Infrared technology and application

Research on packaging technology for 40 K dual-band long-wave detectors
Wang Xiaokun, Chen Junlin, Luo Shaobo, Zeng Zhijiang, Li Xue
2024, 53(3): 20230654. doi: 10.3788/IRLA20230654
[Abstract](59) [FullText HTML] (11) [PDF 2390KB](35)
  Objective   Cryogenic optical technology is a crucial support technology for weak target and multispectral infrared detection. In order to achieve precise temperature control and prevent contamination in the cryogenic optical system, it is common to integrate the cryogenic optics with the detectors inside a cryocooler.  Methods   A specific hyperspectral camera requires the integration of a 320×64 quantum well detector and a 320×64 type II superlattice, co-planarly assembled with dual-band micro-filters to create a long-wave dual-band detection dewar assembly. The required operating temperature for the detector is 40 K, and it is achieved using a pulse tube cryocooler.The dewar adopts a windowless design and is integrated with the cryogenic optical system cryocooler using flexible bellows for hermetic sealing and precise alignment adjustments.  Results and Discussions   Addressing the challenges of three-dimensional assembly of the dual-band detector at 40 K, low-stress assembly of the detector and filters, and efficient heat transfer between the cryocooler and detector, this study investigates the three-dimensional assembly of the detector (Fig.4-6), a heat layer structure for efficient heat transfer at 40 K with low-stress integration with the detector (Fig.7), low-stress filter support (Fig.15), and the coupling between the dewar and the cryocooler (Fig.12). Innovative approaches such as a three-point Z-axis adjustment assembly method, an Al2O3 carrier composite molybdenum substrate for the detector, a molybdenum support structure for the integrated dual-band filters, and a coupling method with stress isolation for the cryocooler and detector are proposed.  Conclusions  Ultimately, this research achieves a detector flatness better than ±2.06 µm (RMS) at 40 K (Fig.6), low-temperature stress of the detector less than 22.06 MPa (Fig.8), low-temperature deformation of the dual-band filter membrane less than 8.55 µm, and a temperature gradient of 2.6 K (Fig.14) between the detector and the cryocooler. The dewar assembly with a 40 K long-wave dual-band infrared detector has been verified through 2000 hours of continuous operation and 300-on/off cycles, with no significant change in component performance before and after testing, meeting the requirements for engineering applications (Fig.16).
Mid-infrared up-conversion imaging based on chirp polarization crystals
Han Zhaoqizhi, Ge Zheng, Wang Xiaohua, Zhou Zhiyuan, Shi Baosen
2024, 53(3): 20230585. doi: 10.3788/IRLA20230585
[Abstract](73) [FullText HTML] (6) [PDF 2089KB](35)
  Objective  The mid-infrared band (2.5-25 μm) has important applications in the field of spectroscopy and imaging. Spectral migration technique up-converts mid-infrared signal light to visible/near-infrared light through a non-linear frequency process, which is then detected using high-performance detectors based on wide-band gap materials such as silicon. Compared to schemes directly using traditional semiconductor detectors, this technique has the advantages of fast response and room temperature operation. Bulk crystals have large aperture to realize array detection. In particular, chirped polarized crystals have obvious advantages in imaging acceptance bandwidth and field of view due to their large phase-matching bandwidth. Previous up-conversion imaging theory, however, didn't consider the nonlinear process of signal light in the crystal to affect the propagation. Therefore, there is some deviation between the theoretical analysis and the up-conversion imaging results under the weak signal light condition. Based on the basic imaging principle, a simple physical model of the up-conversion imaging process is presented by solving the coupled wave equation using finite difference method and considering the effect of nonlinear process on the optical propagation. On this basis, a theoretical derivation for up-conversion imaging under coherent/incoherent radiation illumination conditions based on chirped polarized crystals is provided.  Methods  A mid-infrared up-conversion detection imaging system based on a chirped polarized crystal is built (Fig.3). The target object is illuminated by the thermal radiation of an electric soldering iron, then the visible light in the signal is filtered out by a band pass filter (BP1). A strong 1 080 nm pump light is directed into the crystal through a dichroic mirror (DM) along with the signal beam. Through a 4f system, the up-conversion results of the target are imaged on the EMC CD. A chirped polarized lithium niobate (CPLN) crystal with a period interval of 0.01 μm and a period range of 21.6-23.4 μm is used in the experiment. The length of the crystals is 40 mm and the cross section size is 2 mm×3 mm. The temperature of CPLN crystal is controlled by a home-made temperature controller, whose fluctuation is ±0.002 ℃.  Results and Discussions  By using a mature spectrometer to measure the spectrum after up-conversion and combining with the law of conservation of energy, the accepted spectrum of the up-conversion process in the corresponding mid-infrared band can be obtained (Fig.4). The corresponding mid-infrared acceptance range is 2 915-3 512 nm, and its full-width of half-max (FWHM) is 597 nm. Due to the low transmittance of the DM at wavelengths greater than 3 400 nm, the actual conversion bandwidth is larger than the direct measurement results, which is in agreement with the numerical calculation results (Fig.2). In contrast, the wavelength acceptance bandwidth of single-period polarized crystals is only on the order of nanometers. In the up-conversion imaging results (Fig.5), the largest one-dimensional size of the target is 3.62 cm, corresponding to 125 mm propagation distance, thus the full angle of the field of view is 16.59°, which is slightly smaller than the numerical calculation result in Fig.2. Under the condition of weak signal light, the background of pattern directly imaged by mid-infrared light through the mercury cadmium telluride thermal imager is full of white noise, making it difficult to identify the target contour information, while the pattern obtained by the up-conversion method with the same power of light has clean background and high signal-to-noise ratio (SNR), which also can realize high SNR of the single photon level imaging (Fig.6-7). In addition, applications of up-conversion imaging under coherent/incoherent radiation illumination conditions are reported. The optical edge enhancement imaging is realized for the objects illuminated by mid-infrared coherent light (Fig.8). Real-time video frame rate imaging of incoherent illuminated objects is realized, and its temperature characteristics can be analyzed (Fig.9).  Conclusions  In the experiment, chirped polarized crystal is used to realize the up-conversion imaging detection of the mid-infrared receiving bandwidth of 597 nm and the field angle of view of 16.59°. By comparing with traditional mercury cadmium telluride mid-infrared detector, the up-conversion imaging technique has obvious advantages in improving the signal-to-noise ratio and sensitivity of imaging, and the low-light imaging of mid-infrared is realized by using the photon flux of 1.05×105 Hz. The paper further shows the application of the up-conversion imaging system to the objects illuminated by correlation light and incoherent light. This work has conducted a comprehensive study on the up-conversion based infrared imaging system, which will provide a basis for the design of various application scenarios and improve the system design.
Research progress and development trends of antimonide-based superlattice infrared photodetectors
Zhang Jie, Huang Min, Dang Xiaoling, Liu Yixin, Chen Yingchao, Chen Jianxin
2024, 53(3): 20230153. doi: 10.3788/IRLA20230153
[Abstract](66) [FullText HTML] (12) [PDF 3184KB](41)
  Significance   Infrared focal plane arrays (FPAs) are indispensable core components in many fields such as aerospace remote sensing, deep space exploration, national defense and security, resource exploration, and industrial control. In recent years, the antimonide-based superlattice is drawing the research interests from all over the world. It has become the prominent candidate to achieve infrared detectors with high-uniform large arrays, extended detection wavelengths to long wave and very long wave, two-color detection and so forth, due to its excellent uniformity, low dark current, relatively high quantum efficiency as well as the tunable detection wavelengths which almost covers the full infrared wavebands from near-infrared (NIR) to very long wave infrared (VLWIR). The basic technical principles of the antimonide-based superlattice for infrared detection, the several development stages and key results, as well as the development trends of the Type-II superlattice infrared focal plane arrays, are sequentially introduced and discussed. As antimonide-based superlattice evolves towards higher pixel density, larger specifications, higher operating temperature, longer detecting wavelength, two-color (multi-color), avalanche devices, it is depicted that the antimonide-based superlattice will always play an important role in many fields especially for infrared sensing and imaging.   Progress  The development process of antimonide-based superlattice focal plane detectors is divided into three stages. The first stage spans from 1980s to the very beginning of 21st century. This stage includes the proposal of the concept of superlattice infrared detection technology, theoretical calculation and analysis of the performance of superlattice detectors, epitaxial growth of superlattice materials (first MBE growth by HRL), and some preliminary research on basic optoelectronic properties. The research results of this stage demonstrate the decent capabilities of superlattice materials for infrared detection. The second stage spans from the very beginning of 21st century to year about 2010. This stage mainly focuses on breakthroughs in key technologies for the preparation of high-performance focal plane devices. Particularly, the advanced heterostructures are studied and prepared to suppress the dark current of superlattice long-wavelength detectors. And the etching and sidewall passivation technologies of superlattice materials are explored to prepare superlattice FPA devices. Through these technical breakthroughs, FPAs with 1024 pixel×1024 pixel (Tab.1) and detecting wavelength longer than 10 μm are achieved. The third stage starts from about 2010 and until now. This stage is mainly about the improvement of superlattice focal plane preparation capabilities and the realization of engineering applications, and government becomes an important strength which quickly and efficiently promotes the developments of superlattice technologies. Under the support of related government agencies, Western countries with more technological accumulation make breakthroughs in key technologies such as superlattice structure design, material growth, and chip preparation processes. The VISTA project dominated by American government is a typical case with successful results and deep influence. FPAs with millions of pixels (up to 6 K×4 K), pixel pitches of less than 10 micrometers (e.g. ~5 μm), operating temperature as high as ~180 K are reported. Such superlattice FPAs have already been used in super transport aircrafts, the International Space Station (Fig.7), hyperspectral equipment and so forth.   Conclusions and Prospects   Since the idea of InAs/GaSb superlattice infrared detector was first proposed, it has been over 30 years during which domestic and foreign researchers have successively obtained a series of infrared detectors with large array, high temperature operation, long wave/multi-color detection, through structural design optimization and preparation technology improvement. Antimonide-based superlattice FPAs show advantages such as high uniformity, high stability, and high preparation controllability, and are widely used in aerospace fields such as infrared remote sensing and imaging. Now, to fabricate detectors with higher performance, higher requirements for superlattice materials are put forward. Essentially, materials with longer minor carrier lifetime, higher quantum efficiency and novel structure are explored. Based on the deeper studies, superlattice infrared focal planes are practically developing towards higher pixel density, larger specifications, higher operating temperature, longer detecting wavelength, two-color (multi-color) detection, avalanche devices, etc.
Infrared thermal imaging detection and defect classification of honeycomb sandwich structure defects
Tang Qingju, Gu Zhuoyan, Bu Hongru, Xu Guipeng
2024, 53(3): 20230631. doi: 10.3788/IRLA20230631
[Abstract](39) [FullText HTML] (7) [PDF 2949KB](23)
  Objective  In order to realize the accurate classification of GFRP/NOMEX honeycomb sandwich structure defect types, an infrared thermal imaging detection system was built to collect heat maps of defects and healthy areas, and a GFRP/NOMEX honeycomb sandwich structure defect classification model was constructed by using convolutional neural network and transfer learning technology to realize quantitative detection of defect categories.  Methods  The experimental study of pulse infrared thermal imaging detection was carried out on the specimen. The training data set was constructed using the data obtained from the experiment, and the fine-tuned convolutional neural network model after transfer learning was trained to realize the quantitative detection of defect categories. Firstly, GFRP/NOMEX honeycomb sandwich structure specimens with delamination, debonding, water accumulation and glue plugging defects were prefabricated, and a pulsed infrared thermal wave detection system was built. The FLIR A655SC infrared thermal imager was used to collect the surface temperature distribution field of the specimens under pulse excitation. Secondly, the defects in the heat map are cut into 90 pixel×90 pixel, and the data are expanded by rotating 90°, 180°, 270°, horizontal flipping, vertical flipping and adding Gaussian noise operations. The pre-trained VGG16, MobileNetV2, ResNet50, InceptionV3, and DenseNet201 convolutional neural network models use transfer learning technology to fine-tune the back-layer structure of the network. Finally, the constructed data set is randomly divided into training set, verification set and test set, and the network is trained. The value \begin{document}$ \varphi $\end{document} and Accuracy are used as evaluation indexes to evaluate the generalization ability and classification effect of the model.  Results and Discussions  The VGG16, MobileNetV2, ResNet50 network, InceptionV3 and DenseNet201 network fine-tuned models based on transfer learning technology are trained (Fig.9). The VGG-16-1 network model has the fastest convergence speed, the network is stable, and the training process has no large fluctuations. At the same time, the confusion matrix is used to describe the classification results of the test set data by the six networks (Fig.10). It can be seen that the six models can realize the classification task of five categories of defects prefabricated by GFRP/NOMEX honeycomb sandwich structure. The values of \begin{document}$ \varphi $\end{document} and Accuracy are shown (Tab.4). The classification Accuracy of VGG16 and ResNet50 fine-tuned models reaches 99.94%, 99.10% and 98.95% respectively, and the scores of five categories of \begin{document}$ \varphi $\end{document} are all higher than 96%. Compared with the two fine-tuning models of VGG16 network, the Accuracy and value of VGG-16-1 are higher than those of VGG-16-2. VGG-16-1 has only one misjudgment for the 1 612 defect data of the test set, and the network convergence speed is fast and stable, achieving a better classification effect. Although the overall score of ResNet50 is not as good as VGG-16-1, its network training speed is fast and can also achieve better classification effect.  Conclusions  The data set is constructed by using the real infrared images collected by the infrared thermal imager detection test, and the data is expanded for small samples. Based on the transfer learning technology, the network model structures of VGG16, MobileNetV2, ResNet50, InceptionV3 and DenseNet201 are fine-tuned, and the stability and convergence speed of the training process are compared and analyzed. Besides, the performance of the network was evaluated using a test set that did not participate in the training. The results show that by fine-tuning the transfer learning operation of the pre-trained classical convolutional neural network model, different types of defects of GFRP/NOMEX honeycomb sandwich structure can be well classified, and the quantitative detection of defect categories can be accurately realized.
Numerical and experimental research on the effect of outlet structural parameters of diverter nozzle on infrared suppressor performance
Du Jiadong, Shan Yong, Zhang Jingzhou
2024, 53(2): 20230459. doi: 10.3788/IRLA20230459
[Abstract](58) [FullText HTML] (13) [PDF 4684KB](34)
  Objective  With the rapid development of advanced infrared detection technology and infrared tracking and striking technology, armed helicopters are increasingly threatened by infrared guided missiles from ground and air in the modern high-tech battlefield. In order to improve the battlefield survivability and combat assault capability of armed helicopters, advanced infrared stealth technology must be developed. The research shows that the use of shielding technology and the improvement of the ejector capacity of the suppressor have a significant effect on reducing the infrared radiation intensity of the exhaust system, but the specific technical means should depend on the structure of the infrared suppressor. For the diverter nozzle ejector infrared suppressor, limited to the size and shape of the helicopter, it is difficult to improve the ejector capacity of the diverter nozzle and reduce the exhaust and wall temperature in a limited space. Therefore, it is necessary to discuss the modification scheme of the diverter nozzle outlet to reduce the infrared radiation intensity of the diverter nozzle ejector infrared suppressor.   Methods  A physical model was established including diverter nozzle, gas-collecting chamber, ejected gas inlet, curved mixing tube, covering shelter, and outer cover (Fig.1). The structured and unstructured hybrid grids were established, and the infrared radiation of the infrared suppressor was calculated by the forward-backward ray-tracing method. The calculation method is verified by experimental data (Tab.1-2,Fig.9). By comparing the pumping coefficient, total pressure recovery coefficient, outlet and wall temperature distribution of the mixing tube and infrared radiation intensity of the diverter nozzle ejector infrared suppressor (Fig.10-14), the effect of outlet structural parameters of diverter nozzle on infrared suppressor performance is analyzed from multiple perspectives.   Results and Discussions   The experimental data are used to verify the calculation method. The pumping coefficient and total pressure recovery coefficient of the infrared suppressor under different diverter nozzle outlet structures are compared and analyzed (Fig.10). The exhaust temperature distribution of the mixing tube outlet plane of the infrared suppressor under different diverter nozzle outlet structures is shown (Fig.11). The temperature distribution of the outer mixing tube wall surface of the infrared suppressor under different diverter nozzle outlet structures is shown (Fig.12). And the infrared radiation intensity distribution of the infrared suppressor with different diverter nozzle outlet configurations on the horizontal and lead hammer detection surfaces in the 3-5 μm band (Fig.13) and 8-14 μm band is shown (Fig.14).   Conclusions  Compared with the original model, the pumping coefficient of the Lobe_1 with a certain expansion angle is slightly reduced, the total pressure recovery coefficient of the Lobe_1 is reduced, and the peak exhaust temperature at the outlet of the intermediate mixing tube is reduced by 65.1 K. For Lobe_1, the wall temperature in the upper and lower areas of the mixing tube is reduced, but the temperature in the local area of the outer wall of the middle and rear sections of the mixing tube is increased. The lobed outlet structural (Lobe_2) with an outer expansion angle of 0 increases the pumping coefficient by 3.8%. The total pressure recovery coefficient is basically the same as that of the Lobe_1 model, and the peak exhaust temperature of the intermediate mixing tube is also reduced by 62.8 K, especially the effect of reducing the wall surface temperature of the mixing tube is the best. The outlet of the diverter nozzle with tab structure increases the pumping coefficient by 10.6%, but the total pressure recovery coefficient decreases 0.7%, and the average exhaust temperature of the inner mixing tube decreases by 19.3 K. Tab model has a poor effect on cooling the wall temperature of the mixing tube. In general, both lobe and tab structures play a role in ejection and mixing. In particular, the lobed outlet structure (Lobe_2) has the best effect on reducing the overall infrared radiation of the suppressor, and the infrared radiation intensity in the 3-5 μm band can be reduced by up to 21%, in the 8-14 μm band, the infrared radiation intensity can be reduced by 15%.
Silicon based near-infrared absorption enhancement structure with gradient doping of nano metal particles
Sun Yujia, Chen Fangzhou, Li Xiaozhi
2024, 53(2): 20230519. doi: 10.3788/IRLA20230519
[Abstract](65) [FullText HTML] (19) [PDF 1946KB](25)
  Objective  Silicon based optoelectronics are compatible with CMOS technology, and with the help of mature microelectronic processing platforms, large-scale mass production can be achieved. It has the advantages of low cost, high integration, and high reliability. Among them, the application of silicon based semiconductor detectors in the visible light band has become more mature. However, the commonly used semiconductor materials for near-infrared band detectors have drawbacks such as difficulties in compatibility with existing CMOS processes and high prices. Therefore, expanding the operating frequency range of silicon based semiconductor detectors to the near-infrared band is of great significance. Due to the bandgap width of silicon, there are significant limitations in the absorption of electromagnetic waves by silicon based materials in the near-infrared band, posing serious challenges for the application of silicon based detectors in the near-infrared band.  Methods  In order to break through the bandgap width limitation of silicon and improve the absorption performance of silicon materials in the near-infrared band, a silicon based structure based on gradient doping of nanometallic particles was proposed, based on the near-field enhancement effect generated by local surface plasmon resonance of nanometallic particles. The slow change in doping concentration can effectively solve the severe change in reflectivity caused by refractive index mutation. By applying the Maxwell Garnett equivalent medium theory, the absorption characteristics of composite silicon based structures in the visible and near-infrared bands were simulated, and the effects of two doping concentration changes and two doping metals on the absorption enhancement effect of silicon based materials were compared.  Results and Discussions   The results indicate that the structure has a significant improvement in electromagnetic wave absorption in the near-infrared band. When the doped metal is silver, both decreasing and increasing doping can bring absorption improvement in the 640-1080 nm wavelength range. However, increasing doping can avoid the drastic change in reflectivity caused by refractive index mutations, and its effect is significantly better than decreasing doping(Fig.6). When comparing the effects of different metals, the absorption enhancement band brought by the doping of gold nanoparticles is wider than that of silver nanoparticles. So when choosing gradient increasing doping of gold nanoparticles, the effect is optimal, and the absorption performance can be improved in the 610-1450 nm wavelength range, with a maximum improvement of 10.7 dB(Fig.7).  Conclusions  A silicon based structure that can break through the bandgap width limitation of silicon was proposed, near-infrared absorption enhancement was achieved, and the absorption enhancement effect under different conditions was simulated and analyzed. The proposed structure can effectively enhance the absorption efficiency of silicon based materials in the near-infrared band, which helps to improve the performance of silicon based devices. And by comparing different doping methods and metal selection, it is concluded that gradient increasing doping of gold nanoparticles is the optimal choice. The research results of this article provide important references for the application of silicon based semiconductor detectors in the near-infrared band.
Research of IRFPA ROIC for astronomy
Liang Qinghua, Wei Yanfeng, Chen Honglei, Guo Jing, Ding Ruijun
2024, 53(1): 20230364. doi: 10.3788/IRLA20230364
[Abstract](129) [FullText HTML] (25) [PDF 2605KB](54)
  Objective  Because of the redshift effect, the deepest and most distant universe has been seen at wavelengths closer to the infrared wavelength. The James Webb Space Telescope (JWST), launched on December 25, 2021, focuses its main detector on the infrared detection band. Therefore, infrared observation provides a new technical means for astronomical observation. The core component of infrared payload is infrared focal plane detector. At present, the typical products of mercury cadmium telluride infrared detectors for astronomical applications reported internationally are Hawii-2RG, VIRGO, ALFA (Astronomical Large Focal plane Array), etc., which have been applied in the European Space Agency (ESA). Projects such as the European Space Agency's Euclid probe and NASA's JWST. Because there is still a big gap between the device performance and the advanced level of foreign countries, the progress of infrared astronomy application is relatively slow, and there are few reports about astronomical application detectors in China. Therefore, a 640×512 HgCdTe focal plane readout circuit for the astronomical application is studied.   Methods  Because infrared astronomical observation is characterized by extremely low background radiation and low photon flux, low dark current and low read noise are the key array parameters in order to achieve high signal-to-noise ratio (S/N). Some low-flux observations require observation of several photoelectrons in a very long integration time, so the readout circuit needs to achieve a long integration time to complete the detection of small target signals. An effective power management strategy (Fig.5-6) is used to reduce the power consumption, then reduce the influence of glow on the dark current. At the same time, the digital function of non-destructive readout (Fig.9) is studied to achieve long integration time. And as a ramp sampling strategy (Fig.17), the output noise of the circuit is effectively reduced.   Results and Discussions   The test results of the circuit-coupled shortwave HgCdTe detector are in line with the theoretical design expectation. When the non-destructive readout function of the circuit is turned on, the device can realize ultra-long integral time detection, the dark current of the test device is set to 0.9 e-·pixel−1·s−1 (Tab.2, Fig.25-26) when the power consumption of the circuit is reduced to 14.04 MW at the integration time of 6 000 s. The readout noise is 50e-(10 fF) and 27e-(5 fF) (Fig.28) with two-step gain, respectively, and the nonlinearity is less than 0.1%.   Conclusions  The design of the 640×512 readout circuit for astronomical application and the short-wave IRFPA detector show that reducing the power consumption of the readout circuit is conducive to reducing the influence of the glow on the dark current of the device, and turning on the non-destructive readout function of the readout circuit can realize the long integration time of the detection and improve the signal-to-noise ratio of the device. The focal plane of astronomical applications meets the design expectations, meets the use demand of the infrared focal plane of the large optical platform of the space station, and provides a technical basis for the infrared focal plane research of larger scale astronomical applications in the future.
Effects of infrared-suppressor-integrated exhaust outflow on its aerodynamic and infrared radiation characteristics
Wen Xingyao, Zhang Jingzhou, Shan Yong
2024, 53(1): 20230436. doi: 10.3788/IRLA20230436
[Abstract](73) [FullText HTML] (18) [PDF 6912KB](28)
  Objective  The armed helicopter is in the blind area of radar detection when performing low-altitude missions, but more attention should be paid to the threat of infrared guided weapons. Integrated into the rear fuselage of the helicopter, the infrared suppressor offers excellent stealth capabilities due to its small spatial footprint and the ability of rapid mixing and cooling at short distances. Over the past decades, significant progress has been made in understanding the mechanisms of infrared suppression, enhancing the performance of the suppressor in the areas such as cold-air injection, cold-hot flow mixing, and obscuration of high-temperature components. However, the infrared stealth effectiveness of the suppressor from the top and bottom perspectives has always been suboptimal, necessitating the search for optimal suppressor structures for further improvement. Furthermore, during the helicopter cruising, the suppressor exhaust is inevitably affected by the forward flow. Therefore, it is essential to study the performance of the infrared suppressor under the coupled conditions of forward flow, thermal exhaust, and rotor downwash.   Methods  In this study, an integrated physical model of the infrared suppressor is constructed, which includes the outer skin and the exhaust system (Fig.1). On the basis of the verification of ground model experiment, the simulation of forward flow and variations in the exhaust flow angle are added to assess how these changes affect the flow dynamics, heat transfer, and spatial distribution of infrared radiation intensity within the suppressor. The infrared radiation intensity was calculated using forward-backward ray-tracing method.   Results and Discussions   The results of ground experimental measurement and simulation calculation meet the error requirements, proving the calculation method in this paper is feasible. The increase of the forward flow velocity will increase the ejection coefficient of the lobed nozzle (Fig.10), but will reduce the total pressure recovery coefficient of the exhaust system (Fig.12), and the exhaust of the suppressor is blocked at higher forward flow velocity (Fig.11). Reducing the backward deflection angle γ can solve the problem of poor exhaust, thereby increasing the flow area and improving the total pressure recovery coefficient. However, when the outlet area of the exhaust lobe is constant, its cross-sectional area decreases with the decrease of γ, resulting in a decrease in the ejection coefficient of the exhaust system, an increase in the static pressure in the mixing tube, and a decrease in the total pressure recovery coefficient. When the forward flow velocity increases, the infrared radiation of each band is mainly reduced by reducing the exhaust and internal wall temperature. The installation of a curved deflector at the downwash flow inlet of the suppressor can block the internal high-temperature mixing tube and effectively reduce the infrared radiation intensity at the top of the suppressor (Fig.18). The radiation shielding baffle at the downstream of the exhaust on the longitudinal section makes the suppressor show a high radiation level only in a small range of 30° (Fig.19).   Conclusions  The balance of the advantages and disadvantages brought by changing the backward deflection angle γ of the exhaust lobe determines its influence on the aerodynamic performance of the mixing tube. The external skin downstream of the suppressor exhaust will form a high temperature zone higher than the ambient temperature of about 20 K, and the area of the high temperature zone decreases first and then increases with the decrease of γ. The infrared radiation intensity in the 3-5 μm band is mainly derived from the internal high temperature wall, while the 8-14 μm band is determined by the internal high temperature wall and the external skin. When the forward flow velocity increases from 15 m/s to 55 m/s, the peak infrared radiation intensity of the suppressor decreases by about 50% in the 3-5 μm band and about 20% in the 8-14 μm band. In general, when γ is 60°, the mixing tube has good aerodynamic performance, the local high temperature zone of the external skin is the smallest, and it has good infrared stealth performance at all detection angles.
Numerical simulation of infrared radiation characteristics of near-space aircraft side jet due to angle of attack
Lv Rong, Niu Qinglin, Wang Xiaobing
2024, 53(1): 20230176. doi: 10.3788/IRLA20230176
[Abstract](80) [FullText HTML] (19) [PDF 3451KB](26)
  Objective  Divert and attitude control system's side jet flow is ejected along the normal direction of the projectile during operation, which will form a series of complex structural flow fields called jet interference effects. The high-temperature jet not only generates infrared radiation but also affects the temperature distribution on the surface of the projectile, which ultimately affects the radiation characteristics of the target. In particular, the DACS operation is often accompanied by a change in the angle of attack. The change in the angle of attack causes a significant change in the jet interference effect, which can cause significant changes in the infrared radiation characteristics of the target. In the field of attack-defense mutual countermeasures, both for the stealth and surprise defense of interceptors and for the evasion and identification of interceptors, the urgent concern for the infrared radiation characteristics of targets under high-speed jets is raised. The paper analyzes the effects of the angle of attack on the reignition of the thermal jet field at typical altitudes, and the effects of the angle of attack on the infrared radiation characteristics of the projectile in different spectral bands and at different observation angles.   Methods  With the typical cone-cylinder-flare elastomer as the research object (Fig.1), the three-dimensional N-S equation with chemical reaction source terms is solved. The reaction thermal jet field and the wall temperature of the projectile are calculated in conjunction with the radiative equilibrium wall. The radiative transfer equations are solved based on the statistical narrow band model and the apparent light method from the high temperature database. A Cartesian coordinate system is used to describe the radiation distribution at all possible angles, and the observed angles are represented by the zenith angle θ and the circumferential angle φ (Fig.3).   Results and Discussions   Compared to α=0°, the Mach disk increases at α=10°, the jet expands upward and the high-temperature area increases. However, the Mach disk decreases at α=−10°, the jet is compressed into a limited area of elongated shape, and the local wall temperature at the tail of the projectile increases by about 500 K (Fig.5). The reignition effect increases the intensity of infrared radiation in the MWIR band of the target by about 3.5%, and the degree of radiation intensity increase at α=−10° is enhanced by about 145% compared with α=0° and reduced by about 31.5% at α=10° (Fig.8). The peak radiation intensity of the near-space aircraft proper spectrum is concentrated in the MWIR band, and is strongest in the top view and weakest in the back view, 1 836.6 W/sr and 7.6 W/sr at α=0°, respectively; The total radiation spectrum has two peaks of 2.7 μm (H2O) and 4.3 μm (CO2). The integrated intensity of radiation in the two bands of the same detection surface shows a similar distribution pattern with the change of observation angle and angle of attack, but the difference of radiation intensity values is obvious, which is approximately in line with the pattern that the integrated intensity in the MWIR band is 4 times higher than that in the LWIR band. 4 times the law. In the detection surface 1 described by the zenith angle θ, when α =−10°, the total radiation integral intensity in the top view is enhanced by about 40.2% compared with α = 0°, and reduced by about 28.1% in the top view; When α = 10°, the total radiation integral intensity in the top view is reduced by about 8.6% compared with α = 0°, and enhanced by about 27.8% in the top view; In the detection surface 2 described by the circumferential angle φ, when α =−10°/10°, the total radiation integral intensity is reduced by about 7.5%, and when α =−5°/5°, the total radiation integral intensity is reduced by about 4.8% (Fig.9-14).   Conclusions  When the side jet stream acts, a local hot spot is formed on the wall surface of the projectile. Changes in the angle of attack cause changes in the jet pattern, the temperature distribution at the wall, and the concentration distribution of the gas components, which change the re-ignition level and the radiation intensity. The radiation intensity of the projectile is strongly dependent on the waveband and the observation angle. The total radiation intensity is mainly derived from body radiation. The change of the angle of attack affects the radiation intensity of the target at each observation angle as follows. The radiation intensity of the target in the top view decreases with the negative to the positive angle of attack, and the radiation intensity of the target in the horizontal plane normal to the jet decreases with the increasing value of the angle of attack. This study can provide a theoretical reference for the identification of the target characteristics of the near-space aircraft side jet flow.
Simulation and topological optimization of the thermal stability of the optical axis of the infrared imager
Li Jing, Dong Shulin, Jin Ning, Yang Kaiyu, Yang Dan, Xu Man, Pu Long
2024, 53(1): 20230358. doi: 10.3788/IRLA20230358
[Abstract](70) [FullText HTML] (11) [PDF 2103KB](23)
  Objective  Thermal imaging systems, operating in harsh environments and generating substantial internal heat, are prone to thermal axis deviations, posing a severe threat to their targeting performance. Consequently, the simulation analysis and optimization design of the thermal axis stability for military thermal imaging systems are of paramount importance. This work aims to address these issues and enhance the thermal axis stability of military thermal imaging systems through simulation analysis and optimization design, ensuring accurate targeting performance in adverse operational conditions.   Methods  In order to enhance the thermal axis stability of the infrared thermal imaging system, this study primarily focuses on a key sensitive component of the system, the optical path folding reflector assembly. The research investigates the variations in the thermal axis under different environmental temperatures. To achieve this, a finite element simulation model for the optical path folding reflector assembly is constructed (Fig.1), and a testing system is established (Fig.5). The simulation model demonstrates a high level of consistency with experimental data. Based on this, a topological optimization simulation technique, utilizing a variable density approach, is employed (Fig.3). The primary design objective is to maximize stiffness, while adhering to volume fraction constraints (Fig.4).   Results and Discussions  Through experimental test, it was determined that the optimized design of the folding mirror mount resulted in significant improvements in thermal stability. The high-temperature axial displacement was reduced from 46.1" to 25.5", marking a substantial decrease of 44.7% . Likewise, the low-temperature axial displacement decreased from 92.9" to 51.0", indicating a notable reduction of 45.1% (Fig.6). These outcomes underscore the substantial enhancement achieved in the thermal stability of the folding mirror. Subsequently, the optimized folding mirror was integrated into a specific thermal imaging system for comprehensive system-level test. The testing results confirmed the tangible benefits of the optimization approach. Specifically, the high-temperature axial displacement of the complete imaging system decreased from 0.461 mrad to 0.340 mrad, marking a significant reduction of 26.2%. Furthermore, the low-temperature axial displacement was reduced from 0.485 mrad to 0.296 mrad, representing a substantial improvement of 39.0% (Fig.7). These practical validations affirm the feasibility and effectiveness of the simulation and topological optimization models. In conclusion, this research demonstrates the viability and efficacy of employing simulation and topological optimization techniques, significantly improving the thermal stability of the folding mirror in military infrared imaging systems. The achievements offer a robust foundation for subsequent efforts in lightweight system design and performance enhancements in military infrared thermal imaging systems.   Conclusions  This study, based on a structural thermodynamics simulation model, has significantly improved the consistency between simulation and experimental results for the folding mirror under different temperature conditions. Employing a topological optimization method based on variable density, structural optimization was conducted for the thermal imaging system's folding mirror component. The primary optimization objective was to maximize structural stiffness, which led to the determination of the optimal material distribution within the folding mirror. Firstly, the simulation data of the folding mirror's optical axis thermal displacement before and after optimization was compared, it is evident that the high-temperature axial displacement of the folding mirror decreased from 44.5″ to 17.7″, resulting in a substantial reduction of 60.2%. Similarly, the low-temperature axial displacement of the folding mirror mount decreased from 87.8″ to 43.0″, marking a significant reduction of 51.0%. Secondly, by comparing the experimental test data of the folding mirror's optical axis thermal displacement before and after optimization, it is evident that the high-temperature axial displacement of the folding mirror decreased from 46.1″ to 25.5″, resulting in a substantial reduction of 44.7%. Similarly, the low-temperature axial displacement decreased from 92.9″ to 51.0″, marking a significant reduction of 45.1%. Finally, the experimental test data of the high-temperature axial displacement of the complete infrared thermal imaging system before and after the installation of the optimized folding mirror was compared, it is observed that the high-temperature axial displacement of the imaging system decreased from 0.461 mrad to 0.340 mrad. This reduction represents a significant decrease of 26.2%. Likewise, the low-temperature axial displacement decreased from 0.485 mrad to 0.296 mrad, indicating a substantial reduction of 39.0%. The research results demonstrate that through the application of topological optimization techniques, it is possible to achieve a localized, optimal redistribution of materials within the target structure without altering the original structural installation conditions. This effectively enhances the thermal axis stability of the target structure. The technology allows for a more rational allocation of materials, laying the foundation for further improvements in the thermal axis stability of thermal imaging systems and the lightweight design of the complete imaging system.
Research on the error influence mechanism of infrared temperature measurement of turbine guide vanes with end walls
Zhai Yingni, Liang Zhijie, Meng Xianlong, Liu Cunliang
2024, 53(1): 20230371. doi: 10.3788/IRLA20230371
[Abstract](45) [FullText HTML] (12) [PDF 3587KB](18)
  Objective  With the rapid development of national defense industry and science and technology, more in-depth application and research of gas turbine engines in aviation, power generation, chemical industry, ship and power engineering are also conducted. Due to the complex working environment of turbine blades, the particularity of temperature measurement, and the interference of wall and gas radiation, the traditional temperature measurement technology has been unable to meet its needs. In order to accurately measure the working temperature of turbine blades in complex high-temperature environments, ensure that the highest temperature and temperature gradient on the blade surface are suitable for the blade design life, and improve the safety and efficiency of gas turbine operation, infrared temperature measurement technology was used to correct the temperature of the blades under high operating conditions.  Methods  With a discretized pure three-dimensional model and a radiation correction method based on infrared temperature measurement of turbine blades, the temperature error verification calculation of turbine guide vanes with end walls was carried out using numerical simulation combined with User Defined Function (UDF) custom programming. Custom programming was used to perform reliability verification calculations on the classic concentric sphere model, such as angle coefficients and effective radiation. Based on this method, the angle coefficients of each grid element between the end wall and turbine guide vanes were calculated, and the radiation heat transfer between the blade surfaces was calculated. The surface radiation characteristics distribution of the turbine guide vanes was output, and the radiation energy flow distribution of the turbine guide vanes under this operating condition was derived using Boltzmann's law. We calculated and analyzed the temperature error distribution of turbine guide vanes with end walls under different error influence mechanisms, explored the influence of thermal radiation environment on blade surface radiation characteristics, and discussed the effect of effective radiation on turbine blade temperature measurement.  Results and Discussions  From Figure 8, it can be seen that after convergence, as the inlet blackbody radiation temperature increases from 1400 K to 1800 K, the temperature at the trailing edge and pressure surface of the blade is higher. Under changing the temperature conditions of imported blackbody radiation, the impact on the wall temperature of the blade is mainly concentrated in the pressure surface area of the blade. The pressure surface temperature of the blade is significantly higher than that of the suction surface area, and the second most influential area is mainly the leading edge area of the blade; From Figure 10, it can be seen that as the outlet blackbody radiation temperature increases, the proportion of radiation heat flow rate gradually increases, and there is a significant temperature rise near the trailing edge wall of the suction surface. As shown in Figure 10 (b), (e), (h), the suction surface and trailing edge of the blade are more affected by the outlet blackbody radiation temperature. When the export blackbody radiation temperature is 1600 K, the calculated error of the blade suction surface and trailing edge is about 10 K. The impact area of the export blackbody radiation is mainly in the blade suction surface area, and the temperature rise is relatively small, which has not had a significant impact on the distribution of the outer surface of the blade; When the wall emissivity decreases from 0.8, 0.6, and 0.2, the temperature in the leading edge area of the blade pressure surface is less affected by the emissivity. The temperature error distribution of the effective radiation inverse calculation is shown in Figure 12. The larger the emissivity, the greater the error at the gill area of the blade pressure surface. From the error distribution Figure 13, it can be seen that the influence at the leading edge of the blade is greater than that in the middle area of the blade, and the influence in the pressure surface area of the blade is secondary to that of the suction surface.  Conclusions  When the temperature of imported blackbody radiation is between 1 400 K and 1 800 K, the intensity of imported radiation has the greatest impact on blade heat transfer; Based on the effective radiation and the calculated error distribution, it can be concluded that the main area affected by the inlet radiation temperature is the leading edge area of the blade, with a maximum calculation error not exceeding 2.82%; Through effective radiation and error distribution, it can be seen that the change in outlet blackbody radiation temperature has a relatively small impact on the turbine guide vanes, and the temperature affected area is mainly the leading edge area of the blade. The maximum calculation error shall not exceed 2.35%; The emissivity of the blade surface is positively correlated with temperature. As the emissivity of the blade surface increases, the surface temperature of the blade uniformly rises accordingly. Under real operating conditions, the changes in the physical properties of blade materials are relatively small, and the impact of changes in physical parameters caused by blade temperature changes can be approximately ignored in engine design.
Spectral responsivity of mosaic SWIR detectors
Liao Qingjun, Hu Xiaoning, Huang Aibo, Chen Honglei, Ye Zhenhua, Ding Ruijun
2023, 52(9): 20220890. doi: 10.3788/IRLA20220890
[Abstract](130) [FullText HTML] (22) [PDF 1564KB](60)
  Objective  Hyperspectral imaging can not only get the two-dimensional geometric spatial information of the observed objects, but also obtain the continuous high-resolution spectral information which can reflect the physical and chemical characteristics of the target. It is a very important method for target detection and recognition based on hyperspectral remote sensing information. Spectral range of typical imaging spectrometer is 0.4-2.5 µm due to the ground objects' reflection of solar radiation. Mercury Cadmium Telluride (Hg1-xCdxTe) detectors cover a bandwidth of 0.8-30 µm as the alloy composition of Hg1-xCdxTe material is tuned in terms of cut-off wavelength. Hg1-xCdxTe detectors are the major part of the imaging spectrometer for detection in short waveband. As the swath width of the imaging spectrometer increased, larger scale infrared focal plane array (IRFPA) is needed. Mosaic ultra-large scale shortwave infrared (SWIR) detectors can meet the demand for wide field of view detection in space application. The detector modules for butting have their own spectral responsivity. Hyperspectral imaging demands that the mosaic IRFPA has high uniformity of the spectral response. Therefore, it is necessary to measure and analyse the spectral responsivity specification of the mosaic IRFPA accurately and quantitatively for the hyperspectral imaging application. For this purpose, a method for evaluating the absolute spectral responsivity of the mosaic SWIR detectors is proposed in this paper.   Methods   This paper presents a method for measuring the absolute spectral responsivity accurately and quantitative analysis of the spectral responsivity specification of the mosaic 2 000×256 SWIR detector for imaging spectrometer. The relative response spectrum is measured by a precisely calibrated grating monochromator system. Five optical filters with different center wavelength (CW) and full width at half maximum (FWHM) were chosen to analyze and measure the narrow band responsivity (Tab.1). The center wavelength of the filter is 1225 nm, 1670 nm, 2062 nm, 2420 nm and 2470 nm respectively. The bandwidth is 10 nm and 50 nm, and the cut-off depth is OD3 (optical density). Spectral responsivity is calculated by relative response and narrow-band responsivity.   Results and Discussions   The cut-off wavelength of detector to be tested is 2.6 μm, and its pitch size is 30 μm×60 μm. The integration time of the read-out integrated circuit (ROIC) is 4.4 ms and integration capacity is 65 fF. F number of the Dewar is 0.9. The results of output signal analysis with filter of different CW at different black body temperature show that narrow-band responsivity is much lower than out-of-band response (Tab.2, Fig.3) with 1# filter and much higher (Tab.2, Fig.4) with 5# filter. The possibility of narrow-band signal's accurate measurement at 1200 nm is discussed if the bandwidth is widened to 200 nm and the cut-off depth is adapted to OD4 and OD5 (Tab.3). It shows that narrow band responsivity can be measured precisely only when cut-off depth is smaller than OD5 and FWHM is wider than 200 nm. Based on the result of the analysis, for HgCdTe SWIR detector the measurement error is smallest when the filter's center wavelength is 2470 nm, FWHM is 50 nm, and cut-off depth is OD3 at 80 ℃ black body temperature. The absolute spectral responsivity of four HgCdTe detectors is measured by the relative response curve and narrow-band responsivity (Fig.7). According to the spectral responsivity curve, the responsivity non-uniformity of four detectors can be calculated to be 6.23%, 6.06%, 4.07% at 1 μm, 1.9 μm and 2.5 μm respectively (Fig.8).  Conclusions  In this study, a quantitative method for measuring the spectral responsivity accurately and analyzing the spectral responsivity specification of the mosaic 2000×256 SWIR detector for imaging spectrometer is proposed. The results of this study demonstrated that spectral responsivity of Hg1-xCdxTe SWIR can be measured accurately when the filter's center wavelength is 2470 nm, FWHM is 50 nm, and cut-off depth is OD3 at 80 ℃ black body temperature. Narrow-band spectral response output signal is much larger than signal caused by out-of-band response. The spectral responsivity non-uniformity of the four detectors helps to evaluate the response uniformity of spectral dimension response of 2000×256 SWIR detector quantitatively. The results have demonstrated that the use of this measuring method promotes appropriate application of IRFPA detectors in hyperspectral imaging.
Optimization of nBn dual-band mid-/long-wavelength detector based on InAs/GaSb superlattice
Liu Wenjing, Zhu Lianqing, Zhang Dongliang, Zheng Xiantong, Yang Yichen, Wang Wenjie, Liu Yuan, Lu Lidan, Liu Ming
2023, 52(9): 20220837. doi: 10.3788/IRLA20220837
[Abstract](157) [FullText HTML] (49) [PDF 2250KB](78)
  Objective  Infrared photodetectors are useful for a variety of military and civil applications, such as space science, military equipment, industrial production and so on. Presently, infrared photodetectors are developing towards high performance and low cost to meet the technical requirements. Compared to single color detectors, dual-band infrared detectors covering different atmospheric windows allow for simultaneous acquisition of target information in both wavelengths which is the most obvious advantage. Therefore, the dual-band capability of the detector makes it possible to discriminate between different temperatures and objects, improving the accuracy of temperature measurement and target recognition. Complex infrared backgrounds can be suppressed and it is possible to reduce the false alarm rates significantly in early warning, searching and tracking systems. Mid-long wavelength dual-band infrared detectors based on type II superlattice have great advantages in terms of cost and performance, and have become a popular research topic in the field of new infrared detectors. However, infrared detectors need to reduce dark current density and crosstalk to achieve better performance. The nBn superlattice detector has a unique band gap engineering approach, which can work at a higher temperature and has better thermal stability compared to traditional single color detectors. This leads to better performance and longer operating life in harsh environments. Additionally, the nBn structure has a high absorption coefficient, resulting in a high detectivity and low noise. However, the development of nBn superlattice dual-band detectors faces several challenges, such as the difficulties in fabrication and the limitations in performance. The fabrication of the nBn structure requires precise control of the layer thickness and doping levels, which is a complex process. Besides, the performance of the nBn detector is limited by dark current and temperature. These issues need to be addressed through further research and development. To this end, the paper designs an InAs/GaSb superlattice mid/long dual-band infrared detector with nBn structure to reduce dark current density and crosstalk by simulation of silvaco.  Methods  The materials of the mid-band and the long-band absorber are selected by calculating the band gap of InAs/GaSb using the k.p model to meet the requirements of the design objectives. The mid/long dual-band infrared detectors model with nBn structure is eatablished by silvaco, and the responsivity and dark current density values of the mid/long waveband channels are compared by simulating some device structures at different bias voltages. The effects of the barrier layer thickness, absorber layer thickness, and doping in different regions are analyzed to obtain the best model parameters to reduce the dark current density and crosstalk.  Results and Discussions   By modeling and simulating the nBn type II superlattice mid/long dual-band infrared detector structure, the thickness of the absorber and barrier layers and the doping concentration are optimized to reduce the dark current and the crosstalk in the mid-band and the long-band channel. At 77 K, the cutoff wavelengths of the dual-band detector are 4.8 µm (50%) at 0.3 V and 10.5 µm (50%) at −0.3 V (Tab.8) with the detectivies of 3.9×1011 cm·Hz1/2W−1 and 4.1×1011 cm·Hz1/2W−1 (Tab.9). The dark current density is 4×10−5 A·cm−2 and 1.3×10−4 A·cm−2 respectively (Tab.7). This provides a theoretical basis for subsequent material growth and device processes.  Conclusions  The advantages of the designed superlattice mid/long dual-band infrared detector are simple device structure, low dark current density, and similar detection rate compared with the foreign InAs/InAsSb infrared detectors based on nBn structure and domestic InAs/GaSb infrared detectors based on PπMN structure. The simulation performance will have some differences with the actual device performance, so the subsequent material growth and device process will be carried out to further feedback the simulation, and the device structure will be further improved.
Linear APD hybrid time-of-flight ranging model and readout circuit design
Shao Jiaqi, Chen Honglei, Ding Ruijun
2023, 52(9): 20220892. doi: 10.3788/IRLA20220892
[Abstract](128) [FullText HTML] (51) [PDF 2180KB](59)
  Objective  Currently, 3D image sensors based on time-of-flight ranging have been widely used in military and civil applications, such as astronomical detection, target identification, and unmanned vehicles. They are currently being developed in the direction of high sensitivity, high accuracy, and low power consumption in the future. Hybrid time-of-flight ranging, which can achieve high accuracy and high range of lidar ranging, is based on the principle of indirect time-of-flight ranging while incorporating the notion of direct time-of-flight ranging. It has become one of the development paths of time-of-flight ranging. For this purpose, a hybrid ranging model and a 5×5 array readout circuit with 50 µm center distance are designed based on an APD in linear mode as the detector.  Methods  A two-segment, two-phase hybrid ranging model is built in this paper (Fig.4). Based on this model, the time-of-flight solution was implemented and the error of background light and counter clock frequency was simulated (Fig.6-7). In order to adapt to the model, the readout circuit selects Capacitor Feedback Transimpedance Amplifier (CTIA) as the input stage, outputs a voltage signal through a sample-and-hold circuit, and generates an 8-bit digital signal through a positive feedback comparator and True Single Phase Clock counter (Fig.3). The accuracy of intensity information is determined by calculating the linearity of the analog voltage output (Fig.9). The accuracy of distance measurement is analyzed by combining analog and digital signals, calculating the time of flight in the vicinity of 108.75 m, and comparing the result to the ideal value (Fig.10).  Results and Discussions  The hybrid ranging readout circuit can be passively integrated over a range of 0.5 V to 2.5 V with high injection efficiency. CTIA output voltage has 99.83% linearity (Fig.9). In the hybrid ranging simulations over a range of 108.75 m, the K values were correctly determined for most subperiods. The maximum and average errors in the last subperiod are 11.355 cm and 4.415 cm respectively (Fig.10). This error can be greatly reduced by optimizing the data at the first and last ends. Performance of the readout circuit meets design requirements. The simulation results of the main parameters are compared with the advanced designs at home and abroad in various ranging modes (Tab.1). It can be seen that the small array readout circuit based on LM-APD in the paper achieves a much higher range than indirect ranging at a lower modulation frequency using a medium process. It also achieves a higher accuracy with a very low counter cost and good linearity compared with the direct ranging scheme. It provides a hybrid ranging scheme that can be applied to near-medium range.  Conclusions  In this study, a hybrid ranging model is established and systematically analyzed by combining the advantages of direct ranging and indirect ranging. Based on the model, the intensity of reflected background light and continuous pulse light can be found. By using LM-APD, a 5×5 array with 50-μm pixel center distance two-stage two-phase hybrid ranging readout circuit is designed. It consists of two sub-frames of phase in a single frame, with two steps of integration process in each sub-frame. Both a voltage analog output and an 8 bit counter digital output are available from the readout circuit, which employs CTIA as its input stage. Simulation results show that the analog output achieves 99.83% linearity at a modulation frequency of 20 MHz, and the readout circuit achieves a maximum error of 11.355 cm and an average error of 4.415 cm over a hybrid ranging range of 108.75 m. It extends the range to 29 times that of pure indirect ranging, and the readout circuit has great potential for key performance such as accuracy and range. The preliminary simulation results have shown the advantages of hybrid ranging and verified the feasibility of the hybrid ranging model, providing a theoretical and circuit reference for the design of a larger-scale infrared focal plane 3D imaging readout circuit. Further validation and improvement are pending after the flow of the chip.
Low-power and high-precision SPAD array readout circuit based on built-in clock
Zheng Lixia, Han Yongqi, Wan Chenggong, Zhou Mouzhao, Li Xuyan, Wu Jin, Sun Weifeng
2023, 52(9): 20220896. doi: 10.3788/IRLA20220896
[Abstract](104) [FullText HTML] (12) [PDF 3769KB](46)
  Objective  Using the highly sensitive detection ability of avalanche photoelectricity to weak photon signals, the time of flight can be detected which is obtained after the active laser light source is reflected by the target object. The spatial distance distribution of the measured object, namely the depth of scene information, can be obtained, and the geometric contour image of the target object can be reproduced through relevant algorithms. This Laser Detection and Ranging system composed of APD and readout integrated circuit has the advantages of small size, fast detection rate, high sensitivity, strong anti-interference ability, and is widely used in laser radar, quantum communication, map construction, safe distance detection, unmanned navigation and other fields. With the continuous expansion of the scale of SPAD array and the complexity of application scenarios, higher requirements are put forward for the performance of ROIC. This design focuses on high-precision resolution under low-power constraints. Based on the detailed analysis of the mutual constraints of ROIC array precision, range, area and power consumption, the controllable built-in GRO high-frequency clock drive pixel architecture and event-driven operation mode are adopted to reduce the system power consumption and meet the application requirements of short-range and high-precision ranging imaging.   Methods  The readout integrated circuit for high-precision imaging is established. The ROIC array architecture selects the TDC fully built-in structure, which has unique advantages such as small nonlinearity and good clock phase-splitting uniformity, and eliminates many problems caused by the long-distance routing of polyphase high-frequency clock signals (Fig.1). At the same time, in order to reduce the power consumption, the quantization timing adopts the event-driven quantization method (Fig.3). In order to further pursue higher resolution at rated frequency, the TDC circuit adopts a two-stage structure (Fig.4). In order to ensure clock uniformity and low jitter clock, an external PLL driver with built-in GRO is used to provide the required clock signal (Fig.5).   Results and Discussions  The packaging and related testing of the samples prepared by the MPW chip are completed using the test instrument provided by the laboratory. The PLL outside the array and the GRO inside the pixel meet the requirements, and the GRO function also meets the requirements (Fig.7). The quantization function and performance of the array are tested, the average resolution of TDC is 102 ps (Fig.8). After evaluating the linearity of pixel TDC, the test results show that the differential nonlinearity of TDC array is not greater than 0.8 LSB, and the integral nonlinearity is not greater than 1.3 LSB (Fig.9). The uniformity of TDC array pixels is tested, and the test results show that the total relative deviation is within ± 0.65%, which indicates that the clock frequency and phase generated by each pixel GRO are different (Fig.10). Compared with similar design schemes at home and abroad, the high-precision TDC array designed can obtain larger range with the same accuracy (Tab.1).   Conclusions  In this study, a readout integrated circuit based on built-in clock is designed. The performance of the readout circuit is tested using the test instrument provided by the laboratory. The resolution of the readout circuit is 102 ps, the differential nonlinearity of the pixel TDC is not more than 0.8 LSB, the integral nonlinearity is not more than 1.3 LSB, and the total relative deviation of the uniformity of the TDC array pixel is within ± 0.65%. By testing the performance of the readout circuit, for the sparse photon detection application environment, the circuit can meet the application requirements of short-range and high-precision, and provide stable imaging function for short-range detection.
Numerical simulation of infrared radiation characteristics of the B-2-like aircraft
Lv Rong, Niu Qinglin, Dong Shikui
2023, 52(7): 20220810. doi: 10.3788/IRLA20220810
[Abstract](135) [FullText HTML] (28) [PDF 2910KB](57)
  Objective  The B-2-like aircraft is the only active strategic bomber with excellent stealth performance in the world, and its low detectability is attributed to its unique radar absorbing coating and small radar cross section. However, the high-temperature gas from the exhaust plume cannot be directly concealed and eliminated, becoming a potential main source of infrared radiation. For B-2-like aircraft, the infrared radiation may comes from the high-temperature components such as the engine's high-temperature plume, skin, and nozzle. The exhaust plume of an engine often contains components such as CO2, H2O, and CO, which can emit intense infrared radiation at specific wavelengths through vibrotational transitions at high temperatures. In addition, the skin subjected to aerodynamic heating will also emit a continuous spectrum that follows Planck's law. This paper numerically analyzes the infrared radiation characteristics of the B-2 like aircraft at different observation angles under a representative flight condition (12 km@0.8 Ma), including the spectrum, integrated radiances, and synthetic IR image.  Methods  Taking the B-2-like aircraft as the research object (Fig.3), the flow and thermal characteristic parameters of the engine nozzle are calculated by using the segmental specific heat method in the ideal gas state. The Navier-Stokes equation is solved based on the FVM method to obtain the flow field. The skin temperature is calculated based on the radiation equilibrium wall condition. Based on the statistical narrow-band (SNB) model, the physical properties of radiating gases are calculated, and the radiation transport equation (RTE) is solved using the light-of-sight (LOS) method. The Cartesian coordinate system is used to describe the radiation distribution in observation angles in 2π space, and the observation angle is described by the zenith angle θ and the circumference φ (Fig.5).  Results and Discussions  The high-temperature regions of the aircraft is mainly located near the handpiece, air intake, engine compartment lid, and nozzle, with the highest temperature approaching 250 K (Fig.7). A significant afterburning effect occurs within a certain range from the nozzle, resulting in an increase of the plume temperature to 540 K, and an increase of the mass fractions of H2O and CO2 to 0.045 and 0.025, respectively (Fig.8). The spectral intensity of the skin is the highest in the top view with a peak value of 596 W/(sr·μm). The peak spectral intensity in the bottom view is 78.2% of that in the top view. The peak spectral intensity in the side, front, and rear views is similar, which is 12.8% of that in the top view (Fig.9). In the top view, the total spectral radiation intensity of the target is nearly 3 orders of magnitude higher than that of the skin, and the spectral peak value is in bands of 2.7 μm, 4.3 μm and 5-8 μm (Fig.12). The integrated radiation intensities of skin in the MWIR and LWIR bands are 8.2 W/sr and 1.9×103 W/sr, respectively (Fig.10-11), and the total radiation intensity of the target is 1×103 W/sr and 2.01×103 W/sr (Fig.13-14). The maximum radiation intensity of the plume of the B-2-like aircraft in the MWIR band is approximately 2 times that of the LWIR band and four times that of the 4.3 μm band. In particular, the radiation intensity in the MWIR band is nearly three orders of magnitude higher than that in the 2.7 μm band (Fig.16).  Conclusions  The radiation intensity of the B-2-like aircraft strongly depends on the wave band and observation angle, and the radiation intensity of the target is the strongest in the top view. The main sources of target radiation intensity in the MWIR band and the LWIR band are the exhaust plume and the aircraft body, respectively. This work can provide a theoretical reference for target characteristic identification of the B-2-like aircraft.
Stray light analysis and suppression of long-wave infrared Dewar component for cold optics
Zhu Haiyong, Chen Junlin, Zeng Zhijiang, Wang Xiaokun, Li Yaran, Wang Xi, Li Xue
2023, 52(7): 20220823. doi: 10.3788/IRLA20220823
[Abstract](98) [FullText HTML] (14) [PDF 2495KB](75)
  Objective  As the main detection spectrum of infrared earth optical payload, infrared spectrum (8-12.5 μm) plays an important role in earth remote sensing. With the development of space imaging optical technology, the requirements for the detection performance of imaging satellites are constantly improving, and the imaging satellites are developing towards high resolution, high spatial resolution and wide radiation. For example, Venezuela’s Remote Sensing Satellite (VRSS) infrared camera, NASA's Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) infrared camera, etc. The infrared imager achieves a spatial resolution of 30 m and a width of 300 km by whiskbroom, which ensures high resolution and improves the imaging width. The influence of stray light on it is particularly prominent when the infrared remote sensing instrument with high resolution and large field of view extracts the remote sensing information of weak targets. If the suppression of stray light is insufficient, the energy distribution on the image plane is uneven, which leads to the decrease of signal-to-noise ratio and modulation transfer function (MTF), and the nonuniformity becomes worse. In severe cases, the detection signal of the detector is annihilated by stray light of background radiation, which results in the failure of the detector. Therefore, the design of stray light suppression for infrared imager is the premise to ensure its on-orbit imaging quality. The long-wave infrared Dewar module is an important part of the imager. Because the optical structure of the Dewar module is close to the detector, the detector is more sensitive to the optical structure, so the design of stray light suppression of the Dewar module is particularly important.   Methods  In view of the above requirements, this research analyzed four key surfaces of spurious radiation in opto-mechanical system, including lens, lens barrel, Dewar window and window cap, among which lens barrel was the main source of spurious radiation (Fig.2). Cryogenic optical design was adopted to reduce stray radiation, including 195 K lens, 180 K lens barrel, 200 K Dewar window cap and window design (Tab.2). In order to realize the low-temperature Dewar design, flexible bellows were introduced into the Dewar package structure to increase the thermal resistance between the refrigerator coupling surface and the window cap, and realize the thermal isolation between the 200 K low-temperature window cap and the 240 K expander (Fig.1). The effects of window, window shell, cold screen structure and surface treatment technology of Dewar module on stray light in Dewar were studied (Fig.6, Fig.8, Fig.9).   Results and Discussions   Based on the analysis above, the innovative results are as follows. (1) The flexible bellows were introduced into the Dewar package structure to increase the thermal resistance between the coupling surface of the refrigerator and the window cap, and the design of 200 K low temperature window and window cap was realized, and the radiation suppression in the optical machine was at a good level (Tab.2). After the measurement, the temperature gradient of cold end and hot end of bellows reached 37-48 K (Tab.1). (2) The cold screen adopted three-stage baffle design, and the filter was integrated in three bands. Considering the assembly and machining accuracy, the cold screen and the filter bracket were separated. The radiation suppression in the optical-mechanical system was at a good level (Fig.10-12, Tab.3).   Conclusions  The main objective is to reduce the radiation stray light of infrared remote sensing instrument with high resolution and large field of view. Reasonable low temperature design is beneficial to restrain the stray radiation of the module, and the flexible bellows shell insulation structure with 0.1 mm wall thickness is an effective means to realize the design of 200 K low temperature window and window cap. As the main source of optical-mechanical stray internal radiation, the influence of lens barrel on it should be considered when considering the processing and design of cold screen and window. This research provides theoretical and technical reference for the design and processing of low-temperature Dewar.
Research on long wave detection of low feature surface aircraft in sea environment
Song Minmin, Lv Tao, Sang Xueyi, Xue Fenfen, Su Jianping
2023, 52(7): 20220807. doi: 10.3788/IRLA20220807
[Abstract](53) [FullText HTML] (7) [PDF 2239KB](31)
  Objective  Most of the new generation of surface aircraft further use stealth, power control and other means to improve their penetration ability, and their infrared radiation energy has dropped significantly, bringing more and more challenges to shipborne air defense. The medium and long wave dual-band infrared detection method effectively utilizes the different characteristics of the target radiation in the two bands to enhance the detection ability of different radiation energy areas of the surface aircraft with low characteristics at the same time.   Methods  The infrared radiation model of an surface aircraft at different detection angles is established by using ray tracing and inverse Monte Carlo method, and the medium-long wave infrared radiation intensity of an surface aircraft at different detection angles is completed. Then, based on the calculation results of side-to-head radiation intensity, the differences of medium-long wave detection under special conditions such as rain and sea fog in the marine environment are compared and analyzed, and the medium-long wave detection data at different distances are obtained by means of the detection test of weak and small targets under the complex sea background in the actual outfield, and the equivalent temperature difference between the target and the sea background is statistically analyzed.   Results and Discussions   The calculation results of medium and long wave infrared radiation intensity distribution of an surface aircraft at different detection angles are shown in Figure 5; The impact of sea haze, overcast rain and other weather on medium-long wave detection is shown in Figure 6 and Figure 7 respectively; The influence of sea clutter on medium and long wave detection is shown in Figure 8 and Table 2. Through the above work, the advantages and disadvantages of medium-wave and long-wave bands under different climate and sea background conditions are statistically analyzed, and the advantages of medium-wave and long-wave composite detection technology are fully verified.   Conclusions  In sunny weather and good visibility, long-wave detection has advantages in weak and small target recognition and anti-sea clutter interference. However, in case of sea fog, rainfall conditions and poor visibility, medium-wave detection is superior to long-wave detection. Therefore, it is necessary to use the medium-long wave composite detection method to learn from each other's strong points and compensate for the weak and small target recognition probability under various sea environment conditions.
Simulation of flow field infrared radiation over reentry vehicle with ablation of carbon-based thermal protection material
Gao Tiesuo, Jiang Tao, Ding Mingsong, Liu Qingzong, Fuyang Aoxiao, Xu Yong, Li Peng, Dong Weizhong
2023, 52(5): 20220606. doi: 10.3788/IRLA20220606
[Abstract](81) [FullText HTML] (32) [PDF 2609KB](32)
  Objective  Hypersonic vehicle travels at a very high speed in atmosphere. Due to the high flight velocity, hypersonic vehicle has to endure very high heating rates on surface, ablative material is widely used in the design of thermal protection system (TPS). During the ablation process, gaseous ablator species are injected into the flow field, these gaseous species can involve inflow air in the chemical reaction, which changes flow field species distribution and temperature distribution, thus changing the target infrared radiation characteristics of hypersonic vehicle. Infrared radiation characteristics are the foundation of aircraft detection, identification and interception. Therefore, it is necessary to study the effect of thermal protection material ablation on aircraft target infrared radiation characteristics. For this purpose, this paper focuses on strategic warhead blunt body configuration with carbon-based thermal protection material. Numerical simulation of flow field and its infrared radiation is conducted, ablation effects on infrared radiation of flow over reentry body are discussed.  Methods  Numerical simulation of flow field is conducted by solving three-dimensional thermal-chemical non-equilibrium Navier-Stokes equations. To simulate the surface ablation effect, surface velocity boundary condition, surface mass balance condition and surface energy balance condition are introduced into the computation process of flow field simulation. Oxidation, catalytic reaction and sublimation reaction of surface ablation material are also taken into account. To simulate the chemical reactions in the flow field, chemical reactions model of high temperature air with gaseous ablator species is used. Based on spectral band radiation model and by solving high temperature gas radiation transport equation, numerical simulation of flow field infrared radiation is conducted, the radiation mechanism of NO, CO, CO2, CN, N2, O, N is considered.  Results and discussion  Numerical simulation results at typical condition agree well with experiments and numerical simulation results in literature (Fig.1-3), the computation model and method are validated. The main ablation product on surface is CO, infrared radiation in the waveband of 0.8-8 μm of flow field mainly comes from the radiation of high temperature CO, NO, CO2 and CN (Fig.4). Ablation effect can increase flow field infrared radiation intensity, this phenomenon is more significant in 3-8 μm waveband than 1-3 μm waveband (Fig.5). Radiation from 3-8 μm waveband mainly comes from CO and NO, mass fraction of these species and flow field temperature increases as flight altitude decreases and flight velocity increases. Due to this, the radiation of 3-8 μm waveband increases as the flight altitude decreases and flight velocity increases (Fig.7-8). Radiation from 1-3 μm waveband in flow field around vehicle body increases as flight velocity increases, the radiation from 1-3 μm waveband in wake flow shows nonmonotonic variation due to the change of flow structure (Fig.7-8).  Conclusions  In this paper, the ablation effects on infrared radiation of flow over reentry body covered with carbon-based thermal protection material is studied. By solving high temperature gas dynamics equations and radiation transfer equations, numerical simulation of thermal protection material ablation flow field and its infrared radiation is conducted. The distribution and changing rules of infrared radiation in different wavebands from ablation flow are analyzed. The study shows that ablation effect has significant influence on infrared radiation of reentry flow, which makes integral radiation intensity of wake flow increase more than one order of magnitude compared with non-ablation case in 3-8 μm waveband; The infrared radiation of ablation flow mainly comes from CO, NO and CO2, and the ablation effect has less effect on the radiation in 1-3 μm waveband; The infrared radiation intensity of ablation flow increases with the decrease of reentry height at the same flight velocity, which weakens with the decreasing reentry velocity at the same flight height in 3-8 μm waveband.
Analysis of airborne infrared detection performance of submarine thermal wake in stratified seawater
Li Yingchao, Pan Ze, Li Guanlin, Shi Haodong, Fu Qiang
2023, 52(5): 20220741. doi: 10.3788/IRLA20220741
[Abstract](257) [FullText HTML] (61) [PDF 1348KB](71)
  Objective  At present, most of the calculation methods for thermal wake detection by MRTD analysis consider the water body as uniformly distributed seawater. The stratified nature of seawater temperature and density has great influence on the inversion accuracy of submarine thermal wake on the surface temperature distribution, rise time and wake rise distance. However, the research at home and abroad mainly focuses on the improvement of MRTD algorithm of infrared system or derivation of the detection ability of infrared detector based on other parameters of the system, as well as the influence of weather and other factors on wake detection, and has not analyzed the influence of seawater stratification on wake detection and inversion. Therefore, the research on infrared radiation detection of thermal wake under the conditions of stratified seawater temperature and density is of great significance to the infrared detection of submarines.   Methods  For the lack of infrared detection of submarine thermal wake under the condition of stratified sea water temperature and density, the calculation error of detection distance and inversion accuracy error of submarine are large. Based on the finite element analysis method, the research on submarine infrared radiation characteristics under the condition of seawater stratification is carried out in this paper. Firstly, the finite element analysis method is used to simulate the floating process of submarine thermal wake in stratified seawater by a full-size submarine model with propeller and bridge characteristics. Then, according to the sea surface infrared radiation model and atmospheric transmission model, the full-link mathematical and physical model of the wake from floating diffusion, atmospheric transmission atmospheric attenuation to sensor detection is built, and the detection distance of the infrared detector to the submarine thermal wake under the condition of layered seawater is calculated according to the specific infrared detector performance parameters.   Results and Discussions   The comparison shows that the stratification condition of seawater has a great influence on the detection of wake. With 95% detection probability, the detection distance of the wake increases by 10.61%, the identification distance of the wake increases by 9.32%, and the recognition distance of the wake increases by 8.28% (Tab.2). In the case of stratified water, the wake is presented as a cold wake on the water surface. The temperature difference between the cold wake and the sea surface is 0.152 K larger than that between the hot wake and the sea surface in the case of non-stratified water. The submarine travels 340 m forward without stratified seawater and 101.8 m under stratified seawater temperature and density. Compared with seawater stratification, the inversion error of submarine without stratification reaches 238.2 m, and the wake temperature difference on the surface is not only 0.152 K, but also cold wake phenomenon. It can be seen that the seawater stratification condition has a great influence on the submarine's inversion accuracy, and even directly leads to incorrect results.   Conclusions  The mathematical and physical model of the wake from floating diffusion, atmospheric decay to full link of sensor detection under the condition of seawater temperature and density stratification is established. The influence of seawater temperature and density stratification on the wake floating speed, the detection distance of the infrared detection system to the wake and the inversion error of the wake are obtained by simulation calculation. That is, it takes 101.8 s for the wake to rise to the surface at 50 m under the condition of stratified seawater temperature and density. Under the same conditions, when the seawater is not stratified, the time taken for the wake to rise to the surface is 340 s, which is much longer than that for the stratified seawater. This is due to the lower underwater temperature of the stratified seawater and the large density difference conducive to the floating of the hot wake. The discovery distance of the delaminated water body wake is 6.451 km, the identification distance of the wake is 1.631 km, and the recognition distance of the wake is 0.824 km. The unclassified detection distance, identification distance and recognition distance are 5.832 km, 1.492 km and 0.761 km, respectively. Compared with seawater delamination, the inversion error of submarine wake is 238.2 m without delamination, the temperature difference of wake on water surface is 0.152 K, and the cold and hot wakes on sea surface are different.
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