Terahertz technology and application
2022, 51(6): 20210648.
doi: 10.3788/IRLA20210648
A tunable broadband, polarization insensitive and incident angle insensitive metamaterial terahertz absorber is proposed, which consists of silicon semi-ellipsoid/semi-spherical structure, graphene, dielectric layer and metal back plate. Based on the known results, the electric field results under different chemical potentials of graphene and different structural conditions were analyzed by simulation under the condition of vertical incident TE wave show that under the synergism of continuous and multimode Fabry-Perot resonances formed by silicon semi-ellipsoid/semi-spherical subwavelength structure and multiple discrete plasma resonances excited by graphene the absorption spectrum is smoothed and expanded so that the structure can achieve a wide range of adjustable absorptivity and a broadband absorption characteristic of nearly 100% absorptivity. When the chemical potential of graphene is around 0.2 eV and 0.9 eV, it can obtain about 5.7 THz and 7 THz wideband terahertz wave absorption (the absorption rate is more than 90%), respectively, and its maximum absorption rate is close to perfect absorption (about 99.8%). In addition, the structure is insensitive to 360° polarization and incident angle higher than 60°. In the above angle range, the absorptivity of the absorber can still be maintained to more than 90%. and the structure has potential applications in terahertz wave detection, spectral imaging and stealth technology.
2022, 51(6): 20210338.
doi: 10.3788/IRLA20210338
The detection of the main components in crude oil samples and the origin traceability is of great significance to the fields of national defense security and ecological environment. At this stage, the measurement of crude oil composition are complicated, high-cost, and have long detection time, which cannot meet the demands of rapid detection of crude oil composition and traceability of the origin of crude oil. Combining with a highly sensitive terahertz detection chip (Based on dual torus toroidal effect) and terahertz time-domain spectroscopy system, the terahertz spectra of crude oil samples from different origins were measured in this paper, and it was found that the frequency shift of the chip resonant peak showed different rules. For two main indicators of sulfur content and residual carbon in crude oil, quantitative analysis can be carried out according to their unique frequency shifts. The calculation of experimental data shows that the relative difference of the average resonance frequency of crude oil from the same origin is about 4.63%, and the relative difference of the average resonance frequency of crude oil from different production areas is about 56.53%, which can clearly distinguish the origin of crude oil. The designed metasurface chip can excite new electromagnetic mode, providing a highly sensitive detection technology, which can be widely used in real-time monitoring of biomolecules or detection of chemical substances (such as crude oil) composition detection, origin traceability and other fields.
2022, 51(6): 20210430.
doi: 10.3788/IRLA20210430
Multilayer bonding structure is widely used in aerospace field, and its bonding strength is the key factor to ensure engineering safety. Different terahertz time-domain spectroscopy parameters such as time-of-flight, energy and amplitude were used to characterize the uniformity of the adhesive layer of multilayer bonding structure, and then evaluate the bonding quality of multilayer bonding structure materials. The uniformity of the adhesive layer was qualitatively analyzed by the terahertz time-domain spectroscopy time-of-flight imaging method. The relative standard deviations of flight time of four experimental samples are 8.78%, 8.09%, 7.30% and 9.57% respectively; Using the energy integration information of terahertz time-domain spectroscopy, the kurtosis and skewness of the energy integration curve were used to qualitatively analyze the uniformity of the adhesive layer. The energy standard deviations of four experimental samples were 0.95, 0.9, 0.71 and 1.01, respectively; In addition, according to the amplitude characteristic information of terahertz time-domain spectroscopy, the uniformity of adhesive layer was quantitatively characterized by amplitude dispersion coefficient. The results show that the time-of-flight, energy integral and amplitude of terahertz time-domain spectroscopy can be use to quantitatively evaluate the adhesive layer uniformity of multi-layer adhesive structures. This method can provide a reliable means for evaluating the adhesive strength of multi-layer adhesive structures.
2019, 48(S1): 211-216.
doi: 10.3788/IRLA201948.S125001
Terahertz(THz) waves occupy a very important position in the electromagnetic spectrum. THz technology is recognized as a major cross-cutting frontier in the international scientific and technology community. Photonic generation of THz signal using a recirculating frequency-shifting loop(RFSL) was proposed and experimentally demonstrated. The frequency of optical source was shifted by the RFSL and beats with each other in a high-speed photodetector to generate a THz signal. In the RFSL, the single sideband(SSB) modulator driven by a radio frequency(RF) signal was a key component for frequency-shifting. The frequency multiplication factor(FMF) of the THz signal was controlled by the lap number circulating in the loop. The frequency of the THz signal increased with the improvement of FMF and equals to the frequency multiplication factor multiplied by the frequency of RF signal. Experimentally, tunable signals from 5 GHz to 20 GHz were generated and the FMF was successfully tuned from 1 to 25. The stability of the power and center frequency was detected when the frequency of the signal was 20 GHz. 0.25 THz signal was finally generated by this system.
2019, 48(2): 225002.
doi: 10.3788/IRLA201948.0225002
A 220 GHz tripler frequency multiplier using no-substrate and space combined structure was designed and realized based on four anodes in parallel-series GaAs planar Schottky diodes. Four Schottky diodes was adopted and divided into two groups. One group with two Schottky diodes placed in the same direction was flip-chiped on the top surface of the slab waveguide metal film and the other group on the bottom surface composed anti-series structure. The efficiency of the circuit was stimulated combined of EM simulator and circuit simulator. The stimulated efficiency was bigger than 3% over the band of 213 GHz to 229 GHz with the input power of 300 mW. An E-band power amplifier was used to drive the circuit to get the output power of the multiplier. The measured output power was bigger than 5 dBm over the band of 213 GHz to 229 GHz with the input power of 300 mW. The efficiency was 1% to 2%.
2019, 48(1): 125001.
doi: 10.3788/IRLA201948.0125001
A spectrally wide-band terahertz modulator based on monolayer graphene on germanium (GOG) was proposed. Utilizing a homemade THz-TDS (Terahertz-time domain spectroscopy) system, it was experimentally demonstrated that the THz modulator can be tuned by a 1 550 nm pump beam in a frequency range from 0.2 to 1.5 THz. The average transmittance of THz decreased from 40% to 22% when the pump power was increased to 250 mW, while the absorption coefficient averaged increased from 19 to 44 cm-1. The maximum modulation depth of the GOG modulator can reach as high as 62% at 0.38 THz and in a frequency range from 0.2 to 0.7 THz, the modulation depth was over 50%. Compared with bare Ge, it was proved that the modulation performance can be moderately enhanced by introducing monolayer graphene. This novel optically controlled graphene based THz modulator provides a feasible method for terahertz applications in communication and imaging.
2019, 48(1): 125003.
doi: 10.3788/IRLA201948.0125003
The parameters of steel bar (such as position, diameter, etc.) play an important role in the safety of the constructed buildings. A measurement method for position and diameter of the steel bar within the building by using terahertz wave was proposed. The terahertz wave was used as the detection signal to realize these functions, which the terahertz wave had a strong penetrability to nonmetal building material (such as cement, brick, lime, etc.) and had the characteristics of almost total reflection to the metal (steel bar). At the same time, compared with the microwave, the terahertz wave was easy to achieve a very narrow antenna beam, which achieved high detection accuracy. And compared with the magnetic detector, it was not influenced by the external magnetic field environment. Theoretical analysis and engineering test show that this method can meet the requirements of actual engineering application.
2019, 48(1): 125004.
doi: 10.3788/IRLA201948.0125004
Terahertz interferometric imaging technique based on the spectral domain, by sampling information of the spectral domain of the target scene to reconstruct the target image. It offers considerable potential in image acquisition rate and resolution for avoidance of scanning each pixel and ability to image with only a handful of detector elements. The terahertz interferometric imaging principle and implementation method were researched, then imaging resolution and effective field of view were focused on. Simulation experiments were carried out to analyze the influence of noise in target scene for imaging quality, and the results show that interferometric imaging is sensitive to noise. The reflection imaging model in security check was focused on which validated the applicability of the principle system. The conclusions from the simulation results may offer some theoretic evidence and technical support to designs of terahertz interferometric imaging system and practical applications.
2018, 47(2): 225001.
doi: 10.3788/IRLA201847.0225001
Considering the terahertz near-field scattering characteristics, a high-frequency terahertz radar cross section (RCS) measurement system was presented based on a CO2 laser pumped terahertz laser and an independent double-deck rotation platform. The reliability of the system was verified by utilizing stainless steel smooth spheres as the standard calibration targets. The error between measurement result and the theoretical value was less than 3 dBsm and the signal-to-noise ratio is better than 24 dB. For the first time, RCS measurement of metal plates was performed with different materials and coatings, and metal cones with different bottom diameter, at a high frequency of 3.11 THz. The RCS difference of pure, anodized, painted aviation aluminum and P304 stainless steel plates, was demonstrated. The RCS of cones with different bottom diameters made of pure aviation aluminum plate was also compared. This work can lay the foundation for further study of the complex target RCS research in the terahertz band.
2018, 47(2): 225002.
doi: 10.3788/IRLA201847.0225002
The modified polypropylene(PP) material has been widely used in dashboard, bumper and other auto parts because of its characteristics of flame retardant, high impact resistance, etc. It is a necessary means to improve the quality of auto parts by using the nondestructive testing technology to detect the modified PP material. A transmission terahertz time-domain spectroscopy(THz-TDS) imaging system and a reflective THz-TDS imaging system were built. The optical parameters of modified PP materials were extracted by adopting the transmission THz-TDS system. The refractive index, one of the optical parameters in terahertz band can be solved through the mathematics model, its value was 1.53. A kind of modified PP material sample with flat bottom holes was designed. The reflective THz-TDS imaging system was adopted for measuring the sample, the deconvolution method was used to filter the time domain THz signal, which largely improved the signal-to-noise ratio. What's more, THz-TDS tomography imaging technology was proposed based on the time of flight. Combined with the measured refractive index, the 3D structure of the modified PP material was reconstructed with the time of flight tomography imaging technique, the thickness accuracy is 0.01 mm.
2018, 47(10): 1025001.
doi: 10.3788/IRLA201847.1025001
In the process of generating terahertz (THz) waves using femtosecond lasers, the plasma absorbs the THz wave energy, and the absorption characteristics have a great application prospects in the THz wave radar detection, plasma stealth, electromagnetic interference research. A measurement system of THz absorption via plasma was designed combining the theoretical analysis, and it was proposed that the interaction between plasma particles was the main reason for the plasma absorption of terahertz waves. The results show that the plasma density, the focal length of the optical lens and the angle of the incident femtosecond laser and the multiplier crystal are the main factors that affect the absorption degree, which provides a more comprehensive theoretical support for the plasma absorption application, it will be helpful to promote the THz wave technology in the military and civilian areas with rapid development.
2018, 47(10): 1025002.
doi: 10.3788/IRLA201847.1025002
The aging of natural rubber products is a common phenomenon in its use, and the essence of aging is that the material itself is flawed and easily affected by external factors. Dielectric spectrum is a macroscopic manifestation of micro-polarization which is the dependence of dielectric constant on electromagnetic frequency or temperature. According to the plastic/rubber hot air aging standard GB/T3512-2014, the thermal oxygen experiment of natural vulcanized rubber was carried out in the experimental chamber of 100℃ for more than 1 000 hours, and the relationship between the dielectric spectrum of samples and aging time was studied. By tracking test, the effective data of complex permittivity and loss tangent value of 0.2-1.2 THz rubber were obtained every 24 hours. Based on the complex permittivity values, the polarization characteristics of the deduced rubber and the statistical microcosmic movement types can be calculated, and the molecular structure changes of the natural vulcanizates characterized by terahertz dielectric spectrum were analyzed. Due to the similarity of the aging of the material, the results can also play a positive role in studying other polymer materials aging.
2017, 46(8): 825001.
doi: 10.3788/IRLA201746.0825001
The dielectric properties of single-crystal MgO were studied by terahertz time-domain spectroscopy in the frequency range extending from 0.5 to 9.5 THz. The refractive index, power absorption, and the complex dielectric function were extracted from experimental data. At low terahertz frequencies band (2 THz), the absorption coefficient was extremely low and increased with increasing frequency. Meanwhile the corresponding refractive index had low dispersion, increasing from 3.12 to 3.15. Two prominent resonances were observed at 3.16 THz and 8.11 THz and were well-described by a multiple-oscillator model through theoretical fitting. The interaction of incident photons and the transverse optical (TO) phonons in the crystal were studied and it gives good evidence to further applications in developing broadband terahertz components and terahertz spectroscopy.
2017, 46(8): 825002.
doi: 10.3788/IRLA201746.0825002
Terahertz interferometric imaging offers considerable potential in many imaging applications due to its simple imaging principle, less detector elements and efficient data acquiring ratio. An interferometric imaging system scheme was proposed based on the research of Terahertz interferometric imaging principle. Simulation experiments were carried out to analyze the impact of imaging frequency, radius of circular array and detector number on imaging quality and frequency bandwidth of the imaging system. The experimental results show that the radius of circular array is smaller while the frequency is higher for available imaging with the other conditions being changeless. Adding detector number would improve the imaging quality but not obvious while bigger than one certain number and the frequency bandwidth of uniform circular array for available imaging is wide. The conclusions from the simulation results may offer some theoretic evidence and technical support for the design of terahertz interferometric imaging system and practical applications.
2017, 46(8): 825003.
doi: 10.3788/IRLA201746.0825003
The influence of groove depth in one dimensional (1D) subwavelength metal grating on THz spoof surface plasmon ploaritons(SPPs) was theoretically investigateal in detail. Two device geometries were proposed including uniform groove depth 1D metal grating and defect groove depth 1D metal grating. The electric field distribution of metal grating was stimulated by employing COMSOL software. For the uniform structure, the dispersion relation of SPPs propagating along grating can be tailored by groove depth. The metal grating with deeper groove has stronger THz electric field distribution and the spoof SPPs is better confined to grating surface. For the defect structure, electric field distribution characteristics of both sides are determined by the defect groove depth, which can be attributed to reflection and scattering of defect. Based on the proposed theoretical stimulation, the two different subwavelength metal grating structures can provide new functionality for THz wave devices such as wave guiding, attenuator and filter.
2017, 46(5): 525001.
doi: 10.3788/IRLA201746.0525001
In order to acquire extinction characteristics of smokes for terahertz (THz) wave, graphite and carbon black powders were mixed respectively into KBr powder with some certain proportions, and the admixtures were pressed into tablets to measure the THz transmission spectrums using THz time-domain spectroscopy (THz-TDS) from 0.2 to 1.1 THz. At the same time, the THz signal was acquired from the pure KBr powder tablet, which was prepared with same method under same condition. Then, absorption coefficients of graphite and carbon black tablets were deduced based on material parameter estimation method. The result indicates that absorption coefficients of those tablets are enhanced with the increasing frequency and they are improved with the proportions of smoke powders at the same frequency. The absorption coefficient of tablet filled with carbon black powder is greater than it of graphite tablet. The final results demonstrate that THz wave has stronger penetration capacity through graphite smoke, and carbon black is a promising jamming material for THz detection.
2017, 46(5): 525002.
doi: 10.3788/IRLA201746.0525002
In many practical applications, it is required that the spot is ring distributed. Therefore, it is important to do the experimental research of converting the terahertz Gaussian beam to a ring beam. In the paper, a phase plate was designed using GS algorithm, converting the Gaussian beam with frequency of terahertz band to a ring beam. The shaping effect of multi-order encoding phase plates was discussed. According to different transmission distances, different simulations were done. Using the PyrocamⅢ as the recording device, beam shaping experiments were carried out on different distance. The experimental results show that the experimental results are close to the simulation results.
Due to the low THz radiation energy and narrow pulse width (picosecond range), as a new spectral analysis method, terahertz time-domain spectroscopy(THz-TDS) technology is nondestructive and high-temporal-resolution when being used to extract optical parameters of samples. Fabry-Prot interference is a crucial obstacle in extracting optical parameters of thin wafers in the THz-TDS through- transmission mode. A reliable algorithm was proposed and tested to simultaneously filter Fabry-Prot interference and obtain precise optical characterization of thin wafers. The algorithm employs a band-stop filter immediately and exclusively designed for every single sample to the initial refractive index and absorption coefficient. Experimental results of doped silicon wafers and amino acid tablets confirming the utility of the algorithm were also presented.
2017, 46(11): 1125001.
doi: 10.3788/IRLA201746.1125001
In order to get different harmonics output of frequency multiplier, a 170 GHz and 340 GHz frequency selective network based on Compact Suspended Microstrip Resonators(CSMRs) filter was designed. The design met the multi-frequency requirements of systems, and the cost was reduced and the system integration degree was increased. In the simulation, the 170 GHz and 340 GHz probes were designed respectively. CSMRs low-pass filter was introduced to increase the isolation degree of 170 GHz and 340 GHz bands. The waveguide height was decreased, the cutoff frequency of the WR.2.8 waveguide was increased below 300 GHz. The measurement module was back-to-back of Selective Network. The simulation results show that CSMSRs filter has S11-18 dB between 20 GHz and 180 GHz,S12-20 dB between 266 GHz and 520 GHz. The back-to-back module S11 is better than -15 dB at 170 GHz and 340 GHz bands, and two ports isolation degree is better than 30 dB. Measurement results show that S11-10 dB and transmission loss is better than 1.2 dB at 150-185 GHz. S11-10 dB between 306 GHz and 355 GHz, and transmission loss is 2 dB, two ports isolation degree is 10-60 dB.
2017, 46(11): 1125002.
doi: 10.3788/IRLA201746.1125002
An automatic recognition algorithm was proposed for recognizing objects concealed on the edge of human body in an image, which was scanned by THz human security system. First, the pretreatment methods, with binarization, filtering, filling, and morphological corrosion and expansion operations, were used to transfer the original THz image into a binary image, whose outline coordinates was later extracted by clockwise contour tracking algorithm. Then, the combinative application of circular template detection and non-minimal, non-maxima suppression algorithm were applied to calculate and select out all the convex and concave points in the extracted profile coordinates. Finally based on the grouping features of these adjacent convex and concave points, together with their distance constraints, the recognition of the edge objects(Objects covered the contour of human, etc.) could be realized. The experimental results, of testing 500 images of different people with different objects hiding on different edge position taking by the THz human security system, show that this algorithm represents quick identification and strong robustness, having the distinct advantages of strong anti-noise ability, high recognition speed and precision, and also it can match well the recognition accuracy of security system to achieve the system's resolution limit by adjusting proper parameters of the algorithm.
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