Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
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Abstract:A gate-recessed AlGaN/GaN high electron mobility transistor (HEMT) on sapphire substrate having fmax of 200 GHz is reported. The gate-recessed device with a T-shaped gate exhibits a maximum drain current density of 1.1 A/mm, and a peak value of 421 mS/mm for extrinsic transconductance with minimum short-channel effects because of an InGaN back-barrier layer. A unity current gain cut off frequency(fT) of 30 GHz and a maximum oscillation frequency(fmax) of 105 GHz were obtained. After removing SiN by wet etching, the fT of the device increase from 30 GHZ to 50 GHz and the fmax increases from 105 GHz to 200 GHz, which are the results of lower Cgs and Cgd after removing of Si3N4.
Abstract:PbTe thin films on CdZnTe(111) substrates were epitaxially grown by Molecular Beam Epitaxy. Prototype photovoltaic mid-IR detectors were fabricated using ZnS thin films as insulated materials, In2O3 as transparent conductive thin films, and metallic In thin films as the Ohmic contact electrodes. The wavelength response of the detectors covers the range from 1.5 μm to 5.5 μm at 77 K, and the detectivity is higher than 2?1010 cm?Hz1/2W-1. The peak detectivity D*λ calculated using R0A data reaches 4.35?1010 cm?Hz1/2W-1 at 77 K. The cut-off wavelength blue shifts and the detectivity decreases as the measurement temperatures rise. The main factors that influence the detectivity and R0A parameters are discussed.
Abstract:InGaAs shortwave infrared focal plane array (FPA) has important application in space remote sensing. In this paper, a new design of readout integrated circuit (ROIC) is presented for a low-noise InGaAs FPA. In order to promote the signal-to-noise ratio, a new correlated double sampling (CDS) circuit is presented for eliminating KTC noise of integration capacitor (0.15 pF) in mode of integration while read. The circuit has been fabricated with 0.5 μm 5 V N-well CMOS process. Test results show that ROIC noise is 1.7?10-4 V and dynamic range is above 80 dB, working well after interfaced with InGaAs detectors.
Abstract:Very-narrow-gap HgCdTe single crystals were multicarrier semiconductor material with multiple electron and hole species in the conduction band. Especially, for p-type HgCdTe single crystals, the evaluation based on conventional measurements at a single magnetic field could lead to erroneous conclusions because of the large ratio of the electron mobility to hole mobility (b=μe/μh≈102). Variable-magnetic-field Hall measurements were performed on bulk-grown HgCdTe single crystals at various temperatures. The mobility spectrum analysis (MSA) technique were employed in this paper. An accurate determination of both the carriers type and the carriers mobility usually involves multicarrier characterization. At the same time, the effect of the autoxidation for the HgCdTe multicarrier system was investigated.
Abstract:The data requirements of all parameters on the performance test of infrared focal plane arrays (IRFPA) was analyzed, and then presented an efficient data acquisition method different from the traditional one. As a result of ADI latest high-performance 16-bit ADC and this new method, a high-efficiency high-accuracy data acquisition system was introduced. By the embedded RMS Hardware Algorithm and the particular combination of external SRAMs, this scheme is not only compatible with conventional test system, but also improves the efficiency of the test system greatly at the same time. Through experiments on HgCdTe 640?512(15 μm) IRFPA, the noise floor of the acquisition system is down to 75 μVrms and the calculation of various parameters can be completed in about 2 seconds. The data acquisition system is proved to be able to meet the demanding requirements for full IRFPA test and will have a great application prospect relatively to the traditional one.
Abstract:A land surface temperature (LST) retrieval algorithm called week-fixed-parameter method was proposed. The new method is achieved by week-fixed sensitive parameters so as to control information flow from MODIS thermal infrared data. Based on the thermal infrared radiative transfer theory, a forward retrieval model was established and 14 parameters were retrieved together. The retrieved parameters included LST, average temperature of atmosphere, six bands’ atmospheric transmittances and surface emissivities in mid-infrared(3~5 μm) and infrared(8~145 μm). The algorithm was tested with both MODTRAN simulated data and MODIS data. Compared with that of split-window algorithm, MODIS temperature products and ground truth, the RMSE is 0.57 K,which is better than that of traditional split-window algorithm. The test indicates that the weak-fixed-parameter method is effective to retrieve LST.
Abstract:The hyper-spectral reflectance of soil was measured by a ASD FieldSpec within 400～1000 nm, then treated with logarithmic transformation. First derivative of soil spectra with different scales of differential window were acquired and denoised by the threshold denoising method based on wavelet transform. From the first derivative of soil spectra, feature parameters used as indicators for soil organic matter content were extracted. Results show that: (1) When the number of the scale of differential window was set as W=1~5, it is difficult to identify the spectrum contour and response feature in first derivative of soil spectra because of much noise. (2) When W=6~15, noise in first derivative of soil spectra is partly removed, and spectrum contour is identified roughly. However spectral response feature resulted from different organic content levels can not be identified clearly. (3) When W=16~30, noise in first derivative of soil spectrua is removed effectively. The coefficient of correlation between organic matter content and feature parameter MD19s is 0.803. MD19s can be used as one of the best indicators for soil organic matter content.
Abstract:FengYun-2 geostationary spectral data consists of 5 channels that locate at visible, near infrared, water vapor and far infrared wavelength. Among these channels, the reflectance of near infrared bands at daytime is the function of cloud particle’s size and thermodynamic phase. The paper proposes a grouped detection method to identify cloud particle’s thermodynamic phase by reflectance of visible, near infrared bands, and brightness temperature of infrared bands. The identified cloud phase was compared with CloudSat products. The example analysis indicated that two kinds of data regarding consistent rate are higher than 97% for high layer ice cloud, including deep convection and cirrus. For low water clouds, the consistency of two kinds of data got 94.98%. It can clearly show the cloud system structure of tropical cyclone, including central convection cloud area, cirrus around and outside water cloud when using cloud thermodynamic phase identified method analysis the cloud properties of tropical cyclon.
Abstract:Different size distributions of aerosol, fog and rain collected. Atmospheric volume scattering intensity characteristics were calculated and analyzed according to Mie scattering theory. The results show that the energy of atmospheric volume scatter concentrated mainly in a narrow area of forward scatter angle. The distributions of volume scattering phase relied on particle size distributions, wavelength and complex refraction index, and was diverse for different type of particles. The atmospheric single scattering albedo was influenced by the wavelength and the imaginary of complex refractive index, and varied in a wide value range. The single scattering albedo of urban aerosols was less than that of fogs in the same wavelength. The single scattering albedo of urban aerosols and fogs were inversely proportional to the wavelength.
Abstract:When the real vegetation is composed of three layers, the accuracy of the traditional three-stage vegetation parameter inversion method becomes lower. To solve this problem, a new polarimetric SAR interferometric coherence model was established. Based on this new model, the reason why the accuracy of the tranditional three-stage vegetation parameter inversion method becomes lower was analyzed and a new vegetation parameter inversion method based on dual-baseline polarimetric SAR interferometry was proposed. Compared to the tranditional inversion method, this new method is more suitable to the three-layer vegetation constructions and has higher accuracy. Experimental results validated the correctness and the superiority of the new method.
Abstract:Based on the technologies of both object spectrum database and biological parametric models, the ground-object spectrum simulation signals were derived with the known LAI values. By use of computer simulation methods, effects of atmospheric condition and remote sensing detectors with assigned spectral sensitivity characteristics were simulated, and RS simulated signals on satellite level were produced. Furthermore, the performances of different sensors in detecting LAI were analyzed and compared, including CBERS-1, SPOT-1 HRV1, LANDSAT-5 TM and NOAA-14 AVHRR. Finally, on the criterion of LAI-detecting sensitivity, the paper designed and tested the best LAI-detecting band, and proposed the method of multiband remote sensing detector's parameter design based on digital simulated signal. The method has certain practical meanings in both the choices and optimums for sensor channels.
Abstract:A sub-harmonic mixer is presented with micro-strip at 3 mm wave length. The key device of the mixer is a pair of GaAs beam lead anti-parallel Schottky diode (type MS8251). According to the request of the local oscillator (LO), radio frequency (RF) and intermediate frequency (IF) networks of sub-harmonic mixer, the large signal impedance of anti-parallel diode pair, which is stimulated with the LO signal alone, is simulated by harmonic balance method firstly. The LO network is designed based on the result above. Then the small signal impedance of anti-parallel diode pair with LO stimulation is simulated and the RF network is designed. A 3 mm waveguide to micro-strip translation is also designed in the paper, and the sub-harmonic mixer is fabricated on the RF-Duroid 5880 with 0.127 mm thick and dielectric constant εr of 2.22. According to the measurement result, the conversion loss which is lower than 15 dB is achieved with the RF ranged from 90 GHz to 95 GHz and the LO frequency of 46.3 GHz.
Abstract:This paper presents a new waveguide-based spatial power combining amplifier at millimeter-wave frequency. In this amplifier, a waveguide-microstrip spatial power dividing/combining network is adopted. A four-way broadband low loss symmetrical power dividing/combining is achieved at millimeter-wave frequency with an easy manufacture processing and convenience of integrating solid-state high power devices. The measured output power of this amplifier is more than 43.4 dBm in 29～31 GHz, and the corresponding power combining efficiency is more than 80%. The obtained output power is more than 25 W in 30~30.6 GHz.
Abstract:We report the design of a wide-band and quasi-omnidirectional tabulate metamaterial absorber in the terahertz regime. Simulated results indicate that the We report the design of a wide-band and quasi-omnidirectional tabulate metamaterial absorber in the terahertz regime. Simulated results indicate that the absorber has a wide-band strong absorption between 4.36 and 4.91 THz, which is polarization insensitive and wide incident angle. Retrieved real parts of the impedance show that by adjusting the electromagnetic response of the metamaterial, the impedance of the absorber could be tuned to match approximatively the impedance of the free space on one side and do not match to the impedance of the free space on the other side, resulting in the minimal reflectance, the minimal transmission and the highest absorbance in the absorption band. Simulated absorbance values under three different loss conditions suggest that high absorbance is mainly due to metallic absorption and dielectric loss can be used to absorb partial energy if there is no metallic absorption. Simulated absorbance values under different electric conductivity values and copper thicknesses suggest that the intensity of metallic absorption can be boosted up by adopting metal of high conductivity or reducing the thickness of metal properly. This absorber may have broad applications in many scientific and technological fields.
Abstract:Multiple visual sensor fusion provides an effective way to improve the robustness and accuracy of visual surveillance system. This paper gives a review of moving object detection with visual-thermal fusion. Firstly, the problem is analyzed, including its procedure, key problems, advantages, testing data sets. Then the existing algorithms are analyzed according to several different rules: fusion strategy, detection method and fusion structure. By comparing different kinds of methods, we analyzed the advantage, disadvantage and applicability. Finally we conclude with discussion on difficulties, challenges and possible future research directions of this kind of method.
Abstract:This paper has proved the data fitting and extrapolating ability of the kernel-driven model in TIR band by simulation of the multi-angle thermal infrared images of Linze grassland acquired in WATER campaign with the model. Additionally, the most suitable kernel-driven model available for multi-angle thermal imagery has been identified. In the feature space of land surface temperature (LST) and a combination of model coefficients which describes the actual surface directional radiative characteristics, a multi-angle thermal infrared dryness index (MTDI) is constructed and extracted out. The correlation coefficient of simulated MTDI and corresponding Temperature-Vegetation Dryness Index (TVDI) is greater than 0.87. It can be inferred that the kernel driven model is also effective in the analysis of directional radiative information in thermal infrared band.
Abstract:The shock layer of high-speed missiles is composed of gas medium with highly uneven temperature distribution. A model for the radiative heat transfer in this layer was developed. With the method of discrete transfer and the model of light transmission, the heat radiation strength of the shock layer was calculated by the line of sight along the seeker detectors. The relations between the shock wave thermal radiation noise and flow parameters were also analyzed and the empirical formula is given. The results showed that for 3~8 μm infrared band, the thermal radiation noise and the Mach number is closely related. The radiation alters very little with the change of flight height (in atmosphere).
Abstract:As the conventional evolutionary clustering optimization methods are often time-consuming and easy to trap in local optimal value in dealing with the problem of change detection. Furthermore, it can not detect the edge accurately for SAR images. We proposed a method for change detection in SAR images based on the clustering analysis. The proposed method takes gray-levels as an input, uses the quantum bit to define the clustering center, searches the optimal cluster center using the quantum-inspired immune clonal algorithm, and gets the global threshold. Finally, the change-detection map is produced. Compared with K&I threshold, it can achieve a better value. Compared with Genetic Algorithm Based Clustering (GAC), the proposed method can search a much better clustering center quickly and effectively. Besides, it can detect the accurate edge and improve the change detection accuracy.
Abstract:A 2mm-band frequency tripler built on quartz was formed by anti-parallel Schottky-barrier varactor diode pair. Its equivalent circuit model had been built and the component parameters were obtained. Then the tripler was designed and realized. Its input signal was fed in by a K connector, and the output signal was fed out by a WR-8 waveguide. When the output signal frequency is between 112.8 GHz and 118.2 GHz, the best conversion loss is 16 dB and the output power is larger than 0 dBm with maximum 2.05 dBm at 118 GHz. The tripler module can supply good local oscillation source for the meteorological measurements.
Abstract:High-resolution time synchronization is the crucial technology of quantum key distribution experiment from ground to satellite. A new scheme of time synchronization was presented. In this scheme, a synchronous pulse which has the same wavelength with the quantum signal was adopted and single photo detector was used to detect the synchronous pulse. High-resolution time measurement module was used to measure the instance of synchronous pulse and signal pulse. This scheme overcomes the problem that the the synchronization laser requires much more resources of satellite and the isolation between the synchronization pulse and quantum single pulse. This system was successfully applied to the 16 km quantum key distribution in free space channel. Synchronous resolution of the system is 1.023 ns and bit rate of the raw key for the quantum key distribution is 8.27 kHz.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335