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:Colloidal PbS quantum dots (QDs) with spectral tunability through quantum size effects were synthesized by chemical solution. By controlling the reaction temperature and preparing proper precursor, we obtained QDs with first absorption peak varied from 833 nm to 1706 nm. The structures, size distribution, and absorption properties of the QDs were measured by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and absorption spectra. Results showed that PbS quantum dots had narrow size distributions with diameters in the range of 2.6～7.0 nm. Based on the near infrared absorption properties of PbS QDs, we fabricated FTO/TiO2/PbS/Au solar cells by controlling the surface properties of PbS QDs on TiO2 film deposited with atomic layer deposition (ALD) and studied the relation between the photocurrent and the characteristic absorption peak of QDs.
Abstract:A revised method to evaluate parameters of solar cell from current-voltage characteristics, under illuminated or non-illuminated conditions, was described. The series resistance(Rs), the shunt resistance(Rsh), the ideality factor(n), and the reverse saturation current density(J0) were extracted using the two diode circuit model from selected regions of the J-V curves. Using the presented model, more parameters with higher fitted precision have been extracted from experimental J-V curves of a CdS/CdTe thin film solar cell than using a single diode circuit one.
Abstract:Thermal characteristics of new substrate-free FPA (focal plane array) with full hollow supporting frame structure are very different from that of traditional substrate FPA. The thermal analysis model which based on temperature-constant substrate assumption is not efficient any more. Therefore, an equivalent circuit model was presented to analyze the thermal response characteristics of substrate-free FPA with electrics and holistic approach. According to this model, the thermal characteristics of substrate-free FPA under non-vacuum environment were analyzed. The result shows that, the substrate-free FPA has excellent infrared imaging performances under atmospheric pressure, while its NETD (noise equivalent temperature difference) is just increased several times than in the vacuum environment.
Abstract:In order to develop millimeter wave electric vacuum radiation source devices with field emission cold cathodes, the electron-optical system using a large area carbon nanotube cold cathode (CNCC) was investigated, which can generate an electron beam with large current and high current density. By adding a mesh grid on the cathode surface of a Pierce electron gun, problems of the electron bunching and high electric field applied to the CNCC surface have been solved. Based on the experimental results of a CNCC, the field emission model was built, by using PIC simulation software, to simulate the Pierce electron-optical system. The effect of the mesh grid on the electron beam has been analyzed. And the influence of the anode voltage and the axial magnetic field for the electron beam radius has been researched. The simulation results of the electron-optical system showed that when the area of cathode is 3.03 cm2, an electron beam with 210 mA at 60 kV can be produced. The current density is 6.7 A/cm2 and the maximum radius of the electron beam is 1 mm.
Abstract:A total output power of 25.5W was achieved after optimizing the transmissivity of the output mirror and the design of the output window in the middle infrared and long infrared dual-band (3～5 μm & 8～12 μm) laser driving by two glow discharge tubes. Power in either single band is greater than 10W. The transverse mode of DF and CO2 laser beam in the middle and long infrared band is TEM00 and TEM20, respectively. An output power of 15.4W was obtained for TEM00 fundamental mode selected with a Φ8mm diaphragm. The dual-band laser can work as light source for research of dual-band or multi-band infrared detector arrays and the related systems.
Abstract:To solve the problem of low interaction efficiency of harmonic gyrotrons, self-consistent theory was used to investigate the dependence of the interaction efficiency on three critical factors; cavity length (quality factor), electronic beam’s velocity ratio and operating voltage. It was found that high efficiency can be achieved by adjusting beam voltage and velocity ratio when the working magnetic field was located at the hard excitation region. Based on the self-consistent nonlinear theory, a W band second harmonic gyrotron oscillator was optimized. Particle in cell computation showed that the efficiency was up to 39.5% when the beam voltage and current was 37kV and 4A, respectively, with velocity spread of 3%.
Abstract:Based on the coupling wave theory and phase re-matching technique, a Q-band TE01-TE11 circular waveguide mode converter for transmitting high power microwave has been designed and analyzed by numerical calculation and simulation. Results of 4-period and 6-period mode converter are demonstrated in this paper. The numerical calculation show that maximum conversion efficiency is 98.82% and bandwidth is over 2.2GHz for 4-period structure. However, for the 6-period one, the maximum conversion efficiency is 99.89% and bandwidth is over 1.7GHz. It also presented the influence of the key parameters on the conversion efficiency. Simulated results from HFSS agreed well with the numerical calculation. Based on the theory and simulated results, a mode converter was fabricated and tested. It turned out that a pure TE11 mode was abtained.
Abstract:A new strong coupling multi-gap output structure has been developed as the output cavity of Ka band sheet beam klystrons. This structure has a better output coupling characteristics and better shape of electric field. Moreover, when the drift tube of the output cavity is cut-off in the operating frequency, an ideal field shape can be obtained as to support more efficient beam-wave interaction. An analysis of the distribution of the surface current supports the design theoretically. A stable output power curve can be observed at the center frequency by using particle-in-cell simulations, where the interaction efficiency is more than 50% and the 3dB bandwidth is about 75MHz.
Abstract:In accordance with the hot issues of infrared detection and guidance, an IR transmission process from target to sensitive array was established to explore the IR signatures of an anisotropic-isothermal sphere model. The energy probability density distribution function was employed to describe the energy intensity levels of sensitive array units. The energy distributions of detector units were abtained with the aid of the Monte Carlo Method. The relationship between target directional IR radiation characteristics and energy distributions on the sensitive array was revealed. It indicates that in the case of the equal hemispherical emissivity of far-field small targets, increasing the emissivity in the near-normal direction can appreciably enhance the IR intensity of the image-center unit and improve the IR intensity contrast among the image units.
Abstract:Dim small target detection problem in infrared complex background was formulated as a binary classification problem of background and target in the theoretical framework of Markov random field (MRF). Based on the posterior probability model of MRF, a method using prior information of target SCR (signal-to-clutter ratio) and local statistic characteristic of infrared image was proposed to construct the posterior probability model of observed image. The classic iterated conditional mode (ICM) was used to estimate the optimal labeling image. Simulation and experimental results show that the proposed algorithm effectively reduces the false labeling probability of background, while maintaining a high probability of correct labeling of target. In addition, for using image’s local statistic characteristic in modeling, the proposed algorithm also reduces the correlation between labeled results and model parameters which contributes to improvement on the convergence speed of estimating the optimal labeling.
Abstract:On the basis of the cardinalized probability hypothesis density (CPHD), track-before-detect (TBD) algorithm is able to effectively solve the detection and tracking of weak point target with unknown target number. A detailed study of the CPHD algorithm which starts from the standard CPHD filter to the practicalities of TBD is presented. The updated expression for calculating particle weight of CPHD-TBD algorithm was deduced. Meanwhile, according to the physical means of the target distribution of CPHD, its update calculation in TBD has been implemented. Ultimately the combination of the CPHD and TBD has been achieved. The method to use it was introduced. The CPHD-TBD algorithm changes the way of target number estimation essentially compared with the PHD-TBD, resulting in accurate information of target distributions. Simulation results demonstrated that the proposed algorithm can estimate the number and states of targets more stability and accurately than the existing PHD-TBD algorithm.
Abstract:The traditional methods for 3D building extraction from high resolution monoscopic SAR imagery extract the footprint from bright lines caused by double bounce between ground and wall, then estimate height from features such as layover, shadow etc. However, it is very common that bright lines of buildings with large aspect angles are unrecognizable in SAR imagery, which makes these traditional methods useless. A new method was proposed for 3D extraction of these kinds of buildings from a single high resolution amplitude SAR image. This method relies on the constraint of geometrical model, assuming a parallelepipedic 3D building model. The performance of this new method were validated on test SAR data over two urban area.
Abstract:Two nonlinear dimensionality reduction methods were proposed based on image Euclidean distance. Considering the physical characters of hyperspectral imagery, the methods introduced image Euclidean distance into traditional manifold dimensionality reduction. Compared with other methods, our methods have several advantages. The introduction of image Euclidean distance not only considers hyperspectral image’s spatial relationship, but also preserves the local feature of datasets well. Thus the proposed methods can discard efficiently the redundant information from both the spectral and spatial dimensions. The experiment results demonstrated that the proposed methods have higher classification accuracy than other methods when applied to hyperspectral image classification.
Abstract:One-dimensional compressive sensing measurement data based on Gaussian measurement matrix not only well retain sparse signal’s energy, but also inherited sparse signal’s direction information. However in the one-dimensional compression sensing model, direction information can not be applied to sparse signal reconstruction and examination. Two-dimensional compressive sensing model was proposed based on sparse features of change area in the remote sensing image. By use of energy and direction information, sparse signal reconstruction algorithm (2DOMP) was constructed based on two-dimensional compressed sensing. Theoretical analysis and experimental results demonstrated that signal reconstruction ability of 2DOMP algorithm is stronger than other methods. Meanwhile, the concepts of directional remote sensing and directional change are put forward based on the fact that very little measurement data are required to recovery sparse signal by compressive sensing.
Abstract:Based on the bio-optical properties of water constitute in the Taihu, Chaohu, Dianchi lake and Sanxia reservoir, bio-optical retrieval model for the suspended particle matter and chlorophyll-a were established according to the radiance transfer model and genetic optimization algorithm. The measured data in situ was used to test this optimized model. The results indicate that, the model can remove the influence of noise on the final retrieval precision in a certain degree. The retrieval precision of this model in the Taihu, Chaohu, Dianchi lake and Sanxia reservoir is different due to the variation of suspended particle matter and chlorophyll-a bio-optical properties. However, in general, this model can retrieve the concentration of suspended particle matter and chlorophyll-a with a preferable precision. Two parameters, mean absolutely percentage error (MAPE) and root mean square error (RMSE) which represent the retrieval precision of suspended particle matter, can reach to a value of 23% and 15.13mg/L, respectively (the number of sampling points is 228). The retrieval precision of chlorophyll-a (MAPE and RMSE) can reach to 26% and 17.68μg/L, respectively with the same number of sampling points.
Abstract:Panchromatic remote sensing image with high spatial resolution has been applied in military reconnaissance, ground surveillance and other areas. A simulation method for high spatial resolution panchromatic remote sensing image is presented .The data source of the simulation is a kind of the airship remote sensing image. The low-altitude wide-field images were classified according to typical surface features. Then these images and the multi-spectral images were fitted to different typical features. The high spatial resolution panchromatic simulation image was composed by the fitting results. The simulation precision was assessed. Compared with satellite panchromatic remote sensing images, high spatial resolution panchromatic simulation image has the same spatial resolution, panchromatic band, wide view and so on. This method provides accurate data source for the satellite panchromatic remote sensing image simulation.
Abstract:Conventional phase unwrapping methods will fail when the height variation of highly steep terrain exceeds half of the ambiguity height. In the millimeter-wave band, this problem is particularly severe. The three-baseline millimeter-wave InSAR phase unwrapping method based on cluster analysis was studied. In cluster analysis, isolating the peaks on the wave curve of the histogram is improved. The mask on the shadow cast by the steep terrain is proposed in order to improve the cluster analysis. The validity of the proposed method was testified by both simulation and an example of its application.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335