Abstract:Conductivity type conversion (CTC) describes the process resulting in a p-to-n or n-to-p conductivity change in doped or unintentionally doped mercury cadmium telluride (MCT) materials. The thorough understanding of CTC mechanisms involves the knowledge of diverse fields of electrical science, physics, chemistry and etc.. The related progress to date has been primarily empirical. By summarizing and analyzing some related papers published in recent years, this review describes the MCT/CTC research progress of MCT/CTC with emphasis on ion beam milling techniques.

Abstract:The non-dispersive infrared gas analysis technique and its application in sulfur dioxide measurement are presented. The absorbance acquisition and concentration retrieval in non-dispersion sulfur dioxide analysis are analyzed. By taking the third-order polynomial as a fitting model, the calibration curve is obtained with the nonlinear least-square. The measurement accuracy of the system is analyzed and the measurement error less than 2 \% is derived. The result shows that the non-dispersive infrared technique can measure the sulfur dioxide accurately and it can also be used in the analysis of other gases.

Abstract:To study the optical path difference of a ray passing through a Fourier Transform infrared spectroscopy (FTIR), the symmetric analysis and geometrical optics methods are used to analyze the optical path expression when the ray is passing through one to three plates and a general optical path expression when a ray is passing through arbitrary plates is derived. On the basis of above analysis, the accurate expression of the optical path difference reduced by two arms of a Michelson interferometer with respect to the incident angle is analyzed. Finally, the condition for field widening is given. This research is of great significance to the design of a wide field FTIR.

Abstract:A pyroelectric infrared sensor equiped with a multiple reflection optical device was used to receive the infrared radiation emitted from a human body. By collecting and analyzing the signatures of the analog signals outputted from the pyroelectric infrared sensor, the location information of the human body could be extracted. When a person was passing through the area to be observed at a different distance from the infrared sensing node, the maximum peak of the infrared signal would be decreased with the increasing of the distance from the person to the infrared sensing node. A novel method for target localization based on the maximum peak of infrared signals outputted from the pyroelectric infrared sensor was designed. Compared with the centroid localization algorithm, the maximum localization error of this method was reduced by 87.89 %.

Abstract:According to the characteristics of THz images, some digital image processing methods such as threshold division and edge detection are used to segment the pistol from a THz image. Then, the effective signatures of the pistol are extracted and automatic recognition and judgment are implemented on the image. If hazardous or suspicious goods are found, an alarm signal is generated. The experimental result shows that this method can effectively discriminate the pistols concealed in clothes from other metal goods such as pens, keys and ornaments which people usually carry. It can be used to automatically identify the contraband goods such as pistols in the THz images in a security check.

Abstract:The characteristics of terahertz (THz) radiation of small-aperture spiral photoconductive antennas are studied. By using the THz time-domain spectroscopy to measure the THz radiation spectra of a spiral photoconductive antenna, its time-domain emission spectra are obtained. Then, the corresponding frequency domain spectra are obtained via fast Fourier transform. At the same time, the THz radiation characteristics of two spiral photoconductive antennas with different apertures are compared with each other. The experimental result shows that the intensity of a THz signal can be enhanced with the increase of bias voltage. For same bias voltage and pump power, the photoconductive antenna with a smaller aperture has a higher radiation power.

Abstract:This paper is aim to estimate SPAD value of apple leaf using hyperspectral red edge parameters. With Fuji apple leaf of different phenophase as the research object, hyperspectral reflectance and SPAD value were measured by the ASD FieldSpec 3 spectrometer and the chlorophyll meter SPAD-502, respectively. The hyperspectral characteristic and variation rule of SPAD value were analyzed to florescence, spring shoots pause growth period, autumn shoots pause growth period and maturity period of apple. The correlations between the red edge parameters and apple leaf SPAD values were studied. The estimating models for apple leaf SPAD value were established. The results showed that the variation rules of reflectance curve waveform of apple leaf were similar to different phenophase.The leaf SPAD value increased gradually from the start of florescence and reached to the peak in the autumn shoots pause growth period, and then began to decline. The experience estimating models were established between the hyperspectral red edge parameter λr and leaf SPAD value and the correcting models were built to leaf SPAD value based on partial least squares in different phenophase. The best estimating effects of their models were the autumn shoots pause growth period. The test accuracy of their models was 94.2%, and 96.7%。The stability and precision of apple leaf SPAD value estimation model is higher by partial least squares. This study provided theoretical basis and technical support in the application of apple leaf chlorophyll content using hyperspectral remote sensing for the rapid, non-destructive estimation, nutrition diagnosis and efficient management.

Abstract:The non-invasive lubricant acid value measurement method based on a visible and near-infrared spectroscopy is studied. The visible and near-infrared spectra of the lubricant in the region from 475 nm to 975 nm are obtained. A visible and near-infrared spectral detection model is established by using a least square support vector machine. By combining the uninformative variable elimination with the successive projection algorithm, effective spectral wavelengths are selected. Among the 500 variables, only eight wavelength variables namely 498 nm, 553 nm, 591 nm, 874 nm, 893 nm, 910 nm, 935 nm and 951 nm are selected. The least square support vector machine model based on those eight wavelength variables has obtained a prediction set of 0.9546, a root mean square error of 0.0081 and a residual predictive deviation of 4.5663. This prediction result shows that the visible and near-infrared spectroscopy can be used to measure the acid value of lubricant non-invasively. Compared with the standard acid value measurement method, it has the advantages of fastness, non-invasion and low cost. Meanwhile, it is also an effective algorithm for spectral variable selection.