Youtang Gao

Model for the brightness uniformity of fluorescence screen of image intensifier

The three elements of photoelectrical cathode, microchannel plate and fluorescence screen are important parts to imaging quality of low light and ultraviolet Image intensifier. To do research and analysis work on the Fluorescence screen parameter testing have practical significance to the understanding of the performance of fluorescence screen and then can help to know where improvement should be made and then achieve a best performance entire tube, This article mainly introduce the testing theory of the brightness uniformity of fluorescence screen of Image Intensifier and how to build a mathematic model.

Study of photoemission mechanism for varied doping GaN photocathode

Negative electron affinity (NEA) GaN photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive threshold and so on. The quantum efficiency is an important parameter for the preparation and evaluation of NEA GaN photocathode. The varied doping GaN photocathode has the directional inside electric field within the material, so the higher quantum efficiency can be obtained. The varied doping NEA GaN photocathode has better photoemission performance. According to the photoemission theory of NEA GaN photocathode, the quantum efficiency formulas for uniform doping and varied doping NEA GaN photocathodes were given. In the certain condition, the quantum efficiency formula for varied doping GaN photocathode consists with the uniform doping. The activation experiment was finished for varied doping GaN photocathode. The cleaning method and technics for varied doping GaN photocathode were given in detail. To get an atom clean surface, the heat cleaning must be done after the chemical cleaning. Using the activation and evaluation system for NEA photocathode, the varied doping GaN photocathode was activated with Cs and O, and the photocurrent curve for varied doping GaN photocathode was gotten.

Research on the performance of thermal shock and stress with infrared optical domes

The development of infrared optical materials is always closely related to the research and exploration of material science. The infrared optical domes bears shock and produces stress when the infrared optical domes mounted on the missile moving at a high speed is shocked by high temperature. According to aerodynamics theory and thermo shock theory, the surge current will be transferred to optical parts through holding up layer and warms the surface of optical parts when infrared optical parts are shocked by high temperature. A compress stress is formed on the hot external surface of optical parts forms and a tension stress is formed on the internal surface or optical parts under the circumstance of the edge of optical parts being fixed. The windows of optical parts become curvature radius of lens with the function of pressure difference which can cause aberration change. The brittle fracture of material will be caused if peak stress is beyond the strength which is permitted for infrared materials. Therefore, limits to design of windows thickness is proposed in this paper.

Analysis of thermal shock strength and quality factor with infrared optical domes

The development of infrared optical materials is always closely related to the research and exploration of material science. The infrared optical domes bears shock and produces stress when the infrared optical domes mounted on the missile moving at a high speed is shocked by high temperature. According to principle of energy balance in fracture mechanics proposed by D.P.H. Hasselman, the author analyzed the crack extension and derived the relationship between Infrared optical materials window model and thermal shock quality factor. Meanwhile, strong or weak of thermal shock for different samples whether they are thin or thick are compared through the operation of queuing algorithm. The conclusion is the internal surface of the domes isn’t heated when the window model is the thermal shock quality factor of thick sample and the heating time is between heating time constant and diffusion time constant. On the other hand, the internal surface of the domes is being heated when the window model is the thermal shock quality factor of thin sample and the heating time is between the two time constants. The most optical domes parts in practice is belong the thin model. For the thin model, reducing the thickness of optical parts can improve their thermal shock ability but mechanical impact stress factor should be considered comprehensively to design optical parts.

Noise research of microbolometer array under temperature environment

Thermal noise and steady performance of infrared sight has always been the concern of military production under temperature test conditions. According to military optical instrument environmental test standard of GJB1788-93 and MIL-STD-810F in infrared detector test method, the test procedure and test method of 320×240 α-Si micro-bolometer array of UL01011-type were given in detail. By using thermal noise theory and mathematical model analysis method, the noise models of Johnson noise, 1/ f noise, noise caused by electrothermal effect in temperature shock test condition, preamplifier noise and other noise models of micro-bolometer array were established and analyzed. Noise models under temperature environment were analyzed. The results are as follows: the basic noise of micro-bolometer array is the temperature fluctuating noise (thermal noise) which consists of background radiation fluctuation noise and thermal conductivity noise. In addition, there is Johnson noise, 1/ f noise, noise caused by electrothermal effect and preamplifier noise etc. Among them thermal noise, Johnson noise and 1/ f noise is the main noise source which determines the limited performances of micro-bolometer array.

Motion detection and estimation in low-level-light video sequence

This article introduces motion detection and estimation of low-level-light video sequence, and, motion detection, motion estimation and variational problem. Low-level-light video sequence different form others, the time and space domain noise in the signal not only limit the lowest illuminance of the system but also make the image show random glitter. In this paper how to improve the signal-to-noise ratio (SNR) of low light level image is discussed too. The results show that models and estimation algorithms in low-level-light video sequence can lead to improve reliability and accuracy of the estimated motion.

Averaging algorithm of reticle images in low-level-light weapon sight based on impact condition

The novel approach to the image noise problem of reticle images based on impact condition in low-level-light weapon sight is proposed in this paper. The condition and process of the low-level-light weapon sight impact experiment were analyzed, and then averaging algorithm of reticle images consists of two parts has been applied on the experiment. First averaging and smoothing using a rotating mask methods were operated on Gaussian noise, to obtain a matching precision with in 0.05 mil. Second the well known efficient median filtering smoothing method is performed to obtain the higher matching precision. The potential of this averaging method is shown in the experimental results of reticle images in low-level-light weapon sight based on impact condition.

Iterative infrared image restoration

Iterative infrared image restoration is concerned with the improvement of infrared imagery acquired in the presence of varying degradations. The degradations can arise from a variety of factors: common examples include undersampling of the infrared image data, uncontrolled platform or scene motion, system aberrations and instabilities, noise characteristic of the infrared detector. In this paper, the mathematic models of infrared image blur and sampling and noise models are discussed. The iterative infrared image restoration problem is discussed, too. We show the origin and restoration infrared images which are used in the application of iterative infrared image restoration. By assessing subjectively and objectively to restoration infrared images, we have verified this kind of model and the feasibility of the iterative infrared image restoration.

A kind of real-time infrared image enhancement algorithm

A new algorithm which is suitable for FPGA to the real-time infrared image enhancement is proposed in this paper. In order to reduce Infrared image noise, we use the accumulation of the combining sequential neighbor frames, and use the nonlinear expanding of gray histogram to enhance contrast ratio. This kind of algorithm has considered infrared image characteristic and vision characteristic of the human eye synthetically, and guarantee real-time character of image process, at the same time, also give consideration to the advantage of the FPGA design. This method can be realized easily on hardware without damaged enhancement result. Finally, quality of enhanced image is evaluated through a model. It has verified the enhancement result of this kind of algorithm, and offered reliable assurance for further treatment of the infrared image. Use in the image system of the infrared video, the effect of image Enhancement is obvious.

Thermal research of infrared sight signal processing circuit board under temperature shock environment

Thermal stability technology of signal processing circuit infrared sight is studied under temperature shock. Model parameters and geometry is configured for FPGA devices (EP1C20F400C8), solder material and PCB. Signal circuit boards of full array BGA distribution are simulated and analyzed by thermal shock and waveform through engineering finite element analysis software. Because solders of the whole model have strong stress along Y direction, initial stress constraints along Y direction are primarily considered when the partial model of single solder is imposed by thermal load. When absolute thermal loads stresses of diagonal nodes with maximum strains are separated from the whole model, interpolation is processed according to thermal loads circulation. Plastic strains and thermal stresses of nodes in both sides of partial model are obtained. The analysis results indicate that with thermal load circulation, maximum forces of each circulation along Y direction are increasingly enlarged and with the accumulation of plastic strains of danger point, the composition will become invalid in the end.