The optical system with variable F-number can simultaneously meet the requirements of sensitivity in wide field of view and the requirements of resolution in narrow field of view, and variable F-number infrared detector is an important part of the optical system. Due to the thermal contact resistance, the temperature of the diaphragms is much higher than that of the cold shield of traditional detector, which means the thermal radiation of the diaphragms would adversely affect the performance of the FPAs. Based on the radiation theory, the effect of thermal radiation of the diaphragms on the performance of FPAs was studied from response signal and NETD, respectively. Furthermore, a MW FPAs and a LW FPAs were calculated by the theory of this paper. The results suggest that the temperature of the diaphragms must be 197K or less if the variation of the performance of the MW FPAs does not exceed 10%. And the temperature of the diaphragms must be 152K or less if the variation of the performance of the LW FPAs does not exceed 10%. The research of this paper has certain guiding significance for the design of Dewar assembly with variable F-number.
The MMR (Micro Miniature Refrigerator) is a novel Joule-Thomson cryocooler manufactured by micro-machining technology, its axial length is significantly shorter than the traditional Joule-Thomson cryocoolers that are used in infrared detectors. So MMRs can greatly reduce the size of infrared detectors once they are successfully integrated. To study the working mechanism of MMRs a micro-channel flow calculation model is established considering the gas compressibility, the Joule-Thomson effect at the throttling section and the distributed Joule-Thomson effect along the micro channels and the calculation model is verified with experiments. The characteristics of heat transfer, micro-channel distribution and heat losses are further investigated, leading the model to describe the working condition of the MMR more correctly. The temperature and pressure distribution in the micro channels and the theoretical cooling performance of the MMR is thus obtained, and a set of MMR geometry parameters with superior theoretical cooling performance are acquired. Furthermore, a MMR prototype is fabricated, and a testing platform is built and the cooling performance of the prototype is experimentally studied. The experimental results agree well with the prediction of the calculation model. The MMR prototype achieves 110K and 119K cooling temperature under 10MPa N2 and Ar working condition, the cooling power reaches 231mW and 479mW, and the cool down time is 250s and 70s respectively. As a result, the cooling performance of the MMR prototype can meet the cool down requirement of infrared detectors, providing a new approach to infrared detectors’ miniaturization.
The vibration of a single-piston linear Stirling Cryocooler caused by the compressor operation seriously affects the component performance and imaging quality of the infrared detector, so in terms of vibration abatement, the use of a vibration absorber has become an important way of vibration damping. While during using the vibration absorber, the damping variation is an important factor affecting the vibration damping performance. Hence, through the experimental analysis of the damping variation of the vibration absorber, it is identified in this paper that the main reason for the damping variation is the variation of mass and amplitude of the vibration absorber, which affects the deformation of the plate spring and the internal friction energy dissipation of the material. It is discovered in the experiment that at the same amplitude, the damping variation is the most stable when the mass of the vibration absorber is 28.6g~36.4g and the amplitude is 1.6~2.1mm. In the end, a vibration-damping experiment is also carried out for the compressor using a vibration absorber with a mass of 33.1g. When the compressor operates at a working frequency of 75Hz and an input power of 6W, its vibration acceleration can be decreased from 42.274m/s2 before vibration damping to 3.047m/s2 .
The SC100H linear Stirling cryocooler is designed by Kunming Institute of Physics. The characteristics of the magnetic circuit of the moving magnet linear oscillation motor used in SC100H was analyzed by the theoretical and experimental methods. In this study, a theoretical model of the motor was established, and its structure was simplified for easy analysis and calculation. Using the equivalent circuit methods and principle of electromechanical energy conversion, the relationship between the thrust characteristic and relative position of the mover in the motor was analyzed. The thrust characteristics of the motor at different input currents were tested by a tension test system. The results were consistent with that predicted from the theoretical analysis. Taken together, this study provided a good basis for the design and optimization for the structure and operation parameters of the motor.
The moving magnet linear compressors are very popular in the tactical miniature stirling cryocoolers. The magnetic circuit of LFC3600 moving magnet linear compressor, manufactured by Kunming institute of Physics, was studied in this study. Three methods of the analysis theory, numerical calculation and experiment study were applied in the analysis process. The calculated formula of magnetic reluctance and magnetomotive force were given in theoretical analysis model. The magnetic flux density and magnetic flux line were analyzed in numerical analysis model. A testing method was designed to test the magnetic flux density of the linear compressor. When the piston of the motor was in the equilibrium position, the value of the magnetic flux density was at the maximum of 0.27T. The results were almost equal to the ones from numerical analysis.
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