Study On Miniaturization Of Image Intensifier And Analysis Of Refrigeration Performance

Image intensifier is a kind of imaging device detecting weak light. It's commonly used to detect weak light signals and transient optical signals. Through optical-electric conversion in photocathode, multiplication in microchannel plate (MCP) and electric-optical imaging in anode, image intensifier can amplify very weak light signal (usually invisible and transient) to a signal we can directly observe. Nowadays, image intensifier is very popular in many fields such as military, astronomy, public security, police, biomedical etc. According to the requirement in many practical applications, the trends is to develop image intensifier with higher sensitivity, higher resolution and compact size. The research result shows that photocathode thermal noise takes up almost 90% of total noise of the image intensifier. So reducing the temperature of photocathode to inhibit the thermal noise is essential to improve the performance of image intensifier.Based on the SJTU-I image intensifier, the work of this thesis mainly focuses on two points: 1. Design and implementation of portable image intensifier. 2. Study on the performance of refrigeration and noise inhibitation.In order to make the image intensifier system more compact, we take steps as follows: 1. Choose semiconductor refrigeration as the mean of photocathode refrigeration due to its advantages such as small volume, fast response, high control accuracy and so on. 2. Design a spindle type heat sink and use it to dissipate heat with cooling fans instead of water cooling. As a result, some parts with large volume such as water pump and refrigerator can be removed. 3. Design a drive chassis and image intensifier shell. Drive chassis supplies all inputs the image intensifier needs and the shell includes other function elements such as pulse-produce circuit, high voltage model and refrigeration system. In order to make the shell as small as possible, we customize the high voltage models with small volume and design the pulse-produce circuit on a 35mm?35mm printed circuit board.In order to find out if our design can meet the requirement, we use commercial software COMSOL to simulate the refrigeration system performance with the spindle type heat sink. The simulation result shows that photocathode can reach -5.91℃(the minimum temperature)when the work voltage of the semiconductor refrigeration piece is around 6V. We test the actual performance of system. It is found that the optimal work voltage of the semiconductor refrigeration piece is between 6V and 7V. Under the optimal voltage, temperature of photocathode can decrease from 21℃to below zero and finally become stable around 4℃. This performance meets the project requirement. Under this situation, photocathode noise decreases 5.87dB.There are some possible ways to further improve the refrigeration performance of the image intensifier. 1. Use two-stage semiconductor refrigeration piece instead of one-stage one. 2. Enlarge the speed of the cooling fans. 3. Improve the material of heat sink and the shell structure design. In order to find how much the first two ways affect on the refrigeration performance, we simulate these situations in COMSOL. The results show that: 1. The refrigeration performance using two-stage semiconductor refrigeration is much better than that using only one-stage. The performance is best when the voltage of the first-stage is 3.5V and the voltage of the second-stage is 5V. The minimum temperature can reach -23.81℃. 2. Faster speed of the cooling fans brings more efficient refrigeration, especially when the voltage of the semiconductor refrigeration piece is high.