The Absorbing Layers, Radiation Modulation And Micro-scanning Of Pyroelectric Detectors

The advantages of pyroelectric detectors make them widely used in the field ofdetection and security. Generally, a pyroelectric detector consists of infrared lens,absorbing layers, choppers, focal plane array, and readout circuit and so on. Theabsorbing layers is to translate the infrared radiation of objects to temperature change,so an ideal absorbing layer will absorb all the radiation; pyroelectric detectors arefundamentally ac. coupled devices, requiring the scene radiation to change, usually bymodulation through a chopper at field rate, before impinging on the detector area;micro-scanning is a new emerging technology that can improve the spatial resolutionand decreasing frequency aliasing. This paper focus on these aspects and the contentsare as followings:Firstly, the commonly used absorbing layers in infrared detectors are introduced,we choose the composite multilayer films as absorbers in consideration of the cost andtechnical difficulty. This kind of absorber usually places the thin metal film onequarter of wavelength in front of an opaque, reflecting metal film via a dielectric layer.This optical cavity is capable of absorbing nearly100%of the incident radiation atone wavelength, but the total average absorption is not ideal. We have expanded onthis configuration by adding a dielectric layer in front of the thin metal film, whichprotects the thin metal layer from abrasion and corrosion and can greatly broaden the region of high-IR absorption. The average absorption can be as much as98%amongthe wavelength of7~14microns.Secondly, I have a summery on the radiation modulation technology and analyzedtheir advantages and disadvantages. For the commonly used Archimedes spiral shapedchopper, I proposed the method to calculate its influence on the exposure time andexposure sequence of pixels in FPA, which pave the way for choosing the reasonableparameters of the chopper.Thirdly, for the micro-scanning part, it’s easy to find the way to choose the exactshape and tilt angle of the plates of the Archimedes spiral shaped micro-scanner. Ihave calculated the exposure sequence of the pixels in order to obtain the differencebetween their real exposure time, which will do help the subsequent imageprocessing.My work is of practical value for focusing on the pyroelectic detectors.