A new approach to shutterless operation of microbolometer based infrared cameras

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2021-2-03
Çavdar, Semih
This thesis presents an algorithm for the shutterless operation of microbolometer based infrared imaging systems. The active material of the microbolometer used in the thesis is vanadium oxide and it is produced in METU MEMS Center. The array size of the microbolometer is 480x640 and pixel pitch is 17 μm. The microbolometer has a CTIA type readout circuit which consists of detector and reference resistance. Voltage values are optimized at steady-state considering interactions between pixels in the focal plane array (FPA). An algorithm to find these interactions and optimum voltage values is proposed. Output distributions of the pixels obtained with the method are analyzed and residual nonuniformity (RNU) values are compared to standard methods which are sweep and binary search. These methods and the proposed algorithm are applied to five different samples. Improvement in the operability is observed and RNU values are decreased generally half of the value found with standard methods. A method is proposed to find optimum voltages for each 1 °C by using at least two calibration points although TCR of vanadium oxide material has nonlinear temperature characteristics. 2-point correction, which contains gain and offset coefficients, is used as the software-based correction to improve the uniformity. Gain and offset coefficients are modeled for temperature and a way to estimate these coefficients is presented. Temperature drift, which is used to explain alterations in pixel outputs against small temperature variations, is modeled for 1 °C interval and the temperature drift compensation method is also proposed. The proposed shutterless algorithm is applied to three different microbolometers for the temperature range between 0 °C to 50 °C. RNU values are kept below 1% with the algorithm and decreased down to around 0.5% at low temperatures. The PSNR values calculated from infrared images are about 50 dB. Temperature drift compensation provides good stability at the pixel outputs and maximum shift at the output is observed around 6%. The proposed algorithm decreases the number of required calibration temperatures down to 12 from 51 which means a lower calibration time of around 76%. It requires lower memory space about 84% of the standard method by decreasing the array number from 102 to 16. The results show that the proposed algorithm can be used in the shutterless application for microbolometers.

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Citation Formats
S. Çavdar, “A new approach to shutterless operation of microbolometer based infrared cameras,” M.S. - Master of Science, Middle East Technical University, 2021.