Performance Optimization of the SLEEPIR Sensor Towards Indoor Stationary Occupancy Detection

To enable passive infrared (PIR) sensors to detect stationary occupants, we recently invented a synchronized low energy electronically chopped PIR (SLEEPIR) sensor consisting of PIR sensor, a polymer dispersed liquid crystal (PDLC) infrared shutter and a driving circuit. By electrically chopping the long-wave infrared (8-
$12~\mu \text{m}$
) radiation received by the PIR sensor, the SLEEPIR sensor can detection both stationary and moving occupants. In this paper, we developed a theoretic model to better understand the output of the SLEEPIR) sensor, and thus optimize its fabrication process and detection performance. The model indicated that its performance is mainly depending on the effective modulation and response time of the PDLC shutter in addition to the time constants of the PIR sensor. We empirically found that the effective modulation and response time are largely dependent on the frequency and amplitude of the driving signal, as well as the mass ratio, cell gap and cooling rate of the PDLC shutter. In the end we obtained optimized parameters that can produce the maximal SLEEPIR output, and experimentally validated our obtained optimal parameters and fabrication conditions.