SLEEPIR: Synchronized Low-Energy Electronically Chopped PIR Sensor for True Presence Detection

Passive infrared (PIR) sensors are widely used in motion sensing and lighting control. However, stationary occupants always trigger false-negative detects of PIR sensors and result in uncomfortable lighting swings and short lifetime of electronic appliances. To address this issue, a synchronized low-energy electronically chopped PIR (SLEEPIR) sensor is developed in this letter for true presence detection, where a liquid crystal (LC) optical shutter is proposed to electrically chop signals received by the PIR sensor in the long-wave infrared (LWIR) region (8-12 μm), where human skin radiates the most. Utilizing the anisotropic absorption property of the LC material, the shutter shows high modulation with a low driving voltage (V
_rms
= 4.17 V). Instead of using the mechanical shutters previously developed by our group that are driven by motors, the SLEEPIR sensor reduces the power consumption,weight, volume, and noise level by 90.5%, 83.8%, 82.6%, and 100%, respectively, while maintaining high sensitivity and reliability. Thanks to the high modulation of the LC shutter in the LWIR region, the experimental results show that the SLEEPIR sensor could detect stationary occupants with high accuracy within the range of 4.0 m and with a large field-of-view of 100°.