Owing to the unique features of passive sensing, low cost, large detection range and wide field of view (FOV), the pyroelectric infrared (PIR) sensors are widely used for smart home applications based on motion detection, such as light control, intrusion detection. However, due to the pyroelectricity on which their sensing principles are based, PIR sensors cannot detect stationary objects, which confines their applications to advanced sensing systems, e.g. stationary occupancy sensing. To address this issue, this paper develops a novel chopped PIR (C-PIR) sensor for detecting the presence of both moving and stationary occupants, which consists of a chopper, a servo motor, a Fresnel lens, PIR sensing elements and a controller. Theoretical analysis is conducted to reveal the working principles of the proposed C-PIR sensor. A prototype of the C-PIR sensor is fabricated and experiments are conducted to find the optimal option of the chopper material, and the optimal values of the thickness, and the chopping frequency. Results show that the proposed C-PIR sensor can sense human presence no matter if the occupant is moving or not. In experiments, the preliminary prototype shows its detection range up to 4.0 m for stationary occupant sensing and 8.5 m for moving occupant sensing. Meanwhile, the C-PIR sensor maintains the same performance of the field of view as its traditional PIR sensor counterpart. Thus, the C-PIR sensor has great potential to provide accurate occupancy information for smart building energy management.

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