What do Passive Infrared (PIR) sensors, often pyroelectric, primarily look for in a moving target?
The change in the IR signature caused by a person moving across their field of view.
Passive Infrared (PIR) sensors are a specific and common application of quantum detectors, typically utilizing pyroelectric materials for operation, especially in security systems. A pyroelectric material generates an electrical charge specifically when its temperature undergoes a change. Therefore, PIR sensors are often optimized not to measure the absolute temperature of an object but rather to detect the *rate of change* in the infrared energy incident upon them. As a warm body, like a person, moves across the sensor's field of view, it causes rapid fluctuations in the incident IR energy across the sensor elements, which the pyroelectric material detects as a change in temperature, triggering the alarm.
