Application principle of pyroelectric infrared sensor in modern smart home

Pyroelectric human body infrared sensor is a kind of device that converts the infrared emitted by human or animal into electrical signal. It can be used to detect the existence of human body, so it is widely used in electronic products such as safety device, anti-theft alarm, induction door, automatic lamps and intelligent toys.

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Pyroelectric human body infrared sensor can detect the infrared emitted by human body, but the detection distance is relatively close, generally within 2m. In order to improve the detection distance, a Fresnel lens is usually installed in front of the light receiving surface of the sensor, which can make the detection distance reach more than 10m.

The lens is usually made of transparent plastic and is divided into several equal parts according to a certain manufacturing method. Fresnel lens has two functions: one is to focus the light; the other is to divide the detection area into several bright and dark areas. When a person enters a bright area of the detection area, the infrared light emitted by the human body is focused by the corresponding lens of the light area, and then irradiates to the sensitive element through the filter of the sensor, and the sensitive element generates voltage. When the person goes to the dark area, the infrared light of the human body cannot reach the sensitive element, and the voltage at both ends of the sensitive element will change, that is, the voltage at both ends of the sensitive element changes with the light The frequency of the output signal of the sensor is related to the speed of human moving between the light and dark areas in the detection range. The faster the moving speed is, the higher the frequency of the output signal is. If the person does not move within the detection range, the sensor will output a fixed voltage.