Pyroelectric sensor is a kind of sensor, also known as human body infrared sensor, used for life burglar alarm, visitor notification, etc., the principle is to release the charge through the amplifier into a voltage output.
The piezoelectric ceramic dielectric can maintain a polarization state after being polarized, which is called spontaneous polarization. Spontaneous polarization decreases with increasing temperature and the temperature drops to zero at the Curie point. Therefore, when the material is exposed to infrared radiation and the temperature rises, the surface charge will decrease, which is equivalent to releasing a part of the charge, so it is called pyroelectric. The discharged charge is converted to a voltage output by an amplifier. This is how the pyroelectric sensor works.
When the radiation continues to act on the pyroelectric element and its surface charge is balanced, the charge is no longer released. Therefore, the pyroelectric sensor cannot detect constant infrared radiation.
Working principle: The human body has a constant body temperature, generally at 37 degrees, so it will emit infrared rays with a specific wavelength of about 10UM. Passive infrared probes work by detecting infrared rays of about 10UM emitted by the human body. The 10 UM infrared rays emitted by the human body are enhanced by the Philippine filter and collected on the infrared sensing source. The infrared sensing source usually adopts a pyroelectric element, which loses the charge balance when receiving the temperature change of the infrared radiation of the human body, and discharges the charge outward, and the subsequent circuit can generate an alarm signal after being detected and processed.
Pyroelectric effect: When some crystals are heated, an equal number of oppositely charged charges will be produced across the crystal. This phenomenon of polarization due to thermal changes is called pyroelectric effect.
Fresnel lens: According to the Fresnel principle, the Fresnel lens is divided into two types: refractive and reflective. Its role is to focus and refract (reflect) the pyroelectric infrared signal on the PIR. Second, the detection area is divided into a number of bright areas and dark areas, so that moving objects entering the detection area can produce a modified pyroelectric infrared signal on the PIR in the form of temperature changes, so that the PIR can generate a change electrical signal. The sensitivity of the pyroelectric human body infrared sensor (PIR) is greatly increased.