A Pyroelectric Infrared Sensor is a sensor that can detect infrared radiation or changes in infrared radiation and is widely used in security systems, electronic equipment, and automatic control systems. Its working principle is based on the pyroelectric effect of the material.

Pyroelectric effect refers to the weak electric charge generated by some materials when the temperature changes or the radiation energy changes, this effect is caused by the thermal vibration of atoms or molecules. The pyroelectric effect was first discovered by the German physicist Pierre Louis Antoine Becquerel in 1880. The researchers later discovered that the pyroelectric effect could be applied to infrared sensing technology.

Pyroelectric infrared sensor is usually composed of infrared sensing element, light filter, amplifier circuit and output circuit. It works as follows:

1. Material selection: The materials used in pyroelectric infrared sensors are usually some crystal materials that are more sensitive to infrared radiation, such as lithium triborate (LiTaO3), dual-polarized gallium arsenic (GaAs), lithium tantalate (LiNbO3) and so on. These materials have a large pyroelectric effect and can quickly generate an electric charge in response to radiation or temperature changes.

2. Detection mechanism: When infrared radiation or temperature changes act on the pyroelectric material, the atoms or molecules in the material begin to vibrate irregularly, which leads to the separation of positive and negative charges. The electrode structure in a pyroelectric sensor senses the resulting charge through changes in electromagnetic induction or potential distribution.

3. The role of the filter: pyroelectric sensors usually use a filter to select a specific infrared wavelength range. Filters block other wavelengths of light, allowing only specific infrared wavelengths to pass through. This can avoid the impact of stray light on the sensor, improve the sensitivity and reliability of the sensor.

4. Amplifier circuit and output circuit: the small electrical signal detected by the sensor needs to be amplified by the amplifier circuit to improve the signal-to-noise ratio of the sensor. The amplified signal is converted by the output circuit into a voltage or current signal that is actually available for controlling other electronic devices or for data processing.

In general, the working principle of pyroelectric infrared sensors is to convert infrared radiation or temperature changes into weak electrical signals through the pyroelectric effect of materials, and then process these signals through the filter, amplification circuit and output circuit to achieve the detection and measurement of infrared radiation or radiation changes.