The pyroelectric infrared sensor detects infrared rays emitted by people or certain animals and converts them into electrical signal output. It is a new type of high-sensitivity infrared detection element that can detect infrared rays emitted by the human body. It can detect the change of infrared energy radiated by the human body in a non-contact form, and convert it into a voltage signal for output. It amplifies the output voltage signal to drive various control circuits, such as power switch control, anti-theft and fire alarm and so on.
a. Pyroelectric effect: When some crystals are heated, an equal number of charges with opposite signs will be generated at both ends of the crystal. This kind of electric polarization caused by thermal changes is called the pyroelectric effect.
b. When the temperature does not change, the bound charge on the spontaneous pole surface of the crystal is neutralized by free electrons from the air, and the spontaneous polarization moment cannot be expressed. When the temperature changes, the center of gravity of positive and negative charges in the crystal structure shifts relatively, the spontaneous polarization changes, and the charge depletion occurs on the crystal surface.
c. The pyroelectric infrared sensor uses the pyroelectric effect, which is a temperature-sensitive sensor.
d. When the pyroelectric sensor does not detect the human body radiation or the human body is still, due to the polarization of C1 and C2, the infrared light energy on C1 and C2 is equal and balanced, the photocurrent with opposite polarity and equal energy counteracts each other in the loop, there is no current in the loop and the sensor has no output.
e. When the people moves, the infrared radiation leads the two equivalent capacitances of the sensor sensitive unit to produce different polarization charges, and then the electric signal will be output. Therefore, this kind of sensor is only sensitive to the movement or motion of the human body, and is not sensitive to stationary.