Infrared sensors can be divided into:

(1) A heat type that converts a part of infrared rays into heat, and uses the heat to extract output signals such as resistance changes and electromotive force.

(2) Photoelectric effect of absorbing energy difference using semiconductor migration phenomenon and quantum type using photoelectromotive force effect due to PN junction.

The thermal phenomenon is commonly known as the pyrothermal effect, among which the most representative ones include Thermal Bolometer, Thermopile and Pyroelectric elements.

The advantages of the thermal type are: it can be operated at room temperature, the wavelength dependence (the sensitivity of different wavelengths has a great change) does not exist, and the cost is cheap;

Disadvantages: low sensitivity, slow response (mS spectrum).

Advantages of quantum type: high sensitivity, fast response (spectrum of μS);

Disadvantages: must be cooled (liquid nitrogen), wavelength dependence, high price;

Infrared sensors, in particular, use the sensitivity in the far-infrared range for human detection. Infrared wavelengths are longer than visible light and shorter than radio waves. Infrared rays make people think that they are only emitted by hot objects, but this is not the case. All objects in nature, such as humans, fire, ice, etc., all emit infrared rays, but their wavelengths are different depending on the temperature of the object. . The body temperature of the human body is about 36-37°C, which emits far infrared rays with a peak value of 9-10μm, and objects heated to 400-700°C can emit intermediate infrared rays with a peak value of 3-5μm.