PassiveInfrared Ray

It is mainly made of a material with high pyroelectric coefficient, such as lead zirconate titanate ceramics, lithium tantalate, triglyceride titanium sulfate, etc. to make the detection element with a size of 2*1mm. Install one or two detection elements in each detector, and connect the two detection elements in series with reverse polarity to suppress the interference caused by the rise of their own temperature. The detection element converts the detected and received infrared radiation into a weak voltage signal, which is amplified by the field effect tube installed in the probe and output outward. In order to improve the detection sensitivity of the detector and increase the detection distance, a Fresnel lens is generally installed in front of the detector. The lens is made of transparent plastic. The upper and lower parts of the lens are divided into several equal parts. It is a kind of lens with a special optical system. It can amplify the signal by more than 70 decibels in cooperation with the amplifying circuit, so that the movement of people within 20 meters can be measured.
The Fresnel lens uses the special optical principle of the lens to produce an alternating "blind zone" and "high-sensitivity zone" in front of the detector to improve its detection and reception sensitivity. When someone walks in front of the lens, the infrared rays emitted by the human body will alternate from the "blind area" to the "high sensitive area", so that the received infrared signal is input in the form of sudden strong and weak pulses, thereby strengthening its energy amplitude .
The central wavelength of infrared radiation radiated by the human body is 9~10--um, and the wavelength sensitivity of the detection element is almost stable in the range of 0.2~20--um. A window equipped with a filter lens is opened at the top of the sensor. The wavelength range of light that this filter can pass is 7~10--um, which is suitable for the detection of human infrared radiation, and other wavelengths of infrared rays are filtered. The sheet is absorbed, thus forming an infrared sensor specially used to detect human body radiation.