Do You Know the Types of Infrared Sensors?(2)

According to the different ways of energy conversion, infrared sensors can be divided into photon type and pyroelectric type.

Photon infrared sensor

Photon infrared sensor is a sensor that works by using the photon effect of infrared radiation. The so-called photon effect refers to that when the infrared ray is incident on some semiconductor materials, the photon flow in infrared radiation interacts with electrons in semiconductor materials, changing the energy state of electrons, thus causing various electrical phenomena.

By measuring the changes in electronic properties in semiconductor materials, we can know the strength of the corresponding infrared radiation. The types of photon detectors mainly include inner photodetectors, outer photodetectors, free carrier detectors, QWIP quantum well detectors, etc.

The main characteristics of a photon detector are high sensitivity, fast response speed, and high response frequency, but the disadvantage is that the detection band is narrow and generally works at low temperature (to maintain high sensitivity, liquid nitrogen or thermoelectric refrigeration are often used to cool the photon detector to a lower working temperature).

Pyroelectric infrared sensor

The pyroelectric infrared sensor uses the thermal effect of infrared radiation to cause the temperature change of the component itself to detect some parameters. Its detection rate and response speed are not as good as the photon sensor.

However, because it can be used at room temperature and its sensitivity is independent of wavelength, it has a wide range of applications. Pyroelectric infrared sensors based on the pyroelectric effect of ferroelectrics have high sensitivity and have been widely used.

The pyroelectric effect when some insulating materials are heated, with the rise of temperature, an equal number of charges with opposite symbols will be generated at both ends of the crystal. This kind of polarization caused by thermal change is called the pyroelectric effect. The pyroelectric effect has been used in pyroelectric infrared sensors in recent ten years. The crystal that can produce a pyroelectric effect is called pyroelectric, also known as a thermoelectric element. Materials commonly used in thermoelectric components include single crystal, piezoelectric ceramics, and polymer films.

The structure of pyroelectric infrared sensor consists of the following four main parts:

① Aluminum substrate and field effect transistor (FET) constituting the circuit;

② Ceramic materials with pyroelectric effect;

③ Window materials that limit the incident infrared wavelength;

④ Shell TO-5 type pipe cap and socket.

When the detector element is used alone, it has the shortcomings of short detection distance and difficulty to deal with the subsequent circuit of the obtained signal. Therefore, at present, infrared assemblies are mostly used for detection. The infrared assembly is composed of a pyroelectric infrared sensor, a lens, a measurement conversion circuit, and a sealed shell]. The lens can expand the detection range and improve the sensitivity of measurement; The measurement conversion circuit can complete signal processing processes such as filtering and amplification; The sealed shell can prevent the wrong action caused by external noise. This kind of assembly has a small volume, low cost, and various functions, so it is widely used.

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