How much do You Know about the Application of Infrared Sensors?

From the current application, infrared sensors have the following advantages:

1. Environmental adaptability is better than that of visible light, especially at night and in bad weather;

1. It has good concealment. Generally, it receives the signal of the target passively, which is safer and more confidential than radar and laser detection, and is not easy to interfere;

1. Because of the temperature difference and emissivity difference between the target and the background, the ability to identify camouflaged targets is better than that of visible light;

1. Compared with the radar system, the infrared system is small in size, light in weight, and low in power consumption;

According to the above performance characteristics of infrared sensors, we can develop a variety of infrared detectors.

Using its optical effect:

1. Photoconductive detector: also known as photosensitive resistance. After the semiconductor absorbs enough photons, some carriers in the body change from a bound state to a free state, which increases the conductivity of the semiconductor. This phenomenon is called the photoconductivity effect. Photoconductive detectors made of photoconductive effect can be divided into polycrystalline thin film type and single crystal type.

1. Photovoltaic detector: mainly uses the photovoltaic effect of the p-n junction. Infrared photons with energy greater than the band gap excite electron-hole pairs in and near the junction region. The existing junction electric field makes the holes enter the p region and the electrons enter the N region. There is a potential difference between the two parts, and the external circuit has a voltage or current signal. Compared with photoconductive detectors, the background limit detection rate of photovoltaic detectors is 40%, which does not need external bias electric field and load resistance, does not consume power, and has high impedance.

1. Light emission Schottky barrier detector: metal and semiconductor contact to form Schottky barrier. Infrared photons are absorbed by PtSi through the Si layer, so that electrons obtain energy to transition to the Fermi level, leaving holes to cross the barrier and enter the Si substrate. Electrons in the PtSi layer are collected to complete infrared detection.

1. Quantum well detector (QWIP): two kinds of semiconductor materials are alternately grown in thin layers by artificial methods to form a superlattice, and there is a sudden change in the energy band at its interface so that electrons and holes are limited in low potential energy wells, thus quantizing energy to form a quantum well.

Infrared detectors can be made by using the principle of electronic transition of energy levels in quantum wells. Because only the polarization vector perpendicular to the growth surface of the superlattice acts in the incident radiation, the photon utilization is low; The ground state electron concentration in the quantum well is limited by doping, and the quantum efficiency is not high; Narrow response spectral region; Low temperature is demanding.

Using its thermal effect:

1. Liquid mercury thermometer and pneumatic Golay cell: take advantage of the thermal expansion and contraction effect of materials.

1. Thermocouple and thermopile: the thermoelectric effect that temperature gradient can generate thermoelectric electromotive force between different materials are used.

1. Quartz resonator uncooled infrared imaging array: infrared detection is realized by using the principle that resonance frequency is sensitive to temperature.

1. Bolometer: use the thermal effect of the resistance or dielectric constant of the material - the temperature rise caused by radiation changes the resistance of the material - to detect thermal radiation. Due to the high-temperature coefficient of semiconductor resistors, they are most used. Thermometers and bolometers are often called "thermistors".

1. Pyroelectric detector: when some crystals, such as triglyceride sulfate and strontium barium niobate, are exposed to infrared radiation, the temperature rises, causing changes in the intensity of spontaneous polarization. As a result, a small voltage is generated between the two outer surfaces of the crystal perpendicular to the direction of spontaneous polarization, so that the power of infrared radiation can be measured.

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