Pyroelectric effect
In nature, any more than the absolute temperature (-273K) objects will have
infrared spectra, objects at different temperatures the wavelength of infrared energy released is not the same, so the level of infrared wavelengths is related to temperature, and radiation energy size and surface temperature.
1μm wavelength of visible light is usually less, but more than 1μm light the human eye can not see, but can be an appropriate instrument to detect the energy oradiation.
When some of the crystal is heated, the crystal will have an equal number of both ends of the opposite sign of charge, such as heat of changes in the polarization phenomenon, known as the pyroelectric effect. Typically, the crystals produced by the spontaneous polarization bound charge is attached to the air from the surface of free electrons in the crystal and in its spontaneous polarization electric moment can not be
demonstrated. When the temperature changes, positive and negative charges in the crystal structure of the relative center of gravity shifts, the spontaneous polarization changes, the crystal surface will have run out of charge, charge depletion is proportional to the polarization degree of the situation, Figure 1 shows the pyroelectric The principle effect of the formation.
Pyroelectric effect can produce a crystal or call the pyroelectric pyroelectric
body components, the material commonly used in single crystal (LiTaO3, etc.), piezoelectric ceramic (PZT, etc.) and polymer film (PVFZ, etc.) [ 2]
When represented LiTaO3 pyroelectric material is self-polarized state, the absorption of infrared incident, the crystallization of the surface temperature change, since the polarization has changed, crystal surface charge becomes imbalanced, the imbalance taken out of charge voltage can be measured by infrared. Pyroelectric materials produced only when the temperature changes the voltage, if the infrared radiation has been, there is no imbalance in voltage, if no infrared radiation, the crystal surface charge on the in an unbalanced state, so the output voltage
Pyroelectric infrared sensors, infrared light irradiation due to gain or lose
heat and shelter, resulting in voltage output. In principle should be independent of the wavelength, but the material made by the pyroelectric sensor has a light transmission window, the translucent windows and wavelength selection of a relationship. To SiO2 as the window material, such as sensors, it can almost all visible light, while others near the window material can only 4μm wavelength of light, and some wavelengths of light through 6.1μm, and some through 8μm ~ 14μm wavelength of light, so use a different window materials which can be confirmed that the heat generated by the wavelength of light.
Quantum-type infrared detector
Quantumponse, response sensitivity and infrared wavelength. The energy generated by each incident photon E = hc / λ = 1124λ
Where, h - Planck constant, h = 4.14 × 10-15 (evs) = 6.625 × 10-34 (JS) c - the speed of light, c = 3 × 1010cm / s
1μm infrared light energy 1.24eV, 10μm infrared light energy of 0.12eV,
compared with the visible light, infrared light energy smaller. Quantum-type infrared sensor light conductive type and is divided into two kinds of light force. Components of light conductive material PbS, PbSe, Hg, Cd, Te, etc., it is the use of infrared radiation to reduce the characteristics of impedance detection signal to obtain; and light force type is in Ge, IrSb formed on a substrate such as semiconductor PN Results, when the infrared radiation generated when the light force, Ge band gap for the 0.6ev, Ge diode of 0.6μm and 1.9μm more sensitive to infrared light, infrared light when the wavelength of the incident in the 0.6μm ~ 1.9μm, in the PN junction force formed with the increase of the amount of incident light, thereby detecting amplified output signal.
Pyroelectric sensor
Pyroelectric
sensor
using
the
pyroelectric
effect
is,
is
a
temperature-sensitive sensor. It consists of oxides or ceramic piezoelectric crystal components, the component made of two surface electrodes, when the temperature within the sensor monitoring the change ΔT, the pyroelectric effect in the two electrodes will produce the charge ΔQ, ie between two electrodes in a weak voltage ΔV.
Pyroelectric infrared sensors and thermocouples are based on the principle of
thermoelectric thermoelectric infrared sensors. Different pyroelectric infrared sensors is the thermoelectric coefficient is much higher than the thermocouple.
Chart
Pyroelectric infrared sensor structure and the internal circuit shown in Figure
2.
Sensors are mainly case, interference filters, pyroelectric component PZT,
FET, FET and other components.
Filter
Human central wavelength of infrared radiation 9 ~ 10 - um, the wavelength
sensitivity of the detection component in 0.2 ~ 20 - um range is almost constant. The top of the sensor chip has opened a window with filter, this filter through the wavelength range of 7 ~ 10 - um, just right for the detection of infrared radiation in the human body, while the other infrared wavelengths by the filter film to be absorbed, thus forming a special body for detection of infrared radiation sensor. Thermoelectric components
Thermoelectric materials will be a certain thickness of the sheet, and in its metal electrodes deposited on both sides, and then power on its polarization, this will
make the pyroelectric detectors. As the voltage increases polarization is extremely nature and therefore, the detection element is polarized positive 、 negative in nature.
Thermoelectric element within the Seebeck coefficient by the high iron titanate ceramic lead and mercury, and lithium tantalate 、 Triglyceride iron sulfate, and its polarization changes with temperature. In order to suppress the temperature change due to their interference can be generated process will be the same two features reverse thermoelectric element connected in series or poor way of balancing the circuit, to suppress its own temperature as a result of the interference. Thus able to detect objects in non-contact infrared energy emitted changes and converts it to electrical signal output.
FET impedance transformation
Pyroelectric infrared sensors in the structure aims to introduce complete FET
impedance transformation. Thermoelectric element as is the charge output signal, resistance up to 104MΩ, so the introduction of the N-channel JFET common drain pipe should be connected in the form of that the source follower to complete the impedance transformation.
Because of its high output impedance, so the sensor has a field effect
transistor for impedance transformation. Pyroelectric effect will be produced by the charge ΔQ with combination of ions in the air disappeared, when the ambient temperature stability constant, ΔT = 0, the sensor no output. When the body into the detection zone, because the body temperature and ambient temperature differential, resulting in ΔT, is a signal output; if the body does not move into the detection zone, the temperature does not change, the sensor has no output, so this sensor can detect body or animal activities.
Reference Selection
The commonly used models of pyroelectric infrared sensors are P228,
LHl958, LHI954, RE200B, KDS209, PIS209, LHI878, PD632 and so on. Pyroelectric