Certain crystalline substances are electrically polarized, and a change in heat causes them to change their polarization proportionally. The crystal manifests its change in polarization by temporarily generating a detectable voltage across itself. Scientists call the behavior of such crystals the Pyroelectric effect and the phenomenon as Pyroelectricity. Sensors made of such crystals are pyroelectric sensors and they are infrared sensors with a host of applications with the underlying technology relying on the pyroelectric effect.
With pyroelectric sensors, it is possible to detect infrared radiation or heat emanating from substances. Different materials and chemicals absorb infrared radiation at specific wavelengths. Therefore, pyroelectric sensors can detect the presence of a specific material or chemical by sensing the change in a specific wavelength of IR that the substance is blocking. Two basic types of pyroelectric sensors are available—passive and active.
Passive pyroelectric sensors can measure or detect infrared rays that an object generates as an IR emitter. Active pyroelectric sensors require the presence of an absorber between itself and the IR source, to be able to detect the wavelengths that the absorber is absorbing. The industry uses pyroelectric sensors primarily to detect motion, gas, food, and flame, among others.
Motion sensing can use either active or passive pyroelectric sensors. Active pyroelectric sensors are useful in instances where the emitter and sensor are far apart over a very long distance. A garage door safety sensor is a simple example. Anything blocking the infrared signal across the opening of the door sends a signal to stop it from lowering. Passive pyroelectric sensors can be very sensitive in detecting the source of heat directly, such as from a human body. The user can configure the sensor to detect the presence or absence of any object, including a human body, radiating enough IR.
Monitoring and detecting the presence of gasses is another popular application for pyroelectric sensors. The setup requires the presence of an IR emitter and an active sensor across a sample of the gas. The pyroelectric sensor checks for the presence of a specific wavelength—the absence of which means the gas absorbing the specific wavelength is present in the sample. Using optical IR filters, manufacturers can tune the sensors to a specific wavelength, permitting only that wavelength to pass through to the sensing element.
Like pyroelectric gas sensors, manufacturers can calibrate pyroelectric food sensors to detect food-related substances. For instance, pyroelectric food sensors can differentiate between fat, lactose, and sugar, as they absorb different IR wavelengths. In fact, these general pyroelectric sensors are useful for monitoring many types of commercial, industrial, and medical substances or processes, depending mainly on their configuration.
Pyroelectric flame sensors can easily detect flames as they are strong emitters of IR. They are useful not only in detecting the presence of flames, pyroelectric sensors can also differentiate between sources of flames. Triple IR flame detection systems do this by comparing three specific IR wavelengths, and their ratios to each other. This helps to detect flames to a high degree of accuracy—very useful in fire protection systems and in smart homes, furnace monitoring, and forest fire detection.
