Tag Archives: Pyroelectric Effect

What is the Pyroelectric Effect?

With the electronic industry trending more toward automated devices, their safety and reliability are assuming the utmost importance. Pyroelectric sensors help to make these devices work properly, by indicating changes that require specific types of reactions. Many types of ceramic materials can absorb infrared rays and generate an electrical signal in response.

Certain crystalline materials demonstrate Pyroelectricity. These materials, which are electrically polarized, demonstrate a change in their polarization when they undergo a change in temperature. The change in polarization of the crystal material generates a temporary but detectable voltage across it. Different materials exhibit differences in pyroelectric coefficients that show their sensitivity to temperature.

Infrared radiation heats pyroelectric ceramic crystals to generate a detectable voltage. It is possible to detect the infrared rays the object is generating by using passive infrared sensors. The sensor can detect the wavelengths that the pyroelectric ceramic crystal absorbed when it is in position between the hot object and the sensor. Pyroelectricity has several applications.

Motion Sensors—Typically, there are two types of infrared motion sensors, active and passive. Active infrared sensors have a long range of operation, and the emitter and sensor can be far apart. A garage door safety sensor is a good example of an active sensor. Anything blocking the infrared beam across the opening of the garage door generates a signal to prevent the garage door from moving.

Passive infrared sensors can also detect motion by sensing infrared radiation or heat direct from a source. Such sensors can detect the presence, or absence, of an object emitting heat, such as a human body.

Pyroelectric motion sensors can be surface-mount devices and are highly sensitive. Manufacturers offer them in single-pixel configuration or as a 2×2 pixel configuration, allowing users to determine the direction of the motion it has detected. The sensors have a high dynamic range and a fast response time that ensures rapid and accurate motion detection.

Gas Sensors—Infrared pyroelectric sensors can detect and monitor gases. In fact, this is one of their most popular applications. The sensors operate by directing infrared radiation from an emitter through a sample of the gas. The detector senses if a certain IR wavelength is present on the other side. If the sensor does not detect that wavelength, it means the gas that absorbs this wavelength is present in the sample. Optical IR filters allow fine-tuning the sensor to a specific wavelength, thereby permitting only the desired wavelength to pass through to the sensing element.

Pyroelectric gas sensors are available in small SMD packages and most have a digital I2C output, although analog outputs are also available. The sensor consumes very low power but offers high sensitivity and extremely fast response times.

Food Sensors—Similar to gas sensors, infrared pyroelectric food sensors can detect food-related substances like sugar, lactose, or fat. These are typically general IR spectroscopy sensors for monitoring commercial, medical, or industrial substances or processes.

Flame Sensors—With pyroelectric elements, it is easy to construct sensors for detecting flames. As flames are strong, flame sensors, apart from detecting the presence of the flame, can also discriminate the source of the flame. Typically, they compare three specific IR wavelengths and their interrelated ratios. This allows them to detect flames with a high degree of accuracy.

Pyroelectric Sensors

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.