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.