Pyroelectric detectors are light sensors that use the pyroelectric effect. They are widely used to detect laser pulses, otherwise known as continuous-wave of light, mainly in the spectral region of infrared. These detectors are mostly used as the central part in several optical energy meters at room temperature. Compared to other sensors such as photodiodes, pyroelectric detectors have a broader spectral reaction.
The basic principle of how a pyroelectric detector operates is ferroelectric crystal material with electrodes on the sides. One of the two electrodes is coated with a black material exposed to UV light or any other radiation. As the light hits the exposed surface, the crystals are heated because heat is conducted from the electrodes. When the heat of the crystal, they produce a pyroelectric voltage that can be detected. If the voltage is constant, the current can also be detected.
Constant electrical power cannot be measured because the voltage fades away, and the device will be satisfactory. Pyroelectric detectors are therefore not suitable for detecting the intensity of a continuous-wave of light. These detectors are classified as thermal detectors because of their heating effect. They respond to the heating effect on the radiation rather than react. Operational amplifiers are used to detect the charges based on field-effect transistors because of their low current leakage.
Spectral response is the sensitivity of the material used as the photo sensor for UV light. This is vital because not all parts of the radiation spectrum are visible. Thermal Detectors have a wide range of spectral responses that require the only absorption of sufficient broadband. Pyroelectric sensors can use infrared filters that transmit light in a range of specific wavelengths.
Sensitivity and Dynamic Range
Pyroelectric detectors are used in the nanojoule and microjoule region to determine the pulse energies. Some of the sensors can measure a noise floor that is below 100 pJ. Furthermore, higher energies of up to 10 μJ can be determined. Other detectors can measure much higher pulses of several joules, but high noise nanojoules cannot be determined.
Standard detection bandwidth for pyroelectric detectors ranges between several kilohertz up to tens of kilohertz. Such bandwidth is fast, making this detector faster than thermopiles and thermocouples. This is possible because of the small thermal capacity made by compact crystal detectors. To make the sensor respond quickly, use thin metal objects that have processed ends that minimize thermal capacity.
In this principle, pyroelectric detectors are supposed to absorb the full spectrum of the incident light with such a possible high sensitivity. Furthermore, if you want a fast response, use thin absorbing coatings sitting on a metallic electrode that has enhanced absorption due to the surface structure. Doing this allows a substantial amount of reflectivity to be used in the detection.
Pyroelectric detectors can be used in other applications, including satellite-based infrared detection, fire detection and detection of people in motion detectors. The technology also allows the detection of dangerous gases such as carbon monoxide by using a specific filter. The technology has improved with additional components such as digital outputs and amplifiers.