A pyroelectric detector or sensor is an infrared sensitive optoelectronic component that is specially used to detect electromagnetic radiation in a wavelength from 2-14 µp. It is basically a motion detection technology that offers both digital as well as analog detectors to serve various applications in smart homes, burglary detection, IOT, smart city, and security systems.
These pyroelectrics are available in single, dual, and quad element configurations. There are also a wide range of different infrared sensor surfaces, meaning that there is enhanced performance and sensitivity.
How does a pyroelectric detector work?
Pyroelectric crystals typically have a rare asymmetry because of their single polar axis. This causes their polarization to fluctuate with temperature. This pyroelectric effect is used in sensor technology. For this, a thin pyroelectric crystal is layered vertical to the polar axis with electrodes.
On the upper electrode of the crystal, an absorbing layer, usually black is applied. When this layer gets into contact with infrared radiation, the pyroelectric layer heats up and surface charge arises. If the radiation is switched off, a charge of the opposite will originate, but the charge will be very low.
Before the predetermined internal resistance of the crystal equalizes the charges, low-leakage current field-effect transistors, and very low-noise convert the charges into a signal voltage.
Types of pyroelectric detectors
As already mentioned, there are various types of pyroelectrics detectors. Here are some of the various types of pyroelectric detectors.
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Single-element pyroelectric detector
Single-element pyroelectric detectors are usually applied for gas and temperature measuring applications on single or dual-channel variants, which is one output per element. Single-element pyroelectric detectors are offered as thermally compensated devices. The principle of gas monitoring application is known as NDIR, and it requires detectors with narrow-band optical filters for maximum performance. Thankfully, these pyroelectric detectors manufacturers provide a wide range of ideal windows for those gases that show an absorption band in the IR spectral range.
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Four-element pyroelectric detectors
The four-element pyroelectric detectors typically have four sensing elements and can be configured in a wide range of geometrical forms. The most popular design today is known as “Quad”, which basically has two pairs of elements in square from layout. Due to the spacing and polarity of the elements, there are different variations available. The majority of these applications for such sensors are often ceiling-mount sensing devices.
These Quad designs are also available in single-channel and dual-channel outputs. Latest versions of Quad include the enhanced functionality known of the Dual-element Low-Power DigiPyro, offering a Dual-Channel Quad DigiPyro with sensitivity adjust, window time, sleep mode, and bandwidth selection.
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Dual-element pyroelectric detectors
These types of pyroelectric detectors are adequately established because the performance standard in motion detection. It features two sensing elements connected to one another in reverse polarity to provide an AC-signal with motion and common mode rejection for non-moving radiation. This type of pyroelectric detector has various window sizes to match various fields-of-view.
Performance parameters
- Spectral response
As typical of thermal detectors, the spectral response can be very broad; one just requires adequately broadband absorption. A pyroelectric sensor may have an infrared filter that transmits only light in a specific range of wavelengths.
- Surface reflectivity
Logically, a pyroelectric detector should absorb all incident light because of the high sensitivity. However, for a fast response, one may want to use a thin absorbing coating that sits on a metallic electrode or a reflecting one equipped with processed surface structure for improved absorption. This means that there could be a significant reflectivity in practice.
- Active area
The active area is often a rectangular area or a circular disk with a diameter between a few millimeters. Subsequently, detectors for higher pulse energies have larger active areas.
- Maximum pulse width
For a pyroelectric detector to work efficiently, the input pulses must be adequately short. The maximum allowed pulse width generally varies between different models- for instance, it can be tens of microseconds.
- Sensitivity and dynamic range
These types of detectors are often used to detect pulses energies in the nanojoule or microjoule region. Pulse energies as high as 10uj can sometimes be allowed. Other devices are also pretty much optimized for much higher pulse energies.
- Detection bandwidth
Pyroelectric detectors’ typical detection bandwidth is a number of kilohertz. It can also be even tens of kilohertz. Of course, this is pretty much fast compared to other types of thermal detectors, such as thermopiles and thermocouples. This is because of the small thermal capacity of the compact detector crystal. For a faster response, you can use thin metallic electrodes with a processed absorbing surface, limiting the thermal capacity.
Suppliers usually specify the maximum bandwidth allowed. Maximum bandwidth can be used to monitor pulse energy fluctuations of a Q-switched laser. But if it’s a case of measuring just the average pulse energy, you could just use a slow thermal detector.
- Respond to sound
Each pyroelectric crystal material is also piezoelectric. This means that a pyroelectric detector will also respond to incoming sound waves, i.e., it acts as a microphone. However, such response to sound can be curbed. For instance, that can be achieved by shielding or mounting of the crystal.
Choosing the right pyroelectric detector supplier
If you are planning to purchase a pyroelectric detector, it is important that you do your due diligence. With so many pyroelectric detector suppliers in the market, it can be quite a daunting task to find one with high-quality devices.
When it comes to choosing the right supplier, you need to start by checking if they are certified. The supplier must be certified to sell, service, and install various types of pyroelectric detectors. Being certified proves that they are knowledgeable and can be trusted.
Pay attention to the reputation of the supplier too. Of course, you want to associate your company with reputed suppliers. Finally, you need to pay attention to the amount of money the suppliers are charging for their pyroelectric detectors because some suppliers tend to sell their detectors expensively compared to others.
