How Does a Pyroelectric Detector Work?

Pyroelectric crystals have a rare asymmetry due to their single polar axis. This causes their polarisation to change with temperature. This so-called pyroelectric effect is used in sensor technology. For this, a thin pyroelectric crystal is coated perpendicular to the polar axis with electrodes. On the upper electrode of the crystal, an absorbing layer (black layer) is applied. When this layer interacts with infrared radiation, the pyroelectric layer heats up and surface charge arises. If the radiation is switched off, a charge of the opposite polarity originates. However, the charge is very low. Before the finite internal resistance of the crystal can equalise the charges, extremely low-noise and low leakage current field-effect transistors (JFET) or operational amplifier (OpAmp) convert the charges into a signal voltage. Thermopiles, too, belong to the group of thermal detectors, however, the measuring effect is less significant. While pyroelectric infrared detectors show a good signal/noise ratio up to modulation frequencies of 4 kHz, e.g. in FTIR spectrometers, thermopiles produce good results up to modulation frequencies of specific Hertz only.

PYROMID® multi channel detectors from InfraTec

Experiment: The Pyroelectric Effect

Changing the temperature of the crystal material lithium tantalate (LiTaO3) changes its polarisation. When the crystal is heated and cooled, a surface charge with opposite polarity is created. These charges equalize through the visible sparks between the top and bottom surfaces.

Der Pyroelektrische Effekt – mit einem schwarz beschichteten LiTaO3 Kristall

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Pyroelectric Detector with Integrated Beam Splitter by InfraTec

In addition to the pyroelectric crystal, a pyroelectric infrared detector by InfraTec contains optical and micro-mechanical components. Two-channel and four-channel pyroelectric detectors with integrated beam splitter and integrated CMOS amplifier are micro-systems consisting of components which function thermally, electronically and optically.

As pyroelectricity is a characteristic of a subgroup of piezoelectric crystals, a pyroelectric detector reacts to airborne and solid-borne sound. This effect is often called microphony. However, a patented fastening of the pyroelectric chip by InfraTec reduces these negative effects for pyroelectric detectors dramatically so that in many cases these negative effects are in the order of magnitude of other interference voltage or of the inherent noise of the infrared detector only.

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InfraTec offers five different product groups including approximately 50 standard pyroelectric detectors. Choose your suitable infrared detectors with the help of our detailed detector search.

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