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Pyroelectricity is a phenomenon where certain materials, such as minerals and crystals, can produce electricity when their temperature changes. This effect is used in temperature sensors, like passive infrared detectors in security systems. Pyroelectricity was first observed by Theophrastus in 314 BC. When a crystal is heated or cooled, electric charges form on opposite sides of the mineral, which can be harnessed as an electric current. Pyroelectricity is not practical for generating energy, but it is useful in sensors. Pyroelectric sensors can detect heat sources, like fire, and can be combined to detect temperature changes over a large area, like a thermal imaging camera.
Pyroelectricity is a scientific phenomenon that allows special materials to create electricity when they change temperature. Minerals and crystals are the most common substances to produce this effect. These materials are commonly used to build temperature sensors, such as the passive infrared detectors used in security systems.
The word pyroelectricity comes from the Greek term “pyr”, which means fire. The first observation of the pyroelectric effect occurred in 314 BC when the ancient philosopher and scientist Theophrastus noted that tourmaline minerals create electrical attraction when heated. Several scientists studied this phenomenon during the 18th century, but it wasn’t until the 19th century that researchers fully understood its cause.
All crystals have electrical, mechanical and thermal properties. These three properties are able to interact. In piezoelectric crystals, for example, physical force such as bending a mineral will generate electricity. Similarly, pyroelectricity results from the interaction of the thermal and electrical properties of a crystal.
When a crystal is heated or cooled, electric charges form on opposite sides of the mineral. These charges can be harnessed as an electric current by placing electrodes on the surfaces of the crystals. Electricity flows in one direction when heat increases and in the opposite direction when heat decreases.
The amount of electricity produced by the pyroelectric effect is usually not enough to power other devices. This means that pyroelectricity is not a practical method of generating energy. However, the small electrical signal of a crystal is very useful in sensors. Pyroelectric materials can be combined with other electronic devices to indicate when a temperature change has occurred.
Passive infrared detectors are a common application of pyroelectric signals. These devices are also known as motion detectors and are often placed in homes and businesses as part of a security system. Each detector contains a wide angle lens and a pyroelectric crystal. When a person passes in front of the sensor, the heat from their body causes the crystal to generate pyroelectricity and the alarm is triggered.
Pyroelectric sensors can be used to detect other heat sources, such as fire. Unlike traditional smoke detectors, a sensor using pyroelectricity can detect a real flame even if smoke is not present. These types of sensors are useful in applications such as gas heaters, where they can detect if a pilot flame has been properly lit.
A collection of these sensors can be combined to detect temperature changes over a large area. An array of these sensors can function like a thermal imaging camera and can show temperature changes caused by people or vehicles. This technology is often used by military and law enforcement agencies as a form of night vision.
