THERMOELECTRIC DEVICE

any of a class of devices that either convert heat directly into electricity or transform electrical energy into pumped thermal power for heating or refrigeration. Such devices are based on thermoelectric effects involving interactions between the flow of heat and of electricity through solid bodies. The first important thermoelectric phenomenon was discovered in 1821 by Thomas Johann Seebeck, a German physicist. Known as the Seebeck effect, this phenomenon concerns the generation of an electric current or voltage in a circuit composed of two different conducting materials in cases in which the junctions between them are maintained at different temperatures. The flow of heat from the hotter to the cooler junction produces a current. Jean-Charles-Athanase Peltier of France discovered another important thermoelectric effect in 1834. He found that, when a direct current flows through a circuit composed of different conductors, one junction between the materials is cooled while the other is heated, depending on the direction of the current flow. This phenomenon, called the Peltier effect, is essentially the inverse of the Seebeck effect and constitutes the basis for thermoelectric refrigeration. A third major thermoelectric effect was discovered by the English physicist William Thomson (later Lord Kelvin) during the mid-1850s. The Thomson effect involves the reversible generation of heat when a current flows in a single conductor along which there is a temperature gradient. The first and for many years the only useful thermoelectric device was the thermocouple, an instrument for measuring temperature whose operation is based on the Seebeck effect. Growing knowledge of solid-state physics in general and semiconductor materials in particular finally led to the development of practical thermoelectric-power generators and refrigeration systems during the 1950s. Thermoelectric devices have a variety of applications. Metallic thermocouples, for example, are used in science laboratories and in industry to measure and control temperature, particularly in furnaces and other inaccessible or hazardous locations. Compact, durable thermoelectric generators are employed in remote equipment with moderate power requirements, such as telephone repeaters, Arctic weather stations, and unattended navigation buoys. Such devices have also been used aboard Earth-orbiting spacecraft, and in miniaturized form they have been employed as a power source for electronic cardiac pacemakers. Thermoelectric cooling devices are used for temperature control in various kinds of electronic equipment to improve performance. Other applications include the employment of thermoelectric coolers to preserve blood plasma and antibiotics during storage and transport.