The basic TEC unit is a thermocouple, which consists of a p-type and n-type semiconductor elements, or pellets. Copper commutation tabs are used to interconnect pellets that are traditionally made of Bismuth Telluride-based alloy.
Thus, a typical TEM consists of thermocouples connected electrically in series and sandwiched between two Alumina ceramic plates. The number of thermocouples may vary greatly - from several elements to hundred of units. This allows to construct a TEM of a desirable cooling capacity ranging from fractions of Watts to hundreds of Watts.
When DC moves across TEM, it causes temperature differential between TEM sides. As a result, one TEM face, which is called cold, will be cooled while its opposite face, which is called hot, simultaneously is heated. If the heat generated on the TEM hot side is effectively dissipated into heat sinks and further into the surrounding environment, then the temperature on the TEM cold side will be much lower than that of the ambient by dozens of degrees. The TEM's cooling capacity is proportional to the current passing through it. TEM's cold side will consequently be heated and its hot side will be cooled once the TEM's polarity has been reversed.