New Self-regulating Ceramic PTC Thermistor Heating Elements with Strongly Improved Performance

Positive Temperature Coefficient (PTC) thermistors are electrical resistors with an exponentially increasing resistance within a small temperature range. This behaviour is used in several switching and sensor applications, among them self-regulating heating elements (PTC heaters). These PTC heaters work like usual ohmic heaters but are independent on external regulation. This is due to their intrinsic power reduction that occurs by exceeding a tuneable temperature threshold, thus making the behaviour of PTC heaters fast, smart and tough. Until now, the geometries of such heaters have been simple cuboids or disks. Nowadays, owing to the ceramic injection moulding (CIM) technology, heaters with appropriate geometric designs can be produced, which opens new fields of application. For example, the combination of mechanical and electrical functions in the same component is possible. In addition, alternative electrode arrangements for the electric excitation can be proposed. Here, a recent ongoing investigation is presented, showing that the design of the electrodes influences the performance of the heater in a substantial manner. This article explains the self-regulating characteristic of PTC heaters and gives an overview on the underlying mechanism. In comparison with common designs, the advantage of alternative electric and geometric designs is introduced here. It is also shown that by new designs of the devices the heat transfer from the heater into a medium is increased by a factor of two and more. In certain cases the heat output is as high as 1 MW/m(2).