High power self-regulating heater

Abstract

An improved performance ferromagnetic self-regulating heater. Constant alternating current is applied to a layered structure including at least one ferromagnetic layer. One or more layers of non-magnetic material is added to the ferromagnetic layer in such a way that the power factor of the heater is very significantly increased above its value in the absence of at least one of the layers. The alternating current flows through the different layers in varying quantities depending on layer composition, temperature and Curie point of the ferromagnetic layer. The structure generates heat by resistive heating as a function of the power applied. In one embodiment a single layer of non-magnetic, high-resistance material is in intimate electrical and thermal contact with one surface of the ferromagnetic material. Below the effective Curie temperature of the ferromagnetic layer the current is mainly confined in the non-magnetic layer which heats with greater efficiency due to better resistive and impedance chararacteristics. In a second embodiment a further non-magnetic, low-resistance layer is added to the opposite surface of the ferromagnetic material. Here the majority of the current is switched from the high-resistance to the low-resistance layer as the heater approaches effective Curie. Accordingly, impedance matching circuit losses can be substantially reduced and energy is saved in high power systems based on the power factor.