High power self-regulating heater

An electrically resistive heating element, comprising:

• a non-magnetic substrate of high thermal and electrical conductivity,
• a ferromagnetic layer having a first planar face in intimate thermal and electrical contact with said substrate,
• a further non-magnetic layer of high electrical resistivity in intimate thermal and electrical contact with an opposite planar face of said ferromagnetic layer, and
• said ferromagnetic layer being sufficiently thin that upon the application of a constant current of sufficient magnitude to cause the ferromagnetic layer to approach its Curie temperature the majority of the current switches from said nonmagnetic layer of high electrical resistivity into said nonmagnetic substrate.

An electric heater comprising

• a high resistance element,
• a low resistance element,
• a ferromagnetic element,
• said ferromagnetic element located between and in thermal and electrical contact with said high resistance and said low resistance elements, and
• means for switching a current between said high resistance and low resistance elements,
• said means including means for connecting said elements in parallel to a source of high frequency constant current of sufficient magnitude to heat said ferromagnetic element to a temperature approaching its Curie temperature.

An electric heater comprising

• a high resistance element,
• a low resistance element,
• a ferromagnetic element,
• said ferromagnetic element located between and in thermal and electrical contact with said high resistance and said low resistance elements, and
• means for switching a current between said high resistance and low resistance elements,
• said means including means for developing in said elements a high frequency current generated by a constant current source of sufficient magnitude to heat said ferromagnetic element to a temperature approaching its Curie temperature whereby to reduce materially the permeability of said ferromagnetic element.