Importance

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Abstract

An autoregulating electrically shielded heater employs a structure of two magnetically permeable members of different Curie temperatures and preferably differing resistivities. The two members are in electrical contact with one another; having at their interface a very low resistivity layer or member provided by copper or a like material. A first of the electromagnetic members has the lower Curie temperature and high resistivity while the other of said members has the higher Curie temperature of the two and preferably lower resistivity. A constant current a.c. source is connected to induce currents in the members parallel to their interface. Below the Curie temperature of the first member, current is substantially confined to a narrow region along a surface remote from the interface. Above the Curie temperature, some of the current spreads into the low resistance layer or member and into the second electromagnetic member where it is confined, due to skin effect to a narrow region adjacent the interface. The I.sup.2 R heating is greatly reduced, 6 to 1 in a typical case, so that autoregulation of temperature occurs near the Curie temperature of the first member. Since the current in the second electromagnetic member is limited in its penetration by skin effect, a low frequency power supply may be employed in a thin device without radiation of the electromagnetic field.

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First Claim