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A self regulating heating device for a mirror is disclosed including a substrate having an electrical buss system deposited on one surface including a plurality of interdigitated electrodes and two buss bars. Stripes of positive temperature coefficient resistive material are printed perpendicularly

A self regulating heating device for a mirror is disclosed including a substrate having an electrical buss system deposited on one surface including a plurality of interdigitated electrodes and two buss bars. Stripes of positive temperature coefficient resistive material are printed perpendicularly over the buss system to form a plurality of heater areas and exposed substrate areas. A first adhesive layer is deposited over the resistive layer and adheres to the exposed areas of the substrate. An electrical barrier layer is secured to the first adhesive layer and a removable protective covering is secured by the second adhesive layer. The buss bars are tapered such that the power density at any point along their length is substantially equal to the average power density of the heater areas.

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A heating device comprising: a planer electrically insulative substrate; an electrical buss system on one surface of said substrate, including a pair of buss bars and two electrode patterns having a plurality of spaced apart parallel interdigitated electrodes, adjacent electrodes of said plurality o

A heating device comprising: a planer electrically insulative substrate; an electrical buss system on one surface of said substrate, including a pair of buss bars and two electrode patterns having a plurality of spaced apart parallel interdigitated electrodes, adjacent electrodes of said plurality of interdigitated electrodes connect to different ones of said pair of buss bars, each buss bar extending from one of a pair of terminal connection points along generally opposite portions of a peripheral edge of said substrate; an electrically resistive layer of material having a positive temperature coefficient, and resistive layer deposited over said electrical buss system in a plurality of parallel spaced apart stripes orientated perpendicular to said interdigitated electrodes defining a plurality of heater areas between adjacent electrodes; a first adhesive layer deposited over said electrically resistive layer including the spaces between said spaced apart stripes, whereby said adhesive layer contacts and adheres to said substrate in areas of said substrate between said heater areas; an electrically insulative barrier layer on said adhesive layer; a second adhesive layer on said electrically insulative barrier layer; and means providing for achieving a predetermined power density at any location along each of said buss bars from said respective terminal connection point to a free end of each buss bar substantially equal to an average power of all of said heater areas.