| 摘要 |
A self-regulating resistive electric heating element consists of a two- layer laminate, the first layer having high electrical conductivity and low magnetic permeability and being itself, as described a laminate comprising a sandwich of cutting steel 21, Fig. 2, between two layers of metal 23 such as silver or copper, and the second layer 25 having a high permeability and a low conductivity and being of ferromagnetic material. If an r.f. current is passed through such an element using an additional conductive layer 29 insulated 27 from the element as the return conductor, at low temperatures the majority of the current will pass, owing to the skin effect, through the thin ferromagnetic layer and thereby cause heating, but as the temperature rises towards the Curie point of the ferromagnetic layer, its permeability falls, the skin depth increases, and as a consequence less current is carried by the ferromagnetic layer and more by the other layer 21, 23, which results in a net drop in the rate of generation of heat. As described the composite heating element is sharpened to a cutting edge 15 and forms part of a surgical scalpel. <IMAGE> |
