Rapid Response Thermopiles*

A technique has been developed for the evaporation of bismuth and of antimony upon thin cellulose nitrate so that the metals have comparatively low electrical resistivities and comparatively high thermal e.m.f.’s. A procedure has been developed for making bismuth-antimony radiation thermopiles in which units of 50 thermal junctions have a receiving area of ~0.11 cm2 and a resistance of ~70 ohms. These units are called “folded thermopiles.” The response of several folded thermopiles of different design operated at atmospheric pressure has been studied over a range of frequencies. The “folded” thermopiles are faster than any thermopiles reported heretofore, yet the response is greater for all frequencies above 5 cycles per second than for evaporated thermocouples operated in a vacuum. The thermopiles are rugged, relatively free of microphonics, and show very little noise in addition to “Johnson noise.”