A hand held probe unit has an infrared sensitive thermopile mounted in a metal housing kept at a constant reference temperature by a regulator circuit. A waveguide tube, surrounded by a thermally insulative probe, directs infrared emissions to the thermopile. The thermopile and regulator circuit of the...http://www.google.com.au/patents/US4602642?utm_source=gb-gplus-sharePatent US4602642 - Method and apparatus for measuring internal body temperature utilizing infrared emissions
