Use of Peltier effect for small signal amplification and conversion

It is possible to use thermocouples operating as heat pumps with small temperature gradients to effect the control of elements whose properties are temperature dependent. This enables the construction of a number of electrical and optical signal transducers. The cooling or heating gain of a thermocouple used as a heat pump is proportional to the ratio of the cold or hot junction temperature to the temperature drop across the thermocouple. As this temperature gradient becomes quite small, the efficiency of such converters theoretically rises without limit. Under these conditions, the thermocouple can control any device whose properties change sharply in a narrow temperature range. Simple circuits for small signal amplification, frequency conversion, and detection were discussed. The gain of one such amplifier was plotted as a function of the input signal using various metal-semiconductor phase transition devices; the detection gain was plotted as a function of the input signal for a posistor and a metal-semiconductor phase transition device. Gains on the order of 100 and more were obtained with the latter. While such devices have the advantage of electrically isolating the input from the output, the speed is governed primarily by the rate of the thermal processes and is approximately inversely proportional to the square of thermocouple branch length. The speed is presently limited to tens of milliseconds, though with the transition to film technology, it may increase by a few orders of magnitude.