Thermal switches and transistors
Like an electronic transistor, a thermal transistor consists of two segments (the source and the drain) as well as a third segment (the gate) through which the input signal is transferred (top). Crucially, negative differential thermal resistance (NDTR) is possible between the source and drain segments, which allows a heat current to be amplified. Calculations reveal that when the gate temperature (TG) rises, both the drain current (JD) and the source current (JS) increase by a factor of almost 100. In particular, the gate current JG = JS – JD is zero when TG ≈ 0.03 and TG ≈ 0.14. Because the source current is so very different at the two temperatures, we can turn the transistor “off” by making TG = 0.03 and switch it “on” by making TG = 0.14. By making the thermal resistance between the output (O) and the gate very small, the temperature of the output (TO) is always close to TG. This switch function means that a thermal transistor can also be used to carry out thermal logic operations such as NOT, AND and OR.