Rev. Sci. Instr. 82, 094901 (2011)

There are a number of parallels between thermal and electric currents. With the design of a thermal analogue of an electrical inductor, Olaf Bossen and Andreas Schilling not only add to the collection, but also enable a new approach to high-precision calorimetry.

Heat capacity can be measured by monitoring the response to an oscillating heating power. One of the advantages of the technique is that the accuracy of a measurement can be improved by temporal averaging. In such experiments, typically the temperature amplitude is monitored and, as the measurement time t is increased, the statistical uncertainty decreases as t−1/2.

Bossen and Schilling now propose, and demonstrate, an approach in which the heat capacity is related not to the amplitude of the temperature oscillation, but to its frequency. The statistical uncertainty then decreases significantly faster, as t−3/2. The key to their technique is a construction that neatly combines an electrical conductor, Peltier elements and an amplifier to act as a thermal inductor. When this device is connected to a sample of unknown heat capacity C, a resonant circuit can be built that supports autonomous oscillations, at a frequency proportional to C−1/2.