A Comparison of Thermoelectric Devices Evaluation Results obtained with a Harman Method Based and a Porcupine Method Based zT meters

A comparison is presented of results obtained for the series resistance R and the dimensionless figure of merit zT of a number of different thermoelectric devices with two instruments based on alternative approaches. One is a commercial zT meter (DX 3065) manufactured by RMT and based on the Harman method, and the other one is a prototype realized at the Politecnico di Torino and based on the porcupine method. All devices were evaluated with both instruments at three different temperatures (20°C, 25°C and 30°C) in a climatic chamber, and results were compared. As expected from the theoretical analysis, the porcupine method consistently returned lower R values than those obtained by the Harman approach. Values obtained for zT with the two instruments are instead much more aligned, which is unexpected if thermoelectric effects are assumed to be correctly accounted for. A discussion of such results is offered, with comments on extrapolations which are introduced in both approaches in order to infer relevant quantities.