Characterization of thermoelectric modules for powering autonomous sensors

The characterization of three commercial thermoelectric modules, which are designed for cooling/heating applications, is presented to employ the devices for power conversion, i.e., as thermoelectric generators (TEGs). The thermoelectric theory is briefly summarized at first, taking into account the relationship between the effective temperature difference across the TEG junctions and the temperature difference applied externally, considering insulating ceramic plates having finite thermal conductance. The thermoelectric modules have been characterized in terms of open-circuit output voltage and output power density for different temperature gradients and load conditions. Measurement techniques and experimental data are reported, which show the possibility of using thermoelectric devices for energy-harvesting applications. A comparison of the results from the tested devices with the performance data of commercial TEGs that are specifically designed for power harvesting is then presented, and the main characteristics of the two device typologies are discussed. A TEG was then used to supply an autonomous system that interfaces with a temperature sensor and periodically transmits the measurement information via an RF link. Experimental data show that the system works correctly and sends the RF signal when the temperature difference that is applied across the TEG is higher than 34 K.