Innovative thermal energy harvesting for zero power electronics

Thermal gradients, commonly present in our environment (fluid lines, warm fronts, electronics) are sources of energy rarely used today. This paper aims to present innovative approaches of thin and/or flexible thermal energy harvesters for smart and autonomous sensor network applications. The harvester system will be based on the collaborative work of interrelated energy nodes/units, which will be either piezo-thermofluidic converters (use of rapid thermal cycles of a working fluid) or piezo-thermomechanic converters (use of the mechanical energy developed by rapid snapping of micro-switches). The two kinds of energy nodes convert a heat flux into storable electrical energy through a piezoelectric transducer. Miniaturization of the energy nodes will lead to increased thermal transfer rates and consequently increased harvested power. To effectively use thermal energy sources in varying environments, the nodes will be adaptive versus different thermal gradients (in a predefined temperature range) and will possibly influence each other. The concept is unique in the sense that it is based on a matrix structure of micro or mini energy nodes which will work together in a collective approach to optimize the harvested energy, and which do not require the use of radiators as classical Seebeck approach, thanks to the controlled thermal resistance. This opens the door to new properties and features of the object, with better performances. It could therefore be declined on flexible substrates, allowing conformability around the sources of potential heat for low power applications.