Energy-Harvesting based on Piezoelectrets

In this research work, a novel vibration Energy Harvester based on Flourethylenepropylene (Teflon-FEP) polymer-electrets is investigated and optimized, for generating few milliwatts of electrical power.

Since FEP is inexpensive, very flexible and also provides excellent flame and chemical resistance, as well as low-temperature toughness, there are considerable advantages over conventional piezoceramics (e.g. PZT). Because electrets are surrounded by a static electric field, they are the electrical analogue to permanent magnets, from which the concept derives. Electretes are dielectric materials with quasi-permanent electrical polarization or excess electrical charge.

The generator itself (see figure) consists of two FEP-foils bonded together by means of fusion-bonding, so that a large number of micron-sized cavities are hollowed out. A bilateral metallization of the bonded films allows an electrical breakthrough within the air-filled cavities, by applying high voltage. The tops and bottoms within the cavities are thereby charged with different polarity.

If the generator is mechanically excited, the mechanical stress yields a change in compensation charges, which is why displacement currents can flow through a connected load resistor. The electro-mechanics phenomenon is also referred to as quasi-piezoelectric effect, because the same theoretical approach is applicable for those Energy Harvesters. This work focuses on the miniaturization of the Harvester by means of a micro-system-technology-based approach.

Schematic of a FEP-based energy-harvester consisting of two thermoformed and fusion bonded FEP-foils.

Using piezoelectric PP-foils as energy-source for LEDs

Energy-Harvesting based on large Barkhausen jumps

In addition to the known transducer principles, such as the piezoelectric or thermoelectric approach, magnetic concepts have also promising new possibilities for energy harvesting. Thus, the magnetic Wiegand effect has long been used for magnetic field sensors. Despite relatively small energy yields, the Wiegand effect has also recently been proposed as an interesting principle for energy harvesting. To further develop this magnetic energy-harvesting principle, the Wiegand wire is replaced by alternative bistable, magnetic materials. These should be miniaturizable and thus be integrable in semiconductor processes. For this purpose nano- and micro wires with large bark living jump are to be realized and be combined with a readout coil on a chip with the method of the electro-chemical deposition.

a) Schematic representation of nanowires surrounded by a readout coil on a chip
b) Principle of the wiegand effect and external magnetic field