Ferroelectrets are piezoelectric polymers that feature noteworthy piezoelectric coefficients. The term ferroelectret is used since such films show a hysteresis effect upon charging and charge reversal. A synonymous term frequently used is piezoelectrets. These materials have been known for only about 20 years. They consist of a cellular polymer, often polypropylene (PP), containing gas voids of several μm in thickness and diameter. Such films are permanently charged by corona discharge or by contact electrification, resulting in barrier discharges in the voids. After charging, the films exhibit a reversible piezoelectric effect.
Energy Harvesting and Self-Sufficient Sensors
Combining factories with the Internet is the concept behind the fourth industrial revolution called as ’Industry 4.0’. However, industrial revolutions have so far been triggered not only by new data technologies, but also in combination with new energy sources. In fact, sensor networks that do not require batteries and transmit their data by wireless technologies are increasingly being used for monitoring of widely dispersed production and process engineering plants. In this context, energy harvesters are seen as the driving force behind this revolution as a way to provide these devices with the energy they need where electric power is not readily available.