Functionality of Piezo & Pyro Sensors
The core of the PyzoFlex® technology is made up of an array of screen-printed sensors. A sensor element is composed of a polarized ferroelectric polymer layer, embedded between two printed electrodes, which forms a capacitive element. This polymer layer contains ferroelectric crystallites whose dipole moment can be aligned by polarization in an electric field.
After this poling activation, charges are generated in the sensor layer by the smallest changes in pressure or temperature and the charge flow to the electrodes are interpreted as voltage signals via special multiplexing electronics in a personal computer. The detected signal height is proportional to the strength or speed of the contact - that is, while these parameters can be measured, the site of contact cannot be identified.
The basic materials used in the PVDF class ferroelectric co-polymers are very stable, i.e., they are very UV and weather resistant, flame-retardant and highly chemically durable. By means of a low-temperature sol-gel process that is currently patent-pending, this material can be formulated into a paste and, thus, made printable. The sensor array is currently printed on PET film, up to A3 wide, with only four different materials needed. In the future, the technology will also be produced on the roll-to-roll pilot plant (at the JOANNEUM RESEARCH - MATERIALS Institute in Weiz) using gravure. Thus, it is now possible to produce square-meters sheets of sensors scale cost-effectively. Once polarized, the dipole orientation remains stable over countless cycles of stimulation so long as the Curie temperature of about 130°C, which marks the transition between the ferroelectric and paraelectric phase, is not exceeded.
Each mechanical movement of the PyzoFlex® film (pressure, flutter, bending) generates an electrical charge. The film, therefore, works not only as a sensor, but also as a mechanical to electrical energy converter. Combined with electronics suitable for energy harvesting, a power per unit area in the range of uW / cm2 to MW / cm2 can be generated.