Emfit is elastic, permanently charged ferro-electret film that converts mechanical stress into proportionate electrical energy and conversely, it mechanically expands when voltages of opposite polarities are applied. Emfit film is also pyroelectric, converting heat into electrical charge, but with less intensity compared to piezoelectric pvdf film. Our dynamic Emfit sensors offer unique design and performance advantages, as they are thin, flexible and robust.
Piezoelectricity and Quasi-Piezoelectricity
"Piezoelectricity" refers to changes in the internal polarization of a dielectric material for small changes in stress and vice versa. A material can be piezoelectric if its crystalline symmetry is inherently assymmetric, i.e. it lacks an inversion centre. There are several polymers in which piezoelectricity can be induced by external electric field, which permanently alignes electrical dipoles in the material.
Two slabs of nonpolar dielectric material containing a monocharge of opposite polarities may induce an electric signal like piezoelectric materials. The signal will be induced, if the thickness of an aircap between the slabs is changed. In this case the signal does not originate from piezoelectricity.
Emfit film consists of thin polymer layers separated by air voids. When an external force is applied, the thickness of the film changes. As the thickness of the film changes, the thickness of the polymer layers will change much less than the thickness of the air voids due to their lower stiffness. The electromechanical signal of Emfit film thus mainly arises from the movement of the charged polymer layers with respect to the other layers and is not of piezoelectric origin. Because of it's difference in working principle compared to piezoelectric materials, yet producing charge upon pressure change like them, several scientists have recently begin to call Emfit film as "quasi-piezoelectric".