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 Piezopolymers produce variable voltage when subject to periodical mechanical stress. We have developed a proprietary technique to remotely sense motion when a piece of polymer embedded into fabric or paper is rotating on a roller against another roller or against a fabric. The invention is used by heavy industries such as pulp & paper manufacturing where it contributes to minimize the downtime caused by production stops.
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Piezopolymer film – how does it work? | |
Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. The word is derived from the Greek - piezein, which means to squeeze or press. In a piezoelectric crystal, the positive and negative electric charges are separated, but symmetrically distributed, so that the crystal overall is electrically neutral. When a stress is applied, this symmetry is destroyed, and the charge asymmetry generates a voltage. Piezoelectric materials also show the opposite effect where application of an electrical field creates mechanical stress (distortion) in the crystal. Because the charges inside the crystal are separated, the applied voltage affects different points within the crystal differently, resulting in the distortion. Several decades ago the piezoelectric effect was discovered in certain polymeric materials, such as polyvinyl difluoride, PVDF.
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Microphones and Loudspeakers | |
Piezo-polymers are relatively soft, cheap to produce and they have paved the way for numerous industrial applications. For example, in microphones, the piezoelectric sensing element converts mechanical distortion due to acoustic waves into an electric signal, while in a loudspeaker the voltage applied to a piezoelectric membrane is converted into mechanical motion that generates sound waves.
The voltage across the thickness of the piezopolymer that arises due to charge separation can be relatively large, in some cases several tens of volts. If one connects two sides of a piezoelectric film via a resistor, the charge separation decays and the material becomes electrically neutral. The discharge time is usually rather short, in the order of a few microseconds and the generated electric pulse can be detected remotely.
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Microcantilever defelections | |
Another application of piezoelectric polymer films is to remotely
measure the deflection of, or actuate, a micro cantilever beam. The piezoelectric film deposited onto one side of a cantilever is used as a
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