Ferroelectrets are flexible and conformable polymer transducer materials with a dominant longitudinal piezoelectric effect. They can be used in a wide range of transient pressure sensing applications. We present concepts for thin, flexible ferroelectret-keyboards (and advanced pressure sensors) based on ternary coded polarization patterns in a multilayer configuration. The decoration of a cellular polypropylene ferroelectret with a heteropolar polarization pattern of high resolution is a technical challenge. We discuss several concepts for achieving such polarization patterns and demonstrate a flexible 300 μm thin 3-layer keyboard where the combined signals of every single layer allow to encode and detect a total number of 26 keys.
Kogler, A., Buchberger, G., Bauer, S., & Schwödiauer, R. (2010). Heteropolar ferroelectrets for ultrathin flexible keyboards and tactile sensors. In Procedia Engineering (Vol. 5, pp. 717–720). Elsevier Ltd. https://doi.org/10.1016/j.proeng.2010.09.209