Flexible, large-area sensors and microphones

Flexible, large-area sensors and microphones made with thin sheets of packaging foam may be possible. Via a simple charging process, the foam can be turned into a ferroelectret, a material that combines the permanently polarized electric dipoles of a ferroelectric substance with a large piezoelectric effect whereby a slight deformation generates a significant voltage. (See the article on ferroelectrets in (Physics Today, February 2004, page 37 .) Physicists at the Johannes Kepler University (Linz, Austria) and at Princeton University have shown that ferroelectret films can muster electric fields big enough to activate a thin-film FET made of amorphous silicon. Combining those two technologies—ferroelectrets and FETs—the researchers have demonstrated working versions of flexible microphones and touch sensors, about a centimeter across and 70 microns thick. Lead investigator Ingrid Graz says that their new form of soft electronics can be scaled up and may be useful for producing items like flexible paper-thin keyboards, flexible microphones for mobile phones, active noise-control devices, toys, hearing aids, and surround-sound systems. Someday it might even be used as prosthetic skin. (I. Graz et al., Appl. Phys. Lett. 89 , 073501, 2006 http://dx.doi.org/10.1063/1.2335838 ).