Berlin 2008 – scientific programme
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DF: Fachverband Dielektrische Festkörper
DF 2: Electric, electromechanical and optical properties I
DF 2.5: Talk
Monday, February 25, 2008, 11:40–12:00, EB 107
Cellular polymer ferroelectrets for generation and detection of air-borne ultrasound — •Petr Bartu1, Mario Dansachmüller1, Ivan Minev2, Ingrid Graz2, Nikita Arnold1, and Siegfried Bauer1 — 1Soft Matter Physics, Johannes Kepler University, Linz, Austria — 2Nanoscience Centre, University of Cambridge, UK
Charged cellular polypropylene ferroelectrets can be used as sensors and transducers in many applications (e.g. pressure measurements, microphones and loudspeakers). The suitability of different materials for generating and detecting air-borne ultrasound can be compared by means of a figure of merit (fom) F = k4/Z2, where k and Z denote the materials longitudinal coupling factor and acoustic impedance respectively. By comparison with piezoelectric ceramics and ferroelectric polymers, soft cellular foams possess the largest fom F.
In order to demonstrate the coupling quality of cellular ferroelectrets to air, samples of charged cellular polypropylene are investigated in an acoustical interferometer arrangement in a transmitting as well as in a reflecting mode. Due to the good coupling to air, Fabry-Perot resonances are observed together with the electromechanical thickness extension resonance of the cellular ferroelectret foam. Using a plane wave acoustical model, the observed Fabry-Perot resonances are confirmed and a straightforward derivation of the fom F is presented. Work partially supported by the FWF.