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Abstract
Improvement of ferroelectret transducers for air-coupled ultrasonic applications was demonstrated on the base of optimization of the ferroelectret electromechanical properties and adjustment of the ferroelectret transducers to the ultrasonic system. Controlled inflation of the polypropylene ferroelectret films results in an increase of the coupling factor in two and the figure of merit in ten times. Integration of a pre-amplifier with high impedance matching increases the ferroelectret transducer sensitivity in ∼ 40 dB. Ferroelectret transducers are characterized by the broad transmission band with smooth amplitude-frequency dependence and provide a well shaped and short pulse transmitted through the air.
Acknowledgments
We are indebted to Prof. Dr. Reimund Gerhard and Werner Wirges (University of Potsdam, Germany), to Prof. Dr. Siegfried Bauer (Johannes Kepler University Linz, Austria) and to Dr. Mika Paajanen (VTT Processes, Tampere, Finland) for stimulating discussions on the ferroelectret topic. The work was supported by the Academy of Sciences of the Czech Republic (Project No. AVOZ 10100520) and by the Grant Agency of the Czech Republic (Project No. 202/06/0403).