Enhanced electromechanical response of ferroelectret ultrasonic transducers under high voltage excitation

Abstract

Polypropylene based ferroelectret films exhibit a strong electromechanical activity and provide a promising solution for the air coupled ultrasonic (ACUS) transducers. Ultrasonic transmission between two air coupled ferroelectret transducers in dependence on the amplitude and polarity of the high voltage exciting pulse revealed a strongly non-linear electromechanical response of the ferroelectret transmitter which provides an increase in the transmitter efficiency. The authors present a simple model describing both promotion and competition of the piezoelectric and electrostriction contributions, as well as increase in the transducer constant under high voltage excitation. Enlargement of the inverse transducer constant of the polypropylene ferroelectret film by a factor of 4 was demonstrated. The non-linear properties of the polypropylene ferroelectrets result in a strong increase in their ACUS figure of merit under the high voltage excitation, which exceeds the results of their technological optimisation. Consequently, enhancement of the ACUS system transmission by 12 dB and signal to noise ratio by 32 dB was achieved.

DC-Biased Piezoelectret Film Transducers for Airborne Ultrasound

“…(2), directly proportional to the d 33 -coefficient of the piezoelectric material used. DC-biased and stacked piezoelectrets have effective d 33 -values of up to 1500 pC/N in the ultrasonic range until about 100 kHz, compared to values of 80 to 400 pC/N reported before for conventional piezoelectrets [43]. Thus, if all the other parameters, such as transducer size and measuring distance, are the same, the present transducers are capable of delivering nearly four times the sound pressure compared to existing systems.…”

“…A number of papers about the use of ferroelectrets as transmitters and receivers of airborne ultrasound and about the use of ferroelectret transducers in transmit-receive and in Downloaded by [Monash University Library] at 12:05 04 December 2014 pulse-echo systems have recently appeared in the literature [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. These papers document the large progress that has been achieved in this field.…”

Interpretation of the Thickness Resonances in Ferroelectret Films Based on a Layered Sandwich Mesostructure and a Cellular Microstructure

“…Another possibility could be the increase of the frequency bandwidth by the convenient design of the thickness resonances of the different layers involved and their potential coupling. Finally, as in many cases FE films in transducers are operated in the nonlinear regime [51], the areas of the film with more flattened cells may become more important as they are more likely to respond in a non-linear way. Future work will focus on the analysis of the electromechanical response of FE films to determine if it is possible to extract any information about the distribution of the d 33 value across the film thickness and to study the possibility of improving FE transducers (air-and water-coupled) by engineering this layered structure.…”

Modification of Mechanical and Electromechanical Resonances of Cellular Ferroelectret Films Depending on the External Load

“…In the latter case, the main advantage is the extremely low acoustic impedance of these materials that facilitates the coupling to the air; they are normally operated using the thickness resonances of the films. In addition, the possibility to operate these films in the electrostrictive regime under high voltage excitation offers an important improvement of transducer efficiency [ 34 , 35 ]. Applications of FE-based air-coupled transducers have mainly been oriented towards non-destructive testing of materials.…”