Generation and detection of broadband airborne ultrasound with cellular polymer ferroelectrets

Abstract

Cellular polypropylene ferroelectrets are useful for broadband airborne ultrasound generation and detection up to the fundamental thickness extension resonance. The authors show that the coupling of ferroelectrets to air alters the electromechanical resonance of the foam. In an acoustical cavity, Fabry-Perot resonances are obtained, which is in excellent agreement with the plane wave model calculations. For material assessment in airborne ultrasound applications, a figure of merit is used based on the electromechanical coupling factor and acoustical impedance of the material. The good coupling of ferroelectrets to gases results from the small acoustical impedance of the material.

Fluoroethylenepropylene ferroelectrets with patterned microstructure and high, thermally stable piezoelectricity

“…8 Interferometrically determined frequency responses measured at four different positions on a laminated FEP film. The two ordinate scales are related by (7) and both scales apply to all curves. The sequence of curves from top to bottom at 1 kHz is indicated in the legend box respectively.…”

“…The third measurement was taken in the middle of another bubble, while the last measurement was carried out somewhere between bubbles. The measured vibration amplitudes of the sample surface are given on the left axis of the figure and the resulting d 33 coefficients according to (7) are given on the right axis. The three measurements taken in the center of a bubble are similar to typical measurements made on conventional PP ferroelectrets: A slightly decreasing d 33 coefficient with increasing frequency followed by the first resonance at a frequency in the 100 kHz range.…”

“…Since the first such films, made of polypropylene (PP), were developed in Finland about 15 years ago [4], the polarization, charge storage, mechanical properties, and piezoelectricity have been intensively investigated. Owing to their unique features, such as large piezoelectric d 33 coefficients, flexibility, light weight, and low cost, many applications have been suggested [1][2][3][4][5][6][7][8][9]. Some devices based on PP ferroelectret films, such as movement monitors and non contact vital monitors [5], are commercially available right now.…”

“…Some devices based on PP ferroelectret films, such as movement monitors and non contact vital monitors [5], are commercially available right now. Many other applications, such as microphones [6], ultrasonic transducers [7], flexible ferroelectret field-effect transistors [8], and ferroelectret accelerometers [9] are being developed in some laboratories. Unfortunately, the relatively poor stability of d 33 in PP ferroelectret films, with working temperatures normally lower than 60°C, limits their applications when the devices are required to work at elevated temperatures.…”

DC-Biased Piezoelectret Film Transducers for Airborne Ultrasound

“…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.…”