Wide-band piezoelectric polymer acoustic sources

Abstract

The design of a wideband acoustic source made of the piezoelectric polymer polyvinylidine fluoride (PVDF) is described. The source was developed for the characterization and absolute calibration of ultrasonic hydrophone probes. Construction details are described and performance characteristics of the wideband PVDF transmitter, including its transmitting voltage response and directivity patterns, are compared with theoretical predictions in the frequency range up to 40 MHz. The Krimholtz-Leedom-Mattaei (KLM) model was used to examine the influence of the PVDF polymer film thickness, the backing acoustic impedance, the cable length, and the electrical source resistance on overall transmit transfer characteristics. A comparison is made with traditional piezoelectric ceramic acoustic sources, and it is shown that piezopolymer transmitters exhibit some improved properties and are well suited for certain ultrasound dosimetry applications. In particular, the polymer sources have been found useful in measurements based on swept-frequency excitation. Those measurements allow characterization of transmitters and receivers to be performed as a virtually continuous function of frequency.

Effect of temperature on the pulse‐echo performance of ultrasonic transducers fabricated with PVDF film

“…PVDF is particularly suited to applications requiring short, highly damped, pulses with wide bandwidths and is common in non-destructive testing (NDT) or imaging applications where good temporal resolution is required. Its low acoustic impedance and inherently damped polymeric structure enable impulse responses with a ring-down of only one to two cycles to be achieved without the need for ¼ wave acoustic impedance matching layers or electrical impedance matching, unlike most standard piezoceramic transducers [2].…”

Calibration of ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz

“…As already mentioned, TDS calibration was used in this work to calibrate hydrophones by substitution technique in the frequency range from 250 kHz to 1 MHz as shown in Figure 2. The calibration was performed in the following way: First, the continuous spectrum of previously calibrated reference hydrophone was obtained by placing the reference hydrophone at the focal plane of an ultrasonic transducer source [27] using the X-Y-Z micro-manipulator. The reference hydrophone was previously calibrated by the National Physical Laboratory, NPL, UK.…”

Study on Pulse Compression Ultrasonic Imaging by a Stacked M‐Sequence Encoding Probe

“…However, with phased array flaw detection systems, multiple elements must be controlled in parallel, which makes devices complex and expensive; moreover, aperture area of line-arrayed probes unavoidably grows large as compared to a single probe. Polymer piezoelectric oscillators, though being inferior to ceramic oscillators in terms of sensitivity, feature good fabricability and broadband frequency characteristic due to high dynamic internal loss [8,9]. Thus, in this study, we aimed at a new imaging method that requires fewer elements with relatively small aperture and can do without scanning so as to implement simpler ultrasonic imaging.…”

“…In this context, we resorted to a stacked M-sequence encoding probe [7]-a single-probe design using piezoelectric polymer films and offering high orthogonality. Polymer piezoelectric oscillators, though being inferior to ceramic oscillators in terms of sensitivity, feature good fabricability and broadband frequency characteristic due to high dynamic internal loss [8,9]. Another advantage is that delamination is unlikely to occur because acoustic impedance of the adhesive is close to that of the polymer film.…”