Simplified technique for the calibration and use of a miniature hydrophone in intensity measurements of pulsed ultrasound fields

Abstract

A simplified technique for calibration of the response of a miniature hydrophone as a function of frequency was evaluated experimentally for reproducibility and for its uncertainty in calibration of hydrophones intended for intensity measurements in broadband medical ultrasound fields. In this hydrophone calibration technique, the known total acoustic power passing through a plane lying normal to an ultrasound beam is compared with the surface integral of the intensity over that plane. Broadband source transducers calibrated by the National Bureau of Standards were driven in a narrow-band tone-burst mode to calibrate the hydrophone at multiple discrete frequencies. A least squares polynomial fit to the discrete values provided a continuous estimate curve of the hydrophone intensity response factor (Kf2) as a function of frequency. Good reproducibility of this multipoint technique was demonstrated by an independent, but similar, calibration of the hydrophone by the Bureau of Radiological Health. This hydrophone was then employed to measure acoustic intensities and power in broadband fields of typical pulse echo systems. If the variation in Kf2 is adequately small over the frequency spectrum of the measured pulse and the wave pressure is not so high as to be producing large nonlinear effects, a ±30% uncertainty in SPTA intensity can be achieved by use of a single Kf2 value determined either at the center frequency of the pulse or as the mean of the Kf2 values at the center and half-power frequencies of the spectrum of the pulse. In those cases where the variability of Kf2 exceeds ±1.5 dB over a one-octave range centered about the center frequency of the pulse’s spectrum, use of an effective Kf2 value determined by a deconvolution technique is recommended.

The impact of piezoelectric PVDF on medical ultrasound exposure measurements, standards, and regulations

“…The first published result, titled "Safety Standard for Diagnostic Ultrasound Equipment," defined several exposure quantities based on hydrophone measurements [143]. Some of the background work for this document was presented and published in 1981 [144], [145]. In these papers, the superiority of PVDF as a hydrophone transducer material for medical ultrasound field measurements was documented.…”

Polymeric Piezoelectric Transducers for Hydrophone Applications

“…As thick-film PVDF became available in 1979, Meyers 45 built a series of large hydrostatic mode thick-film hydrophones by encapsulating a single PVDF sheet in polyurethane. These hydrophones had the expected higher FOM h due to the increased film thickness but the frequency response was unsatisfactory due to the presence of undesired low frequency resonances.…”

Determination of Sensitivity Versus Frequency Characteristics of Miniature Ultrasonic Hydrophones Below 1 MHz Using Planar Scanning Technique

“…7 In this work, the applicability of the planar scanning technique was examined as an alternative method for low-frequency calibration of the probes. Although measurements using the planar scanning technique have been reported in the megahertz range of frequencies, [8][9][10] it appears that this technique has not been explored at frequencies below 1 MHz. In the following sections, a brief description of the principles of the technique is given, and the results of the low-frequency calibration of a PVDF bilaminar membrane hydrophone are presented.…”