Comparison of an acousto-optic and a radiation force method of measuring ultrasonic power

Abstract

During the interim period while nationally acceptable methods of measurement of referential standards for ultrasonic power are being developed, comparisons are needed among measurment techniques currently used. This is particularly necessary for determining the acoustic power from ultrasonic medical devices. Such a comparison was made between an optical and a radiation force technique to measure the ultrasonic power output of a 1-MHz 1-in.-diameter PZT crystal from 70 mW to 2.3 W total acoustic power. The optical technique follows the theory of Raman and Nath, assaying the diffraction of monochromatic light by ultrasound. In addition, a correction factor is introduced into the calculation of the phase retardation parameter and eliminates the need to determine the pathlength of the light through the sound. The radiation force technique relates the change of position of an air-backed, self-centering, reflecting float to the ultrasonic power. A linear regression analysis between the square of the voltage applied to the crystal and the measured power of each method was used. For a 99% confidence level, there is no statistical difference between the measurements over the range of power investigated, although the variance of the optical measurements was significantly lower than that of the radiation force. Subject Classification: 35.65, 35.80; 85.24.

Acoustic radiation pressure in laterally unconfined plane wave beams

“…In a similar experiment, Haran et al [24] report independent, simultaneous assessments of the acoustic power generated from a 1 MHz acoustic transducer from acousto-optic Raman-Nath diffraction measurements and measurements from a force balance in water using the Langevin equation. Critical to their assessment from the Raman-Nath measurements is the value 1.46 × 10 −10 Pa −1 assumed for the piezo-optic coefficient.…”

“…The radiation pressure generated by an acoustic wave is used in a variety of applications such as acoustic radiation force-based elasticity imaging [1][2][3][4][5][6][7][8][9], acoustophoretic drug delivery [10], acoustic tweezers [11][12][13][14][15], the characterization of atomic force microscope cantilevers [16,17], and the calibration of ultrasonic transducers [18][19][20][21][22][23][24]. The search for the proper understanding of radiation pressure in acoustic fields has been controversial and elusive since the pioneering efforts of Lord Rayleigh [25], Brillouin [26,27], Hertz and Mende [28], and Langevin [29,30] in the early twentieth century and has continued to the present time .…”

“…Such an experiment has been reported by Breazeale and Dunn [23] of the absolute pressure amplitude of a progressive, plane wave obtained using a force balance, three different optical techniques, a thermoelectric probe, and a direct assessment of the transducer output utilizing the piezoelectric constant. Experiments by Haran et al [24], have also been reported employing Raman-Nath diffraction measurements of the intensity of a progressive, plane wave impinging on a calibrated force balance. The measurements of Breazeale and Dunn [23] and Haran et al [24] are shown to provide tentative evidence for the validity of the present model, but reveal that more accurate and precise measurements are necessary for model confirmation.A critical analysis of Lagrangian and Eulerian coordinates and quantities is presented in section 2.…”

“…Experiments by Haran et al [24], have also been reported employing Raman-Nath diffraction measurements of the intensity of a progressive, plane wave impinging on a calibrated force balance. The measurements of Breazeale and Dunn [23] and Haran et al [24] are shown to provide tentative evidence for the validity of the present model, but reveal that more accurate and precise measurements are necessary for model confirmation.A critical analysis of Lagrangian and Eulerian coordinates and quantities is presented in section 2. The analysis is necessary to understand errors made in previous derivations of the acoustic radiation pressure and to provide the framework for a radical (though mathematically punctilious and physically realistic) departure from previous approaches to resolve the long-lasting confusion surrounding the subject.…”

“…Experiments by Haran et al [24], have also been reported employing Raman-Nath diffraction measurements of the intensity of a progressive, plane wave impinging on a calibrated force balance. The measurements of Breazeale and Dunn [23] and Haran et al [24] are shown to provide tentative evidence for the validity of the present model, but reveal that more accurate and precise measurements are necessary for model confirmation.…”