Measurement of Sound Fields Using Mach–Zehnder Interferometer

Abstract

In this paper, we propose a method of noncontact measurement of sound fields, radiating from an ultrasonic transducer, using a Mach–Zehnder interferometer. The deviation of refractive index, which depends on sound pressure, was transformed into the intensity of the interference light using the interferometer, in which a light beam passes through the measured object. Projection data used in the computerized tomography (CT) method along the optical axis was obtained by single linear scanning in the range of ±40 mm and was electronically quadrature-detected as the complex amplitude. The 36 projections were acquired by the rotation of the sound fields in the range of 0≤θ≤π (rad) with an interval of π/36 rad. Finally, the complex sound fields were reconstructed in the region of 48×48 mm2 by the CT method. The plane of reconstruction was 5 mm apart from the plane of the transducer. The ultrasonic transducer used in the experiment was driven at a frequency of 1.416 MHz and had a diameter of 8.0 mm. The experimental results were approximately in agreement with the numerical results.

Optical Computerized Tomography for Visualization of Ultrasonic Fields Using Michelson Interferometer

“…Therefore, the reconstruction image seems to faithfully show the radiated sound fields. As a whole, higher-contrast projection images than the previously obtained ones 21) are obtained.…”

“…16,17) Projection images can be utilized for computerized tomography (CT). 15,[18][19][20][21] We have proposed a method for the two-dimensional reconstruction of sound fields radiated from an ultrasonic transducer in water using an optical CT (O-CT) method and a quadrature detector. 20,21) However, clearly visualized sound pressure distributions cannot be obtained in complex sound pressure measurement using the Mach-Zehnder interferometer, especially in the phase distribution.…”

“…15,[18][19][20][21] We have proposed a method for the two-dimensional reconstruction of sound fields radiated from an ultrasonic transducer in water using an optical CT (O-CT) method and a quadrature detector. 20,21) However, clearly visualized sound pressure distributions cannot be obtained in complex sound pressure measurement using the Mach-Zehnder interferometer, especially in the phase distribution. On the other hand, in the measurement using the Michelson interferometer, the test light may pass sound fields twice and the detection sensitivity also becomes twice.…”

“…We obtain visualized distributions of the amplitude and phase of sound fields radiated from an ultrasonic transducer, which is much clearer in comparison with the result obtained by the conventional technique. 20,21) In the following sections, the measurement principle, experimental method and visualization results are described.…”