Measurement of Sound Fields Using Mach–Zehnder Interferometer

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.