Hiroyuki Masuyama

Measurement of Temperature Distribution Using Acoustic Reflector Array

We propose an ultrasonic measurement of temperature distribution. Using the system, we aim to measure temperature distribution to be used for a sophisticated air-conditioning system. The system consists of a loudspeaker (SP), a microphone (MIC) and an acoustic reflector array. Sound velocity is dependent on air temperature along the propagation path, and is measured from the time of flight (TOF) of sound. A measurement area is partitioned into a 1×3 grid. The sound velocities in each partitioned grid square were obtained by arranging the SP, MIC and three reflectors appropriately. We created a temperature gradient in a grid square of the measurement area using an electrical heat source to confirm that the system detects an area of heat concentration. The product of area length (m) and area temperature (°C) corresponds to the amount of heat (m°C) in that area. The amount of heat measured by the system showed good agreement with the amount of heat estimated using thermocouples, which were installed as reference. The method has the advantages of noncontact sensing, a quicker response and a simpler composition, over conventional temperature measurement systems.

Optical Computerized Tomography for Visualization of Ultrasonic Fields Using Michelson Interferometer

We propose a method for the noncontact visualization of ultrasonic fields using the Michelson interferometer and optical computerized tomography (O-CT). The light source of the interferometer is a He–Ne laser. The test light passing through radiated sound fields is interfered by the reference light. Therefore, the index of refraction gradient including sound pressure information is transformed into the intensity of the interference light that can be electrically acquired by an avalanche photo-diode. Projection data along the optical axis is obtained by single linear scanning in the range of ±32 mm and electronically quadrature-detected as complex amplitude. Thirty-six projections are acquired in the range of 0≤θ<π (rad), and complex sound fields are reconstructed in a region of 64×64 mm2 by CT. The experimental results are in agreement with the numerical results.

Generation of Bessel Beam from Equiamplitude-Driven Annular Transducer Array Consisting of a Few Elements

We present a method for generating a nondiffraction beam using an annular transducer array. In this method, each element is driven with equiamplitude and with an antiphase from its neighboring elements. Theoretical and experimental analyses of an array of this type have been carried out, and the feasibility of this method is confirmed. The beam from a continuous wave is shown using radiated pressure magnitude distributions and it is shown that there exist most suitable values of the width and number of elements. When the array is driven by a burst signal, the beam propagates as a plane wave which has an amplitude corresponding to the zeroth-order Bessel function of the first kind, J0. Since this beam is realized by an annular array consisting of a few elements, it suggests the possibility of a transducer of this form developing into a source which generates nondiffraction beams.

Determination of Sound Velocity in Three-Dimensional Space by Optical Probe

We propose a method of determining a three-dimensional sound velocity using a Michelson interferometer, optical computerized tomography (O-CT) and near-field acoustical holography (NAH). Ultrasonic waves affect the phase of the test light passing through radiated sound fields. The zeroth-order diffraction light including sound pressure information is electrically acquired by an avalanche photodiode (APD). Projection data along the optical axis is obtained by single linear scanning in the range of ±30 mm and electronically quadrature-detected as a complex amplitude. Eighteen projections are acquired in the range of 0≤θ<π rad, and the complex sound fields are reconstructed in a region of 40×40 mm2 by O-CT. Then another plane separated by 1 mm is propagated using NAH from the acquired sound fields, and the same plane is reconstructed. Comparing the phase of the reconstructed and propagated sound fields in wave number domain, we determine the three-dimensional sound velocity in a region of 40×40×1 mm3. The experimental results are in agreement with the reference value.

Indirect Measurement of Vibrating Surface of Ultrasonic Transducer Using Optical Computerized Tomography and Acoustical Holography

We propose a method for the indirect measurement of the vibrating surface of an ultrasonic transducer using a combination of the Michelson interference method, optical computerized tomography (O-CT), and acoustical holography (AH). Ultrasonic fields affect the phase of a light passing through the fields. The phase change, including information on the sound pressure, is acquired using a Michelson interferometer. Projection data along the optical axis is obtained by one-way linear scanning, and complex sound fields are reconstructed in a region of 64×64 mm2 by CT using 36 projections. Then using AH, the complex sound pressure in the vibrating surface of the transducer is reconstructed in a region of 24×24 mm2, which is 10.0 mm distant from the transducer, using the acquired sound fields. The method does not require that the light irradiates the vibrating surface of the transducer. The experimental results are in agreement with the numerical results.

Quadratic-Curve Approximation of Impulse Responses to Calculate Radiated Fields from Rectangular Transducers

A new approximation of the impulse response to calculate speedily acoustic radiated fields from a rectangular transducer is proposed. The conventional approximation causes considerable error in some cases. The proposed method approximates the time derivative of the response with the inclined straight lines in the interval between its discontinuities. This means the graph of the response itself is approximated with quadratic curves. We call this method the quadratic-curve approximation. Numerical calculation indicates that the quadratic-curve approximation reduces error with little increase in computational load.

Nondiffraction beam generated from an annular array driven by uniform velocity amplitude

This paper presents a method for generating J/sub 0/ beam approximately using an annular array. In this method, each element is driven by an anti-phase from its neighboring element and at the same amplitude. The validity of this method is verified with simulations and experiments and is shown to the generation of nondiffraction beam from the array consist of few elements. Using an annular array consisting of 5 elements driven by a continuous wave, simulation results and experimental results using piezoelectric rubber annular array transducer show good agreement. Driving by RF burst signal, the pulse from the annular array arrives slightly earlier than that of an ideal J/sub 0/ source.

Reconstruction of Three-Dimensional Sound Field from Two-Dimensional Sound Field Using Optical Computerized Tomography and Near-Field Acoustical Holography

We propose a method for reconstruction of a three-dimensional sound field using optical computerized tomography (O-CT) and near-field acoustical holography (NAH). The center of a transducer is the origin, and a sound wave is radiated along the z-axis. An ultrasonic wave affects the phase of light passing through the sound field, and the phase change is determined using a Michelson interferometer. Projections of the underwater sound field were obtained by mechanical scanning, and the sound field was reconstructed from 18 of these projections by O-CT. To determine sound velocity for reconstruction of the three-dimensional sound field, two-dimensional sound fields at z = 40 and 41 mm were reconstructed using O-CT in a region of 28 ×28 mm2. The sound velocity was determined to be 1508 m/s using inverse analysis of NAH. Using NAH and the determined sound velocity, the three-dimensional sound field of 28 ×28 ×5 mm3 was reconstructed from the two-dimensional sound field at z = 40 mm. The sound field reconstructed using NAH was in good agreement with the sound field reconstructed using O-CT.

Directional Trimming of Radiated Ultrasonic Beam Using Decentered Annular Transducer Array

By using a decentered annular transducer array, the directional trimming of radiated ultrasonic beams is examined. In the proposed method, the number of array elements for decentering is minimized, so the decentering operation is more simplified in comparison with that in the conventional decentering method. From the results of the calculation for the examination of the aspect of the radiated beam, it is shown that the center of the generated narrow beam moves at a sound axial distance from the sound source that is determined by the actual decentered element, and that the slippage of the center of the beam is proportional to the decentering ratio of the decentered element. From these results, the directional trimming of the radiated beam is confirmed. The technique presented here is highly simplified; thus, its applicability should be high in the production of practical sound sources.

Sound source with direction-variable beam using annular transducer array

We present a method for generating a narrow beam such that the direction of radiation is variable using an annular array. A sound source using this method has a clearance between each neighboring element of the array. These clearances are applied to decentring the array elements and the direction of radiated ultrasonic beam becomes controllable. The validity of this method is confirmed with numerical calculations, and it is shown that the beam radiated at a direction of 15 degrees from the perpendicular of the source plane still keeps the sharp profile. The sound source fabricated by this method has small, simple and planar structure, and it suggests the capability of a sound source based on this method developing into various acoustic devices.