Showing papers by "Masahiko Hirao published in 1995"
TL;DR: In this article, the exact solution to the Helmholtz equation with a Dirichlet boundary condition is obtained to study three-dimensional ultrasonic diffraction phenomena and derive the numerical data of amplitude loss and the phase shift for correcting induced errors.
Abstract: The exact solution to the Helmholtz equation with a Dirichlet boundary condition is obtained to study three‐dimensional ultrasonic diffraction phenomena and derive the numerical data of amplitude loss and the phase shift for correcting induced errors. Calculation is made for near‐field diffraction, for the rectangular transducers, and for the transducers with strength distribution on the radiating area. In the near field, where the wavelength and the propagation distance are comparable with each other, the longitudinal and shear waves undergo different diffraction. For transducers having a noncircular shape and a strength distribution on the area, both the amplitude loss and the phase shift experience different tendencies from the classical work on the circular piston source. Use of diffraction data specific to each measurement condition is then necessary to correct the errors. The calculated results are verified for pulse‐echo measurements using a shear‐wave electromagnetic acoustic transducer.
13 citations
01 Jan 1995
TL;DR: In this paper, a new method of measuring the attenuation is presented, which employs electromagnetic acoustic resonance (EMAR) which is a combination of resonance method and electromagnetic acoustic transducers (EMATs).
Abstract: The accurate measurement of ultrasonic attenuation is very important, since it has a great utility in the wide area of materials characterization. In this paper, a new method of measuring the attenuation is presented, which employs electromagnetic acoustic resonance (EMAR) [1–3]. The EMAR is a combination of resonance method and electromagnetic acoustic transducers (EMATs). At a resonance, many reflection echoes are coherently overlapped each other, which serves to provide an easily measurable signal intensity, compensating in excess for the inefficient transduction with EMATs. Use of a noncontacting or weakly coupling EMAT for the attenuation measurement has a pronounced advantage of eliminating the extra energy losses, which otherwise occur with the conventional contacting or immersion tests based on the piezoelectric transducers.
4 citations