Hirotsugu Ogi 교수

This study is devoted to deducing exact elastic constants of an anisotropic solid material without using any advance information on the elastic constants by incorporating a displacement-distribution measurement into resonant ultrasound spectroscopy (RUS). The usual RUS method measures free-vibration resonance frequencies of a solid and compares them with calculations to find the most suitable set of elastic constants by an inverse calculation. This comparison requires mode identification for the

The coupling mechanism of the electromagnetic acoustic transducer (EMAT) for bulk waves has been studied by examining the magnetic-field dependence of the wave amplitudes. A spiral elongated coil placed on a thin plate of low carbon steel excites and receives the longitudinal and the shear waves propagating in the thickness direction in the presence of the bias magnetic field. The field dependences of the bulk-wave amplitudes are measured using the electromagnetic acoustic resonance both for the

A noncontacting resonant-ultrasound-spectroscopy (RUS) method for measuring elastic constants and internal friction of conducting materials is described, and applied to monocrystalline copper. This method is called electromagnetic acoustic resonance (EMAR). Contactless acoustic coupling is achieved by energy transduction between the electromagnetic field and the ultrasonic vibrations. A solenoidal coil and static magnetic field induce Lorentz forces on specimen surfaces without using a coupling

All independent components of the elastic constants, internal friction, and piezoelectric coefficients of synthetic α-quartz have been simultaneously determined by resonance ultrasound spectroscopy coupled with laser-Doppler interferometry. Seventeen crystals obtained from Z and X regions with various infrared-absorption values were used; for each crystal, a complete set of the coefficients was determined using 72 resonance frequencies, which were measured by a needle-transducer tripod in a vacu

This paper presents advanced techniques to determine all independent elastic-stiffness coefficients C/sub ij/, the associated internal friction Q/sub ij//sup -1/, and piezoelectric coefficients e/sub ij/ of monocrystal langasite (La/sub 3/Ga/sub 5/SiO/sub 14/) using a single rectangular parallelepiped specimen. Langasite's crystal structure belongs to the trigonal system with point group 32, and thus possesses six independent C/sub ij/, two e/sub ij/, and two dielectric coefficients /spl epsiv//

We report simultaneous measurement of the complete set of elastic and piezoelectric coefficients of lithium niobate (LiNbO3), which has trigonal crystal symmetry (3m point group) and thus six independent elastic-stiffness coefficients Cij, four piezoelectric coefficients eij, and two dielectric coefficients κij. We used a single specimen: an oriented rectangular parallelepiped about 5 mm in size. Our measurement method, acoustic spectroscopy, focuses on the crystal’s macroscopic resonance freque

This paper presents a contactless technique to measure shear bulk wave resonance frequencies of an isolated quartz crystal in a flow cell. The line antenna placed outside the cell generates and detects the resonance frequencies in a wireless-electrodeless manner. It is revealed that this mechanism relies on the quasistatic electric field. A 0.3-mm-thick AT-cut quartz was used, and its overtone resonance frequencies up to 80 MHz were measured in liquids. Exact vibrational analysis was carried out

A nonlinear acoustic measurement is studied for fatigue damage monitoring. An electromagnetic acoustic transducer (EMAT) magnetostrictively couples to a surface-shear-wave resonance along the circumference of a rod specimen during rotating bending fatigue of carbon steels. Excitation of the EMAT at half of the resonance frequency caused the standing wave to contain only the second-harmonic component, which was received by the same EMAT to determine the second-harmonic amplitude. Thus measured su

Electromagnetic acoustic resonance is applied for determining the frequency dependence of the ultrasonic attenuation and the average grain size of low-carbon steels. Use of a noncontacting electromagnetic acoustic transducer (EMAT) makes it possible to isolate the attenuation within the plate specimens. The method relies on the Lorentz force mechanism to couple the EMAT to the specimen surfaces and then eliminates the other losses, which may otherwise occur with the contacting piezoelectric tran

We studied the interrelationship of elastic and piezoelectric properties with the lattice structure and crystal physics of paratellurite $(\ensuremath{\alpha}\ensuremath{-}{\mathrm{TeO}}_{2}).$ Tetragonal paratellurite ${(D}_{4}^{4},P422)$ shows six independent elastic constants ${C}_{\mathrm{ijkl}},$ the associated internal friction ${Q}_{\mathrm{ijkl}}^{\ensuremath{-}1},$ and one piezoelectric coefficient ${e}_{14}.$ We determined simultaneously these material coefficients using resonant ultra

This paper describes the design principles of a line-focusing electromagnetic acoustic transducer (LF-EMAT) and the results of a feasibility test for detecting slit-type defects in metals. The LF-EMAT excites shear vertical (SV) elastic waves and focuses them to a line in a metal body. It consists of a permanent magnet block and a meanderline coil, whose spacing is continuously varied so that the excited SV waves become coherent on a focal line after traveling oblique paths. The measured directi

Resonances of coherent acoustic phonons were excited and detected by femtosecond light pulses for determining the normal elastic constant of ultrathin platinum films. The elastic constant increases with the decrease of the film thickness, exceeds the bulk value at the thickness near 5 nm, and significantly increases at low temperatures. It shows a correlation with the normal lattice distance. Thus, this Letter provides evidence of the stiffness enhancement in ultrathin films caused by lattice an

We studied the relationship between elastic constants and microstructure in sputtered vitreous ${\text{SiO}}_{2}$ thin films using pump-probe picosecond laser ultrasound. The delayed probe light pulse is diffracted by the acoustic wave excited by the pump light pulse, inducing Brillouin oscillations, seen as reflectivity change in the probe pulse, whose frequency can be used to extract the sound velocity and elastic moduli. Theoretical calculations were made to explain the asymmetric response of