Masahiko Hirao

Complete mode identification for resonance ultrasound spectroscopy.

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 measured resonance frequencies, which has been difficult and never been free from ambiguity. This study then adopts a laser-Doppler interferometer to measure the displacement-distribution patterns on a surface of the vibrating specimen mounted on pinducers; comparison of the measured displacement distributions with those computed permits us to correctly identify the measured resonance frequencies, leading to unmistakable determination of elastic constants. Because the displacement patterns are hardly affected by the elastic constants, an exact answer is surely obtained even when unreasonable elastic constants are used as initial guesses at the beginning of the inverse calculation. The usefulness of the present technique is demonstrated with an aluminum alloy and a langasite crystal.

Electromagnetic acoustic resonance and materials characterization

Abstract This paper reviews the operation principles and several applications of electromagnetic acoustic resonance (EMAR). EMAR is an emerging ultrasonic spectroscopy technique for nondestructive and noncontact materials characterization, relying on the use of electromagnetic-acoustic transducers (EMATs) and the superheterodyne circuitry for processing the received reverberation signals excited by long radio-frequency (RF) bursts. The transduction occurs through the Lorentz force mechanism and, for ferrous metals, the dynamic response of magnetostriction and the magnetic force as well. Weak coupling of the EMATs is now essential to realize the high accuracy of measuring ultrasonic velocities and attenuation in conducting materials. High signal to noise ratio is achieved by receiving the overlapping coherent echoes at resonant frequencies. Small changes in the related material properties are well detectable. The spectral response can be interpreted for simple geometries such as plate, cylinder and sphere. EMAR has been proven to be powerful for industrial purposes because of its robustness, the omission of surface preparations and the capacity for simple measurement in a short time. Stress application varies the propagation velocities of ultrasonics and then shifts the resonant frequencies in longitudinal and shear modes in the parallel-sided geometries. Promising applications include the two-dimensional stress distribution in thin plates, the axial stress in railroad rails and the residual stresses around the weldments. In addition, the attenuation is precisely measurable at resonant frequencies and can evaluate the grain size of polycrystalline metals. Furthermore, the EMAR technique serves for developing the basic research on the effects of the metallurgical changes on ultrasonics, leading to the damage estimation of the fatigued, crept or thermally aged metal parts.

Anisotropic elastic constants of lotus-type porous copper: measurements and micromechanics modeling

Abstract We studied the elastic constants of a lotus-type porous copper, regarding it as a composite material showing hexagonal elastic symmetry with the c-axis along the longitudinal direction of the pores. We used the combination of resonance ultrasound spectroscopy and electromagnetic acoustic resonance methods to determine the elastic constants of the composite. The resulting Young’s modulus E∥ decreases linearly and c33 does slowly with porosity, while E⊥ and c11 drop rapidly and then slowly. Micromechanics calculations considering the elastic anisotropy of the copper matrix can reproduce the measured anisotropic elastic constants. This indicates that the elastic properties of various types of porous metals can be predicted and designed with the present approach using micromechanics modeling.

170-MHz electrodeless quartz crystal microbalance biosensor: capability and limitation of higher frequency measurement.

We develop a highly sensitive quartz crystal microbalance (QCM) biosensor with a fundamental resonance frequency of 170 MHz. A naked AT-cut quartz plate of 9.7 microm thick is set in a sensor cell. Its shear vibration is excited by the line wire, and the vibration signals are detected by the other line wire, achieving the noncontacting measurement of the resonance frequency. The mass sensitivity of the 170 MHz QCM biosensor is 15 pg/(cm2 Hz), which is better than that of a conventional 5 MHz QCM by 3 orders of magnitude. Its high sensitivity is confirmed by detecting human immunoglobulin G (hIgG) via Staphylococcus protein A immobilized nonspecifically on both surfaces of the quartz plate. The detection limit is 0.5 pM. Limitation of the high-frequency QCM measurement is then theoretically discussed with a continuum mechanics model for a plate with point masses connected by elastic springs. The result indicates that a QCM measurement will break down at frequencies one-order-of-magnitude higher than the local resonance frequency at specific binding cites.

Acoustic spectroscopy of lithium niobate: Elastic and piezoelectric coefficients

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 frequencies and is sensitive to any property that affects those frequencies. We overcame the principal obstacle to precise measurements—mode misidentification—by using laser-Doppler interferometry to detect the displacement distribution on a vibrating surface. This approach yields unambiguous mode identification. We used 56 resonances ranging in frequency from 0.3 to 1.2 MHz and determined the Cij and eij with known κij. The ten unknowns always converged to the same values even with unreasonable initial guesses. The Cij ...

Nonspecific-adsorption behavior of polyethylenglycol and bovine serum albumin studied by 55-MHz wireless-electrodeless quartz crystal microbalance.

The nonspecific binding ability of polyethylenglycol (PEG) and bovine serum albumin (BSA) on modified and unmodified surfaces is quantitatively studied by a wireless-electrodeless quartz crystal microbalance (WE-QCM). PEG and BSA are important blocking materials in biosensors, but their affinities for proteins and uncoated substrates have not been known quantitatively. The WE-QCM allows quantitative analysis of the adsorption behavior of proteins on the electrodeless surfaces. Affinities of PEG, BSA, human immunoglobulin G (hIgG), and Staphylococcus protein A (SPA) for alpha-SiO(2)(quartz), Au thin film, PEG, and BSA are systematically studied by the homebuilt flow-injection system. PEG shows low affinities for the SiO(2) surface (K(A)=4.2x10(4) M(-1)) and the Au surface (K(A)=6.6x10(4) M(-1)), but BSA shows higher affinity for the SiO(2) surface (K(A)=1.4x10(6) M(-1)). Both PEG and BSA show low affinities for hIgG (K(A) approximately 1.5x10(5) M(-1)). However, the number of binding sites of PEG to hIgG is significantly larger than that of BSA, indicating that blocking for hIgG is favorably achieved by BSA, rather than PEG.

Effect of applied stresses on magnetostriction of low carbon steel

Abstract We have measured the magnetostriction of low carbon steel specimens while applying magnetic fields, being both parallel and perpendicular to the uniaxial applied stress. An individual domain of a polycrystalline steel is elongated in its magnetization direction, which coincides with one of the crystallographic axes, 〈100〉. The magnetization appears as a result of the domain wall movement induced by the applied magnetic field. The rotation of the domain magnetization participates, when the field becomes larger. As the magnetic field is increased, the magnetostriction in the magnetization direction first increases and then shows a maximum when the rotation of the domain magnetization starts to occur. Since the stress affects the domain structure through magnetoelastic interaction, the maximum magnetostriction shows the stress dependence. The magnetoelastic interaction tends to increase the volume of the domains being either parallel to the tensile stress or perpendicular to the compressive stress. The amount of the domain wall movement, equivalently the maximum magnetostriction, is thus larger for the magnetization which is either perpendicular to the tensile stress or parallel to the compressive stress. In the experiment, the maxima of magnetostriction, up to 17 × 10−6, were measured with sufficient accuracy using semiconductor strain gauges attached to the specimens. The results support the above physical prediction. We found that the stress dependence of the maxima is almost insensitive to the relation between the rolling direction and the loading direction, which ensures that the magnetostriction method is suitable for the residual stress measurement.

Observation of higher stiffness in nanopolycrystal diamond than monocrystal diamond

Diamond is the stiffest known material. Here we report that nanopolycrystal diamond synthesized by direct-conversion method from graphite is stiffer than natural and synthesized monocrystal diamonds. This observation departs from the usual thinking that nanocrystalline materials are softer than their monocrystals because of a large volume fraction of soft grain-boundary region. The direct conversion causes the nondiffusional phase transformation to cubic diamond, producing many twins inside diamond grains. We give an ab initio-calculation twinned model that confirms the stiffening. We find that shorter interplane bonds along [111] are significantly strengthened near the twinned region, from which the superstiff structure originates. Our discovery provides a novel step forward in the search for superstiff materials.

Elastic-stiffness mapping by resonance-ultrasound microscopy with isolated piezoelectric oscillator

A resonance-ultrasound microscopy has been developed for mapping a material’s elastic constant in a localized surface region. It detects the effective elastic modulus through a resonance frequency of free vibrations of a solid probe touching the specimen via a small tungsten-carbide bearing. Langasite (La3Ga5SiO14) crystal is used as a probe because of the low sensitivity of its elastic constants to temperature and its high piezoelectric coefficients. The vibration of the probe is excited and detected with a surrounding solenoid coil. This noncontacting acoustic coupling isolates the probe vibration and measures the resonance frequency with an accuracy better than one part in 105. This microscopic method is applied to a composite material consisting of silicon-carbide (SiC) fibers in titanium-alloy matrix. The stiffness distribution inside a single fiber was determined.

Resonance acoustic-phonon spectroscopy for studying elasticity of ultrathin films

Ultrahigh-frequency phonon resonances were excited in ultrathin films (∼5nm) by femtosecond light pulses, and their resonance frequencies were measured to determine the through-thickness elastic constants. The studied materials were Pt and Fe. The elastic stiffness increases with decreasing film thickness for both materials, whereas the normal strain showed opposite thickness behavior. Analysis of the wave propagation using the third-order elastic constants explained these trends.