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A varifocal concave–convex lens using ultrasound and transparent viscoelastic gel is reported. The configuration of the lens is simple and thin, consisting of four pieces of a piezoelectric ultrasound transducer, a glass disk, and a transparent silicone gel film. It uses a combination of the ultrasound resonant flexural standing- and traveling-wave modes excited by in-phase and four-phase drives so that the lens can change its shape to both concave and convex by switching the resonance mode with the same structure. The acoustic radiation force (ARF) originated from the resonant flexural vibration modes changed the surface profile of the gel. Convex and concave deformation were generated at the center of the lens at the resonance frequencies of 38 and 60 kHz, respectively, indicating that a varifocal concave–convex lens could be fabricated by controlling the driving frequency, voltage amplitude, and phase differences among the ultrasound transducers. The deformational displacement on the lens surface and the change in the focal length increased with the input voltage amplitude. The optical microscopic images observed through the lens were enlarged $1.28\times $ (reduced $0.92\times $) in the convex (concave) mode with 20 ${V}_{\text {pp}}$. The response time for focusing and the temperature stability under operation were evaluated. By switching the resonance vibration modes of the lens through the input signals to multiple ultrasound transducers, the variable-focus function with both concave and convex lenses was achieved in the same configuration. [ABSTRACT FROM AUTHOR]

A pump–probe system with a subnanosecond pulsed laser is expected to be a compact and inexpensive transient spectroscopic system that enables nondestructive and noncontact evaluations of the physical properties. However, an improvement in the sensitivity and a theoretical model to complement the measurement signal are necessary to obtain the transient signal precisely because of the low sensitivity and large time resolution. We have developed a highly sensitive pump–probe system with a subnanosecond pulsed laser that combines signal amplification based on surface plasmon resonance (SPR) in this study. An integrated theoretical model of the transient response obtained by a subnanosecond pump–probe under the SPR condition was proposed. Our model consisted of the profile descriptions of the used pulse source, temperature change, generated thermoelastic stress, estimated permittivity change in the metal film, and estimated reflectivity change. The theoretical estimations in the time domain and the incident angle dependence were compared with those of the experimental results to verify our theory. As a result, the estimations were well in agreement with the experimental results. Moreover, the signal-amplification mechanism based on SPR was discussed using our theory. The amplification was caused by the broadening of the resonant curve of SPR and the shift of the resonant angle, which seemed to come from the increase in the electron–phonon scattering rate and the thermal expansion of the metal film, respectively. A clear mechanism of SPR-based signal amplification of the subnanosecond pump–probe was identified through experimental and theoretical approaches. [ABSTRACT FROM AUTHOR]

Diabetic patients have a higher risk of bone fracture than those without diabetes, despite a normal bone mineral density. This higher riskmay result fromthe deterioration of collagen because of glycation. The objective of this study was to investigate the elastic properties of glycated collagen using the micro-Brillouin scattering technique. Using single-layer uniaxial collagen films with a thickness of approximately $30~\mu \text{m}$ , the longitudinal wave velocities, propagating in the parallel andperpendiculardirectionswith respect to the collagen fiber orientation, were measured in dry and wet film specimens. The wave velocities in the glycated collagen specimens decreased as a function of glycation time. This decrease depended on the direction of collagen fiber alignment and wave propagation. The lowest velocity due to glycation in thewet filmswas foundwhen the ultrasound propagated perpendicular to the fiber direction. These results indicate that the glycation of collagen in the bone may also reduce bone elasticity and suggest that the effects of glycation on collagen films may be anisotropic. [ABSTRACT FROM AUTHOR]

Piezoelectricity in bone is thought to be a mechanism by which ultrasound promotes the healing of bone fractures. However, a few studies have been conducted in the more clinically relevant megahertz range. To understand the piezoelectricity in bone, we fabricated ultrasound transducers using bone samples as piezoelectric materials and identified the longitudinal ultrasound radiation and reception in the megahertz range. The maximum transmitting sensitivity of the bone transducer was 140 mPa/V, which was nearly 1/1000 of a polyvinylidene difluoride (PVDF) transducer that has better electrical properties and piezoelectricity. The resonance frequencies of the transducer depend on the plate thickness and angle between the bone axis (alignment direction of the hydroxyapatite crystallites) and ultrasound propagation direction, reflecting the anisotropic character of the bone. The reception and transmission sensitivities of the bone transducers also depend on the plate thickness and angle, showing maximum values at off-axis angles. These results indicate the existence of both piezoelectricity and inverse piezoelectricity in bone, which may be key factors in understanding the bone healing by low-intensity biophysical (electrical or mechanical) stimulation. [ABSTRACT FROM AUTHOR]

The viscosity and the surface profile of a thixotropic gel were controlled via ultrasound vibrations. The ultrasound device consisted of two piezoelectric lead zirconate titanate transducers glued to each end of a 60-mm-long rectangular glass substrate. It generated a 71-kHz flexural standing wave along the length. A 0.9-mm-thick thixotropic gel film made from silicone oil and hydrophobic fumed silica was formed on the glass substrate. The ultrasound vibration decreased the film viscosity, and its surface profile could be changed by the acoustic radiation force acting from the gel to the surrounding air, generated by the flexural vibration of the substrate. The transient response of the surface profile was observed by switching the ultrasound excitation ON and OFF. When the excitation was switched OFF, the gel displacement gradually decreased, but the surface profile did not return to that of the initial steady state, indicating that the viscosity recovered in time to preserve the surface profile. When a pulsed megahertz (MHz) signal was used to control the gel deformation, the surface profile rapidly approached the initial steady-state profile after the excitation. [ABSTRACT FROM AUTHOR]

This paper investigates acoustic levitation and noncontact transportation techniques for use with planar objects. An acoustic levitation system was developed which consists of a 1-mm-thick and 400-mm-long bending plate along with two bolt-clamped Langevin-type transducers (BLTs) that have stepped horns. A plane reflector was installed parallel to the vibrating plate to generate an ultrasound standing wave between the reflector and the plate. The sound pressure distribution in the ultrasound waveguide was calculated via finite-element analysis to investigate the effects of levitation of a planar object in the standing-wave field. A 1-mm-thick polystyrene plate was levitated along the nodal line of the acoustic standing wave in the waveguide. By controlling the driving phase difference between the two BLTs, the position at which flexural vibration occurs on the vibrating plate could be shifted along the length direction, and the trapped planar object could be moved by 9 mm along the same direction when the phase difference was varied from 0° to 360°. [ABSTRACT FROM AUTHOR]

It is difficult to perform 2-D imaging of elastic properties using the Brillouin scattering technique because the weak thermal phonon signal in the sample leads to low measurement accuracy and long measurement times. To improve the phonon signal, we artificially induced acoustic phonons using a ScAlN thin-film piezoelectric transducer, which has a giant piezoelectricity. The film was grown using RF magnetron sputtering of a ScAl alloy target on a silica glass bar sample. Using a microwave probe, the electric power applied to the film was 1 mW at 875 MHz. We obtained the enhancement of the Brillouin scattering signal in the silica glass bar sample due to the induced phonons. Compared with and without the induced phonons from the ScAlN film transducer, the peak intensity improved by nearly 3 orders of magnitude. This technique can significantly shorten the time required for the Brillouin scattering measurements. [ABSTRACT FROM AUTHOR]

We have experimentally investigated wave velocities and refractive indices in bulk and film samples [a GaN single-crystal plate and c-axis-oriented Sc{x}{\text{Al}}({{1} - {{x}})}{\text{N}} $(x= 0.00-0.63)$ films] by Brillouin scattering (BRS). All of the piezoelectrically unstiffened elastic constants and the ordinary refractive index of the GaN single-crystal plate were determined from the reflection-induced ${{\varTheta {\text A}}}({{{\text {RI}}\varTheta {\text A}}})$ scattering geometry and the combination of 90R and 180° scattering geometries. The uncertainties of the measured wave velocities were approximately 0.17% (${{{\text {RI}}\varTheta {\text A}}}) and 2.5% (combination technique). In addition, the longitudinal-wave velocities of \textS\textc{x}{\text{A}}{{\text {l}}({{1} - {{x}})}}{\text{N}} films propagating in the normal direction were obtained by the combination technique. The maximum uncertainty was approximately 3.3%. The shear-wave velocities and refractive indices of \textS\textc{x}{\text{A}}{{\text {l}}({{1} - {{x}})}}{\text{N}} films were also investigated by the 90R scattering geometry using velocities measured by high-overtone bulk acoustic resonators. The softening trends of the elasticity were obtained from the measured longitudinal- and shear-wave velocities, although there were large uncertainties in the Brillouin measurement system owing to thermal instability. [ABSTRACT FROM AUTHOR]

This paper investigates a two-dimensional ultrasonic manipulation technique for small objects in air. The ultrasonic levitation system consists of a rectangular vibrating plate with four ultrasonic transducers and a reflector. The configuration of the vibrator, the resonant frequency, and the positions of the four transducers with step horns were determined from finite element analysis such that an intense acoustic standing-wave field could be generated between the plates. A lattice flexural vibration mode with a wavelength of 28.3 mm was excited on the prototype plate at 24.6 kHz. Small objects could get trapped in air along the horizontal nodal plane of the standing wave. By controlling the driving phase difference between the transducers, trapped objects could be transported without contact in a two-dimensional plane. When the phase difference was changed from 0° to 720°, the distance moved by a small particle in the orthogonal direction was approximately 29 mm, which corresponds with the wavelength of the flexural vibration on the vibrating plate. [ABSTRACT FROM AUTHOR]