SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Ultrasonics

28

The purpose of this study was to clarify whether p38 MAPK is involved in the process of low intensity pulsed ultrasound (LIPUS) induced osteogenic differentiation of human periodontal ligament cells (HPDLCs).

Concepts: Periodontal ligament

28

The purpose of the present simulation study is to reveal how confining surfaces with different mechanical properties affect the acoustic response of a contrast agent microbubble. To this end, numerical simulations are carried out for three types of walls: a plastic (OptiCell) wall, an aluminium wall, and a biological tissue. For each wall, the behaviour of contrast microbubbles of three sizes is investigated. The spectral characteristics of the scattered pressure produced by the microbubbles are compared for two cases: the bubble oscillates far away from the wall and the same bubble oscillates in the immediate vicinity of the wall. The results of the simulations allow one to make the following main conclusions. The effect of the OptiCell wall on the acoustic bubble response is stronger than that of the aluminium and tissue walls. Changes in the bubble response near the wall are stronger when bubbles are excited above their resonance frequency. Considering changes in the fundamental and the 2nd harmonic with respect to the peak values of these components at different bubble radii, it is found that the changes are stronger for smaller bubbles and that the changes in the 2nd harmonic are stronger than those in the fundamental. These results allow one to gain an insight into conditions under which the effect of an elastic wall on the acoustic response of a contrast agent microbubble is easier to be detected.

Concepts: Resonator, English-language films, Wave, Acoustics, Sound, Resonance, The Wall, AnyLogic

28

For the ultrasonic testing at the wheel seat of railway axles, quantitative investigation of the reflection and transmission phenomena at the axle-wheel interface is important. This paper describes the influence of the axle-wheel interface on the ultrasonic testing of a fatigue crack in a wheelset by applying the spring interface model. The normal and tangential stiffnesses were identified experimentally for an as-manufactured wheelset at the normal incidence, and the reflection coefficient for the shear-wave oblique incidence was calculated. A parametric study was performed to clarify the influence of these interfacial stiffnesses on the incident-angle dependence of the reflection coefficient. The calculated reflection coefficient at the incident angle of 45° qualitatively explained the relative echo-height decrease due to the presence of a wheel observed experimentally for a wheelset in fatigue loading by rotating bending. The quantitative difference between the experimental and calculated results was considered to be due to the reduction of the effective interference of shrink fit by the wear at the axle-wheel interface during the fatigue loading as well as by the applied bending moment. For the estimated relative echo-height decrease to agree with the experimental results, the interfacial stiffnesses were found to be smaller than the values identified for the as-manufactured wheelset by a factor of 0.5-0.7.

Concepts: Snell's law, Refraction, Research, Total internal reflection, Geometrical optics, Angle of incidence, Wheel, Axle

28

It has recently been demonstrated that it was possible to individually trap 70μm droplets flowing within a 500μm wide microfluidic channel by a 24MHz single element piezo-composite focused transducer. In order to further develop this non-invasive approach as a microfluidic particle manipulation tool of high precision, the trapping force needs to be calibrated to a known force, i.e., viscous drag force arising from the fluid flow in the channel. However, few calibration studies based on fluid viscosity have been carried out with focused acoustic beams for moving objects in microfluidic environments. In this paper, the acoustic trapping force (F(trapping)) and the trap stiffness (or compliance k) are experimentally determined for a streaming droplet in a microfluidic channel. F(trapping) is calibrated to viscous drag force produced from syringe pumps. Chebyshev-windowed chirp coded excitation sequences sweeping the frequency range from 18MHz to 30MHz is utilized to drive the transducer, enabling the beam transmission through the channel/fluid interface for interrogating the droplets inside the channel. The minimum force (F(min)(,)(trapping)) required for initially immobilizing drifting droplets is determined as a function of pulse repetition frequency (PRF), duty factor (DTF), and input voltage amplitude (V(in)) to the transducer. At PRF=0.1kHz and DTF=30%, F(min)(,)(trapping) is increased from 2.2nN for V(in)=22V(pp) to 3.8nN for V(in)=54V(pp). With a fixed V(in)=54V(pp) and DTF=30%, F(min)(,)(trapping) can be varied from 3.8nN at PRF=0.1kHz to 6.7nN at PRF=0.5kHz. These findings indicate that both higher driving voltage and more frequent beam transmission yield stronger traps for holding droplets in motion. The stiffness k can be estimated through linear regression by measuring the trapping force (F(trapping)) corresponding to the displacement (x) of a droplet from the trap center. By plotting F(trapping) -x curves for certain values of V(in) (22/38/54V(pp)) at DTF=10% and PRF=0.1kHz, k is measured to be 0.09, 0.14, and 0.20nN/μm, respectively. With variable PRF from 0.1 to 0.5kHz at V(in)=54 V(pp), k is increased from 0.20 to 0.42nN/μm. It is shown that a higher PRF leads to a more compliant trap formation (or a stronger F(trapping)) for a given displacement x. Hence the results suggest that this acoustic trapping method has the potential as a noninvasive manipulation tool for individual moving targets in microfluidics by adjusting the transducer’s excitation parameters.

Concepts: Fluid dynamics, Fluid mechanics, Viscosity, Liquid, Surface tension, Fluid, Reynolds number, Drag

28

The control problem in ultrasound therapy is to destroy the tumor tissue while not harming the intervening healthy tissue with a desired temperature elevation. The objective of this research is to present a robust and feasible method to control the temperature distribution and the temperature elevation in treatment region within the prescribed time, which can improve the curative effect and decrease the treatment time for heating large tumor (⩾2.0cm in diameter). An adaptive self-tuning-regulator (STR) controller has been introduced into this control method by adding a time factor with a recursive algorithm, and the speed of sound and absorption coefficient of the medium is considered as a function of temperature during heating. The presented control method is tested for a self-focused concave spherical transducer (0.5MHz, 9cm aperture, 8.0cm focal length) through numerical simulations with three control temperatures of 43°C, 50°C and 55°C. The results suggest that this control system has adaptive ability for variable parameters and has a rapid response to the temperature and acoustic power output in the prescribed time for the hyperthermia interest. There is no overshoot during temperature elevation and no oscillation after reaching the desired temperatures. It is found that the same results can be obtained for different frequencies and temperature elevations. This method can obtain an ellipsoid-shaped ablation region, which is meaningful for the treatment of large tumor.

Concepts: Heat, Acoustics, Control theory, Physical quantities, Feedback, Sound, Length, Depth of field

27

A simulation study of Rayleigh wave devices based on a stacked AlN/SiO₂/Si(100) device was carried out. Dispersion curves with respect to acoustic phase velocity, reflectivity and electromechanical coupling efficiency for tungsten W and aluminium Al electrodes and different layer thicknesses were quantified by 2D FEM COMSOL simulations. Simulated acoustic mode shapes are presented. The impact of these parameters on the observed Rayleigh wave modes was discussed. High coupling factors of 2% and high velocities up to 5000 m/s were obtained by optimizing the AlN/SiO₂ thickness ratio.

Concepts: Operations research, Wave, Acoustics, Group velocity, Waves, Wave mechanics, Rayleigh wave, Surface acoustic wave

25

Geometrical and material property changes cause deviations in the resonant conditions used for noncollinear wave mixing. These deviations are predicted and observed using the SV(ω1)+L(ω2)→L(ω1+ω2) interaction, where SV and L are the shear vertical and longitudinal waves, respectively, and ω1, ω2 are their frequencies. Numerical predictions, performed for the scattered secondary field in the far field zone, show three field features of imperfect resonance conditions: (1) rotation of a scattered beam, (2) decrease in the beam amplitude, and (3) beam splitting. The response of the nonlinear ultrasonic wave mixing technique is verified experimentally in two ways: (1) detection of a kissing bond between two polyvinyl chloride (PVC) plates, and (2) detection of subsurface micro-cracks in polymethyl methacrylate (PMMA). A predominant decrease in nonlinear wave energy is observed in both experiments. Beam rotation and splitting is observed in the kissing-bond experiment, while a minor increase in the nonlinear wave energy up to 100% is observed in the micro-cracked PMMA specimen.

Concepts: Causality, Fundamental physics concepts, Electromagnetic radiation, Wave, Frequency, Sound, Waves, Window

24

Laser pulses focused near the tip of an elastic wedge generate acoustic waves guided at its apex. The shapes of the acoustic wedge wave pulses depend on the energy and the profile of the exciting laser pulse and on the anisotropy of the elastic medium the wedge is made of. Expressions for the acoustic pulse shapes have been derived in terms of the modal displacement fields of wedge waves for laser excitation in the thermo-elastic regime and for excitation via a pressure pulse exerted on the surface. The physical quantity considered is the local inclination of a surface of the wedge, which is measured optically by laser-probe-beam deflection. Experimental results on pulse shapes in the thermo-elastic regime are presented and confirmed by numerical calculations. They pertain to an isotropic sharp-angle wedge with two wedge-wave branches and to a non-reciprocity phenomenon at rectangular silicon edges.

Concepts: Quantum mechanics, Optics, Light, Optical fiber, Pulse, Wave, Acoustics, Physical quantity

23

The influence of the width of the gap between the free side of the piezoelectric lateral electric field excited resonator and the metal film placed on the dielectric plate on the frequencies of the parallel and series resonances was experimentally and theoretically studied. The measurements were carried out in the temperature range of 14-45 °C. It has been shown that the change of the gap width from 0 up to 3.5 mm leads to the change of the parallel resonant frequency on 1.3% at the constant temperature. At the same conditions the change of the series resonant frequency does not exceed 0.07%. Theoretical analysis quantitatively confirmed the experimental dependencies of the aforementioned frequencies on the gap width at the room temperature. At that the maximum difference between the theoretical and experimental values of the parallel and series resonant frequencies in all cases does not exceed 1.2%. The obtained results may be used as the basis for the development of the sensors for the measurement of the displacement in the interval of 0.2-2 mm in the temperature range of 15-45 °C.

Concepts: Resonance, Acoustic resonance

23

The effect of a thin layer with the finite surface conductivity located near the lateral electric field excited resonator on its characteristics is studied theoretically and experimentally. It has been shown that for the fixed distance between the free side of the resonator and conducting layer with increasing the surface conductivity of the layer the resonant frequency of the parallel resonance remains initially practically constant, then sharply decreases in a certain range and then insignificantly changes. For the fixed value of the layer conductivity the parallel resonant frequency increases at the increase in the gap between the resonator and layer and then achieves the saturation. The maximum change in the frequency of the parallel resonance corresponds to a zero gap when the layer conductivity varies over the wide range is equal to ∼1%. The frequency of the series resonance decreases only by ∼0.08% due to the change in the layer conductivity. The obtained results may be useful for the development of the gas sensors based on the lateral electric field excited piezoelectric resonator conjugated to the gas sensitive film, the conductivity of which changes in the presence of the given gas.

Concepts: Resonator, Resonance, Acoustic resonance, Standing wave, Mechanical resonance