Particle Displacement Amplitude Research Articles

Love‐like wave dispersion in a highly non‐homogeneous viscoelastic orthotropic layer under the effect of non‐local elasticity

This paper examines the effects of non‐local elasticity on the propagation of Love‐like waves in a Voigt‐type viscoelastic layer over an elastic half‐space. The model's geometry is considered orthotropic, highly non‐homogeneous, and initially stressed media in the context of non‐local continuum mechanics. The non‐homogeneity functions are regarded as binomial functions with a positive real exponent. Two different non‐local parameters have been defined by considering different internal characteristic lengths for the layer and half‐space. Modified Bessel functions of the first and second kinds are used to determine displacement functions. Asymptotic representations of derivatives of modified Bessel's functions have been derived to get the compact form of the dispersion equation. A comparison of phase velocity equations with classical Love wave equations has demonstrated the validity of our model. It is found that different modes of Love‐like waves are dispersive and highly affected by the attenuation coefficient. Additionally, non‐local parameters significantly influence the limitation of phase velocity modes of Love‐like waves. The phase and damped velocity versus non‐local parameters have been depicted with the effect of different parameters in the model. It has been found that the non‐local parameters decrease the particle displacement amplitude in elastic half‐space and rapidly eliminate waves with depth.

Analysis of the Effect of Electrode Materials on the Sensitivity of Quartz Crystal Microbalance.

This paper investigated the effect of electrode materials on the performance of quartz crystal microbalance (QCM) sensors by means of theoretical calculation, experiment, and finite element analysis methods. First, we calculated the particle displacement amplitude and thus obtained the mass sensitivity function distribution of QCMs with gold, silver and aluminum electrodes, and found that the QCM with the gold electrode has the highest mass sensitivity at the center of the electrode. Then, we tested the humidity-sensing performance of QCMs with gold, silver, and aluminum electrodes using graphene oxide (GO) as the sensitive material, and found that the QCM with the gold electrode has higher humidity sensitivity. Finally, we used the finite element analysis software COMSOL Multiphysics to simulate the specific electrode material parameters that affect the sensitivity of the QCMs. The simulation results show that the density and Young’s modulus of the electrode material parameters mainly affect the sensitivity. The results of this paper are instructive for optimizing QCM sensor performance and improving the capability of QCM quantitative analysis.

Video microscopy-based accurate optical force measurement by exploring a frequency-changing sinusoidal stimulus

Optical tweezers are constantly evolving micromanipulation tools that can provide piconewton force measurement accuracy and greatly promote the development of bioscience at the single-molecule scale. Consequently, there is an urgent need to characterize the force field generated by optical tweezers in an accurate, cost-effective, and rapid manner. Thus, in this study, we conducted a deep survey of optically trapped particle dynamics and found that merely quantifying the response amplitude and phase delay of particle displacement under a sine input stimulus can yield sufficiently accurate force measurements. In addition, Nyquist-Shannon sampling theorem suggests that the entire recovery of the accessible particle sinusoidal response is possible, provided that the sampling theorem is satisfied, thereby eliminating the requirement for high-bandwidth (typically greater than 10 kHz) detectors. Based on this principle, we designed optical trapping experiments by loading a sinusoidal signal into the optical tweezers system and recording the trapped particle responses with 45 frames per second (fps) charge-coupled device (CCD) and 163 fps complementary metal-oxide-semiconductor (CMOS) cameras for video microscopy imaging. The experimental results demonstrate that the use of low-bandwidth detectors is suitable for highly accurate force quantification, thereby greatly reducing the complexity of constructing optical tweezers. The trap stiffness increases significantly as the frequency increases, and the experimental results demonstrate that the trapped particles shifting along the optical axis boost the transversal optical force.

The Rapid Detection Technology of Lamb Wave for Microcracks in Thin-Walled Tubes

Thin-walled tubes are a kind of pressure vessel formed by a stamping and drawing process, which must withstand a great deal of sudden pressure during use. When microcrack defects of a certain depth are present on its inner and outer surfaces, severe safety accidents may occur, such as cracking and crushing. Therefore, it is necessary to carry out nondestructive testing of thin-walled tubes in the production process to eliminate the potential safety hazards. To realize the rapid detection of microcracks in thin-walled tubes, this study could be summarized as follows: (i) Because the diameters of the thin-walled tubes were much larger than their thicknesses, Lamb wave characteristics of plates with equal thicknesses were used to approximate the dispersion characteristics of thin-walled tubes. (ii) To study the dispersion characteristics of Lamb waves in thin plates, the detection method of the mode was determined using the particle displacement–amplitude curve. (iii) Using a multi-channel parallel detection method, rapid detection equipment for Lamb wave microcracks in thin-walled tubes was developed. (iv) The filtering peak values for defect signal detection with different depths showed that the defect detection peak values could reflect the defect depth information. (v) According to the minimum defect standard of a 0.045-mm depth, 100,000 thin-walled tubes were tested. The results showed that the missed detection rate was 0%, the reject rate was 0.3%, and the detection speed was 5.8 s/piece, which fully meets the actual detection requirements of production lines. Therefore, this study not only solved the practical issues for the rapid detection of microcracks in thin-walled tubes but also provided a reference for the application of ultrasonic technology for the detection of other components.

A method to estimate the absolute ultrasonic nonlinearity parameter from relative measurements

The ultrasonic nonlinearity parameter (β) is determined from the particle displacement amplitudes of the fundamental and second-order harmonic components in an ultrasonic wave propagated through a material. This parameter is generally referred to as the absolute parameter. However, measuring the second harmonic component is especially difficult because its amplitude is usually much smaller than those of signals in typical ultrasonic measurements. For this reason, most studies use the relative parameter determined using the measured electric signal amplitudes of the fundamental and second harmonic ultrasonic waves. However, in many occasions, the absolute parameter is needed for a quantitative assessment of material degradation. This study proposes a method to estimate the absolute parameter from a measured relative parameter along with a proportionality constant between normalized absolute and relative parameters. This method is based on the observed fact that the ratio of between normalized relative and absolute parameters is identical after compensating proportionality constant. The method was experimentally validated for Al6061-T6 alloy specimens heat-treated for different aging times. The parameter determined through the proposed method were compared with the absolute parameters which were measured separately. The results show that these two parameters were close to each other within the measurement errors.

Acoustic particle displacement resonator

A simple device consisting of a waveguide and two loudspeakers is proposed for generation of low-frequency standing acoustic field with high amplitude of acoustic velocity and particle displacement, which is primarily intended to be used for stabilization of electric discharges in acoustic field. A coupled model of loudspeakers and nonlinear wave equation including waveguide radius variability, thermoviscous attenuation in boundary layer and minor losses is developed. The results of the conducted experiments validate the model revealing that the minor losses and acoustically generated turbulence in the boundary layer represent an important means of acoustic energy dissipation in this and similar applications.

Relative excitation of the seismic shear waves Sn and Lg as a function of source depth and their propagation from Melanesia and Banda arcs to Australia

SUMMARY. - Seismic activity associated with the collision of the continentalpart of the Australian plate with the oceanic Melanesian arcs along Papua NewGuinea and the Banda arc provides an unusual opportunity to study the relativeexcitation of the seismic shear waves Sn and Lg. These waves are produced byearthquakes located along the arcs in the upper 200 km of the earth and arerecorded by the Australian WWSSN Stations at Charters Towers (CTA) and AliceSprings (ASP). The paths to these stations are predominantly continental. The dataclearly show that for events located at crustal depths, Lg is the predominant phaseon the records and Sn is either absent or very weak. For events deeper than about50-70 km, Sn becomes the predominant phase on the records. These observationsarc in qualitative agreement with the explanations of Sn and Lg as highermodes of surface waves, for the particle displacement amplitudes are maximumwithin the crust for Lg and maximum within the lid of the lithospheric mantlefor Sn. The data suggest that either the crustal wave guide for Lg is moreefficient than that for Sn, or that Lg is more easily excited than Sn. No clearLg is observed from shallow earthquakes when the length of the segment of thepath crossing oceanic structure is greater than about 200 km. Also, widespreadQuaternary volcanism within the « stable » area of central Papua New Guineato the south of the mobile belt does not seem to affect the efficient transmissionof high-frequency (1 Hz) shear energy.The paths from events located along the New Hebrides, Solomon, and NewBritain arcs to Australia traverse oceanic structure, and no Lg is observed fromthese paths. The inefficient propagation of Sn along these paths from bothshallow and intermediate-depth events can be explained as follows: 1) Forthe New Hebrides case, the inefficiency of Sn propagation for paths exceedingabout 20° distance is related to the relatively young age (Lower to MiddleEocene) of the suboceanic lithosphere of the Coral Sea. As proposed by CHINN,ISACKS and BARAZANGI (1979), such relatively thin lithosphere is probably not anefficient wave guide for shear energy of about 1 Hz 2). The inefficiency of Snpropagation from events located along the northern Solomon and the New Britainarcs is probably due to anomalous attenuation in the uppermost mantle beneaththe Woodlark basin and beneath southeastern Papua New Guinea. 3) Theinefficiency of Sn propagation from events deeper than about 150 km locatedin the westernmost part of the northerly-dipping Benioff zone of the NewBritain arc could be due either to structural isolation of the nearly verticaldescending segment of the plate in which the events occur, or could be due tostructural complexity of the plates in the region which interrupts the waveguide for Sn to the Australian stations. This structural feature could be theresult of the collision of the Australian plate and the New Britain arc.

Numerical study of the performance of thermally isolated thermoacoustic-stacks in the linear regime

A simplified calculus model to investigate on the transverse heat transport near the edges of a thermally isolated thermoacoustic stack in the low acoustic Mach number regime is presented. The proposed methodology relies on the well known results of the classical linear thermoacoustic theory which are implemented into an energy balance calculus-scheme through a finite difference technique. Details of the time-averaged temperature and heat flux density distributions along a pore cross-section of the stack are given. It is shown that a net heat exchange between the fluid and the solid walls takes place only near the edges of the stack plates, at distances from the ends not exceeding the peak-to-peak particle displacement amplitude. The structure of the mean temperature field within a stack plate is also investigated; this last results not uniform near its terminations giving rise to a smaller temperature difference between the plate extremities than that predicted by the standard linear theory. This result, when compared with experimental measurements available in literature, suggests that thermal effects localized at the stack edges may play an important role as sources of the deviations found between linear theory predictions and experiments at low and moderate Mach numbers.

Computation of the time-averaged temperature fields and energy fluxes in a thermally isolated thermoacoustic stack at low acoustic Mach numbers

A simplified calculus model to investigate on the transverse heat transport near the edges of a thermally isolated thermoacoustic stack in the low acoustic Mach number regime is presented. The proposed methodology relies on the well-known results of the classical linear thermoacoustic theory which are implemented into an energy balance calculus-scheme through a finite difference technique. Details of the time-averaged temperature and heat flux density distributions along a pore cross-section of the stack are given. It is shown that a net heat exchange between the fluid and the solid walls takes place only near the edges of the stack plates, at distances from the ends not exceeding the peak-to-peak particle displacement amplitude. The structure of the mean temperature field within a stack plate is also investigated; this last results not uniform near its terminations giving rise to a smaller temperature difference between the plate extremities than that predicted by the standard linear theory. This result, when compared with experimental measurements available in literature, suggests that thermal effects localized at the stack edges may play an important role as sources of the deviations found between linear theory predictions and experiments at low and moderate Mach numbers.

Flowing water decreases hydrodynamic signal detection in a fish with an epidermal lateral-line system

The lateral-line system of the common bully, Gobiomorphus cotidianus, is unusual in that it possesses an extensive array of superficial neuromasts. Fish were trained to orientate to a small vibrating bead (50 Hz). By manipulating the amplitude of vibration to determine the threshold level for the behaviour, the hydrodynamic detection capabilities of the common bully were characterised in both still- and flowing-water. In still water, the common bully attained a detection threshold (calculated as the amplitude of water particle displacement at the snout) of 3.3 × 10−5 cm at 50 Hz. Successive elevations in the background flow caused a 10-fold decrease in detection sensitivity. At a background flow of 4.5 cm s–1 the detection threshold increased to 3 × 10−4 cm. These findings demonstrate that a lateral-line system that lacks sub-surface canal neuromasts is most sensitive in still-water conditions (low-noise). However, this system is compromised under flowing-water conditions such that sensitivity is reduced at current velocities >1.5 cm s–1.

Numerical Simulation of Stack-Heat Exchangers Coupling in a Thermoacoustic Refrigerator

The Navier‐Stokes equations for an unsteady and compressible flow are solved numerically to investigate the flow near the stack of a thermoacoustic refrigerator. The computational domain is a resonator “slice” including the resonator end but not the source. An incoming wave is introduced into the domain using the method of characteristics. Also included in the domain is a stack plate and two heat exchangers. The effects of the acoustic Mach number and geometrical parameters on refrigerator performance is investigated. Of special interest are some nonlinear temperature oscillations, which are not predicted by linear models and are due to acoustic propagation, and coupling between the stack plate and the heat exchangers. It is shown that the maximum heat pumping occurs fo ra stack/heat exchanger separation that is of the order of one particle displacement amplitude.

Improvement of NOx Removal by Silent Discharge in Acoustical Standing Wave Field.

The purpose of this study is to discuss the effects of sound wave on discharge and NOx removal. Against this backdrop, we removed NOx from NO/N2 mixed gas by superimposing silent discharge and sound wave in an acoustical standing wave field. As the results, NO removal rate and efficiency increase with increasing sound pressure. In particular, highest NOx removal rate is obtained when the electrode is located at the node point of sound pressure distribution, that is, at the maximum point of the particle velocity. This result shows significant improvement on NO removal by superimposing silent discharge and sound wave. Furthermore, NO removal rate decreases with increasing resonance frequency, for the reason of decreasing amplitude of particle displacement. Therefore, it is considered that NO removal rate relates to particle velocity and amplitude of particle displacement.

Mechanoreception, a possible mechanism for food fall detection in deep-sea scavengers

There is strong evidence in the literature that energy supply for deep-sea scavengers is largely restricted to food falls of dead vertebrates such as fish and mammals. The problem for any scavenger inhabiting the seafloor is the unpredictability both in space and time of food fall events. It is generally accepted that chemoreception is one of the major means by which marine organisms detect food sources. Another major source of potential information, however, may come from hydroacoustic stimuli, which have long-range penetration. Such hydroacoustic stimuli will either arise when a large carcass hits and impacts the seafloor or during food consumption of scavengers producing feeding noises. The intensity and transmission characteristics depend upon sediment properties, size, weight and composition of the carcass as well as on size and mouthpart morphology of feeding individuals. In this study the relevance of hydroacoustic stimuli for food fall detection has been investigated in the pandalid shrimp Pandalus borealis Krøyer, 1838. The sensitivity of P. borealis to particle displacement amplitude was found to be close to values measured in other crustaceans. Based on 228 single experiments carried out with five specimens, our results indicate that low-frequency noises may be helpful in detecting food fall events but only in the near-field. In this paper we suggest that the impact of a sinking carcass at the seafloor is a likely source producing elastic waves at the water–seafloor interface. Based on both empirical findings and general theoretical calculations of elastic waves originating from a sinking object hitting the seafloor we conclude that such “micro seismic events” may allow resting scavengers even several hundred metres away to detect a food source.

An experimental study of heat transfer from a cylinder in low-amplitude zero-mean oscillatory flows

This is the report of an experimental study on the convective heat transfer behavior from a cylinder in an intense acoustic field which is representative of a strong zero-mean oscillatory flow. The measurements are based on a steady state technique in which, at equilibrium, a predetermined rate of heat dissipation in the cylinder is balanced by the convective cooling action of the acoustic field. Only low-amplitude cases have been treated for which the particle displacement amplitude in the oscillatory flow is small on the scale of the cylinder diameter. Two distinct flow regimes have been identified. The first regime, consistent with theory, is the laminar attached flow regime which shows the expected square root dependence of the Nusselt number, Nu, on the appropriate Reynolds number, which in this case is the streaming Reynolds number, R s. The second regime, which is less well understood, is predicted to be an unstable regime in which vortex shedding is prevalent, contributing to higher heat transfer rates. Suitable correlations have been provided for both regimes for the case of air, and suggestions have been included to extend them to other Prandtl number gases for which they are likely to be used. This work could find application in the design of heat exchangers for thermoacoustic engines.

Stress-wave displacement polarizations and aftenuation in unidirectional composites: Theory and experiment

The wave propagation mechanism of changes in displacement polarizations was studied in unidirectional graphite/epoxy composite materials. Change in Displacements can be large enough to cause a transition in the mode or displacement polarizations from longitudinal to transverse. These unusual mode transitions are a result of the peculiar elastic anisotropy observed in only a few crystals and unidirectional graphite/epoxy composities at high-fiber volume fractions Theoretical calculation of these mode transitions were compared with experimental measurements Mode transitions occur when the wave vector orientation is varied from 51.9° to 74.4° in unidirectional samples of T300/5208 graphite/epoxy composite with a 0.6°-fiber volume fraction. Energy flux deviation and particle displacement directions and amplitudes also were compared with theory. To show this mode transition, an attenuation study was performed. The attenuation coefficient, measured in units of reciprocal time, does not appear to depend on the wave vector orientation and the wave type (quasi-transverse and quasi-longitudinal waves) at 5-MHZ frequency. But the attenuation coefficient, expressed in units of reciprocal length, does depend on the wave type and the wave vector orientation because the wave velocity is included in the calculation of this coefficient. Previous studies have focused on how anisotropy and attenuation influence the stress wave speed (eigenvalues), but in this study we focused more on how the same parameters influence the displacement polarizations (eigenvectors) of the same propagating waves. Because eigenvalues and their corresponding eigenvectors are both solutions of the same eigenvalue problem, more attention should be given to measurement of the eigenvectors.

Multifrequency evaluation of different immunosorbents on acoustic plate mode sensors.

Previous studies of acoustic plate modes on ZX-LiNbO3 have indicated that practical mass-sensitive immunosensors can be implemented by using devices with higher frequencies of operation and/or by improving techniques for the immobilization of antibodies. However, it is also known from these studies that the viscoelastic properties of aminosilane films, used for the covalent immobilization of antibodies on the crystal surface, cannot be ignored in the sensor response. In the present work, in an attempt to study the effect of viscoelasticity of the binding film, three different films with different viscoelasticity and binding capacities, an aminosilane, a dextran, and a poly-(etherurethane)-based immunosorbent (XP-5), were prepared on the sensor surface for the immobilization of antibodies. Immunochemical reactions were monitored by the acoustic plate mode sensor at three different frequencies, thus allowing the direct observation of the frequency dependence of mass sensitivity with different films. Depending on the type of immunosorbent, the sensitivity at the third harmonic was enhanced by a factor of 2-5 with respect to the fundamental response. A third acoustic mode at a closely spaced frequency to the third harmonic yielded lower sensitivity values, which indicates that sensitivity depends not only on the frequency of device operation but also on particle displacement amplitude and components of the selected wave. Since antigen binding capacities of the different immunosorbents were determined independently by a modified ELISA test, sensor responses can also be correlated to the immunosorbent structure, and hence the viscoelastic properties. A dual delay line configuration was used which compensates for second-order effects such as temperature variations and nonspecific adsorption.

Stress-Wave Displacement Polarizations and Attenuation in Unidirectional Composites: Theory and Experiment

Abstract The wave propagation mechanism of changes in displacement polarizations was studied in unidirectional graphite/epoxy composite materials. Change in Displacements can be large enough to cause a transition in the mode or displacement polarizations from longitudinal to transverse. These unusual mode transitions are a result of the peculiar elastic anisotropy observed in only a few crystals and unidirectional graphite/epoxy composities at high-fiber volume fractions. Theoretical calculation of these mode transitions were compared with experimental measurements. Mode transititons occur when the wave vector orientation is varied from 51.9° to 74.4° in unidirectional samples of T300/5208 graphite/epoxy composite with a 0.6°-fiber volume fraction. Energy flux deviation and particle displacement directions and amplitudes also were compared with theory. To show this mode transition, an attenuation study was performed. The attenuation coefficient, measured in units of reciprocal time, does not appear to depend on the wave vector orientation and the wave type (quasi-transverse and quasi-longitudinal waves) at 5-MHz frequency. But the attenuation coefficient, expressed in units of reciprocal length, does depend on the wave type and the wave vector orientation because the wave velocity is included in the calculation of this coefficient. Previous studies have focused on how anisotropy and attenuation influence the stress wave speed (eigenvalues), but in this study we focused more on how the same parameters influence the displacement polarizations (eigenvectors) of the same propagating waves. Because eigenvalues and their corresponding eigenvectors are both solutions of the same eigenvalue problem, more attention should be given to measurement of the eigenvectors.

Low-frequency propagation modes in a liquid-filled elastic tube waveguide

Axisymmetric propagation in a liquid-filled elastic tube waveguide is considered, with emphasis on the two modes existing down to zero frequency. Previous work by Del Grosso is used as the basis of the theoretical description of modal phase velocities and particle displacement profiles in such waveguides. It is shown that certain combinations of material properties can produce a mode which, in the zero frequency limit, has plane-wave motion in the liquid. Two examples of waveguides with very different wall compliance, aluminum/water and PVC/water, are studied numerically and experimentally. Numerical calculations are used to show the frequency dependence of phase velocity in all waveguide modes and the radial dependence of complex particle displacement amplitude in the two low-frequency modes (ET0 and ET1). Contrasting behavior in the two waveguides is seen—approximate plane-wave motion in the liquid occurs in the ET0 mode of the aluminum/water waveguide, but in the ET1 mode of the PVC/water waveguide. Experimental measurements of the frequency dependence of phase velocity in the ET0 and ET1 modes of these waveguides are also presented. Good agreement with numerical predictions is obtained in both cases, although experimental difficulties more severely limit the frequency range of measurement in the PVC/water waveguide.

Absolute ultrasonic displacement amplitude measurements with a submersible electrostatic acoustic transducer

An experimental technique for absolute measurement of ultrasonic wave particle displacement amplitudes in liquids is reported. The technique is capable of measurements over a frequency range of two decades with a sensitivity less than one angstrom. The technique utilizes a previously reported submersible electrostatic acoustic transducer (ESAT) [Rev. Sci. Instrum. 50, 31 (1979)] featuring a conductive membrane stretched over a recessed electrode. An uncertainty analysis shows that the displacement amplitude of an ultrasonic plane wave incident on the ESAT can be experimentally determined to better than 2.3%–4%, depending on frequency, in the frequency range of 0.5–15 MHz. Membranes with lower and more uniform areal densities can improve the accuracy and extend the operation to higher frequencies.

Boundary-layer transition problems for forced and for thermally driven gas oscillations

The transition of the acoustic (Stokes) boundary layer from laminar to turbulent flow has been observed and also to some extent theoretically explained for forced oscillations of a gas column in a tube. The pertinent critical Reynolds number is the ratio of the particle displacement amplitude to the Stokes boundary layer thickness. For thermally driven acoustic oscillations, there seems to be no experimental evidence for the occurrence of turbulence, in “ordinary” gases that have a Prandtl number of the order 1. For gases with high thermal conductivity (i.e., with near-zero Prandtl number), theory predicts extremely high amplitudes of the second-order velocity (associated with acoustic streaming) in the thermal boundary layer. Even for very weak acoustic oscillations, this means a “shortcut to turbulence.” If the tube or channel width is reduced to the order of the thermal boundary layer thickness, then acoustic streaming effects are drastically reduced and laminar flow is to be expected.