Showing papers on "Acoustic wave published in 2008"

Surface acoustic wave biosensors: a review

Abstract: This review presents an overview of 20 years of worldwide development in the field of biosensors based on special types of surface acoustic wave (SAW) devices that permit the highly sensitive detection of biorelevant molecules in liquid media (such as water or aqueous buffer solutions). 1987 saw the first approaches, which used either horizontally polarized shear waves (HPSW) in a delay line configuration on lithium tantalate (LiTaO3) substrates or SAW resonator structures on quartz or LiTaO3 with periodic mass gratings. The latter are termed “surface transverse waves” (STW), and they have comparatively low attenuation values when operated in liquids. Later Love wave devices were developed, which used a film resonance effect to significantly reduce attenuation. All of these sensor approaches were accompanied by the development of appropriate sensing films. First attempts used simple layers of adsorbed antibodies. Later approaches used various types of covalently bound layers, for example those utilizing intermediate hydrogel layers. Recent approaches involve SAW biosensor devices inserted into compact systems with integrated fluidics for sample handling. To achieve this, the SAW biosensors can be embedded into micromachined polymer housings. Combining these two features will extend the system to create versatile biosensor arrays for generic lab use or for diagnostic purposes.

Focusing microparticles in a microfluidic channel with standing surface acoustic waves (SSAW)

Abstract: We introduce a novel on-chip microparticle focusing technique using standing surface acoustic waves (SSAW). Our method is simple, fast, dilution-free, and applicable to virtually any type of microparticle.

Isotropic angle-domain elastic reverse-time migration

Abstract: Multicomponent data usually are not processed with specifically designed procedures but with procedures analogous to those used for single-component data. In isotropic media, the vertical and horizontal components of the data commonly are taken as proxies for the P- and S-wave modes, which are imaged independently with the acoustic wave equations.This procedure works only if the vertical and horizontal components accurately represent P- and S-wave modes, which generally is not true. Therefore, multicomponent images constructed with this procedure exhibit artifacts caused by incorrect wave-mode separation at the surface.An alternative procedure for elastic imaging uses the full vector fields for wavefield reconstruction and imaging. Thewavefieldsarereconstructedusingthemulticomponentdata as a boundary condition for a numerical solution to the elastic wave equation. The key component for wavefield migration is theimagingcondition,whichevaluatesthematchbetweenwavefields reconstructed from sources and receivers. For vector wave fields, a simple component-by-component crosscorrelation between two wavefields leads to artifacts caused by crosstalk between the unseparated wave modes. We can separate elastic wavefields after reconstruction in the subsurface and implement theimagingconditionascrosscorrelationofpurewavemodesinstead of the Cartesian components of the displacement wavefield.Thisapproachleadstoimagesthatareeasiertointerpretbecause they describe reflectivity of specified wave modes at interfaces of physical properties.As for imaging with acoustic wavefields, the elastic imaging condition can be formulated conventionally crosscorrelation with zero lag in space and time and extendedtononzerospaceandtimelags.Theelasticimagesproduced by an extended imaging condition can be used for angle decomposition of primary PP or SS and converted PS or SP reflectivity. Angle gathers constructed with this procedure have applicationsformigrationvelocityanalysisandamplitude-variation-with-angleanalysis.

Particle concentration and mixing in microdrops driven by focused surface acoustic waves

Abstract: We report the use of focused surface acoustic waves (SAWs) generated on 128° rotated Y-cut X-propagating lithium niobate (LiNbO3) for enhancing the actuation of fluids and the manipulation of particle suspensions at microscale dimensions. In particular, we demonstrate increased efficiency and speed in carrying out particle concentration/separation and in generating intense micromixing in microliter drops within which acoustic streaming is induced due to the focused SAW beneath the drop. Concentric circular and elliptical single-phase unidirectional transducers (SPUDTs) were used to focus the SAW. We benchmark our results against a straight SPUDT which does not cause focusing of the SAW. Due to the increased wave intensity and asymmetry of the wave, we found both circular and elliptical SPUDTs concentrate particles in under 1 s, which is one order of magnitude faster than the straight SPUDT and several orders of magnitude faster than conventional microscale devices. The concentric circular SPUDT was found ...

Interfacial destabilization and atomization driven by surface acoustic waves

Abstract: Surface acoustic wave atomization is a rapid means for generating micron and submicron aerosol droplets. Little, however, is understood about the mechanisms by which these droplets form due to the complex hydrodynamic processes that occur across widely varying length and time scales. Through experiments, scaling theory, and simple numerical modeling, we elucidate the interfacial destabilization mechanisms that lead to droplet formation. Using a millimeter-order fluid drop exposed to surface acoustic waves as it sits atop a single-crystal lithium niobate piezoelectric substrate, large aerosol droplets on the length scale of the parent drop dimension are ejected through a whipping and pinch-off phenomenon, which occurs at the asymmetrically formed crest of the drop due to leakage of acoustic radiation at the Rayleigh angle. Smaller micron order droplets, on the other hand, are formed due to the axisymmetric breakup of cylindrical liquid jets that are ejected as a consequence of interfacial destabilization. ...

Wave propagation and instabilities in monolithic and periodically structured elastomeric materials undergoing large deformations

Abstract: Wave propagation in elastomeric materials undergoing large deformations is relevant in numerous application areas, including nondestructive testing of materials and ultrasound techniques, where finite deformations and corresponding stress states can influence wave propagation and hence interpretation of data. In the case of periodically structured hyperelastic solids, the effect of deformation on the propagation of acoustic waves can be even more dramatic. In fact, transformations in the periodic patterns have been observed upon application of load due to microstructural elastic instabilities, providing opportunities for transformative phononic crystals which can switch band-gap structure in a sudden, but controlled manner. Here both analytical and numerical techniques are presented for assessing the influence of finite deformations on the propagation of elastic waves in both monolithic as well as periodically structured elastomeric materials. Both elastic instabilities and propagation of acoustic waves are strongly influenced by geometric pattern, material properties and loading conditions, giving different opportunities for tuning and manipulating the location and presence of instabilities and phononic band gaps

Microfluidic mixing via acoustically driven chaotic advection.

Abstract: Mixing presents a notoriously difficult problem in small amounts of fluids. Herein, surface acoustic waves provide a convenient technique to generate time-dependent flow patterns. These flow patterns can be optimized in such a way that advected particles are mixed most efficiently in the fluid within a short time compared to the time pure diffusion would take. Investigations are presented for the mixing efficiency of a flat cylinder that is driven by two surface acoustic waves. The experimental results favorably agree with model calculations of the flow patterns and the advective transport.

Piezoelectric-on-Silicon Lateral Bulk Acoustic Wave Micromechanical Resonators

Abstract: This paper reports on the design, fabrication, and characterization of piezoelectrically-transduced micromechanical single-crystal-silicon resonators operating in their lateral bulk acoustic modes to address the need for high-Q microelectronic-integrable frequency-selective components. A simple electromechanical model for optimizing performance is presented. For verification, resonators were fabricated on 5-mum-thick silicon-on- insulator substrates and use a 0.3-mum zinc oxide film for transduction. A bulk acoustic mode was observed from a 240 mum times 40 mum resonator with a 600-Omega impedance (Q=3400 at P=1 atm) at 90 MHz. A linear resonator absorbed power of -0.5 dBm and an output current of 1.3 mA rms were measured. The same device also exhibited a Q of 12 000 in its fundamental extensional mode at a pressure of 5 torr.

Ion acoustic waves in the plasma with the power-law q-distribution in nonextensive statistics

Abstract: We investigate the dispersion relation and Landau damping of ion acoustic waves in the collisionless magnetic-field-free plasma when the plasma is described by the nonextensive q -distributions of Tsallis statistics. We show that the increased numbers of superthermal particles and low velocity particles can explain the strengthened and weakened modes of Landau damping, respectively, with the q -distribution. When the ion temperature is equal to the electron temperature, the weakly damped waves are found to be the distributions with small values of q .

Interferometry by deconvolution: Part 1 — Theory for acoustic waves and numerical examples

Abstract: Interferometry allows for synthesis of data recorded at any two receivers into waves that propagate between these receivers as if one of them behaves as a source. This is accomplished typically by crosscorrelations. Based on perturbation theory and representation theorems, we show that interferometry also can be done by deconvolutions for arbitrary media and multidimensional experiments. This is important for interferometry applications in which (1) excitation is a complicated source-time function and/or (2) when wavefield separation methods are used along with interferometry to retrieve specific arrivals. Unlike using crosscorrelations, this method yields only causal scattered waves that propagate between the receivers. We offer a physical interpretation of deconvolution interferometry based on scattering theory. Here we show that deconvolution interferometry in acoustic media imposes an extra boundary condition, which we refer to as the free-point or clamped-point boundary condition, depending on the measured field quantity. This boundary condition generates so-called free-point scattering interactions, which are described in detail. The extra boundary condition and its associated artifacts can be circumvented by separating the reference waves from scattered wavefields prior to interferometry. Three wavefield-separation methods that can be used in interferometry are direct-wave interferometry, dual-field interferometry, and shot-domain separation. Each has different objectives and requirements.

Acoustic Metameterial with Negative Modulus

Abstract: We present experimental and theoretical results on an acoustic metamaterial that exhibits negative effective modulus in a frequency range from 0 to 450 Hz. One-dimensional acoustic metamaterial with an array of side holes on a tube was fabricated. We observed that acoustic waves above 450 Hz propagated well in this structure, but no sound below 450 Hz passed through. The frequency characteristics of the metamaterial has the same form as that of the permittivity in metals due to the plasma oscillation. We also provide a theory to explain the experimental results.

Acoustic-counterflow microfluidics by surface acoustic waves

Abstract: In this letter, we demonstrate an unexpected surface-acoustic-wave (SAW)-driven pumping effect in hydrophobic polydimethilsiloxane (PDMS)-lithium niobate (LiNbO3) microchannels. Atomization within the fluidic channel followed by SAW-assisted coalescence leads to liquid counterflow with respect to the SAW propagation direction. This physical mechanism is contrasted with the acoustic-streaming process driving isolated drop displacement on piezoelectric substrates. This principle is shown not to be readily applicable to the present microchannel case. The proposed device geometry can be exploited to integrate micropumps into complex microfluidic chips, improving the portability of micro-total-analysis systems.

Non-normality and nonlinearity in combustion-acoustic interaction in diffusion flames

Abstract: The role of non-normality and nonlinearity in flame–acoustic interaction in a ducted diffusion flame is investigated in this paper. The infinite rate chemistry model is employed to study unsteady diffusion flames in a Burke–Schumann type geometry. It has been observed that even in this simplified case, the combustion response to perturbations of velocity is non-normal and nonlinear. This flame model is then coupled with a linear model of the duct acoustic field to study the temporal evolution of acoustic perturbations. The one-dimensional acoustic field is simulated in the time domain using the Galerkin technique, treating the fluctuating heat release from the combustion zone as a compact acoustic source. It is shown that the coupled combustion–acoustic system is non-normal and nonlinear. Further, calculations showed the occurrence of triggering; i.e. the thermoacoustic oscillations decay for some initial conditions whereas they grow for some other initial conditions. It is shown that triggering occurs because of the combined effect of non-normality and nonlinearity. For such a non-normal system, resonance or ‘pseudoresonance’ may occur at frequencies far from its natural frequencies. Non-normal systems can be studied using pseudospectra, as eigenvalues alone are not sufficient to predict the behaviour of the system. Further, both necessary and sufficient conditions for the stability of a thermoacoustic system are presented in this paper.

Gold nanorod arrays as plasmonic cavity resonators.

Abstract: Hexagonal 2D arrays of Au nanorods support discrete plasmon resonance modes at visible and near-infrared wavelengths when coupled with light at normal incidence (kz). Reflectance spectra of nanorod arrays mounted on a thin Au baseplate reveal multiple resonant attenuations whose spectral positions vary with nanorod height and the dielectric medium. Simulations using 3D finite-element method calculations reveal harmonic sets of longitudinal standing waves in cavities between nanorods, reminiscent of acoustic waves generated by musical instruments. The nodes and antinodes of these quarter-wave plasmon modes are bounded, respectively, at the base and tips of the array. The number of harmonic resonances and their frequencies can be adjusted as a function of nanorod height, diameter-spacing ratio, and the refractive index of the host medium. Dispersion relations based on these standing-wave modes show strong retardation effects, attributed to the coupling of nanorods via transverse modes. Removal of the metal ...

ACOUSTICS2008/677 Theory of resonant acoustic transmission through subwavelength apertures

Abstract: The discovery of the phenomenon of extraordinary optical transmission through a two-dimensional array of subwavelength holes in a metallic film has opened a new line of research within optics. The key role played by surface plasmons in transferring light eciently from the input side of the metal film to the output region was soon realized. This fundamental knowledge enabled extension of this surface-plasmon ability to achieve extraordinary optical transmission and strong collimation of light in a single hole surrounded by a finite periodic array of indentations. Here, we show how these ideas developed for electromagnetic radiation can be transferred to other classical waves such as acoustic waves.

Impedance-acoustic tomography ∗

Abstract: In this work we present a new hybrid imaging technique that combines electrical impedance tomography (EIT) with acoustic tomography. The novel technique makes use of the fact that the absorbed electrical energy inside the body raises its temperature, thus leading to expansion effects. The expansion then induces an acoustic wave which can be recorded outside the body and consequently be used to calculate the absorbed energy inside the body, from which the electrical conductivity can be reconstructed. In other words, we try to combine the high contrast of EIT with the high resolution of ultrasound.

Extremal transmission and beating effect of acoustic waves in two-dimensional sonic crystals.

Abstract: The extremal transmission of the acoustic wave near the Dirac point in two-dimensional (2D) sonic crystals, being inversely proportional to the thickness of sample, has been demonstrated experimentally for the first time. Some unusual beating effects have been observed experimentally, when the acoustic pulse transports through the 2D sonic crystal slabs. Such phenomena are completely different from the oscillations of the wave in a slab or cavity originating from the interface reflection or the Fabry-Perot effect. They can be regarded as an acoustic analogue effect to Zitterbewegung of the relativistic electron. The physical origination for the phenomenon has been analyzed.

Wave-number-explicit bounds in time-harmonic scattering

Abstract: In this paper we consider the problem of scattering of time-harmonic acoustic waves by a bounded, sound soft obstacle in two and three dimensions, studying dependence on the wave number in two clas...

Dust-acoustic wave modulation in the presence of superthermal ions

Abstract: A study is presented of the nonlinear self-modulation of low-frequency electrostatic (dust acoustic) waves propagating in a dusty plasma, in the presence of a superthermal ion (and Maxwellian electron) background. A kappa-type superthermal distribution is assumed for the ion component, accounting for an arbitrary deviation from Maxwellian equilibrium, parametrized via a real parameter κ. The ordinary Maxwellian-background case is recovered for κ→∞. By employing a multiple scales technique, a nonlinear Schrodinger-type equation (NLSE) is derived for the electric potential wave amplitude. Both dispersion and nonlinearity coefficients of the NLSE are explicit functions of the carrier wavenumber and of relevant physical parameters (background species density and temperature, as well as nonthermality, via κ). The influence of plasma background superthermality on the growth rate of the modulational instability is discussed. The superthermal feature appears to control the occurrence of modulational instability, ...

Far-field image magnification for acoustic waves using anisotropic acoustic metamaterials

Abstract: A kind of two-dimensional acoustic metamaterial is designed so that it exhibits strong anisotropy along two orthogonal directions. Based on the rectangular equal frequency contour of this metamaterial, magnifying lenses for acoustic waves, analogous to electromagnetic hyperlenses demonstrated recently in the optical regime, can be realized. Such metamaterial may offer applications in imaging for systems that obey scalar wave equations.

Dynamics of the Solar Magnetic Network. II. Heating the Magnetized Chromosphere

Abstract: We consider recent observations of the chromospheric network and argue that the bright network grains observed in the Ca II H and K lines are heated by an as-yet-unidentified quasi-steady process. We propose that the heating is caused by dissipation of short-period magnetoacoustic waves in magnetic flux tubes (periods less than 100 s). Magnetohydrodynamic (MHD) models of such waves are presented. We consider wave generation in the network due to two separate processes: (1) transverse motions at the base of the flux tube and (2) the absorption of acoustic waves generated in the ambient medium. We find that the former mechanism leads to efficient heating of the chromosphere by slow magnetoacoustic waves propagating along magnetic field lines. This heating is produced by shock waves with a horizontal size of a few hundred kilometers. In contrast, acoustic waves excited in the ambient medium are converted into transverse fast modes that travel rapidly through the flux tube and do not form shocks, unless the acoustic sources are located within 100 km from the tube axis. We conclude that the magnetic network may be heated by magnetoacoustic waves that are generated in or near the flux tubes.

Evaporative self-assembly assisted synthesis of polymeric nanoparticles by surface acoustic wave atomization.

Abstract: We demonstrate a straightforward and rapid atomization process driven by surface acoustic waves that is capable of continuously producing spherical monodispersed submicron poly-e-caprolactone particle aggregates between 150 and 200 nm, each of which are composed of nanoparticles of 5‐10 nm in diameter. The size and morphologies of these particle assemblies were determined using dynamic light scattering, atomic force microscopy and transmission electron microscopy. Through scaling theory, we show that the larger particle aggregates are formed due to capillary instabilities amplified by the acoustic forcing whereas the smaller particulates that form the aggregates arise due to a nucleate templating process as a result of rapid spatially inhomogeneous solvent evaporation. Minimization of the free energy associated with the evaporative process yields a critical cluster size for a single nucleus in the order of 10 nm, which roughly corresponds with the dimensions of the sub-50 nm particulates. M This article features online multimedia enhancements

Alignment of particles in microfluidic systems using standing surface acoustic waves

Abstract: We report on the use of standing surface acoustic waves, formed on a single-crystal piezoelectric substrate, to organize micron-scale latex particles into an array comprising a series of lines in an adjacent microfluidic system. The lines of particles are formed parallel to the substrate surface and perpendicular to the surface acoustic wave vector. They extend across the width of the acoustic beam aperture, with a periodicity of one-half the surface acoustic wavelength. The position and spacing of the particle arrays can be altered by adjusting the acoustic wave frequency within the device passband. We discuss the mechanism responsible for the formation of the lines, which could be widely applicable to the alignment of microscopic objects held in suspension.

Phononic band-gap crystals for radio frequency communications

Abstract: We report on the experimental and theoretical observation of a phononic band-gap crystal operating in the megahertz regime. Our experimental data show over 25dB suppression of bulk acoustic waves, and our theoretical models predict almost linear scaling to the gigahertz frequencies, thus laying the foundation for the implementation of such devices in radio frequency communications. We further argue that cavities in such systems offer a unique opportunity to couple acoustic energy into a resonator utilizing piezoelectric materials, while at the same time allowing the realization of a resonance cavity in high-Q materials such as silicon oxide, silicon, and tungsten.

Microfabricated VHF acoustic crystals and waveguides

Abstract: Microfabricated acoustic crystals have been designed and experimentally verified. The acoustic crystals are realized by including tungsten (W) scatterers in a SiO2 matrix. Wide frequency ranges where acoustic waves are forbidden to exist (acoustic bandgaps, ABG) are formed due to the large acoustic impedance and mass density mismatch between W and SiO2. The acoustic crystal structures are fabricated in a 7-mask process that features integrated aluminum nitride piezoelectric couplers for interrogating the devices. Acoustic crystals in a square lattice have been measured at 67 MHz with greater than 30 dB of acoustic rejection and bandwidths exceeding 25% of the midgap. Single and multimode acoustic waveguides have been realized by defecting the acoustic crystals through removal of a subset of the W scatterers. These waveguides achieve relative transmission of up to 100% for the propagating modes.

Hypersonic Modulation of Light in Three-Dimensional Photonic and Phononic Band-Gap Materials

Abstract: The periodicity of the dielectric constants in artificially grown structures is generally accompanied by a periodicity of the acoustic impedance. With regard to their acoustic properties they may therefore behave as phononic crystals, in analogy to photonic crystals for light. If the structure acts as a photonic crystal operating in the visible, then it shows the features typical of phononic crystals for hypersonic (� 10 10 Hz) acoustic waves. The combination of

Ion acoustic solitary waves with adiabatic ions in magnetized electron-positron-ion plasmas

Abstract: Linear and nonlinear ion acoustic waves in the presence of adiabatically heated ions in magnetized electron-positron-ion plasmas are studied The Sagdeev potential approach is employed to obtain the energy integral equation in such a mulitcomponent plasma using fluid theory It is found that electron density humps are formed in the subsonic region in magnetized electron-positron-ion plasmas The amplitude of electron density hump is decreased with the increase of hot ion temperature in electron-positron-ion plasmas However, the increase in positron concentration and obliqueness of the wave increases the amplitude of nonlinear structure The increase in positron concentration also reduces the width of the nonlinear structure in a magnetized multicomponent plasma The numerical solutions in the form of solitary pulses are also presented for different plasma cases The results may be applicable to astrophysical plasma situations, where magnetized electron-positron-ion plasma with hot ions can exist

Receptivity of a hypersonic boundary layer over a flat plate with a porous coating

Abstract: Two-dimensional direct numerical simulation (DNS) of receptivity to acoustic disturbances radiating onto a flat plate with a sharp leading edge in the Mach 6 free stream is carried out. Numerical data obtained for fast and slow acoustic waves of zero angle of incidence are consistent with the asymptotic theory. Numerical experiments with acoustic waves of non-zero angles of incidence reveal new features of the disturbance field near the plate leading edge. The shock wave, which is formed near the leading edge owing to viscous–inviscid interaction, produces a profound effect on the acoustic near field and excitation of boundary-layer modes. DNS of the porous coating effect on stability and receptivity of the hypersonic boundary layer is carried out. A porous coating of regular porosity (equally spaced cylindrical blind micro-holes) effectively diminishes the second-mode growth rate in accordance with the predictions of linear stability theory, while weakly affecting acoustic waves. The coating end effects, associated with junctures between solid and porous surfaces, are investigated.

Stability analysis of thermally induced spontaneous gas oscillations in straight and looped tubes

Abstract: A gas in a tube spontaneously oscillates when the temperature gradient applied along the wall of the tube is higher than the critical value. This spontaneous gas oscillation is caused by the thermal interaction between the gas and the tube wall. The stability limit of the thermally induced gas oscillation is numerically investigated by using the linear stability theory and a transfer matrix method. It is well known that an acoustic wave excited by the spontaneous gas oscillation occurring in a looped tube is different from that in a straight tube with two ends; a traveling acoustic wave is induced in a looped tube, whereas a standing acoustic wave is caused in a straight tube. The conditions for the stability limits in both tube types were calculated. The calculated and measured conditions were compared and were found to be in good agreement. Calculations performed by varying the value of the Prandtl number of the gas were used to determine the reasons for the existence of the stability limits of the looped and straight tubes.

Material parameters and vector scaling in transformation acoustics

Abstract: The degree to which the coordinate transformation concept first demonstrated for electromagnetic waves can be applied to other classes of waves remains an open question. In this work, we thoroughly examine the coordinate transformation invariance of acoustic waves. We employ a purely physical argument to show how the acoustic velocity vector must transform differently than the E and H fields in Maxwell's equations, which explains why acoustic coordinate transformation invariance was not found in some previous analyses. A first principles analysis of the acoustic equations under arbitrary coordinate transformations confirms that the divergence operator is preserved only if velocity transforms in this physically correct way. This analysis also yields closed-form expressions for the bulk modulus and mass density tensor of the material required to realize an arbitrary coordinate transformation on the acoustic fields, which we show are equivalent to forms presented elsewhere. We demonstrate the computation of these material parameters in two specific cases and show that the change in velocity and pressure gradient vectors under a nonorthogonal coordinate transformation is precisely how these vectors must change from purely physical arguments. This analysis confirms that all of the electromagnetic devices and materials that have been conceived using the coordinate transformation approach are also in principle realizable for acoustic