Showing papers on "Acoustic wave published in 2007"
Patent•
AT&T1
TL;DR: In this paper, an improved technique for acoustic sensing involves, in one embodiment, launching into a medium, a plurality of groups of pulse-modulated electromagnetic-waves, and the energy scattered by the medium is detected and used to determine a characteristic of the environment of the medium.
Abstract: An improved technique for acoustic sensing involves, in one embodiment, launching into a medium, a plurality of groups of pulse-modulated electromagnetic-waves. The frequency of electromagnetic waves in a pulse within a group differs from the frequency of the electromagnetic waves in another pulse within the group. The energy scattered by the medium is detected and, in one embodiment, may be used to determine a characteristic of the environment of the medium. For example, if the medium is a buried optical fiber into which light pulses have been launched in accordance with the invention, the presence of acoustic waves within the region of the buried fiber can be detected.
269 citations
TL;DR: Two universal reconstruction methods for photoacoustic computed tomography are derived, applicable to an arbitrarily shaped detection surface, by calculating the far-field approximation, a concept well known in physics, where the generated acoustic wave is approximated by an outgoing spherical wave with the reconstruction point as center.
Abstract: Two universal reconstruction methods for photoacoustic (also called optoacoustic or thermoacoustic) computed tomography are derived, applicable to an arbitrarily shaped detection surface. In photoacoustic tomography acoustic pressure waves are induced by illuminating a semitransparent sample with pulsed electromagnetic radiation and are measured on a detection surface outside the sample. The imaging problem consists in reconstructing the initial pressure sources from those measurements. The first solution to this problem is based on the time reversal of the acoustic pressure field with a second order embedded boundary method. The pressure on the arbitrarily shaped detection surface is set to coincide with the measured data in reversed temporal order. In the second approach the reconstruction problem is solved by calculating the far-field approximation, a concept well known in physics, where the generated acoustic wave is approximated by an outgoing spherical wave with the reconstruction point as center. Numerical simulations are used to compare the proposed universal reconstruction methods with existing algorithms.
239 citations
TL;DR: It is reported that the transmission of an incident acoustic wave through a one-dimensional acoustic grating can also be drastically enhanced, showing that the coupling between the diffractive wave and the wave-guide mode plays an important role in EAT.
Abstract: Recently, there has been an increased interest in studying extraordinary optical transmission (EOT) through subwavelength aperture arrays perforated in a metallic film. In this Letter, we report that the transmission of an incident acoustic wave through a one-dimensional acoustic grating can also be drastically enhanced. This extraordinary acoustic transmission (EAT) has been investigated both theoretically and experimentally, showing that the coupling between the diffractive wave and the wave-guide mode plays an important role in EAT. This phenomenon can have potential applications in acoustics and also might provide a better understanding of EOT in optical subwavelength systems.
237 citations
TL;DR: In this paper, the authors show how these ideas developed for electromagnetic radiation can be transferred to other classical waves such as acoustic waves, and show how to use surface plasmons in transferring light efficiently from the input side of the metal film to the output region.
Abstract: The discovery of the phenomenon of extraordinary optical transmission through a two-dimensional array of subwavelength holes in a metallic film1 has opened a new line of research within optics. The key role played by surface plasmons in transferring light efficiently 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 indentations2. Here, we show how these ideas developed for electromagnetic radiation can be transferred to other classical waves such as acoustic waves.
228 citations
TL;DR: In this paper, the linear and nonlinear properties of the ion-acoustic waves (IAWs) were investigated by using the quantum hydrodynamic equations together with the Poisson equation in a three-component quantum electron-positron-ion plasma.
Abstract: The linear and nonlinear properties of the ion-acoustic waves (IAWs) are investigated by using the quantum hydrodynamic equations together with the Poisson equation in a three-component quantum electron-positron-ion plasma. For this purpose, a linear dispersion relation, a Korteweg-de Vries equation and an energy equation containing quantum corrections are derived. Computational investigations have been performed to examine the quantum mechanical effects on the linear and nonlinear waves. It is found that both the linear and nonlinear properties of the IAWs are significantly affected by the inclusion of the quantum corrections. The relevance of the present investigation to dense white dwarfs (where the electron-positron annihilation can be unimportant) is discussed.
228 citations
Book•
09 Aug 2007
TL;DR: In this article, the fundamental principles and device design techniques for surface acoustic wave filters are discussed, as well as the latest technologies for low bandpass filters such as unidirectional transducers, resonators in impedance element filters, double-mode SAW filters and transverse-coupled resonators using waveguides.
Abstract: This book gives the fundamental principles and device design techniques for surface acoustic wave filters. It covers the devices in widespread use today: bandpass and pulse compression filters, correlators and non-linear convolvers and resonators. The newest technologies for low bandpass filters are fully covered such as unidirectional transducers, resonators in impedance element filters, resonators in double-mode surface acoustic wave filters and transverse-coupled resonators using waveguides.The book covers the theory of acoustic wave physics, the piezoelectric effect, electrostatics at a surface, effective permittivity, piezoelectric SAW excitation and reception, and the SAW element factor. These are the main requirements for developing quasi-static theory, which gives a basis for the non-reflective transducers in transversal bandpass filters and interdigital pulse compression filters. It is also needed for the reflective transducers used in the newer devices. It is a thorough revision of a classic on surface acoustic wave filters first published in 1985 and still in print. It uniquely combines easy-to-understand principles with practical design techniques for all the devices in widespread use today. It includes complete coverage of all the latest devices which are key to mobile phones, TVs and radar systems; and, a new foreword by Sir Eric Albert Ash.
223 citations
TL;DR: In this article, a dielectric substance is laminated on one surface of a piezoelectric material and an IDT and reflectors are disposed as electrodes at a boundary between the piezelectric materials and the dielectrics.
Abstract: A dielectric substance is laminated on one surface of a piezoelectric substance, and an IDT and reflectors are disposed as electrodes at a boundary between the piezoelectric substance and the dielectric substance, and the thickness of the electrodes is determined so that the acoustic velocity of the Stoneley wave is decreased less than that of a slow transverse wave propagating through the dielectric substance and that of a slow transverse wave propagating through the piezoelectric substance, thereby forming a boundary acoustic wave device.
218 citations
Book•
22 Oct 2007
TL;DR: In this article, a variational formulation of the wave equation is proposed for continuous systems with axially translating strings, and the initial value problem is solved using Laplace transform and forced vibration analysis.
Abstract: Preface . 1 Vibrations of strings and bars. 1.1 Dynamics of strings and bars: the Newtonian formulation. 1.2 Dynamics of strings and bars: the variational formulation. 1.3 Free vibration problem: Bernoulli's solution. 1.4 Modal analysis. 1.5 The initial value problem: solution using Laplace transform. 1.6 Forced vibration analysis. 1.7 Approximate methods for continuous systems. 1.8 Continuous systems with damping. 1.9 Non-homogeneous boundary conditions. 1.10 Dynamics of axially translating strings. Exercises. References. 2 One-dimensional wave equation: d'Alembert's solution. 2.1 D'Alembert's solution of the wave equation. 2.2 Harmonic waves and wave impedance. 2.3 Energetics of wave motion. 2.4 Scattering of waves. 2.5 Applications of the wave solution. Exercises. References. 3 Vibrations of beams. 3.1 Equation of motion. 3.2 Free vibration problem. 3.3 Forced vibration analysis. 3.4 Non-homogeneous boundary conditions. 3.5 Dispersion relation and flexural waves in a uniform beam. 3.6 The Timoshenko beam. 3.7 Damped vibration of beams. 3.8 Special problems in vibrations of beams. Exercises. References. 4 Vibrations of membranes. 4.1 Dynamics of a membrane. 4.2 Modal analysis. 4.3 Forced vibration analysis. 4.4 Applications: kettledrum and condenser microphone. 4.5 Waves in membranes. Exercises. References. 5 Vibrations of plates. 5.1 Dynamics of plates. 5.2 Vibrations of rectangular plates. 5.2.1 Free vibrations. 5.3 Vibrations of circular plates. 5.4 Waves in plates. 5.5 Plates with varying thickness. Exercises. References. 6 Boundary value and eigenvalue problems in vibrations. 6.1 Self-adjoint operators and eigenvalue problems for undamped free vibrations. 6.2 Forced vibrations. 6.3 Some discretization methods for free and forced vibrations. References. 7 Waves in fluids. 7.1 Acoustic waves in fluids. 7.2 Surface waves in incompressible liquids. Exercises. References. 8 Waves in elastic continua. 8.1 Equations of motion. 8.2 Plane elastic waves in unbounded continua. 8.3 Energetics of elastic waves. 8.4 Reflection of elastic waves. 8.5 Rayleigh surface waves. 8.6 Reflection and refraction of planar acoustic waves. Exercises. References. A The variational formulation of dynamics. References. B Harmonic waves and dispersion relation. B.1 Fourier representation and harmonic waves. B.2 Phase velocity and group velocity. References. C Variational formulation for dynamics of plates. References. Index.
203 citations
TL;DR: The acoustic negative-birefraction phenomenon in a two-dimensional SC is reported, for the first time, even with the same frequency and the same 'polarization' state, showing great impacts on both fundamental physics and device applications.
Abstract: Optical birefringence and dichroism are classical and important effects originating from two independent polarizations of optical waves in anisotropic crystals1. Furthermore, the distinct dispersion relations of transverse electric and transverse magnetic polarized electromagnetic waves in photonic crystals can lead to birefringence more easily2,3,4,5,6. However, it is impossible for acoustic waves in the fluid to show such a birefringence because only the longitudinal mode exists. The emergence of an artificial sonic crystal (SC) has significantly broadened the range of acoustic materials in nature7,8,9,10,11,12,13,14,15,16,17,18 that can give rise to acoustic bandgaps and be used to control the propagation of acoustic waves. Recently, negative refraction has attracted a lot of attention and has been demonstrated in both left-handed materials and photonic crystals19,20,21,22,23,24,25,26. Similar to left-handed materials and photonic crystals, negative refractions have also been found in SCs14,15,16,17,18. Here we report, for the first time, the acoustic negative-birefraction phenomenon in a two-dimensional SC, even with the same frequency and the same ‘polarization’ state. By means of this feature, double focusing images of a point source have been realized. This birefraction concept may be extended to other periodic systems corresponding to other forms of waves, showing great impacts on both fundamental physics and device applications.
173 citations
TL;DR: In this article, a two-dimensional phononic-crystal plate consisting of circular steel cylinders which form a square lattice in an epoxy matrix is studied first using the finite-difference time-domain (FDTD) method.
Abstract: Propagation of acoustic waves in a phononic-crystal plate and related waveguides are analyzed in this paper. A two-dimensional phononic-crystal plate consisting of circular steel cylinders which form a square lattice in an epoxy matrix is studied first using the finite-difference time-domain (FDTD) method. The Bloch theorem is employed to deal with the periodic condition, and the traction free condition is set on the top and bottom boundaries of the plates. The dispersion curves and displacement fields are calculated to identify the band gaps and eigenmodes. With the existence of a complete band gap in the phononic-crystal plate, an acoustic waveguide is presented accordingly. Eigenmodes of acoustic waves inside the waveguides are indicated, and the modes are affected by the geometry arrangement of waveguides. Inside the phononic-crystal plate waveguides, wave propagation is well confined within the structure.
168 citations
TL;DR: It is shown that the Green's function can be retrieved from waves that are excited throughout the volume by spatially uncorrelated injection sources with a power spectrum that is proportional to the local dissipation rate.
Abstract: The Green’s function of acoustic or elastic wave propagation can, for loss-less media, be retrieved by correlating the wave field that is excited by random sources and is recorded at two locations. Here the generalization of this idea to attenuating acoustic waves in an inhomogeneous medium is addressed, and it is shown that the Green’s function can be retrieved from waves that are excited throughout the volume by spatially uncorrelated injection sources with a power spectrum that is proportional to the local dissipation rate. For a finite volume, one needs both volume sources and sources at the bounding surface for the extraction of the Green’s functions. For the special case of a homogeneous attenuating medium defined over a finite volume, the phase and geometrical spreading of the Green’s function is correctly retrieved when the volume sources are ignored, but the attenuation is not.
TL;DR: In this article, a (3+1)-dimensional spherical Kadomtsev-Petviashvili model is constructed with symbolic computation, 4th-ordered and with variable coefficients, in spherical geometry with both azimuthal and zenith perturbations existing.
Abstract: Dust-ion-acoustic waves in a cosmic dusty plasma is investigated, in spherical geometry with both azimuthal and zenith perturbations existing. (3+1)-dimensional spherical Kadomtsev-Petviashvili ((3+1)DsKP) model is constructed with symbolic computation, 4th-ordered and with variable coefficients. Auto-Backlund transformation and (3+1)DsKP nebulons are analytically obtained for such a generic model. Astromechanical and physical implications are discussed, of the supernova-shell-type expanding bright and Saturn-F-ring-type expanding dark (3+1)DsKP nebulons. Possibly observable nebulonic effects are proposed for future cosmic experiments.
TL;DR: In this article, the authors investigated the effect of acoustic forcing at various frequencies on flame heat release behavior and found that the phase shift of the flame fluctuation from the imposed acoustic wave seems to be very closely coupled to the vortices generated at the flame boundary due to shear mixing, thus inducing the alternating toroidal structures.
TL;DR: An acoustic radiance transfer method, which can handle both diffuse and nondiffuse reflections, is derived and used to predict several acoustic parameters of a room model and provides results as accurate as current commercial room acoustic prediction software.
Abstract: An integral equation generalizing a variety of known geometrical room acoustics modeling algorithms is presented. The formulation of the room acoustic rendering equation is adopted from computer graphics. Based on the room acoustic rendering equation, an acoustic radiance transfer method, which can handle both diffuse and nondiffuse reflections, is derived. In a case study, the method is used to predict several acoustic parameters of a room model. The results are compared to measured data of the actual room and to the results given by other acoustics prediction software. It is concluded that the method can predict most acoustic parameters reliably and provides results as accurate as current commercial room acoustic prediction software. Although the presented acoustic radiance transfer method relies on geometrical acoustics, it can be extended to model diffraction and transmission through materials in future.
TL;DR: In this article, a damage detection and damage localization system based on fiber Bragg grating sensors is presented, which is used to detect and locate damage in structures such as those found in aerospace applications.
Abstract: The aim of this study is to present the results of testing a damage detection and damage localization system based on fiber Bragg grating sensors. The objective of the system is to detect and locate damage in structures such as those found in aerospace applications. The damage identification system involves Bragg gratings for sensing ultrasound by detecting the linear strain component produced by Lamb waves. A tuneable laser is used for the interrogation of the Bragg gratings to achieve high sensitivity detection of ultrasound. The interaction of Lamb waves with damage, e.g., the reflection of the waves at defects, allows the detection of damage in structures by monitoring the Lamb wave propagation characteristics. As the reflected waves produce additional components within the original signal, most of the information about the damage can be found in the differential signal of the reference and the damage signal. Making use of the directional properties of the Bragg grating the direction of the reflected acoustic waves can be determined by mounting three of the gratings in a rosette configuration. Two suitably spaced rosettes are used to locate the source of the reflection, i.e., the damage, by taking the intersection of the directions given by each rosette. A genetic algorithm (GA) can be used to calculate that intersection and to account for any ambiguities from the Lamb wave measurements. The performance of the GA has been studied and optimized with respect to the localization task. Initial experiments are carried out on an aluminum structure, where holes were drilled to simulate the presence of damage. The results show very good agreement between the calculated and actual positions of the damage.
TL;DR: In this paper, the quantum hydrodynamic model for plasmas is employed to study the dynamics of the nonlinear quantum dust acoustic (QDA) wave in a nonuniform quantum dusty plasma (QDP).
Abstract: The quantum hydrodynamic model for plasmas is employed to study the dynamics of the nonlinear quantum dust acoustic (QDA) wave in a nonuniform quantum dusty plasma (QDP). Through the reductive perturbation technique, it is shown that the quantum hydrodynamical basic equations describing the nonlinear QDA waves yield a modified Korteweg-de Veries equation with slowly varying coefficients in the system inhomogeneity. Applying generalized expansion method, it is found that the system admits only rarefactive solitons. The properties of the solitons such as the velocity, the amplitude and the width of the nonlinear QDA waves are analyzed using appropriate choice for initial ion and electron density numbers. For the homogeneous QDP, no critical value is found. Because of the system inhomogeneity, a new criticality is found forcing with the usage of new stretching coordinates. A higher evolution equation with third-order nonlinearity is derived at the critical values. The solution of the latter equation admits rarefactive shock wave attached with an amplitude factor. The present investigations should be useful for researches on astrophysical plasmas as well as for ultra small micro- and nano-electronic devices.
TL;DR: In this paper, the quantum ion-acoustic wave in single-wall carbon nanotubes is studied with the quantum hydrodynamic model, in which the electron and ion components of the nanotsubes are regarded as a two-species quantum plasma system.
Abstract: The quantum ion-acoustic waves in single-wall carbon nanotubes are studied with the quantum hydrodynamic model, in which the electron and ion components of the nanotubes are regarded as a two-species quantum plasma system. An analytical expression of the dispersion relation is obtained for the linear disturbance. Numerical results show that the frequency of the ion-acoustic wave strongly depends on the nanotube's radius in the long-wavelength cases.
TL;DR: In this article, the penumbral trans-sunspot wave propagation was investigated using a Fourier phase difference analysis, and the dispersion relation for radiatively cooling acoustic waves, modified to incorporate an inclined propagation direction, fits well the observed phase differences between the pairs of photospheric and chromospheric pixels.
Abstract: We seek to clarify the nature of running penumbral (RP) waves: are they chromospheric trans-sunspot waves or a visual pattern of upward-propagating waves? Full Stokes spectropolarimetric time series of the photospheric Si I λ10827 line and the chromospheric He I λ10830 multiplet were inverted using a Milne-Eddington atmosphere. Spatial pixels were paired between the outer umbral/inner penumbral photosphere and the penumbral chromosphere using inclinations retrieved by the inversion and the dual-height pairings of line-of-sight velocity time series were studied for signatures of wave propagation using a Fourier phase difference analysis. The dispersion relation for radiatively cooling acoustic waves, modified to incorporate an inclined propagation direction, fits well the observed phase differences between the pairs of photospheric and chromospheric pixels. We have thus demonstrated that RP waves are in effect low-β slow-mode waves propagating along the magnetic field.
TL;DR: In this article, full-image micro-PIV analysis in combination with images of transient particle motion is used for experimental studies of acoustic radiation forces and acoustic streaming in microfluidic chambers under piezo-actuation in the MHz range.
Abstract: We show that full-image micro-PIV analysis in combination with images of transient particle motion is a powerful tool for experimental studies of acoustic radiation forces and acoustic streaming in microfluidic chambers under piezo-actuation in the MHz range. The measured steady-state motion of both large 5 µm and small 1 µm particles can be understood in terms of the acoustic eigenmodes or standing ultra-sound waves in the given experimental microsystems. This interpretation is supported by numerical solutions of the corresponding acoustic wave equation.
TL;DR: The present computer simulation results suggest that MAT-MI can reconstruct conductivity images of biological tissue with high spatial resolution and high contrast and in the present simulation study, a two-layer spherical model is used.
Abstract: We have conducted computer simulation and experimental studies on magnetoacoustic-tomography with magnetic induction (MAT-MI) for electrical impedance imaging. In MAT-MI, the object to be imaged is placed in a static magnetic field, while pulsed magnetic stimulation is applied in order to induce eddy current in the object. In the static magnetic field, the Lorentz force acts upon the eddy current and causes acoustic vibrations in the object. The propagated acoustic wave is then measured around the object to reconstruct the electrical impedance distribution. In the present simulation study, a two-layer spherical model is used. Parameters of the model such as sample size, conductivity values, strength of the static and pulsed magnetic field, are set to simulate features of biological tissue samples and feasible experimental constraints. In the forward simulation, the electrical potential and current density are solved using Poisson's equation, and the acoustic pressure is calculated as the forward solution. The electrical impedance distribution is then reconstructed from the simulated pressure distribution surrounding the sample. The present computer simulation results suggest that MAT-MI can reconstruct conductivity images of biological tissue with high spatial resolution and high contrast. The feasibility of MAT-MI in providing high spatial resolution images containing impedance-related information has also been demonstrated in a phantom experiment
TL;DR: In this article, the authors constructed a novel apparatus based on subharmonic ultrasound for the accurate imaging of closed cracks, where linear and nonlinear responses not only from the tip but also from other parts of cracks were observed in fundamental and sub-harmonic images, which were changed with varying closure stress.
Abstract: The authors constructed a novel apparatus based on subharmonic ultrasound for the accurate imaging of closed cracks. Linear and nonlinear responses not only from the tip but also from other parts of cracks were observed in fundamental and subharmonic images, which were changed with varying closure stress. The subharmonic images always gave an accurate length of partially closed cracks, in contrast to the fundamental images in which the crack length was underestimated. Significant similarities in generation and resonance phenomena of subharmonic waves, acoustic emission, and the vibration of microbubbles are discussed.
TL;DR: The propagation of acoustic waves in a square-lattice phononic crystal slab consisting of a single layer of spherical steel beads in a solid epoxy matrix is studied experimentally, in good agreement with theoretical predictions.
Abstract: The propagation of acoustic waves in a square-lattice phononic crystal slab consisting of a single layer of spherical steel beads in a solid epoxy matrix is studied experimentally. Waves are excited by an ultrasonic transducer and fully characterized on the slab surface by laser interferometry. A complete band gap is found to extend around 300 kHz, in good agreement with theoretical predictions. The transmission attenuation caused by absorption and band gap effects is obtained as a function of frequency and propagation distance. Well confined acoustic wave propagation inside a line-defect waveguide is further observed experimentally.
TL;DR: In this paper, it was shown that a locally resonant sonic material is capable of totally reflecting low-frequency sound at a frequency where the effective dynamic mass density can approach positive and negative infinities.
Abstract: Elastic and electromagnetic waves are two types of classical waves that, though very different, nevertheless display many analogous features. In particular, for the acoustic waves, there can be a correspondence between the two material parameters of the acoustic wave equation, the mass density and bulk modulus, with the dielectric constant and magnetic permeability of the Maxwell equations. We show that the classical mass density, a quantity that is often regarded as positive definite in value, can display complex finite-frequency characteristics for a composite that comprises local resonators, thereby leading to acoustic metamaterials in exact analogy with the electromagnetic metamaterials. In particular, we demonstrate that through the anti-resonance mechanism, a locally resonant sonic material is capable of totally reflecting low-frequency sound at a frequency where the effective dynamic mass density can approach positive and negative infinities. The condition that leads to the anti-resonance thereby offers a physical explanation of the metamaterial characteristics for both the membrane resonator and the 3D locally resonant sonic materials. Besides the metamaterials arising from the dynamic mass density behavior at finite frequencies, we also present a review of other relevant types of acoustic metamaterials. At the zero-frequency limit, i.e., in the absence of resonances, the dynamic mass density for the fluid–solid composites is shown to still differ significantly from the usual volume-averaged expression. We offer both a physical explanation and a rigorous mathematical derivation of the dynamic mass density in this case.
TL;DR: In this paper, the authors exploited the resonance that occurs at the minimum frequency thickness product of the first order symmetric (S1) and of the second order antisymmetric (A2) Lamb modes.
Abstract: An original method for material characterization with acoustic waves is presented. The measurement of the longitudinal and shear wave velocities in thin isotropic plates or shells is performed locally on the same face without any mechanical contact. We exploit the resonance that occurs at the minimum frequency thickness product of the first order symmetric (S1) and of the second order antisymmetric (A2) Lamb modes. At these frequencies the group velocity vanishes, whereas the phase velocity remains finite. Then, the energy, which cannot propagate in the structure, is localized in a zone of diameter half the wavelength. The vibrations are excited in the thermoelastic regime by a laser pulse and detected at the same point by an optical interferometer. For these two Lamb modes we have computed the variations of the frequency thickness product versus Poisson’s ratio. The resonance frequency ratio, which is independent of the plate or shell thickness, provides an absolute and local measurement of Poisson’s rat...
TL;DR: In this article, a correction to the theoretical prediction of longitudinal mode vibration in thin, slender beams was reported, and numerical simulations were performed that adjusted Poisson's ratio until the acoustic wave speed matched that measured in the experiments.
Abstract: This letter reports on a correction to the theoretical prediction of longitudinal mode vibration in thin, slender beams. Thin magnetostrictive strips were fashioned from Metglas™ and subjected to a modulated magnetic field to determine resonant frequency and acoustic wave propagation speed. The results indicated that current analytical solutions were not adequate to predict behavior. Numerical simulations were performed that adjusted Poisson’s ratio until the acoustic wave speed matched that measured in the experiments. The results indicated that the current equations, formulated using the plane-strain modulus, should be modified by using the plane-stress or biaxial modulus.
TL;DR: In this paper, a newly developed extension of ray theory which accounts for mode transmission and conversion between fast and slow magnetoacoustic waves, as well as simple wave mechanical calculations, was used to find that strong surface magnetic fields, as may be found in solar and stellar active regions, have several related but distinct effects on seismic waves: transmission/conversion, shortened travel times, a directional filtering of acoustic waves entering the overlying atmosphere, and a tendency to more closely align velocities with the field as height increases in the atmosphere.
Abstract: Using a newly developed extension of ray theory which accounts for mode transmission and conversion between fast and slow magnetoacoustic waves, as well as simple wave mechanical calculations, we find that strong surface magnetic fields, as may be found in solar and stellar active regions, have several related but distinct effects on seismic waves: transmission/conversion, shortened travel times, a directional filtering of acoustic waves entering the overlying atmosphere, and a tendency to more closely align velocities with the field as height increases in the atmosphere. Magnetic field inclination is particularly relevant to these effects. Here, we briefly review these findings, and present some new results on ray travel times and magnetic filtering. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, a technique for obtaining a far-field asymptotic solution to the 3D Green's function in terms of the modal solutions to the forced 2D problem is presented.
Abstract: The design of transducers to excite and detect guided waves is a fundamental part of a nondestructive evaluation or structural health monitoring system and requires the ability to predict the radiated guided wave field of a transmitting transducer. For most transducers, this can be performed by making the assumption that the transducer is weakly coupled and then integrating the Green’s function of the structure over the area of the transducer. The majority of guided wave modeling is based on two-dimensional (2D) formulations where plane, straight-crested waves are modeled. Several techniques can be readily applied to obtain the solution to the forced 2D problem in terms of modal amplitudes. However, for transducer modeling it is desirable to obtain the complete three-dimensional (3D) field, which is particularly challenging in anisotropic materials. In this paper, a technique for obtaining a far-field asymptotic solution to the 3D Green’s function in terms of the modal solutions to the forced 2D problem i...
TL;DR: In this article, the presence and power of high frequency acoustic waves at high spatial resolution were studied using the Hinode/SOT Ca II H-line and blue continuum broadband observations.
Abstract: We use Hinode/SOT Ca II H-line and blue continuum broadband observations to study the presence and power of high frequency acoustic waves at high spatial resolution. We find that there is no dominant power at small spatial scales; the integrated power using the full resolution of Hinode (0: 05 pixels, 0: 16 resolution) is larger than the power in the data degraded to 0: 00 5 pixels (TRACE pixel size) by only a factor of 1.2. At 20 mHz the ratio is 1.6. Combining this result with the estimates of the acoustic flux based on TRACE data of Fossum and Carlsson (2006, ApJ, 646, 579), we conclude that the total energy flux in acoustic waves of frequency 5–40 mHz entering the internetwork chromosphere of the quiet Sun is less than 800 W m � 2 , inadequate to balance the radiative losses in a static chromosphere by a factor of five.
TL;DR: Results from the first statistical study of waveform capture data during 67 interplanetary (IP) shocks with Mach numbers ranging from approximately 1-6.m are described, consistent with theory suggesting IAWs provide the primary dissipation for low Mach number shocks.
Abstract: We describe results from the first statistical study of waveform capture data during 67 interplanetary (IP) shocks with Mach numbers ranging from approximately 1-6. Most of the waveform captures and nearly 100% of the large amplitude waves were in the ramp region. Although solitary waves, Langmuir waves, and ion acoustic waves (IAWs) are all observed in the ramp region of the IP shocks, large amplitude IAWs dominate. The wave amplitude is correlated with the fast mode Mach number and with the shock strength. The observed waves produced anomalous resistivities from approximately 1-856 Omega.m (approximately 10(7) times greater than classical estimates.) The results are consistent with theory suggesting IAWs provide the primary dissipation for low Mach number shocks.
Journal Article•
TL;DR: In this article, the authors measured the acoustic wave velocities in standing trees of five softwood species by the time-of-flight (TOF) method and found that the observed tree velocity was significantly higher than log velocity.
Abstract: Acoustic wave velocities in standing trees of five softwood species were measured by the time-of-flight (TOF) method. Tree velocities were compared with acoustic velocities measured in corresponding butt logs through a resonance acoustic method. The experimental data showed a skewed relationship between tree and log acoustic measurements. For most trees tested, observed tree velocities were significantly higher than log velocities. The results indicate that time-of-flight measurement in standing trees is likely dominated by dilatational or quasi-dilatational waves rather than one-dimensional plane waves. To make appropriate adjustments of observed tree velocities, two analytical models were developed for the species evaluated. Both the multivariate regression model and dilatational wave model were effective in eliminating deviation between tree and log velocity and reducing variability in velocity prediction.