Acoustic resonance scattering from a submerged anisotropic sphere

The resonance scattering theory (RST) is applied to the problem of sound scattering from an elastic transversely isotropic solid sphere suspended in an ideal acoustic fluid medium. The normal mode expansion technique in conjunction with the Frobenius power series solution method is utilized to deal with the material anisotropy. The presented model, which degenerates to the simple isotropic solution in the case of very weak anisotropy, is initially employed to study sensitivity of various resonant modes of vibration to perturbations in elements of the stiffness matrix. Employing a rigid background subtraction, the target’s spectrum of resonances is extracted from the relevant modal backscattering form functions and subsequently traced and discussed through Regge pole trajectory plots. Also, the backscattering form function and resonance spectra, along with the dispersion curves for selected transversely isotropic solid spheres with distinct degrees of material anisotropy, are calculated and discussed. The various modes of propagation associated with the Rayleigh, Whispering Gallery, and fluid-borne Scholte-Stoneley surface waves are identified and examined. Published in Russian in Akusticheskiĭ Zhurnal, 2008, Vol. 54, No. 2, pp. 205–218. The text was submitted by the authors in English.     

Extraordinary Resonant Scattering in Imperfect Acoustic Cloak

We present a systematic study on the extraordinary resonant scattering in imperfect acoustic cloak by means of acoustic scattering theory. Analysis results demonstrate that the resonances are inevitable due to the perturbation to the ideal clo~k, and specific resonance modes are excited by specific order waves. The strength of resonance is determined by the magnitude of perturbation and each order wave＇s sensitivity to the perturbation. Further studies reveal the unique scattering characters of different resonance modes.     

The effect of the size,shape, and structure of metal nanoparticles on the dependence of their optical properties on the refractive index of a disperse medium

The effect of the size, shape, and structure of gold and silver nanoparticles on the dependence of their extinction and integral scattering spectra on the dielectric environment has been investigated. Calculations were performed using the Mie theory for spheres and nanoshells and the T-matrix method for chaotically oriented bispheres, spheroids, and s cylinders with hemispherical ends. The sensitivity of plasmon resonances to variations in the refractive index of the environment in the range 1.3–1.7 for particles of different equivolume size, as well as to variations in the thickness of the metal layer of nanoshells, was studied. For nanoparticles with an equivolume diameter of 15 nm, the maximal shifts of plasmon resonances due to variation in the refractive index of the environment are observed for bispheres and the shifts decrease in the series nanoshells, s cylinders or spheroids, and spheres. For particles 60 nm in diameter, the largest shifts of plasmon resonances occur for nanoshells and the shifts decrease in the series bispheres, s cylinders or spheroids, and spheres. All other conditions being the same, silver nanoparticles are more sensitive to the resonance tuning due to a change in the dielectric environment.     

Acoustic resonance scattering from a multilayered cylindrical shell with imperfect bonding

The method of wave function expansion is adopted to study the three dimensional scattering of a time-harmonic plane progressive sound field obliquely incident upon a multi-layered hollow cylinder with interlaminar bonding imperfection. For the generality of solution, each layer is assumed to be cylindrically orthotropic. An approximate laminate model in the context of the modal state equations with variable coefficients along with the classical T-matrix solution technique is set up for each layer to solve for the unknown modal scattering and transmission coefficients. A linear spring model is used to describe the interlaminar adhesive bonding whose effects are incorporated into the global transfer matrix by introduction of proper interfacial transfer matrices. Following the classic acoustic resonance scattering theory (RST), the scattered field and response to surface waves are determined by constructing the partial waves and obtaining the non-resonance (backgrounds) and resonance components. The solution is first used to investigate the effect of interlayer imperfection of an air-filled and water submerged bilaminate aluminium cylindrical shell on the resonances associated with various modes of wave propagation (i.e., symmetric/asymmetric Lamb waves, fluid-borne A-type waves, Rayleigh and Whispering Gallery waves) appearing in the backscattered spectrum, according to their polarization and state of stress. An illustrative numerical example is also given for a multi-layered (five-layered) cylindrical shell for which the stiffness of the adhesive interlayers is artificially varied. The sensitivity of resonance frequencies associated with higher mode numbers to the stiffness coefficients is demonstrated to be a good measure of the bonding strength. Limiting cases are considered and fair agreements with solutions available in the literature are established.     

Pure elastic resonance scattering for submerged elastic objects with separable geometries

I.IntroductionTheResonanceScatteringTheory(RST)wasdevelopedasabasicmethodtoanalyzesoundscatteringfromelasticobjectsimmersedinwater.Itwasusedtocylindricalandspher-icalgeometries,includingsolidandshellobjects.TheRSTinvestigatesmainlytheresonancespectrumofscatteredwavefromanelasticobjectexcitedbytheincidentwave.Theresonallcespectrum,namedthe'AcousticSpectroscoPy',reflectsmaterialcharactersoftheobjectsandcanbeusedtoidentifythetarget.Theresonallcespectraareisolatedbysubtractingfromthescattere…     

On the contribution of circumferential resonance modes in acoustic radiation force experienced by cylindrical shells

A body insonified by a constant (time-varying) intensity sound field is known to experience a steady (oscillatory) force that is called the steady-state (dynamic) acoustic radiation force. Using the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of a resonance field and a background (non-resonance) component, we show that the radiation force acting on a cylindrical shell may be synthesized as a composition of three components: background part, resonance part and their interaction. The background component reveals the pure geometrical reflection effects and illustrates a regular behavior with respect to frequency, while the others demonstrate a singular behavior near the resonance frequencies. The results illustrate that the resonance effects associated to partial waves can be isolated by the subtraction of the background component from the total (steady-state or dynamic) radiation force function (i.e., residue component). In the case of steady-state radiation force, the components are exerted on the body as static forces. For the case of oscillatory amplitude excitation, the components are exerted at the modulation frequency with frequency-dependant phase shifts. The results demonstrate the dominant contribution of the non-resonance component of dynamic radiation force at high frequencies with respect to the residue component, which offers the potential application of ultrasound stimulated vibro-acoustic spectroscopy technique in low frequency resonance spectroscopy purposes. Furthermore, the proposed formulation may be useful essentially due to its intrinsic value in physical acoustics. In addition, it may unveil the contribution of resonance modes in the dynamic radiation force experienced by the cylindrical objects and its underlying physics.     

Accurate transport cross sections for the Lennard-Jones potential

It is well-known that in open quantum systems resonances can coalesce at an exceptional point, where both the energies and the wave functions coincide. In contrast to the usual behaviour of the scattering amplitude at one resonance, the coalescence of two resonances invokes a pole of second order in the Green’s function, in addition to the usual first order pole. We show that the interference due to the two pole terms of different order gives rise to patterns in the scattering cross section which closely resemble Fano-Feshbach resonances. We demonstrate this by extending previous work on the analogy of Fano-Feshbach resonances to classical resonances in a system of two driven coupled damped harmonic oscillators.     

Scattering and active acoustic control from a submerged piezoelectric-coupled orthotropic hollow cylinder

A general exact analysis for three-dimensional scattering of a time-harmonic plane-progressive sound wave obliquely incident upon an arbitrarily thick bilaminated circular hollow cylinder of infinite extent, which is composed of a cylindrically orthotropic axially polarized piezoelectric inner layer perfectly bonded to an orthotropic outer layer, is presented. An approximate laminate model in the context of the so-called state space formulation along with the classical T-matrix solution technique involving a system global transfer matrix is employed to solve for the unknown modal scattering and transmission coefficients. Numerical example is given for an air-filled and water-submerged two-layered elasto-piezoelectric hybrid (steel/PZT4) hollow cylinder insonified by an obliquely incident unit-amplitude plane sound wave. Following the acoustic resonance scattering theory (RST), the total form function amplitude together with the associated global scattering, the far-field inherent background, and the resonance scattering coefficients of the nth normal mode are computed as a function of dimensionless frequency for selected angles of incidence, piezoelectric layer thickness parameters, and electrical boundary conditions (i.e., open/closed circuit or active). Also, the electrical voltage coefficients required for partial or complete cancellation of the reflected sound field are calculated. Limiting cases are considered and good agreements with the solutions available in the literature are obtained.     

Acoustic radiation force of a Bessel beam on a porous sphere

The possibility of using acoustic Bessel beams to produce an axial pulling force on porous particles is examined in an exact manner. The mathematical model utilizes the appropriate partial-wave expansion method in spherical coordinates, while Biot's model is used to describe the wave motion within the poroelastic medium. Of particular interest here is to examine the feasibility of using Bessel beams for (a) acoustic manipulation of fine porous particles and (b) suppression of particle resonances. To verify the viability of the technique, the radiation force and scattering form-function are calculated for aluminum and silica foams at various porosities. Inspection of the results has shown that acoustic manipulation of low porosity (<0.3) spheres is similar to that of solid elastic spheres, but this behavior significantly changes at higher porosities. Results have also shown a strong correlation between the backscattered form-function and the regions of negative radiation force. It has also been observed that the high-order resonances of the particle can be effectively suppressed by choosing the beam conical angle such that the acoustic contribution from that particular mode vanishes. This investigation may be helpful in the development of acoustic tweezers for manipulation of micro-porous drug delivery carrier and contrast agents.     

Influence of Coating Layer on Acoustic Wave Propagation in a Random Complex Medium with Resonant Scatterers

We investigate the influence of coating layer on acoustic wave propagation in a dispersed random medium consisting of coa.ted fibers.In the strong-scattering regime, the characteristics of wave scattering resonances are found to evolve regularly with the properties of the coating layer.By theoretical calculation,frequency gaps are found in acoustic excitation spectra in a random medium.The scattering cross section results present the evolution of scattering resonances with the properties of the coating layer,which offers a good explanation for the change of the frequency gaps.The velocity of the propagation quasi-mode is also shown to depend on the filling fraction of the coating layer.We use the generalized coherent potential-approximation approach to solve acoustic wave dispersion relations in a complicated random medium consisting of coating-structure scatterers.It is shown that our model reveals subtle changes in the behavior of the acoustic wave propagating quasi-modes.     

Using simple particle shapes to model the Stokes scattering matrix of ensembles of wavelength-sized particles with complex shapes: possibilities and limitations

We investigate to what extent the full Stokes scattering matrix of an ensemble of wavelength-sized particles with complex shapes can be modeled by employing an ensemble of simple model shapes, such as spheres, spheroids, and circular cylinders. We also examine to what extent such a simple-shape particle model can be used to retrieve meaningful shape information about the complex-shaped particle ensemble. More specifically, we compute the Stokes scattering matrix for ensembles of randomly oriented particles having several polyhedral prism geometries of different sizes and shape parameters. These ensembles serve as proxies for size-shape mixtures of particles containing several different shapes of higher geometrical complexity than the simple-shaped model particles we employ. We find that the phase function of the complex-shaped particle ensemble can be accurately modeled with a size distribution of volume-equivalent spheres. The diagonal elements of the scattering matrix are accurately reproduced with a size-shape mixture of spheroids. A model based on circular cylinders accurately fits the full scattering matrix including the off-diagonal elements. However, the modeling results provide us with only a rough estimate of the effective shape parameter of the complex-shaped particle ensemble to be modeled. They do not allow us to infer detailed information about the shape distribution of the complex-shaped particle ensemble.     

水中微小波纹圆柱体声散射低频共振调控

塑料类高分子材料甲基丙烯酸甲酯-亚克力(PMMA)圆柱中亚音速Rayleigh波低频隧穿共振可引起反向散射增强,在低频标准散射体设计等领域具有重要应用价值.提出一种微弱形变的规则波纹表面结构,可实现水中PMMA圆柱反向散射低频共振频率的无源调控.利用微扰法推导了水中微弱形变规则波纹圆柱反向散射低频共振频率偏移的近似解,讨论了波纹微扰系数、周期对规则波纹圆柱共振频率偏移的影响规律.基于Rayleigh波相位匹配方法分析了低频共振频率偏移的机理.研究表明:微弱形变规则波纹圆柱中亚音速Rayleigh波沿微弱形变波纹表面传播,与光滑圆柱体相比,传播路径的改变引起Rayleigh波传播相位变化,导致了Rayleigh波低频共振频率发生偏移.最后开展了微弱形变规则波纹圆柱体声散射特性水池实验,获取了其反向散射共振频率,明显观察到了规则波纹圆柱共振频率偏移现象,与理论预报结果吻合较好.     

复动量格林函数方法对n-α散射研究

在复动量表象下引入格林函数,建立了复动量格林函数方法.把这种方法应用于n-α散射系统,计算其散射相移.提取n-α系统的共振态并研究共振态对能级密度、相移和散射截面的贡献.在不引入任何非物理参数的前提下,离散化薛定谔积分方程得到束缚态、共振态和连续谱.通过分析散射态物理量可以更好地理解共振态以及非共振连续谱态.在n-α系统中的成功应用,证明了该方法的正确性.     

An exploration in acoustic radiation force experienced by cylindrical shells via resonance scattering theory

In nonlinear acoustic regime, a body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force (RF). This force is a second-order quantity of the velocity potential function of the ambient medium. Exploiting the sufficiency of linear solution representation of potential function in RF formulation, and following the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of the resonant field and a background (non-resonant) component, we will show that the radiation force is a composition of three components: background part, resonant part and their interaction. Due to the nonlinearity effects, each part contains the contribution of pure partial waves in addition to their mutual interaction. The numerical results propose the residue component (i.e., subtraction of the background component from the RF) as a good indicator of the contribution of circumferential surface waves in RF. Defining the modal series of radiation force function and its components, it will be shown that within each partial wave, the resonance contribution can be synthesized as the Breit-Wigner form for adequately none-close resonant frequencies. The proposed formulation may be helpful essentially due to its inherent value as a canonical subject in physical acoustics. Furthermore, it may make a tunnel through the circumferential resonance reducing effects on radiation forces.     

Echo features used by human listeners to discriminate among objects that vary in material or wall thickness: implications for echolocating dolphins

Echolocating dolphins extract object feature information from the acoustic parameters of echoes. To gain insight into which acoustic parameters are important for object discrimination, human listeners were presented with echoes from objects used in two discrimination tasks performed by dolphins: Hollow cylinders with varying wall thicknesses (+/-0.2, 0.3, 0.4, and 0.8 mm), and spheres made of different materials (steel, aluminum, brass, nylon, and glass). The human listeners performed as well or better than the dolphins at the task of discriminating between the standard object and the comparison objects on both the cylinders (humans=97.1%; dolphin=82.3%) and the spheres (humans= 86.6%; dolphin= 88.7%). The human listeners reported using primarily pitch and duration to discriminate among the cylinders, and pitch and timbre to discriminate among the spheres. Dolphins may use some of the same echo features as the humans to discriminate among objects varying in material or structure. Human listening studies can be used to quickly identify salient combinations of echo features that permit object discrimination, which can then be used to generate hypotheses that can be tested using dolphins as subjects.     

A new spectral resonance of metallic nanorods

The extinction, integrated scattering, and absorption spectra of gold and silver nanorods with random and regular orientation are studied. The calculations are performed for spheroids, circular cylinders, circular cylinders with hemispherical ends (T-matrix method), and rectangular prisms (discrete dipole approximation). A new quadrupole resonance is discovered that arises between the usual plasmon dipole resonances excited by a field longitudinal or transverse with respect to the symmetry axis. The new resonance can be excited only by a TM incident wave and is the greatest for orientation of the symmetry axis of the particle at an angle of 54° with respect to the light beam.     

Circumferential resonance modes of solid elastic cylinders excited by obliquely incident acoustic waves

When an immersed solid elastic cylinder is insonified by an obliquely incident plane acoustic wave, some of the resonance modes of the cylinder are excited. These modes are directly related to the incidence angle of the insonifying wave. In this paper, the circumferential resonance modes of such immersed elastic cylinders are studied over a large range of incidence angles and frequencies and physical explanations are presented for singular features of the frequency-incidence angle plots. These features include the pairing of one axially guided mode with each transverse whispering gallery mode, the appearance of an anomalous pseudo-Rayleigh in the cylinder at incidence angles greater than the Rayleigh angle, and distortional effects of the longitudinal whispering gallery modes on the entire resonance spectrum of the cylinder. The physical explanations are derived from Resonance Scattering Theory (RST), which is employed to determine the interior displacement field of the cylinder and its dependence on insonification angle.     

Acoustic elliptical cylindrical cloaks

By making a comparison between the acoustic equations and the 2-dimensional (2D) Maxwell equations, we obtain the material parameter equations (MPE) for acoustic elliptical cylindrical cloaks. Both the theoretical results and the numerical results indicate that an elliptical cylindrical cloak can realize perfect acoustic invisibility when the spatial distributions of mass density and bulk modulus are exactly configured according to the proposed equations. The present work is the meaningful exploration of designing acoustic cloaks that are neither sphere nor circular cylinder in shape, and opens up possibilities for making complex and multiplex acoustic cloaks with simple models such as spheres, circular or elliptic cylinders.     

Super scattering phenomenon in active spherical nanoparticles

Localized surface electromagnetic resonances in spherical nanoparticles with gain are investigated by using the Mie theory. Due to the coupling between the gain and resonances, super scattering phenomenon is raised and the total scattering efficiency is increased by over six orders of magnitude. The dual frequency resonance induced by the electric dipole term of the particle is observed. The distributions of electromagnetic field and the Poynting vector around nanoparticles are provided for better understanding different multipole resonances. Finally, the scattering properties of active spherical nanoparticles are investigated when the sizes of nanoparticles are beyond the quasi-static limit. It is noticed that more highorder multipole resonances can be excited with the increase of the radius. Besides, all resonances dominated by multipole magnetic terms can only appear in dielectric materials.     

The design of Helmholtz resonator based acoustic lenses by using the symmetric Multi-Level Wave Based Method and genetic algorithms

Sonic crystals can be used as acoustic lenses in certain frequencies and the design of such systems by creating vacancies and using genetic algorithms has been proven to be an effective method. So far, rigid cylinders have been used to create such acoustic lens designs. On the other hand, it has been proven that Helmholtz resonators can be used to construct acoustic lenses with higher refraction index as compared to rigid cylinders, especially in low frequencies by utilizing their local resonances. In this paper, these two concepts are combined to design acoustic lenses that are based on Helmholtz resonators. The Multi-Level Wave Based Method is used as the prediction method. The benefits of the method in the context of design procedure are demonstrated. In addition, symmetric boundary conditions are derived for more efficient calculations. The acoustic lens designs that use Helmholtz resonators are compared with the acoustic lens designs that use rigid cylinders. It is shown that using Helmholtz resonator based sonic crystals leads to better acoustic lens designs, especially at the low frequencies where the local resonances are pronounced.