Acoustic wave propagation along cladded fibers of cubic crystalsymmetry

An approximate method is proposed to analyze the acoustic wave propagation characteristics in nonpiezoelectric cladded fibers of cubic crystal symmetry. The fiber axis coincides with the crystalline Z axis. This approximate method utilizes coupled mode equations and the exact solutions for the corresponding cladded isotropic fiber are used as the approximation base. We concentrate our analysis on cubic fibers with weak anisotropy where the first order approximation obtained from the coupled mode equations can provide accurate results. Dispersion curves of a few lower order flexural, torsional and radial-axial modes in such a fiber with infinite cladding are presented for the first time. Higher order approximations are also discussed. We show the accuracy of the perturbation formula, reveal that the torsional and radial-axial modes are not pure in cubic fibers, and inspect the modal birefringence phenomenon     

Acoustic wave propagation in piezoelectric fibers of hexagonalcrystal symmetry

An exact analysis is presented for acoustic wave propagation in cladded acoustic fibers having a core and an infinite thick cladding both made of piezoelectric hexagonal crystal of 6 mm point group symmetry. The crystalline Z axes of both the core and cladding coincide with the fiber axis. A general dispersion equation is derived for all the acoustic modes propagating along the fiber axis. Two simpler and independent equations which represent the dispersion relations of torsional and radial-axial modes can be separated from the general dispersion equation. It has been found that the radial-axial and general flexural modes are piezoelectrically active while the torsional modes are not. Approximate dispersion relations for pure guided modes in weakly guiding weakly piezoelectric fibers which are much simpler than the exact ones are also given. Numerical results are only presented for pure guided modes. Exact and approximate dispersion curves of several lower order pure guided flexural, radial-axial and torsional modes in a weakly guiding ZnS fiber are compared and they are in good agreement     

Leaky guided wave propagation along imperfectly bonded fibers in composite materials

Leaky guided modes propagating along embedded fibers in a composite material can be used for characterizing the fiber-matrix interface. This principle can be applied to real composites containing small-diameter fibers by using laser interferometric detection of very fine lateral resolution on the order of a few microns. The main purpose of this paper is to develop the analytical tools needed to assess the sensitivity of guided wave inspection to interface properties in composite materials. Typically, the sound velocity is much lower in the matrix than in the fiber and the guided modes are strongly attenuated by leaking their energy into the matrix as they propagate. As a result, the velocity of the lowest-order axisymmetric longitudinal mode decreases while its attenuation increases with increasing interfacial stiffness between the fiber and the matrix. It is shown that loose fibers can be readily identified from early signals produced by fast guided modes. In the case of a well-bonded fiber-matrix interface, these guided modes are slowed down and strongly attenuated by the loading of the matrix depending on the fiber diameter and the interfacial stiffness of the interface. Interestingly, the relative difference between the well-bonded and free fibers is greater at low frequencies. Therefore, good sensitivity to the sought interfacial stiffness can be achieved at a few MHz, i.e., when the fiber diameter is still much smaller than the acoustic wavelength. Our analytical results show that the leaky guided mode technique is mainly sensitive to the transverse interfacial stiffness of the fiber-matrix interface. At typical ultrasonic frequencies between 1 and 20 MHz, the technique works best in the 10¹¹–10¹³ N/m³ interfacial stiffness range which is one or two orders of magnitude lower than the optimal sensitivity range of the more conventional bulk velocity and reflection methods.     

Acoustic wave propagation in Laves-phase compounds

We have studied the acoustic wave propagation in the hexagonal structured materials TiCr₂, ZrCr₂ and HfCr₂. In this paper, we have calculated the orientation dependence of three types of acoustic wave velocity and Debye average velocity using second order elastic constants. The six second order elastic constants are calculated for these materials at 300 K using Lenard-Jones Potential. An anomalous behaviour in orientation dependent acoustic wave velocity is obtained which is due to the combined effect of elastic constants and density. These velocity data are important for their structural information and to differentiate them from third group nitrides.     

Acoustic wave propagation in disordered microscale granular media under compression

We investigate the effect of dynamic and uniaxial static loading on the wave speeds and rise times of laser generated acoustic waves traveling through a disordered, multilayer aggregate of 2 \(\mu {\mathrm {m}}\) diameter silica microspheres, where the excited dynamic amplitudes are estimated to approach the level of the static overlap between the particles caused by adhesion and externally applied loads. Two cases are studied: a case where the as-fabricated particle network is retained, and a case where the static load has been increased to the point where the aggregate collapses and a rearrangement of the particle network occurs. We observe increases in wave speeds with static loading significantly lower than, and in approximate agreement with, predictions from models based on Hertzian contact mechanics for the pre- and post-collapse states, respectively. The measured rise time of the leading pulse is found to decrease with increasing static load in both cases, which we attribute to decreased scattering and stiffening of the contact network. Finally, we observe an increase in wave speed with increased excitation amplitude that depends on static loading, and whether the system is in the pre- or post-collapse state. The wave speed dependence on amplitude and static load is found to be in qualitative agreement with a one-dimensional discrete model of adhesive spheres, although the observed difference between pre- and post-collapse states is not captured. This investigation, and the approach presented herein, may find use in future studies of the contact mechanics and dynamics of adhesive microgranular systems.     

Analysis of cladded acoustic fibers of hexagonal crystal symmetry

A cladded acoustic fiber consisting of a core and an infinite thick cladding both having a hexagonal crystal symmetry is analyzed. The crystalline Z axes of both core and cladding are parallel to the fiber axis. Dispersion equations and field distributions for all modes are derived, and previously reported results for the isotropic case are retrieved. Numerical results for a few lowest-order pure guided torsional, radial-axial and flexural modes are shown. Material considerations are discussed.     

Solitary wave propagation in tunable liquid crystal-filled dual-core photonic crystal fibers

In this paper, we introduce the mathematical model and the necessary constraint conditions of solitary wave propagation through dual core photonic crystal fibres (PCF) filled with liquid crystal. Using the Ansatz method, we derived analytically the necessary formulas to support soliton wave propagation in the new proposed type of coupled bi-refringent fibres. We evaluated dispersion and coupling coefficients by solving wave equations using the vector finite element method. These values can be tuned either by applying external perturbations such as heat or electric field or even altering the geometry of the PCF. Based on the constraint conditions derived from analytic formulas and numerical simulation, we determined the wavelength range for which the soliton waves will be supported without any distortion. The wavelength range can be adjusted by tuning the PCF.     

In-line optical fiber sensors based on cladded multimode tapered fibers

The use of uniform-waist cladded multimode tapered optical fibers is demonstrated for evanescent wave spectroscopy and sensors. The tapering is a simple, low-loss process and consists of stretching the fiber while it is being heated with an oscillating flame torch. As examples, a refractive-index sensor and a hydrogen sensor are demonstrated by use of a conventional graded-index multimode optical fiber. Also, absorbance spectra are measured while the tapers are immersed in an absorbing liquid. It is found experimentally that the uniform waist is the part of the taper that contributes most to the sensor sensitivity. The taper waist diameter may also be used to adjust the sensor dynamic range.     

Analysis of weakly guiding cladded acoustic fibers of hexagonal crystal symmetry

An approximate analysis of the weakly guiding cladded acoustic fiber consisting of a core and infinite thick cladding both with hexagonal crystal symmetry is presented. The crystalline Z axis is parallel to the fiber axis. Weak guidance conditions require that the stiffness constants of the core are slightly less than those of the cladding, and the density of the core and cladding are almost the same. Approximate dispersion and cutoff equations are derived for all pure guided modes. Dispersion curves of several lower-order guided torsional, radial-axial and flexural modes are evaluated using both exact and approximate formulas and they are in good agreement. A simple approximate dispersion equation for leaky (longitudinal-type) modes is also obtained.     

A new approach to the analysis of piezoelectric cladded acoustic fibers

In this paper, a new effective analysis method is proposed for the piezoelectric cladded acoustic fiber of hexagonal crystal symmetry. Interpreting all quantities appearing in the boundary conditions as state variables, a first-order differential equations system is obtained to investigate the waves in cladded acoustic fiber of hexagonal symmetry. This approach makes possible the analysis of cladded fibers by the general transmission-matrix technique. By using this method, dispersion relations for all modes are easily obtained. Examples of several materials are given. This method can also be applied in the analysis of the multilayered cylindrical fiber for which the individual layers have hexagonal symmetric piezoelectrical material.     

Acoustic wave propagation in continuous functionally graded plates: an extension of the Legendre polynomial approach

The propagation of guided waves in continuous functionally graded plates is studied by using Legendre polynomials. Dispersion curves, and power and field profiles are easily obtained. Our computer program is validated by comparing our results against other calculations from the literature. Numerical results are also given for a graded semiconductor plate. It is felt that the present method could be of quite practical interest in waveguiding engineering, non-destructive testing of functionally graded materials (FGMs) to identify the best inspection strategies, or by means of a numerical inversion algorithm to determine through-thickness gradients in material parameters     

Elastic wave propagation with kinematic discontinuity along a non-ideal interface between two isotropic elastic half-spaces

The problem of wave propagation along the interface between two elastic, isotropic, and homogeneous half-spaces is studied when the half-spaces are coupled through a vanishingly thin layer of Voigt material. It is assumed that the separation, 2H, between the half-spaces, and the complex rigidity-modulus, , of the layer are both vanishingly small, but the complex quantity /2H remains finite.In a series of experiments in which two blocks of elastic materials with or without lubricant/couplant at the interface are subjected to an external load normal to the interface, the variation of the speed and attenuation of interfacial waves, generated and detected by piezoelectric transducers, was measured as a function of external load. Assuming a nonlinear relation between external load and /2H, the experimental data is interpreted theoretically, and the best-fit parameters of the nonlinear relation are determined.For the 13 cases of interfaces studied, with or without lubricant/couplant, satisfactory agreement was found between experiment and theory, except in one case. Even in this case, the agreement is satisfactory in the lower range of load. It is hoped that this study will be useful in developing nondestructive methods of testing the bonding conditions at an interface between elastic materials by means of interfacial wave properties.     

Acoustic energy during pop-in crack propagation

The acoustic energy emitted during a brittle multiple pop-in fracture process in DCB specimens has been measured and its values have been correlated with the mechanical parameters. An approximate formulation has also been developed in order to explain the behaviour of the emitted acoustic energy to the temperature.     

波浪滑翔器声学应用分析

波浪滑翔器作为一种跨界面无人自主航行器具有独特的优势,既可以作为水下与水面通信的中继节点,又可以搭载观测设备在大洋上长期自主航行,实现长时序、大范围观测.利用波浪滑翔器搭载声学负载组成声学探测节点,由多个节点按一定的轨迹运行组成特殊接收阵型可以提高水下目标检测概率.文章利用波浪滑翔器搭载自容式水听器在青岛近海开展了海上...     

Ferroelectrically active acoustic wave propagation

The ferroelectrically active acoustic wave equation including electrostriction effects is derived from nonlinear constitutive equations of stress and electric displacement for ferroelectric materials exhibiting significant electrostrictive strain. Electrically controllable acoustic wave propagation is predicted by solving the equation as a function of various acoustic variables, e.g., wave excitation, polarization, dc bias, etc. As examples, the elastic, piezoelectric, and ferroelectric acoustic waves and the electromechanical coupling factors are computed as a function of wave propagation in the [100]-[010] plane of BaTiO3 under thickness excitation mode.     

Cyclotron wave propagation in silver

Azbel'-Kaner cyclotron resonance in metals is accompanied by electromagnetic waves propagating in a direction perpendicular to the magnetic field. Taking into account the anisotropy of the silver Fermi surface, the dispersion relation for these waves is calculated in the limit where the wavelength is much smaller than the orbit diameter of the electrons. Thus it is shown that a number of previously observed oscillations in the surface impedance of a semiinfinite silver specimen arise from points of zero-group velocity on the dispersion relation. Physically, the oscillations reflect a matching of the electron-orbit diameter with an integer number of wavelengths. They may, therefore, be looked upon as geometric resonances in the surface impedance, complementary to the temporal cyclotron resonances. The surface impedance is calculated under the assumption of specular surface scattering. Satisfactory agreement with experiments is obtained by using an independent-particle model for the electron gas and band parameters based on APW calculations. The influence of the Fermi-surface geometry is demonstrated by comparing with calculations for a cylindrical and a spherical Fermi surface. The electric field in the metal is calculated for selected magnetic fields, and the expected result of a transmission experiment is presented. Finally, the absence of Fermi liquid effects in the experiments is briefly discussed.     

Non-symmetrical wave propagation in arteries

Summary For a better understanding of the effects of initial stress on flow in elastic tubes, the propagation of a harmonic and non-symmetrical wave in an initially stressed thick cylindrical shell filled with an inviscid fluid is studied. Although the blood is known to be a non-Newtonian fluid, for simplicity, it is assumed to be a non-viscous, while the elastic tube is considered to be isotropic and incompressible. Utilizing the theory of small deformations superimposed on large initial static deformation, for a non-symmetrical perturbed motion the governing differential equations are obtained in cylindrical polar coordinates. Due to variability of the coefficients of the resulting differential equations of the solid body, the field equations are solved by truncated power series method. Applying the boundary conditions, the dispersion relation is obtained as a function of inner pressure, axial stretch and the thickness ratio. It is observed that the wave speed of the non-symmetrical wave is large as compared to the axially symmetrical case. Various special cases are also discussed in the paper.     

Light propagation along periodic metal-dielectric layers

Analysis and experiments on TE and TM waves along periodically laminated metal-dielectric layers are described; the waves propagate parallel to the layers. Aluminum (Al) and silica (SiO2) are chosen as the metal and the dielectric, respectively. We find that the attenuation for TE waves is much higher than that for TM waves. Typically, alphaTE/alphaTM ranges from 10(3) to 10(4). Thus, an optical polarizer can be made in a multilayer structure.