Electrical characteristics of Cu-PS-Si structures

The effect of ambient humidity on the current-voltage characteristics of Cu-PS (porous silicon) structure was investigated. The humidity-voltaic effect, i.e. the generation of open-circuit voltage (V _oc) in Cu-PS interface in humid atmosphere (up to 300 mV at 95% relative humidity) in dark and day-light illumination is discovered. Humidity-stimulated open-circuit voltage generation is caused by hydrogen component of water-vapor of ambient. The possible mechanism of hydrogen-stimulated voltage generation in Cu-PS interface is suggested. Besides this effect, annealing in the range of 60–200°C in air on V _oc of Cu-PS structures was studied and decrease of values of V _oc depending on duration of annealing was discovered. These changes were attributed to diffusion of oxygen from air and oxidation of copper film. (V _oc – t) data were used for estimation of diffusion coefficients of oxygen in Cu film. The temperature dependence of the oxygen diffusion coefficient in Cu films are described by the relation D = 5.2 × 10^–7 exp(-0.44/kT). The results of this research showed that Cu-PS structures can be perspective for using as hydrogen sensors.     

The spectrum of dipole-exchange spin waves in tangentially-magnetized metal-ferroelectric-ferromagnet-ferroelectric-metal sandwich structures

An equation describing the dipole-exchange spin waves in tangentially magnetized metal-ferroelectric-ferromagnet-ferroelectric-metal symmetric planar sandwich structures has been derived within the framework of the Green function tensor formalism for the Maxwell field equations. Changes in the wave spectrum in response to variation of the layer structure parameters are theoretically studied.     

Dispersion characteristics of the surface electromagnetic-spin waves in ferrite-ferroelectric-dielectric-metal structures

Dispersion characteristics of the surface hybrid electromagnetic-spin waves propagating in a layered structure comprising a ferrite film on a ferroelectric plate and a metal screen at a certain distance from the ferroelectric plate surface were experimentally studied. The experimental data are compared to the results of calculations performed within the framework of a previously developed theory. The theoretical and experimental dispersion characteristics show good coincidence.     

Stress waves in layered rocks

Summary In this paper two problems will be solved analytically: the reflection of plane stress waves at a free boundary and the reflection and refraction of plane stress waves at a welded interface separating two dissimilar materials. In particular, stress reflection and refraction coefficients will be derived and the superimposed state of stress in regions of wave interference will be calculated. The solutions are visualized in a series of examples by means of computer-generated isochromatic fringe patterns. They show the partition of stress between reflected and refracted waves, stress distribution in regions of wave interference and demonstrate stress wave propagation in laycred structures.     

Generation of dissipative structures in self-oscillating ring systems upon parametric interaction of spin waves

A quasi-periodic sequence of pulses in a self-oscillating ring system with a resonant amplifier and a ferromagnetic film has been generated upon three-wave parametric interaction of spin waves. It is established that the generated pulses are analogs of dissipative bright solitons, which are formed as a result of competition between amplification and loss, as well as between time dispersion and nonlinearity. To describe the mechanism of formation of these structures, we have proposed a model in the form of three parametrically coupled differential equations with amplification and a differential equation of linear oscillator. Under certain assumptions, this model has analytical solutions in time in the form of structures with a profile similar to that of bright solitons.     

Synthetic phase tuning of guided waves

A novel method has been developed to generate and manipulate multi-mode guided waves. This technique uses a linear phased array whose elements are activated according to a prescribed time delay profile obtained from the dispersion curves. It is shown that a desired guided wave mode can be tuned by synthetically constructing a virtual wave from individually acquired waveform data. In addition to the development of such a synthetic phase tuning (SPT) technique, a pseudo pulse-echo (PPE) operation scheme is also developed for nondestructive testing. Experimental results are compared with those obtained by more traditional techniques using variable angle wedges and array transducers. It was shown that the new technique is convenient, robust, and flexible in utilizing multi-mode guided waves for nondestructive evaluation (NDE). It is a dynamic method that can produce desired guided wave modes propagating in the desired direction without any mechanical alignment. The advantages and limitations of the technique are addressed     

SAW device modeling including velocity dispersion based on ZnO/diamond/Si layered structures

Surface acoustic wave (SAW) filter properties of ZnO/diamond/Si structures are calculated including velocity dispersion. The conventional SAW device modeling has previously been developed for bulk substrates. However, layered materials exhibit SAW velocity dispersion. The null frequency bandwidth of typical layered ZnO/diamond/Si structures is narrower than that calculated by conventional SAW device modeling techniques due to the velocity dispersion of the layered structures. The null frequency bandwidth of layered structures was calculated by the delta function model and the equivalent circuit model, including velocity dispersion, and compared with the experimental results. The dispersive equivalent circuit (DEC) model for layered structures is also presented. The results of these analysis are compared with the experimental results which show very good agreement.     

A simple closed form dispersion equation for shear types of surface waves propagating in periodic structures

A closed-form dispersion relation is found for shear surface acoustic waves (SAWs), namely, Bleustein-Gulyaev waves (BGWs), surface transverse waves (STWs), and leaky waves, propagating in periodic structures in the frequency range corresponding to the Bragg stopband. Changes in the spatial structure of the waves mutually reflecting on the grating as well as bulk wave scattering are considered. A comparison with numerically obtained dispersion curves for leaky waves on 36-LiTaO (3) shows good agreement.     

Non-linear dispersion of Stokes waves

Summary Asymptotic solutions representing slowly varying wavetrains are obtained for two-dimensional irrotational surface waves of finite amplitude on water of finite depth (Stokes waves) by means of a formal perturbation procedure. The resulting partial differential equations for wavenumber, frequency, amplitude, mean waveheight and mean velocity are identical with those found by Whitham [1], [2] using the averaged Lagrangian density method.     

Shear waves in a piezoceramic layered structure

The propagation of SH-type wave is studied in a composite structure consisting of alternating polymeric layers and porous piezoelectric layers. The porous piezoelectric materials of the composite structure are assumed to have 6mm symmetry and their poling direction is along z-axis. Layers of the polymer are considered as isotropic dielectric elastic material. Solutions of the field equations for the porous piezoelectric material and for the polymeric material are obtained. Two cases, first when the direction of propagation of the SH-type wave is taken along the direction normal to the layering of the composite structure, and second when the propagation direction is taken along the layering, are considered for the derivation of the phase velocity. The dispersion and the stop-pass band behavior of the Floquet wave is also discussed. Numerical results for phase velocity and stop band effect are presented for a periodic system of alternating PZT-5H and polythene layers. The influence of volume fraction on phase velocity and stop band effect is discussed.     

The peculiarities of energy characteristics of acoustic waves in piezoelectric materials and structures

This paper is devoted to detailed theoretical investigation of energy density and power flow of homogeneous (bulk) and inhomogeneous (surface and plate) plane acoustic waves in piezoelectric materials and structures. The analysis of these waves in different materials of various crystallographic orientations allowed us to establish some energy regularities. These regularities are the same for instantaneous energy characteristics of homogeneous waves and for time-average energy characteristics on unit of aperture of inhomogeneous waves if the electrical energy and power flow in vacuum are taken into account. It has been shown that, for strong piezoactive waves, the electric energy density may exceed the mechanical energy density more than three times.     

Theory for the measurements of dispersion characteristics in waveguiding structures with a scanning near-field optical microscope

A theory is presented for the interpretation of scanning near-field optical microscope measurements on pulses propagating in waveguiding structures. It is shown how the dispersion characteristics of the propagating guided modes may be derived from such experiments. Then it is demonstrated how to calibrate the scanning tip position and to derive experimental values for reflection and transmission of modes in identical single-mode waveguides connected to a photonic device such as a micro cavity.     

On the sensing and tuning of progressive structural vibration waves

Progressive flexural waves can be generated only in finite structures by fine tuning the excitation and the boundary conditions. The tuning process eliminates the reflected waves arising from discontinuities and edge effects. This work presents and expands two new methods for the identification and tuning of traveling waves. One is a parametric method based on fitting an ellipse to the complex spatial amplitude distribution. The other is a nonparametric method based on the Hilbert transform providing a space-localized estimate. With these methods, an optimization-based tuning of transverse flexural waves in a one-dimensional structure, a vibrating beam, is developed. Existing methods are designed for a single frequency and are based on either combining two vibration modes or mechanical impedance matching. Such methods are limited to a designated excitation frequency determined by a specific configuration of the system. With the proposed methods, structural progressive waves can be generated for a wide range of frequencies under the same given system configuration and can be tuned in real time to accommodate changes in boundary conditions. An analytical study on the nature of the optimal excitation conditions has been carried out, revealing singular configurations. The experimental verification of the sensing and tuning methods is demonstrated on a dedicated laboratory prototype. The proposed methods are not confined to mechanical waves and present a comprehensive approach applicable for other physical wave phenomena.     

钢轨垂直振动模态导波频散曲线、波结构及检测应用*

频散曲线和波结构是钢轨导波检测时设计检测方法和分析回波波形的基础。首先介绍了半解析有限元计算任意截面弹性波导中导波传播的频散曲线和波结构的基本方法。然后应用该方法求解了U60型钢轨中垂直振动模态的导波频散曲线和波结构,并讨论了频散曲线和波结构在钢轨轨头缺陷导波检测中的应用。最后采用模态力锤实验及时频联合分析的方法验证了频散曲线数值计算结果。钢轨轨头横向裂纹垂直振动模态导波检测的有限元数值模拟和实验表明该模式导波是检测钢轨轨头缺陷的有效检测模式波型。     

Interactions between spin waves and elastic waves in one-domain ferromagnetic insulators

The interaction between spin waves and the elastic waves is theoretically investigated in the ferromagnetic insulators which are made to behave like one-domain bodies by means of an applied magnetic field. The free energy of the material, that is, the potential of stresses, is derived by continuum approximations of a microscopic model, and the physical meaning of various contributions in the free energy is discussed. The dipole-dipole interaction which may be considered to be a long-range interaction is approximated by a nearest neighbor interaction. As an application of the theory, interactions of spin waves and elastic waves are studied. A correspondence between the microscopic and the continuum theories of ferromagnetic resonance is presented.     

Transverse surface waves in an FGM layered structure

The existence and propagation behavior of Love waves in a functionally graded material (FGM) layered structure are theoretically investigated in this paper based on the three-dimensional equations of linear electricity. The Wentzel–Kramers–Brillouin (WKB) method is applied to obtain the analytical solutions in the FGM layer. The dispersion equation for a Love surface wave in this kind of structure is obtained in a simple mathematical form, where the material property variation of the FGM layer is arbitrary. First, the solution is used to study the effect of the gradient coefficients on the dispersion curves and the phase velocities of Love waves. Then, the influence of gradient coefficients on the stress and displacement fields is discussed in detail. The reported results are important in the design of surface acoustic wave (SAW) devices with high performance.     

Velocity dispersion of acoustic waves in cancellous bone

Measurement of ultrasonic attenuation and velocity in cancellous bone are being applied to aid diagnosis of women with high fracture risk due to osteoporosis. However, velocity dispersion in cancellous bone has received little attention up to now. The overall goal of this research was to characterize the velocity dispersion of human cancellous bone based on a spectral analysis of ultrasound transmitted through the bone specimens. We have followed a systematic approach, beginning with the investigation of a test material, moving on to the investigation of bone specimens. Particular attention is given to diffraction effect, a potential source of artifacts. Parametric images of phase velocity (measured at the center frequency of the pulse spectrum), slope of attenuation coefficient (dB/cm/MHz) and velocity dispersion were obtained by scanning 15 bone specimens. We have demonstrated that the diffraction effect is negligible in the useful frequency bandwidth, and that the ultrasonic parameters reflect intrinsic acoustic properties of bone tissue. The measured attenuation showed approximately linear behavior over the frequency range 200 to 600 kHz. Velocity dispersion of cancellous bone in the frequency range 200 to 600 kHz was unexpectedly found to be either negative or positive and not correlated with the slope of attenuation coefficient. There was a highly significant correlation between the slope of attenuation coefficient and phase velocity at the center frequency of the spectrum. This behavior contrasts with other biological or nonbiological materials where the local form of the Kramers-Kronig relationship provides accurate prediction of velocity dispersion from the experimental frequency dependent-attenuation for unbounded waves.     

Electrical resistivity anisotropy in layered p-SnSe single crystals

Single crystals of p-type SnSe were grown by both direct vapor transport (DVT) and chemical vapor transport (CVT) techniques. The d.c. electrical resistivity anisotropy has been investigated for the first time in these layered crystals. The DVT grown crystals exhibited a large anisotropy ratio and also a higher activation energy compared to that of CVT grown crystals. The electron microscopic examination revealed the presence of a large concentration of stacking faults in the DVT grown crystals. The resistivity anisotropy is accordingly discussed in terms of stacking disorder.