Nonlinear surface acoustic waves: realization of solitary pulses and fracture

A laser-based technique for the contact-free generation and detection of strongly nonlinear surface acoustic wave (SAW) pulses with amplitudes limited by the materials strength has been developed. The effects of nonlinear propagation of short elastic surface pulses with finite strength in isotropic solids, such as fused quartz, anisotropic solids, such as silicon, and dispersive media were investigated. Solitary surface wave propagation was observed in layered structures for normal and anomalous dispersion. In addition, a SAW-based method for evaluating the critical fracture stress of anisotropic brittle solids, such as single crystal silicon, is introduced.     

Nonlinear surface acoustic waves: silicon strength in phonon-focusing directions

The anisotropy of the elastic properties of single-crystal silicon manifests itself in features of both the linear and nonlinear surface acoustic wave (SAW) propagation. Directions showing the phonon-focusing effect and strong nonlinearity were employed in contact-free and notch-free laser-based fracture experiments, yielding the intrinsic strength of silicon. The critical tensile stress values vary between 2.5 GPa and 7 GPa for the different crystallographic planes and directions of SAW propagation investigated.     

Nonlinear compression of giant surface acoustic wave pulses

The nonlinear propagation of very high-amplitude surface acoustic wave (SAW) pulses in polycrystalline aluminum and copper was studied. A nonlinear compression and an increase of the SAW pulse amplitude have been observed. SAW pulses were numerically simulated with a nonlinear evolution equation including local and nonlocal nonlinear terms.     

Nonlinear response of photorefractive lithium tantalate and niobate at acoustic frequencies

An amplification of the intensity of pump oscillations is observed experimentally at frequencies from 100 Hz to 1 kHz during photoinduced light scattering and holographic-type parametric scattering in photorefractive lithium tantalate and niobate. Possible ways are analyzed for explaining the existence of a photorefractive response in these crystals over times of 10⁻²–10⁻³ s, which are five orders of magnitude shorter than the Maxwell time. Zh. éksp. Teor. Fiz. 112, 1490–1498 (October 1997)     

Nonlinear acoustic propagation and focusing

Two model equations of nonlinear acoustics are considered. The implications of a point transformation between forms of the generalised Burgers equation (GBE) is discussed. New exact and asymptotic solutions are obtained. The dissipative Zabolotskaya-Khokhlov (DZK) equation describing acoustic wave propagation with allowance for transverse amplitude variation is studied. By considering a transformation onto the GBE, solutions exhibiting caustic behaviour are presented. A mechanism for the control of such singularities is presented along with a comparison with shock formation time.Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 9EW, England. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 8, pp. 783–787, August, 1993.     

声表面波器件变频快速模拟方法

声表面波器件的级联有限元模拟方法是从整体结构中分离出若干独立的基本单元,通过基本单元边界矩阵的级联实现有限长器件结构的模拟.在实际设计中,通过优化叉指换能器的指条周期,激发出不同波长的声表面波,调整声表面波器件的谐振频率,这导致级联有限元模拟方法存在频繁的单元建模与数据传输过程.为提高模拟效率,该文提出了一种波长(频率...     

Theoretical simulation of a rotary motor driven by surface acoustic waves

A simulation model for theoretically studying the operation behavior of a rotary motor driven by surface acoustic waves (SAWs) is proposed. According to the model, some simulation results are obtained as follows: (1) as the rotor is excited by the SAWs, the motor experiences two phases, i.e., the acceleration phase and the steady phase; (2) the normal vibration amplitude A of SAWs has a very weak effect on the acceleration in the first phase but an enhancing effect on the steady velocity of the rotary motor; (3) as the number of the contact points between the rotor and the stator increases, the motor rotates more steadily; (4) as the rotor radius becomes smaller, both the acceleration and the steady angular velocity become greater. These features are in agreement with the experimental results.     

FE simulation of laser generated surface acoustic wave propagation in skin

Advances in laser ultrasonics have opened new possibilities in medical applications, such as the characterization of skin properties. This paper describes the development of a multilayered finite element model (FEM) using ANSYS to simulate the propagation of laser generated thermoelastic surface acoustic waves (SAWs) through skin and to generate signals one would expect to observe without causing thermal damage to skin. A transient thermal analysis is developed to simulate the thermal effect of the laser source penetrating into the skin. The results from the thermal analysis are subsequently applied as a load to the structural analysis where the out-of-plane displacement responses are analysed in models with varying dermis layer thickness.     

Numerical simulation of evaluation of surface breaking cracks by array-lasers generated narrow-band SAW

Most of the factors limiting the extensive application of laser-based ultrasonic for nondestructive evaluation of surface breaking crack are its poor sensitivity, low efficiency relative to conventional contact ultrasonic methods and limit on the dimension of the cracks. For this reason, a new technique that multiplepulse narrow-band ultrasound generated by laser arrays has been proposed. It is found that crack detection dependent on spectrum of narrow-band ultrasound generated by laser arrays can be operated with low amplitude requirements. In this paper, the narrow-band ultrasound generated by pulse laser arrays interacting with surface breaking cracks has been simulated in detail by the finite element method (FEM) according to the thermoelastic theory. The pulsed array lasers were assumed to be transient heat source, and the surface acoustic wave (SAW) which propagating on the top of the plate was computed based on thermoelastic theory. Then the frequency spectrums of both reflected waves by crack and transmission ones through crack were compared with the direct waves. Results demonstrate that multiple-frequency components of the narrow-band ultrasound were varied with change of the depth of surface breaking cracks significantly, which provides the possibility for precise evaluation of surface breaking cracks.     

Nonlinear response of uniaxial ferromagnets and applications to surface magnetostatic waves

The nonlinear susceptibilities of uniaxially anisotropic ferromagnets are obtained analytically. The expressions show that the anisotropy effect on the first- and second-order components means just an increased H_1a (the first-order anisotropy field) of the dc field H₀ along the anisotropy axis, but the third-order components are complicated and new terms appear. Applying the above results to surface magnetostatic waves in the films, we find new magnetostatic modes from the joint effect of the anisotropy and nonlinearity since higher powers of frequency are introduced in the dispersion equation by the nonlinearity and anisotropy. Very obvious non-reciprocity is seen from the dispersion curves.     

Nonlinear frequency shift in surface acoustic wave resonator operating as a gas sensor

The shift in the resonance frequency of a two-port quartz surface acoustic wave (SAW) resonator operating as a gas sensor without a selective layer is studied versus the power of an SAW excited in the resonator. At working frequencies of the resonator (≈389 MHz) placed in the flow of moisture-containing nitrogen gas, an anomalously large positive shift of the resonance frequency is observed as the SAW power exceeds 1 mW. This shift is one order of magnitude larger than that due to the nonlinear amplitude-frequency effect, which is known for quartz SAW resonators. Possible physical mechanisms underlying this phenomenon are analyzed. Experimental data indicate that such a shift is associated with the influence of a powerful SAW on sorption processes taking place on the active surface of the resonator rather than being a direct consequence of heating of the SAW substrate by the powerful SAW.     

基于AlN声表面波滤波传感器器件的有限元仿真

声表面波器件是一种利用压电材料的压电效应与逆压电效应工作电子器件, 文章首先详细描述了声表面波器件的设计与仿真过程,运用有限元分析的方法分别计算了利用声表面波的 SAW 器件与利用体波的 BAW 器件的性能与各项参数,对相关的器件进行了计算分析,分别用上述方法研究了基于 AlN 薄膜的声表面波器件和悬臂梁结构的体波器件,推导得出了器件的电学导纳与频率之间的关系, 通过分析器件的导纳-频率曲线,推导出器件内部声波的模式以及合适的工作频率,最终得出在 IDT 周期为 8 微米的情况下,SAW 器件的理想工作频率是 0.7-1.95GHz,BAW 器件的理想工作频率在 0.6-3.2GHz 的结果。     

Nonlinear oscillation and acoustic scattering of bubbles

The scattered acoustic pressure and scattered cross section of bubbles is studied using the scattered theory of bubbles. The nonlinear oscillations of bubbles and the scattering acoustic fields of a spherical bubble cluster are numerically simulated based on the bubble dynamic and fluid dynamic. The influences of the interaction between bubbles on scattering acoustic field of bubbles are researched. The results of numerical simulation show that the oscillation phases of bubbles are delayed to a certain extent at different positions in the bubble cluster, but the radii of bubbles during oscillation do not differ too much at different positions. Furthermore, directivity of the acoustic scattering of bubbles is obvious. The scattered acoustic pressures of bubbles are different at the different positions inside and outside of the bubble cluster. The scattering acoustic fields of a spherical bubble cluster depend on the driving pressure amplitude, driving frequency, the equilibrium radii of bubbles, bubble number and the radius of the spherical bubble cluster. These theoretical predictions provide a further understanding of physics behind ultrasonic technique and should be useful for guiding ultrasonic application.     

Optical method for measuring the amplitude response of surface acoustic wave devices

The amplitude response of acoustic surface wave (SAW) devices up to the highest frequencies can be determined in an optical way without electric shielding. This makes it possible to use the method for fast nondestructive testing and control in SAW-device production as well.     

Structural-borne acoustics analysis and multi-objective optimization by using panel acoustic participation and response surface methodology

This paper is aimed to investigate the structural-borne acoustics analysis and multi-objective optimization of an enclosed box structure by using the panel acoustic participation (PAP) and response surface methodology (RSM). The acoustic frequency response function is applied to achieve the critical frequency of interest under each excitation. The PAP analysis is then carried out at all critical frequencies and the remarkable acoustic panels are identified. The correlation coefficient matrix method is proposed for reselecting and grouping the positions of acoustic panels identified to paste damping layer to control noise. With the help of faced central composite design, an efficient set of sample points are generated and then the second-order polynomial functions of sound pressure response at each critical frequency are computed and verified by the adjusted coefficient of multiple determination. The functional relationships between sound pressure responses and the thicknesses of damping layers are investigated, and multi-objective optimization of the thicknesses of damping layers is developed. The results indicate that, by using the PAP and RSM, the structural-borne acoustics at critical frequencies are calculated conveniently and controlled effectively. The optimization process of the explicit optimization model proposed in this paper is simple and the computational time is saved.     

Interaction of hydrogen with palladium surface: FIM and FEM studies

In the present paper, we focus on the geometrical and electronic changes in palladium surface structure which appeared during its interaction with hydrogen in the presence of an external electric field. The interaction process was examined by using the field ion microscopy (FIM) as well as the field emission microscopy (FEM) techniques. In order to study the geometrical changes in substrate surface structure, the distance distribution function (DDF) was constructed on the basis of FIM patterns of both a clean and hydrogen-covered palladium surface. The electronic changes were examined by the measurement of the total energy distribution (TED) of electrons emitted from the palladium tip surface. The most pronounce examples of such changes are an expansion of the equilibrium interatomic distance in palladium surface and a shift of the Fermi level of the metal. These changes may be explained among others by palladium hydrides formation. This process is the most efficient if the field strength exceeds 23 V/nm.     

Efficient simulation of surface tension-dominated flows through enhanced interface geometry interrogation

In this paper, three improvements for modelling surface tension-dominated interfacial flows using interface tracking-based solution algorithms are presented. We have developed an improved approach to curvature estimation for incorporation into modern mesh-based surface tension models such as the Continuum Surface Force (CSF) and Sharp Surface Force (SSF) models. The scheme involves generating samples of curvature estimates from the multitude of height functions that can be generated from VOF representations of interfaces, and applying quality statistics based on interface orientation and smoothness to choose optimal candidates from the samples. In this manner, the orientation-dependence of past schemes for height function-based curvature estimation is ameliorated, the use of compact stencils for efficient computation can be maintained, and robustness is enhanced even in the presence of noticeable subgrid-scale disturbances in the interface representation. For surface tension-dominated flows, the explicit capillary timestep restriction is relaxed through timescale-separated slope limiting that identifies spurious modes in curvature evolution and omits them from contributing to surface force computations, thus promoting efficiency in simulation through the use of less timesteps. Efficiency in flow simulation is further promoted by incorporating awareness of interface location into multigrid preconditioning for Krylov subspace-based solution of elliptic problems. This use of interface-cognizance in solving problems such as the Helmholtz equation and the Poisson equation enables multigrid-like convergence in discontinuous-coefficient elliptic problems without the expense of constructing the Galerkin coarse-grid operator. The key improvements in the surface tension modelling and the numerical linear algebra are also applicable to level-set-based interfacial flow simulation.