Nonlinear surface acoustic wave pulses in solids: Laser excitation, propagation, interactions (invited)
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Laser techniques enabled generation of very high amplitude pulses with acoustic Mach numbers about 0.01. Such waves drive the medium into the nonlinear elastic regime and shock fronts can be formed during their propagation. As an intense surface acoustic wave (SAW) propagates, the temporal evolution of the wave shape provides information on the nonlinear acoustic parameters and the nonlinear elastic constants of the material. The nonlinear propagation of SAW pulses exhibits different types of nonlinear behavior depending on nonlinear acoustic constants. Changes of a SAW pulse shape were calculated using a nonlinear evolution equation. Measurements of SAW pulses in polycrystalline stainless steel have demonstrated that a compression of the pulse takes place in this material corresponding to a positive parameter of the local nonlinearity, which was evaluated by fitting the parameters of the evolution equation to the experimental data. Numerical simulations of a dispersive propagation of nonlinear SAWs in a system comprised of a substrate with a film were performed. A formation of a relatively stable portion of the waveform was found in agreement with recent observations of soliton-like SAW pulses.Keywords:
Nonlinear acoustics
Acoustic wave equation
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The paper deals with parametric excitation of nonlinear standing waves in acoustic resonators. There are a number of methods which enable to generate intensive acoustic fields confined to resonators. The acoustic system, which is composed of an acoustic resonator and source, is often bulky and expensive. For this reason we designed a method which is inexpensive and at the same time enables miniaturization of the discussed acoustic system. This method is based on the use of a parametric acoustic piston source which radiates an amplitude modulated ultrasonic waves. The carrier ultrasonic wave is the finite amplitude one hence the nonlinearity of the fluid enables to self-demodulate the amplitude modulated ultrasonic waves. The approximate solutions were found for the used model equation. From the realized analysis it follows that parametric excitation of nonlinear standing waves inside of the acoustic resonators represent a perspective method.
Nonlinear acoustics
Piston (optics)
Acoustic wave equation
Acoustic dispersion
Acoustic interferometer
Standing wave
Physical acoustics
Parametric array
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Acoustic sensor
Physical acoustics
Acoustic wave equation
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Abstract : This report discusses five projects all of which involve basic theoretical research in nonlinear acoustics. (1) Pulsed Finite Amplitude Sound Beams are studied with a recently developed time domain computer algorithm that solves the KZK nonlinear parabolic wave equation. (2) Nonlinear Acoustic Wave Propagation in a Liquid Layer is a study of harmonic generation and acoustic soliton information in a liquid between a rigid and a free surface. (3) Nonlinear Effects in Asymmetric Cylindrical Sound Beams is a study of source asymmetries and scattering of sound by sound at high intensity. (4) Effects of Absorption on the Interaction of Sound Beams is a completed study of the role of absorption in second harmonic generation and scattering of sound by sound. (5) Parametric Receiving Arrays is a completed study of parametric reception in a reverberant environment.
Parametric array
Nonlinear acoustics
Physical acoustics
Harmonic
Acoustic wave equation
Acoustic theory
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Laser techniques enabled generation of very high amplitude pulses with acoustic Mach numbers about 0.01. Such waves drive the medium into the nonlinear elastic regime and shock fronts can be formed during their propagation. As an intense surface acoustic wave (SAW) propagates, the temporal evolution of the wave shape provides information on the nonlinear acoustic parameters and the nonlinear elastic constants of the material. The nonlinear propagation of SAW pulses exhibits different types of nonlinear behavior depending on nonlinear acoustic constants. Changes of a SAW pulse shape were calculated using a nonlinear evolution equation. Measurements of SAW pulses in polycrystalline stainless steel have demonstrated that a compression of the pulse takes place in this material corresponding to a positive parameter of the local nonlinearity, which was evaluated by fitting the parameters of the evolution equation to the experimental data. Numerical simulations of a dispersive propagation of nonlinear SAWs in a system comprised of a substrate with a film were performed. A formation of a relatively stable portion of the waveform was found in agreement with recent observations of soliton-like SAW pulses.
Nonlinear acoustics
Acoustic wave equation
Autowave
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To generate acoustic waves with abnormal transmission characteristics different from those of traditional natural acoustic materials, we studied the propagation of acoustic waves in resonant phononic crystals. We identified the vibration mechanism of 2D three-component locally resonant phononic crystals. Using the finite element software COMSOL, an acoustic propagation model of a tubular structure based on acoustic metamaterials was constructed, and the local resonance characteristics of the acoustic waves and the original cells were used to simulate the propagation characteristics of the acoustic waves. We found that after low-loss wavefront propagation, most of the incident acoustic waves were absorbed by the model and reconverged with the outgoing acoustic waves on the other side of the model. Acoustic metamaterials with different layers emit acoustic waves at different locations, and thus, the propagation distance can be controlled by the design of the acoustic metamaterials. In addition, the propagation characteristics of the acoustic waves tend to be better at frequencies close to the resonance frequency. Because of the flexibility and the controllability of the acoustic metamaterials, the structure can be designed according to the actual situation to achieve the resonance frequency needed to propagate acoustic signals. This can improve the efficiency of acoustic propagation and provide new ideas for actual underwater acoustic source detection and acoustic communication.
Physical acoustics
Ion acoustic wave
Acoustic wave equation
Acoustic interferometer
Rayleigh Wave
Acoustic space
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Acoustic wave equation
Duplexer
Physical acoustics
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By introduction of the high-order thermal expansion coefficients and the high-order thermal elastic constants of material,the equations of surface acoustic wave propagation in a semi-infinite quartz crystal have been solved and the wave velocities at different temperature have obtained.Numerical results showed that temperature change has strong effect on wave velocities of surface acoustic wave propagation in AT-cut and ST-cut quartz crystal.Then we investigated the frequency-temperature characteristics of surface acoustic wave propagation in ST-cut quartz crystal and found that the frequency shift caused by temperature change is significant.
Crystal (programming language)
Acoustic wave equation
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