Showing papers on "Acoustic interferometer published in 2014"

Sub-optical wavelength acoustic wave modulation of integrated photonic resonators at microwave frequencies

Abstract: Light–sound interactions have long been exploited in various acousto-optic devices based on bulk crystalline materials. Conventionally, these devices operate in megahertz frequency range where the acoustic wavelength is much longer than the optical wavelength and a long interaction length is required to attain significant coupling. With nanoscale transducers, acoustic waves with sub-optical wavelengths can now be excited to induce strong acousto-optic coupling in nanophotonic devices. Here we demonstrate microwave frequency surface acoustic wave transducers co-integrated with nanophotonic resonators on piezoelectric aluminum nitride substrates. Acousto-optic modulation of the resonance modes at above 10 GHz with the acoustic wavelength significantly below the optical wavelength is achieved. The phase and modal matching conditions in this scheme are investigated for efficient modulation. The new acousto-optic platform can lead to novel optical devices based on nonlinear Brillouin processes and provides a direct, wideband link between optical and microwave photons for microwave photonics and quantum optomechanics. Acousto-optic modulators use acoustic waves to control light on a chip. Here, the authors achieve modulation in nanophotonic resonators using microwave frequency surface acoustic waves with wavelength smaller than the optical wavelength towards highly integrated devices on silicon.

Symmetrical and anti-symmetrical coherent perfect absorption for acoustic waves

Abstract: We investigate tunable acoustic absorption enabled by the coherent control of input waves. It relies on coherent perfect absorption originally proposed in optics. By designing appropriate acoustic metamaterial structures with resonating effective bulk modulus or density, we show that complete absorption of incident waves impinging on the metamaterial can be achieved for either symmetrical or anti-symmetrical inputs in the forward and backward directions. By adjusting the relative phase between the two incident beams, absorption can be tuned effectively from unity to zero, making coherent control useful in applications like acoustic modulators, noise controllers, transducers, and switches.

Imaging of acoustic fields using optical feedback interferometry

Abstract: This study introduces optical feedback interferometry as a simple and effective technique for the two-dimensional visualisation of acoustic fields. We present imaging results for several pressure distributions including those for progressive waves, standing waves, as well as the diffraction and interference patterns of the acoustic waves. The proposed solution has the distinct advantage of extreme optical simplicity and robustness thus opening the way to a low cost acoustic field imaging system based on mass produced laser diodes.

Embedded ultrasound sensor in a silicon-on-insulator photonic platform

Abstract: A miniaturized ultrasound sensor is demonstrated in a silicon-on-insulator platform. The sensor is based on a π-phase-shifted Bragg grating formed by waveguide corrugation. Ultrasound detection is performed by monitoring shifts in the resonance frequency of the grating using pulse interferometry. The device is characterized by measuring its response to a wideband acoustic point source generated using the optoacoustic effect. Experimental results show that the sensor's response is dominated by the formation of surface acoustic waves.

Spatial separation of spoof surface acoustic waves on the graded groove grating

Abstract: In this paper, a rigid surface decorated with an array of grooves with graded widths is proposed to get spatial separation of the spoof surface acoustic waves. Because of the intermodal coupling between forward and backward modes on the graded structure, the spoof surface acoustic waves with different frequencies stop propagating ahead and reflect back at different positions of the graded groove grating. The intensity of acoustic field is effectively enhanced near the propagation-stop position due to the slow group velocity. We believe that such system with the capability of energy concentration and wave spatial arrangement by frequencies has potential applications in acoustic wave coupling and absorption.

Advanced numerical technique for analysis of surface and bulk acoustic waves in resonators using periodic metal gratings

Abstract: A numerical technique characterized by a unified approach for the analysis of different types of acoustic waves utilized in resonators in which a periodic metal grating is used for excitation and reflection of such waves is described. The combination of the Finite Element Method analysis of the electrode domain with the Spectral Domain Analysis (SDA) applied to the adjacent upper and lower semi-infinite regions, which may be multilayered and include air as a special case of a dielectric material, enables rigorous simulation of the admittance in resonators using surface acoustic waves, Love waves, plate modes including Lamb waves, Stonely waves, and other waves propagating along the interface between two media, and waves with transient structure between the mentioned types. The matrix formalism with improved convergence incorporated into SDA provides fast and robust simulation for multilayered structures with arbitrary thickness of each layer. The described technique is illustrated by a few examples of its application to various combinations of LiNbO3, isotropic silicon dioxide and silicon with a periodic array of Cu electrodes. The wave characteristics extracted from the admittance functions change continuously with the variation of the film and plate thicknesses over wide ranges, even when the wave nature changes. The transformation of the wave nature with the variation of the layer thicknesses is illustrated by diagrams and contour plots of the displacements calculated at resonant frequencies.

Determination of acoustic speed for improving leak detection and location in gas pipelines

Abstract: The commonly used cross-correlation technique for leak location requires that the acoustic speed is known and invariable. In practice, the gas leakage-induced acoustic waves propagate along multiple paths including in-pipe gas and pipe wall, and the acoustic waves in different transmission paths exhibit different acoustic speeds and different dispersive behaviors, which bring a great challenge for leak detection and location in the gas pipelines. In this study, based on the vibration theory of cylindrical elastic thin shell, the wavenumber formulae in different transmission paths are derived to predict the acoustic speeds and the acoustical coupling between the in-pipe gas and the pipe wall is analyzed to determine the dominant transmission path. In addition, the velocity dispersions in the dominant transmission path are suppressed by selection of a characteristic frequency band of the gas leakage-induced acoustic waves. The theoretical predictions are verified in the experiment and the results show that the theoretical acoustic speed is slightly larger than the measured acoustic speed. Thus, the theoretical acoustic speed formula is modified considering the effect of the structural loss factor and consequently the location error using the modified acoustic speed is reduced by two times compared to that using the theoretical acoustic speed.

Passive acoustic measurements of wind velocity and sound speed in air.

Abstract: Random acoustic fields generated by uncorrelated sources in moving media contain information about the propagation environment, including sound speed and flow velocity. This information can be recovered by noise interferometry. Here interferometric techniques are applied to road traffic noise. Acoustic travel times and their nonreciprocity are retrieved from two-point cross-correlation functions of noise. The feasibility of passive acoustic measurements of wind velocity using diffuse noise is experimentally demonstrated for the first time. The accuracy of the interferometric measurements of sound speed and wind velocity is confirmed by comparison with in situ measurements of wind, air temperature, and humidity.

Alternative Designs of Acoustic Lenses Based on Nonlinear Solitary Waves

Abstract: In the last decade, there has been an increasing attention on the use of highly- and weakly-nonlinear solitary waves in engineering and physics. These waves can form and travel in nonlinear systems such as one-dimensional chains of particles. When compared to linear elastic waves, solitary waves are much slower, nondispersive, and their speed is amplitude-dependent. Moreover, they can be tuned by modifying the particles' material or size, or the chain's precompression. One interesting engineering application of solitary waves is the fabrication of acoustic lenses, which are employed in a variety of fields ranging from biomedical imaging and surgery to defense systems and damage detection in materials. In this paper, we propose the design of acoustic lenses composed by one-dimensional chains of spherical particles arranged to form a line or a circle array. We show, by means of numerical simulations and an experimental validation, that both the line and circle arrays allow the focusing of waves transmitted into a solid or liquid (the host media) and the generation of compact sound bullets of large amplitude. The advantages and limitations of these nonlinear lenses to attain accurate high-energy acoustic pulses with high signal-to-noise ratio are discussed.

A method for the frequency control in time-resolved two-dimensional gigahertz surface acoustic wave imaging

Abstract: We describe an extension of the time-resolved two-dimensional gigahertz surface acoustic wave imaging based on the optical pump-probe technique with periodic light source at a fixed repetition frequency. Usually such imaging measurement may generate and detect acoustic waves with their frequencies only at or near the integer multiples of the repetition frequency. Here we propose a method which utilizes the amplitude modulation of the excitation pulse train to modify the generation frequency free from the mentioned limitation, and allows for the first time the discrimination of the resulted upper- and lower-side-band frequency components in the detection. The validity of the method is demonstrated in a simple measurement on an isotropic glass plate covered by a metal thin film to extract the dispersion curves of the surface acoustic waves.

Efficient excitation of guided acoustic waves in semiconductor nanorods through external metallic acoustic transducer

Abstract: We demonstrate that guided acoustic waves inside a nanorod can be excited through an external metallic acoustic transducer. By attaching gold nanodisks on top of GaAs nanorods, the femtosecond optical excitation on the external acoustic transducer enables the generation of guided acoustic waves in the rods. The propagation behavior and mode shape of the observed guided acoustic waves are analyzed. These observations would not only lead to the development of superior external transducers for acoustic imaging, but also provide an experimental system for the study of the acoustic phonon transport behavior in nanorods and nanowires.

Microaccelerometer based on surface acoustic waves

Abstract: This paper proposes an idea of an accelerometer based on surface acoustic waves. Such devices should be able to survive high shocks (up to 65 000 g) and still be small, energy efficient and low-cost. Theory basics, design concepts, experimental and modeling results are discussed.

On the wavenumber spectra for sound within subsonic jets

Abstract: This paper explores the nature of sound spectra within subsonic jets. Three problems of increasing complexity are presented. First, a point source is placed in a two-dimensional plug flow and the sound field is obtained analytically. Second, a point source is embedded in a diverging axisymmetric jet and the sound field is obtained by solving the linearized Euler equations. Finally, an analysis of the acoustic waves propagating through a turbulent jet obtained by direct numerical simulation is presented. In each problem, the pressure or density field is analyzed in the frequency-wavenumber domain. It is found that acoustic waves can be classified into three main frequency-dependent groups. A physical justification is provided for this classification. The main conclusion is that, at low Strouhal numbers, acoustic waves satisfy the d'Alembertian dispersion relation.

Acoustic Vector-Corrected Impedance Meter

Abstract: We describe the development of a novel instrument intended for the measurement of the acoustical reflection coefficient of materials. The instrument effectively implements a one-port vector-corrected network analyzer in the acoustic, rather than the electromagnetic, domain. Employing the well-documented methods of error correction familiar to microwave engineers, this instrument permits automated measurement of an acoustic impedance presented to a waveguide port. A dual-directional coupler allows a working frequency range of well over an octave. In principle, a set of six couplers would allow measurement from 100 to 50000 Hz.

Measuring oblique incidence sound absorption using a local plane wave assumption

Abstract: In this paper a method for the measurement of the oblique incidence sound absorption coefficient is presented. It is based on a local field assumption, in which the acoustic field is locally approximated by one incident- and one specularly reflected plane wave. The amplitudes of these waves can be determined with an unidirectional sound intensity probe. The local active- and incident acoustic intensity are straightforwardly obtained. The area-averaged sound absorption coefficient is calculated after spatial integration of these quantities over the surface area of interest. Alternatively, one may use a three-dimensional intensity probe. In that case, the determination of the amplitudes of the plane waves can be formulated as a least-squares problem. Measurements performed for a sound absorbing foam demonstrate that accurate results can be obtained, even under non-ideal acoustic conditions. Measurements carried out for a periodic absorber show that the method is accurate below the cut-on frequency of scattering as long as the amplitude of the evanescent surface waves is significantly smaller than that of the specularly reflected wave.

Near-surface Full Waveform Inversion Using Surface Waves and Reflected Waves

Abstract: We investigate the capacity of extracting near-surface shear-wave velocity by considering dispersive surface waves and non-dispersive reflected waves. We show that indeed the full waveform fitting of these waves requires a dedicated approach by using lateral spatial and frequential coherence for surface waves and by explicitely introduces the fitting of reflected waves in the inversion formulation. On a simple example as a two-layers model, lateral variations of the velocity are reconstructed while the low-wavenumber content of the velocity could be improved through reflection waves. Combining these two sources of information on the shear-wave velocity could improve our shear-wave velocity imaging in the near-surface context.

Noncontact determination of thin films conductance by SH0 plate acoustic waves

Abstract: The paper is devoted to the development of noncontact acoustic method of the determination of thin film conductance by using shear-horizontal zero order (SH0) acoustic waves in thin piezoelectric plates The method is based on the registration of changes in velocity and attenuation of acoustic waves in a piezoelectric plate due to placing the structure “film under study–dielectric substrate” on the certain distance from the plate The limits of measured values by the suggested method are determined The theoretical data are compared with the experimental results

Solid-state motion sensors on acoustic waves. Theory and experiment

Abstract: The results of theoretical and experimental researches of bulk acoustic wave propagation into rotating isotropic solid-state medium are represented. The wave parameters, dependent from rotation velocity, which can be used as an informative signal, are found. Some fundamentally new concepts for motion sensor design, based on bulk acoustic waves, are offered.

Sound Source Identification and Acoustic Contribution Analysis Using Nearfield Acoustic Holography

Abstract: The main goal of the present paper is to provide a method of source identification. Firstly, statistically optimal near-field acoustical holography (SONAH) techniques are applied to locate sound sources with the reflected sound field. In the presence of reflection plane parallel and perpendicular to the source plane, the incoming wave and reflected waves are separated based on the acoustic superposition principle and acoustic mirror image principle to satisfy the condition of the sound sources reconstruction using SONAH. Secondly, contribution of noise source to the special field point is analyzed and noise source ranking of interior panel groups are evaluated based the proposed three step acoustic contribution method. Finally, this method is verified experimentally.

Investigation of the Space Distribution of the Velocity of Surface Acoustic Waves in Plastically Deformed Steel by the Laser Method

Abstract: We study the influence of plastic deformation of St.3 steel on the velocity of Rayleigh surface acoustic waves measured by the method of laser recording. It is shown that plastic strains lead to the formation of anisotropy of the acoustic properties mainly determined, according to the data of evaluation of residual mechanical stresses, by the texture of steel.

Characterization of the Sound Field Generated by an Ultrasonic Transducer in a Solid Medium by Rayleigh-Sommerfeld Back-Propagation of Bulk Acoustic Waves Measured with Double-Pulsed TV Holography

Abstract: The established approach for the characterization of sound beams is the acquisition of experimental data by measuring the acoustic field pressure distribution in a fluid medium, which is usually done with point detectors (hydrophones, microphones) or arrays of detectors. From these point measurements, important characteristics of the sound field emitted by the transducer (such as the axial and transversal beam profiles, focal length or beam spread) can be derived. When the propagation medium is a solid, these characteristics are normally obtained from the measurement of pulse-echo signals that arise from the interaction of the sound beam with targets placed in the material, such as metal balls embedded in plastics, or flat-bottom or side holes drilled in metallic blocks [1]. These measurements are more difficult to perform and provide a sparser set of data compared to the immersion techniques.

Coupling Electron Waves and Laser Waves

Abstract: In this chapter, we go back to laser–plasma interaction by addressing the coupling of the laser waves with the electron plasma waves. So we derive the so-called Raman instability model. In the case of the fixed-ion assumption, it leads to a three-wave coupling system that shows the same structure as the system of Brillouin instability. In the second part of this chapter, we deal with the modelling of the interaction of an ultra-intense laser pulse and a plasma. This leads to the so-called Euler–Maxwell system. We give some mathematical properties of this system and we show how an envelope description may be useful in some cases.

X-ray analysis of surface and pseudo-surface acoustic waves propagation in disordered La3Ga5SiO14 and ordered Ca3TaGa3Si2O14 crystals

Abstract: X-ray diffraction on disordered La3Ga5SiO14 (LGS) and ordered Ca3TaGa3Si2O14 (CTGS) crystals modulated by surface (SAW) and pseudo-surface acoustic waves (PSAW) with wavelength of A=6 μm was studied using a double axis X-ray diffractometer at the BESSY II synchrotron radiation source. The propagation of SAW and PSAW leads to sinusoidal modulation of the crystal lattice and gives rise to diffraction satellites on the rocking curve, with the intensity and angular divergence between the diffraction satellites depending on the wavelength and amplitude of the crystal lattice acoustic modulation. The analysis of diffraction spectra enables the determination of the amplitude and acoustic wavelengths, power flow angles of acoustic energy propagation.

Extraction of energy from gravitational waves by laser interferometer detectors

Abstract: In this paper we discuss the energy interaction between gravitational waves and laser interferom- eter gravitational wave detectors. We show that the widely held view that the laser interferometer gravitational wave detector absorbs no energy from gravitational waves is only valid under the approximation of a frequency-independent optomechanical coupling strength and a pump laser without detuning with respect to the resonance of the interferometer. For a strongly detuned interferometer, the optical-damping dynamics dissipates gravitational wave energy through the interaction between the test masses and the optical field. For a non-detuned interferometer, the frequency-dependence of the optomechanical coupling strength causes a tiny energy dissipation, which is proved to be equivalent to the Doppler friction raised by Braginsky this http URL.

Parametric interaction of acoustic waves in a resonant nonlinear layer

Abstract: The degenerate parametric interaction of acoustic waves in a nonlinear resonator (plane-parallel layer placed into an external linear medium and irradiated by primary harmonic waves with frequencies ω and 2ω incident along the normal) is investigated. The amplitudes of secondary waves at combination frequencies ω and 3ω in the external media are determined. The method for determining the nonlinearity parameter of the medium in the layer is considered; the method is based on measuring the amplitude of the secondary wave at frequency ω or 3ω, which is emitted by the layer into the external medium in the forward or reverse (relative to the direction of propagation of primary waves) direction.

Transmission of Acoustic Waves from a Solid Cylinder into a Liquid and Equivalent Acoustic Impedances

Abstract: We discuss the feasibility of the one-dimensional theory by which the transmission of acoustic waves from a solid cylinder into a liquid is analyzed with the acoustic impedance. For this purpose, experiments were performed on a cylinder made of Cu with a size of 1.98mm o © 51.96mm t . The frequency of acoustic waves was varied from 0.80 to 1.3MHz. The characteristics of the Pochhammer mode in the solid cylinder are clarified by certain equivalent acoustic impedances. At low frequencies from 0.80 to 1.0MHz, several definitions of the equivalent acoustic impedances work effectively. At intermediate frequencies near 1.1MHz, the equivalent impedances available are those defined near the lateral surface of the cylinder. At high frequencies from 1.15 to 1.3MHz, the experimental transmission rate of acoustic waves decreases considerably, and the adequate impedance is obtained using the energy flux and the axial component of the velocity field in the cylinder.

Resonances and nonuniformities in CMUT elements or arrays

Abstract: We determine the response of individual cells of a CMUT array immersed in water using the small-signal equivalent circuit of a single cell and radiation impedances. Using a numerically efficient technique, we are able to simulate large arrays. The results indicate the presence of resonances at low frequencies where Rayleigh-Bloch waves are excited on the surface of the array. Reflections from the edges cause standing-wave patterns. Above the cut-off frequency of Rayleigh-Bloch waves, no standing-wave pattern exists. However, there is nonuniformity among cell velocities mainly due to unequal radiation impedance seen by the cells. Rayleigh-Bloch waves and nonuniformity in cell velocities do not cause a significant degradation in the point spread function, but the oscillations extend the duration of impulse response, limiting the dynamic range.

The Frequency Range of an Optical Receiver in the Registration of Surface Acoustic Waves

Abstract: The upper limit of the frequency range of a broadband optical receiver of surface acoustic waves based on a two-beam laser interferometer and depending on the diameter of the laser beam in the reception area on the sample surface is determined theoretically and experimentally. It is shown that the frequency range of the developed receiver is 0.05–53 MHz and in the limit can reach 1 GHz.

Fiber laser sensing system for double-frequency sound wave detection

Abstract: The invention relates to a fiber laser sensing system for double-frequency sound wave detection. The system comprises a fiber DBR grating, a rotary part, a 980/1550 wavelength division multiplexer, a pump laser, an optical isolator, a polarization controller, a polarizer and a photoelectric detector, wherein 980nm laser pumped by the pump laser is emitted and then input to the fiber DBR grating via the 980/1550 wavelength division multiplexer, the rotary part keeps the fiber DBR grating rotating, external double-frequency sound waves from different directions act on the fiber DBR grating which keeps rotating, the rotating grating is sensitive to one frequency of sound waves at one angle and is sensitive to the other frequency of sound waves at the other angle, information of the double-frequency sound waves is modulated into transmitted light waves, the light wavelength is converted to 1550nm, and the light waves are reflected back to the 980/1550 wavelength division multiplexer; and the light waves are input to the polarization controller via the optical isolator that prevents photo echo, and then two polarization states are converted into electrical signals in the same direction via the polarizer. The system can simultaneously detect the sound waves of two different frequencies.