Acoustic interferometer

About: Acoustic interferometer is a research topic. Over the lifetime, 1493 publications have been published within this topic receiving 19355 citations.

Real Time Imaging of Surface Acoustic Waves on Crystals and Microstructures

Abstract: The use of acoustic pulses to image materials is well-known in echography or sonar applications. We are extending this field by generating point-excited sound pulses on solid surfaces with ultrashort laser pulses and imaging the resulting surface wave propagation in real time. To see the tiny vibrations of the surface, smaller in amplitude than the dimensions of a single atom, we use another set of laser pulses for scanned probing. The typical surface phonon wavelength is of the order of a few microns, corresponding to frequencies up to 1 GHz. With such a system we can watch coherent acoustic wave packets in two dimensions rippling across crystal surfaces and microscopic landscapes.

Refraction and Scattering of Sound by a Shear Layer

Abstract: The angle and amplitude changes for acoustic waves refracted by a circular open jet shear layer were determined. The generalized refraction theory was assessed experimentally for on axis and off axis acoustic source locations as source frequency varied from 1 kHz to 10 kHz and free stream Mach number varied from 0.1 to 0.4. Angle and amplitude changes across the shear layer show good agreement with theory. Experiments confirm that the refraction theory is independent of shear layer thickness, acoustic source frequency, and source type. A generalized theory is, thus, available for correcting far field noise data acquired in open jet test facilities. The effect of discrete tone scattering by the open jet turbulent shear layer was also studied. Scattering effects were investigated over the same Mach number range as frequency varied from 5 kHz to 15 kHz. Attenuation of discrete tone amplitude and tone broadening were measured as a function of acoustic source position and radiation angle. Scattering was found to be stronger at angles close to the open jet axis than at 90 deg, and becomes stronger as the acoustic source position shifts downstream. A scattering analysis provided an estimate of the onset of discrete tone scattering.

Time-resolved detection of propagating Lamb waves in thin silicon membranes with frequencies up to 197 GHz

Abstract: Guided acoustic waves are generated in nanopatterned silicon membranes with aluminum gratings by optical excitation with a femtosecond laser. The spatial modulation of the photoacoustic excitation leads to Lamb waves with wavelengths determined by the grating period. The excited Lamb waves are optically detected for different grating periods and at distances up to several μm between pump and probe spot. The measured frequencies are compared to the theoretical dispersion relation for Lamb waves in thin silicon membranes. Compared to surface acoustic waves in bulk silicon twice higher frequencies for Lamb waves (197 GHz with a 100 nm grating) are generated in a membrane at equal grating periods.

Use of dual waves for the elimination of reverberations in drill strings

Abstract: Drill-string waves can be used to transmit acoustic and seismic information from the bottom hole to the surface. Because the drill string is a heterogeneous assembly, the investigated signal is disturbed by reverberations. Removal of the reverberations generated in the drill string is obtained by measuring acceleration and strain, which have opposite reflection coefficients and are used as dual waves. Addition of the dual waves makes it possible to remove part of the drill-string reflections and improve the signal-to-noise ratio.

Energy Quantity Estimation in Radiated Acoustic Fields

Abstract: Energy Quantity Estimation in Radiated Acoustic Fields Eric B. Whiting Department of Physics and Astronomy, BYU Master of Science Energy quantities, which are calculated from pressure and particle velocity, yield a great deal of information about acoustic fields. Errors in pressure or particle velocity estimation lead to bias errors in the estimation of energy quantities. The bias errors arise from different probe configurations and processing methods. Two processing methods are examined: the traditional method and the recently developed Phase and Amplitude Gradient Estimation (PAGE) method. These two methods are compared to investigate how each estimates pressure and particle velocity and the subsequent bias errors in a plane wave, standing wave, and spherical spreading wave field. Analytical expressions are derived for the energy quantity estimation using ideal onedimensional probes. A simulation of the field from a baffled circular piston and measurements using ideal two-dimensional probes is computed. Compared to the traditional method, the PAGE method significantly extends the range of frequencies for which the results are accurate. It is found that a probe with a center microphone significantly reduces the estimation error and extends the usable range of frequencies. The PAGE method with unwrapping, perfectly matches the analytical results for plane waves, while the traditional method is only good at wavelengths that are large compared to the probe size. Furthermore, the PAGE method has a constant bias error in spherical wave fields due to the 1/r decrease in pressure. The traditional method has a frequency dependent bias error that is much worse at higher frequencies. Lastly, the PAGE method has the same or worse error for the standing wave. As an application of energy quantities, acoustic intensity is used to develop an equivalent source model for jet noise from an F-22 at military and afterburner engine conditions. An optimization is used to find the bestmatching wavepacket model for measured intensity vectors. The results are compared to another intensity method of estimating the source region and source directivity, and the two methods have good agreement.