Acoustic interferometer

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

Detecting acoustic-emission signals with fiber-optic interference transducers

Abstract: Results of the analysis of acoustic-emission signals generated due to ultrasonic waves propagating in a polymer composite material and registered with piezoelectric and fiber-optic sensors are presented. The fiber-optic sensors were arranged into an adaptive interferometer based on using a dynamic hologram formed in a photorefractive crystal. Reducing the setpoint fading has made it possible to improve the noise immunity and sensitivity of the measurement system when using an adaptive interferometer on a photorefractive crystal. Optical fibers in the interferometer’s measurement system served as sensors of ultrasonic waves and were built into a polymer composite material when the sample was manufactured. The sample was a rectangular plate made of a multilayer fiberglass material. It has been discovered that the sensitivity of the adaptive interferometer makes it possible to detect acoustic- emission signals generated by a Hsu–Nielsen source. When determining the speed of sound in the polymer composite material, peculiarities of registering a group wave by fiber-optic sensors have been established that are due to the anisotropy of the medium the wave propagates in and the distributed character of sensor placement in the studied composite material. The wavelet transform has been used to separate the informative component of the wanted signal.

Influence of circumferential partial coating on the acoustic radiation from a fluid-loaded shell

Abstract: Acoustic compliant coatings are a common approach to mitigate the radiation and scattering of sound from fluid-loaded submerged structures. An acoustic compliant coating is a coating that decouples an acoustic source from the surrounding acoustic medium; that is, it provides an acoustic impedance mismatch (different density and speed of sound product). Such a coating is distinct from an ordinary compliant coating in that it may not be resilient in the sense of low stiffness, but still provides an acoustic impedance mismatch. Ideally, the acoustic coating is applied uniformly over the entire surface of the fluid-loaded structure to minimize the acoustic radiation and scattering. However, in certain instances, because of appendages, it may not be practically possible to completely cover the surface of a fluid-loaded structure to decouple it from the adjacent acoustic medium. Furthermore, there may be some inherent advantages to optimizing the distribution of the coating around areas from which the acoustic radiation appears to be dominant. This would be analogous to the application of damping treatment to a vibrating structure in areas where the vibration levels are highest. In the case of the acoustic radiation the problem is more complex because of the coupling between the acoustic fluid and the structure. In this paper, the influence of a partial coating on the acoustic radiation from a fluid-loaded, cylindrical shell of infinite extent and excited by either a line force or an incident plane acoustic wave is examined. The solution to the response and scattered pressure is developed following the procedure used by the authors in previous work on the scattering from fluid-loaded plates and shells. The coating is assumed to be normally reacting providing a decoupling layer between the acoustic medium and the structure; that is, it does not add mass or stiffness to the base structure. The influence of added mass or stiffness of the coating can be included as an added inhomogeneity and treated separately in the solution.

Interferometric detection of acoustic waves at air-solid interface applications to non-destructive testing

Abstract: In this paper, some properties of acoustic waves at the air-solid interface are reviewed and laser-ultrasonics is used to optically excite and detect these waves. In comparison with the leaky Rayleigh wave, a large amplitude is observed for the acoustic disturbance which is composed of Scholte and lateral waves. However, it is apparent from theoretical results, taking source terms into account, that the normal displacement of these waves cannot be large in such an interface. Another explanation for the high-intensity fluctuation measured is the optical heterodyne detection of the refractive index variation induced in the fluid. This assumption is experimentally checked by probing the acoustic field parallel to the surface of the sample. The potentialities of these waves in non-destructive testing are also investigated. It is clearly shown that the transmitted, reflected, or diffracted acoustic fields provide useful information about the position or the size of structures intercepting the propagation path. Indeed, glass plate thickness or steel block position can be easily determined using a time of flight analysis. This suggests a lot of new applications in the sizing of structures where noncontact measurements on inaccessible parts would be necessary.

III Interaction of Light and Acoustic Surface Waves

Abstract: Publisher Summary This chapter describes the interaction of light and acoustic surface waves. It discusses two major areas in the interaction of light and acoustic surface waves. One is the light diffraction by acoustic surface waves and the other is the interactions of optical guided waves and acoustic surface waves. The study of light diffraction by acoustic surface waves results in a convenient optical probing technique to study the propagation characteristics of acoustic surface waves that are needed for the design and utilization of acoustic surface wave devices. The interest in the interaction of light and acoustic surface waves began after the recent advance of acoustic surface technology. In designing acoustic surface wave devices, it is necessary to have a detailed knowledge of the propagation characteristics of these waves on any isotropic or anisotropic substrate. Optical probing of acoustic surface waves based on the light diffraction by acoustic surface waves has become a convenient tool in studying and utilizing these waves.

Detection of acoustic second harmonics in solids using a heterodyne laser interferometer

Abstract: Acoustic second harmonic generation in solids is difficult to measure and often requires careful sample preparation. In this paper, a heterodyne interferometer modified to measure acoustic fundamental and second harmonics is presented. It requires relatively little sample preparation and it provides noncontact, wideband, absolute, and pointlike measurements. It is shown that the output of an ideal heterodyne interferometer does not contain any even harmonics of a single‐frequency acoustic signal. Odd harmonics, however, are produced in calculable amounts. A detailed model of the interferometer is introduced to account for various sources of spurious second harmonics and the model is experimentally verified. Three methods of calibration for the absolute measurement of surface displacement are presented. Measurements of the nonlinearity parameter, β, of a fused quartz sample are shown to agree with literature values.