Distortion Of Acoustic Wave Research Articles

Non-destructive evaluation of corrosion in steel liner plates embedded in concrete using nonlinear ultrasonics

Nuclear containment structures employ a leak-tight steel liner to avoid any unwanted particle release into the exterior environment. The steel liner can be embedded in concrete which creates large continuous areas where the steel plate is in direct contact with surrounding concrete. The impact of the aging of concrete structures due to the presence of structural discontinuities, such as the presence of foreign matter and a delamination gap at the embedded steel–concrete interface, is investigated for small laboratory-scale specimens manufactured with a novel inlay technique by nonlinear ultrasonic evaluation. A Total Damage Index (TDI) which combines several parameters related to acoustic wave distortion into a single damage index to rank the specimens is introduced. The findings in this work indicate that severe corrosion, the presence of foreign matter, and delamination gap in the steel–concrete interface can be detected using nonlinear ultrasonic techniques based on higher-harmonic analysis and modulation intensity using continuous ultrasonic probe excitation and an impactor to modulate the signal. The results obtained using the TDI are consistent with attenuation, a conventional parameter used in corrosion detection.

Acoustic and thermal numerical modelling of transcranial ultrasound thermal therapy

Ultrasound has long been recognized as a therapeutic tool with potential to treat disorders throughout the brain. However, the attenuation and distortion of acoustic waves caused by the skull has been a significant challenge to the development and clinical application of transcranial ultrasound therapies. Numerical models, such as the use of finite difference method, can be prohibitively expensive in required computational resources. While some numerical models can be computationally prohibitive, the ray-tracing modelling method used in the CIVA Healthcare simulation platform has been shown to be an efficient and computationally inexpensive method of modelling transcranial focused ultrasound, and can be coupled to Pennes’ bioheat transfer equation to model temperature in biological tissue. The present work quantifies the sensitivity of transcranial ultrasound to clinically relevant uncertainties in the physical properties of the skull (i.e., shear conversion, wave speed), and combines the ray-tracing acoustic model with a numerical thermal model to provide a versatile and unified software platform for use in clinical ultrasound treatment planning. Results are compared with experimentally measured thermal rise from transcranial focused ultrasound using a clinical Insightec ExAblate 650 kHz 1000-element system, and shown to exhibit a high degree of accuracy. [This work is supported by the Focused Ultrasound Foundation.]

Nonlinear crosstalk in broadband multi-channel echosounders.

Distortion of acoustic wave caused by nonlinear propagation transfers acoustic energy into higher harmonics of the transmitted signal. When operating several broadband echosounders with non-overlapping frequency bands to cover a wide frequency range, higher harmonics generated by one band may interfere with the fundamental band of others. This interference (i.e., crosstalk) can adversely affect the measured backscattered amplitude frequency response and in some circumstances, appears as spurious targets above and/or below the main target in pulse-compressed echograms. The nonlinear propagation of frequency-modulated acoustic waves in a directional beam was modeled and used to assess methods to reduce the deleterious effects of harmonic components in the signal, and was also compared to field experiments using the seabed echo and a metallic target sphere, with good agreement. Two methods are shown to materially reduce crosstalk: (1) reduction in transmit power, which reduces crosstalk amplitude by a larger amount than the associated reduction in transmit power, and (2) selection of a proper Fourier window length in the processing stage. The effect of crosstalk was small (<0.4 dB or 10%) for area backscattering measurements, but could be several dB for target strength measurements at different frequencies, depending on the transmit signals and processing parameters.

Analysis and prediction of shock formation in acoustic energy transfer systems

Losses associated with nonlinear wave propagation and exhibited by acoustic wave distortion and shock formation compromise the efficiency of contactless acoustic energy transfer systems. As such, predicting the shock formation distance and its dependence on the amplitude of the excitation is essential for their efficiency, design, and operation. We present an analytical approach capable of predicting the shock formation distance of acoustic waves generated by a baffled disk with arbitrary deformation in a weakly viscous fluid medium. The lossless Westervelt equation, used to model the nonlinear wave propagation, is asymptotically expanded based on the amplitude of the excitation. Because the solutions of the first- and second-order equations decay at different rates, we implement the method of renormalization and introduce a coordinate transformation to identify and eliminate the secular terms. The approach yields two partial differential equations that can be solved to predict the formation distance either analytically or numerically much faster than time-domain numerical simulations. The analysis and results are validated with solutions obtained from a nonlinear finite element simulation and previous experimental measurements.

Intracranial Applications of MR Imaging-Guided Focused Ultrasound.

Initially used in the treatment of prostate cancer and uterine fibroids, the role of focused ultrasound has expanded as transcranial acoustic wave distortion and other limitations have been overcome. Its utility relies on focal energy deposition via acoustic wave propagation. The duty cycle and intensity of focused ultrasound influence the rate of energy deposition and result in unique physiologic and biomechanical effects. Thermal ablation via high-intensity continuous exposure generates coagulative necrosis of tissues. High-intensity, pulsed application reduces temporally averaged energy deposition, resulting in mechanical effects, including reversible, localized BBB disruption, which enhances neurotherapeutic agent delivery. While the precise mechanisms remain unclear, low-intensity, pulsed exposures can influence neuronal activity with preservation of cytoarchitecture. Its noninvasive nature, high-resolution, radiation-free features allow focused ultrasound to compare favorably with other modalities. We discuss the physical characteristics of focused ultrasound devices, the biophysical mechanisms at the tissue level, and current and emerging applications.

이종 해양로봇의 협력제어를 위한 지능형 경로 계획 및 추종

Abstract In real system application, the path planning and following system for the coordinated control of heterogeneous marine robots based on the underwater acoustic communication has the f ollowing problems: surface and underwater robots have different maneuvering properties, an underwater robot requires more effective operating, it has a limited communication range because of the transmission loss (TL) of ac oustic wave, it has a communication error because of the Doppler distortion of acoustic wave, and further, it requires an easy design procedure in terms of its structures and parameters. To solve these problems, an intelligent path pl anning algorithm using the evolution strategy (ES) and the fuzzy logic controller (FLC) based on system modeling, is p roposed. To verify the performance of the proposed algorithm, the path planning and following of an underwater rob ot is performed according to the maneuvering of a surface robot. Simulation results show that the proposed algori thm effectively solves the problems.

Acoustic Pressure Waveforms Measured in High Speed Jet Noise Experiencing Nonlinear Propagation

An experimental study has been carried out in a controlled environment in a large anechoic chamber at Boeing to clarify certain features associated with the nonlinear distortion of acoustic waves. The test points were chosen to yield both subsonic and supersonic convective Mach numbers. Both spectral and time-domain analyses have been performed to elucidate nonlinear effects. The spectral analysis indicates that there is agglomeration of energy at the higher frequencies as the propagation distance increases. The time-domain analysis shows strong positive peaks in the pressure signals; the skewness values of the acoustic signals jump from ∼0.05 to ∼0.3, when the convective Mach number is increased from low subsonic values to just above unity. An examination of the Morfey-Howell nonlinear indicator reveals that energy is transferred from the spectral peak to the higher frequencies as a consequence of long-distance propagation. It is established that the convective Mach number is a critical parameter that may be used to identify the onset of nonlinear effects. When the value exceeds unity, there is a dramatic difference in the wave characteristics. In addition, a set of high-quality data has been generated that can be used to guide the development and the validation of prediction methods for nonlinear propagation.

Phase Inversion: Inferring Solar Subphotospheric Flow and Other Asphericity from the Distortion of Acoustic Waves

A method is proposed for analyzing an almost monochromatic train of waves propagating in a single direction in an inhomogenous medium that is not otherwise changing in time. An effective phase is defined in terms of the Hilbert transform of the wave function, which is related, via the JWKB approximation, to the spatial variation of the background state against which the wave is propagating. The contaminating effect of interference between the truly monochromatic components of the train is eliminated using its propagation properties. Measurement errors, provided they are uncorrelated, are manifest as rapidly varying noise; although that noise can dominate the raw phase-processed signal, it can largely be removed by low-pass filtering. The intended purpose of the analysis is to determine the distortion of solar oscillations induced by horizontal structural variation and material flow. It should be possible to apply the method directly to sectoral modes. The horizontal phase distortion provides a measure of longitudinally averaged properties of the Sun in the vicinity of the equator, averaged also in radius down to the depth to which the modes penetrate. By combining such averages from different modes, the two-dimensional variation can be inferred by standard inversion techniques. After taking due account of horizontal refraction, it should be possible to apply the technique also to locally sectoral modes that propagate obliquely to the equator and thereby build a network of lateral averages at each radius, from which the full three-dimensional structure of the Sun can, in principle, be determined as an inverse Radon transform.

Space charge measurement in thick dielectric materials by pulsed electroacoustic method

The new application of pulsed electroacoustic (PEA) method to measure space charge profiles in several millimeters thick polymers such as power transmission cable was proposed. In this method, space charge profiles are detected as acoustic wave signals that are generated by the space charge profiles existing in the sample under stimulation of an electric pulse. In most polymer samples, such as cross-linked polyethylene (XLPE) widely used in XLPE cable (CV cable), however, the acoustic wave form is obviously distorted as it propagates through the thick polymer. The acoustic wave distortion cannot be negligible when applying this method directly to very thick samples (several millimeters thick). To recover the wave form and obtain the accurate space charge profiles, it is necessary to study the attenuation and dispersion characteristics of the sample and remove their effects to the propagating acoustic wave. So-called ‘‘deconvolution processing’’ using ‘‘Jacobi method’’ was employed in this report to obtain the undistorted wave form. The principle of the data processing method is introduced and some examples for recovering the wave form are given to verify the effectiveness of the data processing method.

A Study on the Scalar Wave Equation for Nonlinear Surface Acoustic Wave Distortion

A new definition and interpretation of nonlinear parameter β and scalar potential φ of the one-dimensional phenomenological nonlinear scalar equation of surface acoustic waves (SAW) are proposed. This definition made it possible to solve the problem of SAW waveform distortion caused by its nonlinearity. Finally, the discontinuity length of the SAW propagating along the X-axis on 128°-rotated Y-cut LiNbO3 was obtained by means of this definition.

Effects of attenuation, dispersion, and high sound-pressure levels on acoustic wave distortion in horns

High-power sound sources have received a lot of attention in the past few years due to renewed interest in industrial applications of high-intensity sounds such as the acoustic agglomeration of aerosols or combustion enhancement. Most high-power sound sources require a horn to match the source impedance to the medium where the sound is radiated. Such horns introduce distortion in the initial waveform, which can be detrimental to the agglomeration or combustion enhancement process. Boundary-layer attenuation smooths the wave shape while dispersion breaks up the symmetry of the waveform. Horn-induced dispersion is usually the dominant dispersion mechanism, resulting in strong peaks in the waveform. Finally, due to the very high acoustic levels at the horn throat, finite-amplitude effects are responsible for a significant amount of distortion at high frequencies. Simple examples of waveform distortion due to these various mechanisms are shown. The effects of sound-pressure level, horn design, and frequency on distortion are illustrated for an exponential horn and several initial wave shapes. Experimental results are presented that compare very well with theory.

Acoustic loading in straight pipes

Based on linear one-dimensional acoustics, a geometrically perfect elastic waveguide would respond to an oscillatory internal pressure only in the presence of path deflectors (elbows and branches). In practice, a significant elasto-acoustic interaction results even in straight conduits as a result of manufacturing tolerances. A theoretical model of the linear acoustic loading in straight pipes is developed that considers the acoustic wave distortion due to perimeter, axial, and wall thickness nonuniformities.