The Doppler technique has traditionally been the method used to extract motion information from ultrasonic echoes reflected by moving tissues. The Doppler technique has been around for a long time, and has been extensively reviewed and analyzed in the literature. Recently, time-domain methodologies for estimating tissue motion have gained in popularity. Time-domain methods have advantages over Doppler methods in many applications, and as of yet have not been comprehensively reviewed. An overview of time-domain techniques that have appeared in the literature over the past few years is presented. Their potential advantages over Doppler are examined, and the individual techniques are compared. >

Current time-domain methods for assessing tissue motion by analysis from reflected ultrasound echoes-a review

The utilization of signal processing techniques in nondestructive testing, especially in ultrasonics, is widespread. Signal averaging, matched filtering, frequency spectrum analysis, neural nets, and autoregressive analysis have all been used to analyze ultrasonic signals. The Wavelet Transform (WT) is the most recent technique for processing signals with time-varying spectra. Interest in wavelets and their potential applications has resulted in an explosion of papers; some have called the wavelets the most significant mathematical event of the past decade. In this work, the Wavelet Transform is utilized to improve ultrasonic flaw detection in noisy signals as an alternative to the Split-Spectrum Processing (SSP) technique. In SSP, the frequency spectrum of the signal is split using overlapping Gaussian passband filters with different central frequencies and fixed absolute bandwidth. A similar approach is utilized in the WT, but in this case the relative bandwidth is constant, resulting in a filter bank with a self-adjusting window structure that can display the temporal variation of the signal's spectral components with varying resolutions. This property of the WT is extremely useful for detecting flaw echoes embedded in background noise. The detection of ultrasonic pulses using the wavelet transform is described and numerical results show good detection even for signal-to-noise ratios (SNR) of -15 dB. The improvement in detection was experimentally verified using steel samples with simulated flaws.

Signal detection and noise suppression using a wavelet transform signal processor: application to ultrasonic flaw detection

Interest in the interaction of acoustic waves with particulate mixtures has a long history—dating back to the work of Rayleigh in the 19th century. This interest has intensified over the last fifteen years as advances in electronics and instrumentation science have brought the possibility of using ultrasound to characterize colloidal mixtures both in the laboratory and in-process, and in both of these contexts a small number of instruments are currently in use. The characterization of colloidal mixtures by ultrasound requires a formal theoretical basis which relates the properties of the mixture, particularly the dispersed phase particle size distribution (PSD), to the complex wavenumber governing propagation. The number of theoretical treatments is vast, having evolved over more than a century. This paper is intended to provide a review of these developments in a form which will enable new researchers in the field to climb a very steep learning curve in a relatively short time. We discuss definitions and production techniques for colloidal mixtures and the basic physical phenomena underlying wave propagation through them. We identify two approaches to the propagation problem—scattering and coupled-phase; these are treated both separately and comparatively, particularly in relation to limitations that arise when the concentration of particles is high and the basic theories break down. We introduce the basic method for the measurement of PSD and show how dynamic effects such as flocculation and crystallization can be observed and modelled. The core of all ultrasonic characterization procedures is the physical measurement of the ultrasonic wave attenuation coefficient and phase velocity as functions of frequency; here we discuss these techniques on the basis that what is observable or measurable about a colloid depends on both its physical properties and the frequency bandwidth available for measurement. This paper concludes with our view on future developments of measurement technique and theoretical treatments.

https://iopscience.iop.org/article/10.1088/0034-4885/68/7/R01/pdf

Ultrasound techniques for characterizing colloidal dispersions

http://ecasp.ece.iit.edu/publications/1978-1987/Ultrasonics1982%20Newhouse%20SSP.pdf

Flaw-to-grain echo enhancement by split-spectrum processing

Ultrasound image enhancement: A review

Application of random signal correlation techniques to ultrasonic flaw detection

A random signal flaw detection system has been devel- oped with a signal-to-noise ratio enhancement approximately10 000 times greater than conventional ultrasonic pulse-echo systems.Ex- perimental results are presented which demonstrate thatthe system can penetrate highly absorbent materials suchas plexiglass,high- density siliconnitride and alumina at greater distances than is possible with conventional pulse-echo systems. The systemis shown to detect echoes fromgrain boundarieswhich indicate that the system could have applications in microstructure evaluationof materials. Finally, the possible applicationof this systemto accurate sound velocity mea- surement in strongly absorbing materialsis discussed.

N.M. Bilgutay

Papers

Flaw-to-grain echo enhancement by split-spectrum processing

Application of random signal correlation techniques to ultrasonic flaw detection

Evaluation of a Random Signal Correlation System for Ultrasonic Flaw Detection

Flaw-to-grain echo enhancement

Flaw Visibility Enhancement by Split-Spectrum Processing Techniques