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

Ultrasound image enhancement: A review

We demonstrate that a simple acoustic time-of-flight experiment can measure the state of charge and state of health of almost any closed battery. An acoustic conservation law model describing the state of charge of a standard battery is proposed, and experimental acoustic results verify the simulated trends; furthermore, a framework relating changes in sound speed, via density and modulus changes, to state of charge and state of health within a battery is discussed. Regardless of the chemistry, the distribution of density within a battery must change as a function of state of charge and, along with density, the bulk moduli of the anode and cathode changes as well. The shifts in density and modulus also change the acoustic attenuation in a battery. Experimental results indicating both state-of-charge determination and irreversible physical changes are presented for two of the most ubiquitous batteries in the world, the lithium-ion 18650 and the alkaline LR6 (AA). Overall, a one- or two-point acoustic measurement can be related to the interaction of a pressure wave at multiple discrete interfaces within a battery, which in turn provides insights into state of charge, state of health, and mechanical evolution/degradation.

Electrochemical-acoustic time of flight: in operando correlation of physical dynamics with battery charge and health

The effects of a broadband signal on the performance of a side-scan synthetic aperture sonar, including detail on the necessary spatial sampling and resolution tradeoffs, are discussed. The mathematical description of the echo signals and the consequent image reconstruction algorithms are shown for a step-and-go scenario that ignores the Doppler effect. Extra modifications for the Doppler effects are introduced with some discussion of their probable impact. Simulated echoes and image reconstructions on hypothetical targets show the limiting performance and some of the effects of narrowband reconstruction approximations on broadband signals. For comparison, images taken from a CTFM 15-30 kHz sonar especially designed as a synthetic aperture sonar are presented. >

Broad-band synthetic aperture sonar

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

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

Application of random signal correlation techniques to ultrasonic flaw detection

Flaw Visibility Enhancement by Split-Spectrum Processing Techniques

: This report describes four areas of work In the first area random signal beam forming techniques are developed which make it possible to transmit several independent beams from a phased array using the same number of incoherent noise sources Following this ultrasound beam scanning techniques are demonstrated in which random signal correlation systems and RF correlation systems using quadrature phase techniques are used in methods for scanning the intensity profile of ultrasound transducer beams using respectively broadband signals and narrow band signals In addition two types of deconvolution procedure are described and demonstrated which have been successful in improving the effective resolution of ultrasound correlation systems when viewing surface features Finally the design and construction of a random signal correlation system is described which uses an electronic delay line (Author)

http://ieeexplore.ieee.org/iel5/10274/32707/01533371.pdf

Random Signal Flaw Detection

Nondestructive testing of targets c onsisting of a finite number of thin layers using backscattered ultrasound echoes is highly desirable in material evaluation. These targets can be examined by an ultrasound pulse-echo system from uhich acoustical parameters sensitive to the inhomogeneity of the samples are extracted. In practice, extracting these parameters is difficult if nor impossible because of: l) limitation o f system spatial resolution, and 2) multiple reflection uithin the target. In this study the system resolution has been improved by using transducers uith the largest possible banduidth taking into account the increase in absorption and scattering, and applying a subtraction technique uhen the signal-to-noise ratio is high. In addition, the r everberation echoes are also identified and classified by decoupling the components of the backscattered echoes. These techniques have been adapted for measuring support

/pdf/ultrasound-imaging-through-highly-reverberant-thin-layers-10eck5za0w.pdf

V.L. Newhouse

Papers

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

Application of random signal correlation techniques to ultrasonic flaw detection

Flaw Visibility Enhancement by Split-Spectrum Processing Techniques

Random Signal Flaw Detection

Ultrasound Imaging Through Highly Reverberant Thin Layers