Long and Intermediate Wavelength Flaw Reconstruction

An automated multiviewing ultrasonic transducer and a first generation signal processing program have been developed for the purpose of detecting and characterizing flaws in materials. The multiviewing transducer has been designed and developed to exploit advances in theoretical inverse elastic wave scattering in the long and intermediate wavelength regime made in recent years. The signal processing algorithm has been assembled as a first step in the development of a decision-tree algorithm for flaw characterization. First results that have been obtained in a completely automatic mode are given in this paper. It is concluded that this new long and intermediate wavelength, model-based reconstruction is feasible and potentially very useful in quantitative NDE applications on real systems

Ultrasonic Imaging and the Long Wavelength Phase

Elastodynamic and acoustic wave scattering play an essential role in various inspection methods such as sonar and ultrasonic tomography. Recently there has been considerable interest in the implications of long wavelength elastodynamic scattering for the characterization of flaws in elastic solids [1-6]. If the scattering amplitude is expanded as a power series in the frequency, the leading term is real and varies as the frequency squared. The next term varies as the frequency cubed and is purely imaginary. The evaluation of the phase variation in the long wavelength limit requires the ratio of these terms. Most effort to date has been invested in understanding the dependence of the coefficient of the frequency squared term on the size, shape, orientation and material properties of the scatterer. Richardson [3] and Kohn and Rice [4] have shown that, for an anisotropic elastic inclusion in an otherwise isotropic and homogeneous elastic space, the coefficient depends on at most 22 parameters. In addition, efficient numerical programs have been constructed to evaluate this coefficient for ellipsoidal inclusions. Other work has related it to the stress intensity factor for flaws which are crack-like [5]

Technique for Generation of Unipolar Ultrasonic Pulses

Substantial progress has been made in recent years in the development of inverse elastic wave scattering theories for use in ultrasonic nondestructive evaluation (NDE). These include theories that are applicable in different ultrasonic frequency ranges and include formulations in various approximations [1–15]. It is by application of these inverse scattering solutions to ultrasonic inspection results that quantitative measures of the size, shape, and orientation of a flaw can be determined