NDTnet 1998 Aug, Vol.3 No.8

Abstract

Ultrasonic Reflection Tomography (URT) results from a linearization of the Inverse Acoustic Scattering Problem, named Inverse Bom Approximation (IBA).
The goal of URT is to get reflectivity images from back-scattered measures. It's a Fourier synthesis problem and the first step is to correctly cover the frequency space of the object. For this inverse problem, we use the classical algorithm of tomographic reconstruction by summation of the filtered back-projections.
In practice, only a limited number of view are available, typically one hundred eighty, with our mechanical architecture, and the frequency band-width of the used pulses is very limited, typically one octave.The resolving power of the system is then limited by the band-width of the pulse.
Low and high frequency can be restored by use of a fast deconvolution algorithm that enhance resolution.We used a deconvolution technique based on the Papoulis method. The advantage of this technique is a real conservation of the all frequency information of signals.
The enhancement procedure was tested on an image of an aluminium rod. In this case, the wavelength is longer than the section of the rod, six mm for the wavelength against four mm for the section of the rod. The frequency of the transducer is two hundred fifty kilohertz. In this case, the Bom approximation is not respected and theoretically the reconstruction is impossible.
We can see the result and the improvement of the resolution on those two images.

Fig. : without deconvolution ; Fig. : after Papoulis deconvolution

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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