The influence of roughness, angle, range, and transducer type on the echo signal from planar interfaces

Jens E. Wilhjelm, Peter C. Pedersen, Søren Mehl Jacobsen

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Abstract

The received electrical echo signal from a pulse-echo system insonifying a planar interface was measured for varying degrees of rms roughness [0 to 0.29 mm (0 to 1.7 /spl lambda/)], angles of incidence, /spl theta/, (-7/spl deg/ to 7/spl deg/), and ranges to a planar or focused transducer. The effect of varying a is quantified in terms of the energy of the received signal, E(/spl theta/), and the normalized spectrum of the received signal. E(/spl theta/) is approximately Gaussian when using a planar transducer or a focused transducer with the reflecting interface located at or beyond the focal point. For focused transducers with the interface located closer than the geometrical point of focus, two maxima can sometimes be observed when varying the incident angle. As is generally known, the width of E(/spl theta/) is strongly dependent on transducer type, e.g., for a smooth interface, the -3 dB width for a 25.4 mm diameter 5-MHz planar and focused transducer was approximately 0.5/spl deg/ and 4/spl deg/ (at the focal point), respectively. E(0/spl deg/) as a function of surface roughness, R/sub q/, was nearly linear on a decibel scale, with a slope of -109 dB/(R/sub q///spl lambda/) and -61 dB/(Rq//spl lambda/) for planar and focused transducers, respectively. The characteristic nulls present in the normalized spectra of the echo signal at non-normal incidence tend to vanish with increasing R/sub q/ when using planar transducers. For focused transducers, the normalized spectra change from relatively flat to monotonically decreasing as R/sub q/ increases, and they exhibit reduced amplitude with increased incident angle.
Original languageEnglish
JournalI E E E Transactions on Ultrasonics, Ferroelectrics and Frequency Control
Volume48
Issue number2
Pages (from-to)511 - 521
ISSN0885-3010
DOIs
Publication statusPublished - 2001

Bibliographical note

Copyright: 2000 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE

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