The effects of material attenuation on acoustic resonance scattering from cylindrical tubes

Abstract

This paper presents the effects of material attenuation on acoustic resonance scattering (ARS) from cylindrical shells for the purpose of applying it to ultrasonic nondestructive evaluation (NDE). Complex wave numbers are introduced to include the effects of material attenuation. Resonance widths versus resonance frequencies with attenuation neglected have been numerically analyzed (up to k(1)a = 230) for five (S-0, A(1), S-1, S-2, and A(2)) modes not only to determine resonance frequency regions in which attenuation effects must be investigated intensively, but also to select appropriate frequencies from an NDE point of view. It has been found that frequency regions of interest are those which have relatively narrow resonance widths but not too narrow ones. Material attenuation results in a decrease of resonance peak amplitude as much as an increase of resonance width. The increase of resonance width attributed to material attenuation alone is linearly related to attenuation coefficients and its proportional constants are dependent on the types of modes. The ratio of the resonance width caused by material attenuation alone to that caused by radiation damping governs the relationship between resonance width and amplitude.