Abstract
Two different kinds of experimental methods allow the isolation of resonances of cylindrical elastic targets immersed in water: a quasiharmonic one, the method of isolation and identification of resonances (MIIR) [G. Maze et al., J. Acoust. Soc. Am. 73, 41 (1983)] and an impulsive one, the short‐pulse MIIR [P. Pareige et al., Phys. Lett. A 135, 143 (1989)]. In both cases the experimental results only involve the spectral amplitude of the signal, so that the information provided by the phase spectrum is never used. A new method is proposed which uses the evolution with the frequency N of the ratio Im(N)/Re(N) of the complex number provided by the FFT of the whole backscattered temporal signal (for details see O. Lenoir, preceding abstract). The Im/Re spectra are compared to the spectra obtained by the two previous methods. Several elastic and viscoelastic cylinders and tubes are investigated. That the Im/Re spectrum provides as much information as the backscattered and resonance spectra obtained by the two different MIIR can be noticed. The first two methods allow the identification of the mode number of each isolated resonance; in the same way the Im/Re ratio at a given frequency versus the azimuthal angle is studied. The signification of the symmetric shape of the so‐obtained angular diagrams is discussed.
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