SCATTERING OF VIBRATIONAL WAVES IN PERTURBED QUASI-ONE-DIMENSIONAL MULTICHANNEL WAVE-GUIDES

We investigate the scattering properties of vibrational waves in pertu rbed quasi-one-dimensional multichannel waveguides in the harmonic app roximation. Local defects are introduced by changing the masses or the spring constants of the perfect waveguide. For both types of defects we find resonances in the continuum. These are due to the coherent cou pling between local defect states and propagating states. Beyond the s imilarity with the quantum-mechanical case of electron scattering and associated Fano resonances, the scattering behavior of vibrational wav es appears to be more complex. This complexity can be attributed to th e vector character of the vibrational amplitudes and to additional pos sibilities for mode-mode coupling by the defects. To illustrate the me thod a detailed discussion of the transmission spectra is presented fo r the generic case of a double chain containing defects, which shows a lready the essential characteristic features of a multichannel system.