VIBRATION TRANSMISSION THROUGH SYMMETRICAL RESONANT COUPLINGS

The transmission of vibration through a symmetric junction is considered. The problem is introduced using a stretched string with a general point attachment, and then a result is derived which encapsulates the important aspects of the transmission behaviour for a wider class of systems. These are systems that consist of two semiinfinite sections of identical, one-dimensional structure having only one propagating wavetype (but any number of evanescent ones), joined through any linear system that satisfies a condition of symmetry. For such systems, it is shown that there will in general be a set of frequencies of perfect transmission and perfect reflection, in a number and pattern which can be described in terms of the behaviour of the junction alone. Representative examples are presented, based on the behaviour of bending beams and thin circular cylinders with attached structures providing wave reflection. The implications of this result are explored for sea coupling loss factors, and for the interpretation of SEA model predictions when such resonant coupling structures are present.