ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

4aSA8. Anomalous attenuation in disordered networks.

J. Dickey

G. Maidanik

David Taylor Res. Ctr., Annapolis, MD 21402

J. D'Archangelo

U.S. Naval Acad., Annapolis, MD 21402

A two-dimensional ``jungle gym'' is modeled as a network of connected dynamic systems, each characterized by a propagation wave number, loss factor, and length. The response of the network to an out-of-plane harmonic drive is calculated as a function of frequency. When the systems are all identical (i.e., a regular lattice) the modes are well defined and identifiable as being either modes of the individual systems or global modes of the network. Further, the pass and stop band structure in the network is distinct. When the system lengths are not regular, and in particular when they are randomly distributed, the modes are not easy to classify and the transmission of waves through the network is profoundly affected. This tends to destroy both pass and stop bands giving rise to an attenuation which is an average of the pass and stop bands, i.e., an ``amber'' band (since pass bands are green, stop bands are red and amber bands lie in between). In other words, perturbing the lengths gives rise to a structure whose attenuation (and transmission) from one point to another far exceeds that which would be expected based on the propagation loss of the constituent systems.