Andres Larraza William F. Coleman Anthony A. Atchley
Phys. Dept., Code PH/La, Naval Postgraduate School, Monterey, CA 93943
A nonlinear effect in an acoustic duct is described for waveguide modes above the first cutoff frequency, whereby a finite extent modulation of the nonlinear mode splits into two disturbances moving with two different velocities of propagation. That is, for each bit of information input, there will be two bits output. The effect was first predicted by Whitham for nonlinear dispersive media [G. B. Whitham, Linear and Nonlinear Waves (Wiley--Interscience, New York, 1974)]. An experiment to verify this phenomenon will be discussed. The apparatus consists of a 21-m-long, 7-segment, thick-walled aluminum tube with a 2-in. internal diameter. Two high-intensity compression drivers arranged in a push--pull configuration are mounted at one end to drive a mode above the first cutoff frequency. A 3-m anechoic termination spanned the length of the last segment at the other end. A physical explanation of the effect, a simplified perturbative treatment of the problem, and possible applications to fiber optic communications will be presented. [Work supported by ONR and NPS Direct-Funding Program.]