Folded semi-infinite waveguide

Abstract

An experimental study has been made of the propagation of low-frequency longitudinal sound waves along parallel, non-collinear, straight solid aluminum rods joined together at the ends to form a folded waveguide. Results show that tone bursts propagated outward on the input section of the waveguide successively reverse direction of propagation at the joints to enter succeeding rods. No reflections are produced if the joints are impedance matched to the characteristic mechanical impedances of the rods. Thus a very long echo-free waveguide can be provided in a relatively small space. Since the impedance match at the joints is independent of frequency, the folded waveguide can be used to obtain long time delays of broad-band audio signals. Also, in a given space, the folded waveguide allows independent measurement at lower frequencies than is otherwise possible of the amplitudes and phases of narrow-bandwidth tone-burst signals incident upon, transmitted through, and reflected from a target attached to the waveguide. [Research supported by the National Science Foundation.]