A granular acoustic diode

Diodes, which allow electricity to flow in only one direction, have been the key to the development of modern electronics. Creating acoustic analogues that restrict sound transmission to one direction has proven challenging. In no small part that’s because wave propagation is inherently symmetric: A system’s transmission is unchanged if the source and detector are reversed (see Physics Today, May 2016, page 14). There have been some successes in creating acoustic diodes, transistors, and logic elements, but most have relied on nonlinear media that distort the waveforms. Now Tianzhi Yang (Tianjin University) and Jian-Guo Cui and Li-Qun Chen (Shanghai University) demonstrate a simple, nondispersive system for nonreciprocal acoustic propagation: a one-dimensional chain of 23 beads. The flexibility to select the number, shape, stiffness, and arrangement of the component elements in such granular crystals facilitates the tailored engineering of their behavior. (See the article by Mason Porter, Panayotis Kevrekidis,...