Reversible Hardware for Acoustic Communications Reversible computation has been recognized as a potential solution to the technological bottleneck in the future of computing machinery. Rolf Landauer determined the lower limit for power dissipation in computation and noted that dissipation happens when information is lost, that is, when a bit is erased. This meant that with reversible computation, conserving information conserves energy as well, and as such can operate on arbitrarily small power. There were only a few applications and use cases of reversible computing hardware. Here, we present a novel reversible computation architecture for time reversal of waves, with an application to sound wave communications. This energyefficient design is also a natural one, and it allows the use of the same hardware for transmission and reception at the time reversal mirror.

Realtime reversible iterative arrays Iterative arrays are onedimensional arrays of interconnected interacting finite automata. The cell at the origin is equipped with a oneway readonly input tape. We investigate iterative arrays as acceptors for formal languages. In particular, we consider realtime devices which are reversible on the core of computation, i.e., from initial configuration to the configuration given by the time complexity. This property is called realtime reversibility. It is shown that realtime reversible iterative arrays can simulate restricted variants of stacks and queues. It turns out that realtime reversible iterative arrays are strictly weaker than realtime reversible cellular automata. On the other hand, a nonsemilinear language is accepted. We show that realtime reversibility itself is not even semidecidable, which extends the undecidability for cellular automata and contrasts with the general case, where reversibility is decidable for onedimensional devices. Moreover, we prove the nonsemidecidability of several other properties. Several closure properties are also derived.