Non-reciprocal wave propagation in discretely modulated spatiotemporal plates
Abstract We investigate non-reciprocal wave propagation in spatiotemporal phononic plates. Specifically, the first aim of this manuscript is to propose a general formulation of the Plane Wave Expansion Method (PWEM) that, in contrast with previous works, is applicable to any class of 2D spatiotemporal unit cells whose properties can be expanded in traveling plane waves. The second aim is to exploit this analysis tool in order to study a class of phononic materials capable of violating mirror symmetry in reciprocal space, therefore breaking reciprocity principle along different propagation directions in physical space. This is obtained by considering the plate elastic properties to be discretely modulated in space and continuously in time. Theoretical dispersion profiles are validated and compared with numerical simulations.
This work describes a method for providing robustness to errors from a binary symmetric channel for the SPIHT image compression. The source rate and channel rate are jointly optimized by a stream of fixed-size channel packets. Punctured turbo codes are used for the channel coding, providing stronger error protection than previously available codes. We use a subset of the puncturing patterns that are well chosen and that leads to the best source rate. The rate allocation scheme presented obtains all necessary information from the SPIHT encoder, and does not require image decompression.