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Estimating channel capacity and power transfer efficiency of a multi-layer acoustic-electric channel

Recent research has shown that acoustic waves can be used to transmit data and power through metallic barriers. In this paper, we extend this work to consider the case where the channel consists of multiple layers of different materials. In particular, a steel-water-steel type of interface i.e., a layer of water sandwiched between two steel walls, is investigated. A pair of 1 MHz resonant (25.4 mm diameter) piezoelectric transducers are co-axially aligned and mounted on the dry side of each steel wall to form the channel. This channel is acoustic-electric in nature and is modeled as cascade of layers and interfaces in MATLAB. Each layer (single material) and interface is interpreted as transmission line in the acoustic domain. Experimental channels are implemented and the measured channel characteristics are compared to those obtained using the model. The power transfer efficiency and channel capacity are determined using the measured channel data. To maximize the capacity and reduce interference, it is assumed that data transmission is performed using orthogonal frequency division multiplexing (OFDM). The width of water column is varied and its effect on the power transfer efficiency and data capacity are shown. Results indicate that a channel formed by two steel walls of 15.97 mm and 10.92 mm thickness separated by 88.3 mm water column is capable of supporting data rates of several megabits/sec and of transferring power with more than 30 percent efficiency.