Time reversal data communications on pipes using guided elastic waves: Part II. Experimental studies

Abstract

Embedded sensors in large civil structures for structural health monitoring applications require data communication capabilities between sensor nodes. Conventional communication modalities include electromagnetic waves or acoustical waves. However, ultrasonic guided elastic waves that can propagate on solid structures such as pipes for a great distance have rarely been studied for data communication purposes. The multi-modal and dispersive characteristics of guided waves make it difficult to interpret the channel responses and to transfer useful information along pipes. Time reversal is an adaptive transmission method that can improve the spatial and temporal wave focusing. Based on the focusing effect of time reversal, we have developed a data communication technique using guided waves in a highly dispersive pipe environment. In this paper, we experimentally demonstrate the data communication using time reversal pulse position modulation (TR-PPM). Three-step laboratory tests have been performed using piezoelectric transducers in a pitch-catch mode. We first measure the channel responses between the transmitter and the receiver on a pipe. We then carry out the time reversal transmission by reversing the sounding signal and feeding it back to the same channel. Finally, we perform the time reversal communication experiment by sending the modulated time reversal signals as a stream of binary bits at a given data rate. A series of experiments are conducted on steel pipes. Experimental results demonstrate that time reversal pulse position modulation for data communications can be achieved successfully using guided elastic waves.