Multiple input single output configurations to improve performances and robustness of acoustic power transfer

Powering and communicating with sensors placed behind metal walls is required in various applications such as submarine hulls, pressurized tanks or pipes. Acoustic power transfer (APT) is an excellent option to supply these sensors without making through holes. However, the power transfer performances of APT systems can be strongly degraded by the destructive interferences of emitted waves, typically when the receiver diameter is smaller than the transmitter's one. In this paper, the use of multiple transmitters to focalize acoustic waves on a receiver is analyzed and the equations determining the optimal magnitudes and phases of the input voltages are presented. We experimentally validate that the efficiency and the transmitted power are strongly improved with the proposed technique. The transmitted power and the efficiency are multiplied by two for aligned transducers while the transmitted power is multiplied by up to 45 for misaligned transducers. It is hence demonstrated that using multiple emitters is particularly well suited for industrial applications where high power and high robustness are needed. Moreover, it paves the way toward the power supply of non-aligned distributed sensor nodes, which are of particular interest in structural health monitoring.