P3F-5 An Ultrasonic Through-Wall Communication System with Power Harvesting

Electromagnetic "wireless" techniques are ineffective for communicating through a solid steel barrier due to the shielding effect of the metal. Although holes can be made in the barrier to allow wires to pass through, they are often undesirable because they can reduce the integrity of the barrier. In contrast, ultrasound propagates readily through steel and can be used to convey information without degrading the barrier. Since it may be inconvenient to periodically access the sensor side of the barrier, it is also desirable to make the sensor/communication system operate for an indefinite period without servicing. Power harvesting can be used to derive electric power for the circuits from the ultrasonic power applied at the other side of the barrier, making batteries unnecessary. This paper describes an ultrasonic communication system with power harvesting using two ultrasonic transducers and continuous-wave ultrasound techniques. Experimental results are presented, which were obtained using a 5.7 cm thick steel block with 2.54 cm piezoelectric transducers at 1 MHz. The data shows reliable communication at rates of up to 55 kbps and power delivery of over 0.25 W.