Through-wall communication of low-rate digital data using ultrasound

Wireless communication is ineffective for communicating through a solid steel wall due to the shielding effect of the metal. In some cases, holes can be made in the wall to allow wires to pass through, enabling the transport of electronic data. However, holes are often undesirable because they can reduce the integrity of the wall. This paper describes several approaches for using ultrasound to communicate low-rate digital data through a steel wall. The techniques minimize the complexity and power consumption of the communications hardware on the side of the wall from which the data is being sent, supporting applications in which a sensor may be either permanently embedded in a structure or is difficult to reach for servicing. Both pulsed and continuous-wave ultrasound techniques are described. Experimental data is presented showing the performance of the techniques when implemented using 1 MHz transducers mounted on a 15.24 cm (6 inch) thick steel wall. The results show that data rates on the order of 500 bits per second are readily available using simple communications techniques. Higher rates are possible if equalization is used to mitigate the effects of the multipath propagation within the steel block.