Two ultrasonic transducer through-wall communication system analysis.

The use of ultrasound to convey data from one side of a metallic wall to the other side is presented. A communication channel is established by attaching two ultrasonic crystals to either side of the wall. The outside transducer injects a continuous ultrasonic wave into the wall. The inside transducer operates as an energy harvester and signal modulator. The outside transducer also receives the modulated signal reflected back from the wall containing the inside transducer. A sensor on the inside provides analog data (e.g., temperature) that is then digitized. The digitized bits are used to vary the electrical load applied to the electrical terminals of the inside transducer by changing its acoustic impedance in accordance with the data bits. The impedance changes, in turn, modulate the amplitude of the reflected ultrasonic signal. This modulated signal is detected at the outside receiving (as well as transmitting) transducer, where it is then demodulated to recover the data. Additionally, some of the acoustic power received at the inside transducer is harvested to produce the electrical power needed to operate the communication and sensor system on the inside. Digital data communication rates exceeding 50 000 bits/s are achieved.