Modeling of an ultrasonic communication system

This paper discusses the use of ultrasound to convey data from one side of a metallic wall to the other side. A communication channel is established by attaching a set of three ultrasonic transducers to the wall. The first transducer injects a continuous ultrasonic wave into the wall. The second transducer is mounted on the inside and operates as a receiver and signal modulator. The third transducer is installed on the same side as the first transducer and receives the signal that is reflected from the inside transducer. A sensor on the inside provides analog data that is then digitized. The digitized bits are used to vary the electrical load applied to the electrical terminals of the inside transducer, 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 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 theelectrical power needed to operate the communication and sensor system on the inside. The entire system (ultrasonic, solid wall, and electronic) is modeled in the electrical domain through electro-mechanical analogies. This approach enables the simultaneous examination of the ultrasonic and electronic components. The electric circuit simulation package PSpice is used to simulate the communication system, which assisted in the analysis and optimization of the communication channel. Both simulation and experimental results are presented and discussed.