Underwater Ultrasound Communication Based on PMUTs with DC Bias Voltage

The use of sound waves for underwater communication is more effective than electromagnetic waves due to their lower energy attenuation coefficient in water. This paper introduces a low-power communication modulation technique using piezoelectric micromechanical ultrasonic transducers (PMUTs). The technique involves using DC bias voltage and pulse polarity for signal modulation, allowing PMUTs to support underwater acoustic communication without the need for high-frequency carriers or complex circuit designs. The driving signal is designed to overlay a pulse signal on a slowly varying DC bias cycle. Ultrasound signals generated by PMUTs under DC biases of 3 V and -3 V were captured by an ultrasonic probe and converted into electrical signals with peak amplitudes of approximately 55 mV and 92 mV, respectively, demonstrating the amplitude modulation effect induced by the DC bias. Additionally, activating PMUTs with pulse signals of varying polarities produced signals with inverse phases, indicating the phase modulation effect of pulse polarity. These results demonstrate the potential for using different DC bias voltages of PMUTs for underwater communication and suggest the possibility of high-order modulation and low-power communication based on DC bias.