Development of Micromachined Piezoelectric Near-Ultrasound Transducers for Data-over-Sound

Data-over-sound is an emerging technology for digital data communication which uses frequencies at the upper bounds of human hearing, usually between 15 kHz to 25 kHz. We report the successful development of Micromachined Piezoelectric Near-Ultrasound Transducers for low power data-over-sound applications. Lead zirconate titanate thin films used in Piezoelectric Micromachined Ultrasonic Transducers can have high residual tensile stresses ranging from 300 MPa to 1.5 GPa. These stresses raise the resonant frequencies of the transducers, making it a challenge to fabricate low frequency devices. Using the optimum dimensions by estimating the net residual stress inside the fabricated diaphragm, a low power transducer with a target frequency range of 17 kHz to 21 kHz was fabricated, capable of generating as much as 83 dB of sound pressure level at a distance of 5 cm for continuous operation.