A High Output Multi-Frequency Ultrasonic Transmitter Based on Nonlinear Harmonic Enhancement

Multi-frequency ultrasound devices have shown great potential in imaging and range-finding applications for their capabilities in balancing sensing spatial resolution and penetration depth. Traditional multi-frequency ultrasound devices are typically achieved by integrating highfrequency and low-frequency transducer elements, but suffer from mutual radiation impedance coupling. Here, by utilizing the inherent harmonic response of a single nonlinear mode curved Sc -doped AlN piezoelectric micromachined ultrasonic transducer (PMUT), a novel method to generate multi-frequency ultrasound outputs with balanced magnitudes is presented. Significant enhancements of the vibration harmonics of the PMUT diaphragm were achieved through excitation signal tuning. Increasing frequency sweep continuous sine wave excitation was implemented to induce nonlinear behavior, further increasing the harmonic amplitudes. The proposed method yielded harmonic vibration outputs with intensities comparable to, or surpassing, those of the fundamental vibration mode. Consequently, with optimized modulation of the excitation frequency and the driving voltage, the second and even third-order harmonics of the PMUT can be effectively utilized for multi-frequency transmission.