An Ultrasonic Actuator with Amplitude-Modulated Quasi-Monopolar Pulses Based on Dual-Frequency PMUT

Low-frequency modulated high-frequency ultrasonic technology is widely used in haptics and neuromodulation based on ultrasonic stimulation. Traditional amplitude modulation produces bipolar signals with low modulation efficiency due to the cancellation of positive and negative sound acoustic pressures. This paper presents a monopolar modulation method based on a dual-frequency piezoelectric micromachined ultrasonic transducer (PMUT), alternating positive and negative sound pressures in a single low-frequency cycle can significantly enhances effective low-frequency acoustic pressure, achieving a Peak-to-Peak Pressure (PPP) ratio of 4.78 at one quasi-monopolar pulse. For continuous modulation, the paper demonstrates the operation down to 150 kHz, enabling the generation of arbitrary low-frequency waveforms. Moreover, the independent PMUT arrays also allow operation across three or more frequencies to get higher PPP ratio, showcasing its potential for advanced haptic and neuromodulation technologies.