Acoustic-Black-Hole-Enabled bimorph ultrasonic transducers with enhanced vibration and radiation efficiency

Bimorph ultrasonic transducers are widely used in ultrasonic atomizers, piezoelectric buzzers, and wearable ultrasound monitoring systems. Advancing technologies demand that these devices exhibit higher vibration displacement, improved acoustic impedance matching, and enhanced overall radiation efficiency. To address these demands, an acoustic-black-hole-enabled bimorph ultrasonic transducer (ABH-BUT) is proposed, wherein a power-law thickness taper reduces local flexural wave velocity and focuses vibrational energy. This mechanism significantly enhances vibration displacement, the electromechanical coupling coefficient, and acoustic radiation efficiency. The transfer matrix method calculates the ABH-BUT's resonance frequencies, while a conventional stepped disk bimorph ultrasonic transducer serves as a reference. Vibration modes, electrical impedance, and near-field acoustic pressure distributions of both transducers are evaluated using finite element analysis and experimental measurements. Comparative results demonstrate that, under identical vibration modes, the acoustic-black-hole profile effectively improves the electromechanical coupling coefficient and acoustic radiation efficiency. This study provides a novel design framework for advanced trilaminar piezoelectric flexural ultrasonic transducers.