Extraordinary acoustic transmission and enhanced focusing by metasurface ultrasonic transducers.

To realize the synergistic optimization of energy transfer efficiency and spatial control accuracy in high-intensity focused ultrasound (HIFU) therapy, an extraordinary acoustic transmission (EAT) and enhanced focusing by metasurface ultrasonic transducer (EAFT) is proposed. By coupling a piezoelectric element with a sub-wavelength grooved lens designed based on Wood's anomaly and Fabry-Pérot resonance, the device achieves precise wavefront modulation. Compared with conventional acoustic focused transducers (CAFT), the proposed design enhances the peak focal pressure by 33%, improves the electroacoustic efficiency by over 10% and reduces the transverse full width at half maximum (FWHM) from 2.3λ to 1.6λ. When further compared with the clinically equivalent CAFT* configuration with identical focal length, the EAFT still achieves a 15.7% increase in peak focal pressure and a 16.8% reduction in FWHM, demonstrating that the performance enhancement originates from the metasurface engineering rather than geometric focal shortening. Both simulation and experimental results confirm the excellent performance of the designed transducer in terms of focal energy confinement and sidelobe suppression. This work provides a novel acoustic solution with high energy efficiency, compact design, and millimeter-scale spatial resolution, offering great potential for precise tumor ablation therapy and advanced micro-scale processing.