Obstacle-crossing Self Focused Acoustic Transducer based on Bessel Beams

This paper introduces a Self-Focused Acoustic Transducer (SFAT) based on Bessel beams, designed to overcome obstacles and maintain focal precision in complex environments. Focused ultrasound is widely used in biomedical applications, but conventional methods like Fresnel zone plates struggle with obstacle-crossing capabilities and stability of the focal point. The proposed SFAT leverages the diffraction-free and deep-focus properties of Bessel beams by superposing multiple inclined beams, achieving a longer focal length and improved resistance to obstruction. The transducer, fabricated using MEMS processes, consists of a Piezoelectric Transducer (PZT-5A) and a Polydimethylsiloxane (PDMS) film with air cavities, generating a binary acoustic field. COMSOL simulations show that the SFAT provides a focal depth of 7 mm and exhibits a 5% reduction in acoustic pressure with an obstacle present, compared to 17% with a Fresnel zone plate. Additionally, the focal point drift is minimized to 0.13 mm, validating the design's superior obstacle-crossing capability. We successfully fabricated a prototype and experimentally demonstrated its ability to trap PDMS particles in water, even with an obstacle present. These results validate the potential applications of the SFAT in biomedical and acoustic manipulation fields.