Rotation-free high order Bessel beam acoustic transducer for particle trapping

Acoustic particle trapping demonstrates significant potential across various disciplines, encompassing biology, chemistry, and engineering. One particularly noteworthy technique is the utilization of acoustic Bessel beams, distinguished by their exceptional attributes, such as diffraction-free properties, self-healing capabilities, and concentrated energy. Consequently, these beams have proven to be particularly effective for particle trapping applications. Specifically, the implementation of high order Bessel beams (HOBB) allows for the capture of positive impedance contrast particles, owing to the presence of a low-pressure zone along the propagation axis. However, one noteworthy challenge arises from the rotation of trapped particles induced by HOBB, which becomes problematic for long-term observation requirements. To address this concern, we introduce a novel approach using a compact ultrasonic transducer equipped with a Micro-Electro-Mechanical Systems (MEMS)-based acoustic lens. This setup enables the generation of dual Bessel beams, effectively trapping particles without inducing rotation. Notably, the combined effect of the dual Bessel beams ensures particle trapping devoid of rotation, as the transverse phase distribution of the second-order Bessel beam cancels out any rotational effects, thus circumventing the observation-related difficulties encountered in traditional HOBB implementations.