Reconfigurable generation of order-controllable acoustic orbital angular momentum beams

Acoustic vortex beams carrying orbital angular momentum (OAM) have attracted a broad research interest in the past 20 years. Due to the orthogonality of OAM beams with different orders, a wealth of interesting applications have been developed, including communications, particle manipulation, and imaging. Although many techniques have been reported to generate acoustic OAM beams, it still remains a formidable challenge to generate reconfigurable and order-controllable OAM beams via a cost-effective manner. In this work, we propose a balanced-ternary-based approach to generate reconfigurable order-controllable acoustic OAM beams in water. We cascade three engineered spiral phase plates and manipulate them in a reconfigurable manner to generate 26 different OAM modes at ultrasonic frequencies. Experimental results demonstrate the good quality and high purity of all the generated OAM beams. According to this method and theory, we can flexibly extend our design to generate acoustic OAM beams with arbitrarily high orders. This work provides a new paradigm for the reconfigurable and order-controllable generation of acoustic OAM beams and may facilitate many OAM-based applications.