Self-induced long-distance acoustic pulling in phononic crystal waveguides

Acoustic pulling provides an additional degree of freedom for precise acoustic manipulation in acoustofluidics, with applications in separation, assembly, and cell characterization. However, most current approaches rely on elaborately designed scattering to redistribute momentum and generate pulling forces, which inevitably produces strong backward-propagating waves and consequently limits the realization of sustained long-distance pulling. Herein, we propose a novel strategy for long-distance acoustic pulling through a self-induced intensity gradient field generated by the manipulated object itself. Using a phononic crystal with a precisely engineered bandgap structure, we establish a unique transmission mode that propagates as a guided mode in the absence of the object but becomes prohibited upon object insertion, resulting in the formation of a bandgap. This inhibition leads to persistent negative intensity gradient fields in the object, yielding continuous acoustic pulling forces. By leveraging phononic crystals with precisely engineered bandgap structures, we establish a distinct transmission regime that gives rise to a continuous negative intensity gradient within the object, thereby generating a sustained acoustic pulling force. Furthermore, this approach accommodates a broad range of object sizes and offers a versatile platform for acoustic manipulation in biomedicine and related fields.