Acoustic-induced strong interaction between two periodically patterned elastic plates

We study the acoustic-induced interactions between a pair of identical elastic plates perforated with periodical structures. Tremendous mutual forces, both repulsions and attractions, have been observed in subwavelength regime. The dramatic effect stems from the resonant enhancement of the local field sandwiched between the double plates. The parameter-sensitivity of the magnitude and the sign of the interaction (i.e. repulsion or attraction) depend directly on the vibration morphology of the resonant mode. In practical applications, the sign of the interaction can be switched by controlling the external frequency. Both the adjustable magnitude and the switchable sign of the contactless interaction endow this simple and compact double-plate structure with great potential in ultrasonic applications.