Anomalous wave control by an adaptive elastic metasurface shunted with negative capacitance circuit

A metasurface is an artificially engineered structure that has received extensive research attention recently because of its ability to modulate wavefronts arbitrarily. A metasurface can be designed to either passively or actively manipulate wave propagation. Among the types of metasurfaces, an adaptive metasurface is more advantageous because of its tunability for various functionalities in a wide frequency range without structural modification. In this paper, an adaptive elastic metasurface composed of piezoelectric stacks shunted with negative capacitance circuit is proposed to actively control the propagation of elastic longitudinal wave. Through tuning of the negative capacitance via an external electrical circuit, an effective and tuned Young's modulus of the proposed metasurface is obtained. This tuning allows adaptive phase velocity manipulation of the propagating wave, resulting in full 2π phase span coverage. Additionally, analytical modeling and numerical analysis are used to study the transmission and phase shift of the proposed metasurface unit cell connected to a negative capacitance shunt. Both analytical and numerical results show excellent agreement. Based on numerical findings, the proposed elastic metasurface proficiently demonstrates multiple functionalities at broadband frequencies by distributing the required phase response tuned by the corresponding negative capacitance.