Adaptive non-Hermitian elastic metasurface with piezoelectric shunting circuits for broadband perfect absorption of flexural waves

In this paper, we propose an adaptive non-Hermitian elastic metasurface (ANEM) composed of symmetrical piezoelectric pillars, whose stiffness and loss are modulated by shunted tunable circuits, to examine its perfect absorption of flexural waves for beam and plate models. The tunable perfect absorption and corresponding mechanisms are theoretically and numerically studied by cooperating with the inductance-resistance (LR) and negative capacitance-resistance (NCR) circuits. Especially, the broadband perfect absorption is realized by a hybrid circuit composed of LR and NC connected in parallel without tuning the circuit parameters, achieved through the simultaneous radiation-dissipation balance at electrical and mechanical resonances. The broadband and wide-angle perfect absorption of flexural waves in plate is numerically and analytically demonstrated. Besides, the high-efficiency asymmetric absorption in plate is achieved by ANEMs with the multiple reflection effect, and the perfect asymmetric absorption is further realized at the exceptional point. The broadband or asymmetrical perfect absorption only rely on the resistance in shunting circuits without needing additional damping material. Our design opens a new route for wave absorption by ultra-compact configuration, which may have potential applications in low-frequency vibration and noise suppression.