We design and experimentally demonstrate a linear active elastic metasurface for real-time and simultaneously multifunctional wave control on a steel plate. The metasurface consists of an array of circuit-controlled piezoelectric patches bonded on the plate separated by thin slots for active wave phase modulations. Our experiments illustrate that by properly programming digital circuits of metasurface unit cells, wave steering directions and paths can be arbitrarily tuned in real-time, which also has an excellent agreement with numerical simulations. We further explore that multiple wave control functions can be integrated into one within the circuits to achieve a simultaneously multifunctional wave control device by using only one metasurface layer. Our numerical results prove the feasibility of the design for broadband and oblique incident applications. The active metasurface breaks the time-revisal symmetry and behaves nonreciprocal propagations of elastic waves. Our design can be simply extended for other elastic wave mode control and wave mode conversion. We believe that the proposed active elastic metasurface could open new avenues for novel and unconventional real-time elastic wave control applications.
A great deal of research has been devoted to controlling the dynamic behaviors of phononic crystals and metamaterials by directly tuning the frequency regions and/or widths of their inherent band gaps. Here, we present a novel approach to achieve extremely broadband flexural wave/vibration attenuation based on tunable local resonators made of piezoelectric stacks shunted by hybrid negative capacitance and negative inductance circuits with proof masses attached on a host beam. First, wave dispersion relations of the adaptive metamaterial beam are calculated analytically by using the transfer matrix method. The unique modulus tuning properties induced by the hybrid shunting circuits are then characterized conceptually, from which the frequency dependent modulus tuning curves of the piezoelectric stack located within wave attenuation frequency regions are quantitatively identified. As an example, a flexural wave high-pass band filter with a wave attenuation region from 0 to 23.0 kHz is demonstrated analytically and numerically by using the hybrid shunting circuit, in which the two electric components are connected in series. By changing the connection pattern to be parallel, another super wide wave attenuation region from 13.5 to 73.0 kHz is demonstrated to function as a low-pass filter at a subwavelength scale. The proposed adaptive metamaterial possesses a super wide band gap created both naturally and artificially. Therefore, it can be used for the transient wave mitigation at extremely broadband frequencies such as blast or impact loadings. We envision that the proposed design and approach can open many possibilities in broadband vibration and wave control.