Title: The oretical and experimental analyses of tunable active metamaterials via use of feed-forward/back controllers
Abstract: Metamaterials are engineered materials with either periodic or non-periodic elements whose properties depend on the designed elements, and these properties may not be available in nature. Over the years, metamaterials have shown incredible applications in manipulating electromagnetic, acoustics, and elastic waves, such as wave focusing, bending, and cloaking by carefully engineering their physical properties (e.g., stiffness, density) or dimensions. Researchers use passive and active metamaterials. Passive designed structures are fixed and not reconfigurable or reprogrammable. On the other hand, active metamaterials can simultaneously have passive elements features and are re-programmable and tunable, leveraging the space-time modulations. So, here in this project specifically, we use piezoelectric sensors and actuators as smart elements to design new active devices. Two devices that are introduced here are (i) active baffle (ii) mechanical diode.Decrease the fluid movements in the semi-full fluid containers is one of the open researches in fluid-structure and metamaterial. Most of the researchers focus on passive elements to suppress the wave movements in the fluid. Here, the first active baffle, containing a flexible structure and a pair of piezoelectric sensor and actuator in each element, is introduced. The problem of fluid-structure vibration is viewed from several viewpoints, including analytical methods and numerical techniques. The boundary control technique is also used to control the multi-modal vibration of the fluid and structure. The simulation results for the analytical models validate the proposed controller. They indicate that the piezoelectrically-excited beam is able to suppress the vibrations of the whole fluid very effectively and quickly. Another open research that has recently become of interest is breaking reciprocity in mechanical structures and controlling the direction of wave propagation. These systems have potential applications in localizing energy and designing mechanical logic circuits. Here, we introduce the first experimental demonstration of a broadband mechanical diode, which can be reconfigured to represent wave nonreciprocity. This is achieved by using spatiotemporal stiffness modulation with piezoelectric patches in a closed-loop controller. Using a combination of analytical methods, numerical simulations, and experimental measurements, the results show that contrary to the conventional methods, this device is stable, less complicated, reconfigurable, and precise over a broad range of frequencies.--Author's abstract