A Variable Shape Metastructure Based on Controlled Bistable Structural Elements

The so-called hybrid position feedback controller is an unstable-then-stable position feedback controller, which is a second-order single-degree-of-freedom system in nature. This hybrid controller takes advantage of the resonant mode of a bistable system about one equilibrium position, destabilizes the system, and dynamically induces snap-through between the two equilibria. In this dissertation, a new multi degree of freedom metastructure concept that utilizes the hybrid position feedback controller is introduced. An arbitrary number of bistable “segments” or “structural elements” are attached to each other in a serial (or parallel) manner to generate a “distributed” bistable structure – also referred to as a metastructure. Due to the simplicity of the hybrid controller, the physical implementation of the proposed approach can be realized using simple circuit elements fully distributed and integrated in the structure. This new metastructure inherits the multiple bistable positions that its building blocks have; hence, the structure becomes multi-stable. It can maintain the equilibrium positions without consuming power and can achieve many equilibrium shapes. This research shows that in the series metastructure configuration, the equilibrium distribution critically depends on the stiffness distribution of the system. By tuning the stiffness for each DOF, any arbitrary shape can be achieved. Furthermore, the equilibrium employed in the feedback signal to attain the desired stable state must be adjusted according to the principles outlined in this dissertation to prevent non-zero control force in equilibrium states. Failure to incorporate this adjustment may result in unnecessary static control effort. The proposed metastructure concept can be used in various applications, such as: locomotion in bioinspired systems, undulatory motion, morphing aerodynamic surfaces, wave guiding, filtering, and vibration attenuation, amplification, and control. The concept can also be used in energy harvesting to enable maximum power extraction for a given broadband vibratory input.