# A Review on Vibration Control Using Piezoelectric Shunt Circuits
## 3 Experimental Studies  
In this section, attention is directed to the experimental work on the piezoelectric shunts for vibration suppression over the last five years, in addition to the highly cited references that were published earlier. By highly cited, we considered papers that are cited at least 100 times in all time. [PERSON] and [PERSON] [107] systematically examined the performance of an integral piezoelectric circuitry design that leverages the energy harvesting capacity to supply power to a negative capacitance (NC) element to enhance the passive vibration suppression of inductive shunt. An analytical model that links the NC internal parameters with vibration suppression performance and net power of the system is developed and experimentally validated. The parametric influence of NC element design on system performance is experimentally investigated. It is identified that a vibration suppression enhancement with positive net power is indeed feasible. It is further identified that proper selection of the NC value and the divider resistance can lead to a programmable design that may further enhance the system performance. [PERSON] et al. [108] presented a tunable piezoelectric metasurface for achieving modulation of flexural waves over a broad working frequency range. Based on the developed electromechanical coupling model, the piezoelectric patch with a shunt resistor-inductor circuit is analyzed, and the functional unit of metasurface with only two piezoelectric patches is designed for modulating the flexural wave in a thin plate. By using [PERSON]'s circuit and considering the effect of impedance in the circuit, the arbitral phase shift in the functional unit is experimentally achieved by adjustable shunt circuits. [PERSON] and [PERSON] [93] demonstrated the capabilities of a programmable nonlinear synthetic impedance circuit in emulating Duffing shunts with hardening or softening cubic inductive nonlinearities, along with numerical simulations based on approximate analytical solutions. A bimorph piezoelectric cantilever under harmonic base excitation is used as the host structure in the experiments and simulations. The capabilities of the synthetic impedance circuits with digital control enable precise tuning for both hardening and softening cases. Approximate analytical solutions using the method of harmonic balance, time-domain numerical simulation, and experimental measurements are compared for various mechanical excitation amplitudes and frequencies, considering a set of cubic nonlinear coefficients for hardening and softening scenarios. The results show a very good agreement between the model simulations and experimental results for both hardening and softening cases at all tested parameters. [PERSON] and [PERSON] [109] suggested a novel way to attain passive hardening stiffness by introducing an electrical component in a shunt circuit for passive nonlinear piezoelectric vibration isolation or energy harvesting applications, and the induced structural nonlinearity is demonstrated experimentally. A passive nonlinear component is suggested to be a hardening capacitor obtained from the P-N junction. An analytical model is derived for a parallel connected macro-fiber composite (MFC) piezoelectric material attached bimorph configuration on a cantilever beam and the model is solved numerically. MFC integrated bimorph model, and P-N junction approximate model are presented. The frequency response of the coupled system is obtained by using numerical models and experiments. Both numerical analysis and experiments validated the hardening stiffness effect of the P-N junction. [PERSON] et al. [71] proposed a semi-active control method based on a piezoelectric smart cantilever beam with a passive shunt circuit for vibration control. The proposed passive shunt circuit for the vibration control principle is analyzed and the modeling of the piezoelectric smart -cantilever beam with the passive shunt circuit is developed. Finally, a prototype is manufactured, and the measurement system is constructed.