# A Review on Vibration Control Using Piezoelectric Shunt Circuits
## 3 Experimental Studies
The experimental results show that the force transmissibility is reduced about 57.75% at resonant frequency. [PERSON] et al. [118] experimentally investigated a metastructure with piezoelectric unit cells shunted to self-tuning resonant circuits to enable adaptive behavior in the resulting system dynamics with focus on vibration attenuation. Synthetic inductor circuits are combined with digital potentiometers to enable real-time tuning of the resonant shunts. A microcontrollerunit was employed to detect the excitation frequency and properly adjust the resonant circuits. Experimental results are presented for a base-excited, locally resonant, piezoelectric plate. [PERSON] and [PERSON] [119] proposed a shunt tuning method, in which a consistent correction for the influence from residual vibration modes is included by an effective modal capacitance, evaluated from measured charge and voltage amplitudes in short- and open-circuit conditions, respectively. The robustness of the proposed method is verified experimentally for both a free beam and a free plate structure with four shunted piezoceramic patch pairs. A stable and fully passive inductor is produced by winding a copper wire around a magnetic core, which requires precise inductance tuning to determine the final number of turns. It is demonstrated that the effective modal capacitance interpolates consistently between the blocked and static capacitances, commonly used for single-mode tuning of piezoelectric inductive-resistive shunts. [PERSON] et al. [120] investigated the system parameters which affect the electromechanical coupling coefficient, a metric for measuring the effectiveness of mechanical-to-electrical energy conversion. For that purpose, a thorough investigation is performed to determine the critical system parameters and their combined effects on the electromechanical coupling coefficient of laminated composite plates with surface-bonded piezo patches. First, the first four natural frequencies of the electromechanical system are obtained using the Rayleigh-Ritz method for various patch sizes. Then, the electromechanical coupling coefficient variations for a different set of system parameters are presented. Later, to demonstrate the applicability of the developed methodology for a broader frequency range, four independently shunted piezo pair are attached to the plate. [PERSON] et al. [121] presented a strategy to optimize, in terms of damping efficiency, the geometry of piezoelectric patches as well as their placement on the host elastic structure. This procedure is based on the maximization of the modal electromechanical coupling factor (MEMCF) of the mechanical vibration mode to which the shunt is tuned. It was found that the patches' thickness is an essential parameter and that several configurations are possible, depending on the considered vibration mode. Experiments are also proposed to validate the model. [PERSON] et al. [122] investigated the vibration reduction in one- and two-dimensional thin structures by means of several piezoelectric transducers shunted with a proper electric network system. A further numerical optimization problem on the spatial distribution of the piezoelectric elements allows to achieve better performance. Numerical case studies of two relevant systems, a double-clamped beam and a fully clamped plate, allow to take into account issues relative to the proposed approach. Laboratory experiments carried out in real time on a beam clamped at both ends consent to validate the proposed technique. [PERSON] and [PERSON] [123] analyzed the enhancement of piezoelectric stack transducers by means of the negative capacitive shunting. Stability has been thoroughly studied, starting from the electrical admittance curve of the transducer; a method has been introduced that quantifies the stability margins of the shunted structure. Two different implementations (series vs. parallel) are investigated, and the lack of robustness of the parallel one is demonstrated. Next, this technique is experimentally applied on a truss structure.