# A Review on Vibration Control Using Piezoelectric Shunt Circuits
## 1 Introduction
Common types of shunt circuits include resistive (R), resonant (RL), and more complex configurations involving capacitors and negative capacitance, each tailored to specific vibration control needs. Due to their remarkable characteristics and diverse uses, piezoelectric materials have drawn a lot of attention in the fields of materials science and engineering. There are two types of piezoelectric effect: the direct effect, where the material converts the mechanical strain into an electrical charge, and the reverse effect, where the material converts an applied electrical potential into a mechanical strain [7]. The direct effect is usually used when the piezoelectric material functions as a sensor, whereas the reverse effect is commonly used when the piezoelectric material functions as an actuator. The piezoelectric fabulous features were exploited to develop active control systems that can be utilized in a variety of industries, including healthcare [8,9], energy harvesting [10], and sensor technologies [11]. Among the numerous applications of piezoelectric materials, their usage in vibration damping systems has emerged as a potential topic of research. [PERSON] [12] suggested the use of a piezoelectric patch that is connected to electrical elements to transform the structure's vibrational energy into electrical energy. The mechanical-electrical analogy can be used to explain how the mechanical damping system and the electric circuit are related. The structure's mass, stiffness, damping, and force excitation are equivalent to the electrical circuit's inductance, capacitance, resistance, and voltage, respectively. Researchers classified piezoelectric shunt circuits into three categories depending on their control methods: passive, active, semi-passive, or semi-active. The electrical elements in the shunt circuits, as well as the existence of any external power source, determine which type is used, with each having unique benefits and limitations. The passive technique relies on the inherent ability of the piezoelectric material to absorb vibrational energy, resulting in passive energy dissipation without any external power source. On the other hand, active methods utilize sensors and actuators to achieve vibration sensing and activation to suppress vibration in real time [13]. An active control system usually requires powerful power amplifiers and high-performance digital signal processors, which are inappropriate for space applications, to drive actuators. Despite being simpler to construct than active control systems, passive control methods are less resistant to system disturbances [14]. Therefore, the interest in semi-active and semi-passive control systems has increased because of their potential to successfully offer vibration damping using piezoelectric materials. These systems combine the benefits of adaptability and energy efficiency to provide an adaptable way of reducing vibrations in various applications. It is essential to keep in mind that while active control systems can be used to limit low-frequency vibrations, passive shunt circuits can be highly effective at damping high-frequency excitations. Additionally, semi-passive and semi-active techniques are necessary for good control over wide frequency bands, where the hybrid methods combine the best attributes from active and passive approaches [15]. Piezoelectric shunt circuits have been implemented in aerospace applications, including the damping of wing flutter in aircraft and satellite panels; automotive in reducing noise and vibration in chassis or engine mounts; civil engineering in stabilizing bridges and buildings against wind or seismic loads; and precision machinery in suppressing micro-vibrations in optical systems and manufacturing equipment. This review provides a comprehensive overview of the current state of the art on vibration suppression using piezoelectric shunt circuits, covering their fundamentals, types, applications, recent developments, and future directions.