The improvement of reliability of circuits based on operational amplifiers in piezoelectric shunt

Piezoelectric shunt is an approach useful in different fields, such as vibration control and isolation as well as structural health monitoring. In several applications, the shunt circuits include one or more operational amplifiers. This can be due either to the ease of implementation of some electrical components (e.g. inductances with high value, negative resistances to compensate possible parasitic ones) or to increase the performance of the system. Indeed, increasing the coupling between the hosting structure and the piezoelectric element improves the performance of the system. A common approach for the increase of the coupling is the use of negative capacitances in the shunt circuit, which are based on operational amplifiers. A main issue when dealing with these types of circuits is related to the risk of saturation of the outputs of the operational amplifiers, which can lead to non-proper functioning of the piezoelectric system and even to system instability. This manuscript focuses on shunt circuits based on negative capacitance to propose two different approaches, which can be even employed together, for lowering the outputs of operational amplifiers without affecting the system behaviour and performance. The two methods are described analytically and are then shown to be reliable and feasible through an experimental campaign. The first proposed method allows a reduction of 50 % of the voltage output of the operational amplifier, while the benefit provided by the second proposed method can be larger or smaller depending on the modal data of the system. As mentioned, the two methods can be coupled to reach a voltage output reduction larger than 50 % .