Design of smart lightweight structures: Simultaneous optimization of mechanical and shunt circuit parameters

Modern passenger cars are increasingly restrained to lower CO2 emissions and therefore to reduce weight. In order to accomplish that, the replacement of metals by lightweight composite materials is a viable solution. However, this can significantly change the NVH behavior of the vehicle, thus requiring new design techniques. One well-known technique uses shunted piezoelectric transducers, which are applied to a mechanical structure and connected to an electronic circuit. When correctly designed, the shunt can significantly attenuate the vibration of the system without excessive mass addition. Much research has been done in the last decades to analyze various types of shunts in terms of their potentials and characteristics. Nevertheless, they are not yet integrated in many technical structures, not only because of high costs, but also due to the high effort to design the electronics effectively together with the mechanical structure and transducer. This paper presents a methodology for a global design of a smart structure, instead of isolated sub-systems, where different functions of the electromechanical system (host structure, actuators and electronics) are simultaneously optimized. The design optimization focuses on numerical and experimental analyses of composite materials, with bonded piezoelectric ceramic transducers and connected to a semi-active shunt network, more precisely a resistor-inductor circuit with a negative capacitance. Here in particular, the negative capacitance has to be built through a synthetic circuit (negative impedance converter). It is based on an operational amplifier, a fact that increases the number of variables in the optimization process and makes the real values diverge from the theoretical ones. From the mechanical side, the material layup and the part geometry are the main design variables, whereas for the actuator, its position and dimensions are crucial. As an application example, a composite part together with a piezoelectric actuator is improved by parametric optimization, regarding its mass, its static and dynamic behavior. At this phase, the generalized electromechanical coupling coefficient (GEMCC), which describes the modal energy transfer between the mechanical and the electrical systems, is one of the main design variables, since it dictates the performance of the semi-active vibration control. Finally, the parameters of the electronic shunt network are optimized to minimize the mechanical response of the structure.