**1. Introduction**

694 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

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Corresponding Author

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, Utku Boz, Serkan Kulah and Mustafa Ugur Aridogan

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**Author details** 

*Koç University, Turkey* 

Ipek Basdogan\*

**5. References** 

Piezoelectric shunt damping is a well known technique to damp the vibrations of mechanical structures. This technique relies on the piezoelectric effect that converts mechanical energy into electrical energy. A damping effect on the host structure is observed when the electrical energy is dissipated. In order to optimize the damping performance, the transferred energy as well as the dissipated energy must be maximized. The transferred energy depends on the piezoelectric constants as well as the vibration mode and the location of the piezoelements within the structure. While higher piezoelectric constants generally increase the amount of transferred energy, the location can typically only be optimized for one eigenform of the structure. As a consequence, the piezoelectric transducer can be placed in such a way that it only affects one eigenform of the system. One measure for the coupling of the piezoceramics is the generalized coupling coefficient, which is defined for every vibration mode and generally takes different values for the individual modes. The design of the electrical shunt aims at maximizing the energy dissipation. Different networks have been developed, which can be classified into the categories passive, active, linear or non-linear. The best choice of network depends on the performance target, the availability of electrical power supply and the vibration behavior and excitation type of the mechanical structure.

Passive resonant circuits have been among the first networks for piezoelectric shunt damping. Forward studied inductance-resistance networks for the damping of optical systems [4] which were tuned to the resonant frequency of the mechanical system. Hagood and von Flotow then studied the performance and tuning of these *LR*-networks in more detail [7]. They described the shunted piezoceramics as a frequency depending stiffness and damping element and they showed the analogies of *LR*-shunted piezoceramics and tuned mass dampers. They obtained from calculations that the damping effect grows with the piezoelectric coupling coefficient. The standard *LR*-network can only be tuned to one frequency, therefore in the subsequent years new circuits were proposed that are capable to damp several frequencies at the same time [2, 9]. These networks basically consists of multiple *LR* branches that are tuned to the individual frequencies to be damped.

©2012 Neubauer et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In order to enhance the limited damping performance of passive shuntings, active elements have been proposed. The mostly studied element is a negative capacitance, which can be realized by a negative impedance converter circuit [5]. Initially considered by Forward [3], a negative capacitance proves to be able to increase the effective piezoelectric coupling factor. Especially the combination of passive networks with active elements is a promising approach. This class of networks is called 'active-passive hybrid piezoelectric network' (APPN) by Tang [21]. Most prominent APPN networks are a negative capacitance with a resistor and a negative capacitance with an inductor and resistor.

The drawback of these linear resonant networks is that they all must be tuned to a certain frequency, which has to be known in advance and which should not change during operation. For many applications they are therefore not suitable. In these cases adaptive, non-linear networks are a better choice. The most common one is the 'synchronized switch damping on inductor' (SSDI) technique, which consists of an *LR*-branch and a switch that can connect and disconnect the network to the electrodes of the piezoceramics [10]. For the case of monoharmonic excitation the switch is closed at the moments of maximum deformation of the piezoceramics. In this moment, the electrical charge is inverted via the inductance. The inductance value is very small in order to realize a fast inversion. When fully inverted, the switch is closed so that the charge cannot flow anymore. During the following half period of excitation the charge stays nearly constant, so that the piezoceramics generates a force acting against the deformation velocity. The resulting force signal is nearly rectangular shaped. Like for the passive *LR* shunting the damping strongly depends on the electrical damping ratio, which can be set by the resistance value. A small damping results in a good inversion of the charge, which amplifies the stationary charge amplitudes and the dissipated energy. The adaptive capability of the SSDI technique comes from the triggering of the switching times. Therefore, typically one additional sensor is used which monitors the vibration of the mechanical structure. Due to this triggering, the force signal from the piezoceramics is always in phase with the structure vibration and the performance is only minimally dependend on the excitation frequency.
