**1. Introduction**

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Mechanical vibrations cause undesirable effects such as noise and acoustic signature and consequences of severe vibrations may lead to a decrease in service life of machines, or even cause damages on the components. In order to reduce vibration levels in ground, marine and aerospace applications as well as nano and micro devices, active control methods for vibration and noise reduction has been proposed in the last decade.

In 1980s, the usages of large structures as the components of the space vehicles were resulted in new challenges in vibration control since these structures are lightly damped and have long decay times. Researchers were motivated to design and implement active vibration control to these lightly damped structures with piezoelectric materials. In one of the first research studies relevant to this area, Bailey and Hubbard [1] designed an active damper system by using piezoelectric material as distributed actuator for the vibration suppression of a cantilever beam. Subsequently, Crawley and Luis [2] developed and experimentally verified the analytical model of piezoelectric materials. The main contribution of Crawley and Luis was the accurate prediction of performance and effectiveness of piezoelectric materials when they are used as actuators. While passive isolation techniques are not generally feasible and efficient for low frequency vibration suppression; aforementioned initiative studies showed that piezoelectric materials can be used to suppress the low frequency vibration. Indeed, Ro and Baz [3] investigated and compared the overall effectiveness of the active and passive treatments for vibration and noise reduction. Their results revealed that active treatments such as bonded piezoelectric patch actuators can significantly reduce the vibration and noise radiation better than the passive treatments. Currently, different types of piezoelectric elements are available in market which can be employed widely as actuators and sensors for active vibration reduction of structures.

© 2012 Basdogan 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 the literature, there are published review articles discussing fundamental aspects of active vibration control. Rao and Sunar [4] published a review paper on the use of piezoelectric materials as sensors and actuators for control of flexible structures. In this review paper, they presented the general framework of structural control strategies and presented the applications in various fields. One of the most common application areas is aerospace industry, since the aerospace structures are flexible and have limited tolerance for vibration. In a different review study, Loewy [5] presented the key applications of smart structures in aeronautical applications with potential usages. In this work, smart materials are categorized in terms of their energy-exchange capabilities. The benefits of using smart structures in aeronautical applications are also presented.

The active vibration control systems should be feasible and reliable to be used in marine, aerospace and automotive applications. The reliability and feasibility of the control systems are related to dynamics of piezoelectric actuators and implementation of controller algorithms. Thus, it is needed to predict performance of the piezoelectric sensor and actuators embedded in control systems before implementation and production. For this purpose, Chee et al. [6] presented the modeling approaches for performance investigation of piezoelectric materials. As discussed in their article, analytical and finite element modeling of piezoelectric materials with host structures can be built using the linear constitutive piezoelectric equations only for low actuation authority. In case of high actuation authority; the nonlinearities occurs and different methodologies should be considered.

The choice of the controller type and optimal positioning of sensors and actuators are other important aspects of design and implementation of active vibration control systems. There are also published technical review papers discussing the controller algorithms and optimal placement of actuators and sensors. For instance, Alkhatib and Golnaraghi [7] reviewed the controller architectures and presented the general design procedures for the active vibration control systems. In this review paper, the advantages and disadvantages of different controller architectures with various application examples are presented. Specifically that review paper states that the active damping system is advantageous when the vibration suppression is aimed only around resonance frequencies. It is also noted that the active damping system ensures stability when collocated sensor and actuator pairs are used. In another review paper, Gupta et al. [8] concentrated on the optimal positioning of piezoelectric sensors and actuators. In this technical review, the optimization techniques are presented based upon six optimizing criteria, namely (i) maximizing modal forces/moments applied by piezoelectric actuators, (ii) maximizing deflection of the host structure, (iii) minimizing control effort/maximizing energy dissipated, (iv) maximizing degree of controllability, (v) maximizing degree of observability, and (vi) minimizing spill-over effects. Gupta et al. presented the optimal positioning results in the literature in a tabular form for beam and plate like structures.

For robust and adaptive active vibration control systems, the structural modeling techniques and estimation of uncertainties are important. A comprehensive methodology for the design and validation of a robust controller is presented by Iorga et al. [9]. In their paper, structural modeling techniques with uncertainty analysis are explained and *H*∞ controller design is pursued by placing emphasis on robust control concepts.

The piezoelectric materials also attracted attention of the researchers working on noise reduction. In a review paper on smart structures and integrated systems, Chopra [10] stated that most of the applications for aerospace vehicles are focused on minimization of vibration levels; however, interior and exterior noise reduction, using piezoelectric materials is also a potential research area for transport vehicles. Hanselka [11] named the use of smart materials in active noise and vibration control as an innovative technology and gave an application example of active noise reduction. In that application, piezoelectric materials served as sensors and actuators to reduce structural-borne noise and the results showed that the application of current developments is possible and advantageous.

This chapter is organized as follows. In section 2, the design procedure and algorithms for active vibration and noise control systems are explained briefly. In section 3, a proportional velocity feedback implementation for active vibration control system developed in our laboratory is presented. Finally, the vibration and noise reduction performance of the controller is discussed.
