**3.1. System architecture**

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

response) .

**Figure 3.** Example FRF of a system

controller performance is presented.

9, and 12].

stated in section 2.2 there are different types of the control algorithms and for each type of the controller, system identification is essential. This system identification can be carried out via a vibration testing & analysis methods. Aim of such method is to extract Frequency Response Functions (FRF) where these functions presents the system response to a specific input in frequency range of interest by means of magnitude and phase. A representative FRF is shown in Fig. 3 for a structure where piezoelectric materials are used as bonded patch actuators (to excite the structure) and LDV as velocity sensor (to measure the vibration

The modal (resonance) frequencies of the systems are indicated in magnitude plot of FRFs as sharp peaks where the active damping systems are most effective. In active damping systems, the higher frequency modes may deteriorate the stability due to phase lag. Such effects of the higher frequency modes can be suppressed by including the low-pass filters. On the other hand, model based controllers use mathematical relations which in turn represents the system response based on FRF. Since the scope of this chapter is devoted only to proportional analog velocity feedback controller, more detailed information on modelbased controllers and mathematical system representations can be found in references [6, 7,

In this section an active vibration control system using an analog velocity feedback algorithm is described. At first, the system architecture is explained. Later, the controller design and implementation steps are discussed. In the final step, the evaluation of the

**3. Application of analog velocity feedback controller** 

The structure used in this study is a rectangular box (1 x 1 x 2 m) and shown in Fig. 4. The surrounding cavity walls are constructed using wood filled concrete with a thickness of 10 mm. This box is separated inside with a thin plate to obtain two enclosed compartments. The two compartments are used for investigation of vibration and noise transmission. The thin steel separation plate (1 x 1 m) in the rectangular box has a thickness 1.8 mm and clamped along on all four edges.

**Figure 4.** Rectangular box for vibration and noise reduction experiments

In the presence of mechanical and acoustical vibrations, the thin separation plate transmits the vibration and noise to the compartments. By attenuating vibrations of the separation plate, the noise radiation can be also reduced. In this study, the piezoelectric patch actuators bonded on the separation plate are employed as actuators to control and suppress vibration. The piezoelectric actuator is a PI Dura-act 875 bender type piezoelectric patch. This type of patch is compact, lightweight and insulated so it can be easily attached to the host structure and it does not add additional weight. The mechanical properties of the steel and piezoelectric patches are given in Table 1.

Since the piezoelectric materials generate high strain on the host structure, the most effective position for the piezoelectric patch is around the high strain regions on the host structure. In fact, for a clamped-clamped plate, the maximum curvature (highest strain region) changes over the surface for each vibration mode. The maximum curvature of the first mode of a clamped-clamped plate occurs at the center and along the edges; whereas in the second vibration mode, maximum curvature is in the middle of the upper and lower halves of the plate. After these high strain regions are identified, the piezoelectric patches are attached to the center and upper-left (-35 cm, 35 cm from the left upper corner) of the plate in order to suppress first two modes. For suppression of vibration and noise, two piezoelectric patches are used in independent and pair configuration. Fig. 5 shows the thin-separation plate and piezoelectric patches.

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


**Table 1.** Mechanical properties of host structure and piezoelectric patch

**Figure 5.** Thin steel plate with piezoelectric patches
