ABSTRACT
Chapter 5 presents a semi-active approach to control. In brief, it consists of controlling changes in the parameters of an object, in particular switching, in such a way that energy is absorbed and dissipated accordingly. Energy is thus only needed to control these changes and is not introduced into the vibroacoustic system. The concept of shunt circuits has been developed by moving it from a passive to a semi-active level. Shunt circuits known from literature are based on piezoelectric elements glued to a vibrating plate. The authors have additionally proposed a completely different approach. One of them, appropriate for two-panel walls, consists in the use of controlled links placed at selected locations between the panels, in such a way that, depending on the frequency ranges dominating the noise, the frequency response of the wall is altered so as to produce anti-resonant valleys in those ranges, thus increasing its acoustic isolation. Another approach involves a single-panel wall. It is based on using a concentrated mass and moving it on a mandrel attached to the panel, thereby changing the frequency response. Both of the proposed approaches have proven to be a very effective method of shaping the vibrating response of the structure.
