smart technologies for safety engineering

Smart Technologies in Vibroacoustics 305
subjected to harmonic excitations modeled as a directly applied uniform pressure. The design
of panels and the final qualitative results of the analysis will be briefly described in this section.
Another design of an active panel made up of a single elastic plate and a layer of poroelastic
material will also be presented (see Section 8.9.3). This model will be thoroughly examined
in Section 8.10 (an abridged discussion of preliminary investigations can also be found in
Reference [11]). An important interaction of the panel with an acoustic medium (the air) will
also be taken into account. The panel is active because piezoelectric patches are fixed to the
elastic faceplate and form a piezo-actuator, which can be used to affect the bending vibrations
of the faceplate; in this way, the vibroacoustic transmission through the panel can be controlled.
In Section 8.10 the final accurate modeling of the entire hybrid panel and the results of relevant
frequency analyses concerning the panel design are given. Finally, numerical testing of active
and passive behaviour of the panel is performed.
8.9.2 Active Sandwich Panel
In Reference [7] a model of a prototype sandwich panel made up of two elastic faceplates and
a poroelastic core was investigated. The panel is active, so an antisymmetric piezo-actuator
composed of two co-located piezoelectric wafer elements is mounted on one of the elastic
faceplates, which is termed the active faceplate. Both elastic faceplates are simply-supported.
As a matter of fact, the whole prototype is a small cell of panel but larger panel surfaces can
be obtained by juxtaposing the cells. Figure 8.6 presents the assembly and finite element mesh
of one quarter of the panel cell, where advantage was taken of the symmetry by applying
appropriate boundary conditions on the lateral faces.
The panel is subjected to a uniform pressure excitation (acting on the passive faceplate)
and the bending vibrations of the active faceplate can also be excited by voltage applied to
Figure 8.6 FE model of one quarter of an active sandwich panel