Concurrently engineered active composite sandwich panels

The objective of this study was to design, fabricate, and test an active panel capable of significantly reducing the radiated sound power from a vibrating structure. To accomplish this objective, a cascaded flextensional actuator was embedded in a composite sandwich panel consisting of inner and outer E-glass/epoxy face sheets separated by a foam core where portions of the core were removed to accept a high performance actuator. The actuator consisted of a cascaded flextensional, mechanical amplifier driven by two, co-fired, multi-layered, piezoceramic stacks. The stack displacements were amplified by the cascaded flextensional to generate the levels of surface normal vibrations of the panel's composite face sheets to produce the desired sound power reductions. A prototype active composite sandwich panel containing a single embedded cascaded flextensional actuator was fabricated and an experiment was conducted to evaluate its dynamic response. Dynamic finite element analyses were performed to simulate the experiment. Good correlation was obtained between the predictions and the experimental results. Final testing was conducted in air in a sound transmission loss facility to determine the levels of sound pressure reduction achievable with the prototype active composite sandwich panel. Up to a 25 dB reduction in sound pressure level was obtained over the frequency band of interest.