Compliant-backplate Helmholtz resonators

The results of a theoretical and experimental investigation into compliant-backplate Helmholtz resonators are presented. The motivation for this study is to develop a prototype energy-reclamation module based upon a Helmholtz resonator that uses a compliant piezoelectric backplate. To establish a baseline case, rigid backplate Helmholtz resonators are first designed using a lumped element model and then tested in a plane-wave tube. The plane-wave tube, in the Interdisciplinary Microsystems Lab at the University of Florida, permits characterization in a known acoustic field at frequencies up to 20 kHz. After this initial testing, the rigid backplate of the resonator is then replaced by a compliant piezoelectric diaphragm and tested in the plane-wave tube. The experimental results are compared to theory based on lumped element modeling of the Helmholtz resonator with a compliant diaphragm. The compliant-backplate configuration results in a lower resonant frequency relative to the rigid-backplate configuration. Finally, the potential for extracting useful energy from broadband pressure fluctuations outside the resonator (e.g., from a grazing turbulent boundary layer) and converting this energy to its electrical form via electromechanical transduction is evaluated. [Work funded by NASA Langley Research Center.]