The Wavenumber-Frequency Filtering Characteristics of Compliant Layers.

Techniques for the measurement of the wavenumber-frequency filtering characteristics of compliant layers mounted on an elastic structure and subject to unsteady pressures are developed and demonstrated. In order to measure the performance of the layer at arbitrary wavenumbers and frequencies, an array of shakers was fabricated and used to generate a standing wavepattern of force where the maximum spectrum levels of the input forces could be concentrated at selected wavenumbers independent of the selected frequency. Arrays of thin film transducers were designed, fabricated, and used to measure the wavenumber- frequency pressure spectra above and below compliant layers. The wave-number frequency admittances of a coated and uncoated beam were used to determine the effectiveness of compliant layers in reducing the vibration response of the beam as a function of wavenumber and frequency. The development of the shakers, transducers, and data processing algorithms is described. Measurement results of the effectiveness and pressure transmission loss are presented as functions of frequency at different drive wavenumbers for several compliant layers with different properties. The pressure spectra above and below the layers, velocity spectra of the beam response, and admittances of the coated and uncoated beam are presented and analyzed as functions of wavenumber and frequency.