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Microperforated panel absorbers are best considered as the combination of the perforate and the backing cavity. They are sometimes likened to Helmholtz resonators. This analogy is true in the sense that they are most effective at the resonant frequencies of the panel-cavity combination when the particle velocity is high in the perforations. However, unlike traditional Helmholtz resonators, microperforated absorbers are broader band and the attenuation mechanism is dissipative rather than reactive. It is well known that the cavity depth governs the frequency bands of high absorption. The work presented here focuses on the development, modeling and testing of novel configurations of backing constructions and materials. These configurations are aimed at both dialing in the absorption properties at specific frequencies of interest and creating broadband sound absorbers. In this work, several backing cavity strategies are considered and evaluated.

Several sources of vibration are felt by a driver of an automobile. Road and engine excitation are the primary sources of vibrations and they are transmitted to the driver by the steering wheel, the floor and the seat. Active vibration control has been a well established method of controlling vibration, but its use has been limited to research laboratories and high end applications. This paper describes an approach of implementing a cost effective active vibration control system applied to a steering column. The active control system has been designed to eliminate the engine idle vibrations being transmitted to the steering wheel. The system is comprised of piezoelectric actuators, sensors and low cost electronics to drive the actuators in an appropriate manner. The first bending mode of the steering column was addressed. The efficacy of the solution was compared to the current production solution (a viscoelastic tuned mass damper tuned for such frequency).

Piezoelectric materials have been used in the past to reduce noise and vibration in several different applications, but the use of these materials to enhance noise reduction for automotive exhaust systems is a new application of this technology. The work detailed herein shows how an inductive shunt circuit may be used to improve the noise reduction performance of a baffle-less automotive muffler system. The absence of interior baffles in the muffler minimizes backpressure and improves fuel efficiency of the upstream engine system. We designed and built a prototype system utilizing an IM7/bismaleimide composite for the muffler body, stainless steel end caps and PZT 5A piezo-ceramic for the passive/adaptive element. By matching the acoustic resonance of the cavity inside the muffler with that of the structure surrounding it, a fully coupled system was achieved.