The possibility of a broadband noise reduction of piezoelectric smart panels is experimentally studied. A piezoelectric smart panel is basically a plate structure on which piezoelectric patches with electrical shunt circuits are mounted and sound-absorbing material is bonded on the surface of the structure. Sound-absorbing material can absorb the sound transmitted at the midfrequency region effectively while the use of piezoelectric shunt damping can reduce the transmission at resonance frequencies of the panel structure. To be able to reduce the sound transmission at low panel resonance frequencies, piezoelectric damping using the measured electrical impedance model is adopted. A resonant shunt circuit for piezoelectric shunt damping is composed of resistor and inductor in series, and they are determined by maximizing the dissipated energy through the circuit. The transmitted noise-reduction performance of smart panels is tested in an acoustic tunnel. The tunnel is a square cross-sectional tube and a loudspeaker is mounted at one side of the tube as a sound source. Panels are mounted in the middle of the tunnel and the transmitted sound pressure across panels is measured. When an absorbing material is bonded on a single plate, a remarkable transmitted noise reduction in the midfrequency region is observed except for the fundamental resonance frequency of the plate. By enabling the piezoelectric shunt damping, noise reduction is achieved at the resonance frequency as well. Piezoelectric smart panels incorporating passive absorbing material and piezoelectric shunt damping is a promising technology for noise reduction over a broadband of frequencies.

The transmitted noise reduction (NR) of passive and active hybrid panels is experimentally studied. The concept of hybrid panels is based on a combined approach for noise controls: a passive approach for mid and high frequencies and an active approach for low frequencies. Active and passive hybrid panels are demonstrated. An active-hybrid single panel is made with a plate structure on which piezoelectric sensor/actuators are bonded in conjunction with a simple controller. Sound absorbing material is bonded on the structure to effectively reduce the transmitted noise in mid frequencies. An active-hybrid double panel is also made by using another single plate to maintain an air gap. To prove the concept of hybrid panels, an acoustic measurement experiment is performed. Instead of using the active control system, a passive shunt damping is used for the NR in low frequencies. This is called a passive-hybrid panel. The use of sound absorbing material and an air gap is effective for noise control in mid and high frequencies. Meanwhile, the active approach and the passive shunt approach are useful for noise control at lower resonance modes. These hybrid panels demonstrate the potential for NR at broadband frequencies.

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In this paper, noise reduction performance of piezoelectric smart panels is experimentally studied. Piezoelectric smart panel is comprised of plate structure on which piezoelectric sensor/actuators are bonded and sound absorbing materials. The concept ofpiezoelectric smart panels is to combine passive and active strategies such that the noise reduction can be effectively achieved over a broad frequency range. The noise reduction performance is tested on an acoustic tunnel. The tunnel is made of a guided tube having a square cross section and loud speaker is installed at one end as a sound source while nonreflection terminator is attached at the other end. The panels can be mounted in the middle of the tunnel and the transmission as well as reflection ofpanels can be measured.Noise reduction performance of a single plate with absorbing material shows a good result at mid frequency region but little effect in the resonance frequencies. When the active control scheme is activated, a remarkable noise reduction is observed at the resonance. The combined use of absorbing materials and piezoelectric active devices brings the simultaneous noise reduction in mid and low frequency regions. It can be concluded that piezoelectric smart panels incorporating passive absorbing material and active piezoelectric devices, is a promising technology for noise reduction in a wide band frequency.

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