Vibroacoustic studies of perforated plates, plate with piezoelectric ceramic attachments and shunt circuits

Abstract

Low-frequency noise control remains a challenging task due to the weak inherent dissipation of traditional sound absorption materials in this region. The acoustic resonators can work at low frequencies, while the effective bandwidth is narrow, and the required volume is large. The passive structures and semi-passive control strategies are explored in this thesis to improve the bandwidth of noise control in the low-frequency range.

A passive corrugated micro-perforated panel (MPP) is studied to tackle the dips of the absorption curves caused by anti-resonance. The results show that the absorption is enhanced at the dips of the absorption curves because multiple modes are excited at the peak and dip frequencies, and the absorption by the non-resonating modes gives rise to performance improvement. However, it is also found that when the higher non-resonating modes are excited to help improve absorption, the dissipation from original resonant modes deteriorates. This is the limitation of a purely passive system.

To break the limitations of wavelength and total volume while maintaining good robustness and low control cost, the semi-passive shunt method is explored. Such circuit is shunted to the piezoelectric ceramic (PZT) patch. The shunted PZT patch is attached to a conventional MPP to construct a smart MPP absorber. Multiple branches are added to the shunt circuit, and hence it can resonate with the PZT patch at multiple frequencies and improve the sound absorption at low frequencies. The results show that the shunted PZT patch controls the vibration of the MPP and improves the Helmholtz absorption at multiple low frequencies.

A smart side-branch silencer is then constructed with an array of shunted PZT resonators mounted on a thin plate forming part of the wall in the duct, and the device is backed by a side-branch cavity. This smart silencer can filter out selected incident waves. The sound attenuation performance is found to benefit from the sound reflection and absorption by the light plates attached with shunted PZT arrays. Both simulated and measured results demonstrate that extra sound attenuation peaks can be added by the electrical resonances of PZT patches.

To adapt to different incident wave spectra, a time-domain design approach is proposed using the metal-oxide-semiconductor field-effect-transistor (MOSFET) in the shunt circuit to form a temporal modulated material. This new composite material consists of a lightweight structure attached with shunted PZT patches, and the time sequence of the working circuit is controlled with the MOSFET. The material is designed to improve the sound isolation band by optimizing the time sequence of multiple resonant shunts working at different frequencies. The results show that the time-varying shunted PZT can make the electrical resonances effective at multiple frequencies, and the total absorbed energy is distributed to multiple frequencies to broaden the effective bandwidth. Hence, broadband sound isolation is achieved with the proposed temporal modulated material, which is lightweight and without a sensor.