Host: The Japan Society of Mechanical Engineers
Name : Dynamics and Design Conference 2018
Date : August 28, 2018 - August 31, 2018
An acoustic metamaterial sound-insulator based on Helmholtz resonators is developed by using light weight plastic foam. Small Helmholtz resonators are embedded periodically within the sub-wavelength throughout the plate of plastic foam. This plate of plastic foam covers an elastic plate with an air gap and a double-wall insulation system is organized. This system exhibits extraordinary high sound transmission loss in the frequency range between these two resonances compared with the sound transmission loss by a conventional double-wall insulation system. This characteristic can be realized since the equivalent stiffness of the air gap becomes negative in that frequency range. The theoretical analysis gives the expression of the equivalent stiffness of the air gap between the elastic plate and the insulator with resonators. Numerical calculations are also performed by using representative unit cell to demonstrate the acoustic performance of the developed system, an elastic steel plate of 1 mm is covered with a plastic plate of 35 mm thick where the resonators that has a resonance around 2 kHz. Air gap of 5 mm between these two plates gives resonant transmission loss around 800 Hz. The finite element analysis utilizing COMSOL Multiphysics gives higher transmission loss than a conventional double-wall from 0.8 kHz to 2.0 kHz. Measured transmission loss of the system is also higher by 10 dB than one by the conventional double wall without resonators.
