A Study On The Structural Design And Sound Insulation Of Plate-type Acoustic Metamaterials

Low-frequency sound wave is characterized by long wavelength and high sound penetration.An effective insulation of low-frequency noise usually involves the usage of thick and/or highdensity materials(i.e.,mass law).Membrane type acoustic metamaterials,a composite material which demonstrates excellent sound insulation properties with relatively light weight can be used for low-frequency noise control.However,the performance of membrane type acoustic metamaterials is affected by the membrane pre-tension and durability problems which restrict its usage in practical applications.Plate type acoustic metamaterials which do not require pretension and can endure a larger normal impact can overcome the problems for better industrial applications.However,existing plate type acoustic metamaterials are characterized by high sound insulation peak frequencies and a narrow sound insulation band.To lower the sound insulation peak frequency and to improve the sound insulation performance of plate type acoustic metamaterials,this thesis presents a structural design of a new plate type acoustic metamaterial coupled with multiple distributing masses on the plate.A two-layer design of a coupled plate-type acoustic metamaterial is further presented aiming for a broadband sound insulation.In this thesis,an electro-acoustic analogy and the transfer matrix method are employed first to derive the acoustic impedance and sound insulation of a single-layer plate type acoustic metamaterial.The sound insulation result calculated is verified by that of finite element simulation and experimental test using sound impedance tubes.Multiple distributing masses are then introduced and attached to the plate to reduce the sound insulation peak frequency and the broaden the sound insulation band.A parameter analysis is also included in the study to understand the key parameters of the design affecting the sound insulation of the multiple distributing masses plate type acoustic metamaterial.A new two-layer paralleled plate type acoustic metamaterial is designed aiming to improve the sound insulation and the sound insulation bandwidth.The superior sound insulation performance of this new metamaterial design is verified by simulation and experimental results.In the last main chapter of this thesis,a perforated plate-type acoustic metamaterial is designed to replace the cover of the compressor compartment of a refrigerator to reduce the noise propagation for the working noise generated by the compressor.The effectiveness of the design is verified by the experimental noise measurement at the laboratory.