Membrane-type acoustic metamaterials (MAMMs) have been studied for more than a decade. It has been disclosed to be efficient to attenuate low pitched noise by ultra-thin materials, which seems to turn against the mass-density law in nature. By various designs of the membrane resonators, low transmission and perfect absorption have already been achieved by different experiments. When the symmetry of membrane surface is broken, additional eigenmodes and anti-eigenmodes will be generated. Off-centred decorated membrane resonator (ODMR) is an ideal candidate for studying the manipulation of those new modes. The specific motions of the decoration are critical to discover the control factors of mode manipulation. Besides, V-shape impedance tube is applied to examine the effects of tilted incident angle to the sample surface. Power dependent properties in membrane oscillator are also observed by varying input signals in V-shape tube. Non-linearity in membrane-type metamaterials is then revealed to be responsible for power dependent effects. The non-linearity in membrane resonators not only leads to different transmission coefficients, but also causes frequency-shifting among spectra. Therefore, composite metamaterials are designed to produce asymmetry in transmission. Thanks to the power dependent effects, asymmetric transmission takes place in dual-layer membrane resonators.
| Date of Award | 2022 |
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| Original language | English |
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| Awarding Institution | - The Hong Kong University of Science and Technology
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| Supervisor | Zhi Yu YANG (Supervisor) |
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Transmission asymmetry by sound power dependency in non-linear acoustic metamaterials
LAU, P. H. (Author). 2022
Student thesis: Master's thesis