Abstract
摘要:過去幾年中,本計畫主持人針對具有共振微結構的超穎聲學材料(Acoustic Metamaterial)進行一系列的研究,也建立了一些數學模型來研究探討該結構性材料的動力行為。研究結果預測了此結構性材料的特殊動力行為,例如材料具有等效負質量密度及等效負彈性常數的存在。另外,利用波傳實驗,亦顯示出此結構性材料具有濾波及阻波的能力。這些發現強烈顯示出此種新人工超穎材料具有很多未來潛能,有機會開創出一個新工程研究領域及研發許多科學及工程應用。
本研究旨將延伸前述創新研究,並發展數項細部研究方向。基本上,由於超穎材料的學理根本在於材料內的微結構,因些我們一部分的研究重心將放在進行創新的微結構設計。新的微結構將使結構性材料具有新的性質與功能。接著,主要的研究重心將放在二維超穎材料的折射特性。利用微結構造成的動力特性,此材料將具備等效負質量密度以及等效負彈性模數,且數值均隨著外力頻率大小而改變。而雙負材料常數所造成的動力特性、特殊現象、及隱含意義,將由理論與數值模擬加以分析。此二維超穎材料的實驗原型也會在實驗室製造並驗証理論與數值所預測的特殊動力性質。最終,本研究亦會提出並建議具潛能的實際應用。
另外,本研究的一部分目標在於探討二維超穎材料的雙異向性質,即質量密度與彈性模數同時具備異向性。此結構材料的雙異向性將以理論與數值方法研究。其中,非傳統的微結構連體理論以及新的多位移自由度連體理論將會被加以探討與研究來預測此結構性材料的動力特性。
本研究的另一項主要目標在於探討並開發此新結構性材料的潛在應用。其中一項可能的應用是在離岸式風力發電機的主要基底結構附加上超穎多功能結構。而超穎結構的概念即原自於超穎材料。附加的超穎多功能結構不但可以吸收獲取海浪的能量,並可以減少海浪為離岸式風力發電機所造成的振動,進而保全及延長主結構體的壽命。此外,對於超穎多功能結構在海浪波動及能量轉換的探討與認識,將製造許多工程應用上的機會與新挑戰。
最後令人期望的是,經由本研究成功的進行,有機會帶給未來工程材料與結構顯著的衝擊ー特別是多功能材料與結構。所發展的科學技術亦可為相關產業帶來衝擊與成長。此必為行政院國家科學委員會所鼓勵與樂見。
Abstract: In the past few years, the present PI has investigated acoustic metamaterials with locally resonant microstructures by employing theoretical models. A number of unusual dynamic behaviors such as the existence of negative effective mass/mass density or negative elastic modulus in some metamaterials have been found. In addition, wave propagation experiments were conducted on the metamaterial to demonstrate its capability in blocking/filtering dynamic disturbances. These findings strongly indicate that this new class of emerging man-made metamaterials has tremendous potential in opening up a new field of material engineering and numerous novel applications.
The present research will enlarge the scope of the study in acoustic metamaterials in a number of directions. Since the heart of a metamaterial is its constituent man-made microstructure, we will develop new locally resonant microstructures for making new metamaterials to attain new properties/functions. The main emphasis will be placed on 2D metamaterials that can exhibit unusual refraction characteristics. The proposed metamaterial is frequency-dependent and its effective mass density and elastic modulus may become simultaneously negative in certain frequency range. The implication of double negativity will be investigated, and the dynamic characteristics of the proposed metamaterial will be studied both by analytical and numerical approaches. Prototypes of these metamaterials will be made and experimentally evaluated to verify their unusual properties predicted by the analytical and numerical models. Potential applications will be identified and suggested.
In addition, part of our effort will be focused on the bi-anisotropy properties of the proposed metamaterials. Dynamic behaviors of such metamaterials will be investigated analytically and computationally. Nonconventional microstructure continuum theories as well as a new multi-displacement continuum theory will be developed and used to study the dynamics behavior of these metamaterials.
In this research, a significant effort will be made to explore possible applications of this class of new metamaterials. Specifically, we will employ meta-structures in addition to the offshore wind turbines to perform energy harvesting function in addition to being a wave blocker/filter, as well as other potential interesting functions yet to be explored. Such a meta-structural concept can be used to build multifunctional structures. Moreover, the coupling of wave motion and energy conversion in the meta-structure may provide many new challenges in engineering as well as opportunities in novel applications.
We anticipate that, if successfully carried out, the proposed research will have substantial impact on the future development of engineered materials and structures, especially multifunctional materials and structures. The technology developed could be beneficial to related industries. This shall be of interest to the National Science Council.
Keyword(s)
超穎材料
多功能材料與結構
波傳與振動
負質量密度
負彈性模數
Metamaterials
Multi-functional materials and structures
Wave propagation and vibration
Negative mass density
Negative elastic modulus