聲學超常材料的等效負材料特性

Equivalent Negative Material Properties of an Acoustic Metamaterials

王聖智(Sheng-Chih Wang) ； 張怡玲(I-Ling Chang)

《中華民國振動與噪音工程學會論文集》 2014 (2014/06) Pp. 218-225

摘要

本研究著重於有效負質量密度超常材料的波衰減和能量轉移機制，且所使用的超常材料（metamaterial）是由彈簧與質量塊組成的晶格系統，藉由等效彈簧質量塊系統可以計算出等效質量密度與彈簧常數和正規化頻率的關係式，經由關係式作圖可觀察出在特定頻率範圍內會出現負的質量密度與彈簧常數，當強制頻率在共振頻率附近時，波振幅會有衰減的現象，而其能量轉移的機制可以藉由外力作功來模擬晶格內能量流的變化，結果發現外力所做的功會儲存在晶格系統內部的質量塊，且儲存在內部質量塊的能量只是暫時性的，將會隨著外力所做的負功而被移除，故能量流會以循環的方式在晶格系統內變化，這種行為所設計出的超常材料主要是用來防止壓力波的通過。

關鍵字

超常材料 ； 負質量密度 ； 負彈簧常數

並列摘要

This study focused on wave attenuation and energy transfer mechanisms of a metameterial with negative effective mass density or spring constant. The metamaterial was composed of a lattice system of springs and masses. The equivalent mass density or spring constant as a function of dimensionless frequency could be calculated for the spring-mass system with substructures. It is noticed that the equivalent mass/spring constant were negative at particular frequency range. When a periodic force with frequency close to the local resonance frequency of the substructure was applied, the wave would not propagate far into the spring mass system. The mechanism of the energy transfer can be studied using external work, and it was found that external work was stored temporarily in the internal mass of lattice system, which would be removed later by negative work.