摘要
文章作者提出了一种结构简单、易于实现的薄膜型声学超常介质,不仅从实验上证实了它能够在100Hz到1000Hz的低频范围内以200倍的幅度打破声波衰减的质量密度定理,而且还给出了相应的理论解释.由于薄膜弱小的弹性模量,对于一块周边被硬边框所固定的小面积的弹性薄膜而言,仍然存在着各种不同的低频振荡模式.这些振荡模式的本征频率可以通过在薄膜的中央放置一个小的质量块而调整.文章作者惊奇地发现,在位于两个最低的本征频率之间的某个特定频率处,入射的声波几乎完全被反射,此时整个薄膜面内的平均法向位移为零.借助于有限元数值模拟方法,也发现在全反射频率附近薄膜的动态质量密度是负的.实验结果和理论计算符合得非常好.与此同时还发现,微波在某些频率全透射通过金属分型结构的现象可以用类似的机制来解释,而且这些全透射频率也是位于两个局域共振频率之间.
We present the experimental realization and theoretical explanation of a membrane-type acoustic metamaterial of very simple structure,capable of breaking the mass density law of sound attenuation in the 100—1000Hz regime by a significant margin（~200 times）.Due to the membrane＇s weak elastic moduli,low frequency oscillation patterns can be found even in a small elastic film with fixed boundaries defined by a rigid grid.The vibrational eigenfrequencies can be tuned by placing a small mass at the center of the membrane sample.Near-total reflection is achieved at a frequency in between two eigenmodes where the in-plane average of the normal displacement is zero.By using finite element simulations,a negative dynamic mass is explicitly demonstrated at frequencies around the total reflection frequency.Excellent agreement between theory and experiment is obtained.We also show that the present mechanism can explain the phenomenon of total microwave transmission through subwavelength slits in metallic fractals,at frequencies intermediate between two local resonances.
出处
《物理》
CAS
北大核心
2010年第4期243-247,共5页
Physics
