We propose a tapered phononic beam with a broad low-frequency band gap for flexural waves. A unit cell of the phononic beam consists of two identical uniform parts and a thickness- and width-varying part sandwiched between them. Thickness and width profiles and uniform beam length are controlled to change the shear and rotational stiffnesses of the phononic beam, changing the starting and ending frequencies of the first band gap. By identifying the effects of those geometrical parameters on band structures, we determine the parameter values that enable the phononic beam to yield an ultra-broad and ultra-low band gap from 3.6 Hz to 237.9 Hz with a small lattice constant of $\lambda$/25. For experimental realization, a finite phononic beam with three unit cells is fabricated by wire electric discharge machining and its displacement transmission is measured through impact hammer tests. Particularly low transmission of -35 dB to -10 dB is observed at the band-gap frequency range. We briefly present ongoing works to enhance the structural robustness of the phononic beam by changing geometrical parameters or material of a thin and narrow part.

我们提出了一种弯曲声波的锥形声子束，其低频带隙较宽。声子束的晶胞由两个相同的均匀部分以及夹在它们之间的厚度和宽度变化部分组成。控制厚度和宽度分布以及均匀的束长度，以改变声子束的剪切刚度和旋转刚度，从而改变第一带隙的开始和结束频率。通过确定这些几何参数对能带结构的影响，我们确定了使声子束产生从3.6 Hz到237.9 Hz的超宽和超低带隙且具有较小晶格常数的参数值。$\lambda$/ 25。为了进行实验实现，通过电火花加工制造了具有三个单位单元的有限声子束，并通过冲击锤测试测量了其位移传递。在带隙频率范围内观察到特别低的-35 dB至-10 dB的传输。我们简要介绍了正在进行的工作，通过更改几何参数或薄而窄的部分的材料来增强声子束的结构鲁棒性。