Fig. 1. Model design of the acoustic metamaterial: (a), (b) Schematic diagram and equivalent circuit diagram of the two-dimensional SHS; (c), (d) schematic diagram and equivalent circuit diagram of the two-dimensional HT; (e), (f) schematic diagram and equivalent circuit diagram of the coupled structure of SHS and HT; (g) schematic diagram of the tunable acoustic metamaterial obtained by the deformation and optimization of the coupled structure.可调声学超材料的模型设计　(a), (b)二维SHS的结构示意图和等效电路图; (c), (d)二维HT的结构示意图和等效电路图; (e), (f)SHS和HT耦合后的结构示意图和等效电路图; (g)进一步变形优化得到的可调声学超材料模型的结构示意图

Fig. 2. Simulated comparison of the absorption performance of tunable acoustic metamaterial: (a) Absorption coefficient for different rotation angles of the inner split ring as a function of frequency; (b) real parts and imaginary parts of the relative impedance for different rotation angles of the inner split ring as a function of frequency; (c) comparison of the theoretical and simulated resonant frequency as a function of rotation angle.仿真得到的可调声学超材料的吸收性能对比　(a)不同内腔旋转角度下的吸收系数随频率的变化; (b)不同内腔旋转角度下的相对阻抗实部与虚部随频率的变化; (c)理论和仿真得到的共振频率随内腔旋转角度的变化关系

Fig. 3. Comparison of the sound energy and local speed distributions at different frequencies: (a), (b) Sound energy and local speed fields at 500 Hz; (c), (d) sound energy and local speed fields at 1000 Hz; (e), (f) sound energy and local speed fields at 1600 Hz.不同频率下的声能量和空气介质局域速度分布图对比　(a), (b) 500 Hz处的声能量和空气局域速度图; (c), (d) 1000 Hz处的声能量和空气局域速度图; (e), (f) 1600 Hz处的声能量和空气局域速度图

Fig. 4. Photographs of sample prepared by 3D printing technology: (a) Assembled whole sample; (b) outer split cavity; (c) top seal; (d) inner split ring; (e) bottom seal.3D打印制备的样品实物图　(a)组装成整体的样品; (b)外层开口腔体; (c)顶部密封端; (d)内层可旋转开口腔体; (e)底部密封端

Fig. 5. Experimental absorption coefficient of the sample at different rotation angles (i.e. 0°, 90°and 180°, respectively) of the inner split ring as a function of frequency.实验测试得到的样品在不同内腔旋转角度(分别为0°, 90°和180°)下的吸收系数随频率的变化