Defect modes in the phononic crystal based on Helmholtz resonators with point defect

Defect mode can be created by introducing point defect in the one-dimensional crystal containing Helmholtz resonators. Based on the acoustic transfer matrix method and finite element method, the relationship among the defect mode, the geometrical parameters of the defect cell, and the acoustic field distribution in the structure at the frequency of the defect mode was studied. The results show that the defect mode moves to the edges of the local resonant forbidden band with the increase of the coupling effect between the defect cell and the perfect cells. In addition, acoustic energy localization is also observed due to the existence of the defect state. The research result will be of help for designing new acoustic filters and energy concentrators.