Self-Collimation Effect In Two-dimensional Phononic Crystal And Its Application Research

As a kind of new artificial periodic material, phononic crystal was proposed by analogy with natural crystal and photonic crystal. It has potential application prospects in many fields such as mechanical vibration, integrated acoustics and acoustic communication. In recent years, the anomalous dispersion in photonic crystal has attracted lots of interest, due to their unique properties in passing band. The unique properties include negative refraction, sonic focusing, and self-collimation effect. Of which, the latter provides a new method to manipulate the light waves in integrated optical device. Compared with the conventional waveguides, self-collirnation-based wave propagation is much better, because of no coupling and reflection losses. Great progress has been made in designing light devices based on self-collimation effect, such as channelless waveguide, beam splitter and interferometers. However, the researches of theory and application on self-collimation effect in phononic crystal are just beginning.According to the present research situation on photonic crystal and phononic crystal, we analyze the self-collimation effect systematically in the paper. Meanwhile, we explore the possible applications of self-collimation effect in phononic crystal. Using finite element method, we have studied the following several aspects in this paper.(1) Proceeded from two basic conceptions (group velocity and equi-frequency contour line) at first, we analyze the refraction phenomena of light waves in the reciprocal lattice space. The principle of self-collimation effect is then introduced. We analyze the propagation of self-collimation-based light waves in photonic crystal.(2) Two kinds of acoustic beam splitters are proposed. The two-dimensional (2D) PC employed herein comprises rigid steel rods arranged in a square lattice and immersed in water. Circular and square steel rods are respectively adopted in model 1 and model 2. The acoustic beam splitter is formed by changing the rods’radius along with the diagonal direction of model 1, or changing the rods’orientation along with the diagonal direction of model 2. The calculated results show that the splitting efficiency of two splitters can be controlled by changing the radii of the circle rods or the orientations of the square rods. The two splitters we proposed are compact-sized and flexible to split. Moreover, for model 2, we have discussed the acoustic propagation phenomenon when the length of the square rods is changed. The results show that the total transmission/reflection range decreases/increases as the side length increases. In addition, there is a quasi-linear relationship between the orientation of the transflective point and the square rods’length.(3) We investigate the acoustic directional radiation based on self-collimation effect How the rods’orientation affects the directional radiation frequency. Firstly, we calculate the equi-frequency contour line with different rods’orientations. The results show that the directional radiation frequency changed with the changing of rods’orientation. But the corresponding normal direction keeps steady in the changing process which means the propagation direction of acoustic waves keeps unchanging. We can see the results clearly through the acoustic field distributions. The finding will apply to tuning the frequency of acoustic wave device. Besides, we also study the effect of structure truncating on acoustic fields distribution. We truncate the corner of the structure along +45° direction with different orientation cases. The results show that when rods’rotating angle θ=45°, the radiation branch along+45° suppresses other three branches while there are no similar results in other rotating angle. The finding will help us understand the acoustic directional further.These three aspects of the study illustrated that it is possible to research the self-collimation in phononic crystal. The theory analysis and the simulation results demonstrated that this subject is effective and feasible. The paper provides a new idea for the research of anomalous dispersion in phononic crystal.