Research On Elastic Wave Propagation Characteristics Of Internal Mass Cycle Structure

By analogy with "metamaterials" and "photonic crystals" in the field of optical physics, such concepts have spurred a renewed interest in the frontiers of acoustic materials. "Acoustic metamaterials" and "Phononic crystals" are the artificial periodic composite structures/composite materials with the periodic array of elastic modulus and mass density. The interaction between elastic wave and the internal periodic structure results in a special dispersion relation, furthermore the band between dispersion curves is called the band gap. It provides some new ideas for the control of vibration and noise of engineering and technology. With the proposed of locally resonant phononic crystals, the researchers reduce the wavelength corresponding to bandgap frequency to two orders of magnitude. It opens up a new way for the design of new acoustic devices or the control of low-frequency noise (vibration).The miniaturization and high efficiency of acoustic metamaterial are the interest goals for people in practical applications. Since the phononic crystals can be designed, the specific design of primitive cell structure and parameters of material is a good way to optimize the performance of phononic crystals. The theme this dissertation focused on is performance optimization of phononic crystals. The performances of low frequency, broadband and high efficiency are proposed by designing new phononic crystals. The following aspects have been considered:(1) the study on negative effective parameters of three resonance mass-spring microstructure, additionally, the filter characteristics and the band gap characteristics of three resonance phononic crystals are also discussed; (2) the influence of defect for band gap and the adjustment of defect modes; (3) the band gap characteristics and band gap regulation for hexagonal honeycomb phononic crystals, which has a feature of mass-spring microstructure. The main conclusions of this dissertation are listed as follows:(1) Three resonance systems can achieve negative effective mass, and the frequency range corresponding to negative effective mass can be adjusted. Much more interesting, the low frequency and broadband band gap phenomenon can be found in three resonance phononic crystal. In addition, there are number of methods for band gap adjusting. Furthermore, the filter characteristic of three resonance phononic crystal tends to ideal with the increase of periods. (2) The position of defect mode will move to the low frequency region when increasing the mass of defect, furthermore, the defect modes have a tendency to move to the low-frequency region if the defect is away from the incentive end. (3) The broad band gap phenomenon also can be found in hexagonal honeycomb phononic crystals which have mass-in-mass system, more specifically, the frequency position and bandwidth of band gap can be adjusted.