Research On Filtering Characteristics Of Phononic Crystals In Ultrasonic Frequencies

Phononic crystals has been widely used in various fields in recent years due to its band gap mechanism and artificial controlled technology of the motion state of the sound wave.Filtering characteristics of phononic crystals are researched using the band gap characteristics,focusing functions and defect structures in ultrasonic frequencies.Based on elastic wave, lattice and band theory, the phononic crystals about two dimensional three component locally resonant structure is designed by lead, rubber and epoxy.On the basis of the tetragonal lattice and the material parameters, the structure of triangular lattice, hexagonal lattice and complex lattice are designed by defect states changing the array of scatter. The band structures of four different lattice types are simulated based on the plane wave expansion method and the finite element method. The result shows that pass band frequencies ranges have a better convergence effect. When frequencies enter the stop band range, such as frequencies are unable to resonate with the phononic crystals or quickly attenuated in the process of the internal transmission of the phononic crystals, the aim of filter is reached.The tetragonal lattice structure can be designed as a band-stop filter or low pass filter according to the different structures of the array in 10 MHz. The triangular lattice structure is a band-pass filter in 1100 kHz. The structure of hexagonal lattice and complex lattice are multi-channel filters in 200 kHz. It better achieved the adjustablity of the filter frequencies to change the range of pass band and stop band of the phononic crystals by altering their lattice structure types.Three dimensional triangular lattice phononic crystals structure is designed based on two dimensional profile and the simulation of finite element method is carried out. The result is consistent with that of the two dimensional profile structure. The matrix material of triangular lattice structure is made by material parameters set in simulation and 3D printing technology.Based on it, and penetrated by lead core and filled with rubber, the synthesis of phononic crystals structure is finished. Finally, transmitting and receiving modules of ultrasonic testing are designed. The test is carried out using ultrasonic probes with seven different frequencies in the range of 40 kHz to 1000 kHz. Trafficability characteristic of each frequency is observed from the amplitude level of output first wave. The experimental results obtained with phononic crystals are consistent with simulation results. Output amplitude obtained without phononic crystals is not significantly enhanced or attenuated. The results verify filtering performance of the triangular lattice structure of phononic crystals.