Abstract:

This paper deals with  the acoustic band gaps in periodic composite materials, and gives out a new attenuation mechanism. Using the modified reflection and transmission matrices method, we considered the periodically stratified porous media as 1D phononic crystal, investigated the band gap properties of plane P\|waves propagation. It is shown that there is a series of stop bands when the characteristic P\|wave velocities of the two media are different and the stop band frequencies satisfy that lattice thickness is integer multiples of average P\|wave half\|wavelength. The bandwidth and attenuation of the low\|frequency stop band correspond to the difference of velocity. And with the same velocity difference, they are much greater when the difference is caused by porosity variations and partial saturation, compared with grain\| and frame\|parameter variations. When the lattice thickness is in the magnitude of meters or decades meters, the low\|frequency stop band is within the seismic band of frequencies. 

Key words: seismic attenuation, phononic crystal, acoustic band gap, reflection and transmission matrices method