COMPLEX WAVENUMBER ANALYSIS OF FLEXURAL WAVES IN PLATE STRIP WITH PERIODIC ACOUSTIC BLACK HOLES

Acoustic Black Hole (ABH) structures are attractive for potential applications in broadband vibration suppression and wave manipulation. Moreover, the ABH lattice structures are favored for achieving broadband bandgap (BG) in lightweight design. Some reported works demonstrated the BG generation in an infinitely large periodic ABH plate, within which wave propagation in all directions is considered. The BG generation is contributed by the ABH-induced local resonance and Bragg scattering. In this work, a plate strip with periodic ABHs is presented and the wave characteristics of different flexural waves are discussed by complex wavenumber analysis. Results show that there exist two different flexural waves in such plate strip configuration for BG generation due to the finite width of strip configuration. By scrutinizing the complex wavenumber characteristic, it is observed that, within the BG satisfying the Bragg condition, there exist two flexural waves usually characterized with different attenuation ratios, but with the same attenuation ratios for the BG not satisfying the Bragg condition. The complex wavenumber characteristic is also discussed for two different periodic cells with considering the symmetry: one irreducible unit cell with embedded single ABH and with double ABHs. Results show that, due to the resonance mode of finite structure falling into the predicted BG ranges, the broadband and continuous attenuation band is difficult to be warranted by employing an asymmetrically irreducible unit cell when compared with the symmetric one. Results from the irreducible unit cell with two ABH indentations has potential in realizing broadband attenuation band in practical application.