Extending and lowing band gaps in one-dimensional phononic crystal strip with pillars and holes

• The one-dimensional strip with hybrid pillars and holes is innovatively studied.
• Gap difference between 1D phononoic crystal strip and 2D plate is discussed.
• Extremely low and wide gap can be obtained with pillar-hole strip.
• Combination of pillars and holes is an effective way to gain low-wide gaps.
• Gap can be modulated flexibly with geometrical parameters.
• The hybrid strip is applicable in integrated acoustic device with low and wide gap.

Effectiveness of extending and lowing gaps in one-dimensional phononic crystal strips is conducted by periodically patterning pillar-type strip with holes. Finite element method is applied to the hybrid unit to calculate band structures and eigen modes. Transmission spectra and displacement fields are investigated to confirm the gap effect in the studied hybrid strips. Numerical results show that, the one-dimensional hybrid strip can open lower and wider gaps. Compared with two-dimensional phononic crystal plate, band structures of phononic crystal strip show different group velocities and frequencies in low-order bands, different eigen modes of gap edge because of boundary condition difference. The effectiveness of modulating gaps with strip width is investigated. Gap degeneration happens to adjust lower gap edge downward. Besides, hybrid structure with double-side pillar leads to more resonance bands than that with single-side pillar. Vibration mode of pure pillar type structure located in lower edge of the gap of hybrid single-side pillar-type structure, and some resonance modes in the hole-type strip are reserved in hybrid single-side pillar structure. Resonance in hybrid double-side pillar structure is introduced by vibration of the double-pillar character, to create more flat bands. Furthermore, gap sensitivity to geometrical parameters of pillars and holes is also investigated.