  The terahertz transmission properties of symmetrical and asymmetrical annular
apertures arrays (AAAs) are investigated both experimentally and numerically.
It is found that only odd order resonant modes are observed for the symmetrical
structures but both odd and even order resonances can be shown for the
asymmetrical structures. Breaking the symmetry of AAAs by gradually displacing
the H-shaped AAAs to U-shaped AAAs allows an intensity modulation depth of 99%
of the second order resonance. Simulation results verify the experimental
conclusions well. This result provides a tremendous opportunity for terahertz
wavelength tunable filtering, sensing, and near-field imaging.
