  Transmission through sub-wavelength apertures in perfect metals is expected
to be strongly suppressed. However, by structural engineering of the apertures,
we numerically demonstrate that the transmission of transverse electric waves
through periodic arrays of subwavelength apertures in a thin metallic film can
be significantly enhanced. Based on equivalent circuit theory analysis,
periodic arrays of square structured subwavelength apertures are obtained with
a 1900-fold transmission enhancement factor when the side length $a$ of the
apertures is 10 times smaller than the wavelength ($a/\lambda=0.1$). By
examining the induced surface currents and investigating the influence of the
lattice constant and the incident angle to the resonant frequency, we show that
the enhancement is due to the excitation of the strong localized resonant modes
of the structured apertures.
