Device structure and simulation results. (a) Illustration of the SBE structure. (b) Simulation model for the eight-tip Siemens-star aperture. (c) Simulation model for the SBE structure. (d) Simulated transmission spectra for the Al-based SBE (e) FDTD simulations of the electric field component (E) distribution for the circular subwavelength aperture (left) and the eight-tip Siemens-star aperture (right). The colour bar values are given on a logarithmic scale and normalized by the THz source powe