THz transmission through Sierpinski fractal structures on copper foils by FDTD simulation

The enhanced transmission spectra and reflection spectra of sub-wavelength fractal structure named Sierpinski fractal structure are presented by means of finite-difference-time-domain (FDTD) simulation. It is found that there are several transmission peaks in the transmission spectra and several reflection peaks in the reflection spectra. The transmission peaks appears red shift and increases with increasing of side length of center square holes when keeping the period of array as a constant. To investigate the physical mechanism of the enhanced transmissions, we simulated the incidence and transmission of THz radiation field at certain transmission peak and show the propagation and distribution of the interior electromagnetic field by the electromagnetic design software named CONCERTO. It is found that different transmission peaks are caused by the different level of square holes. Further analysis reveals that the transmission enhancement is from the interaction of the complicated waveguide coupling effect and the local resonance of electric field. Our simulation is helpful for the understanding of THz wave propagation and THz transmission through the fractal structures of the metal foil.