Multilayer homogenization and experimental demonstration of artificial plasma matched with free space

A multilayer homogenization technique based on a cascade product of three transfer matrices has been proposed for a general artificial medium comprising periodically stacked impedance sheets. This method has been demonstrated to precisely predict the parameters of structures that mimic artificial plasma with different electrical sizes of the unit cell, while the simple Drude plasma model describes well only structures with a unit cell much smaller than the wavelength. Using the multilayer homogenization technique, we have found some effective permeability that is automatically neglected in the conventional Drude plasma approximation which only considers permittivity. It can seriously affect the desired impedance matching with free space above the plasma frequency. To improve the impedance matching, and thus reduce ripples above the plasma frequency, it is necessary to design unit cells with high equivalent self-inductance. According to theoretical and numerical results, we have demonstrated that the replacement of straight strips with zigzag strips of the same width can considerably improve the quality of the impedance matching. This work opens the route to new designs of high-pass filters based on artificial plasmas with flat transmission above the cutoff frequency. A proof-of-concept experiment is shown.