| Metamaterial(MM),which consists of a periodic array with sub-wavelength dimensions,has recently attracted considerable interest due to its special electromagnetic characteristics generated by the rich resonant effects in MM.The assessment criteria of resonance is quality factor(Q-factor),but it is difficult to be improved largely because of the ohmic loss of metal and the radiative loss.The conventional methods of achieving high Q-factor are all based on surface mode resonance,there are indeed some effect on suppressing the radiative loss but little.MM can be consider to a kind of grating due to its periodicity,so grating diffraction by which electromagnetic wave can be coupled into the waveguide is also exist in MM,the resonance caused by this effect is called guided mode resonance(GMR).This kind of resonance can suppress largely the radiation of energe to free space because of the guiding function of waveguide on electromagnetic wave,and can achieve extremely high Q-factor which has been verified in the region of grating.In this paper,we proposed the GMR in MM based on single metal ring at the first time,and studied its basic regulating principle with different structure parameters,then we presented two ways of controlling the spectral width to achieve high Q-factor which took the unit cell consisted of two metal closed rings and split rings for example respectively:(1)The unit cell is consist of polymide film with the period of 2d along x-axis and d along y-axis,and two metal closed rings evenly distributed on the surface of polymide film,so the distance of two rings and the real period is all d now,GMR with the grating period of d will be stimulated when the electromagnetic wave incident because a two-dimensional grating effect exists.Once the two rings move towards each other or reversely which lead to that the distance of adjacent two rings are different,GMR with the grating period of 2d will be stimulated,and we can control the Q-factor and amplitude of GMR through adjusting the amount of movement,this is due to the reason that modulation depth changes.The smaller the distance moved,the higher Q-factor but weaker amplitude,and in simulation,the value of Q-factor can reach up to 104.Then on this basis,the influence on GMR with different thickness of planar waveguide is discussed,a thiner and lower loss material is good for realizing ultra high Q-factor.At last,we fabricated a sample by the method of laser induced and non-electrolytic plating with copper,the test result through THz-TDS is well coincide with simulation.(2)The unit cell is consist of polymide film with the period of 2d along x-axis and d along y-axis,and two metal split rings evenly distributed on the surface of polymide film,but the gaps are distributed in the top and bottom of the rings respectively.GMR with the grating period of 2d will be also stimulated when the two rings rotate at the same time or the two gaps move towards each other or reversely,it is obvious that the smaller angle or movement,the higher Q-factor and weaker amplitude of GMR will be achieved,and in simulation,the value of Q-factor can also reach up to 104.In addition,we proposed a method to control the spectral width of EIT-like caused by the coupling of GMR and dipole resonance,and gave the demonstration in simulation.At last,we also fabricated a sample by the method of laser induced and non-electrolytic plating with copper,the test result through THz-TDS is well coincide with simulation. |
PDF Full Text Request