Abstract ThisChapter evaluated the simulation studies that have been conducted on aring-type split ring resonators (SRR) and Cascaded Split ring resonators (CSRR).
The study has been conducted to understand the properties of metamaterialstructure when light fall horizontally. When light falls along the x-axis, theproposed structure shows the properties of the double negative material due tonegative refractive index. Moreover, it was noticed that the left-handedbehavior of the structure is affected by the width of the continuous wire, aswell as distance between the centers. Additionally, the left-handed behavior ofthe structure affected by lattice constant was also studied. 6.
1 Design and Simulation of Split Ring Resonator6.1.1 Simulation Technique (SRR)The FDTD method wasused to simulate the structure. S-parameters were deduced by using the S-parameteranalysis tool.
Figure 6-1 has shown the unit cell. It consists of two materials: glass substrateand split ring resonator made of copper. The unit cell has following dimensions.
The thickness of the substrate is 250nm, width of metal wires is 140nm, length of the metal wires of the outer ring is2000nm, and the gap between the inner ring and the outer ring is 147nm. (a) (b)Figure ?6?1 (a) Horizontal incident light and(b) Parameters. Figure6-2 shows the Split Ring Resonators simulation results i.e. Transmission,Refractive index, permittivity and permeability.
This structure shows double negative metamaterials properties because permittivityand permeability indicate a negative result at around 9.7 THz. When wechange the wire width from 50nm – 140nm and retaining the length constant at140nm, the Figure 6-3 shows the Split Ring Resonators simulation results i.e.Transmission, Refractive index, permittivity and permeability. There is achange in the transmission and permittivity by varying the width and from thiswe can conclude it as a Left handed metamaterial. By increasing in width therefractive index is changing but no change is found in permeability. As the refractiveindex change, it becomes more negative in nature.
Figure6-4 shows the Split Ring Resonators simulation results i.e. Refractive index,permittivity and permeability by changing the gap ‘g’ in SRR structure.
From thefigure 6-4, it can be seen that results is changed when we varying the gap ‘g’from 500nm – 700nm. Decrease in the gap moving this to the left side.By retainingthe lattice constant ax fixed and changing the ay from 1500nm – 2400nm, Figure6-5 shows the Split Ring Resonators simulation results i.e. Refractive index,permittivity and permeability. From the figure 6-5, it can be observed obviouslythat result is changed when the lattice constant ax is increasing, and with theincrease in lattice constant ay the waves are moving towards left direction.
By retainingthe lattice constant ay fixed and changing the ax from 2200nm – 2600nm, Figure6-6 shows the Split Ring Resonators simulation results i.e. Refractive index,permittivity and permeability. From the figure 6-6, it can be observed obviouslythat result is changed when the lattice constant ay is decreasing, and with thedecrease in lattice constant ax the waves are moving towards left direction. Figure ?6?2 (a) Shows the structure transmission spectra simulation, (b, c, and d) are the results deduced from thesimulation data shows real part of thepermittivity, permeability, andrefractive index, respectively.Figure ?6?3 (a) Structure simulated transmission spectra withdifferent widths. (b, c, and d) the real part of the permittivity, permeability, and refractive index,respectively.
Figure ?6?4 Extracted results of the structure with effective parameters:(a), (b) and (c) are the permittivity, permeability,and refractive index, respectively. Figure ?6?5 Shows the structure extracted effective parameters:(a), (b) and (c) are the permittivity, permeability, and refractive index,respectively. Figure ?6?6 Showsthe structure extracted effective parameters: (a), (b) and (c) are the permittivity, permeability,and refractive index, respectively. 6.2 Designand Simulation of Cascaded Split Ring ResonatorThe FDTD method was used to simulate the structure. Toextract the S-parameters, S-parameter analysis tool was used with frequencyunit in THz.
Each calculation is based on 100 frequency samples. Figure 6-7shows the unit cell 3D design and its parameters. It consists of threematerials: SiO2 as a substrate, Si as a waveguide and split ring resonator madeof gold. The frequency range of 216 THz was selected to simulate the structure.
The unit cell has following dimensions. The thickness of the substrate is340nm, thickness of the waveguide is 220nm, width of metal wires is 40nm, lengthof the metal wires of the outer ring is 230nm, and the gap between the innerring and the outer ring is 40nm. Figure ?6?7 (a)Shows 3D design of the structure, and (b) parameters 6.2.1 Simulation Technique (SRR)Figure 6-8 showsthe simulation results of the Split Ring Resonators i.e. Transmission,Refractive index, permittivity and permeability. As this structure has doublenegative metamaterials properties due to which permittivity and permeabilityshows a negative result at around 219 THz.
Figure6-9 shows the Split Ring Resonators simulation results i.e. Refractive index,permittivity and permeability by changing the width of the wires from 20nm –40nm. There is a change in the transmission and permittivity by varying thewidth and from this we can conclude it as a Left handed metamaterial. By increasingin width the refractive index is changing but no change is found in permeability.
As the refractive index change, it becomes more negative in nature. Figure ?6?8(a) Simulation result of the structure wavelength spectra. (b, c, and d) are the simulation data results of the real part of permittivity, permeability, and refractive index respectivelyFigure ?6?9 Shows the structure transmissionspectra simulation: (a, b and c) the realpart of the refractive index, permeability,and permittivity respectively.
6.3 SummaryTo understand the properties ofmetamaterial structure the simulation studies have been conducted on aring-type Split ring resonators (SRR) and cascaded split ring resonators (CSRR).When the light is incidented horizontally, the structures (SRR) and (CSRR)shows a NRI which indicate the properties of the double negative material (DNG)and left-handed material (LHM) at the near-infrared range. Moreover, it was noticedthat the left-handed behaviour of the structure is affected when we change thedifferent parameters of the structures.
