Preface

"Metamaterial" is a man-made material with special properties that is not found in nature. This material can regulate basic physical characteristics such as frequency, amplitude, phase and polarization of electromagnetic waves. THz metamaterials are metamaterials that regulate electromagnetic waves with frequencies in the terahertz range. This case simulates the passive metamaterial described in the paper Chen et al. Active terahertz metamaterial devices^[1] and analyzes the surface current density of the metamaterial.

Simulation settings

Device introduction

The THz metamaterial used in this case consists of a gallium arsenide (GaAs) substrate and a gold (Au) layer on its surface. Its structure is shown in the figure below. The thickness of gold used in the reference is $0.2 \mu m$, which is much smaller than the wavelength used in the simulation (130$\mu m$ - 1200$\mu m$), so 2D Structure can be used in this case to build the gold layer. Since the simulation structure and the source are symmetrical in the X direction, we use Symmetric boundary conditions in the $X_{min}$ and $X_{max}$ directions.

Parameters	A	D	G	W
Value ($\mu m$)	36	10	2	4

Material

The gold material is represented with the Drude model (which contains the plasma frequency $\omega_p$ and the collision frequency $\gamma_p$). At the low frequency limit ($\omega_p << \gamma_p$), the Drude model can be expressed as a simple conductive model, so this case uses the Perfect electric conductor(PEC) instead of gold.

Simulation results

Reflectivity and transmissivity

According to the T data obtained by the Frequency-Domain Field and Power(FDFP) monitors on the top and bottom of the device, the reflectivity (R) and transmissivity (T) of the structure are plotted as a function of frequency as follows. It can be seen that the resonance frequencies of the metamaterial device are approximately 0.66THz and 1.7THz, which are consistent with the results of the reference as shown in Figure3a.

Electric field distribution and surface current density

The attached script file can be used to plot the electric field distribution and surface current density distribution on the surface of the metamaterial device at a resonance frequency of 0.66THz. To plot the surface current density distribution, you need to click the set icon in the Figure window and configure it as shown in the figure below.

The results are plotted in the figure below. At a resonance frequency of 0.66THz, the electric field is highly concentrated at the split gaps, and there is no significant surface current on the metal lines connecting the metasurface elements.

References

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1. H.-T. Chen et al., "Active terahertz metamaterial devices", Nature 444, 597-600 (2006) ↩︎