Abstract
Combined with experimental and simulated results, the resonances and metamaterial-induced transparency have been theoretically investigated using the Lorentz oscillator model for terahertz metamaterials with unequal-length bar structures. The bar spacing has an impact on the spectral evolution, implying that the coupling between metal bars varies correspondingly in one unit cell and the adjacent cells. Different from the evidence that the strongest coupling occurs in double bar structures when the bar spacing is uniform in the entire sample, the coupling in 3 bar structures is more complicated due to the weakened coupling with the middle bar and increased coupling between the other 2 bars by further increasing the bar spacing. The dependence of calculated transmission spectra on the damping rate and coupling coefficient is demonstrated, showing that the fitting parameters could control and tune the resonant dips, the transparency peaks, and even the quality factors of the spectra regularly. Furthermore, the sensing properties have been investigated by simulating the spectral evolution with the overlayers of different refractive indices to optimize the sensing parameters. Our obtained results could advance the understanding of resonance coupling and offer the possibility to further study the modulation and biosensing in the coupled terahertz devices.
Highlights
Engineered materials, usually known as metamaterials, have exhibited novel electromagnetic phenomena which do not exist in natural materials, such as negative refractive index [1, 2], electromagnetic cloaking [3,4,5,6], sensing [7, 8], and near-perfect absorption [9, 10]
The relationships between γ and the full width half maximum (FWHM) of the resonant dips for M1, M2, and M3 are plotted in Figure 2C, showing the FWHM increases with γ and will saturate by further increasing the damping rate
We systematically investigated and analyzed the Lorentz oscillator model from a single resonator to three resonators combined with the experiment and simulation to explore the underlying coupling mechanism, especially the influence of the spacing between bars on the spectral evolution in the double-bar and 3-bar structures
Summary
Engineered materials, usually known as metamaterials, have exhibited novel electromagnetic phenomena which do not exist in natural materials, such as negative refractive index [1, 2], electromagnetic cloaking [3,4,5,6], sensing [7, 8], and near-perfect absorption [9, 10]. Where x is the displacement of the oscillator, ω0 is the natural frequency of the oscillator, γ is the damping rate, and g is the geometric parameter indicating the strength of each oscillator coupled to the incident field and related to effective charges and effective masses. If another oscillator is added in this system, we can obtain the dynamics of a pair of oscillators coupled under the incident field termed as the bright–bright mode. Frequencydependent THz transmission spectra of our designed structures can be obtained from the aforementioned formula
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