Article

Effect of metal permittivity on resonant properties of terahertz metamaterials

School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Optics Letters (Impact Factor: 3.29). 08/2008; 33(13):1506-8. DOI: 10.1364/OL.33.001506
Source: PubMed

ABSTRACT

We investigate the effect of metal permittivity on resonant transmission of metamaterials by terahertz time-domain spectroscopy. Our experimental results on double split-ring resonators made from different metals confirm the recent numerical simulations [Phys. Rev. E 65, 036622 (2002)] that metamaterials exhibit permittivity-dependent resonant properties. In the terahertz regime, the measured inductive-capacitive resonance is found to strengthen with a higher ratio of the real to the imaginary parts of metal permittivity, and this remains consistent at various metal thicknesses. Furthermore, we found that metamaterials made even from a generally poor metal become highly resonant owing to a drastic increase in the value of the permittivity at terahertz frequencies.

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Available from: Ranjan Singh
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    • "Characterizing the structure responses has been made easier because of the well-known properties of the embedded metallic (e.g., Cu, Au) designs. In the THz regime, Singh and his colleagues have studied the material characteristics extensively [10– 16], including optically thin metamaterials [10], effects on resonance due to (i) material permittivity [11] and (ii) nearest neighbor interactions [13]. Metamaterials in the THz regime are of interest because of their applications [17]. "
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    ABSTRACT: The concept of a single frequency band, single high-refractive-index metamaterial has been extended and applied in the design of dual frequency band, dual high-refractive-index metamaterials in the THz regime. The structure design consists of twenty five unit cells with a surface area of 250 um by 250 um and a thickness of 5 um. Each cell has metallic structures embedded in a polyimide substrate. The return loss (S-parameter) analysis shows two strong electric responses at two frequency ranges, and the extracted constitutive parameters suggested high values of simultaneous dielectric constant and permeability at these frequencies. Results retrieved from the S-parameters also show high refractive index values. A first peak refractive index of 61.83 was observed at a resonant frequency of 0.384 THz, and another peak refractive index of 19.2 was observed at the resonant frequency 1.416 THz. Analysis show that higher refractive index at the second resonance frequency band is achievable through redesign of the structures, and modifications could lead to a single structure with multiple frequency, multiple high-refractive-index metamaterials that can be put to practical use.
    Full-text · Article · Aug 2012 · Physics Research International
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    • "It has been shown that metal conductivity as well as thickness can affect metamaterial resonance [25] [26], though such tunability is through design and fabrication. Noble metals are still the choice for fabricating metamaterial structures because of their high conductivity, which, however, makes the resonance tuning rely on the integration of additional materials able to respond to external stimuli. "
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    ABSTRACT: Through the integration of semiconductors or complex oxides into metal resonators, tunable metamaterials have been achieved by a change of environment using an external stimulus. Metals provide high conductivity to realize a strong resonant response in metamaterials; however, they contribute very little to the tunability. The complex conductivity in high-temperature superconducting films is highly sensitive to external perturbations, which provides new opportunities in achieving tunable metamaterials resulting directly from the resonant elements. Here we demonstrate ultrafast dynamical tuning of resonance in the terahertz (THz) frequency range in YBa_2Cu_3O_7-\delta (YBCO) split-ring resonator arrays excited by near-infrared femtosecond laser pulses. The photoexcitation breaks the superconducting Cooper pairs to create the quasiparticle state. This dramatically modifies the imaginary part of the complex conductivity and consequently the metamaterial resonance in an ultrafast timescale. We observed resonance switching accompanied with a wide range frequency tuning as a function of photoexcitation fluence, which also strongly depend on the nano-scale thickness of the superconducting films. All of our experimental results are well reproduced through calculations using an analytical model, which takes into account the SRR resistance and kinetic inductance contributed from the complex conductivity of YBCO films. The theoretical calculations reveal that the increasing SRR resistance upon increasing photoexcitation fluence is responsible for the reduction of resonance strength, and both the resistance and kinetic inductance contribute to the tuning of resonance frequency.
    Full-text · Article · Nov 2011
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    • "The incident angle is fixed at . The Drude permittivity of metals at terahertz frequencies can be approximated by [10], where is the dc conductivity, is the damping rate and is the vacuum permittivity. Here we have assumed S/m and s , which are typical values for silver [11]. "
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    ABSTRACT: Enhanced transmission through metallic gratings with narrow slits is a well-known phenomenon for TM polarized waves at optical and microwave frequencies. A similar though fundamentally different phenomenon, i.e., enhanced reflection at terahertz frequencies, is reported here for the geometrical complement of the structure with narrow slits. The latter phenom- enon cannot be related to the former by Babinet's principle, as their origin is quite different, and both are observed for the same polarization. This phenomenon is explored by studying the field profiles within the grating, and is attributed to the presence of TM cavity modes at specific frequencies. A simple formula is given to anticipate the frequencies at which the anomalies appear. The accuracy of this formula is verified by using a rigorous numerical approach. Index Terms—Metallic grating, enhanced reflection, enhanced transmission.
    Full-text · Article · Nov 2011 · IEEE Transactions on Terahertz Science and Technology
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