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Research Papers

Tunable Negative Refractive Index Metamaterials Based on Thermochromic Oxides

[+] Author and Article Information
Yimin Xuan

School of Energy and Power Engineering,
Nanjing University of Aeronautics and Astronautics,
Nanjing 210016, China;
School of Energy and Power Engineering,
Nanjing University of Science and Technology,
Nanjing 210094, China

Qiang Li

School of Energy and Power Engineering,
Nanjing University of Science and Technology,
Nanjing 210094, China

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received March 18, 2012; final manuscript received December 11, 2012; published online July 26, 2013. Assoc. Editor: Zhuomin Zhang.

J. Heat Transfer 135(9), 091502 (Jul 26, 2013) (6 pages) Paper No: HT-12-1120; doi: 10.1115/1.4024459 History: Received March 18, 2012; Revised December 11, 2012

A tunable metamaterial is proposed by combining a thermochromic oxide with a fishnet structure. The reflection and transmission coefficients are calculated by finite-difference time-domain (FDTD) method. The effective electromagnetic parameters of the metamaterial are retrieved on the basis of these data. The results reveal that an effective negative refractive index is obtained by this proposed structure and the wavelength region with negative refractive index can be self-regulated by simply tuning the temperature, which is of importance to extend the applications of negative refractive index materials. The effects of structural sizes on the negative refractive index are discussed. The size-dependence indicates that the wavelength range in which the apparent refractive index is negative can be tuned to be located at the desired position by dexterously tailoring the structural parameters.

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Figures

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Fig. 1

Schematic diagram of (a) a slab and (b) a unit cell of a metamaterial structure with square arrays of apertures. The periodic structure has a lattice period of a and aperture radius of r. The thicknesses of LSMO, MgF2, and Ag are dLSMO, dMgF2, and dAg, respectively.

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Fig. 7

The real part of effective refractive index for dMgF2 = 0.05 μm (solid line), 0.1 μm (dashed line) and 0.2 μm (dotted line)

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Fig. 5

The real part of effective refractive index for different film thickness of LSMO: dLSMO = 0.05 μm (solid line), 0.1 μm (dashed line), and 0.2 μm (dotted line)

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Fig. 3

The magnitude (a), phases (b), and transformed phases, and (c) of reflection and transmission coefficients for temperature of 250 K (left) and 295 K (right). |S11| and |S21| are the magnitudes of reflection and transmission coefficients, ϕ11 and ϕ21 are the phases of reflection and transmission coefficients.

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Fig. 2

Schematic diagram of collecting surfaces for the reflected and transmitted electromagnetic fields

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Fig. 6

The magnitude of reflection and transmission coefficients (a) and the real part of its effective refractive index (b). The inset is the schematic diagram of the metamaterial with hexagonal arrays of apertures.

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Fig. 4

The retrieved effective parameters of the metamaterial: effective values of permittivity ɛ (a), permeability μ (b), impedance Z (c), ɛ1μ2+ɛ2μ1 (d), and refractive index n (e) for temperature of 250 K (left) and 295 K (right). ɛ1 and ɛ2 are the real and imaginary part of permittivity, μ1 and μ2 are the real and imaginary part of permeability.

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