Research ArticleMATERIALS SCIENCE

Electrically switchable metadevices via graphene

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Science Advances  05 Jan 2018:
Vol. 4, no. 1, eaao1749
DOI: 10.1126/sciadv.aao1749
  • Fig. 1 Electrically tunable metadevices.

    (A) Schematic representation of the hybrid metamaterial system consisting of SRR capacitively coupled to the graphene electrodes. The capacitive coupling is defined by the SRR-graphene separation, d1. (B) Small-signal equivalent circuit model of the metadevice. SRR is represented by the L, R, and C lump circuit elements; the graphene layer is modeled by the variable sheet resistance, RG, and quantum capacitance, CQ. Cc models the capacitive coupling. (C and D) Spectra of the magnitude and phase of the transmittance (S21) at various bias voltages. The color bar shows the bias voltage. (E and F) The variation of the amplitude and phase of the transmittance with the bias voltage.

  • Fig. 2 Investigating coupling distance dependence (d1) of the metadevice performance.

    (A) Variation of the resonance amplitude (Res. ampl.) with d1 and bias voltage in the forward direction. Although the bias voltage damps the resonance at the damping regimes, it changes the radiation pattern of SRRs without changing its amplitude in the resonance regimes. (B) Resonance amplitude as a function of bias voltage at various d1, extracted from (A). The solid lines represent damping and dash lines represent resonance regimes. (C) Modulation of transmission amplitude at resonance with bias voltage as a function of d1. Modulation is maximum at dc = 2.4 mm. (D) Schematic drawing for the metadevice structure used in finite element simulation together with simulated electric field distribution on SRR at 6- and 0.4-kilohm sheet resistance (Rs) of single-layer graphene at d1 = 2 mm. (E) Simulated variation of resonance amplitude of SRR arrays with d1 for Rs = 6 and 0.4 kilohm. The inset shows calculated resonance amplitude variation with experimentally measured ones. (F) Simulated and measured resonance amplitude modulation as a function of d1. The blue scattered circles are experimentally measured amplitude modulation in decibel scale.

  • Fig. 3 Near-field characterization of the active metadevices.

    (A) Near-field scanning technique to map the local scattering parameter (S21) of the device. Scattering parameter provides the magnitude of the local electric field along the direction of the antenna. (B to D) Spatial map, spectrum, and average resonance amplitude of the local scattering parameter of the metadevices probed by a monopole antenna at different graphene-SRR distances at 0 V. (E to G) Voltage dependence of the spatial map, spectrum, and resonance amplitude of the local scattering parameters of device at d1 = 3 mm.

  • Fig. 4 Electrically reconfigurable, spatially varying digital metamaterials.

    (A) Schematic drawing of a digital metamaterial with individually addressable pixels. Controlling the charge density on individual pixels allows us to reconfigure the local dielectric constant. (B and C) The spectra of the calculated real and imaginary part of the effective dielectric constant of a single pixel under different bias voltages. (D and E) The spatial map of the real part of the effective dielectric constant of the device at the resonance condition for different voltage configurations. The effective dielectric constant of the pixels is controlled by passive matrix addressing.

  • Fig. 5 Frequency-tunable active metadevices.

    (A) Schematic drawing of the designed three-layer frequency-tunable metadevice structure. In a unit cell, two SRRs are coupled to a LR at d2, and a graphene capacitor is coupled to both of them at d1 below the LR layer. (B) Small-signal circuit model to represent the three-layer metadevice. (C) Transmission spectrum showing the resonances of coupled (d2 = 3.5 mm) and uncoupled SRR and LR metasurfaces. (D) Experimentally measured variation in the transmission spectrum of the three-layer metadevice by means of bias voltages applied to graphene capacitor at d1 = 1.35 mm and d2 = 3.50 mm. (E) Transmission spectrum showing the resonance damping of LR-like resonance with bias voltage. (F) Transmission spectrum showing the shift in the frequency of the SRR-like resonance with bias voltages without varying its amplitude.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao1749/DC1

    section S1. Fabrication and characterization of graphene supercapacitors

    section S2. Microwave performance of active metadevices in near-field

    section S3. Electromagnetic modeling and simulation of active metadevices

    section S4. Imaging near-field extinction pattern of a square SRR

    section S5. Electrically reconfigurable, spatially varying digital metamaterials

    section S6. Frequency-tunable active metadevices

    section S7. Performance of active metadevices in far field

    section S8. Microwave performance of various metadevices in near-field

    fig. S1. Image of growth, transfer, and etching processes.

    fig. S2. Characterization of single-layer graphene.

    fig. S3. Large-area graphene supercapacitor and its characterization.

    fig. S4. Fabrication of large-area SRR structures.

    fig. S5. Near-field microwave measurement setup.

    fig. S6. Modulation of resonance amplitude in percent scale.

    fig. S7. Modulation of resonance amplitude in decibel scale.

    fig. S8. Detailed analysis for electrical switching of square SRRs.

    fig. S9. Time response of the metadevices.

    fig. S10. Conductivity of graphene.

    fig. S11. Simulating performance of metadevices working in microwave.

    fig. S12. Simulated transmission spectrum of active metadevices working in microwave.

    fig. S13. Dependence of the resonance amplitude modulation to the period of SRRs in arrays of them in microwave.

    fig. S14. Simulating performance of metadevices working in terahertz.

    fig. S15. Simulating performance of metadevices working in far IR.

    fig. S16. Simulating performance of metadevices working in mid IR.

    fig. S17. Simulating performance of metadevices working in near IR.

    fig. S18. Simulating performance of metadevices working in visible.

    fig. S19. Simulating performance of metadevices in near IR using Au metal with its frequency-dependent n-k constants.

    fig. S20. Simulating performance of metadevices in visible using Au metal with its frequency-dependent n-k constants.

    fig. S21. Dependence of optimum coupling distance to resonance wavelength ratio (Formula) on λr.

    fig. S22. Device structure and experimental setup used for imaging near-field extinction pattern of SRRs.

    fig. S23. Variation of extinction pattern with coupling distance d1 at 0 V.

    fig. S24. Variation of extinction pattern with bias voltage at d1 = 3 mm.

    fig. S25. Variation of extinction pattern with bias voltage at d1 = 3.5 mm.

    fig. S26. Device structure of large-area, pixelated, reconfigurable metadevices.

    fig. S27. Transmission (S21) patterns of pixelated, reconfigurable metadevices obtained by passive matrix addressing.

    fig. S28. Real part of patterned dielectric constant on a large-area metadevice.

    fig. S29. Imaginary part of patterned dielectric constant on a large-area metadevice.

    fig. S30. Voltage response of transmission (S21) and retrieved dielectric constants in pixelated metadevices.

    fig. S31. SRR arrays coupled to LR arrays.

    fig. S32. Finding optimum d1 to achieve maximum shift in resonance frequency of SRRs at d2 = 3.5 mm.

    fig. S33. Transmission spectrums showing the shift in resonance frequency of SRR arrays while damping the resonance amplitude of LRs.

    fig. S34. Coupling two identical SRR arrays.

    fig. S35. Tuning resonance frequency of SRR arrays coupled to its twin.

    fig. S36. Active tuning of magnetic resonance.

    fig. S37. Active tuning of electric resonance excited by a horizontally traveling electromagnetic waves on SRR arrays by graphene supercapacitor.

    fig. S38. Electrically switchable metadevices made of a dense SRR arrays measured in far field.

    fig. S39. Switching transmission amplitude and phase of various type metamaterials coupled to graphene supercapacitors by sweeping bias voltage from 0 to −1.5 V in near-field.

    fig. S40. Switching transmission amplitude and phase of various type metamaterials coupled to graphene supercapacitors by sweeping bias voltage from 0 to −1.5 V measured in near-field.

    fig. S41. Schematic drawings of metamaterials fabricated throughout this work with their dimensions.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Fabrication and characterization of graphene supercapacitors
    • section S2. Microwave performance of active metadevices in near-field
    • section S3. Electromagnetic modeling and simulation of active metadevices
    • section S4. Imaging near-field extinction pattern of a square SRR
    • section S5. Electrically reconfigurable, spatially varying digital metamaterials
    • section S6. Frequency-tunable active metadevices
    • section S7. Performance of active metadevices in far field
    • section S8. Microwave performance of various metadevices in near-field
    • fig. S1. Image of growth, transfer, and etching processes.
    • fig. S2. Characterization of single-layer graphene.
    • fig. S3. Large-area graphene supercapacitor and its characterization.
    • fig. S4. Fabrication of large-area SRR structures.
    • fig. S5. Near-field microwave measurement setup.
    • fig. S6. Modulation of resonance amplitude in percent scale.
    • fig. S7. Modulation of resonance amplitude in decibel scale.
    • fig. S8. Detailed analysis for electrical switching of square SRRs.
    • fig. S9. Time response of the metadevices.
    • fig. S10. Conductivity of graphene.
    • fig. S11. Simulating performance of metadevices working in microwave.
    • fig. S12. Simulated transmission spectrum of active metadevices working in microwave.
    • fig. S13. Dependence of the resonance amplitude modulation to the period of SRRs in arrays of them in microwave.
    • fig. S14. Simulating performance of metadevices working in terahertz.
    • fig. S15. Simulating performance of metadevices working in far IR.
    • fig. S16. Simulating performance of metadevices working in mid IR.
    • fig. S17. Simulating performance of metadevices working in near IR.
    • fig. S18. Simulating performance of metadevices working in visible.
    • fig. S19. Simulating performance of metadevices in near IR using Au metal with its frequency-dependent n-k constants.
    • fig. S20. Simulating performance of metadevices in visible using Au metal with its frequency-dependent n-k constants.
    • fig. S21. Dependence of optimum coupling distance to resonance wavelength ratio (d1opt.r) on λr.
    • fig. S22. Device structure and experimental setup used for imaging near-field extinction pattern of SRRs.
    • fig. S23. Variation of extinction pattern with coupling distance d1 at 0 V.
    • fig. S24. Variation of extinction pattern with bias voltage at d1 = 3 mm.
    • fig. S25. Variation of extinction pattern with bias voltage at d1 = 3.5 mm.
    • fig. S26. Device structure of large-area, pixelated, reconfigurable metadevices.
    • fig. S27. Transmission (S21) patterns of pixelated, reconfigurable metadevices obtained by passive matrix addressing.
    • fig. S28. Real part of patterned dielectric constant on a large-area metadevice.
    • fig. S29. Imaginary part of patterned dielectric constant on a large-area metadevice.
    • fig. S30. Voltage response of transmission (S21) and retrieved dielectric constants in pixelated metadevices.
    • fig. S31. SRR arrays coupled to LR arrays.
    • fig. S32. Finding optimum d1 to achieve maximum shift in resonance frequency of SRRs at d2 = 3.5 mm.
    • fig. S33. Transmission spectrums showing the shift in resonance frequency of SRR arrays while damping the resonance amplitude of LRs.
    • fig. S34. Coupling two identical SRR arrays.
    • fig. S35. Tuning resonance frequency of SRR arrays coupled to its twin.
    • fig. S36. Active tuning of magnetic resonance.
    • fig. S37. Active tuning of electric resonance excited by a horizontally traveling electromagnetic waves on SRR arrays by graphene supercapacitor.
    • fig. S38. Electrically switchable metadevices made of a dense SRR arrays measured in far field.
    • fig. S39. Switching transmission amplitude and phase of various type metamaterials coupled to graphene supercapacitors by sweeping bias voltage from 0 to −1.5 V in near-field.
    • fig. S40. Switching transmission amplitude and phase of various type metamaterials coupled to graphene supercapacitors by sweeping bias voltage from 0 to −1.5 V measured in near-field.
    • fig. S41. Schematic drawings of metamaterials fabricated throughout this work with their dimensions.

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