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Meta-Materials for High Frequency Applications

Meta-Materials for High Frequency Applications. Hao Xin September 27 th , 2007. H. Xin. U. Arizona - Low Energy Physics Seminar. Outline. -. Introduction Two-dimensional tunable electromagnetic crystals Antenna in low refractive index medium Thermal emission control Summary.

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Meta-Materials for High Frequency Applications

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  1. Meta-Materials for High Frequency Applications Hao Xin September 27th, 2007 H. Xin U. Arizona - Low Energy Physics Seminar

  2. Outline - • Introduction • Two-dimensional tunable electromagnetic crystals • Antenna in low refractive index medium • Thermal emission control • Summary

  3. What is Meta-Materials - Artificial composite materials that have special properties (electromagnetic here) that may or may not exist for natural materials Double Negative Materials Left-Handed Materials Negative Refractive Index* Electromagnetic / Photonic Crystal Band Gap Structure Often due to inhomogenities embedded in host media Periodic media or effective media description Not limited to EM properties * R. A. Shelby et al., Science, Vol 292, p. 77, 2001; R. W. Ziolkowski and N. Engheta, IEEE Trans. Antennas & Propagation, Vol. 51, p. 2546, 2003

  4. Brief History - • Concept existed long time ago – resurrected recently * • In 1898, J. C. Bose: rotation of polarization plane by man made twisted structures • In 1914, K. F. Lindman: small wire helix • In 50 – 60’s, artificial dielectrics • Many periodic structures have been studied • Left-handed media / Negative index of refraction • In 1968, Veselago considered  < 0, µ < 0 media • Poynting vector opposite of phase velocity, n < 0 • In 2000, Smith et al demonstrated first example • Electromagnetic crystal / band gap structures • In 1887, multi-layer film studied by Lord. Rayleigh • In 1987, Yablonovich & Johns independently suggested 2-D & 3-D band gaps R. W. Ziolkowski and N. Engheta, IEEE Trans. Antennas & Propagation, Vol 51, p. 2546, 2003

  5. Permittivity and Permeability Space -

  6. Many Applications with Designed , µ 2Electrically Small Antennas 1Perfect Lens n = -1 3,4Cloaking - 1. J. B. Pendry, PRL, Vol. 85, p. 3966, 2000; 2. R. W. Ziolkowski and N. Engheta, IEEE Trans. Antennas & Propagation, Vol 51, p. 2546, 2003 3. J. B. Pendry et al, Science, Vol. 312, p. 1780, 2006; 4. A. Alu and N. Engheta, Optics Express, Vol. 15, p. 3318, 2007

  7. Outline - • Introduction • Two-dimensional tunable electromagnetic crystals • Antenna in low refractive index medium • Thermal emission control • Summary

  8. Electromagnetic Crystal (EMXT) - *Sievenpiper surface 1-D Dielectric Layers 2-D Dielectric Rods • Periodic dielectric structures: photonic crystal (PXT) • Forbid EM wave propagation – band gap • Metal – dielectric structures for microwave and millimeter wave applications Metal – Dielectric Structures * Sievepiper et al, IEEE Trans. on Microwave Theory & Tech., Vol. 47, p. 2059

  9. Two-Dimensional EM Crystal Surface - * Sievepiper et al, IEEE Trans. on Microwave Theory & Tech., Vol. 47, p. 2059

  10. EMXT as Impedance Surfaces(Artificial Magnetic Conductor) - • Resonant frequency fres (band gap center) • Frequency dependent effective surface impedance • f = fres, high impedance (0o reflection phase) • f < fres, inductive • f > fres, capacitive • Tuning mechanism allows controllable EM boundary condition Edge to Edge Capacitance Substrate Inductance

  11. Unique Properties of EMXT Surfaces In phase reflection Within band gap, no current can flow I -

  12. Possible Applications y E H x z j E Field H Field Current Tunable EMXT - • Antenna Ground Planes • Low-profile antennas • Mutual coupling reduction • Smaller ground plane • EM surfaces: TEM waveguide • Quasi-optical systems • Tunable EMXT – Arbitrary EM boundary condition achieved • Phase shifters / phased arrays • Filters / Switches • Circular / Linear Polarizers Flush mounted Monopoles TEM Waveguide Waveguide Phase Shifter

  13. Bias Bar Tunable EMXT Surface - InP Quantum-Barrier Varactor EMXT Unit Cell of a Tunable EMXT • Design for effective surface impedance: ZS(f,,V) • - Waveguide modes simulated • Design optimization: trade-off between loss and tuning • 30 – 50 GHz fres measured with 0 – 12 V bias • - Useful TEM operation bandwidth 25 – 50 GHz

  14. Measured GaAs Schottky Diode Peformance - • RF characterization up to 50 GHz • CPW test structures • Much better performance compare to InP HBV • Three fold increase of cutoff frequency • Much lower EMXT loss measured • GaAs process: easier packaging

  15. Lower Level Metal Higher Level Metal MEMS Varactors - MEMS-Tuned EMXT Photo Surface Profile • Advantages: • Extremely low loss • Micro-second tuning time • Simulation shows good tunability • Much cheaper to produce than varactor • Reliability and yield

  16. EMXT Under Test Tunable Band Gap Demonstrated - • Reflection measurement to determine center of band gap • Band gap can be tuned within nano-seconds from 30 to 50 GHz

  17. Waveguides Using EMXT Surfaces TEM Waveguide Metallic Waveguide y E H x z j E Field H Field Current Tunable EMXT - • Normal metallic rectangular waveguide • Sinusoidal electric field distribution / fixed propagation • Cutoff behavior • EMXT surface replace metallic waveguide walls • Any desired boundary conditions possible • Real time control of propagation can be achieved

  18. • Analog tuning • Fast • Low Cost • New phased array architecture • Average loss 6.5 dB measured ‘Beta’’ rad/cm InP Hetereo-Barrier Varactor EMXT Waveguide Phase Shifter 38 GHz Tunable EMXT Example – Phase Shifter - Effective phase control by tuning the waveguide EM boundary conditions

  19. Phased Array Antenna EMXT sidewalls 30 25 20 15 10 5 0 5 10 15 20 25 30 ... 2β β 0 Bias controls -

  20. 20-mm EMXT Other Components – Filters / Switches - Tunable Band-Stop Filter Tunable Band-Pass Filter Shutter Switch

  21. Outline - • Introduction • Two-dimensional tunable electromagnetic crystals • Antenna in low refractive index medium • Thermal emission control • Summary

  22. Near zero index media Source Low Refractive Index Media • Wavefront transformer 1 • Highly directive beam ³ • Waveguide tunneling2 Longer wavelength • Zero phase delay lines 4 • Relaxed tolerance in nano-scale fabrication *1 Andrea Alù, “Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern”, Phys. Rev. E, 75, 155410, 2007 *2 Ma´rio Silveirinha, “Tunneling of Electromagnetic Energy through Subwavelength Channels and Bends using ε-Near-Zero Materials”, Phys. Rev. Lett., 97,157403 (2006) *3 S. Enoch, “A Metamaterial for Direct Emission”, Phys. Rev. Lett., 76, pp. 213902, Nov. 2002 *4 R. W. Ziolkowski, “Propagation in and scattering from a matched metamaterial having a zero index of refraction,” Phys. Rev. E, 70, pp. 046608, 2004

  23. z x y a a 2r Simple Effective Low-Index Medium - Wire Array • 2D or 3D metallic wire array works as effective low-index media • Can be treated using plasma theory for free electrons with reduced density

  24. Simple Effective Low-Index Medium - Wire Array Host medium permittivity Host medium permittivity ۪=1 Host medium permittivity ۪=1 Host medium permittivity ۪=1 Decompose When • Effective  of wire array close to 0 around plasma frequency

  25. Plasma Theory – Self Consistency - • Plasma theory is self-consistent • The wire array can be used as effective medium

  26. Free space n2< 1 medium Free space Free space Free space Antenna Embedded in n < 1 medium - Beam Narrowing Effect Snell’s Law: n1 sinθ1 = sinθ1= n2 sinθ2, if n2 < 1, θ1 < θ2

  27. Effective  and µ of Wire Array µ=n*z =n/z • Similar trend for calculated and extracted  • Deviation due to finite wire radius • Apparent magnetic response above 30 GHz due to Bragg reflections (EM crystal effects)

  28. Monopole antenna z y x Monopole Antenna in Wire Medium • Monopole antenna embedded in n < 1 wire media to test the beam narrowing effect • Expect focused beam in x-y plane

  29. Experimental Result – Return Loss • Reasonable agreement between measurement and simulation • Multiple resonances seen – more complicated than simple effective medium theory predicts

  30. Experimental Result – Radiation Pattern Beam Width at 9.5 GHz n = 0.42 2θ1 = 2sin-1[n1 /(n2 sin θ2)] = 2sin-1[1 /(0.42×sin 45◦)] = 34.6◦ • Radiation pattern agrees excellently • Consistent with Snell’s law: measured and simulated beam widths are 34◦ and 37◦

  31. Self-assembled periodic nano-structures Future Work - • Loss and bandwidth are critical issues for some applications • Active material / device to compensate (Gain) • Higher frequency: THz & up • Self-assembled nano-fabrication • Practical applications • Enhanced sensors

  32. Summary - • Meta-materials have very interesting properties • Several interesting examples New components New methods for designing and understanding • 2-D tunable EMXT • Large band gap tuning; new waveguide components • Low-index antenna • Thermal emission control via 3-D EMXT

  33. Acknowledgement - Rongguo Zhou Ziran Wu T-C Chen Lu Wang Dr. Bruce Zhang A. Young Prof. R. Ziolkowski Prof. M. Kim Dr. A. Higgins Dr. H. Kazemi Dr. M. Rosker Prof. C. Walker DARPA, ARO, Teledyne Scientific Company, Raytheon

  34. Outline - • Introduction • Two-dimensional tunable electromagnetic crystals • Antenna in low refractive index medium • Thermal emission control • Summary

  35. Idea: EM Band Gap Material as Radiation Source • Radiation suppressed within EM crystal band gap • Photon Density of States peak at specific frequencies --- Emission enhancement • Low cost, efficient, and compactthermal THz source • Advanced band gap engineering --- Tunable sources and signature control • Similar effects observed at Infrared region

  36. Theoretical Principles To the first order, photon density of states decides thermal radiation power intensity directly EM crystal Modified DOS, therefore modified thermal radiation Peak EnergyShift Gap Normal Blackbody radiation

  37. Silicon Woodpile Blackbody EM Crystal Example: Silicon Woodpile Structure (WPS) • Woodpile thermal radiation intensity calculated • Energy gap around 200GHz • Sharp peak around 300GHz • Up to 9 times higher emission achievable Silicon rod width w, height D/4 The crystal has a FCT lattice

  38. EM Crystal Example: Tungsten Woodpile Structure Metallic structure can be easily heated by electric current --- Higher temperature and more power emitted • Tungsten woodpile with band gap around 475GHz designed • Photon DOS calculated with HFSS • Up to factor of 5 enhancement available Enhancement = EM crystal emission / normal blackbody emission

  39. EM Crystal Fabrication Silicon woodpile chosen as preliminary case study because of its simple and robust mechanical fabrication process A series of grooves were cut into both the front and back faces of Silicon wafer. Each wafer made up one half of the woodpile structure unit cell . Assembly done by stacking wafers together with the help of pre-registered alignment marks

  40. EBG Sample Characterization • A 18-layer Silicon woodpile sample is fabricated and characterized by independent methods • Vector network analyzer, Fourier transform spectroscopy, and time-domain THz spectroscopy results agree with simulation • Confirmed band gap at 200 GHz • The design, simulation and fabrication processes verified

  41. Emission Measurement Setup • Fourier Transform Spectrometer with 4.5GHz resolution • Silicon woodpile and blackbody samples as radiation source • Precise sample temperature control • Liquid Helium cooled bolometer detector • Optical chopper and lock-in amplifier applied to increase S/N

  42. Experimental Results: Calibration Run • Calibration run is taken with the unmounted heating stage at 61℃ • Good spectrum repeatability • Most expected atmospheric absorption lines are resolved • Beam splitter nulls every 500GHz are observed 150-400GHz signal is small due to FTS and bolometer interior beam optics

  43. Experimental Data Calibration Sample emission + Sample reflection + Sample transmission + Aperture signal - Chopper signal = BB: blackbody, SUR: surroundings, HE: heating element, RT: room temperature Calibrated Data

  44. Comparison of WPS and Blackbody Emission • Averaged data of three runs • Indication of band gap • Enhancement at certain frequencies

  45. Similar Results at Other Temperatures

  46. Advanced Band Engineering: Metallic Cavity Array • Narrow band peak possible: sharpness and peak value depends on box size variations (conservatively assumed a 1% dimension tolerance) • Thermal source power estimation at room temperature: 100 cm2 emission area, enhancement factor of 1000, at 1 THz with 10 GHz bandwidth, 30 mW of total power

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