Metamaterials - Concept and Applications

1
Metamaterials - Concept and Applications

• Dr Vesna Crnojevic-Bengin
• Faculty of Technical Sciences
• University of Novi Sad

• March 2006

2
Overview

• Microwave passive circuits
• Metamaterials
• Definition
• Examples
• LH metamaterials
• Idea
• Phenomena
• Realization
• LH microstrip structures
• Resonant and non-resonant structures
• Applications

3
Microwave Passive Circuits

• Rationale

4
Problem

• Dimensions ? Performances
• End-coupled ms resonator
• Antennas narrow beam with only one source
  element?
• Classical theory large source
• Metamaterials ENZ substrate

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Antenna on ENZ Substrate
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Metamaterials

• Characteristics
• Definition
• Types
• Examples

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Material Characteristics

• Rel. permitivity er
• Rel. permeability µr
• Rel. index of refraction
• Rel. characteristic impedance

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Extreme values of er and µr

• Metamaterials
• EVL Epsilon Very Large
• ENZ Epsilon Near Zero
• MVL Mu Very Large
• MNZ Mu Near Zero
• MENZ Mu and Epsilon Near Zero
• HIMP High Impedance
• LIMP Low Impedance
• HIND High Index
• LIND Low Index

µr
er
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Definition

• Metamaterials are artificial structures that
  exhibit extreme values of effective er i µr.

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Example HIMP and LIMP
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Metamaterials Do Not Exist

• Artificial materials
• Periodic structures
• Period much smaller then ?
• ? Homogenization of the structure
• ? Effective values of er and µr

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Examples of Metamaterials
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Left-Handed MM

• First Ideas
• Development
• Realization
• Applications

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Other Quadrants?

• Single-negative MM erlt0 or µrlt0

µr
evanescent mode (plasma,metals_at_THz)
propagation mode (isotropic dielectrics)
er
evanescent mode (ferrites)
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Veselagos Intuition

• Double-negative MM erlt0 and µrlt0 ?

µr
propagation mode (isotropic dielectrics)
evanescent mode (plasma,metals_at_THz)
er
evanescent mode (ferrites)
?
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Conditions of Existence

• No law of physics prevents the existence of DN MM
• Generalized entropy conditions for dispersive
  media must be satisfied ( )

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Veselagos Conclusions

• Propagation constant ß is real negative
• ? Propagation mode exists
• ? Antiparalel group and phase velocities
• ? Backward propagation (Left-hand rule)
• ? Negative index of refraction

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Synonyms

• Double-Negative (DN)
• Left-Handed (LH)
• Negative Refraction Index (NRI)
• (Metamaterials)

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Left-Handed Metamaterials

• Double-negative MM erlt0 and µrlt0

µr
propagation mode (isotropic dielectrics)
evanescent mode (plasma,metals_at_THz)
er
propagation mode (Left-Handed MM)
evanescent mode (ferrites)
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Apparent Paradox

• Group velocity increases with frequency
• ? superluminal propagation ?!?
• Explanation
• LH MM is a dispersive media, where
• Pulse can be superluminally propagated
• Group velocity does not bear a well defined
  physical meaning
• Velocity relevant to energy propagation is not
  group velocity but front velocity, always
  smaller then c

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Consequences of LH MM

• Phenomena of classical physics are reversed
• Doppler effect
• Vavilov-Cerenkov radiation
• Snells law
• Lensing effect
• Goss-Henchens effect

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Snells Law

• !!!

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Lenses

• Direct consequence of reversed Snells law

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But Alas...

• Everything so far was what if...
• Can single- or double-negative materials really
  be made?

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First SN MM J. B. Pendry

• erlt0 - 1996. µrlt0 - 1999.

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Why is ?r negative?

• Plasmons phenomena of excitation in metals
• Resonance of electron gas (plasma)
• Plasmon produces a dielectric function of the
  form
• Typically, fp is in the UV-range
• Pendry fp8.2GHz

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Why is µr negative?
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Experimental Validation

• Smith, Shultz, et al. 2000.

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LH MS Structures

• Resonant and non-resonant structures
• Applications

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Resonant LH Structures

• Split Ring Resonator (SRR)
• ? Very narrow LH-range
• ? Small attenuation
• Many applications, papers, patents
• Super-compact ultra-wideband (narrowband) band
  pass filters
• Ferran Martin, Univ. Autonoma de Barcelona

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Wide Stopband

• Garcia-Garcia et al, IEEE Trans. MTT, juni
  2005.

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Complementary SRR

• Application of Babinet principle - 2004.
• CSRR gives e0

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LH BPF CSRR / Gap

• November 2004.
• Gaps contribute to µ0
• Low attenuation in the right stopband

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BPF CSRR / Stub

• August 2005.
• 90 BW
• Not LH!!!

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Three Elements

• CSRR/Gap steep left side
• CSRR/Stub steep right side
• 2 BW

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Multiple SRRs and Spirals

• Crnojevic-Bengin et al, 2006.

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Fractal SRRs

• Crnojevic-Bengin et al, 2006.

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Non-Resonant LH Structures

• June 2002.
• Eleftheriades
• Caloz Itoh
• Oliner
• Transmission Line (TL) approach
• Novel characteristics
• Wide LH-range
• Decreased losses

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Conventional (RH) TL

• Microstrip

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LH TL

• Dual structure

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A Very Simple Proof

• Analogy between solutions of the Maxwells
  equations for homogenous media and waves
  propagating on an LH TL
• Materials LH TL

!!!
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Microstrip Implementation

• Unit cell

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Dispersion Diagrams
RH TL LH TL
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Is This Structure Purely LH?

• Unit cell

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CRLH TL

• Real case RH contribution always exists

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LH TL Characteristics

• Wide LH-range

Caloz, Itoh, IEEE AP-S i USNC/URSI Meeting, juni
2002.
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2-D LH Metamaterials
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Applications of LH MM

• Guided wave applications
• Filters
• Radiated wave applications
• Antennas
• Refracted wave applications
• Lenses

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Guided Wave Applications

• Dual-band and enhanced-bandwidth components
• Couplers, phase shifters, power dividers, mixers)
• Arbitrary coupling-level impedance/phase couplers
  
• Multilayer super-compact structures
• Zeroth-order resonators with constant field
  distribution
• Lai, Caloz, Itoh, IEEE Microwave Magazin, sept.
  2004.

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Dual-Band CRLH Devices

• Second operating frequency
• Odd-harmonic - conventional dual-band devices
• Arbitrary - dual-band systems
• Phase-response curve of the CRLH TL
• DC offset additional degree of freedom
• ? Arbitrary pair of frequencies for dual-band
  operation
• Applications
• Phase shifters,
• matching networks,
• baluns, etc.

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Dual-Band BLC Lin, Caloz, Itoh, IMS03.

• Conventional BLC operates at f and 3f
• RH TL replaced by CRLH TL
• ? arbitrary second passband

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CµS/CRLH DC Caloz, Itoh, MWCL, 2004.

• Conventional DC
• ? broad bandwidth (gt25)
• ? loose coupling levels (lt-10dB)
• CRLH DC
• ? 53 bandwidth
• ? coupling level -0.7dB

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ZOR Sanada, Caloz, Itoh, APMC 2003.

• Operates at ß0
• Resonance independent of the length
• Q-factor independent of the number of unit cells

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SSSR Crnojevic-Bengin, 2005.

• LZOR?/5
• LSSSR?/16
• Easier fabrication
• More robust to small changes of dimensions

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Radiated Wave Applications

• 1-D i 2-D LW antennas and reflectors
• ZOR antenna, 2004. - reduced dimensions
• Backfire-to-Endfire LW Antenna
• Electronically controlled LW antenna
• CRLH antenna feeding network

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Backfire-to-Endfire LW Antena

• Operates at its fundamental mode
• Less complex and more-efficient feeding structure
• Continuous scanning from backward (backfire) to
  forward (endfire) angles
• Able to radiate broadside

• Liu, Caloz, Itoh, Electron. Lett., 2000.

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Electronically Controlled LW Antenna

• Frequency-independent LW antenna
• Capable of continuous scanning and beamwidth
  control
• Unit cell
• CRLH with varactor diode
• ß depends on diode voltage

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Antenna Feeding Network
Itoh et al, EuMC 2005.
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Refracted Wave Applications

• Most promising
• Not much investigated - 2-D, 3-D
• Negative focusing at an RHLH interface
• Anisotropic metasurfaces
• Parabolic refractors...

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Current Research...

• Subwavelength focusing
• Grbic, Eleftheriades, 2003, (Pendry 2000)
• NRI lense with er-1 and µr-1 achieves focusing
  at an area smaller then ?2
• Anisotropic CRLH metamaterials
• Caloz, Itoh, 2003.
• PRI in one direction, NRI in the orthogonal
• Polarization selective antennas/reflectors

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Future Applications

• Miniaturized devices based ZOR
• MM beam-forming structures
• Nonlinear MM devices for generation of ultrashort
  pulses for UWB systems
• Active MM - dual-band matching networks for PA,
  high-gain bandwidth distributed PA, distributed
  mixers
• Refracted-wave structures compact flat lenses,
  near-field high-resolution imaging, exotic
  waveguides
• SN MM ultrathin waveguides, flexible
  single-mode thick fibers, very thin cavity
  resonators
• Terahertz MMs medical applications
• Natural LH MM currently not known to exist
• SF MM - chemists, physicists, biologists, and
  engineers tailor materials missing in nature

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Main Challenges

• Wideband 3-D isotropic LH meta-structure

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Main Challenges

• Development of fabrication technologies(LTCC,
  MMIC, nanotechnologies)
• Development of nonmetallic LH structures for
  applications at optical frequencies
• Miniaturization of the unit cell
• Development of efficient numerical tools

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Conclusion

• LH materials one of the top ten scientific
  breakthroughs of 2003.
• Science, vol.302, no.5653, 2004.
• MMs have a huge potential and may represent one
  of the leading edges of tomorrows technology in
  high-frequency electronics.
• Proc. of the IEEE, vol.93, no.10, Oct.2005.