modelado de metamateriales para aplicaciones en...
TRANSCRIPT
ModeladoModelado de de MetamaterialesMetamateriales paraparaAplicacionesAplicaciones en en AntenasAntenas
Raj MittraElectromagnetic Communication Laboratory
Penn State UniversityE-mail: [email protected]
TITLES, TITLESTITLES, TITLES——POSSIBLE POSSIBLE CHOICESCHOICES
META 101ALL YOU WANTED TO KNOW ABOUT
METAMATERIALS BUT WERE AFRAID TO ASKWHAT’S NEW ABOUT METAMATERIALSMETAMATERIALS—THE HOLY GRAIL!METAMATERIAL MODELING FOR ANTENNAS
FINALLY, WE SETTLE ON:
A CASE FOR METAMATERIAL MODELING
CLASSIFICATON OF METAMATERILS
Loughborough Antennas and Propagation Conference – 2006 F. Bilotti – Potential Applications of Matamaterials in Antennas
εRe[ ]
μRe[ ]
DPS∈ℜk
DNG∈ℜk
ENG
k ∈ℑMNG
∈ℑkMNZMNZ
ENZ
ENZ
RegularDielectricsDPS
Taxonomy of Metamaterials
Double Negative (DNG) materials (Periodicity d << λ)
Elements and distances between them are much smaller than a wavelength (Effective medium concepts, simultaneous effective negative permittivity and permeability)
Have several names including left-handed materials, backward-wave materials, Negative Index of Refraction (NIR) materials, etc.
Electromagnetic Band Gap (EBG) materials (Periodicity d ~ λ)
Element Distances are on the order of half a wavelength or more (Periodic medium concepts)
Photonic crystals, Photonic Band Gap materials (PBG), Artificial Magnetic Conductors (AMC), High Impedance Surfaces (HIS)
Electromagnetic Communication Lab
Acknowledgement:
The viewgraphs 5-22 are from Prof. Yang Haoof Queen Mary College, University of London
In a paper published in 2001, Rodger Walser from the University of Texas, Austin, coined the term 'metamaterial' to refer to artificial composites that '...achieve material performance beyond the limitations of conventional composites.' The definition was subsequently expanded by Valerie Browning and Stu Wolf of DARPA (Defense Advanced Research Projects Agency) in the context of the DARPA Metamaterials program that started also in 2001. Their basic definition:– Metamaterials are a new class of ordered composites that
exhibit exceptional properties not readily observed in nature. These properties arise from qualitatively new response functions that are: (1) not observed in the constituent materials and (2) result from the inclusion of artificially fabricated, extrinsic, low dimensional inhomogeneities.
Periodic Structures in Nature and Daily Life
A bending light under the conservatory roof
Natural Periodic Structures
Bee hive
Crystal structure
Butterfly wings
Artificial DielectricsThe first ever known metamaterials, which mimic natural materials: high contrast lossless dielectrics and absorbers Usually consist of artificially created 'molecules': dielectric or metallic inclusions of certain shape. These 'molecules' can be distributed and oriented either regularly or randomly.The dimensions of the 'molecules' and characteristic distances between neighboring ones is much smaller than wavelength.Can be described in terms of material parameters (permittivity) The first artificial dielectric was invented by W.E. Kock and used in design of low-weight dielectric lenses at microwaves
[1] W. Kock, “Metallic delay lenses”, Bell Syst. Tech. J., vol. 27, pp. 58-82, 1948.
[2] R. Collin, Field Theory of Guided Waves. IEEE Press, Piscataway, NJ, 1990.
Wire Mediumplasma-like frequency dependent permittivity
negative below plasma frequencypositive but less than unity above omega0
2
201)(
ωωωε −=
J. Pendry, A. Holden, W. Steward, and I. Youngs, “Extremely low frequency plasmonsin metallic mesostructures”, Phys. Rev. Lett., vol. 76, no. 25, pp. 4773-4776, 1996.
Permittivity of Artificial Dielectrics
[1] J. Brown, “Artificial dielectrics," Progress in dielectrics, vol. 2, pp. 195-225, 1960.[2] W. Rotman, “Plasma simulations by artificial dielectrics and parallel-plate media," IRE Trans. Ant. Propag., vol. 10, pp. 82-95, 1962.
Artificial Magnetics
Magnetic inclusions: a) split-ring-resonator, b) swiss rollJ. Pendry, A. Holden, D. Robbins, W. Stewart, “Magnetism from conductors and enhanced nonlinear phenomena”, IEEE Trans. Microwave Theory Techn., vol. 47, no. 11, pp. 195-225, 1999.
Permeability of Resonant Magnetics
Characteristic sizes giving negative μ–PendryJ et al IEEE Trans MTT472075 1999–a ~ λo/ 2
Left-handed Medium (LHM): Material with Simultaneous
Negative ε and μ
V.G. Veselago, “The electrodynamics of substances with simultaneously negative values of ε and μ,” Soviet Physics Uspekhi, vol. 10, pp. 509-514, 1968.
Right-handed VS Left-handed
Right-handed medium: vectors E, H and k form right triple of vectors
Left-handed medium: vectors E, H and k form left triple of vectors
Backward waves at beginning of 20th century
H. Lamb [1] may have been the first person who shown theexistence of backward waves (the waves which phase moves inthe direction opposite from that of the energy flow) in mechanical systems. Seemingly, the first person who discussed the backwardwaves in electromagnetism was A. Schuster [2]. On pp. 313-318 Schuster gives a speculative discussion of its implications foroptical refraction. H.C. Pocklington in [3] showed that in a specific backward-wave medium, a suddenly activated sourceproduces a wave which group velocity is directed away from thesource, while its velocity moves toward the source.[1] H. Lamb, “On group-velocity”, Proc. London Math. Soc., vol. 1, pp. 473-479, 1904.[2] A. Schuster, An Introduction to the Theory of Optics, Edward Arnold, London, 1904.[3] H. Pocklington, “Growth of a wave-group when the group velocity is negative”, Nature, vol. 71, pp. 607- 608, 1905.
Backward waves in left-handed transmission lines in 50ths
[1] G.D. Malyuzhinets, “A note on the radiation principle”, Zh. Tekh. Fiz., Vol. 21, pp. 940-942, 1951. [2] A. Grbic and G. Eleftheriades, “Periodic analysis of a 2-D negative refractive index transmission line structure,” IEEE Trans. Antennas Propagation, vol. 51, no. 10, pp. 2604-2611, 2003.
Positive and Negative Refraction
Positive refraction: from ordinary dielectric to ordinary dielectric
Negative refraction: from ordinary dielectric to left-handed medium
Negative Refraction in 40s
Academician L.I. Mandelshtam
(1879-1944)
Imaging by Pendry’s Perfect Lens
far field
near field
Photonic (electromagnetic) CrystalsPeriodical structures with lattice periods comparable to wavelengthsBand gaps: frequency bands where the material does not support propagating wavesSpatial and frequency dispersion: material parameters depend on the wave vector as well as on the frequencyStrong localization of photons and inhibited spontaneous emission due to photonic bandgaps
[1] E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics andelectronics,” Phys. Rev. Lett., vol. 58, no. 20, pp. 2059–2062, 1987.[2] S. John, “Strong localization of photons in certain disordered dielectric superlattices,”Phys. Rev. Lett., vol. 58, no. 23, pp. 2486–2489, 1987.
Example of Photonic Crystal with Complete Bandgap
E. Yablonovitch, T. Gmitter, and K. Leung, “Photonic band structure: the face-centered-cubic case employing nonspherical atoms,” Phys. Rev. Lett., vol. 67, no. 17, pp. 2295–2298, 1991.
QUESTION, QUESTIONQUESTION, QUESTION
Q. SO WHAT EXOTIC THINGS WOULD YOU DO WITH METAMATERIALS, IF YOU HAD THEM?
Inductive Coupling: Inductive Coupling: the author, the author, AmalAmal GraafstraGraafstra, , and his girlfriend, and his girlfriend, Jennifer Jennifer TomblinTomblin, , have matching RFID have matching RFID implants.implants.
BAN & MonitoringBAN & Monitoring
hearing
implant
Blood pressure
Vision
EEG
NE
TWO
RK
Heartmonitoring
Glucose
HandsetHandset evolutionevolutionSizeWeightPrice
FunctionalityDesign
1990 2000Antennas:
• Size reduction: effect on polarisation, bandwidth, efficiency and manufacturing tolerances
• Reduced ground plane: effect on matching, bandwidth, patterns and user interaction
• Price reduction: low cost elements
Antennas for mobile terminalsAntennas for mobile terminals
Customised antennas forspecific applications
Internal mobile phoneantennas
Antennas forPCMCIA cards
AAppplicaplicattionsions• Mobile phones
• GSM modules for customised applications
• PCMCIA
• Special terminals- Emergency phones- Code bars readers- Credit cards terminals…
• Mobile phones
• GSM modules for customised applications
• PCMCIA
• Special terminals- Emergency phones- Code bars readers- Credit cards terminals…
Effect of the componentsEffect of the components• Limited available volume
• Circuits and components
• Antenna: only component with physical limitations for miniaturisation!
• Limited available volume
• Circuits and components
• Antenna: only component with physical limitations for miniaturisation!
iPoDsiPoDs and Implants and Implants Future of Future of body centricbody centric communicationscommunications
RFID (Radio Frequency Identification ) RFID (Radio Frequency Identification ) SystemSystem
* Technology for automatic identification of objects
* Application : logistics,security system,animal tracking transportation and manufcacturing process control
Why are Metamaterials interesting?They require combining expertise in the fields of electrical engineering and materials science.Artificial Dielectrics and their Applications:– Explore Metamaterials and – Investigate their viability in enhancing antenna
performance.Antennas and Metamaterials:– Size Reduction– Other Improvements, e.g., bandwidth, directivity
and pattern shape.– They can make objects dissapear (cloaking)*Fine print—That’s the promise anyway!!
HOW DID WE GET STARTED ON THEDNG STUFF? WHAT WOULD THEY DO FOR US ONCE WE HAVE THEM?
V.G.Veselago, SOV. Phys, 10, 5091968
Engineered media that have a negativeindex of refraction ( negative permittivity andPermeability)
Perfect reconstruction, High Transverse Wave vectors Imaginary Longitudinal component Evanescent Fields
The ‘Perfect Lens’
LET’S BEGIN WITH A LITTLE HISTORY
• Metamaterials are artificial materials that
exhibit electromagnetic responses generally
not found in nature.
• Engineered media that have a negative index
of refraction ( negative permittivity and
permeability )
• Predicted in 1968 by V.G.Veselago
• E,H and K form a left-handed system of
vectors Composite Metamaterial (CMM)
D.R.Smith and S.Schultz, UCSD
V.G.Veselago, SOV. Phys, 10, 509,1968
Realization of Metamaterials
Realization of Conventional Metamaterial
Negative ε• Thin metallic wires are arranged periodically• Effective permittivity takes negative values below plasma frequency
Negative μ• An array of split-ring resonators (SRRs) are arranged periodically
( Koray Aydin, Bilkent University, Turkey Sep 6 , 2004 )
Realization (contd.)
Extraction of constitutive effective Extraction of constitutive effective parameters from Sparameters from S--parameters for parameters for
normalnormal incidenceincidence
Effective ParametersEffective Parameters
Inversion Method
• Can be applied to both simple and complex structures
• Can use both numerical and experimental data
• S-parameters for metamaterials are more complex
• Ambiguities in the inversion formulas
Equations used in the inversion approachEquations used in the inversion approach
Compute Z:
Compute n:
Compute effective μand ε:
221
211
221
211
)1()1(
SSSSZ
−−−+
±=
Conditions used: Z’ > 0 and
<= 1-
})]'[ln(]2)]"{[[ln(100 dinkdink
oeime
dkn −− −+−= π
210 XiXe dink −±=−Y =
( 2 different roots )
( 2 different roots )
( )221
211
21
11 SSS
X +−=2
(branches with different m)
n”<=0, ε”<= 0 and μ” <= 0
Iterative approach to pick n such that n is continuous
zneff /=ε nzeff =μ and
Example 1: 2Example 1: 2--D infinite array of dipoles for normal incidenceD infinite array of dipoles for normal incidence
X
Y
Z
Plane wave source EY
Plane of reflection
Plane of transmission
Unit cellBC used
X and Y: PBCZ: PML
Ei, Et and Er are the contributions from the zerothFloquet mode measured on the corresponding planes.
(1) By enforcing ε” <0 and μ” <0, only m=0 can be solution.
(2) By enforcing n”<0, the correct root can be determined.
(1)(1)
(2)
Solutions for all branches ( m=0, Solutions for all branches ( m=0, --1 and +1) and 2 roots1 and +1) and 2 roots
Determine the solutionby using ref. (1):
Extracted parameters: 2Extracted parameters: 2--D infinite array of dipolesD infinite array of dipoles
X
Y
Z
Plane wave source EY
Plane of reflection
Plane of transmission
Unit cellBC usedX and Y: PBC
Z: PML
Example 2: 2Example 2: 2--D infinite array of splitD infinite array of split--rings for normal incidencerings for normal incidence
Extracted parameters: 2Extracted parameters: 2--D infinite array of splitD infinite array of split--ringsrings
Note: The shaded area represents the non-physical region, where ε” or μ” > 0. In this region, we choose the branch that best connect n just before and after this band.
X
Z
Y
Plane wave source EY
Plane of reflection
Plane of transmission
Unit cellBC used
X and Y: PBCZ: PML
Example 3: 2Example 3: 2--D infinite array of splitD infinite array of split--rings + dipoles for normal incidencerings + dipoles for normal incidence
Extracted parameters: 2Extracted parameters: 2--D infinite array of splitD infinite array of split--rings+dipolesrings+dipoles (1(1--layer)layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
22--D Infinite array of splitD Infinite array of split--rings + dipoles ( 2rings + dipoles ( 2--layer )layer )
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Extracted parameters: 2Extracted parameters: 2--D infinite array of splitD infinite array of split--rings+dipolesrings+dipoles (2(2--layer)layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
22--D Infinite array of splitD Infinite array of split--rings + dipoles ( 3rings + dipoles ( 3--layer )layer )
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Extracted parameters: 2Extracted parameters: 2--D infinite array of splitD infinite array of split--rings+dipolesrings+dipoles (3(3--layer)layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
22--D Infinite array of splitD Infinite array of split--rings + dipoles ( 4rings + dipoles ( 4--layer )layer )
Extracted parameters: 2Extracted parameters: 2--D infinite array of splitD infinite array of split--rings+dipolesrings+dipoles (4(4--layer)layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Comparison of effective parameters for 1 to 4Comparison of effective parameters for 1 to 4--layer splitlayer split--ring + dipolering + dipole
Note: The effective parameters for 1-4 layers are almost the same, except that more resonant peaks can be seen for more layers.
Refraction in DNG Prisms
DNG DPS
Metamaterial Design using Metamaterial Design using SRRsSRRs and Dipolesand Dipoles
Front view Top view
Top view of a metamaterial prism
L1 L2
g
d
w
z
x
t
y
x
�w
y
x
LeLe--Wei Li, Wei Li, HaiHai--Ying Yao, and Wei Ying Yao, and Wei XuXuNational University of Singapore, Kent Ridge, SingaporeNational University of Singapore, Kent Ridge, SingaporeQunQun WuWuHarbin Institute of Technology, Harbin, ChinaHarbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
Simulation ResultsSimulation Results
Distribution of electric field component Ez(r,t) in rectangular linear around a metamaterial prism at f=16.21 GHz
LeLe--Wei Li, Wei Li, HaiHai--Ying Yao, and Wei Ying Yao, and Wei XuXuNational University of Singapore, Kent Ridge, SingaporeNational University of Singapore, Kent Ridge, SingaporeQunQun WuWuHarbin Institute of Technology, Harbin, ChinaHarbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
Simulation ResultsSimulation Results
Electric field component Ez(r,t) distribution due to a metamaterial prism
LeLe--Wei Li, Wei Li, HaiHai--Ying Yao, and Wei Ying Yao, and Wei XuXuNational University of Singapore, Kent Ridge, SingaporeNational University of Singapore, Kent Ridge, SingaporeQunQun WuWuHarbin Institute of Technology, Harbin, ChinaHarbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
Scattering PatternScattering Pattern
Distribution of electric field component Ez(r,t) in polar plot due to a metamaterial prism at f=16.21 GHz
LeLe--Wei Li, Wei Li, HaiHai--Ying Yao, and Wei Ying Yao, and Wei XuXuNational University of Singapore, Kent Ridge, SingaporeNational University of Singapore, Kent Ridge, SingaporeQunQun WuWuHarbin Institute of Technology, Harbin, ChinaHarbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
Negative Refraction in a Slab
Plane wave
θ ??DNGDNG
SLABSLAB
Comprising Comprising of Periodicof Periodic
Structures Structures
EBG Array Settings: Oblique incidence (EBG Array Settings: Oblique incidence (TMzTMz))
Array settings:Ele. Separation: 2.25 mm x 5 mm x 4 mEle. Separation in λ: 0.1125 x 0.25 x 0.20Total number: 38 x 17 x 6 = 3876Total number falls within beam width = 34 ( X: 10, Y
85.5 mm = 4.3 λ85 mm = 4.3 λ
24 mm = 1.2 λ
22 mm = 1.1 λ
FDTD Computational domainPhsyical size: 85.5 mm x 85 mm x 67 mm
Cell number: 680 x 684 x 536 = 2.5 x 108 cells
λ = wavelength at 15.0 GHz
Guassian beam
θ = 30o
Vertical Field Distribution Vertical Field Distribution at 14.4 GHzat 14.4 GHz
Free space Dielectric Slab EBG Array
P1P2
P4Array ( 6 layers )
P4: YZ Plane
Free space Dielectric Slab EBG Array
P4: Transmission region
Transverse Field distribution P4 and P5 at 15.0 GHz
Free space Dielectric slab EBG Array
P5: ~1 wavelength behind the array
P4: ~2/3 wavelength behind the array
Transverse Field distribution P2 and P3 at 16.0 GHz
Free space Dielectric slab EBG Array
P3: ~1/3 wavelength behind the array
P2: Right behind the slab/array
Transverse Field distribution P4 and P5 at 17.5 GHz
Free space Dielectric slabEBG Array
P5: ~1 wavelength behind the array
P4: ~2/3 wavelength behind the array
Vertical Field Distribution Vertical Field Distribution at 15.6 GHzat 15.6 GHz P1
P2
P4Array ( 6 layers )
Free space Dielectric Slab EBG Array
P4: YZ Plane
Free space Dielectric Slab EBG Array
P4: Transmission region
Ring DimensionsSide length – 3mm Thickness - 0.25mmGap - 0.5mm
Waveguide DimensionsX-band waveguideWidth – 19.25mmHeight – 10.625mm
Terminated by PML walls to avoid reflections
The SRR was placed vertically with the gap-bearing side parallel to the direction of propagation.
Voltage Measurementpoints
y
z
x
RingField Planes
SINGLE & MULTIPLE LAYER SRR
Before theresonance
After theresonance
Amplitude
Amplitude
Phase
Phase
Field Distributions Confirm the Resonant Permeability Behavior
Ring DimensionsSide length – 3mm Thickness - 0.25mmGap - 0.5mm
Waveguide DimensionsX-band waveguideWidth – 19.25mmHeight – 10.625mm
Terminated by PML walls to avoid reflections
The SRR was placed vertically with the gap-bearing side perpendicular to the direction of propagation.
Voltage Measurementpoints
y
z
x
RingField Planes
SRR Design : Perpendicular Orientation
• Comparison of reflection and transmission coefficients obtained from measurements and simulations (Dimensions Scaled)
• Comparison of real parts of effective permittivity and effective permeability
S-parameters and Effective Parameters: Parallel Orientation
Comparison of reflection and transmission coefficients obtained from measurements and simulations (Dimensions scaled)
Comparison of real parts of effective permittivity and effective permeability
Perpendicular Orientation - Results
• Comparison of real parts of effective permittivity and effective permeability
• Comparison of reflection coefficients obtained from simulations for the three cases
Composite Unit Cell - Results
Distance d of the points from the source
Increase in phase ( phase advance) for points away from the source in the frequency range where the effective parameters are simultaneously negative.
Phase of the field measured at three different points along the waveguide inside the DNG unit cell
Sourced
y
z
Confirmation of Backward Wave Propagation
Verification
x
y
Pass Band below cutoff
Waveguide BC-SRRS
Coaxial feed
37600
8.4 GHz 8.6 GHz
62000
76300
8.8 GHz
74000
8.7 GHz
79400
9.1 GHz
68700
8.9 GHz
Ez in XY-plane
Hz in YZ-plane
x
y
• SRRs are coupled as seen from the magnitude and phase distributions of the E and H fields
• The axial magnetic moment does not exist and so cannot cause negative permeability.
• Wave tunneling might be due to a resonance wave propagation along the SRR chain
z
y8.7Ghz
Simulation and Field Analysis
Waveguide DimensionsWidth – 10.66mmHeight – 4.2mmCut off – 14.07GHz
Ring DimensionsSide length – 1.7mm Thickness - 0.25mmGap - 0.48mm
Cut Off
Pass Band below Cutoff
Regular Half-wavelength Resonance of the SRR ( Negative Permeability)
z
y
Magnitude Phase
Magnitude and Phase of Ex nearthe SRR
Transmission Coefficient
K – Band Wave Guide
Ex (13.65GHz) Ex(13.95GHz)
Hx(13.65GHz) Hx(13.95Ghz)
• Components of E and H fields normal to theSRR plane
z
y
Half wavelength Resonance Full wavelength Resonance
• Magnitude of the fieldsis more than 3 times higher than that at other frequencies
• Separation ~ 0.35Ghzand the fact that the Half-wavelengthresonance occurs at twofrequencies indicates thata slow wave modepropagates through theSRR waveguide below cutoff
9.97e+005 4.89e+005
1.03e+003 3.07e+002
Field Distributions
Electromagnetic Communication Lab
Next 3 Slides are courtesy of Prof. HosseinMossallei of Northeastern University
1 layer and 3 Layer Periodic Array of Spheres1 layer and 3 Layer Periodic Array of Spheres
h=2.5 cm
3-Layer with h=2.5 and d=1.5 cmx
yz
d
Diameter = 1 cmεr=40
Tripod FSS Tripod FSS –– Layered StructuresLayered Structures
0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0frequency (GHz)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% o
f Pow
er R
eflec
ted
normal incidenceTE at 30
o
TM at 30o
Ty
L1
L2
Tz
mmTmmTmmLmmLangleflare
z
y
44.240.148.040.0
240
2
1
=
===
o
d=0.02 mm
0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0frequency (GHz)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% o
f Pow
er R
eflec
ted
normal incidenceTE at 30
o
TM at 30o
0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0frequency (GHz)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% o
f Pow
er R
efle
cted
normal incidenceTE at 30
o
TM at 30o
D=1 mm
1-Layer
2-Layer2 of 2-Layer
Sphere Dielectric and Coupling PerformanceSphere Dielectric and Coupling Performance
Coupling and Resonance Behavior
εr=20
x
yz εr=10
260
nm520 nm
160 nm
εr
H-Field in y-x plane
Mag
netic
Dip
ole
Elec
tric
Dip
ole
Normal Mode
Elec
tric
Dip
ole
Mag
netic
Dip
ole
Reverse Mode
TIME TO RAISE A FEW ??TIME TO RAISE A FEW ??
THE PERFECT LENS?
Refraction in DNG Prisms
DNG DPS
Equivalent Medium ApproachIt is a Common practice to replace an artificial dielectric with its equivalent ε and μperform an analysis of composite structures (antenna + medium) using the equivalent medium.
But this can lead to significant errors and wrong conclusions
Single layer
R T...
Multiple layers
Exit angle?
.
.
.
.
.
.
.
.
.
Floquetharmonics
Negative Retraction in a Slab
Plane wave
θ ??DNGDNG
SLABSLAB
Imaging with DNG Lens
Field distribution along z in the RHS of Lens
or ?
0 ZIsource
DNG LENS
Field Distribution
0 ZI 0 7 Z
Field Distribution
Question?
Images?
Can we resolve two longitudinally-spaced sources with a DNG lens?
DNGDNG
LensLens
NEXT ?NEXT ?
SMALL ANTENNAS WITH VERY HIGH DIRECTIVITIES?
DPS
ENG
Performance Enhancement of Small Antennas
Small Antenna
(length << λ)
Thin shell,
Radius << λ
Big Q?? Can we violate
Chu limit?
Artificial Magneto-Dielectric Substrates
Performance Enhancement of Wire and Patch Antennas Using Artificial MaterialsPekka Ikonen(1), Stanislav Maslovski(1), Kostantin Rozanov(2), Murat Ermutlu(3), and Sergei Tretyakov(1)(1)Radio Laboratory / SMARAD Center of Excellence Helsinki University of Technology(2)Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow, Russia(3)Nokia Networks, Finland
Clockwise from top right:– A single unit-cell design.– A two unit-cell design.– Fabricated single unit-cell BW
TL.
1.2mm
Multilayered Loop Inductors
Parallel-Plate Capacitors
Transmission Line Approach
Based on Transmission Line (TL) circuit models:
RH-TL– Regular microstrip line– Lowpass in nature
LH-TL– Inductance/Capacitance interchanged– Series/Parallel arrangements inverted– Highpass in nature
Loading a MPA
Microstrip Patch Antenna (MPA):
– Normally λ/2 a side.– TL structure loads sides.– Size reductions.
Antennas tested:– 7.55 GHz λ/4 (69% area
savings).– 485 MHz λ/6 (87% area
savings).– 348 MHz λ/8 (93% area
savings).
Patch
via to ground plane
Loading Strip
Width=2.25 ”Length=0.125”
@ 4303.5" 0.4 f MHzλ ==
Height = 0.01875” = 18.75 mils
via = 0.04375” = 43.75 mils
Y
X
Ground PlaneY
X
Z9=rε
Size-Reduction of MPA:
(a)(a) (b)(b)
(c)(c)
Ez field distribution between patch and ground @ f=430 MHz(a)(a)
Ex field distribution between patch and ground @ f=430 MHz
Ey field distribution between patch and ground @ f=430 MHz
(b)(b)
(c)(c)
via
loading stripProbe feed
YX
2 22
1 1
2
1 tan( )
2 ( )
r yy
r y
r
kY k h
k
Y
εε
γ ε
=
=
8.232 ≈rε
L
b
x
y
z
PMC
PMC
PMC
PMCPMC
PMC1rε
3rε
2rε
Partially filled Cavity
d
a’
a
h
(1)
(3)
(2)
Simulation results based on theoretically calculated effective dielectric constant:
Directivity Enhancement of a Class of Patch
Antennas using Metamaterial Superstrates
Directivity Enhancement of a Class of Patch Directivity Enhancement of a Class of Patch
Antennas using Metamaterial Antennas using Metamaterial SuperstratesSuperstrates
Motivation
◈ In the past, array antennas had been widely used for applications requiring high directive antennas.
◈ However, array antennas require a complex feed network, and it makes difficulty in fabrication of array antennas and cause losses.
◈ A simple way to obtain high directivity with one or a few radiators is necessary. Metamaterial superstrates
BeamArray and complex feed network Superstrate
Patch
High Directivity
Candidates for Metamaterial Superstrates
◈ Periodic structures such as FSSs and EBGs act as spatial angular filters with transmission and reflection pass and stop bands, and can be used to enhance directivity of a class of antennas being placed above them.
Woodpile EBGStacked
dielectric layerDielectric rod
EBG FSS
◈ Two approaches for the analysis of antennas with metamaterial superstrates1. Fabry-Perot Cavity (FPC) Antenna Partially Reflecting Surface (PRS)
2. Leaky Wave Antenna
11.76cm
9.66cm
1.00 cm
εr=2.2, t=20mil
L1=1.33cm, dl=1.0cm
Fabrication and Measurement Results of the 7×28 Strip Dipole FSS Composite
Measured Maximum Directivity: 19.5dB
FSS superstrate printed on a commercial available dielectric material
11.5 12 12.5 13 13.5Frequency(GHz)
10
12
14
16
18
20
22
Gai
n(dB
)
simulationmeasurement
-80 -60 -40 -20 0 20 40 60 80angle(degree)
-40
-35
-30
-25
-20
-15
-10
-5
0
pow
er(d
B)
E-plane(12.5GHz)H-plane(12.5GHz)E-plane(simul)H-plane(simul)
20×10 Thin FSS Superstrate
Fabrication and Measurement Results of the 20×10 Thin FSS Composite (1)
εr = 2.2,
t = 2.0828 mm
< top view > < back view >
< side view >
The design parameter valuesFSS array size: 10 × 20a = 12, b = 6dl_l = 8.7, dl_u = 11.2dw_l =1, dw_u = 4h = 16, Lg=2.0828
h = 13
8.41 and 11.67 GHz
Two FSS layer are etched in same substrate whose thickness is only 2.0828 mm
Must we use DNG superstrate and other metamaterials and look for focusing effects for directivity enhancement?
DNG
Ground planeMicrostrip patch
DNG
Ground plane
Ground plane Microstrip patch
Metamaterials with frozen modes and other Special Characteristics
Q. Can we achieve higher directivity than is possible for a uniformly illuminated aperture of the same size as that of the antenna + superstrate composite?
Ground planeMicrostrip patch
FSS
TE mode E-field when θ=1, φ=90
TM mode E-field when θ=1, φ=0
S11 ~ -1.4 dB at 13 GHz
Phase ~ 360 deg at 13 GHz
S21 ~ -6 dB at 13 GHz Phase ~ -90 deg at 13 GHz
Can’t find any resonant mode at 13 GHz but reflection phase
Dual-layer simulation
Single-layer (red line) dipole compare to dual-layer (blue line)
L = 1.2
L = 1.3L = 1.4
Geometry of a fabricated dipole strip FSS composite and its unit cell.
Comparison of the simulated and measurement results: (a) directivity and (b) radiation pattern
EBG SUBSTRATESEBG SUBSTRATES
DO THEY ENHANCE ANTENNA PERFORMANCE?
REF: EuCAP’06 PAPER BY LIVERPOOL U
CONVENTIONAL MSACONVENTIONAL MSA
SLOT ANENNA ABOVE HISSLOT ANENNA ABOVE HIS
RETURN LOSS CHARACTERISTICS OF RETURN LOSS CHARACTERISTICS OF ANTENNA ABOVE HIS ANTENNA ABOVE HIS
ALTERNATIVE TO VESELAGO ALTERNATIVE TO VESELAGO LENS?LENS?
Source plane
Image plane
Imaging Device
Distribution of electric fieldDistribution of electric field
a) near the front interface b) near the back interface
Near field scan resultsNear field scan results
Distribution of electrical field at the source and image planes.Confirmation of λ/15 resolution and 18% bandwidth reported!
P.A. Belov, Y. Hao, S. Sudhakaran, “Subwavelength microwave imaging using an array of parallel conducting wires as a lens”, Phys. Rev. B, vol. 73, 033108, 2006.
Intensity distributionIntensity distribution
a) near the front interface b) near the back interfaceResolution is λ/15!
P.A. Belov, Y. Hao, S. Sudhakaran, “Subwavelength microwave imaging using an array of parallel conducting wires as a lens”, Phys. Rev. B, vol. 73, 033108, 2006.
AMC Ground DesignsAMC Ground Designs
Response of AMC GroundResponse of AMC Ground
AMC GroundAMC Ground
Antenna over AMC GroundAntenna over AMC Ground
SUMMARY QSUMMARY Q’’SSQ1.DNG’S ARE INTERESING CONCEPTUALLY, BUT IS THIS LENS BUSINESS REALY PRACTICAL? IT DOESN’T ACTUALLY WORK LIKE A CONVNTIONAL OPTICAL LENS; THE MATERIAL IS NOT ISOTROPIC; AND, LOSSES AND BANDWIDTH CAN BE PROBLEMS.
Q2.OK, SO EVEN IF WE PUT THE LENS BUSINESS ASIDE, HOW ABOUT THEIR USE AS SUBSTRATES, SUPERSTRATES ABD SHELL COVERS FOR SMALL ANTENNAS? SHOULD WE ONLY LOOK FOR DNG’S FOR THESE APPLICATIONS?
MORE QUESTIONSMORE QUESTIONS
Q3.CAN WE GET MORE DIRECIVITY FROM A SMALL ANTENNA COMPOSITE (ANTENNA + SUPERSTRATE) BY USING METAMAERIALS, THAN IS POSSIBLE TO REALIZE FROM THE APERTURE SIZE OF THE COMPOSITE?Q4.CAN WE GET GOOD BACKLOBE SUPPRESSION FROM A GROUNDPLNE, WHOSE SIZE IS COMPARABLE TO THAT OF THE ANTENNA (∼λ/2),BY USING METAMATERIALS?SHOULD ALL MANNER OF IMAGING SYSEMS BE LABELED AS LENSES?
A FEW MOREA FEW MOREQ5.DO THE EFFECTIVE PARAMETERS REMAINUNCHANGED WHEN WE VARY THE THCKNESS OF THE METAMATERIAL SLAB, OR CHANGE THE INCIDENT ANGLE?Q6.FOR SMALL ANTENNA/SUPESTRATE COMPOSITES, SHOULD WE BE LOOKING AT THE SIZE OF THE ANTENNA OR THA OF THE COMPOSITE WHEN COMPARING DIRECTIVITIES?Q7.IS THERE A SPECIFIC ADVANTAGE TO BE GAINED IN USING EBG’S WITH SMALL PERIODICIIES WHOSE CELL SIZE IS MUCH SMALLER THAN A WAVELENGTH?
BIG QUESTION(S)??BIG QUESTION(S)??
SO, WHERE DO WE GO FROM HERE?HOW DO WE REALIZE LOW LOSS, ISOTROPIC, ESSENTIALLY NON-DISPERSIVE METAMATERIALS THAT ARE LOW COST AND CAN BE INTEGRATED WITH SMALL ANTENNAS TO IMPROVE THEIR FUNCTIONALIY AND PEFORMANCE?
Resonator Array structures for Resonator Array structures for metamaterials?metamaterials?
Higher Frequencies pushing into the THz rangeSpherical resonators instead of cylindrical resonatorsFree space optical testing.
1 mm diameter silica spheres. Fabricated by Amanda Baker
W0RTH A LOOK?W0RTH A LOOK?COURTESY OF ELENA SEMOUCHKINA (PENN STATE)COURTESY OF ELENA SEMOUCHKINA (PENN STATE)
A WORD ABOUT SIMULATIONA WORD ABOUT SIMULATION
Antenna-metamaterial composites requireheavy duty computing power to model
(Note: We routinely simulate upward of billion-unknown-category problems)
1 mm diameter silica spheres. Fabricated by Amanda Baker
Resonator Array structures for metamaterials?
• Higher Frequencies pushing into the THz range
• Spherical resonators instead of cylindrical resonators
• Free space optical testing.