Tianxia Zhao

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Beauty and Application of Periodic Structures
Tianxia Zhao
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Introduction

• Periodic structures in nature have fascinating
  characteristics.
• When these structures interact with
  electromagnetic waves many unique features result
  such as stop-band, pass-bands, and band-gaps.
• Various terminology have been used to classify
  these structures depending on the domain of the
  applications in filter design frequency
  selective surface(FSS), photonic crystals and
  band-gaps(PBG), and meta-materials and
  Electromagnetic band-gaps(EBG).
• Broadly speaking, EBG structures are 3-D periodic
  objects that prevent the propagation of the
  electromagnetic waves in a specified band of
  frequency for all angles of arrival and for all
  polarization states of EM waves.
• Brief introduction for each terminology and some
  representative application will be given at each
  section.

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Outline

• Natural periodic structures
• Periodic structures in EM
• Phased array antenna
• Leaky wave antenna
• Frequency selective surface(FSS)
• Photonic crystal(photonic band-gap PBG
  structures)
• 1D PC
• 2D PC
• 3D PC
• Metamaterials and EBG(electromagnetic band-gap
  structure)

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Natural Periodic Structures
Crystal structure
Butterfly wings
Bee hive
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Section I Periodic structures in
electromagnetic applications

• Part 1. Phased array antenna
• application in radar system and
  satellite TV or
• communication
• Part 2. Leaky wave antenna
• leaky wave antenna changes a
  wave-guiding structure into a
• radiating structure
• Part 3. Frequency selective surface
• FSS as band-pass, band-stop filters,
  and application in
• radomes, thermovoltaic system

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Part I What is Phased Array antenna

• Phased-array antennas contain a multitude of
  radiating elements, typically arranged in a
  rectangular or triangular tessellation.
• Array of Antenna element with phase ( and
  sometimes, the amplitude) of each element being a
  variable.
• Phased Array antenna can control the radiation
  beam direction and pattern shape including side
  lobes.
• When the phase change is accomplished by varying
  the frequency, its called frequency scanning
  arrays.

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The structure of Phased array antenna
Single antenna element and its radiation pattern
Phased array antenna and its radiation pattern
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Phased array antenna in radar application

• Extreme beam agility
• Mechenical scanning takes 1 second while
  electronic scanning takes less than 1 ms.
• Reducing antenna radar cross section
• Advanced beam forming capabilities
• High reliability and Less structural intrusion

Radiation deflected from threat antenna
Stationary phased array antenna
Phased array antenna application in radar system
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Phased array antenna Application in DBS
Big Ugly dish(BUD)
The planar microstrip antenna array
Direct broadcast satellites
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Part II 2D Leaky-Wave Antenna

• Guiding Stucture In electromagnetics and
  communication engineering and optics, a waveguide
  is a physical structure that guides any
  electromagnetic waves or light. Metallic,
  dielectric waveguide and planar transmission line
  are all wave guiding structures.
• Leaky wave antenna changes a guiding
• structure into a radiation structure.

Metallic Waveguide
Leaky wave antenna radiation from a guiding
structure
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2D Periodic Leaky-Wave Antenna
y
z
x
x

h
b
W
a
L
2D LWA using metal patches
z
x
h
2D LWA using slots
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Design principle of 2D LWA

• The source launches a parallel-plate mode (n1)
  that is leaky due to radiation through the
  PRS.
• The substrate thickness h controls the beam
  angle.
• The PRS controls the beamwidth.

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Radiation Pattern Slot LWA
Slot LWA
Hplane patterns for ?r 2.2 (Slot
LWA) changing substrate thickness f 12 GHz, l
0.6 cm, w 0.05 cm, a 1.0cm, b 0.3 cm
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Applications of LWA

• Leaky-wave application based on the higher order
  modes of planar transmission lines possess the
  advantage of higher gain, wider bandwidth,
  frequency scanning.
• LWA can be made electronically steerable using a
  tunable ferroelectric material whose dielectric
  properties is controlled by a bias voltage
  applied to the traveling waveguide.
• Leaky wave waveguide antenna used in vehicular
  radar antenna arrays that can be blended into
  surfaces curved in two dimensions.

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Frequency Selective Surface(FSS)

• What is FSS?
• A FSS is any surface construction designed as a
  filter for plane waves
• Angular/frequency dependence
• Band pass/ band stop behavior
• FSS characteristics
• Typically narrow band
• Periodic, typically in 2 dimensions
• FSS Degrees of Freedom
• Element type dielectric or metallic/circuit
• Element size,shape and loading
• Element spacing and orientation

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printed dipole FSS structures
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Complementary surfaces-slot FSS
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Slot Vs Dipoles FSS
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Applications of FSS

• Traditional Applications
• Radomes
• Dichroic subreflectors
• Reflect array lense
• Recent Applications
• RFID
• Collision avoidance
• RCS augmentation
• Robotic guided paths
• EMI protection
• Photonic bandgap structures
• Waveguide or cavity controlled coupling
• Low-probability of intercept systems(e.g.
  stealth)

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FSS applications- radome
Radome must be transparent at operating
frequency. Radome protects antenna from the
environment. Radome will affect the antenna
pattern by refraction from radome wall, loss from
radome materials and multiple reflection, and
increased sidelobes from multiple reflection.
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FSS radome
Bandpass radome is constructed from one or more
metallic screens sandwiched between dielectric
slabs
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Application of FSS with antenna
Surface wave elimination
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application of FSS
Thermovoltaic system
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Section II- PBG structure
Butterfly P. Nireus
The blue-green color on several species of
African butterflies is caused by the nanoscale
structure of the insects wings
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Explaination for butterfly wings

• Optical physicist studied the scales that make up
  the brightly colored regions of the creatures
  wings.
• These scales contain a pigment that absorbs
• light at wavelengths of around 420
  nanometers-
• roughly sky blue- and radiates it at 505 nm
• in the blue-green region where butterfly
• eyes are particularly sensitive.
• Underneath the pigment slab
• are layers of reflective surfaces
• natural versions of
• distributed bragg reflector mirrors.
• The butterfly's "mirrors" are tuned
• to reflect blue-green light.

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What is bragg reflector

• What is distributed bragg reflector
• In guided wave optics, a distributed Bragg
  reflector (DBR) is a structure formed from
  multiple layers of alternating materials with
  varying refractive index, or by periodic
  variation of some characteristic (such as height)
  of a dielectric waveguide, resulting in periodic
  variation in the effective refractive index in
  the guide. Each layer boundary causes a partial
  reflection of an optical wave, and for waves with
  optical wavelength such that the many reflections
  combine with constructive interference, a high
  quality reflector is formed.

Lights with different colors reflected by the
evenly-spaced data track of CD surface at
different angles
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Explanation of butterfly wings

• Just above the mirror, is a slab of material
  filled with hollow cylinders of air that run
  perpendicular to the mirror. These cylindrical
  holes channel the light away from the reflector,
  preventing it from getting trapped. The slab, is
  what optical physicists call a photonic crystal.
• The combined effect of the reflectors and the
  structure of the slab, is a much brighter
  blue-green fluorescence than could be achieved
  with pigment alone.
• The brighter wings allow the butterflies to
  better signal to each other.

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photonic crystal(photonic bandgap structure)

• Photonic crystals are periodic dielectric or
  metallo-dielectric nanostructures
• PC or PBG structure affect the propagation of
  electromagnetic wave (EM) in the same way as the
  periodic potential in a semiconductor crystal
  affects the electron motion by defining allowed
  and forbidden electronic energy bands.
• The absence of allowed propagating EM modes
  inside the structures, in a range of wavelengths
  called a photonic bandgap,
• Optical phenomena such as inhibition of
  spontaneous emission, high-reflecting
  omnidirectional mirrors and low-loss-waveguiding
  among others.

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1D photonic crystal

• Application of 1D photonic crystal
• Perfect dielectric mirror
• The reflectivity of photonic crystals derives
  from their geometry and periodicity, not a
  complicated atomic-scale property (unlike
  metallic components mirror).
• For the frequency range of interest, the
  material should be essentially lossless.
• Such materials are widely available all the way
  from the ultraviolet regime to the microwave.

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2D photonic crystal fiber

• Photonic-crystal fiber, which use a nanoscale
  structure to confine light with radically
  different characteristics compared to
  conventional optical fiber for applications in
  nonlinear devices, guiding exotic wavelengths,
  and so on.

Conventional optical fiber
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2D photonic crystal fiber

• Hollow-core Bandgap Fibers

Photonic Crystal
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Application of 2D photonic crystal
Waveguides and junctions
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3D Photonic crystal
I.
II.
Experimental realization of the three-dimensional
layer-by-layer structure
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light emitting diodes (LED)

• Light-emitting diodes use semiconductor material
  that converts electrical current to light of a
  particular wavelength.
• The improved design of ultra-high-efficiency
  light-emitting diodes can borrow from butterfly
  wings.
• The butterfly wings Distributed Bragg reflectors
  are not perfect. Some light always becomes
  trapped on the surface of the reflector and is
  lost.
• But in each scale, sitting just above the mirror,
• cylindrical holes (photonic crystal.)
  channel the light away from the reflector,
  preventing it from getting trapped.
• Light-emitting diodes based on this design
  principle would be much more efficient than
  today's models, which scatter light in all
  directions, causing much of the light they
  produce to be reabsorbed by the devices'
  material.

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Section III- Metamaterials

• a. Metamaterial is an artificial material whose
  permittivity and permeability are both negative.
• b. Why it is artificial? Such materials possess
  engineered effective electromagnetic properties
  resulting from response functions not found in
  constituent materials and not readily observed in
  nature.

Negative refraction index
Positive refraction index
a. Based on definition of J.Pendry 2000
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Introduction

• Difference between PBG and meta-material
• PBG exhibit stop bands as a result of Bragg
  reflection
• and often implies structure in higher
  frequency regions (optics).
• Metamaterial is a general electromagnetics
  term which covers
• optics and photonics. It is an object
  that gains its (electromagnetic) material
  properties from its structure rather than
  inheriting them directly from the materials it is
  composed of. PBG materials are an example of an
  artificial visible light metamaterials.
• Negative e already exist at optical frequencies,
  but less
• explored at lower frequencies.
• Natural material exist with a
  negative permittivity typically
• ferroelectrics.
• Negative permeability (µlt0) is the
  challenge.
• Wires and SRR (split ring resonators) are
  conducting elements
• that can be possible artificial
  structures, especially at lower
• frequencies.

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Metamaterial design- negative µ
SRR-split ring resonator
From Dana V. Radovic etc. XII telecom Forum
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Metamaterial design- negative e

• To obtain negative permittivity medium, thin
  metallic wires are arranged periodically.
  Effective permittivity takes negative plasma
  frequency.
• Negative e and µ can be achieved simultaneously.

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Metamaterial Application
Negative phase velocity, reversal of Doppler
Effect and Backward Cerenkov radiation are
interesting novel physical properties emerging
from left-handed metamaterials phenomena. Science
magazine listed metamaterial top ten
breakthrough in 2003
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Summary

• In this presentation, many applications based on
  periodic structures are introduced.
• For phased array antenna, the control of phases
  from different array element will change the
  total radiation pattern.
• For leaky wave antenna, the type of wave (wave
  number) is changed from guided mode to leaky
  radiation mode.
• Inspired by some fascinating phenomenon from
  periodic structures new nanostructured devices at
  optical frequencies combines the electronic
  functions are being designed, PBG,EBG or
  metamaterials can lead to revolutionary optical
  components.

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Thank you
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Band-Structure(Brilloun Diagram)
a period, k0 2? / ?0 , ? 2 ? / ?g
?-1 a ?0 a - 2?