The nano Rectenna Project Design and Applications of UWB ...

The nano Rectenna Project

Design and Applications of UWB Nano-Antenna Arrays

Zeev Iluz, Yuval Yifat, Doron Bar-Lev, Michal Eitan, Yoni Kantarovsky, Yoav Blau, Yael Hanein, Koby Scheuer, and Amir Boag

School of Electrical EngineeringTel Aviv University, Tel Aviv 69978, Israel

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Largest of the 7 universities in Israel with ~ 28000 students

Tel Aviv University

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Why Nanoantennas?

Field localization• Breaks the diffraction

limit (10-50nm resolution) - Imaging

• Smaller photodetectors (less dark current, faster response) - Detection

• Increasing resolution - information processing

Field enhancement• Up to 40dB power

enhancement• Increased

effective absorption cross section

• Enhancing nonlinear optics

Field detection• Phase

sensitive detectors

Design flexibility• Wavelength

scaling* – Hybrid detectors

• Load dependence response –sensing, active antennas

Coupling from near to far field• Efficient

surface phenomena detection

* P. Bharadwaj, B. Deutsch & L. Novotny, "Optical Antennas", Adv. Opt. Photon. 1, 438-483 (2009).

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Plasmonics and nano-antenna projects

Broadband antennas

Nonlinear optics

Particle trapping

D A E B F G

HolographySensors

Rectennas


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UWB Antennas and Rectennas• Motivation• Rectenna concept• Dual-Vivaldi design• Fabrication• Performance evaluation• Rectifying devices• Conclusion and

Applications


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Contemporary and Future World Energy Consumption 1990-2035*

Contemporary and Future World Energy Consumption By Fuel*

*The US Energy Information Administration (EIA) website

Qua

drill

ion

BTU

Qua

drill

ion

BTU

• Technology = Power

• Primary energy resources lead to pollution (e.g. global warming)• Possible solution – Renewable energy, particularly solar energy

Motivation for Solar Energy Harvesting


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• The energy from 1hr of sunlight striking the earth ( ) ~ 1 year of consumed energy worldwide ( in 2001*)

• Two main commercial technologies:• Concentrating solar power (CSP) systems• Photovoltaics (PV)

Both technologies at present have low efficiency !

Wednesday,

Nano Rectifying Antennas f S l E H ti

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J20103.4 ⋅

J20101.4 ⋅

*The UN Development Program (2003) World Energy Assessment Report

A CSP System Typical Solar Cell

World insolation map

http://upload.wikimedia.org/wikipedia/commons/9/91/Moody_Sunburst.jpg

http://upload.wikimedia.org/wikipedia/commons/9/91/Moody_Sunburst.jpg


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Any optical rectenna system will include:

1. Receiving antenna

2. Non linear load that rectifies the AC field

induced at antenna terminals3. In 1964, Raytheon demonstrateda helicopter powered by 2.45 GHzrectenna system.

The helicopter flew for over 10 hours

Alternative approach: optical rectenna system


General Concept• NanoAntenna + high-frequency diode• EM radiation excites AC in nano-antenna• The high-frequency diode rectifies the AC

current• The outcome:

Detection + Second Harmonic Generation

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Guidelines for efficient rectenna1. Wideband (both impedance matching & radiation

efficiency)

2. Integrated antenna-to-waveguide device (matching

manipulations)

3. DC power lines that do not interact with antenna

operation (array configuration)

4. Metal’s skin depth


The Skin Depth of Gold

Visible spectrum

• Skin depth ~ 13 nm in IR band

• Antenna thickness > 40-50 nm 12


The Dual Vivaldi antenna geometry

zx

( )end end,x z

( )start start,x z

1 25 nmW =

250 nmL =

2 500 nmW =

• Classical Vivaldi - slot antenna with exponential taper • UWB impedance matching• End-fire radiation• Our approach: two end-fire Vivaldi antennas, placed opposite to one another• Peak gain at the antenna broadside direction. 13


Both parallel plate waveguide gaps were excited coherently and in phase, using ports across the gaps:

Port 1Port 2

The parallel plate impedance ~ 0 1 / 78.5 ,Z W hη= = Ω 377η = Ω14


Array configuration for Power harvestingSeries DC connection – no need for DC interconnects

Slight tuning of Design Parameters

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Dual Vivaldi Antenna: Simulation results

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The return loss > 9.5 dB between (129% impedance bandwidth).

0.7 3.25μm−


How does it work ?

17Benefits of coupling for wideband operation !


The Dual Vivaldi input resistance and reactance

Multi resonance behavior - finite size traveling wave configuration

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y-xy-z

Non symmetric far-field pattern due to the Quartz substrate

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Antenna configuration

Far-field directivity patterns in the y-x (vertical) and y-z (horizontal) planes


The Dual Vivaldi radiation efficiency

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The radiation efficiency remains higher than 85% between (122% efficiency bandwidth).0.78 3.23μm−


Visible Range AntennasAluminum Wideband

Efficiency 60-70 %

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The Fabrication Process

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The antennas structure, composed of a 7 nm adhesion

promotion layer of Cr followed by 33 nm of Au, was

patterned using E-beam lithography.

Both Open and Short circuits were fabricated.


Fabrication Results

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W

H

c

g

SINGLE ANTENNA SPECIFICATIONAnt MeasuredAnt Design596580W[nm]471470H[nm]3125g [nm]5040c[nm]

ARRAY SPECIFICATION1.791.79dx[um]

0.470.47dy[um]


Array Fabrication

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Open Circuit Short Circuit


The Reflection Measurement Setup

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Design Verification

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How to measure impedance of Nano-Antennas?

How to measure impedance of Nano-Loads?

Coupling Antennas to Loads


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An infinite antenna array unit cell, as a loaded scatterer:

212, ( , ) 2, (0,0)

2,11

22 22

22 22

12 21 12

21 12 2 (01 ,0)2,

CBA

, ) 1( 2+

1hL hh hv

vh v

hTE m n TE

TM

h v

v h v vn vLTM m

S S S SS S S SS

aab

S SS S

b

Γ

= ⋅

− Γ

The incident, scattered, and reradiated waves can be related by S-parameters’ network equations:

A load influence B Tx. & Rx. characteristics

C structural scattering


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open short load2, ( , ) 2, ( , )2, ( , )

11 open short2, ( , )2, ( , )

2TE m n TE m nTE m n

TE m nTE m n

b b bS

b b

+ − ×=

−

( )open load2, ( , ) 2, ( , )

21 12 112, (0,0) 2, (0,0)

1TE m n TE m nh h

TE TE

b bS S S

a a

= − −

Illuminating the array with a single mode and using 3 different loads (“open”, “short” and matched load) we determine antenna parameters:

Unknown load reflection coefficient measurement:

( )unknown load2,TE( , ) 2, ( , )

unknown open load unknown open2, ( , ) 2, ( , ) 11 2,TE( , ) 2, ( , )

m n TE m n

TE m n TE m n m n TE m n

b b

b b S b b

−Γ =

− + −


The S-parameters Measurement Setup in RF

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The maximum error in the return loss is 3%, which is less than the resistor manufacturing tolerances (5%).

RF Direct (simulation) vs. Scattered (measurements)


RF measurements for unknown load (R=2 KΩ)

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Typical error of 9% and a flat response vs. frequency, as expected


High Frequency Diodes

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CNT diodes

A single CNT connecting Ti electrode (Schottky) with Pt electrode (Ohmic) on a Quartz substrate.

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CNT diodes model

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Carbon nanotubes


Dual Vivaldi + MIM

Au

Al

nm isolation layer Al

Aunm isolation

layer

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Main Achievements• Arrays of regular and nano-gapped nano antennas (using E-beam

lithography)• Full antenna model was constructed and various antennas were

simulated• Comparison between simulation and experimental data (good

correspondence• Dual-Vivaldi UWB antennas• High efficiency validated (both numerically and experimentally)• CNT & MIM diodes were fabricated and successfully realized

including electrical characterization. Novel methods suited for high resolution patterning of these structures were developed

• CNT & MIM diodes are studied

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Additional Applications Particle Trapping and

Sensing

Refractive Index Sensing

Reflectarrays

Second and Higher Harmonic Generation

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Trapping and sensing nano-objects using nano-antennas


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Sensors: trapping and identify nano-particles


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Sensors: trap and identify nano-particles


Trapping with DEP

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• Dielectric particles manipulated through high-gradient electric fields

• Force depends on:– Particle Geometry– Dielectric properties of

particle– Dielectric properties of

medium

( )( )

( ) ( )

Re ( ) ( )DEP

m f

t t

K t tε

= ⋅∇ =

= Γ ⋅∇

F μ E

E E

2p m

fp m

Kε ε

ε ε−

=+

3sphere 4 RπΓ =


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Optical DEP – numerical simulation• E-field distribution

calculation performed with CST

• Motion equations found from DEP force:

• MC motion simulations performed

DEP randdm fdt

= + −v F F v

DEP force

Random motion

Friction (medium and

geometry dependent)


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DEP Experimental setup• Trapping setup is

added on characterization setup

• Sample is placed at bottom of basin

• Chip illuminated with high power source (Pin=1W)

A B


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Preliminary results


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Detection concept - summary• Antenna array placed

under particle colloid• Array illuminated• DEP trapping occurs• Resonance change in

antenna• Scattering properties

modified• Detection through

optical scattering

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Refractive Index Sensor concept

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Wood’s anomalyThe impinging beam excites a surface wave on the surface.Accompanied by strong variations in the amplitudes of the Bragg diffraction lobes.


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Splitting Mechanism

xdiff Gmk

±=

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Theory vs. ExperimentsFOM and sensitivity depends on incident angle and surrounding RI.

∆λFWHM

𝑆𝑆 =𝑑𝑑𝜆𝜆𝑑𝑑𝑑𝑑

𝐹𝐹𝐹𝐹𝐹𝐹 =𝑆𝑆

Δ𝜆𝜆𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹

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Theory vs. Experiments

n=1.36 n=1.404

Tilting the impinging beam by ~0.5º yields a narrow peak.Sensitivity of S>1000RIU and FOM~150-210

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Phased reflectarraysInduce an arbitrary phase profile using nano-antennas.Conceptually similar to SLMs but with sub-wavelength resolution.The challenge: Design a set of antennas covering 2π phase shiftwith low sensitivity to fabrication tolerances.Our solution: Employ coupled dipole-patch antennas.

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Beam-Shaping: The unit-cellThe combination of dipole and patch antennas provides multiple multi-curve phase response.Modifying the dipole length and patch width allows for tuning the phase response.

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Beam-Shaping: deflect-array fabrication

A B C

A B C

D A E B F G

D A E B F G

20° deflection45° deflection

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Nano-Antenna reflection holographyDesign a phase reflector which generates an arbitrary beam shape.High efficiency & resilience to fabrication errors.


AlgorithmA

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Hologram Efficiency


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Nano-imprinting lithography (NIL)• Avoid expensive E-beam lithography

• Single master can be reused indefinitely

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High Harmonic Generation

Tightly focus light on a nonlinear materialGeneration of higher harmonics.Re-emit the higher harmonics.No need for phase matching, etc.

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Maximizing SHG

Pump and Polarization effects-numerical results:(a) FH field distribution for propagation from the

LiNbO3 or the Air;(b) The LiNbO3 effect on the field enhancement in

recessed and on-top Bowtie nanoantennas.

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Experimental setup FH source is a femtosecond fiber mode locked laser.

λ=1550 nm, pulse duration: 150 fs, repetition rate: 80 MHz Beam is linearly polarized and its power is monitored

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Experimental results Generation of SH signal observed experimentally The intensity of the SH signal scales as the square

of the intensity of the FH power. Thisis a clear sign of SHG.

SH signal depends strongly onpolarization of the FH pump.This is a clear indication ofthe importance of the nano antennas in the process.

Conversion efficiency is notyet determined as collection efficiency is unknown.

0 5 10 15 20 250

500

1000

1500

FH [mW]

SH [p

W]

FH z-polarizedz polarized Quadratic FITFH y-polarizedy polarized Quadratic FIT


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SummaryNano-antennas may provide an inexpensive, efficient and simple solution for various nano-photonics applications.

Nano-Rectennas for power harvesting and detection fabricated and characterized.

Beam deflection and wide-angle holography using nano-antennas demonstrated with efficiencies exceeding 50%.

High sensitivity slot-antenna based RI sensor with record high sensitivities and FOM demonstrated.

Rapid optical sensing possible through trapping with nano-antennas

Nano-antennas can facilitate efficient HHG on surfaces.

The nano Rectenna Project Design and Applications of UWB ...

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