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The nano Rectenna Project
Dual Vivaldi UWB nanoantenna
for optical applications Zeev Iluz, Yuval Yifat, Doron Bar-Lev, Michal Eitan, Yoni Kantarovsky, Yuav Blue,
Yael Hanein, Koby Scheuer, and Amir Boag
School of Electrical Engineering
Tel Aviv University, Tel Aviv 69978, Israel
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The nano Rectenna Project
Outline
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• The motivation: solar energy harvesting using optical
nanoantennas
• The Dual Vivaldi antenna – geometry simulation results
• The fabrication process
• The measurements setup – using far field instead of
near field
• Design verification
• Future research
The nano Rectenna Project
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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, October 5, 2011
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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
The motivation
The nano Rectenna Project
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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 terminals
3. In 1964, Raytheon demonstrated a helicopter powered by 2.45 GHz rectenna system. The helicopter flew for over 10 hours
Alternative approach: optical rectenna system
The nano Rectenna Project
General Concept
• NanoAntenna + high-frequency diode
• EM radiation excites AC in nano-antenna.
• The high-frequency diode rectifies the AC current.
• The outcome – IR detection + Second Harmonic Generation.
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The nano Rectenna Project
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Guidelines for efficient IR rectenna
1. 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)
The nano Rectenna Project
• 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. 7
The Dual Vivaldi antenna
The nano Rectenna Project
The simulation setup:
• CST MWS - Finite Elements Frequency Domain solver.
• Unit cell boundary condition: dx=1790 nm, dy=470 nm higher
modes (grating lobes) at the azimuth plane.
• Materials: the complex indices of refraction for all metals was
imported.
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Two phase simulations:
1. Place ports at the slot line edge
S parameters.
2. Normal incident scattering
EM field.
The nano Rectenna Project
Phase 1: both parallel plate waveguide gaps were excited coherently and in phase, using ports across the gaps:
Port 1 Port 2
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The nano Rectenna Project
Dual Vivaldi Antenna: S parameter
simulation results
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The return loss > 9.5 dB between
(129% impedance bandwidth). 0.7 3.25μm
The nano Rectenna Project
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.
The nano Rectenna Project
Initial fabrication results
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W
H
c
g
SINGLE ANTENNA SPECIFICATION
Ant Measured Ant Design
596 580 W[nm]
471 470 H[nm]
31 25 g [nm]
50 40 c[nm]
ARRAY SPECIFICATION
1.79 1.79 dx[um]
0.47 0.47 dy[um]
The nano Rectenna Project
Array Fabrication
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“Open” Circuit
“Short” Circuit
The antenna arrays size is 150 µm X 150 µm, with approximately 26,000 elements.
The nano Rectenna Project
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• To equally excite all nano-antennas in the array (in amplitude and in phase), the
array was positioned at the waist of the incident Gaussian beam.
• The lateral pitch of the arrays the 1st order Bragg diffraction lobe at 60º @
λ=1550.2 nm for a normally incident excitation beam.
• The spectral response of the antennas was obtained by sweeping the excitation
wavelength through the measurement range for different rotation positions of the
array.
Measurements setup
By rotating the stage, the
entire optical spectrum of
the laser was covered.
The nano Rectenna Project
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Measurements at 780 nm were performed using a similar
optical setup with a few differences:
(a) a Si detector was placed at an angle of 26º relative to the
incident beam in accordance with the Bragg condition.
(b) the laser source was a non-tunable, wideband ultra-fast
laser.
The nano Rectenna Project
Design verification
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The nano Rectenna Project
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Efficiency:
• Only the ±1 lobe can be measured.
• Excellent agreement between simulation and
measurements.
• Summing all lobes results in radiation efficiency
exceeding 90%.
The nano Rectenna Project
CNT diodes
A single CNT connecting Ti electrode (Schottky) with Pt electrode (Ohmic) on a
Quartz substrate. The minimal distance between the electrodes is less than 1mm.
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Future research
The nano Rectenna Project
TAU Nanorectenna
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Dual Vivaldi broken
Antenna (model + experiment)
Dual Vivaldi broken
Antenna (2 Metals + Carbon
nanotubes)
NiAu
TiAu
Made at TAU
The nano Rectenna Project
Short Vivaldi + MIM
Au
Al
Sub nm
isolation layer Al
Au
Sub nm
isolation layer
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The nano Rectenna Project
Thank you
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