Nano-rectenna Project

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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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


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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

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 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


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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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)


• 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 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.


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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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 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.


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]


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.


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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.


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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.


Design verification

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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%.


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


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


Short Vivaldi + MIM

Au

Al

Sub nm

isolation layer Al

Au

Sub nm

isolation layer

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Thank you

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Nano-rectenna Project

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