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 Engineering Tel Aviv University, Tel Aviv 69978, Israel
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Tel Aviv University
Largest of the 7 universities in Israel with ~ 28000 students 3 The nano Rectenna Project
Why Nanoantennas?
Field Field Field Design Coupling localization enhancement detection flexibility from near to • Breaks the diffraction • Up to 40dB power • Phase • Wavelength far field limit (10-50nm enhancement sensitive scaling* – Hybrid • Efficient resolution) - Imaging • Increased detectors detectors surface • Smaller effective phenomena photodetectors (less absorption cross detection dark current, faster section • Load dependence response) - Detection • Enhancing response – • Increasing resolution nonlinear optics sensing, active - information antennas processing
* P. Bharadwaj, B. Deutsch & L. Novotny, "Optical Antennas", Adv. Opt. Photon. 1, 438-483 (2009). Plasmonics and nano-antenna projects
Broadband antennas Rectennas Particle trapping
D A E B F G
Nonlinear optics Sensors Holography 5 The nano Rectenna Project
UWB Antennas and Rectennas • Motivation • Rectenna concept • Dual-Vivaldi design • Fabrication • Performance evaluation • Rectifying devices • Conclusion and Applications
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Motivation for Solar Energy Harvesting • Technology = Power Quadrillion BTU Quadrillion BTU Quadrillion
Contemporary and Future World Contemporary and Future World Energy Consumption 1990-2035* Energy Consumption By Fuel*
• Primary energy resources lead to pollution (e.g. global warming) • Possible solution – Renewable energy, particularly solar energy
*The US Energy Information Administration (EIA) website 7 The nano Rectenna Project
• The energy from 1hr of sunlight striking the earth ( 4.3⋅1020 J ) ~ 1 year of consumed energy worldwide (4.1⋅1020 J in 2001*) • Two main commercial technologies: • Concentrating solar power (CSP) systems • Photovoltaics (PV)
World insolation map
A CSP System Typical Solar Cell Both technologies at present have low efficiency !
*The UN Development Program (2003) World Energy Assessment Report 8 Nano Rectifying Antennas 8 Wednesday, f S l E H ti The nano Rectenna Project
Alternative approach: optical rectenna system
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 9 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: Detection + Second Harmonic Generation
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Guidelines for efficient 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) 4. Metal’s skin depth 11 The nano Rectenna Project
The Skin Depth of Gold
Visible spectrum
• Skin depth ~ 13 nm in IR band
• Antenna thickness > 40-50 nm 12 The nano Rectenna Project
The Dual Vivaldi antenna geometry
( xzend, end )
( xzstart, start ) x z = W1 =25 nm W2 500 nm
L =250 nm • 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 The nano Rectenna Project
Both parallel plate waveguide gaps were excited coherently and in phase, using ports across the gaps:
Port 2 Port 1
The parallel plate impedance ~ Z 01=η Wh/ = 78.5 Ω , η =377 Ω 14 The nano Rectenna Project
Array configuration for Power harvesting Series DC connection – no need for DC interconnects Slight tuning of Design Parameters
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Dual Vivaldi Antenna: Simulation results
The return loss > 9.5 dB between 0.7− 3.25μm
(129% impedance bandwidth). 16 The nano Rectenna Project
How does it work ?
Benefits of coupling for wideband operation ! 17 The nano Rectenna Project
The Dual Vivaldi input resistance and reactance
Multi resonance behavior - finite size traveling wave configuration
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Far-field directivity patterns in the y-x (vertical) and y-z (horizontal) Antenna configuration planes y-x y-z
Non symmetric far-field pattern due to the Quartz substrate
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The Dual Vivaldi radiation efficiency
The radiation efficiency remains higher than 85% 0.78− 3.23μm between (122% efficiency bandwidth). 20 The nano Rectenna Project
Visible Range Antennas Aluminum Wideband
Efficiency 60-70 %
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The Fabrication Process 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.
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Fabrication Results
c
H g
W
SINGLE ANTENNA SPECIFICATION Ant Design Ant Measured W[nm] 580 596 H[nm] 470 471 g [nm] 25 31 c[nm] 40 50 ARRAY SPECIFICATION dx[um] 1.79 1.79 dy[um] 0.47 0.47 23 The nano Rectenna Project
Array Fabrication Open Circuit Short Circuit
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The Reflection Measurement Setup
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Design Verification
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Coupling Antennas to Loads
How to measure impedance of Nano-Antennas?
How to measure impedance of Nano-Loads?
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An infinite antenna array unit cell, as a loaded scatterer:
The incident, scattered, and reradiated waves can be related by S-parameters’ network equations: b a 2,TE ( m , n ) ΓL SS21h 12h SS 21hv 12 SS22hh 22 hv 2,TE (0,0) = + ⋅ b2,TM( m,)n 1−ΓS11 L SS21vh 12 SS 21 vv12 SS22vh 22 vv a2,TM (0,0) A B C 28 A load influence B Tx. & Rx. C structural scattering characteristics The nano Rectenna Project
Illuminating the array with a single mode and using 3 different loads (“open”, “short” and matched load) we determine antenna parameters: bbopen+ short −×2 bload = 2,TE ( m , n ) 2,TE ( m , n ) 2, TE ( m , n ) S11 open short bb2,TE ( m , n ) − 2,TE ( m , n )
bbopen load SS =−−2,TE ( m , n ) 2, TE ( m , n ) 1 S 21hh 12 ( 11 ) aa2,TE (0,0) 2,TE (0,0)
Unknown load reflection coefficient measurement:
bbunknown− load Γ= 2,TE(mn , ) 2, TEmn ( , ) unknown open load unknown open b2,TEmn ( , )−+ b 2, TEmn ( , ) Sb 11( 2,TE(mn , ) − b 2, TEmn ( , ) )
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The S-parameters Measurement Setup in RF
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RF Direct (simulation) vs. Scattered (measurements)
The maximum error in the return loss is 3%, which is less than the resistor manufacturing tolerances (5%). 31 The nano Rectenna Project
RF measurements for unknown load (R=2 KΩ)
Typical error of 9% and a flat response vs. frequency, as expected
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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
Carbon nanotubes
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Dual Vivaldi + MIM
nm isolation layer Au Au nm isolation layer Al
Al
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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 The nano Rectenna Project
Sensors: trapping and identify nano-particles
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Sensors: trap and identify nano-particles
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Trapping with DEP • Dielectric particles manipulated through high-gradient electric fields • Force depends on: FDEP =(μE()tt ⋅∇) () = – Particle Geometry = Γε Re{Kt }(EE ()⋅∇) () t – Dielectric properties of mf εε− particle pm 3 K f = Γ=sphere 4π R – Dielectric properties of εεpm+ 2 medium
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Optical DEP – numerical simulation • E-field distribution dv mf=+−FF v calculation performed dt DEP rand with CST Friction DEP Random (medium and • Motion equations force motion geometry dependent) found from DEP force: • MC motion simulations performed
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DEP Experimental setup
• Trapping setup is A B added on characterization setup • Sample is placed at bottom of basin • Chip illuminated with high power source (Pin=1W)
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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
47 Refractive Index Sensor concept
48 Wood’s anomaly The 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
kdiff = ±mGx
50 Theory vs. Experiments FOM and sensitivity depends on incident angle and surrounding RI.
∆λFWHM
= = 𝑑𝑑𝜆𝜆 𝑆𝑆 𝑆𝑆 𝐹𝐹𝐹𝐹𝐹𝐹 𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹 𝑑𝑑𝑑𝑑 Δ𝜆𝜆 51 Theory vs. Experiments Tilting the impinging beam by ~0.5º yields a narrow peak. Sensitivity of S>1000RIU and FOM~150-210
n=1.36 n=1.404
52 Phased reflectarrays
Induce 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 shift with low sensitivity to fabrication tolerances. Our solution: Employ coupled dipole- patch antennas.
53 Beam-Shaping: The unit-cell The 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.
54 Beam-Shaping: deflect-array fabrication
A B C D A E B F G
A B C
D A E B F G
20° deflection 45° deflection
55 Nano-Antenna reflection holography Design a phase reflector which generates an arbitrary beam shape. High efficiency & resilience to fabrication errors.
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Algorithm
A Hologram Efficiency
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Nano-imprinting lithography (NIL) • Avoid expensive E-beam lithography
• Single master can be reused indefinitely 59 High Harmonic Generation
Tightly focus light on a nonlinear material Generation of higher harmonics. Re-emit the higher harmonics. No need for phase matching, etc.
60 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.
61 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
62 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. This 1500 is a clear sign of SHG. FH z-polarized z polarized Quadratic FIT . SH signal depends strongly on FH y-polarized polarization of the FH pump. y polarized Quadratic FIT This is a clear indication of 1000 the importance of the nano
antennas in the process. SH [pW] . Conversion efficiency is not 500 yet determined as collection efficiency is unknown. 0 0 5 10 15 20 25 FH [mW] 63 The nano Rectenna Project Summary Nano-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. 64