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 1 The nano Rectenna Project 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 6 The nano Rectenna Project 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 10 The nano Rectenna Project 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 15 The nano Rectenna Project 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 18 The nano Rectenna Project 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 19 The nano Rectenna Project 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 % 21 The nano Rectenna Project 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. 22 The nano Rectenna Project 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 24 The nano Rectenna Project The Reflection Measurement Setup 25 The nano Rectenna Project Design Verification 26 The nano Rectenna Project Coupling Antennas to Loads How to measure impedance of Nano-Antennas? How to measure impedance of Nano-Loads? 27 The nano Rectenna Project 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 ( , ) ) 29 The nano Rectenna Project The S-parameters Measurement Setup in RF 30 The nano Rectenna Project 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 32 The nano Rectenna Project High Frequency Diodes 33 The nano Rectenna Project CNT diodes A single CNT connecting Ti electrode (Schottky) with Pt electrode (Ohmic) on a Quartz substrate. 34 The nano Rectenna Project CNT diodes model Carbon nanotubes 35 The nano Rectenna Project Dual Vivaldi + MIM nm isolation layer Au Au nm isolation layer Al Al 36 The nano Rectenna Project 37 The nano Rectenna Project 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 38 The nano Rectenna Project Additional Applications Particle Trapping and Sensing Refractive Index Sensing Reflectarrays Second and Higher Harmonic Generation 39 The nano Rectenna Project Trapping and sensing nano-objects using nano-antennas The nano Rectenna Project Sensors: trapping and identify nano-particles 41 The nano Rectenna Project Sensors: trap and identify nano-particles 42 The nano Rectenna Project 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 43 The nano Rectenna Project 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 44 The nano Rectenna Project 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) 45 The nano Rectenna Project Preliminary results 46 The nano Rectenna Project 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