Novel electro-magnetic phenomena: and. wireless power transfer

Transcription

1 Novel electro-magnetic phenomena: one-way-waveguides waveguides and wireless power transfer

2 Unidirectional backscattering-immune immune topological electromagnetic states Dr. Zheng Wang Dr. Yidong Chong Prof. John Joannopoulos Prof. Marin Soljačić

3 Metamaterial: optical properties determined from its nano-structure t (rather than its composition) High index of refraction Low index of refraction 3D photonic crystal: a semiconductor for photons Fre equency Allowed Forbidden Allowed Yablonovitch (1987) John (1987)

4 Electronic and Photonic Crystals Peri iodic Me edium atoms in diamond structure ~0.1nm dielectric spheres, diamond lattice ~300nm Ba and Diag gram elec ctron energ gy pho oton frequ uency wavevector wavevector

5 Optical waveguides conventional waveguides photonic crystal photonic crystal waveguides

6 In both conventional and PhC waveguides? T-symmetry REFLECTIONS: IMMUNE TO DISORDER!

7 Topologically-nontrivial Electromagnetic States Integer Quantum Hall Effect : unusual phenomena in a 2D system of electrons in crystals, subjected to a perpendicular strong magnetic field Chiral Edge States (CESs) Unidirectional transport Dissipationless transport in presence of impurities Thouless et al. (1982) Simon (1983) Kohmoto (1985) Haldane (1988) Hatsugai (1993) Enabled by: nontrivial topology of band structure T-reversal symmetry breaking Can one extend these ideas to E&M States in photonic crystals? Haldane & Raghu PRL (2008) Haldane & Raghu, PRL 100, (2008) Raghu & Haldane, PRA 78, (2008) Wang, Chong, Joannopoulos & Soljačić, PRL 100, (2008)

8 Chern number of n-th band: How does this work? Intro to Chern numbers c n : integer always changes abruptly Σ n c n =0 T-symmetric systems c n =0 p? q? p + Δ q - Δ p + Δ q - Δ

9 Hatsugai's Relation Δ Δ T-symmetric T-broken Δ one-way edge modes The # of CESs in a gap = Σ C n over lower bands

10 Break T-symmetry one-way edge states 0 YIG B ~ 0.2T increase H c n changes discontinuously at degenerate-k points

11 Create one-way edge-states at the PhC boundary equency Fre

12 Truly reflectionless! CES waveguide source metal scatterer Absorbing region

13 Truly reflectionless!

14 Contrast with conventional waveguides conventional PhC waveguide CES waveguide

15 Observation: CES DC magnetic field 0.2 Tesla Antenna B CES Waveguide Antenna A Metal Wall Copper Plate Magneto-optical Photonic Crystal (ferrites) Microwave Absorber Waveguide Wang, Chong, Joannopoulos & Soljačić, Nature 461, 772 (2009)

16 Observation: backscattering-immunity Scatterer of variable length (l ) Waveguide

17 Chiral Edge States: Unidirectional transport backscattering-immunity Summary: one-way states enabled by: nontrivial topology of band structure T-reversal symmetry breaking previously known in quantum Hall effect (electronic system) observed for the first time as electromagnetic (photonic) states Dr. Yidong Chong Dr. Zheng Wang Prof. Marin Soljačić Prof. John Joannopoulos

18 WiTricity: non-radiative wireless power transfer

19 Motivation Tesla tower: cca. 1904

20 Wi-Fi (wireless internet) concept: radiation

21 Resonant coupling as energy transfer

22 Resonances in quantum mechanics nonradiative transfer 2 V(r) V(r) h 2m 2 ψ = Eψ Schrödinger equation c 2 2 E 2 = ω E e - quantum tunneling e - Maxwell equation Hydrogen atom proton

23 Magnetic resonances B E Outside: U E «U B Most materials: μ~μ AIR weak interaction with B-field!

24 Examples of magnetic technology Maglev Magnetically levitating bed

25 Coupled mode theory resonant object (Source) resonant object (Device) da dt S D = i ( ω i Γ ) as + iκa D = i( ω i Γ) ad + iκas da dt Q = ω 2ΓΓ

26 Strong Coupling : κ/γ» 1 efficient energy transfer

27 Strong Coupling efficient transfer Karalis, Joannopoulos & Soljačić, Annals of Physics 323, 34 (2008)

28 Experimental results

29 source device 200 cm 30 cm 60W bulb Kurs, Karalis, Moffatt, Joannopoulos, Fisher & Soljačić, Science 317, 83 (2007)

30 same thing, different viewing angle

31 Experimental proof of strongly-coupled regime e

32 source device 200 cm 30 cm 60W bulb efficiency i ~50% (Q~1000)

33 Efficiency vs. distance

34 Comparison with inductive coupling D» L D Efficiency η R /Q 2 L D ~ η R /1,000,000 L» D L Efficiency η R

35 Andre Kurs Prof. Marin Soljačić Prof. J.D.Joannopoulos bulb Prof. Peter Fisher Robert Moffatt Dr. Aristeidis Karalis

36 Experiments with 1 source, 2 devices - different sizes Kurs, Moffatt & Soljačić, Appl. Phys. Lett. 96, (2010)

37 Some potential applications Industrial, military, and household robots Portable personal electronics Electric vehicles

38 Summary: wireless power transfer mid-range non-radiative energy transfer scheme based on strongly-coupled resonances as a powerful concept, it could enable a wide range of applications

39 WiTricity TED talk summer 2009 Eric Giler; CEO, WiTricity Corporation