Assimonis, Stylianos

Fusco, Vincent

Queen's University Belfast Research Portal

(Invited) Planar Perodic Geometries: How to Reflect or AbsorbElectromagnetic Energy in a Specific MannerAssimonis, S., & Fusco, V. (2017). (Invited) Planar Perodic Geometries: How to Reflect or AbsorbElectromagnetic Energy in a Specific Manner. In Metamaterials WorkshopPublished in:Metamaterials WorkshopDocument Version:Other versionQueen's University Belfast - Research Portal:Link to publication record in Queen's University Belfast Research PortalPublisher rights© 2017 QUB and © 2017 The Authors.This work is made available online in accordance with the publisher’s policies. Please refer to any applicable terms of use of the publisher.General rightsCopyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or othercopyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associatedwith these rights.Take down policyThe Research Portal is Queen's institutional repository that provides access to Queen's research output. Every effort has been made toensure that content in the Research Portal does not infringe any person's rights, or applicable UK laws. If you discover content in theResearch Portal that you believe breaches copyright or violates any law, please contact openaccess@qub.ac.uk.Download date:06. Aug. 2018Planar Periodic Geometries: How to reflect or absorb electromagnetic waves in a specific mannerDr Stylianos Assimonis and Prof Vincent Fuscos.assimonis@qub.ac.uk, v.fusco@ecit.qub.ac.ukResearch Fellow, Centre for Wireless Innovation ECIT Institute, Queen’s University Belfast, U.K.Exeter Microwave Metamaterials Meeting, December 2017www.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast @ECIT_QUBOutline• Introduction to electromagnetic periodic geometries• Dispersing Electromagnetic Energy• Absorbing Electromagnetic Energy• Harvesting Electromagnetic Energywww.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast 2Electromagnetic Periodic Geometries• Problems • Mutual coupling reduction on MIMO antennas• Radar Cross Section reduction of an object• Design high-directivity planar antennas• Phase plates design• Electromagnetic energy absorption• Why these geometries• They have unique properties mainly because of the periodicity and hence they efficiently solve all the above problems• Usually they are easily fabricated and have low cost• Depending on electrical size, the operation mechanism and the application are categorized as• Frequency selective surfaces• Electromagnetic Band-Gaps• Metamaterials• Electromagnetic absorbers• ScattersDispersing Electromagnetic energy𝑅 = −1 𝑅 = +1Dispersing Electromagnetic energyIt is possible to disperse electromagnetic energy and thus to reduce RCS by properly placing pec and pmc platesGood news: the phase difference between the two reflection coefficients of the plates matters and not the absolute valuesSide-by-side Chess-boardDispersing Electromagnetic energywww.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast 6Unit-cells with size 10x10x3 mm: the basic geometry (left,unit cell 1) is rotated by 90 deg. right (right, unit-cell 2).Magnitude of the cross-polarized reflectioncoefficient for the both unit-cells.Phase and phase difference of the cross-polarized reflection coefficient for the bothunit-cells.Dispersing Electromagnetic energywww.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast 7The finite planar periodic geometry, which consists of 2x2 lattices, which inturn consists of 4x4 unit-cells (left) and the RCS reduction (right) comparedwith a metallic plate with exactly the same size vs. frequency for normalincidence for both TE/TM polarization: reduction occurs from 10 to 25 GHz.RCS for normal incidence at15 GHz for the finite planarperiodic geometry and for ametallic plate with exactlythe same size: at (θ, φ) = (0,0) point the reduction isabout 20 dB (monostatic co-mparison), while in thegeneral case (bistatic co-mparison) is about 3.5 dBAbsorbing Electromagnetic energyAbsorbers use different mechanism than the diffusersΓ =𝑍M − 𝑍0𝑍M + 𝑍0𝑍M = 𝑍0𝜇M𝜖MFrom the effective medium theory and when the unit-cell is electrically small, the periodic geometry can be represented by the effective relative permittivity 𝜖M and the effective relative permeability 𝜇M, and thusBecause of the ground plane the transmission is vanished. Hence, for perfect absorptionΓ = 0 → 𝑍M = 𝑍0 → 𝜇M = 𝜖MΓ = 0 → 𝑍M = 𝑍0 → 𝜇M = 𝜖MAbsorbing Electromagnetic energywww.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast 9Unit cell with size of a = 8 mm,substrate (FR4) height of 1 mm,copper traces and surface currentdistribution at 10.31 GHz.Absorption efficiency for obliquely incident waves for TE (a) and TM (b) polarization.Absorption A, reflectance R, andtransmittance T: the peak value forthe absorption is found to be95.81% at 10.31 GHz.Kollatou, Theofano M., et al. "A family of ultra-thin, polarization-insensitive, multi-band, highly absorbing metamaterial structures." Progress In Electromagnetics Research 136 (2013): 579-594.Absorbing Electromagnetic energywww.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast 10Super cell of a triple-band absorber,consisting of nine properly scaled ERRs.The dimensions of the bigger, medium,and smaller ERRs are those of Fig. 1scaled by s1 = 1, s2 = 0.8 and s3 = 0.7,respectively.Absorption efficiency of the triple-bandabsorber for obliquely incident waves intwo different cases of polarization: TM (φvariation) and TE (θ variation).Kollatou, T. M., et al. "Multi-band, highly absorbing, microwave metamaterial structures." Applied Physics A 115.2 (2014): 555-561.Surface current distribution at 10.4, 13 and15 GHz.Absorbing Electromagnetic energywww.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast 11Schematic of Hexagon FSS unit cell with p = 6.93 mm, substratethickness of 3.13 mm, lossy traces with surface resistance of 27ohm/sq and photograph of the fabricated, planar periodicstructure consisting of 208 unit-cells. Y Shield HSF-74 electroconductive shielding paint was used to form the elements on thesurface. Y Shield HSF-74 is a graphite and carbon black-basedmaterial, which is reinforced with long conductive fibers.Simulated and measured reflectivity plots for normal (a) and 45 degrees (b) incidence. For the first case the bandwidth is 108%, while for the oblique incidence case is 16% for TE and TM polarization.(a)(b)Zabri, S. N., R. Cahill, and A. Schuchinsky. "Compact FSS absorber design using resistively loaded quadruple hexagonal loops for bandwidth enhancement." Electronics Letters 51.2 (2015): 162-164. Absorbing Electromagnetic energyThe mechanism behind the absorbance: meta-surface (dielectric and metallic parts) acts like a resistor𝑓: frequency, tan 𝛿: loss tangent, 𝜖: relativedielectric permittivity, 𝜇: relative magneticpermeability, 𝜎: metals’ conductivity,Losses on the dielectric and metallicparts to the total incident power fornormal incidence for TE/TM (coppertraces)𝑃𝑑 = 𝜋𝑓 tan 𝛿 𝜖𝜖0ම𝑉d𝐸 2 𝑑𝑉𝑃𝑚 =12𝜋𝜇𝑓𝜎ඵ𝑆𝑚𝐻 2 𝑑𝑆losses on the volume 𝑉d of the dielectric partslosses on the surface 𝑆𝑚 of the metallic partsLosses on the dielectric and metallicparts to the total incident power fornormal incidence for TE/TM(resistive traces)energy dissipates on dielectrics and metalsHarvesting Electromagnetic EnergyIs it possible the captured energy to be delivered to a load?Metamaterial RF Harvesters with conventional rectification system (i.e., diodes)Metamaterial harvesters are like metamaterial absorbers BUT• In metamaterial harvesters• RF power is mainly delivered to a properly placed load, representing the input impedance of a rectifier• In metamaterial absorbers• RF power mainly dissipates on the metallic or dielectricparts of the structure• Metamaterial harvesters usually outperform conventional harvesters because,• are inherit periodic geometries with unit-cell of dimension usually λ/10• each unit cell acts as a small battery• could form compact structures operating at low frequency bands (e.g., FM, TV) which usually carry more powerHarvesting Electromagnetic Energy𝛼 ≈𝜆10Power efficiency: the power delivered tothe rectification system (load) to theincident powerTriple-band (0.9 GHz, 1.8 GHz and 2.45 GHz) metamaterial absorber for RF Energy HarvestingSurface current distributions at the three resonating frequencies at 0.9 GHz, 1.8 GHzand 2.45 GHz• S. D. Assimonis, et. al, "High efficiency and triple-band metamaterial electromagnetic energy harvester," IEEE ELECO, Bursa, 2015, pp. 320-323.Harvesting Electromagnetic Energy0.5λTriple-band metamaterial absorber for RF Energy HarvestingA panel of 5x5 unit-cells(left) is formed. On thebottom a circuit grid ofrectifiers transforms thecaptured RF energy toDC powerHarvesting Electromagnetic EnergyTriple-band metamaterial absorber for RF Energy Harvesting𝑆 = 0.1 to 100 𝜇W/cm2Assuming plane wave which impinges on the panel with power densityFor each unit-cell𝐴𝑖 = Τ𝜆 102 = 11.1 cm2 and 𝑃𝑖𝑛,𝑖= 𝑆𝐴𝑖 = −29.55 to 0.45 dBmFor the whole 5 × 5 panel with dimension Τ𝜆 2 × Τ𝜆 2𝐴 = Τ𝜆 2 2 = 277.39 cm2 and𝑃𝑖𝑛 = 𝑆𝐴 = −15.57 to 14.43 dBmIt is possible to harvest above 20 mW for100 𝜇W/cm2 from a metamaterial absorberpanel with dimension Τ𝜆 2 × Τ𝜆 2Efficiency =𝑃outdc𝑃inRFThank you for your attention!www.ecit.qub.ac.uk ECIT is a Global Research Institute of Queen’s University Belfast 17

(Invited) Planar Perodic Geometries: How to Reflect or Absorb Electromagnetic Energy in a Specific Manner

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(Invited) Planar Perodic Geometries: How to Reflect or Absorb Electromagnetic Energy in a Specific Manner

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