Optimizations for ultra small and wide incident angle metamaterial perfect absorbers at low frequency

ThesisfortheDegreeofDoctorofPhilosophy

Optimizationsforultra-smallandwide-incidentanglemetamaterialperfectabsorbersatlowfrequenc
y

by
BuiXuanKhuyen

February 2018

DepartmentofPhysicsGrad
uateSchoolHANYANGUNI
VERSITY


ThesisfortheDegreeofDoctorofPhilosophy

Optimizationsforultra-smallandwide-incidentanglemetamaterialperfectabsorbersatlowfrequenc
y
by
BuiXuanKhuyen
SupervisedbyProfesso
rYoungPakLee
SUBMITTEDINPARTIALFULFILLMENTOFTHER
EQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
AT
HANYANGUNIVERSITYSE
OUL,SOUTHKOREA
February 2018
©BuiXuanKhuyen,2018

HANYANGUNIVERSITYDE
PARTMENTO F PHYSICS
December2017

TheundersignedherebycertifythattheyhavereadandrecommendtotheG rad uateSchoolforacceptance
a t h e s i s e n t i t l e d " O p t i m i z a t i o n s foru l t r a - s m a l l andw i d e - i n c i d e n t a n g l e metamaterialperfectabsorbersatlowfrequency"byBuiXuanKhuyen in

part ia l f u l f i l l m e n t oftherequirementsfortheDegreeofDoctorofPhilosophy.

ChairmanofCommittee:Prof.JooYullRhee

:J-·d

ExaminingCommittee:Prof.ChaffwanOh

Prof. SangJin Sin

Prof. YoungPak Lee


Acknowledgments
Iw o u l d l i k e t o t a k e thisopportunitytothankthosep e o p l e : withoutt h e i r h e l p s a n d s
u p p o r t s , thisthesiswouldhavenotbeenpossible.Mygreatestthanksmustexpresstomysup erv i
sor , ProfessorYoungPakLee,forhisinvaluableguidance,andendlessencouragementoverpast
fouryears.Iamveryproudtohavetheopportunitytostudyunderh i s supportsinthisfieldofmetamateri
als.My

gratitudealsogoestotheq-

PsiLaboratory,D e p a r t m e n t ofPhysics,HanyangUniversityforprovidingmeafina
ncialsupportintheprofessionalresearchenvironment.
Iw ou l d l i k e to thankA s s o c i a t e ProfessorV u D i n h La m wh o hase nc o ur a ge d i n myc
u r r e n t researches,andDr.NguyenThanhTungwhohasalwayssharedwithmemanyu s
e f u l suggestionsandresearchexperiencesinmetamaterials.Itwouldliketoexpressmyd e e p t h a
n k f u l n e s s t o ProfessorJ o o Y u l l R h e e a n d ProfessorK i W o n K i m f o r l o t s o f i n t e r
e s t i n g discussionsinmystudies.Itisalsoapleasuretothanktheformerandcurrentmemberso
ftheqP s i Laboratorya s w e l l a s myfriendsa t H a n y a n g U n i v e r s i t y f o r thef r i e n d s h i p anda
llthesupportsinpastfouryears.Inaddition,Iwouldliketothanktomyc l o se friends,bothnewand
old,farawayandnearbyfortheircontinuousencouragements,w h i c h arethegreatmotivationsof
mylife.Thankyouall.
Finally,Iowemydeepestgratitudetotheencouragement,thesupport,andthelovefrommyparents,
mywifeandmygrandfather.

I


Contents
ListofFigures

V

Abstract

IX

1. Introduction

1

1.1. Historicaloverview.............................................................................................1
1.2. Frameworkofthethesis.......................................................................................3

2. Theoreticalbackground

5

2.1. Materialclassification............................................................................................5
2.2. Metamaterialsandeffective-mediumtheory............................................................7
2.3. Electromagnetic-parameterretrievalfrommetamaterials........................................8
2.4. Electricandmagneticresponsesinmetamaterials....................................................11
2.5. Impedancematching..........................................................................................16
2.6. Metamaterialperfectabsorbers.............................................................................18

3. Simulationandexperimentofmicrowavemetamaterials

22

3.1. Numericalsimulation........................................................................................22
3.2. Fabricationtechnique...........................................................................................23
3.3. Measurementconfigurationintheradioband.........................................................24

4. Reducingthesizeofsingle/dual-bandMPAbyincreasingtheeffective
inductance of the patterninthe UHFband

26

4.1. Introduction...............................................................................................................26
4.2. Metamaterialmodelandfabrication......................................................................26

4.3. Mechanismofperfectabsorptionat400MHz.........................................................28
4.4. ExaminationonMPAfordifferentincidentradiations.............................................32

II


4.5. Realizationofdual-bandperfectabsorptionviaself-asymmetricstructure....................34
4.6. Summary...................................................................................................................36

5. Scaling downthesizeofMPAbyincreasingtheeffective capacitancev i a
t h e effective couplingcross-sectionoftopandbottomlayersin
theV H F band

37

5.1. Introduction...............................................................................................................37
5.2. Metamaterialschemeandexperiment....................................................................37
5.3. Physicalmechanismoftheperfectabsorptionat250MHz..........................................38
5.4. Estimationfortheperfectabsorptionatawideobliqueincidentangle.........................40
5.5. Summary...................................................................................................................42

6. Miniaturizationforsingle/dualbandMPAbyintegratingtheparasiticcapacitorsandthethroughinterconn
ectsin theVHFband43
6.1. Introduction...............................................................................................................43
6.2. Proposeddesignandmeasurement.......................................................................43
6.3. Mechanismoftheenergyconsumptionofincomingelectromagneticwaveat102M H z
46
6.4. Investigationontheperfectabsorptionforwideincidentangle..................................50
6.5. Realizationofthedual-bandMPAbyutilizingsuper-cellstructure.............................50
6.6. Summary...................................................................................................................52

7. Studyontheminiaturizationfordual/triplebandMPAbyutilizingonlyparasiticcapacitorsintheUHFband

53

7.1. Introduction...............................................................................................................53
7.2. Metamaterialmodelandexperimentalsetup.........................................................53

II


7.3. Mechanismanalysisoftheperfectdual-absorptionpeakat305and
360.5MHz................................................................................................................54
7.4. Valuationofthedual-bandperfectabsorptionforwideincidentangle..........................58
7.5. Extendedstudyontriple-bandperfectabsorption......................................................59
7.6. Summary...................................................................................................................61

8. Conclusionsandperspective

62

Listofpublications

66

Bibliography

68

II

ListofFigures
Fig.2.1Materialclassificationsbasedonsignofεandμμ............................................................6
Fig.2.2DiagramforSparametersmeasurementson(a)ahomogeneous1Dslab(b)aninhomogeneousasy
mmetric1Dslaband(c)asymmetricinhomogeneous1Dslab.A singleunitcellofstructureha
sathicknessofdμ.....................................................................................................10
Fig.2.3

(a)Lattice
ofthinmetallicwiresand(b)itseffectivepermittivity(withradiusr=5 . 0 mandperiodici
tya=40.0mm)......................................................................................................12

Fig.2.4Unit-cellstructureofseveralelectricelements:
(a)singleSRR(b)CWand(c)e q u i v a l e n t - c i r c u i t model..................................13
Fig.2.5Schematicofthemagnetic-resonantelementsas(a)unitcellofCWPstructureand
(b)equivalentLC-circuitmodel.SimplifiedLCcircuitmodelsfor(c)magneticand( d ) electricresonantfrequencies,respectively............16
Fig.2 . 6 ( a ) Schematico f u n i t c e l l f o r t h e f i r s t M P A .
( b ) D i s t r i b u t i o n s o f Ohmica n d dielectriclossesattheresonantfrequency.........19
Fig.3.1FabricationprocessofMPAsamples........................................................................24
Fig.3.2Schematicofthereflection-measurement.....................................................................25
Fig.4.1(a)UnitcelloftheproposedMPA.Photosofthefabricated(b)single-peakand(c)d u a l b a nd samples.Insetsin(b)and(c)aretheunitcells, correspondingtothes i n g l e
- p e a k andthedual-bandMPAstructures,respectively.(d)Experimentalsetu p forthemeasurement........................................................................................27
Fig.4.2(a)Simulatedandmeasuredabsorption

spectraofthesingle-

peakMPA.Redandb l u e dashedarrowsdisplaytheFWHMvaluescorrespondingtothesi
mulatedandt h e experimentalabsorptionspectrum,respectively.Inducedsurfacec
urrentson

(b) thefrontand(c)thebacklayersat400MHz.3-dimensionaldistributionsof(d)


themagneticenergy,(e)theelectric

energyand(f)thepower

lossattheresonantf r e q u e n c y ..................................................................................28
Fig.4 . 3 ( a ) E q u i v a l e n t circuito f t h e discussedM P A .
( b ) S i m u l a t e d a n d calculateda b s o r p t i o n frequenciesaccordingtothera
diusofthequarterofdisk(r)andthew id t h o f slenderw i r e ( w).R e d squareandbluet r i a n g l e symbolsr e p r e s e n t t h e simulatedresults,whilethecalculatedresultsare
denoted in blackdotsand greendiamonds..................................................................30
Fig.4 . 4 ( a ) Simulateda n d ( b ) measureda b s o r p t i o n s p e c t r a o f t h e singlepeakM P A accordingt o the i nci de nta ngl e of E M w a v e f or TE po l a r i z a t i on.
( c ) T he sa m e simulatedabsorptionspectraforTMpolarization................................33
Fig.4.5(a)Dependenceoftheabsorptiononthegap(g2)ofproposeddual-bandMPA.
(b)Simulatedabsorptionspectraaccordingtothepolarizationangle(ϕ)ofEMwave.T h e
insetistheschematicviewofvaryingpolarizationangleϕ.Inducedsurfacec u r r e n
t s onthefrontandthebackmetalliclayersattwoabsorptionpeaksforϕ=
(c) -45oa n d (d)45o.Redand

blackarrowsaredesignated

forthecurrentflowsont h e surfaceoffrontmetalliclayeratlowandhighabsorptionfr
equencies,res pe cti ve ly .........................................................................................35

Fig.5.1(a)Structuralspecificationsoftheunitcell.(b)Zoomedimageof2 ×2u n i t cells
forthefabricatedsample.(c)Arrangementfortheexperimentalsetup...........................38
Fig.5.2(a)SimulatedandexperimentalabsorptionspectraofthesuggestedMPA.D i s t r i b u t i

o n s of

(b)the

inducedsurfacecurrentsonthetopandthebottomlayers,3-

dimensional(c)magneticenergy,(d)electricenergyand(e)powerlossat250M H z .
.....................................................................................................................................39


Fig.5 . 3 ( a ) Simulateda n d ( b ) measureda b s o r p t i o n s p e c t r a o f t h e p r o p o s e d M P A
f o r d i f f e r e n t obliqueincidentanglesofTEpolarization.
(c)Similarsimulateda b s o r p t i o n spectraforTMpolarization............................42
Fig.6.13dimensionalperiodicstructureoftheunitcellofsingleMPAwiththepolarizationo
fEM wave...........................................................................................................44
Fig.6.2.(a)SchematicoftheproposeddualbandMPAstructurewiththepolarizationofE M field.

(b)Illustratedarrangementfor

theexperimental
configuration(bottom)a n d magnificationofthefabricatedsample(top)...............45
Fig.6.3(a)SimulatedeffectiveimpedanceandabsorptionspectrumoftheproposedMPA.3dimensionaldistributionsfor(b)theinducedsurfacecurrents,
(c)themagnetice n e r g y , and(d)thepowerlossattheresonantfrequency................46
Fig.6 . 4 ( a ) E q u i v a l e n t circuito f t h e discussedM P A .
( b ) S i m u l a t e d a n d calculateda b s o r p t i o n frequenciesaccordingtothevalue
oflumpedcapacitor.Red-squareandb l u e c i r c l e symbolsrepresentthecalculatedandthesimulatedresults,respectively.G r e e n t r i a n g l e symbolsmarkthesimulatedabsorption................................................48
Fig.6.5SimulatedabsorptionspectraoftheultrathinMPAaccordingtotheincidentangleo f EMwa
vefor(a)TEand(b)TMpolarizations......................................................................50
Fig.6.6(a)Simulatedand(b)measuredabsorptionspectraaccordingtotheincidentangleo f EMwa
ve, oftheproposeddual-bandMPA.......................................................................52

Fig.7.1SchematicofthesimulationandthemeasurementforultrathinDMPA.( a ) 3dimensionalperiodicstructureoftheunitcell,
(b)experimentalconfigurationoft h e proposedDMPAwiththepolarizationofEMwa
ve........................................................................................................................54
VII


Fig.7.2Physicalmechanismofthedual-bandperfectabsorption.
(a)SimulatedeffectiveimpedanceandabsorptionspectrumoftheDMPA.Distributionsof(b)t
heinduced

VII


surfacecurrentsonthefrontandthebacklayers.3dimensionaldistributionsfort h e powerlossat(c)305and (d)360.5MHz...............56
Fig.7.3PerformanceofthebasicDMPAinwiderangeofincidentangle.
(a)FabricatedD M P A .
( b ) Simulateda n d ( c ) measureda b s o r p t i o n s p e c t r a a c c o r d i n g tothe
i n c i d e n t angleof E M w a v e f or T E polarization.
( d) Evolutionof t he si m ul a t e d a b s o r p t i o n spectrafor TM polarization......59
Fig.7.4Extensiontothetriple-bandMPA.(a)3-dimensionalschematicoftheunitcelland
(b)simulatedabsorptionspectraaccordingtotheincidentangleofEMwavefort r i
p l e - b a n d MPA.................................................................................................60
Fig.8.1Examplesofflexible/broadbandMPA,whichcanbeadaptedinthemilitaryandt h e civilianapplications.Ifthe
wholebattleship(ordrone)iscoveredbyalow-f r e q u e n c y flexible/broadbandMPA,theirexistencecannotbedetectedbythelow-f r e q u e n c y radars..................64

8


ABSTRACT
Optimizationsforultra-smallandwide-incident-angle

metamaterialperfectabsorbersat lowfrequency
BuiXuanKhuyenD
epartmentofPhysicsThe
GraduateSchoolHanyan
gUniversity
Inrecentyears,theadvancesinmaterialsciencehavecontributedtothedevelopmento f b e t t e r
t e c h n o l o g i e s . I n lookingf o r n e w e x c i t i n g materialsa n d effects,a n a r t i f i c i a l m
a t e r i a l named“metamaterial(MM)”wasdesignedandhaschangedourunderstandingoflightmatterinteractionsinnature.MMsareregardedasaclassofcompositematerials,a r t i f i
c i a l l y structuredtoexhibitextraordinarypropertiesthatarenotreadilyobservedinn a t u
r a l materials.FromthefirstMM,whichwastheoreticallyproposedbyV.G.Veselagoi n 1968,the
so-calledlefthandedmaterial(LHM),theunnaturalelectrodynamiceffectsw e r e establishedsuchasthe
doublenegativerefractiveindex(NRI)material,theopposited i r e c t i o n o f electromagnetic( E M )
w a v e propagationa n d i t s p o w e r f l u x , andinverseC h e r e n k o v radiation.In2000,S
mithetal.successfullyfabricatedthefirstNRI.Nowadays,t h e novelpropertiesofMMhavebeeninvestigat
edineveryfrequencyrangefromradiotov i s i b l e f o r practicala p p l i c a t i o n s s u c h a s s l o w l i
g h t , s u p e r r e s o l u t i o n s , s u p e r l e n s , el ectr om agn eti cal ly in du ced transmission,EMcloaking,MMmemory,andwirelesspowert r a n s f e r r i n g .
Int h i s t h e s i s , I s t u d i e d t h e e x o t i c phenomenono f p e r f e c t a b s o r p t i o n i n M
M b y simultaneousoptimizationoftheperfectimpedancematchingandthefundamentalmag
neticres ona nc esat veryl ow f re que nc y. These resultsar epromisingc a n di da t e s fora
p p l i c a t i o n s inradiobroadcastingandtelecommunications.Firstly,ametamaterialperfecta
b s o r b e r (MPA)isdesignedbythesandwichedstructure(metal-dielectric-


metal)at400M H z . T h e r a t i o s o f t h e periodicityo f u n i t c e l l s a n d t h e thicknesst
otheabsorption


wavelength(at400MHz)aredesignedas1/12and1/94,respectively.ThisMPAmaintainst h e impedanc
e-matchingconditionwiththefreespacequitewellinarelativelywiderangeo f i n c i d e n t a n g l e s u p to3 0 of o r b o t h t r a n s v e r s e e l e c t r i c a n d t r a n s v e r s e - m a g n e t i c p o la r i za t i o n . As e l f a s y m m e t r i c s t r uc t ur e wasa l s o i n v e s t i g a t e d t o o b t a i n t h e d ua l ba nd p e r f e c t absorptioninthesamerange.Secondary,Iapplyamodeloffourconnectedsplitsqu a r e resonatorsforaplanarMPAstructure,whichhasathickness240timessmallerthant h e absorptionwavelengthat250MHz.TheperformanceofthisMPAisex
perimentallyt e s t e d f o r a w i d e r a n g e o f i n c i d e n t a n g l e s u p t o 45o.T h e n , b y a d

j u s t i n g t h e lumpedc a p a c i t o r s andtheverticalinterconnects,thisnewkindofMPAisminiat
urizedtobeonlyλ/816andλ/
84foritsthicknessandperiodicitywithrespecttotheoperatingwavelength(at1 0 2 MHz),respectiv
ely.Moreover,Iimprovedthisstructureto realizeanearl y-perfe ct d u a l b a n d absorberinthesamerange.Theresultswereobtainedbybothsimulationandexperime
ntatobliqueincidenceanglesupto50o.Finally,byadaptingonlythelumpedcapacitorsonasim
plemeta-surface,dualbandmetamaterialperfectabsorbers(DMPAs)w i t h thicknessof 1/378and1/320withr
espect totheoperatingwavelength at305and
360.5

MHz,respectively,aredemonstrated.Theoperation

ofthisDMPAis

alsoexploredo v e r awiderrangeofincidentangles(upto55o).Inordertofurtherstudythisinte
gratedmethod,a t r i p l e - b a n d M P A i s c o n s i d e r e d b y usinga n a d d o n c a p a c i t o r . A l l o f t h e a b s o r p t i o n spectraa r e e x a m i n e d b y t h e measurement
i n t h e r a d i o - f r e q u e nc y rangea n d comparedwiththesimulation.
MyapproachcontributessignificantlytothedevelopmentofmultibandMPAsatM H z frequencies.ThiswillbethebasisforultrabroadbandMPAsoperatingatverylowf requency int h e f u t u r e . Ina d d i t i o n , theser e s u


l t s a r e promisingf o r potentialp r a c t i c a l a p p l i c a t i o n s i n t h e r a d i o b a n d , s u c h a s
r a d i o - f r e q u e n c y shieldingdevices,s i n g l e / d u a l - f r e q u e n c y filters,andsingle/
multi-modeswitchingdevices.


Chapter1
Introduction
1.1. Historicaloverview
Thep e r f e c t a b s o r p t i o n behaviori n metamaterial( M M ) i s characterizedb y e l e c t r i c a n d /
o r magneticresonances.Ingeneral,theelectricresponseiscausedbyexcitationoftheelectricresonator
sbytheelectricfieldofincidentelectromagnetic(EM)wave.Ontheotherh a n d , themagneticresponseiso

bservedbytheantiparalleldistributionofinducedcurrentso n theoppositesidesofsubstrate.Theexoticphenomenonofne
arlyperfectabsorptioninM M wasdiscoveredfirstlyin2008[1].Bycontrollingtheeffectiveper
mittivityandtheeffectivepermeabilityofresonant structures,a newMMperfectabsor
ber(MPA)hadau n i t - cells i z e o f λ /
3 0 , muchsmallert h a n t h e previousgenerationo f absorbers[2].I n p a r t i c u l a r , theope
rationalfrequencycanbeselectedflexibly,whichisfrommicrowavetoT H z [1,314],infrared[15-18]andevenopticalregion[19,20].Duetoitscompatibilityw i t h
p e r i p h e r a l devices,MPAsare

greatcandidates

forfuturedevicessuchasbolometers[21,22],thermali m a g e r s [23,24],s o l a r c e l l s [25,
26],b i o - s e n s o r s [27,28],andh i g h subwavelength-resolutioncameras[29].

1


Inordertoexpandthep r a c t i c a l - a p p l i c a t i o n areasofMPAs,thetopics

onomni-

dir ecti onal andmulti-and/orbroadbandabsorptionhavebeeninvestigatedintensively.Fori n s t a
n c e , T a o e t a l .proposeda n i n c i d e n t - a n g l e independentMPAbyusingsplitr i n g r eso n ato rs (SRRs)intheTHzrange[30].TheirMPAconsistsofmetallicSRRs(thickness

2


of200nm)atthetopandcontinuousmetalliclayeratthebottomseparatedbyadielectricspacer.T h
e i r t h e o r e t i c a l modelp r e d i c t e d a n d
t h e experimentalr e s u l t s confirmeda n a b s o r p t i o n of94%at1.6THzforvariousangle
sofincidence.Inthenextyear,Diemetal.t h e o r e t i c a l l y d e s i g n e d a n i n t e r e s t i n g a p p

r o a c h f o r w i d e - a n g l e THzM P A , w h i c h w a s modeledbyatungstenwirearrayatthetopandatungstenplateatthebottomofadielectricl a y e r (silicon-nitridesubstrate)
[31].Theirstructurecanbepreparedbytheplanarf a b r i c a t i o n technique,andexhibitedanearl
y-perfectabsorptionpeakoverawiderangeofi n ci d en t angles(from0to70o).
In2011,Maetal.alsocreatedadualbandMPA,whichincludedthreelayers:agoldmetallicl a y e r w i t h s q u a r e r i n g structuresa t t h e f r o n t , a polyimidedielectricl a y e r a n d a n o t h e r metallicgoldlay
erattheback[32].Thesimulatedspectrumpredictedanearly-p e r f e c t dualpeakabsorptionat2.7and5.0THz.However,themeasuredabsorptionswereonly68%
(at2.7THz)and74%(at5.2THz).Then,inthenear-infraredfrequencyregime,a dualbandperfectplasmonicabsorberwasdemonstratedbyZhangetal.[33].Theyfoundt h a t adualperfectabsorptionwasachievedat1.27and1.70μm,m,whichwascausedbythemagneticr e s o n a n c
e s . M o r e o v e r , t h e d u a l - b a n d MPAmaintainst h e n e a r l y p e r f e c t a b s o r p t i o n atincidentanglesupto50oa n d exhibitspolarizationindependentbehavioratnormalincidence.
Nowadays,thedevelopmentoftelecommunicationdevicesbasedonMPAsisapromisingn
ewfield.Hence,thebenefitsofMPAsarebeinginvestigatedandextendedintor a d i o f r e q u e n c i e s
. T h e r e a r e manye f f e c t i v e r e s o l u t i o n s w h i c h haveb e e n p r o p o s e d f o r