Microwave-absorbingcharacteristicsforthecompositesofTPMaterialsScienceandEngineeringB117(2021)27–36Microwave-absorbingcharacteristicsforthecompositesofthermal-plasticpolyurethane(TPU)-bondedNiZn-ferritespreparedbycombustionsynthesismethodCheng-HsiungPenga,Chyi-ChingHwangb,,JunWanb,Jih-ShengTsaib,San-YuanChenaabDepartmentofMaterialsScienceandEngineering,NationalChaoTungUniversity,Hsinchu300,TaiwanDepartmentofAppliedChemistry,ChungChengInstituteofTechnology,TashiJen,Taoyuan335,TaiwanReceived6June2021;receivedinrevisedform6October2021;accepted14October2021AbstractNiZnferritewiththechemicalformulaNi0.5xZn0.5xM2xFe2O4(M=Co,Cu,orMg,andx=0or0.05)wassynthesizedbyacombustionsynthesismethodusingmetalnitratesandurea((NH2)2CO)asreactants.Thenanocrystalliteofthesematerialsweremixedwithathermal-plasticpolyurethane(TPU)elastomertobeconvertedintoamicrowave-absorbingcomposite.Thecomplexrelativepermittivity(εr=εjε)andpermeability(r=j)oftheabsorberweremeasuredinafrequencyrangeof2–12GHz.Thereectionloss(R.L.),matchingfrequency(fm)andmatchingthickness(dm)werecalculatedusingthetheoryoftheabsorbingwall.Effectsofboththeparticlesizeofferriteandthedopantpresentedintheferriteontheelectromagneticpropertiesandmicrowave-absorbingcharacteristicswereinvestigated.Itwasfoundthatnanoparticlesaround40nmexhibithigherreectionlossthanboththoseobtainedfrommicro-sizedpowdersandthosewithsizelessthan25nm.Also,itwasshownthattheCo-doped,Mg-doped,andCu-dopedNiZnferrite-TPUcompositescouldbedesignedtobemorenegativethan20dB,inafrequencyrangeof2–12GHz,tobecomepromisingmaterialsformicrowave-absorbingapplication.Thesedopedferrite-containingcompositeshavemoreeffectivemicrowave-absorbingcharacteristicscomparedtoundopedone.2021ElsevierB.V.Allrightsreserved.Keywords:NiZnferrites;Microwaveabsorbers;Reectionloss;Combustionsynthesis1.IntroductionMuchattentionhasbeenattractedbymicrowave-absorbingmaterialsduetothefactsthattheycanabsorbenergyfrommicrowaveandthattheycanbewidelyusedinthestealthtechnologyofaircraft,televisionimageinter-ferenceofhigh-risebuildings,andmicrowavedark-roomandprotectionetc.[1,2].Extensivestudyhasbeencarriedouttodevelopmicrowave-absorbingmaterialswithhighefciencyandnewabsorptionmaterials[3–5].Onecriterioninselect-ingtheabsorbingmaterialistodiscoverthelocationofitsnaturalresonanceregion.Thus,astudyofthefrequencyde-pendenciesofthecomplexrelativepermittivity(εr=εjε)Correspondingauthor.Tel.:+88633891716x312;fax:+88633892494.E-mailaddress:cchwang1@ccit.edu.tw(C.-C.Hwang).andpermeability(r=j)ontheabsorbingmaterialhasbeenaeldofinterest.Inthepast,thespinelferriteshavebeenutilizedasab-sorbingmaterialsinvariousformsformanyyears.Also,theferrite-polymercompositesareusefulasabsorbersduetotheirlightweight,lowcost,andgooddesignexibility[1,5,6].Amongthespinelferrites,NiZnferritesarecommerciallyusedaselectromagneticdevicesoperatedinhighfrequencies(10MHz),arisingfromthefactthatmetaldopantscanbeusedtomodifytheelectromagneticpropertiesofNiZnfer-ritesbyincreasingtheresistivityandpermeability[7].Forthispurpose,someattemptsweremadetoverifythecorrela-tionbetweenthematerialconstants,εrandr,andmicrowaveabsorptioninthesinteredferritesthatcontaindivalentmetalions[6–9].Recently,theresearchpursuingtonanocrystallinema-terialsandtheirpropertieshasbeengivenmuchattention0921-5107/$–seefrontmatter2021ElsevierB.V.Allrightsreserved...