J Shanghai Univ(Engl Ed),2011,15(3):185—189 Digital Object Identiifer(DOI):10.1007/s1 1741—01 1-0718—3 4-component 2-D CFDFD method in analysis of lossy circular waveguide with fractal rough surface DENG Hong-wei(邓宏伟) ,ZHAO Yong-jiu(赵永久) ,LIU Bing(刘 冰) ,JIANG Wan-shun(姜万顺) , NING Yue—min(宁日民) 1。College of Electronic and Information Engineering,Nanjing University of Aeronautics and Astronautics,Nanjing 210016, P.R.China 2.The 41th Research Institute of China Electronics Technology'Group Corporation,Qingdao 233006,P.R.China ( ̄)Shanghai University and Springer—Verlag Berlin Heidelberg 2011 Abstract In this paper,equivalent surfcae impedance boundary condition(ESIBC),which takes fractal parameters(D,G) into SIBC,is implemented in the 4.component 2.D compact finite diiference ̄equency domain(2-D CFDFD)method to an. alyze the propagation characteristics of lossy circular waveguide with fractal rough surface based on Weierstrass-Mandelbrot fW.M)function.Fractal parameters’effects on attenuation constant are presented in the 3 mm lossy circulra waveguide,and the attenuation constants of the first three modes vary monotonically with scaling constant fG)and decrease as the fractal dimension(D)increasing. Keywords fractal,roughness,2-D compact fimte diference rfequency domain(2-D CFDFD),equivalent surface impedance boundary condition(ESIBC),attenuation constant Introduction ulate rough surface of the transmission line.Alberto[ J calculated the TE and TM modes for a hollow conduct— In practical engineering,the rough inner surfa ce in’ ing waveguide with random wall roughness.The sta- troduces additional disturbance on the electromagnetic tistical properties associated to the wall roughness are ifeld distribution nearby and increases the propagation consistent with a Gaussian random process.Tsangt5J losses of the circular metal waveguide.A theoretic in— adopted the analytic small perturbation method and the vestigation was reported that the surface roughness numerical method of MoM to analyze the effects of a gave rise to the eddy current losses at microwave fre— random rough surface on the absorption by a metallic quency,and the power dissipation of the rough conduc- surface at microwave ̄equency.However,engineering tor plate was ofund to jncrease by about 60%over that rough surface is neither periodic nor random,thus the for a smooth surface[l11.The full—wave mode—matching Gauss model can not simulate the rough surface accu— method employing the similarity transformation to de— rately. rive the eigenvalue equation for the periodic bumpy re— The f6—8]indicate that machined surface profile gions that mode1 the surface roughness of a WR.10 shows the characters of stochastic,multi—scale and self- f75—1 10 GHz1 waveguide is presented[圳.The attenu- afifnity.The Wleierstrass—Mandelbrot fW—M1 fractal ation losses increase by approximately 60%at 75 GHz, function satisfies all these mathematical properties and 36%at l10 GHz under the particular conditions applied. therefore is widely used to simulate engineering rough Hollmann[3J applied the integral equation method using surface. In addition.the W.M function amended by the equivalent surface impedance boundary condition Bhushan is expressed as fESIBC1 to investigate the effect of surface roughness of a particular microstrip on the attenuation losses.AP— =proximately 22%increased in attenuation constant was G(D-1) E 器, observed at 10 GHz.The mentioned studies of trans— mission line with rough surface are based on simple 1<D<2,7>1, (1) periodic models,such as rectangular model or triangle where D is the fractal dimension and G the scaling con— mode1.The Gauss model is employed in the[4-5]to sier— stant.D reflects the complexity and irregularity of the Received Sept.15,2009;Revised Mar.5,2010 Corresponding author DENG Hong—wei,Ph D Candidate,E—mail:ceceliayanl008@yahoo.com.an 186 profiles curves and both D and G are scale independent. -y iS the fractal scaling parameter and selected to be 1.5 + J Shanghai Univ(Engl Ed),2011,15(3):185—189 m一0.5 m rn一1,J) for the phase randomization and high spectral density. In this paper,the 4一component 2.D compact differ— ence frequency domain(2一D CFDFD1 method which needs less CPU time and memory space[9—10J iS intro- duced to derive propagation constant of lossy circular J- (m+1,n)一 (m+1,n一1) (m+1)h (m,佗)一Hpmh (m,n一 ) (2) waveguide fractal rough surface based on W—M rune— tion.ESIBC which takes fractal parameters into SIBC iS implemented in the method.of which the advantages m=0,1,…,M一1,n=1,2,…,N, are reserved.Fractal parameters’effects on attenuation constant of the lossy circular waveguide are presented and the results are discussed in detail. 1 4-component 2-D CFDFD method Similarly to the treatment in『9—101,it iS assumed that the circular waveguide iS uniform along Z and the wave propagates in the positive Z direction.The trans— verse field components shown in Fig.1 inside the circular waveguide can be expressed by eliminating the longitu— dina1 components from the Maxwell’S curl discrete equa— tions,we have 聍=2 胛=1 n=Ⅳ E E2( ,") ———÷ ● E components …… o Hcomponents Fig.1 Compact 2D lattice 一 ( )=(1— 1 2m((m+0m+1.51 。 )g ̄(7/'t,rt) + 1 (m+1.5H\m+1v(m+1,佗) 一 …)=( 志一 ) (…) + 1 【r、 m—+—O.5 ,(m,佗+1)一日 (m,佗) m mh∞ m一0.5日 (m一1,n+1) 一 (m一1,礼) m (仇,礼+ (1mh)+ ()0 m,n ), m=l,2,…,M,n=1,2,…,Ⅳ, 一:- ̄Hp( m,几) ( (m,It)一 1 2 (m一1,n)+ Ep(m~1,札+1)一 (m~1,n) (m一0.5)h ! ! ± ! ! 2 (m+0.5)h m=1,2,・一,M,佗=1,2,…,Ⅳ j一i'y ( ):( 一 丽) (…) 1 f +碗( (m,几+1)+ (m,n~1) (m+0.5)。圮 1 (m+1,札)一 (m+1,几一1) m+0.5 (仇+0.5)h + (m,n)一 m+0.5()m,h 佗一 m+0,5 (), m=0,1,…,M一1,n=1,2,…,Ⅳ (5) where 7 is the complex propagation constant and o the wave number in free space.^p and h denote mesh sizes in P and directions. It is observed that Ep and H can not be applied in the center point(m=0)because ifeld components that J Shanghai Univ(Engl Ed),2011,15(3):185—189 —187 have no definition will be involved.Then(2)and(5) should be modified to[10] roughness function,which expresses the extent of devi. ationfro,.m the profile midtine.From(9)and(10),we 一 ,: Hp(1n)Hp(1,n-+ (1.5 -......... can obtain s +一ar2 ctan。船 co一 , —....................1) ——一h 0.SH.(O,n)1 (11) + (0,rt)~ 4 N k2h2pN ∑ (0,n), 札) (6) Ac cording to the ESIBCthe field components ,and ontheouter boundary surface shown in Fig2 . .n=0 一 (。,扎) (。,n)+ j 2 I j2 (1,—can be specified as (M,lt') ≈ sHz(M一1,n), 一芸 (0,n+1)+ Ez(M,佗)≈--Ze ( ~1,n). (12) 一j2 (1n-1)一 jN (。,,札一1)), (7) ^ ) where m=0 2 Equivalent SIBC for fractal surface roughness The multiscale nature of fractal function Z( )c0In. posed of the infinite frequency modes superp i ion is displayed by the power spectrum which provi _es the aⅡ卜 plitude of the roughness at all length scalesThe Dower spectrum of the W-M function is given as .一一一’、一’ O Hcomponents ) G2(D一1) Fig・2 ESIBC on outer boundary surface for E口and E 2 1n w(5—2D) where frequency is the reciprocal of wave length. (8) Equations(2)一(5)can not be applied to boundary nodes Oil fractal rough surfaceThey have to be modi.. lfed by applying ESIBC .The parameter m0 obtained from the spectrum is R:=(z(z) )= mo /厂 S(w)dw 】 一 ( —l,n)= (M一1,n) 一 G2(D~1) 1 1 2In7(4—2D) “,f4一。D) D) (9) — (( s+ M—1.5 M——1 ) ( 札) where the low frequency limit 021 corresponds to the sampie length(L),whereas Wh corresponds to the sampling ( 一2,n) interval(AL)which is related to the resolution of th--eo instrument. H p(、M一 1,n)西-Hp (M-1,nConsidering the effect of surface roughness Ra by the 一 ( 一1)^ M—— )/J (13) correction formula given in[3】,the equivalent surface impedance jS expressed as ( ,n)=一譬Ze。HdM—l,佗) fMHp(M,n)~( 一1)Hp(M k(M一0.5)h 一=Zs(1+arctan(¨( )。)), . (10) — JZes where Z8: is the surface impedanceand are the conductivity and the skin depth of the meta1 respectively. is the root mean square of the surface 1,扎)+ (M一1,n+ 188 ,Il, .7 。 一—J Shanghai Univ(Engl Ed),2011,15(3):185-189 ‘ 叠.QNJ_\嚣口墨田蜀0u I10一 Il墨《 kh—M一0.5 p 一—、H M sZe8 f I M—l kh—p M一0.5 Hp(M一1,n) 日 (M一12M(,n+1M)一日 ( 一1, ) 0.5)h 一(15) From surface points and inner points,we can con— clude an eigen problem as 30 31 32 33 34 35 36 37 38 【A]{ )= { ), w,Frequency/GHz (a)TEll h【ere{ ):{ , , , ) , :一等= ,A】a sparse coefifcient matrix.In the pr opagatin g sta- is the phase constant and ol is the attenuation ,and tus, constant caused by the metal loss. 3 Numerical results The attenuation constants of the first three modes (TEn,TMo1,TEo1)are calculated by the 4-component _Ⅷ.A ,s —— ∞口o —10l】《rII10#《 2一D CFDFD method with SIBC in 1ossy circular O O O O O O O 0 metal waveguide with radius r=3 mm and conductivity 如勰 ∞ 如 加 _一_.Ⅲ.A ,s _【 墨∞Il0u口0 晕—I。#《 【_ 。目.aZ)/∞ 是 口00 Il0 对 Il #《 O O 0 O O O O O O O O O O O O 0 O O O O a=5.8×10 S/m(see Fig.3).The numbers of grids in direction of radius and angle are M=I5,N=25 respec— tively.Figure 3 shows that the attenuation constants decrease as frequency going up and are consistent with the theoretical ones[1 l1. 加 M ∞ 如 ∞ 如 Frequency/GHz (b)TMol 0.25 0_20 O.15 O.2O 0.10 50 51 52 53 54 55 56 57 58 Freuqency/GHz 0.O5 (c)TE01 30 35 40 45 50 55 60 Fig.4 Attenuation constants of the first three modes Frequency/GHz for diferent scaling constants G fr=3 mm,o-: 5.8×10 S/m,L--i.5 mm,D=I.8,△L=0.15 m) Fig.3 Attenuation constants of the first three modes in lossy circular waveguide( :1.5×10 S/m,肛r=l, r=3 mm) The effects of fractaI dimension(D1 and scaling COn- stant(G)of fractal rough surface on the attenuation constants of the first three modes are investigated with the other parameters unchanged as shown in Figs4—5. .4 Conclusions In this paper.the 4一component 2一D CFDFD method with ESIBC is introduced to analyze the attenuation losses of the lossy circular waveguide with fractal rough surface based 0n W—M function.The advantages of the 4一component 2一D CFDFD method are reserved by ap- plying ESIBC.Detailed investigation on the fractal pa.. rameters’effects of 3 mIn lossy circular waveguide is It is observed that the attenuation constants vary mono— tonically with G from 0.01 m to 0.04 m in Fig.4whereas the D increases from 1.6 to 1.9,and the at— , presented.The attenuation constants of the first three modes vary monotonically with G and decrease as the D increasing. tenuation constants decrease in Fig.5. t_ -Ⅲ. 盟豆研gu g焉 II尝《 J Shanghai Univ(EnglEd),2011,15(3):185-189 ^I_蜀.a邑 q景u00 g 霉g#《 O O O 0 O O O O O O ^I.—II.△量嚣q曩计—f0 I10口硝 IID≈《 0 O O 0 O O O O 189 ∞ 加 M ∞ 如 ∞ ∞ 加:2 Frequecy/GHz (a)TE,1 40 41 42 43 44 45 46 47 48 Frequency/GHz (b)TMol 50 51 52 53 54 55 56 57 58 Frequency/GHz (c)TEol Fig.5 Attenuation constants of the first three modes for diferent D(r=3 mm,a=5.8x 10 S/m,L=I.5 mm, G=0.02 gm,AL=0.15 gm) References I l I MORGAN S P Jr.Effect of surface roughness oil eddy current losses at microwave frequencies fJ].Journal of Applied Physics,1949,20:352-362. I2】CHEN C D,TZUANG C K C,PENG S T.Ful1.wave anal— ysis of a lossy rectangular waveguide containing rough inner surfaces fJf.IEEE Microwave and GuidedⅥ e Letters,1992,2(51:893-895. I3】HOLLMANN D,HAFFA S,ROSTAN F,WIESBECK W. The introduction of surface resistance in the three- dimensional finite-diference method in frequency do- main[J].IEEE Transactions on Microwave Theory and Techniques,1993,4l(5):893—895. 14『ALBERTO M S,ULISES R C,RAFAEL E L.Efrect of wall random roughness on TE and TM modes in a hol— low conducting waveguide[J】.Optics Communications, 2004,238(416):291-299. 5I TSANG L,Gu X X,BRAUNISCH H.EIj’ect of ran. dom rough surface on absorption by conductors at mi. crowave frequencies IJ1.IEEE Microwave and Wireless Components Letters,2006,16(4):221-223. I61 GANTI S,BHUSHAN B.Generlaized fractal analysis and its surfaces applications to engineering[J].Wear,1995, 180(1/2):17—34. 17I HASEGAWA M,Ltu J C,0KUDA K,NUNOBIKI M.Cal- culation of the fracta1 dimensions of machined surface profiles【J】.Wear,1996,192(112):40—45. I81 JIANG Z D,w_ANG H R,FEI B.Research into the ap. plication of rfactal geometry in characterising machined surfaces『J1.International Journal of Machine Tools and Manufacture,2001,41f13/141:2179-2185. 19]ZHAO Y J,Wu K L,CHENG K K M.A compact 2D full wave ifnite-diference frequency.domain method for general guided wave structures『J1.IEEE 1 ansactions on Microwave Theory and Techniques,2002,50(7): l844—1848. [10]ZHANG Qi,ZHOU Xi—lang,SHEN Wen—hui.AnalySis of transmission characteristics of circular metal waveguide using 2-D FDFD method[J].Journal of Microwaves, 2005,21(2):12-19(in Chinese). [11]POZAR D M.Microwave engineering【M].3th ed.New Jersey:John Wiley&Sons.Inc..2008:1—612. (Editor JIANG Chun-ming) 。