llllll 1 RADIA‘HON OF A POIN? 536905.23 LOCATED AT THE T}? Q? A PROLATE SPHERGH) Thesis for me Degree of M. S. MSCREGAN S?ATE CGiLEGE Eugene C. Hamhes 32'. lIIlIIIlIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII I 1293 917014790 _ g This is to certify that the thesis entitled Panama“ ofa Pom'f DI o/e iot‘qkol CH" We WPO a]? a .Pf‘qulla Sf‘nptmmg presented by cc. C. Hdaimflt, has been accepted towards fulfillment of the requirements for _M'_\70°. Vihereas for the dipole alone, the radiation is symmetric about the z-axis. This type of radiation oattern becomes more pronounced as thL increases. A greater amount of energy is radiated as the soheroids approach the limiting case, where ‘7— , as was predicted by equation (3") . FIG. T -24- 10 FIG. -26- T _ q _ r _ w i ’ a \ a 80.8 \\ oood. / \\ k \ nun; 80.. u aw 12 FIG. I27- n «.9. 80.. EM. 15 FIG. FFFFFF APPENDIX I. II. III. TABLE OF CONTENTS A Magnetic Dipole Near the Tip of the Spheroid. . . . . . . . . . . . . . . . . 51 The Integration in Equation (55). . . . . 55 Formulas Useful in Computation With Prolate Spheroidal Wave Functions. . . . .36 I. - 31 - A Magnetic Dipole Near the Tip of the Spheroid The electromagnetic field can in this case be de- duced from the component £5q> alone. It must satisfy the boundary condition E'f : 0 when g: go (17(5) The calculation for Green's function yields G67; 57') Utmé Gk 2% W (‘5) (3) 3‘? Q1“) 2 mfiaue.) (”RZGWRmu)? >§’ where now . I :2) “Li? (3) 3R; s”) R. (9-9 Ruej'RL LS) an) in order that Gfi7jg'l7)satisfy the same bounds 1y condition as Ehe . The calculation of En? yields an expression analogous to equation (37) , but now: the coefficients of this reqresentation have the form 81: taC. fkm (SM/{ET NUF’R (3.) (“m u where g , is the coordinate of the dipole at any point I of the pos tive z-axis such that €12 go . Now as §,->§°,L u , and therefore 811. as well as the entire field must vanish. A simple physical argument can be advanced to account for this fact. When a magnetic dipole is approached to a perfectly conducting surface, with its magnetic moment perpendicular to it, there will arise surface currents producing an opposing magnetic dipole field vanish, as required by general theory. In the limit of zero distance the effect is complete cancel- lation. II. The Integration in Equation (35) We substitute from equations (34) and (35) into the integral (35). The integration variables are the I primed coordinates g , 7’, and all quantities are re— presented in terms of these. Thus one finds, cf. Fig. 5 and equations 0) , L1) and C5) , that sin e: f/R H?) where R= a J(§'-U0-7")+(§'-§.)‘ (‘9’ f z: aJ(§”-’-l)(|“7'T) (5‘!) also z! =a§‘ , and $2 fig. since 7:: I“; (5 2’) where J- is an arbitrarily small positive number. a In substituting from (5‘!) it will be convenient to write down here just a typical term of the infinite series, and furthermore only that part of the term which varies during the integration, i.e., , ( : 512(7) 11(3) (53) This clearly is the function to be used in finding the field at points (3,7) more distant from the origin I than the dipole D itself (§?§) . (If the near field, such as the current on the spheroid, were desired, Lu’RU. would be reilaced by (”R [L ). The integral breaks Up into three parts, the top, bottom and sleeve of the cylinder. Since the cylinder is infinitesimal in size, those terms with the highest negative power in R predominate, all others can be neglected. Thus on'esobtains _ we , ~3‘fkw 153-??— 5‘77‘9'“ r‘ 7 9R “Ur-3...:— (3 6" 1R 5,1977”? 'hf' d7 ' (5” +4 S,,(I~5)f r7K’é ”fig (3' )RSA p M The choice of prOportions of the cylinder is arbitrary, and if we assume it to be long and slender such that /°<< «(3"; §,) then it is easily snown that the first two integrals cancel each other, while in the tJde '11; Z: "t— r*' ‘II -+ .1 éyi R a‘[u-7'v(§'—I)+<3—§.)j can be expanded by the binominal theorem. I Since the value of the integral over 1‘ must be independent of its size so long as it enclosed the dipole, we may now shrink it arbitrarily close to the point D.and obtain the result that only the first term - 55 - of the binomial exoansion will contribute an amount waich is not arbitrarily small. The calculation yields the result _.’2Lw 311("'$) m (57) a “4”); Jacki,” One finds that the bracKeted expression becomes the IQ coefficient Q , defined in (B7) . Remembering that the actual term of the ex-) . (3 (,5 pansmn (3"!) is not (53) , but “(7 )WRMW\ times (5.5) , and imposing the summation appearing in (3%), one Obtains the final result embodied by equations (37) and (58) (A! III. Formulas Useful in Computation with Prolate Spheroidal have Functions The partial differential equations (/7) and ([8) upon separation of the variables yield two ordinary differential equations (7LI)%SIA +[Afl :2 O (58) Isl 31¢. (59) J- 1 J l --( 4.8. «1? g )ds' 1i” §*— The solution of (5:9 is given by Stratton et.al.5 ‘5 0’3 May)" - i 0/: H (7) “0) The prime on this summation and those which follow indicate that the sum contains only terms even.ir1 *7 if 2(- is even and odd in VI if! is odd. The norm of the angular functions is given by ' , z 00 I l :L I N";[ [7%)] ‘17 2 ggfihiifii (a!) -37- The functions SUE?) possess singularities at 7:1. and therefore must be eliminated as a possible solution in problems where the 7~ axis lies in free space. The radial equation (57) has two fundarinextal (1) solutions, )1? “(3) and I“) . The radial function of the first kind is given by 0" IO. K-l-l/A Q __ A. I 1—1 (62) where the factor I or g are used when l is even or odd, respectively and V'here ___l_' 1.... (as) x" Iii-41k (1:1)!" x ‘Efl.’ toil w» 111 :Jfi-ch #4} (£11). 11 The coefficients CK are found from the recursion formulas 3K(2g+2)CL1+{UK-Hulk}:+1151 +2 4%?! 01:] (a) 5) +£zatCk-1JKGVC’? - 38 _ 4K(2K+2)C.l+ §(:K‘H)2K +A|Q +fiz¢ 1}C‘Q "l ((0‘) Mi? 1 C11 on (L7) ”I a l and (:;:l::: 1:5: ‘4” (7Tf4? m9: 271, We did not use the expansion of the radial function of the second kind as defined by Spencea for two significant reasons, namely (1) his eXpansion is a power series in the variable f-lz' (é‘fUG'U. If one wishes to compute the value of this series in the range 3 just beyond-bl the use of the variable 3-] alone is clearly of advantage; (ii) the coefficients in the expansion given by Spence are determined as infinite series, which do not always converge raoidly, whereas the coefficients of an expansion in the powers ofg'l are detafmined in closed form from the set of (fé previous— ly defined. Consequently, we found the following expansion for( useful: ( .— g)~ +6; afiurf"fifi§:+dzz(gb+dlg +1 (ng (9%} 0k} 1+4 where {=§-l cf: I/ei G": -— as /e.,3 61 = ( 3811“ 2 £061 )/Q7 .1 G; = -- Hels- L625, €1+1e:93)/ef and where 60 :: 2C? :1 e, : (fl-MK,“ 0R. 3C6.“ 4-qu , Q IL e12 aqfi. 3c,“ on cg‘L-z-sc,’ +9c, . . 2 e, ‘-’.- c,“+:.1c,"+mg" on. 5c, ll+2acf~+m€§ where the first alternative corresoonds to evenl , the second to odd ,2 . Finally, the constant K1 is defined in terms of infinite series over the coeffi- cients A), which, however, ravidly converge in the range of our calculation, viz. «40—w K = 3:“. $114: 22.." «1+! 6" ‘ 2&6"? (0&3)?ij .2 ° l "’ Q «.1. :§[Jf(fl+l)(n+a)2%]~l'w Z (.1 "1.94:- i};- L Qfi) ital) (:F‘WF‘Lif ' Keven Aim ('2 i 1.3+! C'1 K‘ 2%. 3"" +1(C.‘9’ :otQ“)‘.‘ ‘ta ° Z[J.(w)tn+z)§"'] 'ZJ (Mani; (7o) .31" (MM-1)} ’- 0H ”:5 = Other radial functions arise in the solution of boundary value yroblems involving Hrol te (I) spheroids. They are linear combinations of RIO. and (”Rm given) in L51) and (b!) . Among these 13(3) RIF—(S) 0“ (S): ORR ,(E) +‘LdRmtv (7’) which for large g takes the form (‘43 (s __ _ 14-16 (71) i”(3) I ) £03 In conjunction uith the assumed time dependence -41- this function satisfies the Sommerfeld radiation con~ dition at infinity. The extensions of the tables of prolate soheroidal constants and functions by Stratton et.al.5 and by Spenceg are given in the following tables. A15 A14 at»: 2 -21. 94014372 -51. 96275891 3 ~24.408312175 -54.45404458 4 -27.91179 CN (04101 -42- II 10 ka ka-5 0003me 10 0.000004 f) -0.000055 6 -0.0008115 0.0058659 6 0.086649 0.97072 -0.055648 0.0005902 -0. 000002 -0.000001l e -0. 000016829 Q 0.00050497 0.0051979 0.068002» 1.0158 ~0.052729 0.0004799 -0.000052 ~0.00005 r 0.0004587 6 -0.0026501 -0.019055 0.042681 6 0.18268 0.95056 -0.07719 0.00288 -0.00002 0.000010 9 -0.0000€364 e -0.00045567 6 0.0056564 0.015012 0.15410 1.0246 -0.074684 0.00246 -0.00006 223,5. ka 0.0000000 0.795116 1.508551 2.07587 2.45897 2.561776 2.452795 2.0675668 1.507590 0.8179867 0.080981 -0.6142452 -1.18185 -1.55095 -1.67654 -1.545167 —1.1805748 —0.658058 0.0000000 - 45 - = 2 0 3:5,}:{82'8 0.000000000 0.716985 1.57558 1.913126 2.28670 2.46921 2.40488 2.12959 1.65492 1.02998 0.52501 —O.57405 —0.990095 -1.59907 -1.58209 -l.49921 -l.16551 -0.65606 0.0000000 L41 Rag-15 0.000000000 1.22076 2.27047 2.99461 5.50957 5.15275 2.55889 1.62687 0.514655 -0.58565 -1.47125 —1.98655 -2.05822 -1.62865 -0.85874 0.9015 . 0.99475 1.64097 1.87500 The table appearing on this page was computed by H. Myers and is reproduced by kind permission. If C0 11:: 5 ka - 2 9.2697 5 6.6629 )nfl. ka - 2. 999.69 6 190.06 ka = 2 4.2142 5 5.9656 c) Ru ,2 =5, ka=2 g .1.005 .00094696 1.020 .0020092 1.044 .0052755 1.077 .004901,4 (11R ' In 5 :1.005 .096646 1.020 .058550 1.044 .049859 1.077 .049565 -44.. ‘X . 4 14.720 14.524 12,946 1751.5 5.6501 9. :5, Ka=3 K :4, ka=2 .004461 .0094066 .015115 .022155 .46222 .26741 .22060 .21015 .00011757 .012558 .00085277 .0018652 .0051594 .0049581 .090415 .057522 .052962 .056820 (#93 I! ‘§;1.005 1.020 1.044 1.077 (1) l R l!- 3:1.005 1.020 1.044 1.077 I :3, ka=2 -45... -262.46 -l52.07 —l46.5 ~2.x 102 52858. 1745.2. -556.5 -1 x 103 :6, ka:5 1:4, ka=2 i=4, 149:5 ~51.977 -1792-1 -166.62 -10.59 «60.65 -2.26 -28. 2.8 4.1 x 103 2.6609 x 105 21525. 591. 2560. 2.1 x 102 7 x102 1.2 x 102 - 4e - BIBLIOGRAPHY Morse, P. M. and H. Feshbach. Methods of Theoretical Physics. Cambridge, Massachusetts: Technology Press. Massachusetts Institute of Technology, 1946. Page, L. Physics Review 65. pp. 98-110, 1944. Spence, R. D. The Scattering of S und From Prolate Spheroids. Final Report. Office of Naval Research. NONE—02400, 1951. Stratton, J. A. Electromagnetic Theory. New York: McGraw-Hill BOOK Company, p. 456, 1941. Stratton J. A., P. M. Morse, L. J. Chu and R. A. Hunter. Elliatic Cylinder and Spheroidal Wave Functions. New York: John Wiley and Sons, 1941. MT“ - "tynygfigyy ~11an 1m: my“ 470