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I HC QUC GIA TP. H CH MINHTRNG I HC KHOA HOC T NHIN
Bo Co Ti Mn Hc Cc Phng Php Thc Nghim Chuyn Ngnh
Vt Liu Chit Sut m
HVCH: Nguyn ng Bch NgaGVHD: V Th Hnh Thu
TP. H CH MINH 2015
Mc Lc
1.Nhng l thuyt ca Veslago v loi vt liu c vm.11.1.Vt liu theo qui
tc bn tay tri21.2.Mi trng truyn sng ngc (Backward wave
media)22.Nhng h qu c bit khi c sng in t truyn i trong mi trng c ng
thi hng s in mi v t thm mang gi tr m32.1.Vt liu chit sut m32.2.Hiu
ng Doppler ngc42.3.Bc x Cerenkov ngc43.Nhng ng dng tim nng ca vt
liu chit sut m53.1.Siu thu knh53.2.Thit b bo v nten v b mt chn la
tn s63.3.Vt liu c kh nng tng hnh64.Ch to vt liu c chit sut m
74.1.Vt liu c hng s in mi m74.2.Vt liu c t thm m84.2.1.Vng tr h lng
nhau84.2.2.Vng h cng hng SRR104.3.Cc cu trc c ng thi hng s in mi v
t thm m124.3.1.M hnh ch H124.3.2.M hnh ch 134.3.3.M hnh
fishnet144.3.4.M hnh dng ch S144.3.5.M hnh SRR i xng kt hp dy lin
tc154.4.Cu trc v tnh cht ca m hnh vng h cng hng lng nhau (SRR) kt
cp vi dy kim loi di t c trong thc nghim16Ti liu tham kho:18
Siu vt liu (metamaterials) l mt loi vt liu nhn to, c hnh thnh
bng cch cu trc ha cc thnh phn vt liu khng ng nht theo mt trt t nht
nh. Cc cu trc ny thc cht l cc mch cng hng in t vi m, ng vai tr nh
nhng nguyn t trong vt liu t nhin. Thay i hnh dng, thnh phn v trt t
ca cc vi cu trc ny cho php to ra mt bc tranh in t v m vi cc tnh cht
l thng khng xut hin cc vt liu truyn thng nh chit sut m, b cong nh
sng, lm chm nh sng ...Vt liu metamaterials (MMs) c th c phn ra thnh
3 loi chnh:- Vt liu c in thm m (electric metamaterial):< 0;- Vt
liu c t thm m (magnetic metamaterial): < 0;- Vt liu c chit sut m
(left-handed metamaterial):n< 0.
Thnh phn in (electric metamaterial), c vai tr to ra in thm m (
< 0). Thnh phn t (magnetic metamaterial), c vai tr to ra t thm m
(< 0). Cc cu trc ny c th c thit k to ra nhng tng tc mong mun vi
trng ngoi. Da trn tng ban u, vt liu chit sut m l s kt hp hon ho ca
hai thnh phn in v t to nn vt liu, ng thi c t thm m v in thm m (
< 0, < 0) trn cng mt di tn s. T dn n nhng tnh cht in t v
quang hc bt thng, trong c s nghch o ca nh lut Snell, s nghch o
trong dch chuyn Doppler, hay s nghch o ca pht x Cherenkov. Mt trong
nhng tnh cht th v na ca vt liu c chit sut m l 3 vect ca sng in ttun
theo quy tc bn tay tri (left-handed set). Do vy, vt liu c chit sut
m cn c gi l vt liu left-handed metamaterials (LHMs). LHMs c th c
thit k v ch to hot ng trn cc di tn s mong mun khc nhau, t vng vi
sng ti vng hng ngoi xa, thm ch ti gn vng nh sng nhn thy.
Nhng l thuyt ca Veslago v loi vt liu c vm.Phng trnh truyn sng in
t trong mi trng vt cht theo Maxwell c dng:
(1)
Phng trnh sng tng qut:
(2)
T gio trnh vt l i cng ta bit rng, l vn tc pha ca sng. Cho nn vn
tc sng in t bng:
l chit sut ca mi trng c sng truyn, v l i lng c trng cho s truyn
sng in t trong mi trng vi vn tc v so vi vn tc c ca sng trong chn
khng.
vl nhng s phc. Trong t nhin, gi tr phn thc ca vca cc loi vt liu
l lun lun dng. Tuy nhin vo cui nhng nm 60 ca th k XX, V.G.Veselago,
nh vt l l thuyt ca X Vit a ra nhng l thuyt ca mnh v loi vt liu c ng
thi phn thc ca vl m.Vt liu theo qui tc bn tay triCc Phng trnh
Maxwell dng vi phn
(3)(3)
i vi sng phng n sc, cc i lng trong phng trnh Maxwell t l vi tha
s pha. Do , cc phng trnh (3) v (3) c th c rt gn thnh:
(4)
Mi trng trong t nhin c vdng th ba vect tun theo qui tc bn tay
phi. V v vy, mi trng ny c gi l mi trng theo qui tc tay phi (RHM
Right Hand Media)
cn i vi mi trng c ng thi vm, phng trnh (4) c bin i nh sau:
(5)
T y ta c th thy cc vect tun theo qui tc tay tri. Do nhng mi trng
ny c Vesselago gi l mi trng theo qui tc tay tri (LHM Left Hand
Media).Mi trng truyn sng ngc (Backward wave media)Dng nng lng mang
theo bi sng in t c xc nh bng vect poynting S
(6)
Ta thy rng trong biu thc trn khng ph thuc vo v, do 3 vect vn tun
theo qui tc bn tay phi bt k vnhn gi tr dng hay m. V vy trong mi
trng vi vm v khng truyn theo cng mt hng na, ngha l hng truyn nng
lng v hng truyn sng l ngc nhau. Th nn mi trng ny c th coi nh l mi
trng truyn sng ngc. S truyn sng ngc ny gy ra nhng tnh cht rt c bit
i vi sng in t truyn trong mi trng c ng thi vm.
S truyn ngc gia vect poynting v vect sngcng dn n vn tc pha ngc
vi vn tc nhm. Do vn tc nhm c nh ngha nh l vn tc truyn nng lng,
trong khi hng ca vect sngcng chnh l hng ca vn tc pha trong nhiu
trng hp. iu ny dn n nhng h qu khc l trong cc hin tng vt l bit nh
hiu ng Doppler, nh lut khc x Snell, nh lut Fresnel v bc x
Cerenkov.Nhng h qu c bit khi c sng in t truyn i trong mi trng c ng
thi hng s in mi v t thm mang gi tr m1.1. Vt liu chit sut mSng in t
truyn i gia hai mi trng trong sut, ng tnh bt k s phi tha mn iu kin
bin ti mt phn cch gia hai mi trng:
(7)
Gi s mi trng (1) c >0 v >0 v mi trng (2) c 0.
Hnh 2.1: ng truyn ca tia sng ti mt phn cch ca 2 mi trng. 1- tia
ti, 2 tia phn x, 3 tia khc x vi mi trng n < 0, 4 tia khc x vi mi
trng n > 0.
Nu gc ti ca mt tia sng 1 ti mt phn cch l th tia khc x s l tia 3
thay v tia 4 nh trong mi trng thng thng, vi cng gc lch l . V do
chit sut t i gia hai mi trng c xc nh da trn nh lut khc x Snell cng
s mang gi tr m
Nhng v nn phi mang gi tr m. Hay chit sut ca mi trng ny bng
T y ta thy rng du ca chit sut n by gi c th c nh ngha da trn du
ca v . iu ny gii thch v sao vt liu vi v
