Tuyen tap bao cao khoa hoc Hoi nghj Khoa hpc ky thuat Do luomg toan quoc lan thu IV Hd Noi, 11 - 2005
NGHIEN curu THIET KETHIET Bj DO L U U TOC MAU B A N G LASER PHUC VU DOAN TUAN HOAN NAO
Bdi Trung Dung Vien I'tng dung cdng nghi- Bd KH&CN
Tdm tdt:
Ky Ihudt do luu tdc man bdng Laser ilua Irin nguyin ly hiiu I'ntg Doppler khi tibdo mdu bl chiiu mdt chiim tia Laser. Cdc tigliieu ci'ai ly thiiyei dd chi'fng minh lifit tdc mdu cd Uen quan mdt Ihiel diu sit dich chuyin ldn sd Laser cita tta sdng trifcJt qua tibdo mdu. Cdn cd vdo hiin tugng ndy ctic nhd nghiin i I'at dii chi tgo ra thii't hi do lini td'c mdu bang Laser.
I. GIOI THIEU
Mtft trong nhiJng i n g dung thuc tidn c i a ky thuat cha'n doan bang Laser la phuang phap Doppler do luu ttf'c mau, phuc vu chan doan mtft stf benh vd tuan hoan man, trong dtf ctf bdnh thi^u nang tuSn hoan nao. Phuong phap nay la kha mtfi me, cac nghidn ciu ly thuydt dSu tidn dupc xua't hidn t i nhung nam 70 c i a thd ky XX. Cho ttfi nay cac thiet bj Laser do luu ttf'c mau da dupc che tao va ing dung b nhidu nutfc cho kd't qua rat tot. 0 Viet nam thid't bj Doppler Laser ctfn kha mtfi me va chua dupc nghien c i u day d i ca ve ly thuyet va thie't bj. Vi ly do nay, trong khutfn kho bai bao nay ttfi se trinh bay nguyen ly do va nguyen ly hoat dfing c i a thid't bj Laser do luu ttf'c mau. Dd'n nay thiet bj da dupc Trung tam Ctfng nghe Laser -Vidn ing dung Ctfng nghe chd tao va boat dtfng ttft.
II. c d s d NGUYEN LY DO LUU TOC M A U
Nguydn ly do trdn co so hidu ing Doppler Laser s i dung mpt ngutfn sang Laser He- Ne, hoac Laser Diode don Mode vung hong ngoai gan. Ngutfn sang chid'u ttfi mtf ctf cac td bao mau chuyd'n dpng vtfi van ttf'c khtfng doi tren mpt khoang each Itfn so vtfi butfc song, thi tia tSn stf sang trupt (tia phan xa) bj djch di bcii hidu ftig Doppler. Tan stf dich chuydn tfnh theo ctfng thic:
o> = KV s KvcosB (I) Vtfi: K la vector truot c i a tia sang (djnh nghTa nhu hidu c i a vector song c i a tia ttfi
va tia trupt).
V la vector v4n ttf'c c i a te' bao mau, v la vSn ttf'c td bSo mau va 9 la gtfc gifla vector van ttf'c va vector truot.
Hinh 1: a. Phd laser chie'u tdi md. b. Phd tia nhifiu x a d o tebao mau
Gia tri van tdc cua ddng chay dugc djnh nghTa:
F^^P(o}yo-dco (2)
6 day P(Ci)) Id pho tfn hifiu ddng chay (kfi ca nhifiu trdng). co : tan sd dich chuyfi'n Doppler.
Gia sfl rdng phdn bd td'c do ddng chay toan phdn dugc ty le bdi he sd a do dd v ^ av. Di^u ndy xay ra khi ddng chay nho chay qua hlnh the' cfi' dinh vdi luu Iugng thay ddi theo bfin ngoai vung quan sat. Khi dd phdn bd van td'c va phd tin hieu dugc ty Ifi theo quan hfi sau:
U(v) -^ U{v/a)/a P ( t o ) ^ P((o/a)/o)
Khi dd gia trj mdi cua tham so ddng chay la:
^-JlvH^W^^ !-''(->"
(3)
(4)
Do dd tham sd' ddng chay ty le thudn vdi do tang td'c do dong chay. Nfi'u nhu luu lugng ddng chay cua tfi' bao la f, thi khi thay a = f,/fo, d day f^ la luu lugng chay chuan boa:
F = f\j\^GF,
(5)(y ddy FQ Id gia trj cua tham sd' ddng chay trong che dd chu^n hod, va gia trj can chinh G.
Tham sd cud'i cung la ty Ifi vdi ddng quang trung binh I. Nfi'u tin hifiu vi phdn dugc dua qua bd loc tdn sd thdp vdi tan sd cat B d dd B > o „ „ , sau dd dua qua bd phat hifin RMS, ddu ra cua lin hifiu se la:
R=\ Jp^,^, ((o)d(o = jo)' P{o))d(o + K1 = ^F-+K1
6 day hdng sd nhifiu K dugc xac djnh bdng:
(6)
K = N"Uda> = ~
i 3(7)
Do K thay doi theo dp khue'eh dai cua ong nhan quang, ntf se dupc xac djnh bang thuc nghidm btfi dat mtft vat co djnh vao thiet bj (F = 0). Cutf'i cing, de loai bo hieu ihig phu thutfc c i a lupng anh sang Laser, ta s i dung tham stf dong chay chuan hoa bang each chia tham stf dtfng chay nhan dupc F cho gfa tri dong quang trung binh I.
4^-
(8)III.THIET KE HE DO LUU TOC MAU BANG LASER a. Kho'i thu t h a p tin hieu do
Hinh 2; So do kho'i nguyen ly mach thu thap tin hieu do
Kenh I
Laser
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c
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I
pholo- deteclor
photo- detector
Igc tdn sd cao
K'
loc tdn sdcao
nh khud'eh dai
II
khufi'ch dai
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bd chia
bg
1
chia
Khuech dai vi sai
VoII(t)
Y>i thie't ke he do trudc hfi't chung ta cdn quan tdm dfi'n phuong phdp thu thap tin hifiu do. Trong thie't kfi' nay sau khi tham khao mdt sd thifi't ke' ciia nude ngoai tdi chgn phuang phdp do da kenh Id phuong phdp thu thap tin kieu. Vl nd cd nhflng uu diem:
• Lam tdng dang ke ty Ifi tin hifiu/nhifiu (SNR).
• Loai bd hifiu qua cac nhifiu loan gdy ra bdi giao thoa cac mode trong chiim tia laser va nhifiu bifin dd cua chum tia phd rdng, cung nhu nhifiu ngudn difin (50 hoac 60 Hz) va mfit sd' nhifiu khac gdy ra khi do cac mach mau be mat.
Tin hifiu Laser trugt tfl md qua hai kenh rieng bifit ciia sgi quang dugc dua tdi hai bd phdt hien quang. Cdc tin hifiu quang ddng nay sau khi khue'eh dai cd the' dugc dua true tifi'p de'n bfi khufi'ch dai vi sai, trong trudng hgp nfi'u tin hifiu hai kenh cdn bdng.
b. So do khdi tdng the va nguyen ly boat dgng
Da va mach mau
^ y ni
-i=
Mach do cdng sudt thu
t
Mach hi^n thi iCL7107
i k
Khtfi tiSn
T
x i l y
,
1 - 1 Photomultiolie
Ngudn dn ap
±I5V
±5V
•'H
— j 1
1^
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Khdi tfnh toan dich chuydn
Doppler
, 1
cl
•^gudn oPMT
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Ngufin cao ap He-Ne *
Ngudn cao
•" ap He-Ne
i
I U Mt
He can chinh
Bifi'n ap
1
Thifi't bj hi^n thi gia trj P la lim lugng vi tudn hoan tuong ddi va ty le vdi van td'c mau trung binh cua te' bao mdu.
P = K x V Vdi: V la vdn td'c mau trung binh cua tfi'bao mau.
K Id he ty le so dgc tritng cd'u tiiic md difffc do vd cdn chinh thiet hi.
Ddu do cua thiet bj la he day quang dan gdm 3 kfinh, gdm kfinh truyen anh sang dd ciJa laser He-Ne budc sdng 623,8 nm chie'u tdi vung mach mdu, va 2 kfinh thu dat ddi xflng dd thu tin hieu phan hdi. Cac tin hifiu quang rat ye'u nay dugc chuyfin thanh tfn hifiu difin nhd 2 dng nhan quang de dfla tdi khfi'i tifin xfl Iy. Tin hieu dien thu tfl cac kenh PMT (ky hifiu IN-1 va IN-2) dugc khufi'ch dai ldp nhd 2 vi mach ICL7650 (Ul va U2). Ddy la vi mach chuyen dung sfl dung ddng nhd va do nhieu tin hieu thd'p. Cdc tin hieu ra duoc khufi'ch dai vi sai bdi vi mach OP-7 (U3) vdi dd khufi'ch dai 10 ldn. Tfn hifiu vi sai dugc Igc ky bdi bd loc tich cue tdn sd cao 2 tdng (vi mach U4 LF353) va bfi Igc tdn sd thd'p 2 tdng (vi mach U5). Tfn hifiu da Igc dugc dua qua mach lap (U7-B) va la tfn hieu R dua sang khd'i tinh todn. Tin hifiu tfl 2 kenh IN-1 va IN-2 dugc tich phdn va khufi'ch dai bdi vi mach OP07 (U6), tao tfn hifiu I cho khd'i linh toan. Mach Igc tan sd cao va tdn sd thd'p dugc thie't ke' la mach loc tfch cue Butterworth bdc 4, tdn sd cdt cua mach Igc tdn sd cao la:
2n\R\R2C' In "^ RVR2C'
651
: 1 IK, R2 = 5 IK, C = 220nF, ta c6 f « 30 Hz. Vtfi mach lpc tSn so thSp, tan stf cat
r'V;;iR2CCl 2a-V
f - ' '
In V R\R2CC\ In V RV R2'CC\ • ' ' 'vdi Rl = 18K, R2 = 33K, C = 2.2nF, Cl = 0.3nF, ta cd f ^ 8 kHz. Nhu vay dai thdng ciia mach thuc tfi' se la 30 Hz - 8 kHz.
Khdi tinh todn: cac khdi nay sfl dung vi inach nhdn chuyfin dung AD533 cua hang Analog Device, cho phep tinh todn vdi dfi chfnh xac cao va tflc thdi. Tfn hifiu R dugc khue'eh dai nhd vi mach U3A, sau dd dua vao mach binh phuong tin hifiu S va cho qua mach tl'ch phan cua vi mach U4.
Tin hifiu I dugc dua qua bd khfi'ch dai dao cua vi mach U3B vdi he sd K, dieu chinh dugc. Tfn hifiu nay va tin hieu <R~> dugc dua vao mach trfl cua vi mach U2B, de tao tfn hieu<R">-K,I.
Mat khdc, tfn bifiu I dugc khufi'ch dai nhd vi mach U l A va dua qua mach binh phuong S, sau dd dua qua mach khue'eh dai ciia vi mach UIB cd hfi sd khue'eh dai K, difiu chinh dugc. Tfn hifiu ra ty Ifi vdi K^I" dugc lap va chinh ofset nhd vi mach U2A.
Cac tin hieu <R">-K|I va K J ' dugc dua vao mach chia D, Kfit qua phep chia dugc dua tdl mach khai can R va lap lai nhd vi mach U5B,
Mach R se cho gid trj 0 khi ke't qua phep chia cd tri so am, nhd Diode mdc tai ddu ra cua mach S. Kfi't qua sau tfnh toan qua IC LF353 tdi ddu METER dfi hien thj nhd IC SL322 Khdi do cdng sud't thu : Cac tin hifiu tfl dng nhan quang PMT dugc dua tdi chuydn mach chgn kenh. Tin hieu tfl kfinh do dugc tfch phan vdi ddng vao cue tha'p nhd nua vi mach LF353, sau dd lap lai nhd nfla kia cua vi mach. Tin hieu nhan dugc dua vao IC SL322 hidn thi 9 vach LED. Cdng suat cang ldn thi sd LED sang cdng tang. Mach nay cho phep danh gia dd ldn tin hieu ddu ra tfl fi'ng nhdn quang, va do can bang tfn hifiu gifla 2 kfinh.
Gidi do vd sal sd phep do. Dua theo cdng thflc: Aflf= vie. f= cX, ta cd: v = XAf do dd vdi dai tdn thifi't kfi' 30 Hz - 8KHz, budc song laser He-Ne 633 nm, cac gia tri van td'c gidi ban tuong flng se la 0.02 mm/s - 5 mm/s. Dfi nhifiu cua thifi't bj thudng vao khoang O.IV, tuong flng vdi sai sd van td'c mau ia khoang 0.1 mm/s.
IV.BAN LUAN
Trong qua trinh chfi' tao vific can chinh thifi't bi gap kha nhifiu khd khdn: do mdt sd nguyfin nhdn: nhifiu ngudn: nhifiu 50 Hz cua ngudn difin, nhilu nhifit cua cac linh kien gdy ra. nhifiu do su khong dn djnh cua cdng sud't laser vd dau thu, nhifiu ngudn cao ap cua dng nhdn quang thudng ldn hon mflc tin hifiu. Mfit nguyen nhan quan trong khac la do thudt toan, bdi tfn hifiu vdo dau bd chia phai dm va gdn bdng khdng, thuc te' gia tri nay thudng cdn dugc can chinh lai.
V, KET LUAN
Do luu td'c mau bang Laser la ky thuat do hien dai dua trfin su phdt trifi'n cua ky thudt Laser. Mdc dii thie't bj da xuat hien nhieu tren tbi trudng do nude ngoai chfi' tao.
Nhung d trong nude chua cd don vj nao nghifin ciru sdu vd ly thuyfi't va thuc nghifim, Vi vSy qua bai vie't nay tdi mong mud'n gidi thieu tdi cdc nha nghifin cflu ky thudt nay. cung nhu flng dung ky thudt do ludng bang Laser. Su phat trien cua thifi't bi do Laser se gop phdn phat trifi'n ky thudt do ludng ndi chung.
652
