Bài giảng kỹ thuật cảm biến phần 6 : Cảm biến quang

Bi ging

K Thut Cm Bin (sensors)

1

Hoang Si Hong

----2011----

Faculty of Electrical Eng., Hanoi Univ. of Science and Technology (HUST),

Hanoi, VietNam

Hoang Si Hong-HUST

5

Ngun tham kho

Note: Bi ging mn hc ny c tham kho, trch dn v lc dch t cc ngun sau:

Sch

- K thut o lng cc i lng in tp 1, 2- Phm Thng Hn, Nguyn Trng Qu.

- Cc b cm bin trong o lng-L Vn Doanh

- Cc b cm bin-Nguyn Tng Ph

- o lng in v cc b cm bin: Ng.V.Ho v Hong S Hng

- Sensor technology handbook (edited by JON WILSON)

- Elements of Electronic Instrumentation and Measurement (Prentice-Hall Company)

- Sch gii thch n v o lng hp php ca Vit Nam

Bi ging v website:

- Bi ging k thut cm bin-Hong S Hng-BKHN(2005)

- Bi ging Cm bin v k thut o:P.T.N.Yn, Ng.T.L.Hng BKHN (2010)

- Bi ging MEMs ITIMS BKHN

- Mt s bi ging v cm bin v o lng t cc trng i hc KT khc Vit Nam

- Website: sciendirect/sensors and actuators A and B

Hoang Si Hong-HUST 2

Ni dung mn hc v mc ch

Ni dung Chapter 1: Khi nim chung v Cm bin (2b)

Chapter 2: Cm bin in tr (2b)

Chng 3: Cm bin o nhit (2b)

Chng 4: Cm bin quang (2b)

Chng 5: Cm bin tnh in (2b)

Chng 6: Cm bin Hall v ho in

Chng 6: Cm bin v PLC(1b)

Mc ch: nm c cu to, nguyn l hot ng v ng dng ca

cc loi cm bin thng dng trong cng nghip v i sng. Nm

c xu th pht trin chung ca cng ngh cm bin trn th gii.



Chng 3: Cm bin quang

Ni dung Khi nim chung v nh sng v ngun sng

Quang in tr, t bo quang in v b nhn quang in

Photodiode

Phototranzito

T bo quang in

Ngun sng

hay ngun thu

nh sng?


Cc khi nim chung v nh sng

- nh sng l mt sng in t, vng nh sng nhn thy c c bc sng

t 0.4 n 0.75m.

- nh sng c tnh cht sng v ht.

- Vn tc nh sng trong chn khng v = 299792 km/s

- Vn tc nh sng trong mi trng vt cht c chit sut n l v = c/n

- Mi lin h gia bc sng nh sng v tn s nh sau: = c/ (chn

ko) v = v/

-Ultraviolet (t ngoi). Infrared (hng ngoi)


Cc khi nim chung v nh sng

- Tnh cht ht th hin qua s tng tc ca n vi vt cht. nh sng l cc

ht phton mang nng lng Ept= h. Trong h l hng s planck =

6,6256.10-34 J.s

- Khi dng nh sng xuyn qua mt cht no c th b hp th hoc tn x


Nguyn l chung

-Bc sng ln nht ca nh sng c th gy nn hin tng gii phng in t vi

iu kin nng lng photon Ept > Edt nng lng lin kt ca in t

max = h.c/Edt-Nh vy iu kin gii phng in t ph thuc vo kiu nh sng v bn cht vt

liu b chiu sng

- Hin tng gii phng cc ht dn di tc dng ca nh sng do hiu ng

quang in s gy nn s thay i tnh cht in ca vt liu. l nguyn l c

bn ca cc cm bin quang in

- S in t c gii phng trong mt giy G = (1-R) /h.c

-:Hiu sut, R: h s phn x v thng lng nh sng


Cc n v o

-Nng lng bc x Q : l nng lng pht x, lan truyn hoc hp th di dng bc

x c o bng Jun (J)

-Quang thng : l cng sut pht x lan truyn hoc hp th, o bng ot (W) v l

i lng c trng cho ngun sng: = dQ/dt

- Cng sng I: l quang thng pht ra theo mt hng di mt n v gc khi,

c n v l W/steradian: I = d/d

- chi nng lng L: l t s gia cng sng pht ra bi mt phn t b mt

dI theo mt hng xc nh v din tch hnh chiu vung gc ca phn t b mt

dAn, c n v l W/steradian.m2 :L = dI/dAn

- ri E: l t s gia quang thng thu c bi mt phn t b mt v din tch

ca phn t , c n v l W/m2 :E=d/dA

- n v th gic /v nng lng

- Thng lng lumen (lm) oat (W)

- Cng candela (cd) oat/sr (W/Sr)

- chi cd/m2 W/Sr.m2

- ri lumen/m2 (lux) W/m

- Nng lng lm.s

- nhy ca mt ngi cc i vi bc sng =0,555 micromet


Cc ngun sng c bn

n si t

n ne-on

Laser

Led

LCD ?


n si t

- L bng thu tinh cha kh him hoc halogen v si t lm bng vonfram. Pht ra

nh sng nhn thy c

- u im: thng lng nh sng ln, di ph rng, c th thay i c thng lng

nh sng

- Nhc im: thi gian s dng ngn hn so vi led, d v, qun tnh ln

Very thin metal wire

emitting light rays when

an electric current passes

though it

tungsten filament


n Led (LIGHT EMITTING DIODE)

- Nguyn l: nng lng (quang nng) c gii phng khi c s ti

hp cp t-l trng phn tip gip p-n v pht sinh ra cc phton.

- u im ca led v led 7 thanh:

+ Tn s hot ng cao, bn tt, tin cy cao, tui th cao (10

nm).

+ Cng sut tiu th b, khng gy st p khi bt u hot ng

+ Khi tng nhit v dng cung cp cho led khng i th cng

sng s gim trung bnh khong 1.5 n 2 mV/ oC

+ Kch thc b c th ghp ni din tch rng

+ Cng sng ph thuc vo dng in i qua, do c th iu

khin c cng sng thch hp

+ Mu sc nh sng ph thuc vo vt liu v d: GaAs: , GaAsP

hoc vng, GaP hoc xanh.

+ Kh nng chuyn mch nhanh ( 1 ns)

+ in p st trn led ph thuc vo mu vi dng thun cung cp c

20 mA

+ Bc x ca led l n sc


How does it work?

P-n junction Electrical Contacts

Recombination

produces light!!

Junction is biased to produce even more

e-h and to inject electrons from n to p for

recombination to happen

g = hc/Eg

A typical LED needs a p-n junction

There are a lot of electrons and holes at

the junction due to excitations Electrons from n need to be injected to p

to promote recombination


Visible LED

Definition:

LED which could emit visible light, the band gap of the materials that we use must

be in the region of visible wavelength = 390- 770nm. This coincides with the

energy value of 3.18eV- 1.61eV which corresponds to colours as stated below:

Violet ~ 3.17eVBlue ~ 2.73eVGreen ~ 2.52eV Yellow ~ 2.15eVOrange ~ 2.08eVRed ~ 1.62eV

Colour of an LED should

emits

The band gap, Egthat the

semiconductor must posses to emit each light

Led in p st p khong 1.6 n 2 VLed da cam in p st p khong 2.2 n 3 VLed l cy in p st p khong 2.7 n 3.2 VLed vng in p st p khong 2.4 n 3 VLed xanh da tri in p st p khong 3 n 5 V


LED 7 thanh


Laser

Laser (c l la-de) l tn vit tt ca cm t Light Amplification

by StimulatedEmission of Radiation trong ting Anh, v c ngha l "khuch i nhsng bng pht x kch thch".

http://vi.wikipedia.org/wiki/Laser

Electron tn ti cc mc nng lng ring bit trong mt nguyn t. Cc mc nng

lng c th hiu l tng ng vi cc qu o ring bit ca electron xung quanh ht

nhn. Electron bn ngoi s c mc nng lng cao hn nhng electron pha trong.

Khi c s tc ng vt l hay ha hc t bn ngoi, cc ht electron ny cng c th

nhy t mc nng lng thp ln mc nng lng cao hay ngc li. Cc qu trnh ny

c th sinh ra hay hp th cc tia sng (photon) theo gi thuyt ca Albert Einstein. Bc

sng (do mu sc) ca tia sng ph thuc vo s chnh lch nng lng gia cc mc.

C nhiu loi laser khc nhau, c th dng hn hp kh, v d He-Ne, hay dng cht

lng, song c bc x ln nht vn l tia laser to bi cc thnh phn t trng thi cht

rn.


Laser


Mt v d v c ch hot ng ca laser c th c miu

t cho laser thch anh.

Di s tc ng ca hiu in th cao, cc electron ca

thch anh di chuyn t mc nng lng thp ln mc

nng lng cao to nn trng thi o nghch mt ca

electron.

mc nng lng cao, mt s electron s ri ngu nhin

xung mc nng lng thp, gii phng ht nh

sng c gi l photon.

Cc ht photon ny s to ra nhiu hng khc nhau t

mt nguyn t, va phi cc nguyn t khc, kch thch

eletron cc nguyn t ny ri xung tip, sinh thm cc

photon cng tn s, cng pha v cng hng bay, to nn

mt phn ng dy chuyn khuych i dng nh sng.

Cc ht photon b phn x qua li nhiu ln trong vt liu,

nh cc gng tng hiu sut khuch i nh sng.

Mt s photon ra ngoi nh c gng bn m ti mt u

ca vt liu. Tia sng i ra chnh l tia laser.


Tnh cht Laser v an ton


- nh hng cao: tia laser pht ra hu nh l chm song song do kh nng chiu

xa hng nghn km m khng b phn tn.

- Tnh n sc rt cao: chm sng ch c mt mu (hay mt bc sng) duy nht. Do

vy chm laser khng b tn x khi i qua mt phn cch ca hai mi trng c chit

sut khc nhau. y l tnh cht c bit nht m khng ngun sng no c.

- Tnh ng b ca cc photon trong chm tia laser.

- C kh nng pht xung cc ngn: c mili giy (ms), nano giy, pico giy, cho php tp

trung nng lng tia laser cc ln trong thi gian cc ngn.

Laser vi cng thp, ch l vi miliwatt, cng c th nguy him vi mt ngi. Ti bc sng

m gic mc mt v thy tinh th c th tp trung tt, nh tnh ng nht v s nh hng cao ca

laser, mt cng sut nng lng ln c th tp trung vo mt im cc nh trn vng mt. Kt qu

l mt vt chy tp trung ph hy cc t bo mt vnh vin trong vi giy, thm ch c th nhanh

hn. an ton ca laser c xp t I n IV. Vi I, tia laser tng i an ton. Vi IV,

thm ch chm tia phn k c th lm hng mt hay bng da. Cc sn phm laser cho dn dng

nh my chi CD v bt laser dng trong lp hc c xp hng an ton t I, II, hay III. (Xem

thm an ton laser)


u im v ng dnghttp://vi.wikipedia.org/wiki/Laser

- Tnh cht ny cho php laser c th lu tr vi gigabyte thng tin trn cc rnh

ca DVD. Cng l iu kin cho php laser vicng sut nh vn c th tp

trung cng sng cao v dng ct, t v c th lm bc hi vt liu trong

k thut ct bng laser. u c CD v DVD hot ng theo cng c ch, duy ch

c iu DVD cha c lng d liu nhiu hn bi s dng tia laser bc sng

ngn hn (650 nano-mt so vi 780 nano-mt ca CD). Bc sng ngn hn cho

php tng tn sut va chm, sn sinh photon v tng ng vi n l d liu. D

kin, th h quang mi da trn cng ngh ghi a laser xanh (vi bc sng

khong 405 nano-mt), c kh nng lu tr nhng b phim cht lng cao (High

Definition- HD).

-My o khong cch bng laser trong qun s l loi thit b quan trng

-Rada laser c chnh xc cao hn rada thng thng, c th hng dn hai tu

v tr ghp ni chnh xc trn khng gian. Tuy nhin, nhng thit b laser u chu

nh hng ca thi tit, tri m hoc ma th khong cch o b gim i nhiu.

- My in laser, xo vt xm, y t

-u im: Ngun n sc, chi ln, bc sng xc nh, thng lng ln,

chm tia mnh, i nh hng cao v truyn i xa

Lu v cu hi


Cn tip phn 5-2 !!!

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Bài giảng kỹ thuật cảm biến phần 6 : Cảm biến quang