Bài giảng kỹ thuật cảm biến phần 7 : Cảm tĩnh điện và một vài cảm biến tiệm cận

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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

6

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Ngun tham kho

Hoang Si Hong-HUST 2

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

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Ni dung mn hc v mc ch

Hoang Si Hong-HUST 3

Ni dungChapter 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) v siu mChng 5: Cm bin tnh in (2b) v mt s cm bin tim cn Chng 6: Cm bin Hall v ho in Chng 7: Cm bin v PLC(1b)

Mc ch: nm c cu to, nguyn l hot ng v ng dng cacc loi cm bin thng dng trong cng nghip v i sng. Nmc xu th pht trin chung ca cng ngh cm bin trn th gii.

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Hoang Si Hong-HUST 4

Chng 5: Cm bin tnh in v tim cn

- Th ng haych ng ?- Khong cchpht hin ?

Ni dung Cm bin in dung v tim cn Cm bin p in

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Hoang Si Hong-HUST 5

V d v cm bin in dung o gia tc Tham kho bi ging ca vin vt l v ITIMS -BKHN (capacitive acceleration sensors)

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Hoang Si Hong-HUST 6

V d v cm bin in dung o gia tc

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Hoang Si Hong-HUST 7

V d v cm bin in dung o gia tc

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Hoang Si Hong-HUST 8

Mt s hng s in mi

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Hoang Si Hong-HUST 9

Cm bin in dung

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Hoang Si Hong-HUST 10

Cm bin p in

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Hoang Si Hong-HUST 11

Cm bin p in

Fig. 3.22. Piezoelectric sensor is formed by applying

electrodes to a poled crystalline material.

The magnitude of the piezoelectric effect in a simplified form can be represented

By the vector of polarization [4]:

P=Pxx +Pyy +Pzz, (3.64)

wherex, y, and z refer to a conventional ortogonal system related to the crystal axes.

In terms of axial stress, , we can write (6)

Pxx=d11xx +d12yy +d13zz,

Pyy=d21xx +d22yy +d23zz,

Pzz =d31xx +d32yy +d33zz, (3.65)

where constants dmn are the piezoelectric coefficients along the orthogonal axes of the

crystal cut. Dimensions of these coefficients are C/N (coulomb/newton) (i.e., charge

unit per unit force).

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Hoang Si Hong-HUST 12

Cm bin p in

The piezoelectric elements may be used as a single crystal or in a multilayer form where

several plates of the material are laminated together. This must be done with electrodes placedin between. Figure 3.24 shows a two-layer force sensor. When an external force is applied, the

upper part of the sensor expands while the bottom compresses. If the layers are laminated

correctly, this produces a double output signal. Double sensors can have either a parallel

connection as shown in Fig. 3.25Aor a serial connection as in Fig. 3.24C.The electrical

equivalent circuit of the piezoelectric sensor is a parallel connection of a stress-induced current

source (i), leakage resistance (r), and capacitance (C). Depending on the layer connection,equivalent circuits for the

(A) (B) (C) (D)

Fig. 3.24. Laminated two-layer piezoelectric sensor.

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Hoang Si Hong-HUST 13

Cm bin p in

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Hoang Si Hong-HUST 14

Cm bin p in thch anh nhiu thnhphn

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Hoang Si Hong-HUST 15

V d v hng tinh th

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Hoang Si Hong-HUST 16

Cm bin p in thch anh nhiu thnhphn

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Hoang Si Hong-HUST 17

Mch o

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Hoang Si Hong-HUST 18

Cm bin p in

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Hoang Si Hong-HUST 19

Cm bin p in-S khuych i in p

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Hoang Si Hong-HUST 20

S khuych i in tch

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Hoang Si Hong-HUST 21

S khuych i in tch

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Hoang Si Hong-HUST 22

Mt s ng dng ca cm bin phn tpin

Piezoelectric Force Sensors

SAW Sensors

Ultrasonic Sensors

(Piezoelectric microphone)

Piezoelectric Accelerometers

PIEZOELECTRIC SENSORS FOR DYNAMIC

PRESSURE

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Hoang Si Hong-HUST 23

Cm bin piezoelectric o lc

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Hoang Si Hong-HUST 24

Cm bin piezoelectric o lc

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Hoang Si Hong-HUST 25

Cm bin p in

Phn bi ging ng dng ca cm bin p in cho o gia tc_ph lc 1Phn bi ging ng dng ca cm bin p in cho o p sut_ph lc 2

Cn tip..