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Department of Mechanical Engineering
MEMS1049
MechatronicsChapter 9
Vibration Sensors 9-5
Department of Mechanical Engineering
PiezoelectricityPiezoelectricity
– In 1880, Pierre Curie and Paul-Jacques Curie (Curie Brothers) studied pyroelectricity in the 1880s, leading to their discovery of some of the mechanisms behind piezoelectricity
– Generating an electric charge in a material when subjecting it to applied stress, and conversely, generating a mechanical strain in response to an applied electrical field
Piezoelectric mat’l
Force or strain
Induced ∆Q, ∆V Piezoelectric mat’l
Induced force or strain
V
Department of Mechanical Engineering
Piezoelectric Effect
In some dielectric materials (crystals, ceramics, polymers) without center symmetry, an electric polarization can be generated by the application of mechanical stresses.----Piezo-electricity
– D = d X, direct effect– x = d E , converse effect
P: polarizationd: piezoelectric coefficient (pC/N or m/V)
Department of Mechanical Engineering
Piezoelectric Effect
Department of Mechanical Engineering
Piezoelectric Effect
Department of Mechanical Engineering
Piezoelectric Effect
Department of Mechanical Engineering
Piezoelectric materials and properties
Piezoelectric Materials– Ceramics
Pb(ZrTi)O3 (PZT), PbTiO3 (PT), etc.– Single crystals
Quartz, LiTaO3, LiNbO3, PZN-PT,etc– Polymers
PVDF and copolymers, nylon, etc.– Composites
PZT-polymer 0-3, 2-2, 1-3 composites, etc.– Thin/thick films
PZT, PT, ZnO and AlN films
Important parameters for piezo- materials– piezoelectric strain coefficient d
(m/V)– piezoelectric voltage coefficient g(V.m/N)– electromechanical coupling k33, k31, kt
– dielectric constant K– electrical resistivity ρ– dielectric loss tangent tanδ– mechanical quality factor Q– acoustic impedance ρc
Property Unit PZT ceramic
PVDF ZnO film
PZT film (4 µm on Si)
d33 (10-12)C/N 220 -33 12 246 d31 (10-12)C/N -93 23 -4.7 -105 d15 (10-12)C/N 694 -12 ? Κ3 ε33/εo 730 12 8.2 1400
tanδ 0.004 0.02 0.03 k31 0.31 0.12 Q 400 ρc (106)kg/m2-
sec 30 2.7
Typical properties of PZT, PVDF, ZnO
Crystalline quartz
0000000000
000
2625
141211
ddddd
d11 = -d12 = -d26/2 = 2.31 pC/N, d14 = -d25 = 0.73 pC/N
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For PZT, BaTiO3 , PbTiO3piezoelectric ceramics
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Piezoelectric Effect
∆L=d31 ·V · L/t, ∆W=d31 ·V · W/t , ∆t=d33 ·V
- When a voltage is applied across the thickness of the piezoelectric materials
- When a force F, is applied, in the length, width or thickness direction
Q3=d31 ·F1/(L/t), Q3=d31 · F/(W/t), Q3=d33 · F
Department of Mechanical Engineering
Be careful about this elastic constant
Piezoelectric Effect
Open circuit voltage
Department of Mechanical Engineering
Piezoelectric Effect
Department of Mechanical Engineering
Piezoelectric Effect
nmtVV
VpmdVdt
tVd
tt
Edx
37.01
/37033
33
333
3333
=∆=
==∆
=∆
=
Department of Mechanical Engineering
Piezoelectricity Piezoelectric Materials
– CeramicsPb(ZrTi)O3 (PZT), PbTiO3 (PT), etc.
– Single crystalsQuartz, LiTaO3, LiNbO3, PZN-PT,etc
– PolymersPVDF and copolymers, nylon, etc.
– CompositesPZT-polymer 0-3, 2-2, 1-3 composites, etc.
– Thin/thick filmsPZT, PT, ZnO and AlN films
Important parameters for piezo- materials– piezoelectric strain coefficient d (m/V)– piezoelectric voltage coefficient g(Vm/N)– electromechanical coupling k33, k31, kt
– dielectric constant K– dielectric loss tangent tanδ– mechanical quality factor Q– acoustic impedance ρc
Property Unit PZTceramic
PVDF ZnOfilm
PZT film(4 µm on Si)
d33 (10-12)C/N 220 -33 12 246d31 (10-12)C/N -93 23 -4.7 -105d15 (10-12)C/N 694 -12 ?Κ3 ε33/εo 730 12 8.2 1400
tanδ 0.004 0.02 0.03k31 0.31 0.12Q 400ρc (106)kg/m2-
sec30 2.7
Typical properties of PZT, PVDF, ZnO
33
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Piezoelectric longitudinal andtransverse effect
Piezoelectric multilayer andbimorph actuators
Piezoelectric Shear mode actuator
Longitudinal multilayer actuatorLarge output force, low displacement
Shear mode actuatorMedium force and displacement
Bending mode actuatorLow force, large displacement
Piezoelectric actuators and sensors
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Piezoelectric actuators and sensors
Department of Mechanical Engineering
Device Considerations
Considering piezoelectric sensors such as vibration sensors (dynamic strain sensor), accelerometers, energy harvesting devices
A simple mass-spring-damper structure
PZT is most often usedFor high temperature transducers.- AlN- Bismuth titanate ceramic (Bi4Ti3O12)- LiNbO3
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Device Considerations
Dynamic equation for forced vibration
( )sFKZDsZZMs a=++2
KDsMssF
sZ a
++= 2
)()(
22
2
21)(
nn
n
ssKFsZ
ωζϖω
++=
ζγγ 2111)(
2 jKFsZ
+−=
( ) ( ) ( )
( )tFtF
tMXtKztzDtzM
a==−=++
ωωω
sinsin2
Mechanical Transfer Function
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Device Considerations
For accelerometers
( ) ( )222 211
ζγγ +−=Y
ζγγωωζϖω 2111
21)(
22222 jssXsZ
nnn +−=
++=
−
Department of Mechanical Engineering
Device Considerations
Electrical Transfer FunctionEquivalent circuit of
piezoelectric Transducers( ) ( )tzKtQ q= ( ) ( )sZKsQ q=
22
2
2)(
nn
nq
ssKK
FsQ
ωζϖω
++=
222 21)(
nnq ss
KX
sQωζϖω ++
=−
The governing equation of the equivalent circuit
ppq R
VdtdVC
dtdzK +=
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Device Considerations
Electrical Transfer Function
τ)()()( sVssVssZ
CK
p
q += 1)()(
+=
ss
CK
sZsV
p
q
ττ
12)(
22
2
+++=
ss
ssKCK
FsV
nn
n
p
q
ττ
ωζϖω
12111)(
222 ++−=
− ss
jCK
XsV
np
q
ττ
ζγγωω
( ) 22
22
2
2
2
124sF
ss
ssKCK
sPnn
n
p
q
+
++
=τ
τωζϖ
ω
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Device Considerations
For multilayer piezoelectric stack
233
3333
233 k
sd
KKC
KTEq
p
q ==⋅ε
( ) 23
22
233
233
1211
4T
ss
jsk
spE
+
+−
=ττ
ζγγ
The maximum output power density
Department of Mechanical Engineering
Device Considerations
Transducer power vs. frequency for different damping coefficient and time constant