Lamb Wave Generation With Piezoelectric Wafer Active Sensors for SHM - Giurgiutiu
21 Piezoelectric Sensors
description
Transcript of 21 Piezoelectric Sensors
Piezoelectric Sensors
Yongrae Roh
Kyungpook National UniversityDaegu, Korea
ContentsContentsI. Piezoelectricity
II. Electromechanical Equivalent Circuit
III. Sensing Principles of Piezoelectric Sensors1. Charge detection sensor2. Resonant sensor3. Ultrasonic wave sensor
IV. Design Methods
V. Application of Piezoelectric Sensors1. Impedance measurement2. Sensor system for SHM3. Bulk wave measurement4. Other examples
VI. Future trend of piezoelectric sensorsFuture trend of piezoelectric sensors
Linear conversion of electro-mechanical energy: reversible
Electrical Energy ↔ Mechanical Energy
(1) direct effect: mechanical energy → electrical energy- sensor, microphone, generator
(2) converse effect: electrical energy → mechanical energy- actuator , speaker, motor
☞ electrostriction, piezomagneticity, magnetostriction
I. PiezoelectricityI. Piezoelectricity
energy(electric)mechanicalinputenergyl)(mechanica electrictoconvertedenergy(electric) mechanical2 =effk
σεσκ σ EsEddED +=+=
Piezoelectric constitutive equations
D = electric displacement field, κσ = permittivityE = electric field, d = piezoelectric constantσ = stress, sE = elastic complianceε = strain
Variations
EeC
EeDE −=
+=
εσ
κε ε
DgE
gDsT
D
βσ
σε
+−=
+=
DhE
hDC D
εβε
εσ
+−=
−=
Anisotropy for piezoelectricity
Elastic stiffness
⎟⎟⎟⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜⎜⎜⎜
⎝
⎛
=
66
5655
464544
36353433
2625242322
161514131211
][
cccsymmetriccccccccccccccccccc
c
Permittivity
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛=
33
2322
131211
.][
εεεεεε
εsym
Piezoelectric constants
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛=
363534
262524
161514
333231
232221
131211
][eeeeeeeee
eeeeeeeee
e
V. M. Ristic, John Wiley & Sons, 1983
① Cubic ; o90, ===== γβαcba
② Tetragonal ; o90, ===≠= γβαcba
③ Orthorhombic ; o90, ===≠≠ γβαcba
④ Monoclinic ; βγα ≠==≠≠ o90,cba
⑤ Triclinic ; o90, ≠≠≠≠≠ γβαcba
⑥ Hexagonal ; oo 120,90, ===≠= γβαcba
⑦ Rhombohedral (trigonal); oo 60,90, ===≠= γβαcba
z
y
x
αβ
γa
b
c
Bravais lattice structures
Symmetric groups in crystals
Crystal symmetric groups
Material constants of PZT
2,
000000000000
][ 121166
66
44
44
33
1311
131211
ccc
ccsymmetric
ccccccc
c −=
⎟⎟⎟⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜⎜⎜⎜
⎝
⎛
=
Elastic stiffness
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛=
33
11
11
.000
][ε
εε
εsym
Permittivity Piezoelectric constants
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛=
0000000
000000
][ 24
15
333231
ee
eeee
1211
212
112
ccc
cE+
−=1211
12cc
c+
=νEquivalent isotropic properties:
Hexagonal 6mm Symmetry
Vibration modes
Thermodynamic energy conversion
Corresponding material constantsHeckman Diagram
Pyroelectricity - thermal effects
0 2000 4000 6000 8000 100003820
3822
3824
3826
3828
3830
3832
3834
3836
Freq
uenc
y [k
Hz]
T im e [10sec]
Oscillation frequency vs. time Pyroelectricelement
Wi
FET
Meas. or displaysystem
DS
FET bias resistor
RG RACA
)()(
etemperaturTonpolarizatiPp
ΔΔ
=
crystal
oscilloscope cTTA−
='κ
Curie-Weiss Law for “ferroelectrics”
A = Curie constant
Tc = Curie-Weiss temperature
Nonlinearity
Hysteresis Loop (Sawer-Tower circuit)
Piezoelectric materials
Single crystals(SiO2, LiNbO3, LiTaO3)
Polycrystalline ceramics(PZT, PbTiO3, BaTiO3)
Polymer: PVDF, Co-Polymer Thin films
Fabrication of piezoceramics
Raw Materials and Weighing
Mixing & Milling
Calcination
Remixing & Remilling
Shaping
Sintering
Post Processing
Characterization
Fabrication process
Crushing roller
Hammer mill
Ball mill
* two sphere sintering mode * densification by sintering
Crystal growth -Growth by a change of state from liquid or gas to solid, or from liquid solution to solid around nucleus
-Nucleus : a small single crystal (seed)
-Growth should be a slow process with a precise control over temperature, composition, time and so on.
-Otherwise, there may be random orientation, coring, and trapping of disordered regions.
Czochralski method① Keeping a melt of a powder in a chamber, just above its melting point
② Insertion of a seed crystal fixed to a rotating tube into the chamber.
③ Placing the seed at the surface of the melt; inoculent
④ Slow withdrawing of the tube with rotation; cooling
⑤ Continuous crystallization of the melt,
while serving as a subsequent nucleus
Single crystal growth
Piezoelectric single crystals
2”3”
0.6210.5050.49kt
0.9220.750.705k33
7,84075007,750Density(Kg/m3)
4,9903,4002,000ε33T at 1KHz
(after poling)
PMN-PTPZT-5A
4,350
28.2
3,600
1,560
34
374
34Acoustic Z
(Mrayl)
4,560Sound velocity
593d33(pC/N)
PZT-5H
Pb(Mg1/3Nb2/3)O3-PbTiO3 Comparison of properties
0-0 1-0 2-0 3-0
1-1 2-1 3-1 2-2
3-2 3-2 3-3 3-3
: polymer
: piezoceramic
Piezocomposite materials
⇒ Tailoring material properties to achieve desired performance
Macro Fiber Composite
*Smart Materials Inc., USA
*NASA, Langley
Electromechanical Analogue
u
R
+
-
V
L Ci
m
k Rm
f
uRkxma
uRdtukdtdumf
m
m
⋅++=
∫ ++= ∫ ++= RIdtICdt
dILV 1
Impedance analogue: u → Im → LRm → R1/k = Cm → C, Cm : mechanical compliance
II. Electromechanical Equivalent CircuitII. Electromechanical Equivalent Circuit
Za Za
Zb-C0
C0
1: Φ
330hC=φ
lWcZkt
ZiZ
ktiZZ
Dt
b
a
ρ=
−=
=
0
0
0
sin
2tan
Equivalent circuit of a piezoceramic plate
KLM (Krimholtz, Leedom and Matthei)
Mason
Redwood
t
W
lPZT
Thickness mode
)1(
1 2
00
Lm
mLm
MEINX
CMiRR
CiR
YYY+−++
++=+=
ωω
φω
LZmM mC
0C0RmR
φ:1
u+
_-V
2/φLZ
2/φmM 2φmC
0C0R
22/φmR
Mi+
_
V
Valid only around a resonance
Input admittance
R0 = electrical resistance
C0 = electrical capacitance
Rm = motional resistance
Cm = motional capacitance
Mm = motional inductance
φ = turning ratio
ZL = load impedance = RL + iXL
V = driving electrical voltage
u = im = motional flux (velocity)
Simplified circuit around a resonance
PZT
Load
Resonance: .electromechanical impedance becomes minimum.electromechanical admittance becomes maximum
Anti-resonance: .electromechanical impedance becomes maximum.electromechanical admittance becomes minimum
→ functions of load impedance ZL = RL + iXL
Impedance curve (magnitude & phase) Admittance curve (conductance & susceptance)
Impedance & Admittance analysis
fm = frequency of maximum admittance
& minimum impedance
fn = frequency of minimum admittance
& maximum impedance
fs = series (motional) resonance
fp = parallel resonance frequency
fr = electrical resonance frequency
fa = electrical anti-resonance frequency
Impedance & Admittance analysis
2
22
2
22
2
22
10
12
n
mn
a
ra
p
speff
fff
fff
f
ffCC
Ck−
≅−
≅−
=+
=
1. Charge detection sensor- accumulation of electric charges- D = κε E + e ε
2. Resonant sensor- change in dynamic properties of the sensor- resonant frequency, Q-factor (f0/Δf)
3. Ultrasonic wave sensor- propagation of ultrasonic waves- flight time, phase shift, amplitude attenuation
III. Sensing PrinciplesIII. Sensing Principles
1. Charge Detection Sensor
D = electric displacement, E = electric field,σ = stress, ε = strainκσ , κε = permittivity e, d = piezoelectric constant
εκ ε eED += σκσ dED +=or
Mechanical stress or strain → electrical charge
Accumulation of electric charges
F = ma with a known “m”→ Measured F is proportional to “a”
AamtgAFtg
tgtEVgE
//⋅⋅⋅=
⋅⋅=⋅⋅=
⋅=→⋅=σ
σ
Piezoelectric accelerometer
Vibrating structure
PZTPZT
Mass, m
F
Piezoelectric force & pressure sensor
Force sensor Impact hammer
Pressure sensor On-road pressure sensor
Piezoelectric gyroscope
Coriolis Force:
F = 2 m ω × v
m : mass of the gyroscope
ω : angular velocity
v : linear velocity
Wx
X
Y
Z
Fy
Wx
Z
X
Y
v
ωx
ωx
v
v
×ωx
F
0
0.5
1
1.5
2
2.5
3
1 2 3 4 5
Angular Velocity (Hz)
Output V
oltage (arb.unit)dVab
dVcd
Angular velocity vs. voltage
PZT
2. Resonant Sensor
Attachment of a piezoelectric resonator to a structure
⇒ Change of structural property
⇒ Change of sensor property
.resonant frequency
.Q-factor (f0 /Δf)
► change in impedance spectra
Change in dynamic properties of a sensor
Electromechanical Impedance Sensor
Output display
PC
Impedance analyzer
3200 3300 3400 3500 3600
2
Impe
danc
e [O
hm]
Frequency [kHz]
Non N=1 N=3 N=5 N=7 N=9
Impedance analysis method
d=1cm, Crack N=1
d=1cm, Crack N=11d=1cm, Crack N=9
d=1cm, Crack N=7d=1cm, Crack N=5
d=1cm, Crack N=3
FEM simulation
Impe
danc
e [O
hm]
Frequency [Hz]2M 3M 4M 5M 6M
1
10
100 -N=1N=2N=3N=4N=5N=6N=7N=8N=9N=10N=11
*N = number of cracks on the aluminum plate
Impedance spectrum vs. N
Piezoceramic Oscillator Sensor
Piezoelectric oscillator sensor - piezoelectric vibrator + oscillator circuit
⇒ simple, accurate, reliable
⇒ high sensitivity⇒ limited detection area Piezoceramic
vibrator
electrode
Oscillatorcircuit
AGC(Automatic Gain Control) AmplifierMaintain amplitude ~ 1Vpp
VariableGainAmp.
VariablePhase Shifter
Piezo-vibrator
Resonant frequency vs. Cracks
PZT-Oscillator sensor
d=1 d=2 d=3 d=4 d=5 d=6 d=7
7000
8000
9000
10000
11000
12000
13000
Cha
nge
in re
sona
nt fr
eque
ncy
[Hz]
Crack length
N=1 N=3 N=5 N=7 N=9 N=1126000
25900
25800
25700
25600
25500
Number of cracks
Cha
nge
in re
sona
nt fr
eque
ncy
[Hz]
Oscillator circuitPiezoceramic patch
+
3. Ultrasonic Wave Sensor
Active method- transmit waves of known properties- receive the wave after through-transmission or reflection- compare transmitted and received wave properties
- Through-transmission or Pulse-echo method
Passive method- detect waves transmitted by external sources- waves of unknown properties - event count, ringdown count, energy distribution analysis, etc.- Acoustic emission method
Type of acoustic waves
Bulk longitudinal (P) wave Bulk transverse (S) wave
Plate mode (Lamb) waveSurface (Rayleigh) wave
Properties of acoustic waves
2/1])21)(1(
)1([ννρ
ν−+
−=
EgVP
Elastic wave velocity
. P wave:
. S wave: 2/1])1(2
[νρ +
=EVS
Transmission and Reflection
. Transmission coeff.:
. Reflection coeff.:
01
12ZZ
ZT+
=
01
01
ZZZZ
R+−
=
E = Young’s modulusρ = densityν = Poisson’s ratio
Applications:
1. Medical Diagnosis
2. Nondestructive Evaluation Test
3. Imaging, Holography Sensor
4. Distance, Level Sensor
5. Thickness Sensor
6. Flow Sensor
7. Structural Health Monitoring
Ultrasonic transducers
wear plate
piezoelectricelement
connector
matchingcircuit
backinglayer
matchinglayer
backingmaterial
Characteristics of ultrasonic transducers
1. center frequency (f0)2. sensitivity (Vp-p)3. S/N ratio4. ringdown time (t-20dB)5. bandwidth (Δf)6. impedance7. directivity (beam pattern)8. distance area characteristics (focus)
Ultrasonic test equipment
Through-Transmission Test
Pulse-Echo Test
transducer
structure
d
A1 A2
Pulse-Echo Test
Sound velocity = 2d /(t2 - t1)Attenuation = 20log | A2 /A1 |
Active ultrasonic wave method
A1 ,t1
A2,t2
A0,t0
defects
A1,t1
structure
Trx Trx
d
Through-Transmission Test
Sound velocity = d /(t1 - t0)Attenuation = 20log |A1 /A0|
A0,t0
Active ultrasonic wave method
Image scanning method
TrxTrx y
x
A scan - line depth scan B scan - vertical plane scan C scan - horizontal plane scan
3.02.01.000
0
.0-1
.01
.1
1
frequency (MHz)
|impe
danc
e|
PS
thickness modepiezoelectric
element
thickness shear modepiezoelectric
element
Impedance spectrum
Types of bulk wave transducers
P wave transducer S wave transducer P-S wave transducer
Single element transducer
Side scan transducer
Flat transducer Point focus transducer
Line focus tranducer
*Panametrics (Olympus)
Dual element transducer
Internal structure Sensor operation
Line array transducer
Array of multiple piezoelectric elements
Linear array Convex array
Linear phased array transducer
Adjustment of the time delay of each element-initial phasing to control beam pattern (beam steering) and focusing (dynamic focusing)
High inspection speedFlexible data processing capabilityHigh resolutionThe capability of scanning without mechanical movement
Beam steering Dynamic focusing
Phase shiftTime delay
Excitation by bulk wave transducers
Excitation by inter-digital transducers
Lamb wave transducer
inputIDT
outputIDT
piezoelectric substrate
Snell’s law→ critical angle for total reflection
Excitation by a piezoceramic patch
Lamb wave propagation
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
1000
2000
3000
4000
5000
6000
Gro
up v
eloc
ity(m
/s)
Frequency(MHz)
S0 A0
S0
A0
Positio
n o
f transducer
from
the P
ZT s
ensor
5 cm
10 cm
30 cm
20 cm
40 cm
25 cm
35 cm
15 cm
Volta
ge(v)
Waveform(thickness of a plate : 1 mm
S0 mode
Time(ms)
Origin
A0 mode
0.064 0.068 0.072
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4B->C, X= 0.05 mNumber of cracks = 1
Volta
ge(V
)
Time(ms)
Crack Length = 0 m Crack Length = 0.02 m Crack Length = 0.04 m Crack Length = 0.06 m Crack Length = 0.08 m
Plate mode (Lamb) wave
Acoustic emission test
Causes of acoustic emission- metallurgical transformation- dislocation movements- plastic yielding- micro-cracking- etc.
Objective.to monitor structural integrity.to detect and locate incipient discontinuities.to monitor the presence and severity of growing cracks,
plastic deformation or delaminations
Passive ultrasonic wave method
Acoustic emission sensor
Passive sensor to detect AE activity
.good sensitivity
.wide bandwidth: audible – several MHz
.low directivity
Applications
Pressure vessels, storage tanks, heat exchangers, piping, reactors, aerial lift devices, nuclear power plantsetc.
IV. Design MethodsIV. Design Methods
1. Analytic analysis
2. Equivalent circuit analysis
3. Finite element analysis
r’r
P
σ
x
zθ
22 aS π=
Rigidbaffle
)](2
sin[2 22)(2
00
00
22
22
rarkecui
deckuip
rarki
arr
ik
−+=
=
−+−
+ −∫
ρ
ηρ η
P nearfield
farfield
P θθρ ω
sin)sin(2
21)(
2
00
kakaJe
rkaAuci krti −=
)(θsax HPP •= ,
where 1J = first order Bessel Function.
A = piston radius
Pax = on-axis pressure
Hs(θ) = directional factor
At a far field
1. Analytic Analysis - single piston source
)(
)sin21sin(
)sin2
sin(),,( krtie
kdN
kdN
rNAtrP −⋅⋅= ω
θ
θθ
)()(),( θθ eax HrPrP •=∴
factor ldirectiona)sin
21sin(
)sin2
sin()( ==
θ
θθ
kdN
kdN
He
pressure axis-on)( where, ==r
NArPax
d
z
x y
12…
N
Radiation pattern
Linear array of simple sources
Accurate, complicatedLimited applicability
1. Analytic analysis - linear array
2/φmRREMM EMC
0C0R
22/φEMR
Mi+
_e
branch motionalin dissipatedPower /Rin dissipatedPower
powerinput elec. Totalbranch motionalin dissipatedPower
powerinput elec. total Radiatedpower Acoustic
2mR φη
η
η
=
=
=
MA
EM
EA
0
2
222
222
2)(||
21
)(||21
ReRRi
RRi
mREMM
mREMM
EM
++
+=
φφ
φφη
cycleperRRindissipatedpowerresonanceatMinstoredenergypeakQ
MMR
MM )(
(2+
=π
⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢
⎣
⎡
++
+=
20
20
00/)(
φ
φEMmR
EMmRE RRR
RRRCwQ
mEM
EM
CNst
NC
NM
NtM
22
112
2
22
4)/(
4
441
πωπ
ωρ
=≅
=≅
l
l
2. Equivalent Circuit – piezoelectric patch
Pσ
x
z
θ
22 aS π=
Rigidbaffle
2. Equivalent circuit – ultrasonic transducer
backingload
piezoceramic matchinglayer 1
matchinglayer 2
acousticlens
acousticload
C MRZ
04Z02Z 03Z 05Z
V0
piezoelectricceramics
connector
matchingcircuit
backinglayer
matchinglayer
backingmaterial
time domain frequency domain
Impedance analysis
⎭⎬⎫
⎩⎨⎧
=⎭⎬⎫
⎩⎨⎧Φ⎟
⎟⎠
⎞⎜⎜⎝
⎛
⎥⎥⎦
⎤
⎢⎢⎣
⎡+⎥
⎦
⎤⎢⎣
⎡−
QFu
KK
KKM
u
uuu
φφφ
φω0002
3. Finite Element Analysis
M = mechanical mass matrix,Kuu = mechanical stiffness, Kφφ = electrical stiffnessKuφ, Kφu = electromechanical stiffnessu = displacement, φ = electrical potentialF = force, Q = electric charge
Commercial FEA software packages
ANSYS®, PZFlex®, ATILA®, CAPA®, …
Accurate, multi-dimensional, various analysesexpensive, time consuming
3. Finite element analysis
0 1x106
2x106
3x106
4x106
5x106
6x106
0
500
1000
1500
2000
2500
2.473 MHz
at 1 mm
at 2 mm
at 3 mm
Mag
nitu
de
frequency
15000 20000 25000 30000 35000 400000
200
400
600
800
1000
1200
1400
1600
1800
2000
19.9 kHz
1(upper PZT)
28 kHz, 308Ω
2(lower PZT)
28 kHz, 213Ω
Impe
danc
e(|Z
|)
frequency
spatial domain frequency domain impedance analysis
음압(소자 전면으로 mesh size를 lamda/8로 동일하게 함)
-5.0E+04
-3.0E+04
-1.0E+04
1.0E+04
3.0E+04
5.0E+04
1.00E-05 1.18E-05 1.33E-05 1.48E-05 1.63E-05 1.78E-05 1.93E-05
시간
음압
(dyne/c
m2)
at 1mm
at 2 mm
at 3 mm
time domain
V. Application of Piezoelectric SensorsV. Application of Piezoelectric Sensors
1. Impedance measurement
2. Piezoelectric Sensor System for platesOscillator sensor: Local measurementLamb wave sensor: Global measurement
3. Bulk wave measurement
4. Other examples
1. Impedance Measurement
Mechanical load- function of structural
conditions
Input Admittance
ZL= mechanical impedance of the plate = RL + i XL
V = input voltage, im = mechanical fluxR0 = internal electrical resistance C0 = electrostatic capacitanceRm = mechanical resistance Cm = mechanical capacitanceLm = mechanical mass ω = frequency
PZT
Thickness Mode Resonator
mmCLπ21
m
m
m CCCC
L 0
0121 +π
fs = unloaded series resonance
fp = unloaded parallel resonance
2/φLZ
2/φmL 2φmC
0C0R
22/φmR
Mi+
_
V
)1(
1 2
00
Lm
mLm
MEINX
CMiRR
CiR
YYY+−++
++=+=
ωω
φω
0 00
2
L L
ZA C
ωω ρΔ Δ
∝ −Frequency Shift:
Frequency (Hz)
Impe
danc
e (O
hm)
Does not require Modal Parameters / Failure ModesMonitor Local Modes at High Frequencies(>100 kHz)
: It Can Detect Incipient-type Damages
Monitoring the of the PZT bonded on the Structure in relation to Structural Damages
0ω
= Initial resonant frequency
= Frequency Shift in response to ΔZ
0ω
ωΔ
1. Impedance measurement
Experimental setup and Procedure
1. Impedance measurement
Measured data (S. H. Park)
2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
x 106
100.3
100.4
100.5
100.6
100.7
100.8
Frequency (MHz)
Imp
edan
ceNo damageDamage Case I-1Damage Case I-2
2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
x 106
100.4
100.5
100.6
100.7
100.8
Frequency (MHz)
Imp
edan
ce
No damageDamage Case I-1Damage Case I-2
PZT 1
PZT 2
2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
x 106
100.3
100.4
100.5
100.6
100.7
100.8
Frequency (MHz)
Imp
edan
ce
No damageDamage Case I-1Damage Case I-2
PZT 3
2 cracks near PZTs 2 & 3Damage Case I-2
Crack near PZT 3Damage Case I-1
-40000
-30000
-20000
-10000
0
10000
Damage Case
Fre
qu
en
cy
Sh
ift(
Hz)
PZT 1
PZT2
PZT3
No damage
Damage I-1
Damage I-2
Impedance vs. Crack configuration
*N = number of cracks on the aluminum plate
Frequency [Hz]
2M 3M 4M 5M 6M1
10
100 -
Impe
danc
e [O
hm]
N=1N=2N=3N=4N=5N=6N=7N=8N=9N=10N=11
856 858 860 862 864 866 868
32.72
32.73
32.74
32.75
32.76
32.77
32.78
32.79
Frequency [kHz]
No crackd=3cm, N=1d=4cm, N=1d=5cm, N=1d=7cm, N=1
Impe
danc
e [O
hm]
Impedance spectrum vs. Crack lengthImpedance spectrum vs. N
2. Piezoelectric Sensor System for plates
PZT oscillatorUltrasonic transducer
local major cracksat a weak region
global minor cracksdistributed over arbitrary places
Oscillator circuit
PZT oscillator sensor: Local measurementUltrasonic sensor: Global measurement
Portable ultrasonic measurement system
Local Detection: PZT Oscillator Sensor
Piezoelectric oscillator sensor - piezoelectric vibrator + oscillator circuit
⇒ diagnosis of the number of cracks⇒ diagnosis of the length of cracks
Piezoceramic vibrator
electrode
Oscillatorcircuit
thickness mode lateral mode
1000 2000 3000 4000 5000 6000
1
10
100
1000
10000
100000 Impedacne Phase
Frequency [kHz]
Impe
danc
e [O
hm]
-120
-100
-80
-60
-40
-20
0
20
40
Magnitude [degree]
4.55 MHz
100 200 300 400 50010
100
1000
10000
100000 Impedacne Phase
-100
-80
-60
-40
-20
0
20
40
60
80
100
Magnitude [degree]
Frequency [kHz]
Impe
danc
e [O
hm]
125 kHz
Compensation of environmental effects
Experimental plate specimen
f1 effects of cracks+ effects of environment
Reference plate specimen
f2 effects of environment
Oscillator Oscillator
PZT 10 cm
50 cm
Frequency counter Frequency counter
Output display
ΠΧ
GPIB GPIB
Experimental plate with damages PZT-Oscillator Reference sensor
Lateral mode analysis & measurement
Crack length vs. frequency shift
FEM analysisMeasurement
d=1 d=2 d=3 d=4 d=5
72200
72400
72600
72800
73000
73200
73400
73600
73800
Freq
uenc
y [H
z]
Length of crackd=1 d=2 d=3 d=4 d=5 d=6 d=7
119000
120000
121000
122000
123000
124000
125000
126000
Length of cracks
Del
ta F
requ
ency
[Hz]
Number of cracks vs. frequency shift: crack length = 3 cm
FEM analysis
N=1 N=3 N=5 N=7 N=9 N=11
124000
124200
124400
124600
124800
125000
125200
125400
125600Fr
eque
ncy
[Hz]
Number of cracks
Measurement
N=1 N=3 N=5 N=7 N=9 N=11125000
125100
125200
125300
125400
125500
Number of cracks
freq
uenc
y [H
z]
Number of cracks vs. frequency shift: crack length = 3 cm
Thickness mode vs. Lateral mode: FEA
Crack length vs. frequency shift
thickness lateral
thickness
lateral
None N=1 2 3 4 5 6
0.9980
0.9985
0.9990
0.9995
1.0000
1.0005
Num. of crack
Nor
mal
ized
freq
uenc
y
N=1 N=3 N=5 N=7 N=9 N=11123800
123850
123900
123950
124000
124050
124100
124150
Freq
uenc
y [H
z]
Num. of Crack
d=1cm 3 5 7 9 11
124000
124200
124400
124600
124800
125000
125200
125400
125600
Impe
danc
e [O
hm]
Frequency [Hz]
0 2 4 6 8 100.994
0.995
0.996
0.997
0.998
0.999
1.000
Y A
xis
Title
X Axis Title
B
Ultrasonic Transducer: (1) Bulk transducer (2) Piezeceramic patch
Crack configuration to be measured(1) Crack position (2) Crack length (3) Crack number
Global Detection: Ultrasonic Transducer
OscilloscopeBulk
transducer
PZT sensor
Piezo-patch
Damage detection scheme
0.1 m
0.05 m
0.05 mCB
0.05 m
Transducer & wedge
crack
PZT
xF
The crack position was changed in the range 5<=X<=15.The position of wedge and transducer is fixed at node B.
α : distance between crack and wedge.
α
0.15 m
Specimen
0.01 m
0.05 m
0.05 m
Transducer ->sensor(Through transmission)
Position of cracks
Number of cracks
Range of crack length
B->CE
from 1 to 3 form 0 to 0.09 mF
D->CEF
Damage scenario
D
Ultrasonic beam width
frequency P/Pax
0.5 MHz 1 MHz
-3 dB 12.7871o 12.7157o
-6 dB 17.6608o 17.5607o
Theoretical Beam Width
0.5 MHz
j i
Voltag
e(v)
1 MHz
Voltag
e(v)
j i
frequency P/Pax
0.5 MHz 1 MHz
-3 dB 10.314o 15.589o
-6 dB 17.734o 19.934o
Beam Width Measurement
Good agreement !
Reconstruction of Original Signals
fp : frequency spectrum of PZT- Sensor (known)fa : frequency spectrum of original signal (unknown)fd : frequency spectrum of distorted signal (known)
fa (ω)*fp(ω) = fd (ω)
fa (ω) = fd(ω)/fp(ω)
= fd(ω)*(1/fp=impedance spectrum(Zp))
fd(ω) ≒ signal of wavelet transformed domain
(1) Crack Position – TOF in a P/E responseTo get the position of a crack (unknown)
The crack position was changed in the range 5<=X<=15.The position of wedge and transducer is fixed at node B.
α : distance between crack and the front edge of the wedge.
0.1 m
0.05 m0.05 m
CB
0.05 m
Transducer & wedge
crack
PZT
x
α
0.2 m
Flying distance = velocity*TOF + constant
0.09 0.10 0.11 0.12 0.13 0.14
-0.10
-0.05
0.00
0.05
0.10
Vol
tage
(V)
T im e(m s)
a =0.010 m a =0.015 m a =0.020 m a =0.025 m
Time response of Pulse-echoed signalsα: 0.2 m
α: 0.15 m
α: 0.1 mThe position of the front edge of wedge : X= 0.20 mfrequency 0.5 MHzExact α 0.10 m 0.15 m 0.20 m 0.25 m
TOF (ms) 0.0898 0.1079 0.1261 0.1445
flying distance (m) 0.1995 0.3002 0.3999 0.5
estimated α(m) 0.0998 0.1501 0.1999 0.25
α: 0.25 m
(2) Crack Length –Amplitude of a T/T responseNormalized amplitude of the first peak of measured signals (driving frequency=0.5 MHz)
0.00 0.02 0.04 0.06 0.08 0.10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Nor
mal
ized
mag
nitu
de
Crack length(m)
Crack 1, X=0.05 m Crack 2, X=0.05 m Crack 3, X=0.05 m Crack 1, X=0.1 m Crack 2, X=0.1 m Crack 3, X=0.1 cm
B->C D->C
0.00 0.02 0.04 0.06 0.08 0.10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Nor
mal
ized
mag
nitu
de
Crack length(m)
Crack 1, X=0.05 m Crack 2, X=0.05 m Crack 3, X=0.05 m Crack 1, X=0.1 m Crack 2, X=0.1 m Crack 3, X=0.1 cm
B->C D->C
0.00 0.02 0.04 0.06 0.08 0.10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Nor
mal
ized
mag
nitu
de
Crack length(m)
Crack 1, X=0.05 m Crack 2, X=0.05 m Crack 3, X=0.05 m Crack 1, X=0.1 m Crack 2, X=0.1 m Crack 3, X=0.1 m
0.00 0.02 0.04 0.06 0.08 0.10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Nor
mal
ized
mag
nitu
de
Crack length(m)
Crack 1, X=0.05 m Crack 2, X=0.05 m Crack 3, X=0.05 m Crack 1, X=0.1 m Crack 2, X=0.1 m Crack 3, X=0.1 m
Normalized amplitude of the first peak of original signals (driving frequency=0.5 MHz)
The amplitudes are continuously decreasing as the crack lengths are increased to enter the ultrasonic beam.
(3) Crack Number – TOF in a T/T response
B->C, X= 0.05
TOF is increasing in proportion to the number of cracks.
Crack number =1 Crack number =2 Crack number =3
0.044
0.045
0.046
0.047
0.048
Length of Cracks(m)
X=0.05 m, B->C
0.080.070.06
TOF(
ms)
Number of Cracks = 1 EA Number of Cracks = 2 EA Number of Cracks = 3 EA
Relationship between in TOF and Flying Distance to determine the number of cracks
CDBcrack
FX
3. Bulk Wave Measurement
Nondestructive Testing Handbook, ASNT, 1991
4. Other Example
V. Giurgiutiu et al, Aerospace America, May 2003
structural neural system, G. R. Kirikera et al, Structural Health Monitoring, 2008Monitoring the health of aeronautical structures,
Igor Bovio, SPIE, 2006
4. Other Example
1. New materials: PZN-PT, PMN-PT, Li2B4O7, thin films
2. New structures: .multi-functional, micro-sensors.resistant to harsh environment
3. Smart sensors: .system integration.coupled with actuators to process self-treatment
4. Sensor network: multi-dimensional, wireless
VI. Future Trend of Piezoelectric SensorsVI. Future Trend of Piezoelectric Sensors
Sensor network application framework, E. Sazonov, et al, 2004