Piezoelectric Transducers—Strain Sensing and Energy Harvesting (and Frequency Tuning) Toshikazu Nishida Interdisciplinary Microsystems Group Department of Electrical and Computer Engineering University of Florida [email protected]http://www.img.ufl.edu
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Piezoelectric Transducers—Strain Sensing and Energy Harvesting (and Frequency Tuning)
Toshikazu NishidaInterdisciplinary Microsystems Group
Department of Electrical and Computer EngineeringUniversity of Florida
Electromechanical coupling methods can be broadly classified according to whether the mechanical forces are produced under the action of electric fields on electric charges or by the interaction of magnetic fields and electric currents.
Five major electromechanical transducers
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Linear, Conservative, Transducers
1) Electrodynamic: motor/generator action are produced by the current in, or the motion of an electric conductor located in a fixed transverse magnetic field (i.e., voice coil, solenoid, etc.).
2) Electrostatic: motor/generator action are produced by variations of the mechanical stress by maintaining a potential difference between two or more electrodes, one of which moves (i.e., condensor microphone, etc.).
3) Magnetic: motor/generator action are produced by variations of the tractive force tending to close the air gap in a ferromagnetic circuit.
4) Piezoelectric: motor/generator action are produced by the direct and converse piezoelectric effect - dielectric polarization gives rise to elastic strain and vice versa (i.e., tweeters, etc.).
5) Magnetostrictive: motor/generator action are produced by the direct and converse magnetostriction effect - magnetic polarization gives rise to elastic strain and vice versa.
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Two-Port Model for Linear Conservative TransducerGeneral Two-Port Theory for L.C. Transducers:
In general, represent by simple two-port networks expressed in either the impedance form or the admittance form
Z-representation:
Two-PortElement
I
-
+
-
+V F
U or
EB EM
ME MO
EB EM
ME MO
V Z I T UF T I Z U
Z TV IT ZF U
= += +
⎡ ⎤⎡ ⎤ ⎡ ⎤= ⎢ ⎥⎢ ⎥ ⎢ ⎥
⎣ ⎦ ⎣ ⎦⎣ ⎦
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Piezoelectric Effect
Prior to poling After poling
33 33 33ES s T d E= +
33 33 33TD d T Eε= +
2 (y)
3 (z)
1 (x)
4 5
6 1-D linear piezoelectric coupling equations
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Piezoelectric Model
Piezoelectric element modeled as a two-port network
CaD short circuit acoustic complianceCeb blocked capacitanceφ electro-acoustic transduction factor
A
aD
dC
φ −=
( ) dA = electro-acoustic piezoelectric charge modulus [C/N] or [m/V]( )
“Performance of B&K 4135, size of Kulite MIC-062, cost of SiSonic”
B&K 4135 Kulite MIC 062 SiSonicBandwidth 4 Hz - 100 kHz DC - 125 kHz 30Hz - 10 kHzNoise Floor ~ 5 dB 100 dBA 37 dBAMax SPL (10%) ~ 172 dB 194 dB ~ 124 dBSize 6.35 mm 1.57 mm 3.75 mm x 4.75 mmCost O ($$$) O ($$) O(<$)Type Capacitive Piezoresistive Capacitive
Ref: Kulite Mic-062Kulite Semiconductor Products, Inc.
Ref: B&K Type 4938 Brüel & Kjær
Ref: SiSonicKnowles Acoustics
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Piezoelectric Microphone Structure
Electrode (Pt or Ti/Pt)
Piezoelectric (PZT)Diaphragm (Si)
Package (Acrylic)
PiezoelectricAnnular
Ring
1.8 mm
TopElectrode
BottomElectrode
SiliconDiaphragm
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Process Flow - Overview
a)
b)
d)
c)
f)
e)
g)
h)
a)
b)
d)
c)
f)
e)
g)
h)
TiO2SiBuried Oxide (BOX) - SiO2Top Electrode - Pt
PZTBottom Electrode - Ti/PtPhotoresist
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Packaging & Experimental Setup
Microphone Package
Experimental Setup
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75 100 125 150 17510
-8
10-6
10-4
10-2
Out
put V
olta
ge [V
]
Input Acoustic Pressure [dB]
DataFit
Experimental Results-Linearity169 dBLinear up to at least
0.75 122.5 1V VSens dB rePa Paμ
= = −
2 0.9995R = Taken at 1 kHzw/ 1 Hz bin
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Experimental Results-Frequency Response
101 102 103-140
-135
-130
-125
-120
Freq [Hz]
Mag
nitu
de [d
B re
1 V
/Pa]
101 102 103
0
20
40
60
Freq [Hz]
Phas
e [d
eg]
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SetupTriple Faraday cageSingle point ground
Faraday cages
Experimental Setup-Noise Floor
Sensor
SR785 Spectrum Analyzer
SR560 Low Noise Pre-amplifier
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1 10 100 1000 1000045
50
55
60
65
70
75
80
85
Freq [Hz]
Mag
nitu
de [d
B re
20 μ
Pa]
Experimental Results-Noise Floor
.
MDS: 47.8 /dB Hz
Setup Noise
Sensor Noise
Noise Floor: 3.7 /nV Hz
Corner frequency (6.7 Hz)
@ f = 1 kHz
[ ]eR MΩ
13.9 1.7
[ ]nFebC
min_avgF 12 nN=
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10 20 30 40 50 60 70 80 90-20
-18
-16
-14
Mag
nitu
de [d
B re
1 μm
/V]
Freq [kHz]
10 20 30 40 50 60 70 80 90
-150
-100
-50
0
Freq [kHz]
Pha
se [D
eg]
.
Experimental Results-Laser Vibrometry
50.8 resf kHz= 5.4Q =
3 49.3 dBf kHz=
21T. Nishida, University of Florida
Benchmarking
B&K 4135 Kulite MIC 062
SiSonicSP0102
UF PiezoMic
¼ Scale Mic
Bandwidth 4 Hz –100 kHz
DC –125 kHz
10 Hz –10 kHz
18 Hz –49 kHz (theo.)47.8 dB169+ dB5 mm x 5 mm???
Noise Floor ~ 5 dB 100 dB (?) 35 dBA
180 Hz –44.8 kHz
28 dB170 dB
3.8 mm
Max SPL (10%) ~ 172 dB 194 dB (?) ~ 115 dB
Size 6.35 mm 1.57 mm 3.76 mm x 6.15 mm
Cost O ($$$) O ($$) O(<$) O(<$)
Frequency Tuning
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Tuning and Energy Harvesting Application: Active Acoustic Liner
Aircraft noise is an ongoing environmental problemTwo main sources
Airframe noisePropulsion noise
Comparison of the Approach Noise Levels for the Boeing 747-400 with Pratt & Whitney 1992 Technology Engines and ADP Engines (NASA/TM-2005-212144, May 2005)
60 70 80 90 100 110
Total Aircraft Noise
Total Airframe
Jet
Turbine
Combustor
Aftfan
Inlet
EPNdB
P&W ADP Engine P&W 1992 Technology Engine
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Active Acoustic Liner - Background
Ref. Rolls Royce, “The Jet Engine”, 1986.
Aircraft engine duct linersProvide impedance boundary conditions for engine ductMinimize the radiation of noise from the duct
Tunable impedance, wide bandwidth, robust, light-weight, inexpensive, etc.
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Self-Powered, Wireless Acoustic Liner Concept
( )U n
controller &communications
energyreclamation
module
tunableelectromechanical
liner cellmicrophones
( ) ( ) ( ), , i t k rp r t p k e ωω − ⋅′ ′=r rrr
n
controller &communications
Acoustic liner specifications
Tunable Helmholtz resonator for impedance modification Energy reclamation module for self-poweringWireless control module for remote tuning
26T. Nishida, University of Florida
Lumped Element Model for Conventional HR
( )2
4
kg, 1 2 m
airaDrad
eff
ka cR ka
A sρ ⎡ ⎤≅ ⎢ ⎥⎣ ⎦
4
8 kg, 1 3 m
airaDrad
eff
ka cM ka
Aρ
πω⎡ ⎤≅ ⎢ ⎥⎣ ⎦
Radiation impedance modeled as a piston in an infinite baffle
Plate parameters found from deflection curve,
( )2
00
0
2R
P
AP
w r rdrVoldV V
π→
→
Δ= =
∫
( )2
00
0
2R
V
aDV
w r rdrVolCP P
π→
→
Δ= =
∫2 2
0
( )2R
aD Aw rM rdrVol
ρ π ⎛ ⎞= ⎜ ⎟Δ⎝ ⎠∫
( )w r
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Tunable Electromechanical Helmholtz Resonator
Electromechanical Helmholtz resonator (EMHR)
Piezoelectric composite backplate (PZT-backplate) instead of conventional solid-wallShunt-loads across the PZT-backplateEM DOFs possible
aNR aDCaNM
aCCaD aDradM M+
Q
INZP EBC LZ
:1φ'Q i
+
−
'P
aDradR
Ref. APC International, Ltd.
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Tuning Performance of EMHR
2 DOF/3DOF: coupled oscillatorShort circuit and open circuit define the capacitive and resistive tuning− 9%
Inductive tuning is not limited to short-circuit and open circuit− >19%
Energy Harvesting
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Meso Acoustic Energy Harvesting - Overview
PowerConverter
Circuit
Acoustic Energy
Pin
Acoustic to ElectricalConversion
PHR
Pin
ElectricalConditioning
Electrical Energy
HelmholtzResonator
Pout
PHR
Pout
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Meso Acoustic Energy Harvester – LEM
aNR aDCaNM
aCCaD aDradM M+
Q
INZP EBC LZ
:1φ'Q i
+
−
'P
aDradR
Electromechanical Helmholtz resonator (EMHR)
Piezoelectric composite backplate (PZT-backplate) instead of conventional solid-wallEnergy harvesting circuit across the PZT output
Same equivalent circuit as tuning circuit
PZT-backplateEH Circuit
Cavity
Neck
Ref. APC International, Ltd.
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Meso Acoustic Energy Harvester – Power vs Load
RLoad
Cbulk
iLoad
VLoad
Load Power(VLoad)
2/RLoad
HR Output • The HR is connected to a rectifier bridge, bulk capacitor and load resistor.• The HR is driven at the resonance of the diaphragm.• The bulk capacitor and load resistor are both swept, the power at the load is measured.
Simplifies deployment of a large numbers of wireless sensorsAvoids need for routing or retrofitting wiringEliminates maintenance costs of battery replacement
ChallengesAmbient waste energy not necessarily dependableHarvestable energy scales down with decreasing volume
Smaller size → less available energy
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Energy Sources for Distributed SensorsSource Power Density