piezoelectric transducers—strain sensing and energy harvesting_2007.03.19-nishida

Piezoelectric Transducers—Strain Sensing and Energy Harvesting (and Frequency Tuning)

Toshikazu NishidaInterdisciplinary Microsystems Group

Department of Electrical and Computer EngineeringUniversity of Florida

[email protected]://www.img.ufl.edu

2T. Nishida, University of Florida

General Transducer System

Modular Transducer System DesignTransducer

device that converts one form of energy to anotherInterface ElectronicsPackaging/System Integration

Packaging-Protected

Transducer SignalProcessing ActuationControl

Display and/orData System

Interface ElectronicsEx

pose

dEx

pose

d


Transducer ClassificationBroad Classification

Energy-ConservingNon-energy Conserving

Specific ClassificationLinear versus nonlinearReciprocal versus anti-reciprocalDirect versus indirect


Linear, Conservative, TransducersLinear, energy-conserving, transducers

Linear: linearization about a mean may be requirednecessary for hi-fidelity transduction of time-resolved signal

Energy-conserving: [Ref. Hunt, Electroacoustics, 1954]

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


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.


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

= += +

⎡ ⎤⎡ ⎤ ⎡ ⎤= ⎢ ⎥⎢ ⎥ ⎢ ⎥

⎣ ⎦ ⎣ ⎦⎣ ⎦


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


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]( )

221A

eb ef efaD

dC C C k

C= − = −

Cef = free capacitancek = coupling factor

CaD

Ceb

φ:1+P-

+V-


Strain Sensing


Sensing Application: Piezoelectric MicrophoneAeroacoustic applications

Full scale (fly-over) or reduced-scale testing (wind tunnels)Noise source localization with arrays

1000’s of micsCost ($$$/channel)

Harsh environmentsOutdoorsPressurized wind tunnels

MEMS potentialMatched amplitude/phase

Good for arraysReduction in costSmaller size

Ref: Bob Dougherty, “Phased Array Beamforming for Aeroacoustics,” AIAA Short Course, May 8-9, 1999


Specifications - Aeroacoustic vs. AudioFrequency Range

Audio20 Hz 20 kHz

AeroacousticFull scale: 45 Hz 11.2 kHz1/nth scale: n*(Full scale)

– ¼ scale: 180 Hz 44.8 kHz

Noise FloorAudio

~ 23 – 37 dBAIntegrated, psycho-acoustic weighted

Aeroacoustic~ 28 - 40 dBNarrow bin for spectral measurement1 Hz bin @ 1 kHz

Acou

stic

Pres

sure

Frequency

Audio Aeroacoustic

Upper Dynamic RangeAudio: ~ 115 - 120 dBAeroacoustic : ~ 170 dB


Microphone Choices

“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


Piezoelectric Microphone Structure

Electrode (Pt or Ti/Pt)

Piezoelectric (PZT)Diaphragm (Si)

Package (Acrylic)

PiezoelectricAnnular

Ring

1.8 mm

TopElectrode

BottomElectrode

SiliconDiaphragm


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


Packaging & Experimental Setup

Microphone Package

Experimental Setup


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


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]


SetupTriple Faraday cageSingle point ground

Faraday cages

Experimental Setup-Noise Floor

Sensor

SR785 Spectrum Analyzer

SR560 Low Noise Pre-amplifier


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=


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=


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


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


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

Existing liner technologyPassive acoustic linerActive acoustic liner

Desirable traits of an acoustic liner

Tunable impedance, wide bandwidth, robust, light-weight, inexpensive, etc.


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


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


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.


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


Meso Acoustic Energy Harvesting - Overview

PowerConverter

Circuit

Acoustic Energy

Pin

Acoustic to ElectricalConversion

PHR

Pin

ElectricalConditioning

Electrical Energy

HelmholtzResonator

Pout

PHR

Pout


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.


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.

Experimental Load Power vs. Resistance

0

0.3

0.6

0.9

1.2

1.5

0 20000 40000 60000 80000 100000

Resistance (ohms)

Pow

er (m

W)

0 nF 1 nF 10 nF 100 nF 1000 nF


Meso Acoustic Energy Harvester – SetupAcoustically excited Plane Wave Tube (PWT)

B&K Pulse SystemTechronAmplifier

Cavity Mic.

Mic.2Mic.1

Incident Mic.

EnergyHarvestingDevice (or

Loads)

Speaker PWTPiezoelectric backplate

Helmholtz resonator

Δ

1x


Meso Acoustic Energy Harvester – Results

Output Power vs. Incident Pressure

0

5

10

15

20

25

30

130 135 140 145 150 155 160

Incident Pressure (dBSPL)

Out

put P

ower

(mW

)

4.7mH Linear Regulator Direct Charging


Energy HarvestingAdvantages

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


Energy Sources for Distributed SensorsSource Power Density

(μW/cm3)Energy Density(J/cm3)

Primary Battery 2880Secondary Battery 1080Ultra-Capacitor 50-100Micro-fuel cell 3500Heat Engine 3346Radioactive 0.52 1640Solar (Outside) 15000*Solar (Inside) 10*Temperature 40*a

Human Power 330Air Flow 380b

Pressure Variation 17c

Vibrations 300

* Denotes sources whose fundamental metric is area.

Notes:a) Demonstrated from a 5°C

temperature differential

b) Assumes air velocity of 5m/s and 5% conversion efficiency

c) Based on 1cm3 closed volume of helium undergoing a 10ºC temperature change once per day.

Roundy, S., Wright, P. K., and Rabaey, J., Computer Communications, 26(11), pg1131-1144


Energy Harvesting ApplicationLocally-powered wireless hydrogen sensor

(2) Harvestable energy scales down with decreasing volume

⇒ Multiple sourcesVibrationSolar

⇒Balancing power budgetPower consumption (dissipation)Power generation

(1) Ambient waste energy not necessarily dependableChallenges addressed as follows:

Carbon fiber reinforced H2gas tank, Photo: Quantum Technologies

Liquid H2 storage tank at NASA KSC, Photo: D. Wood


Block Diagram of Self-powered Sensor System

Solar Cell

Piezoelectric

Energy Reclamation

Circuit

Energy Storage

Available Power

Power Generation (Energy Harvester)

Sensor Microcontroller Transmitter

Power Dissipation (Loads)

Solar Cell

Piezoelectric

Energy Reclamation

Circuit

Energy Storage

Available Power

Power Generation (Energy Harvester)

Sensor Microcontroller Transmitter

Power Dissipation (Loads)


H2 Sensor

S D

ZnO M-NRs

Al2O3 Substrate

Al/Pt/AuS D

ZnO M-NRs

Al2O3 Substrate

Al/Pt/Au

Power considerationsConventional

Pd-SiC Schottky diodes– Require on-chip heater

Nano-structure-basedPt-catalyst coated multiple-ZnO nanorod

– Room-temperature low-power operation (O(100 μW))

0 5 10 15 20 25 30

0

2

4

6

8

10Air10~500 ppm H2

Pt-ZnO nanowires500ppm250ppm100ppm10ppm

Time(min)|Δ

R|/R

(%)

Recent result: single Pt-coated ZnO nanorod– 10x lower power and 3x faster response

Ref. Wang et al., Appl. Phys. A, 81, p. 1117, 2005.


Differential Hydrogen Detection

+

-

-

+

-

+

VDD

GNDGNDEx

pose

d Zn

O

Pass

ivat

edZn

OR

Bia

s

R B

ias

R1

R1

RG

R2

R2

R3

R3

VOUT

+

-

-

+

-

+

VDD

GNDGNDEx

pose

d Zn

O

Pass

ivat

edZn

OR

Bia

s

R B

ias

R1

R1

RG

R2

R2

R3

R3

VOUT

Wheatstone bridgeDifferential H2 signal

Exposed m-ZnO vs. sealed m-ZnO


Controller Considerations

SLEEP

SLEEPTransmitData

AcquireDataSLEEP

SLEEPTransmitData

AcquireDataSLEEP

SLEEPTransmitData

AcquireData

Selection factorsActive currentStandby currentWakeup timePort leakageADC precision

NA1uA in hibernating mode

0.1uA in sleep mode

10uA@32kHzXEMICS XE88LC01A

NA0.6uA standby0.1uA sleep

9uA@32kHzEM Micro EM6617

1uA5 Sleep modes, lowest is 0.2uA

27uA@32kHzAtmel Atmega169

25nA3 Stop modes: from 4.3uA to 25nA

812uA@1MHzMotorola MC9S08G

1uA1uA20uA@32kHzMicrochip PIC16F73

50nA4 low power modes from 0.7uA to 0.1uA

14uA@32kHz, 2.5uA@4kHz and 2.2V

TI MSP430F1122

Port Leakage

Standby CurrentActive CurrentManufacturer and Model

NA1uA in hibernating mode

0.1uA in sleep mode

10uA@32kHzXEMICS XE88LC01A

NA0.6uA standby0.1uA sleep

9uA@32kHzEM Micro EM6617

1uA5 Sleep modes, lowest is 0.2uA

27uA@32kHzAtmel Atmega169

25nA3 Stop modes: from 4.3uA to 25nA

812uA@1MHzMotorola MC9S08G

1uA1uA20uA@32kHzMicrochip PIC16F73

50nA4 low power modes from 0.7uA to 0.1uA

14uA@32kHz, 2.5uA@4kHz and 2.2V

TI MSP430F1122

Port Leakage

Standby CurrentActive CurrentManufacturer and Model


Modes of OperationMSP430 configuration

Minimum supply voltage (2.2V)32 kHz external clockInterrupt-driven control, most of CPU shutdown to conserve power

Level monitoringConstantly monitors H2 sensor and only sends emergency RF pulse above preset emergency threshold

Data transmittingConstantly monitors H2 sensor and sends data periodically, except if sensor value exceeds preset emergency threshold


Wireless Transmission

VDD

GND

VDD

GND

TradeoffsLow-level communication protocol

Low overhead for transmitterHigh overhead for receiverLow functionality for multiple sensors, networking, etc.

High-level communication protocolHigh overhead for transmitterLow overhead for receiverHigh functionality

Simple Colpitts oscillatorOn/Off Keying300 MHzData shifted bit-by-bit from output port to input


Power Budget

Average PowerResistanceHydrogen Level

88.6 uW1500 Ohms500 ppm

84 uW1563 Ohms0 ppm

Average PowerResistanceHydrogen Level

88.6 uW1500 Ohms500 ppm

84 uW1563 Ohms0 ppm

Controller/ transmitter

H2 sensor

20 m transmit distance w/ quarter-wave antenna

Power generation targetVibrationSolar

Variable2.5 uWRemain Idle

0.5ms per bit2.5 uWTransmit 0

0.5ms per bit261 uWTransmit 1

0.3 ms per bit2.5 uWSense Data

12.5ms3.07 mWInitialization

Length in TimeAverage PowerEvent

Variable2.5 uWRemain Idle

0.5ms per bit2.5 uWTransmit 0

0.5ms per bit261 uWTransmit 1

0.3 ms per bit2.5 uWSense Data

12.5ms3.07 mWInitialization

Length in TimeAverage PowerEvent


Mesoscale Piezo-Cantilever Power Generation

D1

D3 D4

D2

VBattery

PZTBimorph-4 C

IBattery

+

-A

R

Piezoelectric cantilever

Piezo Systems, Inc. D220-A4-203YB (32 mm x 6.4 mm x 0.3 mm)

displacement

acceleration

OPTICAL TABLE

Clamp plate

Proof mass

PZT composite beam

Mm & Cms

voltage

Power Amplifier

SHAKER

Spectrum Analyzer Imp. Head

displ. sensor

0

50

100

150

200

250

300

0.00 0.20 0.40 0.60 0.80 1.00 1.20

RMS Acceleration [/g]

Pow

er D

eliv

ered

to B

atte

ry [u

W]


Power Generation—Solar

1.5mm

ConverterController

Charge Pump

13 1215 14

Controller

Testing Schematic (Solar)

vds2 vds

Vbattery

PGateNGate

Solar Panel

vin

NGate

-PGate

Cin

Battery/Load

8 710 9111617

1819

2021

2223

65

43

21

24

25

26 29 30

40

2827

GndSmallSolar Panel

+

-

+

-

L=100uH

Voc

VrefH

Override_N

Enable_N

Override_PEnable_P

3931 …

1.5mm

ConverterController

Charge Pump

1.5mm

ConverterController

Charge Pump

13 1215 14

Controller

Testing Schematic (Solar)

vds2 vds

Vbattery

PGateNGate

Solar Panel

vin

NGate

-PGate

Cin

Battery/Load

8 710 9111617

1819

2021

2223

65

43

21

24

25

26 29 30

40

2827

GndSmallSolar Panel

+

-

+

-

L=100uH

Voc

VrefH

Override_N

Enable_N

Override_PEnable_P

3931 …

Custom DC-DC converter designed and testedMaintains output voltage near optimal voltage for maximum output power independent of load

High efficiency c-Si solar cells (IXYS Semiconductor XOD17-04B


System Integration and Test

ZnO H2 sensor

Self-powered Controller/Tx

N2

500 ppmH

2

Rx/laptop

ZnO H2 sensor

Self-powered Controller/Tx

N2

500 ppmH

2

Rx/laptop

Operation confirmed using mechanical shaker and external lightLevel monitoring modeData transmission mode

Informal vibration application testVacuum pump surface

Vibration Energy Harvesting Piezo Cantilever

Modeling assumptionsLinear Euler-Bernoulli beam theoryPerfect bond assumptionLinear piezoelectric material and reciprocal system


Electromechanical LEM

Lumped Element ModelingAnalytical : provides scalingCircuit : enables complete electromechanical system simulation

F

Mm Cms

CebU

φ : 1

EffectiveCompliance of

Beam

EffectiveMass ofBeam

InputForce

Velocity

ElectromechanicTransduction Factor

BlockedElectrical

Capacitance ofpiezoceramic

I

V

Current

Voltageacross the

piezoceramic

Re

Mechanicaldamping of

beam

Dielectric lossin the

piezoceramic

Rm

MEMS Energy Harvesting


Final structure (front view and top view) Not drawn to scale

SiO2

SiSiO2(BOx)

Ti/Pt PZTPt

Bond pads

Proof mass

Clamp

Cantilever Beams

Au

MEMS Piezoelectric Cantilever


MEMS Piezo Cantilever DevicesSEM pictures of released devices

Device DimensionsPZT-EH-09PZT-EH-07

500 μm

4 mm

2.5 mm

1 μm

1 mm

1 mm

12 μm

1 mm

1 mm

1 μmThickness of PZT

1.8 mmLength of proof mass

2.4 mmWidth of proof mass

500 μmThickness of proof mass

0.5 mmWidth of PZT

0.5 mmLength of PZT

12 μmThickness of beam

0.5 mmWidth of beam

0.5 mmLength of beam

Device DimensionsPZT-EH-09PZT-EH-07

500 μm

4 mm

2.5 mm

1 μm

1 mm

1 mm

12 μm

1 mm

1 mm

1 μmThickness of PZT

1.8 mmLength of proof mass

2.4 mmWidth of proof mass

500 μmThickness of proof mass

0.5 mmWidth of PZT

0.5 mmLength of PZT

12 μmThickness of beam

0.5 mmWidth of beam

0.5 mmLength of beam

PZT-EH-07

PZT-EH-09


MEMS Piezo Generator - ArrayArray of MEMS piezo generatorsSeries and parallel connection.

Resonant Energy Generator Array

Output and ControlPads

Power Processor

Summary


Summary

Piezoelectric transducers offer potential benefits for low power sensing and vibration/acoustic energy harvesting

Transducer may require for low power voltage/charge amplifier

Scaling down energy harvester decreases harvestable powerRequires arrays, low power active converter


Acknowledgements

Former and current studentsDr. Steve HorowitzDr. Anurag KasyapMr. Fei LiuMr. Robert Taylor

Collaborating facultyProf. Mark Sheplak, MAE UFProf. Lou Cattafesta, MAE UFProf. Khai D. T. Ngo, ECE UF/ VTech

SupportNASA LangleyNASA Glenn (NAG 3-2930 monitored by Timothy Smith)


Interdisciplinary Microsystems GroupInterdepartmental Research Group in College of Engineering

IMG initiated in 1998Mechanical and Aerospace Engineering

Mark Sheplak: (98) design, acoustics, fluid mechanicsLou Cattafesta: (99) flow control, acoustics, fluid mechanicsHugh Fan: (03) microfluidics, BioMEMS

Electrical and Computer EngineeringToshi Nishida: (88) noise, strained silicon, energy havestingHuikai Xie: (02) CMOS-MEMS, photonics, bio-imagingDavid Arnold: (05) micromagnetics, micro-power systems

piezoelectric transducers—strain sensing and energy harvesting_2007.03.19-nishida

Documents