Sept 2008M Thompson, Chonbuk National University 1 Piezoelectric PVDF Technology and Medical Applications Overview Mitch Thompson, Ph.D. Vice President,

Sept 2008M Thompson, Chonbuk National University 1

Piezoelectric PVDF Technologyand Medical Applications Overview

Mitch Thompson, Ph.D.Vice President, Technology

Measurement Specialties, Inc.9/19/08


Review of piezoelectric fundamentalsReview of piezoelectric fundamentals

Overview of PVDF Material ScienceOverview of PVDF Material Science

PVDF Medical ApplicationsPVDF Medical Applications

IntroductionIntroductionIntroductionIntroduction


AbstractAbstractAbstractAbstract

There are many Electro-Active Polymers (EAP) with potential for use as biomedical actuators or sensors. These polymers are generally classified as either electronic or ionic depending upon the actuation mechanism. Electronic polymers are electro-mechanically coupled insulators and this family includes ferroelectric, electro-strictive, liquid crystal, and dielectric (Maxwell) materials. In contrast, ionic polymers are generally hydrated and react to ionic transport. This family includes Ionic Polymer Metal Composites (IPMC), ionic gels, conductive polymers (e.g., polypyrrole), and some electro-rheological materials.



There are numerous references in recent literature describing the potential biomedical applications for new/emerging EAP: large displacement actuators for catheter navigation, artificial muscle structures, artificial sphincter cuffs, biologically generated power, fluidic valves, fluid flow and flow control, haptic feedback, polymer peristaltic pumps, and many more. Although these materials and applications represent an exciting field of study, piezoelectric PVDF and P(VDF-TrFE) are by far the most widely deployed EAP in the market today and are therefore the focus of this discussion.



This talk will cover:

The basic physics of piezoelectricity,

An overview of the PVDF manufacturing processes,

A discussion of strengths and limitations

An overview of some specific medical applications.



Coupling between energy forms:Coupling between energy forms:

Nearly all sensing systems depend upon Nearly all sensing systems depend upon the ability to transduce energy from one the ability to transduce energy from one form to another. Without this form to another. Without this transduction, none of the modern transduction, none of the modern medical sensing technologies would be medical sensing technologies would be possible.possible.



Electro-strictiveElectro-magneticMagneto-strictiveMagneto-resistiveElectro-elastic (piezo-electric)Elasto-resistive (piezo-resistive)Magneto-rheologicElectro-rheologicElectro-chemicalOpto-chemicalOpto-electricPiezo-optical

Dielectricbehavior

Elasticstructure

Photooptics

Chemicalbehavior

Magnetic field

Electric field

Some Common Coupling EffectsSome Common Coupling Effects

Material behavior is governedby crystallographic symmetry


Linear ElasticityLinear Elasticity

T s = SStrain ComplianceStress

(Hooke’s Law)

= E

Common Equation Form

klijklij TsS

More Formal Tensor Notation

)stress(

strain)(

j

iij T

Ss

Elastic Compliance

Piezoelectric Fundamentals


Linear DielectricityLinear Dielectricity

E = D Charge Disp. Permittivity Field

V C = Q nmnm ED

Common Equation Form More Formal Tensor Notation

)field(

charge)(

j

iij E

D

Dielectric Compliance



PiezoelectricityPiezoelectricity

+ E d + T s = S

p +T d + E = D

Thermal expansion

Piezo coupling

ΔTemp

Pyroelectric coefficient

)field(

strain)(

)stress(

charge)(

i

j

j

iij E

S

T

Dd

Piezoelectric compliance

Direct effect Converse effect



ijkijkklijklij EdTsS

immijiji EdTsS

13313132121111 EdTsTsTsS

S Strain Tensor α Thermal Coeff Expansion TensorT Stress Tensor d Piezo Strain Tensors Elastic Compliance Tensor p Pyroelectric Charge TensorE Electric Field Tensor Θ Temperature Change

Standard Tensor Contraction Yields

Typical Example

Only E3 is usefulin a thin film

Linear Elasticity Electro-Mech CouplingThermo-Mech Coupling



33332321313333 pTdTdTdED

mjkmjknmnm pTdED

33333 pTdED jmj

T Stress Tensor d Piezo Strain Tensorp Pyroelectric Charge Tensor ε Dielectric PermittivityTensorE Electric Field Tensor Θ Temperature ChangeD Charge Displacement Tensor

Linear Dielectricity Electro-Mech Coupling Thermo-Elec Coupling



iijiji EdTsS 33

33333 pTdED jmj

Piezoelectric materials are Electro-Mechanically Coupledand transduce energy forms




InEnergy Elec

OutEnergy Mech

InEnergy Mech

OutEnergy Elec2

k

factor coupling hanicalElectromec 2 k


PVDF Piezoelectric BasicsPVDF Piezoelectric Basics

133

313 T

dE

2

33

323 T

dE

3

33

333 T

dE

Note Polarity

311

311 E

s

dT

Piezoelectrics transduce energy in BOTH directions

Applied stressResulting field

Applied field

Resulting stress



Elastic Viscoelastic

ε

Lossy Dielectric

ε


PVDF is a polymer


20

398

10000

251189

-60-3003

06090

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Loss Tangent

Freq Hz

Temp C

S8504

PVDF Dielectric PermittivityVersus Temperature, Frequency

PVDF Dielectric Loss TangentVersus Temperature, Frequency

20

251

3981

63096

1000000

-60 -30 0 30 60 90

0.00E+00

2.00E-11

4.00E-11

6.00E-11

8.00E-11

1.00E-10

1.20E-10

1.40E-10

Permittivity

Freq Hz

Temp C

S8504



PVDF Material BasicsPVDF Material Basics

H, C, F stick models of 3 major crystal forms in PVDF.

The a form grows from the melt in normal processing, converted to polar b form by extreme mechanical orientation, which produces a solid state phase transformation.

a, apb g

Ferroelectric Polymers, H.S. Nalwa

PVDF Material Science



H, C, F stick models showing a unit cell projection of the polymer backbone.

Note “non zero” net polarization in b (I) form

ab

gap

H

F





Space filling modelsSolid-State phase transition done byorientation

a (non-polar) b (polar)


c (1) axis

a (2) axis

b (3) axis



PVDF Piezoelectric BasicsPVDF Piezoelectric Basics

PVDF FILM is highly anisotropic -

2 (a) Axis: Transverse direction Axis of minor activity (d32 ≈ d31/10)

1 (c)Axis: Chain backbone axis Stretch direction

Axis of major activity

3 (b) Axis: Thickness direction Axis of minor utility (d33 ≈ d31, stiffer)

≈ 90% of Applications use d31, 10% use d33, d32 not used

Electrodes normal to 3 axis (on flat surfaces)




Displacement/Electric Field (D/E) curve shows dielectric hysteresis - the definition of a ferroelectric material. (25um PVDF shown)

Remnant Polarization

CoerciveField


D/E curve for capacitor




Typical properties of piezo PVDF


MEAS PVDF




Interaction between PVDF crystal forms and processing history.

Only a few routes are physically practical, only one route is commercially feasible.






Rolls of FinishedPiezo Film

Ready to Stock

(>100,000ft2/yr)



Piezo Film Roll~850 ft



Thick Film ElectrodeScreen Printing



Printed Silver InkPatterns on a Single Sheet



Low Raw Material Cost

High part density/sheet



Steel Rule Die Patterning



Laser Patterning








Simple equivalent circuit for PVDF Simple equivalent circuit for PVDF sensorssensors

“g” coefficient quantifies stress

to voltage conversion

g=d/ε

Thickness

LengthWidthCap PVDF

Load impedance forms a HPF with

sensor capacitance


Piezo Film Sensors

(+) PVDF Attributes for Medical (+) PVDF Attributes for Medical ApplicationsApplications Excellent LINEARITY: charge is proportional to applied strain

over very wide temperature and frequency range Large DYNAMIC RANGE: useful over 14 orders of magnitude

(>280 dB) - from fC to mC, nV to kV HIGH VOLTAGE SENSITIVITY: ~18mV/(10-6 strain) Very BROAD BANDWIDTH: from mHz to ~GHz LOW Q factor: can be < 1 in water, < 12 in air HIGH DIELECTRIC STRENGTH: up to 200 MV/m Sustains HIGH STRAINS: >4% >10million cycles have little

effect ROBUST and FLEXIBLE, conforms to 2.5D surfaces LOW COST/AREA, ease of manufacturing in large volume

PVDF Medical Applications


(-) PVDF Attributes for Medical (-) PVDF Attributes for Medical ApplicationsApplications LIMITED UPPER TEMPERATURE: ≤ 125°C (no autoclave) SENSITIVITYVOLT = f(TEMPERATURE, FREQ)

POWER COUPLING EFFICIENCY LOW: (not good for harvesting) VARIABILITY in transducer absolute sensitivity, capacitance

(~PZT) HIGH PYROELECTRICITY (8V/ºC): creates thermal noise at low freq HIGH SOURCE IMPEDANCE: (DC ~ 12), often requires local

buffering and careful EMI/RFI shielding CANNOT BE SOLDERED: reflow/wave soldering NOT possible INTERCONNECTIONS: applications with liquids or high strains COMPETITION: Emerging markets driving ubiquitous sensors,

SMALLER, CHEAPER, SMARTER, HIGHER PEFORMANCE, competition from MEMS and NANO technologies in some areas



A Few Medical Applications Using PVDFA Few Medical Applications Using PVDF

Acoustic bone conduction mic Pedobarography (foot pressure)

Cardiac auscultation Powered pacing leads

Cardio/respiratory pads Prosthetic limb tactile sensing

Catheter pressure detection Rapid eye motion (sleep lab)

Cochlear acoustic implants Snore detection (sleep lab)

Diagnostic catheter imaging Thermometry (infrared sensing)

Fetal phonocardiography Ultrasonic imaging (pulse-echo)

Korotkov sound detection Uterine contraction sensing

Monitoring apnea & SIDS Vascular graft monitor (wrapped)

Osteogenesis



Application: pacemaker activity Application: pacemaker activity sensorsensor

PVDF is used to make complex multi layer sensing elements for an implantable pacemaker activity monitor

PVDF sensing elements

Accelerometer assembly



Application: Contact Application: Contact microphonemicrophone

Apnea sensors

Blood pressure cuff microphone

Pulse Wave Velocity, tonometry

Stethoscope sensor

Curved PVDF sensing structure

Internal protection & buffering

~100V/mm 20Hz – 4kHz


Typical Frequency Response

10 100 1000 10000 Frequency (Hz)

Sen

sit

ivit

y (

V/m

m )

70 60 50 40 30 20 10 0



Application: Contact Application: Contact microphonemicrophone

Typical buffering circuit, contained inside package


Application: electronic stethoscopeApplication: electronic stethoscope

High performance Welch Allyn High performance Welch Allyn stethoscope uses a PVDF stethoscope uses a PVDF acoustic sensoracoustic sensor



Application: sleep lab eye sensorsApplication: sleep lab eye sensors

PVDF is used for REM detection, respiration, and snore detection



Application: infant apnea sensorsApplication: infant apnea sensors

Respironics uses PVDF as a contact microphone to detect irregularities in respiration or cardiac function in infants




Application: Adult apnea sensorsApplication: Adult apnea sensors


Application: Motion sensorsApplication: Motion sensors

Chest wall motion sensor

High Sensitivity

~1000mV/g

~1600mV/mm motion @20Hz

Low Cost/Disposable

Mass loaded PVDF cantilever

PCB mountable1,000 mV/g, 75Hz fo




Application: LDTC on Chest with Application: LDTC on Chest with StrapStrap

First

And Second

Heart Sounds



Application: Motion sensorsApplication: Motion sensors

Wide array of sizes,

shapes, and masses


Displacement versus AppliedVoltage (Converse Effect)

Application: UltrasoundApplication: Ultrasound

PVDF Other Applications




Backing Absorber

Piezo Layer

Matching layer λ/4

Reflected U/S wave

Transmitted U/S wave

Reflecting Target



Application: 30-50MHz UltrasoundApplication: 30-50MHz Ultrasound

“Mason’s Model” used to model the acoustic performance of the struacture using electrical impedance blocks

Z2k

Zp

sink tkp

vp

j

Z1k

Zp tank tkp

2 vp

j

Drive V and return signal port

Backing Piezo Matching Tissue/

water




Typical reflection acoustic waveform

(PVDF-TrFE)




U/S Transducer

Imaged TUMOR in MOUSE

High frequency = high resolution image, requires very thin piezo layer




Images from a mouse vascular system


Application: HIFU Array, disposableApplication: HIFU Array, disposable

HIFU = High Intesity Focused UltrasoundTherapeutic treatment of tumors.Beam steered around rib bones, electronically focused.

Dielectric losses very high, required water cooling, not successful.




Application: Cochlear ImplantApplication: Cochlear Implant

Images from a prototype Cochlear device, tapered cavity resonance, cavity covered with thin film layer

High Freq Low Freq



Application: Non-Contact Patient Application: Non-Contact Patient MonitorMonitor Large PVDF sensor

system under mattress detects:

Respiration Rate

Respiration Activity

Heart Rate

Body Motion

Bed Exit



Application: Baby Breathing/MotionApplication: Baby Breathing/Motion

PVDF sensor system in diaper with remote link monitor for:

Respiration Rate

Heart Rate

Body Motion (or no motion)



Application: Respiration Rate, in Application: Respiration Rate, in MaskMask

PVDF pyroelectric response (8V/ºC) used as an added feature in mask to detect respiration rate


Application: ultrasonic Application: ultrasonic transducerstransducers

80kHz Digitizer Tx Assy Includes IR LEDs

Pen/stylus mountableFull a4 capable


28um PVDF welded into a cylindrical ring, excited with ~600Vpp to chirp 80kHz air ultrasound.

Two receivers “hear” the ultrasound and by Time of Flight – triangulate the 2D position of the pen tip

PVDF cylinder (silver ink)


Ultrasonic digitizer from Pegasus Technologies Ultrasonic digitizer from Pegasus Technologies captures handwriting or drawings from normal captures handwriting or drawings from normal paper, and can send as fax, email, or SMS (text paper, and can send as fax, email, or SMS (text message)message)

Application: ultrasonic digitizersApplication: ultrasonic digitizers



Electronic white boards; piezo film based air ranging ultrasound transducers

Retrofit market for 89 million existing white boards

Real time conference calls over the Internet

Application: ultrasonic Application: ultrasonic digitizersdigitizers

Virtual Ink:Virtual Ink: mimio



Thank you for your time.

Questions?

125°C Stable PVDF

Documents

Sept 2008M Thompson, Chonbuk National University 1 Piezoelectric PVDF Technology and Medical Applications Overview Mitch Thompson, Ph.D. Vice President,