Piezo Film Sensors

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					                                      Piezoelectric PVDF Technology
                                     and Medical Applications Overview
                                                Mitch Thompson, Ph.D.
                                              Vice President, Technology
                                             Measurement Specialties, Inc.
                                                       9/19/08




M Thompson, Chonbuk National University        Sept 2008                     1
Introduction



Review of piezoelectric fundamentals

Overview of PVDF Material Science

PVDF Medical Applications




M Thompson, Chonbuk National University   Sept 2008   2
Abstract
  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.




M Thompson, Chonbuk National University   Sept 2008               3
Abstract
   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.




M Thompson, Chonbuk National University   Sept 2008                 4
Abstract



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.




M Thompson, Chonbuk National University   Sept 2008   5
Introduction
                    Coupling between energy forms:


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




M Thompson, Chonbuk National University   Sept 2008   6
Introduction
     Some Common Coupling Effects

  Electro-strictive                         Elastic              Dielectric
  Electro-magnetic                          structure            behavior
  Magneto-strictive
  Magneto-resistive
  Electro-elastic
    (piezo-electric)                      Electric                    Photo
  Elasto-resistive                        field                       optics
    (piezo-resistive)
  Magneto-rheologic                         Chemical
  Electro-rheologic                                              Magnetic
  Electro-chemical                          behavior             field
  Opto-chemical
  Opto-electric                             Material behavior is governed
  Piezo-optical                             by crystallographic symmetry
M Thompson, Chonbuk National University              Sept 2008                 7
Piezoelectric Fundamentals
    Linear Elasticity

                                                      Elastic Compliance
      Strain         Compliance Stress




               (Hooke’s Law)




               Common Equation Form           More Formal Tensor Notation




M Thompson, Chonbuk National University   Sept 2008                         8
Piezoelectric Fundamentals
    Linear Dielectricity

                                                      Dielectric Compliance
  Charge Disp.           Permittivity Field




              Common Equation Form                More Formal Tensor Notation




M Thompson, Chonbuk National University       Sept 2008                         9
Piezoelectric Fundamentals
    Piezoelectricity
                                           Thermal expansion


                                                                       ΔTemp

                                          Piezo coupling



                                                           Pyroelectric coefficient


                          Piezoelectric compliance




                      Direct effect             Converse effect

M Thompson, Chonbuk National University                    Sept 2008                  10
 Piezoelectric Fundamentals



Standard Tensor Contraction Yields




                                                                          Only E3 is useful
Typical Example                                                           in a thin film




                              Linear Elasticity   Electro-Mech Coupling   Thermo-Mech Coupling


        S            Strain Tensor                   α          Thermal Coeff Expansion Tensor
        T            Stress Tensor                   d          Piezo Strain Tensor
        s            Elastic Compliance Tensor       p          Pyroelectric Charge Tensor
        E            Electric Field Tensor           Θ          Temperature Change
 M Thompson, Chonbuk National University            Sept 2008                                    11
Piezoelectric Fundamentals




            Linear Dielectricity    Electro-Mech Coupling       Thermo-Elec Coupling




        T             Stress Tensor                         d           Piezo Strain Tensor
        p             Pyroelectric Charge Tensor            ε           Dielectric PermittivityTensor
        E             Electric Field Tensor                 Θ           Temperature Change
        D             Charge Displacement Tensor

M Thompson, Chonbuk National University                Sept 2008                                        12
Piezoelectric Fundamentals




                Piezoelectric materials are Electro-Mechanically Coupled
                               and transduce energy forms




M Thompson, Chonbuk National University        Sept 2008                   13
Piezoelectric Fundamentals




M Thompson, Chonbuk National University   Sept 2008   14
   Piezoelectric Fundamentals
        PVDF Piezoelectric Basics
                                         Applied stress
Resulting field




                                                                                   Note Polarity




                                                     Applied field


 Resulting stress                       Piezoelectrics transduce energy in BOTH directions

   M Thompson, Chonbuk National University                Sept 2008                                15
Piezoelectric Fundamentals
                                                  PVDF is a polymer


             Elastic                      Viscoelastic         Lossy Dielectric




                                                                      ε




                                                                          ε




M Thompson, Chonbuk National University           Sept 2008                       16
Piezoelectric Fundamentals


     PVDF Dielectric Permittivity            PVDF Dielectric Loss Tangent
   Versus Temperature, Frequency            Versus Temperature, Frequency




M Thompson, Chonbuk National University   Sept 2008                         17
PVDF Material Science
     PVDF 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                                                g
transformation.                           b           a, ap

                                                         Ferroelectric Polymers, H.S. Nalwa



M Thompson, Chonbuk National University   Sept 2008                                           18
 PVDF Material Science
      PVDF Material Basics
                                                     b                 a
                                           H

                                           F



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

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

                                                     ap                g
                                                           Ferroelectric Polymers, H.S. Nalwa


 M Thompson, Chonbuk National University       Sept 2008                                        19
PVDF Material Science
     PVDF Material Basics
                                                                                    c (1) axis

Space filling models                  a (non-polar)               b (polar)
Solid-State phase
transition done by
orientation




                                                                                    a (2) axis

                                                b (3) axis        Ferroelectric Polymers, H.S. Nalwa


M Thompson, Chonbuk National University               Sept 2008                                        20
PVDF Material Science
     PVDF Piezoelectric Basics
                                                           1 (c)Axis: Chain backbone axis
  PVDF FILM is highly anisotropic -                                   Stretch direction
                                                                      Axis of major activity
                                                           2 (a) Axis: Transverse direction
                                                                       Axis of minor activity
                                                                       (d32 ≈ d31/10)

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

                     Electrodes normal to 3 axis (on flat surfaces)

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


M Thompson, Chonbuk National University        Sept 2008                                  21
PVDF Material Science
     PVDF Material Basics


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


                                                                                          Coercive
                                                                                          Field
 D/E curve for capacitor


                                                                     Ferroelectric Polymers, H.S. Nalwa


M Thompson, Chonbuk National University                  Sept 2008                                        22
PVDF Material Science
     PVDF Material Basics

                      Typical properties of piezo PVDF



                                                                                     MEAS
                                                                                     PVDF




                                                         Ferroelectric Polymers, H.S. Nalwa


M Thompson, Chonbuk National University    Sept 2008                                          23
PVDF Material Science
  PVDF Material Basics



Interaction between PVDF
crystal forms and processing
history.

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




                                                      Ferroelectric Polymers, H.S. Nalwa


M Thompson, Chonbuk National University   Sept 2008                                        24
PVDF Material Science




M Thompson, Chonbuk National University   Sept 2008   25
  PVDF Material Science




Rolls of Finished
   Piezo Film
Ready to Stock

(>100,000ft2/yr)




  M Thompson, Chonbuk National University   Sept 2008   26
 PVDF Material Science




Piezo Film Roll
   ~850 ft




 M Thompson, Chonbuk National University   Sept 2008   27
   PVDF Material Science




Thick Film Electrode
  Screen Printing




   M Thompson, Chonbuk National University   Sept 2008   28
  PVDF Material Science




Printed Silver Ink
  Patterns on a
   Single Sheet




  M Thompson, Chonbuk National University   Sept 2008   29
PVDF Material Science




  Low Raw Material Cost
  High part density/sheet




M Thompson, Chonbuk National University   Sept 2008   30
 PVDF Material Science




Steel Rule Die
  Patterning




 M Thompson, Chonbuk National University   Sept 2008   31
  PVDF Material Science




Laser Patterning




  M Thompson, Chonbuk National University   Sept 2008   32
PVDF Material Science




M Thompson, Chonbuk National University   Sept 2008   33
PVDF Material Science




M Thompson, Chonbuk National University   Sept 2008   34
PVDF Material Science
     Simple equivalent circuit for PVDF sensors


  “g” coefficient
quantifies stress to
voltage conversion
      g=d/ε                                             Load impedance
                                                       forms a HPF with
                                                      sensor capacitance




M Thompson, Chonbuk National University   Sept 2008                        35
Piezo Medical
PVDFFilm SensorsApplications
     (+) PVDF Attributes for Medical Applications
       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




M Thompson, Chonbuk National University   Sept 2008                          36
PVDF Medical Applications
     (-) PVDF Attributes for Medical Applications

       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




M Thompson, Chonbuk National University   Sept 2008                          37
 PVDF Medical Applications
A 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




 M Thompson, Chonbuk National University   Sept 2008                          38
  PVDF Medical Applications
                 Application: pacemaker activity sensor

    PVDF sensing elements




PVDF is used to make                        Accelerometer assembly

complex multi layer sensing
elements for an implantable
pacemaker activity monitor




  M Thompson, Chonbuk National University                   Sept 2008   39
  PVDF Medical Applications
                 Application: Contact microphone

Apnea sensors
Blood pressure cuff microphone
Pulse Wave Velocity, tonometry
Stethoscope sensor




                                                        Curved PVDF sensing structure
                                                        Internal protection & buffering
                                                           ~100V/mm 20Hz – 4kHz




  M Thompson, Chonbuk National University   Sept 2008                                     40
PVDF Medical Applications
               Application: Contact microphone
Typical buffering circuit, contained inside package




M Thompson, Chonbuk National University   Sept 2008   41
PVDF Medical Applications
               Application: electronic stethoscope




                                          High performance Welch Allyn
                                          stethoscope uses a PVDF acoustic
                                          sensor




M Thompson, Chonbuk National University      Sept 2008                       42
PVDF Medical Applications
               Application: sleep lab eye sensors




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


M Thompson, Chonbuk National University   Sept 2008                 43
PVDF Medical Applications
               Application: infant apnea sensors




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


M Thompson, Chonbuk National University   Sept 2008                     44
PVDF Medical Applications
               Application: Adult apnea sensors




M Thompson, Chonbuk National University   Sept 2008   45
PVDF Medical Applications
               Application: Motion sensors

Chest wall motion sensor
High Sensitivity
~1000mV/g
~1600mV/mm motion @20Hz


Low Cost/Disposable




                                                      Mass loaded PVDF cantilever
                                                            PCB mountable
                                                         1,000 mV/g, 75Hz fo




M Thompson, Chonbuk National University   Sept 2008                                 46
PVDF Medical Applications
               Application: LDTC on Chest with Strap




First
And Second
Heart Sounds




M Thompson, Chonbuk National University   Sept 2008    47
 PVDF Medical Applications
                Application: Motion sensors



Wide array of sizes,
shapes, and masses




 M Thompson, Chonbuk National University   Sept 2008   48
 PVDF Other Applications
                Application: Ultrasound


Displacement versus Applied
Voltage (Converse Effect)




 M Thompson, Chonbuk National University   Sept 2008   49
PVDF Medical Applications
               Application: Ultrasound
                                            Reflecting
Backing                     Matching          Target
  Absorber                    layer λ/4




       Piezo Layer            Transmitted
                                                         Reflected
                                U/S wave
                                                           U/S wave
M Thompson, Chonbuk National University     Sept 2008                 50
PVDF Medical Applications
               Application: 30-50MHz Ultrasound
 “Mason’s Model” used to model the acoustic performance of the
   struacture using electrical impedance blocks


                            Backing       Piezo        Matching   Tissue/
                                                                  water




Drive V and
return signal
port


M Thompson, Chonbuk National University    Sept 2008                        51
  PVDF Medical Applications
                 Application: Ultrasound




  Typical
  reflection
  acoustic
  waveform
(PVDF-TrFE)




  M Thompson, Chonbuk National University   Sept 2008   52
PVDF Medical Applications
               Application: 30-50MHz Ultrasound
High frequency = high resolution
image, requires very thin piezo layer
                                          Imaged TUMOR in MOUSE




  U/S Transducer


M Thompson, Chonbuk National University   Sept 2008               53
 PVDF Medical Applications
                Application: 30-50MHz Ultrasound

Images from a
 mouse vascular
 system




 M Thompson, Chonbuk National University   Sept 2008   54
   PVDF Medical Applications
                  Application: HIFU Array, disposable


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

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




   M Thompson, Chonbuk National University   Sept 2008   55
 PVDF Medical Applications
                Application: Cochlear Implant

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




                                   High Freq               Low Freq
 M Thompson, Chonbuk National University       Sept 2008              56
PVDF Medical Applications
               Application: Non-Contact Patient Monitor
                                                      Large PVDF sensor
                                                      system under
                                                      mattress detects:
                                                      Respiration Rate
                                                      Respiration Activity
                                                      Heart Rate
                                                      Body Motion
                                                      Bed Exit




M Thompson, Chonbuk National University   Sept 2008                          57
PVDF Medical Applications
               Application: Baby Breathing/Motion



                                                      PVDF sensor system
                                                      in diaper with
                                                      remote link monitor
                                                      for:
                                                      Respiration Rate
                                                      Heart Rate
                                                      Body Motion (or no
                                                      motion)




M Thompson, Chonbuk National University   Sept 2008                         58
PVDF Medical Applications
               Application: Respiration Rate, in Mask


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




M Thompson, Chonbuk National University   Sept 2008                        59
PVDF Other Applications
               Application: ultrasonic transducers



 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


                                                         80kHz Digitizer Tx Assy
                                                            Includes IR LEDs
                        PVDF cylinder (silver ink)        Pen/stylus mountable
                                                             Full a4 capable



M Thompson, Chonbuk National University      Sept 2008                             60
PVDF Other Applications
               Application: ultrasonic digitizers




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

M Thompson, Chonbuk National University   Sept 2008                    61
  PVDF Other Applications
                 Application: ultrasonic digitizers


    Virtual Ink: mimio
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




  M Thompson, Chonbuk National University   Sept 2008   62
 125°C Stable PVDF



Thank you for your time.


Questions?




M Thompson, Chonbuk National University   Sept 2008   63

				
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