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					                   Tri-Service Power Expo – Norfolk, VA



Power from Plastic:
How Electroactive Polymer
"Artificial Muscles" will Improve
Portable Power Generation in the 21st
Century Military
                                      Presented by
                                    Roy Kornbluh
                                 SRI International
                                            July 2003
What is an Electroactive Polymer?

  Electroactive polymers (EAPs) convert electrical
   energy to mechanical work and vice versa


                        ACTUATOR




                    E      EAP         W

                                       MECHANICAL WORK
     ENERGY
     (ELECTRICAL)


                        GENERATOR OR SENSOR



                                                    TriSevices Power Expo 2003–Page 2
     Many Types of EAPs

   Dielectric
elastomers are
  particularly   Dielectric Elastomer
  promising              a.k.a.                 Conducting Polymers
                  Electroelastomers

        Electrostrictive Polymer      “Artificial                   IPMC
                                      Muscle”

             Thermal and Others                                  Gels


                                        Nanotubes



                    Electroactive Polymer “EAP” Actuators
                                                        TriSevices Power Expo 2003–Page 3
Advantages of Dielectric Elastomer EAP Power

                                                 Polymers are 1/8 the
  Lighter – low density, high                     density of common
   performance, multifunctional polymers             materials used in                     Steel,
                                               engines and generators                       Cu
  Cheaper – inexpensive materials, fewer
   parts, no precision machining                                                   1/8    Polymers
  Quieter – high energy density and
                                             0.5
   compliance of polymers allows quiet                Energy Density (J/cc)
                                            0.45
   primarily sub-acoustic operation with     0.4      Specific Energy
   few moving parts                         0.35
                                                      Density (J/g)

  Softer – rubbery materials are            0.3
                                            0.25
   impedance matched to large motions
                                             0.2
   (e.g. human motion, engines)
                                            0.15
  Versatile – polymers are scale-           0.1

   invariant; systems can be made in        0.05

   variety of form factors (conformal,        0
                                                    Electro-    Piezo-        SRI EAP
   elongated, etc.)                                magnetics   electrics      Materials
                                             Polymers have more than 10 times
                                             higher specific energy density than
                                             other transducers
                                                                           TriSevices Power Expo 2003–Page 4
Dielectric Elastomers: Principle of Operation

 Dielectric elastomers are a type of                    Polymer film
                                                                                                        Voltage off
  EAP that uses an electric field across                           Compliant
  a rubbery dielectric with compliant                              electrodes (on top
                                                                   and bottom
  electrodes                                                       surfaces)
                                                                                                            V
 Variable capacitor generator– energy
  generated as nearly incompressible
                                                                                                        Voltage on
  polymer layers increase in area and
  decrease in thickness when stretched                         BASIC FUNCTIONAL ELEMENT

                                                                          Compliant Electrodes (2)
                               +Vout                                                                              +Vin (low)
                               (high)
                                                 +   +          +          +      +
                                                 _   _          _          _      _

                           Dielectric Elastomer
                                                     EAP STRETCHED


  Energy = ½ Qo2 (1/Cf - 1/Ci)          +Vout        +     +    +     +    +                   +Vin (low)
                                        (high)
  C = er eo x film area/film                         _     _   _     _    _
  thickness
                                                         EAP RELAXED                    TriSevices Power Expo 2003–Page 5
Many Possible EAP Transducer Configurations

                                                       V


   Active                            EXTENDER                             DIAPHRAGM
   Electrode Area
                                                           V
                                 V


               STACK


                     V1                 V                      V
                           BIMORPH              ROLL

                                                                             TUBE

                V2
                     V
                          UNIMORPH




                                                               TriSevices Power Expo 2003–Page 6
Polymer Dielectric Elastomer Materials

 Several elastomers work well                                    .45

 Acrylic and silicone are most                                   .40
                                                                                                            Latest Acrylic
                                                                                                        Energy Density Tests
  promising and have shown




                                  Specific Energy Density [J/g]
                                                                  .35
  exceptional energy density
                                                                  .30
 Acrylic has greater energy
  density but also greater                                        .25

  damping and electrical                                          .20
  leakage
                                                                  .15
 Silicone has exceptional
  temperature range                                               .10                              End of 1999

  (–60 to 260 C)
                                                                                                   Acrylic Tests
                                                                  .05 Verification                           Initial Acrylic
                                                                            of
                                                                                  HS3 Silicone                    Tests
                                                                        Phenomena                  2186 Silicone
                                                                   0
                                                                                     12/98       6/99          12/99                  Time

                                                                          Demonstrated Specific Energy
                                                                                    Density
                                                                                                           TriSevices Power Expo 2003–Page 7
Power Conversion and Management
 Power available from dielectric elastomer EAPs is at a high
  voltage (e.g., 2 kV)
 For most applications we would like to charge batteries at a low
  voltage (3–48 volts)
 Some applications can use high voltage directly (e.g. night
  vision optics, in-boot actuators)
 High-voltage is not all bad: low current can allow for thinner,
  lighter wires and simpler connectors
 Battery or capacitor energy storage is needed to smooth output


      Voltage                                Voltage
                                                                      Output
      Step-Up                Polymer        Step-Down
                             Device



      Battery
                                                        TriSevices Power Expo 2003–Page 8
Multifunctionality

   Dielectric elastomers can combine several functions
ACTUATOR or GENERATOR           SENSOR




          STRUCTURE: Support,
          Transmission, Spring, Damper

                                            » Simpler
                                            » Lighter
                                            » Higher Performance

                                                  TriSevices Power Expo 2003–Page 9
  Artificial Muscle: Dielectric
  Elastomer Actuation
 Dielectric elastomers have             Expanding circle
                                         video shows this
  already shown unique                        principle of
  capabilities in a variety of DoD              operation
  actuator applications
                                     DARPA Artificial        DARPA Bending Rolls
                                      Muscle Rolls




                            Flex – Insect-Inspired
NRO DII Mirror Shape        ONR Robot
Control




                                                              Snake robot segment
                                                                 TriSevices Power Expo 2003–Page 10
 Applications that Can Benefit

 Many DoD power generation applications can benefit
  from the advantages of EAPs




   Engine Generators           Shoe and other          Parasitic Energy Harvesting
                          Human-Powered Generators




                                       Pumps and valves for fuel management
       Wave, Wind Power

                                                               TriSevices Power Expo 2003–Page 11
Harvesting Human Movement

 Several possibilities that do not excessively
  burden the wearer



                                             Heel Strike and Shoe Flexure
                                                         2–20w

   Backpack Suspension          Limb Swing
       and Padding                0.2–3w
         0.5–5w



             Chest or Torso
             Expansion From                   Hand or Leg Cranked
             Breathing or Routine             Generator for Emergency
             Movement                         Back-up (Short-term)
             0.1–1w                           10–100w
                                                     TriSevices Power Expo 2003–Page 12
Enabling a Heel-strike Generator
  Energy from the heel strike is “free” - it would otherwise be
   dissipated as heat
  Energy converted per step with reasonable heel compression
   can be up to 5 J
  Power generated (both feet) during walking is 1W to 10 W
  The amount of electrostrictive polymers needed to convert 5 J is
   less than 50 g or 50 cc.
  Electromagnetic or piezoelectric devices would weigh more than
   10 times this weight
                              Conventional technology
                              (“direct drive”; including
                              piezoelectrics)

  Relative Mass, Size, or                              EAP-based design
       Cost for boots with
  equivalent performance
         and functionality


                                                                 TriSevices Power Expo 2003–Page 13
DARPA Heel-strike Generator
 Developed a heel-strike                                    + Dielectric Elastomer (EAP)
  generator to capture free                      +           _      +
  energy while walking                                   _       _
                                    +Vout
 Demonstrated up to 0.8 J per               +       _               _       +           +Vin
  heel strike
                                                         Base
 Developed multi-layer polymer                                  Compliant Electrodes (2)
                                                         EXPANDED
  fabrication techniques                                       +
                                                         +          +
   » Demonstrated 15 layer device    +Vout       +           _ _ __     +        +Vin
                                                           _


                                                         CONTRACTED




 Heel-Strike generators are
expected to produce 1W of
       power under normal
        walking conditions                                               TriSevices Power Expo 2003–Page 14
Applications of a Heel-strike Generator
                   Boot generator can assist the dismounted soldier in
                    several distinct ways
                     » Power source or battery recharger to reduce battery
                        weight for a mission
                      » Smart Shoes, Multifunctional Footwear - simplify logistics
                        by reducing the number of separate batteries or devices
                        required
                         – power an instrument that should logically be located in a
                            boot for best operation:
                              personal navigation system, medical status monitor,
                                foot warmer
                          – power a device that could be located in a boot for weight
                            or space savings
                              Friendly ID beacon, comm link, magnetometer,
                                chem/bio detector, special battery or capacitor for
                                high-voltage device such as night vision scope
                      » Dynamic Footwear - Actuation or Adaptability for
                        enhanced performance
                         – reduced injury
 OFW Concept             – improved comfort
 Source: Natick
                         – more efficient load carrying
                                                                      TriSevices Power Expo 2003–Page 15
Can EAPs overcome limitations of Small
Portable Power Sources?
   Current small fuel-burning                     MAVs, Land
    engines/generators:                                Robots &
     » Noisy                                      Vehicles need
                                                   efficient and
     » Inefficient (typically 5-7%)           quiet Electrical +
     » Require special fuel mixtures                Mechanical
     » Not inherently hybrids or multifunctional -        Power
          Need separate components for both
          mechanical and electrical energy production
   Batteries:
     » Electric only
     » Low energy density (heavy)
     » Slow to recharge, hard to dispose Future Soldier Systems need efficient and
   Fuel cells:                                    quiet Electrical + Mechanical Power
     » Electric only
     » Limited to certain types of fuel and cannot
         run on dirty fuel
       » Require additional components
         and warm-up time

                                                                   TriSevices Power Expo 2003–Page 16
   Specific Example: Mentor Micro
   Air Vehicle
 DARPA TTO project for a MAV capable of
  operation in cluttered environments
                        Vehicle Specifications:
                        Total Weight (Wet):         550 g
                        Engine                      140 g   Performance:
                        Fuel & Tank                 75g     Hover Duration             8 min.
                        Batteries for electronics   30g     (50g fuel)
                        and servos                          Payload Capacity:          30 to 70g
                        Power required (hover):     98 W




                  Superfly 2.5
     “World’s   First Hovering Ornithopter”
         University of Toronto Institute
        for Aerospace Studies with SRI

                                                                       TriSevices Power Expo 2003–Page 17
DARPA’s Palm-Power Program

 Specific DoD Needs can be seen in DARPA
  Palm Power Program Goals:
   » Convert chemical energy of common fuels to
      mechanical / electrical energy for DoD needs
   » 20 Watt average power level at 12 Volts DC
   » Typical Missions :
      – Three-hour MAV reconnaissance mission - 1000 Whr/kg
      – Three-day Land Warrior mission - 2000 Wh/kg
      – Ten-day special operations reconnaissance mission -
        3000 Wh/kg




                                                       TriSevices Power Expo 2003–Page 18
An All-polymer Engine: The Answer?
    Light: Uses lightweight electroactive polymers instead of metallic
     piston/cylinders + electromagnetic generator
    Can operate sub-acoustically or with quieter external combustion cycles
    Unlike fuel cells and many small engines, can run efficiently on dirty logistics
     fuels
    Low cost and rugged – eliminates parts and bearings
    Can be made in a wide variety of shapes and sizes
                              Electromagnetic             Dielectric elastomer
                              Generator

Crankshaft


                                     Conditioning
   Piston
                                      Electronics
                                                     Conditioning
                        Electrical                   Electronics      Electrical
            Cylinder    Output                                        Output

     Conventional Generator System                  Comparable Polymer Engine System
                                                                        TriSevices Power Expo 2003–Page 19
High Efficiency?

 Polymer engines can potentially be
  much higher efficiency than IC or other
  conventional engines:
   » Lower thermal conductivity of                  1    Practical Cycles
                                          P              Only Approximate
     polymer walls
                                                         Ideal Cycle
   » No sliding surface friction
   » No leakage of expanding fluid              4

   » Can exploit resonance                                             2

   » Opportunity to use novel or optimally                             3
     tuned thermodynamic cycles
       – Expansion pressure controlled         Stirling Cycle              V
         electronically; ability to draw
         power at virtually any point in
         cycle
                                              20% or more?
       – Low inertia
                                                           TriSevices Power Expo 2003–Page 20
 Hybrid Power
 Many DoD applications (e.g. robotics, MAVs) require both mechanical
  and electrical power
 Polymer engine with mechanical and electrical output can eliminates
  entire transducer steps
   » Fuel cells: chemical  electrical  mechanical
   » IC Engine + generator + motor: chemical  mechanical  electrical 
      mechanical
    » Polymer engine: chemical  mechanical + electrical
 Hybrid polymer engine saves parts, weight and is more efficient
                                                           Combustion inside
                                                           EAP roll causes
                                                           linear 23%
                                                           expansion that
                                                           could be used for
                                                           both electrical and
                                                           mechanical output

                                                               TriSevices Power Expo 2003–Page 21
By the Numbers
  Polymer engines promise better overall performance
   than existing electrical and mechanical power sources

                              Power
                 Efficiency   density
     Approach                             Output        Noisy
                     (%)
                              (W/g)
    IC engine        6          2       Mechanical       Very
                                          only
    Fuel Cell       30          0.1      Electrical       No
                                           only
    Electric       20-80        1       Mechanical     Somewhat
    Motor                                 only
    Electrical     70-80        1        Electrical    Somewhat
    generator                              only
    Polymer         20          4       Electrical +      No
    engine                              Mechanical
                                                        TriSevices Power Expo 2003–Page 22
      Can it be done?:Polymer Engine First
      Steps
 Successful demonstration of              DARPA/ARO program aimed at
  polymer engines operating with           addressing the key technical challenge –
  high temperature combustion              Can a polymer “cylinder” survive
  gases (>1000 ºC) for over 3 hrs          combustion?
  at 3 Hz
                                      Air
                                       Air
   » High temperature operation                                     Combustion
                                                                    Combustion
      allows for high                                                chamber
                                                                      chamber
                                    Propane
                                    Propane
      thermodynamic efficiency                                                    Valve
                                               Flow rate    Flame

   » Micro-pitting observed,                   controllers arrester    Spark
                                                                        Spark
                                                                     system &
                                                                     system &
      coatings could prevent pitting                                 generator
                                                                     generator
                                                                    electronics
                                                                     electronics

   » Energy density already          Diaphragm-based                             Roll-based
      similar to batteries
      (500 Whr/g)
 Multiple fuels demonstrated
  (butane, propane, hydrogen)
 External combustion cycle also
  demonstrated

                                                                            TriSevices Power Expo 2003–Page 23
  Other Power Applications of EAPs
 Polymer actuators may offer advantages for
  other power systems
     » Valves & pumps for fuel cells
     » Actuated valves for engines, air
        controls, fuel pumps, etc.
                                                        Polymer diaphragms can
                                                        provide large displacements
Proof-of-principle diaphragm array pump.
                                                        for lightweight pumps




                                           Dielectric elastomer actuator for direct
                                           control of engine valving Power Expo 2003–Page 24
                                                                TriSevices
Simple Sensors

 Simple low-cost large-strain
  sensor is a simple
  embodiment of a generator
 Well suited for:
   » Human motion
      (Plethysmography,
      Kinesiology)
   » Computer input devices for
      virtual reality applications etc.
   » General purpose
      displacement detector for low-
      cost instrumentation and
      measurement
   » Low-cost position, force or
                                          Large variety of sensors can be based
      pressure sensors for
                                                 on dielectric elastomers
      actuators, generators, etc.
                                                               TriSevices Power Expo 2003–Page 25
Power from Plastic?

  EAPs are promising for addressing a variety of
   DoD power generation challenges
  First proof-of-principle devices made and
   tested
    » Variety of transducer configurations
    » Heel-strike generator
    » Polymer engine
  Improved devices are under development
    » Lifetime issues are being addressed
    » Electronics for power management is a key
       challenge



                                                    TriSevices Power Expo 2003–Page 26
Acknowledgements

 DARPA
 MITI/NEDO
 ONR
 NRO
 ARO
 UC Berkeley
 University of Toronto Institute for Aerospace Studies
 The numerous SRI employees who have contributed to the work
  presented here: Ron Pelrine, Qibing Pei, Richard Heydt, Don Czyzyk, Phil
  Jeuck, Marcus Rosenthal, Scott Stanford, Harsha Prahlad, Neville Bonwit,
  Seajin Oh, Shari Shepherd, Joe Eckerle, Jon Heim, John Marlow, Surjit
  Chhokar, Jose Joseph, Dave Flamm, Dave Huestis, Karen Nashold, Jeff
  Simons, Tom Cooper and more.
 See www.artificialmuscle.com


                                                          TriSevices Power Expo 2003–Page 27
Human-Powered Generators

 Large-strain capability of electrostrictive polymers allows for
  simple and efficient integration into generators
   » efficiency is not speed dependent
   » device can weigh 10x less than an electromagnetic generator with
      the same output rating
 Novel generator designs with few moving parts are possible
 Similar devices can also be couple to non-human power
  sources (e.g. engines, wind turbines)
                                        HAND CRANK


                               SLIDER



                                                                     PISTON
         MULTILAYER STACK OF
         ELECTROSTRICTIVE POLYMER
         ELEMENTS                                    Linear generator

                                                      MULTILAYER STACK OF
     Rotary generator                                 ELECTROSTRICTIVE POLYMER
                                                      ELEMENTS




                                                                      TriSevices Power Expo 2003–Page 28
  Lighter Generators for Engines
       High energy density and large strain capability of
        EAPs allows for simple, lightweight and efficient
        integration with combustion engines
       Novel engine/generator designs are may be a
        higher risk/higher payoff alternative
                                                                MULTILAYER STACK OF ELECTROSTRICTIVE POLYMER ELEMENTS
                      PISTON
                                                                                        SLIDER




                                                                                      ROTARY ENGINE

MULTILAYER STACK OF ELECTROSTRICTIVE POLYMER ELEMENTS   ENGINE CRANKSHAFT




             Linear generator/piston                               Rotary generator/engine
               engine combination                                       combination

                                                                                                 TriSevices Power Expo 2003–Page 29

				
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