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Electroactive Polymer (EAP) Actuators as Artificial Muscles: Reality, Potential, and Challenges
Editor(s): Yoseph Bar-Cohen
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Book Description

In concept and execution, this book covers the field of EAP with careful attention to all its key aspects and full infrastructure, including the available materials, analytical models, processing techniques, and characterization methods. In this second edition the reader is brought current on promising advances in EAP that have occurred in electric EAP, electroactive polymer gels, ionomeric polymer-metal composites, carbon nanotube actuators, and more.

"'Electroactive Polymer (EAP) Actuators as Artificial Muscles' is a delightful book dealing with one of the hottest topics in biomedical engineering. Virtually every known method of generating displacement is introduced. This book is a must for anyone interested in actuators and sensors, including physicians and biomedical, chemical, electrical, and material engineers. It is thorough in every way...."

--Steven S. Saliterman, MD, FACP, Chief of Medicine Methodist Hospital; Department of Biomedical Engineering, University of Minnesota

Book Details

Date Published: 18 March 2004
Pages: 816
ISBN: 9780819452979
Volume: PM136

Table of Contents
SHOW Table of Contents | HIDE Table of Contents
Preface / xiii
Topic 1 Introduction
Chapter 1 EAP History, Current Status, and Infrastructure / 3
Yoseph Bar-Cohen
1.1 Introduction / 4
1.2 Biological Muscles / 8
1.3 Historical Review and Currently Available Active Polymers / 8
1.4 Polymers with Controllable Properties or Shape / 10
1.5 Electroactive Polymers (EAP) / 22
1.6 The EAP Roadmap - Need for an Established EAP Technology Infrastructure / 39
1.7 Potential / 41
1.8 Acknowledgments / 42
1.9 References / 43
Topic 2 Natural Muscles
Chapter 2 Natural Muscle as a Biological System / 53
Gerald H. Pollack, Felix A. Blyakhman, Frederick B. Reitz, Olga V. Yakovenko,
and Dwayne L. Dunaway
2.1 Conceptual Background / 53
2.2 Structural Considerations / 56
2.3 Does Contraction Involve a Phase Transition? / 59
2.4 Molecular Basis of the Phase Transition / 62
2.5 Lessons from the Natural Muscle System That May Be Useful for the Design of Polymer Actuators / 68
2.6 References / 70
Chapter 3 Metrics of Natural Muscle Function / 73
Robert J. Full and Kenneth Meijer
3.1 Caution about Copying and Comparisons / 74
3.2 Common Characterizations - Partial Picture / 75
3.3 Work-Loop Method Reveals Diverse Roles of Muscle Function during Rhythmic Activity / 79
3.4 Direct Comparisons of Muscle with Human-Made Actuators / 85
3.5 Future Reciprocal Interdisciplinary Collaborations / 86
3.6 Acknowledgments / 87
3.7 References / 87
Topic 3 EAP Materials
Topic 3.1 Electric EAP
Chapter 4 Electric EAP / 95
Qiming Zhang, Cheng Huang, Feng Xia, and Ji Su
4.1 Introduction / 96
4.2 General Terminology of Electromechanical Effects in Electric EAP / 96
4.3 PVDF-Based Ferroelectric Polymers / 103
4.4 Ferroelectric Odd-Numbered Polyamides (Nylons) / 114
4.5 Electrostriction / 119
4.6 Field-Induced Strain Due to Maxwell Stress Effect / 132
4.7 High Dielectric Constant Polymeric Materials as Actuator Materials /133
4.8 Electrets / 137
4.9 Liquid-Crystal Polymers /141
4.10 Acknowledgments / 142
4.11 References / 142
Topic 3.2 Ionic EAP
Chapter 5 Electroactive Polymer Gels / 151
Paul Calvert
5.1 Introduction - the Gel State / 151
5.2 Physical Gels / 152
5.3 Chemical Gels / 152
5.4 Thermodynamic Properties of Gels / 154
5.5 Transport Properties of Gels / 155
5.6 Polyelectrolyte Gels / 156
5.7 Mechanical Properties of Gels / 156
5.8 Chemical Actuation of Gels / 157
5.9 Electrically Actuated Gels / 158
5.10 Recent Progress / 162
5.11 Future Directions / 164
5.12 References / 165
Chapter 6 Ionomeric Polymer-Metal Composites / 171
Sia Nemat-Nasser and Chris W. Thomas
6.1 Introduction / 172
6.2 Brief History of IPMC Materials / 173
6.3 Materials and Manufacture / 175
6.4 Properties and Characterization / 178
6.5 Actuation Mechanism / 196
6.6 Development of IPMC Applications / 219
6.7 Discussion: Advantages/Disadvantages / 220
6.8 Acknowledgments / 223
6.9 References / 223
Chapter 7 Conductive Polymers / 231
Jose-Maria Sansinena and Virginia Olazabal
7.1 Brief History of Conductive Polymers / 231
7.2 Applications of Conductive Polymers / 233
7.3 Basic Mechanism of CP Actuators / 236
7.4 Development of CP Actuators / 241
7.5 Advantages and Disadvantages of CP Actuators / 249
7.6 Acknowledgments / 252
7.7 References / 252
Chapter 8 Carbon Nanotube Actuators: Synthesis, Properties, and Performance / 261
Geoffrey M. Spinks, Gordon G. Wallace, Ray H. Baughman, and Liming Dai
8.1 Introduction / 261
8.2 Nanotube Synthesis / 262
8.3 Characterization of Carbon Nanotubes / 266
8.4 Macroscopic Nanotube Assemblies: Mats and Fibers / 269
8.5 Mechanical Properties of Carbon Nanotubes / 270
8.6 Mechanism of Nanotube Actuation / 275
8.7 Experimental Studies of Carbon Nanotube Actuators/ 279
8.8 Conclusions and Future Developments / 288
8.9 References / 288
Topic 3.3 Molecular EAP
Chapter 9 Molecular Scale Electroactive Polymers / 299
Michael J. Marsella
9.1 Introduction / 299
9.2 Intrinsic Properties and Macroscale Translation / 301
9.3 Stimulus-Induced Conformational Changes within the Single Molecule / 303
9.4 Final Comments / 311
9.5 References / 311
Topic 4 Modeling Electroactive Polymers
Chapter 10 Computational Chemistry / 317
Kristopher E. Wise
10.1 Introduction / 317
10.2 Overview of Computational Methods / 318
10.3 Quantum Mechanical Methods / 320
10.4 Classical Force Field Simulations / 328
10.5 Mesoscale Simulations / 332
10.6 References / 333
Chapter 11 Modeling and Analysis of Chemistry and Electromechanics / 335
Thomas Wallmersperger, Bernd Kroplin, and Rainer W. Gulch
11.1 Introduction / 335
11.2 Chemical Stimulation / 337
11.3 Electrical Stimulation / 342
11.4 Conclusion / 360
11.5 References / 360
Chapter 12 Electromechanical Models for Optimal Design and Effective Behavior of Electroactive Polymers / 363
Kaushik Bhattacharya, Jiangyu Li, and Yu Xiao
12.1 Introduction / 363
12.2 Introduction to Finite Elasticity / 364
12.3 Optimal Design of Electrostatic Actuators / 369
12.4 Models of Ionomer Actuators / 374
12.5 Reduced Models / 379
12.6 Conclusion / 382
12.7 Acknowledgment / 383
12.8 References / 383
Chapter 13 Modeling IPMC for Design of Actuation Mechanisms / 385
Satoshi Tadokoro, Masashi Konyo, and Keisuke Oguro
13.1 Models and CAE Tools for Design of IPMC Mechanisms / 386
13.2 A Physicochemical Model Considering Six Phenomena / 388
13.3 Gray-Box Macroscopic Model for Mechanical and Control Design / 396
13.4 Simulation Demonstration by Models / 402
13.5 Applications of the Model / 406
13.6 References / 425
Topic 5 Processing and Fabrication of EAPs
Chapter 14 Processing and Fabrication Techniques / 431
Yoseph Bar-Cohen, Virginia Olazabal, Jose-Maria Sansinena, and Jeffrey Hinkley
14.1 Introduction / 431
14.2 Synthesis and Material Processing / 462
14.3 Fabrication and Shaping Techniques / 434
14.4 Electroding Techniques / 441
14.5 System Integration Methods / 449
14.6 EAP Actuators / 452
14.7 Concluding Remarks / 453
14.8 References / 454
Topic 6 Testing and Characterization
Chapter 15 Methods of Testing and Characterization / 467
Stewart Sherrit, Xiaoqi Bao, and Yoseph Bar-Cohen
15.1 Introduction / 468
15.2 Characterization of EAP with Polarization-Dependent Strains / 468
15.3 Characterization of Ionic EAP with Diffusion-Dependent Strain / 498
15.4 Summary of Test Methods / 516
15.5 Conclusion / 516
15.6 Acknowledgments / 518
15.7 References / 518
Topic 7 EAP Actuators, Devices, and Mechanisms
Chapter 16 Application of Dielectric Elastomer EAP Actuators / 529
Roy Kornbluh, Ron Pelrine, Qibing Pei, Marcus Rosenthal, Scott Stanford, Neville Bonwit, Richard Heydt, Harsha Prahlad, and Subramanian V. Shastri
16.1 Introduction / 530
16.2 Dielectric Elastomer EAP�Background and Basics / 535
16.3 Actuator Design Issues / 539
16.4 Operational Considerations / 546
16.5 Examples of Dielectric Elastomer EAP Actuators and Applications / 551
16.6 Artificial Muscles and Applications to Biologically Inspired Devices / 552
16.7 General Purpose Linear Actuators / 566
16.8 Planar and Other Actuator Configurations / 567
16.9 Motors / 573
16.10 Generators / 574
16.11 Sensors / 575
16.12 Summary and Future Developments / 576
16.13 Acknowledgments / 577
16.14 References / 577
Chapter 17 Biologically Inspired Robots / 581
Brett Kennedy, Chris Melhuish, and Andrew Adamatzky
17.1 Introduction / 583
17.2 Biologically Inspired Mechanisms and Robots / 584
17.3 Aspects of Robotic Design / 584
17.4 Active Polymer Actuators in a Traditional Robotic System / 594
17.5 Using Rapid Prototyping Methods for Integrated Design / 596
17.6 Evolutionary Design Algorithms (Genetic Algorithm Design) / 598
17.7 EAP Actuators in Highly Integrated Microrobot Design / 602
17.8 Solving the Power Problem - Toward Energetic Autonomy / 614
17.9 The Future of Active Polymer Actuators and Robots / 616
17.10 References / 617
Chapter 18 Applications of EAP to the Entertainment Industry / 621
David Hanson
18.1 Introduction / 622
18.2 Entertainment and Its Shifting Significance / 626
18.3 Technical Background to Entertainment Application of EAP / 627
18.4 The Craft of Aesthetic Biomimesis in Entertainment / 637
18.5 A Recipe for Using EAP in Entertainment / 647
18.6 Facial Expression Robot - Practical Test Bed for EAP / 647
18.7 Conclusion / 655
18.8 Acknowledgment / 655
18.9 References / 655
Chapter 19 Haptic Interfaces Using Electrorheological Fluids / 659
Constantinos Mavroidis, Yoseph Bar-Cohen, and Mourad Bouzit
19.1 Introduction / 659
19.2 Electrorheological Fluids / 661
19.3 Haptic Interfaces and Electrorheological Fluids / 666
19.4 MEMICA Haptic Glove / 668
19.5 ECS Element Model Derivation / 673
19.6 Parametric Analysis of the Design of ECS Elements / 677
19.7 Experimental ECS System and Results / 679
19.8 Conclusions / 682
19.9 Acknowledgments / 682
19.10 References / 683
Chapter 20 Shape Control of Precision Gossamer Apertures / 687
Christopher H. M. Jenkins
20.1 Introduction / 687
20.2 Shape Control of PGAs / 691
20.3 Shape Control Methodologies Involving Electroactive Polymers / 697
20.4 Conclusions / 702
20.5 Nomenclature / 703
20.6 Acknowledgments / 703
20.7 References / 704
Topic 8 Lessons Learned, Applications, and Outlook
Chapter 21 EAP Applications, Potential, and Challenges / 709
Yoseph Bar-Cohen
21.1 Introduction / 710
21.2 Lesson Learned Using IPMC and Dielectric EAP / 711
21.3 Summary of Existing EAP Materials / 717
21.4 Scalability Issues and Needs / 718
21.5 Expected and Evolving Applications / 719
21.6 EAP Characterization / 746
21.7 Platforms for Demonstration of EAP / 748
21.8 Future Expectations / 749
21.9 Acknowledgments / 751
21.10 References / 752
Index / 757


This book reviews the state of the art of the field of electroactive polymers (EAPs), which are also known as artificial muscles for their functional similarity to natural muscles. This book covers EAP from all its key aspects, i.e., its full infrastructure, including the available materials, analytical models, processing techniques, and characterization methods. This book is intended to serve as reference tool, a technology users' guide, and a tutorial resource, and to create a vision for the field's future direction. In preparing this second edition, efforts were made to update the chapters with topics that have sustained major advances since the first edition was prepared three years ago. Following the reported progress and milestones that were reached in this field has been quite heartwarming. These advances are bringing the field significantly closer to the point where engineers consider EAPs to be actuators of choice. In December 2002, the Japanese company Eamex produced a robot fish that swims in a water tank without batteries or a motor. For power, the robot fish uses an inductive coil that is energized from the top and bottom of the tank. Making a floating robot fish may not be an exciting event, but this is the first commercial product to use an EAP actuator.

EAPs are plastic materials that change shape and size when given some voltage or current. They always had enormous potential, but only now is this potential starting to materialize. Advances reported in this second edition include an improved understanding of these materials' behavior, better analytical modeling, as well as more effective characterization, processing, and fabrication techniques. The advances were not only marked with the first commercial product; there has also been the announcement by the SRI International scientists who are confident they have reached the point that they can now meet the challenge posed by this book's editor of building a robot arm with artificial muscles that could win an arm wrestling match against a human. This match may occur in the coming years, and the success of a robot against a human opponent will lead to a new era in both making realistic biomimetic robots and implementing engineering designs that are currently considered science fiction.

For many years the field of EAP has received relatively little attention because the number of available materials and their actuation capability were limited. The change in this view occurred in the early 1990s, as a result of the development of new EAP materials that exhibit a large displacement in response to electrical stimulation. This characteristic is a valuable attribute, which enabled myriad potential applications, and it has evolved to offer operational similarity to biological muscles. The similarity includes resilient, damage tolerant, and large actuation strains (stretching, contracting, or bending). Therefore, it is natural to consider EAP materials for applications that require actuators to drive biologically inspired mechanisms of manipulation, and mobility. However, before these materials can be applied as actuators of practical devices their actuation force and robustness will need to be increased significantly from the levels that are currently exhibited by the available materials. On the positive side, there has already been a series of reported successes in demonstrating miniature manipulation devices, including a catheter steering element, robotic arm, gripper, loudspeaker, active diaphragm, dust-wiper, and many others. The editor is hoping that the information documented in this book will continue to stimulate the development of niche applications for EAP and the emergence of related commercial devices. Such applications are anticipated to promote EAP materials to become actuators of choice in spite of the technology challenges and limitations they present.

Chapter 1 of this book provides an overview and background to the various EAP materials and their potential. Since biological muscles are used as a model for the development of EAP actuators, Chapter 2 describes the mechanism of muscles operation and their behavior as actuators. Chapter 3 covers the leading EAP materials and the principles that are responsible for their electroactivity. Chapter 4 covers such fundamental topics as computational chemistry and nonlinear electromechanical analysis to predict their behavior, as well as a design guide for the application of an example EAP material. Modeling the behavior of EAP materials requires the use of complex analytical tools, which is one of the major challenges to the design and control of related mechanisms and devices.

The efforts currently underway to model their nonlinear electromechanical behavior and develop novel experimental techniques to measure and characterize EAP material properties are discussed in Chapter 6. Such efforts are leading to a better understanding of the origin of the electroactivity of various EAP materials, which, in turn, can help improve and possibly optimize their performance.

Chapter 5 examines the processing methods of fabricating, shaping, electroding, and integrating techniques for the production of fibers, films, and other shapes of EAP actuators. Generally, EAP actuators are highly agile, lightweight, low power, mass producible, inexpensive, and possess an inherent capability to host embedded sensors and microelectromechanical systems (MEMS). Their many unique characteristics can make them a valuable alternative to current actuators such as electroactive ceramics and shape memory alloys. The making of miniature insectlike robots that can crawl, swim and/or fly may become a reality as this technology evolves as discussed in Chapters 7 and 8. Processing techniques, such as ink-jet printing, may potentially be employed to make complete devices that are driven by EAP actuators. A device may be fully produced in 3D detail, thereby allowing rapid prototyping and subsequent mass production possibilities. Thus, polymer-based EAP-actuated devices may be fully produced by an ink-jet printing process enabling the rapid implementation of science-fiction ideas (e.g., insectlike robots that become remotely operational as soon as they emerge from the production line) into engineering models and commercial products. Potential beneficiaries of EAP capabilities include commercial, medical, space, and military that can impact our life greatly.

In order to exploit the greatest benefit that EAP materials can offer, researchers worldwide are now exploring the various aspects of this field. The effort is multidisciplinary and cooperation among scientists, engineers, and other experts (e.g., medical doctors) are underway. Experts in chemistry, materials science, electro-mechanics, robotics, computer science, electronics, and others are working together to develop improved EAP materials, processing techniques, and applications. Methods of effective control are addressing the unique and challenging aspects of EAP actuators. EAP materials have a significant potential to improving our lives. If EAP materials can be developed to the level that they can compete with natural muscles, drive prosthetics, serve as artificial muscle implants into a human body, and become actuators of various commercial products, the developers of EAP would make tremendously positive impact in many aspects of human life.

Yoseph Bar-Cohen
February 2, 2004


The research at Jet Propulsion Laboratory (JPL), California Institute of Technology, was carried out under a contract with National Aeronautics and Space Administration (NASA) and Defense Advanced Research Projects Agency (DARPA). The editor would like to thank everyone who contributed to his efforts, both as part of his team advancing the technology as well as those who helped with the preparation of this book. The editor would like to thank the team members of his task LoMMAs that was funded by the Telerobotic and the Cross- Enterprise Programs of the NASA Code S. The team members included Dr. Sean Leary, Mark Schulman, Dr. Tianji Xu, and Andre H Yavrouian, JPL, Dr. Joycelyn Harrison, Dr. Joseph Smith, and Ji Su, NASA LaRC; Prof. Richard Claus, VT; Prof. Constantinos Mavroidis and Charles Pfeiffer, Rutgers University. Also, the editor would like to thank Dr. Timothy Knowles, ESLI, for his assistance with the development of the EAP dust-wiper mechanism using IPMC. Thanks to Marlene Turner, Harry Mashhoudy, Brian Lucky, and Cinkiat Abidin, former graduate students of the Integrated Manufacturing Engineering (IME) Program at UCLA, for helping to construct the EAP gripper and robotic arm. A special thanks to Dr. Keisuke Oguro, Osaka National Research Institute, Japan, for providing his most recent IPMC materials; and to Prof. Satoshi Tadokoro, Kobe University, Japan, for his analytical modeling effort. Prof. Mohsen Shahinpoor is acknowledged for providing IPMC samples as part of the early phase of the LoMMAs task. The editor would like also to thank his NDEAA team members Dr. Virginia Olaz�bal, Dr. Jos�-Mar�a Sansi�ena, Dr. Shyh-Shiuh Lih, and Dr. Stewart Sherrit for their help. In addition, he would like to thank Prof. P. Calvert, University of Arizona, for the information about biological muscles. Thanks to Dr. Steve Wax, DARPA's EAP program Manager, and Dr. Carlos Sanday, NRL, for their helpful comments related to the development of EAP characterization methods. A specific acknowledgement is made for the courteous contribution of graphics for the various chapters of this book; and these individuals and organizations are specified next to the related graphics or tables.

The editor would like to acknowledge and express his appreciation to the following individuals, who took the time to review various book chapters of the first edition and particularly those who where not coauthors of this book. Their contribution is highly appreciated and it helped to make this book of significantly greater value to the readers:

Aluru Narayan, University of Illinois/Urbana-Champaign
Paul Calvert, University of Arizona
Sia Nemat-Nasser, Dr. Chris Thomas and Mr. Jeff McGee, University of California, San Diego
Christopher Jenkins, and Dr. Aleksandra Vinogradov, South Dakota School of Mines and Technology
Kenneth Johnson, Brett Kennedy, Shyh-Shiuh Lih, Virginia Olazabal, Jos�-Mar�a Sansi�ena, and Stewart Sherrit, Jet Propulsion Laboratory
Giovanni Pioggia and Danilo de Rossi, University of Pisa, Italy
Elizabeth Smela, University of Maryland
Gerald Pollack, Washington University
Hugh Brown, Paul Keller, Geoff Spinks, and Gordon Wallace, University of Wollongong, Australia
Jeffrey Hinkley, Ji Su, and Kristopher Wise, NASA LaRC
Jiangyu Li, Caltech
Michael Marsella, University of California, Riverside
Miklos Zrinyi, Budapest University of Technology and Economics, Hungary
Mourad Bouzit and Dinos Mavroidis, Rutgers University
Peter Sommer-Larsen, Risoe Research Center, Denmark
Mary Frecker and Qiming Zhang, Pennsylvania State University
Robert Full, University of California, Berkeley
Roy Kornbluh and Ron Pelrine, SRI International
Satoshi Tadokoro, Kobe University, Japan

Also, the editor would like to acknowledge and express his appreciation to the following individuals who took the time to review the 12 chapters that were revised in this second edition and particularly those who where not coauthors of this book. Their contribution is highly appreciated and it helped making this book of significantly greater value to the readers:

Ahmed Al-Jumaily, Wellesley Campus, Auckland, New Zealand
Narayan Aluru, University of Illinois/Urbana-Champaign
Andy Adamatzky, University of the West of England, Bristol, England
Mary Frecker, Penn State University
Kaneto Keiichi, Kyushu Institute of Technology, Japan
David Hanson, University of Texas at Dallas and Human Emulation Robotics, LLC
Roy Kornbluh, SRI International, CA
Don Leo, Virginia Polytechnic Institute and State University
John Madden, University of British Columbia, Canada
Chris Melhuish, University of the West of England, UK
Walied Moussa, University of Alberta, Canada
Jos�-Mar�a Sansi�ena, Los Alamos National Laboratory (LANL)
Stewart Sherrit, Jet Propulsion Laboratory, CA
Peter Sommer-Larsen, Risoe Research Center, Denmark
Geoffery Spinks, University of Wollongong, Australia
Ji Su, NASA Langley Research Center (LaRC), VA
Minuro Taya, University of Washington
Aleksandra Vinogradov, Montana State University
Eui-Hyeok Yang, Jet Propulsion Laboratory, CA

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