IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 16, NO. 1, FEBRUARY2011 107 [4] F. Carpi, A. Khanicheh, C. Mavroidis, and D. De Rossi, “MRI com- patibility of silicone-made contractile dielectric elastomer actuators,” IEEE/ASME Trans. Mechatronics, vol. 13, no. 3, pp. 370–374, Jun. 2008. [5] A. Rajamani, M. D. Grissom, C. D. Rahn, and Q. Zhang, “Wound roll dielectric elastomer actuators: Fabrication, analysis, and experiments,” IEEE/ASME Trans. Mechatron., vol. 13, no. 1, pp. 117–124, Aug. 2008. [6] R. Pelrine, R. Kornbluh, and J. Joseph, “Electrostriction of polymer di- electrics with compliant electrodes as a means of actuation,” Sens. Act. A, vol. 64, pp. 77–85, 1998. [7] R. Pelrine, R. Kornbluh, Q. Pei, and J. Joseph, “High-speed electrically actuated elastomers with strain greater than 100,” Science, vol. 287, pp. 836–839, 2000. [8] M. S. Kushwaha, P. Halevi, L. Dobrzynski, and B. Djafari-Rouhani, “Acoustic band-structure of periodic elastic composites,” Phys. Rev. Lett., vol. 71, pp. 2022–2025, 1993. [9] M. M. Sigalas and E. N. Economou, “Band-structure of elastic-waves in 2-dimensional systems,” Solid State Commun., vol. 86, pp. 141–143, 1993. [10] M. Gei, A. B. Movchan, and D. Bigoni, “Band-gap shift and defect- induced annihilation in prestressed elastic structures,” J. Appl. Phys., vol. 105, pp. 063507-1–063507-7, 2009. [11] D. J. Mead, “Wave propagation and natural modes in periodic systems. Part II: Multi-coupled systems, with and without damping,” J. Sound Vib., vol. 40, pp. 19–39, 1975. [12] D. J. Mead, “Wave propagation in continuous periodic structures: Research contributions from Southampton, 1964–1995,” J. Appl. Phys., vol. 190, pp. 495–524, 1996. [13] W. J. Parnell, “Effective wave propagation in a prestressed nonlinear elastic composite bar,” IMA J. Appl. Math., vol. 72, pp. 223–244, 2007. [14] M. Gei, “Wave propagation in quasiperiodic structures: Stop/pass band distribution and effects of prestress,” Int. J. Solids Struct., vol. 47, pp. 3067–3075, 2010. [15] M. Ruzzene and A. Baz, “Control of wave propagation in periodic com- posite rods using shape memory inserts,” J. Vib. Acoust., vol. 122, pp. 151– 159, 2000. [16] A. Baz, “Active control of periodic structures,” J. Vib. Acoust., vol. 123, pp. 472–479, 2001. [17] C. Goffaux and J. P. Vigneron, “Theoretical study of a tunable phononic band gap system,” Phys. Rev. B, vol. 64, no. 7, 075118-1–075118-5, 2001. [18] S. Nudehi, R. Mukherjee, and S. W. Shaw, “Active vibration control of a flexible beam using a buckling-type end force,” J. Dyn. Syst., Meas., Control, vol. 128, pp. 278–286, 2006. [19] R. M. McMeeking and C. M. Landis, “Electrostatic forces and stored energy for deformable dielectric materials,” J. Appl. Mech., vol. 72, pp. 581–590, 2005. [20] A. Dorfmann and R. W. Ogden, “Nonlinear electroelasticity,” Acta Mech., vol. 174, pp. 167–183, 2005. [21] Z. Suo, X. Zhao, and W. H. Greene, “A nonlinear field theory of de- formable dielectrics,” J. Mech. Phys. Solids, vol. 56, pp. 467–486, 2008. [22] K. Bertoldi and M. Gei, “Instability in multilayered soft dielectrics,” J. Mech. Phys. Solids, vol. 59, pp. 18–42, 2011. [23] R. A. Toupin, “The elastic dielectric,” Arch. Ration. Mech. Anal., vol. 5, pp. 849–915, 1956. [24] M. A. Biot, Mechanics of Incremental Deformations. New York: Wiley, 1965. [25] D. Bigoni, M. Ortiz, and A. Needleman, “Effect of interfacial compliance on bifurcation of a layer bonded to a substrate,” Int. J. Solids Struct., vol. 34, pp. 4305–4326, 1997. [26] D. Bigoni, M. Gei, and A. B. Movchan, “Dynamics of a prestressed stiff layer on an elastic half space: filtering and band gap characteristics of periodic structural models derived from long-wave asymptotics,” Int. J. Solids Struct., vol. 56, pp. 2494–2520, 2008. Power for Robotic Artificial Muscles Iain A. Anderson, Ioannis A. Ieropoulos, Thomas McKay, Benjamin O’Brien, and Chris Melhuish Abstract—Artificial muscles based on the dielectric elastomer actuator (DEA) are an attractive technology for autonomous robotic systems. We are currently exploring their use on EcoBot (Ecological roBot), an autonomous robot being developed by Bristol Robotics Lab that uses microbial fuel cells (MFCs). DEA will provide actuators for fuel cell maintenance and other goals and will increase active mission time through greater mechan- ical efficiency and reduced mass. Artificial muscles use high voltages and running them normally requires voltage converters to boost the voltage on delivered charge several hundred times. A dielectric elastomer generator (DEG) when used with a recently developed self-priming circuit (SPC) can supply the high-voltage power directly to artificial muscle systems. The SPC can also be started using an initial low-voltage charge from another energy harvester such as a bank of MFCs or a solar cell array. This combination could lead to a completely autonomous power source for robotic artificial muscles. We demonstrate a proof-of-concept portable self-primed DEG for harvesting wind energy from moving tree branches. Index Terms—Dielectric elastomer, energy harvesting, fuel cells (FCs), power generation, robots. I. INTRODUCTION Electromagnetic motor technologies that involve dense materials and require transmissions, gearboxes, and cooling for best performance are the main constituents of robotic actuators. But they render robots too heavy to match the performance and agility of animals [1]. Lightweight and soft artificial muscles based on the dielectric elastomer actuator (DEA) are an attractive alternative robotic technology [2] as they are capable of large strains of the order of 100% and have been shown to outperform animal muscle in several respects, including power per unit mass [3]. DEA devices would have fewer running parts and this offers promise of reduced mechanical loss and the prospect of robots that can jump like animals [1]. Thus, there is interest in using them for autonomous robot (AR) systems such as the EcoBot, an AR being de- veloped by Bristol Robotics Lab that harvests all of its energy from the environment. Much of the EcoBot research has focused on harvesting energy from bacteria using onboard microbial fuel cells (MFCs) that convert organic matter such as insects directly into electricity [4], [5]. This energy is stored in an onboard accumulator and then released to power the robot’s systems for tasks that include environmental mon- itoring, data processing, communication, and locomotion. The tasks can require more power than the MFCs can deliver. It follows that the robot’s activity is limited by the amount of time it takes for the energy in the accumulator to reach a critical firing threshold and therefore results in pulsed actuation [4], [5]. We anticipate that by incorporat- ing lightweight artificial muscle systems into EcoBot, we can improve Manuscript received April 9, 2010; revised July 16, 2010; accepted Octo- ber 15, 2010. Date of publication December 30, 2010; date of current version January 12, 2011. Recommended by Guest Editor F. Carpi. I. A. Anderson is with the Biomimetics Laboratory, Auckland Bioengineering Institute and the Department of Engineering Science, University of Auckland, Auckland 1010, New Zealand (e-mail: i.anderson@auckland.ac.nz). I. A. Ieropoulos and C. Melhuish are with the Bristol Robotics Laboratory, Bristol, BS16 1QY, U.K. (e-mail: ioannis.ieropoulos@brl.ac.uk; c.melhuish@ brl.ac.uk). T. McKay and B. O’Brien are with the Biomimetics Laboratory, Auck- land Bioengineering Institute, Auckland 1010, New Zealand (e-mail: thomas. mckay@auckland.ac.nz; b.obrien@auckland.ac.nz). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMECH.2010.2090894 1083-4435/$26.00 © 2010 IEEE