Electrical generator or motor structure – Non-dynamoelectric
Reexamination Certificate
1999-08-20
2003-04-29
Font, Frank G. (Department: 2877)
Electrical generator or motor structure
Non-dynamoelectric
C385S147000, C385S022000, C385S134000, C429S009000, C429S345000, C429S346000, C136S291000
Reexamination Certificate
active
06555945
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to actuators based on electrochemical double-layer induced charge injection in materials having very high specific surface areas. Preferred embodiments include actuators for accomplishing mechanical work; the control of thermal, electrical, and fluid transport; and the switching, phase shift, and attenuation of electromagnetic radiation. The actuators range from large actuators to microscopic and nanoscale devices. These actuators are either directly powered by an externally provided electrical energy input or by chemical or photonic processes that generate electrical energy input. The electromechanical actuators can be operated in the reverse direction to convert an input mechanical energy to an output electrical energy.
2. Description of the Background Art
The background art includes various means for fabricating electromechanical actuators that are based on magnetostrictive, electrostrictive, ferroelectric, electrostatic, or shape-memory actuator processes. Each of these actuator processes has a disadvantage that prohibits an important category of applications. For example, the magnetostrictive, electrostrictive, and ferroelectric actuator processes suffer either from low achievable actuator strains (typically less than 0.1%) or a low modulus that limits the work capability per cycle. The need for high magnetic fields for the magnetostrictive actuator processes and large electric fields for the electrostrictive and ferroelectric actuator processes are other significant disadvantages for important applications.
Faradaic conducting polymer electrochemical actuators were proposed about a decade ago [R. H. Baughman et al., in
Conjugated Polymeric Materials: Opportunities in Electronics, Optoelectronics, and Molecular Electronics, eds
. J. L. Bredas and R. R. Chance (Kluwer, Dordrecht), pp 559-582 (1990)]. Examples of such devices have been described by E. Smela, O. Inganäs, and I. Lundström,
Science
268, 1735 (1995); T. F. Otero and J. M. Sansinena,
Adv. Mater
. 10, 491 (1998); A. Della Santa, D. De Rossi, and A. Mazzoldi,
Smart Mater. Struct
. 6, 23 (1997); M. R. Gandhi, P. Murray, G. M. Spinks, and G. G. Wallace,
Synthetic Metals
73, 247 (1995); J. D. Madden, P. G. Madden, I. W. Hunter, S. R. Lafontaine, and C. J. Brenan, Proceedings—Workshop on Working in the Micro-World, IEEE IROS96, Osaka Japan, p. 9-18, November 1996; and K. Kaneto, M. Kaneko, Y. Min, and A. G. MacDiarmid,
Synthetic Metals
71, 2211 (1995).
Conventional faradaic conducting polymer electromechanical actuators operate by the diffusion of dopant ions to and from solid electrode elements in response to an applied potential. As a result of such diffusion, ions are either inserted or de-inserted from solid electrode elements. As a result of the volume change produced by such dopant insertion and de-insertion processes, the electrodes change dimension and this dimensional change produces the actuator stroke. These ion insertion and de-insertion processes are balanced by electron injection and removal from opposing electrodes. While this electron injection and removal could conceivably produce dimensional changes, these dimensional changes are much smaller than those due to the ion insertion and de-insertion processes for all devices that have been demonstrated. For example, ions having large volume (such as perchlorate) are inserted by diffusion into the conducting polymer electrode, and structurally change the solid polymer by pushing apart polymer chains to cause a dimensional change of the conducting polymer electrode.
Although there has been major development effort focused on making practical devices in accordance with this conventional technology, critically important problems remain. The major problem is that the required dopant insertion and de-insertion processes (called intercalation and de-intercalation) result in slow device response, short cycle lifetimes, hysteresis (leading to low energy conversion efficiencies), and an actuator response that depends on both rate and device history. Such conducting polymer electromechanical actuators use the large faradaic dimensional changes that result from the electrochemical doping of various conducting polymers, such as polypyrroles, polyanilines, polyalkylthiophenes, and polyarylvinylenes. Depending upon the dopant species and whether or not they include solvating species, dimensional changes of from 10% to 30% are conceptually obtainable. Since these dimensional changes occur in weakly bonded directions, the elastic modulus for these directions is low, which limits actuator performance.
There has been a proposal to make an actuator that uses the smaller dimensional changes that are in fiber or sheet directions (R. H. Baughman,
Synthetic Metals
78, 339 (1996)). A further proposal in
Synthetic Metals
78 is an electromechanical actuator that operates analogously to non-faradaic supercapacitors, instead of by the insertion and de-insertion of dopant species in a solid polymeric electromechanical electrode. As proposed, such theoretical non-faradaic actuators might use the change in length of a polymer chain, a graphite sheet, a fiber, or a nanofiber that results from a change in charge. However, although design approaches are suggested, the key problem as recognized in
Synthetic Metals
78 is construction of a practical non-faradaic actuator having very high surface area without destroying mechanical properties. Without both the high surface area and high mechanical properties, a useable mechanical actuator can not be made. The point is that porosity must be introduced in order to obtain high surface area for an actuator electrode having macroscopic dimensions. Known fabrication methods for constructing an actuator electrode having porosity results in actuator electrodes that have mechanical properties reduced to such an extent as to be non-usable. For example, efforts to make an actuator from the high-surface-area carbon fibers produced by Unitika Ltd. failed, since these fibers could not support a useful load in an actuator environment. Moreover, the construction of a useful actuator requires that the actuator electrodes are highly electronically conducting, and the introduction of high surface area is expected to degrade electrical conductivity. Consequently, no viable way was available to make a non-faradaic actuator that could serve a useful function.
For example, the suggested approach in
Synthetic Metals
78 of using carbon nanotubes was unrealizable because the required fabrication and purification technology was unavailable for either the precursor nanotubes or any macroscopic form of such nanotubes, such as nanotube sheets. The synthetic methods available when
Synthetic Metals
78 was published produced nanotubes only as one component among extremely high concentrations of many other components (like fullerenes and weakly bonded carbon particles) that would eliminate the possibility of making a useful actuator. Moreover, the available nanotube samples included major concentrations of chiral and zigzag nanotubes that are semiconducting or insulating. The presence of such poorly conducting tubes would be expected to hinder charge injection, thus eliminating the possibility of obtaining useable actuation. The possibility of using actuators based on the aggregates of carbon nanofibers would be unworkable since no useable method was available for making such aggregates (either as films or fibers) that had the. required surface areas, electrical conductivities, mechanical properties, and freedom from massive contamination levels of degradative impurities. Likewise, it was impossible to make nanoscale actuators since no methods were available to make the electrical and mechanical contacts that were needed for a successful device. Also, no method was available for surrounding the nanoscale actuator with required electrolyte without causing a degradation of the structure of the nanoscale actuator.
The possible application of graphite sheets as actuators was c
Baughman Ray H.
Cui Changxing
Iqbal Zafar
Su Ji
Zakhidov Anvar
Allied-Signal Inc.
Font Frank G.
Mooney Michael P.
Palguta Larry J.
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