ABSTRACT

This paper presents an introduction to ionic-polymer-metal composites and some mathematical modeling pertaining to them. It further discusses a number of recent findings in connection with ion-exchange polymer metal composites (IPMC) as biomimetic sensors and actuators. Strips of these composites can undergo large bending and flapping displacement if an electric field is imposed across their thickness. Thus, in this sense they are large motion actuators. Conversely by bending the composite strip, either quasi-statically or dynamically, a voltage is produced across the thickness of the strip. Thus, they are also large motion sensors. The output voltage can be calibrated for a standard size sensor and correlated to the applied loads or stresses. They can be manufactured and cut in any size and shape. In this paper first the sensing capability of these materials is reported. The preliminary results show the existence of a linear relationship between the output voltage and the imposed displacement for almost all cases. Furthermore, the ability of these IPMC's as large motion actuators and robotic manipulators is presented. Several muscle configurations are constructed to demonstrate the capabilities of these IPMC actuators. This paper further identifies key parameters involving the vibrational and resonance characteristics of sensors and actuators made with IPMC’s. When the applied signal frequency is varied, so does the displacement up to a point where large deformations are observed at a critical frequency called resonant frequency where maximum deformation is observed. Beyond which the actuator response is diminished. A data acquisition system was used to measure the parameters involved and record the results in real time basis. Also the load characterization of the IPMC's were measured and showed that these actuators exhibit good force to weight characteristics in the presence of low applied voltages. Finally, reported are the cryogenic properties of these muscles for potential utilization in an outer space environment of few Torrs and temperatures of the order of -140 degrees Celsius. These muscles are shown to work quite well in such harsh cryogenics environments and thus present a great potential as sensors and actuators that can operate at cryogenic temperatures.
 
 

Keywords: Ionic Polymer-Metal Composite Sensor, Soft Actuator, Artificial Muscles, Biomimetic Sensor, Vibrations, Resonance.
 
 

1. INTRODUCTION
 
 

Ion-exchange polymer-metal composites (IPMC) are active actuators that show large deformation in the presence of low applied voltage and exhibit low impedance. They operate best in a humid environment and can be made as a self-contained encapsulated actuators to operate in dry environments as well. They have been modeled as both capacitive and resistive element actuators that behave like biological muscles and provide an attractive means of actuation as artificial muscles for biomechanics and biomimetics applications. Grodzinsky¹, Grodzinsky and Melcher^2,3 and Yannas, Grodzinsky and Melcher⁴ were the first to present a plausible continuum model for electrochemistry of deformation of charged polyelectrolyte membranes such as collagen or fibrous protein and were among the first to perform the same type of experiments on animal collagen fibers essentially made of charged natural ionic polymers and were able to describe the results through electro-osmosis phenomenon. Kuhn⁵ and Katchalsky⁶, Kuhn, Kunzle, and Katchalsky⁷, Kuhn, Hargitay, and Katchalsky⁸, Kuhn, and Hargitay⁹, however, should be credited as the first investigators to report the ionic chemomechanical deformation of polyelectrolytes such as polyacrylic acid (PAA), polyvinyl chloride (PVA) systems. Kent, Hamlen and Shafer¹⁰ were also the first to report the electrochemical transduction of PVA-PAA polyelectrolyte system. Recently revived interest in this area concentrates on artificial muscles which can be traced to Shahinpoor and co-workers and other researchers ^{11-14, 22-53}, Osada¹⁵, Oguro, Asaka and Takenaka¹⁶, Asaka, Oguro, Nishimura, Mizuhata and Takenaka¹⁷, Guo, Fukuda, Kosuge, Arai, Oguro and Negoro¹⁸, De Rossi, Parrini, Chiarelli and Buzzigoli¹⁹ and De Rossi, Domenici and Chairelli²⁰. More recently De Rossi, Chiarelli, Osada, Hasebe, Oguro, Asaka, Tanaka, Brock, Shahinpoor, Mojarrad^11-69 have been experimenting with various chemically active as well as electrically active ionic polymers and their metal composites as artificial muscle actuators.
 
 

Essentially polyelectrolytes possess ionizable groups on their molecular backbone. These ionizable groups have the property of dissociating and attaining a net charge in a variety of solvent medium. According to Alexanderowicz and Katchalsky¹⁷ these net charge groups which are attached to networks of macromolecules are called polyions and give rise to intense electric fields of the order of 10¹⁰ V/m. Thus, the essence of electromechanical deformation of such polyelectrolyte systems is their susceptibility to interactions with externally applied fields as well as their own internal field structure. In particular if the interstitial space of a polyelectrolyte network is filled with liquid containing ions, then the electrophoretic migration of such ions inside the structure due to an imposed electric field can also cause the macromolecular network to deform accordingly. Shahinpoor^{18,22,25,26,28,29,31-,36} and Shahinpoor and co-workers^{21,23,24,27,30} have recently presented a number of plausible models for micro-electro-mechanics of ionic polymeric gels as electrically controllable artificial muscles in different dynamic environments. The reader is referred to these papers for the theoretical and experimental results on dynamics of ion-exchange membranes -platinum composite artificial muscles.
 
 

The IPMC muscle used in our investigation is composed of a perfluorinated ion exchange membrane (IEM), which is chemically composited with a noble metal such as gold or platinum. A typical chemical structure of one of the ionic polymers used in our research is
 
 

                                        [-(CF₂-CF₂)_n-(CF-CF₂)_m-]
                                                                 |
                                                                O-CF-CF₂-O-CF₂-SO^-₃ …..M⁺
                                                                      |
                                                                    CF₃
 
 

where n is such that 5<n<11 and m ~ 1, and M⁺ is the counter ion (H⁺, Li⁺ or Na⁺). One of the interesting properties of this material is its ability to absorb large amounts of polar solvents, i.e. water. Platinum, Pt, metal ions, which are dispersed through out the hydrophilic regions of the polymer, are subsequently reduced to the corresponding metal atoms. This results-in the formation of a dendritic type electrodes.
 
 

Metallization of Ion-Exchange Membranes
 
 

In Metalizing this material there is a first stage of in-depth molecular metallization and a second stage of surface plating and electroding. Thus, the important stage of compositing is the first stage which can be postulated to take place according to the following chemical reacctions :
 
 

                                                                                                     (1.1)
 
 

                                                                                         (1.2)
 
 

From equations (1.1) and (2.1), it is possible to draw the following:
 
 

                                    (1.3)
 
 

Also, the solid form of LiBO₂ occationally precipitates. Therefore, the overall reaction may be,
 
 

                                             (1.4)
 
 

Now, the biggest question is the source of hydroxyl ions. Apparantely, the following reaction may be possible :
 
 

                                                                         (1.5)
 
 

This indicates 9 moles of LiBH₄ are required for reducting 4 moles of Pt(NH₃)₄²⁺.
 
 
 
 

2-THEORETICAL CONSIDERATION
 
 

A simple one-dimensional model of electrically-induced deformation of ionic polymeric gels is such that :
 
 

s =(1/3)E(C₀, C_i) ( l - l ^-2 ) ,                                                                                                               (2.1)
 
 

s = k (C₀, C_i) E*²                                                                                                                                 (2.2)

where s is the stress, l is the stretch, E(C₀, C_i) is the corresponding Young’s modulus of hyper-elasticity, C₀ is the polymer solid concentration, C_i, (i=1,2,….,N)’s are the molal concentration of various ionic species in the aqueous medium, k (C₀, C_i) is an electromechanical coefficient and E* is the local electric field. Thus bending can occur due to differential contraction and expansion of outer most remote regions of a strip if an electric field is imposed across its thickness as shown below in Figure 1. Since ionic polyelectrolytes are for the most part three dimensional network of macromolecules cross-linked nonuniformly, the concentration of ionic charge groups are also nonuniform within the polymer matrix. Therefore the mechanism of bending is partially related to the redistribution of fixed ions and migration of mobile ions within the network due to the imposition of an electric field. However, recent modeling effort on the sensing and actuation have revealed that this effect may play an insignificant role on the actuation which may be dominated by surface charge interactions. This subject is currently under investigation.
 
 

A simple one-dimensional model of electrically-induced dynamic deformation or vibration of a cantilever beam made with such IPMC artificial muscle strips is given by the following equations :
 
 

(x, t),                                                                                                                     (2.3)

, -C<h <C,                                                                                                                    (2.4)
 
 

,                                                                                                                                          (2.5)
 
 

                                                                                                                                (2.6)
 
 

where F is the body force per unit volume of the muscle, r is the density, e is the strain, subscript c indicates values at the neutral axis of the cross-section of the strip, C is the distance of the outer-most remote fibers, is the local curvature due to an imposed electric field, h is a cross-sectional parameter, E* is the local electric field, x and t are axial location and time variables and subscripts + and -, respectively indicate the values of variable at the outermost remote fibers.

Figure 1. General redistribution of charges in an ionic polymer due to an imposed electric field.

Thus bending can occur due to differential contraction and expansion of outer most remote fibers of a strip if an electric field is imposed across its thickness as shown below in Figures 1 and 2. Numerical solutions to the above set of dynamic equations are presently underway and will be reported later. However, it must be mentioned that the governing equations (1)-(6) display a set of highly non-linear dynamic equations of motion for the IPMC artificial muscles.
 
 

Presently attempts are under way to establish existence and uniqueness of dynamic solutions to the above equations mathematically. However, experimental observations in our laboratory clearly indicate the non-linear motion characteristics of such muscles as well as unique vibrational response and resonance characteristics.
 
 

For detailed dynamics description and analysis of the continuum theory of ionic polymeric gel the reader is referred to Segalman, Witkowski, Adolf and Shahinpoor²⁵. Since polyelectrolytes are for the most part three dimensional network of macromolecules cross-linked nonuniformly, the concentration of ionic charge groups are also nonuniform within the polymer matrix. Therefore the mechanism of swelling and contraction are intimately related to osmotic diffusion of solvent, ions and counterions into and out of the gel. One possible way to describe this mechanism is to model the system by the governing continuum mechanics equations and Neo-Hookean deformation theory. In the next section an analytical relation is presented as described by Segalman, Witkowski, Adolf and Shahinpoor²⁵.
 
 
 
 

3-ION TRANSPORT MECHANISMS
 
 

Let c(X,t) be the solvent concentration, H(X,t) be the ionic concentration, x(X,t) be the position vector of a typical gel element, X be the reference material coordinate, and t be the time such that the governing continuum mechanics equation takes the following forms:
 
 

                                                                                  (3.1)

                                                                     (3.2)

                                                                                                                                   (3.3)

                                                                                                                                    (3.4)

                                                                                                 (3.5)

where x is the displacement, a superposed dot stands for a differentiation with respect to time, D_i,j is diffusion coefficient,  is the source term for the production of ions in the gel, r_g is the gel density, S is the stress tensor, f_b is the body force vector which includes electromagnetic and gravitational terms, e is the specific internal energy of the ionic polymeric gel, q is the heat flux vector, q_c is the chemical energy flux vector, J is the electric current flux vector, E is the electric field vector, and h is the specific source of energy production in the gel. The stress tensor S, is related to deformation gradient field by means of Neo-Hookean type constitutive equation which may be represented by the following equation:
 
 

                                                                                                                    (3.6)

where F = (¶ x/¶ X), I is the identity matrix, superposed T stands for transpose, G(c) is the Young’s modulus, p is an unknown Lagrangian multiplier to be found by solving system of equations 1-12. The solution to this model will enable one to electrically control the polymeric muscle bending and therefore the motion of the swimming robotic structure. For additional references on modeling of IPMC artificial muscles the reader is referred to references [11]-[14] and [22]-53]
 
 

4-BIOMIMETIC SENSING CAPABILITY OF IPMC
 
 

Investigations of the use of ion-exchange-membrane materials as sensors can be traced to Sadeghipour, Salomon, and Neogi⁵⁸ where they used such membranes as a pressure sensor/damper in a small chamber which constituted a prototype accelerometer. However, it was Shahinpoor ³⁹ who first discussed the phenomenon of flexogelectric effect in connection with dynamic sensing of ionic polymeric gels. In this paper the focus is on the application of the IPMC sensor on quasi-static or dynamic displacement sensing where the response of the sensor against large imposed displacements was investigated. To get a better understanding of the mechanism of sensing, more explanation must be given about the general nature of the ionic polymers.
 
 

As shown in Figures 1 and 2, IPMC strips generally bend towards the anode and if the voltage signal is reversed they also reverse their direction of bending. Conversely by bending the material, shifting of mobile charges become possible due to imposed stresses. Consider Figure 2 where a rectangular strip of the composite sensor is placed between two electrodes. When the composite is bent a stress gradient is built on the outer fibers relative to the neutral axis (NA). The mobile ions therefore will shift toward the favored region where opposite charges are available. The deficit in one charge and excess in the other can be translated into a voltage gradient which is easily sensed by a low power amplifier.
 
 

4.1-Quasi- Static Sensing
 
 

The experimental results showed that a linear relationship exists between the voltage output and imposed quasi-static displacement of the tip of the IPMC sensor as shown in Figure 3. The experimental set up was such that the tip of the cantilevered IPMC strip as shown in Figure 2 was mechanically moved and the corresponding output voltage recorded. The results are shown in Figure 3.
 

4.2-Dynamic Sensing
 
 

When strips of IPMC are dynamically disturbed by means of a dynamic impact or shock loading, a damped electrical response is observed as shown in Figure 4. The dynamic response was observed to be highly repeatable with a fairly high band width to 100’s of Hz.. This particular property of IPMC’s may find a large number of applications in large motion sensing devices for a variety of industrial applications. Since these muscles can also be cut as small as one desires, they present a tremendous potential to micro-electro-mechanical systems (MEMS) sensing and actuation applications.

Figure 4- Dynamic sensing response in the form of output voltage of strips
(40mmx5mmx0.2mm) of IPMC subject to a dynamic impact loading as a cantilever.

5-BIOMIMETIC ACTUATION PROPERTIES OF IPMC’s
 
 

5.1- General Considerations
 
 

As mentioned before, IPMCs are large motion actuators that operate under a low voltage compared to other actuators such as peizocerams or shape memory alloys. Table 1 shows a comparison between the capability of IPMC materials and both electroceramics and shape memory alloys. As shown in Table 1, IPMC materials are lighter and their potential striction capability can be as high as two orders of magnitude more than EAC materials. Further, their response time is significantly higher than Shape Memory Alloys (SMA). They can be designed to emulate the operation of biological muscles and have unique characteristics of low density as well as high toughness, large actuation strain and inherent vibration damping.
 
 

 
 
 

Property	Ionic polymer-Metal Composites (IPMC)	Shape Memory Alloys (SMA)	Electroactive Ceramics (EAC)
Actuation displacement	>10%	<8% short fatigue life	0.1 - 0.3 %
Force (MPa)	10 - 30	about 700	30-40
Reaction speed	m sec to sec	sec to min	m sec to sec
Density	1- 2.5 g/cc	5 - 6 g/cc	6-8 g/cc
Drive voltage	4 - 7 V	NA	50 - 800 V
Power consumption	watts	watts	watts
Fracture toughness	resilient, elastic	elastic	fragile

These muscles are manufactured by a unique chemical process in which a noble metal (Pt) is deposited within the molecular network of the base ionic polymer.

Equations (1.1) through (1.5) depict the essence of such chemical compositing which is followed by a surface plating and electroding process. One of the interesting properties of IPMC artificial muscles is its ability to absorb large amounts of polar solvents, i.e. water. Platinum salt ions, which are dispersed through out the hydrophilic regions of the polymer, are subsequently chemically reduced to the corresponding metal atoms. This results-in the formation of dendritic type electrodes. In Figure 5, scanning electron micrographs are shown in two magnifications, with an order of magnitude difference. On the left, a view is given of the edge of an electroded muscle. The Pt metal covers each surface of the film with some of the metal penetrating the subsurface regions of the material. A closer view with x10 magnification is shown in Figure 5 on the right.

When an external direct voltage of 2 volts or higher is applied on a IPMC film, it bends towards the anode. An increase in the voltage level (up to 6 or 7 volts) causes a larger bending displacement. When an alternating voltage is applied, the film undergoes swinging movement and the displacement level depends not only on the voltage magnitude but also on the frequency. Lower frequencies (down to 0.1 or 0.01 Hz) lead to higher displacement (approaching 25mm) for a 0.5cmx2cmx0.2mm thick strip. Thus, the movement of the muscle is fully controllable by the applied electrical source. The muscle performance is also strongly dependent on the water content which serves as an ion transport medium and the dehydration rate gradient across the film leads to a pressure difference. The frequency dependence of the ionomer deflection as a function of the applied voltage is shown in Figure 6. A single film was used to emulate a miniature bending arm that lifted a mass weighing a fraction of a gram. A film-pair weighing 0.2-g was configured as a linear actuator and using 5V and 20 mW successfully induced more than 11% contraction displacement. Also, the film-pair displayed a significant expansion capability, where a stack of two film-pairs 0.2 cm thick expanded to about 2.5 cm wide (see Figure 7).
 
 

.
 
 
 
 
 
 
 
 

Figure 6: The deflection of a IPMC strip as a function of the frequency (0.1, 0.5 and 1 Hz) and the applied voltage.

Figure 7: IPMC film-pair in expanded mode. A reference pair (top) and an activated pair (bottom).

 

5.2- Muscle actuators for soft robotic applications
 
 

IPMC films have shown remarkable displacement under relatively low voltage, using very low power. Since the IPMC films are made of a relatively strong material with a large displacement capability, we investigated their application to emulate fingers. In Figure 8, a gripper is shown that uses IPMC fingers in the form of an end-effector of a miniature low-mass robotic arm.
 
 

To date, multi-finger grippers that consist of 2- and 4-fingers were produced, where the 4-finger gripper shown in Figure 8 was able to lift 10.3-g. This gripper prototype was mounted on a 5-mm diameter graphite/epoxy composite rod to emulate a light weight robotic arm. This gripper was driven by a 5 volts square wave signal at a frequency of 0.1 Hz to allow sufficient time to perform a desirable demonstration of the capability of the Gripper -- opening the gripper fingers, bringing the gripper near the collected object, closing the fingers and lifting an object with the arm. The demonstration of this gripper capability to lift a rock was intended to pave the way for a future potential application of the gripper to planetary sample collection tasks (such as Mars Exploration) using ultra-dexterous and versatile end-effector.
 
 

5.3- Linear and Platform Type Actuators

For detailed dynamics description and analysis of the dynamic theory of ionic polymeric gels the reader is referred to Shahinpoor and co-workers ^11-14,22-70. Since polyelectrolytes are for the most part three dimensional network of macromolecules cross-linked nonuniformly, the concentration of ionic charge groups are also nonuniform within the polymer matrix. Therefore the mechanism of bending is partially related to migration of mobile ions within the network due to imposition of an electric field as shown in Figure 1. However, recent investigation by the author and his co-workers point to a stronger effect due to surface charge interactions which will be reported later. Figure 9 depicts the bending deformation of a typical strip with varying electric field, while Figure 10 displays the variation of deformation with varying frequency of alternating electric field.
 
 

Based on such dynamic deformation characteristics, linear and platform type actuators can be designed and made dynamically operational. These types of actuators are shown in Figure 11 and 12.
 
 

6-LARGE AMPLITUDE VIBRATIONAL RESPONSE OF IPMC’s
 
 

6.1-General Considerations
 
 

Strips of IPMC were used to study their large amplitude vibration characteristics. The IPMC strips were chemically composited with Platinum. A small function generator circuit was designed and built to produce approximately ± 4.0V amplitude alternating wave at varying frequency. In order to study the feasibility of using IPMC artificial muscles as vibration damper, a series of muscles made from IPMC’s were cut into strips and attached either end-to-end or to one fixed platform and another movable platform in a cantilever configuration. By applying a low voltage the movement of the free end of the beam could be calibrated and its response measured, accordingly. Typical data for the frequency-dependence of amplitude of lateral oscillations of the muscle strips subjected to alternating voltages of various forms such as sinusoidal, rectangular, saw-tooth or pulsed were investigated. Furthermore, the static deformation of the strip with voltage as well as the frequency dependence of deflection-voltage curves were evaluated.
 
 

6.2--EXPERIMENTAL OBSERVATIONS
 
 

IPMC artificial muscle strips of about 2-4cmx4-6mm were cut and completely swollen in a suitable solution such as water to swell. The IPMC muscle strip typically weighed 0.1-0.4 grams and its thickness measured about 0.2mm. The strip was then held by a clamping setup between two platinum plate terminals which were wired to a signal amplifier and generator apparatus driven by Labview software through an IBM compatible PC containing an analog output data acquisition board. The amplifier (Crown model D-150A) was used to amplify the signal output of a National Instrument data acquisition card (AT-AO-10). Software was written to produce various waveforms such as sinusoid, square, triangular and saw tooth signals at desired frequencies up to 100 Hz and amplitudes up to 10 volts. When a low direct voltage was applied, the membrane composite bent toward the anode side each time. So by applying an alternating signal we were able to observe alternating bending of the actuator that followed the input signal very closely up to 35 Hz. At voltages higher than 2.0 volts, degradation of displacement output of the actuator was observed which may be due to dehydration. Water acts as the single most important element for the composite bending by sequentially moving within the composite depending on the polarity of the electrodes. The side facing the anode dehydrated faster than the side facing the cathode leading to a differential stresses which ultimately leads to bending of the composite. So, prior to each experiment, the composite was completely swollen in water. The displacement of the free end of a typical 2cmx4mm composite membrane was then measured for the frequency range of 0.1-35 Hz for sinusoid input voltage at 2.0 volts amplitude (Figure 13).
 
 

Resonance was observed at about 20 Hz where the associated displacement was observed to be 7.5mm. It should be noted that as the actuator dehydrated the resonance frequency and maximum displacement varied accordingly. By encapsulating the strips in a plastic membrane such as Saran^R, the deterioration in the amplitude of oscillation decreased with time. However, the initial amplitude of oscillation for the same level of voltage was smaller than the unwrapped case due to increased rigidity of the strip. For our sample actuator the resonance occurred in the frequency range of 12 to 28 Hz.
 
 

Based on such dynamic deformation characteristics, noiseless swimming robotic structures as shown in Figure 14 and cilia assembly-type robotic worlds, similar to coral reefs, as shown in Figure 15, were constructed and tested for collective vibrational dynamics. Furthermore, wing flapping flying machines, schematically shown in Figures 16 and 17 can be equipped with these muscles.
 
 

Figure 17 depicts a simple design similar to early flight mechanisms for insects, in which linear type actuators as depicted in Figures 11 and 12 can be used to operate simple flying machines, (a) direct wing movement, (b) indirect wing movement, (c) asymmetric form

7-LOAD AND FORCE CHARACTERIZATION OF IPMC’s
 
 

7.1-General Considerations
 
 

In order to measure the force generated by strips of these muscles in a cantilever form an experimental set up was designed using a load cell. A load cell (Transducer Techniques, model GS-30, 30 grams capacity) and corresponding signal conditioning module (Transducer Techniques, model TMO-1) together with a power supply was setup and connected to a PC-platform data acquisition and signal generation system composed of a 12-bit analog output board (National Instrument AT-AO-10) and a 16-bit multi-input-output board (National Instrument AT-MIO-16XE-50). A Nicolet scope was used to monitor the input and output waveform. Labview^TM software was used to write a program to generate various waveform such as sinusoid, square, saw tooth, and triangular signals at desired frequencies and amplitudes. The effective length of the membrane was 10mm. . This made the effective weight of the muscle producing a force to be about 20 milligrams. The resulting graphs were then adjusted for initial noise and pre-load and plotted over 5 second period (2.5 cycles). The force capability of these muscles, on average was measured to be about 400 N/Kgm indicating that these muscles can lift almost 40 times their own weight. Figures 18 depict such general trends.

8-Force Improvement By Means of Chemical Tweaking
 
 

It has recently been established that with the tweaking of the chemical composition of IPMC the force capability of these muscles can be greatly improved. This is one of the most important results of the present review. Reported here are a set of data pertaining to force capability and recent force improvement on ionic polymeric platinum composite muscles. The experimental configuration of the muscle when we measure the force, by a force transducer, is in a cantilever form as shown in Figure 2. A voltage is applied to one end by a pair of electrodes and the force against the transducer on the other end is measured. The form of the voltage signal is also important. The best results seem to be produced by a square type of voltage signal. Typically for a square voltage signal of 3 volts max, and 40 milliamps, a muscle strip of 5mmx20mmx0.2mm weighing about 30 milligrams produces a completely reversible force of about 1.2 grams at a frequency of 0.5 Hz. This means a force density of about 400N/Kgm, which roughly means these muscles, could lift 40 times their own weight. Figure 19 depicts the variation of force under a sinusoidal voltage signal in a cantilever configuration in which the muscle strip only comes into contact with a force transducer over half the cycle.

9-Force versus Displacement
 
 

The variations of tip force versus tip displacements in a cantilever configuration was obtained using muscles which were lithium-based muscle strips of  1" by 1/4" dimensions and 0.2mm thick. These muscle strips were tested under a voltage of 2 volts, frequency of 0.5 Hz in a cantilever configuration. The results are shown in Figure 20 below. The results indicate that the behaviour is similar to a piecewise linear spring with large deformation.
 
 

10-CRYOGENIC PROPERTIES OF IPMC ARTIFICIAL MUSCLES
 
 

In this section are reported a number of recent experimental results pertaining to the behavior of ionic polymer metal composites (IPMC) under low pressure (few Torrs) and low temperature (-140 degrees Celsius). These experimental results have been obtained in a cryogenic chamber at NASA/JPL as well as a cryogenic chamber at the Artificial Muscles Research Institute at UNM. The interest at NASA/JPL was to study the actuation properties of these muscles in a harsh space environment such as one Torr of pressure and -140 degrees Celsius temperature. While at UNM the electrical properties , sensing capabilities as well as actuation properties of these muscles were tested in an atmospheric pressure chamber with a low temperasture of -80 degrees Celsius.

In general the results show that these materials are still capable of sensing and actuation in such harsh conditions as the following Figures 21 through 28 display. Furthermore, these IPMC artificial muscles become less conductive, i.e., their electrical resistance increases with decreasing temperature. This result appears to defy the generally accepted fact that resistance of metallic conductors increases /decreases with increasing/decreasing temperature, respectively.

Figure 21- Deflection characteristics of IPMC as a function of time and temperature

Figure 25 (a) clearly shows a remarkable trend which is opposite to the normal trend of resistance-temperature variations in conductors. The graph is showing that as the temperature decreases in IPMC artificial muscles the resistance increases . For any given temperature, there is a range of linear response of V vs. I, which indicates a close to a pure resistor response. This rather remarkable effect is presently under study. However, one plausible explanation is that the colder the temperature the less active are the ionic species within the network of IPMC and thus the less ionic current activities. Since current is voltage over the resistance R, i.e., I=V/R, thus R has to increase to accommodate the decreasing ionic current due to decreasing temperature.
 
 
 

Figure 22: Power consumption of the IPMC strip bending actuator as a function of activation voltage.

Figure 23: Deflection of the bending IPMC strip as function of voltage

 
 
 

    . 

(a)-IPMC strip static (V/I) and dynamic  (V/I) resistance at various temperature.

(b)-The relation between voltage and current for an IPMC strip that was exposed to RT and to -100oC.

Figures 26 , 27 and 28 show the relationship between the temperature, voltage , current, power and displacement in a typical IPMC strips. Note that the behaviour of this material at low temperatures resembles more a semi-conductor type response to colder temperatures rather than a typical metalic conductor.
 
 

 

Figure 26-The relation between the current and the deflection for an IPMC strip that was exposed to room temperature and to -100oC.

Figure 27-The relation between the power and the deflection for an IPMC strip that was exposed to room temperature and to -100oC.

 
 

Figure 28-Deflection and power consumption of the IPMC muscle as a function of temperature with pressure as a parameter. Vpeak=3 V, Freq=0.1Hz.
 
 

11-SUMMARY
 
 

An introduction to ionic polymer metal composites as biomimetic sensors and actuators were presented. Some theoretical modeling on the mechanisms of sensing and actuation of such polymer composites were given. Highly Dynamic sensing characteristics of IPMC strips were remarkable in accuracy and repeatability and found to be superior to existing motion sensors and micro sensors. A new type of soft actuator and multi-fingered robotic hand were made from IPMC artificial muscles and found to be quite superior to conventional grippers and multi-fingered robotic hands. The feasibility of designing linear and platform type robotic actuators made with IPMC artificial muscle were presented. By applying a low voltage the movement of free end of the actuator could be calibrated and its response could be measured, accordingly. The feasibility of designing dynamic vibrational systems of artificial muscles made with IPMC artificial muscle were presented. Our experiments confirmed that these types of composite muscles show remarkable bending displacement that follow input signal very closely. When the applied signal frequency is varied, so did the displacement up to a point where large deformations were observed at a critical frequency called resonant frequency where maximum deformation was observed, beyond which the actuator response was diminished. A data acquisition system was used to measure the parameters involved and record the results in real time basis. The observed remarkable vibrational characteristics of IPMC composite artificial muscles clearly point to the potential of these muscles for biomimetics applications such as swimming robotic structures, wing-flapping flying machines, slithering snakes, heart and circulation assist devices, peristaltic pumps and dynamic robotic cilia-worlds. The cryogenic properties of these materials were quite unique. The fact that they still operated at very low temperatures such as -140 degrees Celsius shows their potential as cryogenic sensors and actuators. Their resistance increased with decreasing temperature, a property that is opposite to all metallic conductors.
 
 

12-ACKNOWLEDGMENT
 
 

The results reported in this manuscript were obtained partially under the NASA LoMMAs Task that is sponsored by NASA HQ, Code Q as part of the TeleRobotics program. Mr. David Lavery and Dr. Chuck Weisbin are the NASA HQ and JPL TeleRobotics program managers, respectively. This research was also partially supported by the Artificial Muscles Research Institute (AMRI) of UNM as well as Environmental Robots Incorporated through a grant from NRL. Thanks are also due to Dr. Kwang Kim for chemical reaction analysis.
 
 

13-REFERENCES
 

1. Grodzinsky, A.J., “Electromechanics of Deformable Polyelectrolyte Membranes”, Sc.D. Dissertation, Dept. of Elec. Eng., MIT, Cambridge, June 1974.
2. Grodzinsky, A. J. and  Melcher, J. R., “Electromechanics of Deformable, Charged Polyelectrolyte Membranes”, Proc. 27th Annu. Conf. Engineering in Medicine and Biology, Vol. 16, 1974, paper 53.2.
3. Grodzinsky, A. J., Melcher, J. R., “Electromechanical Transduction with Charged Polyelectrolyte Membranes”, IEEE Transactions on Biomedical Engineering, Vol. BME-23, No. 6, pp421-433, November 1976.
4. Yannas, I. V., Grodzinsky, A., J., “Electromechanical Energy Conversion with Collagen Fibers in an Aqueous Medium”, Journal of Mechanochemical Cell Motility, vol. 2, pp113-125, 1973.
5. Kuhn,W.,“Reversible Dehnung und Kontraktion bei Anderung der Ionisation eines Netzwerks Polyvalenter Fadenmolekulionen”, Experientia, Vol.V, pp318-319, 1949.
6. Katchalsky, A., “Rapid Swelling and Deswelling of Reversible Gels of Polymeric Acids by Ionization”, Experientia, Vol. V, pp319-320, 1949.
7. Kuhn,W., Kunzle, O., Katchalsky, A., “Verhalten Polyvalenter Fadenmolekelionen in Losung”, Halvetica Chemica Acta, vol. 31, pp1994-2037, 1948.
8. Kuhn, W., Hargitay, B., Katchalsky, A., Eisenberg, H., “Reversible Dilation and Contraction by Changing the State of Ionization of High-Polymer Acid Networks”, Nature, vol. 165, pp514-516,  1950.
9. Kuhn, W., Hargitay, B., “Muskelahnliche Kontraktion und Dehnung von Netzwerken Polyvalenter  Fadenmolekulionen”, Experientia, vol. VII, pp1-11, 1951.
10. Hamlen, R. P., Kent, C. E., Shafer, S. N., “Electrolytically Activated Contractile Polymer”, Nature, Vol. 206, pp1149-1150, 1965.
11. Shahinpoor, M., “Conceptual Design, Kinematics and Dynamics of Swimming Robotic Structures Using Ionic Polymeric Gels”, Proceedings of ADPA/AIAA/ASME/SPIE Conference on Active Materials and Adaptive Structures, Alexandria, VA, November 1991.
12. Segalman, D., Witkowski, W., Adolf, D., Shahinpoor, M., "Electrically Controlled Polymeric Muscles as Active Materials used in Adaptive Structures", Proceedings of ADPA/AIAA/ASME/SPIE Conference on Active Materials and Adaptive Structures, Alexandria, VA, November 1991.
13. Shahinpoor, M., “Conceptual Design, Kinematics and Dynamics of Swimming Robotic Structures Using Ionic Polymeric Gel Muscles”, Smart Materials and Structures Int. J., Vol. 1,  pp. 91-94, 1992.
14. D. Segalman, W. Witkowski, D. Adolf and M. Shahinpoor, "Theory of Electrically Controlled Polymeric Muscles As Active Materials in Adaptive Structures," Int. J. Smart Materials & Structures, vol.1, no.1, pp.44-54 , (1992)
15. Shahinpoor, M., D. Adolf, D. Segalman and W. Witkowski, “Electrically Controlled Polymeric Gel Actuators," US Patent Number 5, 250, 167, October (1993)
16. Shahinpoor, M.,, “Microelectro-Mechanics of Ionic Polymeric Gels as Artificial Muscles for Robotic Applications”, Proceeding of the IEEE Robotics & Automation Conf., vol. 1 , pp. 380-385, 1993.
17. Shahinpoor, M.,, “Nonhomogeneous Large Deformation Theory of Ionic Polymeric Gels in Electric and pH Fields”, Proceedings of the 1993 SPIE Conference on Smart Structures and Materials, Feb. 1-4, Albuquerque, Vol. 1916, pp. 40-50, 1993.
18. Shahinpoor, M.,, “Electro-Mechanics of Bending of Ionic  Polymeric Gels as Synthetic Muscles for Adaptive Structures,", ASME Publication AD-Vol. 35, Adaptive  Structures and Material Systems, edited by G.P. Carman and E. Garcia, Vol. AD-35, pp.11-22, 1993
19. Shahinpoor, M.,, "Design and Modeling of A Novel Spring-Loaded Ionic Polymeric Gel Actuator," Proc. SPIE 1994 North American Conference on Smart Structures and Materials ., February 94, Orlando, Florida, vol. 2189, paper no. 26, pp.255-264, (1994)
20. Shahinpoor, M.,, "Microelectro-Mechanics of Ionic Polymeric Gels As Synthetic Robotic Muscles," Proc. SPIE 1994 North American Conference on Smart Structures and Materials, February 94, Orlando, Florida, vol. 2189, paper no. 27, pp.265-274, (1994)
21. Shahinpoor, M.,, “Micro-Electro-Mechanics of Ionic Polymeric Gels as Electrically Controlled Synthetic Muscles,", Biomedical Engineering Recent Advances, Editor : J.Vossoughi, University of  District of Columbia Press,  Washington, D.C., April 1994, vol.1, pp.756-759, (1994)
22. Shahinpoor, M.,"Electro-Mechanics of Resilient Contractile Fiber Bundles with Applications To Ionic Polymeric Gel and SMA Robotic Actuators" Proc. 1994 IEEE International Conference on Robotics & Automation , vol. 2, pp. 1502-1508, San Diego, California, May (1994)
23. Shahinpoor, M.,, “Electro-Thermo-Mechanics of Spring-Loaded Contractile Fiber Bundles with Applications To Ionic Polymeric Gel and SMA Actuators," Proc. 1994 Int. Conf. on Intelligent Materials, ICIM'94, June 1994, Williamsburg, VA, pp. 1105-1116, (1994)
24. Shahinpoor, M.,, “Continuum electromechanics of ionic polymeric gels as artificial muscles for robotic applications,” Smart Materials and Structures, Vol. 3, pp. 367-372, 1994.
25. Shahinpoor, M.,"Electro-Mechanics of Resilient Contractile Fiber Bundles with Applications To Ionic Polymeric Gel and SMA Robotic Actuators" Proc. 1994 IEEE International Conference on Robotics & Automation , vol. 2, pp. 1502-1508, San Diego, California, May 1994
26. Shahinpoor, M.,, “Micro-Electro-Mechanics of Ionic Polymeric Gels as Electrically Controlled Artificial Muscles," Proc. 1994 Int. Conf on Intelligent Materials, ICIM'94, June 1994, Williamsburg, VA, pp. 1095-1104, 1994
27. Shahinpoor, M.,, “Continuum Electromechanics of Ionic Polymeric Gels as Artificial Muscles for Robotic Applications”, Smart Material and Structures Int. J., Vol. 3, pp. 367-372, 1994.
28. Shahinpoor, M., Mojarrad, M., “Active Musculoskeletal Structures Equipped with a Circulatory System and a Network of Ionic Polymeric Gel Muscles”, Proceedings of the 1994 International Conference on Intelligent Materials, pp. 1079-1085, 1994.
29. Shahinpoor, M., Wang, G., Mojarrad, M., “Elctro-Thermo-Mechanics of Spring-Loaded Contractile Fiber Bundles with Applications to Ionic Polymeric Gel and SMA Actuators”, Proceedings of the International Conference on Intelligent Materials” ICIM’94, Williamsburg, VA., pp. 1105-1116, 1994.
30. Osada,  Y., “Electro-Stimulated Chemomechanical System Using Polymer Gels (An Approach to Intelligent Artificial Muscle System)”, Proceeding of the International Conference on Intelligent Materials, pp155-161, 1992.
31. Oguro, K., Asaka, K., Takenaka, H., “Polymer Film Actuator Driven by Low Voltage”, Proceedings of 4th International Symposium on Micro Machine and Human Science at Nagoya, pp39-40, 1993.
32. Asaka, K., Oguro, K., Nishimura, Y., Mizuhata, M., Takenaka, H., “Bending of Polyelectrolyte Membrane-Platinum Composites by Electric Stimuli, I. Response Characteristics to Various Waveforms”, Polymer Journal, Vol. 27, No. 4, pp436-440, 1995.
33. Guo,  S., Fukuda, T., Kosuge, K., Arai, F., Oguro, K., Negoro, M., “Micro Catheter System with Active Guide Wire Structure, Experimental Results and Characteristic Evaluation of Active Guide wire Using ICPF Actuator”, Osaka National Research Institute, Japan, pp191-197, 1994.
34. De Rossi, D., P. Parrini, P. Chiarelli and G. Buzzigoli, “ Electrically-Induced Contractile Phenomena In Charged Polymer Networks : Preliminary Study on the Feasibility of Muscle-Like Structures,”, Transaction of American Society of Artificial Internal Organs, vol. XXXI, pp. 60-65, (1985)
35. De Rossi,  D., C. Domenici and P. Chiarelli, “ Analog of Biological Tissues for Mechanoelectrical Transduction : Tactile Sensors and Muscle-Like Actuators,”,
NATO-ASI Series, Sensors and Sensory Systems for Advanced Robots, vol. F43,, pp. 201-218, (1988)
36. Alexanderowicz, A.,Katchalsky, A., “Colligative Properties of Polyelectrolyte Solutions in Excess of Salt”, Journal of Polymer Science, Vol. 1A, pp3231-3260, 1963.
37. Shahinpoor, M.,, "Micro-Electro-Mechanics of Ionic Polymeric Gels As Electrically-Controllable Artificial Muscles,", Int. J. Intelligent Material Systems, vol. 6, no. 3, pp. 307-314, 1995
38. Shahinpoor, M.,, “Design and Development of Micro-Actuators Using Ionic Polymeric Micro-Muscles,”, Proc. ASME Design Engn. Technical Conference, Boston, MA, September (1995)
39. Shahinpoor, M., and M.S. Thompson, "The Venus Flytrap As A Model For Biomimetic Material With Built-In Sensors and Actuators," J. Materials Science & Engineering, vol.C2, pp. 229-233, (1995)
40. Shahinpoor, M., "A New Effect in Ionic Polymeric Gels : The  Ionic "Flexogelectric Effect," Proc. SPIE 1995 North American Conference on Smart Structures and Materials,  February 28-March 2, 1995, San Diego, California, vol. 2441,  paper no. 05, (1995) .
41. Shahinpoor, M.,, "Active Polyelectrolyte Gels as Electrically-Controllable Artificial Muscles and Intelligent Network Structures,", Book Paper, in Active  Structures, Devices and Systems, edited by H.S. Tzou, G.L. Anderson and M.C. Natori, World Science Publishing, Lexington, Ky., (1995)
42. Shahinpoor, M., and Y. Osada, "Heart tissue Replacement with  Ionic Polymeric Gels" Proc. 1996 ASME Winter Annual Meeting, San Francisco, California, November 12-18, (1995)
43. Shahinpoor, M.,,” Design, Modeling and Fabrication of Micro-Robotic Actuators with Ionic Polymeric Gel and SMA Micro-Muscles,”,  Proc. 1995 ASME Design Engineering Technical Conference,   Boston,  MA, September (1995)
44. Mojarrad, M.,  and Shahinpoor, M., "Noiseless Propulsion for Swimming Robotic Structures Using Polyelectrolyte Ion-Exchange Membranes,”, Proc. SPIE 1996 North American Conference on Smart Structures and Materials, February 27-29, 1996, San Diego, California, vol. 2716, paper no. 27, 1996
45. Shahinpoor, M., and M. Mojarrad, "Ion-Exchange Membrane-Platinum Composites As electrically Controllable Artificial Muscles,", Proc. 1996 Third International Conference on Intelligent Materials, ICIM'96, and Third European Conference on Smart Structures and Materials, Lyon, France,  SPIE Publication No.  ICIM’96 ,  pp. 1171-1184,  June 1996
46. Shahinpoor, M.,, "The Ionic Flexogelectric Effect" Proc. 1996  Third  International Conference on Intelligent Materials, ICIM'96,  and Third European Conference on Smart  Structures and Materials,  June 1996, Lyon, France
47. Shahinpoor, M.,, “ Ionic Polymeric Gels As Artificial Muscles For  Robotic and Medical Applications, Int. Journal of Science & Technology  vol. 20, no. 1, Transaction B, pp. 89-136, (1996)
48. Mojarrad, M., and Shahinpoor, M.,  "Noiseless Propulsion for Swimming Robotic Structures Using Polyelectrolyte Ion-Exchange Membranes,”, Proc. SPIE 1996 North American Conference on Smart Structures and Materials, February 27-29, 1996, San Diego,  California, vol. 2716, paper no. 27, (1996)
49. Salehpoor, K., Shahinpoor, M., and M. Mojarrad, "Electrically Controllable Ionic Polymeric Gels  As Adaptive Lenses," ,  Proc. SPIE 1996 North American Conference on Smart Structures and Materials, February 27-29, 1996, San Diego, California,  vol. 2716, paper no. 18, (1996)
50. Salehpoor, K.,Shahinpoor, M., and M. Mojarrad, "Electrically Controllable Artificial PAN Muscles,",  Proc. SPIE 1996 North American Conference on Smart Structures  and Materials, February 27-29, 1996, San Diego, California,  vol. 2716, paper no. 07, (1996)
51. Shahinpoor, M., and M. Mojarrad, "Ion-Exchange Membrane-Platinum  Composites As electrically Controllable Artificial Muscles,", Proc. 1996  Third  International Conference on Intelligent Materials,  ICIM'96,  and Third European Conference on Smart  Structures and Materials,  pp. 1012-1017, June  1996, Lyon, France
52. Shahinpoor, M.,, "The Ionic Flexogelectric Effect" Proc. 1996  Third  International Conference on Intelligent Materials, ICIM'96,  and Third European Conference on Smart  Structures and Materials, pp. 1006-1011, June 1996, Lyon, France
53. Shahinpoor, M., and M. Mojarrad, “Biomimetic Robotic Propulsion Using Ion-Exchange Membrane Metal Composite Artificial Muscles, “, Proceedings of 1997 IEEE Robotic and Automation Conference,  Albuquerque, NM,  April (1997)
54. Shahinpoor, M., , Salehpoor, K., and Mojarrad, M.,” Some Experimental  Results On The Dynamic Performance of PAN Muscles,”, Smart Materials Technologies, SPIE Publication No. vol. 3040, pp. 169-173, (1997)
55. Shahinpoor, M.,, Salehpoor, K., and Mojarrad, M., ”Linear and Platform  Type Robotic Actuators Made From Ion-Exchange Membrane-Metal Composites,”, Smart Materials Technologies, SPIE Publication No. vol. 3040,  pp.192-198, (1997)
56. Shahinpoor, M. and Mojarrad, M.,” Ion-Exchange-Metal Composite Sensor Films,”, Proceedings of 1997 SPIE Smart Materials and Structures Conference, vol. 3042-10, San Diego, California, March (1997)
57. Shahinpoor, M. and Mojarrad, M.,” Electrically-Induced Large Amplitude Vibration and Resonance Characteristics of Ionic Polymeric Membrane-Metal Composites,”, Proceedings of 1997 SPIE Smart  Materials and Structures Conference, vol. 3041-76, San Diego,  California, March (1997)
58. Osada, Y., Hasebe, M., “Electrically Activated Mechanochemical Devices Using Polyelectrolyte Gels”, Chemistry  Letters,  pp1285-1288, 1985.
59. Kishi, R., Hasebe, M., Hara, M., Osada, Y., “Mechanism and Process of Chemomechanical Contraction  of polyelectrolyte Gels Under Electric Field”, Polymers for Advanced Technologies, vol. 1, pp19-25, 1990.
60. Brock, D., Lee, W., Segalman, D., Witkowski, W., “A Dynamic Model of a Linear
61. Actuator Based on Polymer Hydrogel”, Proceedings of the International Conference on Intelligent Materials, pp210-222, 1994.
62. Mojarrad, M., Shahinpoor, M., “Ion-exchange-Metal Composite Artificial Muscle Load Characterization And  Modeling”,  Smart Materials Technologies, SPIE Publication No. vol. 3040,  pp. 294-301, (1997)
63. Sadeghipour, K., Salomon, R., Neogi, S., “Development of A Novel Electrochemically Active Membrane and ‘Smart’ Material Based Vibration Sensor/Damper”, Smart Materials and Structures, Vol. 1, pp 172-179, 1992.
64. Tzou, H. S., Fukuda, T., “Precision Sensors, Actuators and Systems”, Kluwer
65. Academic Publishers  1992
66. Rieder, W. G., Busby, H. R., “Introductory Engineering Modeling Emphasizing Differential Models and Computer Simulations”, Robert E. Krieger Publishing Company, Malabar, Florida, 1990.
67. Ugural, A. C., Fenster, S. K., “Advanced Strength and Applied Elasticity”, Elsevier, New York, 1987.
68. Bar-Cohen, Y.,, T. Xue, B. Joffe, S.-S. Lih, Shahinpoor, M.,, J. Simpson, J. Smith, and P. Willis, “ Electroactive polymers (IPMC) low mass muscle actuators, “ Proceedings of 1997 SPIE Conference on Smart Materials and Structures, March-5, San Diego, California, (1997)
69. Shahinpoor,  M., “Artificial Muscles,” ERI Press,  Albuquerque, New Mexico, Pending Publications,  (1999)
70. Furukawa and J. X. Wen, “Electrostriction and Piezoelectricity in Ferroelectric Polymers,” Japanese Journal of Applied Physics, Vol. 23, No. 9,  pp. 677-679, 1984.
71. I. W. Hunter and S. Lafontaine, “A comparison of muscle with artificial actuators,” IEEE Solid-State Sensor and Actuator Workshop, pp. 178-165, 1992.
72. Kornbluh, K., R. Pelrine and J. Joseph, “ Elastomeric dielectric artificial muscle actuators for small robots,” Proceeding of the 3rd IASTED International Conference, June, 14-16, 1995.
73. Pelrine, R., R. Kornbluh, J. Joseph and S. Chiba, “Artificial muscle actuator,” Proc. of the First International Micromachine Sym., Nov. 1-2, pp. 143-146, 1995.
74. Heitner-Wirguin, C.,  “Recent advances in perfluorinated ionomer membranes: Structure, properties and applications,” Journal of Membrane Science, V 120, No. 1,  pp. 1-33, 1996.
75. Bar-Cohen, Y.,  T. Xue, B. Joffe, S.-S. Lih, P. Willis, J. Simpson, J. Smith, M. Shahinpoor, and P. Willis,  “Electroactive Polymers (EAP) Low Mass Muscle Actuators,” Proceedings of SPIE, Vol. SPIE 3041, Smart Structures and Materials 1997 Symposium, Enabling Technologies: Smart Structures and Integrated Systems, Marc E. Regelbrugge (Ed.), ISBN 0-8194-2454-4, SPIE, Bellingham, WA (June 1997), pp. 697-701.
76. Shahinpoor, M., "Active Polyelectrolyte gels As electrically-Controllable Artificial Muscles and Intelligent Network Structure,", Book Chapter in Structronic Systems, Part II, edited by : H.S.Tzou, A. Guran, U. Gabbert, J. Tani and E. Breitbach, World Scientific Publishers, London, pp. 31-85,  (1998)
77. Shahinpoor, M., Y. Bar-Cohen, T. Xue, J. Simpson, J. Smith, " Some Experimental Results on Ion- Exchange Polymer-Metal Composites as Biomimetic Sensors and Actuators, " Proc. SPIE Smart Materials and Structures Conference, March 3-5, 1998, San Diego, California, Publication No. SPIE 3324-37, (1998)
78. Y. Bar-Cohen, T. Xue, M. Shahinpoor, K. Salehpoor, J. Simpson, J. Smith, and P. Willis  " Low-Mass Muscle Actuators Using Electroactive Polymers (EAP),   " Proc. SPIE Smart Materials and Structures Conference, March 3-5,  1998,  San Diego, California Publication No. SPIE 3324-32, (1998)
79. K. Firoozbakhsh, and  M. Shahinpoor,  " Mathematical Modeling of Ionic Interactions and Deformation In Ionic Polymeric Metal Composite Artificial Muscles, " Proc. SPIE Smart Materials and Structures Conference, March 3-5,  1998, San Diego, California Publication No. SPIE 3323-66, (1998)
80. G. Wang and M. Shahinpoor, " Design of A Knee and Leg Muscle Exerciser Using A Shape Memory Alloy Rotary Actuator, " Proc. SPIE Smart Materials and Structures Conference, March 3-5,  1998, San Diego, California, Publication  No. SPIE 3324-29, (1998)
81. Y. Bar-Cohen, T. Xue, M. Shahinpoor, J. Simpson, J. Smith, " Flexible Low-Mass Robotic Arm Actuated by Electroactive Polymers (EAP), " Proc. SPIE Materials and Structures Conference, March 3-5,  1998, San Diego, California, Publication No. SPIE 3329-07, (1998)
82. K. Salehpoor, M. Shahinpoor, and A. Razani, " Role of Ion Transport In Dynamic  Sensing and Actuation of Ionic Polymeric Platinum Composite Artificial Muscles, " Proc. SPIE Smart Materials and Structures Conference, March 3-5,  1998,  San Diego, California, Publication No. SPIE 3330-09, (1998)
83. M. Shahinpoor, Y. Bar-Cohen, T. Xue, J. Simpson, J. Smith, " Some Experimental Results on Ion- Exchange Polymer-Metal Composites as Biomimetic Sensors and Actuators, " Proc. SPIE Smart Materials and Structures Conference, March 3-5,  1998, San Diego, California, Publication No. SPIE 3324-37, (1998)
84. Y. Bar-Cohen, T. Xue, M. Shahinpoor, K. Salehpoor, J. Simpson, J. Smith, and P. Willis  " Low- Mass Muscle Actuators Using Electroactive Polymers (EAP), " Proc. SPIE Smart Materials and Structures Conference, March 3-5,  1998, San Diego, California Publication No. SPIE 3324-32 (1998)
85. Y. Bar-Cohen, T. Xue, M. Shahinpoor, J. Simpson, J. Smith, " Flexible Low-Mass Robotic Arm  Actuated by Electroactive Polymers (EAP), " Proc. SPIE Smart Materials and Structures Conference,  March 3-5,  1998, San Diego, California, Publication No. SPIE 3329-07, (1998)
86. K. Salehpoor, M. Shahinpoor, and A. Razani, " Role of Ion Transport In DynamicSensing and Actuation of Ionic Polymeric Platinum Composite Artificial Muscles, " Proc. SPIE Smart Materials  and Structures Conference, March 3-5,  1998, San Diego, California, Publication No. SPIE 3330-09,  (1998)
87. Y. Bar-Cohen, T. Xue, M. Shahinpoor, J. Simpson and J. Smith,"Flexible, Low-MassRobotic Arm Actuated by Electroactive Polymers and Operated Equivalently to Human Arm and Hand,", Proc. Space'98-Robotics'98 Conference, Third International ConferenceAnd Exposition on Robotics for Challenging Environments, April 26-30,  1998, Albuquerque, New mexicoAmerican Society of Civil Engineers, ASCE Publication, edited by L.A. Demsetz, R.H. Byrne and J.P. Weyzel ,  April (1998)
88. Shahinpoor, M.,“Variation of Electric Field In Ionic Polymeric Metal Composite Artificial Muscles”, Technical Report No. AMRI98-1, AMRI, UNM July (1998)
89. Shahinpoor, M., "Active Polyelectrolyte gels As electrically-Controllable Artificial Muscles and Intelligent Network Structure,", Book Chapter in Structronic Systems, Part II, edited by : H.S.Tzou, A. Guran, U. Gabbert, J. Tani and E. Breitbach, World Scientific Publishers, London, pp. 31-85,  (1998)
90. Shahinpoor, M., Y. Bar-Cohen, T. Xue, J. Simpson, J. Smith, " Some Experimental Results on Ion- Exchange Polymer-Metal Composites as Biomimetic Sensors and Actuators, " Proc. SPIE Smart Materials and Structures Conference, March 3-5, 1998, San Diego, California, Publication No. SPIE 3324-37, (1998)
91. Shahinpoor, M., "Spring-Loaded Ionic Polymeric Gel Actuator,", Owner : US Department of Energy, Sandia National Laboratories, US Patent No. 5,389,222,  Issued February 14, (1995)
92. Shahinpoor, M., Y. Bar-Cohen,  J. O. Simpson, J. Smith, " Ionic Polymer-Metal Composites (IPMC) as Biomimetic Sensors, Actuaotrs and Artificial Muscles-A Review," Int. J. Smart Materials and Structures, vol.7, pp. R15-R30, (1998)
93. S. Learya, M. Shahinpoorb, and Y. Bar-Cohen, " Equivalent Circuit of Ionic Polymeric Metal Composites,", Proceedings of SPIE's 6th Annual International Symposium on Smart Structures and Materials, Electro-active Polymer Actuators and Devices (EAPAD) (ss04), Newport Beach, CA.  1-5 March, 1999.
94. M.Shahinpoor,  "Ion-Exchange Membrane-Metal Composite As Biomimetic Sensors and Actuators, " Edited by Y. Osada and D. De Rossi, Springer-Verlag-Heidelberg, Pending Publication (1999)
95. M. Shahinpoor, Y. Bar-Cohen, J. Simpson and J. Smith, " Ionic Polymer-Metal Composites (IPMC's) As Biomimetic Sensors and Actuators,", in Field-Responsive Polymers, American Chemical Society Publication, ACS-FRP, Edited by J. Simpson and I.M. Khan, Pending Publications, (1999)
96. M. Shahinpoor, "Ionic Polymer Metal Composite As Biomimetic Sensors and Actuators, " in Volume 44, Book No. 2 of Evolving and Revolutionary Technologies for the New Millenium, Published by SAMPE, pp.1950-1960, (1999)
97. M. Shahinpoor, "Electro-mechanics of iono-elastic beams as electrically-controllable artificial muscles,", in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-12, (1999)
98. H. Brett Schreyer, Mohsen Shahinpoor, Kwang Kim, " Electrical activation of PAN artificial muscles,", in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-19, (1999)
99. Amid Keshavarzi, Mohsen Shahinpoor, Kwang J. Kim, and Jeffrey Lantz, "Blood pressure, pulse rate, and rhythm measurement using ionic polymer-metal composites sensors ,", in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-36, (1999)
100. L. Ferrara, M. Shahinpoor, K. J. Kim, B. Schreyer, A. Keshavarzi, E. Benzel and Jeffrey Lantz, " Use of ionic polymer-metal composites (IPMCs) as a pressure transducer in the human spine, ", in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-45, (1999)
101. R. Lumia and M. Shahinpoor, " Microgripper design using electro-active polymers, " in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-30, (1999)
102. T. Rashid and M. Shahinpoor, " Force Optimization of Ionic Polymeric Platinum Composite Artificial Muscles by Means of An Orthogonal Array Manufacturing Method, " in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-28, (1999)
103. K.J. Kim, M. Shahinpoor and R. Razani, "Electro-Active Polymer Materials for Solid Polymer Fuel Cells,", in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-42, (1999)
104. K.J. Kim, and M. Shahinpoor, "Effect of the Surface-Electrode Resistance on the Actuation of the Ionic Polymer-Metal Composite's (IPMC) Artificial Muscles,", in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-43, (1999)
105. Y. Bar-Cohen, S.P. Leary, M. Shahinpoor, J.O. Simpson and J. Smith,"Flexible Low-Mass Devices and Mechanisms Actuated by Electro-Active Polymers, " , in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-38, (1999)
106. Y. Bar-Cohen, S.P. Leary, M. Shahinpoor, J.O. Simpson and J. Smith, "Electro-Active Polymer(EAP) Actuators for Planetary Applications," , in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-05, (1999)
107. S.P. Leary, M. Shahinpoor, and  Y. Bar-Cohen, "Equivalent Circuit of Ionic Polymeric Metal Composites " , in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-09, (1999)
108. C. Liu, M. Shahinpoor, and  Y. Bar-Cohen, "Scaling Laws of Micro-Actuators and Potential Applications of Electro-Active Polymers in MEMS " , in Proc. SPIE Smart Materials and Structures Conference, March 1-5,  1999, New Port Beach, California,  Publication No. SPIE 3669-33, (1999)
109. M. Shahinpoor, "Ionic Polymer Metal Composite As Biomimetic Sensors and Actuators, " Proc. 44th. Int. SAMPE Symposium, Edited by : Dr. Leslie J. Cohen, Jerome, L. Bauer and William E. Davis, Published by SAMPE, pp. 1950-1960, May 23-27, Long Beach, California, (1999)