Biomedical Engineering Reference
In-Depth Information
The impedance terms are determined from curve fit of experimental data. As
discussed in Newbury (2002), these parameters can be determined from a set of three
measurements of the polymer response. The measurements incorporate step-response
and frequency-response data to produce a model that is accurate over a broad fre-
quency range. The frequency ranges tested in Newbury (2002) are 0-20 Hz. Unlike
an ideal transformer, though, this model incorporates a frequency-dependent trans-
former coefficient that produces a frequency-dependent coupling parameter. The
terms in the equivalent circuit are derived in Newbury (2002).
The impedance model shown in equation (6.158) was utilized as a basis for
modeling the coupled system. The model was rewritten with voltage and velocity
as the inputs and force and current as outputs:
=
i
f
g
g
v
u
11
12
(6.159)
g
g
a
21
22
The force at the actuator tip was then written as a combination of the inertial force
of the motor and the resistance force of the sensor.
Several other models of electromechanical coupling have been presented in the
literature. Models based on measured data have been presented by Kanno et al.
(1994, 1996). Models developed from first principles have been proposed by Nemat-
Nasser and Li (2000), Nemat-Nasser (2002), Asaka et al. (1995), Asaka and Oguro
(2000), de Gennes et al. (2000), and Tadokoro (2000). Surveying these models, we
see a number of explanations for the electromechanical coupling in ionic polymer
materials. Most of the debate centers around the relative importance of electrostatic
effects and hydraulic effects within the material. When this chapter was written, it
was not clear which model accurately represented the micromechanics of ionic
polymer materials.
6.7
CONCLUSIONS
This chapter presented a detailed description of various modeling and simulation
techniques and the associated experimental results in connection with ionic poly-
mer-metal composites (IPMNCs) as soft biomimetic sensors, actuators, transducers,
and artificial muscles. These techniques included the continuum electrodynamics of
ionic polymeric gels swelling and deswelling, continuum-diffusion electromechan-
ical model for asymmetric bending of ionic polymeric gels, continuum microelec-
tromechanical models, microelectromechanical modeling of asymmetric deforma-
tion of ionic gels, time dependent phenomenological modeling, steady-state solutions
based on linear irreversible thermodynamics, expanded ion transport modeling, and,
finally, equivalent circuit modeling. An exact expression for the curvature and max-
imum tip deflection of an IPMNC strip in an imposed electric field was also derived.
