Biomedical Engineering Reference
In-Depth Information
replace piezoresistive and piezoelectric sensors with just one sensor for broad fre-
quency range sensing and transduction capabilities.
7.2.1
B
S
T
IPMNC
ASICS
OF
ENSING
AND
RANSDUCTION
OF
S
IPCNC
AND
S
It is so far established that ionic polymers (such as a perfluorinated sulfonic acid
polymer, i.e., Nafion
) in a composite form with a conductive metallic medium (here
called IPMNCs) can exhibit large dynamic deformation if placed in a time-varying
electric field (see fig. 7.1). Conversely, dynamic deformation of such ionic polymers
produces dynamic electric fields (see fig. 7.2). A recently presented model by de Gennes
et al. (2000) presents a plausible description of the underlying principle of electrother-
modynamics in ionic polymers based on internal ion and solvent transport and electro-
phoresis. It is evident that IPMNCs show great potential as dynamic sensors, soft robotic
actuators, and artificial muscles in a broad size range of nano- to micro- to macroscales.
A recent study by de Gennes and coworkers (2000) has presented the standard
Onsager formulation on the underlining principle of IPMNC actuation/sensing phe-
nomena using linear irreversible thermodynamics: When static conditions are
imposed, a simple description of
mechanoelectric effect
is possible based upon two
forms of transport:
ion transport
(with a current density,
J
, normal to the material)
and
, one can assume that this term
is the water flux.) The conjugate forces include the electric field
electrophoretic solvent transport
. (With a flux
Q
E
and the pressure
gradient -
∇
p
. The resulting equation has the concise form of
JELp
=−∇
σ
(7.1)
12
21
QLEKp
=
−
∇
(7.2)
are the membrane conductance and the Darcy permeability, respectively.
A cross-coefficient is usually
where
σ
and
K
L
=
L
=
L
, estimated to be on the order of 10
-8
12
21
(ms
-1
)/(volt-meters
-1
) (Shahinpoor and Kim, 2000a, 2001g). The simplicity of the
FIGURE 7.1
Successive photographs of an IPMNC strip that shows very large deformation
(up to 4 cm) in the presence of low voltage. The sample is 1 cm wide, 4 cm long, and 0.2
mm thick. The time interval is 1 sec. The actuation voltage is 2 V DC.
