Artificial Muscle Gels
Thermal and Others Nanotubes
With these assumptions the electrical and
mechanical aspects of the system are separately
and together lossless in the sense that energy is
conserved during changes of state(from stretched
to compressed and vice versa).
Principle of operation:-
V1 = V bias
____________________ Z-d Z
Consider a general case, Let the electrostatic energy
“U” stored in the initial stage is U=(Q^2/2C) where
C=єA/Z where є is the permittivity of the dielectric.
As the dimensions changes there will be change in
The Second term in the dU comes from the Mechanical
Energy of the polymer.
Consider the situation when dQ=0(That is there is no
external electrical power source during the change of state).
Then we have dU= U*(dZ/Z-dA/A).
As for an elastomer volume is constant we have volume =K
A*Z=K => A*dZ + Z*dA =0
=>dZ/Z = -dA/A
substituting this relation in above relation we have
dU = U*(2dZ/Z) or dU= -U*(2dA/A).
From the above relations we can say that the Electrostatic
energy increases if dZ is ‘+’ that is Z increases, in other way
Electrostatic energy increases if dA is negative ie A
Que: From Where Does this Energy come?
It takes some positive work for any
stretching force to stretch the EAPM , when an
EAPM is stretched by that force it stores the
work done by that force as mechanical energy
in it.(It is analogous to that of stretched
spring).Now when the force is removed it will
convert this mechanical energy to Electrostatic
energy that we can use for power generation.
Practical Approach :The cycle for Power
EAPM in stretched state connected to battery
EAPM in contracted state supplying power to load.
Factors effecting the power generated ‘u’:
As shown previously we have
=>∫dU/U = 2* ∫dZ/Z (integrating under suitable limits)
=>ln (U2/U1) = 2*ln (Z2/Z1)
now we know U2-U1=u;
u=U1* ( (Z2/Z1)^2 -1)
we know U1 =Q^2/(2*C1)
As Q=C1*V (V=V bias) we have
U1 = ½ C1(V^2) and we know that (Z2/Z1)^2=C1/C2
because C1/C2 =A1*Z2/A2*Z1,put A1=K/Z1 and A2=K/Z2.
Substituting these in the above equation for u we have
Factors effecting the power generated ‘u’:
From the above equations we can see that
The Electric energy generated by the EAPM
is directly proportional to the square of bias
Voltage V bias. u œ V^2.
And we can also notice that u œ (Z2/Z1)^2
This ratio depends on the elastic properties of the material like
stress , strain relations. If a material is more elastic than Z2/Z1
increases as now it can be compressed more so as Z1 decreases
and Z2/Z1 increases and u increases.
If a material has more energy storing ability per
unit volume then that will give more generated energy ‘u’
We had assumed there are no losses any where in the system
but in reality there will be some losses because of finite
resistances of electrodes, some leakage current through Dielectric
material ,Hysteresis loss in the polymer etc.
Experimental result matching the theoretical
The voltage wave
generated for one
impact in the case of
As expected we can see the exponential decay of
voltage. EPAM it is on the order
of 150-200 ms [time].
This is one of the
capacitor through significant
drain resistor characteristics of
EPAM. The long pulse
duration and the high
energy density of
EPAM in power generation mode helps in mechanical energy to
be be effectively converted to
electric energy even at low frequencies
Developments and advances in EAPM
Thus we can use EAPM as a medium for power generation
from mechanical energy with efficiency as high as(80%).
There are many areas where this technology has given
fruitful results for power generation.
Some of them include Heel strike generators , Power from
ocean waves , wind etc.
Research is still on for the commercial use of these
SIR international is working in this field and now they are
in the process of developing polymer engine.
They had successfully developed generators and actuators.
Defense Advanced Research Projects Agency’s(DARPA)
Heel strike generator:
DARPA developed a heel-strike + Dielectric Elastomer (EAP)
generator to capture free energy + _ +
while walking +Vout + _
Demonstrated up to 0.8 J per heel _ + +Vin
Developed multi-layer polymer Compliant Electrodes
Demonstrated 15 layer device + +
+Vout + _ _ __ + +Vin
Heel-Strike generators are
expected to produce 1W of
power under normal walking
Other significant contributions from EAPM
Potential applications of EAPM’s cover areas like actuators
sensors , robotics, in medicine as an alternative for the muscle
Applications in robotics for electrically controlled muscle like movements.
IEEE journal :Current Status and Future Prospects of
Electric Generators Using
Electroactive Polymer Artificial Muscle.
IEEE journal: Innovative wave power generation
systems using Electroactive Polymer Artificial muscles.
Book : Dielectric Elastomers as Electromechanical
Edited By: Federico Carpi , Danilo De Rossi,
Roy Kornbluh ,Ronald Perline and
Scientific American article –OCT 2003.
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