What is Dielectric Electro-Active Polymer?
DEAP is an elastic silicone film (dialectric) coated on both sides with a very
thin layer of metal. The film is only 40 µm thick making it very flexible and
elastic. Because of its unique mechanical properties DEAP can be placed
on non-planar surfaces and stretched up to 100% of its length. When the
material is stretched its length and area grows while its thickness reduces,
thus the metal coated layers are moving closer to each other making its capacitance grow. Therefore the DEAP sensor material is a variable capacitor.
The dielectric elastomer material basically functions as a plate capacitor
where an incompressible and highly deformable material is sandwiched between two electrodes as seen in figure 4.1. Each of the silver electrodes is
100 nm thick while the polymer material between them is 80 µm thick (d =
80um). The general equation for a plate capacitor can be used to calculate
the capacitance of the material and is given by:
Which
So, the formula become as the follow and it should be linear
Where E-0 and E-material are the permittivity of the polymer material sandwiched between the electrodes and that of free space, A (Omega*L = A) is the active area of the material and d the distance between the electrodes. Omega is the width and L is the length of the sensor. If the sensor stretched, L and d will change.
The DEAP material is made to work as an actuator; it’s called a cold actuator
meaning that there is no consumption in steady state. But due to the design
it can also be used for harvesting electricity with a very low energy loss,
converting from mechanic to electric energy. The focus at Danfoss PolyPower A/S has mainly been on the material functioning as an actuator.
One of the challenges in working with DEAP material is securing a good and flexible contact to the 100nm thick corrugated silver electrodes of the DEAP
material. The electrical contact should stick to the silver electrode without
destroying it, be flexible enough to follow the strain of the polymer material
without breaking and stay conductive.
If instead the DEAP material is stretched, by some outside source and the charge in capacitance is monitored the material can work as a position, strain or pressure sensor. The large strain capabilities of up to 400 and environmental tolerance towards temperature and humidity make the DEAP material very suitable as sensor material but challenges lays in designing sensors for specific purposes, smart contacts to the flexible DEAP material and shielding the sensors where especially parasitic capacitances are a problem.
History of DEAP
Danfoss PolyPower A/S was founded in 2008, but the foundation of their
product was started back in 1995, when the CEO Jorgen Mads Clausen
started a small research in the possibilities of making polymer bers act
like human muscle ber. Since Danfoss is a manufacturing company, the
use of this material was intended to be in actuators, valves and pumps.
In last five years, Danfoss PolyPower A/S has been the only manufacturer
and commercial distributor of dielectric polymer material as evaluation kits
and prototypes. PolyPower DEAP is a dielectric elastomer material that
is fabricated using a silicone elastomer in conjunction with compliant metal
electrode technology [20].
At Danfoss PolyPower A/S, work has concentrated on establishing the processes and equipment necessary to provide a large scale manufacturing platform for DEAP material. Their developments, in combination with well established existing manufacturing processes have made it possible to establish a roll-to-roll manufacturing process for the fabrication of laminated DEAP structures. The manufacturing process can be subdivided into two main stages; the coating stage, which involves coating of elastomer film, delimination and metalization of the elastomer and the actuator assemble stage, which includes elastomer film lamination. The structure of DEAP and impact parameters can been seen in figure 4.1.
Bibliography
[20] M.Benslimane, P. Gravesen, and P. Sommer-Larsen. ME-chanical properties of dielectric elastomer with smart metallic compliant electrodes. Proc. of SPIE, 4695:150–157, 2002.
