Biomedical Engineering Reference
In-Depth Information
Figure 4.21
Electric scheme of the contact of an object with the substrate.
2
2
(4.45)
ε φ ε φ
Ñ
=
Ñ
d
1
1
d
On a theoretical point of view, the electric potential can be obtained through
the Schwarz-Christoffel conformal mapping, in a similar mathematical approach as
that of Section 4.2.2.2. If the angle is sharp, there is a pole of the transform at the
tip of the wedge (Figure 4.22). This anomalous, localized value of the electric field
may increase the voltage above the dielectric breakdown voltage [22]. This could
explain why dielectric breakdown is sometimes observed when cells or proteins
adhere to the substrate, or when the surface gets crackled after a long period of use.
Work is ongoing to reinforce the level of the dielectric breakdown voltage without
raising the value of the capacitance.
4.2.3 EWOD Microsystems
The principle of EWOD (electrowetting on dielectric) is to use a paving of elec-
trodes embedded in a substrate as displacement paths that the droplets follow step
by step, digitally, upon actuation of the electrodes (Figure 4.23) [23-26].
Figure 4.22
Contour plot of the magnitude of the electric field below a protein sticking to the
surface (Comsol software).
