| When a high voltage (~30 kV) is
applied to a capacitor whose electrodes have different
physical dimensions, the capacitor experiences a net
force toward the smaller electrode (Biefeld-Brown
effect). We have verified this effect by building four
capacitors of different shapes. The effect may have
applications to vehicle propulsion and dielectric pumps.
We review the history of this effect briefly through the
history of patents by Thomas Townsend Brown. At present,
the physical basis for the Biefeld-Brown effect is not
understood. The order of magnitude of the net force on
the asymmetric capacitor is estimated assuming two
different mechanisms of charge conduction between its
electrodes: ballistic ionic wind and ionic drift. The
calculations indicate that ionic wind is at least three
orders of magnitude too small to explain the magnitude of
the observed force on the capacitor. The ionic
drift transport assumption leads to the correct order of
magnitude for the force, however, it is difficult to see
how ionic drift enters into the theory. Finally, we
present a detailed thermodynamic treatment of the net
force on an asymmetric capacitor. In the future, to
understand this effect, a detailed theoretical model must
be constructed that takes into account plasma effects:
ionization of gas (or air) in the high electric field
region, charge transport, and resulting dynamic forces on
the electrodes. The next series of experiments should
determine whether the effect occurs in vacuum, and a
careful study should be carried out to determine the
dependence of the observed force on gas pressure, gas
species and applied voltage. |
