10-06-2017, 07:02 AM
A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high electrostatically stable voltages on a hollow metal globe on the top of the stand. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitor and a very large electrical resistance.
This article discusses a MEMS implementation of a planar
Van de Graaff generator in a standard MUMPs process.It can generate high voltages in autonomous MEMS devices. MEMS power
conversion based on mechanical transport of charge analogous
to the macro-scale Van de Graaff generator is discussed. electrical actuators, micro-combustion
engines, vibrations, etc supply the mechanical energy needed for this conversion.
Basic construction:
In the typical Van de graaff generator a belt consisting of insulated
conductive tiles is positively charged by a voltage source and
the charge is delivered to and deposited in a hollow metal
sphere (a dome). The conductive tiles are charged
by another voltage source with a negative charge of the same
magnitude as the one they delivered up, and then travel back to
ground. A positive charge accumulates on the dome
and potentially very high voltages accumulates on the dome.
MEMS implementation
A planar Van de Graaff generator prototype was designed in
the standard MUMPs process(a surface micromachining process).Also, a metal layer is desirable for the implementation of low-resistance contacts for the shuttle. The generator contains capacitor Cc and Cd
bottom plates, and the contacts for the shuttle.The shuttle is
made of a Poly 1 plate, reinforced with Poly 2.The main contribution to Cp comes
from the capacitance between the shuttle rails and ground.Metal(gold) contacts are needed
to connect the shuttle sequentially to Vc and Vo. semiconductor switching maybe utilised in the design.
full report:
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