Cut electricity consumption with automation - Watt Now Magazine

Now you can build an
entire machine on a
microchip - and it works
By Peter Middleton
Micro-electro-mechanical systems or MEMS — also
known as micromachines in Japan or micro systems
technology (MST) in Europe – uses minute components,
typically between one and one hundred microns for
devices that range from twenty microns to one millimetre.
MEMS is the integration of mechanical elements, sensors, actuators,
and electronics onto a common silicon substrate through modern
micro-manufacturing. The technology — based on the technology
developed for integrated circuits (ICs) — places moving mechanical
mechanisms on the same chips and on the same scale as their electronic
controllers. It is a way of making complex electromechanical systems
using batch fabrication methods similar to those used for ICs, but
merging the electromechanical elements with the electronics.
MEMS accelerometers are quickly replacing the conventional
bulky devices used for air-bag systems in motorcars — because they
are much smaller, more functional, lighter, more reliable, and are
produced at a fraction of the cost. They are used for communications
devices, electrical components
such as inductors and tunable
capacitors and mechanical
micro-switches, which have
huge potential in various
microwave circuits. MEMS
biochips are also being used
for the detection of hazardous
chemical and biological agents
and in micro-systems for highthroughput
drug screening and
selection.
In a paper presented at
the recent 9th international
tribology conference held
in Pretoria, Professor John
Williams of the Cambridge
University Engineering
Department, described one
of the more spectacular
MEMS applications, The Texas
Instrument Digital Micro-mirror Device. It consists of an array of
microscopically small, square aluminium mirrors — totalling more
than half a million — in an area of about 1,5 square centimetres.
Each mirror is approximately 20 μm by 20 μm and corresponds
to a single pixel on a projected display: Each can be individually
addressed and rotated about one or other of its diagonals through an
angle of about 20° at a frequency of more than 100 kHz. These are
now routinely used in data-projectors.
Williams went on to describe the range of micro-actuators for
the conversion of electrical energy into mechanical movement.
Electrostatic comb motors, the standard prime-movers in MEMS
machines, have a set of fixed combs or ‘fingers’ interwoven with
second set, which is able to move. By applying an AC-voltage across
the two capacitive elements, reciprocating motion is achieved at very
high conversion efficiencies.
He also described a thermo-elastic actuator consisting of two
linked miniature cantilevers of greatly differing cross-section. When a
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