IBM of Armonk, New York, has filed patents in Europe (432 573) on a
microwave generator for industrial heating and engraving which abandons
the resonant cavities used in microwave ovens in favour of all solid-state
electrical circuits.
Conventional microwave ovens use a magnetron, a tube amplifier which
converts the kinetic energy of an electron beam into microwaves.
Industrial microwave systems use the same sort of devices because they
now cost less than $5. But the tubes can only run at full power and resonate
only at the allocated oven frequency of 2.45 gigahertz. Control is very
basic: the oven is just switched on and off. But more precise and flexible
control is needed for industrial uses.
IBM claims it can produce microwaves from an solid-state circuit similar
to the tuning circuit of a radio set. This produces a low-power but adjustable
signal which can then be boosted with a fixed-power microwave amplifier.
Thus variations in the power and frequency of the low-level signal from
the circuit changed the power and frequency of the amplified signal.
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The microwave energy is fed into a cavity where it heats the material
being processed. A sensor in the cavity continually monitors the colour
and brightness of the light emitted by the material as it gets red and then
white hot. A feedback loop from the sensor to the circuit then varies the
power and frequency to give very precise heating.
