[Eleanor's comment: This is why we don't "hear" ordinary
radio and TV signals.]
Thus the rate of change (the first derivative) of the
waveform of the pulse is a CRITICAL factor in perception.
Given a thermodynamic interpretation, it would follow that
information can be encoded in the energy and "communicated"
to the "listener".
Communication has in fact been demonstrated. A. Guy (Note
1), a skilled telegrapher, arranged for his father, a retired
railroad telegrapher, to operate a key, each closure and
opening of which resulted in a pulse of microwave energy.
By directing the radiations at his own head, complex mess-
ages via the Continental Morse Code were readily received
by Guy.
Sharp and Grove (note 2) found that appropriate modu-
lation of microwave energy can result in "wireless" and
"receiverless" communication of SPEECH. The recorded by
voice on tape each of the single-syllable words for digits
between 1 and 10. The electrical sine-wave analogs of each
word were then processed so that each time a sine wave
crossed ZERO REFERENCE IN THE NEGATIVE DIRECTION, a brief
pulse of microwave energy was triggered.
[Eleanor's comment: This is, in effect a form of what is
called pulse-RATE modulation.]
By radiating themselves with these "voice modulated"
microwaves, Sharp and Grove were READILY able to hear,
identify, and distinguish among the 9 words. [Typo?]
The sounds heard were not unlike those emitted by persons
with artificial larynxes.
Communication of more complex words and of sentences was
not attempted because the averaged densities of energy
required to transmit longer messages would approach the
current 10 milliwatts per square centimeter limit of safe
exposure.
The capability of communicating directly with a human being
by "receiverless radio" has obvious potentialities both
within and without the clinic. But the hotly debated and
unresolved question of how much microwave radiation a human
being can safely be exposed to will probably forestall
applications within the near future.
...
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