Appeal No. 1999-1742
Application No. 08/730,674
electromagnetic signal, means for mixing signals having the
first frequency from the return signal and a second frequency
different from the first frequency to provide a beat signal
having a beat frequency, and means coupled to receive the beat
signal for determining the presence of the identifier means when
a predetermined beat frequency is received and providing a
signal indicative thereof.
Independent claim 14 calls for an apparatus for sensing the
presence of an object comprising signal means for providing a
first electrical signal having a first frequency during a first
time period and a second electrical signal having a second
frequency during a second, different time period, antenna means
for transmitting an electromagnetic signal at the first
frequency during the first time period in response to said first
electrical signal and for providing an electrical return signal
in response to a received electromagnetic return signal,
identifier means securable to the object for providing an
electromagnetic return signal in response to said transmitted
electromagnetic signal, said electromagnetic return signal
continuing for a time duration past the termination of said
transmitted electromagnetic signal, combiner means for mixing
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