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US 4,054,871 AGranted
Electromagnetic intrusion sensor
AssigneeThe United States of America as represented by the Secretary of the Navy
InventorsJames D. Terrell, Richard O. Giorgis
Life of this patent
Estimating the term…
Abstract
An electromagnetic intrusion sensor for detecting the presence of moving ects within a specified detection range by sensing the interaction between the moving objects and an electromagnetic field generated by the sensor.
Claims29
An electromagnetic intrusion sensor for use in remote locations for extended periods of time, comprising:
- means for transmitting an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency;
- means for receiving said electromagnetic signal upon reflection from objects moving before said means for transmitting;
- a mixer circuit electrically coupled in common with said means for transmitting and said means for receiving, for producing a third signal by mixing said reflected electromagnetic signal with said transmitted electromagnetic signal;
- a filter electrically coupled to said mixer circuit for filtering said third signal by attenuating the carrier frequency components in said third signal;
- a detection stage for providing an output signal in dependence upon the envelope of said filtered third signal and,
- means for detecting variation in amplitude of successive peaks of said output signal components wherein a variation in amplitude thereof represents an intrusion into a standing wave pattern between said transmitted electromagnetic signal and said reflected electromagnetic signal.
3 more elements
An electromagnetic intrusion sensor, comprising:
- means for generating an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency;
- an antenna circuit having an electrical length equal to one quarter of the wavelength of said modulation frequency, for propagating said electromagnetic signals and for receiving echoes thereof;
- a first stage having an input terminal coupled in common with said means for generating and said antenna circuit, for producing an intermediate signal by mixing the components of said electromagnetic signal and said echoes;
- a low pass filter having a cut off frequency less than said carrier frequency, coupled to receive said intermediate signal from said first stage;
- and,
- a second stage for producing an output signal varying in dependence upon the envelope of said intermediate signal passed by said low pass filter.
3 more elements
An electromagnetic intrusion sensor, comprising:
- means for generating an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency
- means for pulsing the operation of said means for generating;
- an antenna circuit having an electrical length equal to one quarter of the wavelength of said modulation frequency, for propagating said electromagnetic signal and receiving echoes thereof;
- a first stage having an input terminal coupled in common with said means for generating and said antenna circuit, for producing an intermediate signal by mixing said electromagnetic signal and said echoes;
- filter means for providing paths of differing impedance to said electromagnetic signal and said echoes and to said intermediate signal;
- and,
- a second stage coupled to receive said intermediate signal from said filter means, for producing an output signal varying in dependence upon said intermediate signal.
4 more elements
In an electromagnetic sensor of the type including:
- a pulse circuit for providing regular periodic pulses of uniform length;
- a transmitter for generating during said pulses a carrier frequency signal modulated in amplitude at a modulation frequency;
- and,
- an antenna circuit for propagating the modulated carrier frequency signal and for receiving echoes thereof;
- a network for detecting the presence of Doppler signals, comprising:
- a first mixed circuit reactively coupled in common with said transmitter for providing an intermediate signal by mixing the modulated carrier frequency signal and said echoes;
- a first low-pass filter having a cut-off frequency below said carrier frequency for separating said carrier frequency from said intermediate signal;
- a second stage coupled to receive said intermediate signal from said first low-pass filter, for providing an output signal in dependence upon the envelope of said intermediate signal;
- a second low-pass filter having a cut-off frequency below said modulation frequency for separating modulation frequency components of said output signal;
- and,
- a sample-hold circuit for providing in response to reception of each of said pulses a step pulse having an amplitude dependent upon the peak amplitude of the output signal during each said pulse.
8 more elements
Dependencies are inferred from the claim text.