Narrow field electromagnetic sensor system and method
First Claim
1. A narrow field electromagnetic sensor, comprising:
- a transmitter which transmits a sequence of electromagnetic signals in response to a transmit timing signal;
a receiver which samples the sequence of electromagnetic signals in response to a receive timing signal, and generates a sampled signal;
a timing circuit which supplies the transmit timing signal to the transmitter and the receive timing signal to the receiver, the receive timing signal gating the receiver to sample a portion of each electromagnetic signal that travels along a direct electromagnetic signal propagation path between the transmitter and the receiver; and
a signal processor coupled to the output of the receiver and responsive to the sampled signal to provide an indication of a characteristic of an object in the direct path between the transmitter and the receiver.
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Accused Products
Abstract
A narrow field electromagnetic sensor system and method of sensing a characteristic of an object provide the capability to realize a characteristic of an object such as density, thickness, or presence, for any desired coordinate position on the object. One application is imaging. The sensor can also be used as an obstruction detector or an electronic trip wire with a narrow field without the disadvantages of impaired performance when exposed to dirt, snow, rain, or sunlight. The sensor employs a transmitter for transmitting a sequence of electromagnetic signals in response to a transmit timing signal, a receiver for sampling only the initial direct RF path of the electromagnetic signal while excluding all other electromagnetic signals in response to a receive timing signal, and a signal processor for processing the sampled direct RF path electromagnetic signal and providing an indication of the characteristic of an object. Usually, the electromagnetic signal is a short RF burst and the obstruction must provide a substantially complete eclipse of the direct RF path. By employing time-of-flight techniques, a timing circuit controls the receiver to sample only the initial direct RF path of the electromagnetic signal while not sampling indirect path electromagnetic signals. The sensor system also incorporates circuitry for ultra-wideband spread spectrum operation that reduces interference to and from other RF services while allowing co-location of multiple electronic sensors without the need for frequency assignments.
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Citations
26 Claims
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1. A narrow field electromagnetic sensor, comprising:
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a transmitter which transmits a sequence of electromagnetic signals in response to a transmit timing signal; a receiver which samples the sequence of electromagnetic signals in response to a receive timing signal, and generates a sampled signal; a timing circuit which supplies the transmit timing signal to the transmitter and the receive timing signal to the receiver, the receive timing signal gating the receiver to sample a portion of each electromagnetic signal that travels along a direct electromagnetic signal propagation path between the transmitter and the receiver; and a signal processor coupled to the output of the receiver and responsive to the sampled signal to provide an indication of a characteristic of an object in the direct path between the transmitter and the receiver. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An electronic trip wire, comprising:
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a transmitter responsive to a transmit timing signal for generating a sequence of RF bursts; a receiver responsive to a receive timing signal for sampling a portion of each RF burst, and for generating a sampled receive signal; a timing circuit for providing the transmit timing signal to the transmitter and the receive timing signal to the receiver so that the receiver samples a portion of each RF burst that corresponds to a direct RF path of the RF burst between the transmitter and the receiver; and an eclipse indicating circuit coupled to the output of the receiver and responsive to the sampled receive signal for providing an eclipse indication when an object obstructs the path of the RF burst along the direct RF path. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. A method of sensing a characteristic of an object, comprising:
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providing a common clock signal at a nominal frequency; deriving a transmit timing signal and a receive timing signal from the common clock signal; transmitting a sequence of electromagnetic signals from a transmitter in response to the transmit timing signal; receiving each electromagnetic signal at a receiver in response to the receive timing signal to provide a sampled signal, the receive timing signal being delayed relative to the transmit timing signal to gate the receiver so that sampling of the electromagnetic signal coincides with arrival of the electromagnetic signal along a direct electromagnetic signal propagation path between the transmitter and the receiver; and providing an indication of a characteristic of the object from the magnitude of the sampled signal. - View Dependent Claims (22, 23, 24, 25, 26)
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Specification