Electromagnetic field perimeter detection apparatus

Claim 2

Detection apparatus comprising: at least one receiving conductor for sensing an electromagnetic field; at least three mutually spaced elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said receiving conductor; alarm indicating circuitry coupled to said at least one receiving conductor for providing an alarm indication in response to a sensed disturbance of said electromagnetic field, said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors.

Claim 3

Detection apparatus according to claim 1 and wherein said elongate transmitting conductors are arranged along a common plane.

Claim 4

Detection apparatus according to claim 1 and wherein said at least one receiving conductor comprises a plurality of receiving conductors.

Claim 5

Detection apparatus according to claim 3 and wherein said alarm indicating circuitry comprises a synchronous receiver coupled to said plurality of receiving conductors.

Claim 6

Detection apparatus according to claim 1 and wherein said alarm indicating circuitry comprises digital circuitry having a resolution of less than one percent of full scale.

Claim 7

Detection apparatus according to claim 1 and wherein said alarm indicating circuitry comprises digital circuitry having a resolution of less than one tenth of one percent of full scale.

Claim 8

Detection apparatus comprising: receiver means for detecting an electromagnetic field; transmitter means operative in an intermittent continuous wave mode for producing an electromagnetic field in a protected region, said transmitter means including at least three mutually spaced elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said receiver means; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; alarm indicating circuitry coupled to said receiver means and being operative to detect small changes in said electromagnetic field over a wide dynamic range.

Claim 9

Detection apparatus comprising: receiver means for detecting an electromagnetic field; transmitter means operative in an intermittent continuous wave mode for producing an electromagnetic field in a protected region, said transmitter means including at least three mutually spaced elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said receiver means; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; alarm indicating circuitry coupled to said receiver means and being operative to detect small changes in said electromagnetic field over a wide dynamic range.

Claim 10

Detection apparatus according to claims 1 or 7 and also comprising a digital memory for signal inputs which include indications of a sensed disturbance of said electromagnetic field.

Claim 11

Detection apparatus according to claim 1 and wherein said alarm indicating circuitry comprises amplifier means and high resolution analog to digital conversion means having at least 18 bits of resolution.

Claim 12

Detection apparatus according to claim 9 and wherein said analog to digital conversion means have 20 bits of resolution.

Claim 13

Detection apparatus according to claim 9 and wherein said analog to digital conversion means comprise: a subtraction circuit receiving an analog input; an amplifier receiving the output of said subtraction circuit; an analog to digital converter receiving the output of said amplifier and providing a digital output; computing means receiving said digital output from said analog to digital converter and providing a digital output which is calculated to provide an output from said subtraction circuit which is within the linear range of operation of the analog to digital converter; and a digital to analog converter receiving the digital output from said computing means and providing an analog output to an input of said subtraction circuit.

Claim 14

Detection apparatus according to claim 1 and wherein said transmitting and receiving conductors are located above the ground surface.

Claim 15

Detection apparatus according to claim 1 and wherein said transmitting and receiving conductors include conductors disposed above and conductors disposed below the ground surface.

Claim 16

Detection apparatus comprising: a plurality of receiver means for detecting an electromagnetic field; transmitter means operative for producing an electromagnetic field in a protected region, said transmitter means including at least three mutually spaced elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said receiver means; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; each of said receiver means defining a sensing zone; alarm indicating circuitry coupled to said plurality of receiver means for receiving signals from said sensing zones and including; means for determining the time relationship between signals from said sensing zones; and means for providing an alarm indication in response to receipt of at least two signals of similar shape having a non-zero time difference within predetermined limits.

Claim 17

Detection apparatus comprising: a plurality of receiver means for detecting an electromagnetic field; transmitter means operative for producing an electromagnetic field in a protected region, said transmitter means including at least three mutually spaced elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said receiver means; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; each of said receiver means defining a sensing zone; alarm indicating circuitry coupled to said plurality of receiver means for receiving signals from said sensing zones and including; means for determining the time relationship between signals from said sensing zones; and means for providing an alarm indication in response to receipt of at least two signals of similar shape having a non-zero time difference within predetermined limits.

Claim 18

Detection apparatus according to claim 14 and wherein said means for determining the time relationship comprises cross-correlation function circuitry for indicating a predetermined correlation of signals of similar shape having a non-zero time difference.

Claim 19

Detection apparatus according to claim 15 and wherein said signals from said plurality of sensing zones comprises at least first and second signals, each proportional to the strength of an intrusion disturbance in one of said plurality of sensing zones.

Claim 20

Detection apparatus according to claim 16 and wherein said first and second signals are produced by a single intrusion disturbance.

Claim 21

Detection apparatus according to claim 16 and wherein said first and second signals are produced by different intrusion disturbances associated with a single intrusion occurrence.

Claim 22

Detection apparatus according to claim 14 and wherein said receiver means comprises a plurality of receivers.

Claim 23

Detection apparatus according to claim 19 and wherein said alarm indicating circuitry comprises a differential receiver coupled to said plurality of receivers.

Claim 24

Detection apparatus according to claim 14 and wherein said receiver means comprise elongated conductors.

Claim 25

Detection apparatus according to claim 14 and wherein said sensing zones are overlapping.

Claim 26

Detection apparatus according to claim 14 and wherein said sensing zones are non-overlapping.

Claim 27

Detection apparatus comprising: a plurality of receiving conductors for sensing an electromagnetic field; at least three elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said plurality of receiving conductors; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; each of said receiving conductors defining a sensing zone; alarm indicating circuitry coupled to said receiving conductors for receiving signals from said sensing zones and including; means for sensing the time relationship between signals from said sensing zones; and means for providing an alarm indication in response to receipt of at least two signals having a non-zero time difference within predetermined limits.

Claim 28

Detection apparatus comprising: a plurality of receiving conductors for sensing an electromagnetic field; at least three elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said plurality of receiving conductors; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; each of said receiving conductors defining a sensing zone; alarm indicating circuitry coupled to said receiving conductors for receiving signals from said sensing zones and including; means for sensing the time relationship between signals from said sensing zones; and means for providing an alarm indication in response to receipt of at least two signals having a non-zero time difference within predetermined limits.

Claim 29

Detection apparatus according to claim 24 and wherein said signals include signals produced by different intrusion disturbances associated with a single intrusion occurrence.

Claim 30

Detection apparatus according to claim 1 or claim 24 and wherein said conductors comprise leaky coaxial cables.

Claim 31

Detection apparatus comprising: at least one receiver conductor for sensing an electromagnetic field; at least three elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said at least one receiver conductor; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; alarm indicating circuitry coupled to said at least one receiving conductor for providing an alarm indication in response to predetermined disturbance of the electromagnetic field, and wherein said at least three transmitting conductors are operative to transmit a pulsed continuous wave signal.

Claim 32

Detection apparatus comprising: at least one receiver conductor for sensing an electromagnetic field; at least three elongate transmitting conductors each coupled to a source of electromagnetic energy and cooperating to produce a desired electromagnetic field along the length of said at least one receiver conductor; said source of electromagnetic energy for each transmitting conductor comprising an AC voltage source of selected amplitude and phase, the selection of amplitude and phase determining the configuration of the overall electromagnetic field produced by said transmitting conductors, there being a non-zero phase relationship between the voltage sources of at least two of said transmitting conductors; alarm indicating circuitry coupled to said at least one receiving conductor for providing an alarm indication in response to predetermined disturbance of the electromagnetic field, and wherein said at least three transmitting conductors are operative to transmit a pulsed continuous wave signal.

Claim 33

Detection apparatus according to claim 27 and wherein said pulsed continuous wave signal is characterized in that the pulse width is sufficiently long such that transient effects are substantially absent.

Claim 34

Detection apparatus according to claim 27 or claim 28 and wherein said at least one receiving conductor includes a plurality of receiving conductors and said alarm indicating circuitry comprises a differential receiver coupled to said plurality of receiving conductors.