WO1994025943A1 - Detecteur de proximite employant des champs magnetiques a polarisation orthogonale reciproque, generes de maniere sequentielle - Google Patents

Detecteur de proximite employant des champs magnetiques a polarisation orthogonale reciproque, generes de maniere sequentielle Download PDF

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Publication number
WO1994025943A1
WO1994025943A1 PCT/US1994/004337 US9404337W WO9425943A1 WO 1994025943 A1 WO1994025943 A1 WO 1994025943A1 US 9404337 W US9404337 W US 9404337W WO 9425943 A1 WO9425943 A1 WO 9425943A1
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WO
WIPO (PCT)
Prior art keywords
magnetic field
operative
magnetic
output signal
response
Prior art date
Application number
PCT/US1994/004337
Other languages
English (en)
Inventor
Donald K. Belcher
Original Assignee
A & H International Products
Harris Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by A & H International Products, Harris Corporation filed Critical A & H International Products
Priority to AU66383/94A priority Critical patent/AU6638394A/en
Publication of WO1994025943A1 publication Critical patent/WO1994025943A1/fr

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Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B21/00—Alarms responsive to a single specified undesired or abnormal condition and not otherwise provided for
    • G08B21/02—Alarms for ensuring the safety of persons
    • G08B21/0202—Child monitoring systems using a transmitter-receiver system carried by the parent and the child
    • G08B21/0263—System arrangements wherein the object is to detect the direction in which child or item is located
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B21/00—Alarms responsive to a single specified undesired or abnormal condition and not otherwise provided for
    • G08B21/02—Alarms for ensuring the safety of persons
    • G08B21/0202—Child monitoring systems using a transmitter-receiver system carried by the parent and the child
    • G08B21/0241—Data exchange details, e.g. data protocol
    • G08B21/0247—System arrangements wherein the alarm criteria uses signal strength

Definitions

  • the present invention relates in general to proximity detectors and is particularly directed to a proximity detection system which employs sequentially generated, mutually orthogonally polarized magnetic fields to determine the proximity of a magnetic field sensor relative to a magnetic field generator.
  • Proximity detection devices are used in a wide variety of applications for determining the relative nearness or separation of an object or person relative to another object or person.
  • An application of such devices that has recently acquired considerable public interest involves using such devices to allow a responsible individual, such as parent or guardian, to monitor the whereabouts of another person in the custody of the responsible individual.
  • a monitoring system that is intended to equip a responsible individual with the ability to monitor the whereabouts of another person, such as a child, is described in the U.S. Patent to Cox, No. 4,598,272.
  • proximity monitoring is performed by equipping each of the parent and the child with a respective radio transmitter - radio receiver pair.
  • the radio transmitter carried by the child is operative to broadcast or radiate a high frequency RF electromagnetic wave to which the receiver in the unit carried by the parent is tuned. Should the level of the received signal monitored by the parent's receiver drop below a prescribed threshold, indicating that the child has moved to location beyond a prescribed distance from the parent, an alarm signal is generated by the parent's device. In response to the alarm signal, the parent may then active its own transmitter which broadcasts a radio wave that has sufficient signal strength to be detected by the child's unit. When the child's unit detects the signal transmitted by the parent's unit, it outputs an audible alarm signal that is loud enough to be heard by the parent, so as to allow the parent to locate the child.
  • a fundamental shortcoming of a high frequency radio wave is the fact that it is subject to multipath propagation, which can be especially severe in the interior of a building.
  • colinearity between the direction of polarization of the broadcast RF signal and the receiver antenna is required for ensuring optimum signal reception.
  • a further problem is the effect of the dielectric distortion effect of the human body (a substantial salt water mass) on the signal, which can typically causing a fluctuation in signal amplitude on the order of 10 - 15dB.
  • the above discussed problems of attempting to receive and accurately detect the signal strength of radiated high frequency (RF) electromagnetic energy in order to monitor the relative proximity between two physically separated sites (e.g. parent and child) are effectively obviated by means of a relatively low frequency magnetic field generator, which is operative to sequentially generate a plurality of magnetic fields having mutually orthogonal polarizations, that are not subject to multipath propagation, human body dielectric distortion, or threshold level imprecision.
  • RF radiated high frequency
  • relatively low frequency is meant time varying magnetic fields on the order of several tens to hundreds of kiloHertz, having a standing wavelength (on the order of a mile or more) which is considerably greater than the maximum allowable operative range of separation between the monitoring and monitored individuals, which may typically be on the order of tens of feet.
  • the novel magnetic field-based proximity detector includes a magnetic field generator which is provided within a first device, as may be carried by a person, animal or object whose whereabouts is being monitored.
  • the magnetic field generator sequentially generates a plurality of magnetic fields of respectively different magnetic field polarizations.
  • the magnetic field generator is operative to sequentially generate three time varying magnetic fields having respective field polarizations that are mutually orthogonal to one another, so that complete coverage, without nulls, is provided for a three dimensional space coordinate system.
  • a magnetic field sensor unit is provided within a second device, carried by another individual, such a parent or guardian monitoring the whereabouts of the person, animal or object.
  • the magnetic field sensor unit is operative to detect magnetic field energy associated with one or more of the magnetic fields generated by the magnetic field generator. While the magnetic field sensor unit may employ only a single detection device, because of a potential reduction in performance due to the presence of nulls, it is preferable that the magnetic field sensor unit include a plurality (two or more) of magnetic field sensors having respective magnetic field polarization sensitivities that are oriented mutually orthogonal with respect to one another. Each of the magnetic field sensors is operative to produce a respective first output signal in response to detecting magnetic field energy generated by the magnetic field generator of at least a predefined level.
  • a signal combining circuit is coupled to each of the magnetic field sensors, and is operative to generate an alarm signal in response to a prescribed failure to receive a first output signal from any of the magnetic field sensors, thereby indicating that the monitored individual is beyond a prescribed range or distance from the monitoring individual.
  • the variation of power density of a magnetic field with respect to distance has a very emphatic inverse proportionality characteristic (to the sixth power of distance)
  • the slope of the signal strength variation is extremely steep over the major portion of the working range of the receiver, thereby allowing an out-of- range threshold to be readily and accurately established.
  • this magnetic field does not radiate as a broadcast RF wave; therefore, the previously described problems of multipath propagation and human body dielectric distortion are non existent. Due to the long wavelength and penetrating nature of the magnetic field in a dielectric, the distortions are non-existent.
  • Figure 1 is a diagrammatic illustration of a proximity detection system in accordance with an embodiment of the present invention
  • Figure 2 is a detailed schematic diagram of the magnetic field generator employed in the proximity detection system of Figure 1; and Figure 3 is a detailed schematic diagram of the magnetic field sensor employed in the proximity detection system of Figure 1.
  • the present invention successfully addresses problems associated with the use of radiated high frequency (RF) electromagnetic energy to monitor the relative proximity between two physically separated sites by employing a relatively low frequency magnetic field generator, which is operative to sequentially generate a plurality of magnetic fields having mutually orthogonal polarizations, that are not subject to multipath propagation, human body dielectric distortion, or threshold level imprecision.
  • relatively low frequency is meant a time varying magnetic field frequency on the order of several tens to hundreds of kiloHertz, which has a standing wavelength (on the order of a mile or more) that is considerably greater than the maximum allowable operative range of separation between the monitoring and monitored individuals, which may typically be on the order of tens of feet.
  • Figure 1 diagrammatically illustrates a proximity detection system in accordance with an embodiment of the present invention comprising a first device, such as a portable housing unit 11, that is adapted to be carried by a person, animal or object whose whereabouts is being monitored.
  • Unit 11 includes a magnetic field generator unit 13 which is operative to sequentially generate a plurality of time varying magnetic fields of respectively different magnetic field polarizations.
  • magnetic field generator unit 13 is operative to sequentially generate three time varying magnetic fields having respective field polarizations that are mutually orthogonal to one another, so that complete coverage, without nulls, is provided for a three dimensional space coordinate system.
  • magnetic field generator 13 may comprise three mutually orthogonal magnetic field generating coils, as diagrammatically illustrated at 15x, 15y and 15z, which are sequentially energized to produce three time varying magnetic fields having respective field polarizations, that are mutually orthogonal to one another.
  • magnetic field flux lines will be established in all dimensions of a three dimensional coordinate space around the unit 11, so as to effectively guarantee reception by a monitoring magnetic field sensor regardless of its orientation (polarization sensitivity) .
  • the proximity system further includes a magnetic field sensor unit 21 which is provided within a second device 23, carried by the individual, such as a parent or guardian, for monitoring the distance or range of the person, animal or object carrying unit 11 from the sensor unit.
  • Magnetic field sensor unit 21 is operative, regardless of its orientation, to detect magnetic field energy associated with one or more of the magnetic fields generated by the magnetic field generator 13.
  • magnetic field sensor unit 21 may employ only a single detection device, because of a potential reduction in performance due to the presence of nulls, it is preferable that magnetic field sensor unit 21 include a plurality (two or more) of magnetic field sensors having respective magnetic field polarization sensitivities that are oriented mutually orthogonal with respect to one another.
  • magnetic field sensor unit 21 includes three magnetic field detector circuits containing sensing coils 25x, 25y, 25Z having respective magnetic field polarization sensitivities that are oriented mutually orthogonal with respect to one another.
  • Each of magnetic field sensors 25x, 25y, 25Z is operative to produce a respective first output signal in response to detecting magnetic field energy generated by magnetic field generator 13 of at least a predefined level.
  • the respective outputs of sensors 25x, 25y, 25z are amplified, summed together and coupled to a comparator 27.
  • Comparator 27 compares the combined or summed outputs of each of the magnetic field sensors with a preselected threshold.
  • FIG. 2 The details of the magnetic field generator 13 employed within the proximity detection system of Figure 1 are schematically illustrated in Figure 2 as comprising a reference oscillator 31 having its output 33 coupled through a clock divider 35 which produces a commutation control signal.
  • Reference oscillator 31 generates a prescribed clock frequency, preferably on the order of several tens to several hundreds of kiloHertz, as indicated previously.
  • Clock divider 35 divides the oscillation signal output of reference oscillator 31 down to a selected switching drive frequency for controlling the sequential energization of a set of magnetic field coils which sequentially produce a set of mutually orthogonal magnetic fields. It has been observed that magnetic field strength is effectively linearly proportional to coil drive frequency, so that a coarse range of operation of the system may be initially established by the selected coil drive frequency. For example, it has been found that a coil drive frequency of 60 KHz will provide a practical sensitivity range on the order of twelve feet.
  • the divided clock signal is supplied to a commutating or step input 36 of switch 37, which sequentially couples the reference oscillator signal on line 38 to respective outputs (three in the illustrated example) over lines 41, 42, 43 to non-inverted drive inputs 51, 52, 53 of respective magnetic field generator circuits 61, 62, 63 and to a select gate 71.
  • Select gate 71 is operative to selectively switch a complementary voltage applied to input 73 to respective output lines 45, 46, 47 to inverting drive inputs 55, 56, 57 of the magnetic field generator circuits.
  • Each of the magnetic field generator circuits is identical, being configured in the manner shown in dotted lines 61, comprising a pair of push pull bipolar transistor drivers 81, 83 coupled to opposite ends of a resonant or tank circuit 85, containing magnetic field generating coil 91 and an associated capacitor 93.
  • the respective coils 81 of magnetic field generator circuits 61, 62, 63 are physically oriented within unit 11, such their respective coil axes are arranged mutually orthogonal to one another.
  • Magnetic coil 25 has a prescribed magnetic field polarization sensitivity that is oriented mutually orthogonal to those of the other coils of the magnetic field sensor unit.
  • Magnetic coil 25 may optionally be enclosed in an electric shield (Faraday screen) 107 to effectively shield the coil from electric fields.
  • the output of amplifier stage 105 is coupled through a bandpass filter 111, which is tuned to the operating frequency of the system, to a second amplifier stage 113.
  • the output of second amplifier stage 113 is coupled to successive amplifier stages 115, 117.
  • Each of amplifier stages 105, 113, 115, 117 provides a given amount of amplification of the monitored input signal (e.g. on the order of 30 - 40 dB) , so as to obtain a prescribed overall signal gain (e.g. on the order of 140dB) .
  • the output of amplifier stage 117 is A.C. coupled to a diode detector stage 121, the output of which is coupled to a summing node 123.
  • Summing node 123 is also coupled to receive the outputs of the diode detectors of the other magnetic field detector circuits within magnetic field sensor 21.
  • magnetic field sensor unit 21 includes a plurality of (two or more, three in the embodiment illustrated in Figure 3) magnetic field detector circuits.
  • Node 123 is coupled to an integrating capacitor 125 which integrated the energy supplied to node 123 from each of the sensor amplifier circuits.
  • the resulting integration voltage is applied as a first input 127 to a comparator 27, a reference input 129 of which is coupled to receive an adjustable reference voltage 131 corresponding to a prescribed sensitivity of the unit.
  • the output of comparator 27 is coupled to a indication device such as a light emitting diode 133 or other alarm indicating element or circuit (for example an audio alarm device) , to provide a readily discernible indication of whether the monitored person or object is 'out of range'. In operation, as long as the monitored individual is within the sensitivity range of the unit, the output of comparator 27 will be above threshold.
  • the magnetic field generator 13 illustrated in Figure 2 may include an encoding mechanism for encoding the signals applied to coils 15.
  • associated decoder circuitry may be coupled in the output path of sensor coil 25 within the circuitry of Figure 3, so that the unit will not be affected by magnetic fields generated by another unit.
  • the above discussed problems of receiving and accurately detecting the signal strength of radiated high frequency (RF) electromagnetic energy for the purpose of monitoring the relative proximity between two physically separated individuals are effectively eliminated in accordance with the relatively low frequency magnetic field generator, sensing system of the present invention which is operative to sequentially generate a plurality of magnetic fields having mutually orthogonal polarizations, that are free from multipath propagation, human body dielectric distortion, or threshold level sensitivity imprecision.
  • RF radiated high frequency

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  • Health & Medical Sciences (AREA)
  • Child & Adolescent Psychology (AREA)
  • General Health & Medical Sciences (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics And Detection Of Objects (AREA)

Abstract

Détecteur de proximité comprenant un générateur de champ magnétique basse fréquence, qui est placé sur une personne sous surveillance, le générateur produisant de manière séquentielle une pluralité de champs magnétiques variant dans le temps ayant des polarisations orthogonales réciproques. Une unité capteur de champ magnétique est placée dans un deuxième dispositif porté par une deuxième personne. L'unité capteur de champ magnétique sert à détecter l'énergie associée à un ou plusieurs des champs magnétiques générés par le générateur de champ magnétique. L'unité capteur de champ magnétique comprend de préférence plusieurs (au moins deux) capteurs de champ magnétique dont les sensibilités respectives à la polarisation du champ magnétique sont orientées orthogonalement l'une par rapport à l'autre.
PCT/US1994/004337 1993-04-30 1994-04-20 Detecteur de proximite employant des champs magnetiques a polarisation orthogonale reciproque, generes de maniere sequentielle WO1994025943A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU66383/94A AU6638394A (en) 1993-04-30 1994-04-20 Proximity detector employing sequentially generated, mutually orthogonally polarized magnetic fields

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US5516693A 1993-04-30 1993-04-30
US08/055,166 1993-04-30

Publications (1)

Publication Number Publication Date
WO1994025943A1 true WO1994025943A1 (fr) 1994-11-10

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT414178B (de) * 2003-05-05 2006-09-15 Werner Dipl Ing Dietrich Verfahren und vorrichtung zur markierung von entfernungsgrenzen

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2289015A1 (fr) * 1974-10-24 1976-05-21 France Etat Procede et dispositif pour la detection de l'eloignement d'un objet par rapport a un point donne
US4136338A (en) * 1977-03-08 1979-01-23 James D. Pauls & Associates, Ltd. Perimeter alarm apparatus
US4598272A (en) * 1984-08-06 1986-07-01 Cox Randall P Electronic monitoring apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2289015A1 (fr) * 1974-10-24 1976-05-21 France Etat Procede et dispositif pour la detection de l'eloignement d'un objet par rapport a un point donne
US4136338A (en) * 1977-03-08 1979-01-23 James D. Pauls & Associates, Ltd. Perimeter alarm apparatus
US4598272A (en) * 1984-08-06 1986-07-01 Cox Randall P Electronic monitoring apparatus

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT414178B (de) * 2003-05-05 2006-09-15 Werner Dipl Ing Dietrich Verfahren und vorrichtung zur markierung von entfernungsgrenzen

Also Published As

Publication number Publication date
AU6638394A (en) 1994-11-21

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