CA2264805C - Device for monitoring the presence of a person using proximity induced dielectric shift sensing - Google Patents

Device for monitoring the presence of a person using proximity induced dielectric shift sensing Download PDF

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CA2264805C
CA2264805C CA 2264805 CA2264805A CA2264805C CA 2264805 C CA2264805 C CA 2264805C CA 2264805 CA2264805 CA 2264805 CA 2264805 A CA2264805 A CA 2264805A CA 2264805 C CA2264805 C CA 2264805C
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sensor
circuit
capacitance
microprocessor
person
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CA 2264805
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CA2264805A1 (en
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Paul Newham
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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/103Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • A61B5/1113Local tracking of patients, e.g. in a hospital or private home
    • A61B5/1115Monitoring leaving of a patient support, e.g. a bed or a wheelchair
    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B21/00Alarms responsive to a single specified undesired or abnormal condition and not otherwise provided for
    • G08B21/18Status alarms
    • G08B21/22Status alarms responsive to presence or absence of persons
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0209Special features of electrodes classified in A61B5/24, A61B5/25, A61B5/283, A61B5/291, A61B5/296, A61B5/053
    • A61B2562/0214Capacitive electrodes
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/04Arrangements of multiple sensors of the same type
    • A61B2562/046Arrangements of multiple sensors of the same type in a matrix array
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/22Arrangements of medical sensors with cables or leads; Connectors or couplings specifically adapted for medical sensors
    • A61B2562/225Connectors or couplings
    • A61B2562/227Sensors with electrical connectors
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/683Means for maintaining contact with the body
    • A61B5/6838Clamps or clips
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6887Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient mounted on external non-worn devices, e.g. non-medical devices
    • A61B5/6892Mats
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B90/00Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
    • A61B90/90Identification means for patients or instruments, e.g. tags

Abstract

A capacitive array (26) is housed within a polyester mat or other appropriate nonconductive substrate material (28) and interconnected with a control module (10). The control module (10) supplies to the capacitive array (26) a suitable oscillator driver current and concurrently senses capacitance value changes within the capacitive array (26) induced through dielectric shifts within the array (26) brought about by the proximity or absence thereof of the patient's body mass. The control module (10) includes a power supply (16), a driver/sensor circuit (18), a calibration/comparator logic circuit (20), a system interconnection integrity circuit (24), and an alarm generation circuit (22). It may also optionally contain a nurse call relay circuit (32) for interconnection to a facility's nurse call system (34).

Description

l0152025303540CA 02264805 1999-03-03W0 98/ 10391 PCT/U S97/ 154951TITLE: DEVICE FOR MONITORING THE PRESENCE OF A PERSON USINGPROXIMITY INDUCED DIELECTRIC SHIFT SENSINGBACKGROUND OF THE INVENTION1. FIELD OF THE INVENTIONThe present invention relates generally to devices for theshift induced capacitive changes. Thepresent invention relates more specifically to the use of suchdevices for the detection and monitoring of the presence or absencedetection of dielectricof a person from a medical bed, chair or other support structureso as to insure the safety of a patient occupying such a structure.2. DESCRIPTION OF THE RELATED ARTA problem well know to medical service providers is that ofmaking sure certain patients remain in their medical bed or chair.Reasons for this include the need to quickly locate the patient,administer medical treatment to the correct patient, and theprevention. of patient injury. Such knowledge is particularlyimportant when patients have become disoriented due to illness ormedication.Medical bed and chair occupancy monitoring systems have beendevised to assist medical providers with monitoring the presenceor absence of a person in their bed or chair. Such systemstypically are equipped with an alarm or are electronically tied toa common monitoring location, Suchsystems principally use some form of pressure sensitive switch astheir key U.S. 4,484,043 and4,565,910, and other similar patents describeswitch mechanisms which are used to open and close a circuit tosuch as a nurses station.sensing element.both Musick et a1,Patent Nos.indicate the evacuation of a bed or chair by a patient. In thethe switch apparatus is housed in a thinrectangular cover which may be placed between the patient and themattress or between the patient and the seating surface. Analternative version of the above described switch mechanism isplaced between the lower surface of the mattress and the uppersurface of the bed frame.above described patents,The switch devices in all of the abovedescribed mechanisms are eachcomprised of two rectangularconductors which run the length of the device, are parallel to eachother and lie one on top of the other. The two conductors areseparated at both ends by a pliable material such as foam and areheld apart from each other through the rigidity of the switchingl01520253035CA 02264805 1999-03-03W0 98/ 10391 PCTIU S97/ 154952apparatus itself. The switch is activated by the pressure of thepatient’s body weight on the device, either directly thereon orindirectly through the mattress. Once this weight is applied, thetwo conductive elements come into contact, the switch is closed,and the system indicates that the patient is in the bed or chair.When the switch is opened by the absence of the patient's weightin the bed or chair, the system then sounds an alarm or sends asignal to the medical facility call system through an appropriateinterface.Such pressure sensitive switching elements, as previouslydescribed, suffer from certain inherent problems. Switchingelements which are placed under the mattress exhibit extremelylimited sensitivity and selectivity in identifying the presence ofa patient in the bed. This is due to the fact that the patient’sweight in the bed is masked by the mattress itself. This maskingeffect tends to result in frequent false alarms due to the switchfailing to close properly, as well as the failure to generate analarm when the switch fails to open, even though the patient is nolonger in the bed. As for pressure sensitive switches placedbetween the patient and the mattress or seating surface, they mustbe extremely thin to afford the patient a reasonable degree ofcomfort. Although such switches exhibit substantially improvedsensitivity and selectivity, the required thinness of the movableswitch elements, their supportive structure and the requireddielectric space between them causes them to have a considerablylimited life.Such switches manufactured asare, therefore,disposal devices whose costs prohibit their broad acceptance anduse.It is,therefore, an object of this invention to provide aproximity induced non-compressive dielectric shift sensing device,which replaces the existing pressure sensitive switches previouslydescribed for the monitoring of the presence of a patient in amedical environment. A further object of this invention is toprovide such a device which either interfaces with occupancymonitoring control modules self-already in use or utilizescontained control module circuitry and controls.It is another object of the present invention to provide aproximity induced non—compressive dielectric shift sensing devicewhich may be used as a portable unit, or may be wholly or partlyl01520253035CA 02264805 1999-03-03W0 98/10391 PCT/U S97/ 154953built into or mounted on a medical bed, chair, mattress, cushionor similar structure to sense the presence or absence of a personnormally occupying the structure.It is a further object of the present invention to provide aproximity monitoring device with a limited and controlled rangethat can reliably detect the presence or absence of a person,thereby decreasing the number of false and unreliable alarms.It is another object of the present invention to provide awhich willeliminate patient discomfort by replacing mechanical pressuresensitive switches in the medical bed or chair with a considerablythinner and more flexible sensing element.proximity monitoring device greatly decrease orIt is a further object of this invention to provide aproximity monitoring device,exhibitthe sensing element of which willlife through theelimination of all moving components within the sensing element.It is a further object of thisconsiderablylengthened serviceinvention to provide aproximity monitoring device whose sensing element is inherentlysimplerin design and to manufacture, less rawand utilizesmaterial, thereby resulting in a lower cost end user product.Additional objects, advantages and novel features of theinvention. will be set forth iJ1 part in the description. whichfollows, and in part will become apparent to those skilled in theart upon examination of the following, or‘ may be learned bypractice of the invention. The objects and advantages of theinvention realized andmay be attained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.SUMMARY OF THE INVENTIONAccording to the present invention, the foregoing and otherobjects and advantages are attained by an electronic device ableto detect and monitor the presence or absence of a person withina pre—defined space. The device generally comprises a capacitivearray housed within a polyester mat or other appropriatenonconductive substrate material which is interconnected with acontrol module. The control module supplies to the capacitivearray a suitable oscillator derived driver current and concurrentlysensescapacitance value changes within the capacitive arrayinduced through dielectric shifts within the array brought aboutl01520253035CA 02264805 1999-03-03W0 98/10391 PCT/US97/154954by the proximity or absence thereof of the patient’s body mass.The monitor/control module generally comprises a power supply, adriver/sensor circuit, a comparator/calibration logic circuit, asystem interconnection integrity circuit and an alarm generationcircuit. It may also optionally contain a nurse call relay circuitfor interconnection to a facilities nurse call system.The driver/sensor circuit provides and senses a suitablecurrent to the capacitive array located in the patient’s bed orchair. The driver/sensor circuit is connected to and controlledby a comparator/calibration logic circuit that is most preferablymicroprocessor based. This logic circuit continually analyzes andoptimizes signals received from and generated by the driver/sensorcircuit. In this way, the logic circuit defines capacitive valueparameters which it interprets to indicate whether a patient is inclose proximity to the capacitive array or absent from that array.In such. manner, the logic circuit determines the presence orShould thecapacitive value change and remain at a level indicative of aabsence of a patient from his or her support structure.patient’s absence from their support structure, the logic circuitwould,after a suitable pre—programmed time delay, instruct analarm circuit to activate. This alarm activation may consistsolely of audible and/or visible alarms on or within the controlmodule or may be directed to a medical facility's nurse call systemthrough an appropriate interface relay circuit contained eitherwithin, or remote to, the control module.In addition to the above described functions, the logiccircuit receives continuous data from the control module systemabout theconnection between the control module and the capacitive sensorinterconnection integrity circuit continuity ofarray and, where appropriate, between the control module and themedical facility's nurse call system.The logic circuit may also, if appropriate, continuouslymonitor the entire system during utilization for service faults andsubsequently generate appropriate alarms.The apparatus of the invention, uses a proximity induced non-compressive dielectric shift sensing mechanism, and thus reliablydetects the presence of absence of a patient from a bed, chair orother support structure, with minimal discomfort to the patient andwith a greatly extended sensor element service life.l0l520253035CA 02264805 1999-03-03W0 98/10391 PCT/US97I154955Still other objects and advantages of the present inventionwill become readily apparent to those skilled in this art from thefollowing detaileddescription, wherein multiple preferredembodiments of the invention are shown and described, simply by wayof illustration of the best mode contemplated by the inventor forcarrying out the invention. As will be realized, the invention iscapable of other and different embodiments, and its several detailsare capable of modifications in ‘Various obvious respects, allwithout departing from the invention. Accordingly, the drawingsand descriptions are to be regarded as illustrative in nature, andnot as restrictive.BRIEF DESCRIPTION OF THE DRAWINGFIG. 1. is a schematic block diagram of a first preferredembodiment of the device's control/monitor module interconnectedwith a sensing element capacitive array.FIG. 2 is a cross-section of the sensing element capacitivearray as shown in Fig. 1.FIG. 2a is a cross-section of the sensing element capacitivearray as shown in Fig. 1.FIG. 3components of the present invention.FIG. 3a isis a plan view of the structures of the variousstrain—reliefstructure and function for the mat of the present invention.a plan view of an alternativeFIG. 4 is a plan view of a preferred location for the sensingelement capacitive array as shown 1 in relation to ain Fig.patient in a medical bed.FIG. 5 is a perspective view of the structure of the deviceof the present invention showing a clip—on connector and a sensingelement capacitive array.FIG. 6 is a plan View of a sensing element capacitive arrayutilizing a combination of blocked and interleaved conductiveelements.FIG. 7 is a plan view of a sensing element capacitive arrayutilizing stacked conductive elements within the sensing element.FIG. 8 is a cross—section of the sensing element shown in Fig.7 taken along the line B.FIG. 9 is a top view of two preferred locations of the sensingelement capacitive array as shown in Fig. 1. in relation to apatient in a medical bed.1O1520253035CA 02264805 1999-03-03W0 98/10391 ~ PCT/U S97/ 154956FIG. 10 is a schematic block diagram of a second preferredembodiment of the device's control/monitor module interconnectedwith a sensing element capacitive array and an in—place nurse callswitch circuit.DESCRIPTION OF THE PREFERRED EMBODIMENTAs generally described above, the device of the presentinvention has practical application in a number of situations. Thedevice may be used to monitor the presence of a person, or animal,within a pre—defined space. The invention described may be usedin hospitals or other medical facilities to monitor the occupancyof medical beds, chairs or other supportive structures whenever itmay be useful to determine thestatus of occupancy of suchstructures. In addition to its use as a stand alone system incombination with such structures, it is possible that the sensingelement capacitive array, through its inherently long service life,could be embedded in or under the surface materials of bed mattresscovers and seating surfaces. In such fashion a medical facilitywould then only have to supply and interconnect the control/monitormodule component. Equivalently, if appropriate, the entiremonitoring system could become anintegral component of anappropriate medical bed or chair on a permanent basis either byoriginal manufacture or by retrofit.Outside the hospital area, the present device may be used innursing homes, intermediate and long-term care facilities, mentalhospitals, and other similar institutions needing to track thepresence of individuals. Thelimited toinstitutional use, but also has practical application as a single,invention is notstand alone device in addition to its potential for becoming abuilt—in device. Such applications could include in—home healthcare and presence monitoring for the increasing number of patientswho choose to have medical care provided in their own homes.Reference is made,therefore, to Fig. 1 for a description ofa first embodiment of the current invention. Fig. 1 shows aschematic block diagram showing control/monitor module (10) for theinvention interconnected through connections (12) and (13)(14).is made up of several circuit components,(16). (16)such as a battery, an external source with an appropriate feed toto oneembodiment of sensing element Control/monitor module (10)including power supplyPower supply may consist of an internal power sourcel01520253035CA 02264805 1999-03-03W0 98/ 10391 PCT/US97/154957control/monitor module (10) or any other appropriate source ofpower known in the art.Additional circuit components disclosed in Fig. 1 includedriver/sensor circuit (18) which provides an appropriate drivercurrent to capacitive array (26) contained within sensing element(14) and concurrently senses capacitive value changes producedwithin capacitive array (26) through dielectric shifts caused bythe proximity or absence of the patient’s Alsodisclosed in Fig. 1 is comparator/calibration logic circuit (20)body mass.which is preferably a microprocessor circuit containing embeddedprogramming suitable to the applicationsComparator/calibration logic circuit (20) with(22) alsoaddition,interfacesdriver/sensor circuit (18) and alarm generation circuit(10). Incomparator/calibration logic circuit (20) receives input data fromsystem (24).Comparator/calibration logic circuit (20) continuously monitors thefunctions bothappropriate driver current to capacitive array (26) embedded withinsensing element (14)contained withincontrol/monitor moduleinterconnection integrity circuitof driver/sensor circuit (18) optimizing theand equivalently continuously monitors andanalyzes signal data from the driver/sensor circuit (18).when the overall system is first activatedcomparator/calibration logic circuit (20) will determine, throughthe capacitive value readings it initially obtains, whether theoverall system is correctly connected (through data derived fromsystem interconnection integrity circuit (24)) and, if such is thecase, then whether a patient’s body mass is already proximal tosensing element (14) or if the patient's body mass is absent. Fromthe data derived from such capacitive value readings,comparator/calibration. logic circuit (20) will set appropriatecapacitive value calibration parameters which, when equaled orexceeded, would indicate the presence or absence of a patient’sbody mass from proximal contact with sensing element (14). Due tovarying environmental conditions (humidity, the presence of absenceof other grounded or nongrounded structures, body mass of theembedded withinsensing element (14) may be subject to comparator/calibration logicpatient, etc ), that the capacitive elements (26)circuit (20) mayy as required, adjust the calibration. of thecapacitive value change parameters.described herein.c101520253035CA 02264805 1999-03-03W0 98/ 10391 PCT/U S97/ 15495The principle signal characteristic utilized bycomparator/calibration logic circuit (20) is not a direct analysis(14), butrestingof capacitive change value derived from sensing elementrather an analysis of the ratio comparing the inherent,"unoccupied" (14) examined alongside a capacitive value caused through a dielectric shift withinsensing elementcapacitance of sensing element(14) when a patient‘s body mass comes into contact(14). It has been. demonstrated throughexperimentation that a suitable ratio differential that provideswith sensing elementaccurate and reliable monitoring function by the invention, shouldbe 3 to 1 or better.The firstelementembodiment of the invention utilizing sensing(14), as shown in plan view in Fig. 1, has experimentallyproduced an inherent, resting capacitance value of approximately15 to 20 picofarads when the capacitive array conductive elementsare each 2 inches wide by 30 inches long, separated by a dielectricinterspace (28) of 2 inches. This overall array is embedded inpolyester substrate matrix (30) of sensing element (14) whoseoverall dimensions are approximately 6 inches wide by 30 incheslong. The proximity application of an adult human body mass tosensing element (14) as shown in Fig. 4, has reliably producedcapacitive value readings in excess of 250-300 picofarads or aratio of 12 to 1 or better.Existing materials utilized for capacitive array (26)manufacture may include copper film, aluminum film silver/carbonconductive ink, etc.In a preferred embodiment sensing element(14) as shown in plan view in Fig. 1 and in cross—section in Fig.2, consists of 1 milaluminum conductivefilm hermeticallysandwiched between two 2.5 mil layers of inert polyester substrate(30).Referencing Fig. 2a, the cross—sectional structure of sensingelement (14)in general, the cross—sectionand more specifically,located at each connection point (13), is described in more detail.As indicated above, a metallic conductive film, 1 mil thick in the(26).Capacitive array component (26) is hermetically sandwiched between(30).a snap connection of the type that is typically used and referredpreferred embodiment, serves as capacitive array componenttwo layers of inert polyester substrateConnector (13) isto as an EKG connector. Attachment of snap connector (13) tol0l520253035CA 02264805 1999-03-03W0 98/ 10391 PCT/US97/154959conductive film (26) is made first by providing a circular windowthrough polyester substrate (30) of a size sufficient to permitdirect Contact between the metallic components of snap connector(13) and the metallic conductive film, and then compressing thetwo—part components of snap connector (13)(26) and compress a circularportion of conductive film (26) between the electrical contactingelements of snap connector (13).together so as topenetrate through conductive filmReinforcing layer (15b) is alsoconfigured with a window through which the electrically conductivecomponents of snap connector (13) are allowed to protrude. Theremaining portion of reinforcing layer (15b) adheres to the outersurfaces and edge of the sandwiched substrate/film/substrate layersas shown. This configuration provides not only an appropriatemeans for reinforcing the edge of sensing element (14) but alsoserves to seal the edge and the area around snap connection (13).Reference is again made to Fig. 1 for further details on theoperation of the electronicsof the present invention. Aspreviously stated, when comparator/calibration logic circuit (20)achieves or exceeds a pre—defined high or low ratio limit set byits calibration circuitry in an ongoing manner, its logic circuitwill determine whethercontrol monitor module (10) enters a"hold" and"monitor activate override" commands to the logic circuit may be"resting", "monitor", or "alarm" state. Appropriategiven by an external operator, such as a patient caregiver throughappropriate switches integral to the circuitry. Under its owncommand, the logic circuit will analyze the initial absence of apatient’s body mass from sensing element (14) when first activated"hold" On proximityapplication of a patient’s body mass to sensing element (14) logiccircuit (20) will sense the increased impedance value generated by(18)removal of the patient’s body mass from sensing element (14) andan equivalent appropriate ratio capacitance value decrease derived(18),Should this "alarm" status exist for longerand will enter a resting or status.driver/sensor circuit and enter a "monitor" status mode. Onfrom driver/sensor circuit logic circuit (20) will enter an"alarm" status mode.than a predetermined, operator programmed time delay, logic circuit(20) will"alarm" mode.instruct alarnl generation circuit (22) to enter‘ anThe purpose of the operator programmed time delay,if required, is to prevent improper or false alarms being generatedl0l520253035CA 02264805 1999-03-03W0 98/ 10391 PCT/U S97/ 1549510by the described device through the transient shifting by the(14).will triggerpatient of his or her body mass adjacent to sensing elementAn "alarm" mode activation by control module (10)activity of nurse call relay circuit (32), which will in turnactivate a medical facility's nurse call system (34) if sointerfaced.Comparator/calibration logic circuit (20) and driver/sensor(18)capacitive value ratio obtainable from sensing elementcircuit interact with each other to produce an optimal(14). Inthis manner, the overall monitoring system becomes highly reliableand adaptable to differing sensing element sizes and designs. Forinstance, a shortersensing element with different inherentcapacitive values would be required for a patient chair or seatingsurface or differing sensing element placements on the patient’ssupport surface (for instance, as shown in Fig. 9).(20) ultimatelyrequire alarm generation circuit (22) to enter an alarm generationShould comparator/calibration logic circuitstate caused by the absence of the patient’s body mass from thesensing element, the alarm status so generated will be maintained,under normal circumstances, even. though the patient reapplieshis/her body mass to the sensing element following the generationof such an alarm. Such programming (which may be overridden by thecaregiving operator) will dissuade the patient from frequentlymoving off and on the sensing element. Comparator/calibrationlogic circuit (20) may also be programmed to perform otherfunctions as required (for instance, automatically shifting to a"monitor" mode from a "resting" or "hold" mode when the patient’sbody mass has been proximal to sensing element (14) for a definedperiod of time). _Driver/sensor circuit (18) is positioned in close attachment(14)fieldcomprises circuitry appropriate for measuring the capacitance in(26)relative to the capacitance value.to sensing element in order to reduce any extraneouselectromagnetic effects. Driver/sensor circuit (18)capacitive array and generating a variable frequency signalThe variable frequency outputthus encodes the capacitance "valuein a signal that is lesssusceptible to interference from extraneous fields. The signal canbe provided through ordinary wire connections (12) in Fig. 1 backto control/monitor module (10).l01520253035CA 02264805 1999-03-03wo 93/10391 PCT/US97/15495llReference is now made to Fig. 3 for a detailed description ofthe structural nature of the system described schematically in Fig.1. Sensing element (14) is structurally much as described in Fig.1, being made of a flexible substrate (30) with embedded flexiblecapacitive array elements (26).(28).encases capacitive array (26).Capacitive array (26) is separatedby interspace (30)Substrate effectively surrounds andAt each end of sensing element (14),(15a) (15b). These layers, as describedgenerally above with respect to Fig. 2, serve the dual purpose ofreinforcing the attachment ends of sensing element (14) and sealingthese ends at the same time.as shown in Fig. 3 arereinforcing layers andAt a first end of sensing element(14), reinforcing layer (l5a) covers the upper and lower surfacesof sensing element (14) and wraps around its edge much in themanner described in Fig. 2 with respect to reinforcing layer (15b).Hole or slot (lla) is punched through the entire structurelayers) and is positioned to facilitate the attachment of a means(14)Likewise, reinforcing layer (15b) is positioned at an opposite(14) and wraps around the edge thereof inthe manner described with regard to Fig. 2. (llb) ispunched through the layers of sensing mat (14) and provides a meansfor attaching this end of sensing element (14)bed. (llb) provides a strain—reliefmechanism as described in more detail below.(fivefor holding sensing element to the patient’s bed.end of sensing elementHole or slotto the patient’sIn addition, hole or slotConductors (17a) and (17b) connect the array elements (26) tothe electronics of the present invention through connection points(13a) and (13b).these connection pointsAs described above, in the preferred embodiment,(13a) (13b)These type of connectors provide a sufficiently rigid,yet removable electrical attachment.and constitute EKG—type snapconnectors.3a shows an alternativepreferred embodiment and function of hole or slot (llb). Tofacilitate a strain—relief function on conductors (17a) and (l7b),Fig.hole or slot (llb) is elongated and provides an aperture throughwhich (l7a) (17b)connection points (13a) and (13b).(17a) (17b) pulls at connection points(l3b) in a that isdisconnection.conductors and pass before connecting toIn this manner, any strain on(13a)result in aconductors andanddirection less likely tol0l5202530La)U1CA 02264805 1999-03-03W0 93/10391 PCT/US97/15495l 2In the preferred embodiment, driver/sensor circuit (18) isencased within a small enclosure immediately adjacent connectionpoints and(13a) (l3b). It is anticipated that in order tominimize external electromagnetic conductorsfield influences,(l7a) and (17b), which are unshielded, would be relatively short.In the preferred embodiment, (17a) (17b)As indicated and describedconductors andareapproximately 3 inches in length.(18) converts the capacitive valuesmeasured from sensing element (14) into a frequency output that isless susceptible to external electromagnetic field interference.This frequency signal is provided by way of connector (12) tocontrol monitor module (10) as shown. In the preferred embodiment,connector (12) is a four-conductor telephone—type cable terminatingin a removable plug insertable into an appropriate telephone—type(10).In the preferred embodiment,above, driver/sensor circuitjack in control monitor modulecontrol monitor module (10)comprises a box shell surrounding the electronics described above.On the external surface of the module enclosure is provided guard(31) which serves the dual purpose of protecting and shielding(19) (33)attachment point for the module through strap slotscontrol button by way of cover panel and acting as an(35). Theattachment of monitor module (10) to the patient's bed is describedin more detail below.In addition, monitor module(IO) retains a plurality of LEDindicators as shown to provide the user (the caregiver or nurse)with indications regarding the status of the system. According to(10)(23),the functions described above and below, monitor moduleincorporates low battery indicator (21), check mat indicatoralarm indicator (26), monitor mode indicator (27) and hold modeindicator (29).Monitor module (10) is connected by way of cable (37) to nursecall system connector (39). Connector (39) terminates in astandard phono jack (41) as is typically utilized in existing nursecall system connections. Connector (39) is intended to provide theelectrical connection to nurse call system (34) shown above in Fig.l .Control monitor module (10) in the preferred embodiment ispowered by a 3 VDC power supply typically provided by two AA typealkaline or lithium batteries. The present invention may alsol0152O253O35CA 02264805 1999-03-03W0 93/10391 PCT/US97/ 1549513operate off of an AC power source with an appropriate AC adaptorcircuit. When operable through an AC adaptor, control monitormodule (10) incorporates an automatic battery backup switch—overcircuit to maintain operation of the device in the event of ACpower interruption or failure. Such battery backup systems arewell known in the art.The low battery indicator (21) shown in Fig. 3 is connectedto the electronics of the present invention so as to provide twostage indications of the internal power supply. Low batteryindicator (21) is configured to begin blinking when the voltage ofthe internal power supply falls below 2.6 VDC. This would beindicative of a non—urgent need to replace the battery within theunit. A second stage low battery indication provided at LED (21)would occur when the power supply voltage falls below 2.48 VDC,indicating a more theconjunction with the blinking low battery LED, an audible signal,as well as a closing (or opening as the case may be) of the nursecall connection would occur.urgent need to replace battery. InIt should be noted that driver/sensor circuit (18) does notrequire a separate power supply to convert the capacitance values(14) to a frequency shift valuesutilized by control monitor module (10).(10) is designed to operate throughmanipulation of a single button to control its mode and status.The LED indicators described above are intended to provide a fullmeasured in sensing elementControl monitor modulesystem visual status identification and indication means for theuser. There are two separate system integrity alarms that areincorporated into the electronics described above. The firstinvolves a disconnected mat state that causes the check mat LED,the alarm, and the nurse call system to activate when the mat isnot connected to the system. A second integrity alarm occurs whenan internal electronic function failure occurs. When such aninternal function failure occurs,(10)control monitor module (10) are configured so as to provide a meanstheall LEDs on control monitormodule are illuminated.In addition, the electronics offor indicating presence of a battery when no LEDs(19)provide a single, short audible tone to indicate the presence ofareilluminated. Pushing control button one time will alsoa battery within the system.l01520253035CA 02264805 1999-03-03wo 93/10391 PCT/U S97! 1549514In general, control monitor module (10) is electronicallyconfigured to provide multiple alarm tones selectable by the useror installer. Three settings that include a "no—alarm" state canbe control LED and SET by a standard DIP switch positioned withinthe enclosure. These DIP switch settings provide the user with theability to select the delay time (the time between the sensing ofan off—the—mat condition and the initiation of the alarm) and theTheselection ofduration and character of the alarm once it is activated.electronics are configured so as to permit theinstantaneous alarm activation once an off—the—mat condition isdetected, if the patient returns to the mat,alarm is immediately silenced.in which case, theAlternatively, three, five or eightsecond delays between an off—the—mat condition and the alarm canbe programmed. When such delays are utilized, it is preferable forthe alarm to remain on even after the patient has returned to themat.The process of installing and activating the system shown inFig. 3 is simple and straightforward. With the appropriatebatteries installed and the connections between control monitormodule (10) and driver sensor circuitry (18) in place, connectionsThree audiblepulses are heard to indicate that the system has been switched onwhen this matare made at (l3a) and (l3b) to sensing element (14).connection. is made. when this matLikewise,connection is removed, a single audible pulse indicates the systemis off. (10)manner to a pressure sensitive switch array mat, two audible pulses(10)function in conjunction with the pressure sensitive mat in a mannerShould control monitor module be connected in likeare triggered. Control monitor module then continues toidentical to its function with the dielectric shift sensing mat ofthe present invention.In the activation process, LED indicators on the front panelflash once to indicate their function and then the single LED hold(29)system will automatically enter a monitor mode after 15 seconds.indicator activates. Once a patient is placed on the mat, theMonitor mode may alternatively be immediately activated by pushing(19).between the hold and monitor mode by repeatedly pushing controlbutton (19).It is anticipated that the system of the present invention cancontrol button The system may be switched back and forthl01520253035CA 02264805 1999-03-03wo 93/10391 PCT/US97/1549515be installed with the elements shown in Fig. 3 or may be installedin conjunction with an existing nurse call activation system withinthe hospital. (10)allow it to activate either a normally open or normally closednurse call switch system.The switches within monitor control moduleReference is now made to Fig. 4 for a detailed description ofthe placement of the apparatus of the present invention on thetypical hospital bed. Bed (39) incorporates a plurality of siderails (38) that facilitate both the attachment and the use of thesystem of the present invention. Patient (40) is positioned.on bed(39) as shown. As described above, the placement of sensingelement (14) of the present invention is best made near the largermass areas of patient (40). In Fig. 4, sensing element (14) ispositioned beneath the upper torso portion of patient (40).Sensing element (14) is placed beneath a mattress sheet or mattresscover (not shown) in an area beneath the upper torso of patient(40). (14)mattress of bed through the use of elastic straps(9b)sensing elementtheSensing element(39)In an alternative embodiment,(14)removable positioning ofis positioned on and held to the(9a)a reverse side ofandas shown.may be provided with adhesive material that(14) onVariousallows sensing elementmattress (39) without permanent attachment to its surface.adhesives are well known in the art to permit such. removableattachment of a flexible surface.Positioned immediately adjacent to sensing element (14) is(18). In the preferred embodiment both theenclosure and the circuitry associated with driver/sensor circuit(18) are sufficiently lightweight and flexible as to easily besuspended by connectors (17a) and (17b) along the side of mattress(39).(not shown) would partially cover driver/sensor circuit enclosure(18). (12) (18) tocontrol monitor module which is more rigidly mounted at adriver/sensor circuitIt is anticipated that the mattress cover or mattress sheetsConductor connects driver/sensor circuit(10)position near the patient on the structural components of bed (39)or on the wall adjacent to the head of the patient’s bed.Attachment to the wall is effected through the use of a wallmounted bracket that appropriately engages and retains strap slots(35).In the preferred embodiment,control monitor module (10) isl0l520253035CA 02264805 1999-03-03WO 98/10391 PCT/US97/1549516attached to bed railing (38) by means of flexible attachment strap(7). Attachment strap (7) slips through strap slots (35)in Fig. 3) (10) to the bed inIt is anticipated(shownand attaches control monitor modulea position serviceable by caregiver personnel.that the the responsible foractivating and monitoring the function of the system of the presentinvention so control monitor module (10)(38). as described above,(37), which may be an electrical cord of any reasonable length,caregiver would be individualis positioned on theoutside of bed railFinally, connectorconnects the system of the present invention to existing nurse callsystem connections.It is anticipated that the flexible structure of the sensingelement of the present invention permits large variations in theTheadaptability of the electronics of the system further permits useof a single sensing element structure in a number of applicationswith variations in the patient body mass thatproximity to the sensing element.placement for association with a particular patient.is brought inReference is now made to Fig. 5 for a description of analternative method for the attachment of the sensor mat. At one(14) is (15).Connector clip (15) is a spring—loaded, two—piece clip of a widthgenerally the same as sensing element (14). Incorporated into clip(15) (18) (13).Connector contains the appropriate conductors to make theend. of sensing element attached connector clipis driver/sensor circuit(12)electrical connection between driver/sensor circuit (18), near theand contact connectionspivot spring point (17) of clip (15), back to control/monitormodule (10) (not shown in Fig. 5).Connection (13) is comprised of a plurality of teeth (notshown) on the interior faces of clip (15) that pierce polyestersubstrate (30) and make contact with capacitive array elements(26). Clip edge (19) encases and surrounds the teeth and exposedconductor areas of connector (13) once it is in place on sensingelement (14).It is envisioned that the healthcare provider could easily(15) (14)need might arise to replace sensing element or to simplyconnect and disconnect clip as thefrom sensing element(14)l0l520253035CA 02264805 1999-03-03wo 93/10391 PCT/US97/1549517relocate it in conjunction with a particular patient. The lengthof sensing element (14) in the preferred embodiment is sufficientso that clip (15) when attached to sensing element (14) would fallnear the edge of the bed in which the patient is located. In thisway, only sensing element (14) is present on the top supportivesurface of the patient’s bed.Fig. 6 is, as mentioned above,(14).of the present invention may dictate alternative parameters for thecapacitive characteristics of sensing element (14).(26)specific capacitive requirementsan alternative embodiment forsensing element Various conditions and various applicationsThe structureof capacitive array elements so that theseis variablecan be met. In Fig. 4, analternative configuration is shown whereby the interface areabetween capacitive elements (26) in the array is increased withoutincreasing the overall length of sensing element (14). Substrate(30) and connections (13) are basically the same as those described(28),characteristic that can, under certain conditions, provide a moreoptimal capacitance ratio to be utilized by the electronics of thepresent invention.above. Interspace however, has a significantly differentFigs. 7 and 8 disclose yet another structural arrangement forsensing element (14) that under certain conditions would providemore optimal capacitive characteristics. capacitive(26) (26a, 26b,These components are laid one on top of another so thatIn Fig. 7,array elementsand 26c).are divided into three componentsthey are concentrically arranged operating a very long interfaceTheconstruction of sensor element (14) as described in Figs. 7 and 8edge for a relatively small linear geometry. actualis best seen in cross—section in Fig. 8 taken along line B in Fig.5. While (26a-26c)vertically stacked, the resultant structure is such as to createthe various array elements are in facta sequence of concentric, coplanar elements that function much inthe same two—dimensionalabove—referenced(28a and 28b)layers of dielectric material such as,way as theconfigurations. Interspaces in this case would befor example, the materialutilized for polyester substrate (30). The primary requirement isthat these layers be flexible and electrically insulative so as tocreate the electrical capacitive array described above.Electrical connections for the embodiment shown in Figs. 7 and1O15202530CA 02264805 1999-03-03W0 98/10391 PCT/US97/15495188 would be made as disclosed at connections (13a, 13b, and l3c).(26a and 26c) in this embodiment,function as a single electrical element of the capacitive arrayCapacitive elements would,with element (26b) functioning as the opposite element.Connections (l3a) through (l3c) are made according to thisarrangement.Reference is now made to Fig. 9 for a detailed description ofan alternative placement of the apparatus of the present inventionon the typical hospital bed. Bed (38) incorporates mattress (39)upon which patient (40) is positioned. As described above, theplacement of the sensing element is best made near the larger massareas of patient and(40). In Fig. 9, positions (42) (44) are thepreferable placement areas where large patient mass elements havethe greatest effect on the capacitance characteristics of thesensing element. Connections by way of the clip means describedabove can be made through either side of bed (38) withcontrol/monitor module (10) positioned where indicated andconnected to nurse call system (34). Various hard—wire or radiofrequency communication links are made from nurse call system (34)to the actual nurse's call station.As depicted in Fig. 9, the sensing element (such as that shownas (14) in Fig. 1) may be located under the patient’s body massWhile theis normally in the area(40) in different locations dependent upon requirement.(40)and while this would normallymajority of the patient’s body massof the individual’s hips/buttocks,be the preferred location (42) for the sensing element to producethe greatest possible coverage of the patient’s body mass and,therefore, should thepatient be prone to incontinence which might affect the sensingthe greatest capacitive value ratio shift;element's capacitive shift value, an alternative placement (44) ofthe sensing element, for instance, under the patient's upper torso(44) of thesensing element may produce a slightly lower maximum capacitiveor shoulders)may be preferred. While this locationvalue, the adaptive nature of the monitoring system described willautomatically compensate for this changed circumstance with noreduction in inherent reliability.It is anticipated that the flexible structure of the sensingelement of the present invention permits large variations in theplacement for association with a particular patient. Thel0l520253035CA 02264805 1999-03-03we 93/10391 PCT/US97/15495l9adaptability of the electronics of the system further permits useof a single sensing element structure in a number of applicationswith ‘variations in the patient body mass thatproximity to the sensing element.is brought inIn addition to being installed in environments where patientmonitoring systems have not been in use, the structures of thepresent invention lend themselves to be retrofit into existingpatient monitor systems previously based upon alternate sensingmechanisms. In many cases, existing electronics are already inplace that provide the link between the patient monitor and thenurse's call system. Fig.indicates how the structures of the present invention can beretrofit to take advantage of the existing electronics in place andstill provide the benefits of the improvements found in the presentinvention.In place of control moduleembodiment of the(10)innerconnect adaptor module(18).sensing element (14) and its capacitive array (26) with interspace(28) (30)above. Within innerconnect adaptor module (50) is input data logicin the above described(so)The structures ofinvention,connects with driver/sensor circuitpositioned within substrate are basically as describedcircuit (52) which in turn is connected with relay circuit (54).Both are provided with power from power supply circuit (16).(16)Powersupply circuit also supplies power through innerconnection(12) to driver sensor circuit (18).Innerconnect adaptor module (50) is connected to the existingswitch—base monitor/control unit (60) through logic circuit (62)contained therein. Connection (64) typically carries an on/offcondition between innerconnect adaptor module (50) and existingswitch base nwnitor/control unit (60). Logic circuit (62) ofswitch base monitor/control unit (60) typically generates anelectrical signal into connections (64) which, if it were using amechanical switch sensor would determine the opening or closing ofcontacts within that sensor.(62) might typically be one—half volt at 25 ndcroamps.Should the contacts of a mechanical switch sensor be closed,The driver current produced by logiccircuitthereby completing the driver circuit, logic circuit (62) of theswitch based monitor/control unit (60) would signal and indicatea monitoring status mode within monitor/control unit (60). Should10 describes just such a situation and101520253035CA 02264805 1999-03-03wo 9s/10391 PCTIUS97/1549520the switch sensor contacts open in such an arrangement then, bysensing an open circuit status, (62)generate an appropriate status signal which would activated alarm(66) (68) to effectively generate analarm condition from monitor/control unit (60).interconnected with the medicalfacility's nearest call system as desired.logic circuit would in turncircuit and relay circuitThis alarm statuscondition may or may not beThe principle effect of the described innerconnect adaptormodule (50) is to replace, in an electrically transparent manner,the contact points of a mechanical switch sensor with those of anappropriate relay circuit (most preferably of a solid state design)which will effectively imitate the mechanical switch sensor fromthe viewpoint of monitor/control unit (60).(14),20 picofarads in a resting, unoccupied state, to 200 picofarads orA capacitance shiftvalue produced by sensing element which might typically bemore in an active occupied state is converted by driver/sensor(18)appropriate oscillator circuit imbedded in driver/sensor circuit(18).kilocycles in a resting unoccupied state to 20 kilocycles in anactive occupied state.circuit to an equivalent frequency‘ drop generated by anThis oscillator driven frequency drop may typically be 100This frequency shift signal is conducted(18) towithin interconnect adaptor modulethrough conductive elements from driver/sensor circuit(52)By analyzing this input frequency shift,(52)input data logic circuit(50).logic circuitthe input datamay determine the active/occupied status orequivalent inactive/unoccupied status of capacitive sensing element(14). (54).within interconnect adaptor module which will open or closeThis data is fed into relay circuit(50),its secondary conducting elements interfacing directly to logic(62) (60). thealternative manufacturer's monitor control unit through(50) (l8)and equivalently and appropriately respond toalso containedcircuit of monitor control unit In this manner,(60)and driver/sensor circuitmay,interconnect adaptor moduledirectly interface,status signals generated by the capacitive sensing elements of thepresent invention.It is anticipated that further embodiments and alternativeapplications of the present invention may be envisioned from theabove description and the attached drawings. Since any number ofpotential applications for identifying the presence or absence of1O15CA 02264805 1999-03-03WO 98/10391 PCT/US97/1549521a person or other animate or inanimate object within a particulardefined space may be desirable, various modifications of thesensing element and the electronics associated with its use arecontemplated.Specific modifications of the geometry of thesensing element shown in the preferred embodiment are immediatelydiscernable from the structures and geometries of the devices andenvironment within which the sensing element is to be placed. Theparticular geometries described above are appropriate primarily forpatient bed configurations and could easily’ be adapted. to beappropriate to,for example, wheelchair environments or othersitting structures. Likewise, placement of the sensing elementsdescribed, with appropriate geometry modifications, could be madein enclosures suitable for retaining animals in veterinary hospitalenvironments. The ability of the system to constantly optimize thecapacitance measurement ratio in a manner that distinguishesbetween occupied and unoccupied states permits significantSuchvariations are anticipated and included within the scope of thevariations in the placement of the sensing element.description of the present invention.

Claims (7)

1. An apparatus for monitoring the presence of a person within a predefined space comprising:
a. a flexible capacitance sensor, said sensor comprising a flexible substrate and a plurality of coplanar conductive elements, said conductive elements adhesively positioned in a spaced relationship on said flexible substrate;
b. an electronic driver circuit, said driver circuit establishing a nominal voltage between said conductive elements of said capacitance sensor; and c. an electronic sensor circuit, said sensor circuit detecting capacitance changes within said capacitance sensor and generating an output signal having frequency variations corresponding to said capacitance changes, said sensor circuit positioned physically adjacent to said conductive elements of said capacitance sensor to minimize interfering effects from external electromagnetic fields, said capacitance changes serving to indicate the presence or absence of said person within said predefined space.
2. The apparatus of claim 1 further comprising a releasable electrical connector for making connection between said flexible capacitance sensor, said electronic driver circuit and said electronic sensor circuit, said releasable connecter comprising a first and a second snap connector device, each of said snap connector devices comprising a male snap element compressibly attached to said conductive elements of said capacitance sensor through an aperture in said flexible substrate, and a female snap element electrically connected to said electronic driver circuit and said electronic sensor circuit.
3. The apparatus of claim 1 further comprising:

d. a microprocessor, said microprocessor receiving said output signal from said sensor circuit and analyzing said frequency variations to determine if said capacitance changes within said capacitance sensor are indicative of a change in the presence of said person within said predefined space, said microprocessor generating a digital signal indicating a presence or an absence of said person within said predefined space; and e. an alarm circuit, said alarm circuit receiving said digital signal from said microprocessor and triggering an alarm device to identify a change in the presence of said person within said predefined space.
4. The apparatus of claim 3 wherein said alarm circuit comprises an existing nurse call alert system within a hospital environment.
5. The apparatus of claim 1 wherein said electronic driver circuit and said electronic sensor circuit are incorporated into a single driver circuit/sensor circuit module positioned physically adjacent to said conductive elements of said capacitance sensor, and said microprocessor is incorporated into a module positioned physically apart from said driver circuit/sensor circuit module, and connected thereto by a length of electrical conductor.
6. An apparatus for monitoring the presence of a person within a predefined space comprising:
a. a flexible capacitance sensor, said sensor comprising a flexible substrate and a plurality of coplanar conductive elements, said conductive elements adhesively positioned in a spaced relationship on said flexible substrate;

b. an electronic driver circuit, said driver circuit establishing a nominal voltage between said conductive elements of said capacitance sensor;
c. an electronic sensor circuit, said sensor circuit detecting capacitance changes within said capacitance sensor and generating an output signal having frequency variations corresponding to said capacitance changes, said sensor circuit positioned physically adjacent to said conductive elements of said capacitance sensor to minimize interfering effects from external electromagnetic fields, said capacitance changes serving to indicate the presence or absence of said person within said predefined space;
d. a microprocessor, said microprocessor receiving said output signal from said sensor circuit and analyzing said frequency variations to determine if said capacitance changes within said capacitance sensor are indicative of a change in the presence of said person within said predefined space, said microprocessor generating a digital signal indicating a presence or an absence of said person within said predefined space; and e. an alarm circuit, said alarm circuit receiving said digital signal from said microprocessor and triggering an alarm device to identify a change in the presence of said person within said predefined space.
7. A patient monitor comprising:

a. a sensor, said sensor comprising a flexible substrate and at least one planar conductive element, said sensor positioned adjacent said patient;
b. means for establishing a nominal voltage between said conductive element and a reference;

c. means for detecting capacitance changes within said sensor and generating an output signal having frequency variations corresponding to said capacitance changes, said detecting means positioned physically adjacent to said at least one conductive element to minimize interfering effects from external electromagnetic fields;

d. a microprocessor, said microprocessor receiving said output signal from said detecting means and generating a digital signal indicating a presence or an absence of said patient adjacent said sensor; and e. means for receiving said digital signal from said microprocessor and triggering an alarm to identify a change in the presence of said patient.
CA 2264805 1996-09-04 1997-09-04 Device for monitoring the presence of a person using proximity induced dielectric shift sensing Expired - Fee Related CA2264805C (en)

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US70839796A 1996-09-04 1996-09-04
US08/708,397 1996-09-04
US08/871,363 US6025782A (en) 1996-09-04 1997-06-09 Device for monitoring the presence of a person using proximity induced dielectric shift sensing
US08/871,363 1997-06-09
PCT/US1997/015495 WO1998010391A1 (en) 1996-09-04 1997-09-04 Device for monitoring the presence of a person using proximity induced dielectric shift sensing

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US6297738B1 (en) 2001-10-02
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US6025782A (en) 2000-02-15
AU4410197A (en) 1998-03-26

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