US3828335A - Radio-wave detector for discovering the movement of persons or objects in a confined space - Google Patents

Radio-wave detector for discovering the movement of persons or objects in a confined space Download PDF

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US3828335A
US3828335A US00341744A US34174473A US3828335A US 3828335 A US3828335 A US 3828335A US 00341744 A US00341744 A US 00341744A US 34174473 A US34174473 A US 34174473A US 3828335 A US3828335 A US 3828335A
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voltage
circuit
oscillator
relay
movement
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G Salmet
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
    • G01V3/101—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil
    • G01V3/102—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil by measuring amplitude
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/22—Electrical actuation
    • G08B13/26—Electrical actuation by proximity of an intruder causing variation in capacitance or inductance of a circuit

Definitions

  • ABSTRACT Movements of persons or articles in a monitored space are detected by a change in the effective capacitance between an antenna and an associated counterpoise defining that space, the antenna being energized by an oscillator whose tank circuit is tuned to a predeter mined radio frequency f 'e.
  • the oscillator works into a tuned monitoring circuit resonant at a different frequency f,,, a capacitive feedback path extending from a tap on the inductive branch of that circuit to an input of the oscillator for applying thereto a control voltage which shifts its operating frequency from f"e to a value fe closer to f,
  • This shift in oscillator voltage is reduced by a lowering of the control voltage through a further detuning of the monitoring circuit by a movement to be detected, with resulting change of the operating frequency to a value fe between 1 'e and fe whereby the change in output voltage due to such detuning is intensified.
  • a load circuit connected to the monitoring circuit includes a normally deenergized relay whose energization in response to the aforementioned voltage change produces a voltage drop across a supply resistor common to the relay and the oscillator whereby this voltage change is further stepped up.
  • the object of my invention is to provide a detector of this nature using just a single such transducer, i.e., a transmitter.
  • the space to be monitored is defined by an antenna and an associated counterpoise connected across a tuned circuit which is coupled to an oscillator whose tank circuit is tuned to a predetermined radio frequency, designated f 'e hereinafter, differing from the resonance frequency of that tuned circuit.
  • resonance frequency f is codetermined by the effective antenna capacitance which in turn is variable by a movement to be detected in the monitored space, the sense of capacitance variation due to such move-' ment being so chosen as to increase the difference between the two frequencies f 'e and f,,.
  • a feedback path between the tuned monitoring circuit, serving to energize the antenna, and the oscillator delivers to an input of the latter, such as a transistor base, a control voltage establishing an operating frequency fe intermediate and frequencies fl, and f 'e, this control voltage varying with changes in the effective antenna capacitance for shifting the operating frequency fe toward frequency f'e, i.e., to a new value fe more remote from resonance frequency 11,, in response to a movement to be detected; the resulting voltage change in the tuned monitoring circuit actuates a responder in a load circuit, connected to the monitoring circuit, for indicating that change.
  • the load circuit includes a differentiation network of long time constant (e.g. seconds); a diode in this network may serve to bypass voltage changes in the monitoring circuit whose polarity is opposite that caused by a movement to be detected.
  • a differentiation network of long time constant e.g. seconds
  • the responder which preferably includes a relay triggerable by an amplifier; when, however, that capacitance varies at a critical rate, a signal is applied to that amplifier to energize the relay.
  • the amplifier comprises an integrator so that the device does not respond to interference picked up via the antenna.
  • the integrator must have a time constant longer than the average very brief duration of domestic, industrial and atmospheric interference.
  • the device In cases in which the device is to detect the presence of living beings, more particularly people, whose approach acts to increase the circuit capacitance and also to damp the tuning circuit, the device is so adjusted that the transmitter operating point is positioned on the descending part of the resonance curve of the tuning circuit i.e., at a frequency a little beyond the exact resonance frequency.
  • the reason for this is that since the capacitance increase in the tuned circuit is the result of the presence of a living being in the transmitter field, so that the resonance frequency of this circuit decreases, and since a living body has a small dielectric constant and therefore increases damping, the difference in transmitted energy due to the displacement of the resonance curve toward the origin and to the flattening thereof is at a maximum. This appreciable reduction in the transmitted field is detected by the differentiation circuit which actuates the responder.
  • the deactivation of the responder can be delayed, preferably via the differentiation network, by using negative detection and by energizing the complete system via a common resistance such as the internal resistance of the power supply or an auxiliary resistance in series therewith.
  • the system according to the invention is of use for protecting the monitored premises or other spaces from intruders and for transmitting recorded messages for advertising, tourist and museum purposes.
  • delayed operation of the responder can be produced and maintained by detection, with a short time constant, of message signals going to a loudspeaker, so that the delay ceases when the speech or sound transmission ceases and the device returns to its supervisory or stand-by state.
  • FIG. 1 is a diagrammatic view of a systemaccording to the invention
  • FIGS. 2a and 2b are diagrams explaining the operation of the system of FIG. 1;
  • FIG. 3 is an equivalent circuit diagram of the transmission circuit of the system
  • FIG. 4 is a partial block diagram of the complete system
  • FIG. 5 is a diagram of its power supply
  • FIG. 6 is a diagram showing how deactivation can be delayed when the system is used with a loudspeaker
  • FIG. 7 is a simplified detail of the diagram shown in FIG. 4.
  • FIG. 1 I have shown a resonant monitoring circuit comprising an inductance L and a capacitor C.
  • One side of the circuit is connected to an antenna A and the other to a counterpoise therefor (here ground).
  • the actual capacitance of the tuned circuit is therefore not C but C Ca, Ca, denoting the antenna-to-counterpoise capacitance.
  • the resonant frequency is therefore:
  • the circuit L-C is energized by a constantamplitude but variable-frequency alternating current I
  • the AC voltages at the circuit terminals in dependence upon frequency are represented by a curve K in FIGS. 2a and 2b.
  • the curve which represents the frequency F is the dotted-line curve K, of FIG. 2a. If, in this case, the transmission frequency f is set at a value fe slightly greater than the resonant frequency f,, the capacitance increase and therefore the frequency variation will of course produce a variation AV of the AC voltage across the circuit.
  • the damping efiect is therefore cumulative with the effect of the extra capacitance if the frequency fe is above the frequency f,,.
  • the movement to be detected causes a decrease in capacitance, as for instance in the case of a surreptitious opening of an armored door, metal shutter, grid or closure lattice; in this case, as shown in FIG. 2b, the oscillator frequency fe is advantageously smaller than the resonant frequency f, of the transmitting circuit L-C.
  • the resonance curve shifts to the right (curve K and as in the previous case there occurs a voltage reduction AV,; in this instance, however, there is no damping variation.
  • the value of AV can be increased to AV as will be shown hereinafter.
  • the offset between the frequencies fe and f can be increased so that operation is shifted to the skirts of the curve K. The choice of the offset or difference between the frequencies fe and f, determines therefore the sensitivity of the system.
  • a fixed-frequency oscillator 0 works through an adjustable resistance R, into an amplifier A, which has a high internal output impedance so as not to damp the oscillatory output circuit consisting of an autotransformer L, preferably of the ferrite-core kind, and a capacitor C,.
  • the lower terminal end of the oscillatory circuit is connected to the counterpoise i.e., to ground in the present case whereas its upper terminal is tied to the antenna A.
  • the resistance R serves to control the drive of the amplifier A, so that at resonance of the circuit L-C, the AC voltage between a point a in the amplifier output and ground is near the maximum which the amplifier A, can provide without being saturated.
  • the amplifier A therefore behaves like a constantcurrent generator.
  • the tap a is so chosen that the total supply direct current under these conditions does not exceed a given low value, e.g. 1 mA, when the apparatus is on standby, so that the system can run for a long time (several months) if battery-energized.
  • FIG. 7 is a very simplified circuit diagram of the oscillator O and the amplifier A.
  • the oscillator O is a Hartley circuit comprising a transistor Tr,, a ferrite-core inductance L, and a capacitor C the elements L, and C forming a tuned circuit.
  • the amplifier A either inverts or does not invert the phase of the signal which it transmits; in this particular case the amplifier A, which comprises a single transistor Tr inverts the phase.
  • a feedback coupling between the tap a and a point g (i.e., the base lead of the transistor Tr, of the oscillator O) is provided by a capacitor C, which therefore feeds back a control voltage that is always in phase quadrature with the normal voltage on lead g.
  • the circuit L-C is tuned exactly to the oscillator frequency fe (f fe), the -out-of-phase control voltage fed back via capacitor C to point g lags with reference to the regenerative feedback voltage from tank circuit L,C, present at point g in the absence of such capacitive feedback, and so the oscillator frequency is altered. It can be shown that the operating frequency decreases in this case. Conversely, if the oscillatory detector circuit L-C, is detuned, the lagging control voltage decreases and the frequency fe increases, tending toward the natural frequency f'e of the tuned circuit L,-C,.
  • the voltage between the point a and ground is normally several tens of volts. A proportion of this voltage is taken off at a top b (FIG. 4) and fed via a rectifying connection, constituted by a diode D to an integrating circuit comprising a resistance R in parallel with a capacitor C
  • a rectifying connection constituted by a diode D
  • the alternating voltage of radio frequency fe (or f'e) developed in the tuned circuit L-C builds up a negative potential, of a magnitude proportional to the radio-frequency voltage, on the ungrounded terminal of integrating capacitor C
  • Autotransforrner tap b is so chosen that the voltage thus detected is large but its detection does not cause appreciable damping of the circuit LC
  • the DC voltage across the resistance R can be something like 50V, whereas the AC voltage between the tap a and ground may be only about 5V r.m.s.
  • the inductance L is adjusted to above the resonance frequency (or if such adjustment cannot be provided, the capacitance C is so adjusted) to give a voltage across the circuit L-C, of about 80 percent of the voltage at resonance.
  • the frequency chosen is approximately 30 KHz, which is low enough for the transmitted voltage and its harmonics not to interfere with radio broadcasting, yet high enough to be able to use high-Q inductances of reduced size.
  • the negative voltage detected at the ungrounded terminal c of network R C is transmitted to a DC amplitier A via a differentiation network (I -R).
  • I -R The function of this network, whose time constant is on the order of seconds, is to transmit at a point d only relatively rapid variations of the voltage at point c signaling the approach of a person, and not to transmit very slow variations, due for example to variations of the ambient temperature or of the supply voltage (upon exhaustion of the cells).
  • the amplifier A energizing a relay R is so designed that for zero or negative voltage at d the voltage across the relay R1 is zero, whereas for even a very small positive voltage (e.g. on the order of 0.1V) at the point d the amplifier A energizes the relay Rll sufficiently for the same to become operative.
  • the input impedance of the amplifier A is very high several megohms so that a very high detected voltage can be produced at the point c with low power consumption.
  • the magnitude of the resistance R should therefore itself also be very high.
  • the amplifier A is a conventional NPN transistor connected as a cathode follower, so as to have a high input impedance, followed by another NPN transistor arranged as a voltage amplifier, in turn followed by a voltage-amplifying PNP transistor driving the relay R
  • One of the stages of amplifier A includes an integrating network Int, having a time constant of 0.2 to 0.5 sec, for general interference suppression.
  • Relay R1 has two contacts r r the former actuating a responder, e.g. triggering an alarm AL, whereas the latter preserves the response by the application of an appropriate voltage +v to one of the transistors of amplifier A This obviates the need for a direct holding contact on the relay; the holding effect of voltage +v can be controlled by any parameter, e.g. as described below with reference to FIG. 6.
  • a diode D can provide very rapid absorption of negative potential variations at that point so that when such variations occur, for instance, at switch-on, the apparatus is immediately ready for operation i.e., there is zero voltage at the point d.
  • the detector is self-restoring to the standby or monitoring state, it is preferable for many uses of the invention to have a signal of limited duration rather than a steady signal.
  • Various auxiliary means are known for providing a delay giving a signal lasting for a few tens of seconds; in the present case, however, there is a very simple way of achieving this result with virtually no addition of extra items.
  • the system consumes, say, 1 mA on standby, its consumption is e.g. 30 mA when relay R1 operates, because of the energy used up by this relay.
  • a resistance Rs (FIG. 5) is connected in series with the associated power supply S and is of such magnitude that the supply voltage energizing the detector part Det of the system drops by e.g. 10 percent when the relay is thus energized, all the AC and DC voltages will decrease in substantially the same proportion. More particularly, the voltage integrated at the point c, which was 50 V, becomes -45 V, and the initial voltage change which triggered the alarm and which was just a few tenths of a volt is converted into a much greater swing as a result of the voltage drop developed across resistor Rs.
  • capacitor C To dissipate this voltage by way of the differentiation network, capacitor C must first discharge through resistor R sufficiently for the voltage at d to decrease to e.g. 0.1 V or less. When this voltage has been reached,
  • the relay R1 returns to normal and stops the responder.
  • the detector operates basically on the principle of varying the state of tuning of a tuned transmitting circuit, the main variation being capacitive and the secondary variation being in the damping, there is no need to use a vertical antenna in association with a counterpoise forming a horizontal mass plane.
  • the antenna its counterpoise can be e.g. two metal strips or even wires connected to the two ends of the oscillatory circuit and extending parallel to each other. The strips can be placed on the ground, if the same is not conductive (floor), or positioned vertically on either side of an entrance which it is required to protect.
  • the sensing element formed by the antenna and its counterpoise can be devised differently to suit individual cases. Inter alia, in a room or the like the antenna can be in the ceiling and the counterpoise can be below it on the floor.
  • the system is highly versatile. For instance, with a vertical antenna 1.50 meters long and a ground plane which is either inherently conductive or made so, e.g.- by latticework, a person can be detected at up to about 8 meters from the antenna i.e., assuming that the antenna is accessible from all directions, the operative area of the system is on the order of 200 m.
  • An obvious use of the system is for protection against unwanted intrusions. It can also be used to detect movement, e.g. for automatic door opening, lighting of passageways (timers), or counting people.
  • its delay feature makes it very suitable for advertising purposes as, for instance, to trigger a tape recorder which broadcasts an advertising announcement or a commentary on an article on show in a museum.
  • FIG. 6 shows one such adaptation of the invention.
  • An endless magnetic tape m contains a text which may be repeated a number of times, the spacing between repetitions being such that the end of the text and the start of its repetition are separated by an interval of a few seconds.
  • a tape recorder MAG containing the tape m is under the control of the movement detector hereinbefore described.
  • the two systems are located near the place where possible clients may pass by.
  • the relay of the detector Det starts the tape recorder MAG.
  • the tape recorder transmits no signal to loudspeaker H, but the relay R1 remains held by the delay means hereinbefore described; in this case the delay is fairly short, e.g. seconds.
  • the tape recorder MAG starts to read out the text through a loudspeaker H.
  • the detector relay R1 locks as a result of detection of the transmitted modulation; the voltage across the loudspeaker H is detected by a network DAL-C, and applied through holding contact r, of relay R1 of FIG. 4 to hold the relay while the lowfrequency modulation i.e., the transmitted message continues.
  • the holding voltage disappears, the relay R1 releases and the tape recorder MAG stops. The procedure can restart when someone else passes nearby.
  • the time constant of the detector network R4 C4 must be long enough for the hold not to be likely to disappear between individual words of the message, and short enough for terminating the hold at the end of the message, e.g. after 2 seconds of silence, so that the system is restored to standby for someone else to pass by. 7
  • recording using a continuous tape can be replaced by any other kind of sound recording, such as one using a disk with automatic return of the pickup arm.
  • a system for detecting movements in a monitored space comprising:
  • an oscillator provided with a tank circuit tuned to a predetermined radio frequency
  • a feedback path between said tuned circuit and said oscillator for delivering to an input of said oscillator a control voltage establishing an operating frequency intermediate said predetermined radio frequency and said resonance frequency to be radiated by said antenna, said control voltage varying with changes in said effective capacitance for shifting said operating frequency toward said predetermined radio frequency in response to a movement to be detected;
  • said load circuit including responder means for indicating a voltage change in said tuned circuit due to a movement to be detected.
  • said differentiation network has a resistive branch and a capacitive branch, said diode means being connected across said resistive branch.
  • said responder means includes a normally de-energized relay and trigger means for energizing said relay in response to a significant voltage reduction in said tuned circuit due to a movement to be detected, said relay and said oscillator being provided with a common direct-current supply, further comprising resistance means in series with said common supply for generating a voltage drop 9 upon energization of said relay to intensify said significant voltage reduction.
  • said differentiation network includes a capacitor and a resistor
  • said load circuit further comprising a rectifying connection and an integrating network inserted between said tuned circuit and said capacitor for charging the latter upon occurrence of said significant voltage reduction, said resistor enabling delayed discharging of said capacitor upon restoration of said effective capacitance to normal whereby said relay remains energized beyond said restoration.
  • said source comprises a recording medium carrying a message to be announced and circuitry for deriving said holding voltage from message signals in the output of said recording means.
  • a system as defined in claim 1 wherein said feedback path is connected to said tuned circuit at a point whose alternating voltage decreases upon variation of said effective capacitance by a movement to be detected, thereby diminishing said control voltage in response to such movement.
  • said oscillator comprises a transistor with a base lead connected to said tank circuit for receiving a regenerative feedback voltage therefrom, said feedback path including a reactance connected to said base lead for superimposing said control voltage upon said regenerative feedback voltage.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
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  • General Physics & Mathematics (AREA)
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  • Environmental & Geological Engineering (AREA)
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US00341744A 1972-03-21 1973-03-15 Radio-wave detector for discovering the movement of persons or objects in a confined space Expired - Lifetime US3828335A (en)

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FR7209800A FR2176499B1 (enrdf_load_stackoverflow) 1972-03-21 1972-03-21

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GB (1) GB1378280A (enrdf_load_stackoverflow)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4215341A (en) * 1977-01-19 1980-07-29 Cole Martin T Intrusion or movement detector
EP0041781A3 (en) * 1980-06-11 1982-07-14 Gentex Corporation Intrusion detection and alarm system
US4380721A (en) * 1980-12-29 1983-04-19 Bullock John W Proximity switch
US5932853A (en) * 1996-09-27 1999-08-03 Inventio Ag Identification system for a lift installation
US6339376B1 (en) * 1999-10-26 2002-01-15 Toyota Jidosha Kabushiki Kaisha Automotive cargo space occupant detector
US20170294808A1 (en) * 2008-03-17 2017-10-12 Powermat Technologies, Ltd. Transmission-guard system and method for an inductive power supply
US20190149196A1 (en) * 2017-11-14 2019-05-16 Nxp B.V. Device detection in contactless communication systems
US11067713B2 (en) * 2013-09-24 2021-07-20 Ontech Security, Sl Electrostatic field sensor and security system in interior and exterior spaces
US11387688B2 (en) 2008-07-02 2022-07-12 Powermat Technologies, Ltd. System and method for coded communication signals regulating inductive power transmissions
US11979201B2 (en) 2008-07-02 2024-05-07 Powermat Technologies Ltd. System and method for coded communication signals regulating inductive power transmissions

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60111983A (ja) * 1983-11-22 1985-06-18 Honda Motor Co Ltd 物体検知装置
GB2455540A (en) * 2007-12-13 2009-06-17 Philip Hodgetts Proximity sensing system to control electricity supply

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2152296A (en) * 1936-09-21 1939-03-28 Talking Advertising Corp Advertising device
US2992420A (en) * 1957-11-08 1961-07-11 Holmes Electric Protective Com Capacity type burglar alarm systems
US3005191A (en) * 1957-07-10 1961-10-17 Mosler Res Products Inc Security alarm system
US3324647A (en) * 1964-08-11 1967-06-13 Parmet Company Proximity detector
US3495353A (en) * 1968-09-23 1970-02-17 Stanley Works Door operating mechanism
US3573783A (en) * 1967-09-13 1971-04-06 R F Controls Inc Proximity sensor

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE970232C (de) * 1937-05-01 1958-08-28 Emi Ltd Anordnung zur Ankopplung einer Hochfrequenzquelle an einen Verbraucher
DE1566723A1 (de) * 1967-04-13 1970-08-06 Johannes Rode Raumueberwachungsanlage

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2152296A (en) * 1936-09-21 1939-03-28 Talking Advertising Corp Advertising device
US3005191A (en) * 1957-07-10 1961-10-17 Mosler Res Products Inc Security alarm system
US2992420A (en) * 1957-11-08 1961-07-11 Holmes Electric Protective Com Capacity type burglar alarm systems
US3324647A (en) * 1964-08-11 1967-06-13 Parmet Company Proximity detector
US3573783A (en) * 1967-09-13 1971-04-06 R F Controls Inc Proximity sensor
US3495353A (en) * 1968-09-23 1970-02-17 Stanley Works Door operating mechanism

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4215341A (en) * 1977-01-19 1980-07-29 Cole Martin T Intrusion or movement detector
EP0041781A3 (en) * 1980-06-11 1982-07-14 Gentex Corporation Intrusion detection and alarm system
US4380721A (en) * 1980-12-29 1983-04-19 Bullock John W Proximity switch
US5932853A (en) * 1996-09-27 1999-08-03 Inventio Ag Identification system for a lift installation
US6339376B1 (en) * 1999-10-26 2002-01-15 Toyota Jidosha Kabushiki Kaisha Automotive cargo space occupant detector
US20170294808A1 (en) * 2008-03-17 2017-10-12 Powermat Technologies, Ltd. Transmission-guard system and method for an inductive power supply
US11837399B2 (en) * 2008-03-17 2023-12-05 Powermat Technologies, Ltd. Transmission-guard system and method for an inductive power supply
US11387688B2 (en) 2008-07-02 2022-07-12 Powermat Technologies, Ltd. System and method for coded communication signals regulating inductive power transmissions
US11979201B2 (en) 2008-07-02 2024-05-07 Powermat Technologies Ltd. System and method for coded communication signals regulating inductive power transmissions
US11067713B2 (en) * 2013-09-24 2021-07-20 Ontech Security, Sl Electrostatic field sensor and security system in interior and exterior spaces
US20190149196A1 (en) * 2017-11-14 2019-05-16 Nxp B.V. Device detection in contactless communication systems
US10511347B2 (en) * 2017-11-14 2019-12-17 Nxp B.V. Device detection in contactless communication systems

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Publication number Publication date
FR2176499B1 (enrdf_load_stackoverflow) 1975-03-21
GB1378280A (en) 1974-12-27
DE2312484A1 (de) 1973-10-04
FR2176499A1 (enrdf_load_stackoverflow) 1973-11-02

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