GB2112144A - Detector - Google Patents

Abstract

A detector, primarily for detecting the placement of an explosive device in a zone of a building or vehicle, has a transmitting element 10 transmitting electromagnetic radiation and at least one receiving element 12, the elements being located in spaced relationship near to the zone to be protected so as to form a transducer. Control means monitor signals received at the transducer and are operable to actuate an alarm system when the electromagnetic field in the zone under protection is disturbed, for example by the placement of an explosive device. A number of such detectors can be coupled via an encoding network 40 to a common transmitter 42 radiating to a receiver external of the building zone or vehicle. The receiver decodes and displays the alarm information. <IMAGE>

Description

SPECIFICATION Detector The present invention relates to a detector for detecting the presence of an object or objects placed in, or in proximity to, a restricted zone or area. The invention is concerned particularly, though not exclusively, with a detector for detecting the placement of an object, such as an explosive device, in proximity to a road vehicle.

In view of the increasing practice of placing explosive devices in unattended vehicles there arises a requirement to detect the placement of an explosive device.

In accordance with the broadest aspect of the present invention there is provided a detector for detecting the presence of an object placed in or in proximity to a restricted zone or area, the detector comprising a transmitting element capable of transmitting electro-magnetic radiation and a receiving element capable of receiving transmitted radiation, in use, the elements being located in spaced relationship near to a zone to be protected so as to form a transducer, and control means monitoring the signals transmitted by and received at the transducer, the control means being operable to actuate an alarm system in response to the placement of an object in the electromagnetic field.

In one embodiment of the invention for use primarily on a road vehicle the alarm system comprises an aerial fitted to the vehicle and arranged to radiate an alarm signal to a receiver unit located at a position remote from the vehicle, the alarm signal lying at a different electromagnetic frequency from that utilised by the transmitting and receiving elements. The receiving unit is conveniently hand held.

In a preferred embodiment of the invention a plurality of sets of transmitting and receiving elements are provided, each set being arranged to cover a specific part of the zone to be protected.

Where, for example, the detector is applied to a road vehicle, the specific parts may be the front and rear bumpers, the offside and nearside sills and the four wheel arches so that in this instance eight sets of elements would be provided.

Accordingly, the control means is arranged to issue an alarm signal in response to a disturbance arising at any one of the specific parts protected.

The control means may discriminate between the specific parts, and issue an appropriate alarm signal or signals, this information being indicated at the receiver unit which may include a display arrangement for this purpose. For example, should two devices be placed upon a vehicle, then the receiver unit would indicate this information to the vehicle driver, for example a chauffeur, together with information regarding the location of the devices to enable the bomb squad to be called to defuse the devices.

The invention will now be described further by way of example with reference to the accompanying drawings in which: Fig. 1 is a schematic electrical layout of one channel of a control unit for monitoring signals transmitted by and received at each set of transmitting and receiving elements, Fig. 2 is a schematic electrical layout of one channel of a receiving unit for use with the control unit of Fig. 1, Fig. 3 is a plan view of a motor car with eight sets of transmitting and receiving elements, Fig. 4 is a diagrammatic illustration of a receiving unit, including a visual display, for use with a motor car fitted as illustrated in Fig. 3 and Fig. 5 is a schematic electrical layout of one channel of a modified control unit to that illustrated in Fig. 1.

It is known that when an object is placed in an electromagnetic field, the field pattern is disturbed which disturbance can be detected by a receiving element.

The degree of disturbance depends on: (a) The transmitting medium (in the case of this invention mainly air).

(b) The shape of the transmitting and receiving elements.

(c) The frequency of radiation.

(d) The relative positions of: (i) the transmitting element.

(ii) the receiving element.

(iii) the object to be detected.

and (i), (ii) and (iii) with any other large objects.

(e) The size and composition of the object to be detected.

In practice difficulties arise in detecting the placement of objects more than 2 or 3 inches away from a specific area (the underside of a car say) without grossly affecting the invironment (e.g.

normal passers-by would be detected rather than a package) and false alarms would result.

The object of this invention is to provide a device which will detect the placement of a small object or package (metallic or non-metallic) 1 8 to 20 inches away from a specific area (say a portion of the underside of a car or a wheel arch).

One channel of a multi channel detector as fitted to a motor vehicle is shown in detail in Fig. 1 A transmitting element 10 and a receiving element 12 (together forming a transducer) are connected in spaced relationship on the underside of the motor vehicle. The transmitting element 10 is fed with an alternating current of 30 KHz and 40 volts from an electronic oscillator 14. The vehicle's own battery supply 1 6 provides the power for the oscillator 14 via an ON-OFF switch 18 and regulator 20. If there are additional channels, the oscillator 14 is connected to feed all of them simulataneously.

In a quiescent state of the detector the receiving element 12 picks up electromagnetic radiation from the transmitting element 10 as an alternating current at 30 KHz but at a low voltage.

This signal is then amplified and filtered at 22 (to reduce the affect of any extraneous electrical noise in the environment) and passed to an amplitude detector 24 in the form of a half-wave rectifier. Hence, the alternating voltage is converted to a direct voltage which is a function of the amplitude of the original received signal. The direct voltage from the amplitude detector 24 is then passed to a further amplifier 26 via a capacitor 28 which will only pass a change or alternating current, so that the output of the amplifier 26 will be near zero when the system is in its quiescent state. If, however, there is an alteration in the voltage received at the receiver element 12 then the amplifier 26 will amplify it.

An amplified voltage resulting from a disturbance at the receiving element 1 2 is passed to a full wave rectifier 30 via capacitor 32 to produce a direct voltage which is a function of the disturbance. A comparator 34 compares the voltage received from the amplifier 30 with a preset voltage set by the trip level potentiometer 36.

The potentiometer 36 is set on the installation of the equipment and is not adjusted thereafter and is necessary to reduce the effect of electronic noise. An output from the comparator 34 will result if the disturbance at the receiving element 1 2 is greater than a predetermined level as set by the trip level potentiometer 36. The comparator output being only a momentary change in voltage is then electronically latched at 38 producing a fixed change in voltage. Additional inputs to the latch (e.g. AUX1 s AUX2) are provided so that additional sensors (e.g. micro switches) can be used which are connected for example to the vehicle doors or bonnet.

The latched outputs from up to eight channels are then brought to an encoder 40 which pulse codes the latched outputs into serial form for transmitting on a 27 MHz carrier wave by a transmitter 42.

Reference is now made to Fig. 2 which shows the receiving unit. The pulsed coded 27 MHz signal from the transmitter 42 (Fig. 1) is detected in a receiver 44 which incorporates a low signal indicator which activates when the receiver is out of range of the transmitter. The output of the receiver 44 is decoded by a decoder 46 to produce eight coded signals. Decoder 46 the dual of the encoder 40 of Fig. 1. Each of the eight signals is in the form of a pulse the width of which indicates which transducer element Fig. 1 has been disturbed. The width of each pulse associated with each channel is determined by eight decoders 48 only one of which is shown in Fig. 2. If the pulse width indicating a disturbance, the decoder 48 provides an output to a switch 50 which energises a visual indicator 52 and audio warning device 54 if the audio ON/OFF switch 56 is closed.A strobe 49 is provided so that each of the eight channels can be made to drive the audio warning device 54.

Fig. 3 shows eitht transducers fixed to the underside of a car in the positions numbered 1 to 8 namely, the front and nearside bumpers, the four wheel arches and the offside and nearside sills.

Each transducer consists of a receiving element 12 and a transmitting element 10 (Fig. 1) made to a specific iength in order to cover the desired portion of the vehicle. Each of the eight transducers (and other sensors as may be desired) are wired to one of the eight channels contained in the transmitter control unit shown in Fig. 1.

It will be appreciated that for each of the eight channels, there is provided an oscillator for energising the transmitter element of the transducer, an amplifier and filter network, half wave rectifier, AC amplifier, full wave rectifier, a comparator (which can be pre-set to the desired sensitivity) a latch (which holds in a fixed state when the transducer has been disturbed) and a re-set to return all circuitry to its quiescent state.

There is also provided in the transmitter control unit an encoder network which enables the information in any combination of the eight channels which might have been disturbed to be transmitted via the transmitter.

The receiver unit of Fig. 4 decodes the information transmitted by the control unit and displays it on a visual indicator having eight lights each corresponding to one of the eight positions shown in Fig. 3. An audible warning indicator 60 is also provided. Additionally, if the receiver does not receive sufficient signal from the control unit because it is too far away or the battery strengths are low, then a low signal indicator 62 will flash.

A control unit is provided which would usually be housed inside the vehicle and in reach of the driver or passenger. This unit contains a charger unit for recharging the internal battery of the receiver unit, the detector system ON/OFF switch, and reset switch. Also provided in this unit is an indicator to show the system is in operation and an indicator to show the system has been triggered.

When the receiver unit is not in use, or it is not desired to remove this unit from the vehicle, it can be housed in the control unit.

When fitted to a motor vehicle, the unit illustrated in Fig. 1 has been found particularly sensitive and can be operated, for example, by a person passing by the vehicle inadvertently brushing against it. The modified control unit of Fig. 5 is designed to overcome this problem and in Fig. 5 like reference numerals have been used to designate like parts to those of Fig. 1.

In Fig. 5 an additional receiving element 11 is provided which is mounted in spaced relationship to the transmitting element 10 and the receiving element 1 2. Alternating current from the receiving element 12 is passed to one input, A, of a two input amplifier 1 3 operating in a differential mode.

Alternating current from the receiving element 11 is passed to the second input, B of the amplifier 13. The output of the amplifier 13 is connected to the amplifier filter 22 in the manner described with respect to Fig. 1.

In operation, should a passer-by brush against a vehicle fitted with the detector, then signals of approximately equal magnitude are received at the two receiving elements 11, 12. These in turn pass signals of approximately equal magnitude to the differential amplifier and hence the amplifier provides no output signal. However,should the passer-by place a device under the vehicle mudguard for example, although signals may well be received at the receiving elements 11, 12, those signals would not be of the same magnitude and accordingly the amplifier 13 would provide an output signal to the amplifier and filter 22 to operate the detector in the manner described with respect to Fig. 1.

If desired, the receiving elements 11, 12 may be in the form of a dipole configuration.

Whilst the invention has been described primarily in relation to the protection of motor vehicles, the invention may equally be applied to unoccupied buildings or structures, for example, by connecting a detector in accordance with the invention in, for example, an entrance porch or doorway.

Whereas in the described embodiment of the invention the use of one receiver unit is described, in practice two or more receiver units may be employed for each zone protected. In the case of a vehicle therefore, not only could the chauffer have a receiver unit but also his passenger. In addition, a further receiver unit may be provided at a central station, for example a police station, to enable a central controller to be altered at the time the explosive device is actually being placed.

Claims (11)

1. A detector for detecting the presence of an object placed in or in proximity to a restricted zone or area, the detector comprising a transmitting element capable of transmitting electromagnetic radiation and a receiving element capable of receiving transmitted radiation, in use, the elements being located in spaced relationship near to a zone to be protected so as to form a transducer, and control means monitoring the signals transmitted by and received at the transducer, the control means being operable to actuate an alarm system in response to the placement of an object in the electromagnetic field.

2. A detector as claimed in claim 1 in which two receiving elements are provided each of which is capable of receiving transmitted radiation from said transmitting element, alternating current from each receiving element being passed to respective inputs of a two-input differential amplifier operating in a differential mode which amplifier passes a control signal to said control means only when the two alternating current inputs thereto are of a different magnitude.

3. A detector as claimed in claim 1 or 2 in which the alarm system comprises an aerial fitted to the vehicle and arranged to radiate an alarm signal to a receiver unit located at a position remote from the vehicle, the alarm signal lying at a different electromagnetic frequency from that utilised by the transmitting and receiving elements.

4 A detector as claimed in claim 3 in which the receiving unit is hand held.

5. A detector as claimed in any one of the preceding claims in which a plurality of sets of transmitting and receiving elements are provided, each set being arranged to cover a specific part of the zone or area to be protected.

6. A detector as claimed in claim 5 in which, when fitted to a raod vehicle, the parts are the front and rear bumpers, the offside and nearside sills and the four wheel arches.

7. A detector as claimed in claim 5 or 6 in which the control means is arranged to issue an alarm signal in response to a disturbance arising at any one of the specific parts protected.

8. A detector as claimed in claim 7 in which the control means discriminates between the specific parts and issues an appropriate alarm signal or signals accordingly, this information being indicated at the receiver unit which may include a display arrangement for this purpose.

9. A detector for detecting the presence of an object placed in or in proximity to a restricted zone or area substantially as herein described with reference to and as illustrated in any one of the accompanying drawings.

1 0. A road vehicle wherever provided with a detector as claimed in claim 1.

11. A building or other structure wherever provided with a detector as claimed in claim 1.