GB2339288A

GB2339288A - Buried object detector apparatus

Info

Publication number: GB2339288A
Application number: GB9816847A
Authority: GB
Inventors: Christopher Keith Richardson
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 1998-07-06
Filing date: 1998-07-06
Publication date: 2000-01-19
Anticipated expiration: 2018-07-06
Also published as: GB2339288B; GB9816847D0; GB9814532D0

Description

2339288 IMPROVEMENTS IN OR RELATING TO BURIED OBJECT DETECTOR APPARATUS

This invention relates to buried object detection apparatus and more especially, but not exclusively it relates to hand held buried mine detectors.

It has been estimated that there are presently at least fifty million mines lying beneath the surface of the ground which were buried during periods of conflict in various parts of the world, such as Cambodia and Afghanistan as well as many other countries. Since the location of individual mines is difficult to establish, civilian casualties due to mines are still high long after conflict in the countries concerned has ceased.

Since many of the countries concerned are poor third world countries, there is a real humanitarian need for simple inexpensive maintenance free mine detection equipment, and it is an important object of the present invention to provide such equipment.

According to the present invention a buried object detector comprises an electrical energy generator which produces electrical energy in response to movement produced as the buried object detector is scanned to and fro in use, an energy store for storing electrical energy produced by said crenerator, and detection apparatus powered by energy from the energy store and operative to provide a siornal consequent upon detection of a ZD buried object.

The I electrical energy generator may comprise a pendulum and an electrical generator arranged to be driven by the pendulum as it sweeps to and fro in response to movement of the buried object detector, thereby to produce an alternating current which is fed via a transformer and a rectifier to at least one capacitor defining the energy store.

The electrical generator may be a d.c. generator which is driven first in one direction and then the opposite direction thereby to produce the alternating current.

The detection apparatus may comprise at least one RF signal source and means for providing an audio signal, which said source and said means are coupled to the store so as to receive therefrom electrical energy and a detector head including a primary detector loop fed from the RF signal source and secondary loops inductively coupled to the primary loop so as to receive therefrom an induced signal when loop coupling is unbalanced by the close proximity of a buried object, thereby to produce in the secondary loops a signal which is utilised to provide an audio output signal indicative of the presence of the buried object.

The primary and secondary loops may comprise conductors supported on a conventional printed circuit board.

The secondary loops may be coupled in a figure of eight configuration.

The secondary loops may be on the opposite side of the printed circuit board to the primary loop.

Alternatively, the primary loop may be coupled to the RF sianal source via a torroidal transformer throuah which a link C) 0 conductor forming part of the primary loop is arranged to pass, two similar' secondary loops being provided within the primary loop in close proximity thereto so as to be inductively coupled therewith, the primary loops being coupled via by a further torrodial transformer throuah which link conductors forming part of the secondary loops are arranged to pass.

Some embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

FIGURE 1 is a somewhat schematic perspective view of buried mine detection apparatus; FIGURE 2 is a somewhat schematic block circuit diagram of the apparatus as shown in Figure 1; FIGURE 3 is a schematic block circuit diagram of one embodiment of the apparatus as shown in Figure 2; FIGURE 4 is a schematic block circuit diagram showing an alternative embodiment of the apparatus as shown in Figure 2; FIGURE 5 is a plan view of an antenna arrangement suitable for use with the detection apparatus as shown in Figure 1; FIGURE 6a is a crenerally schematic block diaerram of a pendulum generator for use with the apparatus as shown in Figures 1 to 5; and CY FIGURE 6b is a circuit diagram. of a power supply for use 0 with the apparatus as shown in Figures 1 to 5 and embodying the t) 0 pendulum generator as shown in Figure 6a.

Refer-rincr now to Figure 1, apparatus for detecting buried Z3 ?- 0 mines comprises a detector head 1, to which is connected a handle 2 which supports detection apparatus 3. In use of the apparatus an operator scans the detector head over the ground and consequent upon detection of a buried mine, the detection apparatus 3, which is electrically coupled to the detector head 1, provides an audio signal which is fed via conductors 4, to head phones 5, which are worn by an operator.

Referring now to Figure 2, the detection apparatus 3, as shown in Figure 1, comprises a power supply 6, which provides electrical energy in response to movement of the apparatus in use, an RF signal source 7, coupled to feed an antenna arrangement 8 forming part of the detector head 1, as shown in Figure 1, and an RF detector and tone generator 9, which feeds the head phones 5, shown also in Ficrure 1.

The apparatus as just before described with reference to Figure 2, may be configured in various ways and one configuration is shown in Figure 3 wherein parts corresponding to tp Figure 2 bear the same numerical designations. In this configuration of Figure 3, the RF detector and audio tone generator 9 of Ficure 1 is shown within a broken line 10 and comprises an RF detector 11, an audio tone generator 12, and a 1 Hz confidence oscillator 13. The antenna arranaement 8 comprises a primary loop 14, which is fed from the RF signal source 7, and a pair of secondary loops 15 and 16. The antenna arrangement is such that RF sig nals in the secondary loops 1 D5 and 16 prod uced by co upling with the primary loop 14 normally cancel so that no signal is fed to the RF detector 11. However, in operation, when the antenna arranaement is brought into close proximity with a mine, the 0 secondary loops 15 and 16 are inductively unbalanced so that a RF signal is fed to the RF detector 11 which produces an audio output signal from the tone generator 12 so as to indicate by means of the head phones 15 that a mine has been detected.

The confidence oscillator 13 is provided to produce in the head phones clicks at a frequency of about 1 cycle per second when the power supply is operating whereby operational confidence in the apparatus is afforded. This is a desirable feature since the power supply produces electrical energy only in response to movement and it is therefore highly desirable to provide some indication to give confidence to the operator that the apparatus is functioning.

As already explained, the apparatus shown in Figure 2 may be configured in various ways. An alternative configuration to the conflauration described in Figure 3 will now be described with reference to Figure 4 which comprises two RF signal sources 17 and 18. The RF signal source 18 produces a signal at 455 kHz which is fed to a mixer 19, whereas the RF signal source 17 produces a signal at 455 kHz plus 200 Hz which is fed to a primary loop 20 of an antenna arrangement 21 comprising Z), Z7 secondary loops 22a and 22b which are coupled in a figure of eight configuration so that signals induced therein from the primary loop 20 normally cancel. If however, the antenna arrancrement 21 is unbalanced by being brought into close proximity with a buried mine, the secondary loops 22a and 22b are unbalanced, and a signal is fed therefrom to the mixer 19 so as to produce an audio output signal at a frequency corresponding 0 0 to the difference between the frequencies of the RF signal sources 17 and 18, i.e. 200 Hz. This audio signal is fed via a low pass filter 23 and an amplifier 24 to head phones 25.

In order to provide operational confidence, as hereinbefore explained, a 2 Hz confidence oscillator 26 is provided coupled to an input of the mixer 19 which is fed from the secondary loops 22a, 22b. The oscillator 26 will provide clicks at 2 Hz in the head phones 25 while a movement driven power supply 27, (which provides power for the signal sources 17, 18, the mixer 19, the confidence oscillator 26 and the amplifier 24), is operational.

Although as shown in Figure 4, a figure of eight secondary loop configuration, 22a, 22b may be provided, in an alternative arranorement, a loop configuration as shown in Figure 5 may be used. Referrina now to Figure 5, an antenna arrangement comprises a printed circuit board 28 which is used to support a primary loop 29 within which similar secondary loops 30a and 30b are provided. Signals from the secondary loops 30a and 30b are coupled to detector apparatus (not shown in Figure 5) by means of a torroidal winding 3 1, through the centre of which link conductors 32 and 33 forming parts of the secondary loops 30b and 30a respectively, are arranged to pass. Similarly, RF signals from a signal source (not shown) are fed to the primary loop 29 via a torroidal winding 34, through the centre of which a link conductor 35, forming part of the primary loop 29 is arranged to pass.

Although the power supply 27 as shown in Figure 4, or the power supply 6, as shown in Figures 2 and 3, which produces 0 electrical energy in response to movement of the apparatus, may take vario, us forms, one particular power supply a-rrancFement is shown in Figures 6a and 6b, which will now be described.

Referring firstly to Figure 6a, a generator 36, which produces electrical energy in response to movement comprises a d.c. generator 3 7, a drive shaft 3 7a of which is coupled via a crank 3 8 to a weight 3 9, which forms part of a pendulum 40 mounted on a pivot 41. The arrangement is such that as the pendulum 40 swings about the pivot 41 in response to movement of apparatus in which it is mounted, the drive shaft 37a of the generator 37 is constrained to rotate first in one direction and then in the other so that the generator produces an alternating electrical output.

Referring now to Figure 6b, the generator 37 is connected to a primary winding 42 of a transformer 43 so as to produce an alternatincr electrical output in a secondary winding 44 of the transformer 43, which is rectified by diode rectifiers 45 and 46, thereby to produce d.c. electrical energy which is stored in a pair of capacitors 47, 48 and made available at power supply output terminals 49 and 50.

Although the frequency of the RF signal source which feeds the antenna as hereinbefore described is about 450 kHz, it is contemplated that higher frequencies of up to say 20 NIHz may be used in accordance with the character of the object to be detected. For example, 450 kHz is especially suitable for the detection of metal objects, whereas higher frequencies may be more suitable for detecting differences in the conductivity or permativity of the ground produced by the presence of buried non-metallic objects.

in order to provide optimum detection of objects fabricated from different materials therefore, the frequency used may be chirped or scanned through a range of frequencies chosen in accordance with the characteristics of an object or objects to be detected.

It will be appreciated that by providing a motion powered buried object detector for mine detection purposes which is simple to use, cheap to produce and maintenance free, many lives may be saved and many casualties involving maiming or disablement may be avoided.

I

Claims

WHAT WE CLAIM IS

1. A buried object detector comprising an electrical energy generator which produces electrical energy in response to movement produced as the buried object detector is scanned to and fro in use, an energy store for storing electrical energy produced by said generator, and detection apparatus powered by energy from the energy store and operative to provide a signal consequent upon detection of a buried object.

2. A buried object detector as claimed in Claim 1, wherein the electrical energy generator comprises a pendulum and an electrical generator arranged to be driven by the pendulum as it sweeps to and fro in response to movement of the buried object detector, thereby to produce an altemating current which is fed via a transformer and a rectifier to at least one capacitor defining the energy store.

3. A buried object detector as claimed in Claim 2, wherein the electrical generator is a d.c. generator which is driven first in one direction and then the opposite direction thereby to produce the alternating current.

0

4. A buried object detector as claimed in Claim 3, wherein the detection apparatus comprises at least one RF signal source and means for providing an audio signal, which said source and said 0 means are coupled to the store so as to receive therefrom electrical -energy and a detector head including a primary detector loop fed from the RF signal source and secondary loops inductively coupled to the primary loop so as to receive therefrom an induced signal when loop coupling is unbalanced by the close proximity of a buried object, thereby to produce in the secondary loops a signal which is utilised to provide an audio output signal indicative of the presence of the buried object.

5. A buried object detector as claimed in Claim 4, wherein the primary and secondary loops comprise conductors supported on a conventional printed circuit board.

6. A buried object detector as claimed in Claim 5, wherein the secondary loops are on the opposite side of the printed circuit board to the primary loop.

7. A buried object detector as claimed in Claim 6, wherein the secondary loops are coupled in a figure of eight configuration.

8. A buried object detector as claimed in any of Claims 1 to 6, wherein, the primary loop is coupled to the RF signal source via a torroidal transformer through which a link conductor forming part 0 tn of the primary loop is arranged to pass, two similar secondary loops being provided within the primary loop in close proximity thereto so as to be inductively coupled therewith, the primary loops being coupled via by a further tor-rodial transformer 0 through which link conductors forming part of the secondary loops are rranged to pass.

9. A buried object detector as claimed in any of Claims 4 to 8, wherein the detection apparatus comprises two RF signal sources, the relative frequency of which is arranged to differ by an audio frequency, one of said signal sources being arranged to feed the primary detector loop and the other of said signal sources being arranged to feed a mixer fed from the secondary loops so that an output signal from the mixer is produced when coupling from the secondary loops is unbalanced consequent upon detection of a buried object, which output signal from the mixer is fed via filter means and an amplifier to head phones.

10. A buried object detector as claimed in any preceding Claim, comprising a confidence oscillator fed from the electrical energy generator and arranged to provide a low frequency signal indicating that the detector is operational.

I

11. A buried object detector substantially as hereinbefore described with reference to the accompanying drawings.

0 0