PERSONAL EMERGENCY COMMUNICATOR

FIELD OF THE INVENTION

This invention relates a personal emergency communicator and has been devised particularly, though not solely, for use in underground mines. BACKGROUND OF THE INVENTION

There is a fast growing call for underground two-way wireless communication.

This is due to recent tragic accidents which may have been avoided if reasonable bidirectional underground communications were possible. However, underground wireless communication is difficult and complex to achieve, particularly when the specification calls for portable "Walkie Talkie" style equipment. The state of the art has not yet effectively achieved this.

There remains the need for individual miners trapped in locations where they do not have access to the mine's infrastructure to be able to transmit information regarding their location and other information relevant to the emergency situation. In most situations this is not able to be effected via conventional wireless "walkie talkie" type equipment as the usual UHF and VHF radios are limited to line of sight communication and suffer severe distance attenuation due to wave guide and skin effects on electromagnetic waves underground. Very high powers are required to get any degree of ground penetration using an EM wave. Rescue teams use HF walkie talkies (27 or 49MHz) which may penetrate a few metres into the rock but also remain very limited in their use underground.

Furthermore, high powered walkie talkies are bulky and difficult to carry around by miners in their day to day operations.

SUMMARY OF THE INVENTION The present invention therefore provides a personal emergency communicator including a signal generating device and a ground antenna connected to the signal

generating device such that upon a signal being generated from the device the signal is transmitted through the ground via the ground antenna where it can be intercepted and received by a through the ground receiver equipped with an equivalent antenna. In one form of the invention the ground antenna comprises a loop antenna. Preferably the loop antenna comprises a coil of wire adapted to transmit the signal from the signal generating device through the ground.

Preferably the loop antenna is provided with a levelling device arranged to facilitate the levelling of the loop antenna in a horizontal plane.

Alternatively, the through the ground antenna comprises an earth current antenna. Preferably the earth current antenna comprises a pair of ground engagement members adapted to be connected to the signal-generating device.

Preferably, the ground engagement members comprise spikes connected to the signal-generating device by conductive wires.

In use, the operator of the personal emergency communicator can drive or force the spikes into the ground or rock fissures at spaced apart locations so that the signal generated by the device is transmitted into the ground where it can be intercepted and . received by the through the ground receiver.

In one form of the invention the personal emergency communicator is powered by a battery such as the battery normally used in a miner's cap lamp. In an alternative form of the invention the personal emergency communicator is powered by a manually operated crank and generator assembly.

Preferably, the personal emergency communicator incorporates an input device such as a keypad enabling the operator to formulate the message to be transmitted. In the embodiment where the ground antenna comprises a loop antenna, the through the ground receiver, also in the form of a loop antenna, may be provided in a

mobile device able to be moved around on the surface of the mine until the received signal strength is maximised thereby providing a good indication of the location of the personal emergency communicator.

Preferably the loop antenna on the surface device is also provided with a levelling device to enable the loop antenna on the through the ground receiver to be accurately aligned with the loop antenna on the personal emergency communicator.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic representation of a personal emergency communicator according to the invention, utilising an earth current antenna;

Figure 2 is a similar view to Figure 1 but showing a personal emergency communicator utilising a loop antenna, and; Figure 3 is a diagrammatic cross sectional representation through a mine showing the use of loop antennae to locate a personal emergency communicator according to the invention, in the mine.

DETAILED DESCRIPTION

In the preferred form of the invention a personal emergency communicator is provided which is a small and light weight device able to be carried on the person of a miner as part of a survival package. The device typically uses Quadrature Amplitude Modulation, Single Side Band transmission QAM SSB at VLF frequencies (50KHz to 100KHz) for ground path communication at low data rates to conserve energy. It is typically powered by a miner's cap lamp battery (or other battery) as a power source. Alternatively it could be powered by a small "crank and generator" assembly of the type

- A - used in some torches and which could be used to provide power for communication and low intensity light.

The "crank and generator" version may also ease difficulties with intrinsic safety approvals in mines from power sources such as batteries. The personal emergency communicator 1 is typically incorporated in a housing which might, for example, have a crank handle 2 protruding from one side which may be turned by the operator to rotate a generator within the device to provide power for communication transmission. The device may also incorporate a keypad 3 which the user may utilise to formulate a message which could be displayed on a LCD screen 4 in a similar manner to a mobile telephone.

The message may be formulated in any suitable manner such as that equivalent to the SMS messaging system of a cell phone or, in a very simple form of the invention, a preset emergency code may simply be transmitted by activating the device by cranking the handle 2, or connecting a power source such as a battery as previously described. In one form of the invention, the signal from the personal emergency communicator 1 is transmitted into two or more wires 5 each terminating in a ground engagement member, typically in the form of a spike. To maximise the signal strength, the spikes are driven into the ground as far apart as possible.

In use, a trapped miner can formulate a message using the key pad 3 and then transmit that message through the wires 5 to the spikes 6 where it is transmitted into the ground and can be intercepted and received by a "through the ground" receiver having a similar ground engagement antenna.

In an alternative form of the invention as shown in Figure 2 the ground antenna may take the form of a loop antenna 7, again attached to the personal emergency communicator 1 by way of wires 5. The loop antenna typically comprises a multi-

winding loop of wire which is as large as practically possible in diameter in order to maximise the effectiveness of transmitting the signal from the loop antenna through the ground.

It is recognised that this embodiment is not as portable as the embodiment shown in Figure 1 and therefore may not be suitable for carrying on the person of a miner during normal mining operations, but the embodiment shown in Figure 2 may well find application at set locations in a mine where it can be delivered by an underground vehicle.

The loop antenna 7 is preferably provided with a levelling device 8 which may take the form of a simple bubble level to enable an operator of the personal emergency communicator to accurately level the loop 7 in a horizontal plane for location purposes as described further below.

Turning now to Figure 3 there is shown a personal emergency communicator of the type previously described with reference to Figure 2 at 9 with its attached loop antenna at 10. In use, the loop antenna is levelled into a horizontal plane using the bubble level 8 as previously described.

In use, when an emergency occurs in the mine and it is recognised that a signal may be being generated from the personal emergency communicator 9, a second mobile communicator 11 may be provided on the surface, also having a similar loop antenna 12 levelled into a horizontal plane by a levelling device 13. The communicator 11 may then be moved around on the surface 14 of the mine until the signal from the underground personal emergency communicator 9 is detected, and then further moved to maximise the signal strength received from the underground communicator 9.

Because of the directional nature of a signal transmitted by the loop antenna 10 and received by a similar loop antenna 12, the maximising of the signal strength

received at the surface device 11 is a good indication that the two loop antennae are orthogonally aligned on the vertical axis 15. Location of the surface device 11 in this manner will therefore give a reasonably accurate indication of the location of the personal emergency communicator 9 in its underground location within the mine and assist in directing rescue operations. Such operations could include the drilling of a borehole from the surface 14 along the axis 15 into the underground cavity 16 in the direct location of the personal emergency communicator 9.

It is an advantage of using through the ground communication of this type (Quadrature Amplitude Modulation, Single Side Band transmission) that the energy level required to generate a signal is low and can typically be provided either by the battery from a miner's cap lamp or from a crank and generator device such as that shown at 2. This overcomes the problem of the alternative forms of communication such as electromagnetic radiation which require high levels of energy in order to penetrate rock formations.