WO2006003448A1

WO2006003448A1 - Proximity sensor

Info

Publication number: WO2006003448A1
Application number: PCT/GB2005/002642
Authority: WO
Inventors: William John Martin; Mark Johnson; Roy Lowey; Stephen Roy Pettitt
Original assignee: William John Martin; Mark Johnson; Roy Lowey; Stephen Roy Pettitt
Priority date: 2004-07-06
Filing date: 2005-07-06
Publication date: 2006-01-12
Also published as: GB0415138D0

Abstract

Disclosed is a proximity sensor for determining proximity to an electromagnetic field, the sensor being arranged to: measure the strength of the field; compare the measured field strength with a predetermined threshold; and create an output signal depending on the result of said comparison. Also disclosed is a corresponding method.

Description

Proximity Sensor

The present invention relates to apparatus for sensing presence in, or proximity to, a particular defined environment. In particular, but not exclusively, the defined environment is a domestic or commercial building including a mains-voltage source. Proximity sensors according to embodiments of the invention find may be used in providing a security system and for alerting wildlife to the presence of a possible predator. Other uses will be apparent to the skilled person.

According to a first aspect of the present invention, there is provided a proximity sensor for determining proximity to an electromagnetic field, the sensor being arranged to: measure the strength of the field/ compare the measured field strength with a predetermined threshold; and create an output signal depending on the result of said comparison.

Preferably, the output signal is arranged to toggle between two values indicating whether the measured signal is higher or lower than the predetermined threshold, and hence indicate whether the sensor is inside or outside an area associated with said field.

Preferably, the electromagnetic field is an electromagnetic field associated with an Alternating Current (AC) power supply.

Preferably, the power supply is a mains electric power supply rated in the range of 100 to 250V at 10 to 100Hz. Preferably, the apparatus is a security system for detecting removal of an associated article from an area defined by the electromagnetic field.

Preferably, the apparatus further comprises a positioning module for determining a location of the apparatus .

Preferably, the positioning module comprises a GPS receiver.

Preferably, the apparatus further comprises a communication module for conveying information to a remote monitoring system.

Preferably, the communication module comprises a cellular telephone engine.

Preferably, the apparatus is arranged to be located internally to the associated article.

Preferably, the apparatus is arranged to be powered from a power supply of the associated article.

Preferably, the apparatus further comprises a backup battery power supply.

Preferably, the apparatus is arranged to be mounted on a collar for a domestic pet and further comprises a sound- emitting device for alerting potential prey to the presence of the pet. Preferably, the apparatus is operable to activate the sound-emitting device only when the sensor determines that it is outside the defined area.

Preferably, the apparatus further includes a light- emitting device.

Preferably, the light-emitting device is operable to emit light in the ultra-violet region.

Preferably, the wavelength of the light emitted substantially includes the range 320-450nm.

Preferably, the sensor is further operable to detect supplemental data, which is added to or modulated onto the AC power supply.

Preferably, the supplemental data is indicative of one of: electrical circuit, location, building, address or system owner.

According to a second aspect of the present invention, there is provided a method of determining proximity to a defined area, comprising the steps of: measuring an electromagnetic field strength, present in the defined area; comparing said measured field strength with a predetermined threshold; determining presence within the field if the measured field strength exceeds the threshold.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows a building and the extent of an associated electromagnetic field according to an embodiment of the invention;

Figure 2 shows an item provided with a security system according to an embodiment of the present invention;

Figure 3 shows an electricity distribution system according to an embodiment of the invention;

Figure 4 shows a shows a schematic representation of a security system according to an embodiment of the invention; and

Figure 5 shows a detailed circuit arrangement of a detector for measuring electromagnetic field strength.

Figure 1 shows a plan view of a building 10, in which is installed, in the usual way, a mains electrical circuit. Depending on the location and/or configuration of the circuit, the voltage and frequency of the mains circuit can differ. For instance, in the United Kingdom, the mains electric specification is nominally 240V at 50Hz. In the United States of America, the mains operates nominally at 110V at 60Hz. There are other variations, but in general, anywhere in the world, the mains voltage is in the range 100 to 250V and has a frequency in the range of 10 to 100Hz. The mains electricity in a typical domestic environment is provided to power certain fixed installations, such as lights, and other devices, which may be plugged into one of a range of provided socket outlet points. Different mains circuits are provided for different purposes, and may be rated to provide different levels of current. For instance, a circuit for providing power to an oven will be rated at a higher current than one providing power to a number of ceiling lights only.

Regardless of the rating of a particular circuit, the circuit carrying Alternating Current (AC) mains electricity has an associated electromagnetic (EM) field. The strength of the EM field varies according to the well- known inverse-square law i.e. the strength of the field is proportional to the inverse of the square of the distance from the radiator (i.e. the cabling carrying the power) . The dotted line 20 in Figure 1 represents a particular value of electromagnetic field strength associated with the mains wiring provided in building 10. The mains wiring 10 is provided in the form of a ring main and provides power to a number of socket outlets (not shown) . In certain installations, the electric part of the EM field will dominate, and in other installations, the magnetic part will. In general, in the following description, any reference to electromagnetic field should be understood to include a reference to an electric and/or a magnetic field.

Embodiments of the present invention make use of the fact that the electromagnetic field can be measured and monitored to determine the proximity to the radiating source i.e. the cabling. Since, in most powered environments, the cabling which carries the electricity is relatively well distributed about the building, the field is similarly evenly distributed. In practice, there may well be areas of a building which are not powered, but this does not generally pose any problems to the operation of embodiments of the invention.

In a first embodiment of the invention, use of a proximity sensor, sensitive to the presence of the electromagnetic field of the mains wiring system, is used to provide a security system which is triggered upon removal of the secured item from an area defined by the electromagnetic field associated with the electrical supply.

Figure 2 shows how a valuable item, in this case a personal computer 100, may be equipped with a security apparatus 200, according to an embodiment of the invention. The security system is preferably installed internally in the item to be protected, but it may be fastened securely to the item, if it is not possible to install it internally.

The computer 100 is connected in the usual way by cable 210 to a power outlet 250. The power outlet or socket 250 is then connected to a mains supply circuit 260.

The security apparatus 200 comprises a detector 300, sensitive to the electromagnetic field generated by the electrical mains system in the premises housing the equipment 100. The detector, 300 is operable to detect the presence of said electromagnetic field, and as long as the field is detectable above a preset threshold, the security apparatus is aware that the equipment 100 is located within a defined area.

It is important to note that the security apparatus 200 does not need to be connected to the mains electrical supply in order to function; it merely needs to be able to monitor the electromagnetic field strength due to it.

However, the security apparatus may be configured to draw its operating power from the mains supply, in which case, it will be provided with a battery backup supply, in case of mains power failure.

In domestic environments the electrical mains is generally distributed around the building in a relatively regular manner, in that each room is normally connected to the mains electrical system. However, in some residential environments and in industrial or commercial environments, such as warehouses, it is possible that certain areas are not subject to an electromagnetic field as required. This may be because whole areas are not wired to the mains electrical system or it could be that the cables are carried in earthed metal conduits which prevent radiation of the field.

In such scenarios, it may be possible to run a suitable unshielded length of cable, or several cables, around the area lacking a suitably strong field so that an electromagnetic field may be Artificially' created.

If the detector 300 detects a drop in the measured electromagnetic field strength, to a level below the preset threshold, then there are two likely explanations. The first is that the item 100 has been moved to a point where the electromagnetic field strength has fallen below the preset threshold, perhaps indicating that the item has been removed from its allocated position. The second possible explanation is that the power supply, supplying power to the electrical mains circuit has been switched off. This may be due to planned maintenance or it could indicate an attempt to bypass other security systems in the premises.

In the second scenario, if the mains power is cut, then the security apparatus 200 will no longer register the presence of a suitable electromagnetic field, and so will assume that it has been removed, triggering certain events as will be described. However, there may be legitimate reasons why the mains power needs disconnecting, such as periodic maintenance, power-cuts or an overloaded circuit resulting in a shutdown.

In order to distinguish between these various possible causes of mains power removal, an arrangement as shown in Figure 3 may be employed.

The electricity supply 220 into the building, enters from the street, usually via an underground cable. It is connected to a master fuse 222, which has a very high rating, and is intended for replacement only by the electricity supply company. The supply 224 leaving the master fuse 222, is connected to a consumer unit or fuse box 230, where individual circuits are created and distributed to various points in the building via a plurality of cables 260. A mains signal detector 240 is provided adjacent the supply cable 224. The mains signal detector is operable to detect the presence of AC in the cable 224. By monitoring the status of the supply cable 224 in conjunction with the status of individual security apparatus 200 in the protected building, it is possible to determine whether there has been a power cut, in which case the detector 240 will detect no signal, or if the power has been cut at the consumer unit 230, in which case there will be a signal detected by detector 240. In the event that maintenance work is in progress which required cutting one or more circuits at the consumer unit 230, notice should be given to a central monitoring station so that allowance can be made for possible false-alarms resulting from the power disconnection.

Figure 4 shows a block diagram of the security apparatus 200. The apparatus 200 comprises a number of functional blocks: mains electromagnetic field strength detector 300; Positioning module 320; communication module 340; and power supply 360. In different embodiments of the invention, one or more of the positioning 320 and communication 340 modules may be absent.

In the preferred embodiment shown in Figure 4, the detector 300 is supplied with an antenna 310 arranged to detect the presence and strength of an electromagnetic field due to the presence of an alternating current mains electricity supply. This electromagnetic field is sometimes known as ^Λmains hum' , and can pose a problem for sensitive electrical equipment where the 50 or 60Hz signal, or harmonics thereof, can cause interference to wanted signals. In embodiments of the invention, however, the presence of this otherwise troublesome signal is turned into an advantage.

The detector 300 includes a threshold detector which can be set by a user, or preset by the manufacturer or installer, which determines a level of electromagnetic field strength below which the apparatus 200 is deemed to be ^Λout of range' of the field 20.

The detector 300 may be made to be sensitive to the fundamental frequency of the mains supply (normally 50 or 60Hz) , or to a higher frequency harmonic. The increased use of switched-mode power supplies has resulted in the increased presence of higher order harmonics in the mains supply.

Figure 5 shows a detailed circuit arrangement for part of the detector 300. The circuit includes a high-impedance operational amplifier followed by a 50 Ohm bandpass amplifier and rectifier. The bandpass filter is centred at a frequency of 50Hz, with the response dropping by about 10% at a frequency of 60Hz. Such a response enables a single design to be used in both 50Hz and 60Hz environments .

The output of the circuit (labelled 0 -IV to PIC analog input) is a voltage indicative of the electromagnetic field strength due to the electrical mains signal. It is this signal which forms an input to a comparator, where it is compared to a threshold to determine whether the sensor is outside a permitted range from the field. The output from the comparator is a logical 1 or 0, indicating position inside or outside the permitted area. The antenna 310 is suitably a short wire antenna, which may be constructed as a trace on a printed circuit board.

When the apparatus 200, and hence the valuable item 100 to which it is attached/integrated, is removed from the presence of the electromagnetic field 20 as detected by detector 300, the apparatus 200 acts to send a pre-coded message to a control centre via communication module 340.

The control module 340 is preferably a mobile telephone engine, examples of which are readily available in single- chip format, or as off-the-shelf circuits available for integration into ASICs (Application Specific Integrated Circuits) . In the embodiment shown here, the communication module 340 is a GSM or third generation mobile phone engine and incorporates an identity module 342, known as a SIM (Subscriber Identity Module) card.

The type of message transmitted to the control centre could include details of time, date, subscriber identity, registered location and, if the positioning module 320 is present, the present location of the apparatus. The message may be sent in any suitable format, such as SMS, MMS or as a recorded/synthesised voice message.

The control centre, located at a remote site, acts on the received messages to inform police and/or other authorities of the possible theft of the identified equipment 100. Appropriate action may then be taken as necessary. The positioning module 320 comprises a GPS (Global Positioning System) receiver which receives radio signals from a plurality of orbiting satellites to determine a location, accurate to a few metres. This module is activated by a signal from the detector 300 indicating that the electromagnetic field 20 strength has dropped below the preset threshold. The positioning module 320 then sends periodic position updates to the communication module 340 so that the present position of the apparatus 200 may be transmitted to the remote control centre.

The presence of GPS information in the information transmitted by the apparatus 200, if removed from its designated secure location, may be used by law-enforcement authorities to track the location of the stolen article in real-time. The location information may be cross- referenced to the location of CCTV (closed-circuit television) systems, which are becoming increasingly commonplace, particularly in urban areas. In this way, it may be possible to acquire visual identification of the remover (s) of the protected item 100.

As an alternative to providing a separate positioning module 320, positional information can be derived from the cellular base station to which the mobile phone engine 340 is currently connected. In this way, relatively coarse positional data can be provided which narrows down the location of the item to a cellular service area. In urban situations, where so-called micro-sites are commonly in use, this can provide valuable positional data and negates the need to provide a separate GPS receiver, lowering the overall cost of the system. In a further embodiment of the invention, the presence or otherwise of an electromagnetic field due to mains wiring is used to control the operation of an audible warning tone emitted from a domestic cat's collar.

It is well known that cats are predatory and it has been estimated that, worldwide, they account for the extinction of more bird species than any other cause except habitat degradation. In the United Kingdom alone, the 8 million domestic cats kept as pets are estimated to kill at least 75 million birds annually. In the USA, the 73 million domestically owned cats are said to kill more than 1.4 billion birds annually. Similar figures apply in other countries where cats are commonly kept as pets.

Cat owners wishing to take steps to prevent or limit predation by their pets are restricted in the practical steps they can take. Traditional techniques include adding a bell to the cat's collar to scare away potential prey before the cat can attack. The presence of the bell on the collar can be annoying to the cat owner as the bell is always active and can be heard whenever the cat moved around the house.

Co-assigned US patent 6519206 discloses a solution whereby a sonic alert on the cat' s collar is activated or deactivated as the cat passes through a particular entrance, such as a cat flap. In this way, when the cat is in the house, the sonic alarm is deactivated, minimising irritation to the owner, but activated when the animal goes outside, thus preventing or limiting predation. However, a drawback with the solution disclosed in US 6519206, is that either the animal has to enter and leave the house through a single entry point, which is equipped with suitable RF apparatus, or multiple such apparatus must be provided at various possible entry points.

Embodiments of the present invention utilise a similar technique to that described above in relation to protection of valuable items to enable/disable a sonic alert on the cat's collar.

The collar is provided with a sensor which is sensitive to the electromagnetic field generated by domestic mains wiring, as described previously. When the cat is in the house, the electromagnetic field strength is stronger than outside the house. A threshold value is determined and preset in the collar-mounted apparatus such that when the cat is in the house, the sonic alarm is silenced. However, when the cat leaves the house by any entry/exit point, and the field strength falls below the threshold level, the sonic alarm is activated, warning any potential prey of the cat's presence.

Embodiments of the invention can also be supplemented with additional features. For instance, the tone of the sonic alarm can be varied from a simple ^Λbeep' , emitted by a piezo-electric sounder, to a more complex, realistic sound of a predator, in order to provide a more natural warning to the potential prey.

A further enhancement is the provision of a light source to the collar. The light source is enabled when the cat is outside the house, as detected by the field strength sensor, and when the ambient light level is below a threshold, as detected by an optical detector, such as an LDR (light dependent resistor) . The light source can provide further warning to potential prey that a cat is in its vicinity.

Tests on birds have shown that the range of light wavelengths to which their eyes are sensitive differs to the range visible to the human eye. In fact, avian vision extends into the ultra violet region (320 - 450nm) , and it is believed that their ability to see in this region assists them with navigation, foraging and hunting.

Embodiments of the invention incorporating a UV light source, such as a flashing UV LED, producing light with a wavelength maximum at 375nm, offer a more effective solution for alerting birdlife to the presence of a cat wearing such a collar. Other potential prey animals may also benefit from such an alerting collar, such as rodents, reptiles and amphibians.

In a further enhancement of embodiments of the present invention, the electrical mains supply may be modulated so that information is coded into the supply voltage signal. Alternatively, additional data can be simply added to the mains signal. The data to be encoded may represent information about the registered address of the valuable item or cat so that embodiments of the invention only operate in proximity to a defined mains voltage source, rather than any mains voltage source. Other data may be encoded in the same way, and may relate to property location, address, a system owner or even a particular electric circuit. The coding which is applied to the mains signal could be a simple analogue modulation, such that a particular frequency is associated with a particular electricity supply. Systems could then be supplied so that a user could select one of a preset number of channels, thus minimising unwanted interaction between neighbouring systems, in much the same way as baby monitors, for instance, allow users a choice of channels.

In a more complex scheme, the information encoded onto the mains signal can be digitally coded, resulting in a more secure system which would be much more difficult to circumvent.

A particularly preferred technique for adding signalling information to the mains signal uses so-called XlO mains- borne signalling technology. This technology is know for use in home-automation systems, whereby individual device may be controlled from a central point. Further information may be obtained from the website: http: /1www.xlO .com.

In principle, systems using XlO technology inject RF signals (approximately 868MHz) into the electrical mains supply at the 50Hz zero-crossing point. Traditionally, the data included in these injected bursts is used to control particular items connected to the mains supply. For instance, by injecting a suitable signal, a lamp may be switched on from a central control point. In more sophisticated systems, burglar alarms may be set, ovens may be switched on or any number of different electrical control operations may be implemented. In embodiments of the present invention, the RF burst injected into the mains electrical system can be used to help ^Λfill in' any dead zones in an operational environment. This is due to the different propagation properties of signals at 50Hz and those at higher RF frequencies as used in XlO systems.

In embodiments of the present invention relating to theft- deterrence/detection, each item to be protected will incorporate a suitable receiver. Likewise, in the pet- collar embodiments of the invention, a suitable receiver will be incorporated into the collar.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any- novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A proximity sensor for determining proximity to an electromagnetic field, the sensor being arranged to:

• measure the strength of the field;

• compare the measured field strength with a predetermined threshold; and

• create an output signal depending on the result of said comparison.

2. A sensor as claimed in claim 1 wherein the output signal is arranged to toggle between two values indicating whether the measured signal is higher or lower than the predetermined threshold, and hence indicate whether the sensor is inside or outside an area associated with said field.

3. A sensor as claimed in claim 1 or 2 wherein the electromagnetic field is an electromagnetic field associated with an Alternating Current (AC) power supply.

4. A sensor as claimed in claim 3 wherein the power supply is a mains electric power supply rated in the range of 100 to 250V at 10 to 100Hz.

5. Apparatus comprising a sensor as claimed in any preceding claim wherein the apparatus is a security system for detecting removal of an associated article from an area defined by the electromagnetic field.

6. Apparatus as claimed in claim 5 wherein the apparatus further comprises a positioning module for determining a location of the apparatus .

7. Apparatus as claimed in claim 6 wherein the positioning module comprises a GPS receiver.

8. Apparatus as claimed in any of claims 5 to 7 wherein the apparatus further comprises a communication module for conveying information to a remote monitoring system.

9. Apparatus as claimed in claim 8 wherein the communication module comprises a cellular telephone engine.

10. Apparatus as claimed in any of claims 5 to 9 wherein the apparatus is arranged to be located internally to the associated article.

11. Apparatus as claimed in any of claims 5 to 10 wherein the apparatus is arranged to be powered from a power supply of the associated article.

12. Apparatus as claimed in claim 11 wherein the apparatus further comprises a backup battery power supply.

13. Apparatus comprising a sensor as claimed in any of claims 1 to 4 wherein the apparatus is arranged to be mounted on a collar for a domestic pet and further comprises a sound-emitting device for alerting potential prey to the presence of the pet.

14. Apparatus as claimed in claim 13 wherein the apparatus is operable to activate the sound-emitting device only when the sensor determines that it is outside the defined area.

15. Apparatus as claimed in any of claims 13 or 14 wherein the apparatus further includes a light-emitting device.

16. Apparatus as claimed in claim 15 wherein the light-emitting device is operable to emit light in the ultra-violet region.

17. Apparatus as claimed in claim 16 wherein the wavelength of the light emitted substantially includes the range 320-450nm.

18. Apparatus as claimed in any of claims 5 to 17, when dependent on either of claims 3 or 4, wherein the sensor is further operable to detect supplemental data, which is added to or modulated onto the AC power supply.

19. Apparatus as claimed in claim 18 wherein the supplemental data is indicative of one of: electrical circuit, location, building, address or system owner.

20. A method of determining proximity to a defined area, comprising the steps of:

• Measuring an electromagnetic field strength, present in the defined area;

• Comparing said measured field strength with a predetermined threshold; Determining presence within the field if the measured field strength exceeds the threshold.