Background to the Invention Tamper-proof closures have been used for many years for sealing drinks bottles. Examples of various efforts of this nature can be found in GB-A-2220648, US- A-5246124 and US-A-4456139. In particular, aluminium screw caps are used in the spirits industry where the screw cap has a collar connected to the cap by shearable or frangible bridges. When the cap is removed from the bottle, the bridges shear and the collar is left around the neck of the bottle. A user can readily determine whether the bottle has been opened by visual inspection of the cap and its collar.

In spite of this technology, unscrupulous merchants will change the contents of a bottle and try to reconnect the collar to its cap by glue or other means, to the point where simple visual inspection does not necessarily give a conclusive indication of whether the cap has been opened.

There is a need for a device which can simply and cheaply be used to determine whether a tamper-proof closure has been tampered with. A notable effort to address this need is found in WO-A-9957035, where magnetic strips are provided, bridging the cap and the collar, so that a change in static or permanent magnetic signature can be detected if the seal between the cap and collar has been broken. The arrangement described requires a modification to the industry standard cap and cannot be used with caps already existing in the marketplace.

The industry demands a high degree of reliability and repeatability of testing and is cognizant of ever more devious attempts by unscrupulous merchants to circumvent existing measures, and there is a further need to improve on existing technology in this regard.

It is also a problem that unscrupulous manufacturers of bottle caps may make unauthorized caps for sealing bottles after the original cap has been broken or for bottling counterfeit produce. Accordingly, there is a need for a means of authentication of a tamper-proof closure to ascertain that it is authentic. WO-A-9738364 describes an electronically interrogated conformable tag for preserving the authenticity of articles such as spirits and perfume bottles. The tag includes an integrated circuit and is permanently damaged upon any attempt of its removal by peeling, detaching or cutting.

It is a problem with existing authentication means that they are either disposed in or on the material of the bottle cap. This means that the supplier of the contents is open to fraud through the cap manufacturer dispensing authentic but unauthorized caps to be applied to a counterfeit bottle or to a bottle that has had its original cap removed.

There is a need to make the authentication available only to the provider of the content of the bottle before the cap is applied and/or for it to be invisible to the eye when inspecting the bottle. There is also a need for authentication to be cheap so that it is available in mass-production and not limited to protection of high-value goods Summary of the Invention According to a first aspect of the present invention, a tamper-detecting device is provided for detecting tampering in a tamper-proof metal closure having shearable bridges which, when sheared, evidence tampering of the closure. The device comprises a primary coil, means for locating the coil adjacent the shearable bridges of a closure and circuit means for measuring a level of inductance for the coil to thereby detect whether the bridges are sheared.

The primary coil preferably forms a loop which is orientated such that its axis of flux is perpendicular to the closure. The loop preferably spans at least two shearable bridges of a closure. It preferably has a curvature that gives it a partial cylinder shape to extend partially around the cap.

In a preferred embodiment, a housing is provided to receive the neck of a bottle or jar having a tamper-proof metal cap thereon for locating the primary coil in the correct position.

Various resonant circuit arrangements can be provided to cause the primary coil to resonate and various detector devices can be provided to detect a characteristic of the coil or the resonant circuit such as the frequency of resonance, magnitude of resonance or resonant amplification. One or more of these characteristics can indicate whether the coil is adjacent an opened or an unopened cap.

In accordance with a second aspect of the invention, a tamper-proof closure for a bottle or jar is provided, having a generally cylindrical screw cap and means for sealing the cap around the neck of the bottle or jar. The closure further comprises a magnetic element located beneath the cap, wherein the magnetic element is permanently magnetized to provide an authenticating magnetic signature for authentication of the closure.

The magnetic element is preferably a disc located beneath a top end of the cylindrical cap. The disc is preferably magnetized across its faces, presenting at least one magnetic pole uppermost and at least one opposite magnetic pole beneath, but the magnetic element may comprise a plurality of north poles and a plurality of south poles.

According to a further aspect of the invention, a device is provided for testing the authenticity of a generally cylindrical tamper-proof screw cap for a bottle or jar, the device comprising first sensing means for sensing the presence of a magnetized element located beneath the cap.

A further sensing means may be provided for sensing the presence of the cap fully inserted into the device for commencing an authentication test, preferably with an indicator for indicating commencement of an authentication test and a result of the test.

A detailed description of the invention in its various aspects and embodiments is now provided, by way of example only.

Brief Description of the Drawings Figure 1 is a diagrammatic elevation view of an embodiment of the invention located adjacent an unopened bottle cap.

Figure 2 is a diagrammatic elevation view of the embodiment of Figure 1 located adjacent an opened bottle cap.

Figure 3 is a diagrammatic cross-sectional elevation view of a second embodiment of the invention.

Figures 4 and 5 are circuit diagrams of a suitable circuit for use in the first and second embodiments of the invention.

Figures 6 and 7 are diagrammatic elevation views of alternative embodiments of the invention with bottle caps or jar caps of different sizes.

Figures 8,9 and 10 are circuit diagrams of an alternative circuit for use with various embodiments of the invention.

Detailed Description of the Preferred Embodiment Referring to Figure 1, a metal bottle cap 10 or similar closure is shown having a conventional tamper-proof collar 11 connected to the cap 10 by shearable metal bridges 12, 13, which are shown as being intact in the figure.

Positioned adjacent the cap 10 is a primary coil 20. The coil is sized and positioned such that it spans the gap between the cap 10 and the collar 11. In the embodiment shown, the coil 20 is sufficiently wide in the annular dimension of the cap that it can span more than one bridge. In the position shown it is seen as spanning two bridges 13 and 14. It will be understood that the coil can be dimensioned to span multiple bridges or a single bridge. When two bridges 13 and 14 of the cap and collar lie within the primary coil 20, the pick up coil 22 is positioned between bridges (i. e. has no bridges within it).

The primary coil has about 100 turns, but the approximate number of turns is not important and a number in excess of about 10 will suffice. It is not necessary for the number of turns to be very large and 1000 turns are more than sufficient.

The coil 20 has a curvature such that it follows the cylindrical curvature of the bottle cap 10.

When a small alternating current is passed through the coil 20, it causes eddy currents to be induced in the metal cap 10 and its collar 11 and between the two. For example, the cap 10, the collar 11 and the bridges 13 and 14 form a loop through which eddy currents can flow. The induction of eddy currents by coil 20 in the metal of the cap 10 is equivalent to the presence of the cap causing a change in the induction of the coil 20.

Referring to Figure 2, the same cap and coils are shown with the bridges 12, 13 and 14 in a sheared state following opening of the bottle cap by a user (either authorised or unauthorised). Good electrical contact can no longer be established between the cap 10 and the collar 11 (e. g. due to oxidation of the aluminium of the pair or due to contact resistance between the pair) and accordingly eddy currents can no longer flow to the same degree between the two. This is equivalent to a change (a reduction) in the inductance of the coil 20.

When the coil 20 is made part of a resonant circuit (described below) the resonant frequency of the circuit changes as a result of breaking of the bridges joining the cap and the collar. The resonant magnification of the circuit also changes and the power of an alternating signal applied to it. This forms the basis of a device for detecting tampering.

The coil 20, the optional coil 21 and (optionally) other coils are mounted in a moulded housing 30 as shown in Figure 3. The housing has a cylindrical recess 31 to receive the cap 10. The depth of the recess is matched to the cap to locate the coils correctly in relation to the cap and its collar. A switch or optical detector 32 is optional to detect when the cap is fully inserted into the recess 31.

The coil 20 is connected to a circuit to form a resonant circuit, an example of which is shown in Figure 4. The coil 20 is shown mounted adjacent a virtual coil 40 which is part of the cap 10 and its collar 11 with a shearable or frangible element 13.

Connected to the coil 20 is a capacitor 41 which forms a resonant circuit with the coil.

The coil and capacitor are shown in parallel connection but they could equally be connected in series. An oscillator 42 is preferably connected across the coil 20 (via a load element 43) to drive the resonant circuit. A detector 44 is preferably connected across the capacitor and/or the coil to detect a characteristic of the resonant circuit. The detector 44 detects the resonant frequency of the resonant circuit in a manner known in the art or alternatively detects the amplitude of resonance.

In operation, the oscillator 42 drives the resonant circuit at either a predetermined fixed frequency or a ramped frequency and the detector 44 detects the resonant frequency or it detects whether the frequency or amplitude of resonance exceeds a threshold.

If the shearable element 13 is broken, the effective absence of the coil 40 in the circuit increases the inductance of the primary coil 20 and causes the resonant frequency to fall. The falling of the resonant frequency below a predetermined threshold is

detected by the detector 44. Alternatively, a reduction in signal amplitude at the expected resonant frequency is detected.

Referring again to Figure 1, the function of the pick-up coil 22 is to assist in ensuring that the cap 10 is at the correct rotational orientation within the recess 31 to ensure that at least two bridges 13 and 14 lie within the coil 20. The operation of the preferred embodiment of the device calls for the circuit to measure a property of the resonant circuit when at least two bridges are located within the coil. A false negative test could result if the test is carried out when only one bridge is in that position.

Accordingly, a resonant circuit similar to that shown in Figure 4 is provided for coil 22.

The user rotates the device relative to the cap 10 while the cap is fully inserted into the recess 31. When the coil 22 detects the presence of a bridge, this indicates that the coil 20 is in the correct position to span two bridges and this causes the coil 20 to take its reading. If the coil 22 does not detect a bridge and neither does the coil 20 detect a pair of bridges, this indicates a tampered enclosure.

An alternative circuit is shown in Figure 5. In this circuit the coil 20 and capacitor 41 are connected in a bridge arrangement with a balancing coil 50 and a balancing capacitor 51. The balancing capacitor 51 matches the capacitor 41. The balancing coil 50 matches the coil 20 in either its stand-alone state or in a state in which it is in proximity with a cap with an unbroken collar seal. A controller 60 is shown with two light-emitting diode indicators 61 and 62. The balancing coil 50 is shown as being an adjustable inductance under the control of the controller 60.

In operation, the user places the device over the cap of a bottle, and the switch or optical detector 32 in the housing 30 initiates a testing cycle when the cap is fully inserted into the recess 31.

At the start of the testing cycle, the controller 60 senses-whether a bridge is present within the pick-up coil 22. This is determined using a circuit similar to that of Figure 4 or the bridge circuit of Figure 5. Until the controller 60 detects that there is no bridge 14 within the coil 22, no indication is given by the first LED 61. When the

controller 60 detects, by means of the coil 22, that the coil 22 has no bridge within its span, the controller 60 begins a measurement using coil 20. This is because the absence. of any bridge within the coil 22 indicates that the coil 20 is correctly positioned to span two bridges or, alternatively, indicates that there are no intact bridges between the cap and the collar.

At the commencement of measuring using the coil 20, the LED 61 illuminates to show that a test is being conducted. The controller 60 through detector 44 detects whether there is an imbalance between the arms of the bridge circuit. If there is an imbalance, this indicates that the bridges 12 and 13 have been sheared and LED 62 illuminates to show a tampered closure.

Alternatively if, following a time-out, LED 61 does not illuminate, this also indicates a tampered closure. If, on the other hand, LED 61 illuminates (indicating commencement of a test) and LED 62 does not illuminate, this indicates an intact closure. Clearly other arrangements of the LEDs can be provided and logic circuitry can be used to give alternative combinations of indicators to the user to provide the user with confidence that (a) a test has been conducted successfully and (b) a positive or negative result of that test is given.

If the device is required for testing different caps of different sizes, shapes or materials within an acceptable range, the controller 60 can control the balancing inductor 50 to match the inductor 50 to the particular cap to be tested. While the inductor 50 is shown as being an adjustable inductor, its inductance can, of course, be adjusted by other means, such as by a parallel or serial controllable capacitance.

The entire circuit of Figure 4 or Figure 5 and its necessary battery power supply can be housed within moulded housing 30. In this way, a cheap, lightweight, portable and easy-to-use device is provided that requires no technical training and gives a simple and reliable indication as to whether a bottle has been tampered with.

Referring to Figure 6, an arrangement alternate to those of Figures 1 to 3 is shown. In this embodiment, the coil 20 has a length that is at least four times its width.

That is to say, the length of arc through which the coil extends around the circumference of the recess 31 is at least four times the vertical dimension of the coil. The coil 20 embraces two or three bridges and preferably at least three bridges spanning between the cap and the collar. The coil extends around an arc that is preferably about one-third of the total circumference of the recess 31, i. e. an arc of approximately 120°, but a smaller arc (e. g. 60° or 90°) or a larger arc (e. g. 180°) is also suitable. The coil 20 is centred over the join between the cap 10 and the collar 11 when the cap is fully inserted into the recess 31. A balancing coil 60 in this case is located in a position removed from the gap between the cap and the collar and is positioned over a part of the cap 10 that consists of continuous material. It is not essential that the balancing coil 60 is located adjacent material that mimics an unbroken cap and seal. In fact the balancing coil 60 need not have the same dimensions as the coil 20. It need not be elongate, but may be circular. Moreover, as will be described with reference to Figure 7, the balancing coil need not even be located adjacent the cap.

Also shown in Figure 6 is a magnetic disc 65, which is preferably made of strontium ferrite magnetic material. The disc 65 is located immediately beneath the upper surface of the cap 10, within the laminated seal of the closure. The disc 65 is magnetized across its faces and serves to permit authentication of the closure after the closure has been attached to the bottle or other article. A Hall effect sensor 66 is located within the moulded housing of the testing device. The sensor 66 will sense the presence or absence of the disc 65 for purposes of authentication.

Referring to Figure 7, an arrangement similar to that of Figure 6 is shown, for testing shorter closures, e. g. caps for jars or pharmaceutical products. In this embodiment, the secondary coil 60 is not located adjacent the cap 10. It is located within the moulded housing. Tests show that this embodiment gives improved reliability and consistency of results, because the inductance of the balancing coil is not dependent on the placement of the cap or the material of the cap.

The device illustrated in Figure 6 or Figure 7 can be formed into a hand-held device that can indicate, through LED indicators, whether the closure has been tampered with and whether the closure is an authentic or a non-authentic closure. Suitable circuitry for this purpose is illustrated in Figures 8 to 10.

The arrangement again uses the effect of the proximity of the closure to two coils having a"shorted turn"effect, where the conductive material of the closure acts as the shorted turn. This has the effect of changing inductance of the coils.

Referring to Figure 8, a first inductor pair 80 is provided, comprising first and second coils 80a and 80b. These coils are wound together or are co-located, one on top of the other. Coil 80a comprises only a few turns (between about 2 turns and about 10 turns). Coil 80b comprises substantially more turns. Coil 80b is a main resonant coil and is connected in parallel with capacitor 85. These elements form a self-oscillating circuit. Coil 80a is a feedback coil. It is connected to the base of a transistor 81 to drive the oscillator. Inductor pair 80 operates on the bottom of the closure, covering the junction between the crimped security ring and the main body of the closure.

A second inductor pair 82 (comprising two coils 82a and 82b identical to coils 80a and 80b) forms a reference oscillator with second transistor 83 and associated capacitors. The second inductor pair 82 operates on the main body of the closure as shown in Figure 6, or separated therefrom as shown in Figure 7.

The capacitor 85 in parallel with coil 80b is adjustable for the purposes of balancing the circuit, but it will be understood that the circuit can be balanced in other ways by adjusting other capacitors, inductances or other components. The outputs from the oscillators formed by inductor pairs 80 and 82 are added together by transistors 88 and 89 and the combined output is provided as output"A".

Referring to Figure 9, the signal at output"A"is rectified by diodes 91 and 92 and integrated by a capacitor 93. This gives a signal across resistor 94 the frequency of which is the difference between the frequencies of the two oscillators, and the amplitude

of which is inversely proportional to the different frequencies. This signal is amplified by an integrated circuit 95, rectified by further diodes 96 and 97 and integrated by capacitor 98 to give a DC level which is inversely proportional to the frequency difference between the two oscillators. This DC level is compared in integrated circuit 100 with a voltage from a potentiometer 102. Integrated circuit 100 acts as a comparator, and its output illuminates a green light emitting diode 105.

The oscillator frequencies are such that if the ring seal of the closure has been broken, inductor pair 80 will produce a lower frequency, so that the difference between the two oscillators will change, giving a different voltage at the input of IC 100, and causing the red light emitting diode 106 to be illuminated.

The circuit operates when the battery power supply is switched on by a microswitch 32, which senses when the closure has fully entered the hand-held device.

In addition to the tamper facility described above, the magnetic disc of Figure 6 or Figure 7 permits the authenticity of the closure to be verified by a programmable magnetic signature existing within the magnetic seal of the closure. An embodiment of this feature is illustrated with reference to Figure 10.

Referring now to Figure 10, Hall effect sensor 66 is situated within the hand- held device and generates a voltage which is compared to the voltage on the wiper of a potentiometer 200. An integrated circuit 202 performs the comparison, to operate a pair of coloured light emitting diodes 204 (red) and 206 (green). The green LED illuminates in the presence of a magnetic pole of the correct polarity, thereby indicating authenticity. The red LED illuminates otherwise.

In the embodiments described with reference to Figures 6 to 9 there is no need for a pick-up coil as described with reference to Figures 1 and 2 (although a pick-up coil could be used to indicate a valid test if desired). The arrangement is sufficiently reliable that the microswitch 32 largely serves to indicate that the closure is fully inserted into the device and a test is under way. Similarly, the sensor 66 can serve to indicate that an

authentic enclosure is present and a valid test is being conducted. If a test (or a valid test) is indicated, the user can be confident that the red/green indicator 105/106 will correctly indicate that the closure has passed or failed the test.

In an alternative embodiment (not shown) the magnetized disc 65 is encoded with a series of north and south polarity rings. In this manner the disc is encoded with a magnetic pattern. For example, four polarised rings can be provided which permit up to 16 different codes. An array of sensors is provided in the device to interrogate the magnetic pattern in the closure, and an electronic comparator checks the code against a preset code and operates the two-colour LED. The preset code is stored in the non- volatile memory device or may be set by a series of miniature slide switches.

The above embodiments and aspects of the invention have been given by way of example only and modifications of detail can be made by one skilled in the art without departing from the scope of the invention.