WO2003090321A1

WO2003090321A1 - Electrical connectors

Info

Publication number: WO2003090321A1
Application number: PCT/GB2003/001612
Authority: WO
Inventors: Joseph Gibson Dawson
Original assignee: Magtrix Connectors Limited
Priority date: 2002-04-20
Filing date: 2003-04-15
Publication date: 2003-10-30
Also published as: AU2003222608A1

Abstract

A method of forming a releasable electrical connection, the method comprising the steps of: providing a first electrical device (2) and a second electrical device (2; 36; 40; 42; 50; 56; 58; 80) said first and second electrical devices being connected by at least one permanent magnet (4) so as to form a releasable electrical connection therebetween said method being characterised by providing said at least one permanent magnet (4) with electrically conducting holding means (6; 100; 200; 210; 220; 300; 400; 500) to retain said magnet. The method is particularly suitable for attaching discrete electronics components such as batteries and electrolytic capacitors to a circuit board.

Description

ELECTRICAL CONNECTORS

The present invention relates to a method and devices for releasably attaching electrical components to and in electrical connection with another electrical device, such as a printed circuit board, by the use of one or more permanent magnetic devices.

Magnetic connectors for physical connection are widely known. GB 2071919 (Schluter) discloses a magnetic connector for ceramic tiles. GB 1589309 (Abe) discloses a magnetic sheet for releasably attaching doors, cladding and the like. GB 1530591 (Long) describes a cylindrical magnetic connector for connecting and securing a door in a doorframe wherein a connector magnet is optionally biased by a spring. GB 1104933 (Clark) discloses a magnetic catch for a door wherein the catch is releasable by rotating a cylindrical magnet magnetically attached to another cylindrical magnet such that the magnets repel and the catch is released. None of the above references disclose the use of a releasably attachable magnetic connector for forming an electrical contact between electronic components.

Known methods of securing electrical and electronic components to printed circuit boards include soldering, clamping, push-fit connectors and a wide variety of clips.

The printed circuit board is the almost universally used vehicle for securing electronics components in a handleable physical, i.e. mechanical, form whilst placing them in working electrical contact. With increasing miniaturisation of components applied to such circuit boards, mechanisms for releasably attaching components to circuit boards, as opposed to permanently soldering them in place, become increasingly delicate. Mechanical clips, clamps and similar devices become increasingly difficult to manipulate manually when sub-miniature and miniature sizes are achieved. The users of such devices, especially when there is a requirement for repeated replacement and withdrawal of a component, run the risk of damaging an attached device or component during the manipulation of such delicate components. In addition stress fractures of printed circuit boards are a known problem particularly with spring loaded and latching connectors. Whilst this can be partially overcome by reducing the forces that such attachment means use to retain a component, this reduces the potential for securely holding such components, in for example, environments which will endure mechanical shock and vibration. There is therefore a need for a means of releasably securing electrical components and in particular electronics components to other electronics components, such as a printed circuit board, in a simple, robust, reliable and yet miniaturised manner such that they may be releasably attached.

According to a first aspect of the invention there is provided a method of forming a releasable electrical connection, the method comprising the steps of: providing a first electrical device and a second electrical device said first and second electrical devices being connected by at least one permanent magnet so as to form a releasable electrical connection therebetween said method being characterised by providing said at least one permanent magnet with electrically conducting holding means to retain said magnet.

The method may be used in the formation of an electrical circuit comprising the electrical connection so formed.

Due to increasing miniaturisation, it is desirable that any method of releasably securing an electrical component also functions as a means of electrical connection to avoid wasting space. It is preferable that such methods of attachment for electrical components directly engage an electrical contact. In addition, when releasably securing components to a circuit board, if there is a difference between the means for making electrical contacts and the means for physically securing an electronics device, it is possible that such a device may be mechanically secured, but not in electrical contact. Or alternatively the device can be in electrical contact, but not sufficiently well mechanically secured. It is therefore desirable to have an electrical contact for electronic components, in releasable association with a printed circuit board, which also achieves the physical retention of such electronics devices on the printed circuit board by the same means such that the integrity of mechanical connection is an indication of the integrity of electrical connection and vice versa.

The electrical devices of the method may be physically attached substantially by the releasable magnetic attachment.

Moreover, when mechanical electrical connectors are used for electronics components, repeated insertion and removal of such components leads to wear on the devices, particularly of mechanically interlocking parts, and thereby the potential for deterioration in any associated electrical contact. In particular, whilst plating such contacts with, for example, gold, can improve such contacts it is expensive to make a coating sufficiently thick that high numbers of repeat contacts may be made without wearing the coating away. There is therefore a need for a method of releasably attaching electrical components wherein the mechanical attachment does not comprise a mechanically interlocking component yet an electrical device is securely retained.

In addition it is desirable to decouple stresses placed on a circuit board by the insertion and removal or components and connectors. Whilst flexible couplings, such as wires may be used, secure physical contact with a device to be connected is still required and such combinations take up additional space and increase complexity in manufacture. There is therefore a need to make secure yet adjustable releasable connections to circuit boards.

The electrical devices of the method may optionally only be physically attached by releasable magnetic attachment. By combining physical securing and electrical contact means the 'real estate' of a printed circuit board may be conserved as is important in miniaturisation.

Also according to the method a permanent magnet comprising an electrical connection between the first and second device may be located on, i.e. attached, other than by means of magnetic attachment or attraction, to the first or second device. Furthermore, the permanent magnet on the first device may directly physically and electrically contact the permanent magnet on the second device by means of magnetic attraction.

Releasably attached electrical devices of the method may be physically attached substantially by magnetic attraction. Releasably attached electrical devices of the method may be physically attached only by magnetic attraction. According to the method of the invention one or more points of magnetic attachment may participate in forming an electrical connection which is part of the electrical circuit. Primary physical and mechanical attachment of a magnet, i.e. attachment of a permanent magnet to that electrical device of which it is part, may be by any conventional mechanical securing means such as soldering, clamping and adhesion.

It is an element of the first to third embodiments of the invention may be that the permanent magnets are in electrical connection with the electrical device secured by said magnet and may form an essential and integral part of an electric circuit so formed. It is therefore implicit in the invention that magnets will be arranged in the appropriate polarity to enable mechanical and electrical connection to occur, if appropriate to a given application. For the puφoses of the invention electrical connection through a conductive surface coating, such as metal plating, of a magnetic substance of a magnet is an electrical connection with the magnet.

According to the method of the invention the holding means may be further provided with a separate electrical conductor. Also according to the method of the invention the electrical connection may form part of an electrical circuit. In addition according to the method of the invention a releasable electrical connection may be carried out by providing that the first or second electrical device is held between two or more permanent magnets so as to form a part of an electrical circuit. Also according to the method of the invention the electrical devices may be releasably electrically connected by magnetic attachment. The method of the invention may include where the electrical devices may be releasably electrically connected only by magnetic attachment. Also according to the method of the a permanent magnet associated with the first device may electrically contact a permanent magnet associated with the second device by means of magnetic attraction to form the releasable electrical connection.

The two or more permanent magnets of the invention may all be primarily attached to one component only, for example a first electrical device. In such a case the other component, a second electrical device may have magnetically attractable electrical contact portions. Where the two or more permanent magnets of the invention may all be primarily attached to one component only, that component is preferably a printed circuit board. The method of the invention includes releasably magnetically attaching, and thereby forming an electrical connection between, a first electrical device and a second electrical device by means of a permanent magnet located on, i.e. attached to the first device.

The first electrical device of the method of the invention may comprise a printed circuit board. The second electrical device of the method of the invention may also comprise a printed circuit board. The method of the invention may be used to releasably connect printed circuit boards together in electrical communication. Circuit boards may be readily changed with minimal mechanical abrasion of the electrical contact points giving the aforementioned advantages.

According to the method of the invention the permanent magnet on the first device directly physically and electrically contacts the permanent magnet on the second device by means of magnetic attraction. Since only magnets of opposite polarity will attract and readily contact one another the method provides a means for ensuring that incorrect connections are not made between electrical contacts thus avoiding any resultant damage.

A wide range of electrical devices are suitable for use in the invention including fuses, batteries, button batteries, resistors, capacitors, lamps, and active components such as transistors and electrical sub-assemblies such as circuit boards, among others. The electrical devices may be electrical or electronic components. The electrical devices may be passive electronic devices in the form of discrete electronics components; such components may be capacitors, the capacitors may be ceramic or electrolytic capacitors. Ceramic capacitors are preferably ceramic disc capacitors. Electrolytic capacitors are preferably axial electrolytic capacitors. The electrical devices may be surge arrestors, for the removal of voltage spikes in supply lines, preferably discrete surge arrestor components with a limited life span. Exhausted components may therefore be conveniently replaced. It is preferable that electrical devices releasably mechanically attached using the invention are secured exclusively by surface portions, which are in electrical contact to form said electrical circuit. Mechanically interlocking means of securing the electrical device or devices may be absent other than any due to physical forces resulting from magnetic attraction and/or repulsion. Mechanical means for securing thereby excluded from optimal working of the invention may therefore include mechanically interlocking means such as latching, intermeshing, clips, screw threads and similar mechanical holding mechanisms. Mechanical guides, supports and the like which are secondary to the magnetic effect of releasable magnetic attachment may be used to help guide a component to the general area where the component is to be located but are not the primary medium of such attachment which, for uses within the scope of the invention, is dictated primarily by magnetic attachment. Devices for use in the invention therefore avoid the wear associated with a mechanically interlocking mechanism whilst retaining the inherent compactness of a method wherein the mechanical and electrical contact are achieved using the same means.

The second electrical device of the invention may be releasably magnetically attached between the two or more permanent magnets and comprise one or more discrete electronic components. Alternatively the second electrical device may consist solely of one or more discrete electronic components. The one or more discrete electronic components may be releasably physically attached by an attractive magnetic force between the permanent magnets so as to sandwich said components between the permanent magnets thereby holding them in place and in electrical contact. This provides a method of replaceably locating electrical components in an electrical device, such as a circuit board. A discrete component comprises an individual electrical function, such as a single resistor, as opposed to sub assemblies of multiple components, integrated circuits and the like.

The method may employ one or more discrete electronic components of consumable characteristics. Consumable characteristics are characteristics that are exhausted during use of the component. Examples include batteries, anti-voltage-surge devices. Such devices are advantageously replaceable during the life of a piece of electrical equipment and the benefits of the invention of easy and repeatable replaceability are more fully utilisable. The second electrical device may comprise one component, particularly when the component is one of consumable characteristics. Any failure of such a device when the consumable characteristics are consumed is therefore limited to a single readily replaceable component.

The method may employ a number of discrete components used together sandwiched between two or more magnets preferably without a circuit board or other connecting means save for direct contact between components. Thereby, by for example, sandwiching various resistors, capacitors and other discrete components between a pair of magnets a compound device may be readily obtained and modified. Other examples include a battery and resistor, or a battery and a diode, by example. However, the method may employ a single discrete component.

In particular it is often desirable to adjust the values of electronic components in an electrical circuit; for example, to tailor a mass-produced circuit to a particular application. Whilst variable resistors and capacitors are widely used for this puφose a need remains for a similar method of varying higher value capacitance by means of readily releasably connecting, both mechanically and electrically, such components to a printed circuit board. The one or more discrete electronic components may be passive components in the form of ceramic disc or electrolytic capacitors, thus, realising a method for providing an effectively variable high value capacitance by interchanging such capacitors. The second electrical device may be a single component to achieve simplicity. The second electrical device may be two or more components to achieve a high degree of flexibility in forming a compound component.

Suitable permanent magnets for use with the invention may be magnets with surface magnetic flux of greater than 1,000 Gauss, more preferably greater than 2,000 Gauss and most preferably between 3,000 and 6,000 Gauss. Such magnets give sufficient magnetic adhesion to create an adequate mechanical securing force whilst also avoiding significant variation in electrical contact when used in devices of miniature and sub-miniature size for use in electronics circuits. Such powerful magnets are advantageous in that they cannot, under normal circumstances, be forced into contact, such as would form an electrical contact as required by the this invention, if surfaces of the same polarity are made to approach. Magnets for the securing of a non-magnetically attractable component between, more particularly by sandwiching such a component between magnets, are preferably of 1,000 surface Gauss or greater more preferably 3,000 surface gauss or greater and may further preferably primarily attached not more than 6mm apart.

Permanent magnets for use in the invention preferably comprise neodymium iron boron magnets. A suitable grade, using industry notation, is N30 a preferred grade is N35H. Such devices may be solid units of magnetised nickel-plated NdFeB made from compacted and sintered powder. A method of making such permanent magnets is to sinter a NdFeB magnet from a powder having a composition comprising 14 parts Iron, 2 parts Neodymium and 1 part Boron. The manufacturing process may comprise the steps of aligning unsintered particles in a mould, compacting, sintering and then metal plating the device so formed. Alternatively particles may be sintered, metal plated and then magnetised. Suitable metals for plating include, nickel, chromium and gold. Optionally the sintered articles may be machined. A plastic coating step may also be incoφorated on surfaces not participating in electrical contact.

Other suitable permanent magnets for use in the invention, particularly the thirteenth to nineteenth embodiments (described below) of the invention, are Samarium-Cobalt magnets. Suitable compositions may include materials having a Samarium to Cobalt ratio of 1:5, more preferably of ratio 2:17 for example.

Permanent magnets for use in the invention may preferably be retained in a retaining means such as a metal cup and may further preferably have a lead attached either directly or to the retaining means. The retaining means may retain the magnet by being crimped about a magnet, by a close interference fit, by a resilient means, by adhesion, by soldering or other means known in the art. If soldering is used the magnet is preferably pre-coated with a solderable material, such as by gold plating, and is magnetised after heat treatment for effecting the electrical connection. Alternatively, as in for example, surface mounting a suitably coated magnet may be attached by a cold soldering mechanism such as ultrasonic welding. The method of the invention therefore may include the locating of surface mount electronic components upon magnets surface mounted on a printed circuit board. Soldering is a non-preferred method of connection to a neodymium iron boron magnet as such magnets may rapidly rust when exposed to a normal atmosphere. If coated, by for example electroplating, neodymium iron boron magnets could be soldered to, however, soldering and similar techniques may give rise to imperfections in the coating resulting in rapid rusting.

Components thus mounted by magnetic attachment to magnets are securely mechanically and electrically connected whilst upon attachment and removal little or no mechanical distortion of parts occurs and, in particular little or no shearing action to potentially wear away a contact surface is present. The method and devices of the invention, using magnets, thereby provide for the releasable magnetic attachment of electrical components without requiring a mechanically interlocking component. Connection of electrical components may be facilitated by the attachment of small steel plates, for example thin discs to act as electrical contact points and magnetically attractable attachment points for use with the present invention. The attachment of magnets to components may also be used particularly if components require attachment in a given orientation.

However, it is also within the scope of the invention to attach magnets to a first electrical device, by for example soldering, wherein the attachment is by means of a flexible wire such that magnetic attachment to second devices of variable geometry may be enabled by moving the magnet on one end of the wire to contact the second device whilst another end of the wire contacts a main body of the first device. Here a principal advantage of the invention is in the ability to obtain secure releasable electrical connection to electrical devices of varying size. A method of realising secure yet adjustable releasable connections to circuit boards is therefore achievable. The devices and method of the invention allows stresses from adjustments to fit varying sizes of devices and from inserting and removing connectors to be significantly decoupled from a circuit board by the use of a flexible elongate electrical connector between a magnet and circuit board. The elongate connector may comprise a single strand of wire or multiple strands of wire, which may or may not be bound together. Stress cracking of printed circuit boards can thereby be significantly attenuated. The elongate connector preferably comprises a single strand of wire. Connection by a method and devices according to the invention wherein a flexible coupling is used between a device, and a magnet attached to a device is particularly advantageous as electrical and mechanical connection of a magnet to a circuit board by soldering is facilitated as the risk of damaging the magnet by prolonged heating from a soldering process is greatly reduced. This is particularly so when an end of an elongate flexible connector remote from an end attached to the magnet is soldered.

Also according to the invention there is a method of releasably attaching one or more discrete electronic components between two permanent magnets located on a printed circuit board. The components are preferably secured by an attractive magnetic force between said magnets more preferably by sandwiching said discrete components between said permanent magnets. The electrical component or components may comprise a magnetically attractable material, more preferably such a magnetically attractable material may be present as surfaces forming an electrical contact portion of the electronic component or components. Suitable components are pen cell type batteries. Particularly suitable components are electrolytic capacitors. Such components may, for example, be added in series to appropriately provide greater variation in available capacitance.

A method of conveniently adjusting the values of electronic components in an electrical circuit, for example, to tailor a mass produced circuit to a particular application can therefore be performed. In particular a method of varying high value capacitance by means of readily releasably connecting both mechanically and electrically capacitors to a printed circuit board can be realised.

Particularly, but not exclusively, when an electrical device, such as a first electrical device, for use with the invention is an electrical sub assembly, more preferably when that sub assembly is a printed circuit board all the magnetically attractable electrical contact points may be between pairs of permanent magnets. This has the advantage that incorrect magnetic attachment of circuit boards, when circuit boards comprise the first and second devices is avoided if the magnets and their polarities are arranged so as to stop incorrect assembly by means of magnetic repulsion. An electrical sub assembly comprises a set of interconnected electrical or electronic components.

In addition in electronics circuits there is often a requirement that many connectors are present. However, when many connectors are present it is necessary to utilise a plurality of connector types and connector pin configurations so as to ensure that inconect connections are not made. However, this solution often requires a large number of different types and shapes of connectors in any given device. This adds complexity to a manufacturing process, to the associated components stocking process and to associated ordering processes and so forth, in electronic circuits' manufacture. It would be preferable that only one sort of connector be used, yet without the potential for any misconnection, for example by the connectors themselves actively avoiding engagement with the wrong sort of connection. There is therefore a need for an electrical connector such that the electrical connector, whilst, mechanically the same as other connectors, may be otherwise modified so that it itself determines which electrical contacts it is capable of making and which contacts it is not capable of making with other connectors which are otherwise mechanically identical.

According to a second aspect of the invention there is provided a system for providing a self selecting connector for releasably establishing two or more electrical contacts between two electrical connectors wherein said connectors are electrically and mechanically connected by means of permanent magnets and wherein the self selection is provided by means of arranging the orientation of the permanent magnets such that only connectors with complementary arrangements of magnets are capable of securing electrical and magnetic connection by means of magnetic attraction between the permanent magnets. Hence, by choice of orientation of the polarity of said permanent magnets such connectors may be made to, or not made to electrically contact the other connector, i.e. the pattern of North or South of the exposed magnetic faces of the electrical connectors can be tailored to attach to magnets in a complementary connector and actively repel for an undesirable connection. The above system is particularly suitable for connecting printed circuit boards to one another.

The system of the invention enables fewer different connector types to be used in an electrical assembly, enables the risk of misconnecting connectors to be greatly reduced as incorrect connections are actively repelled by strong magnets of like polarity and correct connections from magnets of dissimilar polarity form strong electrical and mechanical connections. The connectors thereby effectively self-select which other connectors they are suitable for connection with. In most applications of the invention the use of high strength magnets gives rise to very powerful repulsive forces between connectors of incorrect polarity, thus stopping meaningful electrical contact being made. However, where high voltages are involved the potential for arcing between magnets on close approach may be present. In addition where multiple pole connectors, as in the second aspect of the invention, are used a net attraction between an aggregate of connectors may result and individual contacts may thereby be forced. Particularly, but not exclusively, in the above situations a further embodiment of the invention may be used. Electrically contacting, mechanically securing magnets may be movably located in an insulating housing such that the magnets may move in a housing to approach one another and contact if the faces of the magnets are of opposite polarity and if of like polarity may retreat into the housing to avoid a spark-gap forming or other contact being made. The magnets may be resiliently biased within the housing.

According to a third aspect of the invention there is provided an electrical component for the attachment of other magnetically attractable electrical components, comprising a permanent magnet secured in an electrically contacting electrically conductive mechanical holding means to which means a flexible elongate electrical contact and attachment means is electrically and mechanically attached by magnetic attraction at one end to the electrically contacting electrically conductive mechanical holding means and at the remote end is solderable to a conventional printed circuit board. The flexible elongate electrical contact may be in the form of a wire or metal braiding.

An electrical component according to a third aspect of the invention may comprise one face of said magnet that stands proud of said holding means. An electrical component according to any third aspect of the invention may form a magnetic and electrical connector.

An electrical component for use in the invention and in the method of the invention as described above may comprise a component for modifying an electric current forms the sole electrical connection between the permanent magnet and the holding means and the elongate electrical connector is not in direct electrical contact with the permanent magnet. Suitable components are as described above under discrete devices. A preferable component is a diode, such a device, when used as a battery connector can act to stop current flowing if a battery is incorrectly connected.

The method, devices and system of the invention are particularly advantageous in that optimum electrical contact is obtained as magnets, which form the electrical contact surface in the invention, automatically orientate themselves to give the greatest available surface contact by means of their magnetic attraction.

The method and devices of the invention may be used to form a modular educational system for teaching electronics, comprising a matrix of magnetic connectors between which electronics components can be located as hereinbefore described.

According to a fourth aspect of the invention there is provided a component for use in making an electrical connection comprising a permanent magnet and a holding means for the magnet wherein the holding means completely enclose the magnet for protection against corrosion of or mechanical damage to the magnet.

Also within the scope of the invention is a magnet completely enclosed in a holding means for protection against corrosion of or mechanical damage to the magnet wherein a portion of the holding means does not significantly attenuate the magnetic field strength outside the holder of the magnet.

The holding means for the magnet may comprise a first and a second holder. The first and second holder may be in electrical contact. The second holder may hold the first holder. The completely enclosed magnet may be hermetically sealed in the holding means. One of the first and second holders may be cup shaped. The first holder may hold a magnet. The holder may be cup-shaped and one or more magnets may be held inside the cup. The one or more magnets may be in electrical contact with the cup. If more than one magnet is present then a magnet may be in electrical contact with another magnet. The second holder may also hold a magnet. The second holder may be cup-shaped and one or more magnets may be held inside the cup.

The second holder may hold the first holder by means of inner faces of the cup being adhered to the outer face of the first cup or vice versa. The adhesion may be by mechanical contact or by adhesion. A sealant may be used to seal the two holders completely enclosing the magnet. A suitable sealant may be an epoxy resin. The sealant may also act as an adhesive.

One or both of the holders forming the holding means may comprise a paramagnetic material such as brass or aluminium. One of the holders forming the holding means in addition to a metal holding means may be a plastic. A suitable plastic is a potting compound such as an epoxy resin. A holding means comprising a plastic may comprise a first plastic holder held in a cup-shaped second metal holder. Such a metal/plastic holding means may have no attached electrical contact wires or leads. The holding means may be coated. The coating may be of plastic or metal. A metal coating may be metal plating. The metal plating may be silver plating.

The thickness of the metal holder in at least one area with which an encapsulated magnet is in direct contact may be 0.2mm or less thick, more preferably 0.1mm or less thick. The thickness of said area may be greater than 0.01mm thick, more preferably greater than 0.05mm thick.

The thirteenth to nineteenth embodiments of the invention are particularly suitable for use with ultra high strength magnets as their magnetic field strength falls dramatically with distance from the magnet surface. A Neodymium Iron Boron magnet of surface magnetic flux density of 3000 Gauss in direct contact with a nickel plated brass holding means of thickness 0.1mm gives rise to a magnetic flux density on an outer surface of the component, adjacent to the area of direct magnet contact, of 2500 Gauss.

A metal holding means may preferably comprise a low level of ferromagnetic material such that a magnet is held to the holder so as to facilitate manufacture of components of the invention. A low level may be a level of less than 1% Iron.

The protection against mechanical damage of the magnet may protect against the consequences of mechanical damage to the magnet. Samarium Cobalt and ceramic magnets are particularly fragile and impact insufficient to breach the protection of the holding means may result in a magnet contained in the holding means breaking on sufficiently heavy impact. Sufficiently heavy impacts are present with high strength magnets on allowing such magnets to approach a hard surface by virtue of their own magnetic attraction. High strength magnets are magnets of surface magnetic flux density of greater than 1000 Gauss, Ultra high strength are magnets of surface magnetic flux density of greater than 2000 Gauss. Thus a high or ultra high strength magnet, or even a lower strength ceramic magnet, may be attracted to a steel block, for example, with such force that any resulting impact may readily smash the magnet. Examples of high strength magnets include Samarium-Cobalt and Neodymium-Iron-Boron Magnets. The benefit of components of the fourth embodiment invention as regards mechanical protection may be primarily seen with high strength magnets, particularly Samarium-Cobalt magnets and also with ceramic magnets.

The components of the thirteenth to nineteenth embodiments of the invention preferably retain the magnet in an enclosed space of similar dimensions to the magnet. As the efficacy of a magnet may not be significantly diminished by fracture, be it a metal or ceramic magnet, retaining the portions of a broken magnet in situ enables the component to continue to function effectively even after being subjected to significant mechanical damage which would otherwise render a magnet ineffective. An example of ineffectiveness that can be avoided is that of magnet fragments preferably attaching to items other than the device, for example a steel article and more particularly mechanical apparatus such as gear wheels and the like that can be hindered in their operation, in close proximity.

Mechanical damage refers to damage that would otherwise occur to a magnet not held in a holder of the invention. In particular mechanical damage is damage due to shock and sudden impact rather than continuous or persistent forces.

An electrical component according to the invention may comprise a non-metallic mounting member comprising separable plug and a socket portions for accommodating two of said electrical components according to the invention. Such an electrical component is particularly suitable for forming panel mount and in-line electrical connectors. The electrical components according to the invention may be incoφorated into a pre-formed plug or socket and optionally adhesively retained therein. Alternatively a plug or socket portion may be moulded around one or more electrical components according to the invention.

A battery holder of a device of a sixteenth embodiment of the invention comprises at least two electrical components according to the invention and further comprises a flexible sheet member for holding said at least two electrical components in spaced-apart relationship with said magnet portions being adjacent to terminals of said battery, in use. Such a battery holder is particularly serviceable as the flexibility required of a device required for accommodating and in accepting and removing a battery is obtained by means of the flexible sheet member rather than from any electrical contact leads. In addition the conventional reliance on resilient members to achieve such flexibility is obviated by the use of a magnetic device according to the invention. The flexible sheet member may be formed from any suitable material and a series of battery holders may be provided in a parallel arcangement so as to accommodate a series of pen-cell batteries. Such parallel arrangements may be provided as a bandoleer from which a required number of battery holders may be removed as required. The holder may be adapted for other battery forms such as the dual end connector (e.g. types PP9 / PP3) form.

Examples of the invention will now be described by way of illustration only, with reference to the accompanying drawings, in which:

Figure 1 shows a device of a first embodiment of the invention, in side elevation, as a cross section;

Figure 2 shows an end elevation of the device shown in Figure 1;

Figure 3 shows a second embodiment of the invention, in side elevation, as a cross section;

Figure 4 shows devices of the invention in association with a battery;

Figure 5 shows a side elevation in cross section of devices of the invention when used in conjunction with modular electronic components;

Figure 6 shows devices of the invention, in side elevation in cross section, connecting printed circuit boards;

Figure 7 shows devices of the invention, in side elevation in cross section, resisting connection of two printed circuit boards;

Figure 8 shows an end elevation of a connector of a third embodiment of the invention;

Figure 9 shows a side elevation in cross section of a fourth embodiment of the invention; Figure 10 shows a side elevation in cross section of devices of the fourth embodiment of the invention connected;

Figure 11 shows a side elevation in cross section of devices of the fourth embodiment of the invention resisting connection;

Figure 12 shows a side elevation in cross section of a device of a fifth embodiment of the invention.

Figure 13 shows a side elevation in cross section of a device of a sixth embodiment of the invention.

Figure 14 shows a side elevation in cross section of a device of a seventh embodiment of the invention;

Figure 15 shows a side elevation in cross section of a device of a eighth embodiment of the invention.

Figure 16 shows a side elevation in cross section of a device of a ninth embodiment of the invention;

Figure 17 shows a further side elevation in cross section of the device of a ninth embodiment of the invention;

Figure 18 shows a side elevation in cross section of a device of a tenth embodiment of the invention;

Figure 19 shows a side elevation in cross section of a device of a eleventh embodiment of the invention; Figure 20 shows a side elevation in cross-section of a twelfth embodiment of the invention;

Figure 21 shows an end view of the twelfth embodiment of the invention;

Figure 22 shows a side elevation in cross-section of a thirteenth embodiment of the invention;

Figure 23 shows an end view of the thirteenth embodiment of the invention;

Figure 24 shows a side elevation in cross section of a fourteenth embodiment of the invention;

Figure 25 shows a schematic plan view of an application of devices of the invention;

Figure 26 shows a schematic plan view of a further application of devices of the invention.

Figure 27 shows a partial cross-section of a fifteenth embodiment of the invention;

Figure 28 shows a plan view of a sixteenth embodiment of the invention; and

Figure 29 which shows a cross section of a sixteenth embodiment of the invention along line XXVIII of Figure 28.

In the drawings the same or similar features are denoted by common reference numerals.

Figures 1 and 2 show a first embodiment of the invention 2. A permanent magnet 4 is retained by a push fit in a holder 6 comprising rear face 8 and side wall 12, which are in electrical contact with magnet 4. Holding means 6 also comprises an electrical contact wire 10, which is a tinned copper wire. Magnet 4 comprises a nickel-plated neodymium iron boron magnet of cylindrical form and holder 6 comprises a thin tinned copper shell, which may alternatively be crimped on magnet 4 to hold magnet 4 in place.

Figure 3 shows a device of a second embodiment of the invention 20. Device 20 comprises a device of the first embodiment of the invention 2 with additional plastic sheathing 22. The plastic sheathing 22 extends over the end of the device to effectively recess the electrically contactable portions of the end of the device. Plastic sheathing 22 is attached by heat shrinking a polymeric material over the surface of device 2.

Figures 4 to 7 show applications of devices of the invention, in particular device 2 of the first embodiment of the invention.

Figure 4 shows two devices 2 of the invention , attached to a printed circuit board 30 by solder joints 32, which attach lead wires 34 of devices 2 to a copper track (not shown) on circuit board 30. Devices 2 of the invention are located such that a conventional battery 36 comprising magnetically attractable end components 38 may be placed between magnetic faces of magnets 4 of devices 2 of the invention. Devices 2 of the invention hold battery 36 in place by magnetic attraction and also give electrical contact to the end faces 38 of the battery by electrical contact with magnets 4. Thus a method of retaining a battery in electrical contact on a circuit board is disclosed.

Figure 5 shows devices 2 of the invention attached to a circuit board 30 by solder joints 32. Solder joints 32 are part of the printed circuit of the circuit board 30 via copper tracks thereon (not shown). In between devices 2 of the invention are retained modular elements 40 and 42. Modular element 40 is a resistive element comprising magnetically attractable faces 44, which serve as an electrical contact between the surfaces of resistive device 40 and the resistive composition 46 in the modular device. A capacitive element 42 is also present and this similarly comprises magnetically attractable electrically connectable faces enclosing a capacitive structure 48. In use, as shown in figure 5, devices 2 of the invention may have placed between them a number of different modular elements comprising resistive elements, capacitive elements, inductive elements, conductive spacer elements and so forth, in a manner such that a given resistance, capacitance or inductance may be suitably built up by inserting modular elements between devices 2 of the invention, such that the elements of the invention are retained in physical contact and mechanical support, by magnetic attraction and in electrical contact, by electrical contact with opposite faces of the elements, of the various units. The magnetic attraction and electrical contact may be indirect, as when a modular element is sandwiched between other modular elements. Variations include where a modular element 40 is not magnetically attractable but is retained by the mutual attraction of the magnetic members 4.

Figures 6 and 7 show a further application of the invention. Devices 50 of the invention, 52 comprise magnets 4 as previously described. In device 50 of the invention, magnet 4 is orientated with a North pole away from the base of the retaining holder. Device 52 of the invention has magnet 4 orientated with the South pole away from the base of the retaining holder. Devices 50 and 52 of the invention are connected to circuit boards 56 and 58 by means of solder connections 54 and 60. By placing devices 50 and 52 of the invention in proximity they are attracted one to another and a mechamcal and electrical contact is formed in the junction 62 between the two devices, such that the circuit boards are held in physical and electrical contact. Figure 7 shows the effect of bringing in close proximity devices 50 of the invention with fields orientated in a like manner, such that circuit boards 56 and 58 are no longer able to be brought into mechanical and electrical contact using reasonable force due to repulsion, as illustrated by the double headed anow on the diagram.

Figure 8 shows a third embodiment of the invention. This is an end view of a modified conventional D-type connector, comprising a number of contacts 72 surrounded by an earth shield 74. Such a connector can be connected to a like connector simply by offering up the two faces one to another whereupon magnetic attraction holds the devices in physical and electrical contact. Of particular note is the potential for the arrangement of the magnetic field polarity associated with adjacent magnetic elements 72', 72", 72"' and so forth. By suitably orientating the magnetic fields of these individual units it is possible to make a template which is only magnetically recognisable (by magnetic attraction), by a similar template of another such device, such that a very large multiplicity of connectors may be present in a given device whereby a user is prevented from miscormecting connectors, even though the connectors may otherwise look and appear the same. In such a device care is taken to make sure that combinations of dissimilar magnetic patterns of adjoining elements are not present which are capable of still having a net magnetic attraction.

Figures 9, 10 and 11 show a fourth embodiment 80 of the invention. Magnet 4 is located in electrically insulating housing 82 in which it is slideably movable between opening 86 and further into recess 88. Magnet 4 is fixed to, resiliently biased by and in electrical contact with coil spring 84 which is itself at a remote end fixed to and in electrical contact with electrically conducting end plate 8. End plate 8 is connected to lead 10 for connection into, for example, the body of a connector of the third embodiment or to a printed circuit board (not shown). Use of the fourth embodiment of the invention with the third embodiment of the invention overcomes the stated need for care to be taken in the combinations of magnetic fields.

In use (Figures 10 and 11) close approach of devices of the fourth embodiment wherein the magnetic faces 90 of the magnets 4 are of opposite polarity draws magnets 4 together to form an electrical contact across the faces 90 of the magnets. Close approach of devices of the fourth embodiment wherein the magnetic faces 90 of the magnets 4 are of like polarity leads to magnets 4 retreating into cavity 88 as spring 84 is compressed. Therefore even if the ends 92 of insulating housing 82 are brought into physical contact no electrical contact between the surfaces 90 of magnets 4 occurs. Therefore the potential for sparking across the gap 94 between electrically connected surfaces 90 of magnets 4 is reduced.

Figure 12 shows a fifth embodiment of the invention. A permanent magnet 4 is retained in a holder 100 comprising rear face 8 which is in electrical contact with electrical contact wire 10 and resistor 102 but not in electrical contact with holder 100 side wall 12. Magnet 4 comprises a nickel-plated neodymium iron boron magnet of cylindrical form, the rear face 104 of which is in electrical contact with resistor 102 but not tubular side wall 12.

Alternative components to resistor 102 may be used such as a diode, capacitor or other discrete electronics component.

The terms magnetic adhesion and magnetic attachment refer to an attachment that is due to the force of magnetism leading to adhesion or attachment. The word attachment when not prefixed by the word magnetic is generally used to denote attachment in the normal meaning of the word. A device of the invention may be magnetically attached to another device (i.e. a releasable magnetic attachment) whilst itself being attached to and forming part of a device (e.g. by being soldered to it). Physical attachment by magnetic attachment denotes the physical component resulting from a releasable magnetic attachment, usually present here alongside an electrical attachment.

Figure 13 shows a sixth embodiment of the invention in cross section. A magnet 4 is enclosed inside two cylindrical holders 100, 200. The cylindrical holders comprise cylindrical side walls 204, 212 (respectively) and end faces 8, 202 (respectively) such as to define cups. To the rear face 8 of one holder 100 an electrical contact wire 10 is attached. Contact wire 10 comprises an elongate wire and an enlarged end portion 218 with a flat outer face. The outer face of the end portion 218 of the electrical contact wire is attached to the holder 100 by spot welding. A front face 202 of the second holder 200 can act as an electrical contact face to another device such as a battery. The holders are made of thin brass, for example. The holder 100 to which the electrical lead 10 is attached is silver plated. The holder 200 for abutting another device to make the electrical connection of the invention is nickel plated. Magnet 4 is in electrical contact with both holders 100, 200. The holders 100, 200 are held together by an interference (i.e. push fit) between the inner face of side wall 204 of the first holder 100 and the outer wall of side wall 212 of the second holder 200. Magnet 4 is held in place by an interference fit in the second holder 200 such that the magnet is held by friction against the inner walls of the side walls 212 of the second holder 200. The walls of the holding means are about 0.1mm thick. The magnet may be a ceramic magnet or the higher strength Samarium-Cobalt magnet and or Neodymium Iron Boron magnet. The benefits or retaining a magnet using the sixth embodiment when used under conditions where mechanical impact is likely is seen particularly with ceramic and Samarium-Cobalt magnets.

Alternative constructions of devices according to the sixth embodiment of the invention include inserting an adhesive compound in the space 206 between the inside of side wall 204 of the first holder 100 and the outside of side wall 212 of the second holder 200 to such as to hold the side walls together. Adhesive material may also be placed in the space between the magnet 4 and the rear wall 8 of the first holder. Adhesive material may also be placed in the space 216 between the side wall 212 of the second holder 200 and the magnet 4. A suitable adhesive is an epoxy resin.

Alternative shapes for the holders 100,200 include tubes of octagonal cross section particularly where alternate wall portions are bowed outward such that the holders form a deformable cup so as to deform when a magnet 4 is inserted therein so as to create an effective interference fit without making the devices to close tolerances.

Figure 14 shows a side elevation and cross section of a device of the seventh embodiment of the invention. The seventh embodiment of the invention comprises a magnet 4 enclosed in two holders 100, 202 and in a manner as described for the sixth embodiment of the invention. The seventh embodiment of the invention has additional contact wires 210, 210'. Contact wires 210, 210' contact the cylindrical side wall of the first holder 100. Second holder 200 also has an electrical contact wire 10 attached to the rear face 202 of the holder. The second holder 200 fits inside the first holder 100 and an electrical contact with a further device may be made via face 8 of the first holder 100.

Electrical contact wires for use in the above embodiment of the invention are optional and the invention may be used without electrical contact wires 10, 210, 210' attached. In these cases other means of attachment to electrical devices may be used. Furthermore, components of the invention comprising a metal holder in the form of a cup and a plastics holder in the form of a potting compound are preferably used without electrical contact wires.

In use, devices of the seventh embodiment of the invention may be attached to three different places in a printed circuit board by electrical leads 10, 210, 210'.

Figure 15 shows a side elevation in cross section of a device of an eighth embodiment of the invention. The device comprises a magnet 4 held inside two cylindrical steel containers 210, 220. One of the cylindrical containers 210 has an electrical contact wire attached to one side. The cylindrical holders 210 and 220 are held together by machine screw threads on the outside wall of side wall 212 of the first holder 210 and a machine screw thread on the inside wall of side wall 224 of the cylindrical holder 222. This embodiment of the invention is particularly suitable for larger scale applications. A sealant compound may be used between the machine screw threads when they are engaged hermetically sealing the magnet 4 in the space 226 between the holders.

Figure 16 shows a side elevation and cross section of a device of the ninth embodiment of the invention. Magnet 4 is held in holder 300 to which is attached electrical contact lead 10. Holder 300 is rectangular, here seen in cross section, and retains rectangular magnet 4 between side walls 312 and against rear wall 308. Magnet 4 is retained in holder 300 by adhesive means. Magnet 4 is enclosed in a device of the ninth embodiment of the invention inside holders 300 and holder 320. Cover 320 of holder 300 comprises side walls 324 and rear wall 322. The cover 320 is attached to holder 300 by placing over holder 300 and pushing the holder 300 and cover 320 together as indicated by the arrow on the drawing. On pushing cover 320 on holder 300 a wedge engaging means 330 engages in channel 336 in the holder 300. Wedge engaging means 330 comprises a front angled face 332 and vertical rear face 334 such as to engage in side wall 312 of the holder 300 as shown in Figure 17.

Figure 18 shows a side elevation in cross section of a device of a tenth embodiment of the invention. The device comprises a magnet 4 in a sealed container 400. The sealed container is made of mild steel and an electrical contact lead 10 is optionally attached to rear wall 408 of the holder 400.

Holders of the tenth embodiment of the invention may be constructed by placing a magnet 4 between two cylindrical containers 420 with side walls 412, 424 abutting one another. A weld 440 is then made between the abutting edges of the side walls 412, 424 to seal magnet 4 in the enclosed space thus formed. An electrical contact lead 10 may then be subsequently attached.

Figure 19 shows a side elevation in cross section of an eleventh embodiment of the invention. Magnet 4 is sealed in a container 500. The container 500 is made by placing a magnet 4 in a container 520 wherein the side walls 524 retain magnet 4 by an interference fit. Magnet 4 in container 520 is then abutted against a plate 508 and weld 540 made where the two portions 508, 520 of the device 500 meet.

When devices of the tenth and eleventh embodiments of the invention are made by high temperature welding the devices may be constructed by placing a non-magnetic magnetisable material in place of the magnet 4. The devices are then assembled as described above and a magnet 4 created by magnetising the now encapsulated non- magnetic magnetisable material. This has the advantage that no loss of magnetism will occur due to thermal degradation during the high temperature welding process.

In the sixth to twelfth embodiments of the invention a ceramic magnet may be used. Whilst ceramic magnets may be non-conductive there is no requirement for conductivity when used in these embodiments of the invention since electrical conductivity may be obtained by the external faces of the holders such as 100, 200. In addition negative consequences of the brittle nature of ceramic magnets is largely reduced and any breakage limited by use with the sixth to twelfth embodiments of the invention as any impact of the device with for example a surface can be largely absorbed by the external metal holders of these embodiments of the invention such that the ceramic magnet is protected or, if the magnet is broken it is still retained within the device and the device can still function.

The sixth to twelfth embodiments of the invention are advantageous for the use of magnets comprising iron as such magnets can thereby be used in proximity to coreosion causing materials without the magnet rusting. This is particularly relevant to Neodymium Iron Boron magnets that rapidly rust should there be any defect in any protective coating. Particularly advantageous is the use of a magnet protected by thin walled cans when used with batteries as this protects the magnet should a battery leak.

Figure 20 shows a side elevation in cross-section of a twelfth embodiment of the invention, Figure 21 shows an end view of the same embodiment. Three permanent magnets 4', 4", 4'" are held together by mutual magnetic attraction, the poles of the magnets being suitably orientated to facilitate this, i.e. in a North to South arrangement. The three magnets 4', 4", 4'" are retained in holder 6 of circular cross section by means of a push fit wherein an outer edge of magnet 4' and magnet 4'" abut against side wall 12 of holder 6. The three magnets are also in contact with rear face 8 of holder 6. Holder 6 comprises a thin metal shell of brass coated with silver. Attached to the rear face of holder 6 is electrical contact wire 10, a copper wire coated with silver, which is spot welded to the rear face 8 of holder 6. When seen in end view, Figure 21, a space is present either side of the magnets 4', 4", 4" 'this space 620 may be filled with a potting compound, such as an epoxy resin. The use of such a compound is advantageous as the magnets are more firmly retained in the holder and may be protected from shock and chemical attack where they are coated with the compound.

Figure 22 shows a side elevation in cross-section of a thirteenth embodiment of the invention, and Figure 23 shows an end view of the same embodiment. Three permanent magnets 4', 4", 4'" are held together by mutual magnetic attraction, the poles of the magnets being suitably orientated to facilitate this, i.e. in a North to South arrangement. The three magnets 4', 4", 4'" are retained in holder 600 of octagonal cross-section by means of a push fit wherein an outer end of magnet 4' and magnet 4'" abut against side walls 612 of holder 6 comprising eight faces 614. The three magnets 4', 4", 4'" are also in contact with rear face 608 of holder 600. Holder 600 comprises a thin metal shell of brass coated with silver. Attached to the rear face of holder 600 is electrical contact wire 10, a copper wire coated with silver which is spot welded to the rear face 608 of holder 600. When seen in end view (Figure 23) a space is present either side of the magnets 4', 4", 4'" this space 620 is filled with an epoxy resin potting compound 622. The use of such a compound is advantageous as the magnets are more firmly retained in the holder and may be protected from shock and chemical attack where they are coated with the compound. The octagonal holder has the advantage that magnets held therein have a higher surface area for electrical contact with the holder 600 walls 612 due to the facets 614 of the wall. This is particularly advantageous when the magnets 4', 4", 4'" are cylindrical as little contact will be present with the rear face 608 of the holder 600. In addition the octagonal shape more readily distorts to accommodate the magnets 4', 4", 4'".

Figure 24 shows a side elevation in cross-section of an application of devices of the invention according to a fourteenth embodiment of the invention. An assembly of two circuit boards 700 is shown wherein a base circuit board 58, to which is attached a permanent magnet in a holder 50, supports an upper circuit board 56 to which is also attached further permanent magnets in holders 50'. Magnets in holders 50, 50' on the upper and lower circuit boards are arranged so as to mutually repel one and other (compare Figure 7). The upper circuit board effectively floats due to the magnetic repulsion between the parent magnets in holders 50 and the assembly is held together against excessive movement by securing means 704 and guide means 702. The circuit boards are connected by securing means 704, which comprise a rod like elongate member with end caps 706 and 708. End cap 708 prevents the securing means 704 falling away from the assembly as the connecting means 704 is held only loosely through an orifice 710 in upper circuit board 56, end cap 706 prevents removal of the connecting means 704. Furthermore, guide means 702 may be present wherein the amount of lateral play of magnets 50' on the upper circuit board 56 compared to the corresponding magnets 50 on the lower circuit board 58 is restricted. Guide means 702 comprise an elongate cylinder surrounding cylindrical magnets in holders 50. The fourteenth embodiment of the invention enables a circuit board to be suspended i.e. levitated, for example, as required for a circuit board supporting delicate equipment, which is required to be vibration free. Benefits of cushioning any impact on the circuit boards may also be obtained.

The guide means are optional.

In use, should excessive forces be applied to the floating circuit board 56, the magnets in holders 50 may come into contact, electrical contact, and the device may therefore be provided with circuitry to act upon the electrical contact made between magnets in holders 50 such as to engage a protecting system for any delicate apparatus on the floating circuit board 56. Alternatively a device may be constructed so as to act solely as a switch wherein one circuit board is pushed towards another circuit board specifically for the puφoses of making an electrical contact for switching puφoses. Figure 25 shows a schematic plan view of an application of devices of the invention. Three magnets 4', 4", 4'" in a holder 612 as described previously are rotatably located with respect to detecting means 810, 810'. The detecting means comprise Hall effect switches, alternatively the detecting means may comprise read switches. On rotating the magnets in the holder 612 the detecting means 810, 810' may be suitably activated and thus a switch formed. In particular the rotatable location may be by means of balanced location on a fine pin to form an axis of rotation in the manner of a compass. The holder is therefore capable of orientating itself in alignment with the earth's magnetic field and the Hall effect switches may be used to establish the orientation of the magnets and hence enable direction to be established such as may be required in a direction finder. A further application of devices of the invention is shown in Figure 26 wherein a first holder with magnets 602 is rotatably located with respect to two further rotatable holders with magnets 602', 602". On rotating the holder with the magnets 602 rotational movement is induced in the adjacent magnets in holders 602', 602" wherein detecting means, 810, 810', 810", 810'" are suitably actuated so as to form an electrical connection.

Figure 27 shows a partial cross-section of a fifteenth embodiment of the invention 948 which comprises a panel mount connector 920 and a panel mount connector plug 910. The connector 920 and plug 910 comprise a plastics material, such as Delrin (R), into which magnetic connectors as described in Figure 1 are embedded. The magnetic connectors comprise permanent magnets 4, 4' retained in holders 6 and 6' in which the magnets are in electrical contact, holders 6, 6' are connected to and in electrical contact with wires 10 and 10' which pass through the connector 920 and plug 910 respectively. Plug 910 comprises magnet holder 912 with screw threaded portion 918 to which a plug cover 914 is attached by means of a mating machine screw thread 916. Wire 10 passes through a channel 944 in both parts 912, 914 of the plug 910 such that the wire emerges at an end of the plug remote from the end in which the magnet 4 is present. The emergent end of the wire may be suitably insulated and in normal use is used to attach to a piece of electrical equipment. The panel mount connector 920 comprises a similar permanent magnet 4' in a holder 6' with wire attached 10', the wire passing through a channel 944' in the connector such that the wire emerges at an end of the connector remote from the end in which the magnet 4' is present. The panel connector 920 comprises a recessed end portion 930, the recess comprises a wall 938 which limits lateral movement of the plug 910 when inserted therein and a base portion 926 comprising a face 936 of the magnet 4'. The face 936 of magnet 4' is of opposite polarity to the face 934 of magnet 4 so that the magnets 4, 4' attract. Panel connector 920 comprises, at an end remote from the recessed end, a screw thread 928 on which can be mounted a nut 924 with co-operating screw thread.

In use a panel connector 920 is placed through an aperture in a panel (not shown), such as a metal panel such that thread 928 passes through the aperture and a face of the panel butts against retaining shoulder 942 of the panel connector 920. A nut such as 924 is then placed in engagement with the screw thread portion 928 and tightened so as to firmly locate the panel connector 920 in the aperture of the panel (not shown). The end of wire 10' remote from the magnet may be connected to a piece of electrical equipment.

The fifteenth embodiment of the invention acts to form a releasable magnetic connector between the plug portion 910 and the panel connector 920 by means of inserting the plug 910 into the depression 930 in the connector such that magnets 4 and 4' come into electrical contact as the mutually attracting the faces of the magnets 934 and 936 respectively contact. The wires 10, 10' are thereby also brought into electrical contact thus forming an electrical connection.

The fifteenth embodiment of the invention is particularly advantageous in that axially withdrawing high strength magnets, one from another, when in a configuration as shown in Figure 27 requires a substantial force. A robust yet disconnectable electrical connection therefore realisable. However, high strength magnets are most easily detached from one another by applying a shearing force such that the magnets slide apart and any direct contact is reduced, the magnets being readily detached when little direct surface contact is present. In the fifteenth embodiment of the invention lateral movement of the plug and socket when connected is very limited due to the presence of the walls 938 of the recess 930 in the panel connector 920 which restrict lateral movement of the plug 910 relative to the panel connector 920. A particularly secure connection is therefore obtained as disconnection of the magnets 4, 4' is only possible by axially separating the two magnets, an operation that requires a substantially greater force than when a shearing action is possible.

In a variant on the fifteenth embodiment of the invention the clearance between the panel connector 920 and the plug 910 in the depression 930 can be reduced such that very little lateral or rocking movement of the plug is possible to ease detaching the magnets. Such movement may be further reduced by providing a deeper recess (c.f. 930). Alternatively a large gap may be produced such that the plug 910 may be levered over sideways or rocked such that the faces of the magnets 934, 936 are leverable apart and the plug more easily removed.

Connector parts 932 and 922 are preferably formed by securing a connector as described in Figure 1 in a pre-moulded holder. However, the connectors as described in figures 9 and 12 to 19 may alternatively be used.

Figures 28 and 29 show a sixteenth embodiment of the invention in the form of a battery holder 970. The battery holder according to the sixteenth embodiment of the invention comprises two magnetic connectors 2 as previously described (see Figures 1 or 13, for example) in association with a flexible holder 950 such that a battery holder is created capable of holding a battery 36 such as a pen-cell battery. The holder 950 comprises a sheet of flexible material, such as a plastics material, formed into a U shape. The holder therefore comprises a base section 952 and two upturned end sections 954, 954' which are generally peφendicular relative to the base section 952. The end sections 954, 954' comprise apertures 956 wherein a magnet 4 retained in a holder 6 forming a device according to the first embodiment of the invention 2 is retained. The holder 6 is adapted with a peripheral lip 960 which extends around the rim of the holder 6 such that when holder 6 is pressed through aperture 956 in an end 954 or 954' the magnet/holder combination 2 is retained in the aperture 956 by means of peripheral lip 960 abutting the inner side of end sections 954 and 954' around the periphery of aperture 956.

In use, a holder for a battery, as described above, may comprise part of an electrical circuit wherein connecting wires 10, 10' are suitably connected to the circuit. A battery 36 may be inserted into the battery holder 970 by sliding the battery between the two magnets 4, 4'. Due to the flexibility of the battery holder 950 and the strong attraction of the magnets 4, 4' for the magnetically attractable end faces 38 battery 36 the holder 950 conforms to the dimensions of the battery 36 so as to both securely hold the battery in the holder and also to form an electrical connection with the battery by means of the end faces 38 of the battery 36. The battery holder 970 / battery 36 assembly forms a rigid and dimensionally stable structure.

The flexible holder portion may be made of a suitable size to receive two or more batteries 36 and a corresponding number of magnetic connectors 2 depending upon the application for which the battery holder is intended.

The flexible material for forming the battery holder may comprise any suitable flexible non-conducting material such as stiff paper or cardboard, for example, a disposable battery holder may thus be realised.

Claims

1. A method of forming a releasable electrical connection, the method comprising the steps of: providing a first electrical device (2) and a second electrical device (2; 36; 40; 42; 50, 56, 58; 80) said first and second electrical devices being connected by at least one permanent magnet (4) so as to form a releasable electrical connection therebetween said method being characterised by providing said at least one permanent magnet (4) with electrically conducting holding means (6; 100, 200; 210, 220; 300; 400; 500) to retain said magnet.

2. A method according to claim 1 wherein said holding means is further provided with a separate electrical conductor (10; 34).

3. A method according to either claim 1 or claim 2 wherein the electrical connection forms part of an electrical circuit.

4. A method of forming a releasable electrical connection according to any one preceding claim by providing that the first or second electrical device (36; 40; 42) is held between two or more permanent magnets (4) so as to form a part of an electrical circuit.

5. A method according to any one preceding claim wherein the electrical devices are releasably electrically connected by magnetic attachment.

6. A method according to claim 5 wherein the electrical devices are releasably electrically connected only by magnetic attachment.

7. A method according to any one preceding claim wherein a permanent magnet associated with the first device (56) electrically contacts a permanent magnet associated with the second device (58) by means of magnetic attraction to form the releasable electrical connection.

8. A method according to any one preceding claim wherein the first or second electrical device comprises a printed circuit board (30; 56, 58).

9. A method according to any one preceding claim wherein the first and second electrical devices comprise printed circuit boards (56, 58).

10. A method according to any one preceding claim wherein the first or second device comprises one or more discrete electronic components (36; 40; 42; 102).

11. A method according to claim 10 wherein the one or more discrete electronic components are releasably magnetically attached by means of an attractive magnetic force between two or more permanent magnets.

12. A method according to claim 11 wherein the attractive magnetic force between two or more of the permanent magnets acts to sandwich the one or more components between said permanent magnets.

13. A method according to any one of preceding claims 10 to 13 wherein the one or more discrete electronic components comprise passive electronics components.

14. A method according to any one preceding claim wherein the permanent magnets are magnets with surface magnetic flux of greater than 1,000 Gauss.

15. A method according to claim 14 wherein the surface magnetic flux is between 3,000 and 6,000 Gauss.

16. A method according any one preceding claim wherein the at least one permanent magnet comprises neodymium iron boron magnets.

17. A method according to any one preceding claim wherein said holding means is provided in the form of a cup-shaped holder to receive and retain said at least one permanent magnet.

18. A method according to any one preceding claim wherein said holding means (200;

220; 300; 400; 500) completely encloses said at least one permanent magnet.

19. An electrical component (2) for use in the method according to any one of claims 1 to 18, the electrical component being characterised by comprising a permanent magnet (4), electrically conducting holding means (6; 100, 200; 210; 220; 300; 400; 500) for the magnet and an elongate electrical connector means (10, 34).

20. An electrical component according to either claim 19 or claim 20 wherein said holding means is in the form of a cup-shaped holder to receive and retain said magnet.

21. An electrical component according to either claim 19 or claim 20 wherein said holding means (100, 200; 220; 300; 400; 500) completely encloses said magnet.

22. An electrical component according to either claim 19 or claim 20 wherein the magnet is exposed on one face for the puφose of establishing an electrical contact to another device.

23. An electrical component according to any one preceding claim from 19 to 22 wherein the flexible elongate electrical contact is in the form of a single strand of wire.

24. An electrical component according to claim 21 wherein said holder comprises two mutually inter-engaging cups (100, 200; 210, 220; 300, 320) to enclose said magnet.

25. An electrical component according to claim 24 wherein the two mutually inter- engaging cups are held together by an interference fit.

26. An electrical component according to claim 24 wherein the two mutually inter- engaging cups are held together by screw threads.

27. An electrical component according to claim 21 wherein the holding means (400; 500) comprises a first and a second holder welded together.

28. An electrical component according to any one of preceding claims 19 to 27 wherein the holding means and the magnet are in electrical contact.

29. An electrical component according to any one of preceding claims 21 and 24 to 27 wherein the magnet is a ceramic magnet.

30. An electrical component according to any one of claims 24 to 27 wherein the two holder members are in direct electrical contact.

31. An electrical component according to any one of claims 19 to 30 wherein the holding-means has at least one wall of thickness less than 0.2mm.

32. An electrical component according to any one of claims 19 to 31 wherein the holding means comprises a metal.

33. An electrical component according to any one of claims 21 and 24 to 32 wherein the holding means forms a hermetic seal between the magnet and the outside of the holding means.

34. An electrical component according to any one of preceding claims 19 to 33 wherein attenuation of the magnetic field of the magnet is not greater than 1000 Gauss as measured on a portion of the surface of a component comprising a metal shell of 0.1mm thickness.

35. An electrical component according to claim 22 wherein one face of said magnet stands proud of said holding means.

36. An electrical component according to any one preceding claim from 19 to 35 forming a magnetic and electrical connector.

37. An electrical component according to any one preceding claim from 19 to 36 having a non-metallic mounting member (950) comprising plug (910) and socket (920) portions for accommodating two of said electrical components.

38. A battery holder comprising at least two electrical components (2, 2') according to any one of preceding claims 19 to 36 and further comprising a flexible sheet member for holding said at least two electrical components in spaced-apart relationship with said magnet portions (4) being adjacent to terminals of said battery (36) , in use.