Magnet System

Abstract

System 12 comprises a permanent magnet 14, a switchable magnet system 16 and optionally a magnetic field conduit 18 (e.g. comprising steel or soft ferromagnetic material with coercivity of <1 kA / m) ar

Description

TECHNICAL FIELD The present disclosure relates to magnet systems, in particular AWS systems that operate with the application of a magnetic fields. BACKGROUND Referring GB2571112A a powered magnet system of an AWS includes, with reference to figure 2 thereof, an electromagnet with a coil 12c which surrounds a core 12a, which applies an electromagnet magnetic field. Permanent magnets 11 apply a permanent magnetic field. The current through the coil is controlled by a pulse width modulated (PWM) current. In an unsuppressed state, with the electromagnet in an unpowered state, the permanent magnetic field is arranged to emit a magnetic field, with a field strength above a threshold at a predetermined height above a railway so that it can be detected by a sensor system arranged on a train moving over said railway. In a suppressed state, with the electromagnet in a powered state, the permanent magnetic field is arranged to be suppressed or at least partially attenuated such that an overall magnetic field, is undetected by a train moving over said railway. An AWS system can be arranged with an unpowered magnet system that comprises a permanent magnet to provide a south pole magnetic field, that is detected by said train. Subsequently, a north pole magnetic field provided by said powered magnet system in the unsuppressed state is interpreted as a cancelation of the warning. Alternatively, no signal from the powered magnet system in the supressed state is interpreted as a maintenance of the warning. A drawback of such an arrangement is that the powered magnet has limited applications. For example, it may not be alternatively implemented as the unpowered magnet, due to the direction of the magnetic field. Moreover, in the event of a power failure it may not maintain the supressed state. Therefore, despite the effort already invested in the development of AWS improvements are desirable. SUMMARY The present disclosure provides a magnet. The magnet system comprises: a permanent magnet, to provide a permanent magnetic field; a switchable magnet system to provide a switchable magnetic field and; a magnetic field conduit arranged to guide the permanent and switchable magnetic fields, wherein the magnet system is configured with the permanent and (in some cases) the switchable magnetic fields forming an overall magnetic field. In embodiments, the magnet system is configured to implementing a supressed configuration, in which adjoining poles of the permanent magnet and the switchable magnet system are of the opposed polarity, and in which said overall magnetic field is guided (e.g., with field lines) between the permanent magnet and the switchable magnet system, and between the adjoining opposed poles via the magnetic field conduit. By implementing a switchable magnet system to have switchable poles to provide the supressed configuration, in which the magnetic field conduit provides a guide to guide the permanent magnetic field lines of the permanent magnet and / or the switchable magnetic field of the switchable magnet system, between adjoining opposed poles of the permanent magnet and the switchable magnet system, convenient suppression may be achieved e.g., by providing a short-circuit containment of said fields. In embodiments, the magnet system is configured with an unsuppressed configuration, in which the magnetic field conduit does not guide the permanent magnetic field between adjoining poles. In embodiments, in the unsuppressed configuration, adjoining poles may not be opposed. The magnetic field conduit may not guide the permanent magnetic field between adjoining poles in the unsuppressed configuration because there may be no adjoining poles of opposed polarity (e.g., there may be no poles present in the switchable magnet system since it is switched off or the adjoining poles of the switchable magnet system may be of the same polarity). By implementing a switchable magnet system to have switchable poles to provide the unsuppressed configuration (e.g., by switching off the poles present in the supressed configuration, or by switching them to have the reverse polarity), the magnetic field conduit does not guide the permanent magnetic field between adjoining poles and (unlike for the supressed configuration) the short circuit containment of the magnetic field is no longer implemented. As used herein the term “switchable magnet system” may refer to: a magnet system with a switchable magnetic field that is switchable from an off to an on state, and / or; a magnet system in which the poles may be reversed, e.g., by changing a north pole to a south pole and the converse, to reverse the polarity of the switchable magnetic field. As used herein the term “switchable poles” may refer to poles of the switchable magnet system that can be switched from an off (e.g., with no poles present) to an on state (e.g., with poles present), and / or; poles that can be reversed in polarity, e.g., by changing a north pole to a south pole and the converse. As used herein the term “switchable magnetic field” may refer to the magnetic field emitted by the switchable magnet system. The switchable magnetic field may be switchable in terms of on / off and / or polarity. As used herein the term “adjoining poles” or “adjacent poles” may refer to the proximal most poles of separated magnet systems (e.g., the permanent magnet and the switchable magnet system). In particular, adjoining poles may refer to a pole of the permanent magnet and a separate pole of the switchable magnet system, which are proximal most the magnetic field conduit. Adjoining poles may also (or separately) refer to the other pole of the permanent magnet and the other separate pole of the switchable magnet system, which are distal the magnetic field conduit. Adjoining poles may no for example, refer to poles of the same magnets. As used herein the term “opposed polarity” in respect of the adjoining poles may refer to a pole of the permanent magnet being north or south and the proximal most pole of the switchable magnet system being the other of north or south. As used herein the term “same polarity” in respect of the adjoining poles may refer to a pole of the permanent magnet being north or south and the proximal most pole of the switchable magnet system being the same of north or south. As used herein the term “between adjoining poles” may refer to the magnetic field (e.g. the magnetic field lines) being generally transferred / conveyed, e.g. in a longitudinal direction. It may include field lines being conveyed directly between the poles and / or between the poles when viewed in the laterally and longitudinally defined plane, buy not necessarily directly, e.g., with a depth offset. As used herein the term “guide” in respect of the magnetic field conduit may refer to the influence of the magnetic field conduit used to change a direction of the magnetic field lines and / or flux (e.g. through the magnetic field conduit) compared to the condition of the magnetic field conduit not being present. As used herein the term “overall magnetic field” may refer to the combination of the permanent magnetic field and / or the switchable magnetic field in the suppressed and / or the unsuppressed configuration. In embodiments, with the magnet system implemented in use as said advanced warning system, the magnet system is configured: in the unsuppressed configuration with flux density to be above a first threshold flux density at a predetermined distance above a rail, and; in the suppressed configuration with a flux density to be below a second threshold flux density a predetermined distance above a rail, wherein the first threshold flux density is greater than the second threshold flux density. The first threshold, second threshold and predetermined distance may be selected according to AWS specifications such that the magnet system is compliant, e.g. so that a train can detect the overall magnetic field in the unsuppressed configuration and not detect the overall magnetic field in the unsuppressed configuration. In embodiments, the switchable magnet system is configured not to affect a magnetisation of the permanent magnet. For example, the permanent magnet has a coercivity selected and a coil of the switchable magnet system is arranged so that the permanent magnet is not demagnetised by the coil magnetic field at the location of the permanent magnet. By implementing the permanent magnet not to have its magnetic field coerced by the switchable magnet system, it may be ensured that only the switchable magnet system is switched. In embodiments, the permanent magnet has a coercivity of greater than an intensity of the coil magnetic field at a location of the permanent magnet and / or the coercivity of a switchable polarity permanent magnet in embodiments that include this feature. [Embodiment 1] In embodiments, in the unsuppressed configuration, the switchable magnet system is configured with no poles (e.g., an off state, including with no poles or substantially no poles that would effect the permanent magnetic field of the permanent magnet system, which may occur with a small residual magnetisation remaining of a core). In embodiments, the switchable magnet system comprises an electromagnet with: an optional core (e.g. an iron or air core), and; and a coil (e.g. an iron cored or air cored coil) arranged to apply a coil magnetic field to the core, wherein in the suppressed configuration the core is magnetised to provide said opposed poles (e.g. an on state). In embodiments, in the unsuppressed configuration the core is not magnetised and has no opposed poles (or poles). The electromagnet may be powered in the suppressed configuration and unpowered in the unsuppressed configuration. Such an arrangement where the switchable magnet system may not comprises a permanent switchable magnet (e.g., the core loses, including substantially loses, its magnetic field when unpowered) may be convenient since electrical circuitry to determine a polarity of the poles of the permanent switchable magnet system may be obviated. [Embodiment 2] In embodiments, in the unsuppressed configuration adjoining poles of the permanent magnet and the switchable magnet system are of the same polarity (e.g. north and north or south and south), with said overall magnetic field transmitted around (e.g., the magnetic field lines are guided around) the permanent magnet and the switchable magnet system between opposed poles of the same magnets. By implementing a magnet system to have switchable poles (in polarity) to provide supressed and unsuppressed configurations, the magnet system can permanently, e.g., under the absence of power, maintain either configuration until the poles are switched. By having opposed poles in the unsuppressed configuration, the short circuitry condition of involving the magnetic field conduit can be avoided, e.g. the magnetic field conduit does not act as a guide in the unsuppressed configuration. As used herein the term “around” in respect of the magnetic field transmission may refer to the magnetic field being transmitted generally between opposed poles of the same magnets (e.g., from north to south of the permanent magnet and / or from north to south of the switchable magnet system), including not along a length of the magnetic field conduit and / or including along a length of said magnets, which may be a depth direction. A substantial portion e.g., at least 70 % of the magnetic field may be transmitted in this manner, with a negligible amount of the magnetic field transmitted between the adjoining poles due to them have a same polarity. In embodiments, the switchable magnet system comprises: a switchable polarity permanent magnet, and; a coil arranged to apply a coil magnetic field to effect said switching of the polarity. In embodiments, the coil is arranged to apply the coil magnetic field to the switchable polarity permanent magnet and not (including substantially not) to the permanent magnet (e.g. it is arranged wrapped around the switchable polarity permanent magnet, which can be formed of one more magnets). By implementing switchable magnet system as an electromagnet, the switchable magnet system may be conveniently switched. In embodiments, the magnetic member (e.g., the switchable polarity permanent magnet) has a coercivity of less than 200 or 150 kA / m and / or greater than 17 or 30 kA / m. In embodiments, the magnetic member comprises a semi-hard magnetic material. [Conduit] In embodiments, the magnetic field conduit comprises a soft magnetic (e.g., a ferromagnetic) material, which may have a coercivity of less than 1 kA / m or less than 0.5 kA / m or less than 0.2 kA / m. By implementing the magnetic field conduit to have a low coercivity, it may be conveniently magnetised by the magnetic fields of the permanent magnet and the switchable magnet system to act as a guide and / or carrier for the said field. In embodiments, the magnetic field conduit is elongate and extends in the direction of said elongation between the adjoining poles. By implementing the magnetic field conduit to extend between the poles of the permanent magnet and the switchable magnet system (e.g., with the poles of the switchable magnet system present when powered), it may operate as a convenient guide. As used therein the term “between” in respect of the magnetic field conduit may refer to the ends of the magnet systems each or both being overlapped by the magnetic field conduit in one or more of the: depth; lateral; longitudinal direction, in a manner that bridges between (e.g., disposed between) the magnet systems. In embodiments, the magnetic field conduit is planar and extends in a longitudinal direction and a lateral direction, and the permanent magnet and a magnetic member of the switchable magnet system extend from proximal ends, that comprise said adjoining poles, in a depth (including a counter depth) direction, and said proximal ends are in operative proximity / proximal to the magnetic field conduit. As used herein the term “operative proximity” in respect of the magnetic field conduit and the poles of the proximal ends of the magnetic member of the switchable magnet system may be defined as touching or with a separation of less than 2 mm or 5 mm or 10 mm such that the magnetic field conduit can guide a substantial amount of the magnetic field between the poles. In embodiments, the permanent magnet and a magnetic member of the switchable magnet system sit side by side, e.g., they are longitudinally separated and overlap / are aligned to each other in the depth direction. In embodiments, the adjoining poles of the switchable magnet system and the permanent magnet are arranged longitudinally from each other at the same (including substantially the same) depth (rather than above and below each other, e.g., in use). In embodiments, the magnetic field conduit directly adjoins the adjoining poles of the permanent magnet and a magnetic member (e.g., it may overlap then ends of the poles in the longitudinal and lateral direction and / or may extend in the longitudinal direction therebetween). In embodiments, the switchable magnet system of the magnet system comprises first and second switchable magnet units, which are arranged on opposite sides (e.g., in a longitudinal direction) of the permanent magnet. By implementing first and second switchable magnet units, each with a magnetic member (e.g., a switchable polarity permanent magnet with switchable poles), the magnetic field may be better controlled (e.g., with more symmetry when compared to a single such system) in the supressed and / or unsuppressed positions. The power supply system may be configured to switch the magnetic member (e.g., the poles of the switchable polarity permanent magnet) of the first and second switchable magnet units concurrently or sequentially. In embodiments, with the magnet system implemented in use as said railway advanced warning system (e.g. when mounted on or in operative proximity to a rail such that the magnetic field can be detected by a train in the unsuppressed configuration), the magnet system is configured: with the magnetic field conduit proximal a passing train on a rail, and; and the permanent magnet and / or switchable magnet system distal (e.g. relative the magnetic field conduit) said train. By arranging the magnetic field conduit to be closer to a train (e.g. between the train and the permanent magnet and / or switchable magnet system), it may guide the magnetic field in the supressed position so that its is not detectable by the train. In embodiments, the permanent magnet of the magnet system comprises a base permanent magnet and a field shaping permanent magnet (which may act as or be alternatively configured as a flux plate). The field shaping permanent magnet is arranged to control a shape of the overall magnetic field in the unsuppressed configuration to be generally pyramid shaped with a tip proximal a passing train and a base distal said train. The field shaping permanent magnet may be arranged proximal a train in use with the base permanent arranged distal. The present disclosure provides a magnet system, the magnet system switchable between: a suppressed configuration, in which a magnetic field is supressed, and; an unsuppressed configuration, in which a magnetic field is unsuppressed, wherein the magnet system is configured to maintain both of said configurations without the application of power to the magnet system. The magnet system may implement the features of the magnet system of any preceding embodiment or another embodiment disclosed herein. Since the magnet system can maintain either configuration without power applied thereto it may be safe and reliable is use, e.g., a power failure does not trigger a false change of configuration. The present disclosure provides a magnet system and a power supply system that is configured to supply electrical energy to switch a switchable magnet system of the magnet system. In embodiments, the switchable magnet system is switchable (e.g., by the power supply) between: a suppressed configuration, in which a magnetic field (e.g., an overall magnetic field) is supressed, and; an unsuppressed configuration, in which the magnetic field is unsuppressed. In embodiments, the switchable magnet system is switched by powering, e.g., on and / or off. In embodiments, the switchable magnet system is switched by switching the poles of the switchable magnet system to reverse their polarity. The magnet system may implement any features of any preceding embodiment, or another embodiment disclosed herein. In embodiments, the magnet system comprises a housing arranged to house the magnet system. The housing may comprise a mounting system for connection to rails and / or tracks or other associated member of a railway. By implementing a mounting system the switchable magnet system may be conveniently secured in an operable position on the rail. In embodiments, the magnet system comprises a power supply system configured to supply electrical energy to switch the switchable magnet system to switch the poles thereof. The power supply may conveniently switch the magnet system between the supressed and unsuppressed configurations. In embodiments, the power supply system comprises a rechargeable power source, which is arranged to effect said switching. By implementing a rechargeable power source, the power supply system may act as a self contained unit, which is capable of effecting a predetermined number of switches e.g. 5 - 20 or 5 - 50. In embodiments, the rechargeable power source comprises one or more capacitors arranged to be charged by a power source. By implementing capacitors, e.g., super capacitors, the rechargeable power source may be quickly charger for operation. The capacitors may be arranged to step-up the current / voltage applied to the coil, e.g., with a series or parallel arrangement. In embodiments, the housing is arranged to at least partially house the power supply system, and / or least partially house the rechargeable power source. In embodiments, the power supply system comprises a portable power source, which is arranged to apply power to recharge the rechargeable power source. The portable power source may be separate from the housing. The portable power source may comprise a battery, e.g. a 12 V or 24 V battery. By implementing a portable power source, the magnet system may be operated in a range of applications where there is not an electrical network or it is not convenient to connect to such an electrical network. In embodiments, a portable power source supplies electrical energy to switch the switchable magnet system (e.g. without the rechargeable power source). In embodiments, the power supply comprises a connection to an electrical supply, e.g. a mains or other electrical network. In embodiments, the power supply system is arranged to apply an electrical current (e.g. as a pulse, which may be 5 - 30 V) to the switchable magnet system (e.g. to each of the coils thereof) above a threshold current (e.g. 10-60 Amps) for a predetermined amount of time (e.g. 10 - 200 ms). The power supply system may be arranged to switch the poles of the switchable magnet system to implement the suppressed configuration or unsuppressed configuration. The power supply system may be portable. The power supply system may be configured to implement a predefined number of switches. As used here the term “portable” in respect of the power supply system may refer to one or more of: said system being movable manually without lifting equipment; said system not requiring a separate power input from a mains or other electrical supply network to supply power; operation as a self contained unit. In embodiments, the power supply system comprises a power source and a current booster and / or rechargeable power source, which is arranged to boost and electrical current from the power source to effect said switching. In embodiments, the current booster comprises one or more capacitors arranged to be charged by the power source and to discharge a boosted electrical current. In embodiments, the power source comprises a battery unit, which may be portable. In embodiments, the power supply is portable. In embodiments, the power supply and does not require connection to an electrical energy supply network. By implementing a portable power supply system the advanced warning system may be conveniently installed and removed from a rail, e.g. without heavy lifting equipment and / or an electrical connection to a separate electrical energy supply. Other magnet systems may be implemented with the power supply system, e.g. a powered magnet system with an electro magnet to supress a permanent magnet. The present disclosure provides the magnet system of any preceding embodiment, or another embodiment disclosed herein arranged as an advanced warning system of a railway system. The present disclosure provides the advanced warning system of any preceding embodiment or another embodiment disclosed herein arranged as part of a railway system. The present disclosure provides use of the magnet system of any preceding embodiment or another embodiment disclosed herein for a railway advanced warning system. The present disclosure provides use of the advanced warning system of any preceding embodiment or another embodiment disclosed herein for a railway system. The present disclosure provides a method of supressing a magnetic field of a magnet system. The method may implement the magnet system of any preceding embodiment or another embodiment disclosed herein. In embodiments, the method comprises: switching a switchable magnet system so that adjoining poles of a permanent magnet and the switchable magnet system have an opposing polarity, and; guiding (e.g., by means of a magnetic field conduit or just via the proximity of the adjoining poles) a an overall magnetic field between the opposing polarity poles of permanent magnet and the switchable magnet system. In embodiments, the method comprises switching (e.g., from an unsuppressed state to a suppressed state) a switchable magnet system so that adjoining poles of the permanent magnet and the switchable magnet system are switched from a same polarity to an opposing polarity or are switched from having no polarity to an opposing polarity. The present disclosure provides a method of manufacturing a magnet system. The method may implement the magnet system of any preceding embodiment or another embodiment disclosed herein. In embodiments, the method comprises: arranging a switchable magnet system; a magnetic field conduit, and; a permanent magnet in operative proximity of each other, such that the magnetic field conduit can guide an overall magnetic field between opposing polarity poles of the permanent magnet and the switchable magnet system. The preceding summary is provided for purposes of summarizing some embodiments to provide a basic understanding of aspects of the subject matter described herein. Accordingly, the abovedescribed features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Moreover, the above and / or proceeding embodiments may be combined in any suitable combination to provide further embodiments. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims. BRIEF DESCRIPTION OF FIGURES Aspects, features and advantages of embodiments of the present disclosure will become apparent from the following description of embodiments in reference to the appended drawings in which like numerals denote like elements. Figure 1 is an illustrative view showing a railway system that comprises an embodiment advanced warning system. Figure 2 is an illustrative view showing a first and second example of a magnet system of the advanced warning system of figure 1, in which the magnet system is arranged in a supressed configuration. Figure 3 is an illustrative view showing the first example of the magnet system of the advanced warning system of figure 1, in which the magnet system is arranged in an unsuppressed configuration. Figure 4 is an illustrative view showing the second example of the magnet system of the advanced warning system of figure 1, in which the magnet system is arranged in an unsuppressed configuration. Figure 5 is an illustrative view showing a first example of the magnet system of the advanced warning system of figure 1, in which the switchable magnet system is arranged in an unsuppressed configuration. Figure 6 is a block diagram showing an embodiment power supply system for the switchable magnet system of the advanced warning system of figure 1. DETAILED DESCRIPTION OF EMBODIMENTS Before describing several embodiments of the system, it is to be understood that the system, its formation and its application is not limited to the details of construction or process steps set forth in the following description. It will be apparent to those skilled in the art having the benefit of the present disclosure that the system is capable of other embodiments and of being practiced or being carried out in various ways. The present disclosure may be better understood in view of the following explanations: As used herein, the term “railway system” may refer to a system comprising a network of rails located on tracks for wheeled vehicles running on the rails for transferring passengers and goods. It may include various systems for electrical power transmission, signalling, communication etc. As used herein, the term “advanced warning system” or“AWS” may refer to an arrangement of one or more magnetic field emitting devices, which provide a signal to a train travelling over the AWS when mounted on operative proximity to a rail. The AWS may comprise one or more of: an unpowered magnet system, and; a powered / switching magnet system as defined herein. As used herein, the term “unpowered magnet system” may refer to an arrangement that generates a fixed magnetic field (e.g. a north or south pole magnetic field) for detection by a train. The arrangement may comprise a permanent magnet. The arrangement may not include or require a power supply to generate said field. As used herein, the term “powered magnet system” or “switching magnet system” or “magnet system” may refer to an arrangement that generates in an unsuppressed configuration a magnetic field (e.g. a north and / or south pole magnetic field) for detection by a train. The arrangement may generate in an supressed configuration a magnetic field that is not detectable by a train. The arrangement may comprise a permanent magnet and / or a switchable magnet system. The arrangement may be switchable from between one or more of: a supressed configuration; an unsuppressed north pole magnetic field, and; a unsuppressed north pole magnetic field. The arrangement may not require power to maintain any of the aforesaid configurations. The arrangement may require power to maintain any of the aforesaid configurations. The arrangement may require power for said switching. The arrangement may include a power supply. As used herein, the term “permanent magnet” may refer an object made from a material that is magnetized so as to create its own persistent magnetic field. A permanent magnet may be formed from "Hard" materials with a high coercivity, which may be ferromagnetic or ferrimagnetic and can include: nickel; cobalt; alnico; ferrite, and; other rare-earth metals, that are subjected to processing in a strong magnetic field during manufacture to align their internal microcrystalline structure, making them hard to demagnetize. As used herein, the term “switchable magnet system” may refer to an arrangement of magnetic material in which the north and south poles may be switched in position. Said switching may be implemented by one or more of: a subjecting to a strong magnetic field above the material coercivity to enable demagnetising and remagnetisation; via mechanical switching of the positions of the poles; or other suitable means. A permanent magnet of the switchable magnet system may be formed from "Semi-Hard" materials with a high coercivity, examples include alnico. As used herein, the term “supressed configuration” may refer to an arrangement of the magnet system in which the magnetic field of the magnet system is below a threshold such that it is not detectable by a train. The threshold may be defined at a plurality of distances above a rail (e.g. in the depth direction). Example thresholds for the magnetic field in the suppressed configuration are provided on page 16 in the document AWS and TPWS Interface Requirements, Railway Group Standard (NTRs) GERT8075 Issue: Three, March 2018. These may be summarised as: The maximum flux density produced by a de-energised extra strength AWS electromagnet at 193 mm above rail level shall be 1.2 mT. The maximum flux density produced by a suppressed extra strength AWS magnet at 115 mm above rail level shall be 1.2 mT. As used herein, the term “unsuppressed configuration” may refer to an arrangement of the powered magnet system in which the magnetic field of the powered magnet system is below a threshold such that it is not detectable by a train. Example thresholds for the magnetic field in the unsuppressed configuration are provided on page 15 in the document AWS and TPWS Interface Requirements, Railway Group Standard (NTRs) GERT8075 Issue: Three, March 2018. These may be summarised as height above rail level (mm), Minimum flux density (mT): 120, 6.5; 140, 6.1; 160, 5.7; 180, 5.3; 200, 5.0; 220, 4.6. As used herein, the term “magnetic field conduit” may refer to an arrangement capable of guiding a magnetic field between adjacent poles of opposed polarity. Guiding may refer to a greater extent of magnetic field traveling through or in operative proximity to the magnetic field conduit compared to a like arrangement absent said conduit (e.g. if an air gap were present). The magnetic field conduit may comprises a soft ferromagnetic material, which may have a low coercivity, e.g. of less than 1 kA / m. Examples include mild steel an other low carbon steels. The coercivity may be selected so that it may be magnetised by the magnetic fields of the permanent magnet and the switchable magnet system to act as a guide and / or carrier for the said field. As used herein, the term “power supply” may refer to an implementation of one or more power sources and / or a connection system for connection to an external power network, with power for driving the switchable magnet system of the magnet system. As used herein the term “portable” may refer to an object with a size and / or weight that can be lifted by one or more users without lifting equipment. A weight of a portable object may be of less than 20 kg or 30 kg or 50 kg. A length dimension of a portable object may be of less than 20 or 50 cm in one or more of longitudinal, lateral and depth directions. Portable may be implemented for one or more of: the magnet system; the AWS system; the power supply; a power supply and / or rechargeable power supply of the power supply unit. A portable power supply system may comprise a system that does not require an external connection to a power supply network, e.g. a mains or other electrical supply. [System description] Referring to figure 1, a railway system 2 comprises an advanced warning system (AWS) 4 arranged in operative proximity to a rail 6 to provide a magnetic field (not illustrated in figure 1) that can be detected by a sensor system (not illustrated) arranged on a train 8 moving over said rail 6. In the example advanced warning system (AWS) 4 comprises an unpowered magnet system 10, which is based on a permanent magnet that emits south pole magnetic field. A powered magnet system 12, is arranged downstream of the unpowered magnet system 10, which will be discussed. In variant embodiments, which are not illustrated, the advanced warning system (AWS) 4 can be alternatively configured, e.g., with: a further powered magnet system in place of the unpowered magnet system etc. The rail 6 is orientated to extend in a longitudinal direction 100, with a lateral direction 102 extending between the rails 6 and with a depth direction 104 extending in a direction from a bed of the rail 6 to the train 8. [Powered magnet system general description] Referring to figure 2, the powered magnet system 12 comprises: a permanent magnet 14, to provide a permanent magnetic field; a switchable magnet system 16 to provide a switchable magnetic field and; a magnetic field conduit 18 arranged to guide the permanent and switchable magnetic fields. The magnet system 4 is configured with the permanent and switchable magnetic fields forming an overall magnetic field 20. The permanent magnet 14 has north poles 22 and south poles 24. The switchable magnet system 10 has north poles 26 and south poles 28. The poles are separated in the depth direction 106, as will be discussed. Referring to figure 2 the magnet system 12 is shown in a supressed configuration, in which adjoining north poles 22 and south poles 26 of the permanent magnet 14 and the switchable magnet system 10 respectively are of the opposed polarity, and in which said overall magnetic field 20 is guided between the permanent magnet 14 and the switchable magnet system 16, and between the adjoining opposed poles via the magnetic field conduit 18. The magnetic field conduit 18 acts to capture the leakage flux lines above the magnetic field conduit 18 as illustrated. Referring to a first example of figure 3 and a second example of figure 6 the magnet system 12 is shown in an unsuppressed configuration, in which the magnetic field conduit 18 does not guide the permanent magnetic field (e.g. the overall magnetic field 20) between adjoining poles 22, 28 of the permanent magnet 14 and the switchable magnet system 10. The is because: in the first example the adjoining poles 22, 28 are of the same polarity, and; in the second example the switchable magnet system 10 has no poles (e.g. it is switched off), both examples will be discussed following. The magnet system 12 in the unsuppressed configuration emits a north pole magnetic field above the magnetic field conduit 18, i.e., in the depth direction 104 for detection by a train borne AWS system. In variant embodiments, which are not illustrated, the magnet system in the unsuppressed configuration emits a south pole magnetic field above the magnetic field conduit, i.e., in the depth direction for detection by a train borne AWS system. Such an arrangement may be achieved by a manually movable permanent magnet mounting system or a powered reorientation system that includes a driven actuator. Combinations of the magnet systems may also be provided, e.g. a first South pole emitting magnet system upstream of a second North pole emitting magnet system, or other suitable combinations. The magnet system 12 can be retained in the suppressed and / or unsuppressed without the application of any power thereto (or without including a power sources) as will be discussed. [Magnetic field conduit] The magnetic field conduit 18 comprises a soft ferromagnetic material with a coercivity selected so that it is magnetised by the magnetic fields of the permanent magnet and the switchable magnet system so as to act as a guide and / or carrier for the said fields, such that the fields are guided to short circuit between adjoining opposed poles. It acts in a similar manner to a magnetic core of an electro magnet. A coercivity of the magnetic field conduit 18 is selected to be low such that it does not remain magnetised in an opposing state to the overall magnetic field 20. The magnetic field conduit 18 is planar and extends in the longitudinal direction 100 and lateral direction 102 to fully overlap the poles 22, 24 or 26 of the permanent magnet 14 and the switchable magnet system 16 in a plane defined by the longitudinal direction 100 and the lateral direction 102. The magnetic field conduit 18 is formed from steel. The coercivity of the material is selected so as to be less than the overall magnetic field 20, as will be discussed, at the location of said conduit. In the example, the coercivity is 0.12 kA / m. The magnetic field conduit 18 is physically separated in the depth direction 104 from the poles 22, 24 or 26 of the permanent magnet 14 and the switchable magnet system 16 by an airgap of less than 1 mm. An airgap may be implemented for the magnetic field conduit 18 to increase reluctance and aid in the prevention of the material magnetic field conduit becoming magnetically saturated In reference to figure 1, the magnetic field conduit 18 is arranged between the permanent magnet 14 and switchable polarity permanent magnet 30 and the train 18, hence to adjoin the poles of said magnets which are proximal most the train 8 in use. In variant embodiments, which are not illustrated a second magnetic field conduit may be arranged to short circuit the poles on the other side of the permanent magnet and switchable polarity permanent magnet, this function may also be provide by the housing. Hence the magnetic field conduit and second magnetic field conduit are arranged opposed to each other with the magnets therebetween. In variant embodiments, which are not illustrated: the magnetic field conduit partially overlaps the poles; magnetic field conduit; the magnetic field conduit may have other forms, e.g. a rod; the magnetic field conduit is omitted such that the overall magnetic field is guided between adjoining poles only due to the opposite polarity of said poles; the magnetic field conduit is formed of materials other than steel, e.g. other iron based alloys; the coercivity of the material may be less than 0.1 or 1 or 5 or 15 kA / m; the air gap may be alternatively dimensioned, e.g. less than 2 or 5 mm with an optional minimum of 0.25 mm; the air gap my be omitted, e.g. by means of an in contact connection of by filling said air gap with am maternal that may be electrically insulating. [Permanent magnet] The permanent magnet 14 extends with the poles 22, 24 arranged relative each other in the depth direction 104. The material of the permanent magnet 14 is Samarium Cobalt, Neodymium. The coercivity is in general greater than that of a switchable polarity permanent magnet of the switchable magnet system 16 or than that which can be coerced by the switchable magnetic field as will be discussed. Although this is not a design requirement, which is that the magnetisation of the permeant magnet is not effected by the coil (as will be discussed) and may be achieved by wrapping the coil to direct its magnetic field away from the permanent magnet. A coercivity of the permanent magnet 14 is above 800 kA / m to 3200 800 kA / m. In variant embodiments, which are not illustrated: an alternative material for the permanent magnet is implemented, e.g. another or a composition of a rare earth metals. [Switchable magnet system] The switchable magnet system 16 implements a magnet system with a switchable magnetic field that is switchable from an off to an on state, and / or; a magnet system in which the poles may be reversed, e.g. by changing a north pole to a south pole and the converse, to reverse the polarity of the switchable magnetic field, various examples of which are provide following. [First Example] In a first example of the switchable magnet system 16, referring to figure 3 (which shows the unsuppressed configuration), adjoining north poles 22, 28 and adjoining south poles 24, 26 of the permanent magnet 14 and the switchable magnet system 16 respectively are of the same polarity. Hence compared to the supressed configuration (shown in figure 2), the poles of the switchable magnet system 16 have been reversed. In the unsuppressed configuration of figure 3, due to adjoining poles having the same polarity, the overall magnetic field 20 is transmitted around the permanent magnet 14 and the switchable magnet system 16 between opposed poles of the same magnets. In this position the magnetic field conduit 18 may still guide the flux lines around the magnets. Moreover, the switchable magnetic field may optionally supplement the permanent magnetic field. As used herein the term “around” in respect of the magnetic field transmission may refer to the magnetic field being transmitted generally between opposed poles of the same magnets, including not along a length of the magnetic field conduit. The switchable magnet system 16 comprises a magnetic member, which in the first example is implemented as a switchable polarity permanent magnet 30 and a coil 32. The switchable polarity permanent magnet 30 extends with the poles 26, 28 arranged relative each other in the depth direction 104. The coil 32 is wrapped about a central axis that is aligned in the depth direction 104 and extends through the switchable polarity permanent magnet 30. The coil 32 is arranged to receive and electrical current supplied from a power supply, as will be discussed. The coil 32 can be implemented with any suitable gauge wire and material and number of windings to provide a coil magnetic field to effect said switching of the polarity of the permanent magnet 30. The wire may be copper or aluminium or other suitable material. The coil 32, switchable polarity permanent magnet 30 and permanent magnet 14 are configured to switch the polarity of the switchable polarity permanent magnet 30 and not the permanent magnet 14. In particular, the coil 32 is wrapped around the switchable polarity permanent magnet 30 to provide a concentrated field though the switchable polarity permanent magnet 30. The coil magnetic field and material of the switchable polarity permanent magnet 30 are selected to exceed a coercivity of the switchable polarity permanent magnet 30 so that it can be demagnetised from a first saturated condition, to be remagnetised in a different second saturated condition, in which the poles are reversed (as shown in figure 2 compared to figure 3). The switchable polarity permanent magnet 30 is made of a magnetic material which is semi-hard. In the example it is made of Alnico. The coercivity of the switchable polarity permanent magnet 30 is 48 kA / m, e.g. 600 oersted, such that it is switched with a magnetic field of 1800 oersted (Gauss). In variant embodiments, which are not illustrated: the magnetic member (e.g. the switchable polarity permanent magnet) is arranged as a plurality of separate and adjoining permanent magnets, e.g. four rod shaped magnets arranged about an axis, the coil may individually extend around each of the magnets or around the magnets as a whole; a coercivity of the switchable polarity permanent magnet may be less than 200 or 150 kA / m and / or greater than 17 or 30 kA / m; instead of a coil to switch the polarity of the switchable polarity permanent magnet, the switchable polarity permanent magnet may be rotatable to switch the poles by changing their position rather than via demanganization and remagnetisation, e.g. by either an actuator driven system or via manual switching, which can include a removable support for the switchable polarity permanent magnet that can support the switchable polarity permanent magnet in two positions. [Second Example] In a second example switchable magnet system 16, referring to figure 4 (which shows the unsuppressed configuration), the switchable magnet system 16 is similar to the first example, however it is configured with no poles. Hence compared to the supressed configuration (shown in figure 2: note for the first and second example figure 2 has been used to illustrate the supressed configuration as it is diagrammatically equivalent), the poles of the switchable magnet system 16 have been switched off, as will be discussed. The switchable magnet system 16 comprises an electromagnet with: a magnetic member implemented as a core 30 (rather than the switchable permanent magnet of the first example), and; and a coil 32 arranged to apply a coil magnetic field to the core 30. The power supply powers the coil 32 of the switchable magnet system 16 as will be discussed. Hence in the suppressed configuration (as shown in figure 2) the core 30 is magnetised by electrical current through the coil 32 to provide said opposed poles and in the unsuppressed configuration (figure 4) the core 30 is not magnetised and the poles are not maintained, that is. there are no poles as illustrated. In the second example, electrical circuitry to determine a polarity of the poles of the permanent switchable magnet 30 may be obviated. All other features (where compatible) and the associated variants are as for the first example, which for brevity are not repeated. [Third example implementation] Referring to figure 5, a third example (shown in the supressed configuration) that implements the features of the general example, including either the first or second example of the switchable magnet system discussed in association with figures 2 - 4 is provided, including the associated variants. For brevity, like components use the same numerals and are not discussed. Unlike the first and second example the switchable magnet system 16 comprises first 34 and second 36 switchable magnet units, which are arranged (e.g., symmetrically disposed) on opposite sides of the permanent magnet 14 with respect to the longitudinal direction 100. In this manner, due to the more symmetrical arrangement, in the unsuppressed and / or suppressed configuration a more uniform magnetic field may be provided. The coils 32 can be concurrently or sequentially energised to switch the switchable magnet system 16 by the power supply system as will be discussed. In variant embodiments, which are not illustrate: a single coil wraps around both the magnetic members 30; the first and second switchable magnet units may be alternatively disposed. In the unsuppressed configuration (not illustrated): proximal the magnetic field conduit 18 adjoining poles of the permanent magnet 14 and the magnetic members 30 of the first 34 and second 36 switchable magnet units are all north poles, and; proximal the magnetic field conduit 18 adjoining poles of the permanent magnet 14 and the magnetic members 30 of the first 34 and second 36 switchable magnet units are all south poles. In the suppressed configuration (as illustrated in figure 5) proximal the magnetic field conduit 18 adjoining poles of the permanent magnet 14 and the magnetic members 30 of the first 34 and second 36 switchable magnet units are opposed as north 22 and south 26 respectively, and; distal the magnetic field conduit 18 adjoining poles of the permanent magnet 14 and the magnetic members 30 of the first 34 and second 36 switchable magnet units are opposed as south 24 and north 28 respectively. The magnetic field conduit 18 is as for the general example and is additionally arranged to extend in the longitudinal direction 100 to overlap the magnetic member of the second switchable magnet unit 36. The permanent magnet 14 comprises a base permanent magnet 38 and field shaping permanent magnet 40. The base permanent magnet 38 is as described for the general example. The field shaping permanent magnet 40 is removable and reconfigurable e.g. by using different shape and / or strength magnets for tuning of the shape of the magnetic field in the unsuppressed configuration. In the example, the field shaping permanent magnet 40 has a higher strength magnetic field than the a base permanent magnet 38. A material of the field shaping permanent magnet 40 is made of Neodymium. The field shaping magnet 40 is arranged with opposed poles adjoining a pole of the base permanent magnet 38. In variant embodiments, which are not illustrate: the field shaping permanent magnet comprises more than one magnet, which can be layered on top of each other in the depth direction, and field shaping permanent magnet is omitted. The magnet system 12 includes a base 42, which forms part of a housing (not illustrated), that houses the components of the magnet system 12. The base 42 is formed out of the same material as the magnetic field conduit 18 and therefore provides a similar effect in collecting an guiding the magnetic field between opposed adjoining poles of the permanent magnet 14 and the switchable magnet system 16. In embodiments, with the magnet system implemented in use as said railway advanced warning system, the magnet system is configured: with the magnetic field conduit proximal a passing train on a rail, and; and the permanent magnet distal said train. By arranging the magnetic field conduit to be closer to a train (e.g. between the train and the permanent magnet), it may guide the magnetic field in the supressed position so that its is not detectable by the train. [Fourth example implementation] In a not illustrated fourth example of the powered magnet system of the general example (including the first or second example of the switchable magnet system) and / or the third example may form a repeating unit such that there are multiple such repeating units arranged to adjoin each other in the lateral direction. In a specific fourth example two repeating units of the third example are provided so that there are: two permanent magnets, and; two switchable magnet systems, each with first and second switchable magnet units. The repeating units may share a common (e.g., integrally formed): housing including an integrally formed base, and / or; magnetic field conduit. The first - fourth examples, comprise a housing (not illustrated) arranged to house the magnet system. The housing comprises a mounting system (not illustrated) for connection to rails and / or tracks or other associated member of a railway (e.g. part of a bedding). The mounting system may comprise a bracket or apertures to receive mechanical fixtures, including bolts etc. [Power supply] Referring to figure 6, the advanced warning system 4 of any of the preceding examples includes a power supply system 50 to operate the powered magnet system 12. The power supply system 50 is arranged to supply electrical energy to: switch the poles 26, 28 (e.g., to reverse their polarity or to switch them on depending on whether the first or second example of the switchable magnet system 16 is implemented) of the switchable magnet system 16 to switch between the previously described suppressed configuration or unsuppressed configuration. The power supply system 50 when triggered applies a pulsed electrical current to the or each coil 32 to apply the coil magnetic field to the magnetic member 30. In variant embodiments, which are not illustrated, in which a switchable polarity permanent magnet is rotated to switch its polarity, the power supply system alternatively supplies electrical energy to a suitable actuator for said rotation. In a first example, the power supply system 50 includes: a power source 52, and a rechargeable power source 54. The a power source 52 supplies electrical energy to recharge the rechargeable power source 54 and the rechargeable power source 54 supplies the electrical energy to the magnet system 12. The power source 52 is separate from the housing and is a portable e.g. a 12 V or 24 V battery. In variant embodiments, the power source is alternately implemented, for example as: a different voltage battery; and alternative source, including a fuel cell, and; a connection to an electrical supply, e.g. a mains or other electrical network. The rechargeable power source 54 is arranged in the housing (not illustrated) and receives electrical energy for recharging from the power source 52 via an electrical terminal (as will be discussed) through the housing. In variant embodiments, alternative arrangements are contemplated, for example: the rechargeable power source is not arranged in the housing; the rechargeable power source and the power source are both arranged in the housing with the magnet system; the rechargeable power source and the power source are both arranged in a dedicated separate housing; the rechargeable power source and the power source are both arranged in their own housing. The rechargeable power source 54 is implemented as two super capacitors. In the example the two super capacitors are arranged in series and are 12.5 V, 65 Farad. The rechargeable power source 54 and power source 52 are configured for charging of the rechargeable power source 54 to produce a suitable pulse (as will be discussed), within a period of several minutes, e.g. more than 20 seconds and less than 5 or 10 minutes. The rechargeable power source 54 is configured for 5-100 switches per charge until the electrical current is below the threshold required to effect said switching. In variant embodiments, which are not illustrated, other rechargeable power sources are implemented, for example: the capacitors have other values; other numbers of capacitors are used, e.g. 1 or 4; the capacitors have other arrangements, e.g. in parallel; a rechargeable battery is implemented. The rechargeable power source 54 is configured to apply a pulse, typically as a square wave, of electrical energy to the or each coil 32. The pulse is 24 V at 40 A per coil for 100ms. The pulse may be applied as a single pulse or pulsated. In variant embodiments, the pulse is alternatively configured, for example: 5 - 30 V to each of the coils; 10-60 Amps to each of the coils; for a predetermined amount of time of 10 - 200 ms; the pulse may have different waveforms, e.g. sine or saw toothed. The power supply system 50 includes a user interface 56 to initiate (e.g. with a trigger switch) the application of the electrical current to the or each coil 32. The user interface 56 may also be operable to select a polarity (e.g. with a polarity switch) of the current pulse (e.g. by changing a direction of the electrical current through the coil 32 by switching live and neutral circuit paths). In the first to fourth examples of the magnet system 12, the power supply system 50 is arranged to apply the electrical current to the each of the coils 32 in parallel, such that each coil 32 receives the same, (including substantially the same) electrical energy. During operation the user interface 56 indicates to a user when the super capacitors 54 are charged (e.g. by a volt and / or ammeter indicating crossing of a voltage / current threshold) and therefore that the electrical current can be applied to the or each coil 32. In variant embodiments, which are not illustrated: rechargeable power source is arranged to boost or reduce the current and / or voltage from the power supply, it may for example include a step up or step down transformer. The operability of the magnet system 12 with the first example of the power source enables it to be used where there is no trackside power. Moreover, the energy consumption of the magnet system 12 is low since it can maintain either the suppressed or the unsuppressed configuration without the application of electrical energy from the power supply system 50. In a second example, the power source supplies electrical energy to switch the switchable magnet system directly, thus obviating the rechargeable power source. The magnet system 12 includes a first interface terminal (not illustrated) to receive the electrical energy from the power supply 54 of the power supply system 50. The power supply system 50 includes a complimentary second interface terminal (not illustrated) to enable a removable attachment to the magnet system 12. The configuration of the magnet system 12 may therefore be set and the power supply 52 removed to reduce a likelihood of an unauthorised operator tampering with the advanced warning system 4. The use of capacitors as the rechargeable power source 54 are beneficial in this instance as they gradually discharge over a predetermined amount of time (e.g. over a period of several hours, or up to an hour, or less than a day) rendering the magnet system 12 unswitchable without the power source 54. Moreover, the ability of the rechargeable power supply to be able to perform a predetermined number of switches without the power source 54 connected is beneficial since it enables the power source 54 to be switched with the magnet system 12 remaining switchable. Whilst the magnet system disclosed herein has been descried in conjunction with an advanced warning system of a railway system, it will be understood that the magnet system (including the various disclosed embodiments) may be implemented in other applications, in particular those in which a loss of power to the magnetic system may not change the magnetic state. For example, the magnet system may be implemented in systems for which it would be beneficial not to have emergency back up power systems to maintain power to the magnet system to maintain a particular state, examples include marine, automotive and aerospace sectors. As used in this specification, any formulation used of the style “at least one of A, B or C”, and the formulation “at least one of A, B and C” use a disjunctive “or” and a disjunctive “and” such that those formulations comprise any and all joint and several permutations of A, B, C, that is, A alone, B alone, C alone, A and B in any order, A and C in any order, B and C in any order and A, B, C in any order. There may be more or less than three features used in such formulations. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Unless otherwise explicitly stated as incompatible, or the physics or otherwise of the embodiments, example or claims prevent such a combination, the features of the foregoing embodiments and examples, and of the following claims may be integrated together in any suitable arrangement, especially ones where there is a beneficial effect in doing so. This is not limited to only any specified benefit, and instead may arise from an “ex post facto” benefit. This is to say that the combination of features is not limited by the described forms, particularly the form (e.g. numbering) of the example(s), embodiment(s), or dependency of the claim(s). Moreover, this also applies to the phrase “in one embodiment”, “according to an embodiment” and the like, which are merely a stylistic form of wording and are not to be construed as limiting the following features to a separate embodiment to all other instances of the same or similar wording. This is to say, a reference to ‘an’, ‘one’ or ‘some’ embodiment(s) may be a reference to any one or more, and / or all embodiments, or combination(s) thereof, disclosed. Also, similarly, the reference to “the” embodiment may not be limited to the immediately preceding embodiment. The foregoing description of one or more implementations provides illustration and description, but is not intended to be exhaustive or to limit the scope of the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of various implementations of the present disclosure. LIST OF REFERENCES 2 Railway system 4 Advanced warning system 10 Unpowered magnet system 12 Magnet system 14 Permanent magnet 22 North pole 24 South pole 38 Base permanent magnet 40 Field shaping permanent magnet 16 Switchable magnet system (34 First unit, 36 Second unit) 30 Magnetic member (switchable polarity permanent magnet or core) 26 North pole 28 South pole 32 Coil 18 Magnetic field conduit 42 Base 20 Overall magnetic field 50 Power supply 52 Battery unit 54 Capacitors 56 User interface 6 Rail 8 Train 100 longitudinal direction 102 Lateral direction 104 Depth direction

Claims

1. A magnet system comprising:a permanent magnet, to provide a permanent magnet field;a switchable magnet system to provide a switchable magnet field;wherein the magnet system is configured with the permanent and switchable magnetic fields forming an overall magnetic field, and:a supressed configuration, in which adjoining poles of the permanent magnet and the switchable magnet system are of the opposed polarity, and in which said overall magnetic field is guided with field lines between the permanent magnet and the switchable magnet system, and between the adjoining opposed poles;an unsuppressed configuration, in which adjoining poles of the permanent magnet and the switchable magnet system are of the same polarity, with said overall magnetic field having magnetic field lines which are guided around the permanent magnet and the switchable magnet system between opposed poles of the same magnets.

2. The magnet system of claim 1, wherein the magnet system is configured:in the unsuppressed configuration with flux density to be above a first threshold,in the suppressed configuration with a flux density to be below a second threshold,and the first threshold flux density is greater than the second threshold flux density.

3. The magnet system of claim 2, wherein the switchable magnet system is configured not to affect a magnetisation of the permanent magnet.

4. The magnet system of any preceding claim, wherein the switchable magnet system comprises:a switchable polarity permanent magnet, and;a coil arranged to apply a coil magnetic field to effect said switching of the polarity.

5. The magnet system of claim 4, wherein the switchable polarity permanent magnet has a coercivity of less than 200 or 150 kA / m and / or greater than 17 or 30 kA / m.

6. The magnet system of any preceding claim comprising a magnetic field conduit arranged to guide the permanent and switchable magnetic fields.

7. The magnet system of claim 6, wherein in the unsuppressed configuration the magnetic field conduit does not guide the permanent magnet field between adjoining poles.

8. The magnet system of either of claims 6 or 7, wherein in said overall magnetic field is guided with field lines between the permanent magnet and the switchable magnet system, and between the adjoining opposed poles via the magnetic field conduit.

9. The magnet system of any of claims 6 to 8, wherein the magnetic field conduit comprises a soft ferromagnetic material, which has a coercivity of less than 1 kA / m.

10. The magnet system of any of claims 6 to 9, wherein:the magnetic field conduit is planar and extends in a longitudinal direction and a lateral direction, and the permanent magnet and a magnetic member of the switchable magnet system extend from proximal ends, that comprises said adjoining poles, in a depth direction, and said proximal ends are proximal the magnetic field conduit.

11. The magnet system of any preceding claim, the magnet system is configured:with the poles of the permanent magnet arranged relative each other in a depth direction.

12. The magnet system of any preceding claim, wherein the switchable magnet system comprises first and second switchable magnet units, which are arranged on opposite sides of the permanent magnet.

13. The magnet system of any preceding claim, wherein the magnet system is configured to maintain both of said configurations without the application of power to the magnet system.

14. A magnet system of any preceding claim and a power supply system configured to supply electrical energy to switch the switchable magnet system.

15. The magnet system of claim 14, wherein the power supply system comprises a rechargeable power source, which is arranged to effect said switching.

16. The magnet system of claim 15, wherein the rechargeable power source comprises one or more capacitors arranged to be charged by a further power source.

17. The magnet system of any of claims 14-16, wherein a housing houses the magnet system and / or the rechargeable power source.

18. The magnet system of any of claims 14 to 17, the power supply system comprises a portable power source, which is arranged to apply power to recharge the rechargeable power source.

19. The magnet system of any of claims 14 to 18, wherein the power supply system is portable and does not require connection to an electrical energy supply network.

20. A method of supressing a magnetic field of a magnet system, the method comprising:switching poles of a switchable magnet system so that adjoining poles of a permanent magnet and a switchable magnet system are switched from having a same polarity to having an opposing polarity, and;guiding an overall magnetic field between the opposing polarity poles of the permanent magnet and the switchable magnet system.

21. A method of manufacturing a magnet system comprising:arranging: a switchable magnet system, and; a permanent magnet in operative proximity of each other, such that an overall magnetic field can be guided between opposing polarity poles of the permanent magnet and the switchable magnet system, wherein the switchable magnet system has reversible polarity poles.

22. A method of installing the magnet system of any of claims 1 to 13, the method comprising:arranging the poles of the permanent magnet and the switchable magnet system arranged vertically below each other.T +44(0)30 0300 2000A

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