shaker

Abstract

There is provided a shaker configured for use in a seat, the shaker including: a magnet unit including: a U-yoke, a main magnet positioned within the U-yoke, a flux guide positioned on top of the main magnet, and a counter magnet positioned on top of the flux guide; wherein the U-yoke and the flux guide are configured to guide magnetic flux generated by the main magnet across an air gap between the U-yoke and the flux guide; wherein the counter magnet and the main magnet are oppositely magnetised for reducing stray magnetic flux external to the shaker.

Description

[0001] SHAKER

[0002] This application claims priority to GB2402964.7, filed 29 February 2024.

[0003] Field of the Invention

[0004] The present invention relates to a shaker for transmitting vibrations to an application.

[0005] Background

[0006] Shakers are known devices for transmitting vibrations to an application. Herein, an “application” can be understood as any apparatus to which the shaker may be attached (for example a vehicle seat). Shakers are sometimes known as electrodynamical shakers or electromechanical shakers.

[0007] A shaker, if attached to a car seat (e.g. via a frame of the car seat, via foam of the car seat, or via other coupling features of the car seat), can be used for transmitting vibrations to a person sat in the car seat. Such vibrations can be used to provide a tactile warning to a person sat in the seat, to provide a massage to a person sat in the seat, and / or to enhance a listening experience to a person sat in the seat (e.g. by helping them “feel” bass sounds more strongly).

[0008] The present invention has been devised in light of the above considerations.

[0009] Summary of the Invention

[0010] In use, a shaker may be close to a person. For example, where the shaker is attached to (e.g. mounted in) a car seat, the shaker may be close to the occupant of the car seat. Since a shaker as an electromechanical transducer includes a permanent magnet configured to generate a static magnetic field, the resulting stray field leaking outside of the shaker may permeate the occupant and, in particular, the chest of the occupant.

[0011] The present inventor has observed that a stray magnetic field from a shaker may pose a health risk for an occupant with a cardiac implantable electronic device (abbreviated as CIED below). The CIED may be configured to be temporarily disabled in response to a sufficiently strong static magnetic field, which may be done by medical personnel in specific circumstances, e.g. in the case of cardiac arrest, and should be avoided under other circumstances. As such, the present inventor believes that the risk of a shaker interfering with the CIED should be minimised.

[0012] According to a first aspect of the invention, there is provided a shaker configured for use in a seat, the shaker including: a magnet unit including a U-yoke, a main magnet positioned within the U-yoke, a flux guide positioned on top of the main magnet, and a counter magnet positioned on top of the flux guide; wherein the U-yoke and the flux guide are configured to guide magnetic flux generated by the main magnet across an air gap between the U-yoke and the flux guide; wherein the counter magnet and the main magnet are oppositely magnetised for reducing stray magnetic flux external to the shaker.

[0013] By providing the counter magnet, the stray magnetic flux generated by the magnet unit is reduced and correspondingly the risk of interfering with a CIED is reduced. Moreover, performance of the shaker may not be adversely affected and, in at least some examples, may be improved over a shaker without the counter magnet.

[0014] The counter magnet and the main magnet being oppositely magnetised for reducing the stray magnetic flux may include the main magnet and the counter magnet being arranged such that the same magnetic poles of the main magnet and the counter magnet face towards each other. For example, the magnetic north poles of both the main magnet and the counter magnet may face the flux guide or, alternatively, the magnetic south poles of both the main magnet and the counter magnet may face the flux guide.

[0015] The main magnet and the counter magnet may each be a permanent magnet, such as a rare earth magnet.

[0016] The main magnet and the counter magnet may each be approximately cylindrical.

[0017] The main magnet and the counter magnet may each comprise more than one structural element.

[0018] The shaker may further include a coil assembly. The magnet unit and the coil may be configured to magnetically cooperate so as to cause relative motion of the coil assembly and the magnet unit along a movement axis when the shaker is in use.

[0019] The magnet and the counter magnet may be coaxially arranged with respect to the movement axis.

[0020] Providing of a counter magnet to adjust the static magnetic field of a main magnet is in principle known in the context of electrodynamic loudspeakers. Examples are described in US3067366, GB872194, GB918033, US3593239, JP2001128285, JP2003153380, KR20050080808, JP2006020186, KR20060080014, US2016227325. The counter magnets described in these examples, however, are provided in loudspeakers (as opposed to shakers) and are provided based on different technical considerations and motivations. More particularly, addition of a counter magnet in a loudspeaker is generally described for purposes of increasing the magnetic flux in the air gap whereas reduction of stray magnetic flux, if noted at all, generally considered a side effect.

[0021] The U-yoke and the flux guide may each be understood as a flux guiding element configured to guide magnetic flux generated by the magnet unit and, in particular, generated by the main magnet and the counter magnet. Each flux guiding element may comprise more than one structural element.

[0022] The flux guide may be a washer.

[0023] The U-yoke and the flux guide may be coaxially arranged with respect to the movement axis.

[0024] At least one of (preferably each of) the main magnet, the flux guide, and the counter magnet may have a width in a direction perpendicular to the movement axis that is more than 2 times, preferably more than 3 time, preferably more than 4 times, preferably more than 5 times larger than its thickness in the direction of the movement axis. In some examples, the width of the main magnet or the counter magnet may be more than 10 times larger than its thickness, or more than 15 times larger than its thickness, or more than 20 times larger than its thickness.

[0025] A magnetic moment ratio mmr of the magnet unit may be in a range from 0.2 to 0.9. The magnetic moment ratio mmr may be defined as:

[0026] Here, Brmmis the magnetic remanence of the main magnet; Vmmis the volume of the main magnet; Brcmis the magnetic remanence of the counter magnet; Vcmis the volume of the counter magnet.

[0027] The magnetic moment ratio mmr of the magnet unit may suitably express a technical relationship between the main magnet and the counter magnet and, in particular, how both magnets in combination affect the stray magnetic flux external to the shaker.

[0028] A magnetic moment ratio mmr in the range from 0.2 to 0.9 may quantify a combination of the main magnet and the counter magnet whereby the stray magnetic flux generated by the magnet unit is suitably reduced. In some examples, the magnetic moment ratio mmr may be in the range from 0.3 to 0.8; optionally in the range from 0.4 to 0.7; optionally in the range from 0.45 to 0.65.

[0029] The present inventor has found that magnetic moment ratio mmr with a value in the above described ranges may correspond to an arrangement wherein the stray magnetic flux generated by the magnet unit is reduced by an adequate amount to prevent interference with CIEDs, whilst helping to minimise the amount of (expensive) magnetic material used.

[0030] The magnetic moment ratio mmr may be approximately 0.6, e.g. may be in the range from 0.45 to 0.65.

[0031] In some examples, a magnetic moment ratio mmr in the range 0.45 to 0.65 (e.g. around 0.6) may help to minimise the amount of stray field (see e.g. Fig. 7).

[0032] The magnetic flux guided across the air gap may have a magnetic flux density of at least 0.5 Tesla. The magnetic flux density in the air gap may be up to 1 .2 Tesla. In some examples, the magnetic flux density in the air gap may be around 0.9 Tesla.

[0033] A magnetic flux density of the stray field generated by the magnet unit and external to the shaker may be limited by the combination of the main magnet and the counter magnet.

[0034] In some examples, the magnet unit may be configured such that the magnetic flux density of the stray field does not exceed 0.5mT (milli-Tesla) at a distance of 30mm (millimetres) from the magnet unit; or in some examples does not exceed 0.3mT (milli-Tesla) at a distance of 30mm from the magnet unit.

[0035] In some examples, the magnetic flux density in the air gap may be approximately 1000 times higher than the magnetic flux density of the stray field at a distance of 30mm from the magnet unit.

[0036] The magnetic flux density of the stray field may be measured at a location along the movement axis of the shaker. The magnetic flux density measured at a location along the movement axis may also be referred to as the on-axis magnetic flux density. The magnet unit may have an open end, into which the coil assembly may be received, and a base end opposite to the open end. In some examples, the magnet unit may be configured such that the on-axis flux density does not exceed 0.5mT (milli-Tesla) at a distance of 30mm (millimetres) from the base end of the magnet unit; or in some examples does not exceed 0.3mT (milli-Tesla) at a distance of 30mm from the magnet unit.

[0037] In general, the stray field of the shaker at the side of the base end may be lower than the stray field on the other side with the open end of the magnet unit.

[0038] The shaker may comprise a frame including a seat attachment surface for attaching the shaker to an application (e.g. a seat).

[0039] The shaker may comprise the coil assembly. The coil assembly may include a voice coil attached to a voice coil former. The voice coil former may be attached to the frame. The voice coil former may be configured to position the voice coil in the air gap when the voice coil is at rest. The magnet unit may be configured to move relative to the voice coil along the movement axis of the shaker when the shaker is energised by supplying electrical current to the voice coil.

[0040] The shaker may have a mass of approximately 1 10 grams.

[0041] The shaker may have a resonant frequency in a range of 50 Hz to 100 Hz (Hertz).

[0042] The shaker may be configured to move the magnet unit relative to the frame when the shaker is in use (e.g. by providing an AC current to the coil). The magnet unit may thus form part of a moving mass of the shaker. The moving mass of the shaker may substantially correspond to the mass of the magnet unit (e.g. because other parts of the shaker which move relative to the frame are small). A suspension arrangement by which the magnet unit is suspended from the frame may also make a small contribution to the moving mass, which contribution may be less than 1 or 2 percent of the moving mass.

[0043] The magnet unit may have a mass in a range of 50g to 150g. In some examples, the magnet unit may have a mass of approximately 90 grams.

[0044] The resonant frequency of the shaker may refer to the resonant frequency when the shaker is ‘grounded’. The term ‘grounding’ refers to mechanical grounding, which will be familiar to the skilled person, and approximates mechanical attachment to an infinitely heavy and rigid object. The skilled person will appreciate that grounding of the shaker may in practice be achieved by attaching the shaker to a comparatively heavy and rigid mass. The comparatively heavy mass is heavy in comparison to the shaker and may be, for example, a mass of at least 10 kilograms, or a concrete structure of hundreds of kilograms. In use the shaker may be grounded, for example, as a result of being attached to a seat.

[0045] According to a second aspect, there is provided a seat including a shaker as described above. The shaker may be attached to the seat (e.g. by elastically mounting the shaker in foam of the seat).

[0046] The seat may include a backrest. The shaker may be attached to (e.g. mounted in) the backrest of the seat. The shaker may be arranged, e.g. attached to the seat, so that the air gap of the magnet unit faces away from an occupant of the seat, when the seat is in use.

[0047] The shaker may be arranged, e.g. attached to the seat, so that the base end of the magnet unit faces towards the occupant of the seat.

[0048] By arranging the air gap of the magnet unit to face away from the occupant, or likewise the base end facing towards the occupant, the stray magnetic flux permeating the occupant may be reduced.

[0049] According to a second aspect, there is provided a use of a counter magnet in a shaker as described above in a seat to reduce CIED interference, wherein the countermagnet is used to prevent magnetic flux generated by the main magnet unit from interfering with a CIED implanted in a person sat in the seat.

[0050] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0051] Summary of the Figures

[0052] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0053] Figure 1 is a sectional view of an exemplary shaker.

[0054] Figure 2 is a schematic view of an application for the shaker.

[0055] Figure 3 is another schematic view of the application.

[0056] Figure 4 is another schematic view showing two further applications for the shaker.

[0057] Figure 5 illustrates a stray field of a conventional shaker.

[0058] Figure 6 illustrates a stray field of the exemplary shaker.

[0059] Figure 7 illustrates the relationship between the magnetic moment ratio and the magnetic stray field.

[0060] Figure 8 illustrates a stray field of the exemplary shaker.

[0061] Figure 9 illustrates a stray field of the exemplary shaker.

[0062] Figure 10 is another sectional view of the exemplary shaker.

[0063] Detailed Description of the Invention

[0064] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0065] Figure 1 shows a cross-section of an example shaker 100 for transmitting vibrations to an application.

[0066] The shaker 100 (or “actuator”) is an electro-mechanical transducer configured to convert electrical signals into mechanical forces to generate vibrations. These vibrations may in use be passed to a user, e.g. passing music information to the user through mechanical vibration on the skin of the user. An example application, described below with reference to Figures 2 to 4, is an automotive seat.

[0067] The shaker 100 comprises a frame 110, a magnet unit 120, and a coil assembly 130. In use, electrical current is supplied to the coil assembly 130 such that a magnetic field is generated by the coil assembly 130 to interact with a static magnetic field provided by the magnet unit 120. This causes the magnet unit 120 to move relative to the coil assembly 130 along a movement axis 102 of the shaker 100. Of course, movement of the magnet unit 120 relative to the coil assembly 130 along the movement axis 102 can also be considered movement of the coil assembly 130 relative to the magnet unit 120.

[0068] The frame 1 10 includes an application attachment portion 112 for attaching the shaker 100 to the application. The application attachment portion 112 may include any suitable structure for attachment of the shaker 100 to the application. In this example, the application attachment portion 1 12 is configured to receive a bolt so that the shaker 100 may in use be bolted to the seat frame. Multiple application attachment portions may be provided.

[0069] The magnet unit 120 of the shaker 100 includes a U-yoke 121 , a main magnet 122 (or “first magnet”) positioned within the U-yoke 121 , a flux guide 123 positioned on the main magnet 122 and a counter magnet 124 (or “second magnet”) positioned on the flux guide 123.

[0070] The magnet unit 120 has an open end 125 and a base end 126. The open end 125 and the base end 126 are opposite ends of the magnet unit 120 and correspond to axial ends with reference to the movement axis 102.

[0071] The coil assembly 130 is received into the open end 125 of the magnet unit 120.

[0072] The magnet unit 120 is configured to generate magnetic flux and to guide the magnetic flux across an annular air gap 127. More particularly, the air gap 127 is formed between the U-yoke 121 and the flux guide 123.

[0073] The magnet unit 120 is suspended from the frame 110 by a suspension arrangement that includes a proximal suspension 142 and a distal suspension 144. The proximal suspension 142 interconnects the frame 110 and the magnet unit 120 and the distal suspension 144 interconnects the frame 110 and the magnet unit 120. The proximal suspension 142 is closer to the coil assembly 130 than the distal suspension 144. In this example, the proximal suspension 142 and the distal suspension 144 are attached to the U-yoke 121 of the magnet unit 120.

[0074] The U-yoke 121 has a U-shape when viewed in cross-section, and comprises an annular proximal attachment surface for the proximal suspension 142 at the open end 125 of the magnet unit 120, and an annular distal attachment surface for the distal suspension 144 at the base end 126 of the magnet unit 120.

[0075] The coil assembly 130 includes a voice coil 131 attached to a voice coil former 132. The voice coil former 132 is attached to the frame 110 at a voice coil former attachment surface on the frame 110, and is configured to position the voice coil 131 in the air gap 127 when the magnet unit 120 is at a rest position and the shaker 100 is at rest.

[0076] Figures 2, 3 and 4 illustrate an exemplary application wherein the shaker 100 is attached to an automotive seat 200. According to such applications, the shaker 100 may be attached to the automotive seat 200 by elastically mounting the shaker in the seat foam so as to allow the shaker to pass vibrations to an occupant 300 of the seat 200 through upholstery layers. As such, the shaker 100 is in use close to the occupant 300 who occupies the seat 200. When seated, the occupant 300 is in contact with an external surface 210 of the seat 200; for example a surface 210 of a backrest 220 of the seat 200.

[0077] The magnet unit 120 generates a static magnetic field and some part of this static magnetic field leaks outside of the shaker 100 and is referred to as a stray field. Field lines of the stray field are illustrated in Figures 1 and 2, extending from the shaker 100 into the occupant 300. The stray field is not useful for the generation of Lorentz force on the coil assembly 130 since it is outside of the magnet unit 120 and can therefore be considered as a by-product.

[0078] The magnetic stray field can be a health risk to the occupant 300, for example where the occupant 300 has a CIED 400. The CIED 400, which is a “Cardiac Implantable Electronic Device”, may be implanted in the chest of the occupant 300. Static magnet field are used to temporarily disable at least some examples of CIEDs 400, e.g. in case of a cardiac arrest, and this should be done on purpose only by medical personnel. As such, the static stray field generated by the magnet unit 120 may interfere with nominal operation of the CIED 400. It is therefore desirable to reduce the stray magnetic field. For example, it may be desirable to have a stray field not exceeding 0.5 mT (milli-Tesla) at the surface 210 of the seat 200. A distance between the base end 126 ofthe magnet unit 120 and the surface 210 of the seat 200, which may occupied by seat foam and upholstery such as fabric and leather, may in at least some examples be approximately 30mm (millimetres). It may therefore be desirable to limit the stray magnet field to 0.5mT at 30mm.

[0079] It is known to the present inventor to mount shakers in seats such that the air gap 127 faces away from the occupant 300 to reduce the stray field at the occupant 300, i.e. the open end 125 faces away from the occupant 300, however a further reduction of the magnetic flux density may be needed in order to achieve 0.5mT at 30mm, or less.

[0080] Figure 5 illustrates the stray field of a conventional shaker without the counter magnet 124. In Figure 5, a first contour line 1001 illustrates a magnetic flux density of 0.5mT and a second contour line 1002 illustrates a magnet flux density of 0.3mT. As can be seen in Figure 5, at a distance of 30mm from the base end 126 of the magnet unit 120, the magnetic flux density exceeds 0.5mT with values of around 1 to 2mT at 30mm.

[0081] Figure 6 shows the stray field of the shaker 100 which utilises the counter magnet 124 to reduce the stray field generated by the magnet unit 120. The main magnet 122 and the counter magnet 124 are magnetized with opposing polarity such that the magnetic field of the counter magnet 124 opposes that of the main magnet 122, so that the sum of the magnetic stray fields is smaller than the magnetic stray field with only the main magnet 122 (shown in Figure 5).

[0082] A first contour line 2001 corresponding to a magnetic flux density of 0.5mT and a second contour line 2002 corresponding to a magnetic flux density of 0.3mT are shown in Figure 6. As can be seen, the magnetic flux density of the stray field of the shaker 100 drops to 0.5mT at a distance of less than 10mm from the magnet unit 120, and drops to 0.3mT at a distance of approximately 11 mm. At a distance of 30mm, the magnetic flux density is less than 0.2mT.

[0083] The size and magnetic remanence of the counter magnet 126 have been selected by optimising a magnetic moment ratio mmr of the magnet unit 120: where Brmmis the magnetic remanence of the main magnet in Tesla and Vmmis the volume of the main magnet in cubic metres, and Brcmis the magnetic remanence of the counter magnet in Tesla and Vcmis the volume of the counter magnet in cubic metres.

[0084] The magnetic moment ratio mmr can be defined as the ratio of the magnetic moments of the main magnet 122 and the counter magnet 124. The magnetic moment is:

[0085] 1 m = — VBrHo where p0'sthe magnetic constant (4TTX10-7 [H / m]); V is the volume of the magnet [m3], which may be considered a geometry property of the magnet; and Bris the magnetic remanence [T|, which may be considered a material property of the magnet.

[0086] With reference to the magnetic moment ratio mmr, the loudspeaker designer can choose properties of the magnets 122, 124, such as the shape of the magnets and their magnetic material properties, whilst maintaining a suitable value of the magnetic moment ratio mmr for the envisaged application. For instance, the counter magnet 124 can be chosen flatter or higher for the same volume, or the volume can be reduced if a stronger magnetic material grade (Br) is chosen.

[0087] The higher the magnetic moment ratio mmr, the stronger the counter magnet 124 compared to the main magnet 122.

[0088] If no counter magnet is present, the magnetic moment ratio mmr is zero (cf. Figure 5).

[0089] If the counter magnet 124 is present, the magnetic moment ratio mmr is greater than zero and the stray field is reduced. The degree of reduction depends on the how the product of Vcmand Brcmcompares to the product of Brmmand Brmm, i.e. the value of the magnetic moment ratio mmr.

[0090] In some examples, the magnetic moment ratio mmr is at least 0.2 to reduce the stray field to 0.5mT at 30mm. As the magnetic moment ratio mmr is further increased, optimum value is reached at 0.6 for which the stray field is minimised. If the magnetic moment ratio mmr is further increased from 0.6, the stray field increases as compared to the optimum value (although still reduced as compared to counter magnet being present).

[0091] In some examples, the magnetic moment ratio mmr is in the range from 0.3 to 0.8, optionally in the range from 0.4 to 0.7, optionally in the range from 0.45 to 0.65.

[0092] Figure 7 is a graph showing the magnetic moment ratio mmr against the magnetic stray field. The magnetic stray field is measured at a location along the movement axis 102 at a distance of 30mm from the base end 126 of the magnet unit 120. The magnetic stray field measured at a location along the movement axis 102 may also be referred to as on-axis stray field and, similarly, the magnetic flux density measured at a location along the movement axis 102 may also be referred to as on-axis flux density.

[0093] As can be seen in Figure 7, the magnetic stray field is 1 .5mT for a magnetic moment ratio mmr of zero (0%), i.e. no counter magnet present, and that the stray field is reduced as the magnetic moment ratio mmr is increased until at the optimum value of mmr equal to 0.6 (60%), the stray field is at the minimised value of approximately 0.1 mT. As the magnetic moment ratio mmr is increased further, the stray field is also increased until reaching a value of 0.5mT for mmr equal to 0.9 (90%).

[0094] As such, in some examples the magnetic moment ratio mmr is in the range of 0.2 (20%) to 0.9 (90%) to provide a stray field which does not exceed 0.5mT as measured at a location along the movement axis 102 at a distance of 30mm from the base end 126 of the magnet unit 120.

[0095] In some examples the magnetic moment ratio mmr is in the range of 0.4 (40%) to 0.7 (70%) to provide a stray field which does not exceed 0.3mT as measured at a location along the movement axis 102 at a distance of 30mm from the base end 126 of the magnet unit 120.

[0096] It is noted that a magnetic moment ratio mmr in the range from 60% to 90% may not be economical, because the contribution of the counter magnet to the magnetic field in the air gap is smaller than that of the main magnet, since the main magnet 122 is sandwiched between the U-yoke 121 and the flux guide 123 whereas the counter magnet 124 is in contact only with the flux guide 123. As such, this leads to a larger total (summed) magnet strength and higher cost.

[0097] Figure 8 shows the stray field of the shaker 100 for a magnetic moment ratio mmr of 0.2. As can be seen in Figure 8, the on-axis stray field of the shaker 100 is reduced to 0.5mT at 30mm distance to the base end 126.

[0098] Figure 9 shows the stray field of the shaker 100 for a magnetic moment ratio mmr of 0.9. As can be seen in Figure 9, the on-axis stray field of the shaker 100 is reduced to 0.5mT at 30mm distance to the base end 126.

[0099] The shaker 100 may provide low cost and excellent performance, since it does not need external magnetic shielding which would add extra components, product volume, assembly complexity, and cost. Moreover, the shaker 100 may provide straightforward assembly, since counter magnets are in principle known and their addition may not introduce assembly difficulties.

[0100] Figure 10 is another sectional view of the shaker 100. The shaker 100 has a height 104, which is measured along the movement axis 102, of approximately 27mm.

[0101] The shaker 100 has a width 106, which is measured in a direction perpendicular to the movement axis 102 (measuring the frame 110 excluding the attachment portions 112), of approximately 60mm; and a width 108 (measuring the frame 110 including the attachment portions 112) of approximately 72mm).

[0102] Below, electrical parameters and mechanical parameters of the shaker 100 are specified at ‘0 hour’ and after 1 hour of ‘burn-in’. Here, ‘0 hour’ refers to a shaker in straight-from-factory condition, i.e. new and unused, whereas ‘burn-in’ of 1 hour refers to a shaker which was in straight-from-factory condition but has been operated for 1 hour. The electrical parameters are Re (electrical voice coil resistance at DC), Le (frequency independent part of voice coil inductance), fs (driver resonance frequency). The mechanical parameters are Mms (moving mass), Rms (mechanical resistance of total driver losses), Kms (mechanical stiffness of driver suspension) and Bl (force factor).

[0103] Electrical Parameters (0 hour)

[0104] Re 6.5 Ohm

[0105] Le 0.8 mH [milli-Henry] fs 68.5 Hz [Hertz]

[0106] Mechanical Parameters (0 hour)

[0107] Mms 86.0 g

[0108] Rms 0.8 kg / s

[0109] Kms 15.9 N / mm

[0110] Bl 5.4 N / A

[0111] Electrical Parameters (after 1 hour burn-in)

[0112] Re 6.5 Ohm

[0113] Le 0.8 mH fs 56.1 Hz

[0114] Mechanical Parameters (after 1 hour burn-in)

[0115] Mms 86.0 g

[0116] Rms 2.1 kg / s

[0117] Kms 10.7 N / mm

[0118] Bl 5.4 N / A The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0119] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0120] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0121] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0122] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0123] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:1 . A shaker configured for use in a seat, the shaker including: a magnet unit including: a U-yoke, a main magnet positioned within the U-yoke, a flux guide positioned on top of the main magnet, and a counter magnet positioned on top of the flux guide; wherein the U-yoke and the flux guide are configured to guide magnetic flux generated by the main magnet across an air gap between the U-yoke and the flux guide; wherein the counter magnet and the main magnet are oppositely magnetised for reducing stray magnetic flux external to the shaker.

2. The shaker according to claim 1 , wherein a magnetic moment ratio mmr of the magnet unit is in a range from 0.2 to 0.9, wherein:where Brmmis the magnetic remanence of the main magnet and Vmmis the volume of the main magnet, and Brcmis the magnetic remanence of the counter magnet and Vcmis the volume of the counter magnet.

3. The shaker according to claim 2, wherein the magnetic moment ratio mmr is in the range from 0.3 to 0.8.

4. The shaker according to claim 3, wherein the magnetic moment ratio mmr is in the range from 0.4 to 0.7.

5. The shaker according to claim 4, wherein the magnetic moment ratio mmr is in the range from 0.45 to 0.65.

6. The shaker according to any preceding claim, wherein the magnet unit is configured such that a magnetic flux density of the stray field does not exceed 0.5mT at a distance of 30mm from the magnet unit.

7. The shaker according to any preceding claim, wherein the magnet unit is configured such that a magnetic flux density of the stray field does not exceed 0.3mT at a distance of 30mm from the magnet unit.

8. The shaker according to any preceding claim, further comprising: a frame including a seat attachment portion for attaching the shaker to a seat; a coil assembly including a voice coil attached to a voice coil former, wherein the voice coil former is attached to the frame, wherein the voice coil former is configured to position the voice coil in the air gap when the voice coil is at rest; wherein the magnet unit is configured to move relative to the voice coil along a movement axis of the shaker when the shaker is energised by supplying electrical current to the voice coil.

9. The shaker according to any preceding claim, wherein the shaker has a resonant frequency in a range of 50 Hz to 100 Hz.

10. A seat including a shaker according to any preceding claim, wherein the shaker is attached to a backrest of the seat.

11. The seat according to claim 10, wherein the shaker is arranged so that the air gap of the magnet unit in use faces away from an occupant of the seat.

12. Use of a counter magnet in a shaker in a seat to reduce CIED interference, wherein the shaker is according to any one of claims 1 to 9, and the countermagnet is used to prevent magnetic flux generated by the main magnet unit from interfering with a CIED implanted in a person sat in the seat.

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