Electromagnetic device and associated methods

Abstract

Electromagnetic ("EM") test stirrer (20, 120) for use in EM testing in an EM test chamber (10, 110). The stirrer (20, 120) has a test element (24, 124) with a rotationally asymmetrical geometry. The asymmetrical geometry is defined by a plurality of openings (30, 130), each of the openings extending outwardly from at or proximal a radial centre (52, 152) of the test element (24, 124) along a respective path. The radial centre (52, 152) defines an alignment axis (50, 150) of the EM test stirrer (20, 120).

Description

ELECTROMAGNETIC DEVICE AND ASSOCIATED METHODS

[0001] This invention relates to an apparatus for electromagnetic testing and / or measuring, and associated methods; particularly, but not exclusively, to an electromagnetic (EM) test member or testing device for testing electromagnetic compatibility (EMC) or electromagnetic interference (EMI); and associated test methods.BACKGROUND

[0002] Reverberation chambers are typically large rooms formed with highly conductive walls generally equipped with metal stirrers. The stirrers alter the electromagnetic field distribution within the chamber to provide a more homogenous or uniform test environment. The stirrers can mitigate or at least reduce statistical or environmental variations throughout the EM measurement and testing .

[0003] EMC or EMI testing is performed in the chambers on devices or components of devices. For example, test can be performed for the electromagnetic compatibility of electronic equipment, aerospace, aeronautics, automotive, consumer, commercial / domestic devices / equipment and the like. For example, the different electronic components or devices of an automobile, airplane, satellite or the like can interact electromagnetically with each other and associated environment, since they are influenced by the environment and likewise can themselves influence the environment. Accordingly, their electromagnetic compatibility is typically checked to ensure their proper functioning based upon interaction between them and in a given electromagnetic environment (which can be hostile).

[0004] An electromagnetic compatibility test chamber (ECM or CEM) can be used to perform such tests to measure the electromagnetic compatibility of such devices or its electronic components. The chamber is effectively a faradized test enclosure defining a closed space delimited by walls with high electrical conductivity. In some cases, the working volume is provided by covering the chamber surfaces (walls, ceiling, etc.) with a metallic / metallized envelope of high electrical conductivity.

[0005] The electronic devices or components to be tested can be subjected to strong electromagnetic fields over various frequencies. These tests can be carried out in the EMC test chamber using mechanical mixing means. In some cases, electromagnetic fields with hundreds, sometimes thousands, of volts are produced in the chamber, with (incident) waves being subjected to multiple reflections by a rotating mechanical stirrer (e.g. on a wall / ceiling / floor of the chamber). The mechanical stirrer typically has arotating metal blade to try to electromagnetically homogenise the environment, for statistically isotropic testing.

[0006] Immunity / emission tests can be carried out in accordance with regulatory standards, such as in accordance with International Electrotechnical Commission standards (e.g. I EC TR 61000-1-4:2022; I EC61000-1 -1 :2023; EMC testing specification). In general, the apparatus and methods described herein are suitable for at least such IEC 61000 series testing, the relevant standard being the most recent published standard at the filing date of this application.

[0007] It may be a non-exclusive object of the present invention to overcome or at least mitigate, one or more problems associated with the prior art, such as described herein or elsewhere.BRIEF SUMMARY OF THE DISCLOSURE

[0008] In accordance with the present disclosure there is provided an electromagnetic test member. The electromagnetic test member may comprise an electromagnetic compatibility (“EMC”) test member. The test member may comprise a dynamic test member. The test member may comprise a stirrer. The stirrer may comprise a mechanical stirrer. The stirrer may comprise a rotary stirrer, for rotating about an axis. The test member may extend generally laterally from the axis of rotation, such as perpendicularly thereto. The test member may extend, or at least extend substantially, in a plane perpendicular to the axis for rotation. In at least some examples, the test member comprises a planar test element, the planar test element extending in a plane transverse to the axis of rotation. The test element transverse plane may be offset. The planar test element may be angled relative to the axis of rotation. In at least some examples, the test element may be arranged in an angularly offset plane, the angularly offset plane being at an acute or obtuse angle to the axis of rotation. The axis of rotation may intersect a centre of the test member and / or the test element thereof.

[0009] The test member may be for performing an EM test (e.g. EMC and / or EMI). The test member may be for performing an EM test in an EM test chamber. The test member may be positioned in or on the EM test chamber. The electromagnetic test chamber may comprise a reverberation chamber. The EM test chamber may be for testing equipment and / or products. For example, the EM test chamber may be for testing vehicles. The EM chamber may comprise an automotive EM test chamber. The test member may comprise an automotive test member, configured for testing automotive vehicles and / or components thereof or therefor. The test member may be configured to alter the electromagnetic field distribution within the chamber. The testmember may be configured to provide a statistically isotropic and uniform field environment throughout the EM measurement and testing.

[0010] The test element may comprise a discontinuity, such as a discontinuity in its planar surface. The discontinuity may comprise an opening. The opening may comprise a through-opening. Alternatively the opening may comprise a blind opening, such as a blind-hole. In at least some examples, the opening may comprise both blind and through-portions.

[0011] The opening / s may extend between a radial centre of the element and an outer portion or periphery of the element. The opening / s may extend in a labyrinthine pattern / s. The / each opening may be defined by a curved zig-zag. The / each opening may be defined by a series of curved zig-zags.

[0012] The apexes may be offset. For example, the apexes may be radially misaligned. Each apex may be arranged at a different diametrical position. The apexes may be arranged concentrically, with the apexes misaligned such that no straight line intersects all of the apexes. The apexes may be offset or misaligned such that no more than two apexes are colinear with a straight line or axis through the apexes.

[0013] Each opening may be distinct and unique. Each opening may comprise a series of unique characteristics, the characteristics being unique with respect to each other opening.

[0014] At least a portion of each opening may radially overlap with a portion of an adjacent opening. For example, when viewed along a straight radial line or axis from

[0015] Each straight radius emanating from the centre of the element may provide a discontinuous profile, comprised of a series of material portions defined by one or more spoke / s interspersed by a series of discontinuities defined by one or more of the openings. Accordingly, the element may be bereft of any continuous portions of material extending radially in a straight line from the centre of the element to the periphery of the element.

[0016] Accordingly, in at least some examples, there is provided an electromagnetic (“EM”) test stirrer, wherein the stirrer comprises a test element with a rotationally asymmetrical geometry, the asymmetrical geometry being defined by a plurality of openings, each of the openings extending outwardly from at or proximal a radial centre of the test element along a path.

[0017] The test element may comprise a planar element, such as defined by a flat sheet. The test element may be planar in use. The test member may define a 3-dimensional volume, with a proximal plane extending perpendicular to an alignment axis and a distal plane extending perpendicular to the alignment axis, the distal plane being spaced away from the proximal plane.

[0018] In at least some examples, there is provided an electromagnetic compatibility (“EMC”) test stirrer for use in EMC testing in a EMC test chamber, wherein the stirrer comprises a test element with a rotationally asymmetrical geometry, the asymmetrical geometry being defined by a plurality of openings, each of the openings extending outwardly from at or proximal a radial centre of the test element along a respective path, the radial centre defining an alignment axis of the EMC test stirrer.

[0019] The test stirrer may be rotatable about an axis of rotation, the axis of rotation being colinear with the alignment axis such that the test element extends transversely relative to the axis of rotation, the axis or rotation passing through the radial centre of the test element.

[0020] The test element may be arranged in a plane perpendicular to the alignment axis.

[0021] Alternatively, the test element may be arranged in a plane angularly offset relative to the alignment axis, the angular offset being an acute or an obtuse angle. In at least some examples, the test element may be arranged in a plane angularly offset relative to a plane perpendicular to the alignment axis, the angular offset being in a range between about 5° and about 30°.

[0022] Each path may be labyrinthine, each path comprising a plurality of alternating bends or apexes such that each path defining the openings comprises a sequence of linked progressively longer arcs.

[0023] Each opening may be defined by a series of arcuate portions, the arcuate portions being linked such as to define a radially extending zig- zag. The arcuate portions of each opening may be staggered and at least partially overlapping with respect to adjacent opening / s. The arcuate portions of each respective opening may comprise one or more different properties from the other respective openings.

[0024] Each opening may be unique, the plurality of openings each comprising of different parameters from the other respective openings.

[0025] The stirrer may be mounted or mountable in or on a EM test chamber, such as in or on a ceiling or wall of a EM test chamber. Additionally, or alternatively, the stirrer may be mounted in or on a mobile device, such as a mobile EM stirrer device, the mobile EM stirrer device being movable into or within a EM test chamber, such as to beadjustably positionable relative to a test specimen and / or working volume for performing a EM test. The stirrer may comprise a floor stirrer, being mounted or supported on or in the test chamber floor.

[0026] The opening / s may be defined by an adjacent portion of the test element. Each of the plurality of openings may be separated from an adjacent opening / s by a respective test element portion. The separating test element portion may effectively define a spoke.

[0027] The stirrer may comprise an entirely asymmetrical profile. The stirrer may comprise a different radial profile along each and every radius arranged around the entire 360° about the centre of the stirrer. For example, every radial cross-sectional profile of the stirrer may be unique with respect to every other radial cross-sectional profile.

[0028] The opening may define a labyrinthine opening. The opening may define a meandering opening. The opening may define a zig-zag. The opening may be a continuous opening extending from at or proximal a centre of the test element to or proximal to a periphery of the test element. The opening may extend radially via a series of alternating twists or bends. The opening may be bounded by a series of alternating twists or bends such that the opening does not extend radially outward along a direct continuous radial path. Each of the curves or bends may comprise a unique geometry. Each of the bends or curves may be or become progressively longer with each successive bend or curve progressing away from the centre. Accordingly, a longest curve or bend bounding the curve may be the radially outermost bend or curve.

[0029] The opening may be bounded by a plurality of arcuate edges. Each of the plurality of arcuate edges may run substantially transverse to a radius of the stirrer. Each edge may be curved. Each arcuate edge portion may join another arcuate edge portion. Each arcuate edge portion may join another arcuate edge portion at an acute angle. Each consecutive arcuate edge portion may be centred on a virtual centerpoint offset on alternating opposite lateral sides of the test element. For example, where the opening extends in a general radial direction away from the centre of the test element, each successive arcuate edge portion may be centred on an opposite side of an axis defined by the radial direction, being opposite to the preceding (and also subsequent) arcuate edge portion.

[0030] In at least some examples, the opening may be defined by a pair of adjacent edges. Each edge may be associated with a spoke or leg of the test element.

[0031] In contrast to a continuous helical or spiral opening or a plurality of helical or spiral openings, the opening of the test element may be defined by a series of alternating bends. The opening may extend along a serpentine path. The path may be labyrinthine. The opening / path may comprise a plurality of alternating bends or apexes. Accordingly, the opening may zigzag.

[0032] The element may comprise a continuous annular portion around a periphery. The element may be devoid of opening / s or discontinuities at or around an outer periphery of the element, such as an outer perimeter or circumference. The outer annular portion may link or join the legs or spokes.

[0033] The test element may comprise a continuous annular portion at or proximal an outer periphery of the test element and a continuous unbroken portion at the radial centre, with the openings extending in a zone between an inner diameter defined by an outer diameter of the central continuous unbroken portion and an outer diameter defined by an inner diameter of the outer annular portion.

[0034] There may be three openings such that any centralised circular cross-section of the test element at every diameter in the zone between the outer continuous annular portion and the inner continuous unbroken portion is comprised of three discrete portions of test element material, each separated from adjacent portions by a respective one of the three openings.

[0035] Each leg or spoke of material may comprise any corresponding feature of an opening. For example, the test element may comprise three openings separated by three respective legs or spokes, each leg or spoke comprising arcuate portions, bends, apexes or paths corresponding to the openings defined by the legs or spokes.

[0036] The element may comprise a flat disc with one or more sinusoidal-patterned openings therein. The openings may each define a series of radially-arranged cells. The radially-arranged cells may be respectively of progressive or varying properties, such as associated or associable with different frequencies, waves or reflective properties. The test element may comprise a sinusoidal test element. The cells may define a sinusoidal arrangement (e.g. in a radial direction).

[0037] The plurality of openings may comprise at least three openings. The plurality of openings may comprise three openings such that the element is a tri-spoke element.

[0038] The test member may be rotatable. The test member may be rotatable around its radial centre. The test element may comprise a flat element. The test element may comprise a disc. The test element may comprise a plate. The flat element maycomprise a thickness. The thickness may be defined relative to a diameter or flat area of the element. The thickness may be substantially thinner than the diameter or flat dimension / s of the element. The element may comprise a thin-walled sheet element. The flat element may be flat in use. The flat element may be a planar element, the openings and spokes defining the openings being arranged in a single plane.

[0039] The openings may each comprise distinct properties such that each opening is unique. For example, each opening may comprise a different shape, form or geometry than the other openings.

[0040] The test element may be formed from a sheet material. The opening / s may be formed by subtractive manufacturing, such as via one or more of: stamping, cutting, lasering, milling or the like. The test element may be formed from metal, such as (highly) conductive metal. Conductive may be EM conductive metal.

[0041] There may be a plurality of support members supporting the test element, the plurality of support members comprising differing characteristics from other support members, such as one or more physical property selected from: a support member width, a support member length, a support member shape, a support member angle.

[0042] The test member may comprise a frame. The test element may be mounted in the frame. The frame may comprise a plurality of support members. The plurality of support members may connect the test element to the frame. The frame may comprise a proximal plane extending perpendicular to the alignment / rotation axis and a distal plane extending perpendicular to the alignment / rotation axis, the distal plane being spaced away from the proximal plane. The test member may comprise an annular surround arranged in each of the proximal and distal planes. The support members may extend between the annular surrounds to connect the annular surrounds to each other. The frame may be comprised of the pair of annular surrounds and the support members extending therebetween. The support members may be connected to or at an outer edge or periphery of the test element located therewithin.

[0043] The test stirrer may comprise a plurality of test elements. For example, the stirrer may comprise a pair of test elements, the pair of test elements being arranged in parallel planes with respect to each other, the test elements being separated by a spacing therebetween. One or more support members may extend across the spacing between the plurality of test elements to mechanically connect the test elements to each other.

[0044] The support member may comprise a stirrer element. In at least some examples, the support elements each comprise a folded stirrer element, such as a z- fold stirrer element. The support element / s may (each) define a stirrer element, as such. In at least some examples, the test member comprises a pair of planar test elements, each with three sinuous openings defined by three sinuous legs or spokes, each of the respective legs or spokes of a first test element being mechanically connected to a corresponding leg or spoke of a second test element by a respective z- fold stirrer element, acting as a support member. The support member may comprise a sinusoidal edge / s; with a plurality of waves. The plurality of waves may be defined on a carrier wave (e.g. the edge may be defined by a plurality of secondary waves arranged along a primary wave). Each wave of the sinusoidal edge may be unique with respect to other waves along that edge. The respective first and second edges of each support element may be asymmetrical or at least offset or misaligned. Preferably, each edge is unique and each portion of band defined between the respective pair of edges of each support element is distinct (e.g. of differing length and / or with respective edge portions at differing angles).

[0045] The provision of such z-fold stirrer elements as support members connecting the planar stirrer discs may provide for relatively bigger, longer and wider connections (e.g. compared to support members arranged only at or around the periphery of the planar test element and / or non-folded linear support arms). The improved mechanical connections between the planar stirrer elements may lead to improved stirring, particularly at low frequencies

[0046] The provision of such z-fold stirrer elements as support members connecting the planar stirrer discs may provide for improved (mechanical) stability of the respective spokes or legs of the planar stirrer elements. For example, each cell of each sinuous arm defining the openings in the planar stirrer element may be attached to the support element. Each arcuate portion, particularly proximal the respective apex thereof, may be directly supported by attachment to the z-fold connections of the support member. Accordingly the test member may be relatively strong and rigid (e.g. compared to unsupported planar test elements and / or test elements supported only at edges and / or only with linear arm supports)..

[0047] The test member may be configured to provide up to 20% increased performance at low frequencies. The test member may be configured to provide up to 20% increased performance at low frequencies with respect to conventional stirrers. For example, the configuration of the present stirrer may provide up to 20% increasedperformance with respect to a similar-sized rotatable stirrer with a helical opening, sheet or blade.

[0048] Here, low frequency may be considered to be in a range of around 10MHz to around 500MHz. The frequency may be proportional to the diameter of the stirrer (e.g. inversely). For example, for a 1m diameter sinuous floor stirrer, low frequencies may be considered to be around 300 MHz (since the wavelength (A) of 300 MHz is 1m). For a larger sinuous floor stirrer, such as where the diameter is 4m, then low frequencies may be considered to be about from 50-100 MHz. The test member may be configured for high-field strength applications, such as in a range of 200V / m - 7000V / m.

[0049] The size and / or proportions of the test element / s may be configured according to test requirements. For example, a diameter of the test element may be adapted according to a test and / or test specimen for testing. The size and / or proportions of the test element / s may be configured according to a frequency / ies for testing. The size and / or proportions of the test element / s may be configured according to a size of a working volume for testing.

[0050] The test member may be rotatable or rotated at speeds in a range of around 1 to around 500 revolutions per minute; optionally in a range of around 5 to around 200 revolutions per minute; optionally in a range of around 10 to around 120 revolutions per minute. The test member may be configured to constantly distribute the electromagnetic waves in the chamber. The test member may be configured to assist in providing an electromagnetic field distribution that is locally equivalent to irradiation with an antenna from all directions (omnidirectional).

[0051] The test member may be configured to provide increased uniformity in / across / throughout a working volume, the working volume being adjacent or below the test member. The test member may be configured to provide homogeneity. The test member may be configured to provide uniformity, such as with respect to the environment or location (e.g. spatial uniformity). The test member may be configured to provide isotropy. The test member may be configured to provide uniformity with respect to orientation (e.g. polarisation uniformity).

[0052] The axis of rotation of the test member may be directed towards or though the working volume. The test member, and / or a test element thereof, may be arranged to face the working volume. The test member, and / or a test element thereof, may be positioned side-on to the working volume, such as with a wall or floor stirrer. The test member, and / or a test element thereof, may be positioned above the working volume, such as with a ceiling stirrer.

[0053] The test member may be configured to perform EM testing, such as EMC / EMI and / or immunity / emission tests in accordance with regulatory standards, such as in accordance with International Electrotechnical Commission standards (e.g. IEC TR 61000-1-4:2022; I EC61000-1-1 :2023; EMC testing specifications). In general, the apparatus and methods described herein are suitable for such IEC 61000 series testing standards, the relevant standard being the most recent published standard at the filing date of this application. All standards disclosed herein are to be taken as the latest versions of standards as publicly available on the filing date of this patent application.

[0054] The test member may be mounted or mountable in or as part of the test chamber. In at least some examples, the test member may be fixed to the test chamber. For example, the test member may be fixedly mounted to a ceiling of the test chamber; or at least in a space or volume to be located above a test space, area or product. Additionally, or alternatively, the test member may be positioned adjacent the test space, area or product.

[0055] Additionally, or alternatively the test member may be mobile. For example, transportable into and / or out of the test chamber; and / or moveable within the test chamber. The test member may be or form part of a floor stirrer.

[0056] In at least some examples, a plurality of test members may be provided. For example, a single device may comprise a plurality of test members.

[0057] There may be provided a plurality of test members and / or test devices in a test chamber. For example, the test chamber may comprise one or more ceiling- and / or wall / floor mounted test devices. Each test device may comprise one or more test members.

[0058] According to an aspect, there is provided an EM test chamber, the test chamber comprising at least one test member as described in any other aspect, example, clause, claim or embodiment herein. The test chamber may comprise a plurality of test members. The test chamber may comprise one or more test devices, each test device comprising at least one test member as described in any other aspect, example, clause, claim or embodiment herein. The test chamber may comprise a plurality of test devices. The test chamber may comprise a ceiling stirrer and one or more wall or floor stirrers. In at least some examples, the test chamber comprises at least three stirrers.

[0059] According to an aspect, there is provided a method of using the apparatus according to an aspect, claim, embodiment or example of this disclosure.

[0060] The steps of the method may be in any order.

[0061] According to an aspect of, there is provided an apparatus configured to perform a method according to an aspect, claim, embodiment or example of this disclosure.

[0062] According to an aspect, there is provided a controller arranged to perform a method according to an aspect, claim, embodiment or example of this disclosure. For example, the controller may be arranged to perform an EM test with the apparatus of any claim, example, embodiment, aspect or figure of this disclosure.

[0063] According to an aspect, there is provided a system comprising a controller according to an aspect, claim, embodiment or example of this disclosure, or a system arranged to perform a method according to an aspect, claim, embodiment or example of this disclosure.

[0064] According to an aspect, there is provided computer software which, when executed by a processing means, is arranged to perform a method according to any aspect, claim, embodiment or example of this disclosure, such as for performing an EM test. The computer software may be stored on a computer readable medium. The computer software may be tangibly stored on a computer readable medium. The computer readable medium may be non-transitory.

[0065] Any controller or controllers described herein may suitably comprise a control unit or computational device having one or more electronic processors. Thus, the system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller” or “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. A first controller may be implemented in software run on one or more processors. One or more other controllers may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

[0066] Within the scope of this disclosure it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:FIG. 1 shows an electromagnetic (EM) test chamber defining a working volume with a plurality of stirrers and an example test specimen;FIG. 2 shows the EM test chamber of FIG.1 in plan view;FIG. 3 shows a front view of the EM test chamber of FIG.1;FIG. 4 shows a perspective view of the EM test chamber of FIG.1;FIG. 5 shows a side view of the EM test chamber of FIG.1;FIG. 6 shows an example of a portion of a test member;FIG. 7 shows an annotated view of the test member of FIG.6;FIG. 8 shows a shaded view of the test member of FIG.6;FIG. 9 shows an annotated and shaded view of the test member of FIG.6;FIG. 10 shows a three-quarter view of the test member of FIG.6, with the test member shown from four respective angles in FIGS. 10a, 10b, 10c and 10d respectively;FIG. 11 shows orthographic projections of the test member of FIG.6, with FIGS. 11a, 11b, 11c, 11 d, 11e and 11f showing respective plan, front, back, left, right and % isometric views;FIG. 12 shows an example of a test member, generally similar to that shown in FIG. 6, with FIGS. 12a, 12b, 12c and 12d showing respective front, side, plan and % isometric views; andFIG. 13 shows an example of a test member, generally similar to that shown in FIG. 12, with FIGS. 13a, 13b, 13c and 13d showing respective front, side, plan and % isometric viewsDETAILED DESCRIPTION

[0068] Referring firstly to Figure 1, there is shown an electromagnetic test chamber 10 defining a working volume with a plurality of stirrers 20 and an example test specimen 12. Here there is provided a ceiling stirrer 20a with a single, angularly-offset test element 24a supported in a frame 26a with support members 28a extending between proximal and distal surrounds.

[0069] The stirrers 20a, 20b, 20c are mounted or mountable in or on the EM test chamber 10, such as the ceiling stirrer 20a mounted in or on a ceiling the EM test chamber. Additionally, or alternatively, the floor stirrers 20b, 20c are mounted in or on mobile devices, mobile EMC stirrer devices being movable into or within a EM test chamber, such as to be adjustably positionable relative to the test specimen 12 and / or working volume 14 for performing a EM test. The floor stirrers 20b, 20c are mounted or supported on or in the test chamber floor.

[0070] An axis 50 of rotation of the test member 22 is directed towards or though the working volume 14. The test member 22, and / or a test element 24 thereof, is arranged to face the working volume 14. The test member 22, and / or a test element 24 thereof, is positioned side-on to the working volume, such as with a wall or floor stirrer 20b, 20c. The test member 22, and / or a test element 24 thereof, is positioned above the working volume, such as with a ceiling stirrer 20a.

[0071] Each stirrer 20a, 20b, 20c comprises a test member 22 for performing an EM test (e.g. EMC and / or EMI) in the EM test chamber 10. As shown here, the respective test members 22 are positioned in or on the EM test chamber 10 (here, a reverberation chamber). The EM test chamber 10 is for testing equipment and / or products, such as for testing vehicles as shown here, this particular EM chamber 10 being an automotive EM test chamber. In at least some examples, the test member 22 comprises an automotive test member 22, configured for testing automotive vehicles and / or components thereof or therefor. In each example, the test member 22 is configured to alter the electromagnetic field distribution within the chamber 10. The test member 22 is configured to provide a statistically isotropic and uniform field environmentthroughout the EM measurement and testing. FIGS. 2, 3, 4 and 5 show the EM test chamber of FIG.1 in respective plan, front, perspective and side views.

[0072] FIG. 6 shows an example of a portion of the electromagnetic test member 22, here being a dynamic electromagnetic compatibility (“EMC”) test member 22 in the form of a mechanical rotary stirrer, for rotating about an axis 50. As better seen in FIG. 10, the test member 22 extends generally laterally from the axis 50 of rotation. Here, the test member 22 comprises a planar test element 24, the planar test element 24 extending in a plane transverse to the axis 50 of rotation. In the example shown in FIG.6, corresponding to the ceiling stirrer 20a of FIG. 1 , the test element transverse plane is offset. The planar test element 24 is angled relative to the axis 50 of rotation. Here, the test element 24 is arranged in an angularly offset plane, the angularly offset plane being at an acute or obtuse angle to the axis 50 of rotation (see e.g. FIG. 10). The axis 50 of rotation intersects a centre 52 of the test member 22 and the test element 24 thereof.

[0073] The test element 24 comprises a discontinuity in its planar surface, in the form here of a through-opening 30. In other examples (not shown), the opening comprises a blind opening, such as a blind-hole.

[0074] FIGS. 7, 8 and 9 show respective shaded and annotated view of the test member of FIG.6.

[0075] As best shown in annotated, shaded FIGS. 7 and 9, the element 24 comprises a continuous annular portion 34 around a periphery. The element 24 is devoid of opening / s or discontinuities at or around the outer periphery 34 of the element 24, such as an outer perimeter or circumference. The outer annular portion 34 links and joins the legs or spokes 32a, 32b, 32c.

[0076] The test element 24 also comprises a continuous unbroken portion 36 at the radial centre 52, with the openings30a, 30b, 30c extending in a zone between an inner diameter defined by an outer diameter of the central continuous unbroken portion 36 and an outer diameter defined by an inner diameter of the outer annular portion 34.

[0077] Here, there are three openings 30a, 30b, 30c such that any centralised circular cross-section of the of the test element 24 at every diameter in the zone between the outer continuous annular portion 34 and an inner continuous unbroken portion 36 is comprised of three discrete portions 32 of test element 24 material, each separated from adjacent portions by a respective one of the three openings 30a, 30b, 30c.

[0078] The openings 30a, 30b, 30c are defined by an adjacent portion of the test element 24. Each of the plurality of openings 30a, 30b, 30c is separated from an adjacent opening 30a, 30b, 30c by a respective test element portion. The separating test element portion effectively defines a spoke 32.

[0079] Each leg or spoke 32 of material comprises any corresponding feature of an opening 30. For example, the test element 24 comprises three openings 30a, 30b, 30c separated by three respective legs or spokes 32a, 32b, 32c, each leg or spoke 32a, 32b, 32c comprising arcuate portions, bends, apexes or paths corresponding to the openings 30a, 30b, 30c defined by the legs or spokes 32a, 32b, 32c. The element 24 comprises a flat disc with three sinusoidal-patterned openings 30a, 30b, 30c therein. The openings 30a, 30b, 30c each define a series of radially-arranged cells. The radially-arranged cells are respectively of progressive or varying properties, such as associated or associable with different frequencies, waves or reflective properties. Accordingly, the test element 24 comprises a sinusoidal test element 24, with the cells associated with the bends or apexes defining a sinusoidal arrangement (e.g. in a radial direction). Here, there are three openings 30a, 30b, 30c such that the element 24 is a tri-spoke element.

[0080] The openings 30a, 30b, 30c extend between the radial centre 52 of the element 24 and the outer portion or periphery 34 of the element 24. The openings 30a, 30b, 30c extend in labyrinthine patterns, with each opening 30a, 30b, 30c being defined by a series of curved zig-zags. The apexes of each opening 30a, 30b, 30c are offset and radially misaligned. Each apex is arranged at a different diametrical position, with the apexes being arranged concentrically, with the apexes misaligned such that no straight radius from the centre 52 intersects all of the apexes. Each opening 30a, 30b, 30c is distinct and unique, with each opening 30a, 30b, 30c comprising a series of unique characteristics, the characteristics being unique with respect to each other opening 30a, 30b, 30c.

[0081] At least a portion of each opening 30a, 30b, 30c radially overlaps with a portion of an adjacent opening 30a, 30b, 30c, such as when viewed along a straight radial line from the centre 52. Indeed, each straight radius emanating from the centre 52 of the element 24 provides a different discontinuous profile, comprised of a series of material portions defined by one or more spokes 32a, 32b, 32c interspersed by a series of discontinuities defined by one or more of the openings 30a, 30b, 30c. Accordingly, the element 24 is bereft of any continuous portions of material extending radially in a straight line from the centre 52 of the element to the periphery 34 of the element 24.

[0082] Each path is labyrinthine, each path comprising a plurality of alternating bends or apexes such that each path defining the openings 30a, 30b, 30c comprises a sequence of linked progressively longer arcs. Each opening 30a, 30b, 30c is defined by a series of arcuate portions, the arcuate portions being linked such as to define a radially extending zig- zag. The arcuate portions of each opening 30a, 30b, 30c are staggered and at least partially overlapping with respect to adjacent openings 30a, 30b, 30c. The arcuate portions of each respective opening 30a, 30b, 30c comprises one or more different properties from the other respective openings 30a, 30b, 30c. Each opening 30a, 30b, 30c is unique, the plurality of openings 30a, 30b, 30c each comprising of different parameters from the other respective openings 30a, 30b, 30c. The openings 30a, 30b, 30c each comprise distinct properties such that each opening 30a, 30b, 30c is unique. For example, each opening 30a, 30b, 30c comprises a different shape, form or geometry than the other openings 30a, 30b, 30c.

[0083] The stirrer 20 comprises an entirely asymmetrical profile. The stirrer 20 comprises a different radial profile along each and every radius arranged around the entire 360° about the centre 52 of the stirrer 20. For example, every radial cross- sectional profile of the stirrer 20 is unique with respect to every other radial cross- sectional profile.

[0084] The opening 30a, 30b, 30c defines a labyrinthine opening. The opening 30a, 30b, 30c defines a meandering opening in the form of a zig-zag. Each opening 30a, 30b, 30c is a continuous opening extending from at or proximal the centre 52 of the test element 24 to or proximal to the periphery 34 of the test element 24. Each opening 30a, 30b, 30c extends radially via a series of alternating twists or bends. Each opening 30a, 30b, 30c is bounded by a series of alternating twists or bends such that the opening 30a, 30b, 30c does not extend radially outward along a direct continuous radial path. Each of the curves or bends comprises a unique geometry. Each of the bends or curves is or becomes progressively longer with each successive bend or curve progressing away from the centre 52. Accordingly, a longest curve or bend bounding the curve is the radially outermost bend or curve.

[0085] Each opening 30a, 30b, 30c is bounded by a plurality of arcuate edges. Each of the plurality of arcuate edges runs substantially transverse to a radius of the stirrer 20. Each edge is curved; and each arcuate edge portion joins another arcuate edge portion at an acute angle. Each consecutive arcuate edge portion is centred on a virtual centerpoint offset on alternating opposite lateral sides of the test element 24. For example, where the opening 30a, 30b, 30c extends in a general radial direction awayfrom the centre 52 of the test element 24, each successive arcuate edge portion is centred on an opposite side of an axis defined by the radial direction, being opposite to the preceding (and also subsequent) arcuate edge portion. Here, each opening 30a, 30b, 30c is defined by a pair of adjacent edges. Each edge is associated with a spoke or leg 32 of the test element 24.

[0086] In contrast to a continuous helical or spiral opening or a plurality of helical or spiral openings, the opening 30a, 30b, 30c of the test element 24here is defined by a series of alternating bends. The openings 30a, 30b, 30c extend along a respective serpentine path. The opening / path is labyrinthine, comprising a plurality of alternating bends or apexes such that the opening 30a, 30b, 30c zigzags radially outwards.

[0087] Accordingly, in at least some examples, there is provided an electromagnetic (“EM”) test stirrer 20, wherein the stirrer 20 comprises a test element 24 with a rotationally asymmetrical geometry, the asymmetrical geometry being defined by a plurality of openings 30a, 30b, 30c, each of the openings 30a, 30b, 30c extending outwardly from at or proximal a radial centre 52 of the test element 24 along a path.

[0088] As shown here, the test element 24 comprises a planar element, defined by a flat sheet, with the test element 24 being planar in use. The test element 24 is formed from a sheet material. The openings 30a, 30b, 30c are formed by subtractive manufacturing, such as via one or more of: stamping, cutting, lasering, milling or the like. The test element 24 is formed from metal, such as (highly) conductive metal. The test element 24 comprises a flat element. The test element 24 comprises a disc. The test element 24 comprises a plate. The flat element comprises a thickness. The thickness is defined relative to a diameter or flat area of the element 24. The thickness is substantially thinner than the diameter or flat dimension / s of the element 24. The element 24 comprises a thin-walled sheet element 24. The flat element 24 is flat in use. The flat element 24 is a planar element, the openings 30a, 30b, 30c and spokes 32a, 32b, 32c defining the openings 30a, 30b, 30c being arranged in a single plane.

[0089] There is a plurality of support members 28 supporting the test element 24, the plurality of support members 28 (e.g. 28a for the ceiling stirrer 20a) comprising differing characteristics from other support members 28, including several physical properties here: a support member width, a support member length, a support member shape, a support member angle.

[0090] Here, the test member 22 comprises a frame 26. The test element 24 is mounted in the frame 26, supported by the plurality of support members 28. The plurality of support members 28 connect the test element 24 to the frame 26. Theframe 26 comprises a proximal plane extending perpendicular to the alignment / rotation axis 50 and a distal plane extending perpendicular to the alignment / rotation axis 50, the distal plane being spaced away from the proximal plane. The test member 22 comprises an annular surround 27 arranged in each of the respective proximal and distal planes. The support members 28 extend between the annular surrounds 27 to connect the annular surrounds 27 to each other. The frame 26 is comprised of the pair of annular surrounds 27a, 27b and the support members 28 extending therebetween. The support members 28 here are connected to or at an outer edge or periphery 34 of the test element 24 located therewithin.

[0091] FIG. 10 shows a three-quarter view of the test member 22 of FIG.6, with the test member 22 shown from four respective angles in FIGS. 10a, 10b, 10c and 10d respectively. The test member 22 defines a 3-dimensional volume, with a proximal plane extending perpendicular to an alignment axis 50 and a distal plane extending perpendicular to the alignment axis 50, the distal plane being spaced away from the proximal plane.

[0092] Here, the test element 24 is arranged in a plane angularly offset relative to the alignment axis 50, the angular offset being an acute or an obtuse angle. As shown here, the test element 24 is arranged in a plane angularly offset relative to a plane perpendicular to the alignment axis 50, the angular offset being in a range between about 5° and about 30°.

[0093] The test member 22 is rotatable around its radial centre 52. The test stirrer is rotatable about the axis 50 of rotation, the axis 50 of rotation being colinear with the alignment axis 50 such that the test element 24 extends transversely relative to the axis 50 of rotation, the axis 50 or rotation passing through the radial centre 52 of the test element 24.

[0094] FIG. 11 shows orthographic projections of the test member 22 of FIG.6, with FIGS. 11a, 11b, 11c, 11 d, 11e and 11f showing respective plan, front, back, left, right and % isometric views. The test member 22 is configured to provide up to 20% increased performance at low frequencies, such as with respect to conventional stirrers. For example, the configuration of the present stirrer 20 can provide up to 20% increased performance with respect to a similar-sized rotatable stirrer with a helical opening, sheet or blade.

[0095] Here, low frequency is considered to be in a range of around 10MHz to around 500MHz. The frequency is proportional to the diameter of the stirrer 20 (e.g. inversely). For example, for a 1m diameter sinuous floor stirrer 20b (shown in FIG. 11), lowfrequencies is considered to be around 300 MHz (since the wavelength (A) of 300 MHz is 1m). For a larger sinuous floor stirrer 20b, such as where the diameter is 4m, then low frequencies is considered to be about from 50-100 MHz. The test member 22 is configured for high-field strength applications, such as in a range of 200V / m - 7000V / m.

[0096] The size and / or proportions of the test element 24 / s is configured according to test requirements. For example, a diameter of the test element 24 is adapted according to a test and / or test specimen 12 for testing. The size and / or proportions of the test element 24 is configured according to a frequency / ies for testing. The size and / or proportions of the test element 24 is configured according to a size of the working volume 14 for testing.

[0097] The test member 22 is rotatable or rotated at speeds in a range of around 1 to around 500 revolutions per minute; optionally in a range of around 5 to around 200 revolutions per minute; optionally in a range of around 10 to around 120 revolutions per minute. The test member 22 is configured to constantly distribute the electromagnetic waves in the chamber. The test member 22 is configured to assist in providing an electromagnetic field distribution that is locally equivalent to irradiation with an antenna from all directions (omnidirectional).

[0098] FIG. 12 shows an example of a test member 122 with FIGS. 12a, 12b, 12c and 12d showing respective front, side, plan and % isometric views. The test member 122 shown here in FIG. 12 is generally similar to that 22 shown in FIG. 11 , comprising corresponding features to those of the test member 22 of FIG. 11 , with the features incremented by 100. Accordingly, the test member comprises a test element 122 with a radial centre 152. Not all corresponding feature references are repeated here, for brevity and clarity.

[0099] Here, the test element 122 extends perpendicularly to the axis of rotation 150. The test member 22 extends in a plane perpendicular to the axis 150 for rotation. The test element 124 is arranged in a plane perpendicular to the alignment axis 150. The test stirrer comprises a plurality of test elements 124, shown here as a pair of test elements 124, the pair of test elements 124 being arranged in parallel planes with respect to each other, the test elements 124 being separated by a spacing therebetween. Support members 128 extend across the spacing between the plurality of test elements 124 to mechanically connect the test elements 124 to each other.

[0100] There is a plurality of support members 128 supporting the test element 124. Here, the support members 128 each comprise a stirrer element as such. In this particular embodiments exemplified in FIG. 12, the support elements 128 eachcomprise a z-fold stirrer element. The test member 122 comprises a pair of planar test elements 124, each with three sinuous openings 130a, 130b, 130c defined by three sinuous legs or spokes 132a, 132b, 132c, each of the respective legs or spokes 132a, 132b, 132c of a first test element 124a being mechanically connected to a corresponding leg or spoke 132a, 132b, 132c of a second test element 124b by a respective z-fold stirrer element 128, acting as a support member. The support members 128 each comprise a pair of sinusoidal edge / s; with a plurality of waves. The plurality of waves is defined on a carrier wave (e.g. the edge is defined by a plurality of secondary waves arranged along a primary wave). Each wave of the sinusoidal edge is unique with respect to other waves along that edge. The respective first and second edges of each support element 128 is asymmetrical or at least offset or misaligned. Here, each edge is unique and each portion of band defined between the respective pair of edges of each support element 128 is distinct (e.g. of differing length and / or with respective edge portions at differing angles).

[0101] The provision of such z-fold stirrer elements 128 as support members connecting the planar stirrer discs 124 provides for relatively bigger, longer and wider connections (e.g. compared to support members arranged only at or around the periphery 134 of the planar test element 124 and / or non-folded linear support arms). The improved mechanical connections between the planar stirrer elements 128 can lead to improved stirring, particularly at low frequencies.

[0102] The provision of such z-fold stirrer elements 128 as support members connecting the planar stirrer discs provides for improved (mechanical) stability of the respective spokes or legs 132a, 132b, 132c, of the planar stirrer elements 122. For example, each cell of each sinuous arm defining the openings in the planar stirrer element 122 is attached to the support element 128. Each arcuate portion, particularly proximal the respective apex thereof, is directly supported by attachment to the z-fold connections of the support member 128. Accordingly the test member 122 is relatively strong and rigid (e.g. compared to unsupported planar test elements 124 and / or test elements 124 supported only at edges and / or only with linear arm supports).

[0103] FIG. 13 shows an example of a test member, generally similar to that shown in FIG. 12, with FIGS. 13a, 13b, 13c and 13d showing respective front, side, plan and % isometric views. The test element 124 is mounted in the frame 126. The frame comprises a plurality of support members 128 connect the test element 124 to the frame 126. The support members 128 are connected to or at an outer edge or periphery 134 of the test element 124 located therewithin.

[0104] The plurality of support members 128 connect the test element 124 to the frame 126. The test member 122 comprises an annular frame 127 arranged in each of the proximal and distal planes, with the support members 128 extending between the frames 127a, 127b to connect the frames 127a, 127b.

[0105] The test members shown here 22, 122 are configured to provide increased uniformity in and throughout the working volume 14, the working volume 14 being adjacent or below the test member 22, 122. The test member 22, 122 is configured to provide homogeneity. The test member 22, 122 is configured to provide uniformity, such as with respect to the environment or location (e.g. spatial uniformity). The test member 22, 122 is configured to provide isotropy. The test member 22, 122 is configured to provide uniformity with respect to orientation (e.g. polarisation uniformity).

[0106] The test member 22, 122 is configured to perform EM testing, such as EMC / EMI and / or immunity / emission tests in accordance with regulatory standards, such as in accordance with International Electrotechnical Commission standards (e.g.I EC TR 61000-1-4:2022; I EC61000-1-1 :2023; EMC testing specifications). In general, the apparatus and methods described herein are suitable for such I EC 61000 series testing standards, the relevant standard being the most recent published standard at the filing date of this application. All standards disclosed herein are to be taken as the latest versions of standards as publicly available on the filing date of this patent application.

[0107] Accordingly, there is provided a method of performing an electromagnetic (“EM”) test, the method comprising: providing an electromagnetic (“EM”) test stirrer in an EM test chamber, wherein the stirrer comprises a test element with a rotationally asymmetrical geometry, the asymmetrical geometry being defined by a plurality of openings, each of the openings extending outwardly from at or proximal a radial centre of the test element along a respective path, the radial centre defining an alignment axis of the EM test stirrer; and performing an EM test.

[0108] Accordingly, herein described, there is disclosed an electromagnetic stirrer for use in an EM test chamber, such as an electromagnetic compatibility test chamber. There is also disclosed an electromagnetic compatibility test chamber which comprises a reverberation chamber defined by a wall surface made of a conductive reflecting material, and a vehicle placement area defined so that a motor vehicle to be tested can be placed in the vehicle placement area during an electromagnetic compatibility test. An antenna arranged in the reverberation chamber and can emit electromagnetic radiation energy. One or more EM stirrers can be arranged (e.g. on the ceiling and / orwall and / or floor of the reverberation chamber). During electromagnetic compatibility testing, a motor vehicle to be tested is positioned stationary in the vehicle placement area. The stirrer / s can continuously and periodically change the form between a first limit state and a second limit state. EM is supplied into the reverberation chamber through the antenna to the vehicle placement area in accordance with specified electromagnetic compatibility test requirements.

[0109] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0110] It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as disclosed in any aspect, example, claim or embodiment of this disclosure, and a machine-readable storage storing such a program. Still further, embodiments of the present disclosure may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same. For example, control procedures or parameters and / or associated test information for performing EM testing may be conveyed electronically.

[0111] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0112] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0113] The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims, including with equivalence.

[0114] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. An electromagnetic (“EM”) test stirrer for use in EM testing in an EM test chamber, wherein the test stirrer comprises a test element with a rotationally asymmetrical geometry, the asymmetrical geometry being defined by a plurality of openings, each of the openings extending outwardly from at or proximal a radial centre of the test element along a respective path, the radial centre defining an alignment axis of the EM test stirrer.

2. The EM test stirrer of claim 1 , wherein the test stirrer is rotatable about an axis of rotation, the axis of rotation being colinear with the alignment axis such that the test element extends transversely relative to the axis of rotation, the axis or rotation passing through the radial centre of the test element.

3. The EM test stirrer of claim 1 or 2, wherein the test element comprises a continuous annular portion at or proximal an outer periphery of the test element and a continuous unbroken portion at the radial centre, with the openings extending in a zone between an inner diameter defined by an outer diameter of the central continuous unbroken portion and an outer diameter defined by an inner diameter of the outer annular portion.

4. The EM test stirrer of claim 3, wherein there are three openings such that any centralised circular cross-section of the of the test element at every diameter in the zone between the outer continuous annular portion and the inner continuous unbroken portion is comprised of three discrete portions of test element material, each separated from adjacent portions by a respective one of the three openings.

5. The EM test stirrer of any preceding claim, wherein each path is labyrinthine, each path comprising a plurality of alternating bends or apexes such that each path defining the openings comprises a sequence of linked progressively longer arcs.

6. The EM test stirrer of any preceding claim, wherein each opening is sinusoidal, being defined by a series of arcuate portions, the arcuate portions being linked such as to define a radially extending sinusoidal zig-zag.

7. The EM test stirrer of claim 6, wherein the arcuate portions of each opening are staggered and at least partially overlapping with respect to adjacent opening / s.

8. The EM test stirrer of claim 6 or 7, wherein the arcuate portions of each respective opening comprise one or more different properties from the other respective openings.

9. The EM test stirrer of any preceding claim, wherein each opening is unique, the plurality of openings each comprising of different parameters from the other respective openings.

10. The EM test stirrer of any preceding claim, wherein the EM test stirrer is mounted or mountable in or on a EM test chamber, such as in or on a ceiling or wall of a EM test chamber.

11. The EM test stirrer of any preceding claim, wherein the EM test stirrer is mounted in or on a mobile device, such as a mobile EM stirrer device, the mobile EM stirrer device being movable into or within a EM test chamber, such as to be adjustably positionable relative to a test specimen and / or working volume for performing a EM test.

12. The EM test stirrer of any preceding claim, wherein the test element is arranged in a plane perpendicular to the alignment axis.

13. The EM test stirrer of any of claims 1 to 11 , wherein the test element is arranged in a plane angularly offset relative to the alignment axis, the angular offset being an acute or an obtuse angle.

14. The EM test stirrer of any of claims 1 to 11, wherein the test element is arranged in a plane angularly offset relative to a plane perpendicular to the alignment axis, the angular offset being in a range between about 5° and about 30°.

15. The EM test stirrer of any preceding claim, wherein there is a plurality of support members supporting the test element, the plurality of support members comprising differing characteristics from other support members, such as one or more physical property selected from: a support member width, a support member length, a support member shape, a support member angle.

16. The EM test stirrer of any preceding claim, wherein the EM test stirrer comprises a plurality of test elements.

17. The EM test stirrer of claim 16, wherein the EM test stirrer comprises a pair of test elements, the pair of test elements being arranged in parallel planes withrespect to each other, the test elements being separated by a spacing therebetween.

18. The EM test stirrer of claim 17, wherein one or more support members extend across the spacing between the plurality of test elements to mechanically connect the test elements to each other.

19. An electromagnetic (“EM”) test chamber comprising one or more EM test stirrers as defined in any preceding claim.

20. A method of performing an electromagnetic (“EM”) test, the method comprising: providing an electromagnetic (“EM”) test stirrer in an EM test chamber, wherein the stirrer comprises a test element with a rotationally asymmetrical geometry, the asymmetrical geometry being defined by a plurality of openings, each of the openings extending outwardly from at or proximal a radial centre of the test element along a respective path, the radial centre defining an alignment axis of the EM test stirrer; and performing an EM test.

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