GB2471205A

GB2471205A - Motor or transducer winding with diamond-like carbon (DLC) electrically insulating coatings

Info

Publication number: GB2471205A
Application number: GB1010463A
Authority: GB
Inventors: Benjamin John Ballard; Stephen Scaife
Original assignee: Muirhead Aerospace Ltd
Current assignee: Muirhead Aerospace Ltd
Priority date: 2009-06-19
Filing date: 2010-06-18
Publication date: 2010-12-22
Anticipated expiration: 2030-06-18
Also published as: GB2471205B; GB201010463D0; GB0910627D0

Abstract

The winding comprises a wire comprising an electrically conductive core 3 and electrically insulating coatings 7, 9 of diamond-like carbon (DLC) and maintains the flexibility of the coated wire. The first layer 7 is less than 1 pm thick and comprises relatively inflexible low hydrogen-containing DLC. The second layer 9 has a higher hydrogen content and is more flexible. The total thickness of the DLC layers is 2µm - 5µm. There may be only one or three or more DLC layers. The composition of DLC may vary throughout a layer. The core 3 may have a metallic coating 4 comprising aluminium, titanium or nickel. The coatings 7, 9 may include filler materials such as hydrogen, gaphitic sp2 carbon and/or metals which constitute less than 1 % of the coating by weight. The winding is suitable for high temperature applications of electromagnetic transducer windings such as electric motors, electromagnets, solenoids, field windings, sensors, actuators.

Description

Transducer Windings The invention relates to transducer windings and to electrical insulation, of conductive elements for use in electromagnetic transducers, in particular insulation of current-carrying elements such as wires. Aspects of the invention described herein relate to electromagnetic transducer windings, electro magnets, solenoids, field windings, sensors, actuators and motors comprising electromagnetic windings.

Conductive elements, for example wires, are widely used to carry electrical current.

Copper wires are particularly widely used due to low electrical resistance of the copper material as well as its drawability, corrosion resistance and relatively low cost.

As used herein the term conductive element should be construed broadly. A conductive element such as a wire will generally include a single part or element, but might include a plurality of constituent parts or elements. Aspects of the invention may include cables or other conductive elements, for example comprising a plurality of wires bundled or wound together.

Where a conductive element is to carry a current as in a motor winding, electrical insulation is generally provided. The insulation will be provided in particular in regions where electrical conduction from the element is undesirable such as where turns of a winding lie adjacent to one another, but often all of the element will be provided with insulation except where electrical conduction to another element is specifically required. For example, such insulation may be provided at some or all of the exposed surface of the element for safety and/or to prevent unwanted flow of electricity from the element to adjacent components. In the case of a wire or bundle of wires, such insulation is often provided in the form of a polymer sleeve around the wire or a polymer coating applied to the outer surfaces of the wire. The only parts of the wire thposed from the insulation will usually be parts for connection to other conductive elements.

In some applications, in particular for insulation for wires, the insulation material is chosen such that the insulated wire is flexible. This is not only required for flexibility in connecting components together using the wire, but also so that the wire can be provided, for example wound on a reel for later unwinding in use.

The insulation may for example comprise a polyamide material which is cheap, easily applied to the wire and provides appropriate electrical insulation.

However, such polyamide coatings are not appropriate for where the coated wires are to be used in high-temperature applications. A practical maximum temperature for use of examples of known wires is thought to be between about 200 and 240 degrees C. Examples of temperature limits for the use of particular types of coatings include: Polyester I amide imide 200 degrees C Amide Imide 220 degrees C Polyimide 240 degrees C An alternative coating is ceramic material and some ceramic-coated elements can be used at temperatures up to about 800 degrees C. However, for the ceramic coating to be applied to wires, the wires would need to be processed at 700 degrees C or more and this processing temperature is too high for this option to be appropriate for many applications.

Electromagnetic transducers typically comprise field windings to provide magnetic fields in response to the supply of electrical current. To provide magnetic fields of particular spatial properties such windings are arranged according to particular spatial constraints and often are closely wound. To provide higher magnetic field strengths for a given current large numbers of turns are used. Large numbers of densely packed turns of current carrying wire generate considerable heating effects. Also the use of large numbers of turns of wire increases the volume occupied by field windings so that it is difficult to provide compact electromagnetic transducers. Thus there exists a need in the art for electromagnetic transducers having improved thermal properties and improved power to size ratio.

Examples described herein seek to solve or mitigate at least part of this or other problems.

In a first aspect of the invention, there is provided an electromagnetic transducer winding comprising a wire including an electrically conductive core and further including an electrically insulating coating, the coating including diamond-like carbon (DLC).

Using diamond-like carbon (DLC) can provide a coating on the conductive core which is electrically insulating and which can be used in high-temperature applications, for example temperatures of up to about 400 degrees C or more.

Such temperatures may be found for example in motor applications.

Where reference is made herein to wire, preferably the term is to be interpreted broadly as including for eample any electrically conductive element suitable for providing an electrical connection between two components. This may comprise a thin flexible wire, or may comprise for example a rigid element adapted to extend between the two components. The "wire" may be releasably connectable to one or both of the components, may be permanently connectable to one or both of the components and/or may be an integral part of one or both of the components.

The core may wholly comprise conductive material, or might for example include portions being conductive as well as including non-conductive portions. For example the core may include an inner region of conductive material and one or more coatings on the surface of the conductive material.

Carbon can exist in many forms including crystalline (graphite), glassy (diamond), amorphous (DLC) and other allotropes.

DLC is an amorphous form of carbon that is flexible due to its amorphous structure, hard like diamond and also is stable in almost any atmosphere including corrosive atmosphere up to for example about 400 degrees C. The properties of DLC are exploited in existing applications of the material. For example, its hardness and good wear resistance have led to use of DLC in relation to engine components, for example high wear bearings such as piston wrist pins, cam followers and other sliding surfaces.

DLC also has high lubricity, sterility and inertness, which have led to its use in the coating of catheters and on surgical instruments.

In relation to the present invention, the inventors have identified the possibility of using DLC to provide electrical insulation in electromagnetic transducer windings.

This is of particular advantage for high temperature applications. However, the adhesion and flexibility properties of DLC coatings mean that it has been considered unsuitable for such applications.

Preferably the coating on the core is flexible. Preferably the coating is such that the coated wire can be bent without the coating being cracked or otherwise damaged.

Preferably the coating deforms, elastically or plastically, on bending of the wire such that the integrity of the coating is substantially maintained.

Preferably the coated wire can be bent into an s' shape without significantly cracking or damaging of the coating. Preferably the bend is 90 degrees or more, preferably greater than 135 degrees, preferably the coated wire can be bent 180 degrees or more without significant damage to the coating.

Preferably the coating has the required flexibility at ambient temperature, and/or at temperatures greater than 100, 200 or 300 degrees C, or at temperature up to 400 degrees C. However, in some applications, the flexibility of the coating on the surface of the core is less important. For example where the coated wire is potted in use, the integrity of the coating is of less importance.

Preferably the electrical resistivity of the coating is greater than 1012 or 1013 ohm.cm. Preferably the coating has the particular resistivity at a temperature of degrees C or more, preferably at more than 200 degrees C, more than 300 degrees C or at about 400 degrees C. The hydrogen content of the DLC is preferably between 0 and 0.3%, preferably less than 0.5% in some applications. In one possibility the hydrogen content is of the order of 0.1%. In particularly advantageous examples the hydrogen content increases through the thickness of the coating. In one possibility the doping concentration of hydrogen in the DLC increases from zero at the surface of the wire to approximately 0.1% at or near the surface of the coating. In one possibility the concentration increases continuously. In another possibility the concentration changes discreetly eg. in a stepped fusion.

Preferably, the percentage of graphitic sp2 carbon in the DLC coating is as low as possible, preferably less than 1 % by weight.

Preferably, the percentage content of fillers in the DLC coating is less than 2% or 1% by weight, preferably less than 0.5%, in some preferred examples, substantially no filler is used.

Such fillers may include for example hydrogen, graphitic sp2 carbon, and/or metals.

The thickness of the DLC coating in an example may be less than 10 microns for example about 5 microns or less. In an example, the thickness is between 2 and 5 microns. This has the advantage of providing thermally robust and compact transducer windings.

In one possibility the thickness of the DLC coating is less than 60 microns, preferably less than 40 microns, and still more preferably is 20 microns or less these thicker coatings have the advantage of providing still more effective thermal insulation and a more mechanically robust coating. In other possibilities thicker coatings can be used.

In one possibility the core comprises a plurality of cores so that the wire comprises a multi-stranded wire. This has the advantage of providing a mechanically robust and more flexible wire compared to a single stranded wire of the same cross-sectional area.

A benefit of using DLC as an insulation material for wire is that the required insulation properties can be obtained using a considerably lesser thickness of insulation compared with known coated wire. In some applications, the thickness of the insulation for DLC-coated wire can be considerably less than the typical coating thickness for coated wire of about 10 to 70 microns (depending on the wire thickness). Thus, where DLC is used as insulating material, the electrically conductive core (for example copper wire) can be made thicker for a given size of coated wire, thus improving the efficiency of the product design. This has the benefit of providing more compact windings in an electromagnetic transducer compared with windings insulated using conventional insulating coatings.

Advantageously DLC coated field windings are more easily cooled because the windings themselves are smaller.

For conventional coated Grade 2 copper wire, the thickness of the insulating coating may be about 8 to 40% of the wire diameter for 0.1 mm diameter copper wire, and 1.7 to 5.2% of the wire diameter for a 1.0mm diameter copper wire. This can be contrasted with examples of the present invention in which DLC is used as a material in an electrically insulating coating for copper wire. In examples, the DLC thickness may be a maximum of 5% of the wire diameter of a 0.1mm diameter wire, and a maximum of 0.5% of the wire diameter of a 1.0mm diameter wire. Thus a considerably thinner electrically insulating coating is achievable where DLC is used. Also, by using DLC in the electrically insulating coating, a more consistent coating can be achieved.

A further advantage in the use of DLC in an insulating coating relates to the relatively high thermal conductivity of DLC. For many of the electrically insulating materials commonly used for the coating of wires, the electrically insulating material also provides thermal insulation to the wire core. In contrast, the thermal conductivity of DLC materials can be similar to that of metals, for example up to 700W/rn-K compared with a thermal conductivity of copper of about 400W/rn-K.

The high thermal conductivity of the DLC coating can allow heat to dissipate from the wire core more quickly compared with conventional insulating coatings, thus reducing the temperature of the wire core for a given power input. This is of particular advantage in the construction of high power electromagnetic field windings, such as those used in high power electric motors because heat can be more easily dissipated from the motor windings. Still more advantageously the working life of the motor windings is extended because, in addition to the improved heat dissipation properties, DLC coated wire can operate more reliably at higher In particularly advantageous examples transducer windings comprising DLC coatings operate reliably at temperatures greater than 350°C providing actuators and sensors for use in extreme environments and having extended working life.

The wire may include copper metal and/or any other metal or other component as appropriate.

The wire may comprise a coating, for example a Ni coating.

Preferably the coated wire passes the appropriate insulation resistance test. The coated wire may pass BS EN 60317-0-1 but even if not passing such a test, may nevertheless be usable in some applications,for example motors. DLC-coated wires having insulation resistance less than 500 VAC may be used. The insulation resistance performance may be less important in some applications. For example, in some motors, a wire will be insulated from the stack by, for example, NOMEX so the function of the insulation on the wire is to prevent or reduce conducting from wire to adjacent wire. A considerably lower breakdown value than that of the relevant British Standard or other relevant standard may still be of great value in motor applications and/or other applications. The British Standard also calls for a 20000 hour service life; wires having a considerably shorter life than this may still be very useful, for example in special applications.

A further aspect of the invention provides an electromagnetic transducer, comprising electrically conductive field winding including an electrically conductive core and an electrically insulating coating, the coating including diamond-like carbon (DLC).

In examples of any aspect of the invention, the coated wire or conductive element may comprise the electrically conductive core and two or more layers of coating.

The two or more layers may each include DLC.

Other arrangements are possible. For example one or more layers might not include DLC. Any appropriate arrangement of layers is possible. Different layer arrangements may be provided on different parts of the core. Particular layers may be provided only on one or more portions of the core. Different layers, or no layer might be provided on other portions of the core. Inner and/or outer layers may include DLC. There may be one or more layers of material not including DLC between the conductive core itself and the DLC-containing coating.

In some applications, the adhesion of the DLC-containing layer to the underlying surface, for example the core surface, may be a challenge. In particular for surfaces having a curvature, for example as in a wire, the coating of the layer may be difficult. Also, in some examples of the present invention, the core and/or layer will have flexibility. As the coated core is bent, there will be an increased possibility of failure of the bond between adjacent layers.

The surface of the core has preferably been subject to a preparation step before application of a DLC-containing coating.

According to a further aspect of the invention there is provided a method of forming an electromagnetic field winding comprising a coated conductive element, the method including the steps of: providing a core containing conductive material; applying a coating onto the core, the coating including DLC, and winding the coated conductive element to provide a field winding for an electromagnetic transducer. In an example the electromagnetic transducer comprises one of: a sensor; a synchro; a solenoid; an electromechanical actuator; a motor; a resolver and a generator, or any other winding for generating or sensing a magnetic field.

The coating may be applied to an electrically conductive material in the core.

The coating is preferably applied directly to the electrically conductive material.

The conductive element may comprise a wire. Preferably the wire core includes a metal, for example copper.

Preferably the method further includes the step of preparing the surface of the conductive element prior to the application of the coating.

The preparation may include mechanical cleaning of the surface, preferably using acetone. This cleaning of the surface is thought to improve adhesion of the coating and/or to reduce pitting in the coating of the finished product.

The preparation may include ion bombardment of the surface, for example argon ion bombardment. This step is thought to give better adhesion of the coating and/or better coverage of the surface.

Preferably the method includes the step of applying a further layer, preferably the further layer including DLC. The composition of the two layers may be the same or different. Where the two applied layers have substantially the same composition, it can be seen that in many cases the application of two coats of material can give better adhesion, and better coverage compared with the application of only one coat of the material.

Preferably the method includes modifying the composition of the coating during the coating process so that the composition of the coating changes gradually through the thickness of the coating. In one possibility the coating is doped with hydrogen and the doping concentration increases through the thickness of the coating, from a low value at the surface of the conductor to a higher value at the outer surface of the coating. This has the advantage of providing improved coating properties because DLC with a lower doping concentration adheres more easily to the conductor surface whilst DLC having a higher doping concentration is more flexible and resilient Features described above in relation to the coated element are applicable to the method aspect, and may be applied in relation to the method in any appropriate combination.

Aspects of the invention further provide the use of DLC in a coating composition for coating a wire and/or use of DLC as an electrical insulating coating for a current-carrying element in an electromagnetic transducer.

The invention extends to methods and/or apparatus substantially as herein described with reference to the accompanying drawings.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa.

Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figures Ia and lb show schematically two examples of a transverse section of a coated wire.

Figure 2 shows a DLC-coated wire assembly used in a test.

Figure 3 shows an electric motor comprising an electromagnetic transducer winding.

Figures Ia and lb show schematically two examples of a transverse section of a coated wire. The relative sizes of the wire core and the thickness of the layers is not to scale for clarity.

In the example of Figure la, the coated wire I comprises a wire core 3 including a copper or copper/nickel alloy. The outer surface 5 of the core 3 has been prepared prior to the application of the DLC coatings (for example as described below). The coatings comprise two layers of DLC material. The first layer 7 of DLC is provided directly on the surface 5 of the prepared wire core 3; the second layer 9 of DLC is provided on the surface of the first layer 7. The first layer 7 DLC is very thin, for example less than 1 pm and comprises low hydrogen-containing DLC which adheres well to the core. The low hydrogen-containing DLC is not, however, very flexible. The second layer 9 of DLC has a higher hydrogen content which is more flexible. The total DLC thickness of the two layers 7, 9 is between 2 pm and 5pm.

It will be appreciated that other arrangements could be used. For example, only one layer of DLC might be used, or three or more layers of DLC could be provided.

The composition of the DLC might not be uniform throughout the layer.

In the example described above, the core used does not have any coating provided on its surface.

In an alternative example shown in Figure ib, the core used has a metallic coating 4 comprising aluminium, titanium or nickel. In this example, no preparation of the core is necessary because the first layer of DLC material 7 adheres adequately to the coating, for example to a nickel coating.

In the examples, each layer will generally include a substantially continuous coating covering substantially the whole of the circumferential surface. However, other arrangements are possible. A layer might cover only a part or more than one separate part of the wire.

Other layers and/or other components might be provided. Such other layers or components may provide one or more layers of material, for example between the wire core and a DLC layer, between layers of DLC and/or as an outer layer provided on the DLC.

While the wire core 3 shown in Figure la and lb has a circular cross section, it will be appreciated that the cross section may comprise a different shape. The core might comprise two or more wire components corresponding to two or more different current paths. Thus a coated wire product might include more than one separate wire core.

In the following example, a four step method was used to bond two layers of DLC to a wire core. In summary, the method has the following steps: Step 1: Cleaning of the surface to be coated Step 2: Priming of the surface to be coated Step 3: Applying first DLC layer Step 4: Applying second DLC layer In the following method, the DLC layer is applied to a wire core. The wires cores used had a diameter of between 0.1 and 1.0mm.

Step I The surface to which the DLC is to be applied was cleaned mechanically with acetone at room temperature by hand using an abrasive cloth soaked in acetone.

Other solvents could be used, for example methylethylketone.

Step 2 In this method, the surface is prepared to aid adhesion of the DLC. The priming step comprises argon ion bombardment. The bombardment has the effect of increasing the surface energy of the substrate surface, thus giving an improved bond with the DLC applied in step 3.

Step 3 A first layer of low hydrogen DLC is applied to the prepared wire surface. This provides a first coating on the wire which gives good adhesion to the wire as a result of the preparation of the wire carried out in steps 1 and 2. The thickness of the first layer is less than 1 pm.

Step 4 A second layer of a higher hydrogen-containing DLC is then applied to the coated wire. The method used in applying the second layer is the same as that for the application of the first layer. The thickness of the second layer is such that the total thickness is between 2pm and 5pm.

It will be understood that other methods could be used to form the coated conductive element. For example, different solvents could be used for cleaning the element, or the cleaning step might be omitted. The priming step might be omitted in some examples, for example if a conductive element already having a pre-treatment or coating were used.

Other steps may be carried out in addition to those described.

Any suitable method may be used for applying the DLC to the core. For example a Physical Vapour Deposition (PVD) technique may be used.

Testing Several tests were carried out on the coated wire including the following tests.

Each test was carried out for the DLC-coated wire, and also for a wire coated with the conventional polyamide, for comparison.

1. Pitting The surface of the coated wires was inspected under a microscope to look for pitting. Under the relevant standards, for example BS EN 60317-0-1:1998 Paragraph 14 particularly table 11, some pitting is allowed in winding wire. It is seen by observation that the pitting on the surface of the DLC is not substantially greater than for the polyamide sample.

The Inventors believe that the cleaning of the surface before applying the DLC layer may lead to reduced pitting.

2. Bend test Each wire was bent to an angle of 180 degrees at a bend radius of no more than 1.5 times the wire diameter. The absence of crazing or cracking at the bend indicates a good performance.

It was seen that for the polyamide-coated wire, there was no crazing or cracking.

For some of the samples of the DLC-coated wire there is the possibility of some cracking. Samples in which the hydrogen content of the coating was relatively high, the DLC layer had greater flexibility and the risk of cracking under bending is reduced.

3. Reflex test Following the bend test, the bend wires were straightened to identify any splitting or cracking in the region where the wire had been bent.

For the polyamide-coated wire, a significant split was formed, exposing the copper wire core in an unsatisfactory manner. The DLC layer did not split and did not crack significantly.

4. Insulation Resistance Test AC The insulation reistance of the DLC coating was tested, compared with a conventional polyamide coating.

The insulation resistance test identifies the voltage at which the insulation properties of the coating material breaks down and the material thus ceases to function efficiently as an insulator.

The present test was carried out in accordance with BS EN 60317-0-1:1998 Paragraph 3.2. Figure 2 shows schematically the arrangement used. In summary, a copper bar was cleaned and a sample of each of the DLC-coated wire and the polyamide-coated wire was tightly wrapped around the bar. Figure 2 shows the wire 12 wrapped in ten turns around the bar 10. In this case, the wire diameter was 0.4mm; the diameter of the bar was 12mm.

Tape was applied over the top of the wire to ensure that the wire was pressed tightly against the bar. The whole assembly was heated to a temperature of 200 degrees C for the test.

Increasing AC voltage was applied to each of the wind ings on the bar. The voltage at which the insulation breaks down was noted.

For the polyamide-coated wire (polyamide Grade 1), the breakdown was at 2500 VAC, meeting the BS test for Grade 1 coatings. In the present test, the breakdown for the DLC-coated wire was 450 VAC, lower than the BS test level, but the coated wire is still potentially of great value for some applications, for example as noted above.

In particular, the DLC-coated wire can be used in applications where the temperature of the region of the coated wire is up to 400 degrees C or even higher, whereas the practical temperature limit for some types of known coated wires is between about 200 and 240 degrees C depending on the composition of the coating as discussed above.

Aspects of the invention find particular application in relation to machines or motors in particular for downhole applications for oil and gas exploration and other high power or high temperature applications. An example of a motor is shown in Figure 3. Figure 3 shows a motor/generator assembly comprising a motor/generator 26 and a tool 28 for downhole applications. The motor 26 of Figure 3 comprises an armature 20 carrying a winding 22 comprising a DLC coated wire 24. As will be understood by the skilled practitioner in the context of the present disclosure, the schematic diagram of Figure 3 is merely illustrative and other configurations of motor and downhole tool assembly are within the scope of the invention.

Thus DLC can be bonded to copper wire and thus used as electrical insulation. In particular, DLC can be: -bonded to thin copper wires -used as an electric insulator -sufficiently flexile to be a suitable replacement for polyamide insulation -can provide sufficient insulation in a film only about 2 microns thick, compared with a 200 micron polyamide coating.

It will be understood that the present invention has been described above purely by way of example, and modification of detail can be made within the scope of the invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Claims

CLAIMS1. An electromagnetic transducer winding comprising wire including an electrically conductive core and further including a coating, the coating including diamond-like carbon (DLC).
2. A winding according to claim 1, wherein the core comprises a single conductive element.
3. A winding according to claim 1 or claim 2, wherein the coating on the core is flexible.
4. A winding according to any preceding claim wherein the coating has an electrical resistivity greater than 1012 ohm.cm, for example at a temperature greater than 200 degrees C.
5. A winding according to any preceding claim, wherein the coating is substantially electrically insulating.
6. A winding according to any preceding claim wherein the hydrogen content of the DLC is less than 0.3%.
7. A winding according to any preceding claim wherein the percentage of graphitic sp2 carbon in the DLC coating is less than 1% by weight.
8. A winding according to any preceding claim wherein the percentage content of fillers in the DLC coating is less than 1% by weight.
9. A winding according to any preceding claim wherein the thickness of the DLC coating is less than 10 microns, and preferably is 5 microns or less.
10. A winding according to any preceding claim wherein the wire is a current-carrying wire.
11. A winding according to any preceding claim wherein the concentration of hydrogen in the DLC increases from a first concentration at the surface of the wire to a higher concentration at or near the surface of the coating.
12. An electromagnetic transducer winding according to any preceding claim wherein the wire includes two or more layers of material on the core.
13. A winding according to claim 12, wherein the material of each of the two or more layers includes DLC.
14. A winding according to any preceding claim, wherein the surface of the core has been subject to a preparation step before application of a DLC-containing coating.
15. A winding according to any preceding claim, wherein the core comprises a plurality of cores so that the wire comprises a multi-stranded wire.
16. A winding according to any of claims I to 8 in which the thickness of the DLC coating is less than 40 microns, and preferably is 20 microns or less.
17. A method of forming an electromagnetic transducer winding comprising a coated electrically conductive element, the method comprising the steps of: providing a core containing electrically conductive material; applying a coating onto the core, the coating including DLC, and winding the conductive element to provide an electromagnet transducer winding.
18. A method according to claim 17, wherein the coating is applied onto an electrically conductive material in the core.
19. A method according to claim 17 or claim 18, wherein the electrically conductive element comprises a wire.
20. A method according to any of claims 17 to 19 further including the step of preparing the surface prior to the application of the coating.
21. A method according to claim 20 wherein the preparation includes mechanical cleaning of the surface.
22. A method according to claim 21, wherein the cleaning includes the application of a solvent, for example acetone, to the surface.
23. A method according to any of claims 20 to 22, wherein the preparation includes ion bombardment of the surface, for example argon ion bombardment.
24. A method according to any of claims 17 to 23, further including the step of applying a further layer, preferably the further layer including DLC.
25. A method of forming a winding comprising a coated element according to any of claims Ito 16.
26. A method according to any of claims 17 to 25, wherein the coating is substantially electrically insulating.
27. Use of DLC in a coating composition for coating a wire in an electromagnetic transducer.
28. Use of DLC as an electrically insulating coating for a current-carrying element in an electromagnetic transducer.
29. A transducer winding comprising a coated wire being substantially as herein described preferably having reference to and/or as illustrated in one or more of the figures.
30. A method of forming an electromagnetic transducer winding by coating a wire by a method being substantially as herein described preferably having reference to one or more of the figures.
31. An electromagnetic transducer comprising a winding according to any of claims I to 16 or 29 or a winding produced according to the method of any of claims 17 to 28 or 30.
32. An electric motor comprising electromagnetic transducer according to claim 31.
33. A sensor comprising a transducer winding according to any of claims 1 to 16 or claim 29.
34. A machine comprising an electric motor according to claim 30 and/or an electromagnetic transducer according to claim 29 and/or a sensor according to claim 31.
35. An assembly comprising a plurality of mechanical components and a transducer according to claim 31, an electric motor according to claim 32, a sensor according to claim 33 or a machine according to claim 34.
36. A kit comprising a tool and a machine according to claim 34 or an assembly according to claim 35.
37. A kit of parts for an electromagnetic transducer winding according to any of claims Ito 16.