Electrical insulation in the casing

Abstract

An electrical system including a conductive layer and an insulating layer applied to a surface of a cover, the electrical system including: a first insulating layer for attachment to the cover; a second insulating layer; and a conductive layer encapsulated between the first insulating layer and the second insulating layer. The first insulating layer and the second insulating layer have a predetermined minimum withstand voltage and a predetermined minimum resistance.

Description

Technical Field

[0001] The present invention relates to insulating material provided in an enclosure comprising electrical components. Background Art

[0002] Masks containing electrical wiring are becoming increasingly common in many emerging applications, such as physiological and biomechanical sensing, heating, electrical stimulation, visibility lighting, user interfaces, etc. The basic purpose of this wiring is to transmit electrical signals or currents from one part of the mask to other parts, such as transmitting electrical signals or currents from a set of electrodes located on the chest that contact the skin to an electronic module located elsewhere in the mask. Obviously, this wiring and any accompanying insulating materials need to be flexible and able to withstand the various forces generated when placing and removing the mask, as well as wearing, washing, drying and storing the mask. The mask must typically operate over a range of temperatures and humidities and other environmental conditions (such as fluid and dust exposure). If the mask must be cleaned, the wiring needs to withstand the chemical and mechanical conditions involved.

[0003] There are now many different options to generate such wiring, including copper wires between or within the fabric layers and printed circuits that use screen printing conductive inks, 3D printing, conductive wires in the form of yarn or textiles, sheets or strips of conductive polymers or elastomers. The resistance of such conductors is usually an important factor, especially the stability of the resistance in response to stretching, bending, washing, etc.

[0004] In most cases, insulation is required between conductors to ensure proper operation of the device. There are many options for providing insulation, such as printed dielectric inks or sealants, extruded insulation sheets cut into the desired shape, injection molded plastics, 3D printed materials. Conductive wires can be coated with an insulating film.

[0005] Of particular interest are covers in which the electrical system consists of several layers applied to a textile or fabric surface 1, such as (see Figure 1 ):

[0006] Adhesive layer attaching the structure to the fabric of the cover 3

[0007] Insulation layer 5

[0008] Conductive layer 7

[0009] Insulation layer 9

[0010] This structure can be applied to the skin-facing surface of the cover, the outer surface, or even between the textile layers of the cover. One or both of the insulating layers 5, 9 can have an aperture 11 (see Figure 2 ) to allow electrical connection to the underlying conductive layer 7. The fabric may also have apertures 15 to allow access to exposed conductors.

[0011] In order to obtain a flexible and lightweight finished cover it is desirable that these layers are as thin and flexible as possible. It is also necessary that the conductive layer 7 maintains a minimum conductivity during stretching and bending and that the insulating layers 5, 9 have sufficient electrical resistance and dielectric strength.

[0012] Now there are conductive inks with good tensile properties that can be printed directly onto elastic fabrics. In addition to wiring, it is often necessary to use one or more electrodes for electrical contact with the skin. For example, in electrical stimulation, it is necessary to have a defined skin contact area to ensure that the stimulating current is dispersed at the skin, thereby avoiding high current density. The electrodes can be made of conductive elastomer sheets, conductive inks, conductive textiles, etc. The electrodes can be formed by simply having a window in the overly covered in the insulating layer exposing the conductive layer. An additional layer may be applied to the electrode region to modify its conductivity, eg, to match its conductivity with that of the skin.

[0013] Insulating materials are necessary to limit current flow to desired points in the system. The insulating material provided by isolating the conductors from each other to ensure proper operation of the equipment can be described as a functional insulating material. Insulating materials may also be needed to isolate the conductor from its surroundings to ensure safety. However, the prior art does not address the performance requirements of such insulating materials, let alone their designs. This is especially important when the conductors in contact with the patient and need to isolate them from the ground or from contact with the body parts they do not intend to contact. This insulating material can be called a protective insulating material. Insulating materials can of course have both functional and protective purposes.

[0014] For example, conductive tracks can be printed on the skin-facing side of the cover to prevent leakage of current from the cover into the skin. An insulating layer may be applied to the conductive layer to electrically separate the conductive layer from the skin. Adding an insulating layer covering the printed conductive track will reduce the flexibility of the system, so it is desirable to make it as thin and flexible as possible. On the other hand, it needs to be durable and able to withstand normal wear including washing. The breakdown voltage of a given insulating material depends on its thickness and dielectric strength, so a thickness that is appropriately balanced between flexibility, weight and insulation properties must be chosen. The insulation material on the back of the electrode is also very important. Considering the electrode in contact with the skin located on the skin-facing surface of the cover, the opposite surface of the electrode must be insulated so that no current flows through the cover to the outer surface. This is to prevent leakage of current to users who are likely to use their fingers or hands to touch the outer surface of the cover. For a given application, it is not obvious what the dielectric strength and insulation resistance requirements are for each hazardous situation. For example, if the insulation material in the battery-powered heater circuit worn on the body fails in one place, there is no danger because no leakage current returns the path. Two insulation breaks at different locations could expose the user to leakage current and potential injury. The voltage that stresses the insulation must be considered when choosing a design to achieve the necessary protection.

[0015] Although there have been many publications recently describing various architectures for integrating wiring within a housing, WO2016 / 131936A2 (Schwarz), US215 / 0359485A1 (Berg), US2014 / 0318699A1 (Longinotti), WO2017 / 199026A1 (Kai), GB2555592 (Bungay) do not focus on the challenges of insulating materials. It is worth noting that the market for stretchable insulating inks for wearable applications (Dupont TM The leading supplier of PE773) did not even mention insulation performance.

[0016] The problem, therefore, is to determine how much insulation material is needed to achieve the required safety and functional performance and provide that level of insulation while minimizing the overall stiffness, weight, and thickness of the enclosure.

[0017] In view of the above, an object of the present invention is to mitigate and alleviate the above mentioned disadvantages. Summary of the invention

[0018] According to a first aspect, the present invention provides an electrical system comprising a conductive layer and an insulating layer applied to a surface of a casing, the electrical system comprising:

[0019] a first insulating layer for attachment to the housing;

[0020] a second insulating layer; and

[0021] A conductive layer is encapsulated between the first insulating layer and the second insulating layer.

[0022] Preferably, the conductive layer is attached to both the first insulating layer and the second insulating layer. Preferably, the conductive layer is continuously attached to both the first insulating layer and the second insulating layer.

[0023] Preferably, the first insulating layer has a withstand voltage of at least 200VAC or higher and the second insulating layer has a withstand voltage of at least 100VAC or higher.

[0024] Preferably, the first insulating layer has a resistance of at least 200 kΩ when measured using a conductive surface extending on the surface of the second insulating layer. Further preferably, the first insulating layer has a resistance of at least 200 kΩ when measured using a conductive surface extending on the surface of the second insulating layer. 2 When measured on a conductive surface of 8000 mm, the first insulating layer has a resistance of at least 200 kΩ. Further preferably, when using 8000 mm 2 The second insulating layer has a resistance of at least 200 kΩ when measured by a probe.

[0025] Preferably, the first insulating layer has a thickness of 30 μm or less and a withstand voltage of at least 200 VAC or more.

[0026] Preferably, the first insulating layer has a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more.

[0027] Preferably, the first insulating layer has a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more.

[0028] The second insulating layer may have a thickness of 30 μm or less and a withstand voltage of at least 100 VAC or more.

[0029] The second insulating layer may have a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more.

[0030] The second insulating layer may have a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more.

[0031] Preferably, the first insulating layer has a withstand voltage of at least 1500VAC or higher and the second insulating layer has a withstand voltage of at least 100VAC or higher.

[0032] Preferably, the first insulating layer and / or the second insulating layer is formed from at least two separately applied and bonded insulating material layers, wherein the number of insulating material layers is selected to provide a cumulative thickness which imparts the desired insulating properties to the insulating layer.

[0033] Preferably, each individually applied and bonded layer has a dielectric strength of 15 kV / mm to 20 kV / mm.

[0034] Preferably, each individually applied and bonded layer has a thickness of 8-10 μm, thereby providing a nominal withstand voltage of 120-200 V per layer.

[0035] Preferably, each separately applied and bonded layer is a dielectric ink layer.

[0036] Preferably, the at least two separately applied and bonded layers are formed from at least two separately applied coatings of insulating material, wherein a preceding coating is allowed to cure before applying a subsequent coating, and wherein the number of coatings is selected to provide a cumulative thickness that imparts the desired insulating properties to the insulating layer.

[0037] Preferably, the coating is a dielectric ink coating.

[0038] Preferably, attachment means are provided for attaching the first insulating layer to the casing. The attachment means comprises an adhesive. Other means for attaching the first insulating layer to the casing will be apparent to the skilled person.

[0039] According to a second aspect, the invention provides a method for testing an electrical system applied to a surface of a casing, the electrical system comprising a conductive layer and an insulating layer, the electrical system comprising:

[0040] a first insulating layer for attachment to the housing;

[0041] a second insulating layer; and

[0042] A conductive layer encapsulated between the first insulating layer and the second insulating layer;

[0043] The insulation performance of the first insulation layer and / or the second insulation layer is tested by applying a test voltage between a probe connected to the conductive layer and a conductive plate having a defined area placed on the relevant insulation layer and measuring the resistance or breakdown voltage therebetween.

[0044] Preferably, the conductive plate has a width of at least 1000 mm. 2 The conductive plate may have a defined area of ​​at least 8000 mm 2 limited area.

[0045] Preferably, the shape of the conductive plate is substantially consistent with the shape of the associated insulating layer.

[0046] Preferably, the conductive plate is longer and wider than the insulating layer being tested.

[0047] Preferably, the conductive plate is provided as a 3D phantom having a conductive surface onto which the insulating layer to be tested is applied. Preferably, prior to testing, the relevant insulating layer is attached to a cover and the cover is fitted over the phantom with the insulating layer to be tested facing the phantom.

[0048] Features of the first aspect of the invention may be incorporated into the second aspect of the invention, and vice versa.

[0049] Detailed description of the invention

[0050] The present invention will now be described with reference to the accompanying drawings, which show embodiments of the invention by way of example only. In the drawings:

[0051] Figure 1 An electrical system attached to a textile substrate is shown;

[0052] Figure 2 Shows Figure 1 A hole in the insulating layer of the system to expose the conductive layer;

[0053] Figure 3 is a schematic diagram of the insulation material, which depicts the insulation material and potential error current i on the conductive track inside the cover connected to the skin electrode e , that is, if the wearer touches the failed insulating material, the error current i e May flow in the arms;

[0054] Figure 4 An equivalent circuit diagram showing two skin contact electrodes with contact impedances Z1 and Z2 respectively; and

[0055] Figure 5 A test apparatus for testing insulating materials of an insulating layer of a system is described.

[0056] In order to more fully describe the present invention, it is useful to consider a specific example, namely transcutaneous electrical stimulation. However, it should be understood that the present invention is not limited to this use. Various other applications will be apparent to those skilled in the art. The present invention will be described with reference to Figures 1 to 5 Transcutaneous electrical stimulation is a widely used therapy in which the electronic controller module 17 (see Figure 3 ) generates an electrical pulse and passes through Figure 3 At least two wires 21 and corresponding skin-attached electrodes 23 of part A applied in the embodiment transmit electrical pulses to the subject 19. The wires 21 include embedded wiring or conductive tracks (see Figure 1 and 2The embedded wiring or conductive track extends from the controller module 17 to the electrode 23 and insulates to prevent leakage of current to the skin electrode 23 . These conductive layers may generally be laminated to the skin-facing side 25 of the cover 27 . The insulating layer 9 on the skin side 7a of the conductive layer ensures that current does not leak to the underlying skin when worn, causing irritation in the wrong skin position. Failure of this insulation may cause some discomfort, skin irritation or burns. The insulating layer 5 and the electrode of the conductive layer 7 facing the cover side 7b and the electrode prevent current from leaking into the cover 27 . The cover 27 is usually made of woven or knitted textile made of insulating yarn, but when it becomes wet, it can provide a conductive path to the outer surface 27a of the cover 27. If the user has touched that portion of the wet cover 27 during the stimulation and the insulating layer 5 has failed, the current i e May flow into the hands, arms, and trunk area (see Figure 3 ). The amount of current flowing in this situation will depend on the relative impedance of the hand in contact with the electrode contacts, as they are electrically connected in parallel. The effects of current on the human body are covered in IEC 60479, so it is necessary to ensure that any current resulting from insulation failure is well below the limit that would cause significant harm.

[0057] Figure 4 The equivalent circuit of two skin contact electrodes 23 with contact impedances Z1 and Z2 is shown. An electrical stimulus is applied between nodes 1 and 2. Zc represents the impedance of the body core between the two electrodes 23 and is usually much smaller than the skin contact impedance. Zh represents the impedance of the hand in contact with one of the multiple conductive layers 7 in the event of a fault and is usually higher than Z1 or Z2. The error current i flowing through this branch e It must be as low as possible to ensure safety.

[0058] The inventors have found that the voltage applied to this insulating material between the conductive layer 7 and the hand is approximately half the voltage across the two electrodes 23 connected in series, since the potential at the hand is practically the same as the body core as depicted, see equivalent circuit Figure 4 , which represents the electrical impedance of the two percutaneous electrodes 23 connected in series with the core resistance of the body. As we all know, the entire circuit impedance is determined by the skin contact impedance. For a typical electrical stimulation device with a maximum output of 20Vrms, the stress on the insulator is 10Vrms, even if the peak voltage may be as high as 50V (the electrical stimulation waveform is usually in the form of a low duty cycle pulse sequence, and the peak pulse amplitude is usually a multiple of the root mean square value of the pulse sequence).

[0059] The safety factor chosen for an insulation design depends on the risk associated with the failure. For low-risk applications, a coefficient of 2X may be sufficient, which results in a 20VAC withstand voltage or a peak withstand voltage of 100V. More preferably, a higher safety factor of 5X is used even for low-risk applications. The insulation resistance can be selected to limit the current to a normal operation at an upper limit of 100 μA rms without breakdown, so 50V / 100 μA = 500kΩ.

[0060] For higher risk situations, the safety factor for voltage breakdown can be appropriately increased to 5X, 10X, or 20X. For currents that can flow through a chest at risk of fibrillation, the withstand voltage can be set as high as 500VAC or even 1000VAC, depending on the risk estimate.

[0061] Since the risks associated with insulation failure are different on the skin side and the cover side, it may be appropriate to have different insulation properties on each side. Since the failure of the skin-oriented insulating material will only cause skin discomfort, a 200VAC withstand voltage can be specified, which is more than 20 times the operating voltage. For the cover side, the possibility of injury is higher, so a 500VAC pressure resistance is suitable. Safety standard IEC 60601 (3rd edition) specifies the voltage withstand level of insulating materials at different operating voltages. To provide two methods of protecting patients, it may be necessary to provide insulation at a breakdown voltage of 1000VAC.

[0062] It should be noted that hipot testing is primarily performed with machines that run at mains frequency, in which case the use of "VAC" is appropriate and sufficient. In NMES (neuromuscular electrical stimulation), the current is pulsed, so the use of "Vrms" is more correct.

[0063] Typical dielectric inks, such as SE3102 provided by ACI Materials, have a dielectric strength ranging from 15 to 20 kV / mm. Special inks with higher dielectric strength can be used, but flexibility and tensile properties may not be sufficient. For materials with a strength of 20kV / mm, a screen printing step is usually 10 μm in thickness and the nominal strength of each layer is 200V, so at least three steps are required to establish a 500V resistance. Flexible inks can be used, and by using different printing screen and scraper parameters, the flexible ink can be printed on each layer in a larger thickness.

[0064] Screen printing has inherent variability due to mesh marking, mesh stretching, variations in squeegee pressure, angle, speed, and ink viscosity. Air bubbles may also be present which compromise insulation performance. Therefore, multiple layers are required that cumulatively provide the desired insulation performance. Multiple layers typically require curing time between layers which slows down the manufacturing process, so it is desirable to have as few layers as possible.

[0065] In addition to being able to withstand a given voltage, the insulating layer must also provide sufficient isolation resistance below the breakdown voltage. Standard IEC 60601 requires that the auxiliary current during normal use is less than 100μA. Therefore, at a typical operating voltage of 20Vrms, the insulation should be greater than 200kΩ. The resistance in contact with the hand or finger depends on the contact area. Standard IEC 60479 considers the effects of electric current on human and animal bodies and defines test contact areas that simulate finger-hand contact. The area for fingertip contact is 250mm 2 to simulate, and hand contact corresponds to 8000mm 2 . 1000mm 2 The contact area can also be used to simulate finger contact. Therefore, a suitable insulation test for the cover insulation material for finger contact is to measure (for example using an insulation tester 37) at the maximum working voltage the conductive layer 7 and the area of ​​1000mm placed on the insulating material 5,9. 2 The resistance between the surface probes 35 (see Figure 5 ). However, an area of ​​8000mm can be used 2 A similar test can be performed with a surface probe to test the housing insulation against hand contact.

[0066] The structure needs to be tested withstand voltage after the manufacturing is completed to ensure that the insulating layers 5 and 9 meet the withstand voltage requirements. The entire surface of the insulating layers 5 , 9 needs to be tested, so a probe that can be in contact with each point on the insulating layers 5 , 9 must be used. The shape of the probe or plate may be consistent with the shape of the insulating layers 5, 9 so that the insulating layers 5, 9 can be tested at one time without having to repeat the test multiple times while repositioning the smaller probe. Alternatively, a convenient and fast way to test the cover is to attach it to the conductive bobbin or mannequin and test the resistance between each terminal of the conductive layer 7 on the cover and the conductive bobbin. Such phantoms can be made of wood, plastic or foam with conductive coatings such as metal foils, conductive fabrics, conductive coatings or inks. All terminals of the conductive layer 7 are connected together to form a single electrical node and the resistance and breakdown voltage between the node and the conductive body mode are still faster. The cover can be turned over to test the performance of the insulating layer 5 on the outward-facing surface of the laminate circuit. A variety of phantoms can be provided to test covers of different sizes, or phantoms can be adjusted.

[0067] In the cover made of elastic fabric, the electrical system is preferably stretchable and relaxed so as not to impair the performance of the cover. The stretching of the electrical system inevitably reduces the cross-sectional dimension in the direction perpendicular to the direction of the stretching, which may reduce the pressure resistance of the insulating material. Therefore, it may be necessary to stretch the test sample on the phantom during the test. The phantom sizes used for testing need to be selected to match the size of the cover in order to achieve the desired stretching.

[0068] The jacket may become wet during use and washing. The insulating layers 5, 9 need to withstand moisture and prevent water from entering the layered structure. Therefore, it may be necessary to test the wet jacket to ensure that the safety of withstand voltage and insulation resistance is maintained.

[0069] The insulating layers 5 , 9 may have holes 11 to intentionally expose a portion of the conductive layer 7 . The hole 11c may be formed to allow connection to the skin, or to the connector or another conductor. In a manner similar to a multilayer printed circuit board, it may be useful to have a plurality of conductive layers 7 separated by insulating layers 5 , 9 but with selective openings 11 to allow the conductive layer 7 to form contacts at a particular point. The holes 11 in the insulating layers 5 , 9 may also be made to allow the connector (not shown) to be attached to the conductive layer 7 . Such connections may be, for example, stud compression fasteners, press-fit connectors, adhesives, soldering, simple threaded fasteners or other suitable connectors. After such a connection is made, it is necessary to insulate it. Additional layers may be laminated on the joint, such layers having the same insulating properties as the insulating layer to which it is attached. Other methods may include injection or spraying of injection molding or resin onto the joint.

[0070] There are a variety of methods for making insulating and conductive layers on the cover. WO2017 / 199026 A1 (Kai et al.) describes a method of screen printing continuous layers on textiles. GB2555592 (Bungay et al.) describes an alternative method in which multiple layers are laid on a transfer printing substrate and then applied to the cover using heat or pressure. Likewise, multiple layers may be formed by placing and bonding the forming layers of insulating and conductive materials to tops of each other. For example, the first insulating layer (eg, the insulating layer 5) may be an insulating TPU with a thickness of the order of 100 to 200 μm. The conductive layer 7 may be a conductive wire, a conductive fabric, a metal foil, or may be a conductive ink pattern printed on the first insulating layer 5 . The second insulating layer (eg, insulating layer 9) may be another forming layer of the insulating TPU, or other polymer or printing dielectric ink with a thickness of less than 100 μm. The entire assembly can be bonded to the fabric by an adhesive layer 3 .

[0071] While much of the above describes a layered structure of insulating layers 5, 9 and conductive layer 7 applied to the skin-facing side 25 of the sleeve, the structure may also be applied to the outer surface 27a of the sleeve, or even in a layer between two textile layers 27. Insulation coordination must take into account the risk profile of the specific application.

[0072] Those skilled in the art will appreciate that changes and modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. An electrical system comprising a conductive layer and an insulating layer applied to a surface of a housing, the electrical system comprising: a first insulating layer for attachment to the housing; a second insulating layer; as well as a conductive layer encapsulated between the first insulating layer and the second insulating layer; Wherein, the first insulating layer has a withstand voltage of at least 200VAC or higher and the second insulating layer faces the user's skin when in use and has a withstand voltage of at least 100VAC or higher.

2. The electrical system according to claim 1, wherein when using greater than 8000cm 2 The first insulating layer has a resistance of at least 200 kΩ when measured on the conductive surface.

3. An electrical system according to claim 1 or claim 2, wherein the second insulating layer has a resistance of at least 200 kΩ when measured using a conductive surface extending over a surface of the second insulating layer. 4 . The electric system according to claim 1 , wherein the first insulating layer has a thickness of 30 μm or less and a withstand voltage of at least 200 VAC or more. 5 . The electric system according to claim 1 , wherein the first insulating layer has a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more. 6 . The electric system according to claim 1 , wherein the first insulating layer has a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more. 7 . The electric system according to claim 1 , wherein the second insulating layer has a thickness of 30 μm or less and a withstand voltage of at least 100 VAC or more. 8 . The electric system according to claim 1 , wherein the second insulating layer has a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more. 9 . The electric system according to claim 1 , wherein the second insulating layer has a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more. 10 . The electrical system of claim 1 , wherein the first insulating layer has a withstand voltage of at least 1500 VAC or more and the second insulating layer has a withstand voltage of at least 100 VAC or more.

11. An electrical system according to claim 1, wherein one or each of the first insulating layer and the second insulating layer is formed by at least two separately applied and bonded insulating material layers, wherein the number of the insulating material layers is selected to provide a cumulative thickness that imparts the desired insulating properties to the insulating layer.

12. The electrical system of claim 11, wherein each of the individually applied and bonded layers has a dielectric strength of 15 kV / mm to 20 kV / mm.

13. The electrical system of claim 12, wherein each of the individually applied and bonded layers has a thickness of 8-10 μm, thereby providing a nominal withstand voltage of 120-200 V per layer.

14. An electrical system according to any one of claims 11 to 13, wherein each of the separately applied and bonded layers is a layer of dielectric ink.

15. The electrical system of claim 1, wherein the conductive layer is attached to both the first insulating layer and the second insulating layer.

16. The electrical system of claim 15, wherein the conductive layer is continuously attached to both the first insulating layer and the second insulating layer.

17. The electrical system of claim 1, wherein attachment means are provided for attaching the first insulating layer to the housing.

18. The electrical system of claim 17, wherein the attachment means comprises an adhesive.

19. A method of testing an electrical system applied to a surface of a boot, the electrical system comprising a conductive layer and an insulating layer, the electrical system comprising: a first insulating layer for attachment to the housing; a second insulating layer, the second insulating layer facing the user's skin when in use; as well as a conductive layer encapsulated between the first insulating layer and the second insulating layer; The insulation performance of one or each of the first insulating layer and the second insulating layer is tested by applying a test voltage between a probe connected to the conductive layer and a conductive plate having a defined area placed on the first insulating layer or the second insulating layer and measuring the resistance or breakdown voltage therebetween.

20. The method according to claim 19, wherein the conductive plate has a thickness of at least 1000 mm. 2 or a larger limited area.

21. The method of claim 20, wherein the shape of the conductive plate is substantially consistent with the shape of the associated insulating layer.

22. The method of claim 21, wherein the conductive plate is longer and wider than the insulating layer being tested.

23. The method of claim 19, wherein the conductive plate is provided as a 3D phantom having a conductive surface onto which the insulating layer being tested is applied.

24. The method according to claim 23, wherein: Prior to testing, the first insulating layer or the second insulating layer is attached to a cover and the cover is fitted onto the phantom, with the insulating layer being tested facing the phantom.

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