GB2552004A

GB2552004A - Magnetic stimulation coil arrangment including coolant leak detector

Info

Publication number: GB2552004A
Application number: GB1611766.5A
Authority: GB
Inventors: Biginton Matthew
Original assignee: Magstim Co Ltd
Current assignee: Magstim Co Ltd
Priority date: 2016-07-06
Filing date: 2016-07-06
Publication date: 2018-01-10
Also published as: GB201611766D0

Abstract

The magnetic stimulation (MS) coil arrangement having a housing 8a, 8b for receiving one or more windings of a conductive element and a coolant flow path defined between the housing and windings, and a leak detection arrangement comprising first 2 and second 4 electrodes, associated with potential coolant leak flow pathways, such as join 24, wherein a change of impedance between the electrodes is indicative of a coolant leak. There may be a control arrangement to monitor the impedance. Electrode pairs may be nested, ring shaped, split rings, or elongate with constant separation. There may be coolant inlets 10a, 10b and outlet 14 may which may also be potential coolant leak flow pathways with associated electrodes 2, 4.

Description

(54) Title of the Invention: Magnetic stimulation coil arrangment including coolant leak detector Abstract Title: A magnetic stimulation coil with a coolant leak detection arrangement.

(57) The magnetic stimulation (MS)coil arrangement having a housing 8a, 8b for receiving one or more windings of a conductive element and a coolant flow path defined between the housing and windings, and a leak detection arrangement comprising first 2 and second 4 electrodes, associated with potential coolant leak flow pathways, such as join 24, wherein a change of impedance between the electrodes is indicative of a coolant leak. There may be a control arrangement to monitor the impedance. Electrode pairs may be nested, ring shaped, split rings, or elongate with constant separation. There may be coolant inlets 10a, 10b and outlet 14 may which may also be potential coolant leak flow pathways with associated electrodes 2, 4.

Figure 6

Modelled change in Capacitance between two square plates with a hemispherical water droplet between the plates by varying water droplet radius.

ΓΠ (N un

Γ0

O

Jjd] aouejpedeo l/i ri

Radius of Water Droplet [mm]

Figure 3 φ

Τ3

Ο φ

φ

Ω.

Ο

Ω.

ιΛ

φ

-Ω

Ω

Π3

U

TO

Q,

Π3 ,Ξ φ

tuo

C

Π3 χ

υ σ

_φ φ

“S ο

[jd] aaueipedeo (Ν

ISJ(Ν

Ο

Ν

U5

ΓΜ «Ή <sf

Ο

Number of Water Droplets (Ν

ΠΊ

17 _Q

ΓΜ γΉ

_Ω

07 17

07 17

05^7 17 ο

07 17

-1Magnetic Stimulation Coil Arrangement Including Coolant Leak Detector

The present invention relates to a Magnetic Stimulation (MS) coil arrangement that utilises liquid coolant and further includes a coolant leak detection arrangement.

Magnetic stimulators are utilised for magnetic stimulation of the brain and/or muscular tissue and achieve stimulation by creation of a rapidly changing magnetic field. Electric currents induced by the changing magnetic field cause stimulation of the brain and/or muscular tissue. Known magnetic stimulator arrangements generally comprise a charging circuit for a discharge capacitor, a discharge control for allowing discharge of the capacitor through a magnetic stimulation coil arrangement, and other circuit elements for limiting the effect of undesirable electrical transients. The magnetic stimulation coil arrangement comprises an elongate conductive element wound to form a winding having a plurality of turns. Two windings are typically provided in series for transcranial magnetic stimulation (TMS). The implication of discharge of the capacitor through the winding is that significant amounts of heat is generated meaning that cooling is required to ensure comfort for the patient. Lluid is therefore arranged to flow adjacent to the winding(s) to take heat away from the winding(s) during operation.

Liquid cooled magnetic stimulation coil arrangements are advantageous over air cooled coil arrangements due to improved cooling capabilities. Electrically inert liquids such as flourinert and MIDEL 7131 exist that can be used as the coolant however these fluids are not as effective coolant as water due to water having a comparatively low viscosity and high heat capacity.

Using water and even de-ionised water presents significant challenges due to the potential for leaks from seals and joints that may then become a hazard. Even in the case of electrically inert oils having a leak is not desirable and a means of detecting a potential leak is desirable in order to prevent any potential hazards to the patient during treatment.

According to the present invention there is a magnetic stimulation coil arrangement comprising one or more windings, each winding formed of a conductive element wound to

-2define a plurality of turns, a housing for receiving the windings and a coolant flow path defined between the housing and the one or more windings, the housing having at least one potential leak path way from the coolant flow path to external of the housing, the magnetic stimulation coil arrangement further comprising one or more leak detection arrangements for detecting a coolant leak through associated one or more potential leak flow pathways, each of the leak detection arrangements comprising a first and a second electrode arranged such that a potential leak pathway is defined between the first and second electrode, wherein a change in impedance between the electrodes is indicative of a coolant leak.

The present invention provides a solution to this problem by using capacitive sensing and the fact that water has a high permittivity to detect a leak around a seal instantly and enable restriction of normal operation of the MS coil arrangement.

The MS coil arrangement is for external use for a patient. The MS coil arrangement is preferably a Transcranial Magnetic Stimulation (TMS) coil arrangement.

The change in impedance between the first and second electrode is measured dependent upon whether the electrodes are bare electrodes i.e. they are un-insulated or are coated to provide insulation. In the event the electrodes are bare electrodes then resistance and/or capacitance is measured between the electrodes. In the event the electrodes are insulated then capacitance can be measured.

The electrodes are spaced apart to define the leak flow pathway. A control arrangement is preferably provided configured to monitor the electrical impedance between the first and second electrodes and restrict current flow through one or more winding(s) upon detection of a threshold change in the monitored impedance.

The control arrangement is preferably further configured such that the magnetic stimulation coil arrangement enters a safe a mode whereby current is not passed through the one or more windings in the event of detection of the threshold change.

-3The first electrode may be nested in the second electrode. The first and second electrodes may be elongate. The separation between the first and second electrodes is beneficially substantially constant.

The first and second electrodes may be ring shaped and may be circular however the shape of the electrodes depends upon the shape of the potential leak pathway. The first and second electrode may be split rings. The split between opposing ends of the electrode significantly limits current in an otherwise non-split loop from the changing magnetic field from the one or more windings.

The housing may comprise one or more inlet and/or outlet ports and the leak flow pathway is defined between an inlet or outlet port and a conduit in communication with the inlet or outlet port. The inlet/outlet ports are beneficially for enabling coolant to flow into and/or out of the housing and/or enabling the conductive element into and/or out of the housing, and/or enabling wires into and/or out of the housing, wherein a leak flow pathway is defined between the housing and a conduit for carrying the coolant and/or conductive element and/or wires.

It will be appreciated that a potential coolant flow pathway is present between the housing and the carrier for the elongate conductive element formed into the winding(s) and the conductive element extending to the electrodes. An access port must therefore be provided in the housing and the leak flow pathway defined between the housing and the conduit. Additionally, coolant must flow into and out of the housing and access ports may be provided accordingly in the housing, and a coolant conduit may be secured relative to the housing. However, access ports define a potential leak flow pathway which must be sealed. Accordingly, the first and second electrodes are positioned such that the leak flow pathway is defined therebetween.

At least one of the leak detection arrangements may be positioned on the housing for use in detecting potential leak flow pathways from the housing. This is useful in the event of a crack or hole arising in the housing which could potentially occur through accidental impact for example during operation. A plurality of leak detection arrangements may be

-4provided for example on the surface of the housing which would detect a leak should coolant flow out of the housing and between the first and second electrodes.

A further potential leak flow pathway is within the housing such as in the event that the winding(s) are potted and/or otherwise encapsulated within the housing. In such a configuration coolant flows between the inside of the housing and the housed or potted winding(s) and a leak occurs in this inner housing or potting material towards the winding(s). Thus, the leak is inwardly to the windings rather than outwardly through the housing.

The housing may comprise a first and second coupled housing portion, and a leak flow pathway may be defined between the first and second coupled portions. The provision of first and second coupled housing portions is beneficial for assembly purposes and the first and second housing portions are provided separately and during assembly receive the one or more windings therebetween. The first and second housing portions are then coupled together however a potential leak flow pathway is defined at the join between the first and second housing portions. The first electrode is beneficially retained relative to the first housing portion and the second electrode is beneficially retained relative to the second housing portion.

The first electrode may be termed a terminal electrode and the second electrode may be termed a ground electrode. The first and second electrodes may be insulated. In the event of utilisation of bare electrodes resistance and/or capacitance is measured therebetween whereas utilising insulated electrodes the capacitance is measured therebetween.

It will be understood that multiple electrodes may be provided. For example there may be multiple ground electrodes and/or multiple terminal electrodes.

A plurality of leak detection arrangements may be provided in series. This minimises the number of conductive pathways into the housing. The leak detection arrangements may also be provided in parallel.

-5Aspects of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a water droplet present between two electrodes as shown in figure la and in figure lb the finite element modelled electric field is presented with and without a water droplet.

Figure 2 is a graphical representation of the change in capacitance from modelling the system as presented in figure la with varying water droplet radii.

Figure 3 shows a leak detection arrangement according to an exemplary embodiment of the present invention, figure 3b shows water droplets between the electrodes, figure 3c shows additional water droplets between the electrodes and figure 3d shows the electric field produced from this electrode arrangement.

Figure 4 is a graphical representation of the change in capacitance for an increasing number of water droplets between the electrodes of figure 3 a.

Figure 5 is schematic perspective view of a magnetic stimulation coil arrangement according to an exemplary embodiment of the present invention.

Figure 6a and b are schematic perspective and plan views respectively of an exemplary embodiment of the present invention showing the various locations of leak detection arrangements.

Figure 7 is a schematic plan view of an exemplary embodiment of the present invention showing a number of leak detection arrangements in series.

Figure 8a and b is schematic representation in plan view of exemplary embodiments of the present invention showing the variety of electrode shapes and configurations that may be utilised.

-6Figure 9 shows further exemplary embodiments in figures 9a and b of alternative electrode configurations and figure 9c shows the field output from the electrode configuration of figure 8b.

Figure la shows two electrodes. The first electrode 2 is set at a voltage V and will be termed the terminal and the second electrode 4 is set as ground. Represented between the two electrodes 2,4 is situated a hemispherical water droplet 6.

Figure lb shows the finite element modelled electric field shown in a cross-sectional view around the first and second electrodes 2,4 with no water droplet present and with a 15mm water droplet 6 present. As is clearly shown the water droplet shields the electric field.

Figure 2 shows the change in capacitance from modelling for the system shown in Figure la with varying water droplet radii. As can be seen the larger the size of the water droplet the larger the change in capacitance between the first and second electrodes 2,4. Water has a relative permittivity of ~80 whereas air has a relative permittivity of 1 and since capacitance is proportional to permittivity then any amount of water small or large will produce a measureable change in capacitance. If oils for example are used instead of water as the coolant they also have a much larger relative permittivity than air.

Figure 3a shows leak detection arrangement that may be used to detect fluid leaks around a sealed joint. First and second nested split loop electrodes 2,4 (ground and terminal) are shown. The split limits current in an otherwise non split loop from the changing magnetic field from the MS coil. It will be appreciated that a loop with no split may be utilised by shorting or grounding the first and second electrodes thus preventing generation of a current through the individual electrodes and causing them to become passive just before a pulse of charge is passed through the winding(s). This is also good practise even with a split loop. Alternatively the signal whilst firing may simply be ignored. .

The inner split loop electrode 2 is placed around a sealed joint where liquid could leak. The outer split loop electrode 4 is placed around but spaced apart from the inner split loop electrode. If liquid were to leak from the sealed joint then the liquid would inevitably flow

-7between the two electrodes 2,4 causing a measurable change in capacitance. Figure 3d shows the electric field produced from this electrode arrangement. Figure 3b shows eight small water droplets between the electrodes and 3d shows thirty two droplets.

Figure 4 is a graphical representation of the change in capacitance for an increasing number of water droplets between the first and second electrodes 2,4 shown in Figure 3 a, where the capacitance increases as the number of water droplets increases.

Figure 5 is a schematic perspective representation of a water cooled MS coil arrangement housing. The housing 8 in this example has two inlets 10a and 10b for fluid to flow into and around the first and second respective windings located within the housing 8. These inlets 10a, 10b have to be sealed to the housing at locations indicated by reference numerals 12a and 12b. There is one outlet 14 in this exemplary embodiment where liquid exits the coil. This outlet 14 must also be sealed to the housing at joint 18. Thus, inlet and outlet ports are present in the housing 8 leading to potential leak flow pathways.

Additionally, the winding typically has two wires 16 stemming from the winding externally to the housing 8. There may also be temperature sensors and other electronic components within the coil head which require further electrical cables 20 to stem from the coil head externally to the housing 8. All these wires and cables must be sealed at joint 22. The housing 8 may comprise two portions 8a, 8b arranged to cooperate having a join which must also be sealed at joint 24.

In this example there are five potential seals/joins that may leak. In the case of the seals 12a, 12b, 18 and 22 the leak detector arrangement could be implemented at each joint to rapidly detect any leak in any one of these seals. In the case of seal 24 around the peripheral edge of the housing 8 opposing first and second electrodes 2,4 that follow the contour of the housing 8 may be implemented.

Figure 6 shows a perspective schematic representation of a water cooled the MS coil arrangement housing 8 shown previously in Figure 5. Figure 6a shows first and second

-8electrodes 2,4 placed either side of the join 24 between the first and second housing portions 8a, 8b allowing any leaks from this join 24 to be detected.

Figure 6b is a plan view of the coil housing shown in Figure 5. A pair of split loop electrodes 2,4 have been placed around the two inlets 10a and 10b and the outlet 14 respectively allowing for detecting leaks around these joints. Also in this embodiment a pair of electrodes 2,4 have been placed around the seal between the housing 8 and wires/cables to the windings.

Figure 7 shows the arrangement of the first and second electrodes included in the leak detection arrangement shown in Figure 6b. In this embodiment the electrodes 2,4 have been connected in series with twisted wire 28 connecting them. The electrodes 2,4 could alternatively be connected in parallel or the wires replaced with metal tracks for example.

There are numerous potential shapes, sizes and dimensions of electrode 2,4 that could be used in an electrode arrangement without departing from the invention. In addition capacitivly coupled electrodes may be used where such additional electrodes are passive and disconnected metal is placed adjacent or between the ground and terminal electrodes or active where multiple grounds per terminal or multiple terminals per ground are provided.

As a way of showing the many shapes of electrodes that may be used Figure 8a shows a pair of electrodes that span the housing in an irregular shape 30. Figure 8b shows several possible designs to include as examples only a squiggle 32, straight lines 34, triangles 36, spirals 38, hexagons 40, solid square patches 42 and solid triangular patches 44.

Figure 9 is a schematic presentation of further exemplary electrodes 2,4 showing in Figure 9a a pair of coombe electrodes 2,4. Figure 9b is a schematic representation of first and second electrodes 2,4 with several passive pieces of metal 46 positioned between the electrodes 2,4. Figure 8c shows the field output from the structure shown in Figure 8b.

-9It is appreciated that the first and second electrodes may be driven by a DC or AC power supply to enable measurement in the impedance change. It will further be appreciated that embodiments have shown the electrodes 2,4 on the outside of the housing 8. It is appreciated that the electrodes may be located in the housing 8 itself to detect water leaks into the housing 8 and windings enclosed therein, where the windings may be embedded in potting and/or additional housings.

It is appreciated that leak detector arrangement(s) could also be placed on the underside/patient side of the housing 8 (opposite side to the connector).

It is also appreciated that the leak pathway may be the housing itself in the form of a defect or crack, and thus leak detector arrangements may be positioned on or integrated into the housing to detect such an eventuality, in a number of alternative configurations as shown in Figure 8 for example.

The present invention has been described by way of example only and it will be appreciated to the skilled addressee that modifications and variations may be made without departing from the scope of protection afforded by the appended claims.

Claims

1. A magnetic stimulation (MS) coil arrangement comprising one or more windings, each winding formed of a conductive element wound to define a plurality of turns, a housing for receiving the windings and a coolant flow path defined between the housing and the one or more windings, the housing having at least one potential leak pathway from the coolant flow path to external of the housing, the magnetic stimulation coil arrangement further comprising one or more leak detection arrangements for detecting a coolant leak through associated one or more potential leak flow pathways, each of the leak detection arrangements comprising a first and a second electrode arranged such that a potential leak pathway is defined between the first and second electrode, wherein a change in impedance between the electrodes is indicative of a coolant leak.

2. A magnetic stimulation coil arrangement according to according to claim 1 further comprising a control arrangement configured to monitor the electrical impedance between the first and second electrodes and prevent current flow through the one or more windings upon detection of a threshold change in the monitored impedance.

3. A magnetic stimulation coil arrangement according to according to any preceding claim wherein the first electrode is nested in the second electrode.

4. A magnetic stimulation coil arrangement according to according to any preceding claim wherein the first and second electrodes are elongate.

5. A magnetic stimulation coil arrangement according to according to claim 4 wherein the separation between the first and second electrodes is substantially constant.

6. A magnetic stimulation coil arrangement according to according to any preceding claim wherein the first and second electrodes are ring shaped.

7. A magnetic stimulation coil arrangement according to according to claim 6 wherein the first and second electrodes are split rings.

-118. A magnetic stimulation coil arrangement according to according to any preceding claim wherein the housing comprises one or more inlet and/or outlet ports, and the leak flow pathway is defined between an inlet or outlet port and a conduit in communication with the inlet or outlet port.

9. A magnetic stimulation coil arrangement according to according to any preceding claim wherein the housing comprises a first and second coupled housing portions, and a leak flow pathway is defined between the first and second coupled housing portions.

10. A magnetic stimulation coil arrangement wherein at least one of the leak detection arrangements is positioned on the housing for use in detecting potential leak flow pathways from the housing.

11. A magnetic stimulation coil arrangement according to any preceding claim wherein one of the first or second electrodes is a terminal electrode and the other of the first electrode and the second electrode is a ground electrode.

12. A magnetic stimulation coil arrangement according to according to any preceding claim wherein the first and second electrodes are insulated.

13. A magnetic stimulation coil arrangement according to according to any preceding claim comprising a plurality of leak detection arrangements provided in series.

14. A magnetic stimulation coil arrangement according to according to any of claims 112 comprising a plurality of leak detection arrangements in provided in parallel to one another.

15. A magnetic stimulation coil arrangement as hereinbefore described with reference to the accompanying drawings.

Intellectual

Property

Office

GB1611766.5

1-15

Application No: Claims searched: