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You are here: BAILII >> Databases >> England and Wales High Court (Patents Court) Decisions >> City Technology Ltd v. Alphasense Ltd [2000] EWHC Patents 56 (25th October, 2000) URL: http://www.bailii.org/ew/cases/EWHC/Patents/2000/56.html Cite as: [2000] EWHC Patents 56

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City Technology Ltd v. Alphasense Ltd [2000] EWHC Patents 56 (25th October, 2000)

Before: MR. DAVID YOUNG Q.C.

Sitting as a Deputy Judge of the High Court

B E T W E E N

Mr. Iain Purvis instructed by Messrs. Walker Morris, Leeds
appeared on behalf of the Claimant

Mr. Mark Platts-Mills Q.C. and Mr. Robert Onslow instructed by Messrs Hewitson Becke & Shaw, Cambridge appeared on behalf of the Defendant

Hearing dates: 10th, 11th, 12th and 13th October 2000

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J U D G M E N T
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David Young Q.C.

DATED: 25 October 2000

1. The Claimants City Technology Limited are proprietors of UK Patent No. 2,094,005 which relates to electro-chemical gas sensors - in particular carbon monoxide gas sensors which were originally developed for the National Coal Board in the early 80s. In this action they claim that the Defendants gas sensors, in particular their carbon monoxide gas sensors infringe claims 1-3, 7-9 and 11-15 of their patent. The Defendants deny infringement and counterclaim for the revocation of the patent on the grounds that the alleged invention is obvious and does not involve an inventive step having regard to US Patent N. 3,755,125 (Shaw) and/or in the alternative common general knowledge.

U.K. Patent No. 2,094,005

2. The patent in suit claims a priority date of 3rd February 1991. Having pointed out that there is an increasing demand for small compact reliable and relatively inexpensive gas sensors for safety monitoring, pollution control, fire detection and flue gas analysis it states that a particular problem with such gas sensors is to ensure an adequate electrolyte connection between the electrodes regardless of the orientation of the instrument and the changes in volume of electrolyte with changes in ambient humidity.

1. An objective of the invention is stated to be to provide a small compact sensor that is simple in construction and has a high degree of integrity, reliability and freedom from the proneness to leakage and the problems of adequate electrolyte connection.

2. A typical electrolyte used in such sensors is an acid such as 10-N sulphuric or 50% phosphoric acid. It is therefore necessary to ensure that in the construction of the cell, any materials including the electrodes in contact with such strong acid electrolyte must be compatible. The electrodes as described are constructed from porous PTFE support tape to which a catalyst/PTFE mixture is bonded over a smaller circular area. The catalyst in question is finely divided platinum black and it was common ground that such electrodes were generally known from their use in fuel cells - indeed it was accepted that the knowledge of such electrodes would be part of the common general knowledge in the relevant art.

3. The porous PTFE support for the electrode allows the gas being sensed to pass through it but being hyphophobic is impervious to the acid electrolyte. Thus the electrolyte can be conveniently contained between two electrodes namely a sensing anode electrode where the carbon monoxide is electrochemically oxidised and the counter electrode where a reduction process must take place e.g. the reduction of oxygen by the hydrogen ions produced by the oxidization of the carbon monoxide. Such electrodes are separated by separators made from hydrophilic material such as glass fibre paper.

4. The electro chemical principles as to how such gas sensors function are well known. Optionally one may have a third reference electrode to control the base line of the sensor output or the potential of the sensing electrode (see e.g. Figures 3 and 5).

5. The subject of the patent in suit is the particular structure of a gas sensor in the sense of the arrangement of elements which per se are known but which if arranged in the manner claimed provide a sensor fulfilling the stated objective.

3. The relevant claims are as follows:

6. Claim 1- A compact and leak-resistant electrochemical gas sensor in the form of an electro-chemical cell assembly comprising

7. (i) a first planar (sensing) electrode

8. (ii) a second planar (counter) electrode comprising

9. (a) a planar hydrophobic porous support

10. (b) said support having an opening therein

(iii) a planar hydrophilic non-conducting porous separator interposed between said first and second electrodes and in contact therewith and being in contact with

(iv) a hydrophilic non-conducting porous wick passing through said opening and extending into

(iv) an electrolyte chamber partially filled with an electrolyte contacting said wick

said assembly permitting access of a gas to be sensed to the sensing electrode and providing an electrolytic connection between the sensing and counter electrodes in all orientations of the assembly.

11. Claim 2 - A sensor according to claim 1, wherein the wick passes through a hole or slit in the counter electrode.

12. Claim 9 - A sensor according to anyone of claims 1 to 8 wherein the sensing electrode is an anode for the detection and measurement of oxidisable gases.

13. Claim 11- A sensor according to claim 9 wherein the counter electrode is an oxygen reduction cathode receiving its oxygen from ambient air.

14. Claim 13 - A sensor according to claim 11 or 12, wherein one or both of the counter electrode and reference electrode comprises a hydrophobic porous support which extends to the surface of the assembly and permits oxygen to diffuse to the electrode.

15. 4. The novelty of the cell assembly claimed in claims 1 and 2 lies in arranging a wick to pass through an opening (hole or slit) in the counter electrode and its support and thereby allow electrolyte to be drawn up from a reservoir or chamber and by capillary action to continuously wet a hydrophilic separator which is in contact with both electrodes. It is stated that such an arrangement provides a compact and leak-resistant sensor that allows electrolytic contact between the electrodes in all orientations.

16. 5. At page 2 line 21 to page 3 line 3 it is stated that the wick may be integral with the separator and that the wick arrangement ensures an adequate supply of electrolyte to the space between the electrodes independently of any volume change or attitude of the cell and also permits close spacing of the electrodes with consequent reduction in size of the sensor.

17. 6. Whilst there was evidence as to the meaning of the word wick, such evidence was neither admissible or helpful and I propose to give the word its ordinary meaning namely as a bundle of fibres (or woven material) which allows liquid to be drawn up through it - such as a wick for a lamp.

18. There was also a dispute as to the meaning of claim 13. At page 5 lines 17 to 21 the counter electrode is stated to be an oxygen reduction electrode receiving its oxygen supply from the ambient air "by radial diffusion inwardly through the porous PTFE tape from the perimeter of the tape".

19. 7. Again at page 8 line 27 to page 9 line 6 it is stated that ingress of oxygen to the perimeter of the counter electrode occurs via the clearance between the current collectors 6 and 7 and the slots in the O-ring retaining ring 12. To ensure good distribution around the perimeter a narrow, shallow annular channel may be cut in the bottom plate 17 with an outside diameter the same as the inside diameter of 13. From the perimeter the oxygen diffuses radially inwardly along the porous PTFE support of the counter electrode to the counter electrode catalyst, the PTFE tape retaining sufficient diffusibility for this purpose even when compressed by the O-ring 12

20. 8. Reading these passages which provide the only basis for claim 13, I have no doubt that applying a purposive construction to claim 13 it requires the hydrophobic porous support to extend to the surface of the assembly to permit oxygen to diffuse to the electrode from the outside surface or perimeter of the support radially inwards as at least a route for the required oxygen at the counter electrode. That is the whole purpose of extending the support to the surface of the assembly.

Infringement

21. 9. A product description of the Defendants carbon monoxide sensor is to be found in Core Bundle Part C TAB 7 and various photographs of its parts in Part F.

22. The exploded drawing below illustrates the sensor which has three electrodes, namely sensing electrode (8), reference electrode (13) and counter electrode (15) - all three electrodes consist of a platinum black PTFE mixture supported on a porous PTFE tape. The counter electrode has an opening in its centre facing downwards i.e. in the opposite direction to the sensing electrode. Sandwiched between the electrodes are various separators (9), (11), (12) and (14) which when assembled are all in contact with each other to allow electrolyte to be held between them. Below counter electrode (15) is a separator (16) which is in contact with a wick (9) threaded through a slot in the reservoir cup top. The wick (19) which has two legs extending into the reservoir co-operates with the centre of separator (16) to form a wick arrangement which when the sensor is assembled passes through the opening in the counter electrode (15) and forms an electrolytic connection with the electrolyte held by the separators sandwiched between the electrodes.

23. When fully assembled plastic top cap (2) and the plastic body (22) are welded together so that ambient air can only enter the system from the top downwards or the bottom upwards.

10. (a) Infringement of claims 1 and 2

24. The only issue is whether feature (iv) of claim 1 is taken which requires the hydrophilic non conducting wick to pass through the opening in the counter electrode support (or the counter electrode itself).

25. The Defendants contend that the wick is to be construed as a unitary item which extends from the reservoir through such opening and does not include the wick (19) and a separator (16).

26. It is contended that separator as used in the patent is distinct from the wick having a different function. The wick supplies the electrolyte to the separators which maintain the electrolyte in contact with the electrodes and also separate them to create the necessary electrolytic path. Reliance is placed on claim 6 where the wick is required to pass through an opening of a separator. The Claimants rely on the reference that the wick and separator may be integral to indicate that the roles of the wick and separator are not distinct and that both are made from the same or similar hydrophilic porous material. Whether therefore a separator (so called) is a wick or part of a wick will depend on its function i.e. whether it is supplying electrolyte to the separator sandwich.

27. 11. Section 125(3) requires the Protocol on Interpretation of Article 69 of the EPC to be applied. It states:

28. The Protocol outlaws what can be termed strict literal and also liberal interpretation using the claims as a guideline. The correct approach is to achieve a position between those extremes "which combines a fair protection for the patentee with a reasonable degree of certainty for third parties".

12. In Improver Corporation v. Remington Consumer Products Limited [1990] FSR 181 Hoffmann J. suggested at page 189 that the court when applying the Protocol should ask these questions:

"(1) Does the variant have a material effect upon the way the invention works?

If yes, the variant is outside the claim. If no-

(2) Would this (i.e. that the variant had no material effect) have been obvious at the date of the publication of the patent to a reader skilled in the art. If no, the variant is outside the claim. If yes -

(3) Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention. If yes, the variant is outside the claim.

On the other hand, a negative answer to the last question would lead to the conclusion that the patentee was intending the word or phrase to have not a literal but a figurative meaning (the figure being a form of synecdoche or metonymy) denoting a class of things which included the variant and the literal meaning, the latter meaning, the latter being perhaps the most perfect, best-known or striking example of the class".

29. Hoffman J went on to explain that the first two questions involved considerations of fact, but the last was a question of construction.

30. 13. Assuming in the Defendants favour that on a literal construction of the word wick there must be a unitary tape a bundle of fibres which extends from the reservoir through the opening in the support, I have no doubt that both the requirements of the Improver questions and the Protocol to Article 69 are satisfied. Thus assuming the variant in this case is the combined use of a single wick (19) and the centre of the separator (16) which allows the electrolyte to be transported from the reservoir to the separators sandwiched between the electrodes, such arrangement clearly has no material effect upon the way the invention works as it will allow electrolyte to be maintained within the separators at all orientations of the sensor (Question 1 of Improver). As to whether such a fact have been obvious at the date of publication of a patent to the reader skilled in the art. I have no doubt that the close contact of the hydrophilic wick (19) with the hydrophilic separator (16) when assembled will allow electrolyte to be so transported to the separators just as a single wick would do so as described in the patent (Question 2 of Improver). Finally as to whether from the language of the claim it was to be understood that the patentee intended that it was an essential requirement that the wick should be a unitary piece extending from the reserving through the support opening. I consider there is no good reason why the claim should be so narrowly construed particularly in the light of the teaching that the wick may be made integral with the separator. (Question 3) The essence of the invention seems to be how the electrolyte is conveyed to the separators sandwiched between the electrodes, namely by means of a hydrophilic wick arrangement which transports the electrolyte from the reservoir to the separators through an opening in the counter electrode support. This seems to me precisely how the Defendants wick (19) and separator (16) function. Applying the Protocol, such an interpretation combines a fair protection for the patentee with a reasonable degree of certainty for third parties - a narrowed interpretation would be unfair to the patentee.

14. (b) Infringement of claim 13

31. Initially there was a dispute as to precisely what reduction reactions take place at the counter electrode. However it is now common ground that the principal reduction reaction is that of oxygen and the Defendants accept that there are in fact two ways the oxygen will arrive at the counter electrode. Firstly the oxygen that is dissolved in the acid electrolyte will provide sufficient oxygen to monitor levels of up to 100 to 200 ppm of carbon monoxide. However the Defendants sensor is guaranteed to monitor up to 1000 ppm of carbon monoxide.

32. 15. The second way it is accepted by both parties oxygen will reach the counter electrode is by a route that was referred to as inside the O ring route; namely some of the air being monitored will diffuse through an outer annulus portion of the sensing electrode support (8) it will flow past the outer periphery of separator (9) and diffuse through PTFE washer (10), then it will flow past the outer pheriphey of separator (12), reference electrode (13) and separator (14) to finally diffuse through the support of counter electrode (15) where it will contact the counter electrode itself.

33. This second route was not appreciated by the Defendants until the Claimants expert witness (Dr. Wykes) had referred to the same and calculated that such a route would indeed provide sufficient oxygen to monitor carbon monoxide levels up to 1000 ppm.

34. Neither of such routes would fall within claim 13 which (on my construction) requires oxygen to be transported radially inwardly from the surface of the assembly to the counter electrode via its hydrophobic porous support.

35. 16. As regards the claimed route, whilst it is accepted by the Defendants that it is one which is theoretically possible, they contend that given the existence of the first two routes it is highly improbable that significant levels of oxygen will diffuse radially inwardly given that the oxygen will have to pass through the porous support which has been compressed by the O ring. The evidence was that as assembled the downward pressure exerted via the O ring is in the region of 200 and 400 psi. Precisely what effect such pressure will have on the porous support will depend on the nature of the support prior to being compressed. Dr. Safell the Technical Director of the Defendants states that the porous supports in the Defendants' sensor are made from Mupor hydrophobic porous tapes having similar morphology and structure to Goretex and Zitex. However the precise porosity of the tape before it is compressed is not known and the Claimants chose not to carry out what were described by Prof. Williams (the Defendants expert) as a relatively simple experiment to determine whether indeed oxygen does indeed diffuse radially from the surface of the assembly to the counter electrode via its support. That such an experiment could have been conducted is clear from similar earlier experiments conducted by Chan Henry which are referred to in a report dated July 1983 which forms part of a thesis he submitted to the City University - see Table 3.1 of CH Vol part 14 pp 15 & 16. Dr. Wykes in part D of his Supplemental Report contends that even applying pressure some twelve times greater than that applied to the Defendants sensor, oxygen will still diffuse through a porous PTFE tape. Prof. Williams in answer to this relied on micrographs of cross-sections of the electrode support under pressures that he understood to be closely similar to that under the O ring seal in the Defendants device. The micrographs illustrate that the pore structure appears to be substantially closed up. However as is clear from the micrographs themselves the pressure applied to such tapes was of the order of 7000 psi and therefore as was accepted by Prof Williams could not be relied upon. Prof Williams also criticised Dr. Wykes approach in applying the wrong diffusion coefficient on the grounds that as the pores became smaller a different diffusion known as Knudsen diffusion occurs. What one is left with therefore is pure speculation as to how much, if any, oxygen will diffuse radially inwardly from the perimeter of the support of the counterelectrode. On the basis that sufficient amounts of oxygen can reach the counter electrode by other routes which provide less resistance to oxygen diffusion - in particular via the inside of the O ring which seems the most likely route for the oxygen - I consider that the Claimants have not established claim 13 is infringed by the Defendants device. The Claimants did not contend that the inside of the O ring route was an immaterial variant to the radial route via the outer periphery of the support.

Validity

36. 17. The patent in suit is addressed to persons interested in the design and manufacture of gas sensors. Such a person (or group of persons) would have knowledge in the basic principles of electrochemistry and in general the operation of electrochemical cells.

37. 18. Professor Williams (the Defendants Expert) who is Professor of Chemistry at University College London and is clearly someone of considerable distinction in the field of electrochemistry had no or little knowledge about electrochemical cells used as gas sensors prior to being retained by the Defendants. He had never constructed or used electrochemical gas sensors. Therefore his knowledge was gained solely from literature searches of Chemical Abstracts and patent literature which he conducted for the purposes of this case. He was not aware of electrochemical gas sensors on the market as of the priority date or indeed who were the main players in terms of their production.

38. 19. Dr. Wykes (the Claimants Expert) worked for the Mining Research and Development Establishment of the National Coal Board from 1974 to 1983 at the time they decided to commission the Claimants to produce the electrochemical gas sensor which became the subject of the patent in suit. Dr. Wykes describes himself as at that time as having knowledge of electrochemical sensing of gasses somewhere between that of the informed user and that of a cell designer. In Appendix A to his Report Dr. Wykes states that public sources of information whilst good on basic electrochemistry and on engineering applications were much poorer on industrial sensors - sensor manufacturers literature was generally unhelpful and patents were often a better source of constructional details - however how well any particular cell would perform could only be reliably obtained by direct testing.

Common General Knowledge

39. 20. Whilst there was some debate as to what constituted the relevant common general knowledge which the skilled person would possess, in the end there was a considerable measure of agreement. Mr. Purvis for the Claimants referred me to the recent case (as yet unreported) of Davina Wheatley v. Drillsafe Ltd 5th July 2000 (C.A) where Aldous L.J. (para 42) recites a passage from his earlier judgment in Beloit Technologies Inc. v. Valmet Paper Machinery Inc. (1977) RPC 489 at 494. In particular Mr. Purvis relied upon the following passage as being apposite to this case, namely:

40. Citing the well known indeed "common general knowledge" passage of Luxmoore J. from British Acoustics Film 53 RPC 221 at 250

42. 21. Aldous L.J. expressed some doubt as to whether "accepted without question" set too high a test and substituted for it the words "generally regarded as a good basis for further action". The following matters were accepted by the parties to be part of the common general knowledge, namely:

43. 22. The Defendants also contended that the use of electrodes with holes passing through them was part of the common general knowledge. This was disputed by the Claimants.

44. In support of their contention, reliance was placed on Prof Williams' First Report (para 6.2.4.- conclusion 3) - "the use of electrodes with holes passing through them was generally known".

45. This statement was supported by reference to the following matters

(i) making an electrode in the form of a ring

46. Prof. Williams Day 3/353²⁵, 253⁴

(ii) production on an industrial scale of chlorine e.g. the Billiter diaphragm cell which had a flat cathode electrode with holes in it filled with asbestos fibre immersed in brine which percolates through the holes - (Bundle E2/19, Fig. 5-7).

(iii) a polyelectrolyte cell for the electrolysis of organic reagents as illustrated in a book edited by N.L. Weinberg called Techniques of Chemistry (see Bundle E2 17 Fig 2.34) holes cut in a cylindrical anode allow electrolyte to pass from the central reservoir radially therethrough to be absorbed by the polyelectrolyte which because of its ion exchange properties allows current to flow. Such cells have been used in the hydrodimerization of acrylonitrile to adiponitrile. An industrial version of this cell is illustrated in Industrial Electrochemistry by D. Pletcher (1982) Fig 6.4 (See Bundle E2/18).

47. 23. Such industrial applications all relate to the synthesis of chemicals by some form of electrolytical method which are far removed from the sort of compact gas sensor cells the subject of the patent. In addition the Defendants (Prof. Williams) relies on the following patents to illustrate that holes in electrodes were well known:

(v) US 3,239,444 (Heldenbrand) (1966): relates to a polargraphic oxygen sensing cell in which the counter electrode is a stack of consumable anode discs having a central hole which is immersed in electrolyte Again there was no evidence such a cell has ever been put into practice.

(vi) UK 1200595 (Bergman) (1970) Fig 6 illustrates as one construction an electrical cell having a cylindrical silver anode. It does not relate to a planar electrode with a hole or slot in it.

(viii) US 3,767,552 (Lauer) (1973) relates to an electrochemical gas sensor having a consumable porous lead anode in the shape of a cylindrical block having a central hole which is filled with electrolyte. There is no evidence that such a sensor has ever been put into practice.

49. 24. Apart from the Bergman patent there is not only no evidence that any of the cell devices have ever been put into practice but there is no evidence that any of such patents would be familiar to the notional skilled team of addressees. Whilst there was some evidence that the Bergman cell would have been familiar to persons such as Dr. Wykes (See Wykes First Report para 46) such cells were not constructed using a planar electrode with an opening in it.

50. None of such prior art has been pleaded as rendering the patent in suit obvious and apart possibly from the Bergman and Belliter cells none of the prior art referred to by Prof. Williams constitutes common general knowledge.

51. 25. It follows that when designing an electrochemical gas sensor cell at the priority date of the patent in suit (3rd February 1981) the assumed notional skilled person or persons would have no particular reason to consider constructing a cell having an opening in the counter electrode support and/or the counter electrode itself yet alone to provide such an opening to allow a wick to pass through the opening in order to transport electrolyte from a reservoir to the hydrophilic separator located between the electrodes.

52. 26. I consider the Defendants approach based on common general knowledge is one which the courts have consistently condemned. Starting with the well known fuel cell electrodes and hydrophilic separators sandwiched between them it is contended that there is only one way to construct the cell if it is to be compact, namely to locate the reservoir underneath the counter electrode and provide a wick which can only be located either to pass around the counter electrode and its support or through an opening in it.

53. As can be seen from the prior art referred to, electrochemical cells may have electrodes which are cylindrical (either hollow or solid with a hole in the centre) or planar - hence a sensor could be constructed using electrodes having any one of a number of configurations and the question of whether or where a reservoir for the electrolyte will be required will depend on the choice of configuration of the electrode. Likewise the question of whether or where a wick will be required will depend on (1) the electrode configuration (2) the requirement and location of the reservoir.

54. 27. Mr. Platts-Mills Q.C. for the Defendants contended that the claimed integers the subject of claim 1 of the patent in suit are a mere collocation of integers each integer being part of a cell designer's common general knowledge. I do not accept the claimed integers are a mere collocation as each of the integers interact with each other to provide the claimed cell.

55. To assume one is going to design a gas sensor cell using planar platinum black/PTFE electrodes on a porous PTFE support and end up with the requirement of separators, a reservoir and a wick all of which items are individually well known items and to so arrange them to provide an opening in the counter electrode and/or its support through which the wick will pass is the hindsight approach which depends on first knowing that those are the required items.

US 3,755,125 (Shaw)

56. 28. The Defendants contend that claims 1 and 2 are obvious in the light of Shaw.

57. As best seen from Figs 2 and 3 hereunder Shaw relates to an electrochemical gas sensor which is constructed by forming a stack of hydrophilic non-conducting disc-like separators 42 and 44 which are sandwiched between two wire mesh electrodes 41 and 46. Located below this assembly is a reservoir 11 which is filled with an absorbent sponge like material 39 which retains the electrolyte and prevents it sloshing about. Integral with the four lower disc separators 42 are wicks 43 which are spaced circumferentially at 90^o and depend downwardly so that they are in contact with the absorbent filler 39 - the four wicks are accommodated in four notches in the body which retains the assembled unit.

FIG 3

FIG 4

58. 29. It is common ground that the novelty of the construction of the sensor the subject of claim 1 of the patent in suit resides in two features namely:

59. 30. Thus applying the four steps advocated by Oliver LJ in Windsurfing Inc. v Tabur Marine (Great Britain) Ltd (1985) RPC 59 at 73 the question is whether when viewed without any knowledge of the alleged invention those differences over Shaw constitute steps which would have been obvious to the skilled man or whether they require any degree of invention.

60. I bear in mind in particular the warning against ex post facto analysis of Lord Russell in Non-Drip Measure Company Ltd v. Strangers Ltd 60 RPC 135 at 142. Quoting the well known words of Moulton LJ from British Westinghouse Co. v. Braulik he stated that "nothing is easier than to say, after the event, that the thing was obvious and involved no invention".

61. 31. The Defendants case was that by taking a series of simple modifications to the Shaw device one could arrive at the device the subject of claims 1 and 2.

62. The first step is to substitute the wire mesh electrodes with the fuel cell type electrodes comprising a PTFE mixture and catalyst on a PTFE support particularly at the sensing electrode due to their higher activity and efficiency. Such electrodes were part of the skilled persons common general knowledge and Dr. Wykes accepts an improvement to the Shaw device would be to use such an electrode as the sensing electrode (See para 70 of Dr. Wykes First Report).

63. However it was clear from the cross-examination of Prof. Williams (Day 3/288) that the substitution of the wire mesh counter electrode 41 by a platinum/PTFE fuel cell type electrode is not a simple matter. The counter electrode does not rest on the reservoir itself but is merely supported at its periphery on a shoulder in the body of the device. For reasons not explained by Shaw there is a substantial gap between the counter electrode and the reservoir and whilst a wire mesh electrode of the type described by Shaw is structurally self supporting, a platinum/PTFE electrode on a PTFE porous tape support would not be. Thus to accommodate such an electrode the device would require a shelf underneath it to give it support. In addition because the PTFE support is non conducting, gold conductor ring 40 would only function if the electrode was inverted and this would lead to problems of how to maintain electrolyte at its face with a separator underneath for electrode. Alternatively the gold conductor ring could be placed on top of the PTFE/platinum electrode which would mean altering the location of the electrical wire 38.

64. 32. Having made such substitution of PTFE electrodes for wire mesh electrodes it was Prof. Williams evidence that he had no reason to believe it would not work (Day 3/298, 300) so that there would appear to be no reason to consider further modifications to the device.

65. In particular Prof. Williams accepted there was good reason to have four wicks spaced around the periphery to allow a uniform supply of electrolyte from all sides of the sensor. Prof. Williams would not have used a single tab at one edge (See Day 3/303¹²-304²⁶),

66. 33. As regards the idea of placing a wick through an opening in the counter electrode Prof. Williams' evidence under cross examination (Day 3/305^9-20) was as follows:

69. In re-examination (Day 3/354⁸) in response to what he meant by "rigidly" Prof. Williams evidence was:

76. 34. This evidence is precisely the sort of ex post facto analysis referred to by Lord Russell and Moulton L.J. The idea of having a wick passing through an opening in the counter electrode is an idea which is novel per se. Prior to the patent in suit, wicking arrangements in electrochemical cells in so far as cells had such arrangements were via the side of the electrodes i.e. through the natural gap caused by the electrode separation - see Dr. Wykes First Report para 43 and the Hersch cell. Dr. Wykes' evidence (First Report para 70) was that even if he thought of reducing the Shaw wicking arrangement to one wick it would not have occurred to him to cut a hole in the electrode or its support unless one had appreciated the benefits of doing so.

77. 35. One such benefit of a wicking arrangement in which the electrolyte passes through an opening in the support of the counter electrode is that the electrolyte footprint is confined to the centre of the cell due to the hydrophobic nature of the support - thus proneness to leakage of electrolyte is improved - one of the principal objectives of the patent in suit.

78. 36. Having considered the evidence, I consider the concept of a wick arrangement through an opening in a hydrophobic support for the counter electrode is a clever solution to providing a compact leak-resistant sensor and is not obvious in view of Shaw. Hence I conclude claims 1 and all claims appendant thereto are valid.

37. Conclusions

1. I find the Defendants device infringes claims 1 and 2, but not claim 13. Although no separate argument was addressed on the other subsidiary claims, it seems to me that from my findings at least claims 3, 7-11 and 14 are also infringed.

2. I find claim 1 and all appendant claims to be valid.