OPTIMISED THERMOCHROMATIC MATERIALS

Abstract

This invention relates to optimisation of the temperature range of thermochromic liquid crystal materials and to related methods and devices for temperature monitoring and measurement. The invention also relates to methods and devices for the improved registering of objects in contact with thermochromic liquid crystal materials.

Claims

1-30. (canceled)

31. A method for monitoring or measuring temperature using thermochromic liquid crystal (TLC) material, comprising analysing colours revealed as the TLCs transition from transparent to colour and/or from colour to transparent, including colours imperceivable by the human eye and/or colours extending beyond the temperature range set by a TLC manufacturer.

32. The method according to claim 31, wherein said analysis of colours extends a lower and/or an upper end of the nominal temperature range of the TLC material.

33. The method according to claim 32, wherein the temperature range is extended beyond the lower end of the nominal range of the TLC material by analysis of the colours revealed as the TLCs transition from transparent to red.

34. The method according to claim 33, wherein the colours include hues represented by approximately 330° to 355° in a Hue Saturation Value (HSV) colour space, where 0° is pure red.

35. The method according to claim 32, wherein the temperature range is extended beyond the upper end of the nominal range of the TLC material by analysis of the colours revealed as the TLCs transition from violet to transparent.

36. The method according to claim 35, wherein the colours include hues represented by approximately 240° to 360°, preferably 290° to 355°, in the Hue Saturation Value (HSV) colour space, where 0° is pure red.

37. The method according to claim 31, wherein the colour analysis at least partially excludes colours starting from the transparent to red transition to yellow to green hues.

38. The method according to claim 37, wherein which hues are represented by a range from between about 0° to 90° in the HSV colour space, where 0° is pure red, and wherein said exclusion reduces artefacts.

39. The method according to claim 31, wherein said colour analysis comprises analysing only a Hue (H) component of a Hue/Saturation/Value (HIV) colour space and determining temperature from said H component alone.

40. The method according to claim 31, wherein said analysis is carried out on at least one image of said TLC material.

41. The method according to claim 31, wherein specific colours of the TLCs are correlated to specific temperatures by reference to a calibration table or curve fitting formula.

42. The method according to claim 41, wherein said curve fitting formula allows an extrapolation and/or an interpolation of temperature values.

43. The method according to claim 31, wherein the temperature monitored or measured is of an object or subject in contact with TLC material, said method comprising analysing at least one heatmap generated by contacting said object or subject with said TLC material and monitoring or deriving the temperature of the object or subject from analysis of any one or more colours revealed as the TLCs transition from transparent to colour and/or from colour to transparent, wherein said analysis includes colours imperceivable by the human eye and/or colours extending beyond the temperature range set by the TLC manufacturer, wherein said contact is direct or indirect, wherein the subject is a mammal.

44. A method for monitoring or measuring hand or foot temperature in a subject, comprising (i) contacting hand(s) or foot/feet of a subject with a substrate comprising thermochromic liquid crystals (TLCs), wherein said contacting generates a heatmap on said substrate; (ii) analysing the heatmap for colours revealed as the TLCs transition from transparent to colour and/or from colour to transparent, wherein said analysis includes colours imperceivable by the human eye and/or colours extending beyond the temperature range set by the TLC manufacturer; and (iii) monitoring for points of elevated temperature (“hotspots”) and/or reduced temperature (“cold spots”) on said heatmap.

45. The method according to claim 44, wherein a presence of hotspots or colds spots is determined by analysing the heatmap generated for anomalies by comparing the heatmap generated to itself or to one or more previous heatmaps taken from the same subject and/or to reference heatmaps or temperature values.

46. The method according to claim 44, wherein said TLC material is applied to a surface of a substrate and/or is embedded in a substrate.

47. The method according to claim 46, wherein the TLC material is comprised in a thermochromic liquid crystal sheet (TLCS).

48. The method according to claim 46, wherein said TLCS additionally comprise a black layer or another colour suitable for providing contrast.

49. The method according to claim 48, wherein said black or contrasting layer is replaced by a layer of electrochromic material.

50. A thermochromic liquid crystal sheet (TLCS), comprising (a) TLC material applied to the surface of a substrate and/or embedded in a substrate, and (b) a layer of electrochromic material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0090] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0091] FIG. 1 is a schematic representation of a device for measuring temperature accordance with the invention.

[0092] FIG. 2 illustrates the colour transitions of a typical TLCS.

[0093] FIG. 3 is a flow chart of steps carried out in one embodiment by the device of the invention.

[0094] FIG. 4 shows how artefacts are reduced by excluding TLCS colours associated with lower temperatures.

[0095] FIG. 5 is a flow chart detailing the image processing steps carried out in one embodiment to derive temperature values from the images.

[0096] FIG. 6 shows a temperature extrapolation method used to estimate temperatures outside the TLCS temperature range.

[0097] FIG. 7 is a representation of a TLCS comprising a sheet of electrochromic material.

[0098] The present invention will now be described with reference to the following non-limiting examples. Furthermore, elements or components that are described with reference to any Figure may be interchanged with those of other Figures or other equivalent elements without departing from the spirit of the present teaching.

[0099] FIG. 1 shows a schematic representation of a temperature measuring device 100 for measuring the temperature of subject or object 105. The device 100 comprises an enclosure 101 with transparent panel 102 on which a TLCS 103 is placed. The TLCS has one surface comprising the thermochromic liquid crystal layer, which surface faces camera 104, and another surface comprising backing material which comes into direct contact with subject or object 105. A computer 106 is operatively connected to camera 104 and one or more optional light sources 107 for illuminating the TLCS. An optional proximity sensor 108 informs the computer 106 when a subject or object 105 makes contact with the TLCS 103.

[0100] FIG. 2 shows the colour gamut 200 produced by TLCS 103. The full gamut 201 includes all the colours of the rainbow or the visible spectrum 202, which are discernible by the naked eye and constitute the temperature range for off-the shelf TLCS. The outermost rainbow colours red (at the lower end of the spectrum) and violet (at the higher end of the spectrum) eventually fade into transparency, revealing the colour of the TLCS substrate backing material. The temperature interval is short for the transparent to red transition 203. For the violet to transparent transition 204 the interval is significantly longer, in some TLC materials it can be longer than the design interval 202 set by manufacturers. The range 205 indicates an example of the subrange of colours analysed in the methods of the invention.

[0101] FIG. 3 shows an example flowchart 300 of steps when using the device 100. In 301 the computer 106 receives a continuous real-time image stream from camera 104 and retains the respective last image of the stream in the computer’s memory. In 302 sensor 108 signals the presence of object or subject 105 on the TLCS surface 102 and the continuous loop terminates. In 303 the computer 106 immediately enters into a second continuous loop where it captures and stores in computer memory still images from camera 104 at discrete time intervals. In 304, when a prescribed amount of time has passed, the second continuous loop is terminated. In 305, the computer immediately commences with the analysis of the images stored in the memory, including the image stored previously in 301.

[0102] FIG. 4 shows the use of a subsection of the full colour gamut 201. 401 is an enlarged view of TLCS 103 in device 100 captured by camera 104. The TLCS sheet is not in contact with subject or object 105 and is therefore only exposed to ambient temperatures surrounding device 100. A temperature which is below the point where the TLCS colour transition from transparent to red occurs. 401 should therefore show only the substrate colour of TLCS 103, which is black in this instance. However, 401 shows spurious features such as highlights and reflections emanating in this case from the illumination 107 inside device 100.

[0103] Restricting image processing by the computer 106 to the colour gamut shown in 402, excluding regions 403 and 406, results in a processed version of the previous area 405 where the amount spurious features is significantly reduced.

[0104] FIG. 5, flowchart 500, shows the steps involved in processing the images stored in the computer memory as described above and shown in 301 and 303 of FIG. 3. Any time after completion of block 305 the processing starts: block 501 of FIG. 6.

[0105] In a first step, the pre-contact image stored in block 301 is pixel-wise subtracted from all images stored in block 303. This isolates the object in these images. Standard image processing algorithms known to persons having ordinary skill in the art are then used to create a mask from the isolated object. Further processing of all images is restricted to the area covered by the mask, block 502.

[0106] By using only a subsection of the full colour gamut 201 spurious features are removed from all images, block 503.

[0107] A calibration look-up table of the sort known to persons having ordinary skill in the art is then used to pixel-wise translate colour values into a temperature map for each image, block 504.

[0108] Using the known time interval between image captures in continuous loop 303 a pixel-wise extrapolation of the values in the temperature maps resulting from block 504 can be performed by applying measurement task-appropriate curve-fitting algorithms. Such extrapolation can produce pixel-wise approximations of the eventual temperatures at points that lie beyond the upper limit of the extended TLCS temperature range 205, block 505.

[0109] The extrapolated temperature values generated in block 505 are stored in computer memory for further use such as permanent storage onto computer readable media. They may also be displayed in a variety of formats known to persons having ordinary skill in the art, including in the form of a false-colour image, block 506.

[0110] The graph 600 of FIG. 6 illustrates an example for estimating temperatures outside both the designed temperature range of TLCS 202 and the extended range 204. Measurement point 601 results from the retained last image in computer memory in block 301. Several more points between 602 and 603 result from the continuous loop in block 303.

[0111] Using knowledge of the underlying mechanism of the heat transfer between object 105 into the TLCS 103 and the transparent panel 102 an approximating equation can be derived that results in curve T, 604. In most cases this curve will be an inverse exponential function of the generalised form provided in equation (1) but other functions are possible, e.g. in the case of actively heated or cooled objects 105.

[0112] The equation (1) describing curve T 604 can then be used to interpolate the temperature measured for object 105 for any moment in between the discrete measurement points 601 to 603 and to extrapolate the temperature for any later point in time such as 606.

[0113] FIG. 7 shows a TLCS 103 comprising a transparent bottom sheet 701 in contact with transparent panel 102. One or more layers of liquid crystal material 702 forms the next layer. A sheet of electrochromic material 703 forms the topmost layer. Together with the bottom sheet 701 it protects the liquid crystal material from chemical or mechanical damage. The electrochromic sheet changes it optical property from opaque to transparent by applying a control voltage via electrical contacts 704. All three layer of TLCS 103 are bonded together either by an adhesive or, in the case of the liquid crystal layer 702 by adhesion of the liquid crystal paint to its substrate.

[0114] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, mean “including but not limited to”, and do not exclude other components, integers or steps. Moreover, the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0115] Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.