GB2497790A - Temperature sensor - Google Patents

Abstract

There is provided an apparatus and method for measuring a thermal property of a medium under study, comprising at least two temperature sensing elements 120a and 120b and a material 110 of known thermal properties sandwiched between the at least two temperature sensing elements. A processing unit 200 is arranged to provide an adaptive filter to adaptively filter the outputs of the at least two temperature sensing elements to provide an indication of the thermal properties of the medium under study. The material may be an insulator and together with the sensing elements forms a compound sensor 100 such as may measure the relative temperature of the respective elements. The adaptive filter may be one of Least Mean Square, Wiener or Kalman filtering. An application of the sensor is detecting the fill level of a bladder by detecting a change in the temperature of an abdomen adjacent to the bladder.

Description

Title: Temperature sensing apparatus and method

Description

Field of the invention

This invention relates to an apparatus and method for measuring a change in thermal properties of a medium, and in particular to measurement of thermal properties where access to the medium is restricted.

Background of the invention

Methods for the identification of thermal responses or properties of a medium exist, but they require full access to the medium under study. This is not always possible in situations such as construction or medical applications.

Accordingly, it is desirable to provide alternative and improved apparatuses and methods to perform these measurements, particularly without causing disturbance to the medium.

Summary of the invention

The present invention provides an apparatus for measuring a thermal property of a medium under study, comprising at least two temperature sensing elements, a material of known thermal properties sandwiched between the at least two temperature sensing elements, and a processing unit arranged to provide an adaptive filter to adaptively filter outputs of the at least two temperature sensing elements to provide an indication of a thermal properties of the medium under study.

Optionally, the material of known thermal properties comprises an insulator, and may comprise any one of: wrapped fibre glass; high R value plastics; insulating cloths; printed circuit board substrate.

Optionally, the at least two temperature sensing elements are arranged in two groups, wherein a group is located on each side of the material of known thermal properties to form a compound sensor having the material of known thermal properties sandwiched between the two sensor groups.

Optionally, the outputs of the at least two temperature sensing elements are indicative of a relative temperature of the respective temperature sensing element.

Optionally, the adaptive filter may be any one of: a Least Mean Square filter; a Recursive least square filter; a Weiner filter; or a Kalman filter.

Optionally, the filter comprises a number of taps suitable for the respective application/use case, and/or may have a step size of the filter comprising a scaling factor, with a step size, p, chosen to best adapt to the respective application/use case.

Optionally, the thermal property is a thermal characteristic response of the medium under study.

Optionally, the apparatus further comprises a DSP to carry out at least a portion of the adaptive filtering calculations in hardware.

Optionally, the temperature sensing elements are formed from any one or more of: deposited resistive materials; preformed materials; pre-formed thermistor arrangements; pre-formed metallic resistor arrangements; or pre-formed semiconductor arrangements.

Optionally, the at least two temperature sensing elements and material of known thermal properties form a compound sensor, and the processing unit is operably coupled to the compound sensor by a wireless link or wired link.

Optionally, the apparatus measures a fill level of a bladder by determining a maximum and minimum change in temperature of an abdomen adjacent the bladder during use and correlating said change in temperature with observed fill levels of the bladder in a calibration process.

Optionally, the apparatus further comprises a memory to store adaptively filtered values derived from the at least two temperature sensing elements and pre-determined trends determined from previously acquired data from the at least two temperature sensing elements.

There is also provided a method for measuring a thermal property of a medium under study, comprising sampling an output from at least two temperature sensing elements arranged across a medium of known thermal properties to sandwich the material between the at least two temperature sensing elements, and using an adaptive filter to adaptively filter the sampled outputs to provide an indication of one or more thermal properties of the medium under study.

Optionally, the thermal property may comprise any one or more of: a temperature of a medium under study; a change in temperature of the medium under study; a rate of change of temperature of the medium under study.

Optionally, the method further comprises filtering the output from the at least two temperature sensing elements to remove noise, prior to applying to the adaptive filter.

Optionally, the medium under study is a portion of an abdomen immediately adjacent a bladder, and the method further comprises determining a fill level of a bladder from the one or more thermal properties.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Embodiments of the invention provide an apparatus for measuring a change in the thermal properties of a medium, the apparatus comprising two temperature sensors sandwiching a medium of known thermal properties, to form a compound sensor. The compound sensor may then be affixed to the medium in such as way as to insure good thermal contact (or to the surroundings of the medium), to allow measurement. An adaptive algorithm may be employed on one or more of the outputs of the compound sensor, to match the transfer function of the medium to the sensor outputs, thereby providing an estimated thermal characteristic response for medium under study.

The apparatuses and methods provided may allow measurement of the thermal properties of a medium without removal of the medium from its surroundings. This has applications in construction, industrial processes, medical and other fields where access to the medium under study is limited. For example, allowing measurement of the thermal properties of the bladder without direct access to the bladder (which avoids the need for unwanted invasive techniques).

Further analysis of the thermal properties of the bladder may allow assessment of the characteristics, function or fill level of the bladder.

An exemplary use of embodiments of the invention is to provide the ability to measure the change in thermal characteristics of a medium without the need to remove the medium from its surroundings, and in particular where access to only one surface of a medium under study (or a surface nearest the medium) is available.

The sensors used are typically of solid construction to allow for good conductive contact with the medium to be measured. The signal outputs of said sensor may be fed into a processing unit for analysis, and for example may determine the change in thermal properties over time.

Embodiments of the invention may therefore provide one or more apparatuses for measuring a thermal property of a medium under study (i.e. sensor) of reduced complexity, size and/or cost

compared to the sensors of the prior art.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

Figure 1 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses multiple tracks of a temperature sensitive material which has been deposited on a substrate to provide a temperature measurement over an area; Figure 2 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses a single area of temperature sensitive material deposited on the substrate to provide a temperature measurement at the centre point; Figure 3 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses multiple coils of a temperature sensitive material in a wire to provide a temperature measurement over an area; Figure 4 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses a single coil of temperature sensitive material in a wire to provide a temperature measurement in a much smaller area.

Figure 5 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses an array of discrete temperature sensitive components to provide a temperature measurement over an area; Figure 6 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses a single discrete temperature sensitive component to provide a temperature measurement at the centre point; Figure 7 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses an array of discrete temperature sensitive elements in a different, elongated, form factor to provide a temperature measurement over an area; Figure 8 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses a single discrete elongated temperature sensitive element to provide a temperature measurement over a smaller area; Figure 9 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that uses a flexible substrate; Figure 10 schematically shows an example sensing element of a compound sensor according to embodiments of the invention that includes attachment members; Figure 11 schematically shows a first example sensing element of a compound sensor according to embodiments of the invention that uses a strengthening back plate; Figure 12 schematically shows a second example sensing element of a compound sensor according to embodiments of the invention that uses a strengthening back plate; Figure 13 schematically shows an example of a complete compound sensor formed from two sensing elements according to embodiments of the invention; Figure 14 schematically shows an example use of a compound sensor according to embodiments of the invention for measuring the temperature of an otherwise inaccessible furnace interior; Figure 15 schematically shows an example use of a compound sensor according to embodiments of the invention for measuring the temperature of an otherwise inaccessible bladder; Figure 16 schematically shows an example use of a compound sensor according to embodiments of the invention for measuring the temperature of an otherwise inaccessible wall or soil portion; Figure 17 schematically shows an example wireless processing unit for compound sensors according to embodiments of the invention; Figure 18 schematically shows an example wired processing unit for compound sensors according to embodiments of the invention; Figure 19 schematically shows an example combined wired and wireless processing unit for compound sensors according to embodiments of the invention; Figure 20 schematically shows an example adaptive algorithm for use in embodiments of the invention; Figure 21 schematically shows the application of the example adaptive algorithm in embodiments of the invention; Figure 22 shows a graph of outputs signals used in embodiments of the invention.

Detailed description of the preferred embodiments

Because the illustrated embodiments of the present invention may for the most part be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.

The disclosed apparatus for measuring or sensing a thermal property of a medium comprises a compound sensor, comprising at least two sensor elements separated by a medium of known thermal response (such as an insulator), and a processing unit operably coupled to the compound sensor in use, and arranged to analyse the outputs of the at least two sensing elements, using an adaptive algorithm. The method comprises analysing the output of the at least two sensor elements to determine a transfer characteristic for the medium being sensed, the medium being sensed being located on one side of the compound sensor. The method may further comprise further analysis of the transfer characteristic to determine another property of the medium, or a status of the entity including the medium, such as, for example, bladder fill level.

Sensor construction The compound sensor comprises at least two temperature sensing elements 120 sandwiching a material 110 with known thermal transfer characteristics, and preferably with highly insulating properties. The temperature sensing elements 120 preferably provide an accurate reading of the temperature at a predetermined location or point (for example, a central point), and preferably have a fast reaction time.

The temperature sensing elements 120 on either side of the insulating material 110 may be constructed in a number of different ways using differing techniques and components. Figures 1 to 12 show different example embodiments of the sensor elements 120 that can be used on either side of the insulator 110, to form a one side (1OA to 1OM) of the compound sensor 100.

Examples include, but are not limited to: deposited resistive materials (as shown in Figure 1 as an array, Figure 2 as a point); preformed materials, such as a wire (as shown in Figure 3 as an "array" over a larger area, Figure 4 as a loop around a smaller area); pre-formed thermistor arrangements (as shown in Figure 5 as an array, Figure 6 as a centre point), pre-formed metallic resistor arrangements (as shown in Figure 7 as an array over a larger area, Figure 8 as a single element over a smaller area); pre-formed semiconductor arrangements, or other functionally similar component arrangements. When the temperature sensing elements are formed as an array of individual sub-elements (e.g. an array of thermistors, or the like), each individual temperature sensing sub-element may be addressed individually (i.e. in parallel) or together as a whole (e.g. in series, as show in Figure 5), to provide location specific temperature readings, or a single temperature reading for the whole area.

When the temperature sensing elements 120 are formed by deposition of a resistive material on a substrate 110, the resistive material may be laid in tracks covering a large area (e.g. Figures 1, 3, etc.) in order to average out the readings, or it/they could be deposited in a block at a particular point (e.g. centre point, as shown in Figure 2). The location of the particular point can be varied according to the needs of the particular use case for the compound sensor 100. Multiple blocks may also be used. The resistive material could include, but is not limited to, a thermistor compound, a metal (e.g. platinum, silver, gold, copper, or any other suitable metal) or any other material suitable for deposition that has a known thermal response.

Advantages of using deposited resistive materials may include: the ability to take the temperature from an area of the thermal junction not just a point; the ability to be flexible with the medium to be measured (as shown in Figure 9) and/or substrate on which the resistive material is deposited; providing a thin form, that results in less thermal losses in the sensor elements (and increased flexibility). Calibration curves may need to be determined for deposited resistive material to accurately sense temperatures with any arbitrary form or shape of deposited resistive material sensor element arrangement. It may be useful to utilise deposition materials that have increased flexibility, to reduce the existence or extent of any fractures under heavy bending during use.

If the particular use case means it would be advantageous to have a flexible sensor (e.g. when the compound sensor 100 is attached to a flexing entity, such as body), it is possible to construct the compound sensor 100 using a flexible substrate hUb, which could include but is not limited to: flexible printed circuit boards, flexible plastics, cloth and the like. This would then allow the compound sensor to mound to the shape of the medium to be measured; this is described in Figure 9.

When the temperature sensing elements 120 are formed using preformed materials, such as a wire laid onto a substrate, the wire may be arranged to provide a large area for sensing (e.g. Figures 1, 3, etc.), or may just be formed as a loop (e.g. Figure 4). The material used in the wire may include but is not limited to: platinum, copper or any other conductive material suitable for use in temperature sensing wire, which has known a thermal response.

Advantages of using temperature sensing elements 120 that are formed using preformed materials, such as a wire, include the ability to take the temperature from an area, not just a single location or point, whilst being smaller than deposition, improved flexibility, and a wire is thin so there is less thermal loss. Wires in particular may be arranged on a range of different substrates.

Calibration curves may need to be determined for preformed materials such as wire, and may need to be secured down to the substrate of the sensor elements to minimise undesirable movement.

Any gaps around the wire may introduce thermal radiation instead of conduction; therefore embedding the wire into the substrate may be preferable.

Pre-formed thermistor arrangements may comprise using thermistors either on a circuit board (or other suitable substrates) or with leads. The temperature sensing element 120 may be constructed with an array of thermistors to measure temperature over an area, and/or use one thermistor for a fixed point. If using an array, the characteristics of the thermistors used are preferably known, to allow accurate calculation of the thermal response curve, and similar to one another to provide a uniform thermal response over the area, as disclosed in more detail below.

The types of thermistor element used may be chosen for the particular thermal response characteristics desired, and being a pre-formed component, they will typically have known standard thermal responses, or can be specified to be made with a suitable thermal characteristic.

Preformed thermistors may have particularly good linearity over a small temperate range, and their operative linear temperature range may be suitably matched to the particular target application (e.g. around 30-40 degrees Celsius in the case of bladder assessment, or in the hundreds or thousands of degrees, in the case of furnace temperature measurement). Embedding the thermistors into the substrate of the compound sensor 100 may be useful in avoiding gaps that would otherwise provide for radiation instead of conduction. Adjustments to the analysis routine may be useful in removing the effect of any thermal lag due to the size of the preformed thermistors. This may be achieved, for example, by subtracting a predefined transfer function describing the thermistor casing away from the adaptive target.

Pre-formed metallic resistor arrangements may be used for the temperature sensing elements 120, and comprise using components such as platinum resistors, again either in an array or using a single unit with leads. If using an array, the response may need to be calibrated.

Platinum resistors have known standard thermal response, good accuracy, and fast speed of response. Any gaps around the platinum resistors may introduce thermal radiation instead of conduction; therefore embedding the platinum resistors into the substrate 110 may be preferable.

Pre-formed semiconductor arrangements may also be used, such as comprising one or more diodes (or transistors arranged as a diode), either alone as a point sensor element, or in an array as an area sensor element, to sense the temperature. The semiconductor arrangements may be preferably come from the same batch thereby exhibiting similar thermal properties.

At least two temperature sensing elements 120 formed from any of the above described arrangement may be formed into a compound sensor 100 by placement on a suitable substrate(s) 110. There are numerous substrates that may be used to mount or form each sensor element.

These include but are not limited to: Flexible printed circuit board. This substrate medium allows a degree of flexibility to the design of the compound sensor 100, thereby allowing the compound sensor 100 to be mounted to the medium being measured more easily (or comfortably). If solid temperature sensing elements such as thermistors or diodes are used, however, a rigid material may be preferably used to prevent the affixing means (such as solder) from snapping. Deposition of a temperature sensing conductor/resistive material onto the flexible printed circuit boards directly may allow improved flexibility of the compound sensor 100.

Standard circuit board may be used for the substrate, especially if the temperature/thermal sensing elements 120 are formed from solid elements, such as preformed thermistors, and the like.

Standard circuit board medium allows little flexing movement thus ensuring the affixing means (such as solder joints) holding the individual thermal sensing elements to the substrate to remain intact. However the thickness and thermal resistance of the standard circuit board material may need to be taken into account when analysing (by the processing unit) the outputs of the at least two sensing elements forming the compound sensor.

Other materials onto which conductive materials may be printed or otherwise affixed may also be used to form the compound sensor 100, such as plastics, cloth and the like.

The compound sensor 100 comprises, in addition to the at least two temperature sensing elements 120, a material 110 between the temperature sensing elements with a known thermal transfer characteristic, so that a temperature sensing element 120 is located either side of the material (e.g. see figure 14). Preferably this medium is an insulator, to reduce thermal transfer (by conduction) between the two sensor elements, thereby allowing improved analysis as described below. Therefore, it is possible to use the insulator as the substrate, particularly for active thermal sensing elements such as the leaded platinum resistors or thermistors, as they may be bonded directly to the insulator, eliminating the need for separate substrate.

The material with known thermal response, such as an insulator, that is sandwiched between the at least two sensing elements may usefully have a high thermal resistance to allow the sensor time to detect a difference in temperature between the junction between the first sensor element and one side of the insulator, and the junction between the other side of the insulator and the second sensor element, i.e. to introduce a thermal lag. This insulator may be constructed in a number of ways, these include but are not limited to: wrapped fibreglass, which has the advantage of being relatively flexible; plastics with a high thermal resistance, which may be rigid but are cheap to produce; insulating cloths, which may be particularly flexible, and thin to allow a small compound sensor.

The compound sensor may also require a method of affixing to the medium under test. This could be achieved in numerous ways, and may include but is not limited to a wings' style fixing means 130, as shown in Figure 10. Such a formation provides a surface to affix to, possibly by the use of a glue or thermal adhesive on the sensor face.

In the case of using discrete thermal sensitive components or other components which require soldering or another form of inflexible attachment, it may be advantageous to provide a strengthening backing 140 (i.e. backing plate), added to the compound sensor, which would be operable to stop or at least reduce the wear on older joints, and the like; this is depicted in Figure 11. Meanwhile, in Figure 12, there is shown the use of a thicker substrate material 140, which also may provide enough rigidity to prevent flexing.

The different thermally sensitive components/elements 120 described in Figures 1 to 12 illustrate the options available when constructing one half of the compound sensor 100 (i.e. found on one side, or other of the insulting material 110). The compound sensor 100, however, is comprised of two such sensing element arrangements, positioned around an insulating material, as depicted in Figure 13. The sensing element arrangements located on the different sides of the insulating material may utilise different thermally sensitive components to one another, depending on the use application.

The following figures depict some uses for the compound sensor 100 (operably coupled to a processing unit 200, as described in more detail below), in situations where only one side of the apparatus or medium under test is accessible. Figure 14 shows the use on a furnace wall, to measure the otherwise inaccessible inside of the furnace 1400. This figure also shows the three layered construction of the compound sensor 100, formed from a first temperature sensing element portion 120a immediately adjacent the medium under study, a second temperature sensing element portion 120b on the opposite side (relative to the medium under study) of a central material (e.g. insulator) 110 sandwiched between the two temperature sensing element portions 120a and 12Db. Figure 15 shows a usage on the human body, measuring the bladder 1500. Figure 16 depicts the use on a wall or the ground 1600 in general.

Processing unit The compound sensor is typically coupled to a processing unit 200 during use, either through wired or wireless means, to process the output of the compound sensor 100 to provide meaningful data output to a user. An example of a wireless processing unit is depicted in Figure 17.

In this Figure, there is shown a compound sensor 100 feeding into a wireless transceiver 150 to thereby send a signal indicative of the output of the compound sensor 100 to another wireless transceiver 250 in the processing unit 200. The Processing Unit 200 also contains a controller 210 to receive the signals from the wireless transceiver 250, for processing by the controller 210 in conjunction with a digital signal processor (DSP) 230, which performs the necessary calculations for the adaptive algorithm in use. The controller 210 is also optionally operably coupled to a memory 210 for use with the control and processing calculations being carried out by the controller/DSP respectively. The controller may also have inputs 205 and outputs 207 to allow external control of the overall system, and external data upload/down load. The wireless transceiver 250 may also provide data connections to other suitably equipped wireless equipment for similar or different purposes. All the components of the processing unit 200 may be powered by using suitable power circuits 240, deriving power from batteries, or a wired connection to a power supply, or the like. Use of the discrete DSP chip is optional, depending on the complexity of the calculation. Low complexity calculations may be handled by a general purpose processor in the controller 210 alone, with only higher complexity algorithms requiring use of an external DSP.

While wireless transceivers are depicted in this figure, separate dedicated wireless transmitters and receivers may be used instead.

In Figure 17, the compound sensor 100 is operably coupled to a wireless transmitter 150 in the same sensor package, to communicate with the processing unit 200. This would enable the easy use of the module and enable it to be placed in areas which are sealed or have hostile environments. However, for certain use cases, e.g. in industrial applications, the compound sensor 100 may simply be connected to the processing unit 200 using a wired connection, as shown in Figure 18.

In other use cases, for example medical sensing applications, it may be beneficial to have the processing unit 200 embedded directly into the compound sensor assembly, as shown in Figure 19.

The processing unit 200 may be a separately housed unit operably coupled to the output of the compound sensor 100, arranged to carry out the adaptive algorithm calculations that provide an indication of the transfer function of the medium to which the compound sensor is attached, and any related function derivable from the calculated transfer function that could be of use (such as fill level of a bladder).

There are various options open for implementation of the processing unit 200. Some of these include, but are not limited to: The adaptive algorithm may be implemented in a Digital Signal Processor (DSP) chip with a host processor taking the resulting data. This sort of system allows the complexity of the adaptive algorithm to be changed with little worry that processing power will become an issue.

The adaptive algorithm may be implemented on a host processor with enough calculation power to perform the calculations itself quickly enough, without using a DSP. This allows the bill of materials and cost to be reduced (since there is no DSP), but more complex adaptive algorithms could tax the processor, potentially resulting slower operation.

A wireless link could be provided to a master box; in this case the processing unit may communicate its status back to a main hub. This may be useful in medical applications, such as monitoring patients in a ward where one display may be desired for multiple patients. Such an embodiment eases data collection from multiple devices, but may push the power/calculation requirements of the processing unit up.

Sensor drive circuitry, in the case of the compound sensor being attached by one or more wire(s) to the processing unit, the implementation of the drive circuitry for the compound sensor could take place in the processing unit, thereby allowing the compound sensor portion to be cheap and disposable, which is particularly useful in medical use cases, for maintaining sterile conditions and the like.

Sensor reading conversion may also be used when the sensor is attached via wire. In such a case, it would be an option to include the Analog to Digital Converter (ADC) that converted the analog output of the compound sensor into digital signals ready for processing by the processing unit and/or DSP in the processing unit.

In the case where the compound sensor is provided in a wireless form (i.e. the compound sensor communicates with the processing unit wirelessly -see below for more details), a corresponding wireless link may be provided to the processing unit. This may take the form of a low power, ultra-low bit rate communications standard (using a corresponding transmitter and receiver/ transceiver chip to provide the wireless link) to keep the power requirements down.

An on-board power source, such as a battery, may be provided in order to power the device and peripherals. This may include corresponding converters to provide the specific voltages specified by the components used, such as processing unit (adaptive algorithm processor), wireless link processors and the like.

Other inputs and outputs to the processing unit may include buttons for inputting parameters, a direct data input for remote control and the like, lights in order to simply display a state to a user or a more complex display device, such as LCD: OLED and the like.

Suggested layouts of the system are described in Figures 17 through 19, and cover the sensor being equipped with a wireless transceiver to communicate with the base unit and/or alternatively using wires to achieve communication. The system could also be combined into a more integrated form, such as for example, an all in one sensing plaster, depending on the application.

Adaptive filtering process The processing unit 200 is arranged to carry out an adaptive algorithm to approximate the thermal response of the compound sensor 100, and hence the medium under study. A number of different adaptive algorithms may be used, for example but is not limited to: LMS, least mean squares, RLS, Recursive least square, Weiner, and Kalman. The application is not limited by the type of adaptive algorithm used, provided the algorithm adapts (for example adapting its tap weights) to approximate that of the medium to be measured.

An example of the adaptive algorithm 300 overview is described in Fig 20, where the output of the compound sensor, u(n) 310 is filtered by a transversal filter 320, under the control 325 of an adaptive weight-control mechanism 330 that also takes the output of the compound sensor u(n) 310 as an input. The other input to the adaptive weight-control mechanism 330 is an error signal e(n) 360, derived from the output 340 of the transversal filter 320 being subtracted 350 from a desired response d(n) 370). This is to say, the adaptive algorithm 300 computes the error between the output from the filter and the desired output of the system. From this computed error, updated tap weights can be computed for the next iteration of samples.

Figure 21 shows a more detailed version 400 of the adaptive algorithm that may be used. In particular, use of an adaptive filter 410 to determine a value of an unknown system 430.

There will now be described an embodiment that uses the Least Mean Squares (LMS) approach, because it is a simple, yet effective form of the suitable adaptive processes available.

In the LMS algorithm, the number of taps of the filter, which equals the filter size, is defined as M, where the M-by-1 tap input vector is: u(n) = [it(n), u(n-1), ..., u(n-M+1)]T The desired response at time n is d(n).

The error signal for the weight control mechanism is e(n) = d(n) -filter output (i.e. a negative feedback loop), and the M-by-1 tap weight vector, Adapting at iteration n, using the estimation error, e(n), the tap input u(n-k) is computed for k =0,1,.. M-1.

The result defines the correlation, VQk, applied to the tap weight at iteration n+1 (i.e. the next iteration in the sequence). A scaling factor may be used in the calculations with a positive step size, p. The recursive update of the tap weights in a steepest decent algorithm may be: *(n + 1) = *(n) + Jiu(n) [cI(n) -u" As such the filter output is *(n) = [ (ii), (ii) (n)f The estimation of the error signal is then e(n) = d(n) -v(n) For each iteration of n, the error signal e(n) = d(n)-T1(n)u(n) may be calculated and used in the calculation for the next tap weights, using: *(n + 1) = *(n) + iu(n)e(n) Where the iteration starts with an initial guess of *(O) and each subsequent iteration requires knowledge of u(n), d(n) and *(n).

Applying these above examples of an adaptive LMS algorithm to the overall apparatus for measuring or sensing a thermal property of a medium presented, it may be seen that, in order to avoid instability in the adaptive filter, the use of small step sizes may be advantageous. However, using smaller step sizes may lengthen the convergence time. So, in test situations with a small thermal mass, or any fast acting thermal influences, the use of small(er) step sizes may not be appropriate. Furthermore, with materials having large thermal capacity (or mass), and therefore a long impulse time, it may be advantageous to extend the filter (i.e. increase the number of taps, M).

This is because, the length of filter metric is a function of sample speed, so the two are linked and may be chosen accordingly. For a system with a very fast thermal response, a fast sample time might be desirable. However, this may require a longer filter than a similar system with a slower sample rate. Accordingly, such optimisations may need to be considered on a per application/use case basis, using details about the item (or combined system) under test.

The apparatus for measuring or sensing a thermal property of a medium may operate on some assumptions being made, such as: the internal temperature of the medium may be considered a constant self-regulating source; the temperature changes experienced on the ambient side (i.e. the side away from the medium under study) may fluctuate and over time may be assumed to be a bandwidth limited Gaussian white noise source; the thermal characteristics of the sensors elements are known. In these ways, the changes (in temperature) to which the apparatus adapts may be considered due to the changes in the temperature on the side of the compound sensor attached to the medium under study, and therefore characterise that medium's thermal response. This allows the medium under study to be the only unknown in the system, and hence allows its response to be measured.

Using the thermal input to the compound sensor, on the temperature sensing element on the ambient temperature side, and monitoring the difference between the filter estimated medium under study side and the actual medium under study side (i.e. the desired input of the adaptive filter), the adaptive filter can adjust the filter tap weights to approximate the thermal characteristics of the medium to which it is attached.

This process can be demonstrated by using the adaptive filter to characterise the compound sensor's impulse response using a random thermal input. An example output can be shown in the graphs of Figure 22.

The output(s) of interest from the adaptive algorithm may be the tap weights themselves or the area under a graph plotting the change in tap weights, or a combination of factors from the system. Tracking any one or more of these results may allow the real-time tracking of the changes (to temperature, and hence any property of the medium that depends on temperature) the medium is undergoing. For example, in the use case of tracking bladder fill level, the temperature of the area adjacent (i.e. in front of) the bladder is dependent on the fill level of the bladder. Therefore, the tracking of the thermal characteristic of the area immediately adjacent the bladder may be used to determine a relative fill level of the bladder, thereby providing a system to inform a patent when micturition is possible or advised. Calibration may be used to link measured temperatures to specific fill levels of a bladder for each patient (or more generally) measured in alternative and more complex ways (e.g. x-ray, or the like). Such a calibration step may be an initial one off exercise.

There are a number of ways this data could be used to display to the end user, these include but are not limited to: activating an alarm, light, or rumble pack when the filter reaches a certain point, to alert the user of the situation; reporting the results back in real time to a hub which graphs the filter weights and provides a visual representation to a supervising user, who can then act upon the information (useful when supervising a medium, or an unconscious patient); simply logging the data for later assessment, without direct outputs at the time; or a combination of the above, for redundancy and later offline analysis.

Further processing of the output of the measurement apparatus may also be implemented in various applications such as but not limited to: palliative uses in the medical field, such as where the sensor is applied to the abdomen and is used to monitor the change in thermal characteristics of the bladder in relation to its filling. A learning algorithm and/or calibration may be used to monitor the filter properties in both the empty and full bladder states and then, using a control input to signify micturition, provide a prediction of when the user will need to micturate. The output of such prediction processing could be displayed on a graphical screen, activate a light, alarm, or rumble pack when a predefined time threshold is reached.

Connectivity The compound sensor may be formed as a unit separate from the processing unit, but operably coupled to the processing unit. As such, any suitable method to connect the two may be used. These methods may include but is not limited to: Wired connection, e.g. using twisted wire, which is a simple way of connecting the compound sensor to the processing unit. However, it might not be feasible if the processor unit is positioned at distance, since this may cause a hazard in use. The resistance, capacitance and/or electromagnetic radiation receiving nature of the wires may introduce interference to the temperature measurement, therefore may benefit from drive circuitry adapted to mitigate these problems. Furthermore, if used in a medical application, the use of a wired connection may not be preferable, for safety or discretion for the user.

Some example embodiments use a wireless connection to link the compound sensor to the processing unit or other external equipment (e.g. central control units and the like). The wireless connection embodiments may be implemented in a number of different ways, for example: The processing unit may be independent of the compound sensor. In such an implementation, the compound sensor readings may be digitised on the compound sensor unit prior to transmission to the processing unit. This may be done with high resolution and accuracy, for instance a 24bit ADC with suitable filtering to eliminate noise. Any correction curves or calibration pertaining to the compound sensor may be performed on device prior to transmission, so the processing unit can be sensor independent. The advantage of a separate processing unit is the ability to build a data trend over time, longer battery life, higher processing power and options for expanded communications to external equipment.

The processing unit 200 and compound sensor 100 may be implemented on a single intelligent sensor unit, hence removing the need for a separate processing unit. In this scenario, the combined sensor and processing unit may use wireless communication links to connect to the outside world, to provide centralised assessments of the results, and the like.

The wireless communication links may use any suitable standard, for example Bluetooth, Zigbee, Ultrawideband, 802.llx or a similar or more up to date technology. The wireless connection method may allow for connecting less frequently to a central control unit, for example a consultant's PC to diagnose problems or analyse trends and download the sensor unit's history.

Using a sensor incorporating a commonly found networking protocol connection would make it possible to continually/periodically communicate with a smart phone. In this way, the smart phone becomes the processing unit by running a suitable set of computer readable instructions, (e.g. an app'). This reduces costs, and provides instant access to remote help, and the like. The app/custom software on the smart phone may process the information and display statistics information or generate alerts for the user based on the individual user's preferences. This form of processing may allow for more advanced sending of information to a central server over GPRS/ 30/40 networks, including the possibility of logging position and/or time, or any other data provided by the smart phone.

The processing portion of the invention may also be implemented as a computer program for running on a computer system, at least including executable code portions for performing steps of any method according to embodiments the invention when run on a programmable apparatus, such as a computer system or enabling a programmable apparatus to perform functions of a device or system according to embodiments the invention.

A computer program may be formed of a list of executable instructions such as a particular application program and/or an operating system. The computer program may for example include one or more of: a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a suitable computer system.

The computer program may be stored internally on a computer readable storage medium or transmitted to the computer system via a computer readable transmission medium. All or some of the computer program may be provided on computer readable media permanently, removably or remotely coupled to the programmable apparatus, such as an information processing system. The computer readable media may include, for example and without limitation, any one or more of the following: magnetic storage media including disk and tape storage media; optical storage media such as compact disk media (e.g., CD-ROM, CD-R, Blueray, etc.) digital video disk storage media (DVD, DVD-R, DVD-RW, etc) or high density optical media (e.g. Blueray, etc); non-volatile memory storage media including semiconductor-based memory units such as FLASH memory, EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatile storage media including registers, buffers or caches, main memory, RAM, DRAM, DDR RAM etc.; and data transmission media including computer networks, point-to-point telecommunication equipment, and carrier wave transmission media, and the like. Embodiments of the invention are not limited to the form of computer readable media used.

A computer process typically includes an executing (running) program or portion of a program, current program values and state information, and the resources used by the operating system to manage the execution of the process. An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the system.

The computer system may for instance include at least one processing unit, associated memory and a number of input/output (I/O) devices. When executing the computer program, the computer system processes information according to the computer program and produces resultant output information via I/O devices.

Moreover, the terms "front," "back," "top," "bottom," "over," "under" and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

The connections as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices.

Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections.

For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connections that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals.

Each signal described herein may be designed as positive or negative logic. In the case of a negative logic signal, the signal is active low where the logically true state corresponds to a logic level zero. In the case of a positive logic signal, the signal is active high where the logically true state corresponds to a logic level one. Note that any of the signals described herein can be designed as either negative or positive logic signals. Therefore, in alternate embodiments, those signals described as positive logic signals may be implemented as negative logic signals, and those signals described as negative logic signals may be implemented as positive logic signals.

Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality.

Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.

Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. For example, Application specific Integrated Circuits (ASIC), Field Programmable Gate Array (FPGA), or the like.

Alternatively, the examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner. For example, discrete packaged dies including Central Processing Unit (CPU), memory (e.g. RAM), Flash RAM, DSP, networking protocol stacks, and the like Also for example, the examples, or portions thereof, may implemented as soft or code representations of physical circuitry or of logical representations convertible into physical circuitry, such as in a hardware description language of any appropriate type.

Also, the invention is not limited to physical devices or units implemented in non-programmable hardware but can also be applied in programmable devices or units able to perform the desired device functions by operating in accordance with suitable program code, such as mainframes, minicomputers, servers, workstations, personal computers, notepads, personal digital assistants, electronic games, automotive and other embedded systems, cell phones and various other wireless devices, commonly denoted in this application as computer systems'.

However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word comprising' does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms a" or "an," as used herein, are defined as one or more than one. Also, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Unless otherwise stated as incompatible or the physics or otherwise of the embodiments prevent such a combination, the features of the following claims may be integrated together in any suitable and beneficial arrangement. This is to say that the combination of features is not limited by the claim forms, particularly the form of the dependent claims.

In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader scope of the invention as set forth in the appended claims.

Claims (1)

1. <claim-text>Claims: 1. An apparatus for measuring a thermal property of a medium under study, comprising: at least two temperature sensing elements; a material of known thermal properties sandwiched between the at least two temperature sensing elements; and a processing unit arranged to provide an adaptive filter to adaptively filter outputs of the at least two temperature sensing elements to provide an indication of a thermal properties of the medium under study.</claim-text> <claim-text>2. The apparatus of claim 1, wherein the material of known thermal properties comprises an insulator.</claim-text> <claim-text>3. The apparatus of claim 1, wherein the insulator comprises: wrapped fibre glass; high R value plastics; insulating cloths; printed circuit board substrate.</claim-text> <claim-text>4. The apparatus of claim 1, wherein the at least two temperature sensing elements are arranged in two groups, wherein a group is located on each side of the material of known thermal properties to form a compound sensor having the material of known thermal properties sandwiched between the two sensor groups.</claim-text> <claim-text>5. The apparatus of claim 1, wherein the outputs of the at least two temperature sensing elements are indicative of a relative temperature of the respective temperature sensing element.</claim-text> <claim-text>6. The apparatus of claim 1, wherein the adaptive filter is any one of: a Least Mean Square filter; a Recursive least square filter; a Weiner filter; or a Kalman filter.</claim-text> <claim-text>7. The apparatus of any preceding claim, wherein the thermal property is a thermal characteristic response of the medium under study.</claim-text> <claim-text>8. The apparatus of any preceding claim, further comprising a DSP to carry out at least a portion of the adaptive filtering calculations in hardware.</claim-text> <claim-text>9. The apparatus of any preceding claim, wherein the temperature sensing elements are formed from any one or more of: deposited resistive materials; preformed materials; pre-fornied thermistor arrangements; pre-formed metallic resistor arrangements; or pre-fornied semiconductor arrangements.</claim-text> <claim-text>10. The apparatus of any preceding claim, wherein the at least two temperature sensing elements and material of known thermal properties form a compound sensor and the processing unit is operably coupled to the compound sensor by a wireless link or wired link.</claim-text> <claim-text>11. The apparatus of any preceding claim, wherein the apparatus measures a fill level of a bladder by determining a maximum and minimum change in temperature of an abdomen adjacent the bladder during use and correlating said change in temperature with observed fill levels of the bladder in a calibration process.</claim-text> <claim-text>12. The apparatus of any preceding claim, further comprising a memory to store adaptively filtered values derived from the at least two temperature sensing elements and pre-deterniined trends determined from previously acquired data from the at least two temperature sensing elements.</claim-text> <claim-text>13. A method for measuring a thermal property of a medium under study, comprising: sampling an output from at least two temperature sensing elements arranged across a medium of known thermal properties to sandwich the material between the at least two temperature sensing elements; and using an adaptive filter to adaptively filter the sampled outputs to provide an indication of one or more thermal properties of the medium under study.</claim-text> <claim-text>14. The method of claim 15, wherein the thermal property comprises any one or more of: a temperature of a medium under study; a change in temperature of the medium under study; a rate of change of temperature of the medium under study.</claim-text> <claim-text>15. The method of claim 14 or 16, further comprising filtering the output from the at least two temperature sensing elements to remove noise, prior to applying to the adaptive filter.</claim-text> <claim-text>16. The method of any of claims 15 to 17, wherein the medium under study is a portion of an abdomen immediately adjacent a bladder, and the method further comprises determining a fill level of a bladder from the one or more thermal properties.</claim-text> <claim-text>17. A method substantially as herein described with references to the accompanying drawings.</claim-text> <claim-text>18. An apparatus substantially as herein described with reference to the accompanying drawings.</claim-text>