WO2008078271A1

WO2008078271A1 - Device and method for measuring core temperature

Info

Publication number: WO2008078271A1
Application number: PCT/IB2007/055173
Authority: WO
Inventors: Alexander Padiy; Amy Oi Mee Cheung; Olaf Such
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2006-12-20
Filing date: 2007-12-17
Publication date: 2008-07-03
Also published as: CN101568814A; EP2095081A1; JP2010513911A; KR20090103883A

Abstract

The present invention provides a device for determining a core temperature of a body, such as a human body. Thereto, the device comprises a structure having a first and second side, and respective first and second temperature sensors, as well as a modulator means for lowering a temperature of the second sensor by changing a heat flux between the first side and the second side at a position of said second temperature sensor. The modulator means can lower the temperature by controlling heat flux without adding heat, but by controlling thermal coupling, which makes it inherently safe, and often much less power consuming.

Description

DEVICE AND METHOD FOR MEASURING CORE TEMPERATURE

FIELD OF THE INVENTION

The present invention relates to measuring a core temperature of an object. In particular, in a first aspect, the invention relates to a device for measuring a core temperature of an object, comprising a structure having a first side to be positioned against the object, and a second side substantially opposite said first side, a first temperature sensor positioned and arranged for measuring a temperature at the first side, and a second temperature sensor positioned and arranged for measuring a temperature at the second side.

In a second aspect, the invention relates to a method for measuring a core temperature of an object, comprising positioning a first temperature sensor in a position for measuring a surface temperature of said object, positioning a second temperature sensor and a structure having a first side and a second side, such that the structure is present between the first temperature sensor and the second temperature sensor, with the first temperature sensor at the first side and the second temperature sensor at the second side, measuring a first temperature value at the first side with the first temperature sensor and a first temperature value at the second side with the second temperature sensor, measuring a second temperature with the first temperature sensor and a second temperature with the second temperature sensor, and calculating the core temperature from said respective first and second temperatures.

BACKGROUND OF THE INVENTION

Document US Pat. No. 6,886,978 discloses a thermometer for measuring the temperature inside a live body, comprising a first temperature sensor and a second temperature sensor, a thermally insulating member being disposed between the first and second temperature sensor, and a heater for heating the live body, the first sensor measuring temperature proximal to the heater, and the second temperature sensor measuring temperature at a position on the live body opposite the heater across the insulating member.

The known device, and the corresponding method, have a disadvantage in that it bears the risk of overheating or burning the live body, which is undesirable. OBJECT OF THE INVENTION

It is an object of the present invention to provide a device, and in a second aspect a method, that is safer for measuring temperatures, in particular for a live body.

SUMMARY OF THE INVENTION

The above object is achieved, according to the invention, with a device for measuring a core temperature of an object of the type mentioned above, wherein the device comprises a modulator means for lowering a temperature of the second sensor by changing a heat flux between the first side and the second side at a position of said second temperature sensor.

The device according to the present invention is safer than the known device. The above mentioned known device also works according to the principle of measuring temperatures of a double sensor structure at different heat fluxes, to derive a core temperature, but uses heating to establish such different thermal fluxes. Firstly, normal surface temperatures of living bodies are between about 25 ⁰C and up to about 40 ⁰C, while pain is perceived at temperatures as low as 45 ⁰C. In case the thermal insulator fails, or the device is inadvertently reversed in position, such temperatures will be experienced by the living body. Furthermore, a danger zone starts at temperatures of about 45-50 ⁰C. This means that there is only a very small safe temperature window for the known device, which causes noisy measurements and long measurement times.

Contrarily, the present invention achieves the goal of changing thermal flux through a modulator means by which a lower temperature is achievable. This is e.g. achieved by influencing heat transport, instead of generating heat as in the prior art. Note that e.g. temperatures down to a few ⁰C do not pose a problem for living bodies, at least for the small surface being measured. This means that temperature differences of up to 30 to 40 ⁰C are achievable, which reduces measurement noise and allows more accurate measurements, since a time derivative of the temperature will often also be larger, and there is still no necessity for strong thermal coupling (high conductivity).

An important advantage of the present invention is that it allows much lower power designs, as will be elucidated further below.

In the present context, when the temperature of the second temperature sensor is meant, this is to be understood to mean the temperature of the second side at or adjacent the position where the second temperature sensor is present, or at least the part of that side that is relevant for the thermal flux. Moreover, it is preferably for increasing the measuring accuracy if the heat flux is changed significantly, i.e. by at least 10%, although smaller changes are not excluded.

Furthermore, the first side is the side to be positioned against the object, i.e. applied to or placed in sufficient thermal coupling therewith for a temperature to be measured. It is noted that in some cases, to be discussed below, a symmetrical design is possible. In that case, the first and second sides would be interchangeable. In other, nonsymmetrical cases, the first side and second side will be recognizable to the skilled person. Moreover, the first temperature sensor need not be fixed on the first side, but could be moveable with respect to that side, as long as that sensor is positionable between the object to be measured and the first side. In a preferred case, the first temperature sensor is fixed onto or even embedded into the first side. Similarly, the second temperature sensor need not be, but preferably is, fixed onto or even embedded into the second side.

As a general remark, the objects of which a core temperature can be measured are not limited to living bodies such as human bodies. They may also be for example containers with a certain content, such as (heated) milk bottles for babies, or containers with dangerous contents, such as chemicals in a process environment.

In particular, the modulator means are arranged to switch between a first heat flux state and a second heat flux state, wherein an energy consumption of the device in a steady state thereof is substantially unchanged. This reflects the advantage that the modulator means need not produce heat to influence the heat flux, which not only reduces power consumption, but also prevents risks of overheating.

Preferably, the steady state energy consumption is substantially zero for both the first and the second heat flux state. In this particular embodiment, in principle the lowest steady state energy consumption is achievable, because use is made of a change in the passive properties of the device to influence heat flux. For the purpose of the invention, a substantially zero energy consumption means that there is substantially no heating. Other consumption of energy, for purposes of measuring, calculating etc. are not considered here. It will be clear that, by adding a simple power source such as a battery, in order to power incidental energy consumption for measuring, calculating etc., a very long useful life is achievable. Hence, in an advantageous embodiment, the device is cordless and comprises an energy source, preferably a battery. Note however, that it is not strictly necessary to be free from energy consuming modulator means to obtain at least a part of the advantages such as temperature safety. The modulator means may be arranged for lowering the temperature to a temperature that is below a temperature that is attainable by the device when measuring the core temperature of said object without the device consuming any power. It is noted that the known device mentioned above would per se allow a lowering of the temperature, even though not intended, by simply starting with a measurement with active heater, and subsequently carrying out a measurement with the heater turned off. However, a temperature below the equilibrium temperature in said latter situation is not attainable, and the risks of the higher temperatures stay the same. Contrarily, the present invention always allows lowering the temperature to below said equilibrium temperature in the situation without any external supply of energy to the device (apart from thermal energy from the object or the ambient, which for the present purpose is not meant with external energy), as will become clear below. One could also state that the known device cannot actively lower a temerature by performing its function, since it can only add heat, and thus increase temperatures. The present device can actively lower a temperature by switching from a first heat flux state (e.g. the better isolated state) to the second state. For the moment, suffice it to state that actively lowering the temperature is safer than increasing the temperature. In particular, a thermal coupling between a first of the first side, the second side and ambient, and an other of the first side, the second side and ambient is variable. In this embodiment, heat flux is influenced by the way it is coupled to other parts of the device.

Advantageously, the structure has a thermal conductance which is at least locally variable. In other words, the thermal conductance between the first and the sensor, or at least between parts of the respective first and second side at or near a position of the respective temperature sensor, is variable. The modulator means may comprise or be part of the structure. The local variability ensures the possibility of two different measurements of the object's surface temperature, which allow the calculation of the core temperature, according to techniques known per se, and which will be elucidated further below. It is noted that document US 5,816,706 also performs two measurements with different thermal conductivities having a known ratio. However, the conductivity is not variable locally, but is rather set to different fixed values on different positions of the device. This bears the risk of variations within the object to be measured, such as blood perfusion differences in a living body or difference in the contact resistance between the body and the two stacks of the sensors, which introduces inaccuracies in the measurement. Furthermore, the need of different positions, at a mutual distance, makes the device rather large. Moreover, producing a device with different thermal conductivities having a known and time independent ratio poses manufacturing problems. All these problems are absent in the present device. The modulator means could be a means by which the thermal coupling is variable, hence a passive means, or a means that varies the thermal coupling, hence an active means. A passive means may be user-settable, e.g. by moving or the like, while an active modulator means may be set by the device itself, or by a control signal or the like. This choice between active and passive modulator means is intended to be provided throughout this disclosure.

In a particular embodiment of the present invention the structure comprises a first structure part at its first side, and a second structure part at its second side, the modulator means being arranged to vary a thermal coupling between said first and second structure part. In this embodiment, the structure, which may be a separate part in the device, or may substantially comprise the whole device with the exception of the two sensors, is divided in two subparts, i.e. structure parts, in each case one structure part corresponding to one of the first and second sides. Introducing the variable thermal coupling between the first and second structure parts, the desired variable temperature at the second temperature sensor is achievable, for a different thermal coupling introduces a different thermal flux. This in turn causes a temperature change, which can be measured, e.g. by sampling, which in turn allows to calculate core temperature et cetera. According to the present invention, in an alternative or additional embodiment, the modulator means are arranged to vary the thermal coupling between the second side at a position of said second temperature sensor and ambient. This is another way of providing a variable total heat flow. Examples will be elucidated below.

In particular, the modulator means are arranged to provide a variable distance between said first and second structure part. The variable distance ensures a well controllable variable thermal coupling, that decreases with increasing distance.

In a special embodiment, at least one of the first and the second structure part comprises a protruding pin directed such that a tip of said protruding pin is pointing towards an opposite one of said at least one of the first and the second structure part. Small variations in distance between the protruding tip, i.e. the apex thereof, and an opposite structure part can lead to large changes in the overall thermal conductance. Such high sensitivity to small distance variations is due to the thermal field "crowding" near the tip of the pin. It allows a low-cost robust implementation.

Herein, it would be advantageous if the modulator means, or in particular the actuator, that changes the distance between the tip of the pin and the opposite is controlled by a control unit. In a particular embodiment, at least one of the first and the second structure part comprises a first material with a first specific thermal conductivity (air, vacuum, a fluid or solid material), and the protruding pin comprises a second material with a second specific thermal conductivity that is higher than the first specific thermal conductivity, and preferably comprises a metal, more preferably at least one of aluminium, copper and silver. By providing a pin with high thermal conductivity, the crowding of the thermal field is even more pronounced and this provides a higher sensitivity. The pin can be made of any high thermal conductivity material, but is preferably made of a metal, although graphite etc. is also suitable. In a particular embodiment, the protruding pin is moveable with respect to said opposite one of said at least one of the first and second part, and preferably the modulator means is arranged for moving the protruding pin. Herein, the modulator means may be considered to be the movable protruding pin itself. In the case that the modulator means are arranged for moving the protruding pin, they may be considered to be the pin mover means or even the combination of the pin and the pin mover means. In every case in this embodiment, it is sufficient if the pin itself is movable. The structure parts need not be movable with respect to each other, and the pin could be movable through an opening in one or both of structure parts. It is also possible for the pin to be e.g. rotatable or tiltable in order to provide a varying thermal coupling between the two structure parts. In a special embodiment, the modulator means comprises a piezo-actuator for moving the protruding pin. A piezo-actuator is well suited for moving a pin over small distances. However, any other suitable actuator for moving the protruding pin may also be used, such as coil actuators.

In an advantageous embodiment, the structure comprises a cavity, wherein the modulator means comprise a mover means for moving a thermal coupling material at least partially into said cavity. In this embodiment, in a first situation, the cavity is for example substantially empty between the first and second temperature sensor. In a second situation, the mover means moves a thermal coupling material into the cavity between the first and second temperature sensor. The presence of the thermal coupling material may provide a different thermal coupling, as is desirable in the present invention. It is also possible for the mover means to move a thermal coupling material into the cavity, to thereby displace another thermal coupling material already present in the cavity.

In particular, the mover means comprises a fan or pump, the material comprising air or a gas. By being able to move or pump an air or other gas into the cavity, or along a part of the device, such as a structural part, the coupling may be varied, in particular if the ambient temperature differs from the object's surface temperature. Although the fan or pump may consume an amount of energy, this is mostly much less than the energy required to heat the material. In another embodiment, the thermal coupling material has a specific thermal conductivity that is at least twice that of atmospheric air at room temperature. Preferably the specific thermal conductivity is at least 1 W/mK, more preferably at least 50 W/mK. In this way, there will be a large difference in thermal coupling between the first and second structure with and without the thermal coupling material. In general, the higher the difference, the more accurate the measurement will be.

In another embodiment, the thermal coupling of the second side to ambient is variable, preferably the modulator means being arranged to (actively) vary said thermal coupling. Again, a means is provided for changing the heat flux without substantially using energy, but simply influencing the way in which it is given off to ambient, or taken up from it. In a special embodiment, the structure comprises a variable heat sink. In particular, the variable heat sink is thermally coupled to the second structure part, or e.g. between the first and second structure part. Since it is variable, it may sink variable thermal fluxes. The heat sink may comprise a fixed heat sink element and a heat flux modulating element having a variable heat resistance. The heat flux modulating element may be provided between any of the first side, the second side and the heat sink on the one hand, and any (not the same) of the second side, the heat sink and ambient. Herein, as in all of the text, the word 'element' may refer to both a single entity and to an assembly of two or more constructional parts. Furthermore, here, as in all cases, for the measurements to provide a sufficiently accurate result, it would be preferable if the change in heat flux would be at least 10%. In particular, the heat sink could also be thermally variably coupled to the structure, in particular to the second side, for example by means of movable thermal conductors that may be brought into contact with the heat sink, or vice versa.

In an embodiment, the heat sink comprises at least a first heat sink part that is movable with respect to at least one of the second heat sink part and the first structure part. Preferably, the first heat sink part is rotatable or translatable, or both, such that a varying area of the second part is shielded from ambient, or both. This is a simple embodiment of a variable heat sink, which makes a variable contact with ambient and can thus sink variable thermal fluxes to ambient. This in turn allows different temperatures and time derivatives of temperatures to be reached at the second temperature sensor. In a special embodiment, the modulator means for lowering the temperature comprises an active cooler means for cooling the second sensor. Again, this is not meant to cool just the second sensor, but to cool the part of the second side that is at, near or adjacent the second sensor. This should reflect the new temperature that is established at, near or adjacent the second sensor. The active cooler means is preferably arranged to extract thermal energy from the device or at least from the second part at, near or adjacent the second sensor, when the active cooler means is switched on to a state in which energy is consumed thereby. Although the temperature at the second temperature sensor may be lowered by varying the thermal flux, providing an active cooler means allows more control over the cooling and often allows a lower temperature to be achieved.

Advantageously, the cooler means has a variable cooling power, that is settable to at least two different non-zero values. This is a case in which the device consumes energy in both situations. However, an advantage is that the temperature difference, and thus the measurement accuracy, can be higher, while the device as a whole is still safe for the user. In a particular embodiment, the cooler means comprises a Peltier element. A

Peltier element is a small, efficient and well controllable cooler means. Furthermore, a Peltier element also allows heating, which offers the possibility of carrying out a first measurement with an active cooler means and a second measurement with an active heater means. This allows a very large difference of temperature at the second temperature sensor, and thus a very high accuracy.

In another embodiment, the cooler means comprises an evaporator for evaporating a fluid. Such an evaporator forms a suitable means for lowering the temperature at the second temperature sensor without consuming energy. In a special embodiment, the evaporator comprises a pump means for moving fluid. Preferably, the evaporator comprises a fluid reservoir, in particular filled with fluid. This fluid is preferably a fluid that evaporates rapidly and/or with a large latent heat. An example could be ethanol.

In a particular embodiment, the device comprises a fan means that is arranged to displace a gas, preferably air, along at least a part of the second side of the structure. A fan means provides a suitable and well controllable means for lowering the temperature at the second temperature sensor. This holds in particular in the case that the fan means can cooperate with a heat sink, and also in the case that the device comprises an evaporator, and preferably both. The combination of an evaporator and a fan means, possibly with a heat sink, provides a very effective means of lowering the temperature that is also well controllable in order to be independent of ambient temperature or air flow. Preferably, the fan means are variably controllable fan means, in order to select a suitable temperature.

In an embodiment, the device comprises a read out device for reading out a temperature signal from the first and the second temperature sensor. Such a read out device may be a display that displays the respective temperature. It could also be a device that outputs an electrical or digital signal corresponding to the temperature, or any other suitable outputting device.

In a special embodiment, the device comprises a calculation unit arranged to calculate a core temperature from respective temperature signals from the first and the second temperature sensor. The calculation unit may comprise a computer device or e.g. any other circuitry or device for calculating a temperature. The calculation unit may be programmed to calculate the temperature according to mathematical techniques known in the art. One of the methods that can be used is based on the following formula:

This formula and its quantities will be elucidated in the description of the drawings. A general remark to be make with respect to this formula is that a larger temperature difference will generally cause a larger time derivative of T_Sj which allows a more precise determination of the core temperature. For this formula, a temperature trend is measured, and a number of measurements is required. It is also possible to use alternative measuring methods, and accordingly embody the device, in particular the control unit and the calculating unit. An example could be to measure the temperatures of the two sensors in two steady-state situations corresponding to two different and constant heat fluxes, consecutively, by switching with the modulator means. Also possible are mixtures of such methods, e.g. a method in which the steady-state temperature is extrapolated by temperature readings from the sensors. Such extrapolation can most of the time be approximated by an exponential curve of the form A+B*exp(-C*t), and the steady-state temperature at t = ∞ can be estimated by fitting the available initial part of the temperature curve by the exponent A+B*exp(-C*t). After determining the coefficients A, B and C of the exponent, the steady- state temperature T(t=∞) can be estimated since T(t=∞)=A. Then, with the respective steady-state temperatures, suitable formulas may be used to find the core body temperature. For example, one could use a formula like _τ J (T₁₃ - T₁JT₁, - (T_2a - T₂JT_la ξ (T₁₃ - T₁J - (T₂₃ - T₂J where

Tia and T^ are the first and second side's temperature in the first heat flux situation, T_2a and T₂b are the first and second side's temperature in the second heat flux situation, and

K₂ where

Ki and K₂ are the thermal conductivities in the first, the second state, respectively. In this case, it is assumed that the thermal conductivity between the first side and the second side is the predominant factor, and are either known, or are determined from further measurements, according to techniques known to the skilled person.

In any case, the skilled person has a number of ways of deriving the core temperature from measured temperatures at the first and second sides. In an advantageous embodiment, the device comprises a control unit, wherein the control unit is arranged to control said modulator means. In this way, the control unit can adapt the modulator means in a case in which a particular change of a setting of the modulator means is advantageous for determination of the core temperature. For example, depending on T_s, a different variation of thermal coupling or a different setting for a cooler means etc. may be advantageous. Preferably, the control unit is arranged to maintain the respective heat flux at a substantially constant level, in order to improve accuracy. Advantageously, the control unit comprises the calculation unit, or in other words the control unit and the calculation unit are preferably integrated into one unit.

In a particular embodiment, the modulator means are settable to a plurality of states, preferably two, states with different predetermined heat flux between the first and the second side. In this embodiment, with examples as already shown above, the modulator means can set two heat fluxes, to obtain two different situations, each with a different equilibrium temperature or temperature development curve. More preferably, the control unit is arranged to switch between the plurality, in particular the two states, with a variable frequency, such that the resulting heat flux is controllable to a predetermined substantially constant level. In this way, in principle any heat flux between the two extreme values, a low and a high conductance, is settable, and thus the device may be adapted to provide a sufficiently different heat flux, without having to rely on such extreme values. Although it is also possible to provide a continuously variable heat flux with an appropriate modulator means, having discrete values can have advantages as to stability and accuracy of the device. The method of controlling may be compared to pulse width modulation method, or high- frequency time-multiplexing, between the stable states. Different effective thermal coupling can be achieved by tuning the ratio of time intervals during which the device is in the different states. Preferably, the switching frequency should be substantially higher than the speed of heat propagation through the structure, faster than 1-10 Hz in a typical case. A relay- type switch or any other mechanical structure can be used for the purpose. In a special embodiment, the device comprises a control unit arranged to obtain first respective temperature signals from the first and the second temperature sensor in a situation wherein said heat flux has a first value, and to obtain second respective temperature signals from the first and second temperature sensors in a situation wherein heat flux has a second value, and to calculate the core temperature from the first and second respective temperature signals.

This is an embodiment in which the device itself can carry out the required measurement and determine the core temperature. It can also be possible to provide the device with a transmitter for transmitting temperature value to some external calculation unit. This latter embodiment could be helpful for central monitoring the core temperature of various objects, such as various patients in a hospital.

In a further advantageous embodiment, the device according to the invention comprises an optical sensor, preferably an SpO2 and/or an StO2 sensor, with a light source, preferably comprising at least one LED. Although the modulator means according to the present invention allows the advantageous of safer low temperature measurements, it is not excluded to include a heater element in order to obtain a changed heat flux. Advantageously, in the case of a SpO2 and/or a StO2 sensor, a light source will be present and/or a thermistor. In each case, they will be likely to produce heat when functioning. This heat may be used to generate a variable heat flow. In order words, very efficient use is made of heat that is generated anyway. Preferably, the light source comprises at least one LED. Such a light source is very compact and may be provided close to for example the second temperature sensor.

In an advantageous embodiment, the first side has a shape that is outwardly curved, and preferably the structure comprises a member with a shape that is outwardly curved, preferably such that the part where the first temperature sensor is present projects from the first side. In this way, the first temperature sensor will contact the object to be measured in a suitable way, and a reliable contact can be provided. In particular, a member may be provided for that function, unto which the first temperature sensor is attached or attachable. Preferably, a member is arranged to be able to exert a spring force or resilience that is able to press the first side, and thus the first temperature sensor, onto the object.

Thereto, advantageously, the member comprises a flexible material, preferably a spring, in particular a leaf-spring. Herein, "flexible" means that the shape is visibly alterable when exerting a normal force with a human finger. An advantage of the member being flexible is that for example changes such as movements in the object to be measured, in particular a human body (the skin), can be accommodated more easily.

Preferably, the member is of a substantially uniform thickness. In such a case, the heat flow will be more even in the structure, in particular in the member. This greatly simplifies the calculations, and allows relatively simply approximations to hold validly.

In an embodiment, the member is layered. Preferably the member comprises a layer of kapton ™ or neoprene, and/or comprises a layer of a good thermal conductor on at least one surface of the member. Such a layered structure allows an even temperature distribution at the first side and the second side of the member, and advantageously also at the first and second side of the device as a whole. Again, this simplifies heat flow and calculations and increases the accuracy of the temperature measurement. Herein, a thermal conductor is good if it has a thermal conductivity of at least 1 W/mK, and preferably comprises a metal layer. Furthermore, another layer, preferably a central layer, comprises a good thermal insulator, such as kapton ™ or neoprene, which combine a low thermal conductivity with desirable resilient properties. Other materials are not excluded.

In an advantageous embodiment, the device comprises a holding construction for holding the device in a stabile position onto the object. Although the device could also be useful without such a holder construction, for example by holding it manually in a desired position, its usefulness could be increased by providing such a holding construction. In that case the device could be left unattended and still perform its function reliably. In particular, the holding construction comprises sidewalls around the member and/or fixation means for fixating the device onto the object, more preferably comprising an adhesive layer and/or a strap. Such sidewalls may be advantageous to provide a pretension to the member, which is useful for establishing a reliable contact with the object. Furthermore fixation means preferably comprise an adhesive layer and/or a strap in order to fixate the device to the object. Of course, depending on the object, other fixation means may be contemplated. In a second aspect, the invention also relates to a method for measuring a core temperature of an object, comprising positioning a first temperature sensor in a position for measuring a surface temperature of said object, positioning a second temperature sensor and a structure having a first side and a second side, such that the structure is present between the first temperature sensor and the second temperature sensor, with the first temperature sensor at the first side and the second temperature sensor at the second side, measuring a first temperature with the first temperature sensor and a first temperature with the second temperature sensor, changing a heat flux between the first side and the second side, measuring at least one second temperature with the first temperature sensor and at least one second temperature with the second temperature sensor, calculating the core temperature from said respective first temperatures and said respective at least one second temperatures. The method according to the invention is generally a counterpart of the device, and provides generally the same advantages, which thus will generally not be repeated here.

A general remark to be made here is that, instead of first and second temperatures, it is also useful to first and second temperature trends. In other words, in each of two situations, i.e. different thermal coupling or active cooling or the like, the first and second temperature, or at least the first temperature is sampled in time. All this will be further elucidated in the detailed description of embodiments.

In an embodiment, the heat flux is changed by varying the thermal coupling between a first of the first side, the second side and ambient and an other of the first side, the second side and ambient. In these ways of controlling heat flux, each possibility may be used, such as varying the thermal conductivity between the first and second side, or varying the thermal coupling between the second side and ambient, and so on.

In a particular embodiment, the heat flux is changed by cooling the second side. This is the method counter part of a device according to the invention, comprising an active cooler.

Advantageously, in the method according to the invention, use is made of a device according to the invention. In such a case, a reliable core temperature measurement is possible, mostly with very low energy consumption, and without a risk of burning.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, with reference to the drawings that show a number of illustrative and non- limiting embodiments, and which show in: Figures Ia through Ie show diagrammatically various embodiments of the device according to the invention; and Figure 2 is a schematic diagram that may be useful in understanding the invention.

DETAILED DESCRIPTION OF EXAMPLES

The devices are shown diagrammatically, not to scale and in an elevational cross sectional view.

Figures Ia through Ie show various embodiments of the device according to the invention.

The device, generally denoted 1, in figure Ia comprises a first structure part 2 and a second structure part 3, with a first temperature sensor 4, a second temperature sensor 5, respectively, which are connected to a control and/or calculation unit 6 (hereinbelow: control unit).

7 are actuators, 8 denotes a thermally conducting pin, and the device is positioned onto skin 9 of a body part.

The device comprises a kind of double layer structure with, on each side, a temperature sensor 4 and 5. The distance between the two-structure part 2 and 3 can be varied by means of actuators 7.

The actuator could be inflatable actuators, piezo-electrical actuators etc. They may be coupled or connected to the control unit 6. By changing the distance, in the direction of the arrows A, the thermal coupling between the first and second structure parts 2 and 3 may be varied. The sensitivity of the change in this coupling may be increased with optional pin 8. The tip or apex of this pin 8 may be positioned on or close to the opposite structure part in the situation of close approximation of the first and second structure parts 2 and 3. By operating the actuators 7, the distance may be increased, and the thermal coupling may be decreased strongly. For example, pin 8 is made of a highly conductive material such as aluminium or copper, while first and second structure parts 2 and 3 may also be made of a conductive material, such as a metal. The actuators 7 could also be conductive, but could also be thermally insulating to prevent influencing the measurements. The first and second temperature sensors could be any useful type of temperature sensor, such as a thermistor, a thermocouple, NTC/PTC resistors, etc. The sensors 4, 5 could be attached to the structure parts 2, 3, or could be connected thereto via a wire (not shown). The sensors are connected to the control unit 6, that preferably comprises a display for showing the respective temperatures. Preferably, the control unit 6 comprises a calculation unit for calculating the core temperature, and is arranged to display said temperature.

The device 1 is shown positioned on skin 9 of a body part. It could also be positioned on any type of container with contents of a certain temperature to be measured, such as baby milk or the like.

Figure Ib shows an embodiment with a van 10, a heat sink 11, a fluid container 12 containing fluid 13 and a channel 14 in second structure part 3. As a general remark, in all of the drawings, similar parts are denoted by the same reference numerals.

The fan is arranged to be able to move air through the space between the first and second structure parts 2, 3. This changes the thermal coupling between those structure parts. This change is increased if heat sink 11 is provided, which is preferably made of a thermally well conducting material, such as aluminium or copper. Multiple heat sinks may be provided, and they could also be provided on the first structure part 2, or both.

Alternatively or additionally, there is provided a fluid container 12 with a fluid 13 that easily evaporates. The fluid 13 may reach the space between the structure parts 2, 3 through a channel 14. There, the fluid evaporates and becomes a cloud of evaporated fluid 15. The latent heat cools the device and changes the heat flux. The fan 10 may increase this effect through forced air movement, e.g. in the direction of the arrow.

Figure Ic shown an embodiment of device comprising a core material 16, sandwiched between a first conductive layer 17 and a second conductive layer 18.

19 denotes a Peltier element and 20-1, 20-2 denote first and second movable heat sink parts.

This embodiment shows a sandwich structure, in which a core material 16, in this case e.g. kapton ™, is sandwiched between 2 conductive layers 17 and 18, such as aluminium layers. The later elements ensure a homogeneous temperature distribution on both sides of the device.

Peltier element 19, or another cooling device, is provided in thermal contact with the second side, i.e. second conductive layer 2. When switching on the Peltier element, the temperature at the second side may be lowered, causing a temperature change for the second temperature sensor 5. 20-1 and 20-2 denote a first and a second movable heat sink part. The first heat sink part 20-1 is shown being moved to open, along the direction of arrow B, and similar for the second part 20-2. By opening or closing the movable heat sink parts 20-1, 20-2, the thermal coupling of the second side, second conductive layer 18 may be changed, which again ensures a different heat flux and thus a different temperature at the second temperature sensor 5.

Figure Id diagrammatically shows a device that is more suitable for use in an ear or the like. The device comprises a substrate 21, at least one LED 22 and at least one optical sensor 23. The substrate 21 could e.g. be shaped to be radially insertable into the auditory meatus. The substrate 21 could comprise a somewhat flexible, shape restoring material such as various rubbers. The device according to figure Id has been embodied as a combination of a core temperature sensor with a SpO2 or StO2 sensor. Such a sensor, as is well known, comprises at least one, and preferably at least 2 LEDs 22 and an optical sensor 23. When using this device, the heat flux through the device, from the first temperature sensor 4 to the second temperature sensor 5 through the substrate 21 may be changed by operating the one or more LED's 22. These produce heat which is conveyed through the substrate 21 and may thus vary the temperatures. This embodiment is an example of a device that is suited both for measuring blood and/or tissue oxygenation and body core temperature, and not just an in-ear skin surface temperature or tympanic temperature, which are less accurate. It is noted that details about measuring blood and/or tissue oxygenation are deemed known to the skilled men, and will not be discussed further here.

Figure Ie diagrammatically shows an embodiment of the device with a favourable fixation assembly. The device comprises a flexible member 24 in a holding structure 25 with fixation means 26. Also shown are preferred positions for the first and second temperature sensor 4, 5, as well as a respective alternative position 4', 5'.

This embodiment comprises a flexible member 24, made of for example neoprene. The flexible member 24 projects outwardly. Preferably, the first sensor 4 is present at the top of the bulge of the flexible member 24. The member 24 is furthermore fixated between fixation means 26 on a holding structure 25, which could be integrated.

This device insures good coupling between the first sensor 4 and the object to be measured, such as a body part. In use a person might move the body part, which could cause movement of the device with respect to the body part. The present embodiment decreases the risk of inadvertent shifting of the device with respect to the body part. The holding structure 25 could comprise means for attaching the device as a whole to the body part, such as a strap of adhesive strips (not shown). The fixation means may simply be a clamp for fixing the flexible member or any other device or means with a similar purpose. A general remark to be made here is that various embodiments or even parts thereof, could be combined if desired. For example, the layered structure of the embodiment of figure Ic could be combined with the flexible member 24 of the device of figure Ie. The skilled person will easily make such combination and could be guided, although not necessarily so, by the description of the figures and the general introductory part of this application.

Figure 2 is a schematic diagram that may be useful in understanding the invention.

In the diagram, a device 1 is positioned on body part 28. The device schematically comprises first and second structural parts 2, 3 with a first and second temperature sensor 4, 5, and in between a medium 27. The medium has a thickness of ha and a thermal conductivity λ_d.

The body part 28 generally and schematically comprises skin 9 and a body core 29, while 30 represents the skin surface and 31 represent a virtual interface between the skin and the body core. The skin, i.e. the layer that is taken to be the skin in the model as will be explained below, has a thickness h_s and a thermal conductivity λ_s.

In the model, it is for example assumed that the temperature profile in the skin is essentially linear in depth, and ranges from the true body core temperature in the body core 29 to the skin surface temperature or the temperature at the first sensor 4. The body core temperature T_core may be determined by solving a system equations according to

— = oc — - dt dx

T = T_core at x = 0

T = T_S

TYY - λ — = q_s at x = h_s dx wherein

T = temperature t = time x = depth α = λ/pc_p λ = thermal conductivity p = density

C_p = specific heat q_s = heat flux through the skin surface 30

The quantity q_s can be measured by means of the two temperature sensors 4 and 5. After rewriting the above equations, with the assumptions that the thermal response time of medium 27 is faster than that of the skin i.e. αa »α_s, this gives

q = -λ — at x = 0 dx

q_s = -λ — at x = h dx

Furthermore assuming a linear temperature profile in depth, q_c can be approximated as

K from which it follows that

h h ²

The unknown quantities are T_core , — - and -^- , while the quantities T_s , q_s λ s 2(X₅ dTs and are the measured quantities. By measuring those quantities at a series of different dt moments in time t_l5 a matrix of coupled equations is obtained

where

\ ^≡ qM h h ²

One assumption is that T_core , — - and -^- are time-independent during the measurements. λ i 2cc₅

The system of equations can be solved e.g. by means of a least squares minimisation (LMS) procedure, or any other suitable mathematical method. This then provides the body core temperature, and also the heat flux through the skin surface. Note that, in general, the device and the method, according to the invention may thus also be used to determine other quantities than just the core body temperature.

The sampling moments t_x should be chosen at the assumptions on linearity of the temperature profile and of dT/dt in depth hold, which comes down to sampling moments during periods when the skin temperature T_s changes more slowly than the characteristic

propagation time in the skin τ — .

The presently shown embodiments and methods are deemed just illustrative and non-limiting, while the scope is to be determined by the appended claims.

Claims

CLAIMS:

1. A device for measuring a core temperature of an object, comprising

- a structure having a first side to be positioned against the object, and a second side substantially opposite said first side;

- a first temperature sensor positioned and arranged for measuring a temperature at the first side;

- a second temperature sensor positioned and arranged for measuring a temperature at the second side; wherein the device comprises a modulator means for lowering a temperature of the second sensor by changing a heat flux between the first side and the second side at a position of said second temperature sensor.

2. The device according to claim 1, wherein the modulator means are arranged to switch between a first heat flux state and a second heat flux state, wherein an energy consumption of the device in a steady state thereof is substantially unchanged, in particular the steady state energy consumption being substantially zero for both the first and the second heat flux state.

3. The device according to any preceding claim, wherein a thermal coupling between a first of the first side, the second side and ambient, and an other of the first side, the second side and ambient is variable, in particular the modulator means being arranged to vary said thermal coupling, and more in particular said thermal conductivity of the structure.

4. Device according to any preceding claim, wherein the structure comprises a first structure part at its first side, and a second structure part at its second side, the modulator means being arranged to vary a thermal coupling between said first and second structure part.

5. Device according to claim 4, wherein the modulator means are arranged to provide a variable distance between said first and second structure part.

6. Device according to any preceding claim, wherein the structure comprises a cavity, wherein the modulator means comprise a mover means for moving a thermal coupling material at least partially into said cavity.

7. Device according to claim any of claims 3-6, wherein the structure comprises a variable heat sink, in particular comprising at least a first heat sink part that is moveable with respect to at least one of a second heat sink part and the first structure part, the first heat sink part preferably being rotatable, or being translatable such that a varying area of the second part is shielded from ambient, or both.

8. Device according to any preceding claim, wherein the modulator means for lowering the temperature comprises an active cooler means for cooling the second sensor, such as a Peltier element and/or an evaporator for evaporating a fluid, and/or a fan means that is arranged to displace a gas, preferably air, along at least a part of the second side of the structure.

9. Device according to any preceding claim, comprising a calculation unit arranged to calculate a core temperature from respective temperature signals from the first and the second temperature sensor.

10. Device according to any preceding claim, comprising a control unit arranged to obtain first respective temperature signals from the first and the second temperature sensor in a situation wherein said local heat flux has a first value, and to obtain second respective temperature signals from the first and second temperature sensors in a situation wherein said heat flux has a second value, and to calculate the core temperature from the first and second respective temperature signals.

11. Device according to any preceding claim, further comprising an optical sensor, preferably an SpO2 and/or an StO2 sensor, with a light source, preferably comprising at least one LED.

12. Device according to any preceding claim, wherein the first side has a shape that is outwardly curved, and preferably the structure comprises a member with a shape that is outwardly curved, in particular the member comprising a flexible material, preferably a spring, more preferably a leaf-spring.

13. A method for measuring a core temperature of an object, comprising

- positioning a first temperature sensor in a position for measuring a surface temperature of said object; - positioning a second temperature sensor and a structure having a first side and a second side, such that the structure is present between the first temperature sensor and the second temperature sensor, with the first temperature sensor at the first side and the second temperature sensor at the second side, the structure having a thermal coupling between the first side and the second side; - measuring a first temperature with the first temperature sensor and a first temperature with the second temperature sensor;

- changing a heat flux between the first side and the second side;

- measuring at least one second temperature with the first temperature sensor and at least one second temperature with the second temperature sensor; - calculating the core temperature from said respective first temperatures and said respective at least one second temperatures.

14. Method according to claim 13, wherein the heat flux is changed by varying the thermal coupling between a first of the first side, the second side and ambient and an other of the first side, the second side and ambient and/or by cooling the second side, and wherein in particular use is made of a device according to any of claims 1-13.