Sensor unit for a portable computer system and integration of the sensor unit

The invention relates to a sensor unit (2) for determining the core body temperature by means of measured values which can be determined outside the body on a surface, comprising at least one heat flow sensor (20, 20′), and at least one temperature sensor (21, 21′), which can be easily compactly produced and installed and allows optimized determination of the core body temperature. This is achieved in that the sensor unit (2) comprises at least one monolithic heat flow sensor (20, 20′) in the form of a sandwich-like structure consisting of multiple layers of different materials and at least one temperature sensor (21, 2′), which are soldered onto a circuit board (22) at a distance from one another or onto the circuit board (22) at the same height along a longitudinal direction of the circuit board (22), wherein the sensors (20, 21) are connected to an analog-to-digital convener (25) and a microcontroller (26) via wires or strip conductors, the electronic components (20, 21, 25, 26) can be connected to the electronics of a portable computer system by means of connecting wires (3), and the sensor unit (2) or the circuit board (22) with electronic components (20, 21, 25, 26) arranged thereon is at least partially enclosed by a sensor unit sleeve (28) in the transverse direction of the circuit board (22).

RELATED APPLICATIONS

This application is a national phase of PCT/EP2017/082994, filed on Dec. 15, 2017, which claims the benefit of Swiss Application No. 1695/16, filed on Dec. 21, 2016. The entire contents of these applications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention describes a sensor unit for determining the core body temperature by means of measured values, which can be determined outside the body on a surface, comprising at least one heat flow sensor and at least one temperature sensor, a portable computer system with a sensor unit, and the manufacture of a sensor unit comprising at least one measuring sensor and electronic components on a printed circuit board, and the integration of the sensor unit into a housing of a portable computer system, or into an adhesive pad for attachment onto the skin.

PRIOR ART

Portable technical data processing devices with measuring capabilities are of known art in various configurations, with or without a housing, as parts of clothing, or in the form on jewelry. These portable computer systems or wearable computers are the subject matter of the research field “wearable computing”. The wearable computers or portable computer systems have at least one sensor unit, with which data is collected via at least one sensor from the real world. The measured data is then either processed in the portable computer system itself or transferred to another computer, in particular to a smart phone. The user can view the recorded data and process it further. The portable computer system comprises a housing, in which a sensor unit and electronics are integrated. As a rule the electronics have at least one microcontroller and one read-out/storage unit, which are connected to the sensor unit.

One example of a wearable computer, or portable computer system, is an activity tracker, also called a fitness or health armband, smart band, or fitness tracker. Using software operated in the electronics, data from at least one sensor of the sensor unit are collected, further processed, stored in a memory as necessary, and/or forwarded to a smart phone. Accordingly, data relevant to fitness and health, such as running distances, energy consumption, and also, in some cases, heart rate, body temperature, oxygen content in the blood, or sleep quality, can be determined.

Here the determination of the internal body temperature, or core body temperature, by means of a portable computer system is of interest. The non-invasive and continuous determination of internal body temperature, as measured on the skin, is important for patient monitoring in hospitals, for the prevention of heat stroke in athletes, or for the determination and monitoring of the circadian cycle for the diagnosis of sleep disorders and other illnesses.

In the simplest case, the sensor unit of the portable computer system is based on a temperature sensor to determine the skin temperature in combination with thermal insulation over the sensor and its surroundings. The purpose of the insulation is to keep the skin temperature as close as possible to the core body temperature. In many cases the method is inaccurate and unsuitable for use under changing external conditions.

To improve the measurement of the core body temperature, the sensor unit of the portable computer system may include a so-called double temperature sensor, as recorded in DE10038247. Here two temperature sensors are separated from one another by a thermal insulator with a known thermal resistance. In most cases this method requires a calibration measurement so as to determine the thermal, resistance, which depends on the person and also the location of the measurement.

The double sensor method has multiple disadvantages. One severe problem is represented by the thermal parasitic heat losses between the two temperature sensors, which can lead to strong deviations. These must be resolved by thermal insulation and by complex compensation algorithms, as described in DE102005004933. Another disadvantage lies in the size of the system. In order to achieve good sensitivity, the temperature difference in application must be sufficiently large, which means that the material between the two temperature sensors must have a certain minimum thickness. This makes the sensor system rather chunky and bulky and less suitable for ease of integration into housings of prior art.

The sensor units of known art for determining the core body temperature are not yet suitable for ease of integration into the housing of a portable computer system. In order to avoid parasitic heat losses, thermal insulators and additional structures are required, resulting in a complex design, and making it difficult to integrate the sensor unit into the housing of a portable computer system. A further disadvantage is the measurement inaccuracy of the sensor units of known art when determining the core body temperature.

WO02078538 presents the determination of the core body temperature with the aid of a heat flow sensor, which is attached to the skin of a user. The heat flow sensor forms part of a sensor unit, which here too must be attached in a complex manner to a computer system. In WO2005092177 another sensor unit is described that is suitable for the measurement of the core body temperature, which comprises, amongst other items, a heat flow sensor, and can likewise be connected to a portable computer system. This has brought us closer to the goal of determining the core body temperature as accurately as possible, but the manufacture of the sensor unit and the integration of the sensor unit in the portable computer system remains complicated and cumbersome.

PRESENTATION OF THE INVENTION

The object of the present invention is that of creating a compact sensor unit that can easily be installed, either for installation in a portable computer system, or for mounting on or in an adhesive pad, which allows an optimised determination of the core body temperature.

An opportunity is created, by which to simplify the manufacture of the sensor unit, and to simplify the attachment of the sensor unit onto or into a housing of a portable computer system, or onto or into an adhesive pad.

With the sensor unit as presented thermophysiological data on a body, especially the internal body temperature, or core body temperature, can be measured, whereby heat flows and surface temperatures are determined. Other parameters can be: the heat output of the skin, calorie consumption, calorie intake, blood pressure, blood sugar, internal temperature at a particular point on the body, compensated skin temperature, etc.

In particular, a method is described that allows the coupling of a sensor unit to a housing of a portable computer system, or its attachment onto or into an adhesive pad, or by means of a tape, with a few operative steps.

DESCRIPTION

A portable computer system0is here represented in the form of an armband having a hollow interior11with a housing1. The housing1is laid, with a skin contact side10, onto the skin H of a user. A heat flow occurs from the body of the user, across the skin H, crossing the housing1of the portable computer system0, into the interior11; in the detail ofFIG.1athe heat flow through the housing1is marked as Qinto Qout. People and animals are possible users.

A sensor unit2, which is specified in more detail below, is inserted into the housing1, detachably or non-detachably attached, and electrically connected to the electronics (not shown) of the portable computer system0. The sensor unit2is at least partially surrounded by a sensor unit sleeve28and is pressed into the housing1, that is to say, it is bonded in with adhesive, or encapsulated. The sensor unit sleeve28is manufactured from a thermally conductive material, in particular silicone. By using a material with a similar thermal conductivity to that of the heat flow sensor itself, as described later, it is possible to homogenise the heat flow and thus minimise parasitic heat flows. Furthermore, a good thermal conductivity means that the temperature measured is closer to the skin temperature. The conductivity of the sensor unit sleeve28in our case should lie between 0.3 and 10 W/mK; optimally between 0.8 and 3 W/mK. For metrological reasons, the sensor unit2should be located as close as possible to the user's skin, but in principle can be arranged anywhere in the heat path.

In the embodiment as shown inFIG.1aa through hole12is provided, which crosses the housing1completely, into which a completely encapsulated sensor unit2is inserted. The sensor unit sleeve28protrudes slightly from the through hole12and from the skin contact side10, and when in use comes into contact with the skin H of the user. The heat flow from the skin H, and thus from the body, via the skin, through the sensor unit sleeve28and the sensor unit2, adjusts itself during use, and can be used to determine the core body temperature.

As shown inFIG.1b, a cavity in the form of a blind hole13can also be arranged in the housing1of the portable computer system, into which the sensor unit2with a partially surrounding sensor unit sleeve28is introduced. Here too the sensor unit2including the sensor unit sleeve28is inserted into the blind hole13in the form of a plug, and is thus detachably connected to the housing1.

To increase the stability of the mounting of the sensor unit2with the sensor unit sleeve28in the housing1, the sensor unit sleeve28can extend across the housing1, as shown inFIG.1c. This creates a thermal path such that the thermal equilibrium between the environment and the body adjusts itself as quickly as possible. Accordingly, the sensor unit sleeve28extends from the skin contact side10to a side of the housing1remote from the skin contact side10, and thereby crosses the housing1.

FIGS.2ato2dshow embodiments of the sensor units2for determining the core body temperature. The aim is to create a sensor unit2that is as compact as possible, mechanically robust, and in the best case is flexibly configured.

The basis of the sensor unit2is a printed circuit board22, onto which at least one heat flow sensor20and at least one temperature sensor21are soldered. The printed circuit board22can be executed in a rigid or flexible manner, and, in addition to strip conductors made from an electrical conductor, comprises insulating material, preferably a fibre-reinforced plastic. Optimally, the material of the at least one printed circuit board22has a thermal conductivity of between 0.3 and 10 W/mK, and preferably between 0.8 and 3 W/mK, such that a homogeneous heat flow is guaranteed.

The various sensors20,21are placed on soldering surfaces on the printed circuit board22and attached with solder. The at least one heat flow sensor20and the at least one temperature sensor21are arranged spaced apart from one another along a longitudinal direction. The heat flow sensor20and the temperature sensor21are attached onto the same side of the printed circuit board22.

Other components, in particular blocks made from thermally insulating materials23and thermal capacitances24, are also attached onto the printed circuit board22. The thermal insulator23and the thermal capacitance24are bonded to the printed circuit board22with an adhesive such as an acrylic, epoxy or polyurethane or, if the material permits, are soldered on.

In order to keep the thermal transfer resistance between components as low as possible, for example between the heat flow sensor20and the thermal capacitance24, a thermally conductive adhesive should be used in the case of adhesive bonding.

Electronic components such as an analogue-to-digital converter25, a microcontroller26, and a read-out/storage unit27, can also be attached onto the printed circuit board22in an electrically conductive manner. To achieve sufficiently high measurement signals, however, it is sufficient to attach only the analogue-to-digital converter25onto the printed circuit board22, and to arrange the microcontroller26and the read-out/storage unit27at a distance from the printed circuit board22by means of wires or so-called flex-rigid printed circuit boards, a layered arrangement of plastic and copper layers, which form a flexible composite printed circuit board.

Connecting wires3are arranged leading away from the printed circuit board22; these transmit the measured signals, or processed signals, to the electronics of the portable computer system0. Optionally, the connecting wires3can also be formed by flexible printed circuit boards or strip conductors, to which the electronic components can be connected.

In order to increase the stability of the sensor unit2and to achieve a homogeneous heat flow, the printed circuit board22, populated with the components, is at least partially surrounded by the sensor unit sleeve28. While the variants shown inFIGS.2aand2dshow a sensor unit2completely encapsulated in a sensor unit sleeve28, the other embodiments here are only provided with a sensor unit sleeve28on their side of the sensor unit2that subsequently faces towards the skin H.

The sensor unit sleeve28does not necessarily have to consist of only one material. For example, a silicone that is more compatible with the skin can be arranged adjacent to the skin, and a thermally conductive silicone can then be applied up to the printed circuit board22. The printed circuit board22itself has a thermal conductivity that is similar to that of the sensor unit sleeve28. Above the printed circuit board22there is another 0.5 cm of thermally conductive silicone, and then a metal rod, or a silicone-filled metal rod, up to the top of the housing. Tests have shown that it does not matter whether the at least one heat flow sensor20and the at least one temperature sensor21are located on the same side of the printed circuit board22, or on opposite sides. The measurements of the heat flow, using the heat flow sensor20, and the temperature, using the temperature sensor21, are used to determine the actual core body temperature.

InFIG.2athe sensor unit2has two heat flow sensors20,20′ and one temperature sensor21, soldered to the skin-facing side of the printed circuit board22. Here a thermal insulator23is attached, at the height in the longitudinal direction of a heat flow sensor20, on the side of the printed circuit board22that is free of heat flow sensors. In the variant shown inFIG.2b, a thermal capacitance24is attached, at the height in the longitudinal direction of a heat flow sensor20, on the side of the printed circuit board22that is free of heat flow sensors. In this manner a heat flow is measured through a first heat flow sensor20and a thermal insulator23, or a thermal capacitance24, as is a heat flow through a second heat flow sensor20′. The two measured values, together with the measurement of the temperature by means of the temperature sensor21, enter into the determination of the core body temperature. In accordance with a prior calibration of the heat flow sensor measurement with and without the thermal insulator23or the thermal capacitance24, the determination of the core body temperature can be optimised.

The thermal insulator23has a high thermal resistance, whereby the thermal conductivity λ of the material of the thermal insulator23is very low. As shown inFIG.2a, the heat flow through the first heat flow sensor20differs from the heat flow through the second heat flow sensor20′ by virtue of the thermal insulator23. A foamed plastic material is used as the thermal insulator23, whereby the heat flow through the first heat flow sensor20is lass than that through the second heat flow sensor20′. The decisive factor is the difference between the two heat flows, from which the core body temperature can be better determined, with the aid of an algorithm. This design ensures that the sensor unit2is more robust with respect to changes in the thermal coupling between the sensors20,20′,21,21′ and the skin H. The heat flow difference is taken into account in the determination, for which reason the properties of the thermal insulator23must be known and experimentally determined and calibrated. The thermal conductivity λ of the thermal insulator material23should be of the order of that for air (λair=0.024 W/m/K), i.e. between 0.01 W/m/K and 0.1 W/m/K.

Materials for the sensor unit sleeve28can include polymers such as polypropylene, PES, PE, PET, polyethylene, acetal, nylon, polybutylene terephthalate, polysulfone, PPS, polycarbonate, Teflon, polyester, PMMA, PSU, PEEK, TPE, TPU, parylene or PTFE. Ethylene-propylene-diene rubber (EPDM) and polypropylene have preferably been chosen. The at least one printed circuit board22, that is to say, the material of the printed circuit board22, can also be part of the sensor unit sleeve28. FR-4 or FR4, a composite material of epoxy resin and glass fibre fabric, can, for example, be used as the material for the printed circuit board22. As of known art to the person skilled in the art, the thermal conductivity of the materials can be improved or adapted by a specialised form of manufacture (e.g. by the addition of particles) such that the material has a similar thermal conductivity to that of the sensor unit itself.

Accordingly, the thermal capacitance24has a very low thermal resistance and the material has a very high thermal conductivity, that is to say, a very high value of λ. The thermal capacitance24should absorb the heat to the maximum extent. Here too, the heat flow through the first heat flow sensor20differs from the heat flow through the second heat flow sensor20′. Thermally conductive silicone has been successfully used as the material. However, metals can also be used. The thermal conductivity λ of the material of the thermal capacitance24should be significantly higher than the thermal capacitance of air (λair=0.024 W/m/K), i.e. greater than 0.1 W/m/K.

The thermal insulator23and the thermal capacitance24are attached to the printed circuit board22with a suitable adhesive. If copper or brass is used, this can be soldered onto the printed circuit board22.

The variant depicted inFIG.2cshows a heat flow sensor20and two temperature sensors21,21′, whereby a thermal insulator23is attached onto the heat flow sensor side of the printed circuit board22, which is located opposite the temperature sensor21′ at the same height in the longitudinal direction of the printed circuit board22. The temperature sensor21is connected directly to the printed circuit board22, but is spaced apart from the thermal insulator23. This allows two different temperature measurements by means of the two temperature sensors21,21′ arranged at a distance from one another in the longitudinal and transverse directions.

The electronic components of the sensor unit2, the at least one heat flow sensor20, the at least one temperature sensor21, the analogue-to-digital converter25, the microcontroller26and the read-out/storage unit27, encapsulated in an integrated circuit29(IC), can be aggregated in a chip housing, and, together with the printed circuit board22, form the sensor unit2. In practice, the encapsulation is achieved either by the application of adhesive to both sides, or by a casting process. The integrated circuit29, that is to say, the chip housing, is soldered onto the printed circuit board22. By virtue of the compact design of the integrated circuit29, the manufacture of the sensor unit2can be simplified even further.

FIG.2dshows a sensor unit2, whereby the two heat flow sensors20,20′ are soldered onto the same side of the at least one printed circuit board22, spaced apart from one another in the longitudinal direction. A thermal capacitance24is arranged on the side of at least one printed circuit board22that is free of heat flow sensors, at the height of the first heat flow sensor20in the longitudinal direction. In addition, a thermal insulator23is arranged on the side of the at least one printed circuit board22that is free of heat flow sensors, at the height of the second heat flow sensor20′ in the longitudinal direction. On the side that is free of heat flow sensors, a metal plate30is arranged so as to be in contact with the thermal insulator23and the thermal capacitance24, and running parallel to the printed circuit board22. The metal plate30can also be arranged so as to be in contact with, and/or partially covering, a block made from a thermally conductive material on the printed circuit board22, or the sensor unit sleeve28.

By means of the metal plate30, which is preferably made from aluminium and can be rigid or flexible, a thermal equilibrium is achieved with the same external temperature along the metal plate30, and the measuring accuracy can be increased.

Since the aim should be to save space with the integration of the sensor unit, especially in ears, the configuration of the thermal insulator23and/or the thermal capacitance24can be modified. Here the thermal insulator23or the capacitance24does not have to be arranged on the printed circuit board22, but can also be incorporated into the latter. Here, for example, a thermal insulator23is shown running within the cross-section of the printed circuit board22, whereby this thermal insulator can be an insulating layer, for example an air pocket. The thermal conductivity is increased by introducing thermovias, for example Cu vias, which are configured as thermal capacitances24in the form of blind holes, or through holes, filled with copper. In addition, a thermal capacitance24could also be designed as concealed thermovias, so-called “buried vias”, which are not shown here.

As shown inFIG.2f, the printed circuit board22, together with the integrated circuit29, is almost completely surrounded on both sides by the sensor unit sleeve28. Connection of the connecting wires3to the electronics of a portable computer system0is readily possible.

Deployable heat flow sensors20,20′, which in particular can be soldered onto the printed circuit board22, can be found in EP2938980 and WO2016128247 of the applicant, the contents of which are referenced here. Miniaturised and/or thin monolithic heat flow sensors with low thermal invasiveness can be deployed, which are mechanically sufficiently robust and can be soldered onto the surface of the printed circuit board22. A sandwich-like structure, consisting of multiple layers of different materials, including metals and at least one electrically insulating matrix layer, is selected for this purpose. Such a monolithic heat flow sensor20,20′ forms a closed body on at least one side and a number of sensing junctions between different metal layers. Temperature sensors21have been of known art for a long time, and variously configured temperature sensors21can be used. All temperature sensors21of known art that can be soldered onto the printed circuit board22, or onto another printed circuit board, can be used as the temperature sensors21. Amongst others, infrared sensors can be used for temperature measurement; these must not be surrounded by a sensor unit sleeve28. In a preferred embodiment, the sensor unit2comprises multiple printed circuit boards22, whereby the at least one heat flow sensor20,20′ is arranged on one printed circuit board22, and an infrared sensor for purposes of temperature measurement is arranged on another printed circuit board, which is arranged spatially separated from the first printed circuit board22. By means of appropriate wiring, measured values from at least one heat flow sensor20,20′ on the first printed circuit board22, and measured values from the infrared sensor on the second printed circuit board, can be processed in the read-out/storage unit27. Although the infrared sensor is part of the sensor unit2, it must remain free of the sensor unit sleeve28. The easiest way to achieve this is to arrange the infrared sensor on the second circuit board.

FIG.3shows a sensor unit2with a partially round printed circuit board22, or more particularly, a partially round cross-sectional area with cavities A in a plan view onto the side of the sensor that subsequently faces the skin surface. For the sake of simplicity, a sensor unit sleeve28is omitted here, so that the heat flow and temperature sensors20,21protruding from the side of the sensor are visible. The strip conductors on the printed circuit board22run along a circular path that is as long as possible, as indicated by the dashed arrow, along the printed circuit board22to the temperature sensor21and the heat flow sensor20in the centre of the printed circuit board22. This virtually prevents any thermal heat loss or any interfering heat input caused by heat conduction from the connecting wires3.

In particular, by the arrangement of the two kidney-shaped cavities A, in each case adjacent in the longitudinal direction to the heat flow and temperature sensors20,21, bordering a bridge, whereby a central printed circuit board disk is formed, a thermally-undisturbed mounting of the temperature sensor21and the heat flow sensor20is achieved. By virtue of the cavities A′ in the edge region, any interfering heat flow between the contacts of the connecting wires3and the sensors20,21is also further reduced.

A sensor unit2fitted with a sensor unit sleeve28is shown inFIG.4a. The sensor unit sleeve28partially covers the electrical components and the printed circuit board22. When in use, as shown inFIG.4balong the cross-sectional line B-B, the sensor unit2with its sensor unit sleeve28is laid or pressed onto the skin H of a user, and the measurement of heat flows and temperatures can thus take place, and the current core body temperature can be determined using algorithms of known art. Here the sensor unit sleeve28also extends onto the side of the printed circuit board22facing away from the skin, and the sensor unit sleeve28is surrounded by an adhesive pad4.

After the manufacture of the sensor unit2with the sensor unit sleeve28attached, the printed circuit board22together with the protruding sensor unit sleeve28can be attached in a cavity12′ of the adhesive pad4, which is of known art from medical technology, and serves, for example, for the attachment of electrodes to the skin. The connecting wires3can be connected to the electronics of a medical device, either before or after the attachment of the sensor unit2in the adhesive pad4. The adhesive pad4is manufactured from the same materials as the thermal insulator23and has an adhesive layer that is compatible with the skin, e.g. as is of known art from the company 3M.

The thermal conductivity λ of the material of the thermal adhesive pad4should be of the order of that for air (λair=0.024 W/m/K), i.e. between 0.01 W/m/K and 0.1 W/m/K.

In order to introduce the sensor unit2as easily as possible into a housing1of a portable computer system0, the following methods are used.

Preferred Manufacturing and Integration Method

FIG.6show a method for the integration of a sensor unit2into a housing1of a portable computer system0. A sensor unit2is used to cover a through hole12in the housing1in such a way that the edges of the printed circuit board22close off the through hole12. Here the electronic components such as the heat flow sensor20and the temperature sensor21, are positioned at the height of the through hole12, or protrude into the through hole12. The printed circuit board22can be bonded to the walls of the housing1by means of adhesive. As a result of covering the through hole12with the printed circuit beard22, in a further step the through hole12can be filled, for example with a silicone mass, so as to form the sensor unit sleeve28. Here, the filling inFIG.6bis executed in such a way that a part of the sensor unit sleeve28protrudes from the through hole12in the direction of the skin contact side10. The positioning of the printed circuit board22is carried out as indicated by the arrow. The sensor unit2is executed as described above, but is only fitted with the sensor unit sleeve28after the printed circuit board22has been fixed in place. The through hole12is filled from the direction of the interior11of the housing1.

The connecting wires3from the printed circuit board22to the electronics (not shown) can either be connected before the casting or filling process, or only after the cavity12has been filled.

In order to obtain accelerated heat conduction, and to maintain an equilibrium between the environment and the body, a metal rod M, which crosses the interior11of the housing1and is in contact with the exterior of the housing1, is attached onto the side of the printed circuit board22facing away from the body, pointing in the direction of the interior11and at the height of the heat flow sensor20. Depending on the embodiment, this metal rod M can also be thermally insulated on its side walls.

It is also possible to use another manufacturing method, which is described inFIGS.7ato7c. After the manufacture of the sensor unit2, it is placed in a casting mould5, whereby the connecting wires3protrude from the casting mould5. The walls of the casting mould5can be made either from metal or a plastic material.

In the next step, the casting mould5is filled with a material that later forms the sensor unit sleeve28. The sensor unit2is enclosed by the material on all sides, such that the printed circuit board22and all components are enclosed by the sensor unit sleeve28. After curing, the enclosed sensor unit2can be placed in a cavity12,13in the housing1of a portable computer system0, and pressed into it in a detachably held manner. The thermally sufficiently conductive material of the sensor unit sleeve28makes close contact with the walls of the cavity12,13, which prevents it from slipping out unintentionally. The sensor unit2embedded in the sensor unit sleeve28forms a plug, which remains in the cavity12,13.

To improve the retention, a suitable adhesive can be used, which is distributed over the walls of the cavity12,13before the sensor unit2encased in the sensor unit sleeve28is pressed in. Correspondingly, a non-detachable connection can also be achieved.

The casting mould5used here can optionally be used as a lost mould, can remain connected to the sensor unit2, or can be removed before the sensor unit2is mounted in the cavity12in the housing1.

In practice, when the sensor unit2is placed on the skin H, measured values from the at least one heat flow sensor20,20′ and the at least one temperature sensor21,21′ are recorded, from which the core body temperature can be determined, using a variety of algorithms. Calibration measurements are necessary for the most accurate determinations possible, and the types and thicknesses of the materials used must be known. Multiple possible algorithms are of known art, which lead to useful results in the determination of the core body temperature.

The sensor unit2is preferably inserted into the sensor unit sleeve28in such a way that the sensor unit sleeve28is partially arranged so as to protrude from the housing1, away from the walls of the housing1. The thermal coupling of the sensor unit2, or more particularly, the sensors20,21, is then optimised accordingly.

The sensor unit sleeve28could be a sleeve or a cylinder made from PVC, for example, which is filled with the thermally conductive material. This cylinder could also be made of an insulating material (foam), so as to better define the thermal path.

In one variant, the sensor unit2can have multiple printed circuit boards22, separated from one another, on which temperature sensors21,21′ and heat flow sensors20,20′ and/or other electronic components can be arranged, separated from one another. All the printed circuit boards22should then be at least partially surrounded by at least one sensor unit sleeve28. If an infrared sensor is used as the temperature sensor21,21′, it must not be surrounded by the sensor unit sleeve28.

LIST OF REFERENCE SYMBOLS