Sensor arrangement

A sensor for measuring a physiological signal and a method for manufacturing such a sensor. Such a sensor includes a flexible substrate and at least one electrode, which has a signalling surface, which faces in the same direction as the first surface of the flexible substrate. In addition, the sensor includes a signal transmission conductor, which is connected electrically to the electrode. The signal transmission conductor is attached in a watertight manner to the second surface of the substrate. The sensor is reliable, economical to manufacture, and comfortable to the user.

The present application claims priority to FI 20065391, filed in Finland on Jun. 8, 2006, which designated the United States, and on which priority is claimed under 35 U.S.C. §120, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to sensor devices. In particular the invention relates to new sensor for measuring a physiological signal from the skin. Such sensor typically comprises a substrate, a signal electrode, and means from transmitting a signal electrically. In addition, the invention relates to a method for manufacturing sensor, to a heart rate belt, and to apparel.

2. Description of Background Art

Traditional heart-rate meter heart rate bands and heart rate belts generally comprise a body made of plastic, on the surface of which there are two local electrodes to be placed against the chest. Electronics for transmitting a heart rate signal, typically to a wristop device, are built into the plastic body. Conductors from the electrodes to the electronics also run inside the body, which is generally attached against the chest with the aid of a flexible band.

Because plastic heart rate bands are relatively thick and can feel uncomfortable in use, heart rate belts and sensor utilizing textile materials in particular have been developed recently. One such is disclosed in WO publication 2005/032366. In the solution depicted in it, the electrodes and transmission conductors are surfaced with a conductive material directly in the textile material. The transmission conductors can afterwards be coated with an insulating material, so that only the electrodes remain in contact with the skin and the quality of the signal improves. However, the laminate then remains on the surface of the product at the conductors, so that the breathability of these locations is reduced and they may feel uncomfortable against the skin.

WO publication 2002/071935 (FI 110915) discloses a heart rate sensor, in which there are electrodes containing conductive fibres, at the ends of which there is a moisture-retaining layer to improve the electrical contact of the electrodes with the skin. This solution also has a problem with the placing of the signal transmission conductors relative to the fibre material, particularly with creating both reliable contacts with the electrodes for them and good electrical insulation.

WO publication 2003/082103 discloses a heart rate sensor, with electrodes made by moulding through a textile material. The electrical conductors can be added to the mould, in order to attach them securely to the electrode moulding. However, the electrical conductors remain loose of the surface of the fabric and liable to mechanical stresses acting on them. They can also be attached as part of the textile with the aid of thermo-compression, but then a powerful interference signal may connect to them from the skin through the fabric.

US publication 2005/0043641 discloses a device intended to measure heart rate, which can be detachably attached to a flexible band, or piece of apparel, with the aid of hooks in it. Though it can be attached to many different pieces of apparel, it does not eliminate the problem of discomfort when using traditional heart rate bands.

SUMMARY AND OBJECTS OF THE INVENTION

The invention is intended to eliminate the defects of the state of the art disclosed above and for this purpose create a new type of flexible sensor, which is manufactured on a textile substrate, and which is reliable and easily manufactured.

In the sensor according to the invention for measuring a physiological signal, the outer layer is a flexible and moisture-permeable substrate, which has an outer surface (first surface) and an inner surface (second surface) opposite to this. A signal transmission conductor is arranged in a watertight manner on the inner surface of the substrate, so that interference signals cannot connect directly from the skin through the substrate. An electrode, with a signalling surface facing in the same direction as the outer surface of the flexible substrate, is in turn connected electrically to the transmission conductor.

In the method according to the invention for manufacturing sensor, a flexible substrate is taken, which has an inner surface and an outer surface opposite to this. A signal transmission conductor, which is electrically connected to the electrode, is attached to the second surface of the substrate. The electrode is positioned relative to the substrate in such a way that its signalling surface faces in the same direction as the outer surface of the substrate.

The substrate is preferably a textile material or some other fibre manufacture. The electrode can be made of, for example, metal, or a conductive plastic, elastomer, individual fibres, or of a fibre material, such as a woven or knitted fabric. The transmission conductor can be of metal, a conductive plastic, a conductive rubber, a conductive elastomer, a conductive ink, a conductive polymer, a coating with a metal-particle content, a conductive fibre, a pack of fibres, or a fibre manufacture such as a conductive fabric.

The sensor typically comprises a construction of at least three layers, in which there is a substrate layer that remains against the skin, a first insulating layer, and a conductor layer. Further, yet another insulating layer is typically arranged on the second surface of the conductor layer as a fourth layer. The task of the insulating layer is to prevent liquid, for example, perspiration that accumulates in the substrate during exercise, from reaching the conductor layer and thus to prevent an electrical contact arising with the signal conductor and undesirable interference connecting with the electrode signal.

Considerable advantages are gained with the aid of the invention. In the construction according to it, it is possible to combine flexibility of the structure and reliability of the signalling with the sensor's comfort in use. In particular, it permits the use of durable textiles substrates of a tested comfort, directly against the skin either entirely or nearly entirely in the whole area of the sensor. The transmission conductor of the signal is protected against stress, moisture, and electrical interference on the second side of the textile.

The construction according to the invention can also be manufactured entirely form the inner surface of the substrate, in which case the outer surface coming against the user remains untouched, except for the electrode openings. Thus, for example, the comfort and breathability of the textile substrate remain good, even at the conductors. The conductors also remain behind the textile layer, well protected from mechanical stress.

With the aid of the invention, the construction of a sensor product can also be implemented in such a way that the conductor structure remains in such a position in the finished sensor product that no elongating forces act on it when the product bends, or at least such forces are considerably smaller in the outer layers of the product. Thus such unstretchable and poorly stretchable conductor materials too can be used, which has been impossible in earlier solutions.

In particular, such a construction, in which the substrate, the first insulating layer, the conductor/electrode layer, and the second insulating are joined together as a pack, is advantageous in terms of manufacturing technique and use. If the insulating layers are attached to each other at the edges, a conductor structure will be achieved, which is insulated from moisture travelling both parallel to the surface and at right angles to the surface, and which is, in addition, thin and flexible. Such a structure can implemented in both a heart rate belt and in apparel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIG. 1, the substrate is marked with the reference number10. An opening11is made in it for an electrode contact. A moisture-insulating intermediate layer12is attached permanently on top of the substrate. An opening13, which can essentially coincide with the opening11can also be made in the intermediate layer. The openings11and13can, of course, also be made later in a single work stage. The electrode15is positioned relative to the opening11in the substrate and to the opening13in the intermediate layer, so that there is a contact connection to its signalling surface from the outer surface of the substrate10(from the skin). The signal transmission conductor14is attached on top of the intermediate layer12. Thus the signal transmission conductor14is attached to the substrate10with the aid of the electrically insulating and watertight layer12, which is located between the strip-like signal transmission conductor14and the substrate10. At one end, the conductor is connected electrically to the electrode15. At the other, its other end it is connected to the electronics module, or to the module's installation means19.

The substrate can be, for example, of a textile material manufactured from natural fibres and/or artificial fibres. The material can be woven or non-woven. It is preferably self-breathing, i.e. permeable by air and water vapour, and often also water. Thus is creates a comfortable feeling against the user's skin.

InFIG. 2a, the construction is further extended by adding a second intermediate layer16and surface layer18. The layer16ensures that the signal transmission conductor14will be watertight also from the second side. The layers12and16are attached directly to each other at the sides, so that the signal transmission conductor layer14remains watertight between them.

According to one embodiment, the substrate continues unbroken from the sensor side facing against the skin to the side opposite to the sensor. Thus the substrate can surround the pack formed of the signal transmission conductor and the intermediate layer or intermediate layers from all sides, in which case both surfaces of the sensor will be formed of an unbroken material. Applied to the embodiment ofFIG. 2a(and ofFIG. 2b, to be examined in greater detail hereinafter), the substrate10and surface layer18thus consist of the same unified material, which is bent at the sides of the sensor, in such a way that it encloses the other layer inside it. It is possible to use, for example, a sensor surface element arranged in a tubular form, inside which the other layers of the sensor are placed. The other layers can be laminated as a ready pack before being placed inside the tubular surface layer. Alternatively, a planar substrate layer can be bent over the layers to the other side of the sensor after the application of the other layers and a joint can be formed on this side, for example, with the aid of adhesive. Opening for the electrodes15and the electronics module connection are made in the tubular surface element. With the aid of the embodiments described, a tidy appearance is created in the edges of the sensor and the use of separate surface-layer elements is avoided.

According to one preferred embodiment, the second intermediate layer16is electrically insulating. It will then be possible to apply a second conductor structure on top of it. Such a second conductor structure can be used to create a second signal path, or electrical shielding layer. Thus with the aid of such a construction it is also possible to increase the sensoring channels, or electromagnetic interference coming from the direction of the second surface can be effectively eliminated. The intermediate layers12and16are preferably of the same material. Always depending on the thickness and conductor structures of the intermediate layers, there can be several such layers, with no significant increase in the thickness of the sensor. More conductors can also be manufactured in a single layer and/or they can be overlapped in different layers.

According to one preferred embodiment, a conductor layer shielding from electromagnetic interference is arranged under and/or on top of the signal transmission conductor (transfer path)14, with the aid of the insulator-conductor layering technique described above. Two shielding layers can further be connected electrically to each other at the edges, in order to form a complete jacket for the signal transmission conductor14.

According to one embodiment, the intermediate layers12and/or16include electrically insulating laminates. The necessary conductor layers are applied to the substrate10and/or with each other on top of the laminates, before they are layered. Such a manufacturing manner is very easy to implement, cheap, and also retains its flexibility after the application of several layers. The laminate is preferably of a barrier type, generally a thin layer attached with the aid of heat, pressure, heat and pressure, or adhesive. For example, many seam laminates used in the apparel industry are suitable for this purpose. The laminate can at the same time also extend to the environment of the electrode15, as illustrated inFIGS. 1 and 2a. Thus it reinforces the areas of the substrate10in the vicinity of the electrode15, and possibly even prevents the substrate10from fraying around the hole11made in it.

According to one embodiment, the signal transmission conductor (transfer path)14includes a conductor substance, such as a conductive ink, a conductive polymer, or a coating with a metal-particle content, which can be spread in a fluid form. Such a conductor substance is spread on the support layer, the intermediate layer12and/or16being preferably used as such. In such a case, a surface of the intermediate layer is preferred wherein it is possible to print directly onto the surface, i.e. the surface is print-ready. According to one aspect of the invention, a new use is indeed offered for a laminate attached to a textile substrate, as a base for a conductor material to be applied in a liquid form.

The signal transmission conductor14can also comprise a conductor applied in a solid form, such as a rubber or elastomer conductor, a metal conductor, a conductive fibre, or a conductive textile. In this case too, the conductor14is preferably attached to the support structure or intermediate layer described above. Particularly TPU elastomer is well suited to this purpose.

According to one preferred embodiment, the signal-transmission conductor14is non-metallic, in which case its conductivity can be in the range of, for example, 10−10-10−2% of the conductivity of a metal (copper). The permanent integration of non-metallic conductors with the layered construction presented is typically simpler than that of a metallic conductor, for example, using processes used in the textile industry.

The electrode15and the signal transmission conductor14can form a unified structure and/or consist of the same material, particularly if a conductive substance produced in a solid form is used.

An intermediate layer attached to the substrate10, like the laminate described above, can be arranged to make the sensor non-stretchable or poorly stretchable. In that case too the flexibility of the structure will advantageously remain good. In particular, a non-stretchable intermediate layer will be appropriate, if a poorly stretchable signal conductor is used. By means of the pack construction described, the situation is thus achieved, in which the laminate layer or layers, possibly together with the textile layers, carrying the forces acting on the sensor.

FIG. 2bshows a construction particularly suitable for heart rate belts. In it there is additionally a layer17, which is arranged on top of the electrodes15and the signal transmission conductor14, but under the electronics module, or its installation zone19. Thus, it formed a base for the installation zone19. In the layer17, there are openings171, through which the overlapping of the layers can be implemented in such a way that the signal transmission conductor14is taken through the opening171, or a contact between the signal transmission conductor14and the installation zone19is made at the location of the opening171. At the same time, the layer17can also act as moisture protection for the signal transmission conductor14, and thus replace the intermediate layer16for this purpose. In the construction shown, mainly, for example, the textile-like surface layer18of the laminate layer16is used to attach the surface layer18to the sensor. At the same time, however, it protects and covers the openings171and thus protects the contacts from moisture.FIG. 3shows the sensor of the present invention including a flexible substrate30, and at least one electrode35on intermediate layer32. The electrode35has a signalling surface, which faces in the same direction as the first surface of the flexible substrate30. In addition, the sensor comprises a signal transmission conductor34, which is connected electrically to electrode35. Signal transmission conductor34is attached in a watertight manner to the second surface of the substrate30, with electrode35being position directly above opening31of substrate30. The sensor according to the invention is reliable, economical to manufacture, and comfortable to the user.

It can be seen fromFIGS. 4a-4cthat the electrode45is arranged on the substrate40in such a way that there is a direct contact connection from the side of the first surface of the substrate40to the signalling surface47. The signalling surface47is preferably at least on the same level as the first surface of the substrate40, as inFIGS. 4aand4c. In some applications, it can also be deeper than the level of the surface of the substrate40in the manner shown inFIG. 4b, particularly in the case of very thin substrates and/or when using electrodes with a very large surface area. In the figures, the laminate or other intermediate layer is marked with the reference number42, and the signal transmission conductor, which is connected to the electrode and directly on top of the laminate42, is marked with the reference number44.

An opening for the electrode45is preferably made in the substrate40. The electrode45can be arranged at the location of the opening, or through the opening to, or through the surface of the substrate40, using several different techniques. It can be brought to it as a ready fixed piece, in which case it is generally attached directly to the substrate40, or to an intermediate layer arranged on top of it, in which there is preferably also an opening. If necessary, it is possible to use adhesives. The electrode45can also be vulcanized, or sewn onto the substrate40. Part of the substrate40can also be treated to become conductive, for example, by impregnating it with a conductive substance, or coating the fibres of the substrate40with a conductive substance. Suitable conductive substances are conductive polymers, inks, and adhesives. The electrode45can also be insulated at the sides, in such a way that it is not in electrical contact with the substrate40in these parts, or at all, in which case the signal will connect to the electrodes45only through the signalling surface47, even when the substrate40is wet.

With reference toFIG. 5, the sensor structure can, after the application of the electrode55and the signal transmission conductor54, be advantageously extended, in such a way that the signal transmission conductor54remains in an inner layer of the sensor structure. This preferably takes place in such a way that the stretch of the transmission conductor54when the finished structure is bent is substantially less than that of the outer layers50,56of the structure. Thus, such material layers50,52,56,58, or layer constructions, with relatively similar elongation and bending properties, are preferable on both sides of the signal transmission conductor layer54. Their elongations generally differ from each other by 30% at the most and preferably by less than 15%. In that case, the signal transmission conductor54will remain essentially on the zero axis of the bending elongation of the structure. Such an embodiment will protect the conductor from unnecessary elongation and contraction when using the sensor, and permit the sensor to be packed in a small space, for example a roll, without damage. The washing of the sensor, especially machine washing, will also stress the signal transmission conductor layer54mechanically, if it is wrongly located relative to the layers of the sensor.

The sensor according to the invention is suitable for use particularly in detecting the heart rate of the heart from the skin, for example, from the chest. Thus the sensor also typically comprises a second electrode like that described above and a second corresponding signal conductor to be place on a different side of the chest. The sensor can also be used for measuring other electrical functions or properties of the body. Examples are measurement of the conductivity of the skin and of fat percentages, as well as the detection of muscle activation.

The sensor can be manufactured as part of a heart rate belt, or as a permanent part of, for example, underwear, sports apparel, a head band, or brassiere, in which case the textile material of these can act as such as the substrate of the sensor. It can be made to be extremely thin and dense, thanks to its construction, and can be washed without moisture penetrating to the internal parts of the sensor.

For placing on the skin, one of the layers of the layered structured described above can extend outside of the actual sensor area. When integrated in apparel, this layer is typically the substrate layer, but in a heart rate belt application, for example, the elastic belt or band to be stretched around the chest can be manufactured to also continue from some other layer of the structure. Generally, in such a construction there are at least three layers arranged permanently on top of each other, one of which forms the signal conductor layer and one continues as a textile-like or elastic structure, in such a way that it can be arranged around some part of the body, in order to bring the signalling surface of the electrode substantially against the skin. As described above, at least one and preferably two of the layers form in addition a moisture protection for the transmission conductor.

One particular embodiment that can be referred to is a heart rate belt application, in which the sensor structure described is combined with an elastic belt or band, which is made ‘too long’ at the factory, and from which part can be cut off, so that the reaming length of the band will be suitable for the user's body. A connector piece can be attached to the end of the band, which can be fitted to a counter piece connected to the sensor. The band can also be sewn or glued to form a unified loop, in which case no plastic components will be required. The individual fitting of the band can be made by the reseller, for example, in a sports-goods store. In particular, an individually fitted heart rate band makes it possible to avoid the use of plastic length-adjustment pieces, as these are typically thick relative to the actual belt or band, and can be unpleasant during exercise.

In addition, other conductors in addition to the electrode-signal transmission conductors can also be laminated in the sensor structure. Examples of these are antennae and other electrical/optical conductors relating to other electrical/optical functions integrated in the apparel/device totality in question.

With the aid of the sensor structure described, it is also possible to manufacture medical sensors, for example, for electroencephalography (EEG), or electrocardiography (ECG). There can then be tens, or even hundreds of measuring channels. Such sensors are made economical, durable, washable, and comfortable for the patient. Patients' fear of tests can also be reduced by the fact that the signal paths of the various channels can be integrated reliably and unnoticeably in a fabric construction, thus giving the measuring unit a pleasant appearance.

With reference toFIG. 6, the sensor can further comprise an installation zone69for attaching and detaching the electronics module610, to which the signal transmission conductor64can be connected. In that case, the transmission conductor64, disposed on substrate600, is connected electrically to a contact area located in the installation zone69. The installation zone shown inFIG. 7can comprise, for example, the ring structure79, in which metallic contact wires720are integrated. When the electronics module is detachably mounted in the installation zone79, the contact wires720surround and make contact with the electronics module.FIG. 7also shows one possible way to implement the joint730between the signal transmission conductor74and the contact wires720. The joint730is preferably made using a joint moulding technique, which produces a durable joint with good electrical conductivity. The moulding technique can also be used as an aid in creating a durable joint730when using, for example, output conductive substances in the signal transmission conductor64,74. The electronics module can be advantageously installed to be able to be detached later. Typically the contact components in either the installation zone69,79or in the electronic module are flexible when installing the module, to create a good contact. Such a sensor arrangement will also withstand machine washing. The electronics module610can also be connected to the transmission conductors64in other ways, for example, with the aid of press-studs6s, as seen inFIG. 6, for example.

The electronics module typically contains means for transmitting, recording, or displaying a measured physiological signal. Typically it comprises a wireless signal transmitter, the terminal of which being, for example, a wristop computer, a computer, or some other heart-rate monitor.