WO2014094776A1

WO2014094776A1 - A stretchable conductor array

Info

Publication number: WO2014094776A1
Application number: PCT/DK2013/050370
Authority: WO
Inventors: Hans-Erik Kiil
Original assignee: Danfoss Polypower A/S
Priority date: 2012-12-19
Filing date: 2013-11-11
Publication date: 2014-06-26

Abstract

The present invention relate to flexible conductors that may be used as connectors for devices where a stretch is to be expected. The present invention further relate to the conductors forming part of conductor cells in an array of active devices, the conductor cells containing the active devices and connecting them to a power supply, or conductor cells themselves being the active devices, such as pressure sensors in a pressure sensor array.

Description

A STRETCHABLE CONDUCTOR ARRAY

INTRODUCTION

The present invention relate to flexible conductors that may be used as connectors for devices where a stretch is to be expected. The present invention further relate to the conductors forming part of conductor cells in an array of active devices, the conductor cells containing the active devices and connecting them to an electronic circuit being power supply or sensor electronics, or conductor cells themselves being the active devices, such as pressure sensors in a pressure sensor array.

BACKGROUND OF THE I NVENTI ON

An electrical potential difference between two electrically conductive layers located on opposite surfaces of the film structure generates an electric field leading to a force of attraction. As a result, the distance between the conductive layers changes and the change leads to compression of the elastomeric material which is thereby deformed. Such structures can be used for making transducers for various purposes. When implemented as actuators they are sometimes referred to as "artificial muscles" due to certain similarities with a muscle. They can also be used as sensors for sensing strain, deflection, temperature variation, pressure etc., or they can be used as generators for converting mechanical energy to electrical, sometimes referred to as energy harvesting. Herein we will generally refer to these structures as transducers or polymer transducers.

US 6,376,971 discloses a compliant electrically conductive layer which is positioned in contact with a polymer in such a way, that when applying a potential difference across the electrically conductive layers, the electric field arising between the electrically conductive layers forces the electrically

conductive layers towards each other. The electric field thereby deflects the polymer film structure. Such transducers may be used as e.g. pressure sensors, such as disclosed in e.g. WO03056274, WO2004053782, WO2011147414 and US6809462.

It is a known problem within the area of people being hospitalized that if not careful they may tend to get bedsore if not frequently repositioned. For some it is no problem to reposition themselves, but some are more inhibited in the movement and thus needs assistance. Since people do not lie on a mattress with evenly distributed pressures, it therefore may help having an indication of this pressure distribution to help reposition them in the best possible position to avoid injuries. Due to the soft nature of the transducers as they are described in this text they are an obvious choice for forming such pressure sensors, the problem being how to connect the sensors with conductors having a high flexibility too, and

especially where the system does not itself affect the softness / flexibility of the mattress but rather is more soft / flexible than it.

DESCRIPTION OF THE INVENTION

It is an object of embodiments of the invention to provide a conductor which is flexible such that it may be stretched in one or more directions without breaking or cracking thus losing its conductive. According to a first aspect, this object is solved by introducing a stretchable conductor comprising a film structure with at least one layer of an elastically deformable polymer film, the film structure having first and second opposite surfaces, and a first electrically conductive layer arranged on the first surface of the film structure characterized in that, a first surface of the deformable polymer film has a pattern of raised and depressed surface portions, where the

conductive layer is connected to the first surface and takes shape from the pattern, thus being stretchable during elastic deformation of the polymer film in at least one direction In relation to be able to measure the distribution of pressure over an area an array of pressure sensors is introduced through a conductor array comprising at least two layers of the stretchable conductors, wherein the first layer has electrodes forming first rows of first conductive layers is electrically isolated from each other, and the second layer has electrodes forming second rows of second conductive layers, where the first rows are non-parallel to the second rows. Each conductor cell may then comprise active devices such as but not limited to sensors and the flexible conductors operating as electrical connectors to these, or they may themselves be the sensors, or each conductor cell may operate as act as locally and individually stimulated actuator or generators.

When the conductor cells themselves operate as pressure sensors, generators or actuators, it is an advantage to ensure the non-zero potential conductor is shielded from the externals, both due to protecting the externals from the potential, but also to protect the conductor from especial not desired electrical influences from the externals. Therefore a layered structure is formed having this conductor sandwiched between two 0-ptential, or grounded, conductors.

To improve such a sensor it has been found that this internal non-zero potential conductor is formed for two flexible conductors connected such that cracks and imperfections in the one is evened out by the other. In one embodiment these two connected conductors have conductive adhesive between them both to hold them together and also to help re-direct current to by-pass cracks and other imperfections.

One known problem is however in the areas where conductors connects to such sensor arrays, this needs to have a sufficient flexibility or the connection tends to be damaged over time when subdued to constant (mechanical) influences from the externals, such as will be the case for a hospital bed.

This is solved by introducing a first support layer of an essentially un-elastic material arranged to reduce stretchability of connection points. To have the system work, such as where the conductor cells operate as sensors, the system comprises control means adapted to apply an electrical potential between any two of the first and second of the first rows and second rows respectively

In the same manner, when e.g. operating as individual actuator cells, the respective any two of the first and second of the first rows and second rows are applied with a voltage ensuring the respective cell to be actuated in the manner as it is well known. When stretchability of the connection points is reduced, relative movement between the conductor and the electrically conductive layer is reduced, and the transducer may become less vulnerable.

By polymer transducer is hereby meant an element which is capable of converting electrical energy to mechanical energy and reciprocally of converting mechanical energy to electrical energy. This enables the use of the transducer as an actuator which can move an item when provided with an electrical field between the first and second layers of electrically conductive material, and/or the use of the transducer as a sensor which provides a change of an electrical characteristic, e.g. capacitance between the layers of electrically conductive material, upon a change in the flow conditions in the path.

The first electrically conductive layer and the second electrically conductive layer may particularly be made from a material having a resistivity which is less than 10-2 Qcm such as less than 10-4 Qcm. By providing an electrically conductive layer having a very low resistivity the total resistance of the electrically conductive layer will not become excessive, even if a very long electrically conductive layer is used. Thereby, the response time for conversion between mechanical and electrical energy can be maintained at an acceptable level while allowing a large surface area of the composite, and thereby obtaining a large actuation force or fine sensing capabilities for the transducer. The electrically conductive layer may preferably be made from a metal or an electrically conductive alloy, e.g. from a metal selected from a group consisting of silver, gold and nickel. Alternatively other suitable metals or electrically conductive alloys may be chosen. Since metals and electrically conductive alloys normally have a very low resistivity, the advantages mentioned above are obtained by making the electrically conductive layer from metal or from any kind of electrically conductive material, e.g. with a modulus of elasticity which is higher than that of the polymer film - i.e. the electrically conductive layer may have a higher stiffness in the elastic range than the polymer film material. The dielectric material may have a resistivity which is larger than 10¹⁰ Qcm.

Preferably, the resistivity of the dielectric material is much higher than the resistivity of the electrically conductive layer, preferably at least 10¹⁴- 10¹⁸ times higher.

In absolute terms, the electrically conductive layer may have a thickness in the range of 0.01 μηι to 0.1 μηι, such as in the range of 0.02 μηι to 0.09 μηι, such as in the range of 0.05 μηι to 0.07 μηι.

The first and second electrically conductive layers are specified to be stretchable. In practice this can be obtained by making the film structure with polymer films having a surface pattern of raised and depressed surface portions and by applying a corresponding one of the electrically conductive layers onto the surface pattern in a thin layer such that it follows the shape of the polymer film to which it is attached. When the film is elastically deformed, the electrically conductive layer can follow the elastic movement of the film while the pattern is stretched out until the electrically conductive layer is completely stretched. The film structure comprises any number of layers of an elastically deformable polymer film, e.g. one, two, three, four, or five layers of the elastically

deformable film either adhesively joined or simply stacked above each other to form a laminated structure. The elastically deformable film may particularly be made from a dielectric material which herein is considered to cover any material which can sustain an electric field without conducting an electric current, such as a material having a relative permittivity, ε, which is larger than or equal to 2. It could be a polymer, e.g. an elastomer, such as a silicone elastomer, such as a weak adhesive silicone or in general a material which has elatomer like

characteristics with respect to elastic deformation. For example, Elastosil RT 625, Elastosil RT 622, Elastosil RT 601 all three from Wacker-Chemie could be used as a dielectric material.

In the present context the term 'dielectric material' should be interpreted in particular but not exclusively to mean a material having a relative permittivity, ε_Γ, which is larger than or equal to 2.

In the case that a dielectric material which is not an elastomer is used, it should be noted that the dielectric material should have elastomer-like properties, e.g. in terms of elasticity. Thus, the dielectric material should be deformable to such an extent that the composite is capable of deflecting and thereby pushing and/or pulling due to deformations of the dielectric material.

The film may have a thickness between 10 μηι and 200 μηι, such as between 20 μηι and 150 μηι, such as between 30 μηι and 100 μηι, such as between 40 μηι and 80 μηι.

The film and the electrically conductive layers may have a relatively uniform thickness, e.g. with a largest thickness which is less than 110 percent of an average thickness of the film, and a smallest thickness which is at least 90 percent of an average thickness of the film.

Correspondingly, the first and the second electrically conductive layers may have a largest thickness which is less than 110 percent of an average thickness of the first electrically conductive layer, and a smallest thickness which is at least 90 percent of an average thickness of the first electrically conductive layer. The electrically conductive layers may e.g. be applied to one of the polymer film layers in a very thin layer thickness by a coating technique.

A first conductor may be attached to the first electrically conductive layer in a first connection point, and the second conductor may be attached to the second electrically conductive layer in a second connection point. The conductor may be formed as an elongated body like a traditional wire or cable, formed by a woven fabric comprising the conductors e.g. formed as conductive coatings on the surface of the fibers, yarns etc, of the woven fabric. In another embodiment, the conductors may be formed as pouches being circular, oval, or of another shape suitable for establishing the electrically communication with one of the

electrodes.

The conductor may e.g. be highly elastically deformable such that the length of the conductor may be varied, or the conductors may at least be flexibly bendable. First and second support layers made from essentially un-elastic material may be arranged to reduce stretchability of at least one of the first and the second, connection points. This layer may be adhesively attached directly to the surface of one of the contact points. Since the un-elastic material reduces the

stretchability, it may improve the durability of the transducer by reducing fatigue and stress. By un-elastic material is herein meant a material with a higher modulus of elasticity than that of the polymer film. The ratio between a modulus of elasticity of the un-elastic material and a modulus of elasticity of the film may be larger than 50, or even larger than 100 or even larger than 200. By un-elastic material is herein also meant a material though it may be

substantially un-stretchable, at least compared with the dielectric material, it may still be highly bendable.

As already mentioned, the film structure may comprise any number of layers of the elastically deformable polymer film. Particularly, the transducer may include two layers of elastically deformable film which are separated by an intermediate electrically conductive layer structure. The primary advantage of this structure is that a potential difference may be applied between the intermediate electrically conductive layer structure and a common potential of the first and second electrically conductive layers. Particularly, the common potential may be zero, i.e. the first and second electrically conductive layers may be connected to zero or ground, whereas a high potential difference is applied to the intermediate electrically conductive layer structure. The user of the transducer may thereby be protected effectively from the high electrical potential by the first and second electrically conductive layers which form outer surfaces of the transducer.

The intermediate electrically conductive layer structure may comprise at least one, and preferably two intermediate electrically conductive layers being stretchable during elastic deformation of the polymer film.

Two intermediate electrically conductive layers may be adhesively bonded by use of an electrically conductive adhesive, and in that case, an additional conductor which is connected to the intermediate electrically conductive layer structure in an intermediate connection point can be fixed in the conductive adhesive between the intermediate electrically conductive layers.

A further support layer of an essentially un-elastic material may be included in the electrically conductive adhesive applied between the intermediate electrically conductive layers. Since the un-elastic material reduces the stretchability inside the laminated structure between the intermediate electrically conductive layers, it may improve the durability of the transducer by reducing fatigue and stress. The above definition of an un-elastic material still applies, i.e. it has a higher modulus of elasticity than that of the polymer film, e.g. 50 times, or even 100 times, or even 200 times larger.

At least one of the first, the second, and the additional conductors may comprise bendable conductive elements arranged un-stretched in contact with the electrically conductive layer or conductive layer structure to which the conductor is attached. Since the conductors are un-stretched they may be stretched during deformation of the polymer film, and the conductors can thereby follow the movement of the transducer in the contact points. The transducer may further comprise control means adapted to apply an electrical potential difference between at least one of the intermediate

electrically conductive layer structures and the common potential of the first and second electrically conductive layers. As already mentioned, applying a zero potential as the common potential will have the effect of protecting the user against the potential being present on the intermediate electrically conductive layer structure.

At least one of the first and second support layers may be bendable or soft pliable such that it can change shape and easily adapts to the shape of the product in or to which the transducer is applied. In one embodiment, the support layers are as bendable as a piece of cloth or canvas. Particularly, at least one of the support layers may be constituted by a non-woven fabric comprising soft bendable but essentially non-stretchable fibers e.g. having a structure like a soft sheet of cloth etc. The transducer may further comprise a layer of an elastically deformable and / or sealing material covering the film structure, at least some of the electrically conductive layers, and the connection points. Particularly, the transducer may be completely sealed in an elastically deformable sealing material preventing intrusion of water and/or vapor, dust and other contaminants. The transducer may particularly facilitate stretching in one particular direction or in several particular directions, e.g. in two directions being perpendicular. Herein, the ability to stretch the transducer in one direction without being able to stretch the transducer in other directions is referred to as anisotropic stretching

characteristics. The polymer film is already specified as being elastically

deformable, and to provide the anisotropic stretching characteristics, at least one and preferably all of the electrically conductive layers may therefore have anisotropic stretching characteristics.

This can be provided by making the aforementioned surface pattern of raised and depressed surface portions with a particular shape. The surface pattern may e.g. comprise corrugations which render the length of the electrically conductive layers in a lengthwise direction longer than the length of the composite as such in the lengthwise direction. The corrugated shape of the electrically conductive layer thereby facilitates that the transducer can be stretched in the lengthwise direction without having to stretch the electrically conductive layer in that direction, but merely by evening out the corrugated shape of the electrically conductive layer.

The corrugated pattern may comprise waves forming crests and troughs extending in one common direction, the waves defining an anisotropic

characteristic facilitating movement in a direction which is perpendicular to the common direction. According to this embodiment, the crests and troughs resemble standing waves with essentially parallel wave fronts. However, the waves are not necessarily sinusoidal, but could have any suitable shape as long as crests and troughs are defined. According to this embodiment a crest (or a trough) will define substantially linear contour-lines, i.e. lines along a portion of the corrugation with equal height relative to the composite in general. This at least substantially linear line will be at least substantially parallel to similar contour lines formed by other crest and troughs, and the directions of the at least substantially linear lines define the common direction. The common direction defined in this manner has the consequence that anisotropy occurs, and that movement of the composite in a direction perpendicular to the common direction is facilitated, i.e. the composite, or at least an electrically conductive layer arranged on the corrugated surface, is compliant in a direction

perpendicular to the common direction. The variations of the raised and depressed surface portions may be relatively macroscopic and easily detected by the naked eye of a human being, and they may be the result of a deliberate act by the manufacturer. The periodic variations may include marks or imprints caused by one or more joints formed on a roller used for manufacturing the film. Alternatively or additionally, the periodic variations may occur on a substantially microscopic scale. In this case, the periodic variations may be of the order of magnitude of manufacturing tolerances of the tool, such as a roller, used during manufacture of the film.

Each wave in the corrugated surface may define a height being a shortest distance between a crest and neighboring troughs. In this case, each wave may define a largest wave having a height of at most 110 percent of an average wave height, and/or each wave may define a smallest wave having a height of at least 90 percent of an average wave height. According to this embodiment, variations in the height of the waves are very small and a very uniform pattern is obtained.

According to one embodiment, an average wave height of the waves may be between 1/3 μηι and 20 μηι, such as between 1 μηι and 15 μηι, such as between 2 μηι and 10 μηι, such as between 4 μηι and 8 μηι.

Alternatively or additionally, the waves may have a wavelength defined as the shortest distance between two crests, and the ratio between an average height of the waves and an average wavelength may be between 1/30 and 2, such as between 1/20 and 1.5, such as between 1/10 and 1. The waves may have an average wavelength in the range of 1 μηι to 20 μηι, such as in the range of 2 μηι to 15 μηι, such as in the range of μηι to 10 μηι.

A ratio between an average height of the waves and an average thickness of the film may be between 1/50 and 1/2, such as between 1/40 and 1/3, such as between 1/30 and 1/4, such as between 1/20 and 1/5. All electrically conductive layers in the transducer may have identical surface patterns, and they may be arranged to provide stretchability in identical direction.

Due to the deformation of the polymer, the electrically conductive layers move, and the conductor which connects the electrically conductive layer to a power source or sensor electronics must constantly follow the movement of the electrically conductive layer. Fatigue may be experienced over time whereby the conductance of the conductor is reduced or the conductor may fail completely.

Particularly, the transition between the conductor and the electrically conductive layers tend to be fragile and may become damaged by the repeated movement of the transducer.

The stretchable conductors can be produced in webs of potentially endless lengths and the conductor cells may include and / or be transducers, actuators or sensors of any kind such as to monitor humidity, stretch, surface pressure, temperature, shear forces etc.

LIST OF DRAWINGS

Figs. 1a and 1b illustrate a transducer with electrodes on opposite sides of a polymer film structure;

Fig. 2A and 2B illustrates a polymer sheet for making a layer of the transducer with a wavy structure of the electrode;

Fig. 3 illustrates a transducer with two polymer film layers;

Fig.4 illustrates the transducer with conductors and support layers; Fig. 5 illustrates a conductor cell according to the present invention.

Fig. 6 illustrates a conductor array according to the present invention.

Fig. 7 illustrates a conductor cell including an active device.

Figs. 8A and 8B illustrate a stretchable connector interconnecting two conductor cells. Fig. 9 illustrates a compressible dielectric material.

Fig. 10 illustrates a non-compressible but stretchable dielectric material.

Fig. 11 illustrates a conductor cell having a di-electric there between.

Fig. 12 illustrates the conductor array according to the present invention arranged on a matrass also showing flexible connection points. DETAILED DESCRIPTION

It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.

Figs. 1a and 1b illustrate a transducer 1 comprising a film structure 2 comprising at least one layer of an elastically deformable polymer film arranged between first and second electrically conductive layers 3, 4, or just conductive layers 3, 4 or electrodes 3, 4. The first and second electrically conductive layers thereby form electrodes on opposite sides of the deformable polymer film. In Fig. 1a, the transducer is exposed to zero electrical potential difference, and in Fig. 1b the transducer is exposed to a high electrical potential difference. As illustrated in Fig. 1b, the film 2 is expanded, while the electrically conductive layers 3, 4 are evened out, when exposed to an electrical potential difference.

The resistance in the conductors 3, 4 is at least substantially unaffected by the stretching and is thus constant R0.

Fig. 2A illustrates a sheet 5 forming part of one layer of the film structure 2. The sheet has an upper and lower surface 6, 7. The upper surface is provided with a pattern of raised and depressed surface portions thereby forming a designed corrugated profile of the surface. An electrically conductive layer has been applied to the upper surface, e.g. by a deposition technique facilitating a very low layer thickness when compared to that of the sheet. In this way, the electrically conductive layer is formed with the same pattern of raised and depressed surface portions as the upper surface of the sheet.

In terms of everyday physical things, the sheet 5 has a thickness and is pliable and soft like household film. However, it is more elastically deformable than such a film and, once the conductive layer is applied to the upper surface, it has a marked mechanical anisotropy. Fig. 2B illustrates an enlarged section of Fig. 2A where the composite 1 comprises a dielectric film 2 made of a dielectric material having a surface 3 provided with a pattern of raised and depressed surface portions, thereby forming a corrugated profile of the surface 3. The surface 3 is provided with an electrically conductive layer forming a directionally compliant composite as described above. The pattern of raised and depressed surface portions may be designed having various shapes.

The corrugated profile may be represented by a series of well-defined and periodical sinusoidal-like three dimensional m icrostructures. Alternatively, the corrugated profile may have a triangular or a square profile. The mechanical compliance factor, Q, of the corrugated electrode is determined by the scaling ratio between the depth d of the corrugation and the thickness h (see Fig. 2B) of the electrically conductive layer 4, and by the scaling ratio between the depth d of the corrugation and its period P. The most dominating factor is the scaling ratio between the height d of the corrugation and the thickness h of the electrically conductive layer 4. The larger the compliance factor, the more compliant the structure is. It has been found by the inventors of the present invention, that if perfect compliance is assumed, for a scaling ratio between the depth d of the corrugation and its period P, a sinus profile could theoretically elongate approximately 32%, a triangular profile approximately 28% and a square profile approximately 80% compared to the original length. However, in reality this will not be the case since the square profile comprises vertical and horizontal beams, which will result in different compliances, because the vertical beams will bend and thereby generate a very compliant movement in the displacement direction, while the horizontal beams will be much stiffer, since they extent in the displacement direction. It is therefore often desirable to choose the sinus profile.

Referring again to the transducer in Figs. 1a and 1b, the film structure 2 comprises a single layer of an elastically deformable polymer film. This single layer can be constituted by two of the sheets 5, each having an electrically conductive layer deposited on the upper surface. The sheets 5 are arranged with the lower surfaces 7 against each other. This is illustrated by the dotted line 8. Due to the pattern of raised and depressed surface portions, the electrodes 3, 4 may even out as the film 2 expands, and recover its original shape as the film structure 2 contracts along the direction defined by the arrow 9 without causing damage to the electrodes 3, 4, this direction thereby defining a direction of compliance. Accordingly, the laminate 1 is adapted to form part of a compliant structure capable of withstanding deformation and large strains.

As described above, the corrugated surface profile is directly impressed or moulded into each sheet 5 of the dielectric film structure 2 before the electrically conductive layer is deposited. The corrugation allows the manufacturing of a compliant composite using a material for the electrically conductive layers having high elastic moduli, e.g. metal. This can be obtained without having to apply pre-stretch or pre-strain to the dielectric film structure 2 while applying the electrically conductive layer, i.e. the electrodes 3, 4, and the corrugated profile of the finished composite does not depend on strain in the dielectric film 2, nor on the elasticity or other characteristics of the electrodes 3, 4. Accordingly, the corrugation profile is replicated over substantially the entire upper and lower surfaces of the film structure 2 in a consistent manner, and it is possible to control this replication. Furthermore, this approach provides the possibility of using standard replication and reel-to-reel coating, thereby making the process suitable for large-scale production. For instance, the electrodes 3, 4 may be applied to the upper and lower surfaces of the dielectric film structure 2 using standard commercial physical vapour deposition (PVD) techniques. An

advantage of this approach is that the anisotropy is determined by design, and that the actual anisotropy is obtained as a consequence of characteristics of the corrugated profile which is provided on the surfaces of the film structure 2 and the electrodes 3, 4 which follow the corrugated profile.

The transducer shown in Figs. 1a and 1b is designed to have compliance in the direction defined by the arrow 9, and stiffness in the range of the stiffness of the electrically conductive layers 3, 4 in a direction defined by the arrow 10.

However, it may also be compliant in other ways, or may even be formed such that they have compliance in all directions in the 2D-plane. Fig. 2C illustrate an aspect of the invention illustrating a sheet 5 seen from the top and showing an electrode 3 having a section 34 where it operates purely as conductor, and an active section 70, where this active section 70 could form part of an active device 50 (the active devices 50 being internal as they are an internal part of an electrode 3), such as being part of the conductor cells 33 e.g. operating itself as a sensor as to be described later, or could form the contact section to an external active device 50 (the active devices 50 being external to the electrode 4) as it will also be described below.

Fig. 3 illustrates a transducer with two layers 11, 12 of the elastically deformable polymer film with surface electrodes 4, but where the two layers of the film structure are separated by two intermediate electrically conductive layers 13, 14 in contact to each other, optionally in adhesive contact through an electrically conductive adhesive 15. The joined electrically conductive layers 13, 14 are referred to in the following as one intermediate electrically conductive layer structure 13, 14, 15. In the illustration the corrugations of the two layers 11, 12 are parallel to each other. In this disclosure a layer 11 , 12 is to be one

comprising at least an elastically deformable polymer film with an electrode at the surface, in the minimal version as the sheet 5 illustrated in Fig.2, but may include a structure with opposing electrodes as illustrated in Fig. 3. Making a transducer with the embodiment of Fig.3 then would require either laminating one layer with the electrode carrying surface laminated against a surface of another layer without electrode (front-to-back lamination), or the two surfaces without electrode against each other (back-to-back lamination as illustrated in Figs. 1a and 1b). In this way a sandwiched structure is ensured where two opposing electrodes 3, 4 (or conductive layers) are separated by the elastically deformable polymer film.

Alternatively as illustrated in Fig.3 each layer 11, 12 in itself is a transducer having opposing electrodes 3, 4 separated by the elastically deformable polymer film, but when laminated as illustrated the internal electrodes, or conductive layers, 13, 14 operates together as one of the conductive layers 3 and by connecting the outer conductive layers in any possible manner conductively, they will act together as the other of the conductive layers 4. I n even further advanced versions the different kinds of layers 11, 12, either shaped as in Fig.2 or as in Fig.3, may be laminated together in any number and permutation, what matters is that some of the conductive layers are connected to form a first conductive layer 3 and some to form a second

conductive layer 4.

In the following there thus will only be referred to as first conductive layer 3 and second conductive layer 4, though they actually may be composed by a plural of parallel conductive layers.

Fig.4 illustrates a first conductor 16, a second conductor 17, and an additional conductor 18 in electrically conductive communication with the electrically conductive layers 3, 4, and the intermediate electrically conductive layer structure 13, 14, 15 to facilitate an electrical potential between the conductive layers and thereby enable deflection of the film 2 in response to an electrical field. The conductors of traditional transducers are typically made of a stiff material, e.g. a rod shaped material. According to the invention, the conductors may be soft pliable and/or bendable conductors. Each of the conductors 16, 17, 18 may e.g. comprise a plurality of electrically conductive fibers, or yarns.

The areas where the conductors 16, 17, 18 are connected to the electrically conductive layers or layer structure is referred to herein as the connection points. The first and second connection points 19, 20 where the first and second electrically conductive layers 3, 4 are joined to the first and second conductors 16, 17, are covered by first and second support layers 21 , 22 attached

adhesively to the connection points. The support layers are made of an

essentially un-elastic material, e.g. a non-woven material. The support layers thereby reduce stretchability of the transducer in the connection points. The first and second conductors and thus the first and second electrically conductive layers 3, 4 are connected to zero or ground of a power supply, and the

intermediate conductor and conductive layer structure 13, 14, 15 is connected to different electrical potential to cause deformation of the polymer film. The connection of the outer layers to zero or ground protects the user against electric shock, and to shield the transducer from external interaction that e.g. could influence measurements when the transducer acts as a sensor The conductors form part of a soft pliable or bendable cable 23 made e.g. of a woven or non-woven fiber material, such as where conductive material are coated onto the fibers or yarns of a woven material.

Fig. 5 illustrates an alternative relative positioning of the corrugations, illustrated by the lines 24, of the first 11 and second 12 layer respectively are

perpendicular to each other, or at least positioned non-parallel but with

somerelative angle. Rows of conductive layers 3, 4 then could be formed in parallel to the lines 24 of the respective layers 11, 12, or with an angle to them , and the two layers 11, 12 may even have rows of conductive layers 3, 4, such that the first conductive layers 3 extend, or runs, with a different angle to the lines 24 of the corrugations than the second conductive layers. This lamination could for example be suitable for making flexible arrays 30 as illustrated in Fig. 6, where rows 31 of first conductive layers 3, separated and isolated from each other, intersects rows 32 (or columns) of second conductive layers 4, these rows thus extending non-parallel and preferably perpendicular to each other. Since each of the first conductive layers 3 are insulated from each other by polymer film 2 surface not having any conductive material (the same applies to each of the second conductive layers 4), and since the first 3 and second 3 conductive layers are separated by being positioned on opposing sides of at least one polymer film 2 as described above, then an array 30 of individually conductor cells 33 are formed, where each of these may be accessed individually since neither belongs to the same row 31 of the first conductive layers 3 and the same row 32 of the second conductive layers 4. Such conductor cells have the flexibility to take more or less any shape, just as the whole of the sensor array 30 is highly flexible and takes easily shape after any surface whereto it may be applied.

In alternative embodiments some of rows of conductive layers 3, 4 are formed running parallel to the extension of the corrugations and others non-parallel to the direction of the corrugations, such as perpendicular. This e.g. could be that the first conductive layers 3 run parallel and the second conductive layers run perpendicular to the corrugations, or vice versa. The first and second conductive could also just run with respective different relative angles to the extension of the corrugations. Each of the individual conductor cells 33 then may operate as transducer of some kind, by supplying voltage such that they deflect as described above or as sensors such as pressure sensors registering a pressure by a change in capacitance if the first 3 and second 4 conductive layers are pressed closer together. Alternatively they may operate as conductors for other elements, active devices 50 squeezed between the layers, as it shall be described later.

Each of the conductor cells 33 thus is formed of the rows 31 , 32 of first 3 and second 4 conductive layers where these intersect, thus forming areas with opposing conductors. In addition to form active part of the conductor cells 33, in the areas where they are not opposing any conductor each of the rows 31 , 32 of first 3 and second 4 conductive layers further operate as pure flexible (or stretchable) conductors 34, in the present illustration connecting each of the cells 33 to a power supply, however they could with advantage be utilized elsewhere where such a stretchable conductor 34 would be required or just desired.

Especially in the embodiment where the conductor cells 33 comprises or act as sensors it is essential that the resistance of the connecting conductors remains constant since the measurement is based on a changing capacitance, and where the capacitance is linked to the capacitors charge being roughly constant and the voltage, and in the measurement is measured by applying a voltage, it is essential that the resistance of the conductor does not change or it will affect the measurements too, this being due to the wavy shapes of the conductors 3, 4 merely stretching out when the layers 11, 12 are stretched. To learn more how to use e.g. transducers of the kind disclosed in the present disclosure then see e.g. US 6809462.

As also described above, the conductive layers 3, 4 are flexible in that they are shaped due to the surface pattern of polymers, where this pattern may be corrugated thus forming wavy conductive layers, and where the corrugations of the first conductive layers 3 may be perpendicular to those of the second conductive layers 4. However, they may also be parallel, positioned at an angle, or having a whole other pattern e.g. giving compliance in all directions in the 2D-surface plane.

The construction as illustrated in Fig.7 shows an embodiment where the layers 11, 12 does not form the active parts such as being transducers like sensors, generators or actuators themselves, but includes, as also described above, active devices 50 squeezed between at least two layers 11, 12, the active devices in this embodiment being external active devices 50. The active devices 50 is not limited to being sensors, any device may apply to the embodiment where any kind of active devices 50 are to be connected by stretchable conductors. In this case one may refer to external active devices 50 as they are external to the conductive layers 3,4, whereas when the conductive layers 3, 4 themselves form the active devices 50, then one may refer to them as being internal active devices 50, as they are internal to the conductive layers 3, 4.

In this embodiment the first 3 and second 4 conductive layers may be formed at the inside of the laminated structure separated by an additional insulation layer, the one at the outside and the other at the inside, or in any other manner. When one or both of the conductive layers 3, 4 are at the outside, meaning at the opposite site of the respective films 2 relative to the active device 50, then any kind of means to form electrical connection from the electrode to the active device 50 may also be included.

Alternatively to operate as electrical connectors to the active devices 50, the layers 11, 12 of the conductor cells 33 may also act in a mechanical interaction with the active devices, such as by compression on them at variable forces, or alternatively being pushed at variable forces by the active devices 50. Figs. 8A and 8B illustrate the stretchable conductors as stretchable connectors 34 of conductor cells 33, where Fig. 8A illustrates a non-stretched section 34, or at least lesser stretched, and Fig. 8B illustrates a stretched section 34, or at least more stretched. These stretchable connector 34 sections thus forms the flexible / stretchable interconnections between the conductor cells 33. Fig. 9 illustrates one embodiment of the present invention where the conductor cells 33 operates as, or comprises, a pressure sensor e.g. in the form of a compressible di-electric material 60 positioned between two conductors 3, 4, such as between two layers 11, 12 (conductors 3, 4 and layers 11, 12 not illustrated in the figure). Since the di-electric material 60 is compressible it does not need to direct material in the length direction and thus when the electrodes are squeezed together to make a pure push sensor.

Fig. 10 illustrates another embodiment where the di-electric material 61 is non- compressible, or at least not substantially compressible, but is elastic and stretchable, such as the polymer making up the film 2 of the previous

description. In this manner the change in capacitance occurs when the films 2 are stretched thus making a shear and/or stretch sensor.

Each of the two kinds of sensors as illustrated in Figs. 9 and 10 could be used in or as the conductor cells 33 e.g. in an array 30, either in the manner where some of the cells 33 comprises one kind of sensor and other cells another kind of sensor. Alternatively each cell 33 comprises both kinds of sensors and thus comprises more layers 11, 12 than two but the number required according to the number of sensors, or more generally active devices 50, since these embodiments are not limited to sensors of the kinds illustrated in Figs. 9 and 10, but could be any kinds and numbers of active devices 50 possible combined with such sensors.

Fig. 11 illustrates either the compressible 60 or stretchable 61 dielectric between two layers 11, 12 such that a conductor cell 33 is formed that may operate as a sensor, where the resistivity Rs over the conductors 3, 4 are known to be at least sufficiently independent on the stretch of the layers 11, 12 and thus at least sufficiently constant.

Fig. 12 shows one example embodiment of the use of the array 30 according to one aspect of the present invention, the figure showing a mattress 40, e.g. for a hospital bed, where a the array 30 operates as a pressure distribution sensor array that can measure the distribution of pressures on the mattress 40 of a person lying on it. In this manner it is possible e.g. to monitor when and how to reposition the person.

Each of the conductor cells 33 may then operate as pressure sensors in themselves as described above, or they may act as connectors to sensors 50 positioned within the cells between the first and second layers of polymer as illustrated in Fig. 7. Different sensors and / or active devices 50 may also be included either in separate or the same cells 33, as also described above.

Especially, but not exclusively, in the hospital bed example obvious active devices 50 to be included would be temperature and/or humidity/moist sensors. Back to Fig. 12, then also illustrated is connection points 19 of the rows 31 (or 32) to conductors 16, 17, 18. Naturally the other rows would be connected to conductors 16, 17 in the same manner with the support layers 21 making a stable connection to the rows 31 , 32, where the support layers 21 preferably has a flexibility / bendability matching that of the mattress. Such as in the hospital bed embodiment it is frequently observed that patents entering or leaving the bed and the medicals and nurses being at the side of the bed when handling the patient, then they frequently may affect the conductors 3, 4 and connection points 19 especially at the outside edge side 70 of the array 30 meaning the parts external to the array 30 of sensor cells 33, such as illustrated at the edge and side of the mattress 40.

Therefore the present invention also introduces such an edge connection 70 of flexible / stretchable conductors 3, 4 as they have been disclosed above, and the support layers 21 , where the edge connection connects the devices to external electronic devices such as the needed sensor electronics, the power supply etc. Seen too is the stretchable connectors 34 forming electrical interconnections between conductor cells 33.

Claims

CLAI MS

1. A stretchable conductor comprising a film structure with at least one layer of an dielectric elastically deformable polymer film (2), the film structure having first and second opposite surfaces, and a first electrically conductive layer (3) arranged on the first surface of the film structure a first surface of the

deformable polymer film has a pattern of raised and depressed surface portions, where the conductive layer (3) is connected to the first surface and takes shape from the pattern, thus being stretchable during elastic deformation of the polymer film in at least one direction, characterized in that, the first conductive layer (3) comprise a stretchable conductor section (34) and an active section (70) .

2. A stretchable conductor according to claim 1 , wherein the active section (70) contacts an external active device (50) electrically.

3. A conductor array (30) comprising at least two layers (11, 12) stretchable conductors according to claim 1 or 2, wherein the first layer (11) has electrodes form ing first rows (31 ) of first conductive layers (3) electrically isolated from each other, and the second layer (12) has electrodes forming second rows (32) of second conductive layers (4), where the first rows (31) are non-parallel to the second rows (32).

4. A conductor array (30) according to claim 3, where the first (31 ) and second (32) rows forms conductor cells (33) where a first conductive layer (3) of the first rows (31) opposes a second conductive layer (4) of the second rows (32), the conductor cells (33) being or comprising active devices (50) of the conductor array (30).

5. A conductor array (30) according to claim 4, where the conductor cells (33) operate as pressure sensors, the conductor cells (33) themselves form the active deice (50), the active device being an internal active device (50)

6. A conductor array (30) according to claim 4, where an external active device (50) is positioned between the first layer (11) and the second layer (12).

7. A conductor array (30) according to claim 6, where the active device (50) is in electric contact with the first conductive layer (3) and the second conductive layer (4).

8. A conductor array (30) according to any of claims 2-7, where

- a first conductor (16) attached to a first connection point (19) of the first electrically conductive layer (3); and

- a second conductor (17) attached to a second connection point (20) of the second electrically conductive layer (4); wherein the conductor array (30) further comprises a first support layer (21) of an essentially un-elastic material arranged to reduce stretchability of at least the first connection point.

9. A conductor array (30) according to any of the preceding claims 2-8, where the film structure comprises at least two layers (11, 12) of the elastically deformable polymer film, and where the first conductive layer (3) is formed of adjacent layers of the film structure being separated by an intermediate conductive layer structure (13, 14, 15) comprising at least one intermediate electrically conductive layer being stretchable during elastic deformation of the polymer film.

10. A conductor array (30) according to claim 9, where the second conductive layer (4) is formed of two conductive layers positioned and the second

conductive layer (4) is positioned at opposite sides of the intermediate conductive layer structure (13, 14, 15) but is connected electrically thus forming one single electrode (4)

11. A transducer according to claim 9 or 10, where the conductive layer structure comprises two intermediate electrically conductive layers (13, 14) in adhesive

12. A conductor array (30) according to any of the preceding claims 2-11, further comprising control means adapted to apply an electrical potential between any two of the first (3) and second (4) of the first rows (31) and second rows (32) respectively

13. A conductor array (30) according to claim 12 and one of claims 9-11, where the control means is adapted to provide a common electrical potential on each of the conductive layers (13, 14, 15) forming the first conductive layer (3) and to apply a different electrical potential to each of the second (4) electrically conductive layers.

14. A transducer according to claim 13, where the electrical potential of second electrically conductive layers (4) is zero or ground.

15. A conductor array (30) according to any of the claims 4-114, wherein the stretchable conductors further forms stretchable connectors 34 forming electrical interconnections between conductor cells (33).