WO2007073258A1 - Method for providing a film of a magnetoelastic material with a curvature, sensor product obtained by the method and sensor - Google Patents

Method for providing a film of a magnetoelastic material with a curvature, sensor product obtained by the method and sensor

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Publication number
WO2007073258A1
WO2007073258A1 PCT/SE2005/002015 SE2005002015W WO2007073258A1 WO 2007073258 A1 WO2007073258 A1 WO 2007073258A1 SE 2005002015 W SE2005002015 W SE 2005002015W WO 2007073258 A1 WO2007073258 A1 WO 2007073258A1
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WO
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Prior art keywords
polymer
film
characterized
sensor
method according
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PCT/SE2005/002015
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French (fr)
Inventor
Ingrid Gustafson
Stefan Nedestam
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Sca Hygiene Products Ab
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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, E.G. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F13/00Bandages or dressings; Absorbent pads
    • A61F13/15Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
    • A61F13/42Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators with wetness indicator or alarm

Abstract

The present invention relates to a method for providing a film (1) of a magnetoelastic material with a curvature. An amorphous or partly crystalline polymer is coated on one side of the film such that a majority of the applied polymer molecules are at least essentially straightened in a first direction of the film. Thereafter the polymer is immediately solidified such that a majority of the straightened polymer molecules remain at least essentially straightened in the first direction of the film after the solidification. Then a majority of the polymer molecules remaining at least essentially straightened after the solidification are released to an unstraight state, whereby the film is curved in the first direction. Also included are a sensor (5) obtained by the method, a sensor (5), and an absorbent structure and an absorbent article comprising the sensor.

Description

METHOD FOR PROVIDING A FILM OF A MAGNETOELASTIC MATERIAL WITH A CURVATURE, SENSOR PRODUCT OBTAINED BY THE METHOD AND SENSOR

TECHNICAL FIELD The present invention relates to a method for providing a film of a magnetoelastic material with a curvature. In addition, the present invention relates to a sensor product obtained by means of the method and a sensor comprising a film of a magnetoelastic material coated with a polymer layer on one side. Furthermore, the present invention relates to an absorbent structure and an absorbent article comprising the sensor according to the invention as well as a sensoring absorbent system comprising the absorbent structure according to the invention.

BACKGROUND OF THE INVENTION

There are many different types of absorbent articles, such as diapers, diapers of pant type, incontinence garments, sanitary napkins, bed protectors, wipes, towels, tissues, tampon-like products and wound or sore dressings, known today for absorption, retention and isolation of body wastes, such as urine, faeces and blood. Some of the known such absorbent articles comprise a sensor which responds to an event, such as urination or defecation, after absorption onto or into the absorbent article. The response may, for example, be a signal after the event has occurred and may be based on measurement of, for example, wetness, a biological analyte and/or a chemical analyte. The signal of an event enables the user, parent, care taker, nursing personnel, etc. to determine with ease that an event has occurred. One type of sensor that is utilized in some absorbent articles is the magnetoelastic sensor. Magnetoelastic sensors have been described by Grimes et al. (Biomedical Microdevices, 2:51-60, 1999).

A magnetoelastic sensor comprises a piece, typically a strip, of a magnetoelastic material. Suitable materials to be utilized as the magnetoelastic material in a magnetoelastic sensor may be any material with a non-zero magnetostriction and a high magnetoelastic coupling, such as iron-nickel alloys, rare earth metals, ferrites, e.g. spinel type ferrites (Fe3O4, MnFe2O4), silicon-iron alloys, many other different alloys and mixtures thereof. Soft magnetoelastic materials, alloys and mixtures thereof as well as amorphous magnetoelastic materials, alloys and mixtures thereof may be utilized. Examples of amorphous magnetoelastic alloys are metglases such as Fe40Ni38Mo4B18, e.g. Metglas 2826MB™ (Honeywell Amorphous Metals, Pittsburg, PA, USA), (FeCo)80B20, (CoNi)80B20 and (FeNi)80B20. The term "magnetostriction" refers to a phenomenon whereby a material will change dimensions in the presence of an external magnetic field. The size of the dimensional change depends on the magnetization in the material and, of course, on the material properties. The phenomenon of magnetostriction is due to the interaction between the atomic magnetic moments in the material.

The term "a high magnetoelastic coupling" refers to the fact that a material having a high magnetoelastic coupling efficiently converts magnetic energy into mechanical elastic energy and vice versa. When a material that may convert magnetic energy into mechanical elastic energy is excited by a time varying magnetic field, elastic waves mechanically deform the material, which has a mechanical resonant frequency inversely proportional to its length. If the material also is magnetostrictive, it generates a magnetic flux when the material is mechanically deformed, which magnetic flux extends remotely and that may be detected by a pick-up coil.

Furthermore, a magnetoelastic material of a magnetoelastic sensor stores magnetic energy in a magnetoelastic mode when excited by an external magnetic field. When the magnetic field is switched off, the magnetoelastic material shows damped oscillation with a specific frequency denoted as the magnetoacoustic resonant frequency. These oscillations give rise to a magnetic flux that varies in time, which can be remotely detected by a pick-up coil. If a pulsed magnetic field such as, for example, a pulsed sine wave magnetic field is applied to the magnetoelastic material, it will be possible to detect a characteristic resonant frequency, i.e. the magnetoacoustic effect, between the magnetic pulses. The magnetoacoustic resonant frequency is inversely proportional to the length of the piece of magnetoelastic material. Changes in the magnetoacoustic resonant frequency may be monitored so as to measure or detect multiple environmental parameters.

WO 2004/021944 describes a disposable sensoring absorbent structure comprising at least one absorbent layer and at least one sensing device comprising a magnetoelastic film. The sensoring absorbent structure may be comprised in an absorbent article such as, for example, a diaper, a diaper of pant type, an incontinence protector, a sanitary napkin or a bed protector. In one embodiment the sensing device is intended to be utilized for detection of wetness. The magnetoelastic film of the sensing device is then coated with a wetness sensitive polymer which interacts with wetness, e.g. moisture, a liquid or humidity. The wetness sensitive polymer interacts with wetness, such as urine, through absorption or adsorption, whereby the mass of the sensing device is changed. This change in mass will either increase or decrease the magnetoacoustic resonant frequency. Thus, the mass change is measurable and correlates to the amount of wetness interacting with the wetness sensitive polymer. In another embodiment, the magnetoelastic film of the sensing device is coated directly or indirectly with at least one detector molecule adapted to detect at least one target biological and/or chemical analyte in body waste, body exudates or the users/wearers skin. WO 2004/Q21944 is herein incorporated by reference in its entirety.

It is known to utilize magnetoelastic sensors within many other technical fields than absorbent articles. For example, it is known to utilize magnetoelastic sensors in connection with position sensors, identification markers and as anti-theft tags or electronic article surveillance (EAS) tags.

Magnetoelastic materials that may be utilized as the magnetoelastic material in a magnetoelastic sensor are typically produced as a continuous ribbon. However, such ribbons reveal typically a longitudinal curvature or are prone to curve in the longitudinal direction. The longitudinal curvature or tendency to curve in the longitudinal direction may be production-inherent and/or may be provided due to that the ribbon is stored in a rolled form. For example, amorphous ferromagnetic metals are typically produced by rapid solidification from a melt as a continuous ribbon. In such ribbons a production-inherent longitudinal curvature may be seen originating from thermally induced mechanical stresses during rapid solidification.

The fact that the ribbons of magnetoelastic material, which may be utilized for producing magnetoelastic sensors, typically present a longitudinal curvature or are prone to curve in the longitudinal direction is a common problem. Strips of such ribbons of magnetoelastic material are typically used in magnetoelastic sensors. If a ribbon of a magnetoelastic material reveals a longitudinal curvature or is prone to curve in the longitudinal direction, a strip cut from the ribbon will also reveal a longitudinal curvature or will also be prone to curve in the longitudinal direction. Usually, a magnetoelastic sensor is encapsulated or packaged in an encapsulation, a package, a housing or similar device. However, if a strip of a magnetoelastic material utilized in a magnetoelastic sensor reveals a longitudinal curvature or is prone to curve in the longitudinal direction, an encapsulation must have a relatively great height to accommodate the magnetoelastic sensor without inhibiting the oscillations of the sensor. If the magnetoelastic sensor during vibration touches the encapsulation, the magnetoacoustic resonance frequency of the sensor may be disturbed or damped. Thus, the fact that ribbons of magnetoelastic material, which may be utilized for producing magnetoelastic sensors, typically reveal a longitudinal curvature or are prone to curve in the longitudinal direction causes problems with respect to the design of encapsulations. Disturbance of the oscillations of an encapsulated magnetoelastic sensor is a common problem.

Furthermore, it is common to enhance the magnetostrictive effect of the magnetoelastic material of a magnetoelastic sensor by including a magnetic bias field in connection with the magnetoelastic sensor. For example, the magnetic bias field may be generated by a permanent magnetic film or a permanent magnet positioned in proximity to the magnetoelastic sensor. However, if a strip of a magnetoelastic material in a magnetoelastic sensor reveals a longitudinal curvature, or is prone to curve in the longitudinal direction, and if the strip is encapsulated in an encapsulation, a clamping effect may occur due to attractive forces between the magnetoelastic material and a permanent magnet in proximity to the strip of magnetoelastic material. This effect may also imply a risk that the oscillations of the sensor are disturbed or damped due to the fact that the strip of magnetoelastic material touches the encapsulation during vibration.

One known way of counteracting and removing a longitudinal curvature of a ribbon of a magnetoelastic material, or a tendency of a ribbon of a magnetoelastic material to curve in the longitudinal direction, is to provide the ribbon with a transverse curvature. This is described in, for example, US 5,676,767. In the method according to US 5,676,767, a curling fixture is provided in an oven for the purpose of giving a transverse curvature to a ribbon of a magnetoelastic material. The ribbon is drawn longitudinally through the fixture and the fixture has a curl surface, which proceeding in a direction transverse to the longitudinal axis of the ribbon rises and the falls. The heating applied to the ribbon during its passage through the fixture causes the ribbon to conform itself to the curl surface, thereby providing the ribbon with a transverse curvature. The transverse curvature counteracts any longitudinal curvature or tendency to curve in the longitudinal direction and enhances the longitudinal bending stiffness of the ribbon. Thereby, the transverse curvature reduces the above mentioned problems with disturbance of the oscillations of the sensor, the problems with the encapsulation design and the problems with the above mentioned clamping effect. However, this method requires that a heat treatment is applied to the magnetoelastic material in order to counteract a longitudinal curvature. In addition, this method requires the use of a fixture and that the magnetoelastic material is drawn through the fixture. Furthermore, when a magnetoelastic sensor coated with a polymer such as, for example, a wetness sensitive polymer, is to be produced, this method requires an extra process step before the polymer may be coated on the magnetoelastic material.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved method for providing a film of a magnetoelastic material with a curvature.

This object is achieved in accordance with the characterizing portion of claim 1.

In a further aspect of the present invention, there is provided a sensor product produced by the above method. Another object of the present invention is to provide an improved sensor comprising a film of a magnetoelastic material coated with a polymer layer on one side.

This object is achieved in accordance with the characterizing portion of claim 23.

Still other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, wherein like reference characters denote similar elements throughout the several views:

Figure 1a shows a schematic perspective view of a film of a magnetoelastic material that may be utilized as the magnetoelastic material in a magnetoelastic sensor;

Figure 1b shows a schematic perspective view of one example of a strip having a longitudinal curvature;

Figure 2a shows schematically a polymer molecule of an amorphous polymer after the different steps of the method according to the invention when the method comprises a step of fluidizing;

Figure 2b shows schematically a polymer molecule of a partly crystalline polymer after a step of fluidizing, a step of solidifying and a step of releasing of the method according to the invention; Figure 3 shows a schematic perspective view of one embodiment of a sensor according to the invention;

Figure 4 shows a schematic perspective view of one variant of the sensor shown in figure 3, and

Figure 5 shows schematically one non-limiting example of an absorbent article comprising a sensor according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1a shows a schematic perspective view of a film 1 of a magnetoelastic material that may be utilized as the magnetoelastic material in a magnetoelastic sensor. The film 1 of a magnetoelastic material shown in figure 1a is provided in the form of a ribbon 2 and is rolled to a roll 3. The ribbon 2 reveals a longitudinal curvature, which is schematically shown in figure 1a. As above described, a ribbon of a magnetoelastic material that may be utilized as the magnetσelastic material in a magnetoelastic sensor reveals typically a longitudinal curvature or is prone to curve in the longitudinal direction. The longitudinal curvature or tendency to curve in the longitudinal direction may be production-inherent and/or may be provided due to that the ribbon is stored in a rolled form. The term "longitudinal curvature" is herein intended to mean a curvature which has an extension in the longitudinal direction of a film of a magnetoelastic material. Thus, a ribbon of a film of a magnetoelastic material that reveals a longitudinal curvature reveals a curvature in the longitudinal direction of the ribbon, i.e. the ribbon is curved in the longitudinal direction. A strip that is cut from a ribbon revealing a longitudinal curvature or being prone to curve in the longitudinal direction will also reveal a longitudinal curvature or be prone to curve in the longitudinal direction if no further processing of the ribbon is performed before the cut. Figure 1 b shows a schematic perspective view of one example of a strip 4 having a longitudinal curvature, which strip 4 has been cut from the ribbon 2 shown in figure 1a without further processing of the ribbon 2 before the cut.

The present invention provides a method for providing a film of a magnetoelastic material with a curvature, which magnetoelastic material may be utilized as the magnetoelastic material in a magnetoelastic sensor. The magnetoelastic material, to which the method according to the invention may be applied, may be any material with a non-zero magnetostriction and a high magnetoelastic coupling, such as iron-nickel alloys, rare earth metals, ferrites, e.g. spinel type ferrites (Fe3O4, MnFe2O4), silicon-iron alloys, many other different alloys and mixtures thereof. Furthermore, the method according to the invention may be applied to, for example, soft magnetoelastic materials, alloys and mixtures thereof as well as amorphous magnetoelastic materials, alloys and mixtures thereof. Examples of amorphous magnetoelastic alloys are metglases such as Fe4ONi33Mo4Bi8, e.g. Metglas 2826MB™ (Honeywell Amorphous Metals, Pittsburg, PA, USA), (FeCo)80B20, (CoNi)80B20 and (FeNi)80B20. The thickness of the film of a magnetoelastic material that the method according to the invention may be applied to is typically about 0.01-1000 μm, such as 0.01-200 μm, 5-100 μm or 0.01-100 μm.

The method according to the invention may be applied to a film of a magnetoelastic material having the shape of a ribbon or any other shape. Furthermore, the method according to the invention may be applied to a film of a magnetoelastic material being stored in a rolled form or any other form. For example, the method according to the invention may be applied to the film 1 of a magnetoelastic material shown in figures 1a and 1b.

The method according to the invention, for providing a film 1 of a magnetoelastic material with a curvature, comprises the steps of: coating one side of the film 1 with an amorphous or partly crystalline polymer, whereby the coating is performed such that a majority of the applied polymer molecules are at least essentially straightened in a first direction of the film 1 , whereby the mentioned majority of the applied polymer molecules are transferred from a thermodynamically favourable entangled state to a thermodynamically unfavourable straightened state; solidifying the polymer coated on the film 1 immediately after the coating such that a majority of the at least essentially straightened polymer molecules remain at least essentially straightened in the first direction of the film 1 after the solidification, whereby a solidified polymer layer of a predetermined thickness is formed during the solidification, which solidified polymer layer is bound to the film 1 , and releasing a majority of the polymer molecules remaining at least essentially straightened in the first direction of the film 1 after the solidification, whereby released polymer molecules are transferred from the thermodynamically unfavourable straightened state to a thermodynamically favourable unstraight state, whereby the film 1 is curved in the first direction such that the film 1 is provided with a curvature in the first direction, which curvature will counteract any curvature of the film 1 in a direction transverse to the first direction.

Optionally, the method according to the invention may further comprise a step of fluidizing the amorphous or partly crystalline polymer before the step of coating. However, the polymer may also be applied to the film 1 as a semisolid. The term "fluidize" is herein intended to mean to make fluid by dissolution in a solvent or by melting. The term "partly crystalline polymer" is herein intended to mean a polymer which comprises polymer molecules having at least one crystalline part and at least one amorphous part.

The method according to the invention will now be described in more detail when applied to the ribbon 2 of the film 1 of a magnetoelastic material shown in figure 1 a for providing the ribbon 2 with a transverse curvature and when the method comprises a step of fluidizing the polymer before the coating step. The term "transverse curvature" is herein intended to mean a curvature which has an extension in the transverse direction of a film of a magnetoelastic material. Thus, a ribbon of a film of a magnetoelastic material that reveals a transverse curvature reveals a curvature in the transverse direction of the ribbon, i.e. the ribbon is curved in the transverse direction.

In an initial step an amorphous or partly crystalline polymer is fluidized. The polymer may, for example, be a wetness sensitive polymer selected from the group consisting of linear and hydrophilic polymers or physically cross-linked swellable polymer gels based on polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide and co-polymers thereof, polyurethane, polyamides, starch and derivatives thereof, cellulose and derivative thereof, polysaccharides, proteins, polyacrylonitrile, polyethylene imine, acrylate based polymers, and mixtures thereof. A wetness sensitive polymer may interact with wetness, e.g. a fluid, moisture or humidity, through absorption or adsorption. Alternatively, the polymer may be a non-wetness sensitive polymer selected from the group consisting of polyethylene, polypropylene and polystyrene. A non-wetness sensitive polymer may not interact with wetness.

The polymer may, for example, be fluidized by dissolving the polymer in a solvent. The solvent is then selected from the group of solvents consisting of water, alcohols, hydrocarbons, ethers, ketones and chlorinated hydrocarbons. The specific solvent that is suitable for dissolution of a specific polymer depends on the inherent properties of the polymer. Selection of a suitable solvent for a specific polymer should be apparent for a person skilled in the art. The concentration of the polymer in a solvent should be adjusted in order to minimize the efforts in the subsequent method steps. Alternatively, the polymer may be fluidized by melting the polymer.

Following the step of fluidizing the polymer, one side of the ribbon 2, i.e. the film 1 of a magnetoelastic material, is in the method according to the invention coated with the fluidized polymer. After the step of fluidizing, i.e. before the coating, the polymer molecules of the polymer are in a thermodynamically favourable entangled state. When polymer molecules of the polymer are in a thermodynamically favourable entangled state, the polymer molecules of the polymer are more or less entangled individually and/or more or less entangled with each other, i.e. they are not straight. However, according to the invention the coating is performed such that a majority of the polymer molecules applied to the ribbon 2 are at least essentially straightened in the transverse direction of the ribbon 2, i.e. in a first direction of the ribbon 2, during the coating. The expression that "polymer molecules are at least essentially straightened" is herein intended to mean that the polymer molecules are at least essentially straightened/aligned/linearized from their entangled state to an at least essentially straightened/aligned/linearized state. The polymer molecules may thereby be only essentially straightened/aligned/linearized or completely straightened/aligned/linearized. When the polymer molecules are at least essentially straightened they are transferred from the above mentioned thermodynamically favourable entangled state to a thermodynamically unfavourable straightened state, i.e. they are transferred form a disordered state to an ordered state. This will be further described below.

Thus, in the step of coating in the method according to the invention, a majority of the applied polymer molecules are at least essentially straightened in the transverse direction of the ribbon 2 at the same time as they are applied to the ribbon 2. In order to achieve that a majority of the applied polymer molecules are at least essentially straightened in the transverse direction of the ribbon 2 at the same time as they are applied to the ribbon 2, the coating is preferably performed in the transverse direction of the ribbon 2. For example, the coating may be performed by pouring the fluidized polymer into a doctor blade and applying the fluidized polymer to the ribbon 2 by means of the doctor blade. In order to at least essentially straighten the majority of the polymer molecules in the transverse direction of the ribbon 2 at the same time as they are applied to the ribbon 2, the doctor blade is drawn over the ribbon 2 in a transverse direction of the ribbon 2. Suitable gap for the doctor blade and speed with which the doctor blade is drawn are chosen so that the desired effect is achieved.

The polymer molecules that are at least essentially straightened in the step of coating strive for reverting from the thermodynamically unfavourable straightened state to a thermodynamically more favourable state, i.e. to a thermodynamically favourable unstraight state. However, after the step of coating, the polymer coated on the ribbon 2 is immediately solidified according to the invention such that a majority of those polymer molecules that were at least essentially straightened during the coating remain at least essentially straightened in the transverse direction of the ribbon 2 after the solidification. The term "immediately" is in this context used to denote that the solidification is performed immediately or directly after the coating, i.e. before there is time for an essential amount of the straightened polymer molecules to be released from their at least essentially straightened state achieved during the coating. When there is not time for an essential amount of the straightened polymer molecules to be released from their at least essentially straightened state, a majority of the polymer molecules that were at least essentially straightened during the coating will be solidified in the at least essentially straightened state. A solidified polymer layer with a majority of the solidified polymer molecules at least essentially straightened in the transverse direction of the ribbon 2 is thus formed during the solidification. The solidification is preferably performed within ten minutes, such as within five minutes, within one minute, within ten seconds or within five seconds. The resulting solidified polymer layer has a predetermined thickness. The thickness of the solidified polymer layer is about 0.005-500 μm, such as 0.005-100 μm, 2.5-50 μm or 0.005-50 μm.

Furthermore, the polymer is bound to the film 1 during the solidification such that a solidified polymer layer bound to the film 1 is formed. Optionally, the binding of the polymer to the film 1 may be promoted through etching with 1M sulphuric acid.

If the polymer is fluidized in the method according to the invention by dissolving the polymer in a solvent, the step of solidifying the polymer coated on the ribbon 2 comprises solidifying the polymer by rapid evaporation of the solvent. The evaporation must then be performed such that solidification of the polymer molecules is achieved immediately after the step of coating according to the above definition. Thereby, the temperature and the time for the evaporation are respectively selected according to the invention such that an evaporation that is as rapid as possible is achieved, but such that the polymer molecules are not essentially negatively affected. Thus, the temperature and the time for the evaporation are respectively selected based on the inherent properties of the polymer and solvent used.

If the polymer is fluidized in the method according to the invention by melting the polymer, the step of solidifying the polymer coated on the ribbon 2 comprises solidifying the polymer by rapid cooling. The cooling must then be performed such that solidification of the polymer molecules is achieved immediately after the step of coating according to the above definition. Thereby, the temperature and the time for the cooling are respectively selected according to the invention such that a cooling that is as rapid as possible is achieved, but such that the polymer molecules are not essentially negatively affected. Thus, the temperature and the time for the cooling are respectively selected based on the inherent properties of the polymer used.

Following the step of solidifying the polymer coated on the ribbon 2, a majority of the polymer molecules remaining at least essentially straightened in the transverse direction of the ribbon 2 after the solidification are released from the at least essentially straightened state. Released polymer molecules are then transferred from the thermodynamically unfavourable straightened state to a thermodynamically more favourable state. More specifically, the amorphous part(s) of the polymer molecules revert(s) during the release to a more entangled state, whereby the complete molecule is transferred to a thermodynamically favourable unstraight state. When solidified polymer molecules that are at least essentially straightened in the transverse direction of the ribbon 2 revert to an unstraight state, they contract in the transverse direction of the ribbon 2. Since the solidified polymer molecules are bound to the ribbon 2 they exert a transversally bending force on the ribbon 2 due to the contraction. Thereby, the ribbon 2 is curved in the transverse direction such that the ribbon 2 is provided with a curvature in the transverse direction, i.e. a transverse curvature. The transverse curvature will counteract any curvature of the film in a direction transverse to the transverse direction, i.e. in the longitudinal direction. As described above, a transverse curvature counteracts any longitudinal curvature or tendency to curve in the longitudinal direction and enhances the longitudinal bending stiffness of a ribbon consisting of a film of magnetoelastic material.

The release of solidified polymer molecules from the thermodynamically unfavourable straightened state, i.e. the transfer of the amorphous part(s) of the polymer molecules to a more entangled state, will occur spontaneously over time since polymer molecules that are in a thermodynamically unfavourable state strive for reverting to a more thermodynamically favourable state. Thus, the ribbon 2 will be curved in the transverse direction over time. However, the release of polymer molecules may be accelerated by supplying energy to the polymer and/or by adding a softener to the polymer. If the polymer is a wetness sensitive polymer, the release of polymer molecules from the thermodynamically unfavourable straightened state may be accelerated by humidifying the polymer or by heating the polymer or by treating the polymer with ultrasound or by a combination thereof. The term "humidify the polymer" is herein intended to mean to expose the polymer to an atmospheric humidity or to add a solvent to the polymer. The solvent will then act as a softener, i.e. it acts as an agent increasing the mobility of the amorphous part(s) of the polymer molecule(s). For example, the release of polymer molecules of a wetness sensitive polymer may be performed by exposing the polymer to an atmospheric humidity of 100%.

If the polymer is a non-wetness sensitive polymer, the release of polymer molecules from the thermodynamically unfavourable straightened state may be accelerated by heating the polymer or treating the polymer with ultrasound or by adding a solvent to the polymer or by a combination thereof

Figure 2a shows schematically a polymer molecule 9 of an amorphous polymer after the different steps of the method according to the invention when the method comprises a step of fluidizing. In an initial step denoted 10a the polymer molecule 9 is fluidized, i.e. melted or dissolved in a solvent. After the step 10a of fluidizing, the polymer molecule 9 is in a thermodynamically favourable entangled state, i.e. it is entangled. However, even if not shown the polymer molecule 9 may then also be entangled with other polymer molecules.

In a subsequent coating step 10b the fluidized polymer molecule 9 is coated on a film of a magnetoelastic material. At the same time as the polymer molecule 9 is coated on the film it is at lest essentially straightened/aligned/linearized in a first direction of the film. When the polymer molecule 9 is straightened during the step of coating, the amorphous polymer molecule 9 is at least partially disentangled. Thus, the polymer molecule 9 is then transferred to a more ordered state, whereby the entropy is decreased and Gibb's free energy is increased. The result achieved by the step of coating is, thus, a polymer molecule 9 that is at least essentially straightened/aligned/linearized in the first direction of the film.

Then the at least essentially straightened polymer molecule 9 is solidified in a solidification step 10c. The solidification of the polymer molecule 9 is performed immediately after the step of coating such that the polymer molecule 9 is solidified in the thermodynamically unfavourable straightened state. Thus, after the solidification the polymer molecule 9 is still in an ordered state, which is thermodynamically unfavourable. During the solidification the polymer molecule is also bound to the film. Since the polymer molecule 9 after the solidification is in a thermodynamically unfavourable straightened state it strives for reverting to a thermodynamically more favourable state. In a subsequent releasing step 1Od the polymer molecule 9 is released from the straightened state to a more entangled state, i.e. an unstraight state. The release will occur spontaneously over time or may be accelerated by supplying energy and/or by adding a softener. When the polymer molecule 9 reverts to an entangled state, it reverts to a more disordered state, whereby the entropy is increased and Gibb's free energy is decreased. Furthermore, when the solidified polymer molecule 9 is transferred from being straightened in a first direction of the film to an entangled state, it contracts in the first direction of the film. Since the solidified polymer molecule 9 is bound to the film, it exerts then a bending force on the film.

Figure 2b shows schematically a polymer molecule 11 of a partly crystalline polymer after a step of fluidizing 12a, a step of solidifying 12c, and a step of releasing 12d of the method according to the invention. After the step of fluidizing 12a, the polymer molecule 11 is in a thermodynamically favourable entangled state, i.e. it is entangled. However, even if not shown the polymer molecule 11 may then also be entangled with other polymer molecules.

In a subsequent coating step 12b the fluidized polymer molecule 11 is coated on a film of a magnetoelastic material. At the same time as the polymer molecule 11 is coated on the film it is at lest essentially straightened/aligned/linearized in a first direction of the film. When the polymer molecule 11 is straightened during the step of coating, the polymer molecule 11 is at least partially disentangled. The polymer molecule 11 is during the coating transferred to a more ordered state, whereby the entropy is decreased and Gibb's free energy is increased. The polymer molecule 11 is not shown after the step of coating 12b.

After the step of coating 12b the at least essentially straightened polymer molecule 11 is solidified in a solidification step 12c. The solidification of the polymer molecule 11 is performed immediately after the step of coating 12b such that the polymer molecule 11 remain at least essentially straightened after the solidification. After the solidification the amorphous parts of the polymer molecule 11 are still in a disentangled state, whereas the crystalline parts of the polymer molecule 11 may be in a crystalline state. However, the complete polymer molecule 11 is still essentially straightened. Thus, after the solidification the polymer molecule 11 is still in an ordered state, which is thermodynamically unfavourable. During the solidification the polymer molecule is also bound to the film.

In a subsequent releasing step 12d the polymer molecule 11 is released from the straightened state to an unstraight state, i.e. the amorphous parts of the polymer molecule 11 revert to a more entangled state and the complete molecule is thereby transferred to an unstraight state. The release will occur spontaneously over time or may be accelerated by supplying energy and/or by adding a softener. When the polymer molecule 11 is transferred to an unstraight state, it is transferred to a more disordered state, whereby the entropy is increased and Gibb's free energy is decreased. Furthermore, when the solidified polymer molecule 11 is transferred from being straightened in a first direction of the film to an unstraight state, it contracts in the first direction of the film. Since the solidified polymer molecule 11 is bound to the film, it exerts then a bending force on the film.

For example, when the method according to the invention is applied on the ribbon 2, a curvature in the transverse direction may be achieved whereby the longitudinal side edges of the ribbon 2 are 0.1 -4 mm, such as 0.1 - 1 mm, above a horizontal plane when the ribbon 2 is positioned on the horizontal plane.

Even if the method according to the invention has been described when applied to the ribbon 2 of a film 1 of a magnetoelastic material shown in figure 1a, the method according to the invention may be applied to a film of a magnetoelastic material having any other shape than the shape of a ribbon. For example, the method according to the invention may be applied to the strip 4 shown in figure 1b. Furthermore, even if the method according to the invention has been described for providing a film of a magnetoelastic material with a transverse curvature, the method according to the invention may also be applied for providing a film of a magnetoelastic material with a curvature in any desired direction. The step of coating in the method according to the invention is then performed such that a majority of the applied polymer molecules are at least essentially straightened in that direction in which a curvature is desired. For example, if a curvature is desired in a longitudinal direction, the step of coating is performed such that a majority of the applied polymer molecules are at least essentially straightened in the longitudinal direction. The method according to the invention may also be applied on a film of a magnetoelastic material that is essentially plane.

Furthermore, the method according to the invention may also optionally comprise a further step of adding a second polymer to the solidified polymer layer, which second polymer is different from the polymer of the polymer layer. The second polymer may be added to the solidified polymer layer immediately after the solidification step or after the step of releasing. For example, if the polymer of the solidified polymer layer is a non-wetness sensitive polymer selected from the above mentioned group of non-wetness sensitive polymers, a wetness sensitive polymer selected from the above mentioned group of wetness sensitive polymers may be added to, or coated on, the solidified polymer layer. Then the non-wetness sensitive polymer layer is utilized for curving the film 1 and the wetness sensitive polymer, i.e. the second polymer, may be utilized for detection of wetness.

In an alternative, the method according to the invention comprises a further step of adding at least one detector molecule to the solidified polymer layer, which detector molecule is adapted to detect at least one target biological and/or chemical analyte. The detector molecule may be added to the solidified polymer layer immediately after the solidification step or after the step of releasing. For example, if the polymer of the solidified polymer layer is a non-wetness sensitive polymer selected from the above mentioned group of non-wetness sensitive polymers, at least one detector molecule adapted to detect at least one target biological and/or chemical analyte may be added to, or coated on, the solidified polymer layer. Then the non-wetness sensitive polymer layer is utilized for curving the film 1 and the detector molecule may be utilized for detection of biological and/or chemical analytes.

The detector molecule may in one embodiment be adapted to detect a biological or chemical analyte selected from the group consisting of an enzyme or a sequence of enzymes; an antibody; a nucleic acid, such as DNA or RNA; a protein, such as a soluble protein or a membrane protein; a peptide, such as an oligopeptide or a polypeptide; an organelle; parts of a natural or synthetic cell membrane or capside, such as a bacterial or a mammalian cell membrane, or a virus capside; an intact or partial viable or nonviable bacterial, plant or animal cell; a piece of plant or mammalian tissues or any other biologically derived molecule; a lipid, a carbohydrate; a lectin, and mixtures thereof.

In another embodiment the detector molecule may be adapted to detect a biological or chemical analyte selected from the group consisting of pathogenic bacteria; non-pathogenic bacteria, e.g. colonic bacteria; viruses; parasites; bacterial toxins; fungi; enzymes; proteins; peptides; mammalian blood cells, such as human white or red blood cells; hormones; mammalian, including human, blood components, such as blood glucose; urine and its components such as glucose, ketones, urobilinogen, and bilirubin; and mixtures thereof.

The bacteria that the detector molecule may be adapted to detect, pathogenic or not, is selected from the group consisting of Escherichia coli, Salmonela typhi, Salmonella paratyphi, Salmonella enteriditid, Salmonella thyphimurium, Salmonella heidelberg, Staphylococcus aureus, Shigella sonnei, Shigella flexneri, Shigella boydii, Shigella dysenteriae, Vibrio cholerae, Mycobacterium tuberculosis, Yersina enterocolitica, Aeromonas hydrophila, Plesmonas shigelloides,

Campylobacter jejuni, Campylobacter coli, Bacteroides fragilis, Clostridia septicum, Clostridia perfringens, Clostridia botulinum, Clostridia difficile, and mixtures thereof . In still another embodiment the detector molecule is adapted to detect a chemical compound or chemical analyte such as health markers or nutritional markers. Nutritional markers include markers for e.g. metabolic efficiency, nutrient deficiencies, nutrient absorption or malabsorption, food and drink intake, food allergies (e.g. to peanuts), food intolerance (e.g. lactose or gluten intolerance), colonic bacteria ecology (e.g. beneficial bacterias such as bifidobacteria and lactobacillus), and total energy balance. Health markers may include chemical analytes such as heavy metals (e.g. lead, mercury, etc.), radioactive substances (e.g. caesium, strontium, uranium, etc.), fats, enzymes, endogenous secretions, protein matter (e.g. blood casts), mucous, and microorganisms, as described above, that may be related to various health issues such as infection, diarrhoea, gastrointestinal distress of disease, or poisoning. Heavy metals, especially in certain developing countries and in older and/or less affluent areas of developed countries, are serious health risks. For example, lead and mercury poisoning may occur upon the ingestion of these heavy metals from environmental sources (e.g. from lead paint, unregulated heavy industries, etc.) and can be fatal. More commonly, low-level poisoning by these and other heavy metals results in retarded intellectual and/or physical development, especially in children that may occur over a long time and have lasting effects on the individual. Other examples of nutritional markers include calcium, vitamins (e.g. thiamine, riboflavin, niacin, biotin, folic acid, pantothenic acid, absorbic acid, vitamin E, etc.), electrolytes (e.g. sodium, potassium, chlorine, bicarbonate, etc.), fats, fatty acids (long and short chain), soaps (e.g. calcium palmitate), amino acids, enzymes (e.g. lactose, amylase, lipase, trypsin, etc.), bile acids and salts thereof, steroids, and carbohydrates. For example, calcium malabsorption is important in that it may lead to a long-term bone-mass deficiency.

Suitable detector molecules may include any biorecognition element and are further exemplified by carbohydrates, antibodies or parts thereof, synthetic antibodies or parts thereof, enzymes, lectins, DNA (deoxyribonucleic acid), RNA (ribonucleic acid), cells and/or cell membranes or any other molecule with a binding capacity for a defined bioanalyte or chemical analyte.

For example, the detector molecules may be wholly or partially physiosorbed onto the solidified polymer layer of the first polymer on the curved film of a magnetoelastic material using e.g. a cationic polymer such as polyethylene imine (PEI, from e.g. Sigma-Aldrich), a colloidal suspension such as polybead polystyrene (PS) microspheres (from e.g. Scientific Polymer Products), or a hydrophobic polymer such as polystyrene (from e.g. Scientific Polymer Products).

It is obvious to a person skilled in the art that any suitable means of applying the detector molecule than physiosorption onto the solidified polymer layer constituted by the first polymer on the curved film of a magnetoelastic material will be appropriate for other applications. For example, it may be desirable to chemically bind the detector molecule, directly or indirectly, to the solidified polymer layer constituted by the first polymer using any one of a variety of common crosslinker molecules including, but not limited to, glutaraldehyde, N-hydroxysuccinimide, carbodidimides.

Optionally, the method according to the invention may also comprise a further step of cutting the film of a magnetoelastic material into strips of a predetermined size after the solidification step, or after the step of adding a second polymer (if any), or after the step of adding at least one detector molecule adapted to detect at least one target biological and/or chemical analyte (if any) or after the step of releasing. For example, if a film 1 of a magnetoelastic material, to which the method according to the invention has been applied, has the shape of a ribbon, the ribbon may be cut into strips of a predetermined size.

When any of the above described embodiments of the method according to the invention is utilized, a sensor product may be obtained. Figure 3 shows a schematic perspective view of one embodiment of a sensor 5 according to the invention. The sensor 5 according to the invention may be obtained by utilizing the method according to the invention or any other suitable method yielding the same result. For example, the sensor 5 shown in figure 3 may be obtained by applying the method according to the invention to the ribbon 2 shown in figure 1a or to the strip 4 shown in figure 1b. A strip 4 having a longitudinal curvature is schematically shown in figure 3 together with the sensor 5 according to the invention for the purpose of comparing a strip 4 having a longitudinal curvature with the strip 4 constituting the sensor 5, which has a transverse curvature.

The sensor 5 according to the invention comprises a film 1 of a magnetoelastic material. The magnetoelastic material may be any material with a non-zero magnetostriction and a high magnetoelastic coupling, such as iron-nickel alloys, rare earth metals, ferrites, e.g. spinel type ferrites (Fe3O4, MnFe2θ4), silicon-iron alloys, many other different alloys and mixtures thereof. Furthermore, the magnetoelastic material may be any material selected from the group of soft magnetoelastic materials, alloys and mixtures thereof as well as amorphous magnetoelastic materials, alloys and mixtures thereof. Examples of amorphous magnetoelastic alloys are metglases such as Fe4ONi38Mo4B18, e.g. Metglas 2826MB™ (Honeywell Amorphous Metals, Pittsburg, PA, USA), (FeCo)80B20, (CoNi)80B20 and (FeNi)80B20. The thickness of the film 1 of a magnetoelastic material is typically about 0.01-1000 μm, such as 0.01-200 μm, 5-100 μm or 0.01- 100 μm.

The film 1 of a magnetoelastic material is in the sensor 5 according to the invention coated with a polymer layer 6 on one side. In the embodiment shown in figure 3, the film 1 of a magnetoelastic material has the shape of a strip 4 and the polymer layer 6 causes the film 1 to curve in a transverse direction, i.e. a first direction. Thus, the film 1 of a magnetoelastic material reveals a transverse curvature, i.e. it is curved in the transverse direction. The combination of the film 1 and the polymer layer 6 reveals thereby also a transverse curvature. The transverse curvature counteracts any longitudinal curvature or tendency to curve in the longitudinal direction and enhances the longitudinal bending stiffness of the strip 4. The thickness of the polymer layer 6 is about 0.005-500 μm, such as 0.005-100 μm, 2.5-50 μm, 0.005-50 μm or 34 μm.

The polymer of the polymer layer 6 may, for example, be a wetness sensitive polymer selected from the group consisting of linear and hydrophilic polymers or physically cross-linked swellable polymer gels based on polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide and co-polymers thereof, polyurethane, polyamides, starch and derivatives thereof, cellulose and derivative thereof, polysaccharides, proteins, polyacrylonitrile, acrylate based polymers, and mixtures thereof. The wetness sensitive polymer may interact with wetness and in such cases change the mass of the sensor 5. For example, the wetness sensitive polymer may interact with wetness through absorption or adsorption. The change in mass of the sensor 5 due to the interaction with wetness will either increase or decrease the resonant frequency, e.g. the magnetoacoustic resonant frequency. This will be further described below. If the polymer of the polymer layer 6 in a sensor 5 according to the invention is a wetness sensitive polymer selected from the above mentioned group, the sensor 5 may be utilized as a wetness sensor, i.e. a sensor detecting wetness such as a liquid, humidity or moisture. For example, the sensor 5 may then be utilized for detecting body discharges such as body fluids, body waste or body exudates, i.e. urine, faeces, blood, menstruation blood, fluid matters from wounds and sores, rinsing fluid and saliva.

Furthermore, the polymer of the polymer layer 6 may in variants be a non-wetness sensitive polymer selected from the group consisting of polyethylene, polypropylene and polystyrene. The sensor 5 may then, for example, be utilized as an anti-theft device in the art of electronic article surveillance (EAS).

Figure 4 shows a schematic perspective view of one variant of the sensor 5 shown in figure 3. The sensor 5 shown in figure 4 differs from the sensor 5 shown in figure 3 in that a second polymer 7 is coated on the polymer layer 6. The second polymer 7 is different from the polymer of the polymer layer 6. For example, the polymer of the polymer layer 6 of the sensor 5 shown in figure 4 may be a non-wetness sensitive polymer selected from the above mentioned group of non-wetness sensitive polymers and the second polymer 7 may be a wetness sensitive polymer selected form the above mentioned group of wetness sensitive polymers. Then the non-wetness sensitive polymer causes the film 1 to curve in the transverse direction and the wetness sensitive polymer, i.e. the second polymer 7, may, for example, be utilized for detection of wetness. Thus, the sensor 5 may then be utilized as a wetness sensor for detecting body discharges such as body fluids, body waste or body exudates, i.e. urine, faeces, blood, menstruation blood, fluid matters from wounds and sores, rinsing fluid and saliva.

A different variant (not shown) of the sensor 5 shown in figure 4 differs in that at least one detector molecule adapted to detect at least one target biological and/or chemical analyte is coated on the polymer layer 6 instead of the second polymer 7. Thus, in the variant of the sensor 5 shown in figure 4, the polymer of the polymer layer 6 is a non-wetness sensitive polymer selected from the above mentioned group of non-wetness sensitive polymers and the polymer layer 6 is coated with at least one detector molecule adapted to detect at least one target biological and/or chemical analyte. The detector molecule may be any of the above exemplified detector molecules adapted to detect any of the above mentioned biological and/or chemical analytes. In this variant the non- wetness sensitive polymer causes the film 1 to curve in the transverse direction and the at least one detector molecule may be utilized for detection of biological and/or chemical analytes. Thus, the variant of the sensor 5 shown in figure 4 may, for example, be utilized as a sensor for detecting any of the above mentioned biological and/or chemical analytes in body discharges such as body fluids, body waste or body exudates, i.e. urine, faeces, blood, menstruation blood, fluid matters from wounds and sores, rinsing fluid and saliva.

In the embodiments shown in figures 3 and 4 and in the mentioned variant of the embodiment shown in figure 4, the film 1 may, for example, present a curvature in the transverse direction whereby the longitudinal side edges 8 of the strip 1 are 0.1 - 4 mm, such as 0.1 - 1 mm, above a horizontal plane when the strip 1 is positioned on the horizontal plane.

In the embodiments of the sensor 5 according to the invention shown in figures 3 and 4 and the mentioned variant of the embodiment shown in figure 4, the film 1 of a magnetoelastic material has the shape of a strip 4. However, in variants of the embodiments shown in figures 3 and 4 and the mentioned variant of the embodiment shown in figure 4, the film 1 of a magnetoelastic material may have any other suitable shape, such as the shape of a ribbon. Furthermore, in variants of all mentioned embodiments the polymer layer 6 causes the film 1 to curve in another direction than in the transverse direction. The film 1 , and thus the combination of the film 1 and the polymer layer 6, may then reveal a curvature in any desired direction. The curvature in the desired direction will then counteract any curvature in a direction transverse to the desired direction.

When a wetness sensitive polymer comprised in a sensor 5 according to the invention interacts with wetness through, for example, absorption or adsorption, the mass of the sensor 5 changes resulting in a change of the magnetoacoustic resonant frequency of the sensor 5. The change of the magnetoacoustic resonant frequency is detectable and correlates to the amount of wetness that the wetness sensitive polymer has interacted with, i.e. it correlates, for example, to the amount of wetness absorbed or adsorbed by the wetness sensitive polymer. Correspondingly, when a detector molecule comprised in a sensor 5 according to the invention and adapted to detect at least one biological and/or chemical analyte detects such a biological and/or chemical analyte, the mass of the sensor 5 changes resulting in a change of the magnetoacoustic resonant frequency of the sensor 5, which is detectable.

As above described, a magnetoelastic material of a magnetoelastic sensor stores magnetic energy in a magnetoelastic mode when excited by an external magnetic field. When the magnetic field is switched off, the magnetoelastic material shows damped oscillation with a specific frequency denoted as the magnetoacoustic resonant frequency. These oscillations give rise to a magnetic flux that varies in time, which can be remotely detected by a pick-up coil. Thus, the magnetoacoustic resonant frequency is detectable and thereby also a change of the magnetoacoustic resonant frequency. If a pulsed magnetic field is applied to a magnetoelastic material, the magnetoacoustic resonant frequency may be detected between the magnetic pulses. The magnetoacoustic resonant frequency for e.g. a ribbon of a magnetoelastic material is inversely proportional to the length of the ribbon.

For example, a pulsed magnetic field or a pulsed sine wave magnetic field may be applied to the film 1 of a magnetoelastic material of a sensor 5 according to the invention in order to detect the magnetoacoustic resonant frequency of the sensor 5. As mentioned above, the magnetoacoustic resonant frequency may then be detected between the pulses. The amplitude of the pulsed magnetic field must be large enough to magnetize the magnetoelastic material to a certain amount in order to achieve a sufficiently large change in material dimensions. The dimensions of the magnetoelastic material change due to the effect of magnetostriction. The specific magnetic field utilized must be optimised for each magnetoelastic material.

The pulse frequencies used may, for example, be about 10-1000 Hz, such as about 50-700 Hz. The duty cycles of the pulses may, for example, be about 1-90%, such as about 10-50%. If the magnetic field is a pulsed sine wave field, the sine waves may, for example, be about 50-80 kHz. If METGLAS® material from Honeywell is used as the magnetoelastic material, a magnetic field amplitude of the pulsing field may be about 0.05-0.1 mT.

An excitation coil may, for example, be utilized for applying a magnetic field to the magnetoelastic material of a sensor 5 according to the invention. A pick-up coil may, for example, be utilized for collecting the produced signal, i.e. the magnetoacoustic effect. The excitation coil and the pick-up coil may be located in a hand held unit. Furthermore, the excitation coil and the pick-up coil may be located in the same hand held unit or in different hand held units. In an alternative, the same coil may be utilized as both excitation coil and pick-up coil, i.e. both for excitation and detection. WO 2004/021944 is herein incorporated by reference in its entirety for further details regarding the excitation of the magnetoelastic material, detection of the magnetoacoustic resonant frequency as well as changes thereof and devices for detection of the magnetoacoustic resonant frequency.

One way of further enhancing the magnetostrictive effect of the magnetoelastic material in a sensor 5 according to the invention is to include a magnetic bias field. For example, a magnetic bias field may be generated by a permanent magnetic film or a permanent magnet positioned in proximity to the sensor 5. When METGLAS® material from Honeywell is used as the magnetoelastic material, a magnetic bias field of about 0.5-1 mT may be utilized.

The sensor 5 according to the invention may be positioned in contact with or in spaced relation with an absorbent material of an absorbent structure of an absorbent article. For example, the sensor 5 according to the invention may be comprised in an absorbent structure in an absorbent article, such as a diaper, a diaper of pant type, an incontinence garment, a sanitary napkin, a wipe, a towel, a tissue, a bed protector, a wound or sore dressing, a tampon-like product, or similar product. In normal use, an absorbent structure in such an absorbent article serves to absorb, retain and isolate body wastes or body exudates, e.g. urine, faeces, blood, menstruation blood, fluid matter from wounds and sores, rinsing fluid and saliva. When a sensor 5 according to the invention is comprised in such an absorbent structure it will enable easy detection of wetness or a biological and/or chemical analyte, i.e. it will enable easy detection of that an event such as urination or defecation has occurred. The detection is performed by detecting a change of the magnetoacoustic resonant frequency of the sensor 5. Thereby the status of the absorbent structure and, thus, of the absorbent article may be easily monitored by a user, parent, care taker, etc.

For example, the sensor 5 according to the invention may replace the sensing device disclosed in WO 2004/021944 and thus be comprised in the absorbent structures and absorbent articles disclosed in WO 2004/021944. Thus, a sensor 5 according to the invention may be positioned in different positions in an absorbent structure in accordance with the positions of the sensing device in WO 2004/021944 and an absorbent article may also comprise more than one sensor 5 according to the invention. For example, an absorbent article may comprise 1-10 sensors 5.

One non-limiting example of an absorbent article 13 comprising the sensor 5 according to the invention is schematically shown in figure 5. Optionally, the sensor 5 according to the invention may be packaged or encapsulated accurately, not to be exposed to, e.g. mechanical pressure that may affect the resonant frequency or the magnetoacoustic resonant frequency. Then the sensor 5 may be packaged in a way that the wetness or at least one biological and/or chemical analyte can penetrate through the package into the sensor 5, e.g. via pores, slots or holes, in the package material. Suitable encapsulations include encapsulations in the form of tags such as tags from, e.g. Sensormatic, or a similar product. The encapsulations are designed or chosen in each case by a person skilled in the art to fit a specific embodiment.

Furthermore, if the film 1 of a magnetoelastic material of a sensor 5 according to the invention is coated only with a non-wetness sensitive polymer, i.e. if the sensor 5 does not comprise any wetness sensitive polymer or detector molecule, the sensor 5 may in one embodiment be encapsulated in an encapsulation together with an absorbing material, e.g. superabsorbent material (SAP). The encapsulation is then designed to allow liquid to penetrate into the encapsulation and the SAP will exert a mechanical pressure on the sensor 5 when absorbing liquid, moisture or humidity. The mechanical pressure correlates to the amount of e.g. liquid absorbed and will completely or partially dampen the oscillations of the sensor 5. A decrease in the magnetoacoustic effect will be detected when the oscillations are damped, whereby detection of liquid, moisture or humidity may be determined. WO 2004/021944 is herein incorporated by reference in its entirety for further details regarding the encapsulation in this embodiment and how this embodiment works.

Alternatively, if the film 1 of a magnetoelastic material of a sensor 5 according to the invention is coated only with a non-wetness sensitive polymer, i.e. if the sensor 5 does not comprise any wetness sensitive polymer or detector molecule, the sensor 5 may in another embodiment be comprised in an absorbent structure together with a permanent magnet. When the absorbent material of the absorbent structure swells due to uptake of a liquid, humidity or moisture, the absorbent material pushes the permanent magnet closer or away from the sensor 5. This will change the DC magnetic field on the sensor 5, whereby the magnetoacoustic oscillations are affected. WO 2004/021944 is herein incorporated by reference in its entirety for further details regarding the encapsulation in this embodiment and how this embodiment works.

Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices, method steps and products illustrated may be made by those skilled in the art. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

1. A method for providing a film (1) of a magnetoelastic material with a curvature, characterized in, that the method comprises the steps of:
- coating one side of said film (1) with an amorphous or partly crystalline polymer, whereby said coating is performed such that a majority of the applied polymer molecules are at least essentially straightened in a first direction of said film (1), whereby said majority of the applied polymer molecules are transferred from a thermodynamically favourable entangled state to a thermodynamically unfavourable straightened state; - solidifying said polymer coated on said film (1) immediately after said coating such that a majority of the at least essentially straightened polymer molecules remain at least essentially straightened in said first direction of said film (1) after the solidification, whereby a solidified polymer layer (6) of a predetermined thickness is formed during the solidification, which solidified polymer layer (6) is bound to said film (1), and
- releasing a majority of the polymer molecules remaining at least essentially straightened in said first direction of said film (1) after said solidification, whereby released polymer molecules are transferred from said thermodynamically unfavourable straightened state to a thermodynamically favourable unstraight state, whereby said film (1) is curved in said first direction such that said film (1) is provided with a curvature in said first direction, which curvature will counteract any curvature of said film (1) in a direction transverse to said first direction.
2. The method according to claim 1 , characterized in, that the film (1) is a ribbon (2) and that the first direction is the transverse direction of the ribbon (2).
3. The method according to claim 1 or 2, characterized in, that the method further comprises a step of fluidizing said amorphous or partly crystalline polymer before said step of coating.
4. The method according to claim 3, characterized in, that the step of fluidizing said polymer is performed by dissolving said polymer in a solvent.
5. The method according to claim 4, characterized in, that the solvent is selected from the group of solvents consisting of water, alcohols, hydrocarbons, ethers, ketones and chlorinated hydrocarbons.
6. The method according to claim 4 or 5, characterized in, that the step of solidifying said polymer is performed by rapid evaporation of the solvent.
7. The method according to claim 6, characterized in, that the temperature and the time for the evaporation are respectively selected based on the inherent properties of the polymer and solvent used.
8. The method according to claim 3, characterized in, that the step of fluidizing said polymer is performed by melting said polymer.
9. The method according to claim 8, characterized in, that the step of solidifying said polymer is performed by rapid cooling.
10. The method according to claim 9, characterized in, that the temperature and the time for the cooling are respectively selected based on the inherent properties of the polymer used.
11. The method according to any of claims 3-10, characterized in, that the step of coating is performed by pouring the fluidized polymer into a doctor blade and applying the fluidized polymer to said film (1) by drawing the doctor blade over said film (1) in the first direction of said film (1) such that a majority of the applied polymer molecules are at least essentially straightened in the first direction of said film (1) at the same time as they are applied.
12. The method according to any of the preceding claims, characterized in, that the thickness of the film (1) of a magnetoelastic material is about 0.01-1000 μm.
13. The method according to any of the preceding claims, characterized in, that the thickness of the solidified polymer layer (6) is about 0.005-500 μm.
14. The method according to any of the preceding claims, characterized in, that said amorphous or partly crystalline polymer is a wetness sensitive polymer selected from the group consisting of linear and hydrophilic polymers or physically cross-linked swellable polymer gels based on polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide and copolymers thereof, polyurethane, polyamides, starch and derivatives thereof, cellulose and derivative thereof, polysaccharides, proteins, polyacrylonitrile, polyethylene imine, acrylate based polymers, and mixtures thereof.
15. The method according to claim 14, characterized in, that the release of polymer molecules in said releasing step is accelerated by humidifying said polymer or by heating said polymer or by treating said polymer with ultrasound or by a combination thereof.
16. The method according to claim 15, characterized in, that the release of polymer molecules in said releasing step is accelerated by humidifying said polymer, whereby the humidification of said polymer is performed by exposing said polymer to an atmospheric humidity of 100 %.
17. The method according to any of claims 1-13, characterized in, that said amorphous or partly crystalline polymer is a non-wetness sensitive polymer selected from the group consisting of polyethylene, polypropylene and polystyrene.
18. The method according to claim 17, characterized in, that the method further comprises a step of adding a second polymer (7) to the solidified polymer layer (6), whereby the second polymer (7) is a wetness sensitive polymer selected from the group consisting of linear and hydrophilic polymers or physically cross-linked swellable polymer gels based on polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide and co-polymers thereof, polyurethane, polyamides, starch and derivatives thereof, cellulose and derivative thereof, polysaccharides, proteins, polyacrylonitrile, polyethylene imine, acrylate based polymers, and mixtures thereof.
19. The method according to claim 17, characterized in, that the method further comprises a step of adding at least one detector molecule adapted to detect at least one target biological and/or chemical analyte to the solidified polymer layer (6).
20. The method according to any of claims 17-19, characterized in, that the release of polymer molecules in said releasing step is accelerated by heating said polymer or by treating said polymer with ultrasound or by adding a solvent to the polymer or by a combination thereof.
21. A method for producing a sensor (5), characterized in, that the method comprises the steps according to any of claims 1 to 20 and the further step of cutting said film (1) into pieces of a predetermined size.
22. A sensor product (5) obtained by means of a method according to any of claims 1 to 20.
23. A sensor (5) comprising a film (1) of a magnetoelastic material coated with a polymer layer (6) on one side, characterized in, that the polymer layer (6) causes said film (1) to curve in a first direction.
24. A sensor (5) according to claim 23, characterized in, that said film (1) is a strip (4) and said first direction is the transverse direction of said strip (4).
25. The sensor (5) according to claim 23 or 24, characterized in, that the thickness of the film (1) of a magnetoelastic material is about 0.01-1000 μm.
26. The sensor (5) according to any of claims 23-25, characterized in, that the thickness of the polymer layer (6) is about 0.005-500 μm.
27. The sensor (5) according to any of claims 23-26, characterized in, that the polymer of said polymer layer (6) is a wetness sensitive polymer selected from the group consisting of linear and hydrophilic polymers or physically cross-linked swellable polymer gels based on polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide and co-polymers thereof, polyurethane, polyamides, starch and derivatives thereof, cellulose and derivative thereof, polysaccharides, proteins, polyacrylonitrile, polyethylene imine, acrylate based polymers, and mixtures thereof.
28. The sensor (5) according to any of claims 23-26, characterized in, that the polymer of said polymer layer (6) is a non-wetness sensitive polymer selected from the group consisting of polyethylene, polypropylene and polystyrene.
29. The sensor (5) according to claim 28, characterized in, that a second polymer (7) is coated on said polymer layer (6), which second polymer (7) is a wetness sensitive polymer selected from the group consisting of linear and hydrophilic polymers or physically cross- linked swellable polymer gels based on polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide and co-polymers thereof, polyurethane, polyamides, starch and derivatives thereof, cellulose and derivative thereof, polysaccharides, proteins, polyacrylonitrile, polyethylene imine, acrylate based polymers, and mixtures thereof.
30. The sensor (5) according to claim 28, characterized in, that at least one detector molecule adapted to detect at least one target biological and/or chemical analyte is coated on said polymer layer (6).
31. An absorbent structure comprising at least one absorbent layer, characterized in, that it comprises the sensor (5) according to any of claims 22-30.
32. An absorbent article (13), such as a diaper, a diaper of pant type, an incontinence garment, a sanitary napkin, a wipe, a towel, a tissue, a bed protector, a wound or sore dressing, a tampon-like product, or similar product, characterized in, that it comprises the sensor (5) according to any of claims 22-30.
33. The absorbent article (13) according to claim 32, characterized in, that it comprises 1-10 sensors (5) according to any of claims 22-30.
34. A sensoring absorbent system comprising a hand held unit comprising an excitation coil generating a magnetic field to magnetize said magnetoelastic material and optionally a pick-up coil that detects the magnetoacoustic resonant frequency, characterized in, that the sensoring absorbent system further comprises the absorbent structure according to claim 31 , optionally being part of the absorbent articles (13) according to claim 32 or 33.
PCT/SE2005/002015 2005-12-21 2005-12-21 Method for providing a film of a magnetoelastic material with a curvature, sensor product obtained by the method and sensor WO2007073258A1 (en)

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EP2024739A1 (en) * 2006-06-08 2009-02-18 Sca Hygiene Products Ab Method for providing a piece of a film of a magnetoelastic material with an enhanced bending stiffness, product obtained by the method and sensor
CN101461957B (en) 2007-12-19 2012-12-05 天津大学 Organosilicon crosslinked polyvinyl alcohol film coating agent as well as preparation method and application
US8702967B2 (en) 2010-06-17 2014-04-22 Bayer Healthcare Llc Test strip with magneto-elastic-resonance sensor
US9341639B2 (en) 2013-07-26 2016-05-17 Industrial Technology Research Institute Apparatus for microfluid detection
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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2024739A1 (en) * 2006-06-08 2009-02-18 Sca Hygiene Products Ab Method for providing a piece of a film of a magnetoelastic material with an enhanced bending stiffness, product obtained by the method and sensor
EP2024739A4 (en) * 2006-06-08 2011-03-02 Sca Hygiene Prod Ab Method for providing a piece of a film of a magnetoelastic material with an enhanced bending stiffness, product obtained by the method and sensor
US8558052B2 (en) 2006-06-08 2013-10-15 Sca Hygiene Products Ab Method for providing a piece of a film of a magnetoelastic material with an enchanced bending stiffness, product obtained by the method and sensor
CN101461957B (en) 2007-12-19 2012-12-05 天津大学 Organosilicon crosslinked polyvinyl alcohol film coating agent as well as preparation method and application
US8702967B2 (en) 2010-06-17 2014-04-22 Bayer Healthcare Llc Test strip with magneto-elastic-resonance sensor
US9547005B2 (en) 2010-06-17 2017-01-17 Ascensia Diabetes Care Holdings Ag Test strip with magneto-elastic-resonance sensor
US9678034B2 (en) 2011-08-24 2017-06-13 Ascensia Diabetes Care Holdings Ag Analyte sensors and systems including retention tab and methods of manufacturing same
US9341639B2 (en) 2013-07-26 2016-05-17 Industrial Technology Research Institute Apparatus for microfluid detection

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