SE544313C2

SE544313C2 - Liquid detection rfid tag arrangement

Info

Publication number: SE544313C2
Application number: SE2050830A
Authority: SE
Inventors: Lauri Huhtasalo
Original assignee: Digital Tags Finland Oy
Priority date: 2020-07-02
Filing date: 2020-07-02
Publication date: 2022-04-05
Also published as: EP4176383A2; WO2022003613A2; SE2050830A1; WO2022003613A3

Abstract

A liquid and/or moisture detecting RFID tag arrangement (1) comprises a substrate (4, 4’), at least one antenna element (2) arranged on the substrate, and an RFID chip (3) connected to the antenna element(s). At least a part of the substrate forms a water degradable part (4), made of a water degradable material, arranged to dissolve or disintegrate when wetted by a liquid. When the water degradable part disintegrates or dissolves, the response signal from the RFID tag arrangement (1) changes, either to cease, or to be of different content or characteristics. The change in response signal can e.g. be accomplished by a main antenna (2) becoming totally or partly inoperative, by a secondary antenna (5) becoming fully or partly inoperative, or by breaking a detection loop (5’).

Description

LIQUID DETECTION RFID TAG ARRANGEMENT Technical ﬁeld of the invention The present invention is related to a radio frequency identification(RFID) tag arrangement with capability of detecting the presence of moistureand/or liquid. The invention further relates to a method for detecting presenceof moisture and/or liquid.

BackgroundThere are many situations and applications where there is a need to detect the presence of moisture and liquid, such as water.

For example, such detection can be of advantage in many differenttypes of absorbent articles, such as diapers, diapers of pant type,incontinence garments, sanitary napkins, tampon-like products, wound orsore dressings and bed protectors, known today for absorption, retention andisolation of body wastes, such as urine, faeces and blood. Frequent checkingof the status of the absorbent article is often a cumbersome, tedious andlabor intensive task, and may also disturb the user or wound the user'sdignity, whereas prolonged exposure to wetness is not only uncomfortable,but may also e.g. cause painful rashes, urinary tract infections, or aggravateor induce bed sores. lt would be a great benefit for all stakeholders if the needfor changing the diaper could be identified automatically and remotely.

To this end, it is known to use various types of sensors to detecturination or defecation in such products, after absorption onto or into theabsorbent article. Such a sensor may, for example, be based on detection ofwetness, a biological analyte and/or a chemical analyte. When such a sensordetects an event, such as urination or defecation, a detectable response isgenerated. By means of the response, the user, parent, caretaker, nursingpersonnel, etc. may determine that an event has occurred. Thus, sensors inabsorbent articles for detection of an event may be utilized to easily monitor ifan event has occurred, i.e. to easily register the body waste status in anabsorbent article. lt is also known to utilize an RFID tag including various types of Sensors, such as an inductor-capacitor resonator, for detection ofmoisture or liquid in an absorbent article.

However, there are also many other applications and situations wherethere is a need or desire to detect the occurrence of moisture or liquid in acertain location. ln particular, this would be the case where the location ishidden or difficult to see or get access to.

For example, there is often a need to detect presence of moisture orwater in buildings, to detect the occurrence of leakage and the like in thebuilding structure, such a roof leakage and plumbing leakage.

As another example, such detection would be of advantage to evaluatethe water-tightness of various products and structures. For example, carshave compartments which should be watertight after the assembly of the car.However, inspection of their water-tightness can be cumbersome andexpensive.

The presently used detector systems are unfortunately quitecomplicated and need much calibration to provide accurate detection results.The known solutions are also very expensive, resulting in a very limitedpractical use of such systems, despite the great need for detection in manyareas.

There is therefore still a need for an improved RFID tag arrangementfor detection of liquid and/or moisture, and which can provide adequate andreliable detection, and which can be produced to a relatively low cost.

SummaryIt is therefore an object of the present invention to provide a liquid and/or moisture detection RFID tag arrangement and a method for detectionof moisture and/or liquid with such an RFID tag arrangement, which alleviatesat least part of the above-discussed problems, and at least partially addressone or more of the above-mentioned needs.

This object is obtained by means of a liquid and/or moisture detectingRFID tag arrangement and a liquid and/or moisture detecting method inaccordance with the appended claims.

According to a first aspect of the present invention, there is provided aliquid and/or moisture detecting RFID tag arrangement comprising asubstrate, at least one antenna element arranged on said substrate, and anRFID chip connected to said antenna e|ement(s), wherein at least a part ofthe substrate forms a water degradable part, made of a water degradablematerial, arranged to dissolve or disintegrate when wetted by a liquid.

Hereby, a relatively simple RFID tag can be used to detect moistureand/or liquid. When the water degradable part is wetted, i.e. when it comesinto contact with moisture or a liquid, such as water or urine, it will start todisintegrate or dissolve, and will thereby affect the output signal from theRFID tag arrangement. Such an RFID tag arrangement can be produced to avery low cost, since it may use a standard RFID chip, a relatively simpleantenna, and a low-cost substrate. At the same time, the detection becomesvery accurate and reliable.

Compared to previously known solutions, the present RFID tag can beproduced to a cost which is less than at least 1/100 of the cost of suchpreviously known solutions, and most probably less than 1/1000 of this cost.This makes the new RFID tag arrangement useable for many products andapplications where it was previously not practically and economically feasibleto use liquid and/or moisture detection. Further, the low cost makes it possibleto use the RFID tag arrangement as a disposable, for single time use. ln addition, the new RFID tag arrangement may be essentially entirelybiodegradable, and consequently environmentally friendly. ln one line of embodiments, the antenna element is at least partlyarranged on said water degradable part of the substrate, wherein dissolvingor disintegration of the water degradable part makes the antenna elementinoperative. ln such embodiments, the whole substrate can be made of awater degradable material, and form said water degradable part, whichmakes production easier and even more cost-effective. ln such embodiments, the antenna will become inoperative as soon asthe water degradable part dissolves or disintegrates. Thus, a response signalfrom the RFID tag arrangement, e.g. containing only the ID of the RFID tag,can be used as an indication that no water or moisture is present, whereas a lack of response signal can be used as an indication that there is, or hasbeen, moisture and/or liquid present, and that the water degradable part hasbeen disintegrated or dissolved. Thus, the signal from the RFID tagarrangement will here change from a normal signal to no signal upon wetting. ln another embodiment, the RFID tag arrangement may comprise atleast two antenna elements connected to the RFID chip, wherein one of saidantenna elements is arranged on the water degradable part and one of theantenna elements is arranged on a non-water degradable part. The non-waterdegradable part may e.g. be of a different material, connected to the waterdegradable part. However, it may also be of the same water degradablematerial, but protected from becoming wet by a protective layer, or in otherways being arranged in such a way that it is not exposed to the liquid ormoisture. ln such embodiments, one of the antennas will become inoperativewhen the water degradable part dissolves/disintegrates, whereas the otherantenna will still be operative. To this end, the RFID reader may detect thatthere is no moisture/liquid when signals from both antennas are received, andthat there is moisture/liquid present when signals are received from only oneantenna. Thus, the signal from the RFID tag arrangement will here changefrom a normal signal to another signal upon wetting.

The two antennas may e.g. be connected to different ports/pads on theRFID chip, and consequently send out different signals. For example, theantenna which will still be operative after wetting may be used to send out theID of the RFID tag arrangement, whereas the antenna which will becomeinoperative during wetting may send out a signal that no wetting hasoccurred. When the signal indicative of that no wetting has occurred ceases,this may be interpreted by the reader that wetting has in fact occurred.

However, alternatively, the two antennas may be connected to thesame port, and be discernible by e.g. different polarizations or the like.

This solution, with two antennas, is somewhat more complex than thefirst discussed embodiments. On the other hand, this solution is more robustand reliable, since it can here by ensured that the RFID tag is still in operation, even after wetting, and that adequate contact between the RFIDtag and the reader has been established. ln yet another embodiment, the RFID tag arrangement may furthercomprise a detection loop connected to the RFID chip, the detection loopbeing at least partly arranged on said water degradable part. The detectionloop may e.g. be arranged as a conductive line leading between twoports/pads on the RFID chip. Prior to wetting, the detection loop will remainintact, and provide a connection between the two ports. The RFID chip mayuse this to determine that no wetting has occurred, and may include thisinformation in responses sent to the reader. As soon as the water degradablepart starts to dissolve/disintegrate, the detection loop will break, and there willno longer be any connection between the ports. This may then be interpretedby the RFID chip as an indication that wetting has occurred, and thisinformation may then be included in the information sent in response to theRFID reader.

Thus, the signal from the RFID tag arrangement will here change froma first signal, confirming no wetting, to a different second signal, confirmingwetting, after contact with moisture/liquid.

The RFID tag arrangement is preferably configured for operation at afrequency within the ultrahigh frequency range (UHF), such as in the range of860-960 MHz.

The RFID chips may e.g. be a high performance and low-cost IC chip,such as the commercially available NXP UCode 8, NXP G2iL+ and ImpinjMonza 4. NXP UCode 8 has two antenna pads for attaching one antenna,which antenna consists of two antenna conductors. NXP G2iL also has twoantenna pads in accordance with UCode 8 and additionally has two pads forconnecting a separate detecting loop. Impinj Monza 4 has four pads forattaching two separate dipole antennas, each antenna consists of twoseparate antenna conductors.

The antenna and the antenna parts may have various shapes anddimensions, as is per se known in the art. For example, the antenna may be adipole antenna, with antenna parts e.g. extending in a generally lineardirection, or extending in a non-linear way, such as in a meandering form or the like. The parts may also be folded or curved, thereby extending in two ormore directions. However, other antenna designs are also feasible, such aspatch antennas, monopole antennas, and the like.

The RFID tag arrangement may be either passive, i.e. powered by areader's electromagnetic field, or active, i.e. powered by an onboard battery.ln a preferred embodiment, the RFID tag arrangement is passive.

The antennas may be made of any material, as long as the material isconductive. The antennas may be made by the same material, but mayalternatively be made of different materials. For example, the antenna may beformed by aluminum, but other metals, such as silver, and alloys may also beused. Forming of the antenna on the substrate can be made in various ways,as is per se known in the art, such as by printing with conductive ink, such assilver ink, by first providing a conductive layer on the substrate andsubsequently removing or forming this conductive layer into the desiredshape, e.g. by means ofgrinding, cutting or the like. ln particular, the ink may comprise a material having a relatively lowcharacteristic melting point. The solvent can be evaporated by means ofheating at an elevated temperature, by use of photonic curing, or the like. ln one embodiment, the forming of conductive material in a patterncomprise: transferring a conductive material in a pattern corresponding tosaid electrically conductive pattern to a surface of the substrate; and heatingthe conductive material to a temperature exceeding a characteristic meltingtemperature of the conductive material.

The conductive material is preferably in the form of electricallyconductive solid particles. The transferring of conductive material to thesubstrate surface may e.g. comprise direct printing of electrically conductiveparticles as a part of a compound that contains, in addition of the electricallyconductive solid particles, a fluid or gelatinous substance. However, theelectrically conductive solid particles may also be in the form of dry powder.Further, an adhesive area may be created on the surface of the substrateprior to transfer of the particles.

The transfer of the conductive particles and the curing and solidificationmay in particular be made in the way disclosed in one or several of WO 2013/113995, WO 2009/135985, WO 2008/006941 and WO 2016/189446, allof said documents hereby being incorporated in their entirety by reference.

Curing may be effected by heating, or by a combination of heat andpressure. ln case both heat and pressure are used, the curing may bereferred to as sintering.

The formation of the antenna e|ement(s) is preferably made by a dryprocess, thereby not to negatively affect the water degradable part of thesubstrate.

The water degradable material is arranged to disintegrate after arelatively short time when immersed in water, or in other ways wetted. Thewater degradable part may e.g. disintegrate similar to ordinary toilet paper. Atthe same time, the substrate should have a surface and rigidity suitable foruse as a substrate for an RFID tag.

The water degradable material could be tailored for various uses by thechoice of suitable constituents and processing. Thus, the material could betailored to disintegrate very rapidly already at a low degree of wetting, tomake the RFID tag arrangement sensitive to a very low degree of moisture orliquid, or tailored to disintegrate relatively slowly, and only at a high degree ofwetting. Thus, the response time, i.e. the time it takes for the material todisintegrate enough to affect the output signal from the RFID arrangement,could be tailored to be within seconds from when it starts to be wetted, withinminutes, or even longer.

For example, the water degradable material may be sufficientlydisintegrated when immersed in water after a response time in the range of 1second - 15 minutes, and preferably in the range of 10 seconds - 10minutes, and more preferably in the range of 1 minute - 5 minutes.

By water degradable material is here meant a hydrodegradablematerial which breaks down or disintegrates, preferably by hydrolysis, whenplaced in an aqueous environment, such as when being immersed in water.

The water degradable material can e.g. be at least one of a polymer-based material and a cellulose based material. ln one embodiment, the water degradable material comprises at least30 wt% of microfibrillated cellulose and/or nanocellulose.

Additionally, or alternatively, the water degradable material maycomprise 5-70 wt% of a dissolvable polymer, and preferably 10-60 wt%, andmost preferably 20-50 wt%.

The dissolvable polymers may e.g. be at least one of: low molecularwater soluble species, such as dextrins, modified and cold-water solublestarches, modified cellulose derivatives, different types of sugars orhemicelluloses such as xylose, mannose and glucose, and highly hydrophiliccompounds, such as low molecular weight polyvinyl alcohol, PEG andglycole, or mixtures thereof.

Additionally, or alternatively, and in particular for a polymer basedmaterial, the water degradable material may comprise at least one of: PVOH(poly(vinyl alcohol)), starch or cellulose derivatives such as hydroxypropylcellulose, carboxymethyl cellulose, methyl cellulose, hydroxypropylmethylcellulose, gelatin, polyvinyl pyrrolidine, pectin, pullulan, or mixturesthereof. ln an embodiment, the water degradable part is made of at least oneof: paper and polymer film.

The water degradable part of the substrate preferably comprises asingle layer of a generally homogeneous material. However, it is also feasibleto use two or more layer, e.g. arranged in a sandwich construction.

The absorbance of the material is a measure of how much and fastwater is absorbed by the material. This may be measured as a Cobb value,and e.g. in accordance with the ISO 535:014 standard. ln a test for measuringCobb values, a water pillar is arranged over the material to be measured for apredetermined time, and the difference in weight before and after wettingconstitutes the weight of the absorbed water. Different wetting times may beused, such as 60 seconds (Cobb-60), 120 seconds (Cobb-120), but longerand shorter periods may also be used.

A low Cobb value means that only a small amount of water isabsorbed, which generally means that the material maintains its shape andrigidity even after some period of wetting. A higher Cobb value means that agreater amount of water is absorbed. This generally means that the materialwill dissolve/disintegrate more easily during wetting. Thus, finding a material with an adequate Cobb value is an indication that the material maydisintegrate sufficiently fast for the intended need.

The water degradable material may have a Cobb-60 value of at least70 g/m2, and preferably at least 100 g/m2, and more preferably at least 150g/m2. The Cobb value of the water degradable material may be in the rangeof 70-250 g/m2, and preferably in the range 70-200 g/m2, and most preferablyin the range of 80-150 g/m2.

How fast the water degradable material will disintegrate can also becontrolled by suitable additives. For example, the surface can be made moredense and compact using a biobased composition, such as starch. Thesurface can also be made more hydrophobic by suitable additives. Fillers mayalso be used, such as mineral fillers like kaolin, china clay, titanium dioxide,gypsum, talc, chalk, ground marble, ground calcium carbonate andprecipitated calcium carbonate. How fast the water degradable material willdisintegrate can also be controlled by adjustment of the thickness of thesubstrate material.

The water degradable material may e.g. be a web like material,preferably in roll format, and preferably a paper-like, low-cost material.Suitable materials are per se commercially available from manufacturers suchas SmartSolve, UPM Raflatac and Stora Enso. One suitable substratematerial is e.g. a laminate available from UPM Raflatac comprising aDissolvable Paper Plus, adhered to a backing of Honey Glassine 65 by theadhesive RP590.

The RFID tag arrangement is useable as an integrated part ofproducts, such as in absorbent articles, or as discrete RFID tagarrangements, arrangeable in locations where there is a need to monitormoisture and/or liquid, such as in building structures, cars, etc. ln accordance with one aspect of the invention, there is provided anabsorbent article, such as a diaper, comprising a liquid and/or moisturedetecting RFID tag arrangement as discussed in the foregoing.

The absorbent article may be a diaper, but may also be otherabsorbent articles, such as a diaper of pant type, an incontinence garment, a sanitary napkin, a tampon-Iike product, a wound or sore dressing, a bedprotector, or a similar product.

The absorbent product may be arranged to absorb or receive bodydischarges from a user. In the absorbent product, the RFID tag arrangementmay be p|aced within or below a layer of super absorbent po|ymer (SAP) orthe like. When the super absorbent po|ymer is wet, or starts to be wetted, thewater degradable part of the RFID tag substrate will be wetted as well.

According to another aspect of the invention, there is provided amethod for detecting liquid or moisture, comprising: providing a liquid and/or moisture detecting RFID tag arrangementcomprising a substrate, wherein at least a part of the substrate forms a waterdegradable part, made of a water degradable material, arranged to dissolveor disintegrate when wetted by a liquid; wirelessly reading the RFID tag with an RFID reader; and detecting an alteration in the signal from the RFID tag due to dissolvingor disintegration of the water degradable part of the substrate upon exposureof said water degradable part to a liquid or moisture.

In accordance with these aspects, similar features and advantages asdiscussed in the foregoing, in relation to the first aspect, may be obtained.

It will be appreciated that the above-mentioned detailed structures andadvantages of the first aspect of the present invention also apply to the furtheraspects of the present invention.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

Brief description of the drawinqs For exemplifying purposes, the invention will be described in closerdetail in the following with reference to embodiments thereof illustrated in theattached drawings, wherein: Fig. 1 is a top plan view of an RFID tag arrangement in accordancewith a first embodiment; Fig. 2 is a top plan view of an RFID tag arrangement in accordancewith a second embodiment; 11 Fig. 3 is a top plan view of an RFID tag arrangement in accordancewith a third embodiment; Fig. 4 is a cross-sectionai sideview of a substrate in accordance withan embodiment; Fig. 5 is a cross-sectionai sideview of a substrate in accordance withanother embodiment; Fig. 6 is a cross-sectionai sideview of a substrate in accordance withyet another embodiment; Fig. 7 is a schematic illustration of a RFID chip for use in theembodiments of Figs. 2 and 3; and Fig. 8 is a schematic illustration of a system incorporating an RFID tagarrangement.

Detailed description of preferred embodiments ln the following detailed description preferred embodiments of theinvention will be described. However, it is to be understood that features ofthe different embodiments are exchangeable between the embodiments andmay be combined in different ways, unless anything else is specificallyindicated. lt may also be noted that, for the sake of clarity, the dimensions ofcertain components, parts and elements illustrated in the drawings may differfrom the corresponding dimensions in real-life implementations of theinvention, such as the thickness of various layers, the relative dimensions ofthe different antenna parts, etc.

Fig. 1 illustrates an RFID tag arrangement 1 in accordance with anembodiment of the present invention. The RFID tag arrangement comprisesan antenna 2. ln the illustrative example, the antenna is designed as a foldeddipole, comprising two first radiating dipole elements, interconnected by aninterconnecting intermediate feeding part. The feeding part comprises an ICgap (not shown), and an RFID chip 3 arranged over said IC gap, to transmitand receive RF power from the two sides of the antenna.

The dipole antenna may also be designed in many other ways, as isper se known in the art. For example, the antenna and the antenna parts mayhave various shapes and dimensions. Further, even though the antenna is 12 here a dipole antenna, other antenna types may also be used, such as patchantennas, monopole antennas, and the like.

The antenna is arranged on a substrate 4. The antennas may be madeof any material, as long as the material is conductive, such as aluminum,silver, or alloys. For example, it is feasible to use an alloy having a relativelylow melting temperature, such as an alloy comprising tin and bismuth.Forming of the antenna on the substrate can be made in various ways, as isper se known in the art, such as by printing, etc.

The RFID chip may take any of a number of forms (including those ofthe type commonly referred to as a "chip" or a "strap" by one of ordinary skillin the art), including any of a number of possible components and beingconfigured to perform any of a number of possible functions. Preferably, theRFID chip includes an integrated circuit for controlling RF communication andother functions of the RFID tag.

At least a part of the substrate 4 forms a water degradable part, madeof a water degradable material, arranged to dissolve or disintegrate whenwetted by a liquid. ln the illustrative example of Fig. 1, the entire substrate ismade of such a water degradable material, and consequently the waterdegradable part is here the entire substrate.

When the substrate comes into contact with moisture or liquid, thesubstrate will dissolve or disintegrate, and this will make the antenna 2inoperative. Thus, a response signal from the RFID tag arrangement, wheninterrogated by an RFID reader, will be sent only when the antenna isoperative, i.e. when the substrate has not been wetted, and no responsesignal will be sent when the substrate has been wetted, since the substratewill then be disintegrated or dissolved, and the antenna 2 will be inoperative.Thus, the signal from the RFID tag arrangement 1 will here, upon wetting,change from a normal signal, e.g. comprising the RFID tag ID, to no signal. ln the embodiment of Fig. 1, lt is also feasible that only part of thesubstrate forms the water degradable part, as long as the antenna 2 is atleast partly arranged on the water degradable part, and as long as this part ofthe antenna, which will become inoperative upon wetting, will make the entireantenna inoperative, or at least make the antenna operative in a distinctly 13 different way, making it possible to discern from the response signal that theRFID tag arrangement has been exposed to moisture and/or liquid. ln another embodiment, as illustrated in Fig. 2, the RFID tagarrangement may comprise at least two antennas connected to the RFIDchip. A first antenna 2, here similar to the one in the first discussedembodiment, may be arranged on a non-water degradable part 4' of thesubstrate, whereas a second antenna 5 is arranged on a water degradablepart 4 of the substrate.

As will be discussed in more detail in the following, the non-waterdegradable part may e.g. be of a different material and connected to thewater degradable part. However, it may also be of the same water degradablematerial, but protected from becoming wet by a protective layer, or in otherways being arranged in such a way that it is not exposed to the liquid ormoisture. ln the embodiment of Fig. 2, the antenna 5 will become inoperativewhen the water degradable part dissolves/disintegrates, whereas the otherantenna 2 will still be operative. To this end, it may be discerned fromresponse signals from the RFID tag that there is no moisture/liquid whensignals from both antennas are sent, and that there is moisture/liquid presentwhen signals are received from only one antenna. Thus, the signal from theRFID tag arrangement will here change from a normal signal to another signalupon wetting. To make it possible to discern whether signals have been sentfrom both antennas, or only one of them, the two antennas may e.g. beconnected to different ports/pads on the RFID chip, and consequently sendout different signals. For example, the antenna 2 which will still be operativeafter wetting may be used to send out the ID of the RFID tag arrangement,whereas the antenna 5 which will become inoperative during wetting maysend out a signal indicating that no wetting has occurred. When the signalindicative of that no wetting has occurred ceases, this may be interpreted asan indication that wetting has occurred.

However, alternatively, the two antennas may be connected to thesame port, and be discernible by e.g. different polarizations or the like. 14 The embodiment illustrated in Fig. 3 is similar to the one discussed inrelation to Fig. 2. However, in the embodiment of Fig. 3, the RFID tagarrangement 1 comprises a detection loop 5' connected to the RFID chip,instead of the above-discussed second antenna 5. The detection loop is atleast partly arranged on the water degradable part 4. The detection loop maye.g. be arranged as a conductive line leading between two ports/pads on theRFID chip. Prior to wetting, the detection loop will remain intact, and provide aconnection between the two ports. The RFID chip may use this to determinethat no wetting has occurred, and may include this information in responsessent to the reader when the RFID tag is interrogated. As soon as the waterdegradable part starts to dissolve/disintegrate, the detection loop will break,and there will no longer be any connection between the ports. This may thenbe interpreted by the RFID chip as an indication that wetting has occurred,and this information may then be included in the information sent in responseto the RFID reader.

Thus, the signal from the RFID tag arrangement will here change froma first signal, confirming no wetting, to a different second signal, confirmingwetting, after contact with moisture/liquid. lt is to be appreciated by the skilled reader that many other variationsare also feasible. Thus, the water degradable part can be arranged atessentially any location of the substrate, and have essentially any shape anddimensions, as long as disintegration/dissolving of the water degradable partcan lead to a clearly discernible effect for the RFID tag itself, as in theembodiment with the detection loop, or for the receiver of signals sent out bythe RFID tag, as in the above-discussed embodiments of Figs. 1 and 2. ln one embodiment, the substrate may comprise two separate RFIDtags, one being arranged on a water degradable part, and one on a non-waterdegradable part. Prior to being wetted, both RFID tags will respond tointerrogations from an RFID reader. After being wetted, the RFID tag beingarranged on the water degradable part will stop functioning, and thereafter,the RFID reader will only get a response from the RFID tag arranged on thenon-water degradable part.

The water degradable material is arranged to disintegrate after arelatively short time when immersed in water, or in other ways wetted. Thewater degradable material could be tailored for various uses by the choice ofsuitable constituents and processing. Thus, the material could be tailored todisintegrate very rapidly already at a low degree of wetting, to make the RFIDtag arrangement sensitive to a very low degree of moisture or liquid, ortailored to disintegrate relatively slowly, and only at a high degree of wetting.Thus, the response time, i.e. the time it takes for the material to disintegrateenough to affect the output signal from the RFID arrangement, could betailored to be within seconds from when it starts to be wetted, within minutes,or even longer.

The water degradable material can e.g. be at least one of a polymerbased material and a cellulose based material.

The water degradable part of the substrate preferably comprises asingle layer of a generally homogeneous material. However, it is also feasibleto use two or more layer, e.g. arranged in a laminated, sandwichedconstruction.

As discussed in the foregoing, the substrate can be made entirely bythe water degradable material. However, for embodiments where part of thesubstrate forms a water degradable part, and part of the substrate forms anon-water degradable part, these parts may be realized in various ways.Some examples of this will be explained in further detail in the following. ln one embodiment, illustrated in Fig. 4, the water degradable part 4and the non-water degradable part 4' may be made of different materials,wherein the water degradable part 4 is significantly more water degradablethan the non-water degradable part 4”. This could e.g. be accomplished byuse of different grades of paper, different additives, different amounts ofcellulose or dissolvable polymer, etc. 16 The parts could be connected together in various ways. ln the exampleillustrated in Fig. 4, the parts are arranged with a small overlap, andconnected together at the overlap. The connection can e.g. be made withadhesive.

In another embodiment, illustrated in Fig. 5, the non-water degradablepart 4' essentially entirely overlaps the sheet of water degradable materialforming the water degradable part 4. In this embodiment, the part of the sheetthat extends out from the non-water degradable part 4' forms the waterdegradable part 4. The sheets can here be connected together with adhesive,or other per se known lamination technologies.

In yet another embodiment, illustrated in Fig. 6, the sheet of waterdegradable material is partly enveloped inside a material which is less waterdegradable, or non-water degradable. Thus, the enveloped part of the sheethere forms the non-water degradable part 4', whereas the non-enveloped partforms the water degradable part 4. lt is to be appreciated by the skilled reader that other ways of formingparts with distinctly different water degradability are also feasible.

In embodiments where the RFID chip is connected both to an antennaand to another antenna or detection loop, the RFID chip preferably comprisesat least four ports or bumps. Such an RFID chip is schematically illustrated inFig. 7, where the RFID chip comprises two ports 31, 32 connected to an UHFantenna 2, and two ports 33, 34, connected to another antenna, or, as in theillustrative example, a detection loop 5”.

The RFID tag arrangement is useable as an integrated part ofproducts, such as in absorbent articles, or as discrete RFID tagarrangements, arrangeable in locations where there is a need to monitormoisture and/or liquid, such as in building structures, cars, etc.

In an embodiment illustrated in Fig. 8, the RFID tag arrangement 1 isarranged in an absorbent article 6. ln the illustrative example, the absorbentarticle is a diaper, but it may also be other absorbent articles, such as adiaper of pant type, an incontinence garment, a sanitary napkin, a tampon-likeproduct, a wound or sore dressing, a bed protector, or a similar product. 17 The absorbent product may be arranged to absorb or receive bodydischarges from a user. ln the absorbent product, the RFID tag arrangementmay be integrated in the absorbent product, and e.g. be placed within orbelow a layer of super absorbent polymer (SAP) or the like. When the superabsorbent polymer is wet, or starts to be wetted, the water degradable part ofthe RFID tag substrate will be wetted as well.

Upon use, the RFID tag arrangement 1 may be intermittently andregularly interrogated by an RFID reader 7. The RFID reader may be a standalone unit, or be part of a surveillance system or the like. For example, theRFID reader may be connected to a central server 8 by a wired or wirelessconnection. Based on the responses received from the RFID tag arrangementit may be discerned, e.g. in one of the various ways discussed in theforegoing, that wetting of the RFID tag arrangement has occurred. Suchdetermination could be made in any one of the RFID chip, the RFID readerand the central server.

The person skilled in the art realizes that the present invention is notlimited to the above-described embodiments. For example, the generalantenna design may be varied in many ways, as is per se well-known in theart. For example, the dipole elements may be shaped differently than in theabove-discussed embodiments, and the feeding loop, etc., may also haveother shapes. Other type of antennas may also be used, and the antennamay further be adapted for different operational frequencies. Further, thewater degradable part may be realized in many different ways, and may alsohave various shapes, dimensions and locations on the substrate. Further, achange in response signal from the RFID tag arrangement upondisintegration or dissolving of the water degradable part can be accomplishedin various ways, and for example, as exemplified in the foregoing, by makingthe main antenna totally or partly inoperative, by making a secondary antennafully or partly inoperative, by breaking a detection loop, or the like.

Such and other obvious modifications must be considered to be withinthe scope of the present invention, as it is defined by the appended claims. ltshould be noted that the above-described embodiments illustrate rather thanlimit the invention, and that those skilled in the art will be able to design many 18 alternative embodiments without departing from the scope of the appendedclaims. ln the claims, any reference signs placed between parentheses shallnot be construed as limiting to the claim. The word ”“comprising”” does notexclude the presence of other elements or steps than those listed in theclaim. The word “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements.

Claims

1. A liquid and/or moisture detecting RFID tag arrangement (1)comprising a substrate (4, 4'), at least one antenna (2, 5) element arrangedon said substrate (4, 4'), and an RFID chip (3) connected to said antennae|ement(s) (2), wherein a part of the substrate (4) forms a water degradablepart, made of a water degradable material, arranged to dissolve ordisintegrate when wetted by a liquid, and a part of the substrate (4) forms anon-water degradable part (4'), wherein at least one of said at least oneantenna e|ement(s) is arranged on said non-water degradable part (4'), andanother of said at least one antenna e|ement(s) or a detection loop (5)connected to said RFID chip (3) is at least partly arranged on said waterdegradable part (4).

2. The RFID tag arrangement of claim 1, comprising at least twoantenna elements (2, 5) connected to said RFID chip (3), wherein one of saidantenna elements is arranged on said water degradable part (4) and one ofsaid antenna elements is arranged on a non-water degradable part (4').

3. The RFID tag arrangement of claim 2, wherein the two antennaelements are connected to different ports or pads on the RFID chip, andconsequently arranged to send out different signals.

4. The RFID tag arrangement of claim 1, further comprising adetection loop (5') connected to said RFID chip (3), the detection loop (5')being at least partly arranged on said water degradable part.

5. The RFID tag arrangement of any one of the preceding claims,wherein the tag arrangement (1) is configured for operation at a frequencywithin the range of 860-960 MHz.

6. The RFID tag arrangement of any one of the preceding claims,wherein the water degradable material is at least one of a polymer-basedmaterial and a cellulose based material.

7. The RFID tag arrangement of any one of the preceding claims,wherein the water degradable material comprises at least 30 wt% ofmicrofibrillated cellulose and/or nanocellulose.

8. The RFID tag arrangement of any one of the preceding claims,wherein the water degradable material comprises 5-70 wt% of a dissolvablepolymer, and preferably 10-60 wt%, and most preferably 20-50 wt%.

9. The RFID tag arrangement of claim 9, wherein the dissolvablepolymers are at least one of: low molecular water soluble species, such asdextrins, modified and cold-water soluble starches, modified cellulosederivatives, different types of sugars or hemicelluloses such as xyiose,mannose and glucose, and highly hydrophilic compounds, such as lowmolecular weight polyvinyl alcohol, PEG and glycole, or mixtures thereof.

10. The RFID tag arrangement of any one of the preceding claims,wherein the water degradable material comprises at least one of: PVOH,starch or cellulose derivatives such as hydroxypropyl cellulose,carboxymethyl cellulose, methyl cellulose, hydroxypropyl methylcellulose,gelatin, polyvinyl pyrrolidine, pectin, pullulan, or mixtures thereof.

11. The RFID tag arrangement of any one of the preceding claims,wherein the water degradable part (4) is made of at least one of: paper andpolymer film.

12. An absorbent article (6), such as a diaper, comprising a liquidand/or moisture detecting RFID tag arrangement (1) in accordance with anyone of the claims 1-11.

13. A method for detecting liquid or moisture, comprising: providing a liquid and/or moisture detecting RFID tag arrangement (1)comprising a substrate (4, 4'), wherein a part of the substrate forms a waterdegradable part (4), made of a water degradable material, arranged todissolve or disintegrate when wetted by a liquid, and a part of the substrateforms a non-water degradable part (4'), wherein at least one antenna elementis arranged on said non-water degradable part (4'), and another antennaelement or a detection loop (5) connected to said RFID chip (3) is at leastpartly arranged on said water degradable part (4); wirelessly reading the RFID tag with an RFID reader (7); and detecting an alteration in the signal from the RFID tag due to dissolvingor disintegration of the water degradable part (4) of the substrate uponexposure of said water degradable part to a liquid or moisture.