Sensor arrangement for sensing fill state of absorbent article

Abstract

A sensor arrangement for sensing a filled state of an absorbent article having a liquid absorbing layer, the sensor arrangement comprising: a substrate; a plurality of planar capacitors, each planar capacitor comprising a set of at least two corresponding capacitor electrodes, the set of at least two corresponding capacitor electrodes being disposed on or in the substrate close to each other; and a plurality of conductor paths on or in the substrate connecting the capacitor electrodes towards the terminals of the readout circuit, where at least two of the planar capacitors are connected in parallel.

Description

Technical Field

[0001] The present invention relates to a sensor arrangement for sensing the filling state of an absorbent article. The invention particularly relates to improved recognition of a discharge event during which body fluid is released towards a liquid-absorbing layer of an absorbent article. The invention further relates to an absorbent article, such as a diaper. Background Art

[0002] Absorbent articles are used to solve conditions such as leakage problems or incontinence. Such absorbent articles, mostly in the form of diapers, are similarly used for individuals, but are applied and managed by caregivers in the context of nursing homes, hospitals and home care environments. In each of these environments, the filling status and the need to replace the entire absorbent article are of considerable interest, as well as assessing the specific excretion behavior of the individual. The latter in particular is an important input regarding the possibility of forecasting the use of absorbent articles, the planning of replacement schedules and the management of adequate supplies in both independent environments and in the larger context of the above-mentioned nursing homes and the like.

[0003] There are technologies for detecting the filling state of absorbent articles such as diapers, which particularly contemplate the use of conductive threads integrated into the liquid-absorbing layer of the diaper. Since the sensor arrangement is integrated and hardwired with the absorbent article, it needs to be discarded once it is full or needs to be changed. At the same time, measurements of the excretion behavior and related profiles (such as excretion volume and timing) are generally of interest for extended time spans. Initial assessments of possible excretion patterns require at least a few days or weeks of monitoring, while long-term applications in nursing homes under a change warning scheme require daily based sensors.

[0004] There is a desire to separate the sensor arrangement from the absorbent article itself, so that the former can be reused several times, while the latter can be discarded whenever required, while keeping the costs involved low. However, the application of external sensor arrangements suffers from reliability issues, as close or direct contact solutions are not feasible, but other alternatives offer only little sensitivity and / or reliability while being susceptible to external conditions, such as movement of the patient and the immediate proximity of the bed or patient station.

[0005] There therefore exists a need for an improved sensor arrangement to be used in the context of absorbent articles which provides ease of operation as well as reliability. Similarly, there exists a need for a correspondingly improved absorbent article, such as a diaper. Summary of the invention

[0006] The mentioned problems and disadvantages are solved by the subject-matter of the independent claims. Further preferred embodiments are defined in the dependent claims. In particular, embodiments of the invention may provide the substantial benefits which are partly described herein.

[0007] According to one aspect of the present invention, a sensor arrangement structure for sensing the filling state of an absorbent article having a liquid absorption layer is provided, the sensor arrangement structure comprising: a substrate; a plurality of planar capacitors, each planar capacitor comprising a group of at least two corresponding capacitor electrodes arranged close to each other on or in the substrate; and a plurality of conductor paths on or in the substrate, which connect the capacitor electrodes toward terminals of a readout circuit, wherein at least two of the planar capacitors are connected in parallel.

[0008] According to another aspect of the present invention, an absorbent article is provided, which includes a sensor arrangement structure for sensing the filling state of an absorbent article having a liquid absorption layer, the sensor arrangement structure including: a substrate; a plurality of planar capacitors, each planar capacitor including a group of at least two corresponding capacitor electrodes arranged close to each other on or in the substrate; and a plurality of conductor paths on or in the substrate, which connect the capacitor electrodes toward terminals of a readout circuit, wherein at least two of the planar capacitors are connected in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present invention will now be described with reference to the accompanying drawings, which are presented for a better understanding of the concept of the present invention and are not to be considered as limiting the present invention, in which:

[0010] Figure 1 A schematic illustration showing a sensor arrangement for sensing a filling state of an absorbent article according to one embodiment of the present invention;

[0011] Figure 2A and Figure 2B A schematic illustration showing a sensor arrangement in a strip-like configuration according to one embodiment of the present invention;

[0012] Figure 3 A schematic illustration showing the impedance behavior of a sensor arrangement according to an embodiment of the invention;

[0013] FIG. 4A to FIG. 4C A schematic illustration showing a parallel connection of capacitors in a sensor arrangement according to a corresponding embodiment of the present invention;

[0014] FIG. 5A to FIG. 5C A schematic illustration showing an electrode layout of a capacitor in a sensor arrangement according to a corresponding embodiment of the present invention;

[0015] as well as

[0016] Figures 6A to 6C Schematic illustration showing electrode and capacitor configurations in a strip-shaped sensor arrangement according to corresponding embodiments of the present invention. DETAILED DESCRIPTION

[0017] Figure 1 A schematic illustration of a sensor arrangement for sensing the filling state of an absorbent article according to one embodiment of the present invention is shown. Specifically, the absorbent article includes a liquid absorption layer, such as the diaper 9 shown. However, in general, the absorbent article may be any of diapers for children, diapers for adults, pads, protectors, and the like. The liquid absorption layer is a layer comprising or consisting of an absorbent material that is capable of absorbing liquid in a specific context of body fluids (including urine, blood, feces, and similar body fluids). The absorbent material can be arranged to absorb such liquid up to a given capacity and to hold the liquid for a given time. In addition, the absorbent material can be arranged to transport the liquid to an adjacent area so that the nearby absorbent material can absorb the liquid that is not absorbed by the absorbent material upstream toward the liquid source.

[0018] The sensor arrangement 1 is provided for use with such an absorbent article and can be arranged for this purpose so as to be attachable, for example, to the outer side surface 91 of an exemplary diaper 9. The sensor arrangement 1 can take the form of a strip and generally comprises a substrate and a plurality of planar capacitors 11, 12, each capacitor comprising a set of at least two corresponding capacitor electrodes arranged close to each other on or in the substrate. The capacitor electrodes are arranged close to each other in the sense that they do not have their major surfaces facing each other. In other words, the larger surfaces of the electrodes do not face each other and can be arranged in a potentially flexible plane of the sensor arrangement and / or substrate, while the much smaller side surfaces of the conductive material forming the capacitors can be oriented to face each other.

[0019] Because the capacitor is positioned near the liquid absorption layer, at least in the state when the sensor arrangement structure is attached to the absorbent article, the absorbed liquid interacts with the capacitor to change the effective measurable capacitance. The sensor arrangement structure 1 is arranged in this way for sensing the filling state of the absorbent article, and the sensor arrangement structure 1 may include a device for detecting excretion events such as this, evaluating the absorbed volume, and determining a saturation potentially related to the maximum absorption capacity or target absorption capacity. In this way, potential applications of embodiments of the present invention may include any of excretion behavior assessment, excretion monitoring, capacity monitoring, monitoring the need to replace absorbent articles, and similar applications. In order to access the capacitors 11, 12, the absorbent article 1 further includes a plurality of conductor paths on or in the substrate, which connect the capacitor electrodes toward the terminals of the readout circuit.

[0020] According to an embodiment of the invention, at least two of the planar capacitors are connected in parallel. This can be referred to as a so-called capacitor pair if the respective two capacitors forming the pair are connected in series. However, in general, embodiments of the invention assume that a pair is understood in the sense of a group comprising at least two planar capacitors connected in parallel, wherein the group may well also comprise three or more planar capacitors connected in parallel.

[0021] Figure 2A and Figure 2B A schematic illustration of a sensor arrangement in a strip-shaped configuration according to one embodiment of the present invention is shown. Specifically, a sensor arrangement for sensing the filling state of an absorbent article 1 is shown to include a substrate 102 with a plurality of planar capacitors 11, 12 ... The capacitors are spaced apart and arranged in the longitudinal direction or in a longer extension direction of the strip-shaped sensor arrangement 1. Specifically, in this embodiment, the substrate presents an elongated strip-shaped shape along the longitudinal direction of the elongation range, and wherein the planar capacitors are arranged along the longitudinal direction. The term "elongated" should be understood as a strip-shaped sensor arrangement having a length in the longitudinal direction that is longer than the width in the transverse direction. Typically, the length / width ratio is greater than 3. In addition, the longitudinal direction of the sensor arrangement is preferably intended to be aligned with the longitudinal (front / back) extension range of the absorbent article or at least the extension range of the liquid absorption layer therein. Thus, a typical length can be in the range of 150mm to 1000mm, 200mm to 800mm, 300mm to 700mm, for example 490mm, 500mm, 690mm or 700mm. Generally, the sensor arrangement length should be adapted to the length of the absorbent core of the absorbent article, or in other words the length of the region of interest. Typical widths are in the range of 10 mm to 40 mm or 15 mm to 30 mm, for example about 25 mm.

[0022] In general, the substrate may be flexible and configured as a flexible printed circuit board (PCB) with a corresponding and per se known base material and having conductive paths and areas formed from, for example, a copper or metal layer by etching or other types of applicable lithographic techniques. As an alternative to etching, any conductive paths and areas may also be formed by printing, inkjet printing, screen printing and the like.

[0023] In this way, the substrate 102 includes a first surface 1201 and a second surface 1202, wherein the capacitor electrodes are arranged together on one of the first surface and the second surface. Preferably, the capacitor electrodes are arranged together on the first surface 1201, which will be a surface closer to the liquid-absorbent layer of the absorbent article when attached to the liquid-absorbent layer of the absorbent article. In this way, the distance between the capacitor electrodes and the liquid-absorbent layer (where any liquid absorbed is the object of measurement) can be minimized, and the sensitivity of the sensor arrangement as a whole can be optimized.

[0024] In general, the sensor arrangement according to an embodiment of the present invention can be arranged to accompany the liquid absorption layer of an absorbent article. For this purpose, the sensor arrangement 1 can include an adhesive layer 103 facing the absorbent article (e.g., a diaper 9). For example, the adhesive layer 103 can be formed by or include a portion of an adhesive or a hook-and-loop fastener that can attach the sensor arrangement to the absorbent article sufficiently well. However, other ways of fixing or accompanying are generally considered, including that, for example, the sensor arrangement can be incorporated into outer pants, or positioned in some kind of pocket on the inside or outside of the absorbent article.

[0025] However, where an adhesive layer is employed, the material and / or composition of the adhesive layer 103 may be adapted to the specific properties of the surface 91 of the absorbent article 9. For example, an absorbent article in the exemplary form of a diaper 9 may feature a fabric or fabric-like surface 91 to which the hook portion of a hook-and-loop fastener may adhere well. Such an adhesive layer may further provide the benefit of being removable from the absorbent article once the absorbent article needs to be changed. The sensor arrangement may then be easily reused by attaching the sensor arrangement to a new absorbent article (e.g., a diaper) without compromising the integrity of the absorbent article being used, i.e., without destroying or damaging the surface 91 when attaching, being attached and / or being removed. Thus, although the sensor arrangement may be arranged to adhere to the outer surface of the absorbent article, it is equally well adapted to sensing the filling state of the absorbent article while being electrically isolated from the liquid-absorbing layer.

[0026] The absorbent article as a whole may include further components, seals and / or layers. Figure 2BAs shown in , the sensor arrangement structure 1 includes an outer layer 101, which may include or consist of a sealant, such as rubber, paint, silicone, thermoplastics and the like. Similarly, the entire sensor arrangement structure, i.e. the substrate strip of the present embodiment, may be completely silicone-embedded. Considering the situation of sensing the filling state of the absorbent article, then in the specific case of absorbing body fluids, sealing and / or protection from the influence of a humid environment may be desired. In addition, since the sensor arrangement structure can be used several times, it may also be desirable to clean the arrangement structure for hygienic purposes, which may involve, for example, treatment with a detergent and / or disinfectant, heat treatment, radiation treatment and the like. As a further additional layer, a ground plane can be provided, which protects the electrical measurement circuit from the influence of electromagnetic interference (EMI) from the outside. For example, such a ground plane can be implemented by a mesh pattern of conductive material on the second surface 1202 of the substrate 102.

[0027] Figure 3 A schematic illustration of the impedance behavior of a sensor arrangement according to one embodiment of the present invention is shown. As explained, an embodiment of the present invention provides a sensor arrangement for sensing the filling state of an absorbent article with a plurality of planar capacitors, wherein at least two of these planar capacitors are connected in parallel. In particular, an embodiment of the present invention considers sensing the filling state of a liquid-absorbing layer by means of the interaction of the absorbed liquid with the effective dielectric properties of the capacitors. Furthermore, the usual behavior of body fluid discharge is taken into account, wherein the discharge - and the corresponding absorption - is not a continuous process, but rather a process that occurs in events. That is, body fluid is released in so-called discharge events, during which a certain volume of body fluid is discharged during a relatively short time span, while no or almost no fluid is released during intermittent and relatively long time spans (discharge pauses).

[0028] Assuming a single planar capacitor is placed alongside a liquid absorbing layer, the absorbed liquid will change the dielectric properties of the capacitor. The effective capacitance C generally determines the impedance of the capacitor circuit, where the impedance opposes the alternating current presented by the combined effects of resistance and reactance in the circuit.

[0029] Specifically, an AC voltage source may be applied to the capacitor electrodes and the strength of the AC signal reflected by the capacitor in the sense of an AC resistor is measured. This technique is known as such and is often referred to as network analysis (e.g., a corresponding so-called network analyzer is a readout circuit that applies an AC signal to an AC impedance, such as a capacitor, and measures the reflected AC power to determine the impedance value). Thus, the readout circuit may generally include an RF / AC (radio frequency, alternating current) source, a directional coupler, an impedance measurement test set, a so-called "S-parameter" test set, or parts thereof, which generally considers the impedance changes of the entire circuit, including connectors, conductor paths in the sense of impedance matching or well-defined impedance strip lines, which are due to capacitance changes that occur primarily in the capacitor as a result of liquid absorption in the immediate vicinity of the capacitor electrodes.

[0030] In the above assumptions, the capacitance and hence the impedance will change over time, during which one or more insult events occur and the liquid absorbent article contains more and more liquid, acting as a changing capacitor dielectric. The measured impedance will in principle follow Figure 3 The first impedance curve Z1 shown varies over time, since in the time span T1 before the first voiding event the impedance Z1 remains more or less constant, i.e. it is assumed that the impedance value remains within some predetermined limits set to characterize a constant behavior. After the first voiding event during T2 the impedance will change and, for example, drop to a certain first level Z11. After having again remained at a more or less constant level, a further voiding event during T4 will cause the impedance to change again and, for example, assume a certain further level Z12. As shown from Figure 3 As can be seen from the schematic illustration, the difference in impedance between the first level Z11 and the second level Z12 is relatively small and may cause corresponding difficulties for the readout of the sensor arrangement and for evaluating the measured readouts, in particular in the case of identifying and / or counting individual voiding events.

[0031] Since embodiments of the present invention consider a plurality of planar capacitors, and at least two of said planar capacitors are connected in parallel, the readout will be different, although the capacitors are again arranged along the liquid-absorbent layer as in the above case. More specifically, the capacitors are planar, and they are also coplanar with the liquid-absorbent layer, however, this also includes the fact that the "plane" of the sensor arrangement is flexible so as to assume a form that generally follows the curvature of the outer surface of the absorbent article (see Figure 1 and Figure 2B Schematic bend in ).

[0032] As a result, the first discharge event will result in the accumulation of liquid in the first zone or first area. The capacitor facing this zone or area will change its capacitance accordingly and affect the measured impedance. That is, after the first discharge event after time T1 and during time T2, the impedance Z2 will present a value Z21 in time T3. Since the second discharge event during time T4 will result in the accumulation of liquid in a zone different from the first zone, it will affect a further different capacitor. Assuming that this further capacitor is a capacitor connected in parallel with the capacitor affected by the first discharge event, the impedance Z2 of the parallel connection of the two capacitors will reach a value Z22, with the additional feature that the "plateaus" Z21 and Z22 are substantially more different from each other than the plateaus Z11 and Z12 in the case of a single but larger capacitor. Thus, embodiments of the present invention can provide the following advantages: independent discharge events can be more reliably identified by utilizing the much more obvious differentiation behavior of the measured impedance (Z2 relative to Z1).

[0033] FIG. 4A to FIG. 4C A schematic diagram showing the parallel connection of capacitors in a sensor arrangement according to a corresponding embodiment of the present invention is shown. Specifically, Figure 4A In principle, the combination Figure 3 The situation of at least two capacitors being connected in parallel is described by the second impedance Z2. The impedance can be measured via connecting a network analysis circuit to the terminals or connection points T1 and T2 of the two branches of the parallel connection of capacitors C1 and C2.

[0034] also, Figure 4B A schematic illustration of a parallel connection is shown, wherein there are at least two pairs of parallel connected planar capacitors. That is, a first pair of parallel capacitors C1 and C2 and a second pair of parallel capacitors C3 and C4 are provided. The first pair is accessible via terminals T1 and T2, whereas the second pair is accessible via terminals T1 and T3. In this embodiment, a major longitudinal extension of the liquid-absorbing layer and its associated absorption sequence is again assumed, so that a discharge event would, for example, affect C1, then C1 and C2, then C1, C2 and C3, etc. By means of forming several pairs of independently parallel connected capacitors, the readout can be even more improved, since, for example, the second pair C3 / C4 is not affected at all by the first two discharge events.

[0035] also, Figure 4CAnother schematic illustration of a parallel connection is shown, in which there are at least two pairs of planar capacitors connected in parallel. That is, the individual planar capacitors in the pairs of planar capacitors connected in parallel are arranged in an interleaved order. That is, a first pair of parallel capacitors C1 and C3 and a second pair of parallel capacitors C2 and C4 are provided again. The first pair is accessible through terminals T1 and T2, and the second pair is accessible through terminals T1 and T3. However, capacitor C2 is arranged between the parallel-connected capacitors C1 and C3, and capacitor C3 is arranged between the parallel-connected capacitors C2 and C4. In other words, the individual planar capacitors in the pairs of planar capacitors connected in parallel are arranged in an interleaved order so that the individual planar capacitors of a pair are not arranged adjacent to each other. Specifically, such an arrangement can be adopted to maximize the distance between the individual planar capacitors of a pair.

[0036] In this embodiment, again, a major longitudinal extension of the liquid-absorbing layer and its associated absorption sequence is assumed, so that a discharge event would, for example, affect C1, then C1 and C2, then C1, C2 and C3, etc. By means of forming several pairs of independent parallel-connected capacitors and the staggered arrangement, the readout can be improved, since, for example, the initial discharge event can be identified not only by a single capacitor, but even by a single capacitor of a single pair with corresponding single readout lines. Considering such an embodiment can be particularly advantageous when the focus is on identifying the initial discharge event relative to later discharge events, or when the focus is generally on the first group of capacitors rather than the second group of capacitors associated with lower significance and / or importance.

[0037] FIG. 5A to FIG. 5C Schematic illustrations of the electrode layout of a capacitor in a sensor arrangement structure according to corresponding embodiments of the present invention are shown. In principle, these embodiments all take into account that the capacitor electrodes are coplanar, in the sense that the electrode area follows the shape of the substrate, allowing bending and curvature. In general, the 0 volt or ground terminal of the network analysis function is connected to the outer electrode and the signal is connected to the inner circle, or vice versa. Typical dimensions in terms of diameter, width or diagonal extension range from about 15 mm to 25 mm in the transverse direction and from about 15 mm to 70 mm, preferably 30 mm to 60 mm in the longitudinal direction. It is preferred to have a configuration such as Figure 5B The oblong shape of the electrodes in is mainly to achieve good coverage over the strip with small "dead areas" between adjacent electrodes while keeping the number of electrodes reasonable.

[0038] In such Figure 5AIn some of the embodiments shown in , the capacitor electrodes exhibit a pad-like shape 21 , 22 and thereby form a planar capacitor by means of a simple and reliable shape, which is formed with easy contacting, which at least to some extent avoids crossing of conductive paths. Figure 5B and Figure 5C Schematic illustration showing the electrode layout, where the capacitor electrodes present a concentric shape ( Figure 5B : cushion-like shapes 31, 32, such as elliptical; Figure 5C : circular shape 31 ', 32'). This layout can help to concentrate the electric field distribution within the dielectric, i.e. within the liquid absorbent article. Thus, the response can be focused on the liquid positioned in a specific and predeterminable manner, because the trajectory of most of the electric field lines is concentrated to the volume defined by the footprint of the outer concentric electrodes of the concentric electrodes, i.e. the corresponding electrode 32, 32'.

[0039] FIG. 6A to FIG. 6C Schematic illustration showing electrode and capacitor configurations in a strip-shaped sensor arrangement according to corresponding embodiments of the present invention. Fig. 6A Attention is directed to further general aspects of a strip-shaped sensor arrangement 1, which includes, for example, circular and concentric electrode pads for a plurality of capacitors C1, C2, ... C8. A plurality of conductor paths 40, 41, ... 44 are also shown, which are located on or in the substrate 1, connecting the capacitor electrodes toward the terminals of the readout circuit. Specifically, an embodiment is shown in which the sensor arrangement 1 also includes a connector 50 toward the readout circuit. The latter can, for example, be formed by a compact and sealed electronic device that can be interchangeably fixed and connected to the sensor arrangement 1 by being tightly fitted to the connector 50. The mentioned readout circuit can provide suitable and applicable functions, such as power supply, network analysis, data processing, communication, operation, etc.). Other but related embodiments of the present invention contemplate that the sensor arrangement includes such a readout circuit, which can make it possible to omit the connector and implement the readout circuit even on the same substrate on which the capacitor electrodes and / or the conductive paths are constructed. In any way, the readout circuit can also include a transmitter part, wherein only the transmitter part can then be detachable.

[0040] In the present embodiment, the parallel connection of the planar capacitors C1, C2, ... C8 is implemented before the connector 50. That is, all first electrodes of all planar capacitors C1, C2, ... C8 are connected to the first common terminal line implemented by the conductive path 40. The corresponding second electrodes of the capacitors C1 and C5 connected in parallel are connected to the corresponding second common terminal line implemented by the conductive path 41. Similar schemes are applicable to further capacitor pairs C2 and C6, C3 and C7, and C4 and C8. In this way, the planar capacitors are connected in parallel by means of the multiple conductor paths 40, 41, ... 44 on the substrate 1. Conductor paths 40, 41, ... 44 and the electrode pads of capacitors C1, C2, ... , C8 can be implemented as conductive paths and regions of a flexible printed circuit board, including the usual multiple layers and through holes therebetween.

[0041] In one application scenario, the present embodiment may be considered under the assumption that the middle capacitor C4 is intended to represent the main point of urination, with a relatively high probability that this is the capacitor that will first detect wetting. After this, subsequently detecting the impedance change in the pair including capacitors C1 and C5, it may be assumed that capacitor C5 adjacent to the middle capacitor C4 detected liquid absorption, rather than capacitor C1 at the end away from capacitor C5 (but connected in parallel), because none of C2, C3, C6, C7 and C8 were detected as "wetting". Similarly, if after capacitor C4, a pair of capacitors C3 and C7 experienced an impedance change, it may be assumed that liquid absorption occurred near C3 rather than near C7. In this way, the direction of subsequent liquid absorption may also be considered and / or determined.

[0042] Figure 6B A schematic illustration of the configuration of electrodes and capacitors in a strip-shaped sensor arrangement according to one embodiment of the present invention is shown, which focuses on the mutual distances between adjacent capacitors. In particular, the sensor arrangement 1' comprises a plurality of capacitors C1, C2, ..., wherein the mutual distance between two adjacent planar capacitors increases towards at least one end of the substrate 102. In the configuration shown, the distance between capacitors C1 and C2 and, respectively, the distance between C5 and C6 is greater than the distance between capacitors C3 and C4. The capacitors C1, C2, C5 and C6 are positioned closer to the ends of the strip-shaped sensor arrangement 1' than to the capacitors C3 and C4, which are slightly "centered". This embodiment takes into account a specific positioning which may be assumed to be the source of the body fluid. In particular, if the strip-shaped sensor arrangement 1' is to be attached to a diaper 9, such as, for example Figure 1 As shown in , the center of the strip may coincide with or at least be close to the ureteral outlet. Thus, this embodiment may be preferred when the initial voiding event is of particular interest, and it may not be necessary to distinguish one or more subsequent voiding events.

[0043] Figure 6C A schematic illustration of the configuration of electrodes and capacitors in a strip-shaped sensor arrangement according to one embodiment of the present invention is shown, which again focuses on the mutual distances between adjacent capacitors. Specifically, the sensor arrangement 1" includes a plurality of capacitors C1, C2, ..., wherein the mutual distance between two adjacent planar capacitors decreases toward at least one end of the substrate 102. In the configuration shown, the distance between capacitors C1 and C2 and, correspondingly, the distance between C7 and C8 is smaller than the distance between capacitors C4 and C5. Compared to capacitors C4 and C5, which are slightly "centered", capacitors C1, C2, C7 and C8 are positioned closer to one end of the strip-shaped sensor arrangement 1". This embodiment again takes into account a specific location that can be assumed to be the source of the body fluid. However, this embodiment may be preferred when the initial discharge event is less important and subsequent discharge events are of particular interest. In particular, applications taking into account the need and the corresponding time point for replacing the entire absorbent article may want to clearly distinguish discharge events that occur toward the full capacity of the absorbent article.

[0044] Although detailed embodiments have been described, these embodiments are only intended to provide a better understanding of the invention as defined by the independent claims and should not be considered limiting.

Claims

1. A sensor arrangement for sensing a filling state of an absorbent article having a liquid absorbing layer, the sensor arrangement comprising: Base, a plurality of planar capacitors, each planar capacitor comprising a set of at least two corresponding capacitor electrodes arranged close to each other on or in the substrate, and a plurality of conductor paths on or in the substrate, the plurality of conductor paths connecting the capacitor electrodes towards terminals of a readout circuit, Wherein at least two of the planar capacitors are connected in parallel. 2 . The sensor arrangement according to claim 1 , wherein the substrate exhibits an elongated strip-like shape having a longitudinal direction along an elongated extent, and wherein the planar capacitors are arranged along the longitudinal direction. 3 . The sensor arrangement according to claim 2 , wherein a mutual distance between two adjacent planar capacitors increases towards at least one end of the substrate. 4 . The sensor arrangement according to claim 2 , wherein a mutual distance between two adjacent planar capacitors decreases towards at least one end of the substrate.

5. The sensor arrangement according to any one of claims 1 to 4, comprising at least two pairs of planar capacitors connected in parallel.

6. The sensor arrangement of claim 5, wherein the individual planar capacitors in the pairs of parallel-connected planar capacitors are arranged in a staggered order.

7. The sensor arrangement according to any one of claims 1 to 6, further comprising a connector towards the readout circuit.

8. The sensor arrangement according to claim 7, wherein the parallel connection of the planar capacitors is effected before the connector. 9 . The sensor arrangement according to claim 8 , wherein the planar capacitors are connected in parallel by means of the plurality of conductor paths on the substrate.

10. The sensor arrangement according to any one of claims 1 to 9, wherein the capacitor electrode exhibits a pad-like shape.

11. The sensor arrangement according to any one of claims 1 to 9, wherein the capacitor electrodes exhibit a concentric shape. 12 . The sensor arrangement according to claim 1 , wherein the substrate comprises a first surface and a second surface, wherein the capacitor electrodes are arranged together on one of the first surface and the second surface.

13. The sensor arrangement of claim 12, wherein the capacitor electrodes are coplanar.

14. The sensor arrangement according to any one of claims 1 to 13, wherein the substrate is flexible.

15. The sensor arrangement according to any one of claims 1 to 14, arranged to accompany the liquid-absorbing layer of the absorbent article.

16. The sensor arrangement according to any one of claims 1 to 15, further comprising the readout circuit.

17. An absorbent article comprising a sensor arrangement according to any one of claims 1 to 15.

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