Humidity sensing devices and absorbent articles including humidity sensing devices
By employing a capacitive humidity sensing device in absorbent products, utilizing capacitive coupling estimation circuits and biocompatible electrodes, the corrosion and cost problems of existing humidity sensing technologies are solved, achieving efficient and economical humidity sensing results.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- MOLNLYCKE HEALTH CARE AB
- Filing Date
- 2025-01-14
- Publication Date
- 2026-07-31
AI Technical Summary
Existing absorbent products are difficult to effectively sense humidity after absorbing fluids. Conventional methods suffer from corrosion problems or high costs, and large-size electrodes make disposable products uneconomical.
The device employs a first electrode that makes conductive contact with the absorbed fluid, and a second electrode that is separated by a dielectric layer. The humidity is measured using a capacitively coupled estimation circuit. The electrode material is a biocompatible conductive material.
It provides a more cost-effective, compact, and corrosion-insensitive humidity sensor that can accurately detect humidity changes in absorbent products.
Smart Images
Figure CN122497480A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a humidity sensing device and an absorbent article including such a humidity sensing device. Background Technology
[0002] Absorbent products used to absorb fluid from a user's body may lose their ability to maintain the desired level of moisture on the user's skin after absorbing a certain amount of fluid. Therefore, when using regular absorbent products, periodic manual checks may be necessary, which may involve visual inspection or even temporarily partially removing the absorbent product to allow inspection of the skin-side of the product. This latter case is particularly likely if the absorbed fluid is largely transparent. For absorbent products in the form of wound dressings, it is important for the wound healing process to maintain a moisture level below a certain limit and to replace the wound dressing before it reaches its maximum fluid-retaining capacity.
[0003] Therefore, it is desirable to provide improved humidity sensing in absorbent articles. Summary of the Invention
[0004] One object of the present invention is to provide improved humidity sensing for absorbent articles.
[0005] Therefore, according to one aspect of the present invention, a humidity sensing device for sensing humidity in an absorbent article is provided, the humidity sensing device comprising: a first sensing device portion having a first electrode disposed therein, the first sensing device portion being configured such that covering the first sensing device portion with a conductive fluid results in conductive contact between the first electrode and the conductive fluid; a second sensing device portion having a second electrode disposed therein, the second sensing device portion being configured such that covering the second sensing device portion with a conductive fluid results in the second electrode being separated from the conductive fluid by a dielectric layer; and a capacitance estimation circuit coupled to the first electrode and the second electrode, the capacitance estimation circuit being configured to estimate the capacitive coupling between the first electrode and the second electrode.
[0006] The inventors have recognized that existing methods for humidity sensing may not be optimal for use in absorbent articles. Resistive sensing requires the use of conductive measuring electrodes, which can lead to corrosion problems. Alternatively, expensive precious metals may be required, which may be unsuitable for disposable products. Conventional capacitive sensing uses electrically insulated measuring electrodes, thus eliminating the problem of measuring electrode corrosion. However, to obtain reliable measurements indicating the moisture content in absorbent articles, the measuring electrodes may need to be relatively large. This may reduce the number of absorbent articles for which conventional capacitive sensing is feasible. Furthermore, large measuring electrodes may make conventional capacitive humidity sensing devices prohibitively expensive for use in many types of disposable absorbent articles.
[0007] This invention is based on the understanding that a lower-cost and more compact capacitive humidity sensing device for absorbent articles can be achieved by evaluating the capacitive coupling between a first electrode (which is in conductive contact with the conductive fluid absorbed by the absorbent article) and a second electrode (which is separated from the absorbent fluid by a dielectric layer). With this configuration, the absorbent fluid can serve as one of the plates in a parallel-plate capacitor. This provides a relatively large plate area (corresponding to the surface overlap between the absorbent fluid and the second electrode) and a relatively short distance between the plates (corresponding to the thickness of the dielectric layer separating the second electrode and the absorbent fluid), resulting in a relatively high capacitance when there is absorbent conductive fluid in contact with the first electrode and overlapping with the second electrode. This provides a strong dependence between the absorbent fluid area coverage and the capacitive coupling between the first and second electrodes.
[0008] Another insight of the inventors is that the first electrode in the humidity sensing device according to various examples of the invention will not be as sensitive to corrosion as in the case of resistive humidity sensing, because essentially no current will flow through the interface between the first electrode and the absorbed fluid.
[0009] Therefore, aspects of the present invention provide improved humidity sensing in absorbent articles. For example, humidity sensing can be implemented in a more cost-effective and environmentally conscious manner.
[0010] The first electrode disposed in the first sensing device portion may have an exposed conductive surface. This exposed conductive surface may be formed at least partially of a biocompatible conductive material. This may be particularly relevant to absorbent articles intended to cover wounds (i.e., wound dressings). For absorbent articles in the form of hygiene products, biocompatibility may not be required.
[0011] Examples of suitable biocompatible conductive materials may include silver / silver chloride, iridium oxide, boron / boron-doped diamond, noble metals, and oxides of noble metals.
[0012] In an example configuration of a humidity sensing device, the second sensing device portion may partially or completely surround the first sensing device portion. This configuration can be advantageous in making the first electrode relatively small and the second electrode relatively large, while still enabling the humidity sensing device to be sensitive to relatively localized humidity in an absorbent article comprising a humidity sensing device according to this exemplary configuration.
[0013] The second electrode of the second sensing device portion can be arranged on at least two generally opposing sides of the first electrode of the first sensing device portion. This configuration allows the humidity sensing device to sense the presence of absorbed fluid expanding between each of the two generally opposing sides of the first electrode.
[0014] The second electrode of the second sensing device portion may have a geometric centroid that overlaps with the first electrode of the first sensing device portion. This may be advantageous for the ability to symmetrically sense the presence of absorbed fluid in different directions relative to the first sensing device portion of the humidity sensing device. For example, the humidity sensing device may be arranged in an absorbent article such that the first sensing device portion is centered in the region of interest of the absorbent article, for example, at the geometric centroid of a wound dressing.
[0015] In an exemplary configuration of the humidity sensing device according to the present invention, the surface area of the second electrode in the second sensing device portion can be at least twice the surface area of the first electrode in the first sensing device. Increasing the area of the second electrode (whether in absolute value or relative to the area of the first electrode) can improve the sensitivity and / or accuracy of humidity sensing.
[0016] Advantageously, the surface area of the second electrode of the second sensing device portion can be at least five times the surface area of the first electrode of the first sensing device.
[0017] In an exemplary configuration of the humidity sensing device according to the present invention, the longest distance between a point on the outer periphery of the first electrode of the first sensing device portion and a point on the outer periphery of the second electrode of the second sensing device portion can be at least 1.25 times longer than the shortest distance between the points on the outer periphery of the first electrode of the first sensing device portion and the points on the outer periphery of the second electrode of the second sensing device portion. This configuration provides progressively increasing capacitive coupling for increased surface coverage of the absorbed fluid in the absorbent article. The greater the proportion of the second electrode overlapping with the absorbed fluid, the greater the capacitive coupling, provided that the first electrode is also in conductive contact with the conductive absorbed fluid.
[0018] In order to ensure that the increased surface coverage of the absorbent article with the absorbed fluid in a given direction can also lead to an increase in the capacitive coupling between the first electrode and the second electrode of the humidity sensing device, the longest distance extending along a line in the first direction between a point on the outer periphery of the first electrode of the first sensing device portion and a point on the outer periphery of the second electrode of the second sensing device portion can be at least 1.25 times longer than the shortest distance extending along a line in the first direction between a point on the outer periphery of the first electrode of the first sensing device portion and a point on the outer periphery of the second electrode of the second sensing device portion.
[0019] According to an exemplary configuration of the humidity sensing device of the present invention, the second electrode of the second sensing device portion may include: an elongated first sub-portion extending in a first radial direction relative to the geometric centroid of the first electrode of the first sensing device portion; and an elongated second sub-portion extending in a second radial direction relative to the geometric centroid of the first electrode of the first sensing device portion, the second radial direction being different from the first radial direction. This configuration provides gradually increasing capacitive coupling for increased surface coverage of the absorbed fluid in the absorbent article.
[0020] According to an exemplary configuration of the humidity sensing device of the present invention, the second sensing device portion may have a third electrode disposed therein, the third electrode being electrically insulated from the second electrode. The second sensing device portion is configured such that the coverage of the second sensing device portion by a conductive fluid causes the third electrode to be separated from the conductive fluid by a dielectric layer. Furthermore, a capacitance estimation circuit may be connected to the third electrode, the capacitance estimation circuit being configured to estimate a first capacitive coupling between the first electrode and the second electrode, and a second capacitive coupling between the first electrode and the third electrode. Adding a third electrode can improve the accuracy and sensitivity of humidity sensing.
[0021] Humidity sensing devices constructed according to various examples of the present invention can be included in an absorbent article, which further includes a fluid-absorbing pad configured to absorb fluid from a user's body. The humidity sensing device can be arranged in contact with the fluid-absorbing pad such that a first sensing portion and a second sensing portion of the humidity sensing device can be covered by fluid absorbed by the fluid-absorbing pad.
[0022] According to the example, the absorbent article may include a backing layer and a body contact layer that hold a fluid-absorbing pad; the fluid-absorbing pad may be a layered structure that includes at least a fluid retention layer and a fluid-absorbing layer, with the fluid-absorbing layer disposed between the fluid retention layer and the body contact layer; and a humidity sensing device may be disposed between the fluid retention layer and the fluid-absorbing layer. Attached Figure Description
[0023] These and other aspects of the invention will now be described in more detail with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention, in which: Figure 1 This is an illustration of an exemplary absorbent article in the form of a wound dressing placed on a user's arm; Figure 2 yes Figure 1 An exploded view of an absorbent article having an embedded humidity sensing device according to an exemplary embodiment of the present invention; Figures 3A to 3C It has different amounts of absorbent fluid. Figure 2 A cross-sectional view of the absorbent article in the text; Figure 4 This is a top view of a humidity sensing device according to a first embodiment of the present invention; Figure 5 This is a top view of a humidity sensing device according to a second embodiment of the present invention; and Figure 6 This is a top view of a humidity sensing device according to a third embodiment of the present invention. Detailed Implementation
[0024] The present disclosure will now be described more fully below with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are illustrated. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness and to fully convey the scope of the disclosure to those skilled in the art. Similar reference numerals consistently denote similar elements.
[0025] Figure 1 This is an illustration of an exemplary absorbent article 1 in the form of a wound dressing placed on a user's arm 3. Due to the importance of the moisture level in the wound dressing for wound healing, for example... Figure 1 The wound dressing schematically illustrated can be a particularly interesting application of the humidity sensing device according to an embodiment of the present invention.
[0026] Figure 2 yes Figure 1 An exploded view of an absorbent article 1 having an embedded humidity sensing device 5 according to an exemplary embodiment of the present invention. Figure 2 The absorbent product (wound dressing) 1 includes a fluid-absorbing pad 7 configured to absorb fluid from the user's body. In this particular case, the fluid may be exudate from a wound covered by the wound dressing. For other types of absorbent products, the fluid may be urine or blood.
[0027] Humidity sensing device 5 includes a first sensing device part 9 and a second sensing device part 13, wherein the first sensing device part is in Figure 2 The second sensing device portion is schematically indicated by the inner dotted line 11, located between the inner dotted line 11 and the outer dotted line 15. The first sensing device portion 9 has a first electrode 17 disposed therein, and the second sensing device portion 13 has a second electrode 19 disposed therein.
[0028] The first sensing device portion 9 is configured such that the coverage of the first sensing device portion 9 with the conductive fluid results in conductive contact between the first electrode 17 and the conductive fluid, and the second sensing device portion 13 is configured such that the coverage of the second sensing device portion 13 with the conductive fluid results in the second electrode 19 being separated from the conductive fluid by a dielectric layer. The dielectric layer may be included in the humidity sensing device 5 (as illustrated below) or may be a layer of the absorbent article 1.
[0029] like Figure 2 As schematically indicated, the humidity sensing device 5 also includes a capacitance estimation circuit 21 coupled to the first electrode 17 and the second electrode 19, configured to estimate the capacitive coupling between the first electrode 17 and the second electrode 19. Various methods for estimating the capacitive coupling between two electrodes separated by a dielectric layer are known in the art, such as those from various types of capacitive sensors, capacitive touchscreens, and capacitive fingerprint sensors. Since those skilled in the art will find it straightforward to implement suitable capacitive sensing techniques in humidity sensing devices according to various embodiments of the present invention based on the information in this application, detailed information regarding techniques for measuring capacitive coupling is not provided herein.
[0030] In this example configuration, the absorbent article 1 includes a backing layer 25 and a body contact layer 23 that hold the fluid-absorbing pad 7. In this example configuration, the fluid-absorbing pad 7 is a layered structure comprising a fluid retention layer 27, a fluid distribution layer 29, and a fluid absorption layer 31. The fluid absorption layer 31 is arranged closest to the body contact layer 23, the fluid distribution layer 29 is arranged on the fluid absorption layer 31, and the fluid retention layer 27 is arranged on the fluid distribution layer 29. A humidity sensing device 5 can advantageously be arranged between the fluid retention layer 27 and the fluid absorption layer 31. In particular, the humidity sensing device 5 can be arranged between the fluid retention layer 27 and the fluid distribution layer 29.
[0031] Now refer to Figures 3A to 3C The function of the humidity sensing device 5 according to an exemplary embodiment of the present invention is described below. Figures 3A to 3C yes Figure 2 The absorbent product 1 in the middle Figure 2 A cross-sectional view of the section cut by line A-A' in which different amounts of fluid are absorbed by the fluid absorption pad 7 of the absorbent article 1.
[0032] As in Figure 3A As can be seen in the magnified portion, the first electrode 17 has an exposed conductive surface 33, and the second electrode 19 is covered by a dielectric layer 35, which is included in the humidity sensing device 5. The first electrode 17 and the second electrode 19 may be included in a conductive layer formed on a flexible printed circuit board substrate 37. In this case, the conductive layer may be made of copper, for example. The exposed conductive surface 33 may be formed of a biocompatible conductive material suitable for use in the electrodes. Examples of such materials include silver / silver chloride, iridium oxide, boron / boron-doped diamond, noble metals, and oxides of noble metals. For this application, silver / silver chloride may be preferred, primarily for cost reasons. It should be noted that the materials listed are merely examples, and other options exist and / or can be developed. Such additional examples include titanium and titanium nitride, various carbon-based materials (e.g., carbon nanotubes and graphene), and conductive polymers (e.g., PEDOT).
[0033] exist Figure 3A In this process, the absorbent article 1 does not absorb any fluid. There is capacitive coupling C0 between the first electrode 17 and the second electrode 19, but this capacitive coupling C0 is very weak due to the small electrode area and the large distance between the electrodes. To estimate the amount and / or spatial distribution of fluid in the absorbent article 1, this empty-state capacitive coupling can be considered zero.
[0034] exist Figure 3B In this process, the absorbent article 1 has absorbed some fluid 39 (e.g., exudate), which is primarily water and therefore conductive. Figure 3B In the example state, fluid 39 is in conductive contact with the first electrode 17, and fluid covers a portion of the dielectric layer 35 on the second electrode 19 (hereinafter referred to as...). Figure 3B (Right side of the image). As a result, the parallel-plate capacitor (in...) Figure 3B (Schematally shown in the magnified portion on the right) is formed by a fluid 39 conductively connected to the first electrode 17 and a portion of the second electrode 19 covered by the fluid 39. This configuration results in capacitive coupling C between the first electrode 17 and the second electrode 19. a This capacitive coupling is proportional to the area of the second electrode 19 covered by the fluid 39. Of course, this capacitive coupling C... a Compare Figure 3A The capacitive coupling C0 in the dry state shown is much stronger.
[0035] exist Figure 3C In the middle, absorbent products 1 ratio in Figure 3B It absorbed more fluid 39. Figure 3CIn the example state, fluid 39 is in conductive contact with the first electrode 17 and covers most of the dielectric layer 35 on the second electrode 19 (hereinafter referred to as...). Figure 3C (Right and left sides of the middle). This configuration results in capacitive coupling C between the first electrode 17 and the second electrode 19. b The capacitive coupling is proportional to the area of the second electrode 19 covered by the fluid 39. This capacitive coupling C b Compare Figure 3B The capacitive coupling C in the state shown a Stronger. See below for reference. Figures 4 to 6 The different configurations of the humidity sensing device 5 discussed can provide different relationships between the spatial coverage of the fluid 39 in the absorbent article and the resulting capacitive coupling.
[0036] Figure 4 This is a top view of a humidity sensing device 5 according to a first embodiment of the present invention, which has the same... Figure 2 and Figures 3A to 3C The absorbent article 1 shown includes substantially the same structure. Figure 4 In the first example configuration, the second sensing device portion 13 surrounds the first sensing device portion 9. Furthermore, the second electrode 19 of the second sensing device portion 13 is arranged on at least two generally opposing sides of the first electrode 17 of the first sensing device portion 9. In fact, in this example configuration, the second electrode 19 is arranged on all sides of the first electrode 17, such that the presence of fluid can be sensed on all sides of the first electrode 17 as long as the first electrode 17 is covered by fluid. Figure 4 It can also be easily understood that the second electrode 19 has a geometric centroid that overlaps with that of the first electrode 17. This configuration facilitates symmetry in sensing relative to the first electrode 17. Furthermore, the area of the second electrode 19 is significantly larger than that of the first electrode 17. The first electrode 17 and the second electrode 19 are located on a flexible substrate 37. Figure 4 As shown, and also as Figures 3A to 3C As shown in the cross-sectional view, the flexible substrate 37 exists only partially between the first electrode 17 and the second electrode 19. In this configuration, it exists only at the location where the capacitance estimation circuit 21 is arranged, and at the location where the first electrode 17 and the second electrode 19 are connected to the capacitance estimation circuit 21. The humidity sensing device 5 can face upwards (e.g., Figures 3A to 3C (As shown) or arranged face down in an absorbent article. Unless the absorbed fluid at least partially overlaps with both the first electrode 17 and the second electrode 19, the humidity sensing device 5 according to different embodiments of the present invention will not indicate a strong capacitive coupling between the first electrode 17 and the second electrode 19. Figure 4The first embodiment of the invention shown has a simple construction, but a relatively large area of the humidity sensing device 5 overlapping with the absorbed fluid is required before the humidity sensing device can estimate that the absorbent article contains the absorbed fluid. This may be sufficient for some applications. In other applications, it may be desirable to be able to detect when a smaller area is covered by the absorbed fluid and / or provide an indication of the size and / or spatial distribution of the absorbed fluid.
[0037] Figure 5 This is a top view of the humidity sensing device 5 according to a second embodiment of the present invention. Figure 5 The humidity sensing device 5 in the middle can be regarded as Figure 4 The construction of the second electrode 19 in the second sensing device portion 13 is modified such that the second electrode 19 includes elongated sub-portions 41a-41d extending in different radial directions relative to the geometric centroid of the first electrode 17. This construction of the second electrode 19 results in a gradually increasing surface coverage of the absorbed fluid in the absorbent article 1, leading to a gradually increasing capacitive coupling between the first electrode 17 and the second electrode 19, which may be beneficial for some types of absorbent articles (e.g., wound dressings) for at least some applications. Figure 5 An example configuration of the humidity sensing device 5 also shows the longest distance d extending along line 43 in a first direction between a point on the outer periphery of the first electrode 17 and a first point on the outer periphery of the second electrode 19. max Longest distance d max The shortest distance d between a point on the outer periphery of the first electrode 17 and a second point on the outer periphery of the second electrode 19 along line 43 in the first direction. min It is more than 1.25 times longer.
[0038] Figure 6 This is a top view of the humidity sensing device 5 according to a third embodiment of the present invention. Figure 6 The humidity sensing device 5 in the middle can be regarded as Figure 4 The structure is modified in that the second sensing device portion 13 has a third electrode 45, which is electrically insulated from the second electrode 19 and is covered by a dielectric layer. For example... Figure 6 As schematically shown, the capacitance estimation circuit 21 is also connected to the third electrode 45. The capacitance estimation circuit 21 is configured to estimate a first capacitive coupling between the first electrode 17 and the second electrode 19, and a second capacitive coupling between the first electrode 17 and the third electrode 45. This provides improved accuracy in estimating the amount and / or spatial coverage of the absorbed fluid in the absorbent article 1, including the humidity sensing device 5.
[0039] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. In fact, the fact that some measures are described in mutually different dependent claims does not indicate that a combination of these measures cannot be used to provide an advantage.
Claims
1. A humidity sensing device (5) for sensing humidity in an absorbent article (1), the humidity sensing device (5) comprising: A first sensing device portion (9) having a first electrode (17) disposed therein, the first sensing device portion (9) being configured such that the covering of the first sensing device portion (9) by a conductive fluid (39) results in conductive contact between the first electrode (17) and the conductive fluid (39). The second sensing device portion (13) has a second electrode (19) disposed therein, and the second sensing device portion (13) is configured such that the covering of the second sensing device portion (13) by the conductive fluid (39) causes the second electrode (19) to be separated from the conductive fluid (39) by the dielectric layer (35). as well as A capacitance estimation circuit (21) is connected to the first electrode (17) and the second electrode (19), and the capacitance estimation circuit (21) is configured to estimate the capacitive coupling between the first electrode (17) and the second electrode (19).
2. The humidity sensing device (5) according to claim 1, wherein the first electrode (17) disposed in the first sensing device portion (9) has an exposed conductive surface (33).
3. The humidity sensing device (5) according to claim 2, wherein the exposed conductive surface (33) is at least partially formed of a biocompatible conductive material.
4. The humidity sensing device (5) according to claim 3, wherein the biocompatible conductive material is silver / silver chloride or iridium oxide or boron / boron doped diamond, or a noble metal, or an oxide of a noble metal.
5. The humidity sensing device (5) according to any one of the preceding claims, wherein the second sensing device portion (13) surrounds the first sensing device portion (9).
6. The humidity sensing device (5) according to claim 5, wherein the second electrode (19) of the second sensing device portion (13) is arranged on at least two generally opposite sides of the first electrode (17) of the first sensing device portion (9).
7. The humidity sensing device (5) according to claim 6, wherein the second electrode (19) of the second sensing device portion (13) has a centroid that overlaps with the first electrode (17) of the first sensing device portion (9).
8. In the humidity sensing device (5) according to any one of the preceding claims, the surface area of the second electrode (19) of the second sensing device portion (13) is at least twice the surface area of the first electrode (17) of the first sensing device portion (9).
9. The humidity sensing device (5) according to claim 8, wherein the surface area of the second electrode (19) of the second sensing device portion (13) is at least five times the surface area of the first electrode (17) of the first sensing device portion (9).
10. The humidity sensing device (5) according to any one of the preceding claims, wherein the longest distance (d) between a point on the outer periphery of the first electrode (17) of the first sensing device portion (9) and a point on the outer periphery of the second electrode (19) of the second sensing device portion (13) is... max The shortest distance (d) between a point on the outer periphery of the first electrode (17) of the first sensing device portion (13) and a point on the outer periphery of the second electrode (19) of the second sensing device portion (13) is... min It is at least 1.25 times longer.
11. The humidity sensing device (5) according to claim 10, wherein the longest distance (d) extending along line (43) in a first direction between a point on the outer periphery of the first electrode (17) of the first sensing device portion (9) and a point on the outer periphery of the second electrode (19) of the second sensing device portion (13) is... max The shortest distance (d) extending along a line in the first direction between a point on the outer periphery of the first electrode (17) of the first sensing device portion (9) and a point on the outer periphery of the second electrode (19) of the second sensing device portion (13). min It is at least 1.25 times longer.
12. The humidity sensing device (5) according to any one of the preceding claims, wherein the second electrode (19) of the second sensing device portion (13) comprises: The first sub-part (41a) is elongated and extends in a first radial direction relative to the centroid of the first electrode (17) of the first sensing device part (9). as well as The elongated second sub-part (41b) extends in a second radial direction relative to the centroid of the first electrode (17) of the first sensing device part (9), the second radial direction being different from the first radial direction.
13. The humidity sensing device (5) according to any one of the preceding claims. The second sensing device portion (13) has a third electrode (45) disposed therein, the third electrode being electrically insulated from the second electrode (19), and the second sensing device portion (13) is configured such that the covering of the second sensing device portion (13) by the conductive fluid (39) causes the third electrode (45) to be separated from the conductive fluid (39) by the dielectric layer (35); and The capacitance estimation circuit (21) is also connected to the third electrode (45), and the capacitance estimation circuit (21) is configured to estimate a first capacitive coupling between the first electrode (17) and the second electrode (19), and a second capacitive coupling between the first electrode (17) and the third electrode (45).
14. An absorbent article (1), comprising: Fluid absorbent pad (7), the fluid absorbent pad being configured to absorb fluid (39) from the user’s body; as well as According to any one of the preceding claims, the humidity sensing device (5) is arranged to contact the fluid absorption pad (7) such that the first sensing part (9) and the second sensing part (13) of the humidity sensing device (5) can be covered by the fluid (39) absorbed by the fluid absorption pad (7).
15. The absorbent article (1) according to claim 14, wherein, The absorbent article (1) includes a backing layer (25) that holds the fluid absorbent pad (7) and a body contact layer (23). The fluid-absorbing pad (7) is a layered structure comprising at least a fluid retention layer (27) and a fluid-absorbing layer (31), the fluid-absorbing layer being disposed between the fluid retention layer (27) and the body contact layer (23); and The humidity sensing device (5) is arranged between the fluid holding layer (27) and the fluid absorption layer (31).