WO2022255945A2

WO2022255945A2 - A liquid sensor for a diaper and method of manufacturing the same

Info

Publication number: WO2022255945A2
Application number: PCT/SG2022/050369
Authority: WO
Inventors: Jackie Ying; Min Hu
Original assignee: Agency For Science, Technology And Research
Priority date: 2021-06-01
Filing date: 2022-05-31
Publication date: 2022-12-08
Also published as: WO2022255945A3

Abstract

A liquid sensor for a diaper and method of manufacturing the same are provided. The liquid sensor includes a flexible substrate, a first electrode disposed on the substrate and a plurality of second electrodes disposed on the substrate. The substrate is made of an electrically insulating material. Each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes. Each of the second electrodes defines a detection point for receiving a liquid. Each second electrode is configured to provide an output signal indicating a presence of the liquid at the respective detection point. The output signal comprises a potential difference between said second electrode and the first electrode. A wetness level of the diaper is determined based on the output signal of each of the second electrodes.

Description

A Liquid Sensor for a Diaper and Method of Manufacturing the Same

Technical Field

[0001] The present invention generally relates to a liquid sensor for a diaper, and method of manufacturing the same.

Background Art

[0002] Urinary incontinence (Ul) is a prevalent health problem among the elderly, especially for elderly residents in nursing homes and hospitals. Afflicted by dementia, stroke or other advanced neurodegenerative conditions, these residents often have difficulty communicating their toileting needs. As the world’s population ages, the number of elderly and those who suffer from Ul will increase exponentially in the future. It is predicted that by 2030, more than 20% of the world’s population will be over 65 years old, and up to 35% of the population over 60 years old is expected to have problems with continence. Ul is a distressing and costly health problem that affects not only the patients but also their caregivers over an extended period of time.

[0003] Diapering, together with routine checks, is widely used to manage Ul. Standard continence management usually consists of scheduled diaper checks (and changes in case of wet) to shorten the time that patients lie in soiled diapers. Depending on the setting, routine checks by caregivers take place at intervals of 4-6 hours, or up to 5 times a day. However, these routine checks are often a burden to both caregivers and patients. Manual diaper checks are time-consuming for caregivers and intrusive for patients. They are also unpleasant and cumbersome for both parties, as it is not easy to check the diapers without undressing the wearers. If a patient soils his or her diaper shortly after the routine check, he or she may remain in the soiled diaper until the next scheduled check, which could be hours later. Sustained contact with soiled diapers is unhygienic, may lead to degradation of skin integrity, as well as compromise the patient’s dignity and living environment. On the other hand, diapers that are unsaturated or even dry at the point of checking represent wasted time and effort for the caregiver. Therefore, a more effective approach to manage Ul is required to provide quality patient care, eliminate high labour costs, and minimize adverse health impact for the patients.

[0004] Accordingly, a need exists to provide a liquid sensor for a diaper that seeks to address some of the above problems. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

Summary of Invention

[0005] An aspect of the present disclosure provides a liquid sensor for a diaper. The liquid sensor includes a flexible substrate, a first electrode disposed on the substrate and a plurality of second electrodes disposed on the substrate. The substrate is made of an electrically insulating material. Each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes. Each of the second electrodes defines a detection point for receiving a liquid. Each second electrode is configured to provide an output signal indicating a presence of the liquid at the respective detection point. The output signal comprises a potential difference between said second electrode and the first electrode. A wetness level of the diaper is determined based on the output signal of each of the second electrodes.

[0006] Another aspect of the present disclosure provides a monitoring system including the aforementioned liquid sensor, a transmitter unit configured to generate a wireless signal based on an output of the liquid sensor, and a receiver unit configured to receive the wireless signal and generate an alert based on a preset condition.

[0007] Another aspect of the present disclosure provides a liquid sensing method including measuring a potential difference between a first electrode and each of a plurality of second electrodes, the first electrode and the plurality of second electrodes being disposed on a flexible substrate, wherein the substrate is made of an electrically insulating material, wherein each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes, and wherein each of the second electrodes defines a detection point for receiving a liquid, for each of the second electrodes, providing an output signal indicating a presence of the liquid at the respective detection point by detecting a change in the potential difference between said second electrode and the first electrode, and determining a wetness level based on the output signal of each of the second electrodes.

[0008] Another aspect of the present disclosure provides a method of manufacturing a liquid sensor. The method includes providing a flexible substrate made of an electrically insulating material, disposing a first electrode on the substrate and disposing a plurality of second electrodes such that each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes, each of the second electrodes defining a detection point for receiving a liquid. Each second electrode is configured to provide an output signal indicating a presence of the liquid at the respective detection point, the output signal comprising a potential difference between said second electrode and the first electrode. A wetness level of the diaper is determined based on the output signal of each of the second electrodes.

Brief Description of Drawings

[0009] Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Figs. 1a and 1b

[0010] Fig. 1a shows the establishment of potential difference in a liquid sensor between two separate dissimilar electrodes when bridged by electrolyte, in accordance with embodiments of the present disclosure. Fig. 1b shows testing results of potential difference generated by a pair of copper and aluminum electrodes on various human urine samples, in accordance with embodiments of the present disclosure.

Figs. 2a to 2d

[0011] Figs. 2a to 2d show the structure and working principle of liquid sensor for wetness level estimation, in accordance with embodiments of the disclosure.

Figs. 3a to 3d

[0012] Figs. 3a to 3c show characteristics of sensor output for wetness level estimation. Fig. 3d shows a flowchart illustrating a liquid sensing method, in accordance with embodiments of the disclosure.

Figs. 4a and 4b

[0013] Fig. 4a shows a liquid sensor at different stages of manufacture and integration with a diaper. Fig. 4b shows a flowchart illustrating a method of manufacturing a liquid sensor, in accordance with embodiments of the disclosure. Figs. 5a and 5b

[0014] Fig. 5a shows a schematic circuit for wetness data acquisition and transmission, in accordance with embodiments of the disclosure. Fig. 5b shows a photograph of a transmitter prototype for the smart diaper system, in accordance with embodiments of the disclosure.

Fig. 6

[0015] Fig. 6 shows testing of smart diaper with two sensor strips inserted above and below the absorbent layers respectively, in accordance with embodiments of the disclosure.

Fig. 7

[0016] Fig. 7 shows a schematic diagram of a smart diaper system for wetness monitoring of diapers in a nursing home or hospital, in accordance with embodiments of the disclosure.

Fig. 8

[0017] Fig. 8 shows the change of wetness level from the two sensors when saline was gradually poured onto and absorbed by the diaper from laboratory test results, in accordance with embodiments of the disclosure.

[0018] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale. For example, the dimensions of some of the elements in the illustrations, block diagrams or flowcharts may be exaggerated in respect to other elements to help to improve understanding of the present embodiments.

Description of Embodiments

[0019] A smart diaper can solve the problems facing the conventional management of urinary incontinence among the elderly, by providing timely and precise notification to caregivers when the diaper is soiled and needs to be changed. However, the development and commercialization of smart diapers have been slow, hampered at least by the lack of a suitable sensor for effective monitoring of incontinence. A liquid sensor capable of estimating the wetness level of a soiled adult diaper disclosed herein seeks to address some of the above problems.

[0020] The working principle of the liquid sensor is based on the change in potential difference between a plurality of insulated detection electrodes comprising, for example, copper and a non-insulated common electrode comprising, for example, aluminum. The plurality of insulated detection electrodes and the non-insulated common electrode can be printed on a flexible strip (e.g. made from polymer). On each detection electrode, one or more zones can be exposed (e.g. at a fixed pitch) as liquid detection points to contact the absorbent layer of the diaper. These exposed zones can be arranged at an equivalent distance to one another along the strip and can form the markers of an “electronic ruler” for wetness level measurement. When a detection point is in contact with an electrolyte such as urine, a potential difference will be established between the corresponding detection electrode and the common electrode like a galvanic cell structure. This potential difference can be used as a digital output (logic high or low) for the presence of urine. By reading the digital output from all the detection electrodes, the wetness area of a soiled diaper can be estimated using the sensor.

[0021] Thus, the liquid sensor can allow the wetness level of a soiled diaper to be monitored in real time and at an affordable cost. With the help of the sensor, a caregiver can set the alert criteria for diaper change at an optimal time point for each wearer. It can be based on the wetness level of a diaper or the time that a wearer spends in a soiled diaper. Therefore, a sensor-enabled smart diaper in accordance with embodiments of the present disclosure would not only facilitate timely diaper change in frail patients, but also reduce the workload of caregivers and save costs for the healthcare institution.

[0022] Embodiments of the present invention will be described, by way of example only, with reference to the drawings. Like reference numerals and characters in the drawings refer to like elements or equivalents.

[0023] Fig. 1 shows detection of urine as an electrolyte with a galvanic cell structure. Fig. 1a shows the establishment of potential difference in a liquid sensor 100 between two separate dissimilar electrodes 104, 106 when bridged by electrolyte 108 and Fig. 1b shows testing results of potential difference generated by a pair of copper and aluminum electrodes on various human urine samples.

[0024] As shown in Fig. 1a, the basic working principle of the liquid sensor 100 is based on the establishment of a potential difference between dissimilar electrodes 104, 106 separated by an electrically insulating substrate 102. The dissimilar electrodes 104, 106 can be metal or metal oxide that can generate a stable voltage in solution, such as copper and aluminum. A potential difference (or a voltage as signal output) will be generated if the two separate metals are bridged by an electrolyte 108 e.g. urine, regardless of the volume. For example, standard redox potentials of materials at 25°C can be expressed as follows for 1 mol/L of dissolved species at 1 atm of pressure. [0025] Half-cell (positive): Cu²⁺ + 2e^~ = Cu cp°(Cu/Cu²⁺) = +0.159 V

[0026] Half-cell (negative): AI³⁺ + 3e- = AI cp°(AI/AI³⁺) = -1.66 V

[0027] Full cell: 2AI + 3Cu²⁺ = 2AI³⁺ + 3Cu

[0028] Voltage difference between copper and aluminum electrodes in urine can be written as:

where E° is the standard cell potential at the temperature of interest; OAI3₊ and Oc_U2₊ are the chemical activities of Al³⁺ and Cu²⁺ in urine, respectively; 7 is the absolute temperature of the system; z is the number of moles of electrons transferred in the cell reaction; and R and F are the universal gas constant and the Faraday constant, respectively. In the case of a solution with ammonia, the negative half-cell becomes:

[0029] Al(s) + 4(OH ) = AI(OH₄)- + 3e^~ cp°(AI/ AI(OH₄)-) = -2.33 V

[0030] When the diaper is dry, as shown in Fig. 1a, the potential difference between two separate and dissimilar electrodes 104, 106 is almost zero. After the wearer passes urine or wet feces 108, the diaper becomes wet and the two electrodes 104, 106 are bridged to generate a potential difference of ~ 0.6 V (theoretically 2.0 V), which can be easily measured by detection circuit 110 without the need for signal amplification (Fig. 1b). Similar to a simple galvanic cell structure, it offers a very high signal-to-noise ratio due to this principle. This can make it an excellent candidate for monitoring diaper wetness, as a robust sensor is needed to prevent false alarms.

[0031] The wetness level of a diaper can be estimated using the basic working principle described above, but with a slightly different sensor structure design. Figs. 2a to 2d show the structure and working principle of liquid sensor 200 for wetness level estimation. Fig. 2a shows a top view of the sensor 200. Liquid detection points 208 (see Fig. 2c) can be arranged at an equivalent distance to one another on the detection electrodes 206. Fig. 2b shows a cross-sectional view of the sensor strip. Common electrode 204 and the detection electrodes 206 can be printed on different sides of a flexible substrate, where the detection electrodes are partially covered by a layer of insulator. Fig. 2c shows an enlarged view of connecting ends 212 of the electrodes 206. Fig. 2d shows a schematic model of the sensor 200. The sensor 200 can be modeled as a one-dimensional ruler with multiple liquid detection points arranged at equal intervals.

[0032] As shown in Figs. 2a to 2c, a liquid sensor 200 can include a flexible insulator strip 202 with a common electrode 204 (e.g. aluminum) printed on one side and a group of detection electrodes 206 (e.g. copper, Ei to E_n) printed in parallel on the opposing side. The detection electrodes 206 can be embedded in an insulating layer 210. On each detection electrode, only some small zones 208 are exposed (e.g. at a fixed pitch) to contact the absorbent layer of the diaper. The exposed zones 208 are referred herein as the liquid detection points 208. They can be arranged at an equivalent distance to one another on the neighboring detection electrodes.

[0033] In other words, the liquid sensor 200 can include a flexible substrate 202 made of an electrically insulating material, a first electrode 204 disposed on the substrate 202 and a plurality of second electrodes 206 disposed on the substrate. Each of the plurality of second electrodes 206 is electrically insulated from the first electrode 204 and the other second electrodes 206, each of the second electrodes 206 defining a detection point 208 for receiving a liquid. Each second electrode 206 is configured to provide an output signal indicating a presence of the liquid at the respective detection point 208, the output signal comprising a potential difference between said second electrode 206 and the first electrode 204. As will be elaborated below, a wetness level of the diaper can be determined based on the output signal of each of the second electrodes 206. The detection point 208 of one of the plurality of second electrodes 206 can be spaced a predetermined distance away (e.g. distance L as shown in Fig. 2a) along a length of the substrate from the detection point 208 of an adjacent second electrode 206. The first electrode 204 can include aluminum and the plurality of second electrodes 206 can include copper.

[0034] In the embodiment, the liquid sensor 200 can include a liquid impervious layer 210 partially covering each of the plurality of second electrodes 206. The liquid impervious layer 210 is electrically insulating and the detection point 208 of each second electrode 206 comprises a portion of said second electrode 206 exposed by the liquid impervious layer 210.

[0035] As shown in Fig. 2a, if the gap between two neighboring detection electrodes is G, and the distance between the adjacent liquid detection points on the neighboring electrodes is L, then the pitch P of liquid detection points on an electrode is designed as n-L, where n is the number of detection electrodes on the sensor strip. If the electrode gap G is much smaller than the length of the sensor strip, then the sensor strip can be modeled as a “one dimensional ruler”. The repeated groups of detection points (from Di to D_n) on the ruler are designed to eliminate the effect of wet area location on the sensor output.

[0036] Using this ruler, the length of the wet area along the sensor strip can be electrically measured, and thus the wetness level of the diaper can be estimated. Specifically, when a liquid detection point on a detection electrode is in contact with the wet diaper, the potential difference or resistance between the specific detection electrode and the common electrode will be changed. Depending on the output from each detection electrode, the number of liquid detection points in contact with the wet spots on the diaper can be determined, which will roughly correspond to the size of the wet area along the sensor strip. Theoretically, a larger wet area will trigger more detection electrodes. However, due to the limited number of detection electrodes, the full-scale range for this sensor strip is (n - 1) L.

[0037] Figs. 3a to 3c show characteristics of sensor output for wetness level estimation. Fig. 3a shows that the output of the sensor 200 is positively correlated to the size of the wetness area. Fig. 3b shows how the position of the wetness area relative to the detection points 208 can affect the output of the sensor 200. Fig. 3c shows that the same wet area may generate a different output (wetness level) due to the discrete distribution of detection points 208 on the sensor 200.

[0038] The potential difference between each detection electrode 206 and the common electrode 204 can be used as a digital output (logic high or low) to indicate the presence of urine. By reading the digital output from all the detection electrodes 206, the wetness level of a diaper can be estimated as 0, 1, 2, ..., n. The wetness level corresponds to the total number of logical highs from the detection electrodes. Specifically, level 0 reflects dryness while levels 1 to n indicate increasing number of detection points in contact with the wet area. Due to the discrete distribution of detection points, however, both the size and position (relative to the detection points) of the wet area may affect the sensor output. For example, if the wet area (indicated as a small green area in Fig. 3a) is not large enough and happens to lie between two detection points D3 and D4, the output from the sensor will remain at Level 0. However, for the same wetness area, if it happens to lie on a detection point D2 (Fig. 3b), the output from the sensor will change to Level 1 if the wetness area can trigger the liquid sensor. Similarly, depending on the position relative to the detection points, for the same wetness area (indicated as a larger purple area) the output from the sensor might be different. To eliminate this uncertainty, as shown in Fig. 3c, the correspondence between the wetness level and the total number of logical high detection electrodes are redefined. This can help set a minimum wetness threshold for diaper change. For instance, if two detection electrodes are in a logical high state, then the length of the wet area (along the sensor strip) is at least L. In this way, a caregiver could set the alert criteria for diaper change at an optimal time point for each wearer, according to the wetness range on the diaper or the time that a wearer spends in a soiled diaper.

[0039] In other words, with reference to Fig. 3d, a liquid sensing method 300 can include step 302 of measuring a potential difference between a first electrode and each of a plurality of second electrodes, the first electrode and the plurality of second electrodes being disposed on a flexible substrate, wherein the substrate is made of an electrically insulating material, wherein each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes, and wherein each of the second electrodes defines a detection point for receiving a liquid. The liquid sensing method 300 can also include step 304 of providing, for each of the second electrodes, an output signal indicating a presence of the liquid at the respective detection point by detecting a change in the potential difference between said second electrode and the first electrode and step 306 of determining a wetness level based on the output signal of each of the second electrodes. The output signal can include a logic high signal if the liquid is present at the detection point. The step of determining the wetness level can include determining a number of digital high signals and positions of respective second electrodes.

[0040] The sensor strip for quantitative liquid detection is designed based on the structure disclosed above. The sensor strip can be designed to cover the entire length of an adult diaper. It can include one common aluminum electrode and 4 copper detection electrodes. The detection electrodes can be fabricated on a polyimide sheet using the process for flexible printed circuit boards (FPCB). A layer of patterned insulator to expose the liquid detection points and connection ends covers these electrodes. Next, a layer of aluminum was laminated on the other side of the polyimide sheet without copper electrodes. Following that, the individual sensor strips can be cut from the sheet (as shown on the top photographs of Fig. 4a). The fabrication process is suitable for mass production at low cost. The sensor strip can be disposed with the diaper after use.

[0041] Guide sticks were used to insert the flexible sensor strip into the diaper to integrate the sensor with the diaper (as shown on the bottom photograph of Fig. 4b). The sensor strip can be secured by double-sided tapes to the bottom diaper sheet to ensure that the detection points were in contact with the absorbent layer. [0042] In other words, with reference to Fig. 4b, a method 400 of manufacturing a liquid sensor can include step 402 of providing a flexible substrate made of an electrically insulating material and step 404 of disposing a first electrode on the substrate. The method 400 can also include step 406 of disposing a plurality of second electrodes such that each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes, each of the second electrodes defining a detection point for receiving a liquid. Each second electrode can be configured to provide an output signal indicating a presence of the liquid at the respective detection point, the output signal comprising a potential difference between said second electrode and the first electrode. A wetness level of the diaper can be determined based on the output signal of each of the second electrodes. The plurality of second electrodes can be disposed in step 406 such that the detection point of one of the plurality of second electrodes is spaced a predetermined distance away along a length of the substrate from the detection point of an adjacent second electrode. The step 406 of disposing the plurality of second electrodes further comprises disposing a liquid impervious layer partially covering each of the plurality of second electrodes, wherein the detection points of each second electrode comprises a portion of each second electrode exposed by the liquid impervious layer. The first electrode can include aluminum and the plurality of second electrodes can include copper, or vice versa.

[0043] A wireless alert system for smart diapers to monitor incontinence in multiple patients within a hospital ward or a nursing home is disclosed. Each patient can wear a smart diaper with an embedded sensor strip, connected to a transmitter device. The transmitters can transmit sensor readings (e.g. at regular intervals) to a gateway which processes the messages and relays them to a central monitoring computer. With the help of a backend program, the computer stores the data, and hosts a user interface to show caregivers the wetness level of the diapers being monitored. It also provides remote alerts to caregivers by SMS or Telegram bot.

[0044] The transmitters that patients wear should therefore be small, lightweight and power-saving for minimal disruptions. In an embodiment, ZigBee is used as the wireless protocol for signal transmission between the transmitters and the receiving gateway. ZigBee has low power consumption, and its mesh network allows a large number of devices to be connected to it. Nodes can be placed throughout the ward to extend the communication range to the entire area.

[0045] Figs. 5a and 5b show a wireless alert system for diaper wetness monitoring. Fig. 5a shows a schematic circuit for wetness data acquisition and transmission based on ZigBee transceiver module ETRX357 and microcontroller PIC125F635. Fig. 5b shows a photograph of a transmitter prototype for the smart diaper system. The transmitter comprises a Telegesis ZigBee module (ETRX357) with a built-in ceramic antenna, a Microchip PIC12F635 microcontroller, a lithium polymer battery, and a flexible printed circuit connector for the sensor strip. As shown in Figure 5, the ETRX357 is the main module responsible for reading the sensor strip, as well as for communicating with external devices. The module is set as a mobile end device (MED). In other words, the transceiver module ETRX357 can be a processing device configured to measure the output signal of each of the second electrodes and generate a signal with a magnitude indicative of the wetness level of the diaper. The PIC16F636 controls the power to the ETRX357 and is responsible for the sleep cycle of the transmitter to reduce power consumption. Apart from the transmitters, other devices (the routers, the coordinator and the receiver) of the ZigBee system also use the ETRX357 module for data communication.

[0046] Fig. 6 shows testing of smart diaper with two sensor strips inserted above and below the absorbent layers respectively. The smart diaper system is tested in the laboratory to verify the working principle of the liquid sensor and assess the performance of the ZigBee wireless alert system. Two sensor strips were respectively inserted above and below the absorbent layer of an L-sized TENA adult diaper and connected to the wireless alert system via two ZigBee transmitters (see Fig. 6). A saline solution of 0.90% w/v of NaCI was used as simulated urine and poured onto the diaper at a rate of ~ 50 ml/min. Outputs from the two sensors were recorded and compared under the same wetness condition. The results were used to verify the discrete increment of wetness level from the sensor output and to find the optimal position for sensor strip in the diaper. The reliability of the wireless communication system was also tested under different conditions (e.g. node distance, obstacle of walls and battery level, etc.) to mimic the clinical environment.

[0047] Fig. 7 shows a schematic diagram of a smart diaper system for wetness monitoring of diapers in a nursing home or hospital. The smart diaper system 700 can be deployed in a hospital ward. The system can comprise 10 transmitters for patients and 2 transmitters for control and backup, 3 signal routers along the central corridor of the ward to cover the entire area, a ZigBee coordinator, a ZigBee receiver, an SMS gateway and a computer running the monitoring software. The sensor is inserted throughout the length of an adult diaper and centered under the absorbent layer of the diaper, ensuring that it would be in contact with the absorbent material. The transmitter box is attached to the diaper to relay signals from the sensor to the system. When wetness reaches an alert level, a notification is displayed on a computer dashboard and sent to a mobile phone in the form of an SMS. [0048] In other words, a monitoring system in accordance with embodiments of the disclosure can include a liquid sensor 200, a transmitter unit 702 configured to generate a wireless signal based on an output of the liquid sensor 200 and a receiver unit 704 configured to receive the wireless signal and generate an alert based on a preset condition. The preset condition can include the wetness level exceeding a predetermined threshold or a wetness level being detected for at least a predetermined duration. The wireless signal can include a Zigbee signal.

[0049] Fig. 8 shows the change of wetness level from the two sensors when saline was gradually poured onto and absorbed by the diaper from laboratory test results. The accumulation of saline in the absorbent layer led to an increase in the diaper’s wetness level. When saline was gradually poured onto the diaper’s top surface, as shown in Fig. 8, the increase in wetness level was successfully detected and monitored from both sensors with similar outputs. However, the output from the bottom sensor was more stable than that from the top sensor and had less fluctuation. This is because the liquid detection points of the top sensor faced the top layer of the diaper. The output from the top sensor was more easily affected by the absorption of saline from the diaper’s surface layer to the absorbent layer. In contrast, the liquid detection points of the bottom sensor faced the absorbent layer. As saline accumulated in the absorbent layer, gravity caused it to have better contact with the bottom sensor than with the top sensor. Hence, all the sensor strips are inserted at the bottom of the absorbent layer for clinical studies.

[0050] The smart diaper system is a substantial improvement over the conventional approach of periodic routine checks, as it works under an ‘event-driven’ mode, i.e. the diaper change is triggered quickly and only when needed. It can potentially replace inefficient routine checks, thereby increasing productivity within the labor-intensive healthcare industry, minimizing patient discomfort caused by unnecessary routine checks. It also prevents diaper dermatitis and associated infections by reducing the time patients spend lying in soiled diapers.

[0051] It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

1. A liquid sensor for a diaper, the liquid sensor comprising: a flexible substrate, wherein the substrate is made of an electrically insulating material; a first electrode disposed on the substrate; a plurality of second electrodes disposed on the substrate, each of the plurality of second electrodes electrically insulated from the first electrode and the other second electrodes, each of the second electrodes defining a detection point for receiving a liquid; wherein each second electrode is configured to provide an output signal indicating a presence of the liquid at the respective detection point, the output signal comprising a potential difference between said second electrode and the first electrode; and wherein a wetness level of the diaper is determined based on the output signal of each of the second electrodes.

2. The liquid sensor of claim 1 , wherein the detection point of one of the plurality of second electrodes is spaced a predetermined first distance away along a length of the substrate from the detection point of an adjacent second electrode.

3. The liquid sensor of claim 1 or 2, wherein each second electrode defines one or more additional detection points for receiving the liquid, each of the one or more additional detection points spaced a second distance away along a length of said second electrode from an adjacent detection point of said second electrode.

4. The liquid sensor of any one of claims 1 to 3, further comprising a liquid impervious layer partially covering each of the plurality of second electrodes, wherein the liquid impervious layer is electrically insulating, and wherein a detection point of a second electrode comprises a portion of said second electrode exposed by the liquid impervious layer.

5. The liquid sensor of any one of claims 1 to 4, wherein the first electrode comprises aluminum and wherein the plurality of second electrodes comprise copper.

6. The liquid sensor of any one of claims 1 to 4, wherein the first electrode comprises copper and wherein the plurality of second electrodes comprise aluminum.

7. The liquid sensor of any one of claims 1 to 6, further comprising a processing device configured to: measure the output signal of each of the second electrodes; and generate a signal with a magnitude indicative of the wetness level of the diaper.

8. A diaper comprising the liquid sensor of any one of claims 1 to 7.

9. A monitoring system comprising: the liquid sensor as claimed in claim 1; a transmitter unit configured to generate a wireless signal based on an output of the liquid sensor; and a receiver unit configured to receive the wireless signal and generate an alert based on a preset condition.

10. The monitoring system as claimed in claim 9, wherein the preset condition comprises the wetness level exceeding a predetermined threshold.

11. The monitoring system as claimed in claim 9, wherein the preset condition comprises a wetness level being detected for at least a predetermined duration.

12. The monitoring system as claimed in any one of claims 9 to 11, wherein the wireless signal comprises a Zigbee signal.

13. The monitoring system as claimed in any one of claims 7 to 12, further comprising an SMS gateway communicatively coupled to the receiver unit, the SMS gateway configured to transmit a SMS to a device associated with caregivers based on the alert.

14. A liquid sensing method comprising: measuring a potential difference between a first electrode and each of a plurality of second electrodes, the first electrode and the plurality of second electrodes being disposed on a flexible substrate, wherein the substrate is made of an electrically insulating material, wherein each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes, and wherein each of the second electrodes defines a detection point for receiving a liquid; for each of the second electrodes, providing an output signal indicating a presence of the liquid at the respective detection point by detecting a change in the potential difference between said second electrode and the first electrode; and determining a wetness level based on the output signal of each of the second electrodes.

15. The method as claimed in claim 14, wherein the output signal comprises a logic high signal if the liquid is present at the detection point.

16. The method as claimed in claim 15, wherein determining the wetness level comprises determining a number of logic high signals and positions of respective second electrodes.

17. The method as claimed in any one of claims 14 to 16, wherein the liquid comprises urine.

18. A method of manufacturing a liquid sensor, the method comprising: providing a flexible substrate made of an electrically insulating material; disposing a first electrode on the substrate; and disposing a plurality of second electrodes such that each of the plurality of second electrodes is electrically insulated from the first electrode and the other second electrodes, each of the second electrodes defining a detection point for receiving a liquid; wherein each second electrode is configured to provide an output signal indicating a presence of the liquid at the respective detection point, the output signal comprising a potential difference between said second electrode and the first electrode; and wherein a wetness level of the diaper is determined based on the output signal of each of the second electrodes.

19. The method as claimed in claim 18, wherein disposing a plurality of second electrodes comprises disposing the plurality of second electrodes such that the detection point of one of the plurality of second electrodes is spaced a predetermined distance away along a length of the substrate from the detection point of an adjacent second electrode.

20. The method as claimed in claim 18 or 19, wherein disposing the plurality of second electrodes comprises disposing the plurality of second electrodes such that each second electrode defines one or more additional detection points for receiving the liquid, each of the one or more additional detection points spaced a second distance away along a length of said second electrode from an adjacent detection point of said second electrode.

21. The method as claimed in claim 18 or 20, wherein disposing a plurality of second electrodes further comprises disposing a liquid impervious layer partially covering each of the plurality of second electrodes, wherein the liquid impervious layer is electrically insulating, and wherein a detection point of a second electrode comprises a portion of said second electrode exposed by the liquid impervious layer.

22. The method as claimed in any one of claims 18 to 21, wherein the first electrode comprises aluminum and wherein the plurality of second electrodes comprise copper.

23. The method as claimed in any one of claims 18 to 21, wherein the first electrode comprises copper and wherein the plurality of second electrodes comprise aluminum.

24. The method as claimed in any one of claims 18 to 22, further comprising providing a processing device, the processing device configured to: measure the output signal of each of the second electrodes; and generate a signal with a magnitude indicative of the wetness level of the diaper.