GB2565833A

GB2565833A - Wetness sensor

Info

Publication number: GB2565833A
Application number: GB1713669.8A
Authority: GB
Inventors: Huq Ejaz
Original assignee: Oxford Caresense Ltd
Current assignee: Oxford Caresense Ltd
Priority date: 2017-08-25
Filing date: 2017-08-25
Publication date: 2019-02-27
Also published as: GB201713669D0; EP3672545A1; WO2019038550A1

Abstract

A wetness sensor for incontinence products, such as nappies/diapers, has a light source 7 (may be an LED) and detector 8 (may be a phototransistor or photodiode). An expandable portion 6 (may be a hydrogel) increases in volume when in contact with a liquid, and has a reflective surface 18 which reflects light from the source 7 towards the detector 8. The detector 8 generates a signal when the distance between it and the reflective surface 18 decreases. There may be an array of sensors on a flexible substrate 9, arranged in a Y shape, an ellipse, a star, or grid configuration. The expandable portion 6 may be in a housing, and a cap may have a capillary array 13 facilitating liquid ingress. A transparent impermeable barrier 15 may seal the light source 7 and detector 8 from liquid. There may be an external wireless monitoring unit.

Description

Field of the Invention

This invention relates to a sensor, and in particular to a device that can be used to measure wetness in an incontinence product, such as a diaper.

Background of the Invention

Incontinence products such as nappies, diapers, incontinence pads and absorbent briefs are widely sold for both infant and adult users. The use of adult incontinence products in particular is increasing due to factors such as an ageing population and the associated increase in illnesses linked to incontinence. Some users are unable to communicate the need to replace a soiled incontinence product. It is therefore necessary for a carer to periodically make a manual check for soiling, which is demanding on carer time and also negatively affects user dignity.

Various options have been proposed for monitoring soiling of incontinence products. US2013/0162403A1 describes a tag comprising a radio-frequency chip, an antenna, a memory element with electrical storage and output terminals and a coating that becomes electrically conductive when wetted.

Other monitoring solutions involve an indicator that changes colour, positioned within the incontinence product, for example due to a change in pH when wetted with urine.

Summary of the Invention

In one aspect of the invention, a wetness sensor suitable for a diaper or other incontinence product is provided. The wetness sensor comprises an optical sensor. The optical sensor comprises a light source and a light detector; and an expandable element that increases in volume when wetted. The expandable element has a reflective surface which reflects light received from the light source to the light detector and in use the light detector generates a signal when a gap between the light detector and the reflective surface decreases in response to wetting of the expandable element.

A sensor configured in this way is both accurate and reliable and is capable of having a very low profile so that it is unobtrusive to a user when positioned within a diaper.

At least a part of the optical sensor may be supported on a flexible substrate. Optionally, the substrate is suitably part of an elongate flexible polymeric layer, with the optical sensor positioned at a first end of the elongate flexible polymeric layer.

In some embodiments, the wetness sensor comprises a plurality of optical sensors, each respective expandable element being spaced apart from each other intervals along the length of the substrate. This may facilitate selection of the trigger point at which a user or carer is alerted to soiling, such that a lesser or greater degree of soiling may prompt a change of diaper. If a plurality of optical sensors is provided, the number of optical sensors is preferably from 2 to

6. The distance between each optical sensor is preferably from 10 mm to 50 mm.

Preferably, the substrate forms a two-dimensional array linking a plurality of optical sensors. Such an array comprises a plurality optical sensors extending in more than one direction in the plane of a diaper, each optical sensor is supported on the substrate. Use of a two-dimensional array may allow for more accurate detection of wetness independent of the orientation and anatomy of the patient. For example, arrays used in diapers can be configured for genderspecific anatomy and to allow for the effects of gravity on liquid migration within a diaper when a wearer takes any position, including lying down. Particular examples of arrays include a Y-shaped array which may be especially suitable for a male anatomy; an elliptical shaped array which may be especially suitable for a female anatomy; a mesh shaped array and a star shaped array, both of which may be suitable for any gender anatomy.

In an array, each optical sensor or set of optical sensors may be accessed simultaneously to detect the presence or absence of fluid in that particular region. Alternatively, each set may be accessed individually without triggering the others, in an X-Y matrix addressing strategy.

The light source may emit any infrared or visible wavelength of light. Preferably, the wavelength emitted is in the infrared. Preferably the light source is a light emitting diode (LED). In some embodiments, an organic light emitting diode (OLED) is used. An advantage of using OLEDs is that they can be printed onto a polymeric strip, thus facilitating low cost, high throughput manufacturing.

In preferred embodiments the light emitted is pulsed. The modulation frequency may be varied if required for the circumstances of the individual user. The modulation frequency is preferably 1 pulse every 1 to 5 minutes. The length, or cycle, of each pulse is suitably of the microsecond scale. Using a pulsed light source allows the wetness sensor to have a low power consumption.

The wetness sensor preferably operates with a supplied voltage of 5V or less, more preferably 3V or less.

The reflective surface may be a distinct reflective layer, bonded to the surface of the expandable element. A reflective layer is preferably chosen for maximum reflectance of the wavelength of the light source. If an infrared light source is used the reflective layer is preferably opaque and bright white. If a visible red LED is used the reflective layer is preferably opaque and red.

Preferably, the expandable element comprises or is a hydrogel. Hydrogels expand on contact with aqueous liquids and thus are a suitable choice for generating a detectable gap decrease in the wetness sensor.

In preferred embodiments the light detector comprises a light detector component which is a photodiode or a phototransistor. Photodiodes and phototransistors use photons to generate electrons, thus enabling the light detector to generate an electronic signal indicating the gap size. Photodiodes are readily available components that may be provided with a suitably low profile such that the wetness sensor is unobtrusive to the user when placed in a diaper.

Phototransistors are also readily available components that may be provided in a low profile form, with the additional benefit that the signal is amplified. Thus a greater selection of reflective surfaces may be compatible since the reflectance threshold would be lower when a phototransistor is used.

Photodiodes are advantageous because they can be easily and efficiently printable components, thereby facilitating fast manufacture of the wetness sensor and decreasing the overall cost.

Phototransistors are advantageous where a current amplification may be required.

Preferably, the expandable element is contained within a rigid or semi-rigid housing. The housing enables the reflective surface of the expandable element to be separated at a fixed distance from the light source or LED and the light detector in the dry state. The housing is preferably annular.

The housing preferably comprises a cap. The cap preferably comprises a capillary array that is aligned with an outward-facing part of the expandable element. This facilitates liquid ingress and makes use of the capillary effect, drawing in liquid from an incontinence product to the expandable element.

Preferably, a transparent barrier layer, such as a transparent polymeric layer, is positioned between the housing and the substrate. This layer allows the transmission of light from the light source or and to the light detector, whilst sealing the light source and light detector from liquid.

The substrate is suitably part of an elongate flexible polymeric layer, with the optical sensor positioned at a first end of the elongate flexible polymeric layer. Preferably, the elongate flexible polymeric layer has a length of from 200 mm to 350 mm for use in a diaper suitable for an adult.

At a second, distal end of the elongate flexible polymeric layer, electrical contact pads may be provided to facilitate communication with an external control and monitoring unit. Between the electrical contact pads and the light source and light detector are electrical connection lines, such as printed metal lines.

Optionally, the wetness sensor may comprise a sensor coil arranged to induce a current to drive the light source or LED in response to an electromagnetic field generated by a corresponding transmission coil. In this way the need for electrical transmission lines in the diaper may be reduced as the current for the light source or LED is induced rather than transmitted by conductive elements.

Further, the light detector may comprise an optical fibre configured to transport light received from the reflector to a light detector component and arranged such that a gap between an end of the optical fibre and the reflective surface decreases in response to wetting of the expandable element. Thus, the light detector component can be positioned remote of the sensor region. The optical fibre may be configured at a fixed distance from the reflective surface of the hydrogel when the hydrogel is dry. The need for electrical transmission lines is therefore reduced as there are no conductive components carrying current from a power source to the sensor region. The sensor region is passive rather than active.

Optionally, the light source may comprise an optical fibre configured to transport light from a light source component such that light emitted from an end of the optical fibre is reflected by the reflective surface. As above, electrical transmission lines are not required and the light can be emitted toward the reflective surface without an active component in the sensor region. Preferably, in this embodiment the light source emits white light and the reflective surface is configured to reflect red light. Thus, the light can be emitted and detected using the same optical fibre.

The optical fibre in any of the above examples may have an angled end such that the light can be directed toward the reflective surface and controllably reflected.

An external control and monitoring unit may provide power for the light source and light detector and may process signals received from the light detector. The external control and monitoring unit may be configured to clip or otherwise attach onto a waist band of a diaper. Preferably, the external control and monitoring unit is reusable.

In certain embodiments the control and monitoring unit may be housed in a small footprint box made from flexible polymeric material, so that it may not cause discomfort to the patient. The box may be clipped to the waist band of the nappy or attached to the same using Velcro®.

In embodiments in which a current is induced in a sensor coil to drive the light source, the external control and monitoring unit may comprise a transmission coil and a power source configured to generate an electromagnetic field such that a current may be induced in the sensor coil. In embodiments in which an optical fibre either emits or receives light, an optical fibre may be connected to the external control and monitoring unit which may comprise the light detector component or the light source component or both.

Optionally, the external control and monitoring unit may communicate wirelessly with a remote monitoring unit, for example a smartphone, laptop, pager or other device. This may allow a remote carer to be alerted to the need for a fresh diaper. Alternatively, the external control and monitoring unit may itself be capable of emitting an alarm when an alarm set point is reached.

Preferably, the electronic control and monitoring unit comprises an analogue to digital conversion unit; a plurality of indicators, for example one or more of audio, visual and tactile indicators; a wireless communication device; and a power source, for example a rechargeable coin cell providing up to 3.3 volts.

Preferably, the external control and monitoring unit has capability for individual patient identification provided by an RFID chip. This may facilitate remote monitoring of wetness in multiple diapers simultaneously.

The external control and monitoring unit is capable of electrical connection with the wetness sensor. Preferably, the external control and monitoring unit is provided with a clip or Velcro® type mechanism for convenient attachment to a diaper, for example at a waistband. In another preferred embodiment, the external control and monitoring unit is provided with a cable to connect with the wetness sensor. In this configuration, the external control and monitoring unit may be positioned or held in a location more comfortable for the wearer of, e.g. a diaper.

Preferably, the external control and monitoring unit is reusable and detachable from a diaper. Preferably each individual user is provided with a unique external control and monitoring unit.

Preferably, the distance between the light detector and the reflective surface is set such that in the dry state there will be either no photo current or the photocurrent will be below a minimum threshold current such that no alarm is triggered. The initial distance between the light detector and the reflective surface is preferably approximately 3 mm. The sensitivity of the optical sensor is preferably capable of detecting a distance change on the scale of tens of pm. The distance between the light detector and the reflective surface is preferably from 1 mm to 2 mm when the hydrogel has expanded due to liquid ingress.

An incontinence product, such as a diaper, may comprise the wetness sensor of the invention. The wetness sensor of the invention is preferably incorporated into the diaper during manufacture of the diaper. Preferably, the wetness sensor is positioned between a permeable top sheet of the diaper and an absorbent pad of the diaper. This placement may facilitate rapid response to soiling by locating the sensor closest to where liquid enters the absorbent pad, whilst preventing direct contact with the skin of the user.

Optionally the sensor may be placed between the absorbent and the nonpermeable back sheet for increased patient safety and ease of manufacture.

Another aspect of the invention provides a method of detecting soiling of an incontinence product that incorporates a wetness sensor, the method comprising:

a. transmitting light from an LED towards a reflective surface;

b. receiving light reflected from the reflective surface at a light detector; detecting a change in distance between the reflective surface and the light detector consequent to wetting of the incontinence product.

Preferably, the light emitted by the light source is pulsed. This reduces the energy consumption of the wetness sensor.

The method of the invention represents a significant step of improvement in monitoring of wetness in incontinence products. It allows for remote monitoring by a carer and can provide instant information alerting of the need to replace the incontinence product. The method is not dependent on pH and reduces waste compared to diapers without wetness monitoring and compared to previous wetness monitoring solutions.

Preferably, the method further comprises sending the signal by wireless communication to a remote monitoring unit. This may allow a carer to have real time information as to a user requiring a fresh diaper and thus reduce patient discomfort by reducing the time a diaper is still in use when soiled.

Preferably, the method of monitoring wetness in an incontinence product further comprises the step of triggering an alarm when distance between the reflective surface and the light detector is calculated as falling below a predetermined threshold. The alarm may be any type of alarm, such as a visual, audio or tactile alarm. More than one type of alarm may be used, such as a light and a sound simultaneously. In some embodiments the alarm may be triggered by the external control and monitoring unit. In other embodiments, the alarm may be emitted by a remote monitoring device. Alternatively, both the external control and monitoring unit and the remote device may emit an alarm when a predetermined wetness threshold has been passed.

One benefit of the wetness sensor of the present invention is that the wetness trigger point for an alarm can be varied according to user needs. For example, to improve patient comfort it may be desired to trigger an alarm when the incontinence product is partially loaded, rather than leaving it until fully loaded. This is possible because the light detector is able to measure changes in distance on a continuous scale, whereas previously used wetness sensors relied on a binary change of state and so were not tuneable.

Further, a plurality of sensors may be positioned and spaced apart by a predetermined distance such that a time the liquid takes to diffuse to the sensors can be monitored. The relative time at which each of a plurality of sensors is activated may be indicative of a certain volume of liquid.

The present invention is based on a realisation for a low-cost, unobtrusive wetness sensor that can accurately and precisely detect varying degrees of diaper soiling and relay information on wetness to a carer or user without the need to manually and frequently check the diaper. The wetness sensor may obviate the need to manually check for diaper soiling and may reduce waste by ensuring that a diaper is only changed when needed.

Brief Description of the Drawings

Examples of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a simplified schematic of a typical diaper incorporating a wetness sensor in accordance with the invention;

Figure 2A is a schematic cross-sectional view of an exemplary wetness sensor embodying the present invention;

Figure 2B is a schematic cross-sectional view of an exemplary wetness sensor embodying the present invention in which a plurality of optical sensors are present;

Figures 2C, D, E and F show alternative array arrangements of optical sensors according to the invention;

Figure 3A is a schematic cross-sectional view of a portion of the wetness sensor of Figure 2A in its dry state;

Figure 3B is a schematic cross-sectional view of a portion of the wetness sensor of Figure 2 in its wet state;

Figure 4 is a schematic of an optional surface detail of a part of the wetness sensor shown in Figure 2;

Figure 5 is a schematic of an optional arrangement of components of a wetness sensor according to the invention;

Figure 6 is a schematic plan view of the wetness sensor of Figure 2, showing an arrangement at opposing ends;

Figure 7 is a schematic plan view of a part of a wetness sensor embodying the invention, showing its connection to an external control and monitoring unit;

Figure 8 shows an exemplary circuit diagram of an array of optical sensors according to the invention;

Figure 9 shows an exemplary circuit diagram of an individual optical sensor according to the invention;

Figure 10 shows an alternative embodiment of a wetness sensor according to the invention; and,

Figure 11 shows a further alternative embodiment of a wetness sensor according to the invention.

Detailed Description

Figure 1 shows a diaper 1 that incorporates a wetness sensor 2 according to the present invention. The wetness sensor 2 may be positioned on or off-centre relative to the line of symmetry running from the front to the back of the diaper 1. An external monitoring 3 unit is clipped on to a waistband 4 of the diaper 1. The external control and monitoring unit 3 completes electrical connection to an end of the wetness sensor 2. The wetness sensor 2 extends down from the waist band 4 of the diaper 1 towards the crotch area such that the optical sensor may be positioned in the region most likely to be soiled. Details of the wetness sensor are shown in Figure 2.

Figure 1 also shows wireless communication between the external monitoring 3 unit and a remote monitoring unit 5. The remote monitoring unit 5 enables a carer to be alerted to soiling of the diaper 1 without manually checking.

In a preferred example, the wetness sensor 2 is integrated between a permeable top sheet (not shown) and an absorbent pad (not shown) within the diaper 1. The wetness sensor 2 is preferably integrated between the top sheet and absorbent pad during manufacture of the diaper 1 such that the wetness sensor 2 is positioned to facilitate connection with an external control and monitoring unit 3 at the waist band 4 of the diaper 1. The sensor may also be placed between the absorbent layer and the non-permeable back layer.

Figure 2A shows a cross-sectional view of the construction of an example of a wetness sensor 2 in accordance with the present invention. An LED 7 and a light detector 8 are supported on a substrate 9 in a spaced apart relationship. The substrate 9 is a flexible polymeric strip that carries electrical connections used to power the above mentioned optical components and to carry input and output signals to an external control and monitoring unit 3.

An expandable element 6, in this example a piece of hydrogel material, is supported within a rigid annular housing 10, spaced apart from the optical components. The expandable element 6 carries a reflective layer 11, which provides a reflective surface 18, to reflect light transmitted by the LED 7 back across an air gap 12 to the light detector 8. The optical sensor is capable of detecting very small changes in light intensity, corresponding to a gap decrease of 50 pm or less.

The annular housing 10 is bonded to the substrate 9 to prevent liquid ingress, other than to allow contact with an outward facing part of the expandable element 6, via a capillary array 13 which forms part of a housing cap 14. The capillary array 13 encourages the ingress of any liquid which comes into contact with the housing cap 14 when in use. A transparent, impermeable barrier layer 15 is positioned between the substrate 9 and the housing 10 to prevent liquid coming into contact with the optical components, whilst still permitting the passage of light.

As shown, the housing 10 defines a cavity 16 within which the expandable element 6 is supported as well as an air gap 12 into which the expandable element 6 may expand when wetted. The air gap 12 separates the expandable element 6 and the optical components so that any decrease in the gap 12 caused by an expansion of the hydrogel material can be measured.

Figure 2B shows an alternative embodiment of a wetness sensor 2 according to the invention in which four optical sensors are positioned along the length of the substrate 9.

Placing a number of optical sensors at intervals along the length of the elongate flexible polymeric layer, may allow fine-tuning of the point at which a user or carer is alerted to soiling, such that a lesser or greater degree of soiling may prompt a change of diaper. Each optical sensor operates in the same manner as the single optical sensor described above for Figure 2A.

When present in a diaper, the optical sensors further away from the source region of soiling will be actuated only when the absorbent layer of the diaper is very considerably loaded, whilst not being activated when the diaper is only lightly soiled.

Alternatively, a plurality of optical sensors may be arranged in an array, i.e. an arrangement of sensors extending in more than one direction in the plane of the diaper. Exemplary array layouts are shown schematically in Figures 2C, 2D, 2E and 2F, in which optical sensors 22 are denoted by dots and substrates 9 as lines. The sensors may be arranged in any layout suitable for optimum detection of soiling when in use. Examples include a star layout, a Y-shaped layout, an elliptical layout, and a mesh layout. In use, the array would be connected to an external control and monitoring unit (not shown).

The elliptical array layout of Figure 2C is especially suitable for a female anatomy, whilst the Y-shaped array layout of Figure 2D is especially suitable for a male anatomy. The mesh and star-shaped array layouts of Figures 2E and 2F are suitable for any gender user. In each of the layouts shown in Figures 2C-F, the distribution of optical sensors allows for detection of wetness even allowing for the effects of gravity, for example if a user is lying on their side.

Figures 3A and 3B illustrate the detail of the optical components and expandable element of the wetness sensor of Figures 2A and 2B in operation. Figure 3A shows the expandable element in its dry state and Figure 3B shows the expandable element in its wet state. Light is emitted from an LED 7 and reflected back to a light detector 8 by a reflective surface 18. In this example, an expandable element 6 is provided with a separate reflective layer 11 as the reflective surface 18.

The external control and monitoring unit is calibrated to not trigger an alarm in the dry state. As the expandable element is wetted and expands, the reflective layer 11, providing the reflective surface 18, is carried towards the light detector 8 and LED 7, reducing the air gap 12 and thus decreasing the length of the light path. This change results in a higher intensity of detected light and thus a change in signal sent to an external control and monitoring unit. Individual calibration of the alarm set point is possible by using more than one optical sensor, as described above in relation to Figure 2B.

Figure 4 shows an example of surface detail of the reflective surface of the expandable element in accordance with the present invention. In this example, the reflective surface 18 is provided with a notch 19. The notch 19 enables light to be reflected back from the LED 7 to the light detector 8 more efficiently, by directing it more precisely. A reflective layer may be present, but is not shown in Figure 5.

Figure 5 shows an arrangement of the LED 7 and light detector 8 in an exemplary wetness sensor according to the invention. The LED 7 and light detector 8 are offset relative to one another within the substrate 9 such that light is reflected directly towards the light detector 8 from the LED 7, improving the efficiency of the wetness sensor. A reflective layer may be present, but is not shown in Figure 6.

Figure 6 shows the distal ends of an example of a wetness sensor 2 according to the present invention. The LED 7 and light detector 8 are arranged side by side, supported on a substrate 9, at one end and are in electrical connection with electrical contact pads 20 at the opposite end. Electrical connection is facilitated by printed metallic lines 21. Three electrical contact pads are provided at the second end of the elongate flexible polymeric layer: a ground electrical contact pad and line, an electrical contact pad and line for illuminating the LED and an electrical contact pad and line for transmitting sensor output to an external control and monitoring unit.

Figure 7 shows an example of how electrical connection is enabled between the wetness sensor 2 and an external control and monitoring unit 3. The external control and monitoring unit 3 clips on to both the waistband 4 of a diaper and the end of the wetness sensor 2 that comprises electrical contact pads 20. The external control and monitoring unit 3 provides power to the wetness sensor 2 and is able to trigger an alarm or to send a wireless signal to a remote monitoring unit 5 to alert a carer remotely. In this example, the external control and monitoring unit has external dimensions of approximately 40 mm length, approximately 20 mm width and approximately 20 mm depth.

Figure 8 shows an exemplary circuit diagram for an array 23 of optical sensors. Figure 8 illustrates an array of sixteen optical sensors that are arranged in a mesh formation over a given area on a diaper, each one in electrical communication with an external control and monitoring unit 3. Although not shown, other layouts are equally possible, for example the optical sensors arranged in a Y-shape, an elliptical shape, and a star shape.

The optical sensors shown in Figure 8 utilise photodiodes and LEDs. In the circuit shown, each set is simultaneously accessed to detect the presence or absence of fluid in that particular region of a diaper. Shown in Figure 8 is an array of sensors, each individual sensor having an LED and a photodiode arranged adjacent to a reflector and the diode being in series with a load resistor. It will be understood that any suitable circuit configuration for an individual sensor for determining the intensity of light at that location may be used.

Figure 9 shows an exemplary schematic circuit diagram for a single optical sensor in which a phototransistor 8 is used instead of a photodiode as the light detector. The LED 7 and reflective surface 18 are also shown schematically. R_Lrepresents the load resistance and R_D represents the LED resistance.

It has previously been described that an LED, light detector component and reflective surface may each be arranged in an optical sensor region to detect movement of a hydrogel. A series of electrical transmission lines carrying a very low current are arranged to provide the signals to and from the LED and light detector component. Arrangements will now be described which obviate the need for such electrical transmission lines embedded within the diaper.

A first example is shown in Figure 10. In this example, a sensor coil 101 is connected to the LED 7 such than when a current is induced in a coil, the LED can be driven to emit light. Such an arrangement is possible within a diaper due to the low power required to drive the LED to emit a suitable amount of light.

In order to induce a current in the sensor coil 101, a coil 102 is configured to create a magnetic flux which is captured by the sensor coil 101. The coil 102 which creates the electromagnetic field may be configured in the external control and monitoring unit 3, as an external, remote component or, alternatively, may be configure around the periphery of the diaper.

The receiver or transmission coil 102 may be connected to a transmitter which generates an alternating current to create a specific electromagnetic field such as radio waves. In this way, the output of the LED can be configured with a particular signal. Accordingly the signal received in the fibre after reflection may be similarly varied. This has benefits for example in that allows the reception to be paired to a particularly tuned sensor circuit or different signals to be sent down one optical fibre.

In the example illustrated in Figure 10, in order to detect the light emitted by the

LED and subsequently reflected by the reflective surface on the hydrogel, an optical fibre is arranged in a fixed position relative to the reflective surface on the hydrogel. When the light reflects off the reflective surface 18, the light enters an end of the optical fibre. The optical fibre may be preferably connected to the external control and monitoring unit 3 but may be optionally connected to another component within the diaper suitable for detection of the light within the optical fibre. The light travels down the optical fibre so that it can be detected by a light detector in the external control and monitoring unit.

All of the examples described above may equally be applicable to this embodiment. For example, there may be multiple sensor units positioned around the diaper with multiple optical fibres, or one optical fibre, depending on the analysis techniques required. There may be multiple sensor coils and LEDs paired with multiple reflective surfaces. Other examples include, for example, barrier layers or air gaps.

An alternative example is illustrated in Figure 11. In this example a single optical fibre 113 is used through which light is transmitted to the external control and monitoring unit 3. Rather than inducing a current in a coil to drive and LED, light is transmitted down and received from the same optical fibre 113 with a reflective surface configured a fixed distance away from the end of the fibre (when the hydrogel is dry). Preferably white light may be used for transmission which is then reflected off a red surface on the hydrogel such that red light is transmitted down the same optical fibre to reach the monitoring unit. As the reflective surface 18 closes the gap between itself and the optical fibre (which is fixed in position) the intensity of the reflected light will increase. This change can be detected at the receiver end, that is, an indication of an event happening.

Again, features of any of the above examples may be combined with this example. For example multiple optical fibres may be spread in a predetermined pattern around the diaper or air gaps or other light transmitting medium configured between the reflective surface and the light emitting end of the optical fibre.

Examples

A wetness sensor according to the invention was constructed and tested. The optical sensor used was a combination of a Gallium Arsenide based LED operating at 950 nm wavelength and a Silicon based phototransistor operating between 700 and 1200 nm wavelength. The device used was GP2S60 from Sharp™.

A polymeric substrate with perforations to act as capillaries was used to facilitate liquid ingress. Fibrous hydrogel (LIST AG Sweden) was compressed into a disc form. A white thin polymeric disc was glued to the hydrogel disc to form the reflective surface.

The separation between the reflector and the phototransistor was 1 mm prior to wetting of the hydrogel.

A flexible printed circuit strip (FR4) was designed to house the LED and the phototransistor (Sharp™ GP2S60). The device was operated using a programmable Arduino™ platform and a laptop.

The sensor assembly was laid inside a commercial nappy in contact with the diaper absorbent layer and water was poured onto the nappy. As the diaper absorbent layer absorbed the water it expanded. Some of the water in the diaper absorbent layer came into contact with the sensor capillary. The capillary array quickly wicked the water which then caused the hydrogel of the wetness sensor to expand. This expansion caused a reduction in the gap between the reflective surface and the light phototransistor.

Immediately there was a sharp rise in the output current of the phototransistor by 0.70 mA which was displayed a bar graph on the laptop.

The time between wetting the diaper and the bar graph display on the laptop was approximately one minute.

Similar to the above experiment, a flexible sensor mat comprising a square array of 25 sensors (spacing between sensors being 2 cm) was tested to observe water diffusion and to record the volume of water needed to trigger the outer sensors.

600 ml of water was needed to trigger the outmost sensors. It took approximately 30 minutes for the water to reach the outer sensors.

The above experiment proved that it is possible to measure the volume of the 10 liquid inside the diaper.

Claims

1. A wetness sensor for an incontinence product, the wetness sensor comprising an optical sensor, the optical sensor comprising:

a light source;

a light detector; and an expandable element that increases in volume when wetted, the expandable element having a reflective surface which reflects light received from the light source to the light detector, wherein, in use, the light detector generates a signal when a gap between the light detector and the reflective surface decreases in response to wetting of the expandable element.

2. The wetness sensor of claim 1, wherein at least a part of the optical sensor is supported on a flexible substrate.

3. The wetness sensor of claim 1 or 2, wherein the substrate is in the form of an elongate strip or an array, preferably an array.

4. The wetness sensor of claim 3, wherein the substrate is in the form of an array having a Y shape, an ellipse shape, a grid configuration or a star shape.

5. The wetness sensor of any preceding claim, comprising a plurality of optical sensors, each respective expandable element being spaced apart from each other along a length of substrate.

6. The wetness sensor of any of claims 1 to 5, wherein the reflective surface is a reflective layer bonded to the surface of the expandable element.

7. The wetness sensor of claim 6, wherein the expandable element comprises hydrogel.

8. The wetness sensor of any one of claims 1 to 5, wherein the expandable element comprises a pigment that reflects light of the same wavelength as the light source.

9. The wetness sensor of any preceding claim, wherein the light detector comprises a light detector component which is a phototransistor or a photodiode.

10. The wetness sensor of any preceding claim, wherein the expandable element is positioned within a housing and the reflective surface is separated from the light source and the light detector at a fixed distance when dry.

11. The wetness sensor of any of claims 2 to 10, wherein the substrate on which the light source and the light detector are supported is a first end of an elongate flexible polymeric strip, the flexible polymeric strip further comprising:

a. electrical contact pads at a second end of the flexible polymeric strip, distal to the light source and the light detector; and

b. electrical connection lines along the length of the flexible polymeric strip, thereby facilitating electrical communication between the light detector and metal contact pads and between the light source and the metal contact pads.

12. The wetness sensor of claim 9 or 10, wherein a transparent impermeable barrier layer is positioned between the substrate and the housing, thereby providing isolation of the light source and the light detector from liquid.

13. The wetness sensor of any one of claims 10 to 12, wherein the housing comprises a cap, the cap comprising a capillary array aligned with the expandable element, thereby facilitating liquid ingress to the expandable element.

14. The wetness sensor of any preceding claim, wherein the light source comprises a light source component which is an LED.

15. The wetness sensor of claim 14, wherein the wetness sensor comprises a sensor coil, wherein the sensor coil is arranged to induce a current to drive the LED in response to an electromagnetic field generated by corresponding transmission coil.

16. The wetness of any preceding claim, wherein the light detector comprises an optical fibre configured to transport light received from the reflector to a light detector component and arranged such that a gap between an end of the optical fibre and the reflective surface decreases in response to wetting of the expandable element.

17. The wetness sensor of claim 16, wherein the light source comprises an optical fibre configured to transport light from a light source component such that light emitted from an end of the optical fibre is reflected by the reflective surface.

18. The wetness sensor of claim 17, wherein the light source emits white light and the reflective surface is configured to reflect red light.

19. The wetness sensor claims 16 to 18 in which the optical fibre has an angled end.

20. A wetness sensor system comprising the wetness sensor of any preceding claim and further comprising an external control and monitoring unit connectable to the wetness sensor for processing signals generated by the wetness sensor.

21. The wetness sensor system of claim 20, when dependent on claim 14, further comprising a transmission coil and a power source configured to generate an electromagnetic field such that a current can be included in the corresponding sensor coil.

22. The wetness sensor of claim 20, when dependent on claim 16, wherein the optical fibre is connected to the external control and monitoring unit which comprises the light detector component.

23. The wetness sensor system of claims 20 to 22, further comprising a diaper.

24. The wetness sensor system of claim 23, wherein the diaper comprises two or more sheets and where in the optical sensor is integrated between the sheets.

25. The wetness sensor system of any of claims 20 to 24, further comprising a remote monitoring unit capable of wireless communication with the external control and monitoring unit.

26. A method of detecting soiling of an incontinence product that incorporates a wetness sensor, the method comprising:

a. transmitting light from a light source towards a reflective surface;

b. receiving light reflected from the reflective surface at a light

10 detector;

c. detecting a change in distance between the reflective surface and the light detector consequent to wetting of the incontinence product.

27. The method of claim 26, wherein the light emitted by the light source is 15 pulsed.

28. The method of claim 26 or claim 27, further comprising the step of generating an alarm signal when the detected distance is reduced to a predetermined threshold.