Patent Application
20210080398
This invention relates to a sensor including an optical fibre, and in particular to a device that can be used to measure wetness in an incontinence product, e.g. an adult or a baby diaper.
At present, the usual way to check that an incontinent patient's diaper does or does not need changing is to use nursing/caring effort to examine the patient. This involves changing the diaper, possibly unnecessarily, and expending staff time on the checking operation. The consequences of infrequent changing, as well as being uncomfortable and degrading for the patient, also carry significant medical risks. These risks are exacerbated when the patient is bed-bound. The risks of bed sores, other skin inflammations and infection are significant; they can be mitigated by proper hygiene and timely changing.
Various options have been proposed for monitoring soiling of incontinence products. US2013/0162403 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; see WO2010/049829.
US2010/164733 relates to a diaper sensor, using urine as an electrolyte.
US2012/165772 relates to a diaper sensor in which expansion changes or breaks an electrical circuit. This technology therefore has safety issues.
US2009/198202 relates to a magneto-elastic ribbon for use in a diaper. Wetness (or other chemical or biological analyte) is detected via a change in magneto-acoustic resonant frequency.
US2010/305530 relates to a fluid saturation sensor for monitoring wetness in sanitary towels. The sensor may be “resistive or capacitive”.
US2012/157949 (Kimberly-Clark) relates to an incontinence pad that has a visual indicator for wetness. The visual indicator is an “active barrier” that swells when wetted.
U.S. Pat. No. 8,978,452 relates to an electronic wetness sensor for an incontinence product that can be remotely checked via an RFID link. The sensor uses a frangible link, such that contact with urine causes the RF circuit to fail. Remote monitoring of the product is suggested.
According to the present invention, an optical fibre of the type comprising a core and a cladding includes a discontinuity or gap into which liquid can migrate and thereby modify the intensity of light passing through the core. The gap may be formed in the cladding; the thus-exposed surface of the core may then be suitably modified. Alternatively, the gap may extend through the fibre, in which case the separate sections of the fibre are suitably borne on a substrate, in order to maintain their optical alignment.
It will be understood that, here and elsewhere in this specification, the use of the singular includes the plural. Thus, and is indeed preferred, there may be a plurality of gaps (or discontinuities).
Such a fibre can be used as a wetness sensor, and is suitable for use in an incontinence product or a baby diaper. The gap in the fibre provides a sensing region which is responsive to urine when the diaper is wetted. The two ends of the fibre may be connected to a light source and a light detector. The sensing region on the optical fibre may have a gap. The purpose of the gap is a) to allow leakage of the light when the diaper is in a dry state and b) ingress of liquid into the gap, drawn from the absorbent layer in the diaper, when the diaper is wet, using capillary action. The ingress of liquid into the gap allows more light to pass through the gap to the other side of the core, thereby indicating diaper wetting.
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.
The method of the invention represents an improvement in monitoring of wetness in incontinence products. It allows for remote monitoring by a carer and can provide instant information, alerting the carer to 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 a signal by wireless communication to a remote monitoring unit. This allows a carer to have real-time information as to a user's requiring a fresh diaper and thus reduces patient discomfort by reducing the time a diaper is still in use when soiled.
The present invention will be described by way of example only with reference to the accompanying drawings, in which:
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.
The diaper may comprise conventional materials. Generally, disposable diapers are made from absorbent material, e.g. wood/cellulose fibre and polyacrylate material on the inside to absorb the urine, and synthetic materials on the outside. Suitable such materials include polypropylene, polyester, and polyethylene for fitting and to prevent leaking. Incontinence diapers may comprise up to six layers. There are usually three essential layers: in order, a top liquid-permeable layer, a liquid-absorbent layer and a non-permeable layer. The absorbent layer is typically mostly fluff and a small quality of hydrogel. As liquid reaches the absorbent layer, the hydrogel soaks it up from the fluff and swells. Superabsorbent polymer is generally used as hydrogel.
In general, any suitable optical fibre may be used. The core may be of polymethyl methacrylate and the cladding of a fluorinated polymer. The fibre is preferably a step-indexed multimode or a multimode graded or a single mode fibre. A multimode fibre preferably has a diameter of up to 1 mm, e.g. 0.25 mm, and a smaller core diameter, e.g. 0.24 mm. A specific suitable fibre has a numerical aperture 0.5 and acceptable angle of 60 degrees with an attenuation @ 650 nm<0.3 dB/m and operating temperature −40+70 degrees Celsius.
A characteristic feature of this invention is a gap in the fibre. This structured region or sensing gap is typically in the region of 0.05 mm-1 mm in width and 0.25 mm-1 mm in height. The gap may be formed by cutting the fibre or, if primarily only in the cladding, using laser ablation, heated blade or a similar process. The purpose of the gap is to allow light to leak out. A significant portion of the light leaks out of the gap (e.g. approximately 30%) by transmission through or scattering by the material of a diaper, e.g. absorbent layer and the bottom substrate. The remainder (approximately 70%) of the light is transmitted to the other side of the fibre.
As the diaper gets wet, liquid is preferentially wicked into the gap. Liquid in the gap will help to increase the light throughput to the other side of the fibre, resulting in an increased signal at the light detector. Because the refractive index of air in the gap (n=1) is replaced by liquid (urine) with a refractive index in the region of 1.33, which is typically closer to the refractive index of the fibre core (1.49 in the case of polymethyl methacrylate), more light will pass through the core. Additionally, there will be some total internal reflection due to the water-air boundary.
In another embodiment, one or both of the fibre ends in the gap region may be angled to increase light coupling. The angled fibre approach provides enhancement of the effect of liquid bridging the gap. Not only is beam divergence reduced, but the walk-off of the beam due to exiting the angle facet is reduced as the liquid index is closer to the fibre core index. It can be thought of as amplifying the effect of the index change.
As indicated above, the gap may extend through the width of the fibre, such that the fibre is provided in at least two sections. Alternatively, a gap is formed in the cladding, and the fibre includes a roughened surface (for wicking water from the diaper absorbent layer). Roughening may be achieved by, for example, chemical etching, mechanical polishing or physical ablation (e.g. powder blasting). A small section of the fibre, e.g. 0.5-2 cm long, may be roughened. When a diaper including such a fibre is wet, liquid may be wicked either directly from the absorbent layer onto the roughened area or via a microchannel created in the vicinity of the structured region, which increases the quantity of light passing through the fibre, indicating diaper wetting.
In another embodiment, the exposed core region, following cladding removal by roughening, may be further etched to create micro-capillaries in the core, e.g. by a chemical process using a solution such as methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA). This may allow more light to leak out of the fibre when the diaper is in a dry state and more light coupled back into the core as the region is wetted, thus increasing the sensitivity of the sensor.
In another embodiment, the fibre is tapered along its length, in a sensing region. This requires the cladding to be removed. The critical angle when the fibre core is exposed to air is 42° (assuming refractive index n=1.49 for a polymethyl methacrylate core). This means that any light travelling such that its angle to the normal to the fibre wall/air interface is 42° or more will be reflected and travel down the fibre, essentially loss-free. If the cladding is in place this angle increases to 70°, so that only light that is nearer normal to the fibre axis is trapped. If the index outside the core is that of water, n=1.33, then the critical angle is 63°. If light travelling at an angle to the normal of 70° reaches a length of fibre that is bare, then the light is still confined, as it is already travelling at an angle>42° (i.e. 70°). If the fibre is now tapered at a suitable angle (i.e. not too steep, but steep enough that the light has a sufficient number of bounces in the sense region length) then, with each bounce, the ray will be travelling at a smaller angle to the normal between core surface and the outside environment. Eventually, it will reach the critical angle and escape. This will happen earlier if the fibre is clad with water, as the angle only has to reach 63°, not 42°. If the fibre diameter is 250 μm, a beam travelling at 70° to the normal will travel 686 μm before its first bounce, equivalent to 14 bounces along a 1 cm length. If the fibre tapers at 1°, then after this number of bounces it will have reduced its angle by 28°. It should be realised that the fibre will reduce in diameter by 23 μm.
The tapering of the fibre may be implemented in several ways, e.g. having a short length (1-2 mm) of tapering followed by a straight section and repeat of the same over a length of, e.g. 2 cm. A taper of 1° to 2° can be used. A taper provided over a short distance may be followed immediately by a flare (like a bowtie) followed by a straight section and repeat of this pattern over a distance e.g. 2 cm. The flare region will allow refocusing of the light into the core.
Gradually light will leak out of the taper. When the diaper is wet, liquid may be introduced to the tapered region via a micro channel (wicking liquid from the diaper absorbent layer) to increase the quantity of light going through the tapered region.
A product of the invention may comprise one or more microfluidic channels along a section on one or either side of the fibre, including the gap or the roughened region. The microfluidic channel wicks water from the diaper absorbent layer and drains it into the gap or the roughened region. Microchannels in a polymeric material will be essentially hydrophobic; the surface may be treated to render it hydrophilic.
The liquid wicking process is also assisted by pressure created by the diaper loading as the diaper absorbent layer gets wet.
Microchannels between the substrate and the fibre close to the structured region, may be formed using a tape or a similar material. The material is preferably hydrophilic. The channels are created between the tape edge and the fibre.
Microchannels may also be created in the substrate to draw liquid from the diaper absorbent layer into the structured region. Channels measuring up to 2 cm in length and up to 0.5 mm in width may be created in the substrate by a lithography process or physical ablation. In general, any substrate material can be used; however, to assist the wicking process a material having a hydrophilic surface is preferred.
Microchannels may also be created between two separate fibres on a flexible substrate, where the two fibres are in contact. To assist the wicking process, the fibres may be coated with a hydrophilic substance. In this case, a reflective surface may be provided, to reflect light from one fibre into the other.
In summary, the structured fibre has a core that is exposed to liquid that can be drawn from a diaper's absorbent layer such that the refractive index in the structured region is altered by the presence of the liquid. This is analogous to ‘repairing’ the roughened fibre cladding.
The optical fibre may comprise a plurality of sensing regions, spaced apart along the length of the fibre. 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. The number of sensing regions is preferably from 2 to 6, e.g. 3. The distance between each optical sensor is preferably from 1 cm to 10 cm. A plurality of sensing regions, which may be accessed simultaneously, allows quantification of the liquid volume and therefore wetness level in the diaper (low, medium and full).
A sensor of the invention may comprise a single fibre, e.g. with a plurality of sensing regions, or a plurality of such fibres. The provision of more than one sensing fibre allows capture of liquid from a wider area. It may also allow for different possible orientations of the male organ, and may also be beneficial for incontinence assessment. Multi-strand sensors may utilise the same light source but separate photodetectors.
In a preferred embodiment, the sensor includes a reference fibre (without gaps) alongside the sensing fibre. This can be used to account for any change in signal caused by distortion of the diaper during use.
For use in a diaper, one end of the (or each) fibre may be connected to a light source and the other end to a light detector. It will often be convenient that a fibre is bent in a U-shape, so that its ends can be positioned at adjacent points on the waistband of a diaper. For this purpose, the fibre may be, for example, at least 20, e.g. e.g. 50 cm long.
Alternatively, an essentially straight single fibre may be used. A fibre coupler (e.g. 3 db) may then be used, where one end of the fibre may be mirrored or a separate reflective surface may be placed in front of the fibre end.
The fibre may be placed directly in a diaper and attached by, for example, ultrasonic welding. Alternatively, the fibre may be placed on a flexible substrate that is then used to form part of the diaper. The substrate material may be a polymer or a textile which can be either woven or non-woven. The substrate may be hydrophilic, to facilitate liquid wicking from the diaper absorbent layer.
The substrate dimension is typically in the form of a strip. It is preferably 1 cm-1.5 m in length, 1-15 mm in width and up to 1 mm thick. The fibre may be attached to the substrate by, for example, gluing or ultrasonic bonding.
If it extends through the fibre, the gap may be formed before or, preferably, after being positioned on a substrate. This allows the optical alignment of the separate sections of the fibre to be maintained.
In a preferred embodiment of the invention, the fibre (typically in a U-shape) is mounted between two plastics films that are laminated or otherwise bonded together. An aperture is provided in one film at a point corresponding to each sensing gap, and the wicking of liquid from a diaper through the aperture to the gap is preferably enhanced by placing an absorbent or wicking material, e.g. porous tissue, between the films. This material provides a path for liquid form a diaper, through the aperture(s), to the gap(s). This arrangement allows simple, low-cost manufacture of a unitary structure ready for placement in a diaper.
A sensor of the invention may be incorporated in a diaper or other incontinence product, preferably during manufacture. A strip incorporating a fibre of the invention may be placed inside the diaper's non-permeable layer such that the absorbent layer is in contact, directly or indirectly, with the fibre. The sensor strip is preferably placed in the central region, along the length of the non-permeable layer.
In an alternative embodiment, the sensor strip may be embedded within the absorbent layer such that one layer of the absorbent rests on the sensor layer and a second layer of absorbent is under the sensor strip. The absorbent layer rests non-uniformly on the sensor strip with air gaps between the fibre and the absorbent layer.
In another embodiment, the strip is placed under the permeable top layer, above the absorbent layer of the diaper, the sensor region facing the absorbent layer. 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. The strip may have micro-perforations, to allow liquid ingress. In any case, the fibre must have access to the diaper absorbent layer, directly or indirectly.
In order to ensure that the fibre is not damaged during a diaper folding step in manufacture, the radius of curvature of the fibre is preferably not lower than 5 mm. This may be achieved by laying the fibre on the substrate in a particular configuration. One possibility is to fold the fibre, roughly in a figure of eight, such that when the diaper is folded the fibre can expand, without kinking.
To ensure ease of manufacture and convenient use, a connector may be placed at the sensor fibre ends. A complementary interrogator box has two fibres with a connector which is adapted to mate with the sensor fibre ends.
The fibre end or ends may be terminated at the edge of the substrate, and this edge inserted into a soft plastics ‘interrogator box’ comprising a LED, a photodetector, associated electronics and power supply. For ease of insertion, a small length of the substrate may be relatively thick, e.g. by providing an extra layer of the substrate material. Appropriate structuring of the box will allow alignment of the fibre ends with the LED and photodetectors.
In another embodiment, the fibre ends terminate in connector tubes. The mechanical tolerances of the tubes can provide consistent optical alignment. The interrogator box may be clipped or otherwise attached, e.g. using Velcro, to the diaper's waistband.
The light source may emit any infrared or visible wavelength of light. Preferably, the wavelength emitted is in the visible. Preferably, the light source is a light-emitting diode (LED). Alternatively, an organic light emitting diode (OLED) is used. An advantage of using OLEDs is that their manufacture can be low-cost, high throughput.
The light detector preferably comprises a photodiode (photodetector) or a phototransistor. Photodiodes and phototransistors use photons to generate electrons, thus enabling light detection. Photodiodes are readily available components that may be provided with a suitably low profile such that the interrogator box is unobtrusive to the user when placed on the waist in a diaper.
The interrogator preferably comprises a pulsed LED and a photodetector. Signals of order of μW will be received. This is well within the reach of a low-cost photodetector and amplifier. Phototransistors are also readily available components that may be provided in a low-profile form, with the additional benefit that the signal is amplified.
Such components provide sufficient signal to allow the use of a low-cost power consumption amplifier. Because of the signal level, high enough bandwidth (100 KHz or more) is possible, allowing short duty pulses of light for power saving which means battery life greater than 24 hours.
Preferably, 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.
A suitable box sends light down a fibre, and the received light is collected by a photodiode. A 3 dB coupler can be used to allow isolation between the outgoing light and the incoming, without the need for expensive, high-speed, power-hungry, time-division multiplexing.
The noise floor and bandwidth of the amplifier can allow a rapid enough LED pulse with no significant error in the detection signal. The LED is pulsed for two reasons: firstly, it reduces power consumption, to allow the interrogator to be powered by integral batteries for up to 24 hours, and secondly it affords immunity to offsets due to ambient light (DC light), or any other DC offsets affecting the reading. Nevertheless, ambient light should have little or no effect as the fibre in the diaper is in the dark, and the photodiode is enclosed in the interrogator box.
The system can ‘wake up’ by pulsing the LED, acquire the reading and transmit it to a monitor unit (Wi Fi etc.). If background light is a problem, repeat pulsing may be used to eliminate any DC offset.
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. Preferably, in the dry state, the photocurrent will be below a minimum threshold current such that no alarm is triggered.
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.
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 a plurality of gaps can provide a linear array of sensing regions which progressively get activated as the diaper is getting more wet. This can be contrasted with known wetness sensors that rely on a binary change of state and so are not tuneable.
Further, a plurality of sensing regions may be positioned and spaced apart by a predetermined distance such that the time the liquid takes to diffuse to the sensor can be monitored. The relative times at which each of a plurality is sensors is activated is indicative of a certain volume of liquid.
Referring now to the drawings in greater detail,
The following Examples illustrate the invention.
Step-indexed unjacketed multimode optical fibre (fibre diameter 0.25 mm and core diameter 0.24 mm) was used. Other characteristics of the fibre include: core material: polymethyl methacrylate, cladding: fluorinated polymer, numerical aperture: 0.50, acceptance angle: 60 degrees, attenuation @ 650 nm<0.3 dB/m, minimum bending radius: <9 mm and operating temperature −40+70 degrees Celsius.
A 40 cm length of this optical fibre was placed on a 0.1 mm thick flexible substrate. One end was connected to an LED and the other end to a lux meter (photodetector). When the LED was switched on, the lux meter reading was 330 lux. Then three cuts were made in the fibre using a heated blade. The signal in the lux meter dropped to 100 lux after the first cut, 33 lux after the second cut, and 9 lux after the third cut.
The optical fibre-based wetness sensor was then placed inside an incontinence diaper (commercially obtained—TENA), to provide the arrangement shown in
A 5 mm (internal diameter) plastic tube was inserted inside the diaper, ending in the inner permeable layer. The other end of the tube was connected to a mounted plastics bottle filled with saline water (substitute for urine). An adjustable-valve mechanism along the tube allowed control of liquid flow inside the diaper.
Water was introduced inside the diaper at regular intervals (10 ml/min), to a total of 600 ml water. However, the signal in the lux meter remained unchanged at 9 lux. 19 Lux was recorded at 200 ml, corresponding to the first cut, then 28 lux at 340 ml for the second cut, and finally 33 lux for the third cut at 590 ml.
Then microfluidic channels were created in the sensor. This was achieved by wrapping small pieces of plastic tapes on sections of the fibre with gaps.
When water was introduced inside the diaper, the microfluidic channels wicked water from the absorbent layer and filled the gaps in the fibre. Due to the particular placement of the sensor strip inside the diaper, the gaps were progressively filled with water, as water spread across the absorbent layer. This caused the signal in the lux meter to rise gradually. At the end of the experiment, 600 ml of water was introduced inside the diaper, and all three gaps were filled. The effect of having water inside the gaps equated to reintroduction of the cladding, causing more and more light to be coupled to the fibre and the increase in signal. The progressive increase in the signal is also indicative of the quantity of water inside the diaper.
Electronics and associated software were then developed to remotely monitor the water volume on a mobile app. via Bluetooth and WiFi.
The sensor used in this experiment is as shown in
Two step-indexed unjacketed multimode optical fibres of the same type as in Example 1 were used, one acting at the sensing fibre and the other as a reference fibre. A thin (100 micron) transparent plastics strip, 30 cm long and 16 mm wide, was used as the substrate.
The sensing fibre had a length of 59 cm and the reference 57 cm; both were turned into a U-shape, and placed on a substrate using a thin layer of glue. Three pieces of tissue paper (absorbent layer) were put along the width of the fibre sensing regions, using a thin layer of glue to hold them in place.
A second transparent plastic strip having the same dimensions as the substrate was used as the top sheet. The top sheet had three holes covering the three pieces of absorber. The top sheet was then put on the substrate (completely aligned) and the two strips (substrate and top sheet) were then laminated. Following lamination, three equidistant cuts were made in the sensing fibre using a hot blade.
One end of the sensing fibre and one end of the reference fibre were placed in front of a LED, and the other two ends of the fibres (sensing and reference) were put in front of two separate photodiodes (detectors).
Before any cut was made in the sensing fibre, the signal at the photodetector recorded 1000 mV. After the first cut, the signal dropped from 1000 mV to 580 mV, after the second cut it dropped to 200 mV, and after the third cut to 50 mV.
For the reference fibre (without cuts), 800 mV was recorded at the photodetector. The difference between the initial value of 1000 mV for the sensing fibre and 800 mV for the reference fibre was due to some misalignment of the reference fibre.
A commercially procured incontinence diaper was used for the wetness test. The diaper was cut open from inside to insert the laminated sensor strip on top of the non-permeable layer (therefore under the diaper absorbent layer). The diaper (with the sensor strip) was put on a mannequin.
The sensor strip was connected to an electronics box comprising a LED, two photodetectors, signal amplifier and a power supply.
A plastic tube for introducing saline water (substituting for urine) was inserted inside the diaper, and the other end of the tube connected to a water reservoir. Using a control valve allowed control of liquid flow inside the nappy. This was an accelerated test. As the water filled up the first cut (gap in the fibre), the signal after 500 seconds at the photodetector recorded 100 mV (the effect of having water inside the gaps equated to reintroduction of the cladding, causing more and more light to be coupled to the fibre and the increase in signal). The water volume inside the diaper at this point was 125 ml. After 1100 seconds, when water filled up the second cut, the photodetector recorded 200 mV and the water volume inside the diaper was 250 ml. Finally, after 2200 seconds, when water filled the third cut, 400 mV was recorded. At this point the water volume inside the diaper was 625 ml. All through this experiment, for the reference fibre, the photodetector recorded a constant 800 mV, as was expected.
Electronics and associated software have been developed to remotely monitor the water volume on a mobile app, via Bluetooth and WiFi.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1720685.5 | Dec 2017 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2018/053611 | 12/12/2018 | WO | 00 |
