Two-dimensional optical waveguide pressure sensor array

Abstract

A two-dimensional optical waveguide pressure sensor array is disclosed, comprising two or more rows of optical waveguides; two or more columns of optical waveguides, wherein the rows and columns of optical waveguides are deformable and arranged in a planar array to define sensors at the intersections, wherein each intersection comprises one of the row waveguides in contact with one of the column waveguides at its intersection; wherein each intersection further comprises an optical coupling structure configured to enhance bending of the waveguides when pressure is applied to the intersection; wherein the optical coupling structure comprises a layer of a mechanical light scattering material disposed in contact with at least one of the row or column optical waveguides; wherein the optical waveguide pressure sensor array is configured to sense pressure by providing light to the row optical waveguides and measuring the light coupled to its column optical waveguide at each intersection, or vice versa, and wherein the light coupled to the column optical waveguide is dependent on the pressure applied to the intersection as a sensor.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to an optical waveguide pressure sensor array, and more particularly to a two-dimensional pressure sensing system using polymer optical fibers in an optical waveguide pressure sensor array configuration. BACKGROUND

[0002] Pressure sensing systems providing two-dimensional position information are known from, for example, US 4,733,068 and US 2019 / 0302879. From these publications it is known to use an array of optical fiber sensors to measure the spatial distribution of pressure exerted in a two-dimensional structure. Such two-dimensional pressure sensor systems are particularly suitable for measuring and monitoring the specific position and movement of objects and / or persons.

[0003] A pressure sensing system in which the array of sensors is configured from optical fibers, which are polymer optical fibers (POFs), has the advantage that they are inexpensive, robust, flexible and not sensitive to electromagnetic interference (EMI). In such a pressure sensing system, a grid of optical fibers can be provided, in which the optical fibers provided in one direction are connected to light sources (in particular light emitting diodes (LEDs)), while the optical fibers provided in the transverse direction are connected to highly sensitive light receivers. At the intersections, some of the light from one optical fiber can be coupled to the optical fiber at the intersection. Since this light power coupling depends on the pressure exerted on the intersection, each intersection of the grid can act as a local pressure sensor. Such a pressure sensing system requires a modification of the sensors in the array to provide a pressure-dependent light coupling that is sufficiently sensitive. In order to achieve this sufficiently pressure-dependent light coupling, and thus to improve the transmission properties of the sensor system, the sensors can have additional mechanical structures that are configured to enhance the waveguide bending, and thus to improve the transmission properties. Such mechanical structures are ring-shaped, but these structures need to be precisely aligned with the intersection of the optical fibers, which increases the complexity of the system.

[0004] It is therefore advantageous to realize a pressure sensing system using POFs as optical waveguides, which is less complex and has a high precision. SUMMARY

[0005] In a first aspect of the present disclosure, a two-dimensional optical waveguide pressure sensor array is provided, comprising: two or more rows of optical waveguides;

[0006] two or more columns of optical waveguides, wherein the rows of optical waveguides and the columns of optical waveguides are deformable and arranged in a planar array to define sensors in intersections, wherein each intersection comprises one of the rows of optical waveguides in contact with one of the columns of optical waveguides at their intersection;

[0007] wherein each intersection further comprises a light coupling structure configured to enhance the bending of the waveguides when pressure is applied to the intersection.

[0008] wherein the optical coupling structure comprises a layer of mechanical light scattering material arranged in contact with at least one of the row or column optical waveguides;

[0009] wherein the array of optical waveguide pressure sensors is configured to sense pressure by providing light to the row optical waveguides and measuring light coupled to its column optical waveguide at each intersection, or vice versa, and wherein the light coupled to the column optical waveguide is dependent on the pressure applied to the intersection as a sensor.

[0010] Provided is a two-dimensional array of optical waveguide pressure sensors. With such an array of pressure sensors, it is possible to measure the two-dimensional spatial distribution of pressure of an object and / or a person on a certain structure. To this end, the system provides optical waveguides, preferably polymer or plastic optical fibers (POFs).

[0011] The optical waveguides, further referred to as POFs, are provided in a two-dimensional grid of N x M optical fibers, defining Nx M sensors, comprising at least two rows and at least two columns. The skilled person will recognize that in a preferred embodiment, the number of rows and columns is much larger than a 2x2 grid, for example, an 8x8 grid, a 16x16 grid, a 32x32 grid, a 64x64 grid, or with different numbers of rows and columns, like an 8x16 grid or a 16x32 grid.

[0012] POFs are commonly used for low-speed, short-distance optical data communication, they are robust, flexible, and not sensitive to electromagnetic interference (EMI). POFs are cheap and due to their relatively large diameters of core and cladding, they are easy to handle and easy to couple light into. Since they are made of a ductile polymer (e.g. PMMA), they do not break but only stretch when pulled, unlike silica fibers. For the interconnection of two POFs, low-precision connectors can be used, or even skipped, i.e. the interconnection is achieved by simply cleaving and butting the POFs. The large diameter of the core also reduces the impact of small scratches or dust particles on the fiber end face. Due to their bending sensitivity, combined with their ductility, POFs can also be used for sensing.

[0013] It is in principle not possible to detect attenuation in a two-dimensional (2-D) POF-based pressure sensor array only, only in a complex grid of optical fibers. In a two-dimensional grid of crossing POFs, with N POFs running in the x-direction and M POFs running in the y-direction, there are M x N intersections, which cannot be individually detected by measuring the change in attenuation in each POF in the x- and y-direction only, so N+M measurements are lost. Furthermore, POF pressure sensing using fiber Bragg gratings is fundamentally a complex and expensive technology.

[0014] The proposed system has a POF grid in which the fibres in one direction are connected to light sources and the fibres in the perpendicular direction are connected to high sensitivity light receivers. At a cross-over point the fibres are preferably not modified and a very small amount of light from one fibre can be coupled to the fibre at the cross-over point. Because this very small amount of light power coupling depends on the pressure applied at the cross-over point, each fibre cross-over point of the grid can act as a pressure sensor in which the light coupled at the cross-over point or the cross-over point depends on the pressure applied at the corresponding cross-over point. More preferably there is a proportional relationship, more preferably a linear relationship between the light coupled and the pressure applied at the cross-over point.

[0015] The proposed low cost and robust two-dimensional optical pressure sensor principle can be used in many applications such as:

[0016] - for long-term unobtrusive and accurate sleep motion monitoring in non-clinical (home) situations,

[0017] - for detecting the exact position of a person or player in a virtual reality (VR) floor mat so that these people stay in the right area,

[0018] - it can be applied (or woven) under a carpet or under a PVC floor for a privacy-friendly fall detection of (elderly) people.

[0019] - or for detecting the motion of a person during a magnetic resonance scan (MRI), this optical detection method is even immune to very strong magnetic and radio frequency fields (RF),

[0020] - for monitoring the accurate pressure profile of a bedridden person with restricted motion to prevent pressure injuries (e.g. bedsores),

[0021] - in adaptive mattresses where the local pressure is automatically controlled to improve sleep comfort.

[0022] Known two-dimensional optical waveguide pressure sensor arrays based on POFs require light coupling structures in the form of small ring-shaped elements to enhance the waveguide bending of the POFs. Although adding ring-shaped elements can enhance the waveguide bending and thus improve the transmission characteristics, it has the disadvantage that it adds complexity due to the need for precise alignment of each ring with the cross-over point of the optical fibre.

[0023] The insight of the inventor is that to achieve sufficient, detectable, pressure dependent light coupling, the optical fibres do not need to be modified, but remain unaltered and the light coupling structure does not need to be ring-shaped, but can take the form of small patches of light scattering material in various shapes and sizes, which are advantageously applied at each optical fibre cross-over point. The positioning of the patches relative to the cross-over point does not need to be very precise, whereas the position of the rings needs to be precise.

[0024] The light coupling structure is further preferably flexible, for example comprising a white silicone rubber. With a light coupling structure having a layer of flexible light scattering material, the light coupling can be detected in a better way. More in particular, the proposed light coupling structure allows for a more linear transmission characteristic, which not only makes the sensor more accurate, but also simplifies the readout.

[0025] It has been recognized that with the proposed POF based system, whose light coupling structure has one or more layers of light scattering material, the transmission characteristic of the sensor is improved without added complexity, because the light coupling structure with the (preferably flexible) light scattering material not only results in macrobending (a certain minimum bend radius of the optical fiber, below which light will exit the core through the cladding), but also in microbending, which occurs when the optical fiber is touched, resulting in a deformation of the optical fiber in which a small amount of light will exit the core through the cladding. The fact that only a small amount of light exits the core through the cladding is advantageous, because most of the light will stay in the core, thereby entering the next intersection or sensor, where the intensity will be much lower. Therefore, the sensitivity of any further intersection is hardly influenced by the pressure applied to a certain intersection. This makes the system well scalable to a larger two-dimensional matrix.

[0026] With a flexible light coupling structure, instead of being configured as a rigid annular mechanical element as in known light coupling structures, the optical fiber will have a tendency to exhibit more microbending and less macrobending. The use of a layer of light scattering material will improve the transmission characteristic, because the small amount of light that flows out of the core through the cladding will have a greater chance of coupling to the core of the intersecting optical fiber through the scattering material.

[0027] Because of the use of POF, the proposed optical two-dimensional sensing method is robust, fast, flexible, waterproof, not influenced by external electric fields, and does not generate any electric field itself. The method is scalable, because with a limited number of LEDs and optical receivers many sensor points can be detected. It is low cost, because POFs themselves as well as the light scattering patches are cheap, easy to configure and assemble, and ready-made optical and electrical components can be used.

[0028] In embodiments of the disclosure, the pressure sensitive light coupling mechanism allows to build an intersection in which the optical fibers are not modified, so are intact, and the alignment is very tolerant, which makes the POF grid easy to manufacture at low cost. Depending on the size of the patch, different transmission characteristics can be achieved, from exponential to more linear, or even logarithmic dependence, to achieve a large detection range of local pressure. With a rigid ring structure only an exponential characteristic can be obtained, which is only an advantage when you want to detect if the pressure is or is not above a certain threshold level. The flexible (rubber) material also protects the optical fibers from permanent damage by absorbing large forces, so the robustness is improved.

[0029] In one embodiment, the optical coupling structure includes two layers of light-scattering material that are in contact with and disposed on both sides of row and column optical waveguides, wherein the row and column optical waveguides are vertically disposed between or sandwiched between the two layers of light-scattering material.

[0030] According to several embodiments of this disclosure, the optical coupling structure can be applied to both sides of row and column optical waveguides, and can have a layer of light-scattering material on one or both sides, and can have flexible material on either side, or both sides. In the most preferred embodiment, providing optimal transmission characteristics, the optical coupling structure is applied to both sides, and flexible light-scattering material is present on both sides.

[0031] In one embodiment, the two light-scattering materials have substantially the same size and shape and are arranged substantially laterally.

[0032] Although the top and bottom layers of the light-scattering materials may differ in size and shape, in a preferred embodiment with improved transmission properties, these materials are at least substantially the same in size and shape and are arranged laterally.

[0033] In one embodiment, each row waveguide includes a waveguide core surrounded by a waveguide cladding, and each column waveguide includes a waveguide core surrounded by a waveguide cladding, wherein the waveguide claddings of both the row and column waveguides are arranged to make light-transmitting contact at one or more cross sensors.

[0034] In one embodiment, each row waveguide includes a waveguide core surrounded by a waveguide cladding, and each column waveguide includes a waveguide core surrounded by a waveguide cladding, wherein the ratio of the cross-sectional diameter of the waveguide core to that of the waveguide cladding is at least 50:1, preferably at least 75:1, more preferably at least 90:1, and most preferably about 100:1.

[0035] The cladding must be thin enough that a non-negligible amount of light can couple from the core of one fiber to the cross-linking fiber. As the ratio of the core to the cladding cross-sectional diameter increases, light is more likely to couple to the cross-linking fiber. Therefore, this ratio can be at least 50:1, but more preferably higher.

[0036] In an embodiment, the light coupling structure comprises a deformable material layer, wherein the deformable or flexible layer can be provided by the same material as the material providing the light scattering effect. However, according to an embodiment, a separate layer can also be added in the stack of the light coupling structure, which layer only provides the deformation properties. In an embodiment, the deformable material layer comprises silicone rubber. In another embodiment, the deformable material is selected or adapted according to the transmission properties. This means that the material is selected or adapted to optimize the transmission properties such that, when a pressure is applied to the sensor, i.e. the fiber cross-over, the fiber is smoothly bent, resulting in mostly microbends and little macrobends, so that the light is exponentially coupled according to at least mostly linear or logarithmic transmission properties, depending on the size and shape of the patch.

[0037] In an embodiment, the light coupling structure further comprises a rigid material layer, such as polyvinyl chloride.

[0038] In an embodiment, the light coupling structure comprises two layers of light scattering material in contact with and arranged on both sides of the row and column light waveguides, and two layers of rigid material in contact with and arranged on both sides of the two layers of light scattering material, arranged perpendicular between the row and column light waveguides, or sandwiching the two layers of light scattering material with the two layers of rigid material.

[0039] In an embodiment, the light coupling structure is shaped according to a group of shapes consisting of circular, elliptical, rectangular, square, diamond, cross, drill and polygonal, and in particular, the light coupling structure has various dimensions, in particular, the light coupling structure has a cross-sectional diameter of about 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, and in particular, the light coupling structure has a closed structure, in the center of which a deformable material is arranged.

[0040] The light coupling structure can have various shapes and various dimensions. Furthermore, the light coupling structure can have a cross-sectional diameter between 0.5 mm and 3.0 mm. In contrast to known ring-shaped mechanical patches, which are open in the cross-over area so that the optical fiber does not come into contact with the structure in the cross-over area, the light coupling structure according to the present disclosure preferably has a closed structure. Thus, according to the light coupling structure according to the present disclosure, a deformable material, such as flexible silicone, will provide scattering in the cross-over area in addition to macrobending.

[0041] The dependency of the light coupling and the applied pressure can be further optimized by the shaping of the light coupling structure, for example by selecting certain shapes, layer thicknesses, dimensions and materials.

[0042] In an embodiment, the row and column light waveguides are selected from the group comprising: step index plastic optical fiber and graded index plastic optical fiber.

[0043] In one embodiment, the two-dimensional optical waveguide pressure sensor array is configured as a sleep monitoring sensor, applied underneath a mattress, for unobtrusively monitoring sleep-related movements of a person on the mattress. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 A schematic diagram of a two-dimensional optical waveguide pressure sensor array according to a first aspect of the disclosure is shown;

[0045] Figure 2 A top view and two side views of a POF intersection with flexible material on both sides according to one aspect of the disclosure is shown;

[0046] Figure 3 A top view and two side views of a POF intersection with flexible material on one side according to one aspect of the disclosure is shown;

[0047] Figure 4 A setup to measure the sensitivity characteristics of a POF intersection according to one aspect of the disclosure is shown;

[0048] Figure 5 A graph of the receiver output voltage as a function of applied weight without flexible material at the intersection point according to one aspect of the disclosure is shown;

[0049] Figure 6 A graph of the receiver output voltage as a function of applied weight with flexible material on both sides and on one side of the intersection according to one aspect of the disclosure is shown;

[0050] Figure 7 The effect of the size of the scattering material when using light scattering material on both sides according to one aspect of the disclosure is shown;

[0051] Figure 8 The effect of the size of the scattering material when using light scattering material on one side in one aspect of the disclosure is shown. DETAILED DESCRIPTION

[0052] Figure 1A schematic diagram of a real-time two-dimensional (2D) pressure sensing system is shown, which is based on monitoring the local pressure applied on each intersection of a two-dimensional structure embedded in a two-dimensional surface. The system has a two-dimensional POF grid, a photonic module and a data acquisition and control module. The two-dimensional POF grid consists of a grid of SI-POFs (step index POFs) forming a matrix of intersections. The so-called transmitting fibers of the POF grid are connected to LEDs and the receiving fibers are connected to photodiodes of the photonic module. The LEDs are part of the transmitting section of the photonic module and the photodiodes are part of the receiving section of the photonic module. The data acquisition and control module controls the LED transmitters and processes the measurement data obtained from the photodiode receivers of the photonic module. The light coupling between the POFs of an intersection is a function of the local pressure, so by detecting the light power received by the photodiodes the pressure at the intersection can be measured. Due to the very small light coupling effect between the transmitting and receiving SI-POF fibers, high sensitivity light receivers are needed, using transimpedance amplifiers (TIAs) with high gain and high input impedance. Furthermore, due to the fact that only a small amount of light power is coupled out of the transmitting fiber when pressure is applied on the respective intersection, the light remaining in the transmitting fiber and entering the next intersection is hardly reduced. Therefore, the sensitivity of one intersection is hardly influenced by the pressure of other intersections, i.e. the position dependence of the performance of one intersection is negligible. This makes the system well scalable to larger two-dimensional matrices. In order to realize a simple and scalable system, an intersection scanning method is implemented. Figure 1 The data acquisition and control module in the system controls the selector, which selects only one LED at a time, and the intersections are scanned column by column. At the same time the outputs of the photodetectors are read row by row, enabling the data acquisition and control module to perform two-dimensional pressure detection. This solution is easily scalable, because N photodetectors and M LED sources can detect NxM sensor points, where the vertical columns are scanned one by one.

[0053] One innovative feature of the present disclosure is the design of the pressure sensitive light coupling mechanism and the construction of the intersections, where the optical fibers are not modified, so they remain as they are. Furthermore, the design of the intersections is very alignment-tolerant, because the scattering material that increases the sensitivity does not need to be precisely aligned on the intersections. This innovative intersection design makes the POF grid easy to manufacture at low cost. Now two embodiments of the present invention will be introduced: the use of flexible scattering material on both sides (top and bottom) of the intersection, and the use of flexible scattering material on only one side (top or bottom), which makes the structure thinner. These solutions will be discussed below, including their measurement results.

[0054] Solution 1: flexible scattering material on both sides.

[0055] As Figure 2As shown, both sides of the polymer optical fiber (POF) intersection have a flexible light scattering material, for example 10 x 10 x 1.5 mm 3 of white silicone rubber and a thin rigid material, for example hard PVC with a thickness of 0.3 mm. PMMA (polymethyl methacrylate) POF is suitable for visible light, with a loss of <0.5 dB / m in the wavelength range of 400 to 700 nm. To improve the light coupling, the flexible material should scatter the wavelength of the light used as much as possible, with a low absorption coefficient at these wavelengths. Therefore, in the case of red light, a flexible material that is red should be used, and in the case of white light, a flexible material that scatters the broad white light spectrum should be used (so a white material from the outside). In the experiments, white LEDs were used, so a white flexible material was also used, as other colors or even UV did not bring a clear improvement. The ductility of the material must be reversible: when the pressure is removed, the flexible material should return to its original shape, so it should be robust, with no residual deformation after the application of a large pressure. The flexibility and thickness of the material also have an influence on the detection properties. A thicker material will reduce the sensitivity. The flexibility of the scattering material and the POF should be such that, when pressure is applied vertically to the node, the flexible scattering material will press both optical fibers on both sides, so that it will smoothly bend the optical fibers a little. At the same time, the physical contact area of both optical fibers with the flexible scattering material will also increase. Due to the microscopic bending (because the optical fibers touch each other) and the macroscopic bending (because the optical fibers bend smoothly), a small amount of light will escape from the transmitting optical fiber, coupled into the receiving optical fiber. The amount of light coupling is proportional to the applied pressure. Due to the microscopic and macroscopic bending of the optical fibers, the escaped light will be scattered in all directions in the (white) flexible scattering material and will partially be coupled again into the receiving optical fiber. The flexible material makes the sensor grid also very robust. When pressure is applied, the flexible material makes the bending radius of the optical fibers at the intersection more smooth and the force is partially absorbed by the flexible material outside the optical fiber intersection. Without the flexible material, only rigid material, the force would be concentrated on the intersection of the optical fibers, which can lead to permanent deformation. The rigid material concentrates the vertical pressure on the intersection.

[0056] Scheme 2: flexible scattering material on one side

[0057] As Figure 3As shown, one side of the polymer optical fiber cross (e.g. top) has a flexible light scattering material, such as white silicone rubber, and a thin rigid material, such as hard PVC. On the other side (e.g. bottom), the cross has a thin light scattering rigid material, such as white hard PVC, to concentrate the vertical pressure to the cross. If the sensor is laid on a solid surface, this rigid material is not necessary. The flexibility of the scattering material and POFs should be such that when a vertical pressure is applied, the receiving fiber will press and bend the transmitting fiber into the flexible scattering material. At the same time, the physical contact of both fibers with the flexible scattering material will also increase. Because of the microscopic bending due to the fibers touching each other, and the macroscopic bending due to the transmitting fiber bending smoothly, a small amount of light will escape from the transmitting fiber and couple into the receiving fiber. The amount of light coupling is proportional to the applied pressure. The escaped light will be scattered in all directions in the (white) flexible scattering material and the rigid (white) scattering material, and partially couple into the receiving fiber. Also, the flexible material makes the grid of the sensor very robust. When pressure is applied, the flexible material makes the bending radius of the fibers at the cross smoother, and the force is partially absorbed by the flexible material outside the fiber cross. If there is no flexible material, only rigid material, the force will be concentrated on the cross of the fibers, which can cause permanent deformation. The rigid material concentrates the pressure on the cross.

[0058] The proposed system has the following advantages in all or some aspects:

[0059] - The POF fibers keep their original state, i.e. no modification is needed

[0060] - Despite the POFs not being modified, high sensitivity is provided due to the microbending (POFs touching each other), macrobending (fibers being bent at the cross) and the scattering flexible material contacting the fibers at the cross.

[0061] - The positioning of the flexible patch relative to the cross is very forgiving.

[0062] - Very robust, as the flexible material protects the fiber cross.

[0063] - Depending on the size of the patch, different sensitivity characteristics can be achieved, see measurement results below.

[0064] The POF fiber type can be CK20, Mitsubishi Rayon, step index PMMA POF with a diameter of 0.5 mm. The flexibility of the fiber also has an influence on the pressure sensitivity of the optical coupling. From a mechanical point of view, it is known that the force needed to bend a rod increases with the diameter of the rod. Therefore, the smaller the diameter of the fiber, the more flexible the fiber is. Hence, a 0.5 mm diameter POF is more flexible and sensitive than a standard 1 mm diameter POF. Also, the scattering loss of the fiber is important. The fiber must have a relatively high scattering and low absorption loss to obtain a detectable optical signal power at the input of the receiver. Therefore, a silica glass fiber is not suitable, because the scattering loss of silica glass is very low compared to POF. The fiber should also have a thin cladding to prevent influence of adjacent cross-overs, therefore, a step index POF is not suitable. The cladding diameter is preferably 500 μm and the core diameter is 486 μm. The dimensions of the white silicone rubber material are preferably 10 x 10 x 1.5 mm 3 The white LED couples a light power of > 1 mW into the emitting POF. This power depends on the diameter of the fiber core, in general, the larger the fiber core diameter, the more power the LED couples into the fiber. The sensitivity of the photodiode receiver is preferably 0.4 V / nW.

[0065] Measurement results

[0066] A. No flexible material around the cross-over

[0067] To show the influence of the flexible scattering material, first the receiver output voltage is shown as a function of the applied weight, with Figure 2 No flexible material around the cross-over. Figure 5 The shown measurement results are with both surfaces of the rigid hard PVC material around the cross-over a) black light absorbing, b) white light scattering or c) stuck together with white adhesive tape. By using white scattering material or white tape around the cross-over, the sensitivity is much larger for larger weights. However, the output voltage of the optical receiver is always limited (in this case about 3 volts). This limits the pressure range that the sensor can use, in the case of the white tape about 600 g. The output voltage versus weight curve shows an exponential like behavior, see Figure 5 Weights smaller than 200 g are already hardly detectable. By reducing the sensitivity of the sensor, e.g. by reducing the LED output power, the maximum weight is increased, but detecting small weights becomes more difficult. Therefore, these exponential characteristics are not very practical. To detect a larger range, a linear or even a logarithmic characteristic is preferred.

[0068] For sensitive detection, the exponential characteristic is not a problem, whether or not there is a certain pressure.

[0069] Experiments with white silicone sealant to stick the fibers together at the intersection resulted in a low repeatability of the sensitivity characteristics.

[0070] Figure 5 is a plot of the receiver output voltage as a function of applied weight, without flexible material at the intersection:

[0071] a) Black, absorbing, rigid material on both sides of the intersection

[0072] b) White, scattering, rigid material on both sides of the intersection

[0073] c) Fibers stuck together with white adhesive tape

[0074] B. Use of flexible material at the intersection

[0075] Figure 6 shows the receiver output voltage as a function of applied weight for a) using flexible scattering material on both sides of the intersection as shown in Figure 2 and b) using flexible scattering material on only one side as shown in Figure 3 Compared to the results of Figure 5 there is an improvement in sensitivity for small weights and the characteristic is more linear, thus suitable for measuring a larger range of pressures. Because in the structure of Figure 3 one side is flexible and the other is rigid, more macrobending is introduced compared to the intersection with flexible material on both sides. This explains the higher sensitivity of the second scheme.

[0076] Figure 6 is a plot of the receiver output voltage as a function of applied weight:

[0077] a) Flexible scattering material on both sides of the intersection (according to the intersection of Figure 2

[0078] b) Flexible scattering material on one side of the intersection (according to the intersection of Figure 3

[0079] Figure 7 and Figure 8 shows the influence of the size of the scattering material. Figure 7 is in the case of using scattering material on both sides, Figure 8 is when using it on only one side. It can be seen that the size of the scattering material has an influence on the shape of the sensitivity characteristic. For sensitive detection, there is an exponential characteristic with or without a certain pressure, Figure 7 (a) and Figure 8 (a) were obtained using 5 x 5 mm 2 flexible material, which has an advantage. If a more linear characteristic is required, 10 x 10 mm​​2 patch, see Figure 7 (b) and Figure 8 (b). With larger patches, a logarithmic behavior can be obtained, resulting in a wider detection range, see for example Figure 7 (c) and 7(d) and Figure 8 (c) and 7(d).

[0080] Figure 7 is a plot of the receiver output voltage as a function of applied weight, with flexible material on both sides (so according to Figure 2 ), and the dimensions of the flexible material:

[0081] a) 5 x 5 mm 2

[0082] b) 10 x 10 mm 2

[0083] c) 15 x 15 mm 2

[0084] d) 20 x 20 mm 2

[0085] Figure 8 is a plot of the receiver output voltage as a function of applied weight, with flexible material on one side (so according to Figure 3 ), and the dimensions of the flexible material:

[0086] a) 5 x 5 mm 2

[0087] b) 10 x 10 mm 2

[0088] c) 15 x 15 mm 2

[0089] d) 20 x 20 mm 2

[0090] The embodiments described here are able to detect 50 pressure profiles of a person on a mattress in one second, with a 16 x 8 POF grid underneath the mattress, so with 128 intersections.

[0091] This low-cost and robust two-dimensional (2D) optical pressure sensor principle can be used in many applications.

[0092] In a non-clinical (home) situation, for long-term unobtrusive accurate sleep motion monitoring.

[0093] For monitoring accurate pressure profiles of bedridden persons to prevent pressure injuries (e.g. bedsores).

[0094] In adaptive mattresses, local pressure is automatically controlled to improve sleep comfort.

[0095] It can be applied under a carpet (or woven in a carpet), or on a PVC floor for example to detect (elderly) people falling.

[0096] In Virtual Reality (VR) floor mats, the exact position of people / players is detected so that these people / players stay in the right area.

[0097] Having now described several exemplary embodiments of the application, it is to be appreciated that these embodiments are illustrative only and are not intended to limit the scope of the application in any way. Many variations of the described embodiments are possible within the scope of the application, which is defined by the following claims and their equivalents.

Claims

1. A two-dimensional optical waveguide pressure sensor array comprising: two or more rows of optical waveguides; two or more columns of optical waveguides, wherein the rows of optical waveguides and the columns of optical waveguides are deformable and arranged in a planar array to define sensors in intersections, wherein each intersection comprises one of the rows of optical waveguides in contact with one of the columns of optical waveguides at their intersection; wherein each intersection further comprises an optical coupling structure in the form of a patch, the optical coupling structure configured to enhance waveguide curvature when pressure is applied to the intersection; wherein the optical coupling structure comprises a layer of a mechanical light scattering material disposed in contact with at least one of the rows of optical waveguides or the columns of optical waveguides; wherein the optical waveguide pressure sensor array is configured to sense pressure by providing light to the rows of optical waveguides and measuring light coupled to their column of optical waveguides at each intersection, or vice versa, and wherein the light coupled to the column of optical waveguides is dependent on the pressure applied to the intersection as a sensor.

2. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the optical coupling structure comprises two layers of light scattering material in contact with and disposed on either side of the rows of optical waveguides and the columns of optical waveguides, wherein the rows of optical waveguides and the columns of optical waveguides are disposed perpendicularly between the two layers of light scattering material.

3. The two-dimensional optical waveguide pressure sensor array of claim 2, wherein the two layers of light scattering material are substantially the same size and shape and are arranged substantially laterally.

4. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein each row of optical waveguides comprises a waveguide core surrounded by a waveguide cladding, wherein each column of optical waveguides comprises a waveguide core surrounded by a waveguide cladding, wherein the waveguide cladding of the rows of optical waveguides and the columns of optical waveguides are arranged to make transparent contact at one or more intersection sensors.

5. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein each row of optical waveguides comprises a waveguide core surrounded by a waveguide cladding, wherein each column of optical waveguides comprises a waveguide core surrounded by a waveguide cladding, wherein the ratio of the cross-sectional diameter of the waveguide core to the waveguide cladding is at least 50:

1.

6. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the optical coupling structure comprises a layer of deformable material.

7. The two-dimensional optical waveguide pressure sensor array of claim 6, wherein the layer of deformable material comprises a layer of light scattering material.

8. The two-dimensional optical waveguide pressure sensor array of claim 6 or 7, wherein the layer of deformable material comprises a silicone rubber.

9. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the optical coupling structure further comprises a layer of rigid material.

10. The two-dimensional optical waveguide pressure sensor array of claim 9, wherein the layer of rigid material comprises polyvinyl chloride.

11. The two-dimensional optical waveguide pressure sensor array of claim 9 or 10, wherein the light coupling structure comprises two layers of light scattering material in contact with and arranged on both sides of the row light waveguides and the column light waveguides, and two layers of rigid material in contact with and arranged on both sides of the two layers of light scattering material, arranged perpendicularly between the row light waveguides and the column light waveguides and the two layers of light scattering material and the two layers of rigid material.

12. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein the light coupling structure is shaped according to a group of shapes from the group of: circular, elliptical, rectangular, square, and polygonal, wherein the light coupling structure has various or respective dimensions.

13. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein the light coupling structure has a cross-sectional diameter of about 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, wherein the light coupling structure has a closed structure with deformable material arranged in the center of the closed structure.

14. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein the row light waveguides and the column light waveguides are selected from the group consisting of: step index plastic optical fiber and graded index plastic optical fiber.

15. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein the two-dimensional optical waveguide pressure sensor array is configured as a sleep monitoring sensor arranged underneath a mattress for unobtrusive measurement of sleep related movements of a person on the mattress.

16. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein each row light waveguide comprises a waveguide core surrounded by a waveguide cladding, wherein each column light waveguide comprises a waveguide core surrounded by a waveguide cladding, wherein the ratio of the cross-sectional diameter of the waveguide core relative to the waveguide cladding is at least 75:

1.

17. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein each row light waveguide comprises a waveguide core surrounded by a waveguide cladding, wherein each column light waveguide comprises a waveguide core surrounded by a waveguide cladding, wherein the ratio of the cross-sectional diameter of the waveguide core relative to the waveguide cladding is at least 90:

1.

18. The two-dimensional optical waveguide pressure sensor array of any one of claims 1-3, wherein each row light waveguide comprises a waveguide core surrounded by a waveguide cladding, wherein each column light waveguide comprises a waveguide core surrounded by a waveguide cladding, wherein the ratio of the cross-sectional diameter of the waveguide core relative to the waveguide cladding is at least 100: 1.

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