Two-dimensional optical waveguide pressure sensor array

Abstract

The present invention discloses a two-dimensional optical waveguide pressure sensor array comprising two or more row optical waveguides and two or more column optical waveguides, the row optical waveguides and column optical waveguides being deformable and arranged in a planar array to define sensors at cross-points, wherein each cross-point includes one of the row waveguides in contact with one of the column waveguides at its intersection; each cross-point further includes an optical coupling structure configured to enhance waveguide bending when pressure is applied to the cross-point; the optical coupling structure includes a layer of mechanical light scattering material disposed in contact with at least one of the row or column optical waveguides; and the optical waveguide pressure sensor array is configured to sense pressure at each cross-point by providing light to the row optical waveguides and measuring the light coupled into its column optical waveguide, or vice versa, wherein the light coupled into the column optical waveguide depends on the pressure applied to the cross-point that acts as a sensor.

Description

[Technical Field]

[0001] The present invention relates generally to optical waveguide pressure sensor arrays, and more particularly to two-dimensional pressure sensing systems that use polymer optical fibers in an optical waveguide pressure sensor array configuration. [Background technology]

[0002] Pressure sensing systems providing two-dimensional position information are known, for example, from U.S. Pat. No. 4,733,068 and U.S. Patent Application Publication No. 2019 / 0302879. From these publications, it is known to use optical fiber sensor arrays to measure the spatial distribution of pressure applied to 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 people.

[0003] Pressure-sensing systems that use polymer optical fiber (POF) sensors in their arrays offer the advantages of being inexpensive, robust, flexible, and immune to electromagnetic interference (EMI). In such pressure-sensing systems, a grid of fibers is provided, with unidirectional fibers connected to a light source (especially a light-emitting diode (LED)) and transverse fibers connected to a highly sensitive optical receiver. At intersections, light from one fiber can couple into the intersecting fibers. Because this optical power coupling depends on the pressure at the intersection, each of these intersection points in the grid can function as a local pressure sensor. Such pressure-sensing systems require modifications to the sensors in the array to provide sufficiently sensitive pressure-dependent optical coupling. To achieve such sufficient pressure-dependent optical coupling and thereby improve the transduction characteristics of the sensor system, the sensor can have additional mechanical structures configured to enhance waveguide bending and thereby improve the transduction characteristics. While such mechanical structures are ring-shaped, they require precise alignment with the fiber intersections, which increases the system complexity.

[0004] It would therefore be advantageous to provide a pressure sensing system using POF as an optical waveguide with lower complexity and with a high level of accuracy. Summary of the Invention

[0005] In a first aspect of the present disclosure, there is provided a two-dimensional optical waveguide pressure sensor array, comprising: two or more row optical waveguides; two or more column optical waveguides, the row optical waveguides and the column optical waveguides being deformable and arranged in a planar array to define sensors at crosspoints, where each crosspoint includes one of the row waveguides in contact with one of the column waveguides at its intersection; each cross point further includes an optical coupling structure configured to enhance the waveguide bending when pressure is applied to the cross point; the light coupling structure includes a layer of mechanical light scattering material disposed in contact with at least one of the row or column light guides; The optical waveguide pressure sensor array is configured to sense pressure by providing light to row optical waveguides and measuring the light coupled into its column optical waveguide at each cross point, or vice versa, where the light coupled into the column optical waveguide depends on the pressure applied at the cross point that acts as a sensor, thereby providing a two-dimensional optical waveguide pressure sensor array.

[0006] Provided is a two-dimensional optical waveguide pressure sensor array. Such a pressure sensor array can be used to measure the two-dimensional spatial distribution of pressure of objects and / or people on a specific structure. To this end, the system provides an optical waveguide, preferably a polymer or plastic optical fiber (POF).

[0007] The optical waveguide, hereafter referred to as POF, is provided as a two-dimensional grid of N×M fibers defining N×M sensors, the two-dimensional grid including at least two rows and at least two columns. Those skilled in the art will recognize that in preferred embodiments, the number of rows and columns is much larger than a 2×2 grid, for example, an 8×8 grid, a 16×16 grid, a 32×32 grid, a 64×64 grid, or has a different number of rows and columns, such as an 8×16 grid or a 16×32 grid.

[0008] POF is commonly used for low-speed, short-distance optical data communications. It is rugged, flexible, and immune to electromagnetic interference (EMI). Its relatively large core and cladding diameters make it easy to handle and couple light into. Because it is made of a ductile polymer (e.g., PMMA), it is less brittle than silica fiber and stretches rather than breaks when stretched. Low-precision connectors can be used to interconnect two POFs, or they can even be omitted—simply cutting and butt-splicing the POFs. The large core diameter also reduces the impact of small scratches or dust particles on the fiber endface. Due to its bend-sensitive properties, enhanced by its ductility, POF can also be used for sensing.

[0009] A two-dimensional (2D) POF-based pressure sensor array based on detecting only the attenuation within the POF is not possible in principle with a complex fiber grid alone. In a 2D grid of intersecting POFs, with N POFs aligned in the x direction and M POFs aligned in the y direction, there will be M × N intersections, and therefore N + M missing measurements, that cannot be detected individually by measuring only the attenuation variations of each POF in the x and y directions. Furthermore, POF pressure sensing using fiber Bragg gratings is fundamentally a complex and expensive technology.

[0010] The proposed system includes a grid of POFs, with unidirectional fibers connected to a light source and perpendicular fibers connected to a highly sensitive optical receiver. At crossovers, where the fibers are preferably unmodified, very small amounts of light from one fiber can couple into the intersecting fiber. Because this very small optical power coupling depends on the pressure applied to the crossover, each fiber crossover in the grid can function as a pressure sensor, where the light coupled at the crossover point or crossover depends on the pressure applied to the corresponding crossover. More preferably, there is a proportional, and even more preferably, a linear, relationship between the light coupled and the pressure applied to the crossover.

[0011] The proposed low-cost and robust 2D optical pressure sensor principle can be used for many applications, such as: For long-term non-invasive precision sleep and movement monitoring in non-clinical (home) settings, In a virtual reality (VR) floor mat for detecting the exact position of people or gamers so that they stay in the correct area, For privacy-friendly fall detection of (elderly) people, under (or woven into) carpets or, for example, under PVC floors, Alternatively, it can be applied to detect human movement during an MRI scan. This optical detection method is insensitive to very strong magnetic and RF fields. To monitor the precise pressure profile of a person in bed with restricted movement to prevent pressure injuries (e.g., decubitus), In an adaptive mattress, local pressure is automatically controlled to improve sleep comfort.

[0012] Known 2D optical waveguide pressure sensor arrays based on POF require optical coupling structures in the form of small ring-shaped elements to enhance the waveguide bending of the POF. While adding ring-shaped elements can enhance the waveguide bending and thereby improve the transduction characteristics, it also comes with the drawback of increased complexity, as each ring needs to be precisely aligned with the fiber intersection.

[0013] It was the inventors' insight to realise that to achieve sufficient pressure-dependent optical coupling to be detectable, the constituent fibers do not need to be modified but can remain unchanged, and the optical coupling structure does not need to be ring-shaped, but can be used in the form of small patches of light-scattering material of various shapes and sizes that are advantageously applied to each fibre cross-point. The positioning of the patches relative to the cross-points does not need to be highly accurate, but the position of the rings does need to be precise.

[0014] The light-coupling structure is further preferably flexible, e.g., made of white silicone rubber. Using a light-coupling structure with a layer of flexible, light-scattering material allows for improved detection of light coupling. More specifically, the proposed light-coupling structure allows for a more linear conversion characteristic, which not only makes the sensor more accurate but also simplifies readout.

[0015] The proposed system, based on a POF with one or more layers of light-scattering material, recognizes that the (preferably flexible) light-scattering material-based optical coupling structure can improve the sensor's transduction characteristics without adding complexity by preventing not only macrobending (having a specific minimum bend radius for the fiber, where light exits the core through the cladding) but also microbending, which occurs when the fibers come into contact, resulting in strain on the fiber and causing a small amount of light to exit the core through the cladding. The fact that only a small amount of light exits the core through the cladding is advantageous because the majority of the light remains in the core and thus proceeds to the next crossing point or sensor, where its intensity is less likely to be reduced. Therefore, the sensitivity of further crossing points is largely unaffected by the pressure applied to a particular crossing point. This makes the system fully scalable to larger 2D matrices.

[0016] With flexible optical coupling structures, rather than known optical coupling structures configured as rigid ring-shaped mechanical elements, the fibers tend to exhibit more microbending and less macrobending. The use of a light-scattering material layer improves the conversion characteristics because less light exits the core through the cladding, making it more likely to couple into the core of the crossing fiber through the scattering material.

[0017] Because it uses POF, the proposed optical 2D sensing method is robust, fast, flexible, waterproof, and insensitive to external electric fields, and does not generate any electric fields itself. The method is scalable because it can detect many sensor points with a limited number of LEDs and optical receivers. It is also low-cost because the POF itself, as well as the light-scattering patches, are inexpensive, easy to construct and assemble, and can use readily available optical and electrical components.

[0018] In the disclosed embodiments, the pressure-sensitive optical coupling mechanism allows for the construction of crossovers where the fibers remain unmodified and untouched, with very high alignment tolerances, facilitating low-cost manufacturing of POF grids. Depending on the size of the patch, various transfer characteristics can be realized, ranging from exponential to more linear and even logarithmic dependence on local pressure, to achieve a wide detection range. Rigid ring structures only provide exponential characteristics, which are advantageous only when detecting the presence or absence of pressure above a certain threshold level. Additionally, flexible (rubber) materials improve robustness by absorbing large forces and thereby protecting the fibers from permanent damage.

[0019] In one example, the light coupling structure includes two layers of light scattering material in contact with and disposed on either side of row and column light guides, where the row and column light guides are vertically disposed between or sandwiched by the two layers of light scattering material.

[0020] Light-coupling structures according to some embodiments of the present disclosure may be applied to both sides of the row and column light guides and may have a layer of light-scattering material on either one or both sides, with no flexible material on either side, or flexible material on one or both sides. In the most preferred embodiment, which provides the best conversion characteristics, the light-coupling structure is applied to both sides and has flexible light-scattering material on both sides.

[0021] In one example, the two layers of light-scattering material are of substantially the same size and shape and are substantially laterally aligned.

[0022] The top and bottom layers of light-scattering material may be of different sizes and shapes, but in preferred embodiments with improved conversion properties, they are at least substantially the same size and shape and are laterally aligned.

[0023] In one example, each row optical waveguide includes a waveguide core surrounded by a waveguide cladding, and each column optical waveguide includes a waveguide core surrounded by a waveguide cladding, and the waveguide claddings of both the row optical waveguide and the column optical waveguide are arranged for optical transmission contact at one or more intersection sensors.

[0024] In one example, each row optical waveguide includes a waveguide core surrounded by a waveguide cladding, and each column optical waveguide includes a waveguide core surrounded by a waveguide cladding, wherein the ratio of cross-sectional diameter of the waveguide core to 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.

[0025] The cladding is at least thin enough that a non-negligible amount of light can be coupled from the core of one fiber into another crossing fiber. As the ratio of the cross-sectional diameter of the core to the cladding increases, the tendency for light to couple into the crossing fiber increases. Thus, the ratio may be at least 50:1, but is more preferably higher.

[0026] In one example, the optical coupling structure includes a layer of deformable material, where the deformable or flexible layer may be made of the same material that provides the light scattering effect. However, according to one example, a separate layer that only provides deformation properties can be added to the optical coupling structure stack. In one example, the deformable material layer includes silicone rubber. In a further example, the deformable material is selected or tailored to its conversion properties. This means that the material is selected or tailored to optimize the conversion properties so that applying pressure to the sensor, i.e., the fiber crossing point, causes the fiber to bend smoothly, causing mostly microbending and little macrobending, resulting in light being coupled according to an exponential, at least mostly linear, or logarithmic conversion property depending on the size and shape of the patch.

[0027] In one example, the optical coupling structure further includes a layer of rigid material, such as polyvinyl chloride.

[0028] In one example, the light coupling structure includes two layers of light scattering material in contact with and disposed on either side of row and column light guides, and two layers of rigid material in contact with and disposed on either side of the two layers of light scattering material, and is disposed perpendicularly between or sandwiched by the row and column light guides and the two layers of light scattering material comprising the two layers of rigid material.

[0029] In one example, the light-coupling structure is shaped according to one of the group of a circle, an ellipse, a rectangle, a square, a rhombus, a cross, a diamond, and a polygon, wherein, in particular, the light-coupling structure has various sizes, in particular, the light-coupling structure has a cross-sectional diameter of approximately 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, in particular, the light-coupling structure has a closed structure and a deformable material is disposed at the center of the closed structure.

[0030] The optical coupling structure may have various shapes and sizes. Furthermore, the optical coupling structure may have a cross-sectional diameter ranging from 0.5 mm to 3.0 mm. The optical coupling structure of the present disclosure is preferably a closed structure, compared to known ring-shaped mechanical patches that are open at the cross-point region so that the fibers do not contact the structure at the cross-point region. As a result, an optical coupling structure according to the present disclosure, which is provided with a deformable material such as flexible silicone, provides scattering to the cross-point region in addition to macrobending.

[0031] The optical coupling and the dependence of applied pressure can be further optimized by shaping the optical coupling structure, for example, by selecting specific shapes, layer thicknesses, sizes and materials.

[0032] In one example, the row and column optical waveguides are selected from the group consisting of step-index plastic fibers and graded-index plastic fibers.

[0033] In one example, the two-dimensional optical waveguide pressure sensor array is configured as a sleep monitoring sensor applied under the matrass for non-invasive measurement of sleep-related movements of an individual on the matrass. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic diagram of a two-dimensional optical waveguide pressure sensor array according to a first embodiment of the present disclosure. [Figure 2] 1A-1C illustrate a top view and two side views of a POF intersection with flexible material on both sides, according to an embodiment of the present disclosure. [Figure 3] 1A-1C illustrate a top view and two side views of a POF intersection with a flexible material on one side, according to an embodiment of the present disclosure. [Figure 4] FIG. 4 illustrates an arrangement for measuring sensitivity characteristics of a POF intersection, according to an embodiment of the present disclosure. [Figure 5] 10 is a graph of receiver output voltage as a function of added weight for an embodiment of the present disclosure without flexible material at the intersection. [Figure 6] 10 is a graph of receiver output voltage as a function of added weight for an embodiment of the present disclosure having flexible material on both sides and one side of the intersection. [Figure 7] 10 is a graph showing the effect of scattering material size in an embodiment of the present disclosure in which light scattering material is used on both sides. [Figure 8] 10 is a graph showing the effect of scattering material size in an embodiment of the present disclosure where a light scattering material is used on one side. DETAILED DESCRIPTION OF THE INVENTION

[0035] Figure 1 shows a schematic diagram of a real-time two-dimensional (2D) pressure sensing system based on monitoring the local pressure applied per crosspoint on a 2D structure embedded in a two-dimensional (2D) surface. The system includes a 2D POF grid, an optoelectronic module, and a data acquisition and control module. The 2D POF grid is composed of a grid of step-index POF (SI-POF) fibers that form a matrix of crosspoints. The so-called transmit fibers of the POF grid are connected to LEDs, and the receive fibers are connected to photodiodes in the optoelectronic module. The LEDs are part of the transmit section of the optoelectronic module, and the photodiodes are part of the receive section of the optoelectronic module. The data acquisition and control module controls the LED transmitters and processes the measurement data acquired from the photodiode receivers in the optoelectronic module. Because the optical coupling between the POFs at the crosspoints is a function of the local pressure, the pressure at the crosspoints can be measured by detecting the optical power received by the photodiodes. Because the optical coupling effect between the transmit and receive SI-POF fibers is very small, a highly sensitive optical receiver using a transimpedance amplifier (TIA) with high gain and high input impedance is required. Furthermore, when pressure is applied to each crosspoint, only a small amount of optical power is coupled out of the transmitting fiber, so the light that remains in the transmitting fiber and travels to the next crosspoint is barely reduced. Therefore, the sensitivity of a crosspoint is largely unaffected by pressure on other crosspoints, meaning that the positional dependency of crosspoint performance is negligible. This makes the system fully scalable to larger two-dimensional matrices. To achieve a simple and scalable system, a crosspoint scanning scheme is implemented. The data acquisition and control module (Figure 1) controls a selector that selects only one LED at a time, and the crosspoints are scanned row by row. By simultaneously reading the output of the photodetectors line by line, the data acquisition and control module enables 2D pressure detection.This solution is easily scalable, as N photodetectors and M LED light sources can detect N x M sensor points, with vertical columns scanned one by one.

[0036] The innovative features of this disclosure are the design of a pressure-sensitive optical coupling mechanism and the construction of the crossover where the fibers are left unmodified. Furthermore, the crossover design is very alignment-tolerant, as the sensitivity-enhancing scattering material does not need to be precisely aligned at the crossover. This innovative crossover design allows for low-cost and easy manufacturing of POF grids. Two embodiments of the invention are now described: flexible scattering material on both sides (top and bottom) of the crossover, and flexible scattering material on only one side (top or bottom), which allows for a thinner structure. These options are discussed below, including measurement results.

[0037] Option 1: Flexible scattering material on both sides At the crossing of the polymer optical fiber (POF), a flexible light scattering material, e.g., 10 × 10 × 1.5 mm, is used, as shown in Figure 2. 3The flexible material is made of white silicone rubber and a thin, rigid material, such as 0.3 mm thick rigid PVC, on both sides. PMMA (polymethyl methacrylate) POF is suitable for visible light in the wavelength range between 400 and 700 nm, with losses of <0.5 dB / m. To improve optical coupling, the flexible material must scatter the wavelengths of light used as much as possible, clearly possessing a low absorption coefficient at these wavelengths. Therefore, if red light is used, a red flexible material must be used; if white light is used, a flexible material that scatters a wide white light spectrum (and therefore appears white from the outside) must be used. In the experiments, a white LED and, therefore, a white flexible material were used because other colors, even ultraviolet light, did not provide significant improvement. The ductility of the material must be reversible: the flexible material must regain its original shape when pressure is removed, and must be robust without remaining deformation after significant pressure is applied. The flexibility and thickness of the material also affect the sensing characteristics. A thicker material reduces sensitivity. The flexibility of the scattering material and POF must be such that when pressure is applied perpendicular to the node, the flexible scattering material pushes on both sides of both fibers, thus bending them slightly and smoothly. This also increases the physical contact area of ​​both fibers with the flexible scattering material. Due to microbending (due to the fibers touching each other) and macrobending (due to the fibers being bent smoothly), a small amount of light leaks from the transmitting fiber and couples into the receiving fiber. The amount of light coupling is proportional to the applied pressure. The leaked light is scattered in all directions within the flexible scattering material (white) and partially couples back into the receiving fiber due to microbending and macrobending of the fiber. The flexible material also makes the sensor grid very robust. When pressure is applied, the flexible material gives the fibers a smoother bend radius at the crossing, and the force is partially absorbed by the flexible material outside the fiber crossing. Without the flexible material, with only a rigid material, the force would be concentrated at the fiber crossing point, which could cause permanent deformation. The rigid material concentrates normal pressure at the intersection.

[0038] Option 2: Flexible scattering material on one side As shown in Figure 3, a polymer optical fiber intersection is provided on one side (e.g., the top end) with a flexible, light-scattering material such as white silicone rubber and a thin, rigid material such as rigid PVC. On the other side (e.g., the bottom end), the intersection is provided with a thin, light-scattering, rigid material, e.g., white rigid PVC, to concentrate vertical pressure. This rigid material is not necessary if the sensor is placed on a solid surface. The flexibility of the scattering material and POF must be such that when vertical pressure is applied, the receiving fiber bends the transmitting fiber by pushing it into the flexible scattering material. This also increases the physical contact of both fibers with the flexible scattering material. Due to microbending caused by the contact between the fibers and macrobending caused by the smooth bending of the transmitting fiber, a small amount of light leaks from the transmitting fiber and couples into the receiving fiber. The amount of light coupling is proportional to the applied pressure. The leaked light is scattered in all directions in the flexible (white) scattering material and the rigid (white) scattering material and is partially coupled into the receiving fiber. Again, the flexible material makes the sensor grid very robust. The flexible material allows the fibers at the intersections to have a smoother bend radius when pressure is applied, and the force is partially absorbed by the flexible material outside the fiber intersections. Using only a rigid material without a flexible material would concentrate the force at the fiber crosspoints, which could cause permanent deformation. The rigid material concentrates the pressure at the intersections.

[0039] The proposed system has the following advantages in all or some aspects: The POF fiber is left in its original state, i.e., no modification is required. Although the POF remains unmodified, high sensitivity results due to microbending (POFs touching each other), macrobending (fibers are bent at the intersection), and scattering flexible materials at the intersections where the fibers meet. Very forgiving regarding the positioning of the flexible patch relative to the intersection; The flexible material is very robust to protect the fiber crossings; Depending on the dimensions of the patch, different sensitivity characteristics can be achieved, see measurements below.

[0040] The POF fiber type can be CK20, manufactured by Mitsubishi Rayon, a 0.5 mm diameter step-index PMMA POF. The flexibility of the fiber also affects the pressure sensitivity of the optical coupling. From mechanics, it is known that the force required to bend a rod increases with the rod diameter. Therefore, the smaller the diameter of the fiber, the more flexible the fiber. Therefore, a 0.5 mm diameter POF is more flexible and sensitive than a standard 1 mm diameter POF. The scattering loss of the fiber is also important. The fiber must have relatively high scattering and low absorption loss to allow detectable optical signal power at the receiver input. Therefore, silica glass optical fiber is not suitable because silica glass has very low scattering loss compared to POF. Graded-index POF is also not suitable because the fiber must have a thin cladding to prevent the effects of adjacent crossovers. The cladding diameter is preferably 500 pm and the core diameter is 486 pm. The dimensions of the white silicone rubber material are 10 x 10 x 1.5 mm. 3 The optical power coupled into the transmitting POF by the white LED is preferably >1 mW. This power depends on the diameter of the fiber core; generally, the larger the fiber core diameter, the higher the power from the LED coupled into the fiber. The sensitivity of the photodiode receiver is preferably 0.4 V / nW.

[0041] Measurement results A. No flexible material at the intersection To demonstrate the effect of the flexible scattering material, the receiver output voltage as a function of added weight is first shown without the flexible material around the intersection in Figure 2. Figure 5 shows the measurement results when both surfaces of the rigid, hard PVC material surrounding the intersection are attached to each other with a) black light-absorbing material, b) white light-scattering material, or c) white adhesive tape. Using white scattering material or white tape around the intersection significantly increases sensitivity to larger weights. However, the optical receiver output voltage is always limited (approximately 3 volts in this case). This limits the usable pressure range of the sensor to approximately 600 g when using white tape. The output voltage versus weight curve exhibits exponential behavior (see Figure 5). Weights below 200 g are already difficult to detect. Reducing the sensor's sensitivity, for example by lowering the LED output power, increases the maximum weight, but makes detecting small weights even more difficult. Therefore, these exponential characteristics are not very practical. For wider ranges, linear or even logarithmic characteristics are preferable.

[0042] For sensitive detection of whether a particular pressure is present or not, the index characteristic is satisfactory.

[0043] Experiments in which the fibers were glued together at the intersection with a white silicone sealant resulted in less reproducible sensitivity characteristics.

[0044] FIG. 5 is a graph of receiver output voltage as a function of added weight with no flexible material at the intersection: a) Black absorbing rigid material on both sides of the intersection; b) White scattering rigid material on both sides of the intersection; c) The fibers are attached together with white adhesive tape.

[0045] B. Flexible material at the intersection Figure 6 shows the received output voltage as a function of added weight when a) flexible scattering material is used on both sides around the intersection, as shown in Figure 2, and b) flexible scattering material is used on only one side, as shown in Figure 3. Compared to the results in Figure 5, the sensitivity to small weights is improved and the characteristic is more linear, making it suitable for measuring a larger pressure range. In the configuration in Figure 3, one side is flexible and the other is rigid, which introduces more macrobending compared to an intersection with flexible material on both sides. This explains the higher sensitivity of the second option.

[0046] Figure 6 is a graph of receiver output voltage as a function of added weight: a) flexible scattering material on either side of the intersection (per the intersection of Figure 2); b) Flexible scattering material on one side of the intersection (per intersection in Figure 3).

[0047] Figures 7 and 8 show the effect of the size of the scattering material: Figure 7 shows the case where scattering material is used on both sides, and Figure 8 shows the case where scattering material is used on only one side. As can be seen from the figures, the size of the scattering material affects the shape of the sensitivity characteristic. To detect the presence or absence of a specific pressure with high sensitivity, a 5x5mm scattering material is required. 2 The exponential characteristics of Figures 7(a) and 8(a) obtained using a patch of flexible material of 10 x 10 mm are advantageous. If a more linear characteristic is required, 2 Patches of 0.01 mm or less can be applied, see Figures 7(b) and 8(b). Using larger patches results in logarithmic characteristics and a wider detection range (see, e.g., Figures 7(c) and 7(d) and Figures 8(c) and 7(d)).

[0048] FIG. 7 is a graph of receiver output voltage as a function of added weight and size of flexible material with flexible material on both sides (according to FIG. 2): a) 5 x 5 mm 2 b) 10 x 10 mm 2 c) 15 x 15 mm 2 d) 20 x 20 mm 2

[0049] FIG. 8 is a graph of receiver output voltage as a function of added weight and size of flexible material with flexible material on one side (according to FIG. 3): a) 5 x 5 mm 2 b) 10 x 10 mm 2 c) 15 x 15 mm 2 d) 20 x 20 mm 2

[0050] The embodiment described herein is capable of detecting 50 pressure profiles in one second for a person on a mattress with a 16x8 POF grid under the mattress, hence 128 intersections.

[0051] This low-cost, robust two-dimensional (2D) optical pressure sensor principle can be used for many applications.

[0052] For long-term non-invasive precision sleep and movement monitoring in non-clinical (home) situations.

[0053] For monitoring precise pressure profiles of people in bed with restricted movement to prevent pressure injuries (e.g., bedsores).

[0054] In an adaptive mattress, local pressure is automatically controlled to improve sleep comfort.

[0055] It can be applied under carpets (or woven into them) or under PVC floors, for example, for fall detection in (elderly) people.

[0056] In a virtual reality (VR) floor mat that detects the exact position of a person / gamer so that they stay in the correct area.

[0057] The present invention has been described herein according to several exemplary embodiments, which are intended to be illustrative in all respects and not restrictive. Thus, the present invention is capable of many variations in detailed implementation, which variations can be derived by those skilled in the art from the description contained herein. All such variations are deemed to be within the scope and spirit of the present invention as defined by the following claims and their legal equivalents. It should be noted that the present invention includes the following aspects. [Aspect 1] A two-dimensional optical waveguide pressure sensor array, comprising: two or more row optical waveguides; two or more column light waveguides, the row light waveguides and the column light waveguides being deformable and arranged in a planar array to define sensors at cross-points, each cross-point including one of the row light waveguides in contact with one of the column light waveguides at its intersection; each cross point further includes an optical coupling structure configured to enhance waveguide bending when pressure is applied to the cross point; the light coupling structure includes a layer of mechanical light scattering material disposed in contact with at least one of the row or column light guides; The optical waveguide pressure sensor array is configured to sense pressure by providing light to the row optical waveguides and measuring the light coupled into its column optical waveguide at each cross point, or vice versa, where the light coupled into the column optical waveguide depends on the pressure applied at the cross point, which acts as a sensor; a two-dimensional optical waveguide pressure sensor array. [Aspect 2] 2. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the optical coupling structure includes two layers of optical scattering material in contact with and disposed on either side of the row and column optical waveguides, the row and column optical waveguides being vertically disposed between the two layers of optical scattering material. [Aspect 3] 3. The two-dimensional optical waveguide pressure sensor array of any of aspects 1 and 2, wherein the two layers of light-scattering material are substantially the same size and shape and are substantially laterally aligned. [Aspect 4] each row optical waveguide includes a waveguide core surrounded by a waveguide cladding; each column optical waveguide includes a waveguide core surrounded by a waveguide cladding; 4. The two-dimensional optical waveguide pressure sensor array of any of aspects 1 to 3, wherein the waveguide claddings of both the row optical waveguides and the column optical waveguides are arranged for optically transmitting contact at one or more cross sensors. [Aspect 5] each row optical waveguide includes a waveguide core surrounded by a waveguide cladding; each column optical waveguide includes a waveguide core surrounded by a waveguide cladding; 5. The two-dimensional optical waveguide pressure sensor array of any of aspects 1 to 4, wherein the ratio of cross-sectional diameter of the waveguide core to 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. [Aspect 6] 6. The two-dimensional optical waveguide pressure sensor array of any of embodiments 1 to 5, wherein the optical coupling structure comprises a layer of deformable material. [Aspect 7] 7. The two-dimensional optical waveguide pressure sensor array of embodiment 6, wherein the layer of deformable material is a layer of light-scattering material. [Aspect 8] 8. The two-dimensional optical waveguide pressure sensor array of embodiment 6 or 7, wherein the layer of deformable material comprises silicone rubber. [Aspect 9]

[0023] Aspect 9. The two-dimensional optical waveguide pressure sensor array of any of aspects 1 to 8, wherein the optical coupling structure further comprises a layer of rigid material. [Aspect 10] 10. The two-dimensional optical waveguide pressure sensor array of embodiment 9, wherein the layer of rigid material comprises polyvinyl chloride. [Aspect 11] 11. The two-dimensional optical waveguide pressure sensor array of claim 9 or 10, wherein the optical coupling structure includes two layers of light-scattering material disposed in contact with and on either side of the row and column optical waveguides, and two layers of rigid material disposed in contact with and on either side of the two layers of light-scattering material, and is disposed perpendicularly between the row and column optical waveguides and the two layers of light-scattering material with the two layers of rigid material. [Aspect 12] 12. The two-dimensional optical waveguide pressure sensor array of any of aspects 1 to 11, wherein the optical coupling structures are shaped according to one of the group of a circle, an ellipse, a rectangle, a square, and a polygon, and the optical coupling structures have various sizes or corresponding sizes. [Aspect 13] 13. The two-dimensional optical waveguide pressure sensor array of any one of aspects 1 to 12, wherein the optical coupling structure has a cross-sectional diameter of approximately 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, or 3.0 mm, and in particular, the optical coupling structure has a closed structure and a deformable material is disposed at the center of the closed structure. [Aspect 14] Aspect 14. The two-dimensional optical waveguide pressure sensor array of any of aspects 1-13, wherein the row and column optical waveguides are selected from the group consisting of step-index plastic fibers and graded-index plastic fibers. [Aspect 15] 15. The two-dimensional optical waveguide pressure sensor array of any one of aspects 1 to 14, wherein the two-dimensional optical waveguide pressure sensor array is configured as a sleep monitoring sensor disposed under a matrass for non-invasive measurement of sleep-related movements of an individual on the matrass.

Claims

1. A two-dimensional optical waveguide pressure sensor array, comprising: two or more row optical waveguides; two or more column light waveguides, the row light waveguides and the column light waveguides being deformable and arranged in a planar array to define sensors at cross-points, each cross-point including one of the row light waveguides in contact with one of the column light waveguides at its intersection; each cross point further includes an optical coupling structure in the form of a patch having a closing structure, the optical coupling structure configured to enhance waveguide bending when pressure is applied to the cross point; the light coupling structure includes a layer of mechanical light scattering material disposed in contact with at least one of the row or column light guides; The optical waveguide pressure sensor array is configured to sense pressure by providing light to the row optical waveguides and measuring the light coupled into its column optical waveguide at each cross point, or vice versa, where the light coupled into the column optical waveguide depends on the pressure applied at the cross point, which acts as a sensor.

2. 2. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the optical coupling structure includes two layers of optical scattering material in contact with and disposed on either side of the row and column optical waveguides, the row and column optical waveguides being disposed vertically between the two layers of optical 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 substantially laterally aligned.

4. each row optical waveguide includes a waveguide core surrounded by a waveguide cladding; each column optical waveguide includes a waveguide core surrounded by a waveguide cladding; 4. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the waveguide claddings of both the row optical waveguides and the column optical waveguides are arranged for optical transmission contact at one or more intersection sensors.

5. each row optical waveguide includes a waveguide core surrounded by a waveguide cladding; each column optical waveguide includes a waveguide core surrounded by a waveguide cladding; 5. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the ratio of cross-sectional diameter of the waveguide core to the waveguide cladding is at least 50:1, at least 75:1, at least 90:1, or 100:

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 is a layer of light scattering material.

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

9. The two-dimensional optical waveguide pressure sensor array according to 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. 11. The two-dimensional optical waveguide pressure sensor array of claim 9, wherein the optical coupling structure comprises two layers of light-scattering material disposed on either side of and in contact with the row and column optical waveguides, and two layers of rigid material disposed on either side of and in contact with the two layers of light-scattering material, and is disposed perpendicularly between the row and column optical waveguides and the two layers of light-scattering material with the two layers of rigid material.

12. The two-dimensional optical waveguide pressure sensor array of claim 1 , wherein the optical coupling structures are shaped according to one of the group of circles, ellipses, rectangles, squares, and polygons.

13. The two-dimensional optical waveguide pressure sensor array of claim 1 , wherein the optical coupling structures have a cross-sectional diameter of 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, or 3.0 mm.

14. A two-dimensional optical waveguide pressure sensor array as described in any one of claims 1 to 13, wherein a deformable material is disposed at the center of the closed structure.

15. 15. The two-dimensional optical waveguide pressure sensor array of claim 1, wherein the row and column optical waveguides are selected from the group consisting of step-index plastic fibers and graded-index plastic fibers.

16. A two-dimensional optical waveguide pressure sensor array as described in any of claims 1 to 15, wherein the two-dimensional optical waveguide pressure sensor array is configured as a sleep monitoring sensor disposed under the matrass for non-invasive measurement of sleep-related movements of an individual on the matrass.

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