High-resolution two-dimensional indoor positioning using an optical fiber sensor

Abstract

Distributed fiber optic sensing (DFOS) systems include smart mats that (1) identify the positions of people and objects moving indoors, (2) provide two-dimensional visual mapping, and (3) cover blind spots with auxiliary technologies such as LiDAR and RF radar. A DFOS system with a smart mat can be placed almost anywhere indoors and can be used in place of a carpet. By deploying the innovative DFOS systems and smart mats of the present disclosure throughout a building, the latest position information of the building's occupants is provided, blind spots are eliminated, and maintenance costs are reduced, thereby significantly improving the safety and security of the building.

Description

Technical Field

[0001] The present disclosure generally relates to distributed fiber optic sensing (DFOS) systems, methods, and structures. More particularly, it relates to high-resolution two-dimensional indoor positioning using fiber optic sensors.

Background Art

[0002] Indoor positioning of people and objects has become increasingly important because it is crucial for both the safety of occupants and the operation of public infrastructure. Common modern approaches to indoor positioning may utilize cameras or RFID tags. As is well known, cameras raise privacy issues, and RFID technology requires a large number of strategically placed sensors. Other technologies such as GPS, RF radar, LiDAR, etc. also have many operational problems.

Summary of the Invention

[0003] According to aspects of the present disclosure directed to a distributed fiber optic sensing (DFOS) system including a smart mat that (1) identifies the indoor position of a moving person / object, (2) provides two-dimensional visual mapping, and (3) covers any dead zones using complementary technologies including LiDAR, RF radar, etc., advancements in the art are provided.

[0004] In contrast to the prior art, our DFOS system with a smart mat can be placed virtually anywhere indoors and can be configured in place of a carpet. When the DFOS system and smart mats of the present invention are deployed throughout a building, the safety and security of the building are significantly improved by eliminating dead zones, and maintenance costs can also be reduced.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0016] The following merely illustrates the principles of the present disclosure. Therefore, those skilled in the art should understand that they can come up with various configurations that embody the principles of the present disclosure, even if not explicitly described or illustrated in this specification, and that such configurations are within the spirit and scope of the present disclosure.

[0017] Furthermore, all examples and conditional terms given in this specification are for the sole educational purpose of helping those skilled in the art understand the concepts provided by the inventors to facilitate the principles of the present disclosure and this technology, and should not be construed as being limited to the specifically recited examples and conditions.

[0018] Furthermore, all descriptions in this specification regarding the principles, aspects, and embodiments of the present disclosure, as well as all specific examples given therein, are meant to include both their structural and functional equivalents. Moreover, such equivalents are meant to include both currently known equivalents and equivalents developed in the future, i.e., elements developed that perform the same function regardless of their structure.

[0019] Thus, for example, those skilled in the art will understand that any block diagram in this specification is a conceptual diagram specifically showing a circuit that realizes the principles of the present disclosure.

[0020] In this specification, unless otherwise specified, the drawings including figures are not drawn to an exact scale.

[0021] As additional background, note that a distributed fiber optic sensing system interconnects optoelectronic integrators to an optical fiber (or cable) and converts the optical fiber into an array of sensors distributed along the optical fiber. In practice, the fiber becomes the sensor, and the interrogator generates / injects laser light energy into the fiber to sense / detect events along the fiber.

[0022] As will be understood and recognized by those skilled in the art, DFOS technology can be utilized to continuously monitor vehicle movement, human traffic, excavation work, seismic activity, temperature, structural integrity, liquid and gas leakage, and many other conditions and activities. It is used worldwide to monitor power plants, communication networks, railways, roads, bridges, borders, critical infrastructure, onshore and offshore power and pipelines, and downhole applications in oil, gas, and enhanced geothermal power. Distributed fiber optic sensing has the advantage of not being restricted by line-of-site or remote power access constraints and can be deployed in continuous lengths exceeding 30 miles while performing sensing / detection at any point along its entire length depending on the system configuration. Therefore, the cost per sensing point over long distances is far beyond that of competing general technologies.

[0023] Distributed fiber optic sensing measures changes in the "backscattering" of light that occur within an optical sensing fiber when the sensing fiber encounters environmental changes such as events of vibration, strain, or temperature change. As described above, the sensing fiber functions as a sensor over its entire length, providing real-time information regarding the surrounding physical / environment and regarding the integrity / security of the fiber. Further, distributed fiber optic sensing data identifies the exact location of events and conditions occurring at or near the sensing fiber.

[0024] A schematic diagram illustrating a general arrangement and operation of a distributed fiber optic sensing system advantageously incorporating artificial intelligence / machine learning (AI / ML) analysis is exemplified in FIG. 1(A). Referring to FIG. 1(A), it is observed that an optical sensing fiber is connected to an interrogator. Although not shown in detail, the interrogator may include an encoded DFOS system that can adopt a configuration of a coherent receiver known in the art as shown in FIG. 1(B).

[0025] As is well known, modern interrogators are systems that generate input signals for optical sensing fibers and detect / analyze the reflected / backscattered received signals. The received signals are analyzed to generate outputs indicating the environmental conditions that occurred along the fiber. The received backscattered signals are caused by reflections within the fiber such as Raman backscattering, Rayleigh backscattering, and Brillouin backscattering.

[0026] As is understood, modern DFOS systems include an interrogator that periodically generates optical pulses (or any encoded signal) and inputs it into an optical fiber. The input optical pulse signal is transmitted along the optical fiber.

[0027] At positions along the fiber, a small portion of the signal is backscattered / reflected and returned to and received by the interrogator. The backscattered / reflected signal conveys information that the interrogator uses for detection, such as changes in power level indicating mechanical vibrations.

[0028] The received backscattered signal is converted to the electrical domain and processed by the interrogator. Based on the input time of the pulse and the time the signal is detected, the interrogator can determine from which position along the optical sensing fiber the received signal is coming and sense the activities at each position along the optical sensing fiber. Further classification methods may be used to detect and identify events or other environmental conditions including acoustic and / or vibration and / or heat along the optical sensing fiber.

[0029] Figure 2 is a schematic diagram showing an exemplary mapping of a linear optical fiber to a two-dimensional element array according to an aspect of the present disclosure. Referring to this figure, to overcome the limited spatial resolution of the linear optical fiber using the DFOS system, the sensing area is divided into a plurality of square (or other shaped) elements, for example 6 inches × 6 inches, and it should be noted that the fiber sections occupying each element are evenly distributed as shown in the figure. The length of each section is the same as the spatial resolution of the DFOS system. In this way, a one-dimensional linear sensing array can be converted into a two-dimensional sensing element.

[0030] Figure 3 is a schematic flow diagram showing an exemplary workflow of an existing indoor positioning method using the DFOS system according to an aspect of the present disclosure. It should be noted that the method as exemplarily shown in this figure presents several problems. More specifically, it is as follows.

[0031] (Inaccurate positioning)

[0032] The DFOS system detects vibrations generated by people walking. When a person walks on a carpet, the carpet and the floor tiles vibrate together. In the method of laying a linear optical fiber under the carpet to detect the walking position of a person, there is a limit to the spatial resolution for accurate positioning.

[0033] (Unknown vertical distance)

[0034] The linear optical fiber receives all vibrations near the cable, but the vertical distance to the fiber cannot be determined.

[0035] (Inaccuracy in detecting parallel walking)

[0036] In one-dimensional positioning, since only vibrations occurring along the fiber are reported, it is difficult to recognize that there are two people when two people are walking along parallel paths. However, this is common in office buildings because people often walk side by side while talking.

[0037] Figure 4 is a schematic flow diagram showing an exemplary workflow for two-dimensional location identification indoors using DFOS according to an aspect of the present disclosure. As shown in the figure, a DFOS system, such as a distributed vibration system (DVS) or a distributed acoustic sensing (DAS) system, is interconnected with the fibers of a building placed on the floor. The fibers are laid with a smart mat having a specially designed pattern. The smart mat is laid in corridors instead of carpets. When a person walks in a place including the smart mat, the DFOS system detects the person and reports an accurate position within 6 inches (15 cm).

[0038] Figure 5 is a schematic diagram showing an exemplary system configuration and architecture according to an aspect of the present disclosure. A distributed fiber optic sensing (DFOS) system, which can be a distributed acoustic sensing (DAS) and / or a distributed vibration sensing (DVS), can be placed in a control room for centralized monitoring of the entire building. The DFOS system is integrated with an optical switch and connected to the floor fibers to provide location identification functions on multiple floors.

[0039] The design of the fiber-based smart mat is especially designed to easily sense a particularly large area. It is easy to convert a one-dimensional linear sensing array into a two-dimensional element by the zigzag method shown in the figure. However, the main challenge is to improve the actual spatial resolution of the sensing area. The optical fibers are arranged in some special spiral patterns to "pack" the long threads of the optical fibers into a finer grid. This is called a spiral fiber sensing cell.

[0040] FIG. 6 is a schematic diagram showing an exemplary spiral pattern of a template of a fiber sensing cell capable of cascade connection according to an aspect of the present disclosure, (A) shows the input direction and the output direction, (B) shows a complementary pattern for cascade connection to the cell of (A), (C) shows an example of a cell pattern at a corner for cascade connection of two consecutive columns, and the input direction and the output direction are orthogonal to each other.

[0041] Refer to the figure showing various type examples of a spiral fiber sensing cell. Important features of this cell include that there is one input and one output each for easy cascade connection and expansion, and there is no overlap of fibers to avoid fiber damage.

[0042] The input and the output may be parallel ((a) and (b) of FIG. 6) or orthogonal ((c) of FIG. 6). Since (a) of FIG. 5 and (b) of FIG. 6 are symmetric with respect to the vertical axis, they can be arranged at consecutive locations and easily joined. The pattern shown in (c) of FIG. 6 can be used at the end of a sensing region where the fiber needs to rotate to the next column.

[0043] It is difficult to arrange the optical fibers so as to form the complex pattern shown above. Therefore, instead of directly attaching the optical fibers to the floor, EVA foam puzzle tiles are attached, and grooves of the above pattern are processed thereon. In this way, a template for accommodating the optical fibers is created.

[0044] FIG. 7 is a schematic diagram showing the setting of an exemplary smart tile layout system according to an aspect of the present disclosure, including (a) the layout of the leftmost tile (left end tile) of a 2'×2' tile composed of 16 cell patterns having a 6”×6” spatial resolution, (b) a schematic diagram of a fiber cell of a cascade pattern of the left end tile, (c) the layout of the central tile, (d) the cascade pattern of the central tile, (e) the layout of the rightmost tile (right end tile), and (f) the cascade pattern of the right end tile.

[0045] Figure 7 shows examples of template tiles of different patterns. The size of each tile is 2 feet × 2 feet and it contains 16 sensing cell templates. The details are as follows.

[0046] Left end. Figures 7(a) and 7(b) are assumed to start from the left corner, install one column of tiles from left to right, and adopt the cells of pattern 3 at the corner shown in Figure 6(c).

[0047] Central part. Figures 7(c) and 7(d) assume that all central tiles can be used in the combination of pattern 1 and pattern 2 shown in Figures 6(a) and 6(b).

[0048] Right end. Figures 7(e) and 7(f) assume the rightmost template. As shown in Figure 6(c), the cells of pattern 3 are used, and the connection to the second column starts again from template 7(a).

[0049] Figure 8 is a schematic diagram showing the configuration of a smart floor including an exemplary fiber-based smart mat, which includes (a) a configuration of one column of sensing tiles and (b) a diagram of stacking multiple columns to form the entire sensing area according to an aspect of the present disclosure. After laying the form template on the floor, the fibers are laid in the grooves to form the desired pattern. In this way, a rectangular sensing area is formed. This schematic diagram is shown in Figure 7.

[0050] Figure 9 is a schematic diagram showing an exemplary 2’×4’ tile having 32 fiber sensing cell patterns, which is a heat map of the intensity distribution having the point load (upper) of individual cells versus the region of interest (ROI) (lower) according to an aspect of the present disclosure, and Figure 10 is a schematic diagram showing exemplary consecutive screen captures of a walking test of the heat map according to an aspect of the present disclosure.

[0051] These figures show the results of a preliminary test of a small-scale smart floor. The size is 2 feet by 4 feet with a 6-inch by 6-inch grid size. Figure 8 shows the static results of rubbing and walking in the same cell. The upper figure is a mat showing the position of the red square ground truth, and the lower figure shows the received sensing signal in the heat map. The heat map is a direct mapping of the sensing signal along the fiber to a two-dimensional matrix. Warmer and brighter colors indicate higher intensity.

[0052] Figure 11 is a schematic feature diagram showing exemplary features of a system and method according to an aspect of the present disclosure. Here, the present disclosure has been shown using several specific examples, but those skilled in the art will recognize that the present teachings are not limited thereto. Therefore, the present disclosure should be limited only by the claims appended hereto.

Claims

1. An indoor positioning system, comprising: An optical fiber sensor, and An optical interrogator configured to generate an optical pulse, input the generated optical pulse into the optical fiber sensor, and receive a backscattered signal from the optical fiber sensor for optical communication with the optical fiber sensor; An analyzer configured to analyze the received backscattered signal and determine a position where vibration occurs along the optical fiber sensor; A distributed fiber optic sensing (DFOS) system including: At least a part of the optical fiber sensor is arranged along the floor surface and is arranged under a mat placed on the floor surface.

2. The system according to claim 1, wherein the optical fiber sensors are arranged in a pattern without overlap.

3. The system according to claim 2, wherein the non-overlapping pattern is a predetermined pattern selected from a group of predetermined patterns.

4. The system according to claim 2, wherein the non-overlapping patterns are arranged to form a two-dimensional grid.

5. The system according to claim 1, wherein the floor includes one or more grooves formed in the floor surface, and the grooves are sized to receive the optical fiber sensor.

6. The system according to claim 5, wherein the one or more grooves formed in the floor surface form a predetermined pattern.

7. The system according to claim 1, wherein the optical fiber sensor is integrated into a mat forming an optical sensor integrated mat, and the optical sensor integrated mat is formed to have an optical input and an optical output.

8. The system according to claim 7, further comprising a plurality of the optical sensor integrated mats, and each individual one of the optical sensor integrated mats is optically connected to each other to form a continuous optical sensing fiber.

9. Further comprising an optical switch for optical communication with the interrogator and a plurality of optical fiber sensors, The optical switch is configured to provide optical communication between the interrogator and the plurality of optical fiber sensors, The optical interrogator is configured to generate an optical pulse from a laser beam, input the pulse into the plurality of optical fiber sensors via the optical switch, and receive the backscattered signal from the plurality of optical fiber sensors via the optical switch. The parser is configured to analyze the received backscattered signal and determine a position where the vibration occurs along the plurality of optical sensor fibers. The system according to claim 1, wherein at least a part of the plurality of optical sensor fibers is arranged along the floor surface and is arranged under a mat placed on the floor surface.

10. The system according to claim 9, wherein the plurality of optical sensor fibers are arranged in a pattern where they do not overlap.

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