Fabry-Perot cavity-based optical fiber side pressure sensing structure, pressure sensor element and device

Abstract

The invention provides an optical fiber side position pressure sensing structure based on a Fabry-Perot cavity, a pressure sensor element and a device. Belongs to the optical sensor field. In order to solve the problems that an existing sensor is difficult to control in size, poor in wearing comfort, poor in anti-fatigue performance and the like, optical fiber end face side position machining is adopted, a measurement light path is changed through total reflection, and the mechanical property and the miniaturization integration capacity of a sensing element are improved. Besides, the invention also designs a device integrated with the multi-point pressure sensor element, by utilizing the 3D printed PLA substrate for limiting and the PDMS or flexible PET protective film, the uniform arrangement of a plurality of sensor sites in a small area and the preparation of a flexible sensor are realized, and the flexibility is improved while the spatial resolution and the sensitivity are improved. The device is light in structure and convenient to wear, large deformation and concentrated stress are avoided by changing the element structure, the durability of the sensor is improved, and the application scene is expanded.

Description

Technical Field

[0001] The present invention relates to the fields of robot tactile sensing, flexible wearable equipment and optical sensors, and in particular to a flexible optical fiber lateral fingertip multi-point pressure sensor based on a Fabry-Perot cavity. Background Art

[0002] Pressure sensors are widely used in the fields of robots, wearable devices, virtual reality, and smart prostheses. Traditional pressure sensors are mostly rigid sensors. Although they are excellent in stability and accuracy, their inherent rigid structure limits their application in complex curved surfaces or wearable devices. In contrast, flexible pressure sensors can seamlessly fit the surface of target objects due to their thin, bendable, and even stretchable properties, as well as provide a certain shock-absorbing and buffering effect in interactive safety protection, providing a wider and more accurate monitoring and interactive experience. However, existing flexible tactile sensors usually use resistance, piezoresistance, piezoelectricity, capacitance, and electromagnetic principles, combined with materials such as liquid metal, conductive hydrogel, and carbon nanotubes to achieve electrical conversion of tactile signals. Although they can meet basic measurement needs to a certain extent, their working principles and materials have certain defects in sensitivity, working environment, and processing circuits. For example, capacitive sensor nodes are prone to crosstalk and require customized circuit isolation; although electromagnetic sensors do not require cable dragging, they are limited to low electromagnetic interference environments and have low sensitivity in low-frequency areas, and there is signal attenuation, which limits their application; liquid metal sensors change shape, but the packaging is complex, prone to leakage, and there is zero drift. The more common challenge is that the increase in sensing area and nodes has led to a surge in data volume, posing geometric challenges to processing circuits.

[0003] In order to overcome the above limitations, new sensor designs have gradually emerged, striving to achieve wider applicability while maintaining high sensitivity. Compared with traditional technologies, fiber optic sensors have shown excellent performance in harsh environments due to their unique physical properties, such as high bandwidth, anti-electromagnetic interference and excellent stability. In particular, fiber optic sensors based on the Fabry-Perot principle convert external pressure into clearly recognizable optical signals through a simple optical chamber, achieving highly sensitive capture of subtle pressure changes. This sensor not only has excellent linearity and dynamic range, but also has a simple structure, which greatly facilitates integration and installation. However, the existing sensors based on the Fabry-Perot cavity use the end face as the force-bearing element, which concentrates stress when fixed and has poor fatigue resistance, which hinders miniaturization integration, limits the application scenarios and scope, and can only achieve single-point measurement, which is obviously inconsistent with the characteristics of large pressure distribution area and uneven distribution in actual application scenarios, limiting the possibility of multi-point measurement over a larger area.

[0004] In summary, in the field of pressure sensors, there is still a need for sensor solutions with good durability, high sensitivity, high spatial resolution, miniaturized integration, and good flexibility. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention proposes a flexible fiber optic lateral pressure sensing structure based on the Fabry - Perot principle, as well as its sensor implementation and preparation method, sensor device, and application.

[0006] The present invention proposes a fiber optic lateral pressure sensing structure based on the Fabry - Perot cavity, including a lateral total reflection fiber optic element 1, a reflection layer 2, an air cavity 3, and a pressure - receiving reflection layer 4; Among them, the lateral total reflection fiber optic element 1 is made by obliquely cutting one end face of a single - mode fiber. This end face is perpendicular to a certain meridional plane of the fiber, and this end face forms a 45 - degree angle with the corresponding sagittal plane of this meridional plane, and a total reflection metal thin layer is plated on the obliquely cut end face; The reflection layer 2 is a metal thin layer with a reflection function, located at the upper end of the longer side of the processed end face of the lateral total reflection fiber optic element 1, opposite to the processed plane plated with the total reflection layer, and is used to partially reflect light back into the lateral total reflection fiber optic element 1; The air cavity 3 is above the reflection layer 2, is a cavity filled with air, the cavity length is 98% - 102% of the light source wavelength, and the boundary structure of the cavity provides mechanical support for the pressure - receiving reflection layer 4; The pressure - receiving reflection layer 4 is located above the air cavity 3 and is made of a flexible material. The pressure - receiving reflection layer 4 is plated with a metal thin layer with the same reflectivity as the reflection layer 2 on the side in contact with the air cavity 3.

[0007] Preferably, the reflectivity of the metal thin layer in the reflection layer 2 and the pressure - receiving reflection layer 4 is 0.112.

[0008] Preferably, the flexible material is selected from one of polydimethylsilane (PDMS) or flexible polyethylene terephthalate (PET).

[0009] Based on the above - mentioned flexible fiber optic lateral pressure sensing structure, the present invention also proposes a flexible fiber optic lateral multi - point pressure sensor element, which specifically includes a lateral total reflection fiber optic element 1, a reflection layer 2, a hard substrate 5, and a protective coating 6; Among them, a plurality of vertical hole grooves and limiting structures for limiting are provided on the hard substrate 5, and a plurality of lateral total reflection fiber optic elements 1 are respectively placed in a limiting structure of a hard substrate 5; the reflection layer 2 is above the lateral total reflection fiber optic element 1 and is aligned with the vertical hole grooves of the hard substrate 5; the protective coating 6 is located above the hard substrate 5, is made of a flexible material, and is plated with a metal thin layer with the same reflectivity as the reflection layer 2 at the position opposite to the vertical hole grooves at the reflection layer 2, and an air cavity 3 is formed between the protective coating 6 and the reflection layer 2.

[0010] Preferably, six vertical holes and a limiting structure are evenly distributed on the hard substrate 5, and they have different depths, and the depth takes the length parameter of the aforementioned air cavity 3 to distinguish the spectral redshifts corresponding to the optical fiber elements at different positions, so as to realize the distinction of multi-point pressures.

[0011] More preferably, the depth is set according to the length of the air cavity 3, and the lengths of the air cavity 3 from small to large are: 120.9μm, 141.5μm, 169.7μm, 212μm, 282.5μm, 423.5μm.

[0012] More preferably, the vertical holes on the hard substrate 5 are orthogonally and evenly distributed in a 2×3 pattern.

[0013] Preferably, the protective coating film 6 is made of a light-impermeable material, which can avoid the leakage of light in the holes of the vertical hole hard substrate 3.

[0014] Preferably, the hard material is made of polylactic acid (PLA).

[0015] The flexible optical fiber pressure sensor device based on the Fabry-Perot cavity provided in the present invention includes a flexible optical fiber lateral multi-point pressure sensor element 7, an LED light source 8, an optical fiber coupler 9, and a spectrometer 10; In the flexible optical fiber lateral multi-point pressure sensor element 7, the lateral total reflection optical fiber element 1 is respectively connected to the LED light source 8 and the spectrometer 10 through the optical fiber coupler 9.

[0016] The LED light source 8 is used to emit continuous and stable light. The input light of the LED light source 8 is transmitted into the optical fiber lateral pressure sensing element 7 through the optical fiber coupler 9, and the interference light formed after reflection is transmitted into the spectrometer 10 through the optical fiber coupler 9; the spectrometer 10 collects the interference spectrum, and the length change of the interference cavity 3 is obtained according to the change of the interference period in the interference spectrum, so as to inversely deduce the magnitude of the pressure acting on the pressure sensing unit.

[0017] The beneficial effects of the present invention are as follows: 1) The optical fiber lateral pressure sensing structure based on the Fabry-Perot cavity in the present invention makes a breakthrough in structural design. It avoids large-deflection bending during fixation and encapsulation, greatly reduces the concentrated stress of the sensing element, has excellent mechanical properties, can realize high-sensitivity and wide-dynamic-range fingertip mechanical measurement, and has the potential for three-dimensional force measurement, showing great development prospects.

[0018] 2) In the sensor device of the present invention, the mass and volume of each functional element are very small. At the same time, the main functional component, the optical fiber, has high elasticity and flexibility, which is convenient for integrated layout of flexible wearables, improving the comfort of wearing. At the same time, it minimally damages the flexibility and inherent size of the hand itself, making the sensing closer to reality.

[0019] 3) In the present invention, a new integration method is provided by limiting the rigid substrate through the vertical hole and groove structure. Multiple sites are uniformly arranged orthogonally within an area of less than 2 cm², and a large increase in the spatial resolution of the sensor is achieved through the porous groove, making the measurement have higher sensitivity.

[0020] 4) In the present invention, by changing the element structure to change the measurement optical path, the fixed method of concentrating stress due to large deformation at the front end of the sensor is effectively avoided. By skillfully using the processing of the single-mode fiber end face, the convenience and durability of the sensor are greatly improved, providing a broader application scenario and scope.

[0021] 5) The present invention adopts flexible fiber optic sensing, which has the advantages of strong stability, good anti-electromagnetic interference ability, not being easily chemically corroded, and having good biocompatibility in flexible mechanical sensors. It has broad development prospects and a wide application range. By reasonably using the present invention, various related functions can be further realized, such as micro stress measurement, airtight detection, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the flexible fiber side pressure sensing structure based on the Fabry - Perot principle of the present invention; Figure 2 is a schematic diagram of the structure of the flexible fiber side multi-point pressure sensor element of the present invention; Figure 3 is Figure 2 a schematic diagram of the structure of the side total reflection fiber element 1 and the reflection layer 2 of Figure 4 is Figure 2 a side view of the limiting hole and groove; Figure 5 is Figure 2 a top view of Figure 6 is Figure 2 an exploded view of the structure of Figure 7 is a connection schematic diagram of the flexible fiber optic pressure sensor device based on the Fabry - Perot cavity.

[0023] The description of the reference numerals in the drawings is as follows: 1. Lateral total reflection fiber optic element, 2. Reflective layer, 3. Air cavity, 4. Compressed reflective layer, 5. Vertical hole groove structure limiting rigid substrate, 6. Protective coating, 7. Flexible fiber optic lateral multi-point pressure sensor element, 8. LED light source, 9. Fiber optic coupler, 10. Spectrometer. Detailed implementation mode

[0024] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention, rather than limiting the invention. In addition, it should be noted that only the parts related to the invention are shown in the drawings for the convenience of description.

[0025] Embodiment 1 (Optical fiber lateral pressure sensing element based on Fabry - Perot principle) As Figure 1 and Figure 2 shown, the optical fiber lateral pressure sensor based on the Fabry - Perot principle includes a lateral total reflection fiber optic element 1, a reflective layer 2, a rigid substrate 5 and a protective coating 6.

[0026] Among them, 6 vertical hole grooves and limiting structures for limiting are provided on the rigid substrate 5, which are orthogonally and uniformly distributed in a 2×3 pattern, and 6 lateral total reflection fiber optic elements 1 are respectively placed in a limiting structure of a rigid substrate 5; the reflective layer 2 is at the upper end of the lateral total reflection fiber optic element 1 and is aligned with the vertical hole grooves of the rigid substrate 5; the protective coating 6 is located at the upper end of the rigid substrate 5, is made of a flexible material, and a metal thin layer with the same reflectivity as the reflective layer 2 is plated at the relative position of the vertical hole grooves at the reflective layer 2, and an air cavity 3 is formed between the protective coating 6 and the reflective layer 2.

[0027] In this embodiment, the depths of the six vertical hole grooves and limiting structures of the rigid substrate 5 are different, and the depths are set according to the length of the air cavity 3. The lengths of the air cavity 3 from small to large are: 120.9μm, 141.5μm, 169.7μm, 212μm, 282.5μm, 423.5μm, so as to distinguish the spectral redshifts corresponding to the fiber optic elements at different positions, thereby realizing the distinction of multi-point pressures.

[0028] The preparation method of the optical fiber lateral pressure sensor based on the Fabry - Perot principle in this embodiment is as follows: 1) Fabricate the lateral total reflection fiber optic element 1: Attach the single-mode optical fiber to the fixed glass sheet along the 45-degree direction, and cut the optical fiber along the edge of the glass sheet; remove the optical fiber and polish the cut surface, observe the morphology of the polished cut surface, and check the smoothness; after polishing, spray a thin metal film with a certain reflectivity on the 45-degree cut end face with the axis as the center to form a total reflection end face.

[0029] 2) Fabricate the reflective layer 2: Spray a thin metal film with a certain reflectivity above the cutting end face of the single-mode optical fiber to form a reflective layer 2.

[0030] 3) Fabricate the hard substrate 5: Design a hard substrate with single-mode optical fiber limiting vertical hole grooves and limiting structures of different depths, and fabricate the hard substrate by 3D printing.

[0031] 3) Prepare the protective coating 6: According to the size of the hard substrate 5, use flexible materials such as polydimethylsiloxane (PDMS) and flexible polyethylene terephthalate (PET) to make the protective coating 6, and spray a thin metal layer with the same reflectivity as the reflective layer 2 at the position opposite to the vertical hole groove at the reflective layer 2; 4) Assemble the flexible optical fiber lateral multi-point pressure sensor based on the Fabry - Perot cavity: Fill the optical fiber with the reflective layer 2 prepared in step 1) and step 2) into the limiting structure of the hard substrate 5 according to the limit, rotate the optical fiber so that the processing end face forms a 45-degree angle with the upper surface of the hard substrate 5 limited by the vertical hole groove structure and the longest side is placed at the upper end and aligned with the hole groove, and bond and fix it with silicone rubber glue; Place the protective coating 6 at the upper end of the hard substrate 5 limited by the vertical hole groove structure and ensure that its reflective layer is aligned with the hole groove of the hard substrate, and the flexible optical fiber multi-point sensing element based on the Fabry - Perot cavity can be obtained.

[0032] Among them, on the basis of being strictly aligned with the optical path reflected by the lateral total reflection optical fiber element 1, the reflective layer 2 is strictly ensured to be aligned with the hole groove and the reflective layer on the protective coating 6, and the protective coating is parallel to the aforementioned sagittal plane. Its function is to ensure its measurement range and provide a large enough elastic deformation stroke through its own length, and ensure that the measurement of deformation and pressure is more stable.

[0033] Embodiment 2 (Flexible Optical Fiber Pressure Sensor Device Based on Fabry - Perot) The main functional components of the flexible optical fiber pressure sensor device based on the Fabry - Perot cavity include, for example Figure 7 The optical fiber lateral pressure sensing element 7, LED light source 8, optical fiber coupler 9, and spectrometer 10 as shown in the figure. First, connect the lateral total reflection optical fiber element 1 in the optical fiber lateral pressure sensing element 7 to the LED light source 8 and the spectrometer 10 respectively through the optical fiber coupler 9.

[0034] The protective coating 6 is made of a light - impermeable material, which can avoid the leakage of light in the hole groove of the vertical hole groove hard substrate 3 and at the same time avoid the interference of ambient light on the spectrometer 10. The light with different frequency intensities that changes due to the deformation of the protective coating 6 under pressure continues to be completely transmitted to the spectrometer 10.

[0035] The aforementioned input and output light rays both propagate in the lateral total reflection fiber optic element 1. The input light ray of the LED light source 8 is transmitted into the fiber optic lateral pressure sensing element 7 through the fiber optic coupler 9, and the output light ray transmitted from the fiber optic lateral pressure sensing element 7 is transmitted into the spectrometer 10 by the fiber optic coupler 9.

[0036] The LED light source 8 can emit continuous and stable light rays to generate optical signals.

[0037] The working principle of the present invention is as follows: In the working state, the signal light transmitted from the LED light source 8 enters the sensing element through the fiber optic coupler 9. The incident light is transmitted through the optical fiber to the 45° end face mirror, causing the propagation direction of the incident light to change and exit from the side of the optical fiber. When the light ray encounters the reflective layer 2, a part of it is reflected back into the optical fiber along the original path, and the other part continues to exit from the side and enters the air cavity 3. When the light ray encounters the reflective layer 4, a part of it is reflected back into the optical fiber along the original path. There is a phase difference between the two light beams reflected back into the optical fiber by the reflective layer 2 and the reflective layer 4, which will generate interference and exit from the incident end of the optical fiber along the optical fiber. When a force stimulus acts on the flexible pressure sensitive area of the sensor, that is, the projection of the reflective layer of the protective film 6, the protective film 6 deforms, which in turn causes the distance between the reflective layers on the upper and lower surfaces of the air cavity corresponding to the vertical hole groove to decrease, and the length of the interference air cavity becomes smaller, thereby changing the interference period on the interference spectrum. The interference spectrum of the light in the above two parts of the returned light rays is recorded by the spectrometer 10, and the change amount of the interference period can be obtained through computer processing. Assuming that the intensities of the two light beams reflected back into the optical fiber by the reflective layer 2 and the reflective layer 4 are I 1 and I 2, the length of the air cavity 3 is l , the refractive index of air is n , the optical wavelength is λ , then the interference spectrum I total can be expressed as: , and the change amount information of the interference period can be obtained through computer processing, thereby inversely deducing the pressure information.

[0038] The installation method of the sensing element is the same as the aforementioned one, and will not be elaborated here.

[0039] In addition, it should be noted that: The phrase "an embodiment" or "embodiments" mentioned in the specification means that the specific features, structures or characteristics described in connection with the embodiments are included in at least one embodiment of the present invention. Therefore, the phrases "an embodiment" or "embodiments" that appear throughout the specification do not necessarily all refer to the same embodiment.

[0040] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0041] Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. The described fiber side-pressure sensing structure based on a Fabry-Perot cavity, characterized in that, The structure includes a lateral total reflection fiber optic element (1), a reflective layer (2), an air cavity (3), and a pressure - bearing reflective layer (4); Among them, the lateral total reflection fiber optic element (1) is made by obliquely cutting one end face of a single - mode fiber. This end face is perpendicular to a certain meridian plane of the fiber, and the end face forms a 45 - degree angle with the corresponding sagittal plane of the meridian plane. And a total reflection metal thin layer is plated on the obliquely cut end face; The reflective layer (2) is a metal thin layer with a reflective function, located at the upper end of the longer side of the processed end face of the lateral total reflection fiber optic element (1), opposite to the processed plane plated with the total reflection layer, and is used to partially reflect light back into the lateral total reflection fiber optic element (1); The air cavity (3) is at the upper end of the reflective layer (2), is a cavity filled with air, the cavity length is 98% - 102% of the light source wavelength, and the boundary structure of the cavity provides mechanical support for the pressure - bearing reflective layer (4); The pressure - bearing reflective layer (4) is located at the upper end of the air cavity (3) and is made of a flexible material. The pressure - bearing reflective layer (4) is plated with a metal thin layer with the same reflectivity as the reflective layer (2) on the side in contact with the air cavity (3).

2. The fiber side pressure sensing structure based on the Fabry-Perot cavity according to claim 1, characterized in that The reflectivity of the metal thin layers in the reflective layer (2) and the pressure - bearing reflective layer (4) is 0.

112.

3. The fiber side pressure sensing structure based on the Fabry-Perot cavity according to claim 1, characterized in that, The flexible material is selected from one of polydimethylsilane or flexible polyethylene terephthalate.

4. A flexible optical fiber lateral multi-point pressure sensor element based on the pressure sensing structure described in claim 1, characterized in that, It includes a lateral total reflection fiber optic element (1), a reflective layer (2), a rigid substrate (5), and a protective coating (6); Among them, the rigid substrate (5) is provided with a number of vertical holes and limiting structures for limiting. A plurality of lateral total reflection fiber optic elements (1) are respectively placed in the limiting structures of a rigid substrate (5); the reflective layer (2) is at the upper end of the lateral total reflection fiber optic element (1) and is aligned with the vertical holes of the rigid substrate (5); the protective coating (6) is located at the upper end of the rigid substrate (5), is made of a flexible material, and is plated with a metal thin layer with the same reflectivity as the reflective layer (2) at the position opposite to the vertical holes at the reflective layer (2), and an air cavity (3) is formed between the protective coating (6) and the reflective layer (2).

5. The flexible optical fiber lateral multi-point pressure sensor element according to claim 4, characterized in that, Six vertical holes and limiting structures are uniformly distributed on the rigid substrate (5), and their depths are different. The depth takes the length parameter of the air cavity (3) to distinguish the spectral redshift amounts corresponding to fiber optic elements at different positions.

6. The flexible optical fiber lateral multi-point pressure sensor element according to claim 5, characterized in that, The lengths of the air cavities (3) from small to large are: 120.9 μm, 141.5 μm, 169.7 μm, 212 μm, 282.5 μm, 423.5 μm.

7. The flexible optical fiber lateral multi-point pressure sensor element according to claim 4, wherein The vertical holes on the rigid substrate (5) are orthogonally and uniformly distributed in a 2 × 3 pattern.

8. The flexible optical fiber lateral multi-point pressure sensor element according to claim 4, characterized in that, The protective coating (6) is made of an opaque material.

9. The flexible optical fiber lateral multi-point pressure sensor element according to claim 4, characterized in that, The rigid material is made of polylactic acid.

10. A flexible fiber optic pressure sensor device based on the flexible fiber optic lateral multi - point pressure sensor element according to claim 4, including a flexible fiber optic lateral multi - point pressure sensor element (7), an LED light source (8), an optical fiber coupler (9), and a spectrometer (10); In the flexible fiber optic lateral multi - point pressure sensor element (7), the lateral total reflection fiber optic element (1) is respectively connected to the LED light source (8) and the spectrometer (10) through the optical fiber coupler (9); The LED light source (8) is used to emit continuous and stable light. The input light of the LED light source (8) is transmitted into the fiber optic lateral pressure sensing element (7) after passing through the fiber optic coupler (9), and is reflected back into the optical fiber after passing through the reflection layers (2) and (4) to form interference. The interference optical fiber is transmitted into the spectrometer (10) by the fiber optic coupler (9); the spectrometer (10) collects the interference spectrum, and the length change of the interference cavity (3) is obtained according to the change of the interference period in the interference spectrum, so as to inversely deduce the magnitude of the pressure acting on the pressure sensing unit.

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