Bionic flexible touch sensor based on optical fiber MZ interference and preparation method thereof

Abstract

The invention discloses a bionic flexible touch sensor based on optical fiber interference and a preparation method thereof. The sensor comprises a Mach-Zehnder interference type optical fiber sensor formed by dislocation welding of single-mode optical fibers, and a bionic flexible packaging structure used for bearing the optical fiber sensor. The bionic flexible packaging structure adopts bionic octopus sucker array structures which are symmetrically arranged up and down to form a sandwich type flexible structure, the optical fiber interference sensor is arranged in the middle layer of the bionic flexible packaging structure, and supporting optical fibers are arranged on the two sides of the bionic flexible packaging structure to provide mechanical supporting and limiting effects; when external tactile force acts on the bionic octopus suction cup array, the bionic flexible packaging structure deforms synergistically, the deformation is effectively transmitted to a medium area around the optical fiber through the porous structure, the effective refractive index of the medium is changed, and therefore the phase difference of the optical fiber Mach-Zehnder interference structure is modulated, and the optical fiber is obtained. The interference light intensity change is shown in the spectrum analyzer, and optical detection of weak touch force is realized. According to the invention, the structure is simple, the flexibility is high, the anti-electromagnetic interference capability is strong, the preparation process is based on a conventional forming method, the feasibility of array and batch preparation is realized, and the application prospect in the fields of flexible touch sensing and fine force detection is good.

Description

Technical Field

[0001] This invention relates to the field of flexible tactile sensing technology, specifically to a biomimetic flexible tactile sensor based on refractive index modulation mechanism and its fabrication method, belonging to the interdisciplinary field of fiber optic sensing and flexible tactile sensor technology. Background Technology

[0002] With the development of intelligent sensing technology, tactile sensing has significant application value in fields such as robot operation, medical rehabilitation, and precision sensing. In existing tactile sensing technologies, some solutions rely on changes in electrical parameters to achieve signal detection. This type of sensing method usually requires the introduction of conductive materials or circuit structures, is susceptible to electromagnetic interference in complex environments, and has limitations in signal stability and sensitivity under weak force detection scenarios.

[0003] To overcome the above problems, tactile sensing technology based on optical signals has gradually attracted attention. Fiber optic sensors have advantages such as strong anti-electromagnetic interference capability, stable signal transmission, and suitability for long-distance detection, making them suitable for tactile perception in complex environments. Existing fiber optic tactile sensing schemes mostly rely on external forces to cause axial strain, bending, or deformation of the fiber, thereby leading to changes in the optical signal. However, this type of sensing method usually requires large mechanical deformation to produce a significant optical response, and its detection sensitivity is limited under conditions of slight pressure or weak tactile stimulation.

[0004] On the other hand, in order to improve the responsiveness of tactile sensors to weak external forces, some studies have introduced biomimetic microstructures to achieve the concentration and amplification of external pressure, such as designs that mimic biological adsorption structures or surface microstructures. However, existing biomimetic structures are mostly concentrated in the field of electrical tactile sensing. In fiber optic sensing technology, there is still a lack of mature solutions on how to effectively combine biomimetic flexible structures with optical sensing mechanisms so that small external pressures can directly modulate optical signals through changes in the medium.

[0005] Therefore, there is an urgent need for a tactile sensing solution that does not require electrical components, is based on the principle of fiber optic sensing, and combines a biomimetic flexible structure to achieve stable and sensitive optical tactile detection under weak external forces. Summary of the Invention

[0006] This invention addresses the problem that existing tactile sensors struggle to achieve high sensitivity and stable detection under weak force, and also struggle to effectively amplify tactile responses while maintaining flexibility. It provides a flexible tactile sensor based on a single-mode fiber misaligned fusion interference structure and a flexible encapsulation structure. This sensor embeds a single-mode fiber misaligned fusion-formed fiber Mach-Zehnder interference structure within a porous Ecoflex flexible substrate with a biomimetic flexible encapsulation structure (2). External tactile pressure causes a change in the refractive index of the medium surrounding the fiber, which manifests as a change in interference light intensity in a spectrometer, thus enabling the detection of weak tactile forces. The fabrication method includes at least the following steps: S1. Fabrication of a single-mode fiber misaligned fusion splice interferometer sensor; S2. Preparation of a biomimetic flexible encapsulation structure (2) based on a sugar particle sacrificial template; S3. Assembly of the flexible tactile sensor and connection of the testing device.

[0007] The fiber MZ interference sensor (1) in step S1 is composed of a first single-mode fiber (51), a second single-mode fiber (52) and a third single-mode fiber (53) spliced ​​in a staggered manner. Adjacent single-mode fibers are introduced with lateral offset during the splicing process to form mode coupling in the splicing area, thereby forming a fiber Mach-Zehnder interference structure.

[0008] Preferably, the length of the single-mode fiber between the two misaligned fusion splice areas is on the order of centimeters, for example, in the range of 3–10 cm. Within this range, the sensitivity of the fiber optic sensor to changes in the refractive index of the surrounding medium can be improved while ensuring the clarity of the interference fringes.

[0009] In step S2, the biomimetic flexible packaging structure is used to cover and support the fiber MZ interference sensor (1) prepared in step S1, so that external tactile force can be transmitted to the medium around the fiber through the flexible substrate, thereby causing changes in the fiber interference characteristics.

[0010] Furthermore, taking the adsorption and force transmission structure of the octopus sucker as a biomimetic object, a molding mold with an array of biomimetic sucker structures was designed and prepared. The molding mold was obtained by three-dimensional printing, and its inner surface formed a cavity structure to define the shape of the biomimetic sucker array.

[0011] Furthermore, granular sugar material is filled into the molding mold, and the sugar particles serve as a sacrificial template for the subsequent formation of a porous structure; then, Ecoflex 00-30 component A and component B are thoroughly mixed at a mass ratio of 1:1 and injected into the mold, so that the mixture fully coats the sugar particle sacrificial template and fills the biomimetic suction cup array cavity.

[0012] Furthermore, after casting is completed, the mold is placed in a vacuum environment for degassing treatment to remove air bubbles introduced during the Ecoflex mixing and filling process; then the Ecoflex mixture is cured to form a stable elastic structure.

[0013] Furthermore, after curing, the sugar particles sacrificial template are removed by dissolution to obtain an array with an internal interconnected pore structure and an external surface with biomimetic octopus suckers.

[0014] Furthermore, the biomimetic flexible encapsulation structure (2) is an organosilicon elastic substrate, which is prepared by mixing agent A and agent B of Smooth-On's Ecoflex series elastomers in a 1:1 ratio. The organosilicon elastic substrate is sized by a molding die and an array of biomimetic octopus sucker structures is formed on its surface.

[0015] Furthermore, in the process of preparing the organosilicon elastic substrate, by setting particulate soluble material as a sacrificial template in the molding mold and removing the sacrificial template after curing, a connected porous structure is formed inside the organosilicon elastic substrate, thereby enhancing the deformation ability of the flexible substrate under weak tactile force.

[0016] In step S3, the broadband light source (4), single-mode fiber, fiber MZ interference sensor (1), and spectrometer (6) are connected as follows: the broadband light source (4) is connected to one end of the fiber MZ interference sensor (1) through the single-mode fiber, and the other end of the fiber MZ interference sensor (1) is connected to the spectrometer (6); wherein, the broadband light source (4) is used to provide a broadband light source, the single-mode fiber is used to transmit optical signals, the fiber MZ interference sensor (1) is used to optically modulate the external tactile force, and the spectrometer (6) is used to monitor and record the changes in the interference light intensity.

[0017] In step S3, the flexible tactile sensor adopts a sandwich structure with a bionic octopus suction cup array (3) arranged symmetrically on the top and bottom. The middle layer is set as an optical fiber MZ interference sensor (1). Supporting optical fibers (3) are also set on both sides of the optical fiber sensor to provide mechanical support and limiting function, so that the optical fiber sensor maintains a stable spatial position relationship under the action of external tactile force.

[0018] In step S3, when an external tactile force is applied to the upper and lower symmetrical biomimetic octopus suction cup array (3), the sandwich flexible structure undergoes coordinated deformation, causing the medium around the fiber MZ interference sensor (1) located in the middle layer to change from an air state to an organosilicon elastomer state, and its refractive index changes accordingly, which is reflected in the change of interference light intensity on the spectrometer (6); by analyzing the correspondence between the external tactile force and the change of interference light intensity, the detection of the external tactile force is realized.

[0019] In step S3, the wavelength of the broadband light source (4) is 1500-1620nm.

[0020] The working principle of the biomimetic flexible tactile sensor based on the Mach-Zehnder interferometer structure of a misaligned fused single-mode fiber prepared in this invention is as follows:

[0021] When the light emitted by the broadband light source (4) is injected into the first misaligned fusion splice interface through the single-mode fiber, due to the lateral misalignment of the cores of the adjacent single-mode fibers, the incident light undergoes mode redistribution at the misaligned interface. Part of the light energy is coupled from the original core fundamental mode to propagate in the fiber cladding, exciting the cladding mode, while the remaining light energy continues to propagate along the core mode. This forms two optical fields that propagate along the core and cladding respectively, which is equivalent to the beam splitting process in a Mach-Zehnder interference structure.

[0022] The optical field propagating along the cladding interacts directly with the external medium in the misaligned fusion splice section and its adjacent regions, and its effective refractive index is highly sensitive to changes in the refractive index of the surrounding medium. In contrast, the optical field propagating along the fiber core is less affected by the external environment and serves as a relatively stable reference path. When both light paths propagate to the second misaligned fusion splice interface, the cladding mode couples back to the single-mode fiber core, coherently superimposing with the core mode to form a Mach-Zehnder interferometer output.

[0023] The phase difference between the core mode and the cladding mode can be expressed as: in, λ is the effective refractive index difference between the core mode and the cladding mode, L is the equivalent length of the misaligned fusion interference region, and λ is the incident light wavelength.

[0024] The corresponding output light intensity can be expressed as: In the formula, and These represent the light intensities propagating along the fiber core and cladding, respectively.

[0025] In this invention, the fiber MZ interferometer sensor (1) is encapsulated and embedded in a biomimetic flexible packaging structure, and the outer surface of the flexible substrate has an array of biomimetic octopus suction cups. When external tactile force or contact pressure is applied to the biomimetic suction cup array, the flexible substrate undergoes elastic deformation in a local area, and the deformation is effectively transferred to the medium surrounding the optical fiber through the porous structure.

[0026] Because the flexible substrate is in close contact with the fiber cladding, the substrate deformation caused by external forces will lead to a change in the equivalent refractive index around the fiber cladding, thereby altering the effective refractive index of the cladding mode. According to the aforementioned phase relationship, when the refractive index of the external medium changes, the phase difference of the misaligned fusion spliced ​​single-mode fiber (MZI) changes accordingly, ultimately manifesting as interference intensity modulation on the spectrometer (6). By establishing the correspondence between the magnitude of the external tactile force and the change in interference light intensity, highly sensitive detection of minute tactile forces or contact pressures can be achieved.

[0027] In summary, this invention provides a biomimetic flexible tactile sensor based on a single-mode fiber misaligned fusion splice Mach-Zehnder interference structure. This sensor arranges misaligned fusion spliced ​​fibers between biomimetic flexible encapsulation structures (2). When external tactile force acts on the flexible substrate of the biomimetic flexible encapsulation structure (2), it causes deformation of the flexible substrate and changes the equivalent refractive index of the medium surrounding the fiber, thereby causing a change in the interference light intensity of the misaligned fusion splice Mach-Zehnder interference structure, achieving the perception and detection of weak tactile forces. This invention requires no electrodes or electrical signal acquisition units, has a simple structure, high sensitivity, and strong anti-electromagnetic interference capability, making it particularly suitable for applications such as weak force detection and flexible tactile sensing.

[0028] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0029] 1. This invention incorporates the biomimetic mechanism of octopus suction cups in adsorption and force transmission into the design of a flexible tactile sensor. By constructing an array of biomimetic octopus suction cup structures on the surface of a flexible silicone substrate, and forming a connected porous structure within them, minute external tactile forces are effectively concentrated, amplified, and rapidly transmitted at the contact interface. The biomimetic suction cup structure enhances local stress concentration, while the porous structure further improves the deformability and dynamic response performance of the flexible substrate. This allows the flexible substrate to deform more significantly under weak external forces, enhancing the modulation effect of changes in the refractive index of the medium surrounding the optical fiber on the intensity of interference light, and significantly improving the sensor's sensitivity to detecting weak tactile forces.

[0030] 2. This invention employs a staggered fusion splicing of single-mode optical fibers to construct a Mach-Zehnder interference structure. External tactile force induces deformation of a flexible substrate, thereby altering the equivalent refractive index of the surrounding medium and achieving modulation and demodulation of the interference light intensity signal. This tactile sensing method eliminates the need for electrodes, circuits, or electrical signal acquisition units, avoiding the susceptibility of traditional electrical tactile sensors to electromagnetic interference, temperature and humidity changes, and other environmental factors, resulting in high signal stability and reliability. Furthermore, the overall structure of this invention is flexible, small in size, and lightweight, adaptable to complex contact environments such as planar and curved surfaces. The array structure and device size can be customized as needed using 3D printing molds and sacrificial templates, demonstrating excellent engineering feasibility and application expansion potential. Attached Figure Description

[0031] Figure 1 This invention relates to an overall structure of a biomimetic flexible tactile sensor based on fiber MZ interference.

[0032] Figure 2 This is a schematic diagram of a biomimetic flexible tactile sensor detection system based on fiber MZ interferometry.

[0033] Figure 3 This is a schematic diagram of the MZ interference structure of the single-mode fiber misaligned fusion splice fiber of the present invention.

[0034] Figure 4 This diagram illustrates the interference light intensity generated by a biomimetic flexible tactile sensor based on a single-mode fiber misaligned fusion splice MZ interference structure under external tactile force, and shows the fitting relationship curve between the interference wavelength intensity and the magnitude of the tactile force.

[0035] Figure 5 The structure of a single biomimetic octopus suction cup array (21) flexible tactile sensor is shown in three views, including a top view, a front view and a side view. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0037] Example 1: Fabrication of fiber MZ interferometer sensor (1).

[0038] In this embodiment, see Figure 1 A Mach-Zehnder interferometric fiber sensing structure was prepared by using a single-mode fiber misaligned fusion splicing method. The specific method is as follows: First, three commercial single-mode fibers were selected and used as the first single-mode fiber (51), the second single-mode fiber (52), and the third single-mode fiber (53) in sequence. The coating layer of the ends to be fused was removed and cleaned with deionized water and anhydrous ethanol, respectively. Then, the end face of each single-mode fiber was cut flat using a fiber cleaver.

[0039] During the splicing process, a commercial fiber optic fusion splicer is used to perform staggered discharge splicing on two adjacent single-mode fiber segments. By introducing a predetermined offset in the lateral direction, part of the incident light is coupled from the core mode to the cladding mode in the splicing area, while the remaining light continues to propagate along the core. At the second staggered splicing position, the cladding mode couples with the core mode again and forms interference, thus constituting a single-mode fiber staggered splicing Mach-Zehnder interference structure. By controlling the length of each single-mode fiber segment and the staggered splicing parameters, a fiber MZ interference sensor with a stable structure and good interference fringe contrast is obtained (1).

[0040] Example 2: Preparation of biomimetic flexible packaging structure (2).

[0041] In this embodiment, the biomimetic flexible packaging structure is used to cover and carry the fiber MZ interference sensor (1) prepared in Example 1, so as to realize the effective transmission of external tactile force to the medium around the fiber and enhance the deformation response capability under weak force.

[0042] Inspired by the suction and force transmission structure of an octopus sucker, a molding die with an array of biomimetic sucker structures was designed and fabricated. The molding die was manufactured using photopolymerization 3D printing, and its inner surface formed a cavity structure to define the shape of the biomimetic sucker array.

[0043] Preferably, the bionic suction cup array is arranged in a 3×3 configuration, but this can be adjusted according to application requirements. A predetermined spacing is maintained between adjacent suction cup units to balance overall flexibility with localized force concentration.

[0044] The molding die is filled with granular sugar material, which serves as a sacrificial template for the subsequent formation of a porous structure. Then, the A and B components of the silicone elastomer Ecoflex 00-30 are thoroughly mixed at a ratio of 1:1 and injected into the molding die, so that the mixture fully coats the sugar granule sacrificial template and fills the biomimetic suction cup array cavity.

[0045] After casting is completed, the molding mold is placed in a vacuum environment for degassing treatment to remove air bubbles introduced during the mixing and filling of Ecoflex, thereby avoiding the adverse effects of undesigned pores on the mechanical properties and structural uniformity of the flexible substrate; then the Ecoflex mixture is cured to form a stable elastic structure.

[0046] After the Ecoflex elastomer has cured, the sugar particle sacrificial template is removed by dissolution, thereby forming a connected porous structure inside the flexible substrate. At the same time, an array of biomimetic octopus sucker structures is retained on its outer surface, resulting in a biomimetic octopus sucker array (21). The porous structure can produce greater reversible deformation under weak tactile force, thereby improving the sensitivity of the flexible substrate to small external forces.

[0047] Example 3: Overall Assembly of a Bionic Flexible Tactile Sensor

[0048] In this embodiment, the fiber MZ interference sensor (1) prepared in Example 1 is combined with the biomimetic flexible packaging structure (2) prepared in Example 2 to construct an overall structure of a biomimetic flexible tactile sensor for detecting weak tactile force.

[0049] The biomimetic flexible tactile sensor adopts a symmetrical sandwich structure, including a first biomimetic octopus suction cup array (21) on the upper layer, a second biomimetic octopus suction cup array (22) on the lower layer, and an optical fiber MZ interference sensing structure disposed between the first biomimetic octopus suction cup array (21) and the second biomimetic octopus suction cup array (22). The first biomimetic octopus suction cup array (21) and the second biomimetic octopus suction cup array (22) are consistent in structure and materials, and their outer surfaces are both formed with an array of biomimetic octopus suction cup structures.

[0050] The fiber MZ interference sensor (1) is arranged along the planar direction of the flexible substrate and is located in the middle region between the biomimetic flexible packaging structure (2), so that external tactile force can be transmitted to the fiber interference region through the deformation of the biomimetic suction cup array and the porous flexible substrate.

[0051] To improve the stability of the fiber arrangement and the consistency of the force on the flexible structure, a first support fiber (31) and a second support fiber (32) are symmetrically arranged on both sides of the fiber MZ interference sensor (1). The support fiber (3) is basically parallel to the misaligned fusion fiber in the axial direction and is used to limit and support the misaligned fusion fiber under the action of external tactile force, thereby reducing the impact of undesired bending on the interference stability.

[0052] After assembly, the biomimetic flexible packaging structure (2) deforms in tandem under the action of external force, so that the tactile force acting on the sensor surface is transmitted and amplified to the medium region around the optical fiber through the biomimetic suction cup structure and the porous flexible structure, thereby causing changes in the optical fiber interference characteristics and realizing the effective perception of weak tactile force.

[0053] Example 4: Construction of the detection platform.

[0054] In this embodiment, see Figure 1 The detection platform consists of a broadband light source (4), a single-mode optical fiber, a bionic flexible tactile sensor, and a spectrometer (6) connected in sequence. The broadband light source (4) is connected to the input end of the bionic flexible tactile sensor via a single-mode optical fiber, and the output end of the bionic flexible tactile sensor is further connected to the spectrometer (6) via a single-mode optical fiber.

[0055] The broadband light source (4) is used to provide a stable broadband incident light signal, preferably with a working wavelength range of 1500–1620 nm; the spectrometer (6) is used to monitor and record the changes in the interference spectrum output by the bionic flexible tactile sensor in real time.

[0056] During the testing process, the biomimetic flexible tactile sensor is placed on a horizontal worktable. When an external tactile force is applied to the biomimetic flexible encapsulation structure (2), the flexible substrate deforms and changes the equivalent refractive index of the medium surrounding the misaligned fusion fiber, thereby causing a change in the interference conditions in the single-mode fiber misaligned fusion Mach-Zehnder interference structure.

[0057] The change in refractive index is manifested as a shift in the interference spectrum on the spectrometer (6). By analyzing the correspondence between the magnitude of external tactile force and the amount of interference spectrum shift, the quantitative detection of weak tactile force can be achieved.

[0058] In summary, this invention proposes a biomimetic flexible tactile sensor based on a single-mode fiber misaligned fusion Mach-Zehnder interference structure and its fabrication method. Compared to traditional flexible tactile sensors based on electrical signals, this invention uses fiber interference as the core sensing mechanism, eliminating the need for electrodes and complex circuit structures, thus avoiding electromagnetic interference problems. It boasts advantages such as simple structure, stable signal, and strong environmental adaptability. By introducing a vertically symmetrical array of biomimetic octopus suction cups, this invention enables external tactile forces to be transmitted and amplified step-by-step within the flexible structure. This effectively enhances the modulation effect of the equivalent refractive index change of the medium surrounding the fiber on the interference spectrum, significantly lowering the detection limit of weak forces and improving tactile sensing sensitivity. It is suitable for scenarios involving fine touch and small force detection.

[0059] Furthermore, the fabrication method employed in this invention is based on conventional laboratory processes such as 3D printing molds, sacrificial template pore formation, and silicone elastomer molding. It does not involve high-cost or complex micro / nano fabrication techniques, and the fabrication process is simple, low-cost, and highly repeatable, demonstrating feasibility for array-based and mass production. The fabricated flexible tactile sensor has a compliant structure and small size, and can be attached to or integrated onto various curved surfaces, meeting the needs of diverse flexible tactile sensing and human-computer interaction applications.

[0060] The above description is merely a preferred embodiment of the present invention, used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. It should be understood that, for those skilled in the art, various changes, modifications, or equivalent substitutions can be made to the above embodiments without departing from the technical concept and principle of the present invention, and all such changes, modifications, or equivalent substitutions should fall within the scope of protection of the present invention.

Claims

1. A biomimetic flexible tactile sensor, comprising an optical fiber MZ interferometer sensor (1) and a biomimetic flexible encapsulation structure (2); characterized in that: The biomimetic flexible packaging structure (2) consists of a first biomimetic octopus suction cup array (21) and a second biomimetic octopus suction cup array (22) with symmetrical upper and lower parts. The fiber MZ interference sensor (1) is placed between the first biomimetic octopus suction cup array (21) and the second biomimetic octopus suction cup array (22) to form a sandwich-type biomimetic flexible tactile sensor. The fiber MZ interference sensor (1) is formed by staggered splicing of a first single-mode fiber (51), a second single-mode fiber (52) and a third single-mode fiber (53) to form a Mach-Zehnder interference structure. The length of the second single-mode fiber (52) is 3cm-10cm. A first supporting fiber (31) and a second supporting fiber (32) are laid on both sides of the fiber MZ interferometer (1). The first supporting fiber (31) and the second supporting fiber (32) are laid parallel to the fiber MZ interferometer (1) to provide mechanical support and limiting function for the fiber MZ interferometer (1). The molds for the first and second biomimetic octopus suction cup arrays (21 and 22) are prepared using 3D printing technology. The molds are used to define the spatial morphology of the biomimetic suction cup arrays. The first and second biomimetic octopus suction cup arrays (21 and 22) are prepared using a sugar particle sacrificial template pore-forming method. Their interiors are interconnected open-cell foam structures to enhance the ability of the biomimetic flexible encapsulation structure to change the contact medium with the fiber MZ interference sensor (1) under pressure. The first and second biomimetic octopus suction cup arrays (21 and 22) are array-type distribution structures with an array arrangement of n×m, where n ranges from 2 to 10 and m ranges from 2 to 10. When external tactile force is applied to the first and second biomimetic octopus suction cup arrays (21 and 22), the biomimetic flexible encapsulation structure (2) deforms, causing the fiber MZ interference sensor (1) to deform. The equivalent refractive index of the medium surrounding the interference sensor (1) changes, thereby causing a change in the intensity of the interference light output by the fiber MZ interference sensor (1), thus realizing the detection of external tactile force.

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