Lower limb eight-channel muscle deformation FBG optical fiber sensor

Abstract

The invention discloses a lower limb eight-channel muscle deformation FBG optical fiber sensor which comprises a single single-mode optical fiber with eight muscle deformation measuring points and an optical fiber grating demodulator. The single-mode optical fiber is a main body structure of the muscle deformation sensor, and eight FBG (Fiber Bragg Grating) measuring points are sequentially engraved on the single-mode optical fiber along the axial direction and are respectively corresponding to deformation detection of different muscle groups; the fiber bragg grating demodulator is used for transmitting broadband optical signals to the single-mode optical fiber, receiving echo signals reflected by the FBG measuring points and analyzing reflection wavelengths corresponding to the eight FBG measuring points in real time through a wavelength demodulation algorithm, so that strain information of the muscle positions is obtained. The FBG measuring points at different positions are reasonably selected, and a unique spiral distribution mode is adopted, so that synchronous deformation detection of a plurality of key muscles of the lower limb is realized.

Description

Technical Field

[0001] This invention relates to the fields of biomechanical detection and fiber optic sensing technology, specifically to an eight-channel muscle deformation FBG fiber optic sensor for the lower limbs. Background Technology

[0002] Acquiring muscle information is a crucial component of lower limb movement intention sensing technology. Commonly used methods for muscle information acquisition include electromyography (EMG) signal detection and muscle deformation detection. Traditional muscle deformation detection often employs techniques such as resistance strain gauges or piezoelectric sensors. While these methods can achieve basic deformation monitoring in some scenarios, they generally suffer from low sensitivity, insufficient anti-interference capabilities, and poor environmental adaptability, especially struggling to achieve high-precision and stable measurements under complex movement conditions. Furthermore, traditional sensor structures are typically rigid, making it difficult to integrate multiple detection units within a limited space, thus limiting the realization of simultaneous detection of multiple muscle groups.

[0003] Fiber Bragg Grating (FBG) sensing technology, as a novel optical detection method, boasts significant advantages such as high sensitivity, strong resistance to electromagnetic interference, compact structure, and light weight. In recent years, FBG technology has been widely applied to precision measurements in various fields, including strain, temperature, and pressure, providing new solutions for biomechanics and wearable sensing.

[0004] Applying FBG technology to lower limb muscle deformation detection not only enables simultaneous monitoring of multiple muscle groups but also significantly improves the accuracy and stability of deformation measurements, providing highly reliable data support for lower limb movement intention perception. Real-time acquisition and analysis of muscle deformation signals can be used for movement status assessment, early diagnosis of sports injuries, and rehabilitation training monitoring. Furthermore, the flexibility and miniaturization of FBG sensors allow for integration with wearable exoskeletons, smart prostheses, and other devices, providing a crucial data foundation for human-computer interaction and rehabilitation aid design. Therefore, FBG-based lower limb muscle deformation detection technology has significant theoretical value and application prospects in the fields of movement intention recognition and rehabilitation engineering.

[0005] However, there are still some technical limitations in applying fiber Bragg grating technology to the detection of lower limb muscle deformation.

[0006] First, fiber Bragg gratings measure muscle deformation through a strain transfer mechanism, which requires a stable and approximately linear strain transfer relationship between the fiber and the skin, maintaining continuous contact during movement. If the strain transfer structure is poorly designed or the contact method is unstable, it can easily lead to unclear strain coupling, signal attenuation, or nonlinear distortion, thus affecting measurement accuracy and repeatability. Furthermore, when multiple muscle groups need to be monitored simultaneously, using a single fiber to arrange multiple grating units presents challenges such as complex fiber routing paths, mutual interference between different muscle group deformations, and difficulties in optimizing spatial distribution, increasing the complexity of structural design and signal analysis. Summary of the Invention

[0007] To overcome the shortcomings of the existing technology, this invention provides an eight-channel muscle deformation fiber optic sensor for the lower limb. By rationally selecting FBG measurement points at different locations and adopting a unique spiral distribution arrangement, it realizes the synchronous deformation detection of multiple key muscles in the lower limb. This arrangement can cover the main muscle groups involved in the movement of the lower limb and realize the simultaneous acquisition of multi-channel strain signals.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A lower limb eight-channel muscle deformation FBG fiber optic sensor includes a single-mode fiber with eight muscle deformation measurement points and a fiber grating demodulator. The single-mode optical fiber is the main structure of the muscle deformation sensor. Eight fiber Bragg grating (FBG) measurement points are sequentially engraved on it along the axial direction, which are used to detect the deformation of different muscle groups. The fiber grating demodulator is used to transmit broadband optical signals into the single-mode fiber and receive the echo signals reflected by each FBG measurement point. The reflected wavelengths corresponding to the eight FBG measurement points are analyzed in real time through wavelength demodulation algorithm to obtain strain information of each muscle position.

[0009] The single-mode optical fiber with 8 muscle deformation measurement points is engraved with a Bragg grating in the fiber by femtosecond laser direct writing method (by directly writing a grating structure in the fiber core layer with a focused ultraviolet laser). The laser pulse energy is preferably 50–100 μJ and the repetition frequency is preferably 100–500 Hz. By controlling the moving speed of the three-dimensional displacement platform, eight FBG measurement points with different wavelengths are sequentially formed in the fiber optic sensor. The center wavelength range of each FBG measurement point is 1530–1565 nm, and the center wavelength interval between adjacent FBG measurement points is preferably 3–10 nm. The spacing between the Bragg gratings is set between 100 mm and 400 mm according to the muscle distribution position, so as to realize a multi-point series fiber optic grating array.

[0010] The FBG measurement points are the rectus femoris FBG measurement point, vastus lateralis FBG measurement point, biceps femoris FBG measurement point, semitendinosus FBG measurement point, vastus medialis FBG measurement point, gastrocnemius FBG measurement point, tibialis anterior FBG measurement point, and soleus FBG measurement point. The FBG measurement points are the detection locations for muscle deformation.

[0011] Polydimethylsiloxane PDMS11 is embedded at each muscle deformation measurement point. PDMS11 is combined with a single-mode optical fiber to form a flexible sensor. PDMS and curing agent are mixed in a ratio between 10:1 and 20:1, and after pre-curing and secondary curing, a flexible encapsulation with a thickness of about 0.6 mm, a width of 2.4 cm and a length of 3.2 cm is formed.

[0012] This flexible encapsulation has excellent biocompatibility and flexibility, and can be applied to the skin surface through medical dressings to achieve stable adhesion and high strain transfer efficiency.

[0013] During actual measurement, the fiber optic sensor is spirally wrapped around the leg. The fiber optic sensor starts from the inner thigh, passes through the rectus femoris muscle belly region and the vastus lateralis muscle region in sequence; then it goes around from the outer thigh to the back of the thigh, passing through the biceps femoris and semitendinosus muscle belly regions in sequence; then it goes around from the inner thigh to the front of the thigh, passing through the vastus medialis muscle region. The optical fiber transitions from the outer thigh to the back of the calf near the knee joint, passing through the gastrocnemius muscle belly region; then it circles around the inner side of the calf to the front side of the calf, passing through the tibialis anterior muscle belly region; finally, it circles around the outer side of the calf to the back side of the calf, covering the soleus muscle belly region.

[0014] This ensures that each muscle measurement point is located on the skin surface of the corresponding muscle; through the attachment structure of the medical sterile dressing, each muscle deformation measurement point is sequentially attached to the skin surface of the corresponding muscle.

[0015] The attachment structures are the rectus femoris attachment structure, the vastus lateralis attachment structure, the biceps femoris attachment structure, the semitendinosus attachment structure, the vastus medialis attachment structure, the gastrocnemius attachment structure, the tibialis anterior attachment structure, and the soleus attachment structure. The flexible encapsulation of each muscle measuring point can deform synchronously with the human skin surface under aseptic application. Among them, the attachment structures of the rectus femoris muscle correspond to the FBG measurement points of the rectus femoris muscle; the attachment structures of the vastus lateralis muscle correspond to the FBG measurement points of the vastus lateralis muscle; the attachment structures of the biceps femoris muscle correspond to the FBG measurement points of the biceps femoris muscle; the attachment structures of the semitendinosus muscle correspond to the FBG measurement points of the semitendinosus muscle; the attachment structures of the vastus medialis muscle correspond to the FBG measurement points of the vastus medialis muscle; the attachment structures of the gastrocnemius muscle correspond to the FBG measurement points of the gastrocnemius muscle; the attachment structures of the tibialis anterior muscle correspond to the FBG measurement points of the tibialis anterior muscle; and the attachment structures of the soleus muscle correspond to the FBG measurement points of the soleus muscle. This deformation will cause corresponding strain in the FBG grating region of the flexible package, thereby changing the wavelength change fed back by the grating region. This wavelength change is proportional to the strain of the grating region. Ultimately, the muscle deformation is transmitted to the FBG at the muscle deformation measurement point through deformation transmission, and the strain change is linearly reflected by the wavelength of the reflected light, realizing the conversion from muscle deformation signal to light signal wavelength.

[0016] The FBG grid regions are arranged at preset intervals on the single-mode optical fiber.

[0017] For each muscle measurement point, after the FBG grid area is written, place the single-mode fiber at the FBG grid area position on the cover glass, with the FBG grid area in the center. After mixing PDMS and curing agent according to a preset mass ratio, an appropriate amount of the mixture is dropped onto the surface of a glass slide to form a substrate layer.

[0018] During dynamic movements such as walking and flexion / extension, the sensor output optical signal can be fed back in real time to a single channel of the fiber Bragg grating demodulator, which then acquires the changes in reflected wavelength. The demodulator operates in the 1528–1568 nm band with a sampling frequency of 2000 Hz, and can simultaneously detect the feedback wavelength changes of eight muscle measurement points using only a single channel. These wavelength changes are converted into muscle deformation signals through strain calibration, thus enabling the measurement of muscle deformation for eight muscles.

[0019] This sensor can provide precise muscle strain information for motion intention recognition, rehabilitation assessment, and exoskeleton control, thereby providing a more comprehensive assessment of the human body's motion status.

[0020] A method for detecting lower limb muscle deformation using an eight-channel fiber optic FBG sensor includes the following steps: S1. Sensor preparation steps: A single-mode optical fiber with eight muscle deformation measurement points is provided. Eight FBG grid regions are sequentially etched along the axial direction on the single-mode optical fiber to form FBG measurement points for the rectus femoris, vastus lateralis, biceps femoris, semitendinosus, vastus medialis, gastrocnemius, tibialis anterior, and soleus. Each FBG measurement point serves as the detection location for the corresponding muscle deformation. S2, Flexible Packaging Steps: A flexible encapsulation body formed of polydimethylsiloxane alkyl PDMS is set at each FBG gate area position, so that the FBG gate area is embedded inside the flexible encapsulation body, thereby forming a flexible fiber optic sensing unit that can deform synchronously with human skin and muscles. S3. Sensor installation steps: The single-mode optical fiber is arranged in a spiral manner along the surface of the human lower limb, so that each FBG measuring point corresponds to the muscle belly area of ​​the rectus femoris, vastus lateralis, biceps femoris, semitendinosus, vastus medialis, gastrocnemius, tibialis anterior and soleus muscles, and each flexible encapsulation body is attached to the skin surface of the corresponding muscle through an attachment structure composed of medical sterile dressing. S4. System connection steps: The single-mode fiber is connected to the fiber optic demodulator, which sends a broadband optical signal to the fiber and obtains the initial reflection center wavelength of each FBG measurement point as a reference value. S5. Deformation signal acquisition steps: During walking, flexion and extension, or other lower limb movements, the target muscle groups contract and stretch, and the deformation is transmitted through the skin to the flexible encapsulation, which then acts on the corresponding FBG gate area, causing strain at each FBG measuring point and resulting in a change in the reflected wavelength. S6. Wavelength demodulation steps: The reflection wavelength changes of each FBG measurement point were demodulated in real time using a fiber optic grating demodulator, and the wavelength change data of eight muscle measurement points were acquired simultaneously under single-channel conditions. S7. Deformation Calculation and Output Steps: Based on the correspondence between Bragg wavelength changes and strain, the wavelength changes at each FBG measurement point are converted into deformation or strain signals of the corresponding muscles, thereby enabling synchronous deformation detection of the rectus femoris, vastus lateralis, biceps femoris, semitendinosus, vastus medialis, gastrocnemius, tibialis anterior, and soleus muscles.

[0021] The beneficial effects of this invention are: 1. Compared to existing muscle deformation sensors, this invention enables simultaneous detection of multiple muscle deformation signals in a single channel. This invention integrates multiple FBG measurement points with different center wavelengths on a single optical fiber, each corresponding to a different muscle group location. Multi-point synchronous demodulation is achieved through wavelength division multiplexing. Since the FBGs of different wavelengths do not interfere with each other, strain information of multiple muscles can be acquired simultaneously in a single-channel demodulation system, thereby achieving synchronous deformation acquisition of the eight major muscle groups of the lower limb, covering key force-generating muscle groups during movement. The structure is simple and easy to deploy.

[0022] 2. Compared to existing muscle deformation sensors, this invention offers high sensitivity and high linearity. The FBG sensing principle is based on the characteristic that the Bragg wavelength changes linearly with axial strain, exhibiting a strong linear relationship between wavelength change and axial strain. This invention improves the transmission efficiency of muscle deformation to optical fiber axial strain through a flexible PDMS packaging structure, thereby enhancing overall sensitivity. Simultaneously, the optical wavelength demodulation method avoids the electrical noise accumulation problem of resistive sensors, resulting in high detection accuracy and fast dynamic response.

[0023] 3. Compared to resistive or piezoelectric muscle deformation detection methods, this invention has stronger resistance to electromagnetic interference. This invention uses optical signals as the information carrier, acquiring strain information through fiber optic transmission and optical demodulation, without relying on current or voltage signal transmission, and therefore is unaffected by external electromagnetic field interference. This characteristic makes it suitable for wearable applications in exoskeletons, motor drive systems, or complex electromagnetic environments, improving system stability and environmental adaptability.

[0024] 4. The muscle deformation sensor of this invention features a thin, flexible, wearable structure with excellent fit, without affecting natural human movement. This invention uses a PDMS flexible encapsulation substrate to completely cover the optical fiber, forming a transparent sensing structure with low thickness and good flexibility. This structure can closely conform to the skin surface and deform in sync with muscle contraction, improving strain transmission efficiency. Simultaneously, since multiple FBG measurement points are integrated on a single optical fiber, the signal transmission path is simple, eliminating the need for multiple distributed wires, thereby reducing wiring complexity, minimizing interference with natural human movement, and improving wearing comfort and long-term stability. Attached Figure Description

[0025] Figure 1 This is a front view of an eight-channel muscle deformation FBG fiber optic sensor for the lower limbs.

[0026] Figure 2 This is a rear view of an eight-channel muscle deformation FBG fiber optic sensor for the lower limbs.

[0027] Figure 3 This is a flowchart illustrating the fabrication process of a single muscle deformation FBG fiber optic sensor.

[0028] Figure 4 This is a schematic diagram of the strain transmission principle of a muscle deformation sensor.

[0029] Figure 5 This is a schematic diagram of the structure of FBG optical fiber in the PDMS flexible encapsulation layer.

[0030] Figure 6 This is a graph showing the change in FBG wavelength at various muscle measurement points during gait movement. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings.

[0032] To achieve the above objectives, the present invention provides the following specific embodiments: like Figure 1 , Figure 2As shown, the present invention provides an eight-channel muscle deformation FBG fiber optic sensor for the lower limb, including a single-mode fiber 1 with eight muscle deformation measurement points and a fiber optic grating demodulator 10. The single-mode optical fiber 1 is the main structure of the muscle deformation sensor. Eight fiber Bragg grating (FBG) measurement points are sequentially engraved on it along the axial direction, which are used to detect the deformation of different muscle groups.

[0033] The fiber grating demodulator 10 is used to transmit broadband optical signals to the single-mode fiber 1 and receive the echo signals reflected by each FBG measurement point. The reflected wavelengths corresponding to the eight FBG measurement points are analyzed in real time through wavelength demodulation algorithm to obtain the strain information of each muscle position.

[0034] The single-mode optical fiber 1 with eight muscle deformation measurement points includes muscle measurement points numbered 2, 3, 4, 5, 6, 7, 8, and 9. These muscle measurement points correspond to the positions of the rectus femoris, vastus lateralis, biceps femoris, semitendinosus, vastus medialis, gastrocnemius, tibialis anterior, and soleus muscles, respectively. Specifically, these are rectus femoris FBG measurement point 2, vastus lateralis FBG measurement point 3, biceps femoris FBG measurement point 4, semitendinosus FBG measurement point 5, vastus medialis FBG measurement point 6, gastrocnemius FBG measurement point 7, tibialis anterior FBG measurement point 8, and soleus FBG measurement point 9.

[0035] The rectus femoris attachment structure 16, the vastus lateralis attachment structure 17, the biceps femoris attachment structure 18, the semitendinosus attachment structure 19, the vastus medialis attachment structure 20, the gastrocnemius attachment structure 21, the tibialis anterior attachment structure 22, and the soleus attachment structure 23 are respectively set at the corresponding positions of each muscle measuring point to stably attach the measuring point to the corresponding muscle surface, so as to ensure the accuracy of strain transmission and the stability of detection.

[0036] Specifically, when the sensor measures muscle deformation, each muscle measuring point is sequentially attached to the skin surface at the corresponding muscle belly location; The rectus femoris muscle measuring point 2 is applied to the skin surface at the belly of the rectus femoris muscle by aseptic application of the rectus femoris attachment structure 16. The vastus lateralis muscle measuring point 3 is applied to the skin surface at the belly of the vastus lateralis muscle by aseptic application of the vastus lateralis muscle attachment structure 17. The biceps femoris muscle measuring point 4 is applied to the skin surface at the belly of the biceps femoris muscle using the aseptic dressing of the biceps femoris attachment structure 18. The semitendinosus muscle measuring point 5 is applied to the skin surface at the belly of the semitendinosus muscle by aseptic application of the semitendinosus attachment structure 19. The vastus medialis muscle measuring point 6 is applied to the skin surface at the location of the vastus medialis muscle belly by aseptic application of the vastus medialis muscle attachment structure 20. By applying a sterile dressing to the gastrocnemius muscle attachment structure 21, the gastrocnemius muscle measuring point 7 is attached to the skin surface at the belly of the gastrocnemius muscle. The tibialis anterior muscle apposition point 8 is applied to the skin surface of the tibialis anterior muscle belly by aseptic application of the tibialis anterior muscle apposition structure 22. The soleus muscle measuring point 9 is applied to the skin surface of the human soleus muscle belly using the soleus muscle attachment structure 23 aseptically.

[0037] Specifically, during the attachment process, the single-mode optical fiber 1 adopts the following method: Figure 1 and Figure 2 The spiral winding pattern shown is arranged along the surface of the lower limb.

[0038] The optical fiber starts from the inner thigh, passes through the rectus femoris muscle belly region and the vastus lateralis muscle region in sequence; then it goes around the outer thigh to the back of the thigh, passing through the biceps femoris and semitendinosus muscle belly regions in sequence; then it goes around the inner thigh to the front of the thigh, passing through the vastus medialis muscle region.

[0039] Furthermore, the optical fiber transitions from the outer thigh to the back of the calf near the knee joint, passing through the gastrocnemius muscle belly region; then it travels from the inner side of the calf to the front of the calf, passing through the tibialis anterior muscle belly region; finally, it travels from the outer side of the calf to the back of the calf, covering the soleus muscle belly region.

[0040] By using the spiral layout described above, each FBG measuring point can correspond to the target muscle group location, enabling continuous measurement of multiple muscle deformations with a single optical fiber, while ensuring the overall stability and continuity of the optical fiber layout, thus meeting the requirements for simultaneous detection of multiple muscle groups.

[0041] After the attachment is completed, the deformation of the muscle during movement can be transmitted through the skin and the encapsulation layer to the fiber Bragg gratings corresponding to the rectus femoris FBG measurement point 2, vastus lateralis FBG measurement point 3, biceps femoris FBG measurement point 4, semitendinosus FBG measurement point 5, vastus medialis FBG measurement point 6, gastrocnemius FBG measurement point 7, tibialis anterior FBG measurement point 8, and soleus FBG measurement point 9. The corresponding measurement points will reflect different wavelength signals to the fiber Bragg demodulator 10, realizing synchronous strain detection of eight muscles.

[0042] like Figure 3 As shown, each muscle measuring point of the present invention is composed of an FBG grid region 12, a single-mode optical fiber 1, and a flexible substrate 15. During use, the rectus femoris attachment structure 16, the vastus lateralis attachment structure 17, the biceps femoris attachment structure 18, the semitendinosus attachment structure 19, the vastus medialis attachment structure 20, the gastrocnemius attachment structure 21, the tibialis anterior attachment structure 22, and the soleus attachment structure 23 respectively cover the corresponding flexible substrate 15 and are attached and fixed to the skin surface, so that the FBG grid area 12 can generate coordinated deformation with muscle contraction, thereby ensuring the stability of strain transmission and detection accuracy; The FBG grating region 12 is etched using a femtosecond laser direct writing method. The etch pulse energy is approximately 70 μJ, and the repetition frequency is 200 Hz. The movement speed of the three-dimensional displacement platform is controlled within the range of 312–320 μm / s. This invention has a total of 8 muscle measurement points, requiring 8 FBG grating regions to be etched on the single-mode fiber 1 to meet the detection needs.

[0043] Specifically, the FBG gate region 12 is arranged at preset intervals on the single-mode fiber 1.

[0044] In a preferred embodiment, the distance between muscle measuring point 2 and muscle measuring point 3 is approximately 120 mm; the distance between muscle measuring point 3 and muscle measuring point 4 is approximately 170 mm; the distance between muscle measuring point 4 and muscle measuring point 5 is approximately 340 mm; the distance between muscle measuring point 5 and muscle measuring point 6 is approximately 200 mm; the distance between muscle measuring point 6 and muscle measuring point 7 is approximately 50 mm; the distance between muscle measuring point 7 and muscle measuring point 8 is approximately 160 mm; and the distance between muscle measuring point 8 and muscle measuring point 9 is approximately 100 mm.

[0045] The spacing between the aforementioned measuring points is determined based on the linear distance along the fiber optic path between each target muscle group under the spiral winding arrangement. The spacing parameters are designed with reference to the lower limb dimensions of an adult with a height of approximately 170 cm and a weight of approximately 60 kg, to ensure that each FBG measuring point accurately corresponds to the target muscle location, while avoiding positioning deviations due to excessively large spacing or structural interference due to excessively small spacing. The wavelength parameters for FBG inscription range from 1530 nm to 1565 nm, ensuring that the wavelength difference between measuring points is not less than 4 nm during inscription. Muscle measuring point 2 is located at the end closest to the fiber optic demodulator 10, ensuring that its distance from the single-mode fiber 1 connected to the demodulator is not less than 20 cm.

[0046] Specifically, for each muscle measurement point, after the FBG grid region 12 is written, the single-mode fiber 1 at the position of the FBG grid region 12 is placed on the cover glass 13, with the FBG grid region 12 in the center position. After mixing PDMS and curing agent according to a preset mass ratio, an appropriate amount of the mixture is dropped onto the surface of glass slide 13 to form a substrate layer. The mass ratio can be adjusted according to the required flexibility.

[0047] The mixture is pre-cured at room temperature or under controlled temperature to form an incompletely cured matrix 14, which is then used for subsequent embedding of optical fibers and secondary curing.

[0048] After pre-curing, the position of the single-mode fiber 1 is adjusted so that it is located in the middle region along the length of the flexible substrate, and the FBG gate region 12 is located at the center of the substrate.

[0049] Subsequently, PDMS and curing agent are mixed at a preset mass ratio and stirred thoroughly. The mixture is then dropped onto the surface of glass slide 13 to cover the optical fiber and pre-cured substrate. The amount of mixture used is controlled according to the encapsulation size to ensure the formation of a complete encapsulation structure.

[0050] After the mixture is evenly distributed on the cover glass surface and the air bubbles are basically eliminated, the entire measuring point assembly is placed in a constant temperature environment for secondary curing. The curing temperature is preferably within the range of 70℃ to 90℃, and is maintained for a preset time to complete the full cross-linking of PDMS.

[0051] After curing, the glass slide 13 is separated from the formed flexible substrate to obtain the flexible substrate 15. The flexible substrate 15 and the single-mode optical fiber 1 form an integrally cured structure, and the FBG gate region 12 is located in the central region of the flexible substrate. Figure 4 The diagram shown illustrates the strain transfer principle of a single muscle deformation measuring point according to the present invention. The strain transfer path, from the inside out, includes muscle tissue 29, soft tissue 28, skin layer 27, and a flexible encapsulation body 15 disposed on the skin surface.

[0052] The flexible package 15 includes an outer flexible package layer 17, an upper coating layer 26, an FBG layer 25, a lower coating layer 24, and an inner flexible package layer 16.

[0053] The FBG layer 25 is a fiber grating region etched on a single-mode optical fiber; the coating layers 24 and 26 are the original protective coating layers or secondary cladding layers of the optical fiber, used to enhance mechanical protection and strain transmission stability; the inner flexible encapsulation layer 16 and the outer flexible encapsulation layer 17 are preferably formed of PDMS material, used to achieve strain buffering and uniform transmission.

[0054] During muscle contraction, the muscle tissue 29 deforms and is transmitted to the outer flexible encapsulation layer 17 via the soft tissue 28 and skin layer 27. It also forms axial strain with the coating layer and FBG layer 25, thereby causing Bragg wavelength shift and realizing muscle deformation detection.

[0055] During lower limb movement, the target muscle contracts or relaxes, and its lateral or longitudinal deformation first acts on the soft tissue 28 and is further transmitted to the skin layer 27. The local expansion and contraction of the skin layer 27 causes corresponding deformation of the flexible encapsulation layer 17. Since the flexible encapsulation layer 17 is fixed to the skin layer with a medical dressing, the encapsulation layer 17 can move synchronously with the skin layer 27, so that the deformation can be stably transmitted to the coating layer 26 and FBG layer 25 inside the encapsulation.

[0056] A fiber Bragg grating (FBG) is embedded in a flexible encapsulation layer along the fiber axis. When the encapsulation layer undergoes slight stretching or compression, the grating region containing the FBG will experience axial strain, causing a change in the grating period and the effective refractive index of the fiber core, thus resulting in a slight shift in the Bragg reflection wavelength. By detecting the wavelength change of the FBG in real time using a demodulator, the deformation information of the corresponding muscle can be obtained.

[0057] This strain transfer structure utilizes the high elasticity and flexibility of the flexible encapsulation layer to enable muscle deformation to be transmitted to the fiber Bragg grating with high efficiency, thereby improving the sensitivity and stability of the sensor in detecting muscle movement. This structure ensures that instantaneous muscle deformation can be effectively captured during gait, flexion and extension movements, and rapid dynamic actions, achieving synchronous strain monitoring of multiple muscle groups.

[0058] The sensor uses a fiber Bragg grating (FBG) as its detection core. The FBG forms a periodic refractive index variation structure within the optical fiber. When the fiber is subjected to external strain, the grating period and the effective refractive index of the fiber core change, causing a shift in the Bragg wavelength of the reflected light. By monitoring this wavelength shift, the deformation changes of the muscle during movement can be reflected. This principle ensures that the sensor has high sensitivity and a high signal-to-noise ratio.

[0059] like Figure 6 The diagram shown is a schematic representation of the FBG optical fiber in a PDMS flexible encapsulation layer according to an embodiment of the present invention. The encapsulation structure mainly includes: a single-mode optical fiber 1, a flexible encapsulation layer 16, an optical fiber region 12 with an FBG grating, and a flexible encapsulation layer 17.

[0060] like Figure 5 The diagram shown is a schematic representation of the structure of the FBG optical fiber at a single muscle deformation measurement point in the PDMS flexible encapsulation layer in an embodiment of the present invention.

[0061] The lower limb eight-channel muscle deformation FBG fiber optic sensor of the present invention includes eight muscle measuring points disposed on a single-mode fiber 1, each muscle measuring point employing the same or similar encapsulation structure. The encapsulation structure of a single measuring point includes: a single-mode fiber 1, an FBG grid region 12 disposed on the fiber, and flexible encapsulation layers 16 and 17 located on the upper and lower sides of the fiber, respectively. The flexible encapsulation layers are preferably formed of PDMS material. Through this structure, each FBG measuring point can independently sense the deformation of its corresponding muscle group, while the whole structure constitutes a single-fiber multi-channel muscle deformation detection structure.

[0062] In this embodiment, the flexible encapsulation layer 16 is made of polydimethylsiloxane (PDMS) material. PDMS has good elasticity, softness and biocompatibility, can closely adhere to the surface of human skin, and deform synchronously with the skin during movement.

[0063] The FBG is embedded in the central region of the PDMS encapsulation layer. The optical fiber is arranged along the length of the encapsulation layer and has a slightly pre-bent structure to enhance the mechanical flexibility and strain adaptability after encapsulation. The FBG grating area is completely covered inside the encapsulation layer, so that the grating is not directly exposed to the external environment, thereby improving the anti-interference capability and structural stability.

[0064] This encapsulation structure can effectively transfer external strain to the grating region through the skin-PDMS encapsulation layer-FBG transmission chain when muscle deforms, causing a measurable displacement of the Bragg reflection wavelength, thereby achieving high-sensitivity detection of muscle deformation. Figure 5 The encapsulation structure shown illustrates the specific positional relationship of the optical fiber within the PDMS layer, which helps to understand the strain transmission path and the flexible support function of the encapsulation layer.

[0065] like Figure 6 The figure shows the FBG wavelength change curves of various muscle measurement points collected under gait conditions in an embodiment of the present invention. The eight FBG measurement points correspond to the rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, gastrocnemius, tibialis anterior, and soleus muscles of the lower limb, respectively.

[0066] During the test, the eight-channel muscle deformation fiber optic sensor of this invention was attached to the skin surface of the corresponding muscle belly of the subject's lower limb, and the reflected wavelength changes of the eight FBGs were synchronously acquired at a sampling frequency of 2000 Hz using a fiber optic demodulator. The subject performed continuous walking movements according to a natural gait, and the wavelength change data of each FBG was recorded within multiple complete gait cycles.

[0067] like Figure 6As shown, each channel exhibits a wavelength curve that changes with muscle contraction and relaxation during the gait cycle. The curve morphology differs at different muscle measurement points, reflecting the different mechanical functions performed by each muscle during the gait cycle. Each curve shows a continuous and distinguishable wavelength change trend, indicating that the sensor of this invention can measure the deformation information of multiple muscles in real time under dynamic gait conditions, achieving multi-channel synchronous detection.

[0068] This embodiment demonstrates that the muscle deformation FBG sensor of the present invention can reliably acquire muscle strain signals during gait movement without external interference. The obtained wavelength change curves can reflect the dynamic deformation characteristics of each muscle during the gait cycle, and can be used for applications such as movement intention recognition, rehabilitation assessment, and gait analysis. During the test, the eight-channel muscle deformation FBG fiber optic sensor of the present invention was attached to the skin surface of the corresponding muscle belly position of the subject's lower limb. The single-mode fiber 1 was fixed to the surface of each muscle through attachment structures 16-23.

[0069] When the subject performs natural walking or dynamic movements such as knee flexion and extension, the corresponding muscle tissue 29 undergoes periodic contraction and relaxation. The muscle deformation is transmitted sequentially through the soft tissue 28 and the skin layer 27 to the flexible encapsulation layer 17, and axial strain is formed through the coating layer 26 and the FBG layer 25, causing the FBG gate region 12 disposed on the optical fiber to generate Bragg wavelength drift.

[0070] During the gait support and swing phases, different muscles generate deformation signals with varying amplitudes and phases. For example, during the gait support phase, the wavelength changes at the rectus femoris and soleus muscle measuring points are relatively large; during the swing phase, the gastrocnemius muscle measuring point shows a significant response. Each FBG measuring point independently generates a corresponding wavelength change signal, which is synchronously analyzed by a fiber optic grating demodulator, enabling simultaneous monitoring of multiple muscle groups during dynamic movement.

[0071] Similarly, in the knee flexion-extension test, when the knee is flexed, the biceps femoris and semitendinosus probes show wavelength shifts; when the knee is extended, the rectus femoris and vastus medialis probes show enhanced responses. This change clearly reflects the functional division of labor among different muscle groups during flexion-extension movements.

[0072] Therefore, this embodiment not only verifies the strain transfer effectiveness of a single FBG measuring point structure, but also demonstrates the collaborative working capability of the eight-channel overall structure under dynamic gait and flexion-extension motion conditions.

[0073] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the specific implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A lower limb eight-channel muscle deformation FBG fiber optic sensor, characterized in that, It includes a single-mode optical fiber (1) with 8 muscle deformation measurement points and a fiber optic demodulator (10). The single-mode optical fiber (1) is the main structure of the muscle deformation sensor. Eight fiber Bragg grating (FBG) measurement points are sequentially engraved on it along the axial direction, which are used to detect the deformation of different muscle groups respectively. The fiber grating demodulator (10) is used to transmit broadband optical signals to the single-mode fiber (1) and receive the echo signals reflected by each FBG measurement point. The reflected wavelengths corresponding to the eight FBG measurement points are analyzed in real time through wavelength demodulation algorithm to obtain the strain information of each muscle position.

2. The lower limb eight-channel muscle deformation FBG fiber optic sensor according to claim 1, characterized in that, The single-mode fiber (1) with 8 muscle deformation measurement points is written with a Bragg grating by femtosecond laser direct writing method. The laser pulse energy is 50–100 μJ and the repetition frequency is 100–500 Hz. By controlling the moving speed of the three-dimensional displacement platform, eight FBG measurement points with different wavelengths are sequentially formed in the fiber optic sensor. The center wavelength range of each FBG measurement point is 1530–1565 nm, and the center wavelength interval between adjacent FBG measurement points is 3–10 nm. The spacing between the Bragg gratings is set between 100 mm and 400 mm according to the muscle distribution position, thus realizing a multi-point series fiber optic grating array.

3. The lower limb eight-channel muscle deformation FBG fiber optic sensor according to claim 1, characterized in that, The FBG measurement points are the detection locations for muscle deformation, namely the rectus femoris FBG measurement point (2), the vastus lateralis FBG measurement point (3), the biceps femoris FBG measurement point (4), the semitendinosus FBG measurement point (5), the vastus medialis FBG measurement point (6), the gastrocnemius FBG measurement point (7), the tibialis anterior FBG measurement point (8), and the soleus FBG measurement point (9).

4. The lower limb eight-channel muscle deformation FBG fiber optic sensor according to claim 3, characterized in that, Polydimethylsiloxane alkyl PDMS (11) is embedded at each muscle deformation measurement point, and PDMS (11) is combined with a single single-mode optical fiber (1) to form a flexible sensor; PDMS (11) and curing agent are mixed in a ratio between 10:1 and 20:1, and then pre-cured and secondary cured to form a flexible encapsulation (15).

5. The lower limb eight-channel muscle deformation FBG fiber optic sensor according to claim 1, characterized in that, During actual measurement, the fiber optic sensor is spirally wrapped around the leg. The fiber optic sensor starts from the inner thigh, passes through the rectus femoris muscle belly region and the vastus lateralis muscle region in sequence; then it goes around from the outer thigh to the back of the thigh, passing through the biceps femoris and semitendinosus muscle belly regions in sequence; then it goes around from the inner thigh to the front of the thigh, passing through the vastus medialis muscle region. The optical fiber transitions from the outer thigh to the back of the calf near the knee joint, passing through the gastrocnemius muscle belly region; then it circles around the inner side of the calf to the front side of the calf, passing through the tibialis anterior muscle belly region; finally, it circles around the outer side of the calf to the back side of the calf, covering the soleus muscle belly region. This ensures that each muscle measurement point is located on the skin surface of the corresponding muscle; through the attachment structure of the medical sterile dressing, each muscle deformation measurement point is sequentially attached to the skin surface of the corresponding muscle.

6. A lower limb eight-channel muscle deformation FBG fiber optic sensor according to claim 5, characterized in that, The attachment structures are the rectus femoris attachment structure (16), the vastus lateralis attachment structure (17), the biceps femoris attachment structure (18), the semitendinosus attachment structure (19), the vastus medialis attachment structure (20), the gastrocnemius attachment structure (21), the tibialis anterior attachment structure (22), and the soleus attachment structure (23). The flexible encapsulation body (15) of each muscle measuring point can deform synchronously with the human skin surface under the attachment of the sterile dressing structure. Among them, the rectus femoris attachment structure (16) corresponds to the rectus femoris FBG measurement point (2); the vastus lateralis attachment structure (17) corresponds to the vastus lateralis FBG measurement point (3); the biceps femoris attachment structure (18) corresponds to the biceps femoris FBG measurement point (4); the semitendinosus attachment structure (19) corresponds to the semitendinosus FBG measurement point (5); the vastus medialis attachment structure (20) corresponds to the vastus medialis FBG measurement point (6); the gastrocnemius attachment structure (21) corresponds to the gastrocnemius FBG measurement point (7); the tibialis anterior attachment structure (22) corresponds to the tibialis anterior FBG measurement point (8); and the soleus attachment structure (23) corresponds to the soleus FBG measurement point (9). This deformation will cause the FBG grating region (12) in the flexible package (15) to produce corresponding strain, thereby changing the wavelength change fed back by the grating region. This wavelength change is proportional to the strain of the grating region. Ultimately, the muscle deformation is transmitted to the FBG at the muscle deformation measurement point through deformation transmission, and the strain change is linearly reflected by the wavelength of the reflected light, realizing the conversion from muscle deformation signal to light signal wavelength.

7. A lower limb eight-channel muscle deformation FBG fiber optic sensor according to claim 6, characterized in that, The FBG gate area (12) is arranged on the single-mode fiber (1) at a preset spacing.

8. A lower limb eight-channel muscle deformation FBG fiber optic sensor according to claim 7, characterized in that, For each muscle measurement point, after the FBG grid area (12) is written, the single-mode fiber (1) at the position of the FBG grid area (12) is placed on the cover glass (13), with the FBG grid area (12) in the center position; After mixing PDMS and curing agent according to a preset mass ratio, an appropriate amount of the mixture is dropped onto the surface of the glass slide (13) to form a substrate layer.

9. A method for detecting lower limb eight-channel muscle deformation using a fiber optic FBG sensor according to any one of claims 1-8, comprising the following steps: S1. Sensor preparation steps: A single-mode optical fiber (1) with eight muscle deformation measurement points is provided. Eight FBG grid areas (12) are sequentially etched along the axial direction on the single-mode optical fiber (1) to form FBG measurement points (2) for rectus femoris, FBG measurement points (3) for vastus lateralis, FBG measurement points (4) for biceps femoris, FBG measurement points (5) for semitendinosus, FBG measurement points (6) for vastus medialis, FBG measurement points (7) for gastrocnemius, FBG measurement points (8) for tibialis anterior, and FBG measurement points (9) for soleus. Each FBG measurement point serves as the detection location for the corresponding muscle deformation. S2, Flexible Packaging Steps: A flexible encapsulation body (15) formed of polydimethylsiloxane alkyl PDMS (11) is provided at each FBG gate area (12) position, so that the FBG gate area (12) is embedded inside the flexible encapsulation body (15), thereby forming a flexible fiber optic sensing unit that can deform synchronously with human skin and muscles. S3. Sensor installation steps: The single-mode optical fiber (1) is arranged in a spiral manner along the surface of the lower limb of the human body, so that each FBG measuring point corresponds to the muscle belly area of ​​the rectus femoris, vastus lateralis, biceps femoris, semitendinosus, vastus medialis, gastrocnemius, tibialis anterior and soleus muscles, and each flexible encapsulation body (15) is attached to the skin surface of the corresponding muscle through the attachment structure composed of medical sterile dressing. S4. System connection steps: The single-mode fiber (1) is connected to the fiber optic grating demodulator (10), and the fiber optic grating demodulator (10) sends a broadband optical signal to the fiber and obtains the initial reflection center wavelength of each FBG measurement point as a reference value. S5. Deformation signal acquisition steps: During human walking, flexion and extension or other lower limb movements, each target muscle group contracts and stretches, and the deformation is transmitted through the skin to the flexible encapsulation (15), which then acts on the corresponding FBG gate area (12), causing strain at each FBG measuring point and causing a change in the reflected wavelength. S6. Wavelength demodulation steps: The reflection wavelength changes of each FBG measurement point were demodulated in real time using a fiber optic grating demodulator (10), and the wavelength change data of eight muscle measurement points were acquired synchronously under single-channel conditions. S7. Deformation Calculation and Output Steps: Based on the correspondence between Bragg wavelength changes and strain, the wavelength changes at each FBG measurement point are converted into deformation or strain signals of the corresponding muscles, thereby enabling synchronous deformation detection of the rectus femoris, vastus lateralis, biceps femoris, semitendinosus, vastus medialis, gastrocnemius, tibialis anterior, and soleus muscles.

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