A skin-like wearable sensor based on chaotic fiber ring decay oscillation technology

Abstract

The application discloses a kind of wearable sensor based on chaos fiber ring decay ring-down technology, including light source part, fiber ring and data processing device;Light source part is chaos fiber laser;Fiber ring decay ring-down ring includes optical coupler OC-2, optical coupler OC-3, optical isolator ISO and sensing unit;The light splitting ratio of two optical couplers is 95:5, and sensing unit is composed of polydimethylsiloxane packaged fiber bragg grating;The algorithm in data processing device PC includes solving the influence of body surface temperature on FBG stress sensing, the influence of temperature sensitization of PDMS, and the collected chaos signal is autocorrelated and fitted to obtain human motion related data.Carry out human motion detection, solve the influence of body surface temperature on FBG stress sensing.Using PDMS to package FBG, the sensing unit is protected and has the characteristics of skin-like stretchable, and the temperature sensitization of PDMS is easier to measure the body surface temperature.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensors and relates to a fiber optic ring decay sensor, specifically a skin-like wearable sensor based on chaotic fiber optic ring decay technology. Background Technology

[0002] Currently, the demand for flexible sensing devices is growing in the field of medical and health monitoring. In particular, skin-like, stretchable, and wearable stress sensors are essential for a variety of potential applications, including personalized health and rehabilitation monitoring, human motion detection, and soft robotics, enabling real-time and continuous monitoring and providing new opportunities for effective health tracking and improved healthcare quality.

[0003] Many conductive nanomaterials and polymers, such as graphene nanowalls, carbon nanotubes, and Ni polymer composites, have been investigated for use in the design of human body sensors, benefiting from their excellent mechanical flexibility and electrical sensing properties. These electronic sensors can accurately and continuously monitor body temperature, but they suffer from poor biocompatibility due to the use of metallic components. Furthermore, electronic sensors are susceptible to electromagnetic interference (EMI), difficult to miniaturize, and subject to electrical safety issues such as current leakage. A promising alternative for wearable sensor design is the use of fiber optic sensors encapsulated in skin-like materials, which offer skin-like wearability, high sensitivity, light weight, small size, EMI immunity, and inherent electrical safety.

[0004] Fiber Bragg gratings (FBGs) are increasingly attractive for medical applications due to their unique characteristics, such as small size, biocompatibility, immunity to electromagnetic interference, high sensitivity, and multiplexing capabilities. FBGs have been used to develop surgical tools, assistive devices, wearable devices, and biosensors, demonstrating significant potential for medical applications. Current FBG sensors primarily operate on the principle of a broadband light source. After passing through the FBG, a spectrometer is used to measure the reflectance spectrum of the FBG, obtaining the relationship between the center wavelength of the FBG reflectance spectrum and stress or temperature for sensing. A problem arises because the sensing resolution depends on the resolution of the spectrometer used, and spectrometers are generally expensive; higher resolution means higher prices. Using a high-resolution spectrometer increases experimental costs. Furthermore, for sensing units requiring light intensity difference measurements, multiple FBGs are needed for detection at each location. In stress sensing using FBGs, the influence of ambient temperature is often overlooked.

[0005] In recent years, a novel fiber optic sensing technology—fiber optic ring decay (FBG)—has been combined with fiber optic ring-down (FBG) technology, yielding excellent sensing results. By integrating the FBG into the fiber optic ring-down loop, the drift of the FBG's center wavelength caused by temperature or stress is measured and converted into the ring-down time of light within the fiber optic loop. This transforms the wavelength domain change into the time domain, thus eliminating the need for a spectrometer, reducing costs, and improving measurement resolution. Current FBG technologies mostly use pulsed lasers as the light source, with the ring-down time of the pulse intensity as the measured quantity. This pulsed light-based FBG system requires careful design of the fiber optic loop length to avoid crosstalk between pulse signals. Longer loops increase losses within the loop, negatively impacting measurement resolution and pulse signal shape, and the pulsed laser generation device is also relatively complex.

[0006] Polydimethylsiloxane (PDMS, with the molecular formula [Si(CH3)2O)) n PDMS, commonly known as photosensitive silicone, is a reproducible cross-linked elastic polymer material, generally existing in both liquid and solid states. PDMS is optically transparent and, under normal conditions, non-toxic, non-flammable, and possesses good thermal stability, structural plasticity, gas permeability, excellent insulation, and chemical inertness. It is resistant to corrosion, high temperatures, and chemicals, and is also inexpensive, allowing for mass production. Furthermore, its application is simple and quick. Based on these advantages, PDMS is frequently chosen as a sensitizing material for coatings or substrates. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a skin-like wearable sensor based on chaotic fiber ring decay technology.

[0008] A skin-like wearable sensor based on chaotic fiber ring decay technology includes a light source, a fiber ring decay ring, and a data processing device; the light source is a chaotic fiber laser; the fiber ring decay ring includes an optical coupler OC-2, an optical coupler OC-3, an optical isolator ISO, and a sensing unit; wherein the splitting ratio of the two optical couplers is 95:5, and the sensing unit is composed of a polydimethylsiloxane-encapsulated fiber Bragg grating.

[0009] The built-in algorithms of the data processing device PC include addressing the effects of body surface temperature on FBG stress sensing, the effects of PDMS temperature sensitization, and performing autocorrelation and fitting calculations on the collected chaotic signals to obtain human motion-related data.

[0010] According to claim 1, the skin-like wearable sensor is characterized in that the chaotic fiber laser adopts a ring cavity structure, a 980nm semiconductor laser LD is used as the pump source and input to an erbium-doped fiber EDF through a wavelength division multiplexer (WDM), and a 6m long erbium-doped fiber EDF is used as the gain medium; the tunable filter TFGB in the cavity is used to change the output wavelength of the laser, with an adjustment range of 1542-1560nm, and the polarization state of the light is adjusted by a polarization controller PC; the optical isolator ISO determines the unidirectional transmission of light within the ring cavity; 10% of the light is output from the optical coupler OC-1, and 90% of the light continues to circulate within the cavity. The chaotic laser is generated using the nonlinear Kerr effect of the fiber, and the optimal chaotic state is obtained by adjusting the pump source and polarization controller. The output chaotic sequence is observed in real time using an oscilloscope.

[0011] The aforementioned skin-like wearable sensor uses chaotic light generated by a chaotic fiber laser, which enters the fiber ring-down loop through the 5% port of coupler 2. Each time the light circulates through the ring-down loop, the light intensity is attenuated due to losses within the loop. The photodetector PD is connected to the 5% port of optical coupler OC-3. The photodetector PD converts the detected light signal into an electrical signal, which is then displayed on an oscilloscope OSC.

[0012] The aforementioned skin-like wearable sensor, and the data processing device PC with built-in algorithms, include:

[0013] The coefficient of thermal expansion of PDMS is 9.6 × 10⁻⁶. -4 / ℃, the PDMS temperature changes by 20℃ from 20℃ to 40℃, let σ P The stress represents the thermal expansion of the FBG under the influence of PDMS, and T represents the surface temperature.

[0014] c = -13.16416 ± 0.09479(4)

[0015] d = 0.64408 ± 0.0031(5)

[0016] σ P =c+dT(6)

[0017] Based on the Bragg wavelength and grating period formulas for FBG, let the Bragg wavelength (center wavelength) of the reflection spectrum be n, where the effective refractive index of the fiber core is n. eff If the Bragg period is Λ, then

[0018] λ B =2n eff Λ(7)

[0019] The center wavelength shift Δλ B The linear relationship between P and axial stress σ is shown in the following formula, where P eε is the effective photoelastic coefficient, ε is the strain of the FBG, and E is the elastic modulus of the optical fiber, taken as E = 7.0 × 10⁻⁶ in fused silica. 10 Pa; P 11 P 12 ν is the optical stress tensor component, and ν is the Poisson's coefficient of the core material. In fused silica, P 11 =0.121, P 12 =0.270, n eff =1.456, ν=0.17; then

[0020] Δλ B =(1-P e )λ B ε=(1-P e )λ B σ / E(8)

[0021]

[0022] The center wavelength shift Δλ B The linear relationship between temperature and temperature is shown in the following formula:

[0023] Δλ B =λ B K T ΔT(10)

[0024] K T =ξ+α(11)

[0025] Where K T This is the relative temperature sensitivity coefficient of FBG. For fused silica fiber, the thermo-optic coefficient ξ = 0.7 × 10⁻⁶. -5 / ℃, linear thermal expansion coefficient α=5.5×10 -7 Then K T =0.755×10 -5 / ℃;

[0026] Let the wavelength shift of FBG between 20℃ and 40℃ be Δλ. T Where T is the body surface temperature, and T0 = 20℃, then

[0027] Δλ T =λ B K T (T-T0) (12)

[0028] Let Δλ be the wavelength shift caused by the thermal expansion stress of PDMS on the FBG. P ,but

[0029] Δλ P =(1-P e )λ B σP / E=(1-P e )λ B (c+dT) / E(13)

[0030] Assume that the wavelength drift of the FBG is only affected by human motion stress, and is Δλ. F ,but

[0031] Δλ F =(1-P e )λ B σ F / E=(1-P e )λ B (a*x^b) / E(14)

[0032] Let λ be the total wavelength of the FBG within the sensing unit affected by human motion.

[0033] λ=λ B +Δλ T +Δλ P +Δλ F (15)

[0034] Therefore, assuming the body surface temperature is 35℃, T=35℃, σ P = 9.38 N / m 2 ,Δλ T =0.176nm, assuming the overall wavelength of the FBG within the sensing unit affected by human movement at this body surface temperature is λ. 35 ,but

[0035] λ 35 =1550.176nm+(1-P e )λ B (a*x b +c+dT) / E(16)

[0036] The mathematical expressions for the reflection spectrum and chaotic laser spectrum of FBG are as follows:

[0037] P(λ)=P0 exp[-α1(λ-λ0) 2 (17)

[0038] R(λ)=R B exp[-α2(λ-λ B ) 2 (18)

[0039] Here λ0 and λ B These are the center wavelengths of the chaotic laser and FBG reflection spectra, respectively, P0 and R. B α1 and α2 are the power and reflectivity of the chaotic laser and FBG at the center wavelength, respectively. α1 and α2 are the full width at half maximum (FWHM) of the chaotic laser spectrum and the FBG reflection spectrum, respectively.

[0040] The area of ​​overlap between the two is:

[0041]

[0042] The proportion of the overlapping area of ​​the two to the chaotic laser spectrum area is the resulting loss, and the expression for the loss B is:

[0043]

[0044] The decay time of the chaotic autocorrelation peak is:

[0045]

[0046] At this time, the center wavelength of the FBG is the overall wavelength λ affected by human movement during motion, and the body surface temperature is T. Combining formulas (15) and (21), the degree of human movement at this time can be obtained from the decay time result obtained by sensing.

[0047]

[0048] This invention discloses a skin-like wearable sensor based on chaotic autocorrelation fiber ring decay technology. The sensing device consists of two parts: a chaotic fiber laser and a fiber ring decay ring. The chaotic fiber laser employs a ring cavity structure, using a 980nm semiconductor laser as the pump source and a 6m erbium-doped fiber as the gain medium. It generates chaotic laser light using the nonlinear Kerr effect of the fiber. The chaotic laser light enters the fiber ring decay ring through an optical coupler. The fiber ring decay ring consists of two optical couplers, an optical isolator, and a sensing unit. The sensing unit is an FBG encapsulated in PDMS. The elastic modulus of PDMS can be changed by adjusting the mass ratio of PDMS prepolymer to curing agent. Based on the elastic modulus and flexibility of human skin, the PDMS in this invention is prepared by mixing and curing a 10:1 ratio of prepolymer to curing agent. The output of the fiber ring is connected to a photodetector, which is then connected to an oscilloscope. Data from the oscilloscope is acquired and processed by a computer. Sensing and demodulation of the center wavelength of the FBG are achieved by establishing the relationship between the decay time of the chaotic autocorrelation peak in the fiber optic ring decay loop and the degree of human motion.

[0049] The beneficial effects of this invention are: (1) The chaotic laser generated by the chaotic fiber laser has strong anti-interference ability, which can reduce the influence of external noise in the experiment. (2) The autocorrelation of the chaotic sequence is a delta function with a very narrow width. When designing the fiber ring, there is no need to consider the limitation of the ring length on the signal. A shorter ring length can be selected, and the shorter the ring length, the higher the sensitivity. (3) Using FBG as the sensing unit, there is no need to use a spectrometer for demodulation, so that a higher resolution can be achieved. (4) Using the ring decay ring for sensing, there is no need to measure the light intensity difference of the sensing unit, reducing the number of FBGs used. (5) When human movement is performed, the influence of body surface temperature on FBG stress sensing is solved. (6) PDMS is used to encapsulate FBG, which protects the sensing unit and has skin-like stretchable characteristics. The temperature enhancement effect of PDMS makes it easier to measure body surface temperature. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the structure of the chaotic fiber laser used in this invention.

[0051] Figure 2 This is the output timing diagram of the chaotic fiber laser used in this invention.

[0052] Figure 3 This is the output spectrum of the chaotic fiber laser used in this invention.

[0053] Figure 4 This is the autocorrelation graph of the chaotic sequence output by the chaotic fiber laser used in this invention.

[0054] Figure 5 This is a schematic diagram of the optical fiber fading ring used in this invention.

[0055] Figure 6 This is a cascading diagram of the chaotic autocorrelation peaks in an optical fiber cascading loop.

[0056] Figure 7 It is a simulation model of the sensing unit in COMSOL.

[0057] Figure 8 This is a diagram showing the location of the domain probe FBG in COMSOL.

[0058] Figure 9 This refers to the stress variation of the FBG under various simulation levels in COMSOL.

[0059] Figure 10 This is a schematic diagram of an arm (the area marked in bold is the sensing unit).

[0060] Figure 11 This is a schematic diagram of the abdomen (the black area represents the sensing unit).

[0061] Figure 12This is a schematic diagram of the neck (the area marked in bold is the sensing unit).

[0062] In the diagram, LD: semiconductor laser, WDM: wavelength division multiplexer, EDF: erbium-doped fiber, SMF: single-mode fiber, TFBG: tunable filter, OC: optical coupler, PC: polarization controller, ISO: optical isolator, FBG: fiber Bragg grating, PDMS: polydimethylsiloxane, PD: photodetector, OSC: oscilloscope. Detailed Implementation

[0063] The present invention will be described in detail below with reference to specific embodiments.

[0064] The skin-like wearable sensor based on chaotic fiber ring decay technology includes a light source, a fiber ring decay ring, and a data processing device.

[0065] refer to Figure 1 This is a schematic diagram of the light source component of the present invention: a chaotic fiber laser. The chaotic fiber laser adopts a ring cavity structure. A 980nm semiconductor laser (LD) is used as the pump source and input to an erbium-doped fiber (EDF) via a wavelength division multiplexer (WDM). A 6m long erbium-doped fiber (EDF) serves as the gain medium. A tunable filter (TFGB) within the cavity is used to change the output wavelength of the laser, with an adjustment range of 1542-1560nm. The polarization state of the light is adjusted by a polarization controller (PC), and an optical isolator (ISO) ensures unidirectional light transmission within the ring cavity. 10% of the light is output from the optical coupler (OC-1), while 90% continues to circulate within the cavity. The chaotic laser is generated using the nonlinear Kerr effect of the fiber. The optimal chaotic state is obtained by adjusting the pump source and polarization controller. The output chaotic sequence can be observed in real time using an oscilloscope.

[0066] refer to Figure 2 The image shows the output timing diagram of the chaotic fiber laser used in this invention. By adjusting the pump current and polarization controller, the timing diagram on the oscilloscope shows that the output of the chaotic fiber laser gradually enters a chaotic state, exhibiting a disordered, noise-like timing sequence. Based on this characteristic of chaotic sequences, after performing autocorrelation operations, it exhibits a delta-like function shape with an extremely narrow width, as shown in the reference diagram. Figure 4 As shown, this makes the application of chaotic light more widespread.

[0067] refer to Figure 3 The image shows the spectrum of the chaotic fiber laser used in this invention. Different chaotic laser output wavelengths can be obtained by adjusting the filter.

[0068] refer to Figure 5This is a schematic diagram of the fiber optic ring-down ring structure used in this invention. The fiber optic ring-down ring includes optical coupler OC-2, optical coupler OC-3, optical isolator ISO, and sensing unit. The splitting ratio of both optical couplers is 95:5. The sensing unit is composed of a polydimethylsiloxane-encapsulated fiber Bragg grating. Chaotic light generated by the chaotic fiber laser enters the fiber optic ring-down ring through the 5% port of coupler 2. Each time the light circulates within the ring, the light intensity decreases due to losses within the ring. A photodetector PD is connected to the 5% port of optical coupler OC-3. The photodetector PD converts the detected optical signal into an electrical signal, which is then displayed on an oscilloscope OSC.

[0069] The data processing device incorporates algorithms to address the effects of body surface temperature on FBG stress sensing, the temperature-enhancing effect of PDMS, and to perform correlation and fitting calculations on the acquired chaotic signals to obtain human motion-related data. The chaotic autocorrelation peak decay obtained in this device is as follows: Figure 6 As shown in the figure, the chaotic autocorrelation peak exhibits an exponential decay of e^(-e), with the peak value decreasing to e^(-e ... -1 The time is the required ring-down time. The distance between two adjacent autocorrelation peaks in the figure is the time it takes for light to travel one revolution in the ring-down ring. Based on this, the length of the optical fiber ring-down ring used can be calculated to be 5.26m.

[0070] Simulations were performed using a COMSOL-based sensor unit. The entire FBG-containing optical fiber was treated as a quartz cylinder of fiber thickness, covered with a cuboid of PDMS. A cylinder was added to represent a human body part, and its motion was simulated. The sensor unit simulation model was referenced. Figure 7 As shown. Parameters for optical fiber, PDMS, and human skin and bone materials are set, including Young's modulus, Poisson's ratio, and key skin friction coefficients. A domain probe is set to simulate the FBG and its stress and displacement simulation data are exported. The FBG position is referenced. Figure 8 The area indicated by the middle arrow is not located at the direct point of bending. The sensing unit is fixed at both ends to simulate the tensile stress on the FBG when worn on the skin and during movement. A human body part is designated as the displacement, and the sensing unit is moved downwards along the Z-axis at a speed of 0.2 mm / s, compressing it until the fiber is stretched to its maximum ideal range. This simulates the compressive and tensile stress exerted on the sensing unit by joints or muscles during human movement. Since the simulation process for the specified displacement is from 0 mm to 4 mm, the downward compression and bending stretching simulation of the human body part is evenly divided into nine bending levels from level 0 to level 4, based on the displacement distance. Level 0 represents the initial state with no applied stress, i.e., a straight state where the sensing unit does not bend. Level 4 represents the maximum bending strain, i.e., the maximum ideal stretching degree of the sensing unit. The simulation yields a reference value for the stress change of the FBG at each level. Figure 9 As shown, σ FLet σ represent the tensile stress on the FBG, and x represent the stress level. Assume its variation function is fitted as σ. F =F(x), then

[0071] a=15597900±46939.90744(1)

[0072] b=1.88608±0.00247(2)

[0073] σ F =F(x)=a*x^b(3)

[0074] Simulations were performed to enhance the temperature sensing sensitivity of PDMS. The coefficient of thermal expansion of PDMS is 9.6 × 10⁻⁶. -4 / ℃, the PDMS temperature changes by 20℃ from 20℃ to 40℃, let σ P The stress represents the thermal expansion of the FBG under the influence of PDMS, and T represents the surface temperature.

[0075] c = -13.16416 ± 0.09479(4)

[0076] d = 0.64408 ± 0.0031(5)

[0077] σ P =c+dT(6)

[0078] Based on the Bragg wavelength and grating period formulas for FBG, let the Bragg wavelength (center wavelength) of the reflection spectrum be n, where the effective refractive index of the fiber core is n. eff If the Bragg period is Λ, then

[0079] λ B =2n eff Λ(7)

[0080] The center wavelength shift Δλ B The linear relationship between P and axial stress σ is shown in the following formula, where P e ε is the effective photoelastic coefficient, ε is the strain of the FBG, and E is the elastic modulus of the optical fiber (taken as E = 7.0 × 10⁻⁶ in fused silica). 10 Pa). P 11 P 12 ν is the optical stress tensor component, and ν is the Poisson's coefficient of the core material. In fused silica, P 11 =0.121, P 12 =0.270, n eff =1.456, ν=0.17. Therefore...

[0081] Δλ B =(1-P e )λ B ε=(1-P e)λ B σ / E(8)

[0082]

[0083] The center wavelength shift Δλ B The linear relationship between temperature and temperature is shown in the following formula:

[0084] Δλ B =λ B K T ΔT(10)

[0085] K T =ξ+α(11)

[0086] Where K T This is the relative temperature sensitivity coefficient of FBG. For fused silica fiber, the thermo-optic coefficient ξ = 0.7 × 10⁻⁶. -5 / ℃, linear thermal expansion coefficient α=5.5×10 -7 Then K T =0.755×10 -5 / ℃.

[0087] Based on the above sensing principles and combined with the stress and other data simulated by the COMSOL-simulated sensing model, simulation was performed using MATLAB, with the center wavelength λ selected. B =1550.000nm, the following simulation results can be obtained:

[0088] Let the wavelength shift of FBG between 20℃ and 40℃ be Δλ. T Where T is the body surface temperature, and T0 = 20℃, then

[0089] Δλ T =λ B K T (T-T0) (12)

[0090] Let Δλ be the wavelength shift caused by the thermal expansion stress of PDMS on the FBG. P ,but

[0091] Δλ P =(1-P e )λ B σ P / E=(1-P e )λ B (c+dT) / E(13)

[0092] Assume that the wavelength drift of the FBG is only affected by human motion stress, and is Δλ. F ,but

[0093] Δλ F =(1-Pe )λ B σ F / E=(1-P e )λ B (a*x^b) / E(14)

[0094] Let λ be the total wavelength of the FBG within the sensing unit affected by human motion.

[0095] λ=λ B +Δλ T +Δλ P +Δλ F (15)

[0096] Therefore, assuming the body surface temperature is 35℃, T=35℃, σ P = 9.38 N / m 2 ,Δλ T =0.176nm, assuming the overall wavelength of the FBG within the sensing unit affected by human movement at this body surface temperature is λ. 35 ,but

[0097] λ 35 =1550.176nm+(1-P e )λ B (a*x b +c+dT) / E(16)

[0098] The simulation of the relationship between the FBG center wavelength and the fiber ring fading time in the experimental setup used in this invention is as follows:

[0099] The mathematical expressions for the reflection spectrum and chaotic laser spectrum of FBG are as follows:

[0100] P(λ)=P0 exp[-α1(λ-λ0) 2 (17)

[0101] R(λ)=R B exp[-α2(λ-λ B ) 2 (18)

[0102] Here λ0 and λ B These are the center wavelengths of the chaotic laser and FBG reflection spectra, respectively, P0 and R. B α1 and α2 are the power and reflectivity of the chaotic laser and FBG at the center wavelength, respectively. α1 and α2 are the full width at half maximum (FWHM) of the chaotic laser spectrum and the FBG reflection spectrum, respectively.

[0103] The area of ​​overlap between the two is:

[0104]

[0105] The proportion of the overlapping area of ​​the two to the chaotic laser spectrum area is the resulting loss, and the expression for the loss B is:

[0106]

[0107] The decay time of the chaotic autocorrelation peak is:

[0108]

[0109] In summary, the initial center wavelength λ of the FBG used in the experiment... B The wavelength is 1550.000 nm, the reflectivity is 12%, and the full width at half maximum (FWHM) is ≤0.25 nm. The chaotic laser wavelength is set to 1549.998 nm, and the length of the fiber ring-down loop is 5.26 m.

[0110] At this time, the center wavelength of the FBG is the overall wavelength λ affected by human movement during motion, and the body surface temperature is T. Combining formulas (15) and (21), the degree of human movement at this time can be obtained from the decay time results obtained by sensing.

[0111]

[0112] When performing human motion sensing, the sensing unit is attached to the skin of the area to be measured using medical tape. In the absence of motion, the FBG (Fast-Induced Geometric Governance) is only affected by temperature. The FBG wavelength drift can be calculated based on the ring-down time, and the skin temperature can be determined from the wavelength drift. This is used to calibrate the FBG center wavelength when the sensing unit is worn, before motion detection. This method measures the skin temperature of the sensing site while avoiding the influence of temperature on FBG stress sensing. (Reference) Figure 10 The wearable device shown can perform sensor detection of forearm muscle movement when clenching a fist and exerting force; Reference Figure 11 The wearable device shown can sense respiratory rate by detecting abdominal expansion and contraction movements; Reference Figure 12 The wearable device shown can detect and alert users who have been working with their heads down for extended periods by placing the sensing unit vertically against their neck.

[0113] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A skin- like wearable sensor based on chaotic fiber ring decay-oscillation technology, characterized in that, The application relates to a chaotic fiber laser sensor for human body motion detection, which comprises a light source part, a fiber ring and a data processing device; the light source part is a chaotic fiber laser; the fiber ring comprises an optical coupler OC-2, an optical coupler OC-3, an optical isolator ISO and a sensing unit; the splitting ratio of the two optical couplers is 95:5, and the sensing unit is composed of a polydimethylsiloxane (PDMS) packaged fiber Bragg grating (FBG); the data processing device PC has built-in algorithms, which include solving the influence of the body surface temperature on the FBG stress sensing, the temperature sensitization effect of the PDMS, and performing autocorrelation operation and fitting calculation on the collected chaotic signals to obtain human body motion related data. The data processing device PC has built-in algorithms, which include: represents the tensile stress of FBG, x represents the grade, and the change function relationship is fitted as , then: a=15597900±46939.90744（1） ； b=1.88608±0.00247（2）； （3）； The thermal expansion coefficient of PDMS is 9.6 x 10 -4 / °C, the temperature of PDMS changes from 20 °C to 40 °C by 20 °C, and the temperature of the body surface is set to 37 °C. The stress of FBG caused by the thermal expansion of PDMS is represented by T, and the body surface temperature is represented by T. c= ±0.09479（4）； d=0.64408±0.0031（5）； （6）； Based on the Bragg wavelength and grating period formulas for FBG, let the Bragg wavelength (center wavelength) of the reflection spectrum be n, where the effective refractive index of the fiber core is n. eff If the Bragg period is Λ, then: =2 （7）； amount of shift of the center wavelength linear relationship between the axial stress is shown by the following equation, where, is the effective photoelastic coefficient, is the strain of the FBG, E is the elastic modulus of the optical fiber, and ; , is the optical stress tensor component, is the Poisson's ratio of the core material; in fused silica, , , then: （8）； （9）； Amount of shift of center wavelength The linear relationship with temperature is shown in the following equation: （10）； （11）； wherein is the relative temperature sensitivity coefficient of the FBG, for a fused silica optical fiber, the thermo-optic coefficient , the linear thermal expansion coefficient then ; let the wavelength shift variation of the FBG at 20-40℃ be , T is the body surface temperature, T0=20℃, then: （12）； Let FBG wavelength shift change caused by PDMS thermal expansion stress be then: （13）； Let FBG only be subject to the body motion stress wavelength shift changes then: （14）； Let the total wavelength of the FBG in the sensing unit affected by the human body movement be Then: （15）； So, assuming the body surface temperature is 35℃, T=35℃, N / m 2 , =0.176nm, assuming the total wavelength of the FBG in the sensing unit affected by the human body movement at this body surface temperature is , then: （16）； The mathematical expressions of the reflection spectrum of the FBG and the chaotic laser spectrum are respectively: （17）； （18）； and are the center wavelengths of the chaotic laser and the FBG reflection spectrum, respectively, and are the power and reflectivity of the chaotic laser and the FBG at the center wavelength, respectively; and are the full width at half maximum of the chaotic laser spectrum and the FBG reflection spectrum, respectively; the overlapping area of the two is: （19）； The proportion of the overlapping area of the two in the area of the chaotic laser spectrum is the loss caused, and the expression of the loss B is: （20）； The ring-down time of the chaotic autocorrelation peak is: （21）； At this time, the FBG center wavelength is the overall wavelength affected by the human body movement , the body surface temperature is T, and the degree of human body movement at this time can be obtained according to the sensing decay time result by combining formula (15) and formula (21), and the following is obtained: ； （22）。 2. The skin-like wearable sensor of claim 1, wherein, The chaotic fiber laser adopts a ring cavity structure, a 980nm semiconductor laser LD is used as a pumping source and is input into an erbium-doped fiber EDF through a wavelength division multiplexer WDM, and a 6m-long erbium-doped fiber EDF is used as a gain medium; an adjustable filter TFGB in the cavity is used to change the output wavelength of the laser, the adjustment range is 1542-1560nm, a polarization controller PC is used to adjust the polarization state of light, and an optical isolator ISO is used to determine the one-way transmission of light in the ring cavity; 10% of light is output from an optical coupler OC-1, and 90% of light continues to circulate in the cavity; the nonlinear Kerr effect of the fiber is used to realize the generation of chaotic laser, the best chaotic state is obtained by adjusting the pumping source and the polarization controller, and the output chaotic sequence is observed in real time by an oscilloscope.

3. The skin-like wearable sensor of claim 1, wherein, The chaotic light generated by the chaotic fiber laser enters the fiber ring through the 5% port of the coupler 2, and the light intensity is attenuated due to the loss in the ring after circulating in the ring for one cycle; the photoelectric detector PD is connected with the 5% port of the optical coupler OC-3, the photoelectric detector PD converts the detected optical signal into an electrical signal, and then the oscilloscope OSC displays.

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