CN114895404B - Flexible optical waveguide and preparation method and application thereof - Google Patents
Flexible optical waveguide and preparation method and application thereof Download PDFInfo
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Classifications
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- G—PHYSICS
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/1221—Basic optical elements, e.g. light-guiding paths made from organic materials
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- A43—FOOTWEAR
- A43B—CHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
- A43B3/00—Footwear characterised by the shape or the use
- A43B3/34—Footwear characterised by the shape or the use with electrical or electronic arrangements
-
- A—HUMAN NECESSITIES
- A43—FOOTWEAR
- A43B—CHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
- A43B3/00—Footwear characterised by the shape or the use
- A43B3/34—Footwear characterised by the shape or the use with electrical or electronic arrangements
- A43B3/44—Footwear characterised by the shape or the use with electrical or electronic arrangements with sensors, e.g. for detecting contact or position
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Length Measuring Devices By Optical Means (AREA)
Abstract
The invention discloses a flexible optical waveguide, a preparation method and application thereof, and relates to the technical field of sensors. The absorption and scattering of the light by the graphite particles increase the attenuation of the light transmitted from the optical waveguide, thereby improving the detection sensitivity of the flexible optical waveguide sensor. The obtained flexible optical waveguide has the characteristics of high sensitivity, good repeatability and larger stretching ratio, and static and dynamic responses show stable, reliable, sensitive and repeatable performances within the strain range of 90%. The method can be applied to wearable flexible detection equipment, and has wide market prospect.
Description
Technical Field
The invention belongs to the technical field of sensors, and particularly relates to a flexible optical waveguide, a preparation method and application thereof.
Background
At present, the development of stretchable flexible materials capable of conforming to complex curved surfaces has led to a great deal of attention in the flexibility of conventional rigid strain sensors. Particularly in the field of wearable devices, assisted medical and intelligent robotics, such as assisted medical detection devices, human joint motion recognition, prosthetic haptic sensations, and the like. The flexible strain sensor needs to have a high tensile property so as to be able to conform to the complex interface of bending, meet the tensile deformation caused by joint movement, and have a durable durability and a high sensitivity. Miniaturization is a trend of sensors, which makes electronic sensors likely to leak current due to insufficient insulation, while electronic sensors are very sensitive to electromagnetic interference. Thus, there are still difficulties and challenges in practical popularization and application of flexible electronic sensors.
In contrast, the advantages of the strain sensor based on the flexible optical waveguide are highlighted, and the flexible optical waveguide has the characteristics of electromagnetic interference resistance, light weight, small volume, low hysteresis, large bandwidth, convenient signal light transmission and the like of the traditional optical waveguide made of silicon dioxide (the expansion rate is less than 1%) or plastic polymer (the expansion rate is less than 10%), and also has the advantages of high flexibility and large-scale scalability. However, the stretching of the superficial skin due to the movement of the human body joints reaches 30%, which puts higher demands on the stretching performance and sensitivity of the flexible strain sensor in the wearable detection device.
Disclosure of Invention
The invention provides a flexible optical waveguide, a preparation method and application thereof, which are used for solving the problems that the existing flexible sensor is insufficient in tensile property, low in sensitivity, easy to be subjected to electromagnetic interference, low in signal-to-noise ratio during weak signal detection and difficult to apply to wearable detection equipment.
The invention is realized by the following technical scheme:
in a first aspect, the present invention provides a method of making a flexible optical waveguide comprising:
preparing a silicone pre-elastomer from polydimethylsiloxane;
uniformly dispersing graphite particles with the particle size of 0.5-4 mu m in the organosilicon pre-elastomer, wherein the mass percentage concentration of the added graphite particles is 2 multiplied by 10 -3 ～1×10 -2 wt%; and
and standing the obtained mixture in a negative pressure environment to eliminate bubbles, injecting the mixture into a tubular mold, closing two ends of the tubular mold, heating and solidifying the mixture, and performing demolding treatment.
Further, in a preferred embodiment of the present invention, the heating temperature in the above-mentioned heat curing step is 70 to 90 ℃ and the curing time is 0.8 to 1.2 hours.
Further, in a preferred embodiment of the present invention, the inner diameter of the tubular mold is 0.5 to 2mm.
Further, in a preferred embodiment of the present invention, the negative pressure environment has a pressure of 0.8 to 1.2 kg.f/cm 2 。
Further, in a preferred embodiment of the present invention, the silicone elastomer is prepared by mixing polydimethylsiloxane and a curing agent according to a mass ratio of 9-11:1.
In a second aspect, the present invention provides a flexible optical waveguide produced by the above-described production method.
In a third aspect, the present invention provides a flexible optical waveguide strain sensor comprising: light emitting diodes, photodiodes and flexible optical waveguides as above; the two ends of the flexible optical waveguide are provided with optical fiber connectors, and the flexible optical waveguide is respectively connected with the light emitting diode and the photosensitive diode through the optical fiber connectors at the two ends.
Further, in a preferred embodiment of the present invention, the optical fiber connector has a stepped through hole penetrating along the long axis direction, and the flexible optical waveguide extends into the stepped through hole with a corresponding aperture and coincides with the optical coupling surface of the light emitting diode or the photodiode butted with the other end of the stepped through hole.
In a fourth aspect, the present invention provides an application of the flexible optical waveguide in a wearable flexible detection device.
In a fifth aspect, the invention provides an optical waveguide type intelligent shoe, which comprises a power module, a control module, a signal acquisition module, a signal processing module, a voice module and a signal transmitting module which are electrically connected with each other;
the signal acquisition module comprises the flexible optical waveguide sensor, and the flexible optical waveguide sensor is arranged at the metacarpophalangeal joint of the sole.
Compared with the prior art, the invention has at least the following technical effects:
according to the flexible optical waveguide, the preparation method and the application thereof, the graphite particles are doped in the Polydimethylsiloxane (PDMS), the doped graphite particles are uniformly distributed in the space of the PDMS optical waveguide, and the attenuation of light transmitted from the optical waveguide is increased due to the absorption and scattering of the graphite particles to the light, so that the detection sensitivity of the flexible optical waveguide sensor is improved. The obtained flexible optical waveguide has the characteristics of high sensitivity, good repeatability and larger stretching ratio, and static and dynamic responses show stable, reliable, sensitive and repeatable performances within the strain range of 90%. The method can be applied to wearable flexible detection equipment, and has wide market prospect.
The flexible optical waveguide strain sensor provided by the invention has larger flexibility and tensile property so as to be capable of being attached to a complex interface. The stretching of the surface skin caused by the movement of the joints of the human body can reach 30%, the stretching strain of the flexible strain sensor can reach 90%, the stretching deformation of the surface skin caused by the movement of the joints and muscles of the human body can be completely met, and the limitation of the flexible sensor as a wearable flexible sensor can be completely overcome. And has durable durability and high sensitivity.
The optical waveguide type intelligent shoe provided by the invention adopts the strain sensor of the flexible optical waveguide as the signal acquisition module of the intelligent shoe, has the advantages of high flexibility and large-scale scalability, and can realize step counting and speed monitoring of sports. Be applied to auxiliary medical treatment, let leg disease personnel wear this intelligent shoes and carry out rehabilitation training, observe and compare the waveform similarity degree that corresponds the detection when two feet walk, can accurate diagnosis leg disease patient's recovered situation.
Drawings
FIG. 1 is a schematic diagram of a flexible optical waveguide fabrication according to embodiment 1 of the present invention;
FIG. 2 is a schematic structural diagram of a flexible optical waveguide sensor according to embodiment 4 of the present invention;
FIG. 3 is a flow chart of the flexible optical waveguide sensor in example 4 of the present invention;
FIG. 4 is a schematic structural diagram of an optical fiber connector according to embodiment 4 of the present invention;
FIG. 5 is a schematic view of an optical waveguide type intelligent shoe according to embodiment 5 of the present invention;
FIG. 6 is a schematic diagram illustrating the operation of the signal acquisition module according to embodiment 5 of the present invention;
FIG. 7 is a schematic diagram showing the operation principle of the optical waveguide type intelligent shoe according to embodiment 5 of the present invention;
fig. 8 a-8 c are graphs showing the optical loss versus wavelength for different graphite doping conditions in experimental example 1 of the present invention. (a) Parameters of doped graphite are 4 mu m,0, 1 multiplied by 10 -2 、5×10 -3 、2×10 -3 wt%. (b) Parameters of doped graphite are 1 μm,0, 1×10 -2 、5×10 -3 、2×10 -3 wt%. (c) Doped graphite parameters of 0.5 μm,0, 1×10 -2 、5×10 -3 、2×10 -3 wt％；
FIG. 9 is a photograph of 745nm beam incident on doped PDMS prepolymer in Experimental example 2 of the present invention. (a) doping 0.5 μm polyethylene particles. (b) doping 0.5 μm graphite particles;
fig. 10a to 10b show doping parameters c=5×10 in experimental example 2 of the present invention -3 wt%, particle size 0.5 μm. (a) The optical loss and the length of the doped and undoped optical waveguides are corresponding. (b) the length of the optical waveguide was measured 100 times during the stretching cycle. The embedded picture is the initial length corresponding to the length of the 2cm long optical waveguide installed and the length of the strain reaching 100% on the tensile testing device;
FIG. 11 is a graph showing the optical loss with the stretching and releasing at various strain levels in experimental example 2 of the present invention;
fig. 12a to 12c show the optical waveguide sensing mechanism (a) in experimental example 3 of the present invention. (b) an optical waveguide body structure. (c) a strain test;
fig. 13 a-13 d show the change in the strain to 100% attenuation spectrum corresponding to the wavelength of light in experimental example 3 of the present invention. (a) - (c) doping concentration 1X 10 -2 The particle sizes of the particles are respectively 4 mu m,1 mu m and 0.5 mu m. (d) Doping concentration 5×10 -3 wt%, particle size of the particles is 0.5 μm;
fig. 14a to 14e are schematic views showing the structure of the optical waveguide sensor (a) in experimental example 4 of the present invention. (b) sensor physical photographs. (c) dynamic test. The illustration is a smart shoe prototype. (d) - (e) walking at 5km/h, respectively, corresponding waveforms detected when running at 8 km/h;
fig. 15a to 15e show the embodiment of the present invention in which (a) the optical waveguide sensor is integrated at the index finger position of the glove to detect the finger motion in real time, and i-v corresponds to five motion gestures of the finger. (b) Photo of optical loss profile corresponding to finger i-v pose (c) optical waveguide sensor was affixed to the throat of volunteer. (d) - (e) sound the corresponding optical loss waveforms of "hello", "nih and hao", respectively, in rhythm.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the following examples, which are to be construed as merely illustrative and not limitative of the scope of the invention, but are not intended to limit the scope of the invention to the specific conditions set forth in the examples, either as conventional or manufacturer-suggested, nor are reagents or apparatus employed to identify manufacturers as conventional products available for commercial purchase.
The polydimethylsiloxane and curing agent used in this application are silicone elastomers sold under the trade name SYLGARD 184, and the ceramic silicone 10:1 sealant is provided as a two-part liquid component kit. In use, after the liquid components are thoroughly mixed, the mixture cures to form a flexible elastomer.
The following describes specific embodiments of the present invention in detail. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.
Example 1
The embodiment provides a flexible optical waveguide, and a preparation method thereof includes:
(1) The silicone pre-elastomer was prepared in a mass ratio of Polydimethylsiloxane (PDMS) to curing agent of 10:1.
(2) According to the mass percentage concentration of 5 multiplied by 10 -3 A certain amount of graphite particles (the particle diameter of the main particles is 0.5 μm) are added into the organosilicon pre-elastomer, and the mixture is fully stirred, so that the graphite particles are uniformly distributed in the organosilicon pre-elastomer. Next, the PDMS pre-elastomer was put in a negative pressure vessel (1.0 kg. F/cm 2 I.e. a force of 1 kg acts on cm 2 Pressure above) for about 5 minutes to ensure removal of the incorporated air bubbles, and the air bubble-removed PDMS pre-elastomer was introduced into the syringe with care to avoid re-air entrainment during the introduction.
(3) The inner surface of the tubular mold with an inner diameter of 2mm was sprayed with a release agent, and the injection port of the syringe was aligned with one end of the tubular mold, and PDMS pre-elastomer was injected as shown in fig. 1. In order to avoid overflow of the pre-elastomer, plugs are worn at two ends of the tubular mold after filling. And put into an oven for high temperature curing (80 ℃ C., 1 h). Finally, demoulding, namely aligning an injection port of the injector filled with water to one end of the tubular mould, and extruding the solidified PDMS from the tubular mould by water pressure.
Example 2
The embodiment provides a flexible optical waveguide, and a preparation method thereof includes:
(1) The organic pre-silicone elastomer was prepared in a mass ratio of Polydimethylsiloxane (PDMS) to curing agent of 10:1.
(2) According to the mass percentage concentration of 1 multiplied by 10 -2 wt% a certain amount of graphite particles (the particle diameter of the main particles is 2 μm) are added to the silicone pre-elastomer, and the mixture is sufficiently stirred to uniformly distribute the graphite particles in the silicone pre-elastomer. Next, the PDMS pre-elastomer was put in a negative pressure vessel (0.8 kg. F/cm 2 ) The internal rest was carried out for about 6 minutes to ensure removal of the incorporated air bubbles, and the air bubble-removed PDMS pre-elastomer was introduced into the syringe, carefully avoiding re-air incorporation during the introduction.
(3) Spraying a release agent on the inner surface of a tubular mold with the inner diameter of 1mm, aligning an injection port of an injector with one end of the tubular mold, and injecting a PDMS pre-elastomer. In order to avoid overflow of the pre-elastomer, plugs are worn at two ends of the tubular mold after filling. And put into an oven for high temperature curing (70 ℃ C., 1.2 h). Finally, demoulding, namely aligning an injection port of the injector filled with water to one end of the tubular mould, and extruding the solidified PDMS from the tubular mould by water pressure.
Example 3
The embodiment provides a flexible optical waveguide, and a preparation method thereof includes:
(1) The organic pre-silicone elastomer was prepared in a mass ratio of Polydimethylsiloxane (PDMS) to curing agent of 10:1.
(2) According to the mass percentage concentration of 1 multiplied by 10 -3 wt% a certain amount of graphite particles (the particle diameter of the main particles is 4 μm) was added to the silicone pre-elastomer, and the mixture was sufficiently stirred to uniformly distribute the graphite particles in the silicone pre-elastomer. Next, the PDMS pre-elastomer was put in a negative pressure vessel (1.2 kg. F/cm 2 ) The internal rest was carried out for about 4 minutes to ensure removal of the incorporated air bubbles, and the air bubble-removed PDMS pre-elastomer was introduced into the syringe, carefully avoiding re-air incorporation during the introduction.
(3) Spraying a release agent on the inner surface of a tubular mold with the inner diameter of 0.5mm, aligning an injection port of an injector with one end of the tubular mold, and injecting a PDMS pre-elastomer. In order to avoid overflow of the pre-elastomer, plugs are worn at two ends of the tubular mold after filling. And put into an oven for high temperature curing (90 ℃ C., 0.8 h). Finally, demoulding, namely aligning an injection port of the injector filled with water to one end of the tubular mould, and extruding the solidified PDMS from the tubular mould by water pressure.
Example 4
The present embodiment provides a flexible optical waveguide strain sensor, whose structure is shown in fig. 2, comprising:
the light emitting diode 3, the photodiode 4, and the flexible optical waveguide 2 provided in the above embodiments 1 to 3, the optical fiber connectors 1 are provided at both ends of the flexible optical waveguide 2, and the flexible optical waveguide 2 is connected to the light emitting diode 3 and the photodiode 4 through the optical fiber connectors 1 at both ends, respectively.
The flexible optical waveguide strain sensor is prepared by bonding the two ends of the flexible optical waveguide 2 to the optical fiber connectors 1 respectively, as shown in fig. 3. As shown in fig. 4, the inner diameter of the through hole in the optical fiber connector 1 is stepped, and the optical fiber connector 1 has a small end 11 and a large end 12. The inner diameter of the small end 11 is 2mm (equal to the outer diameter of the flexible optical waveguide 2), and the flexible optical waveguide 2 can be inserted into the optical fiber connector from the small end 11 to go deep 5mm. The optical fiber connector 1 is provided with a through hole 13 for dropping ultraviolet curing glue at the small end 11. After the flexible optical waveguide 2 is in butt joint with the optical fiber connector 1, ultraviolet curing glue is dripped from the through hole 13, so that two ends of the flexible optical waveguide 2 are respectively adhered and fixed with the optical fiber connector 1 through the ultraviolet curing glue. The inner diameter of the big end 12 of the optical fiber connector 1 is 3mm, which is slightly larger than the outer diameters of the light emitting diode 3 and the photodiode 4, so that the light emitting diode 3 and the photodiode 4 can be in butt joint with the corresponding optical fiber connector 1. The optical fiber connectors 1 at the two ends of the flexible optical waveguide 2 are respectively abutted with the light emitting diode 3 serving as a light source and the detected photodiode 4, and the light emitting diode 3 or the photodiode 4 can be overlapped with the optical coupling surface of the optical waveguide. And the light emitting diode 3 and the photosensitive diode 4 are respectively packaged by soft sleeves. Thus, the flexible optical waveguide sensor is manufactured.
Example 5
The embodiment provides an optical waveguide type intelligent shoe, the structure of which is shown in fig. 5, and the intelligent shoe comprises a power module, a control module, a signal acquisition module, a signal processing module, a voice module and a signal transmitting module which are electrically connected with each other; wherein the signal acquisition module contains the flexible optical waveguide strain sensor prepared in example 4.
The preparation method comprises the following steps: the flexible optical waveguide sensor manufactured in example 4 was packaged and then embedded in the joint of the sole of the intelligent shoe. The other modules comprise a power supply module, a control module, a signal processing module and a voice module, wherein the signal transmitting module is respectively arranged in the middle of the intelligent sole, all the modules are electrically connected through a CAN wire and are subjected to integral packaging treatment, and thus the intelligent shoe is prepared.
The detection method of the intelligent shoe comprises the following steps: the method comprises the steps that an intelligent shoe starting switch is turned on, a control module in the intelligent shoe wakes up, the states of all other modules in the intelligent shoe are subjected to self-checking, the self-checking in 3S is finished, and if the states of all the modules are normal, a voice module prompts that the modules are normal; if a certain module feeds back the fault in the self-checking process, the language module prompts the fault. If the voice module has no prompt after the self-checking process is finished, the voice module can be judged to be faulty. If the state of each module is normal, each module is in a standby state after being started, and the control module distributes power according to the power of each module, so that each module can work normally.
The intelligent shoe is applied to rehabilitation training of leg disease personnel, the working principle of a signal acquisition module is shown in fig. 6, the intelligent sole part is circularly bent and deformed along with walking, a flexible optical waveguide sensor of the signal acquisition module embedded at the joint of the intelligent sole is stretched and deformed along with bending of the sole, then the light beam passing through the inside of the optical waveguide is absorbed and scattered to change after stretching, and then the light power received by a photodiode is correspondingly changed along with the bending degree, namely, the physical change of movement of the leg disease personnel enables the flexible optical waveguide sensor of the signal acquisition module of the intelligent sole to carry out optical modulation, so that the light power received by the photodiode is correspondingly changed. The light-sensitive diode converts the received optical signal into an electric signal and transmits the electric signal to the signal processing module.
The working principle of the intelligent shoe is shown in fig. 7, the signal processing module analyzes and processes the signals transmitted by the signal acquisition module, filters out some noise signals, amplifies the target signals, transmits the amplified target signals to the control module, and the control module instructs the signal transmitting module to transmit signals in a wireless mode, such as Bluetooth. The remote signal receiving module receives and transmits the wireless signals transmitted by the intelligent shoes to the remote PC display module after recognizing the wireless signals transmitted by the intelligent shoes, and the received signals are displayed on a screen, so that doctors can visually see the signal form and rule, further judge the walking speed, the walking steps and the walking gesture of the leg disease personnel, observe and compare the corresponding waveform similarity degree when two feet walk, and accurately diagnose the rehabilitation condition of the patient. In addition, for the step counting and speed monitoring of walking, a control module can be arranged to control time, and a voice module is used for timing broadcasting.
Experimental example 1
A comparative test was carried out on flexible optical waveguides doped with graphite particles of different concentrations and different particle sizes, according to the method of example 1:
table 1 conditions of graphite particles in experimental examples
The results are shown in fig. 8 a-8 c, and fig. 8 a-8 c show the optical loss versus wavelength for different graphite particles doped. As can be seen from fig. 8 a-8 c, there is a significant difference in the absorption of transmitted light power by the optical waveguides doped with different concentrations of graphite of different particle sizes. The transmission spectrum is used for representing the optical property of the optical waveguide, and analysis of the transmission spectrum shows that compared with an undoped optical waveguide, the loss of the transmission optical power of the graphite-doped optical waveguide is obviously increased, and the local burst of the optical loss is generated at the wavelength of 745 nm. The larger the particle size (smaller the particle diameter) the more the light loss becomes at a constant concentration. When the particle diameter range is constant, the larger the doping concentration is, the more the optical power loss is.
Experimental example 2
For the flexible optical waveguide (doped graphite particles c=5×10) obtained in example 1 -3 wt%, particle size 0.5 μm) for performance testing:
1. the flexible optical waveguide is characterized optically and compared to an undoped flexible optical waveguide. A laser with a wavelength of 745nm was injected into a PDMS pre-elastomer with the same concentration doped with 0.5 μm polyethylene and graphite respectively, as shown in FIG. 9, the pre-elastomer doped with polyethylene was mainly scattered to the injected laser, while the pre-elastomer doped with graphite was scattered and absorbed to the injected laser, and the optical loss was relatively large.
The flexible optical waveguide doped substance provided by the invention is graphite particles, but not graphene, and is mainly based on the following reasons: (1) Graphene is of a lamellar structure, the dispersion difficulty of the graphene in polydimethylsiloxane is high, and a uniformly dispersed mixture is difficult to form, so that stable light loss is difficult to form after the graphene is solidified, the graphene is applied to a strain sensor, errors of different batches are large, and the uniformity is not high. (2) Compared with graphene, the graphite microparticles adopted by the invention have large particle size, the cross section of the graphite microparticles is contracted in the stretching process of the optical waveguide, so that the graphite microparticles distributed on the cross section are gathered, besides the absorption and scattering of the graphite microparticles to light, the channel for light wave propagation of the optical waveguide in the stretching process can be reduced to a certain extent, and the light loss propagated in the waveguide is further increased, so that the graphite microparticles can be used for preparing the flexible strain sensor with higher sensitivity. (3) From the economical point of view, the price of graphite particles is far lower than that of graphene, and the cost can be greatly reduced by adopting the graphite particles.
For an optical waveguide doped with silver nanowires, the tensile strain is <50%, and for a wearable device, an extreme situation of strain overrun is unavoidable. Therefore, the optical waveguide sensor doped with the silver nanowire is used for detecting the joint movement of the human body and has certain unreliability. Rhodamine B is a fluorescent substance, and when the rhodamine B is irradiated by white light in a solution, the rhodamine B absorbs light with a certain wavelength of 540nm, and emits stronger fluorescent light with a wavelength of 620 nm. For the flexible optical waveguide sensor based on intensity, the light intensity received by the photosensitive element at the optical waveguide receiving end loses part of light with the wavelength of 540nm absorbed by rhodamine B, other light with the wavelength is received, and 620nm fluorescence emitted by rhodamine B is also received. Thus, in theory, the light intensity received by the photosensitive element is less lossy relative to the incident light intensity.
Laser light with a wavelength of 445nm is injected from one end of the optical waveguide, and is successively cut off by a cutting method in units of 1cm, and the transmitted light intensity is measured for each cut-off 15 sections so as to calculate the loss coefficient of the optical waveguide. As a result, as shown in fig. 10a to 10b, it is clear from fig. 10 (a) that the optical loss is approximately linear with the increase in the length of the optical waveguide, and the loss coefficients of the doped and undoped optical waveguides are respectively 2.42dB/cm and 0.59dB/cm, and the optical loss of the graphite-doped optical waveguide is significantly higher.
2. The durability test was performed on the flexible optical waveguide, both ends of the flexible optical waveguide were fixed to the tension mechanism, and 500 times of stretching was performed in a cycle until the strain was 100% completely released, and the length was measured once after each 100 times of stretching release, and as apparent from fig. 10 (b), the length of the flexible optical waveguide was unchanged, indicating that the strain sensor based on the optical waveguide had relatively reliable durability.
3. The dynamic response of the flexible optical waveguide was investigated and the difference in optical loss of the flexible optical waveguide during stretching and releasing was tested, and the results are shown in fig. 11. As can be seen from fig. 11, the optical loss corresponding to the stretching and releasing of the flexible optical waveguide was symmetrical, and no hysteresis was observed. Multiple stretching and releasing in the strain range of 90%, and the waveform under the corresponding strain has stable consistency.
Experimental example 3
Strain test experiments on doped graphite induced PDMS optical waveguides
The increased attenuation of the PDMS optical waveguide doped with graphite particles is due to absorption and scattering of graphite particles uniformly distributed in the PDMS optical waveguide space. The sensing mechanism of an optical strain sensor is therefore based on the spectrum of the attenuation change of graphite particles in the transmitted light intensity, characterizing the deformation of the optical waveguide by detecting the loss of light intensity. Beer-Lambert law (Beer-Lambert law) is a basic law of light absorption, and is applicable to all light absorbing substances and has the following relation:
A＝log 10 (1/T)＝Kcl (1)
where a represents absorbance, T represents transmittance, K represents absorption coefficient, c represents concentration of graphite particles, and volume per unit body under strain is constant, i.e., c remains unchanged, l=l 0 (1+ε) represents total length of PDMS optical waveguide doped with graphite, l 0 Represents the initial length of the optical waveguide and epsilon represents the applied axial strain. Theoretically, the absorption coefficient and concentration of a fixed medium remain unchanged, and a beam of monochromatic light is irradiated into the absorption medium, and after passing through a medium of a certain thickness, the light loss amount is in a linear relation with the length of the medium passing through.
For a flexible optical waveguide material with a limited cross-sectional area, as shown in fig. 12 (a), one unit body is arbitrarily stretched inside the flexible optical waveguide material, and the unit body is physically deformed, but the concentration of the graphite particles randomly distributed inside the flexible optical waveguide material is still unchanged. However, from the cross-sectional view of the flexible optical waveguide, the number of the graphite particles in the micron order randomly distributed on the cross section is kept unchanged in the stretched state of the optical waveguide by taking the cross section analysis of the unit thickness, but the cross section area is contracted, so that the optical path in the cross section of the flexible optical waveguide is reduced. The doped graphite particles thus result in a relatively large attenuation of the transmission spectrum, the change in attenuation of the optical waveguide with strain in the stretched state being expressed as:
D(ε)=Kcl 0 ε+Δ(ε) （2）
here delta (epsilon) means that the optical waveguide, when stretched, has a reduced cross-sectional area resulting in a reduced spectral attenuation of the light path. As shown in fig. 12 (b), a flexible PDMS optical waveguide doped with graphite particles, which has a length of 2cm, is prepared, and two ends of the flexible PDMS optical waveguide are respectively bonded with optical fiber connectors through ultraviolet curing glue (ergo 8500), and the optical fiber connectors can be abutted with SMA-905 type optical fibers. The optical fiber connectors at both ends of the optical waveguide were coaxially mounted on a manually controllable stretching device for testing, as shown in fig. 12 (c), and a white light source was passed through the optical fiber and then entered into the flexible optical waveguide, and the transmission spectrum was received and recorded with a spectrometer.
Doped graphite (c=1×10) -2 weight, particle size of 4 μm,1 μm,0.5 μm respectively; c=5×10 -3 wt%, particle size of 0.5 μm) was subjected to transmission spectrum analysis under tensile strain, and the tensile amount of each step of the stretching apparatus was set to 2mm, and the strain was 100% when the 10-time stretching length reached 4 cm. As shown in fig. 13a to 13d, it is clear from fig. 13 (a, b, d) that the optical loss of the three optical waveguides increases linearly with an increase in strain in the range of 90%, and the optical loss exhibits a nonlinear characteristic after the strain exceeds 90%. When the optical waveguide strain exceeds 80% as shown in fig. 13 (c), the optical loss and strain exhibit nonlinear characteristics, which also verifies that the optical attenuation caused by the reduction of the optical path due to the cross-sectional shrinkage is not negligible when the optical waveguide axial tensile strain reaches 90%. Because the maximum strain range of the epidermis is within 30% due to the joint movement of the human body, the graphite-doped optical waveguide is selected as a strain sensor to be used in the field of wearable equipment, and the method has theoretical and economic feasibility.
Experimental example 4
The strain sensor based on the PDMS optical waveguide doped with graphite particles is prepared, as shown in fig. 14 (a) and (b), the length of the optical waveguide section is 2cm, two ends of the optical waveguide section are respectively bonded with optical fiber connectors through ultraviolet curing glue, a light emitting diode is arranged at one end of the optical fiber connector, a photosensitive diode is arranged at the other end of the optical fiber connector, and the light emitting diode and the photosensitive diode are respectively packaged by soft sleeves.
Further, an economical intelligent shoe prototype is manufactured based on the graphite-doped optical waveguide strain sensor. As shown in fig. 14 (c), the flexible strain sensor was embedded at the sole joint of the sole, and a prototype of intelligent shoe worn by volunteer was dynamically tested on a treadmill at speeds of 5km/h and 8km/h, respectively. As a result, as shown in fig. 14 (d, e), one waveform represents walking one step, and the speed is kept constant, and the waveform consistency corresponding to each step is good. The faster the walking speed is, the narrower the corresponding waveform is, the shorter the period is, and the step counting and speed monitoring of the exercise can be realized based on the waveform. The intelligent shoe is applied to auxiliary medical treatment, so that a person with leg diseases wears the intelligent shoe to perform rehabilitation training, and the degree of waveform similarity corresponding to gait of two feet is observed and compared, so that the rehabilitation condition of the patient can be accurately diagnosed.
Further, a test was performed to monitor the movement of the finger joint, and the optical waveguide sensor was adhered to the index finger position of the rubber glove. Fig. 15 (a) shows 5 gestures in which the finger is gradually bent and stretched, from the gesture i-iii strain sensor being gradually stretched, the gesture iii-v strain sensor being gradually released, so that the output optical loss shows a trend of increasing and decreasing. Fig. 15 (b) shows the corresponding light loss change in the posture of the finger i-v, and it can be seen that different motion postures of the finger joint can be accurately monitored.
In addition, the detection sensitivity of the optical waveguide sensor doped with graphite particles was investigated, and the muscle movement was tested by sticking the strain sensor to the throat of the volunteer as shown in fig. 15c, and the optical loss waveforms detected when the sounds of "hello", "nih hao" were emitted as shown in fig. 15 (d, e), and it was seen that the optical loss waveforms had good detection sensitivity. The application test results show that the optical waveguide strain sensor based on the doped graphite particles can be applied to various human motion detection, such as step counting, speed detection and walking gesture auxiliary diagnosis in intelligent shoes in tests, and is reported for the first time.
Table 1 flexible sensor performance comparison
As can be seen from table 1, compared with the flexible optical waveguide strain sensor based on commercial polymer optical fiber and pure PDMS sensor, the proposed graphite doped flexible optical waveguide strain sensor has an effective strain range up to 90%, meets the application requirements of wearable devices, has smaller tensile stress, and can not cause discomfort to the wearer when integrated in an intelligent shoe. The loss strain coefficient, i.e. the sensitivity of the proposed sensor, is high.
In the summary, this applicationPlease propose a flexible optical waveguide based on doped graphite particles, and a preparation method and application thereof. The flexible optical waveguide has the characteristics of high sensitivity, good repeatability and larger stretching rate, and has considerable economy. Under the condition that the material can be obtained economically, the doped graphite particles with the thickness of 0.5 mu m and the concentration of 5 multiplied by 10 are selected by transmission spectrum analysis - 3 wt% of optimal parameters. Experiments have shown that the sensor exhibits stable, reliable, sensitive and repeatable performance in the 90% strain range with static and dynamic responses. The sensor can detect human body movements in real time, such as joint movements, muscle contraction and release, and assist accurate judgment of the walking postures of the two legs in medical treatment, and the like. The novel sensor may have a wider application prospect on wearable devices such as intelligent shoes.
Finally, it should be noted that: the foregoing description is only of the preferred embodiments of the invention and is not intended to limit the scope of the invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A method of making a flexible optical waveguide comprising:
preparing a silicone pre-elastomer from polydimethylsiloxane;
uniformly dispersing graphite particles with the particle size of 0.5-4 mu m in the organosilicon pre-elastomer, wherein the mass percentage concentration of the added graphite particles is 2 multiplied by 10 -3 ~1×10 -2 wt%；
Standing the obtained mixture in a negative pressure environment to eliminate bubbles, injecting the mixture into a tubular mold, closing two ends of the tubular mold, heating and curing the mixture, and performing demolding treatment; the pressure of the negative pressure environment is 0.8-1.2 kg.f/cm 2 ；
Spraying a release agent on the inner surface of the tubular mold, aligning an injection port of the injector with one end of the tubular mold, injecting the PDMS pre-elastomer, putting plugs on two ends of the tubular mold after filling, putting the tubular mold into an oven for high-temperature curing, and finally performing release treatment, aligning the injection port of the injector with water, and extruding the PDMS pre-elastomer from the tubular mold by water pressure;
manufacturing flexible optical waveguides doped with graphite particles with different concentrations and different particle diameters, carrying out a contrast test, and making the optical waveguides have different absorption of transmitted light power; the concentration is unchanged, the larger the particle mesh number is, namely the smaller the particle size is, the more the light loss is; the particle diameter range is unchanged, and the larger the doping concentration is, the more the optical power loss is;
according to the preparation method, flexible optical guided waves are prepared; the obtained flexible optical waveguide has the characteristics of high sensitivity, good repeatability and large stretching rate, and static and dynamic responses show stable, reliable, sensitive and repeatable performances within the strain range of 90%;
a flexible optical waveguide strain sensor comprising: light emitting diodes, photodiodes, and flexible optical waveguides; the two ends of the flexible optical waveguide are provided with optical fiber connectors, and the flexible optical waveguide is respectively connected with the light emitting diode and the photosensitive diode through the optical fiber connectors at the two ends.
2. The method for manufacturing a flexible optical waveguide according to claim 1, wherein the heating temperature in the heating and curing step is 70-90 ℃ and the curing time is 0.8-1.2 h.
3. A method of manufacturing a flexible optical waveguide according to claim 1, wherein the inner diameter of the tubular mould is 0.5-2mm.
4. The method for manufacturing a flexible optical waveguide according to claim 1, wherein the silicone pre-elastomer is prepared by mixing polydimethylsiloxane and a curing agent according to a mass ratio of 9-11:1.
5. The method of manufacturing a flexible optical waveguide according to claim 1, wherein the optical fiber connector has a stepped through hole penetrating in a long axis direction, and the flexible optical waveguide is inserted into the through hole and coincides with an optical coupling surface of the light emitting diode or the photodiode.
6. Use of a flexible optical waveguide prepared according to the preparation method of a flexible optical waveguide of claim 1 in a wearable flexible detection device.
7. The optical waveguide type intelligent shoe is characterized by comprising a power supply module, a control module, a signal acquisition module, a signal processing module, a voice module and a signal transmitting module which are electrically connected with each other;
the signal acquisition module comprises the flexible optical waveguide strain sensor prepared by the preparation method of the flexible optical waveguide according to claim 5, and the flexible optical waveguide strain sensor is arranged at the metacarpophalangeal joint of the sole.
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| CN109540015A (en) * | 2018-11-08 | 2019-03-29 | 清华大学 | A kind of flexible, stretchable fibre optic strain sensor probe and preparation method thereof |
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| CN113566857A (en) * | 2021-04-14 | 2021-10-29 | 北京理工大学 | Human body posture identification method based on optical fiber composite flexible sensor |
| CN113614787A (en) * | 2018-09-04 | 2021-11-05 | 伊爱慕威讯医疗设备有限公司 | Wearable antenna assembly for electromagnetic head imaging |
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| CN113614787A (en) * | 2018-09-04 | 2021-11-05 | 伊爱慕威讯医疗设备有限公司 | Wearable antenna assembly for electromagnetic head imaging |
| CN109540015A (en) * | 2018-11-08 | 2019-03-29 | 清华大学 | A kind of flexible, stretchable fibre optic strain sensor probe and preparation method thereof |
| CN110411490A (en) * | 2019-07-31 | 2019-11-05 | 华中科技大学 | A kind of wearable human action sensor of optical-fiber type |
| CN112225942A (en) * | 2020-10-13 | 2021-01-15 | 中南大学 | Preparation method of strain-temperature dual-response flexible electronic sensor composite material, electronic sensor obtained by preparation method and composite material |
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