Large strain linear double helix structure flexible capacitive sensor and preparation method thereof

Abstract

The present invention provides a method for preparing a large-strain linear double-helix structure flexible capacitive sensor, which relates to the technical field of nanofiber materials. The method comprises: using a water-bath electrospinning method to coat polyamide 6PA6 nanofibers on a conductive core yarn to prepare a nanofiber core-spun yarn; dividing the prepared nanofiber core-spun yarn into two parts, dyeing one part with a neutral dye for color distinction; and winding the dyed fiber core-spun yarn and the white fiber core-spun yarn side by side onto an elastic band to prepare a double-helix structure flexible capacitive sensor. This method solves the problem that, in the prior art, sensors with a strand structure have a relatively small facing area of ​​two electrodes per unit length, resulting in a small capacitance value of the capacitor; and that, in addition, the problem that the sensor has a very small deformation when subjected to external force in both the length direction and the diameter direction, which limits its application in large-strain scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiber materials, in particular to a flexible capacitance sensor with a large strain linear double helix structure and a preparation method thereof. Background Art

[0002] With the continuous development and progress of wearable technology and smart materials, new flexible sensors have gradually attracted widespread attention. This research trend is due to the characteristics of flexible wearable sensors, which are light weight, low cost, good wearability, convenient and wide application, and high efficiency. They have broad application prospects in sports, biomedicine, human-computer interaction and other fields.

[0003] A flexible capacitive sensor is a sensor based on a flexible parallel electrode plate structure. When it is subjected to external mechanical pressure, the distance and relative area between the two plates will change, thereby generating a change in the capacitance signal. This type of sensor has the advantages of simple structure, easy production, good sensitivity and stable performance. It is one of the common sensors in the current research field of flexible wearable devices.

[0004] From a macroscopic perspective, capacitive flexible sensors can be divided into two-dimensional planar structures and one-dimensional yarn-like structures according to their structure; the two-dimensional planar structure generally uses flexible materials such as films and fabrics with conductive properties as electrode plates, and low-modulus insulating materials such as fabrics, polyurethane, and silicone as dielectric layers. The two parts are combined to form a "sandwich" structure of the capacitive flexible sensor.

[0005] Compared with one-dimensional linear structures, two-dimensional capacitive flexible sensors have disadvantages such as poor resilience and unstable signals.

[0006] The preparation method of one-dimensional linear capacitive flexible sensors is mainly to attach a dielectric layer on the surface of the conductive yarn through post-processing methods such as electrospinning, coating, and in-situ polymerization, and then assemble it according to the capacitor principle.

[0007] With the development of materials and technologies, in order to improve the sensing performance and comfort of sensors, both cross-type and multi-layer circular coatings have defects such as complex preparation processes and easy shedding of exposed conductive layers. However, the nanofiber core-spun yarn prepared by coating the surface of conductive yarn with a nanofiber layer through electrospinning technology can improve the mechanical properties of the yarn to a certain extent and protect the conductive layer. The nanofiber insulating coating can also serve as the dielectric layer in capacitive sensors. However, the facing area of ​​the two plates per unit length of the stranded structure sensor is relatively small, and the capacitance value of the capacitor is small. At the same time, the deformation when subjected to external forces in both the longitudinal and diametrical directions is very small, which limits its application in large strain scenarios. Summary of the Invention

[0008] (1) Technical problems solved

[0009] In response to the shortcomings of the existing technology, the present invention provides a large-strain linear double-helix structure flexible capacitive sensor and a preparation method thereof, which solves the problem that the facing area of ​​the two plates per unit length of the strand structure sensor proposed in the above background technology is relatively small, and the capacitance value of the capacitor is small; at the same time, the deformation when subjected to external force in both the length direction and the diameter direction is very small, which limits its application in large-strain scenarios.

[0010] (2) Technical solution

[0011] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0012] A method for preparing a large-strain linear double-helix structure flexible capacitive sensor, comprising:

[0013] The conductive core yarn was coated with polyamide 6PA6 nanofibers by water bath electrospinning to produce nanofiber core-spun yarn.

[0014] The prepared nanofiber core-spun yarn is divided into two parts, one of which is dyed with a neutral dye to distinguish the colors;

[0015] The dyed fiber core-spun yarn and the white fiber core-spun yarn were wound side by side onto the rubber band to prepare a double-helix structure flexible capacitive sensor.

[0016] Preferably, the nanofiber core-spun yarn is prepared by coating polyamide 6PA6 nanofibers on the conductive core yarn using a water bath electrospinning method, comprising:

[0017] Dissolve PA6 powder in formic acid solution and stir thoroughly to obtain an electrospinning solution with a mass fraction of 10-20%;

[0018] Dissolve an appropriate amount of peregrine O in deionized water to obtain a liquid with a concentration of 0.5%-1.2%, which serves as the receiving bath for electrospun nanofibers.

[0019] The left side is the take-up roller and the right side is the unwinding roller;

[0020] The conductive core yarn is first unwound from the unwinding roller on the right side and passes through the upper surface of the receiving bath;

[0021] The receiving bath contains a flat O liquid parallel to the bath surface, with a set of horizontally arranged electrospinning needles above it;

[0022] The needle and syringe are connected by a hose. At the same time, a high-voltage electric field is formed between the needle and the receiving bath. Under the action of the high-voltage electric field, the spinning solution ejected from the syringe is drawn into nanofibers and deposited on the surface of the core yarn.

[0023] After passing through the drying device, it is wound on the take-up roller on the left to finally obtain the nanofiber core-spun yarn.

[0024] Preferably, the conductive core yarn is made of conductive fiber material.

[0025] Preferably, the portion is dyed with a neutral dye for color differentiation, comprising: a dyeing time of 1 hour, a dyeing temperature of 30° C., and a dye concentration of 8%.

[0026] Preferably, the dyed fiber core-spun yarn and the white fiber core-spun yarn are wound onto the elastic band in parallel, and the yarn winding density is 15-30 turns / cm.

[0027] The present invention also provides a large-strain linear double-helix structure flexible capacitive sensor, which is prepared by any of the above-mentioned methods for preparing a large-strain linear double-helix structure flexible capacitive sensor.

[0028] (3) Beneficial effects

[0029] The present invention provides a high-strain linear double-helix structure flexible capacitive sensor and its preparation method. It has the following beneficial effects:

[0030] The present invention adopts water bath electrospinning method to prepare nanofiber core-spun yarn with conductive fiber material as core yarn and PA6 nanofiber as skin layer, and wraps the yarn around rubber band to prepare strain-capacitive sensor.

[0031] The water bath electrospinning technology is used to wrap nanofibers on the surface of the conductive yarn to form a nanofiber core-spun yarn. Then, two nanofiber core-spun yarns are wrapped side by side in a double helix on the rubber band. The conductive yarn serves as the plate of the capacitor, and the nanofiber layer serves as the insulating dielectric layer to form a linear one-dimensional capacitor. Because the rubber band or elastic filament has a large deformation ability, it can be easily changed by stretching its length, thereby changing the distance between the nanofiber core-spun yarns, that is, the spacing between the capacitor plates, to achieve the purpose of changing the capacitance. The sensor exhibits good strain-capacitance sensing performance, and its capacitance value gradually decreases with the increase of the stretching distance. When the strain is small, it has good linearity and sensitivity; with the increase of the strain, the linearity and sensitivity gradually weaken. After a long period of cyclic stretching and cycling, the sensor capacitance value remains stable, with good repeatability and stability. Changes in the stretching speed have basically no effect on its sensing performance, making it suitable for large strain working scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A flow chart of a method for preparing a large-strain linear double-helix structure flexible capacitive sensor provided by an embodiment of the present invention;

[0033] Figure 2A schematic diagram of a water bath electrospinning apparatus in a method for preparing a flexible capacitive sensor with a large strain linear double helix structure provided by an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of the sensing principle of a high-strain linear double-helix flexible capacitive sensor provided by an embodiment of the present invention;

[0035] Figure 4 This is a curve showing the effect of strain on the relative capacitance value of a large-strain linear double-helix structure flexible capacitive sensor prepared based on the method of an embodiment of the present invention.

[0036] Figure 5 The graphs show the monitoring curves of different knee movements using a large-strain linear double-helix structure flexible capacitive sensor prepared based on the method of an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0038] like Figure 1 As shown, a method for preparing a large-strain linear double-helix structure flexible capacitive sensor includes:

[0039] S1 uses water bath electrospinning to coat polyamide 6PA6 nanofibers on the conductive core yarn to produce nanofiber core-spun yarn;

[0040] S2 divides the prepared nanofiber core-spun yarn into two parts, and dyes one part with a neutral dye to distinguish the colors;

[0041] S3 winds the dyed fiber core-spun yarn and the white fiber core-spun yarn side by side onto the rubber band to prepare a double-helix structure flexible capacitive sensor.

[0042] like Figure 2 FIG2 is a schematic diagram of a water bath electrospinning device in a method for preparing a flexible capacitive sensor with a large strain linear double helix structure provided by an embodiment of the present invention;

[0043] Includes: digital syringe, high voltage power supply, hose, drying device, receiving bath, hose, needle, winding roller, unwinding roller, nanofiber, core yarn;

[0044] The electrostatic voltage was 20 kV, the spinning rate was 0.2 mL / h, the core yarn winding speed was 0.16 m / min, and the receiving distance was 5 cm;

[0045] The nanofiber core-spun yarn is prepared by coating polyamide 6PA6 nanofibers on a conductive core yarn using a water bath electrospinning method, comprising:

[0046] Dissolve PA6 powder in formic acid solution and stir thoroughly to obtain an electrospinning solution with a mass fraction of 10-20%;

[0047] Dissolve an appropriate amount of peregrine O in deionized water to obtain a liquid with a concentration of 0.5%-1.2%, which serves as the receiving bath for electrospun nanofibers.

[0048] The left side is the take-up roller and the right side is the unwinding roller;

[0049] The conductive core yarn is first unwound from the unwinding roller on the right side and passes through the upper surface of the receiving bath;

[0050] The receiving bath contains a flat O liquid parallel to the bath surface, with a set of horizontally arranged electrospinning needles above it;

[0051] The needle and syringe are connected by a hose. At the same time, a high-voltage electric field is formed between the needle and the receiving bath. Under the action of the high-voltage electric field, the spinning solution ejected from the syringe is drawn into nanofibers and deposited on the surface of the conductive core yarn.

[0052] After passing through the drying device, it is wound on the take-up roller on the left to finally obtain the nanofiber core-spun yarn.

[0053] Preferably, the core yarn is made of conductive fiber material, and nickel-plated and silver-plated nylon SCP or polyacrylonitrile PAN can be selected.

[0054] Preferably, the portion is dyed with a neutral dye for color differentiation, comprising: a dyeing time of 1 hour, a dyeing temperature of 30° C., and a dye concentration of 8%.

[0055] Preferably, the dyed fiber core-spun yarn and the white fiber core-spun yarn are wound onto the elastic band in parallel, and the yarn winding density is 15-30 turns / cm.

[0056] The dyed core-spun yarn and the white core-spun yarn were wound side by side onto the rubber band to prepare a double-helix structure flexible capacitive sensor.

[0057] In one embodiment, the dyed core-spun yarn and the white core-spun yarn can also be wound onto the elastic filament in parallel.

[0058] An embodiment of the present invention further provides a large-strain linear double-helix structure flexible capacitive sensor, which is prepared using any of the above methods for preparing a large-strain linear double-helix structure flexible capacitive sensor.

[0059] like Figure 3 FIG. 1 is a schematic diagram showing the sensing principle of a large strain linear double helix structure flexible capacitive sensor according to an embodiment of the present invention;

[0060] According to the capacitance calculation formula (ε is the dielectric constant; S is the area of ​​the capacitor plates, cm 2 ; d is the distance between the capacitor plates, cm) It can be seen that the capacitance of the capacitor is proportional to the area of ​​the plates facing each other and inversely proportional to the distance between the plates;

[0061] The sensing principle of the linear double helix structure flexible capacitive sensor of the present invention is as follows Figure 3 As shown, the two groups of nanofiber core-spun yarns can be regarded as two parallel plates, and their facing areas are relatively stable. As the stretching progresses, the spacing between the two groups of yarns increases, that is, the distance between the plates increases, so the capacitance value decreases, and the opposite is true during recovery.

[0062] Compared to the existing conjugate electrospinning method that wraps nanofibers on the surface of conductive yarns, two sets of nanofiber core yarns are vertically interwoven to form a sensor. The sensor as a whole has a two-dimensional planar structure. Pressure is used to change the distance between the two conductive yarns to change the capacitance, thereby achieving the purpose of sensing. However, interweaving has a destructive effect on the nanofibers, making it difficult to ensure the integrity of the nanofiber coating, thus affecting the sensing effect. The sensor size change caused by external force is small, the capacitance change is small, and the sensitivity is low.

[0063] The linear double-helix structure flexible capacitive sensor provided by an embodiment of the present invention utilizes water bath electrospinning technology to wrap nanofibers on the surface of a conductive yarn to form a nanofiber core-spun yarn, and then spirally winds two nanofiber core-spun yarns side by side on a rubber band or elastic filament. The conductive yarn serves as the capacitor's plate, and the nanofiber layer serves as an insulating dielectric layer to form a linear one-dimensional capacitor. Because the rubber band or elastic filament has a large deformation ability, the length can be easily changed by stretching, thereby changing the distance between the nanofiber core-spun yarns, that is, the capacitor plate spacing, to achieve the purpose of changing the capacitance.

[0064] To test the performance of the linear double-helix structure flexible capacitive sensor prepared according to the preparation method in the embodiment of the present invention, the sensor was connected to a capacitance tester. The capacitance value detected by the capacitance tester was used to generate a relative capacitance (Cp / C0)-time curve, where Cp is the real-time capacitance of the sensor during stretching, and C0 is the initial capacitance value of the sensor when it is not stretched, thereby representing the capacitance change of the sensor.

[0065] The stretching speed was fixed at 12 mm / s, and the stretching distances were changed to 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 cm (the strains were 6.67%, 13.33%, 20.00%, 26.67%, 33.33%, 40.00%, 46.67%, 53.33%, 60.00% and 66.67% respectively). The effect of strain on the sensing performance of the sensor was studied. The results are shown in the figure. Figure 4The left half of each curve shows the capacitance change during the stretching phase, while the right half shows the capacitance change during the recovery phase. As can be seen from the figure, during the stretching phase, the capacitance decreases, while the opposite is true during the recovery phase.

[0066] To test the ability of the linear double-helix flexible capacitive sensor, prepared according to the preparation method described in an embodiment of the present invention, to monitor human motion, a human motion test was conducted. The subject's knees were straightened, and the ends of the flexible sensor, unwrapped with nanofiber core-spun yarn, were secured to the subject's thigh and calf above and below the knee using Velcro. The nanolayers on the two nanofiber core-spun yarns at one end were peeled off to expose the inner core yarns. Each was then taped with conductive tape and connected to a capacitance tester via a test chuck. The subject performed exercises such as intermittent and continuous knee flexion, and walking at varying speeds on a treadmill. The capacitance tester recorded the changes in the sensor's capacitance during the exercise in real time.

[0067] Figure 5 Shown are monitoring curves of different knee movements using a large-strain linear double-helix structure flexible capacitive sensor prepared based on the method of an embodiment of the present invention.

[0068] Figure 5 (a) shows the change in sensor capacitance when the subject's knee is bent at different angles. It can be seen that as the knee bends from 0° (I) to 90° (VI), the capacitance value changes immediately with each knee bend and stabilizes when the bending stops.

[0069] Figure 5 (b) shows the capacitance change of the subject's knee when it is bent continuously from 0° to 90°. As can be seen from the figure, during the continuous bending movement, the sensor's C P / C0-relative capacitance, where C p is the real-time capacitance of the sensor during stretching, and C0 is the initial capacitance value of the sensor when it is not stretched (according to the test, in the unstretched state, the C0 of the sensor is 220pF), which is used to represent the capacitance change of the sensor; C P The / C0 value shows a very regular change, and its value fluctuates stably between 0.6 and 1.0.

[0070] Figure 5(c) shows the real-time capacitance signal changes generated by the subject's knee bending while walking (3km / h, 4km / h) and running (6km / h) on a treadmill. It can be seen that both walking and running can produce relatively stable signal changes. Each trough in the curve represents the maximum moment of knee bending, when the sensor is stretched to its maximum position, and each peak is when the sensor returns to its initial position, that is, when the knee is straightened. At speeds of 3km / h and 4km / h, the subject adopts a walking posture, and his stride is adjusted according to the speed, and the stride is large. After the subject adapts to the speed, his steps are almost the same, so at these two speeds, the waveform changes are small, and C P The / C0 value fluctuates steadily between 0.6 and 1.0. At a speed of 6 km / h, the subject is jogging, with a higher frequency, smaller stride, and less knee bending. As a result, the sensor's elongation is lower, and the capacitance signal's variation range is smaller.

[0071] according to Figure 5 (c) It can be calculated that at a speed of 3 km / h, the time spent on taking two steps (because the sensor is fixed to one side of the knee, one waveform change is two steps) is between 1.21s and 1.58s, with an average of 1.39s (cadence 86.4 steps / min); at a speed of 4 km / h, the time spent on taking two steps is between 1.02s and 1.26s, with an average of 1.12s (cadence 107.2 steps / min); at a speed of 6 km / h, the time spent on taking two steps is between 0.71s and 0.84s, with an average of 0.79s (cadence 151.8 steps / min).

[0072] Therefore, in addition to calculating the bending amplitude of the knee based on the capacitance change value, the sensor can also calculate the number of steps and step frequency, thereby realizing human movement monitoring.

[0073] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a large strain linear double helix structure flexible capacitive sensor, characterized in that: include: The conductive core yarn was coated with polyamide 6 PA6 nanofibers by water bath electrospinning to produce nanofiber core-spun yarn. The core yarn is made of conductive fiber material; The prepared nanofiber core-spun yarn is divided into two parts, one of which is dyed with a neutral dye to distinguish the colors; The dyed fiber core-spun yarn and the white fiber core-spun yarn were wound side by side onto the elastic band to prepare a double-helix structure flexible capacitive sensor. The conductive core yarn serves as the capacitor plate, and the nanofiber layer serves as the insulating dielectric layer, forming a linear one-dimensional capacitor structure. The two groups of nanofiber core-spun yarns can be regarded as two parallel arranged electrodes, and their facing areas are relatively stable. As the stretching progresses, the spacing between the two groups of yarns increases, that is, the distance between the electrodes increases, so the capacitance value decreases, and the opposite is true during recovery.

2. The method for preparing a large strain linear double helix structure flexible capacitive sensor according to claim 1, characterized in that: The nanofiber core-spun yarn is prepared by coating polyamide 6 PA6 nanofibers on a conductive core yarn using a water bath electrospinning method, comprising: Dissolve PA6 powder in formic acid solution and stir thoroughly to obtain an electrospinning solution with a mass fraction of 10-20%; Add appropriate amount of Dissolve in deionized water to obtain a liquid with a concentration of 0.5%-1.2%, which serves as the receiving bath for electrospun nanofibers; The left side is the take-up roller and the right side is the unwinding roller; The conductive core yarn is first unwound from the unwinding roller on the right side and passes through the upper surface of the receiving bath; The receiving bath contains a flat bath parallel to the bath surface. Liquid, with a set of horizontally arranged electrospinning needles above; The needle and syringe are connected by a hose. At the same time, a high-voltage electric field is formed between the needle and the receiving bath. Under the action of the high-voltage electric field, the spinning solution ejected from the syringe is drawn into nanofibers and deposited on the surface of the conductive core yarn. After passing through the drying device, it is wound on the take-up roller on the left to finally obtain the nanofiber core-spun yarn.

3. The method for preparing a large strain linear double helix structure flexible capacitive sensor according to claim 1, characterized in that: The one portion is dyed with a neutral dye for color differentiation, including: dyeing time of 1 h, dyeing temperature of 30° C., and dye concentration of 8%.

4. The method for preparing a large strain linear double helix structure flexible capacitive sensor according to claim 1, characterized in that: The dyed fiber core-spun yarn and the white fiber core-spun yarn are wound onto the elastic band in parallel, and the yarn winding density is 15-30 turns / cm.

5. A large strain linear double helix structure flexible capacitive sensor, characterized in that: The large-strain linear double-helix structure flexible capacitive sensor is prepared by the large-strain linear double-helix structure flexible capacitive sensor preparation method according to any one of claims 1 to 4.

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