A flexible strain sensor and a manufacturing method thereof

Abstract

The present application provides a flexible strain sensor and a manufacturing method thereof, wherein the sensor comprises a sensitive layer, a packaging layer and electrode lines, the sensitive layer is wrapped by the packaging layer, the sensitive layer is arranged as an interdigital electrode structure, and the gap between each interdigital electrode is d、 the width of the interdigital electrode w、 and the size of the interdigital electrode finger tip and valley d 0 According to the size constraint greater than the stretching amount L, a pair of parallel plate capacitors are formed, and the electrode lines are respectively connected to the two ends of the sensitive layer interdigital electrode. In this way, the linearity and strain range of the capacitive-based strain sensor are improved.

Description

Technical Field

[0001] This invention relates to the field of sensors, and more particularly to a flexible strain sensor composed of interdigitated electrodes and a method for manufacturing the same. Background Technology

[0002] Advances in microelectronics technology, the rapid development of the internet, and increased public awareness of healthcare have led to a surge in wearable sensor electronic devices. Wearable sensors are widely used in healthcare, motion capture, human-computer interaction, virtual reality (VR) and augmented reality (AR), intelligent robotics, defense, and maintenance. The physical, chemical, biological, and environmental states of the human body can be monitored through various wearable sensors, which can conform well to the skin or clothing for a more comfortable and less burdensome wearing experience.

[0003] Key requirements for wearable sensors include flexibility, sensitivity, high linearity, and good biocompatibility. Flexible strain sensors, as an important component of wearable sensors, can be used to detect movements of various parts of the human body, such as large-scale deformations like bending of the hand, arm, and leg joints, and small-scale deformations like pulse, muscle contraction and relaxation, and swallowing. When used in wearable applications, flexible strain sensors must also meet several additional minimum requirements, including high tensile strength, flexibility, durability, and lightweight design.

[0004] Currently, flexible strain sensors typically consist of a sensing element and stretchable electrodes, or the sensing element can be formed by shaping the electrodes. However, capacitive strain sensors suffer from poor linearity and a limited strain range, thus their performance needs further improvement. Summary of the Invention

[0005] Therefore, the main objective of this invention is to provide a flexible strain sensor and its manufacturing method to improve the linearity and strain range of capacitive strain sensors.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a flexible strain sensor is provided, comprising: a sensitive layer, an encapsulation layer, and electrode wires, wherein the sensitive layer is encapsulated by the encapsulation layer, and wherein the sensitive layer is configured as an interdigital electrode structure, and the gap d between each interdigit, the width w of the interdigit, and the dimension d0 between the fingertip and the base of the interdigit are determined according to the amount of stretching. ,according to Far greater than The dimensional constraints set allow for changes in the capacitor C1 formed by the interdigitated portions resulting from stretching / shrinking. Much greater than the change in capacitance C2 formed by the interdigital fingertip and the base of the finger. This makes the effect of C2 negligible during stretching / contraction, thus forming several pairs of parallel plate capacitors, with the electrode lines respectively connected to both ends of the interdigitated electrodes of the sensitive layer.

[0007] In a possible preferred embodiment, the interdigitated electrode structure of the sensitive layer is configured according to... Greater than or equal to 2.5 times Size constraint settings.

[0008] In a possible preferred embodiment, the sensitive layer is made of carbon fiber plate, which is formed by pressing several pieces of carbon fiber cloth in an overlapping manner.

[0009] In a possible preferred embodiment, the thickness of the carbon fiber plate is 0.05~0.5mm.

[0010] In a possible preferred embodiment, the encapsulation layer is provided with a wire hole, through which the electrode wire extends and connects to both ends of the interdigitated electrode of the sensitive layer.

[0011] In a possible preferred embodiment, the encapsulation layer is made of either polydimethylsiloxane or polyethylene.

[0012] Corresponding to the aforementioned flexible strain sensor, according to a second aspect of the present invention, a method for manufacturing a flexible strain sensor is also provided, comprising the steps of:

[0013] In step S100, carbon fiber cloth is pre-impregnated with epoxy resin, and several pieces of carbon fiber pre-impregnated cloth are stacked horizontally and vertically and pressed into carbon fiber sheets by vacuum heating.

[0014] Step S200: On the carbon fiber plate according to... Greater than or equal to 2.5 times Due to dimensional constraints, the interdigitated electrode structure was fabricated, and electrode wires were connected to both ends of the interdigitated electrode.

[0015] Step S300 prepares an encapsulation layer film to cover the surface of the carbon fiber plate to form an encapsulation.

[0016] In a possible preferred embodiment, the step of preparing the encapsulation layer film includes: S310 preparing a first solution with a dimethylsilane and curing agent ratio of 10:1, pouring it into a mold, defoaming in a vacuum environment for 20-30 minutes, and then heating at 80°C for 1 hour to obtain the encapsulation layer film.

[0017] In a possible preferred embodiment, the encapsulation step in step S300 includes: S320 applying a first solution to the encapsulation surface of the encapsulation layer film, wrapping the encapsulation layer film around the carbon fiber plate from top to bottom, and debubbling in a vacuum environment for 30 minutes, and then letting it stand for 24 to 48 hours to wait for curing to complete the encapsulation.

[0018] Corresponding to the aforementioned flexible strain sensor, according to a third aspect of the present invention, a method for manufacturing a flexible strain sensor is also provided, comprising the following steps:

[0019] In step S100, carbon fiber cloth is pre-impregnated with epoxy resin, and several pieces of carbon fiber pre-impregnated cloth are stacked horizontally and vertically and pressed into carbon fiber sheets by vacuum heating.

[0020] Step S200: On the carbon fiber plate according to... Greater than or equal to 2.5 times Under dimensional constraints, the interdigitated electrode structure and the support rod connecting the carbon fiber plates on both sides of the interdigitated electrode were fabricated, and electrode wires were connected to both ends of the interdigitated electrode.

[0021] Step S300: Prepare a PDMS film to cover the surface of the carbon fiber plate to form an encapsulation, and then cut off the support rod.

[0022] The flexible strain sensor and its fabrication method provided by this invention cleverly design the structure of the interdigitated electrodes, enabling the change in C1 (i.e., the capacitor formed by the overlapping part of the interdigitated electrodes) caused by stretching / contraction to be controlled. The change is much greater than that produced by C2 (i.e., the capacitor formed by the interdigital fingertip and the base of the finger). This makes the influence of C2 negligible during stretching / contraction, thereby greatly improving the linearity of capacitance change during stretching / contraction. Combined with a sensitive layer made of carbon fiber and a PDMS encapsulation layer, the flexible strain sensor formed by multiple pairs of parallel plate capacitors has the advantages of high linearity, wide strain range, and high sensitivity, while also being insensitive to pressure. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 This is a schematic diagram of the overall structure of the flexible strain sensor of the present invention;

[0025] Figure 2 This is a side view schematic diagram of the flexible strain sensor of the present invention;

[0026] Figure 3 This is a half-sectional schematic diagram of the AA side of the flexible strain sensor of the present invention;

[0027] Figure 4 This is an enlarged schematic diagram of the interdigitated electrode structure in the flexible strain sensor of the present invention;

[0028] Figure 5This is a schematic diagram of the interdigitated electrode C1 and C2 capacitor structure in the flexible strain sensor of the present invention;

[0029] Figure 6 Linear fitting data graphs for testing different tensile / contraction strain capacitance changes using the flexible strain sensor of the present invention;

[0030] Figure 7 This is a data graph showing the change in capacitance during tensile strain testing using the flexible strain sensor of the present invention.

[0031] Figure 8 The interdigitated structure parameters of the flexible strain sensor of the present invention are set as follows: Greater than A comparison of the linearity R² of two sensors at 0-100% stretching: one with a stretch greater than 2.5 times T1 and the other with a stretch less than 2.5 times T2.

[0032] Figure 9 This is a step diagram illustrating the manufacturing method of the flexible strain sensor of the present invention;

[0033] Figure 10 This is a process diagram illustrating the fabrication method of the flexible strain sensor of the present invention.

[0034] Explanation of reference numerals in the attached figures

[0035] 1-Encapsulation layer, 2-Sensitive layer, 3-Electrode wire, 4-Support rod, 5-Carbon fiber cloth, 6-Carbon fiber plate. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solutions of the present invention, the specific technical solutions of the present invention will be clearly and completely described below in conjunction with embodiments, so as to help those skilled in the art further understand the present invention. Obviously, the embodiments described in this application are merely some embodiments of the present invention, and not all embodiments. It should be noted that, for those skilled in the art, the embodiments and features in the embodiments of this application can be combined with each other without departing from the concept of the present invention and without conflict. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the disclosure and protection scope of the present invention.

[0037] Furthermore, the terms "first," "second," "S100," "S200," etc., used in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those described herein. At the same time, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. Unless otherwise expressly specified and limited, the terms "set," "arranged," "installed," "connected," and "linked" should be interpreted broadly, for example, as a fixed connection, a detachable connection, or an integral connection; a mechanical connection or an electrical connection; a direct connection or an indirect connection through an intermediate medium; or a connection within two elements. Those skilled in the art can understand the specific meaning of the above terms in this case according to the specific circumstances and in conjunction with existing technology.

[0038] To improve the linearity and strain range of capacitive strain sensors, please refer to [link / reference needed]. Figures 1 to 8 As shown, the flexible strain sensor provided by this invention includes: a sensitive layer 2, an encapsulation layer 1, and electrode wires 3. The sensitive layer 2 is encapsulated by the encapsulation layer 1. The sensitive layer 2 is configured as an interdigital electrode structure, and the gap d between each interdigit, the width w of the interdigit, and the dimension d0 between the fingertip and the base of the interdigit are determined according to the amount of stretching. ,according to Greater than The size constraints are set to form several pairs of parallel plate capacitors, and the electrode lines 3 are respectively connected to the two ends of the interdigital electrodes of the sensitive layer 2.

[0039] Specifically, such as Figures 4 to 5 As shown, the interdigitated electrode structure on the sensitive layer 2 forms two parallel plate capacitors. One of them is a capacitor formed by the overlapping part of the interdigitated electrodes, such as... Figure 5 As shown in the C1 color block area, its capacitance value is represented by... The second is the capacitor formed by the fingertips and the base of the forked fingers, such as... Figure 5 As shown in the C2 color block area, its capacitance value is represented by... This indicates that C2 is a significant parasitic capacitance.

[0040] in Figure 4 The color block area shown is the area A of the overlapping parallel plate capacitor plates formed by a single pair of interdigitated fingers, where A = h * L1, which is the thickness h of the sensitive layer 2 multiplied by the length L1 of the overlapping of the two interdigitated fingers.

[0041] For example, in this example, when the gap between each interdigital finger is set to d = 0.2mm, the width of the interdigital finger w = 0.3mm, the dimension between the fingertip and the base of the interdigital finger d0 = 0.5mm, the overlap length of the two interdigital fingers L1 = 1.5mm, and the thickness of the sensitive layer 2 h = 0.2mm, the sensor test results obtained under these dimensions are as follows: Figures 6 to 7 As shown. According to the formula for a parallel-plate capacitor composed of n pairs of interdigitated electrodes:

[0042] ,

[0043] Where ε is the dielectric constant. Let L1 be the logarithm of the interdigitated fingers. When stretched, L1 decreases, causing a change in capacitance. The stretching direction is the interdigitated finger direction. Based on the above dimensional parameters, the capacitance of the two parts can be calculated separately. , ,in:

[0044]

[0045]

[0046] Therefore, the value of C2 is much smaller than that of C1, when generating When the stretching amount is L...

[0047] The capacitance change generated by C1 ,

[0048] The capacitance change generated by C2 .

[0049] For example, when the capacitance value changes due to a stretch of 0.1 mm, the change in capacitance C1 is 0.1 nε, and the change in capacitance C2 is 0.02 nε. The change in C2 accounts for approximately 17% of the total capacitance change, while the change in C1 accounts for 83%.

[0050] Therefore, it can be seen that the change in capacitance C2 did not significantly affect the linear change in C1. The proportion of the change in C2 in the total change in capacitance is... The larger L is, the lower the proportion; the proportion of the change in C1 capacitance in the total change in capacitance is... The larger L is, the higher its proportion.

[0051] Based on this phenomenon, as long as Far greater than The capacitance of C1 will be much greater than that of C2, as long as Far greater than Then the change in C1 caused by stretching The change in C1 will be much greater than the change in C2. C2, and according to the formula, for the various size parameters of the interdigitated fingers, d and w should be as small as possible, and d0 should be as large as possible.

[0052] In addition, such as Figure 8 As shown, in a preferred embodiment, when Greater than or equal to Linearity is better at ratios of 2.5 or higher, and the effect of C2 can be ignored. Meanwhile, with other quantities fixed, The larger L is, The smaller C2 is, meaning the greater the tensile strain, the more negligible the effect of C2 becomes. This design ensures the linearity of capacitance change during stretching / contraction in the parallel-plate capacitor composed of interdigitated electrodes.

[0053] Furthermore, in order to improve the sensitivity of the flexible strain sensor and make it insensitive to pressure, the sensitive layer 2 of the present invention is preferably made of carbon fiber material. Since carbon fiber does not deform under pressure and has good conductivity, the thickness h of the sensitive layer 2 can remain unchanged, and other parameters can also remain unchanged. Therefore, the capacitance value is not easily changed, thereby making the sensor insensitive to longitudinal pressure and having high sensitivity.

[0054] Furthermore, in order to make the sensitive layer 2 more flexible while maintaining the advantages of carbon fiber material, in a preferred example, the sensitive layer 2 is formed by pressing several pieces of carbon fiber cloth 5 into a carbon fiber plate 6 in a cross-stacked pattern. The preferred thickness of the carbon fiber plate 6 is 0.05~0.5mm, and generally, a larger thickness is preferred under the premise of ensuring processing accuracy and the integrity of carbon fiber interdigitates.

[0055] Furthermore, in optional embodiments, the encapsulation layer 1 is preferably made of either polydimethylsiloxane (PDMS) or polyethylene (PE). In this example, PDMS is preferred as the encapsulation layer 1 to wrap the sensitive layer 2 of carbon fiber material, which can give the sensor as a whole better flexibility and a wider strain range.

[0056] Furthermore, in an optional embodiment, the electrode line 3 can extend from the side of the sensor, such as by passing through the side of the encapsulation layer 1 and connecting to both ends of the interdigitated electrode of the sensitive layer 2, or it can extend from the top / bottom of the sensor, such as... Figure 1 As shown, a wire hole is provided on the encapsulation layer 1, and the electrode wire 3 extends through the wire hole and connects to both ends of the interdigital electrode of the sensitive layer 2.

[0057] On the other hand, corresponding to the aforementioned flexible strain sensor, the present invention also provides a method for manufacturing a flexible strain sensor, such as... Figures 9 to 10 As shown, the specific steps include:

[0058] In step S100, several pieces of pre-impregnated carbon fiber cloth 5 are stacked horizontally and vertically and pressed into carbon fiber board 6 by vacuum heating. The thickness of the selected pre-impregnated carbon fiber cloth is preferably 30 micrometers to 100 micrometers.

[0059] The steps involving vacuum heating include:

[0060] Step S110 involves arranging prepreg carbon fibers overlapping in [0° / 90° / 0° / 90°] in a clamping plate, tightening it, and placing it in a vacuum drying oven, where it is heated at 120°C for 2 hours under vacuum conditions.

[0061] Step S200: On the carbon fiber plate 6, according to... ≥ With a 2.5-fold size constraint, the interdigitated electrode structure was fabricated, and electrode lines 3 were connected to both ends of the interdigitated electrode.

[0062] The interdigitated electrode can be processed using laser processing to etch out a predetermined interdigitated pattern and remove excess interstitial carbon fibers in the sensitive layer 2 structure to form a sensitive structure.

[0063] Step S300 prepares an encapsulation layer film to cover the surface of the carbon fiber plate 6 to form an encapsulation.

[0064] The steps for preparing the encapsulation layer film include:

[0065] S310 is used to prepare a first solution of dimethylsilane and curing agent in a ratio of 10:1. After thorough stirring, the solution is poured into a mold and defoamed in a vacuum environment for 20-30 minutes. Then, it is heated at 80°C for 1 hour to obtain the encapsulation layer film. The thickness of the encapsulation layer film is preferably 0.1 mm to 0.5 mm.

[0066] The encapsulation step in step S300 includes:

[0067] S320 applies the first solution to the encapsulation surface of the encapsulation layer film, wraps the encapsulation layer film around the carbon fiber plate 6 from top to bottom, and removes bubbles in a vacuum environment for 30 minutes, then stands for 24 to 48 hours to wait for curing and complete the encapsulation.

[0068] On the other hand, since processing the interdigitated electrode structure on the carbon fiber plate 6 will divide the carbon fiber plate 6 into two separate parts, in order to maintain the consistency of the interdigitated electrode structure in subsequent processes and facilitate subsequent packaging, in a preferred example, such as Figure 10 As shown, in step S200, while processing the interdigitated electrode structure on the carbon fiber plate 6, a support rod 4 connecting the carbon fiber plates 6 on both sides of the interdigitated electrode will also be processed, thereby maintaining the carbon fiber plate 6 in an inseparable state until the encapsulation is completed in step S300, after which the support rod 4 will be cut off.

[0069] Furthermore, in a preferred embodiment, if it is necessary for the electrode wire 3 to extend from the top / bottom of the encapsulation layer 1, a wire hole can be provided on the encapsulation layer film during the preparation of the encapsulation layer film to allow the electrode wire 3 to be introduced. It is then soldered onto the carbon fiber plate 6 with silver paste and heated to 60°~80° on a heating table for curing. After that, the electrode wire 3, which is located at both ends, can be fixed to the two ends of the interdigitated electrode of the sensitive layer 2. After the encapsulation is completed, the electrode wire 3 can be led out from the wire hole on the encapsulation layer film.

[0070] In summary, the flexible strain sensor and its fabrication method provided by this invention cleverly design the structure of the interdigitated electrodes, enabling the change in C1 (i.e., the capacitor formed by the overlapping part of the interdigitated electrodes) caused by stretching / contraction to be controlled. C1 is much larger than the change produced by C2 (i.e., the capacitor formed by the interdigitated fingertip and the base of the finger). C2 makes the effect of C2 negligible during stretching / contraction, thereby greatly improving the linearity of capacitance change during stretching / contraction. Combined with a sensitive layer 2 made of carbon fiber material and a PDMS encapsulation layer 1, the flexible strain sensor formed by multiple pairs of parallel plate capacitors has the advantages of high linearity, wide strain range, and high sensitivity, while also being insensitive to pressure.

[0071] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The present invention is limited only by the claims and their full scope and equivalents. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

[0072] Those skilled in the art will understand that, besides implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0073] Furthermore, all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0074] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A flexible strain sensor, comprising: The system comprises a sensitive layer, an encapsulation layer, and electrode wires. The sensitive layer is encapsulated by the encapsulation layer. The sensitive layer is configured as an interdigital electrode structure, and the gap d between each interdigit, the width w of each interdigit, and the dimension d0 between the fingertip and the base of the interdigit are determined based on the stretching amount. L, according to Greater than or equal to 2.5 times The dimensional constraints set allow for changes in the capacitor C1 formed by the interdigitated portions resulting from stretching / shrinking. Much greater than the change in capacitance C2 formed by the interdigital fingertip and the base of the finger. C2, thus making the effect of C2 negligible during stretching / contraction, thereby forming several pairs of parallel plate capacitors, with the electrode lines respectively connected to the two ends of the interdigitated electrodes of the sensitive layer.

2. The flexible strain sensor according to claim 1, wherein the sensitive layer is made of carbon fiber plate, and the carbon fiber plate is formed by pressing several pieces of carbon fiber cloth in a cross-over pattern.

3. The flexible strain sensor according to claim 2, wherein the thickness of the carbon fiber plate is 0.05~0.5mm.

4. The flexible strain sensor according to claim 1, wherein the encapsulation layer is provided with a wire hole, and the electrode wire extends through the wire hole and connects to both ends of the interdigitated electrode of the sensitive layer.

5. The flexible strain sensor according to claim 1, wherein the encapsulation layer is made of any one of polydimethylsiloxane and polyethylene.

6. A method for fabricating a flexible strain sensor, comprising the following steps: In step S100, carbon fiber cloth is pre-impregnated with epoxy resin, and several pieces of carbon fiber pre-impregnated cloth are stacked horizontally and vertically and pressed into carbon fiber sheets by vacuum heating. Step S200: On the carbon fiber plate according to... Greater than or equal to 2.5 times Due to dimensional constraints, the interdigitated electrode structure was fabricated, and electrode wires were connected to both ends of the interdigitated electrode. Step S300 prepares an encapsulation layer film to cover the surface of the carbon fiber plate to form an encapsulation.

7. The method for fabricating a flexible strain sensor according to claim 6, wherein the step of preparing the encapsulation layer film includes: S310 is used to prepare a first solution with a dimethylsilane and curing agent ratio of 10:

1. The solution is poured into a mold, defoamed in a vacuum environment for 20-30 minutes, and then heated at 80°C for 1 hour to obtain the encapsulation layer film.

8. The method for manufacturing a flexible strain sensor according to claim 6, wherein the encapsulation step in step S300 includes: S320 applies the first solution to the encapsulation surface of the encapsulation layer film, wraps the encapsulation layer film around the carbon fiber plate from top to bottom, and removes bubbles in a vacuum environment for 30 minutes, then stands for 24 to 48 hours to wait for curing and complete the encapsulation.

9. A method for fabricating a flexible strain sensor, comprising the following steps: In step S100, carbon fiber cloth is pre-impregnated with epoxy resin, and several pieces of carbon fiber pre-impregnated cloth are stacked horizontally and vertically and pressed into carbon fiber sheets by vacuum heating. Step S200: On the carbon fiber plate according to... Greater than or equal to 2.5 times Under dimensional constraints, the interdigitated electrode structure and the support rod connecting the carbon fiber plates on both sides of the interdigitated electrode were fabricated, and electrode wires were connected to both ends of the interdigitated electrode. Step S300: Prepare a PDMS film to cover the surface of the carbon fiber plate to form an encapsulation, and then cut off the support rod.

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