CN114608436B - Bionic high-performance cobweb-shaped flexible strain sensor and preparation method and application thereof - Google Patents
Bionic high-performance cobweb-shaped flexible strain sensor and preparation method and application thereof Download PDFInfo
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- CN114608436B CN114608436B CN202210298237.7A CN202210298237A CN114608436B CN 114608436 B CN114608436 B CN 114608436B CN 202210298237 A CN202210298237 A CN 202210298237A CN 114608436 B CN114608436 B CN 114608436B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
- G01B7/18—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge using change in resistance
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
- A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
- A61B5/6802—Sensor mounted on worn items
Abstract
The invention relates to the technical field of strain sensors, and provides a bionic high-performance spider-web-shaped flexible strain sensor and a preparation method and application thereof. The flexible strain sensor provided by the invention comprises a flexible film, a conducting layer and leads, wherein the surface of the flexible film is provided with a spider web-V-shaped groove bionic structure, the conducting layer is arranged on the surface of the flexible film, and the leads are connected to two ends of the flexible film. The invention provides a cobweb-shaped V-shaped groove combined bionic strain sensor which takes a scorpion slit sensor and a spider web structure as inspiration and couples the two bionic structures, and the sensor gives consideration to the sensing capability of ultra-sensitive vibration and the high stability and durability of the structure. According to the invention, the bionic structure on the surface of the PET substrate is transferred to the surface of the flexible film by a two-time mold-reversing method, and then the flexible strain sensor can be obtained by depositing the conducting layer and the connecting wire.
Description
Technical Field
The invention relates to the technical field of strain sensors, in particular to a bionic high-performance spider-web-shaped flexible strain sensor and a preparation method and application thereof.
Background
Flexible electronic devices are continuously applied to human health monitoring and motion detection, human-computer interaction, intelligent robots and the like, wherein flexible strain sensors are most widely applied due to relatively simple structure, small size and convenient and fast function integration, and the most widely researched flexible strain sensors are wearable strain sensors suitable for being attached to the surface of human skin. Many studies are aimed at improving the performance of the sensor at the present stage, and the method mainly starts from two aspects of functional materials and sensing structures for forming the sensor. The performance of expensive micro-nano materials for improving the sensor is proved, but the preparation cost is too high, so that the common application is not facilitated, researchers aim at high-efficiency bionic sensing structures such as an interlocking structure, a sea urchin-shaped structure, a fish scale laminated structure, an octopus sucker structure and the like, and the bionic structures can improve the sensing performance and reduce the preparation cost.
At present, how to realize the compatibility of high sensitivity and high stability of the flexible strain sensor is a core technical problem in the field. Among the numerous structural designs of flexible strain sensors, the crack structure has the most obvious effect on improving the sensitivity. Choi et al first proposed that a flexible strain sensor was prepared by simulating a spider crack sensing structure, platinum was deposited on the surface of a flexible material polyurethane, and a crack structure was produced by mechanical bending, with a sensitivity (GF) of the sensor as high as 200030. However, the bionic crack structure generates a destructive crack structure on the surface of the functional material in the modes of pre-stretching-stress releasing, mechanical force bending and the like, and the randomness and secondary expansion of the crack generation have adverse effects on the stability and durability of the device. Furthermore, to enhance the stability and durability of the sensor, it can be achieved by improving the compatibility between the different constituent materials of the sensor, such as by Kang et al introducing an intermediate layer of molybdenum between the conductive layer and the base layer, utilizing the molybdenum layer to enhance the adhesion between the base and the metal (Jin Yinbo) layer. Zhang et al prepared a self-healing strain sensor based on unsaturated carboxyl-amine ion interaction using carbon nanotubes/polysiloxane to improve its durability. However, the above preparation methods improve the durability by improving the preparation materials, and the preparation process is complex and is not easy to control, and the cost is high. Therefore, a new sensing structure is still required to be explored to achieve a significant improvement in stability and durability while ensuring high sensitivity.
Fortunately, the biological structures of nature provide inspiration for the design of flexible strain sensing. The scorpions are one of the arachnids which are most sensitive to the micro-nano vibration sensed by the animal kingdom, and the slit receptors of the scorpions can sense the vibration caused by the falling of a sand grain at the position of 20cm around the scorpions, so that the development of the bionic high-sensitivity sensor is promoted. And the stability of spider web structure can effectively resist the load of different degree, alleviate the impact force, damage compensation, guarantees the integrality of function, and this improves stability for bionic sensor and provides the inspiration. The combination of the two biological structure characteristics has important significance for improving the performance of the flexible strain sensor. However, flexible sensors that combine scorpion slot receptors and spider web structures are not currently available.
Disclosure of Invention
In view of the above, the invention provides a bionic high-performance spider-web-shaped flexible strain sensor and a preparation method and application thereof. The flexible strain sensor provided by the invention is novel in structure, realizes the perfect combination of a scorpion suture receptor and a spider web structure, ensures high sensitivity, and obviously improves the stability and durability.
In order to achieve the above object, the present invention provides the following technical solutions:
a bionic high-performance spider-web-shaped flexible strain sensor comprises a flexible film, a conducting layer and leads, wherein the surface of the flexible film is provided with a spider-web-V-shaped groove bionic structure, the conducting layer is arranged on the surface of the flexible film, and the leads are connected to two ends of the flexible film;
the spider web-V-shaped groove bionic structure comprises a plurality of concentric annular V-shaped grooves and a plurality of radial V-shaped grooves; the number of the annular V-shaped grooves is more than or equal to 6; two ends of the radial V-shaped groove are respectively connected with the annular V-shaped groove with the minimum diameter and the maximum diameter; the number of the radial V-shaped grooves is more than or equal to 4.
Preferably, the radial V-grooves and the annular V-grooves have a groove depth of 60 to 140 μm and a groove width of 30 to 80 μm, respectively.
Preferably, the diameter of the circular ring-shaped V-shaped groove with the smallest diameter is 1-3 mm, the radius difference of the adjacent circular ring-shaped V-shaped grooves is 0.5-1.5 mm, and the diameter of the circular ring-shaped V-shaped groove with the largest diameter is 12-20 mm.
Preferably, the number of the radial V-shaped grooves is 4-10, and the included angle between every two adjacent radial V-shaped grooves is 36-90 degrees.
Preferably, the material of the flexible film is a viscoelastic polymer.
Preferably, the flexible film is made of PDMS, rubber or silica gel.
Preferably, the thickness of the conductive layer is 30 to 120nm.
The invention also provides a preparation method of the bionic high-performance spider web-shaped flexible strain sensor, which comprises the following steps:
(1) Scribing a spider web-V-shaped groove bionic structure on a PET substrate, then coating epoxy resin on the PET substrate, heating and curing the epoxy resin, and stripping the cured epoxy resin to obtain an epoxy resin transition layer;
(2) Coating a raw material liquid for preparing a flexible film on the surface of the epoxy resin transition layer, heating and curing the raw material liquid to form a flexible film on the surface of the epoxy resin transition layer, and stripping the flexible film to obtain the flexible film with a spider web-V-shaped groove bionic structure on the surface;
(3) And depositing a conducting layer on the surface of a flexible film with a spider web-V type groove bionic structure on the surface, and then connecting conducting wires on two sides of the flexible film to obtain the bionic high-performance spider web-shaped flexible strain sensor.
Preferably, the carving of the bionic structure of the spider web-V-shaped groove is carried out by a carving machine, the depth of depression of the carving is 2-7, and the pressure value is 2-15.
The invention also provides an application of the bionic high-performance spider-web-shaped flexible strain sensor in the scheme or the bionic high-performance spider-web-shaped flexible strain sensor prepared by the preparation method in human motion detection and voice instantaneity recognition.
The invention provides a bionic high-performance spider-web-shaped flexible strain sensor which comprises a flexible film, a conducting layer and leads, wherein the surface of the flexible film is provided with a spider-web-V-shaped groove bionic structure; the spider web-V-shaped groove bionic structure comprises a plurality of concentric circular ring-shaped V-shaped grooves and a plurality of radial V-shaped grooves; the number of the annular V-shaped grooves is more than or equal to 6; two ends of the radial V-shaped groove are respectively connected with the annular V-shaped groove with the minimum diameter and the maximum diameter; the number of the radial V-shaped grooves is more than or equal to 4. The invention provides a cobweb-shaped V-shaped groove combined bionic strain sensor which takes a scorpion slit sensor and a spider web structure as inspiration and couples the two bionic structures, and the sensor gives consideration to the sensing capability of ultra-sensitive vibration and the high stability and durability of the structure.
The invention also provides a preparation method of the bionic high-performance spider web-shaped flexible strain sensor. According to the invention, firstly, a spider web-V type groove bionic structure is scribed on the surface of a PET substrate, then the bionic structure on the surface of the PET substrate is transferred to the surface of a flexible film (PDMS, rubber or silica gel) through twice mold inversion, and then a conductive layer and a connecting lead are deposited to obtain the flexible strain sensor. The preparation method provided by the invention has the advantages of simple and economical process and repeatability.
Drawings
FIG. 1 is a schematic structural diagram of a bionic high-performance spider-web-shaped flexible strain sensor; wherein: 1-conducting layer, 2-flexible film, 3-spider web-V-shaped groove bionic structure, 4-copper sheet and 5-conducting wire;
FIG. 2 is an enlarged view of the intersection of the annular V-grooves and the radial V-grooves;
FIG. 3 is a schematic structural view of a V-shaped groove;
FIG. 4 is a scanning electron micrograph of a slit receptor of a scorpion, wherein a is the appearance of the scorpion, b is the junction between the tarsal bone and the stone bone, c is the crack structure on the surface cuticle of the slit receptor, and d is the crack structure;
FIG. 5 is a schematic diagram of the structure design and preparation process of a bionic high-performance spider-web-shaped flexible strain sensor (taking PDMS as an example), wherein a is a schematic diagram of the structure design, and b is a schematic diagram of the preparation process;
FIG. 6 is a topography representation diagram of a bionic high-performance cobweb-shaped flexible strain sensor, wherein a is a V-shaped groove stereomicroscope image of the sensor, b is a scanning electron microscope image of a micro-crack generated on a conductive silver layer on the surface of the sensor, and an inset in b is a scanning electron microscope enlarged image of the micro-crack; c is a scanning electron microscope image of the section of the sensor, the dotted line represents the geometric shape and the depth of the V-shaped groove, and d is a scanning electron microscope image of the conductive silver layer on the surface of the bionic sensor;
FIG. 7 is a schematic diagram of the sensing mechanism of a bionic high-performance spider-web-shaped flexible strain sensor;
FIG. 8 shows the stress variation of the tip of a V-groove under different strains;
FIG. 9 is a graph of the angle change of a linear sensor and a spider web sensor in a horizontal bending and stretching condition, wherein a is the linear sensor and b is the spider web sensor;
FIG. 10 is a force cloud of the linear sensor model
FIG. 11 is a force cloud of a spider-web sensor model;
FIG. 12 is a schematic diagram of reference point labeling locations for a linear sensor and a spider web sensor, where a is the linear sensor and b is the spider web sensor;
FIG. 13 is a plot of the incremental angle of reference points for a linear sensor and a spidrome sensor, where a is the linear sensor and b is the spidrome sensor;
FIG. 14 is a schematic diagram of a performance testing experimental device of a sensor in bending and stretching, wherein a is a schematic diagram of a stretching experimental device, and b is a schematic diagram of a bending experimental device;
FIG. 15 is a linear fit of resistance change curves and GF curves of a spider web sensor and a non-structural sensor under different strains;
FIG. 16 shows the results of the test of the number of stabilization cycles of a spider web sensor, wherein the three panels are the relative resistance change curves of 2000-2020, 38000-38020, 78000-78020 cycles;
FIG. 17 shows the results of the measurement of the number of stabilization cycles of the linear sensor, in which 2 small graphs are the relative resistance change curves of 500 th to 520 th and 11500 th to 11520 th cycles, respectively;
FIG. 18 is the response time test results for a spider web sensor;
FIG. 19 is a graph of dynamic pressure of a spider web knot configuration sensor as a function of 0.05kHz vibration;
FIG. 20 is a resistance change curve of a spider web sensor under strain (0% to 2%) during loading and unloading.
Detailed Description
The invention provides a bionic high-performance spider-web-shaped flexible strain sensor which comprises a flexible film, a conducting layer and leads, wherein the surface of the flexible film is provided with a spider-web-V-shaped groove bionic structure;
the spider web-V-shaped groove bionic structure comprises a plurality of concentric annular V-shaped grooves and a plurality of radial V-shaped grooves; the number of the annular V-shaped grooves is more than or equal to 6; two ends of the radial V-shaped grooves are respectively connected with the circular V-shaped grooves with the minimum diameter and the maximum diameter; the number of the radial V-shaped grooves is more than or equal to 4.
In the invention, the schematic structural diagram of the bionic high-performance spider-web-shaped flexible strain sensor is shown in fig. 1, and is explained in detail with reference to fig. 1.
In the present invention, the groove depth of the radial V-grooves and the annular V-grooves is preferably 60 to 140 μm, and more preferably 80 to 120 μm, and the groove width of the radial V-grooves and the annular V-grooves is preferably 30 to 80 μm, and more preferably 40 to 60 μm.
In the present invention, the number of the annular V-shaped grooves is preferably 6 to 10, and more preferably 7 to 8; the diameter of the annular V-shaped groove with the smallest diameter is preferably 1 to 3mm, more preferably 2mm, the radius difference of the adjacent annular V-shaped grooves is preferably 0.5 to 1.5mm, more preferably 1mm, and the diameter of the annular V-shaped groove with the largest diameter is preferably 12 to 20mm, more preferably 16 to 18mm.
In the invention, the number of the radial V-shaped grooves is preferably 4 to 10, more preferably 6 to 8, and most preferably 8; the included angle between two adjacent radial V-shaped grooves is preferably 36-90 degrees, and more preferably 45-60 degrees. In a specific embodiment of the present invention, the included angle between two adjacent radial V-grooves is preferably equal (i.e. several radial V-grooves are uniformly distributed on the circumference of a concentric circle), and is specifically determined according to the number of radial V-grooves, for example, when the number of radial V-grooves is 8, the included angle between two adjacent radial V-grooves is 45 °, and when the number of radial V-grooves is 6, the included angle between two adjacent radial V-grooves is 60 °. In the invention, the radial V-shaped groove is a linear V-shaped groove, the starting point of the radial V-shaped groove is positioned on the circular ring-shaped V-shaped groove with the minimum diameter, the radial V-shaped groove radiates outwards in a linear mode and penetrates through all the circular ring-shaped V-shaped grooves, the end point of the radial V-shaped groove is positioned on the circular ring-shaped V-shaped groove with the maximum diameter, and no radial V-shaped groove passes through the inner part of the circular ring-shaped V-shaped groove with the minimum diameter. In the invention, the specific arrangement mode of the circular ring-shaped V-shaped grooves and the radial V-shaped grooves is shown in figure 1, the enlarged view of the intersection of the circular ring-shaped V-shaped grooves and the radial V-shaped grooves is shown in figure 2, and the structural schematic diagram of the V-shaped grooves is shown in figure 3.
In the present invention, the material of the flexible film is preferably a viscoelastic polymer, more preferably PDMS, rubber (SEPS) or silica gel, and most preferably PDMS; the thickness of the flexible film is preferably 200 to 1000. Mu.m, more preferably 400 to 800. Mu.m. In the present invention, the conductive layer is preferably a conductive metal layer, and more preferably a conductive gold layer or a conductive silver layer, and in a specific embodiment of the present invention, a conductive silver layer is preferably used, which can reduce the cost on the basis of satisfying the conductive requirement; the thickness of the conductive layer is preferably 30 to 120nm, and more preferably 50 to 100nm.
In the invention, the spider web-V-shaped groove bionic structure is specifically positioned on the surface of one side of the flexible film, the conducting layer is specifically positioned on the surface of the flexible film, which is provided with the spider web-V-shaped groove bionic structure, and covers the surface of the V-shaped groove forming the bionic structure, and the conducting layers are attached to the bottom and the inclined plane of the V-shaped groove.
In the present invention, the conductive wires are preferably copper wires, and in a specific embodiment of the present invention, two copper wires are preferably soldered to copper paper, and then the copper paper with the conductive wires soldered thereto is respectively adhered to two ends of the sensor, specifically, to the conductive layer, at the position shown in fig. 1.
The junction of the tarsal bone and the stone bone of the scorpion is provided with a slit receptor which is hypersensitive to the microvibration, a plurality of crack structures are grown on the horny layer on the surface of the slit receptor, as shown in figure 4, a in figure 4 is the appearance of the scorpion, b is the junction of the tarsal bone and the stone bone, c is the crack structure on the horny layer on the surface of the slit receptor, and d is the scanning electron microscope image of the crack structure. When the ground vibration source generates micro-vibration, the vibration is transmitted to the tarsal bones of the scorpions in the ground medium in the form of mechanical wave, so that the tarsal bones are deflected in a micron order to press the slit receptors between the tarsal bones and the stone bones, and then the neurons generate electrophysiological reaction to the micro-vibration. The spider web structure has both a spiral wire buffer load and a radiation wire support web structure, and shows excellent stability under the synergistic effect of the spiral wire buffer load and the radiation wire support web structure. The invention provides a cobweb-shaped V-shaped groove combined bionic strain sensor with a slit-like structure, which is inspired by a high-efficiency sensing structure of a scorpion slit receptor and a spider web structure, and gives consideration to the sensing capability of ultra-sensitive vibration and the high stability and durability of the structure.
The invention also provides a preparation method of the bionic high-performance spider web-shaped flexible strain sensor, which comprises the following steps:
(1) Scribing a spider web-V-shaped groove bionic structure on a PET substrate, then coating epoxy resin on the PET substrate, heating and curing the epoxy resin, and stripping the cured epoxy resin to obtain an epoxy resin transition layer;
(2) Coating a raw material liquid for preparing a flexible film on the surface of the epoxy resin transition layer, heating and curing the raw material liquid to form a flexible film on the surface of the epoxy resin transition layer, and stripping the flexible film to obtain the flexible film with a spider web-V-shaped groove bionic structure on the surface;
(3) And depositing a conducting layer on the surface of a flexible film with a spider web-V type groove bionic structure on the surface, and then connecting conducting wires on two sides of the flexible film to obtain the bionic high-performance spider web-shaped flexible strain sensor.
The method comprises the steps of carving a spider web-V-shaped groove bionic structure on a PET substrate, then coating epoxy resin on the PET substrate, heating and curing the epoxy resin, and stripping the cured epoxy resin to obtain an epoxy resin transition layer. In the invention, the carving of the bionic structure of the spider web-V-shaped groove is preferably carried out by a carving machine, the downward pressing depth value of the carving is preferably 2-7, more preferably 3-6, and the pressure value is preferably 2-15, more preferably 5-10; the invention controls the engraved downward-pressing depth value and the engraved downward-pressing pressure value within the range, and can engrave the V-shaped groove with the size meeting the requirement. In the invention, the epoxy resin is preferably epoxy AB glue; the invention preferably mixes the epoxy A glue and the epoxy B glue (namely the curing agent) according to the weight ratio of 3:1, and then coats the obtained mixture on the PET substrate, in particular to coat the mixture on one surface of the PET substrate with a bionic structure; the coating method is preferably spin coating, the rotating speed of the spin coating is preferably 100 revolutions per minute, and the time of the spin coating is preferably 60s; after the spin coating is completed, the epoxy resin is preferably subjected to vacuum degassing, and specifically, the spin-coated sample is placed into a vacuum degassing machine for degassing. In the present invention, the temperature of the heat curing is preferably 60 ℃ and the time is preferably 1.5h, and the heat curing is preferably performed in an oven. And after curing, peeling off the epoxy resin to obtain an epoxy resin transition layer, wherein the surface of the transition layer is provided with an inverse structure of a bionic structure, and then preparing the flexible film with the bionic structure by taking the epoxy resin transition layer as a mould.
After an epoxy resin transition layer is obtained, coating a raw material liquid for preparing a flexible film on the surface of the epoxy resin transition layer, heating and curing the raw material liquid to form a flexible film on the surface of the epoxy resin transition layer, and peeling the flexible film to obtain the flexible film with the surface provided with a spider web-V-shaped groove bionic structure. In the present invention, the raw material liquid for preparing the flexible film is particularly preferably a raw material liquid for preparing a PDMS film, a raw material liquid for preparing a rubber film, or a raw material liquid for preparing a silicone film, and the components of the raw material liquid are not particularly limited in the present invention, and those known to those skilled in the art may be used. In a specific embodiment of the present invention, when the flexible film is a PDMS film, the raw material liquid preferably includes a PDMS prepolymer and a curing agent, the PDMS prepolymer is preferably in a model of Dow Corning Sylgard184, and the weight ratio of the PDMS prepolymer to the curing agent is preferably 10; the invention has no special requirements on the type of the curing agent, and the curing agent which is well known to a person skilled in the art can be adopted.
In the invention, the raw material liquid for preparing the flexible film is specifically one surface of a bionic structure of an Ardisia purpurea epoxy resin transition layer, and after the coating is finished, vacuum degassing is preferably carried out, and then curing and stripping are carried out in sequence. In the present invention, the vacuum degassing is preferably performed in a vacuum degasser; the invention has no special requirement on the specific conditions of curing, and the curing is carried out according to the conditions well known by the technical personnel in the field according to the specific components of the raw material liquid for preparing the flexible film; when the flexible film is made of PDMS, the heating curing temperature is preferably 80 ℃, and the heating curing time is preferably 2h.
After the flexible film with the surface provided with the spider web-V type groove bionic structure is obtained, a conducting layer is deposited on the surface of the flexible film with the surface provided with the spider web-V type groove bionic structure, and then conducting wires are connected to the two sides of the flexible film to obtain the bionic high-performance spider web-shaped flexible strain sensor. In the invention, the method for depositing the conductive layer is preferably a sputtering method, and the model of the sputtering coating machine is preferably 108auto Cressington sputter coater; in the specific embodiment of the invention, the area of the PDMS membrane is larger, the bionic structure is positioned at the local part of the PDMS membrane, and the invention preferably cuts off the part of the PDMS membrane without the bionic structure and then deposits the conducting layer. The method of connecting the wires has been described above and will not be described in detail here.
The invention also provides an application of the bionic high-performance spider-web-shaped flexible strain sensor in the scheme or the bionic high-performance spider-web-shaped flexible strain sensor prepared by the preparation method in human motion detection and voice instantaneity recognition. In the invention, when the flexible strain sensor is bent or stretched, the resistance of the sensor can be changed, the human body motion detection can be realized by using the resistance change, and the flexible strain sensor has excellent frequency identification capability, so that the flexible strain sensor can be applied to voice prompt identification. The flexible strain sensor combines the characteristics of a scorpion slit sensor and a spider web structure, has high sensitivity, excellent stability and durability, and has wide application prospect in the field. The present invention does not require any particular method for the above applications, and methods known to those skilled in the art can be used.
Fig. 5 is a schematic diagram of the structure design and preparation process of the bionic high-performance spider-web-shaped flexible strain sensor provided by the invention (taking PDMS as an example), wherein (a) is a schematic diagram of the structure design, and (b) is a schematic diagram of the preparation process. The bionic flexible strain sensor is designed based on the hypersensitive sensing ability of a scorpion slit receptor and the high stability of a spider web structure, when the bionic flexible strain sensor is prepared, a mechanical cutting method is used for cutting a V-shaped groove with a spider web structure on a PET film, then an inverted structure is inverted to be molded on epoxy resin of a transition layer, the fluidity of liquid is used for transferring the web structure to a PDMS film, a conductive silver layer is sputtered on the PDMS film with the bionic structure, and finally the strain sensor is connected with wires to obtain the strain sensor.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The type of the carving machine adopted in the embodiment is CAMEO, USA; epoxy AB glue was purchased from Aobang (China) Co., ltd; the model of the spin coater was SC100-SE, purchased from analytical (Beijing) science and technology, inc.; the model of the vacuum degasser is BZF-30, and the vacuum degasser is purchased from Shanghai Boshun industry Co., ltd; the type of the oven is GZX-GF, and the oven is purchased from Longdao instruments and Equipment Co., ltd; PDMS type Dow Corning Sylgard 184; the sputter coater was model 108auto Cressington sputter coater.
Example 1
A preset spider-web structure is engraved on a polyethylene terephthalate (PET) film by using an engraving machine graver, the engraved depression depth value is 5, the pressure value is 3, the depth of an engraved V-shaped groove is 100 micrometers, the width of the engraved V-shaped groove is 80 micrometers, and the finally engraved bionic structure of the spider-web-V-shaped groove comprises 6 concentric circles, the diameter of the smallest circle is 2mm, the diameter of the largest circle is 12mm, the distance between adjacent circles is 1mm, the smallest circle is taken as a starting point, and the largest circle is taken as an ending point and 8 radial V-shaped grooves are engraved at an interval of 45 degrees.
The epoxy AB glue is used for preparing a transition layer, a resin precursor and a curing agent are fully mixed according to the weight ratio of 3:1, then the obtained mixture is uniformly coated on a PET film in a spinning mode, the rotating speed of the spinning mode is 100 revolutions per minute, and the spinning mode is carried out for 60 seconds. Placing the sample into a vacuum degasser to degas for 1h, then placing the sample into a drying oven at 60 ℃ to heat for 1.5h to cure the epoxy resin, stripping the cured epoxy resin from the PET substrate to obtain an epoxy resin transition layer, and taking the epoxy resin transition layer as a mold.
The PDMS prepolymer and the curing agent are mixed according to the weight ratio of 10. Cutting a part with a bionic structure from the PDMS film, wherein the size is 25 multiplied by 15mm, coating a silver layer with the thickness of 100nm on the PDMS film through sputtering, soldering two copper leads on copper paper by tin, and then sticking the copper leads on two ends of the sensor to obtain the bionic high-performance spider-web-shaped flexible strain sensor (subsequently called as a spider-web-shaped sensor).
Comparative example 1
Flexible strain sensor for preparing linear V-shaped groove
The other preparation conditions were the same as in example 1, and only 13 linear V-shaped grooves were used instead of the spider web structure, the depth and width of the V-shaped grooves were the same as in example 1, and the length was 12mm, to obtain a linear V-shaped groove flexible strain sensor (hereinafter referred to as a linear sensor).
Comparative example 2
Preparation of a structureless sensor
Other preparation conditions were the same as in example 1, and only scribing of a spider web structure was omitted to obtain a structure-free sensor.
Morphology characterization and mechanistic analysis:
the obtained spider web sensor was observed at different positions by a stereo microscope and a scanning electron microscope, and the obtained results are shown in fig. 6. As can be seen from a in fig. 6, the sensor surface has an annular groove distribution; when the sensor is bent, microcracks are formed on the surface of the conductive silver layer at the positions of the non-V-shaped grooves due to stretching, as shown in b in FIG. 6, and the insets in b are magnified images of the microcracks. In order to observe the shape of the groove of the sensor, the sensor is broken off under the freezing of liquid nitrogen, the section of the sensor is taken for scanning electron microscope shooting, and the sensor can be clearly seen to be in a V-shaped groove structure as shown in c in figure 6. On top of the sensor is a conductive silver layer, with a thickness of about 100nm, which constitutes the sensor with a flexible base layer PDMS, as shown in fig. 6 at d.
FIG. 7 is a schematic diagram of the sensing mechanism of the spider web sensor, wherein the substrate is PDMS and the functional material is silver; in fig. 7, (i) is a cross-sectional view of a V-shaped groove of the sensor, an included angle θ of the V-shaped groove increases during bending and stretching of the sensor, and the thickness of the conductive silver layer at the tip of the V-shaped groove gradually decreases as shown in ii, iii and iv in fig. 7 (h 1> h2> h 3), and meanwhile, the distance d between the conductive silver nano-particles changes continuously. Firstly, when a sensing element generates small tensile strain, part of the originally contacted conductive silver nano particle units can generate relative slippage to reach a nanoscale tunneling distance, electrons can perform hindered transition between silver atoms to break through a potential barrier to generate a tunneling effect, and can still conduct electricity, but the conduction difficulty is increased to increase the resistance, and at the moment, the calculation formula of the tunneling resistance is shown as formula I:
in formula I: r tunnel Representing the tunnel resistance, V is the potential difference, a is the sectional area of the tunnel, J is the tunnel current density, h is the planck constant, e is the electric quantity, m is the electron mass, λ is the barrier height, and d is the distance between the carbon nanotubes.
In the process of further increasing the opening angle theta, the thickness h of the conductive silver layer is gradually reduced, and then local open circuit occurs, and according to a definition formula (shown in formula II) of conductor resistance, when the cross-sectional area is small, the local open circuit occurs, the number of conductive electronic paths is reduced, and then the resistance is obviously increased.
R = ρ L/S formula II;
in formula II: ρ is the resistivity, L is the length, and S is the cross-sectional area.
FIG. 8 shows the stress variation of the tip of a V-groove under different strains; it can be seen from fig. 8 that the V-groove has a sharp stress concentration characteristic under different strains, and the present invention is directed to designing a sensor by utilizing this particular characteristic of the V-groove.
In addition, the sensor consists of a rigid conductive silver layer and a viscoelastic polymer substrate PDMS, and the long-term service working condition of the sensor is repeated bending and stretching, so that the stability is reduced after a certain period of circulation. The stability is reduced due to two reasons, the first is that repeated bending motion can cause stress concentration at the bottom of the V-shaped groove, and once the concentrated stress f is greater than the allowable material stress delta, the performance of the substrate can be damaged, so that the stability of the sensor is reduced. The second is that the adhesion of the adhesive layer decreases during repeated bending and stretching of the conductive layer and the substrate layer, which generally occurs at the maximum increment of the opening angle of the V-groove.
The angle change of the V-shaped grooves of both structural sensors (straight and spider web) under horizontal bending and stretching is shown in FIG. 9. As shown in fig. 9 a, the angle increment of the whole V-groove is the same under the bending action of the linear V-groove sensor. Compared with the linear V-groove sensor, the angular increment of the V-groove in the mesh sensor is gradually reduced from the middle area to both sides, as shown by b in fig. 9. Further, when fatigue stability degradation occurs at the maximum angular increment, the nearest neighboring regions are sequentially replaced by delaying the stability degradation rate to secure the typical performance of the sensor.
Aiming at the two reasons of the stability reduction of the sensor, in order to further explain the advantages of the spider-web-shaped V-shaped groove structure in stability, a linear V-shaped groove structure is used as a comparison for carrying out finite element analysis. First, it can be seen from the force cloud charts (fig. 10-11) of the two sensor models that the linear V-groove sensor has the highest stress on the middle groove when the same constraint condition is applied, and the maximum stress on the linear sensor is greater than the maximum stress on the spider web sensor (4.021 × 10) -2 MPa>3.821×10 -2 MPa), the stress to which the spider web sensor is subjected is relatively more dispersed. Therefore, the linear sensor can more easily reach the allowable stress value of the material during repeated bending movement, and the material property is more easily damaged.
Secondly, in order to compare the change of the flare angle increment of the two structures during bending and stretching, reference points are marked at different positions of the two sensors (linear type and spider web type), as shown in fig. 12. The V-shaped opening angle increment curves of the two sensor reference points are measured, and the result is shown in fig. 13, wherein a is the V-shaped opening angle increment curve of the linear sensor, and b is the V-shaped opening angle increment curve of the spider-web sensor. The 7 th V-shaped groove of the linear sensor is found to have the largest increment of opening angle by comparison, and the increment reaches 8.9 degrees. When the spider web-like sensor is bent, the maximum increment value of the opening angle of the V-shaped groove is 4.7 degrees and is smaller than that of a linear V-shaped groove sensor (4.7 degrees <8.9 degrees), and the opening angle increment of the V-shaped groove with the same sequence of the spider web-like sensor is smaller, as shown by curves of reference points with the same reference numbers in FIG. 13. In addition, unlike the linear sensor, the net V-shaped groove gradually decreases in angular increment along the groove direction, with the largest angular increment in the middle and symmetrically decreasing on both sides, and it is noted that the angular increment in the linear sensor is larger in the same position in both models, as shown in fig. 13 by the rectangular box mark.
In summary, the linear sensor is most prone to stress concentration in the whole V-shaped groove each time the linear sensor is bent, and once the viscosity of the adhesive layer is reduced due to the excessive stress concentration in the whole V-shaped groove, the stability of the linear sensor is directly affected. Compared with the defect that the whole V-shaped groove structure of a linear sensor is easy to fatigue, the spider-web structure realizes stress dispersion and gradual decrease of the increment of the opening angle through different curvatures of each point, and each ring has the gradual protection function, so that the super-strong durability and stability are shown.
Sensor performance testing
The sensor is bent upwards by pressing the servo motors close to each other, so that the effect similar to stretching is generated, and the sensitivity, stability, durability, response time, frequency identification capability and hysteresis of the sensor are tested.
FIG. 14 is a schematic diagram of an experimental apparatus for testing bending and stretching properties of a spider web sensor. The metal copper sheet pasted with the flexible strain sensor is fixed between the two servo motors with adjustable motion frequency, and the servo motors at the two ends can be close to each other and extrude the sensor to generate an upward bending and stretching-like effect, so that the performance parameters of the sensor can be tested. Sensitivity, the most important performance parameter of a sensor, is defined by GF (Gauge Factor), GF = (Δ R/R0)/Δ ∈, where R0 is the initial resistance of the sensor, Δ R is the difference between the instantaneous resistance and the initial resistance, and Δ ∈ is the strain applied on the sensor. The presence of microcracks at non-V-grooves was found in the sensor structure characterization as shown in fig. 6 b, and the effect of the V-groove structure on the sensor sensitivity was demonstrated by comparing the performance of the spider-web structured sensor provided by the present invention with the unstructured sensor prepared in comparative example 2 through comparative testing experiments.
The sensitivity test result is as follows:
fig. 15 is the relative resistance change for spider web sensors and unstructured sensors at different tensile strains. The fact that the resistance change of the whole sensing element can be divided into two stages for the spider-web sensor through the fitting of the resistance change quantity of the sensor and a strain curve is found, when the sensor is stretched, when the strain is 0% -1.5%, the sensitivity is GF 940.5, and when the distance between the tip of the V-shaped groove and the conductive silver nano particles at the surface microcracks is increased to a certain degree, electrons penetrate through a non-conductive barrier to generate a tunneling effect, and the resistance is increased. When the bending and stretching are continued and the strain range is 1.5% -2.5%, the sensitivity GF reaches 2742.3, because the thickness (h) of the conductive silver layer deposited at the bottom of the V-shaped groove by the sensor is gradually reduced in the process of increasing the opening angle, the number of conductive paths of the conductive silver nano particles at the tip of the V-shaped groove parallel to the current direction is sharply reduced, local open circuit occurs, and the resistance is remarkably increased. By contrast, the sensitivity of the unstructured sensor was 367.1 under the same strain range, further demonstrating the significant effect of the V-groove on the improvement of the sensor sensitivity.
Stability and durability test results:
the stability and the durability are measured by the number of cycle periods that the relative resistance variation of the sensor does not drift or obviously change in the test, and are also important indexes of whether the sensor can be applied for a long time in real life. To demonstrate the stability and durability of a spider web structure sensor, the sensor strain is now varied from 0% to 0.75%, the number of stabilization cycles of the sensor is measured, and to further observe the repeatability of the sensor, the relative resistance changes of 2000-2020, 38000-38020, 78000-78020 cycles of the test sensor are selected. The results of the test of the number of stable cycles of the spider web sensor are shown in FIG. 16, and the three small graphs in FIG. 16 are relative resistance change curves of 2000-2020, 38000-38020, 78000-78020 cycles, respectively. As can be seen from FIG. 15, the stable cycle number of the spider-web sensor is as high as 80000 times, and the relative resistance change curves of 2000-2020, 38000-38020, 78000-78020 cycles show that the relative resistance change amount does not drift or change obviously, which indicates that the spider-web sensor of the invention has better stability and durability.
To further highlight the significant improvement in sensor stability by the spider web structure, the stability of the linear sensor prepared in comparative example 1 was tested and the relative resistance change of the 500-520, 11500-11520 cycle test sensors was selected. As shown in fig. 17, it can be seen from fig. 17 that the linear sensor is relatively stable at 10000 cycles, and the resistance change curve is irregular after 12000 cycles.
Furthermore, the sensitivity and stability of the spider web sensors of the invention were compared to other strain sensors reported in recent literature, and the results are shown in table 1.
TABLE 1 comparison of the Performance of the spider web configuration sensor with other sensors
In table 1:
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response time, frequency identification capability and hysteresis test results:
the response time refers to the time required by the sensor when the output signal jumps and reaches a steady state when external excitation is loaded and unloaded, and is also the basis for real-time monitoring of the sensor.
FIG. 18 is the response time test results for a spider web sensor. As can be seen from fig. 18, the response time of the sensor at the instant loading time is 169ms, and the response time at the unloading time is 195ms, so that the response time of the sensor is about 182ms, and the fast response characteristic shown by the sensor is important for being applied to real-time monitoring.
A modal vibration exciter (JZK-2, sinocera Piezotronics) is used as an input source of a vibration signal, when the vibration signal with the frequency of 50Hz and the amplitude of 10V is input to a sensing element, a resistance output signal of the sensing element is recorded by using a digital multimeter (NPLC: 0.0001), fourier transform is carried out on the recorded resistance signal for carrying out spectrum analysis, and the frequency of an obtained main frequency signal is 49.96Hz and is highly consistent with the frequency of the input vibration signal. Specific detection results are shown in fig. 19, in which fig. 19 shows the change in dynamic pressure of the spider-web knot sensor with 50Hz vibration, and the inset in fig. 19 shows the frequency (50 Hz) measured in the shaded area. As can be seen, the spider web sensor provided by the invention still has response identification capability to vibration signals with the frequency of 50Hz, which shows that the spider web sensor has excellent frequency identification capability.
FIG. 20 is a resistance change curve of a spider web sensor under strain (0% to 2%) during loading and unloading. From FIG. 20, it can be seen that the relative resistance increase fitted curve of the spider web sensor during loading and unloading at 0-2% strain is close, indicating that it has lower hysteresis performance.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A bionic high-performance spider-web-shaped flexible strain sensor comprises a flexible film, a conducting layer and leads, wherein the surface of the flexible film is provided with a spider-web-V-shaped groove bionic structure, the conducting layer is arranged on the surface of the flexible film, and the leads are connected to two ends of the flexible film;
the spider web-V-shaped groove bionic structure comprises a plurality of concentric circular ring-shaped V-shaped grooves and a plurality of radial V-shaped grooves;
the number of the annular V-shaped grooves is 6; the diameter of the circular V-shaped groove with the smallest diameter is 2mm, the radius difference of the adjacent circular V-shaped grooves is 1mm, and the diameter of the circular V-shaped groove with the largest diameter is 12mm; two ends of the radial V-shaped groove are respectively connected with the annular V-shaped groove with the minimum diameter and the maximum diameter; the number of the radial V-shaped grooves is 8, and the included angle between every two adjacent radial V-shaped grooves is 45 degrees.
2. The biomimetic high performance spider web-like flexible strain sensor according to claim 1, wherein the groove depths of the radial V-shaped grooves and the circular ring-shaped V-shaped grooves are independently 60 to 140 μm, and the groove widths are independently 30 to 80 μm.
3. The biomimetic high-performance spider web-like flexible strain sensor according to claim 1, wherein the material of the flexible film is a viscoelastic polymer.
4. A biomimetic high performance spider web-like flexible strain sensor according to claim 1 or 3, wherein the material of the flexible film is PDMS, rubber or silica gel.
5. A biomimetic high performance spider web-like flexible strain sensor according to claim 1, characterized in that the thickness of the conductive layer is 30-120 nm.
6. A method for the preparation of a biomimetic high performance spider web flexible strain sensor according to any of claims 1 to 5, comprising the steps of:
(1) Scribing a spider web-V-shaped groove bionic structure on a PET substrate, then coating epoxy resin on the PET substrate, heating and curing the epoxy resin, and stripping the cured epoxy resin to obtain an epoxy resin transition layer;
(2) Coating a raw material liquid for preparing a flexible film on the surface of the epoxy resin transition layer, heating and curing the raw material liquid to form a flexible film on the surface of the epoxy resin transition layer, and stripping the flexible film to obtain the flexible film with a spider web-V-shaped groove bionic structure on the surface;
(3) And depositing a conducting layer on the surface of a flexible film with a spider web-V type groove bionic structure on the surface, and then connecting conducting wires on two sides of the flexible film to obtain the bionic high-performance spider web-shaped flexible strain sensor.
7. The preparation method of claim 6, wherein the scribing of the bionic structure of the spider web-V type groove is performed by a carving machine, the depth of depression of the scribing is 2-7, and the pressure value is 2-15.
8. The application of the bionic high-performance spider-web flexible strain sensor of any one of claims 1 to 5 or the bionic high-performance spider-web flexible strain sensor prepared by the preparation method of any one of claims 6 to 7 in human motion detection and speech immediacy recognition.
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| CN111649665A (en) * | 2020-06-18 | 2020-09-11 | 西南石油大学 | Cobweb-shaped flexible strain sensor capable of identifying strain direction and preparation method thereof |
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| CN110763132A (en) * | 2019-11-06 | 2020-02-07 | 吉林大学 | Omnidirectional sensing bionic strain sensor and preparation method thereof |
| CN111649665A (en) * | 2020-06-18 | 2020-09-11 | 西南石油大学 | Cobweb-shaped flexible strain sensor capable of identifying strain direction and preparation method thereof |
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