CN112067175A - Flexible capacitive sensor and preparation method and application thereof - Google Patents
Flexible capacitive sensor and preparation method and application thereof Download PDFInfo
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- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/14—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
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- 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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- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/12—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in capacitance, i.e. electric circuits therefor
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Abstract
The invention relates to the technical field of flexible sensors, in particular to a flexible sensor and a preparation method and application thereof. According to the flexible capacitive sensor provided by the invention, the porosity of the dielectric layer is further improved due to the design of the multiple holes and the through holes, so that the elastic modulus of the substrate material is favorably reduced, and the larger deformation is generated under the same stress action. Meanwhile, the polypyrrole is loaded on the filter paper substrate, so that the electrode layer has a rough surface structure, and the performance of the sensor is improved under the synergistic effect of the porous structure and the rough electrode surface structure.
Description
Technical Field
The invention relates to the technical field of flexible sensors, in particular to a flexible sensor and a preparation method and application thereof.
Background
The flexible pressure sensor is one of the key components of future human-computer interfaces, human motion monitoring, electronic skins, soft robots and the like. Pressure sensors can be classified into piezoresistive, capacitive, piezoelectric, and triboelectric devices, depending on the switching mechanism. The capacitive pressure sensor with the advantages of low power consumption, simple equipment manufacturing and the like is mainly used for wearable human motion detection. While a typical capacitive pressure sensor consists of a deformable dielectric material sandwiched between two flexible conductive electrodes. Under the application of pressure, the thickness and area of the dielectric layer will change, resulting in a change in capacitance. However, pure elastic dielectric materials deform very little under pressure, resulting in low sensitivity response, which affects sensor performance improvement. Therefore, by different structural designs, changing the deformation under pressure is critical to the performance of the capacitive sensor. Currently, the design of structures can be divided into two categories: one is the addition of surface microstructure, and the dielectric layer with irregular surface convex structures such as pyramids, columns or wrinkles is obtained by methods such as laser etching or silicon template. The capacitance sensor can obtain higher sensitivity response under smaller pressure, but the deformation of the dielectric layer of the sensor is no longer obvious along with the increase of the pressure due to the smaller deformability of the surface microstructure, and the sensitivity is obviously suddenly reduced. Moreover, the microstructure preparation based on the etching or template process has the advantages of complex process, difficult operation, difficult control and unsuitability for large-area production. For example, chinese patent No. cn201911328978.x discloses a method for manufacturing a capacitive sensor, which is composed of upper and lower electrode layers made of flexible conductive silicone rubber and an intermediate dielectric layer made of pure silicone rubber. After surface microstructures with different roughness are introduced into the electrode layer and the dielectric layer, the sensor has different sensitivities and is used for detecting human body signals. However, the design of the microstructure can only maintain high-sensitivity response under small pressure, the application range is limited, and the pure PDMS film has poor air permeability and is not beneficial to being attached to a human body for detection; chinese patent No. cn2019111300990.x discloses a multifunctional flexible sensor, and a preparation method and application thereof. The functional flexible sensor comprises a bottom layer flexible substrate, a lower surface electrode, a middle dielectric layer, a conductive electrode, an upper surface electrode and a top layer flexible substrate from bottom to top. The surface of the flexible dielectric layer is provided with a microstructure bulge, one end of the upper surface electrode is connected with a lead extraction electrode, and a corresponding notch is arranged at the position of the lead of the upper surface electrode; the invention restores the tactile feeling of the manipulator, realizes the measurement of temperature, distance and stress, reduces the requirements on the number of leads and lead interfaces, and solves the problem of single function of the existing electronic skin. But the metal electrodes reduce flexibility to some extent.
The other type is a sponge-like porous structure, and soluble materials are used as templates of the porous structure. However, the porous structure is limited by the mass ratio of the dissolved material to the substrate material, and has certain limitation on the improvement of the porosity and lower sensitivity. For example, patent No. CN201910936969.2 discloses a method for manufacturing a flexible capacitive sensor. The upper electrode and the lower electrode are made of liquid metal wrapped by flexible materials, and the middle dielectric layer is an elastomer containing a multi-level stepped mesoporous microstructure. The dielectric layer of the multi-layer stepped mesoporous microstructure can realize the positioning of space and the detection of pressure sensing, the design of the mesoporous microstructure can reduce the elastic modulus along with the increase of the porosity of an elastic film, reduce the rigidity of materials, enable the dielectric layer to be easier to deform under the same pressure action, improve the sensitivity of a pressure sensor, and form a regular layered stepped mesoporous structure because the pore diameter distribution in the dielectric layer is arranged from large to small in the vertical direction, thereby effectively controlling the thickness change rate of the dielectric layer and improving the capacitance change linearity of the capacitance sensor. However, the filling of the liquid metal requires a photolithography technique to prepare a mask, and then an adhesion layer is sputtered on the mask, so that the preparation process is complicated and the cost is high.
Disclosure of Invention
The invention aims to provide a flexible sensor, a preparation method and application thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a flexible capacitive sensor, which comprises a first electrode layer, a dielectric layer and a second electrode layer which are sequentially stacked;
the first electrode layer and the second electrode layer independently comprise a filter paper substrate and polypyrrole loaded on the filter paper substrate;
the dielectric layer is an elastomer with a porous structure;
the dielectric layer includes through holes of an array structure.
Preferably, the polypyrrole is supported on the filter paper matrix of 0.0045 +/-0.0005 g per square centimeter.
Preferably, the elastomeric material comprises polydimethylsiloxane, thermoplastic polyurethane or silicone rubber.
The invention also provides a preparation method of the flexible capacitive sensor in the technical scheme, which comprises the following steps:
mixing a dielectric layer material and a pore-forming agent to obtain a mixture;
sequentially pre-curing the mixture in the groove to obtain a pre-cured mixture;
after inserting a cylindrical needle head into the pre-cured mixture, curing, and removing the cylindrical needle head and the pore-forming agent to obtain the dielectric layer;
soaking filter paper in ferric chloride solution, placing the filter paper in a vacuum glass closed container containing liquid pyrrole, and polymerizing to respectively prepare a first electrode and a second electrode;
and preparing the flexible capacitive sensor according to the sequence of the first electrode, the dielectric layer and the second electrode.
Preferably, the mass ratio of the dielectric layer material to the pore-forming agent is 1: (2-4);
the pore-forming agent is sodium chloride and/or sugar.
Preferably, the pre-curing temperature is 80-150 ℃, and the pre-curing time is 3-10 min.
Preferably, the curing temperature is 80-150 ℃, and the curing time is 3-120 min.
Preferably, the concentration of the ferric chloride solution is 1-2 mol/L;
the soaking time is 10-30 min.
Preferably, the polymerization time is 6-24 h.
The invention also provides the application of the flexible capacitive sensor in the technical scheme or the application of the flexible capacitive sensor prepared by the preparation method in the technical scheme in the fields of human-computer interfaces, human body motion monitoring, electronic skins or soft robots.
The invention provides a flexible capacitive sensor, which comprises a first electrode layer, a dielectric layer and a second electrode layer which are sequentially stacked; the first electrode layer and the second electrode layer independently comprise a filter paper substrate and polypyrrole loaded on the filter paper substrate; the dielectric layer is an elastomer with a porous structure; the dielectric layer includes through holes of an array structure. According to the invention, through the design of the porous structure and the through hole, the porosity of the dielectric layer is further improved, the elastic modulus of the substrate material is favorably reduced, and larger deformation is generated under the same stress action. Meanwhile, polypyrrole is loaded on the filter paper substrate, so that the electrode layer has a rough surface structure. Therefore, under the synergistic effect of the porous structure and the rough electrode surface structure, the sensitivity of the sensor is improved.
Drawings
FIG. 1 is an SEM photograph of a dielectric layer and a first electrode prepared in example 1;
FIG. 2 is a schematic structural diagram of a flexible capacitive sensor according to the present invention;
FIG. 3 is a schematic diagram of a process for making a flexible capacitive sensor according to the present invention;
FIG. 4 is an SEM photograph (a) of a via structure of a dielectric layer in example 2, a sensor performance test chart (b) of sensors prepared in examples 1-2 and comparative example 2, and a sensor performance test chart (c) of sensors prepared in comparative example 3 and example 1;
FIG. 5 is a graph showing the capacitance properties of the dielectric layers prepared in comparative examples 1 to 2 and example 1 and the capacitance change rate of the dielectric layers prepared in comparative example 2 and example 1 in a small pressure range of 1 kPa;
fig. 6 is a capacitance response graph of the flexible capacitance sensor prepared in example 1 applied to different parts of a human body.
Detailed Description
The invention provides a flexible capacitive sensor, which comprises a first electrode layer, a dielectric layer and a second electrode layer which are sequentially stacked;
the first electrode layer and the second electrode layer comprise a filter paper substrate and polypyrrole loaded on the filter paper substrate;
the dielectric layer is an elastomer with a porous structure;
the dielectric layer includes through holes of an array structure.
In the invention, the flexible capacitive sensor comprises a first electrode layer and a second electrode layer, wherein the first electrode layer and the second electrode layer independently comprise a filter paper substrate and polypyrrole loaded on the filter paper substrate; the polypyrrole is preferably supported at a level of 0.0045. + -. 0.0005g per square centimeter of the filter paper substrate. In the present invention, the thicknesses of the first electrode layer and the second electrode layer are independently preferably 0.2 ± 0.05 mm.
In the present invention, the flexible capacitive sensor comprises a dielectric layer which is an elastomer of a porous structure; the dielectric layer comprises through holes of an array structure; the arrangement mode of the through holes is preferably as follows: every 1cm2The dielectric layer of (2) comprises through holes with the diameter of 0.8mm and the array of 6 multiplied by 6; or per 1cm2In the dielectric layer of (2), which includes 2.02mm diameter and 2 × 2 array of through holes (the schematic structure is shown in fig. 2), the porosity of the dielectric layer is preferably 78 ± 3%. In the invention, the thickness of the dielectric layer is preferably 2-3 mm, and more preferably 2 mm. In the present invention, the material of the elastomer preferably includes polydimethylsiloxane, thermoplastic polyurethane or silicone rubber, and more preferably polydimethylsiloxane.
The invention also provides a preparation method of the flexible capacitive sensor in the technical scheme, which comprises the following steps:
mixing a dielectric layer material and a pore-forming agent to obtain a mixture;
sequentially pre-curing the mixture in the groove to obtain a pre-cured mixture;
after inserting a cylindrical needle head into the pre-cured mixture, curing, and removing the cylindrical needle head and the pore-forming agent to obtain the dielectric layer;
soaking filter paper in ferric chloride solution, placing the filter paper in a vacuum glass closed container containing liquid pyrrole, and polymerizing to respectively prepare a first electrode and a second electrode;
and preparing the flexible capacitive sensor according to the sequence of the first electrode, the dielectric layer and the second electrode.
In the present invention, all the raw materials are commercially available products well known to those skilled in the art unless otherwise specified.
The invention mixes the dielectric layer material and pore-forming agent to obtain the mixture.
In the present invention, when the dielectric layer is a polydimethylsiloxane layer with a porous structure, the dielectric layer material preferably includes a polydimethylsiloxane prepolymer and a curing agent. In the present invention, the polydimethylsiloxane prepolymer is preferably available from Dow Corning 184A; the curative is preferably available from Dow Corning 184B, USA. In the present invention, the mass ratio of the polydimethylsiloxane to the curing agent is preferably 10: 1.
In the present invention, the preparation method of the dielectric layer material is preferably: and sequentially mixing and defoaming the polydimethylsiloxane and the curing agent to obtain the dielectric layer material. In the present invention, the mixing and defoaming treatments are performed simultaneously; the mixing and defoaming treatment is preferably carried out under stirring conditions, and the stirring rate is not particularly limited in the present invention and may be carried out at a rate well known to those skilled in the art; the stirring time is preferably 10-20 min, more preferably 12-18 min, and most preferably 14-16 min.
In the present invention, when the dielectric layer is a thermoplastic polyurethane layer with a porous structure, a polydimethylsiloxane layer with a porous structure or a silicone rubber layer with a porous structure, the dielectric layer material is preferably thermoplastic polyurethane, polydimethylsiloxane or silicone rubber.
In the invention, the pore-forming agent is preferably sodium chloride and/or sugar; when the pore-forming agent is sodium chloride and sugar cube, the mass ratio of the sodium chloride to the sugar cube is not limited in any way, and the sodium chloride and the sugar cube can be mixed according to any proportion. In the present invention, the pore-forming agent preferably has a particle diameter of 30nm to 800. mu.m, more preferably 200nm to 100. mu.m.
Before mixing a dielectric layer material and a pore-forming agent, and when the pore-forming agent is sodium chloride, preferably, the sodium chloride is pretreated; the pre-treatment is preferably to place sodium chloride in deionized water for full dissolution, then place the sodium chloride in a water bath kettle at 90 ℃, evaporate water to obtain recrystallized sodium chloride and then grind the sodium chloride. When the pore-forming agent is the cubic sugar, the invention has no special limitation on whether the cubic sugar is pretreated, as long as the particle size of the cubic sugar is ensured to be within the range of 30nm to 800 μm.
In the present invention, the mass ratio of the dielectric layer material to the pore-forming agent is preferably 1: (2-4), more preferably 1: (3-4). In the present invention, the mixing is preferably carried out under stirring, and the stirring is not particularly limited in the present invention and may be carried out by a process known to those skilled in the art.
After the mixture is obtained, the mixture is sequentially pre-cured in the groove to obtain the pre-cured mixture. In the present invention, the grooves are preferably grooves each having a length, a width, and a thickness of 1cm and 0.2 mm. According to the invention, the mixture is preferably spread in the groove before being pre-cured in the groove, and the pre-curing is carried out after the surface is scraped flat. In the invention, the pre-curing temperature is preferably 80-150 ℃, more preferably 90-120 ℃, and the pre-curing time is preferably 3-10 min, more preferably 3-5 min.
After the pre-cured mixture is obtained, the pre-cured mixture is solidified after a cylindrical needle head is inserted into the pre-cured mixture, and the cylindrical needle head and the pore-forming agent are removed to obtain the dielectric layer. In the present invention, the cylindrical needle is preferably provided at a rate of 1cm per needle2With inserts of diameter 0.8mm and array 6X 6In a manner of or per 1cm2The diameter of the insert was 2.02mm and the array was 2X 2. In the present invention, the cylindrical needle is preferably kept in an upright state in the pre-solidified mixture. In the invention, the curing temperature is preferably 80-150 ℃, more preferably 90-120 ℃, and the curing time is preferably 3-120 min, more preferably 10-100 min.
In the present invention, the mode of removing the curing agent is preferably: the membrane with the cylindrical needle removed was taken out of the recess and then placed in a 60 ℃ water bath with 1 water change every 1 hour. Until the pore former is sufficiently dissolved.
After removing the pore-forming agent, the present invention also preferably includes drying, preferably natural drying in air.
The preparation method of the flexible capacitive sensor further comprises the steps of soaking the filter paper in ferric chloride solution, placing the filter paper in a vacuum glass closed container containing liquid pyrrole, and polymerizing to respectively prepare the first electrode and the second electrode. In the invention, the concentration of the ferric chloride solution is preferably 1-2 mol/L, more preferably 1.2-1.8 mol/L, and most preferably 1.4-1.6 mol/L. In the present invention, the size of the filter paper is preferably 1X 1cm or more2. The thickness of the filter paper is preferably 0.2-0.3 mm.
In the invention, the soaking time is preferably 10-30 min, more preferably 15-25 min, and most preferably 18-22 min.
The vacuum glass closed container is not particularly limited in the present invention, and any apparatus known in the art may be used. The dosage of the liquid pyrrole is not specially limited, and the loading capacity of the polypyrrole on each square centimeter of filter paper substrate is ensured to be 0.0045 +/-0.0005 g. In the invention, the polymerization temperature is preferably 25 ℃, and the polymerization time is preferably 6-24 h, more preferably 10-20 h, and most preferably 14-16 h.
After the polymerization reaction is completed, the present invention preferably further comprises taking out the filter paper, washing the filter paper with absolute ethyl alcohol and distilled water repeatedly in sequence, and drying the filter paper. The drying temperature is preferably 30-80 ℃, and more preferably 60-70 ℃; the drying is preferably carried out in an oven.
After the first electrode, the second electrode and the dielectric layer are respectively prepared, the flexible capacitive sensor is prepared according to the sequence of the first electrode, the dielectric layer and the second electrode (the preparation process of the flexible capacitive sensor is shown in fig. 3). In the invention, the first electrode, the dielectric layer and the second electrode are preferably fixed by a transparent adhesive tape in a physical attaching mode to prepare the flexible capacitive sensor.
The invention also provides the application of the flexible capacitive sensor in the technical scheme or the application of the flexible capacitive sensor prepared by the preparation method in the technical scheme in the fields of human-computer interfaces, human body motion monitoring, electronic skins or soft robots. The method of the present invention is not particularly limited, and may be carried out by a method known to those skilled in the art.
The flexible capacitive sensor and the method for manufacturing and using the same according to the present invention will be described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.
Note: the mass ratio referred to in the examples is not limited to the unit grade of the amount of each raw material, and may be "g" grade, "kg" grade, t "grade, or the like.
Example 1
Mixing polydimethylsiloxane prepolymer (PDMS, SYLGARD 184A) and curing agent (SYLGARD 184B) for 10min under the condition of stirring according to the mass ratio of 10:1, standing to remove bubbles, and mixing the obtained dielectric layer material and sodium chloride (the particle size is 19 nm-122 mu m) according to the mass ratio of 1:4 under the condition of stirring to obtain a mixture;
spreading the mixture in grooves with length and width of 1cm and thickness of 0.2mm, scraping the surface, pre-curing at 150 deg.C for 3min, and pre-curing in the mixture per 1cm2Inserting cylindrical needles with diameter of 0.8mm and array of 6 × 6, solidifying at 150 deg.C for 10min, taking out the solidified membrane from the groove, and dissolving NaCl in 60 deg.C waterDissolving, changing water every other hour for 1 time, and naturally drying in air to obtain a dielectric layer (with a thickness of 2 mm);
mixing 1X 1cm2Soaking 0.2mm thick filter paper in 1.5mol/L ferric chloride solution for 10min, then placing the filter paper in a vacuum glass closed container containing liquid pyrrole for polymerization for 12 h, taking out the filter paper, repeatedly cleaning the filter paper with absolute ethyl alcohol and distilled water, and drying the filter paper in an oven at 60 ℃ to respectively prepare a first electrode and a second electrode;
placing a dielectric layer between the first electrode and the second electrode in a physical attaching mode to form a sandwich structure, and fixing the sandwich structure by using a transparent adhesive tape to obtain the flexible capacitive sensor (the thickness of the first electrode layer and the second electrode layer is 0.27mm, and the thickness of the dielectric layer is 2 mm);
subjecting the dielectric layer to SEM test, as shown in a and b in FIG. 1, wherein a is SEM image of porous structure of the dielectric layer, and b is SEM image of via structure of the dielectric layer; as can be seen from a and b in fig. 1, porous structures with different sizes are obtained by dissolving salt particles, and a clear through hole structure is obtained on the basis of the porous structures;
the first electrode was subjected to SEM test, as shown in fig. 1c and d, wherein c is an SEM image of the first electrode and d is an SEM image of polypyrrole granules in the first electrode, and as can be seen from fig. 1c and d, the porous and fibrous morphology of the filter paper was maintained at the PPy/filter paper surface, and the polypyrrole granules were uniformly covered on the filter paper surface, and the average diameter was about 228 nm.
Example 2
Mixing polydimethylsiloxane prepolymer (PDMS, SYLGARD 184A) and curing agent (SYLGARD 184B) for 10min under the condition of stirring according to the mass ratio of 10:1, standing to remove bubbles, and mixing the obtained dielectric layer material and sodium chloride (the particle size is 19 nm-122 mu m) according to the mass ratio of 1:4 under the condition of stirring to obtain a mixture;
spreading the mixture in grooves with length and width of 1cm and thickness of 0.2mm, scraping the surface, pre-curing at 150 deg.C for 3min, and pre-curing in the mixture per 1cm2The diameter of the insert is 2.02mm, the array is 2 multiplied by 2 cylinders, after curing is carried out for 10min at the temperature of 150 ℃, the cured film is taken out from the groove, then the film is placed in water at the temperature of 60 ℃ to fully dissolve NaCl, the water is changed for 1 time every hour, and the film is placed in the air to be naturally dried, so that a dielectric layer (the thickness is 2mm) is obtained;
mixing 1X 1cm2Soaking 0.2mm thick filter paper in 1.5mol/L ferric chloride solution for 10min, then placing the filter paper in a vacuum glass closed container containing liquid pyrrole for polymerization for 12 h, taking out the filter paper, repeatedly cleaning the filter paper with absolute ethyl alcohol and distilled water, and drying the filter paper in an oven at 60 ℃ to respectively prepare a first electrode and a second electrode;
placing a dielectric layer between the first electrode and the second electrode in a physical attaching mode to form a sandwich structure, and fixing the sandwich structure by using a transparent adhesive tape to obtain the flexible capacitive sensor (the thickness of the first electrode layer and the second electrode layer is 0.27mm, and the thickness of the dielectric layer is 2 mm);
performing SEM test and sensing performance test on the dielectric layer, wherein a is an SEM image of a through hole structure of the dielectric layer and the diameter of the through hole is about 2.02 +/-0.09 mm, as shown in a and b in FIG. 4; and b is a sensor performance test chart prepared by different pore sizes, the capacitance variation of the sensor with a porous structure and without a through hole is the minimum under the same pressure condition, the variation of the sensor with the porous structure and the large-pore-diameter through hole is higher than that of the sensor without the through hole, and the capacitance variation of the sensor with the porous structure and the small-pore-diameter through hole is the maximum, so that the sensitivity of the sensor is favorably improved.
Comparative example 1
With reference to example 1, the only difference is:
mixing polydimethylsiloxane prepolymer (PDMS, SYLGARD 184A) and curing agent (SYLGARD 184B) under stirring for 10min, standing to remove bubbles to obtain a mixture;
spreading the mixture in grooves with length and width of 1cm and thickness of 0.2mm, scraping the surface, and curing at 150 deg.C for 13min to obtain the dielectric layer.
Comparative example 2
With reference to example 1, the only difference is:
mixing polydimethylsiloxane prepolymer (PDMS, SYLGARD 184A) and curing agent (SYLGARD 184B) for 10min under the condition of stirring according to the mass ratio of 10:1, standing to remove bubbles, and mixing the obtained dielectric layer material and sodium chloride (the particle size is 19 nm-122 mu m) according to the mass ratio of 1:4 under the condition of stirring to obtain a mixture;
and paving the mixture in grooves with the length and the width of 1cm and the thickness of 0.2mm, scraping the surface of the mixture to be flat, curing the mixture at 150 ℃ for 13min, taking out the cured film from the grooves, then placing the film in water with the temperature of 60 ℃ to fully dissolve NaCl, changing the water every other hour for 1 time, and placing the film in air to be naturally dried to obtain the dielectric layer.
Comparative example 3
Based on the embodiment 1, the material of the first electrode and the second electrode is changed from polypyrrole/filter paper to copper foil, and the size is the same as that of the embodiment 1. Commercial copper foil was purchased from Tianjin local market with a thickness of 0.01 mm. The copper foil was made to the desired size with scissors. The copper foil had a smooth surface with no noticeable graininess compared to polypyrrole/filter paper. And (2) placing a dielectric layer between the first electrode and the second electrode which are made of copper foils in a physical attaching mode to form a sandwich structure, and fixing the sandwich structure by using a transparent adhesive tape to obtain the flexible capacitive sensor (the thickness of the first electrode layer and the second electrode layer is 0.02mm, and the thickness of the dielectric layer is 2 mm). The sensor was then tested for sensing performance and compared to a polypyrrole/filter paper electrode as shown in c of figure 4. The copper foil electrode has low roughness because no polypyrrole particles exist on the surface, and the capacitance variation is lower than that of a sensor taking polypyrrole/filter paper as an electrode in a small pressure detection range.
Test example
Respectively carrying out capacitance performance tests on the dielectric layers prepared in comparative examples 1-2 and example 1, and respectively carrying out capacitance sensitivity performance tests on the dielectric layers prepared in comparative example 2 and example 1 under small pressure;
the performance testing device of the capacitance sensor comprises a stepping motor, an LCR digital meter, a mechanical testing system and a computer, wherein pressure is gradually applied through the stepping motor, the mechanical testing system records the change of the pressure, the LCR digital meter records the change of capacitance, and the computer displays output data;
the test results are shown in fig. 5, where a is the capacitance performance test of the dielectric layers prepared in comparative example 1 and comparative example 2, b is the capacitance performance test of the dielectric layers prepared in comparative example 2 and example 1, and c is the capacitance sensitivity performance test of the dielectric layers prepared in comparative example 2 and example 1 under a small pressure, and it can be seen from a in fig. 5 that the capacitance change rate is obviously improved under the same pressure due to the addition of the porous structure. Fig. 5 b shows that the capacitance change rate is further improved by adding the through hole structure on the basis of the porous structure, and the capacitance still maintains the change of the capacitance under the condition that the pressure is as high as 1000 kPa. FIG. 5 c is a graph showing the rate of change in capacitance of the dielectric layers prepared in comparative example 2 and example 1 in a small pressure range of 1kPa, showing that the capacitance sensor of the porous + via structure obtains 1.15kPa-1High sensitivity display of (2).
The flexible sensor described in embodiment 1 is applied to the throat, knee and sole of a human body, and sends out a certain pressure signal through sound production, knee bending and human body walking, the sensor can quickly recognize and send out capacitance responses of different sizes, the capacitance responses are recorded through an LCR digital meter and displayed on a computer, the final test result is shown in a-c of fig. 6, wherein a is the capacitance response applied to the throat, b is the capacitance response applied to the knee, and c is the capacitance response applied to the sole, and as can be known from a-c of fig. 6, when the throat sends out sound, the sensor sends out a corresponding change due to the vibration effect transmitted to the capacitor, and the sensor can detect a slight pressure. In the walking process of a human body, along with the bending of knees and the movement of soles, the sensor changes correspondingly along with the sounding, and the flexible sensor provided by the invention is proved to have good sensing response under high pressure.
The flexible sensor described in example 1 was shaped into fingers and fitted over the finger pad of five fingers (see d in fig. 6) by holding beakers of different weights (see e in fig. 6, 250mL volume beaker with 50mL water, 150mL volume beaker with 150mL water)A 250mL beaker and a 250mL beaker containing 250mL of water with a volumetric capacity of 250 mL) to identify the capacitive response of the sensors, the response results are shown as f in fig. 6, and the change in capacitance of each sensor is marked in the hand schematic as can be seen from f in fig. 6. The results show that the thumb and forefinger graphics have greater force to hold the beaker, the remaining three are used for fine adjustment. As the weight of the beaker increases, the capacitance change of the sensor increases, closely related to the increased force required to hold the beaker. Δ C/C of thumb when beaker was changed from 50mL to 250mL0The value changed from 6.32 to 9.72; from these values, the pressure exerted by the thumb on the beaker varied from 75kPa to 210 kPa. These results demonstrate the potential application of capacitive sensors in human motion monitoring.
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 (10)
1. A flexible capacitance sensor is characterized by comprising a first electrode layer, a dielectric layer and a second electrode layer which are sequentially stacked;
the first electrode layer and the second electrode layer independently comprise a filter paper substrate and polypyrrole loaded on the filter paper substrate;
the dielectric layer is an elastomer with a porous structure;
the dielectric layer includes through holes of an array structure.
2. The flexible capacitive sensor of claim 1, wherein the polypyrrole is supported at a loading of 0.0045 ± 0.0005g per square centimeter of the filter paper substrate.
3. The flexible capacitive sensor of claim 1, wherein the elastomeric material comprises polydimethylsiloxane, thermoplastic polyurethane, or silicone rubber.
4. A method of manufacturing a flexible capacitive sensor according to any of claims 1 to 3, comprising the steps of:
mixing a dielectric layer material and a pore-forming agent to obtain a mixture;
precuring the mixture in the groove to obtain a precured mixture;
after inserting a cylindrical needle head into the pre-cured mixture, curing, and removing the cylindrical needle head and the pore-forming agent to obtain the dielectric layer;
soaking filter paper in ferric chloride solution, placing the filter paper in a vacuum glass closed container containing liquid pyrrole, and polymerizing to respectively prepare a first electrode and a second electrode;
and preparing the flexible capacitive sensor according to the sequence of the first electrode, the dielectric layer and the second electrode.
5. The preparation method according to claim 3, wherein the mass ratio of the dielectric layer material to the pore-forming agent is 1: (2-4);
the pore-forming agent is sodium chloride and/or sugar.
6. The method according to claim 3, wherein the pre-curing temperature is 80 to 150 ℃ and the pre-curing time is 3 to 10 min.
7. The method according to claim 3, wherein the curing temperature is 80 to 150 ℃ and the curing time is 3 to 120 min.
8. The method according to claim 3, wherein the concentration of the ferric chloride solution is 1 to 2 mol/L;
the soaking time is 10-30 min.
9. The method according to claim 3, wherein the polymerization time is 6 to 24 hours.
10. Use of the flexible capacitive sensor according to any one of claims 1 to 3 or the flexible capacitive sensor prepared by the preparation method according to any one of claims 4 to 9 in the fields of human-computer interfaces, human motion monitoring, electronic skin or soft robots.
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