1. The utility model provides a compound flexible sensor which characterized in that, includes conductive fabric layer, first PDMS encapsulated layer, PDMS microchannel layer, PVDF piezoelectric film layer and the second PDMS encapsulated layer that from top to bottom sets gradually, the upper surface on PDMS microchannel layer has the microchannel, the microchannel is used for filling liquid metal mixture.

2. The composite flexible sensor of claim 1, wherein the conductive fabric layer is silver-plated knitted fabric, and electrodes are mounted at two ends of the conductive fabric layer.

3. The composite flexible sensor of claim 1, wherein the number of microchannels in the PDMS microchannel layer is one.

4. The composite flexible sensor of claim 3, wherein the microchannel in the PDMS microchannel layer is serpentine or spiral in shape.

5. The composite flexible sensor according to claim 1, wherein the liquid metal in the microchannel of the PDMS microchannel layer is made of a gallium indium tin alloy or a gallium indium alloy.

6. The composite flexible sensor of claim 1, wherein electrodes are mounted at both ends of the microchannel in the PDMS microchannel layer.

7. The composite flexible sensor according to claim 1, wherein the upper and lower surfaces of the PVDF piezoelectric film layer are respectively provided with flexible interdigital electrodes.

8. A preparation method of a composite flexible sensor is characterized by comprising the following steps:

s1, mixing the PDMS base agent and the curing agent according to a fixed proportion to obtain a liquid mixed polymer;

s2, spin-coating the liquid mixed polymer obtained in the step S1 on a wafer, and curing to obtain a PDMS film;

s3, slowly adding the liquid mixed polymer obtained in the step S1 into a microchannel mold, and scraping the liquid mixed polymer exceeding the upper surface of the microchannel mold after the liquid mixed polymer fills the microchannel mold to obtain a PDMS microchannel layer, wherein the PDMS microchannel layer is provided with microchannels;

s4, respectively adding the liquid metal and the liquid mixed polymer prepared in the step S1 into a spray gun, and alternately spraying the liquid metal and the liquid mixed polymer into the micro-channel through a mask;

s5, adding the liquid mixed polymer obtained in the step S1 into a spray gun, and spraying the PDMS film obtained in the step S2 through a mask to finally obtain a PDMS film with a micro-convex structure;

s6, bonding the product obtained in the step S5 on the upper surface of the product obtained in the step S4 by using an adhesive to play a role of packaging;

s7, adhering a conductive fabric layer on the upper surface of the product of the step 6;

s8, preparing a PVDF solvent, and preparing a PVDF piezoelectric film by using an electrostatic spinning method;

s9, encapsulating the product of the step S8 on the lower surface of the product of the step S6 by a PDMS film.

Background

Since the conventional metal sheet and semiconductor sensor can only be used under the condition of small strain, and have high rigidity, are not easy to bend, and are not suitable for being attached to a human body or being added into wearable equipment, the research on the sensor with high flexibility and high strain sensitivity becomes one of the hot directions for developing intelligent wearable equipment. The flexible sensor has the advantages of high flexibility, high strain, high sensitivity and the like, so that the flexible sensor can be widely applied to the field of wearable electronic products, and can be used for monitoring human body movement and physiological information or used for a human-computer interaction system.

Currently, most available flexible sensors are based on a single sensing mechanism that can only detect one mode of deformation at a time, although it can respond to more than one mode, such as compression, tension, and bending. In practical applications, one input stimulus may induce a combined deformation of multiple modes.

Therefore, how to design a multi-modal flexible measurement mechanism to detect different deformation modes simultaneously is a technical problem to be solved urgently by those skilled in the art.

Disclosure of Invention

The invention aims to provide a composite flexible sensor and a preparation method thereof, which are used for representing one strain behavior through three sensing units simultaneously and avoiding similar induction of a single sensor on different strains.

In order to achieve the purpose, the invention provides the following scheme:

the invention discloses a composite flexible sensor which comprises a conductive fabric layer, a first PDMS (polydimethylsiloxane) packaging layer, a PDMS microchannel layer, a PVDF (polyvinylidene fluoride) piezoelectric film layer and a second PDMS packaging layer which are sequentially arranged from top to bottom, wherein a microchannel is arranged on the upper surface of the PDMS microchannel layer and is used for filling a liquid metal mixture.

Preferably, the conductive fabric layer is a silver-plated knitted fabric, and electrodes are mounted at two ends of the conductive fabric layer.

Preferably, the number of microchannels in the PDMS microchannel layer is one.

Preferably, the microchannel in the PDMS microchannel layer has a serpentine or spiral shape.

Preferably, the liquid metal in the microchannel of the PDMS microchannel layer is made of gallium indium tin alloy or gallium indium alloy.

Preferably, electrodes are installed at two ends of the microchannel in the PDMS microchannel layer.

Preferably, the upper surface and the lower surface of the PVDF piezoelectric film layer are respectively provided with a flexible interdigital electrode.

The invention also discloses a preparation method of the composite flexible sensor, which comprises the following steps:

s1, mixing the PDMS base agent and the curing agent according to a fixed proportion to obtain a liquid mixed polymer;

s2, spin-coating the liquid mixed polymer obtained in the step S1 on a wafer, and curing to obtain a PDMS film;

s3, slowly adding the liquid mixed polymer obtained in the step S1 into a microchannel mold, and scraping the liquid mixed polymer exceeding the upper surface of the microchannel mold after the liquid mixed polymer fills the microchannel mold to obtain a PDMS microchannel layer, wherein the PDMS microchannel layer is provided with microchannels;

s4, respectively adding the liquid metal and the liquid mixed polymer prepared in the step S1 into a spray gun, and alternately spraying the liquid metal and the liquid mixed polymer into the micro-channel through a mask;

s5, adding the liquid mixed polymer obtained in the step S1 into a spray gun, and spraying the PDMS film obtained in the step S2 through a mask to finally obtain a PDMS film with a micro-convex structure;

s6, bonding the product obtained in the step S5 on the upper surface of the product obtained in the step S4 by using an adhesive to play a role of packaging;

s7, adhering a conductive fabric layer on the upper surface of the product of the step 6;

s8, preparing a PVDF solvent, and preparing a PVDF piezoelectric film by using an electrostatic spinning method;

s9, encapsulating the product of the step S8 on the lower surface of the product of the step S6 by a PDMS film.

Compared with the prior art, the invention has the following technical effects:

according to the invention, three different strain sensors are integrated into a whole, so that the space used by various sensors is reduced, and the characteristic of high integration is embodied. The three sensors are used for representing one strain behavior at the same time, so that the phenomenon that strain types cannot be distinguished due to the fact that similar signals are generated by different strain behaviors can be effectively avoided, the representing precision of the strain behaviors is improved, more complex strain behaviors can be distinguished, and the strain behavior sensor has wide application prospects in the aspects of electronic skins and man-machine interaction.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is an exploded view of a composite flexible sensor according to the present embodiment;

FIG. 2 is a cross-sectional view of the composite flexible sensor of the present embodiment;

FIG. 3 is a schematic structural view of a microchannel mold;

FIG. 4 is a schematic diagram of a reticle structure;

description of reference numerals: 100-composite flexible sensors; 1-a conductive textile layer; 2-a first PDMS encapsulation layer; 3-PDMS microchannel layer; 4-a microchannel; 5-PVDF piezoelectric film layer; 6-second PDMS encapsulation layer.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. 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 invention aims to provide a composite flexible sensor and a preparation method thereof, which are used for representing one strain behavior through three sensing units simultaneously and avoiding similar induction of a single sensor on different strains.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

As shown in fig. 1 to 4, the present embodiment provides a composite flexible sensor 100, which includes a conductive fabric layer 1, a first PDMS encapsulation layer 2, a PDMS microchannel layer 3, a PVDF piezoelectric film layer 5, and a second PDMS encapsulation layer 6, which are sequentially disposed from top to bottom. The upper surface of the PDMS microchannel layer 3 is provided with microchannels 4, and the microchannels 4 are used for filling liquid metal mixture.

The conductive textile layer 1 is used as a first strain sensing unit, the conductivity of the first strain sensing unit is influenced by the contact amount between nylon fibers, and the first strain sensing unit is only sensitive to the change of the conductivity generated during stretching. The first PDMS encapsulation layer 2 and the PDMS micro-channel layer 3 form a second strain sensing unit, and the micro-channel 4 is filled with a liquid metal mixture. When tensile or compressive strain occurs, the liquid metal mixture deforms, and the resistance of the liquid metal mixture changes, so that the second strain sensing unit is sensitive to the tensile and compressive strain; the second strain sensing unit is insensitive to bending strain since the length and cross-sectional area of the liquid metal mixture do not change significantly when pure bending strain occurs. And the lower surface of the PDMS microchannel layer 3, the PVDF piezoelectric film layer 5 and the second PDMS packaging layer 6 form a third strain sensing unit, and the PVDF piezoelectric film is used as a sensing layer. When the PVDF piezoelectric film is subjected to one or more of tension, compression and bending, the surfaces of the upper electrode and the lower electrode of the piezoelectric film generate an electric signal, so that the piezoelectric film is sensitive to three strains.

When the composite flexible sensor 100 of the embodiment is used, the composite flexible sensor is fixed on an object to be detected, and various single strains and combinations thereof can be identified by comparing waveforms of the first strain sensing unit, the second strain sensing unit and the third strain sensing unit at the same moment, so that similar induction of different strains by the single sensor is avoided.

Specifically, in this embodiment, the conductive fabric layer 1 is a silver-plated knitted fabric, and electrodes are installed at two ends of the conductive fabric layer 1, so as to output a signal of the first strain sensing unit.

The number of the micro-channels 4 in the PDMS micro-channel layer 3 is one, and the micro-channels 4 are serpentine, spiral and other geometric shapes which can be drawn by one stroke. The liquid metal in the micro-channel 4 is made of gallium indium tin alloy or gallium indium alloy. Because the content of each group of phases in the alloy influences the characteristics of the alloy, such as melting point, conductivity and the like, and further influences the performance of the second strain sensing unit, the content of each group of phases can be adjusted according to actual needs. Electrodes are arranged at two ends of the micro-channel 4 to realize signal output of the second strain sensing unit.

And flexible interdigital electrodes are respectively arranged on the upper surface and the lower surface of the PVDF piezoelectric film layer 5, so that the signal output of the third strain sensing unit is realized.

The embodiment further provides a method for manufacturing a composite flexible sensor, which is used to obtain the composite flexible sensor 100, and the method includes the following steps:

s1, mixing the PDMS base agent and the curing agent according to a fixed proportion to obtain a liquid mixed polymer;

s2, spin-coating the liquid mixed polymer obtained in the step S1 on a wafer, and curing to obtain a PDMS film;

s3, slowly adding the liquid mixed polymer obtained in the step S1 into a microchannel mold, and scraping the liquid mixed polymer exceeding the upper surface of the microchannel mold after the liquid mixed polymer fills the microchannel mold to obtain a PDMS microchannel layer 3, wherein the PDMS microchannel layer 3 is provided with a microchannel 4;

s4, respectively adding the liquid metal and the liquid mixed polymer prepared in the step S1 into a spray gun, and alternately spraying the liquid metal and the liquid mixed polymer into the micro-channel 4 through a mask;

s5, adding the liquid mixed polymer obtained in the step S1 into a spray gun, and spraying the PDMS film obtained in the step S2 through a mask to finally obtain a PDMS film with a micro-convex structure;

s6, bonding the product obtained in the step S5 on the upper surface of the product obtained in the step S4 by using an adhesive to play a role of packaging;

s7, adhering the conductive fabric layer 1 to the upper surface of the product obtained in the step 6;

s8, preparing a PVDF solvent, and preparing a PVDF piezoelectric film by using an electrostatic spinning method;

s9, encapsulating the product of the step S8 on the lower surface of the product of the step S6 by a PDMS film.

In step S1, the ratio of the PDMS base and the curing agent is generally 10: 1, fully stirring the mixture until uniform bubbles are generated, standing the mixture in a vacuum pump of 0.2Mpa for 2 hours, and removing the bubbles to obtain the required liquid mixed polymer.

In step S3, the microchannel mold used may be obtained by machining or 3D printing, and before adding the liquid mixed polymer, the microchannel mold needs to be passivated to facilitate demolding, for example, TMCS steam treatment (30min,2-3 times) may be performed, and after the addition is completed, the microchannel mold needs to be dried in an oven at 80 ℃ for 4-6 h. The microchannel 4 may be formed to have a width of 0.4mm to 2mm and a height of 0.2mm to 1.2 mm. Generally, the smaller the width and height, the greater the sensitivity of the sensing unit.

In steps S4 and S5, the mask may be a laser-processed stainless steel mask or a photo-cured resin processed by a photo-curing printer (which may be treated with a surfactant). The mask plate is provided with a through hole with the shape consistent with that of the micro-channel 4, so that the micro-protrusion-shaped structure on the PDMS film obtained in the step S5 can be embedded into the micro-channel 4.

In step S5, the spraying process of the liquid polymer mixture through the mask plate should be divided into multiple times of spraying, after each time of spraying with a proper height, the mixture is dried in an oven at 80 ℃ for 1 hour, and after solidification and formation, the next spraying is performed until the required height is obtained, and the spraying uniformity needs to be noticed in the spraying process.

In step S7, the conductive fabric layer 1 is a silver-plated knitted fabric, which is made by weaving silver-plated nylon fibers with patterns in a specific direction, and the conductivity of the fabric is affected by the contact amount between the silver-plated nylon fibers, and is only sensitive to the change in conductivity during stretching.

In step S8, the mass ratio of materials in the prepared PVDF solvent is PVDF to DMF to acetone is 1: 3: 7. the PVDF solvent was added to the beaker and heated in a water bath at 50 ℃ for 4 hours. Spinning is started at the voltage of 12kV and the speed of 2.5ml/h after debugging, and the PVDF film is obtained on a collecting device.

The packaging method in step S6 and step S9 includes, but is not limited to, a method of brushing a layer of PDMS solution as an adhesive on the surface to be bonded with a brush and then bonding.

The principle and the implementation mode of the present invention are explained by applying specific examples in the present specification, and the above descriptions of the examples are only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.