Homogeneous integrated bimodal sensor and preparation method thereof

Abstract

The invention relates to a homogeneous integrated bimodal sensor and a preparation method thereof, belongs to the technical field of sensor preparation, and solves the problems of poor measurement stability, small measurement range and complex process flow of a bimodal sensor prepared by adopting an existing method. The method comprises the following steps: (1) designing a coil layer of a plane complementary labyrinth structure; (2) carrying out mold casting to obtain a patterned coil layer substrate; (3) filling and coating the coil layer substrate to obtain a coil layer; (4) performing mold casting to obtain a piezoresistive layer; (5) a supporting frame is obtained through pouring and curing, the size of an inner cavity of the supporting frame is larger than the volume size of the piezoresistive layer, and an air gap layer of the sensor is manufactured after packaging is formed through the height difference; and (6) packaging, and after packaging and curing, the packaging layer and the functional layer substrate are made of the same material. The sensor prepared by the method has a homogeneous integrated structure and a large sensing range, the robustness and durability are improved, and the process preparation flow is simplified.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensor preparation, in particular to a homogeneous integrated bimodal sensor and a preparation method thereof. BACKGROUND

[0002] Compared with traditional rigid sensors, flexible sensors have good flexibility, bendability and conformability, and can better adapt to irregular surfaces and complex environments. Flexible force and tactile proximity bimodal sensors are devices that can perceive and respond to external proximity and tactile stimuli, and are widely used in robots and smart homes to achieve precise force and tactile feedback and environmental perception.

[0003] Existing flexible force and tactile proximity bimodal sensors usually need to integrate multiple sensing elements and circuits in a limited space, which not only increases the structural complexity and manufacturing difficulty of the sensor, but also may cause the reliability of the sensor to decrease due to the complex structure, and the signals of different sensing modalities may have crosstalk, resulting in inaccurate measurement results; the planar capacitors of existing flexible bimodal sensors have a small perceivable distance, and the range of force and tactile is also small; in addition, the use of heterogeneous glue for packaging and combination has poor interface stability and robustness, and is easily affected by external environment, resulting in performance degradation or failure of the sensor.

[0004] Therefore, in order to provide more abundant and reliable sensing information for intelligent devices such as robots, and improve the motion control and human-computer interaction performance of intelligent devices, there is an urgent need for a flexible force and tactile proximity bimodal sensor with better structure and performance. SUMMARY

[0005] In view of the above analysis, the embodiments of the present application aim to provide a homogeneous integrated bimodal sensor and a preparation method thereof, to solve at least one of the problems of poor measurement stability, small range and complex process flow of the bimodal sensor prepared by the existing method.

[0006] In one aspect, the embodiments of the present application provide a preparation method of a homogeneous integrated bimodal sensor, which comprises:

[0007] (1) designing a coil layer with a planar complementary labyrinth structure;

[0008] (2) obtaining a mold for preparing a coil layer substrate according to the structure of the coil layer, pouring, and curing to obtain a patterned coil layer substrate;

[0009] (3) filling and coating the pattern of the coil layer substrate, and curing to obtain the coil layer, wherein the coil layer and the coil layer substrate are mutually embedded into one whole;

[0010] (4) According to the structural design of the piezoresistive layer, a mold for preparing the piezoresistive layer is obtained, pouring and curing to obtain the piezoresistive layer;

[0011] (5) According to the structural design of the piezoresistive layer, a mold for preparing a support frame for placing the piezoresistive layer is obtained, pouring and curing to obtain the support frame, which has a square structure with an open top surface or a square structure with an open top surface and a bottom surface, wherein the inner cavity size of the support frame is greater than the volume size of the piezoresistive layer, and the height difference constitutes the air gap layer of the prepared sensor after packaging;

[0012] (6) Packaging: the square structure support frame with an open top surface and a bottom surface prepared in step (5) is bonded to the packaging bottom surface or directly using a square structure support frame with an open top surface, and the piezoresistive layer is placed inside the support frame; the adhesive is applied on the top surface of the support frame, and the coil layer substrate is placed on the support frame, so that the side of the coil layer substrate filled with the coil layer is in contact with the support frame, and curing is performed to obtain the dual-mode sensor; wherein the bonded coil layer substrate and the support frame together constitute the packaging layer of the sensor, and the coil layer, the piezoresistive layer and the air gap layer therebetween together constitute the functional layer of the sensor;

[0013] Wherein, the material of the packaging layer and the base of the coil layer and the base of the piezoresistive layer are the same.

[0014] Further, in steps (2) and (5), polydimethylsiloxane prepolymer is used for pouring.

[0015] Further, the pouring temperature is 40-60℃, and the time is 70-100min.

[0016] Further, in step (3), a mixture containing conductive carbon and polydimethylsiloxane prepolymer is used for pouring.

[0017] Further, in the mixture, the mass ratio of conductive carbon to polydimethylsiloxane prepolymer is 1:10-1:25.

[0018] Further, the mixture also contains a surfactant.

[0019] Further, in step (4), a mixture containing conductive carbon, polydimethylsiloxane prepolymer and inorganic salt is used for pouring.

[0020] Further, the mass ratio of the inorganic salt, the conductive carbon and the polydimethylsiloxane prepolymer is 20-250:1:10-25.

[0021] Further, in step (5), the height difference between the inner cavity of the support frame and the piezoresistive layer is 0.55-1.45 mm.

[0022] In another aspect, the embodiment of the present application also provides a homogeneous integrated dual-mode sensor, which is prepared by the above method, and comprises a packaging layer and a functional layer, wherein the functional layer is sealed in the inside of the packaging layer; from top to bottom, the functional layer comprises a coil layer, an air gap layer and a piezoresistive layer in sequence, and the packaging layer comprises a coil layer substrate, a support frame and a packaging bottom surface which are bonded in sequence.

[0023] The coil layer and the coil layer substrate are embedded with each other and have a planar complementary labyrinth structure, which is used to provide an edge field capacitance to sense a close object and form a capacitive proximity sense of the sensor.

[0024] The air gap layer is provided by the support frame and is used to provide a space for the deformation of the coil layer when the coil layer is pressed, so as to sense a contact object by using the inter-plate capacitance of the coil layer and form a capacitive force touch of the sensor.

[0025] The piezoresistive layer is fixed in the inside of the support frame and has a porous structure, which is used to provide a resistance to sense a contact object and form a resistive force touch of the sensor.

[0026] The material of the packaging layer is the same as the base material of the functional layer.

[0027] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0028] 1. Compared with the prior art, the present application improves the overall structure and material composition of the sensor: on the one hand, the present application designs the coil layer into a planar complementary labyrinth structure, and adds an air gap layer between the coil layer and the piezoresistive layer, which can expand the sensing distance of the proximity sense of the sensor, expand the range of the force touch, and improve the response speed and sensitivity of the resistive force touch; on the other hand, the material of the packaging layer of the sensor is the same as the base material of the functional layer, which improves the stability of the interface between the parts of the sensor, and makes the sensor have high robustness and durability.

[0029] 2. Compared with the prior art, the patterned coil layer substrate obtained according to the patterning design of the coil layer can not only simplify the preparation process of the subsequent coil layer, but also simplify the packaging process of the subsequent sensor, in addition, it reduces the difficulty of preparing the dual-mode sensor, which is conducive to the preparation of the homogeneous integrated sensor of the present application, improves the preparation efficiency and reduces the cost.

[0030] 3、The application controls the height difference between the support frame inner cavity and the piezoresistive layer through a mold casting process, so that an air gap layer of the bimodal sensor is formed between the coil layer and the piezoresistive layer after packaging each component, the process flow is simple, and the height difference is accurate and easy to control; the air gap layer plays a crucial role in improving the range of contact and force touch of the bimodal sensor, and improving the response speed and sensitivity of the resistive force touch.

[0031] 4、The method of the application adjusts the ratio of conductive carbon and polydimethylsiloxane (PDMS) prepolymer in the raw material for preparing the functional layer, so that the functional layer has good conductivity and measurement stability while maintaining the essential flexibility and deformability of PDMS to the maximum extent, and the excellent chemical inertness and oxidation resistance of conductive carbon can improve the environmental adaptability of the sensor, further ensuring the performance stability and reliability of the sensor in long-term use.

[0032] 5、The application adjusts the amount of inorganic salt in the piezoresistive layer casting raw material, and uses batch casting in the same mold, so as to control the size and gradient change arrangement structure of the porosity in the piezoresistive layer, further improve the sensing sensitivity and sensing range of the piezoresistive layer to external pressure, and improve the force touch sensing ability of the sensor.

[0033] In the application, the above technical solutions can be combined with each other to realize more preferred combination schemes. Other features and advantages of the application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood by implementing the application. The purpose and other advantages of the application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0034] The accompanying drawings are included to provide a further understanding of the application and are incorporated herein and constitute a part of the application. The drawings illustrate embodiments of the application and, together with the description, serve to explain the principles of the application. In the drawings:

[0035] Figure 1 The preparation flow chart of the flexible proximity force touch bimodal sensor of the application;

[0036] Figure 2 The plane complementary labyrinth structure schematic diagram of the coil layer of the flexible proximity force touch bimodal sensor of the application;

[0037] Figure 3 The initial capacitance edge field effect diagram of the flexible proximity force touch bimodal sensor of the application;

[0038] Figure 4 The proximity response principle schematic diagram of the flexible proximity force touch bimodal sensor of the application;

[0039] Figure 5 Schematic diagram of the pressure capacity effect principle of the flexible proximity sense and tactile dual-mode sensor of the present application;

[0040] Figure 6 Schematic diagram of the pressure resistance effect principle of the flexible proximity sense and tactile dual-mode sensor of the present application;

[0041] Figure 7 Schematic diagram of the structure of the flexible proximity sense and tactile dual-mode sensor of the present application (a), schematic diagram of the structure of the pressure resistance layer (b), and schematic diagram of the structure of the coil layer (c);

[0042] Figure 8 Sensor proximity sense response result diagram of the present application;

[0043] Figure 9 Sensor force tactile response result diagram of the present application;

[0044] Reference signs:

[0045] 1 - encapsulation layer; 2 - coil layer; 3 - air gap layer; 4 - pressure resistance layer; 4-1 - first porous sponge layer; 4-2 - second porous sponge layer. DETAILED DESCRIPTION

[0046] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, which form a part of this application, and together with the embodiments of the present application serve to explain the principles of the present application, and are not intended to limit the scope of the present application.

[0047] The existing flexible force tactile proximity sense dual-mode sensor mainly adopts triboelectric type, capacitive type sensor or a hybrid scheme (such as combined with a pressure resistance type sensor), but in the actual manufacturing and application process of the sensor, the following problems exist: the dual-mode flexible sensor usually needs to integrate multiple sensing elements and circuits in a limited space, which increases the structural complexity and manufacturing difficulty of the sensor; at the same time, the complex structure can also lead to reduced reliability of the sensor, and the signals of different sensing modalities can exist crosstalk, resulting in inaccurate measurement results; in the existing research on flexible force tactile proximity sensors, the perceivable distance of the planar capacitive proximity sensor is small, the range of force tactile is small, and the packaging and combined interface stability and robustness are extremely poor, which is easily affected by the external environment, leading to performance degradation or failure of the sensor.

[0048] Therefore, the present application provides a preparation method of a homogeneous integrated dual-mode sensor, which comprises:

[0049] (1) designing a coil layer with a planar complementary labyrinth structure;

[0050] (2) obtaining a mold for preparing the coil layer substrate according to the structure of the coil layer, pouring, and curing to obtain a patterned coil layer substrate;

[0051] (3) filling the pattern of the coil layer substrate, and curing to obtain the coil layer, wherein the coil layer and the coil layer substrate are embedded into one whole;

[0052] (4) obtaining a mold for preparing the piezoresistive layer according to the structure design of the piezoresistive layer, pouring, and curing to obtain the piezoresistive layer;

[0053] (5) obtaining a mold for preparing a support frame for placing the piezoresistive layer according to the structure design of the piezoresistive layer, pouring, and curing to obtain the support frame, wherein the support frame has a square structure with an open top surface or a square structure with open top and bottom surfaces, and the inner cavity size of the support frame is greater than the volume size of the piezoresistive layer, and the height difference constitutes the air gap layer of the prepared sensor after packaging;

[0054] (6) packaging: using an adhesive to bond the square structure support frame with open top and bottom surfaces prepared in step (5) on the packaging bottom surface or directly using a square structure support frame with an open top surface, placing the piezoresistive layer inside the support frame; smearing the adhesive on the top surface of the support frame, placing the coil layer substrate on the support frame, and making the side of the coil layer substrate filled with the coil layer contact the support frame, and curing to obtain the dual-mode sensor, wherein the coil layer substrate and the support frame bonded together jointly constitute the packaging layer of the sensor, and the coil layer, the piezoresistive layer, and the air gap layer therebetween jointly constitute the functional layer of the sensor;

[0055] wherein the packaging layer and the matrix of the coil layer and the matrix of the piezoresistive layer are made of the same material.

[0056] It should be noted that in the preparation process of the existing flexible sensor, heterogeneous glue is used to bond the components of the sensor, and the bonding of the heterogeneous glue makes the combination and packaging interface of the components of the sensor have poor stability, which makes the sensor prone to performance degradation or failure under the influence of external environment, thereby affecting the robustness and durability of the sensor in actual application.

[0057] Therefore, in order to improve the stability and durability of the sensor in actual use while improving the proximity and force tactile perception range of the dual-mode sensor, the materials (packaging materials and functional materials) constituting the sensor and the adhesive for packaging need to be limited.

[0058] Specifically, in steps (2)-(6), the sensor of the present application is designed as a homogeneous integrated structure, i.e., the base material of the coil layer, the base material of the piezoresistive layer, and the material of the coil layer substrate, the support frame, and the packaging bottom surface (or none) are the same, the raw material for preparing the adhesive is the same as the raw material for preparing the coil layer and the support layer, and the basic application adopts a homogeneous integrated structure design for the bimodal sensor.

[0059] Specifically, the material constituting the packaging layer of the present application is polydimethylsiloxane (PDMS), which has high flexibility, low Young's modulus (close to the skin), high chemical stability, good biocompatibility, good environmental resistance, good tensile adaptability, can be worn for a long time, and can improve human-computer interaction performance; and semi-cured PDMS has appropriate viscosity and certain bonding strength.

[0060] It should be noted that the PDMS material constituting the sensor packaging layer is not conductive itself. According to the homogeneous integrated structure design of the present application, when it is used as the base material of the functional layer of the sensor, it needs to be compounded with conductive materials in order to meet the requirement of electrical conductivity of the functional layer.

[0061] Specifically, in steps (3) and (4), in order to make the compounded polymer material have electrical conductivity while maintaining the inherent flexibility and deformability of PDMS, meet the demand of wearable and foldable electronic products, and meet the homogeneous integrated structure design of the sensor of the present application, the present application uses the form of doping conductive carbon particles into the PDMS base material to make the sensor packaging layer material which does not have electrical conductivity have good electrical conductivity, so as to be used as the material constituting the functional layer of the sensor.

[0062] More specifically, in steps (3) and (4), the material constituting the coil layer and the piezoresistive layer of the sensor of the present application is a conductive carbon doped PDMS composite material, wherein the conductive carbon is at least one of carbon nanotubes (CNT), carbon black (CB), graphene (GO), and two-dimensional MXene, the conductive carbon of the present application has a large specific surface area, is easy to disperse, and can provide a high conductive network; preferably CNT, CNT has a high aspect ratio, requires less CNT content to build a conductive network, i.e., has a lower percolation threshold, and has less inherent loss of elasticity of the base material.

[0063] It should be noted that the homogeneous integrated structure design of the bimodal sensor of the present application not only improves the stability of the sensor packaging and the bonding interface, thereby improving the robustness and durability in actual application, but also reduces the difficulty and cost of sensor preparation.

[0064] Since the capacitive sensor realizes the proximity sensing through the capacitive fringe field, and the method for improving the capacitive fringe field sensing distance and accuracy is to increase the tip and edge area of the capacitive electrode, currently researchers enhance the strength of the fringe field by designing the parallel electrode into a cross type, a disc type and a spiral type, which improves the relative performance of the proximity sensing to a certain extent, but such enhancement is at the expense of the pressure sensing capability, and the unbalanced or insufficient dual-mode sensing performance limits the practical application of the dual-mode sensor, and often needs to compromise and trade off the range and performance of the proximity and force touch, and cannot realize the expansion of the performance of the proximity and force touch at the same time in the flexible sensor.

[0065] It should be noted that in order to improve the proximity distance and the force touch range of the dual-mode sensor at the same time, the overall structure of the sensor needs to be designed and the coil layer structure of the capacitive sensor needs to be realized.

[0066] Specifically, in step (1), the coil layer is designed into a planar complementary maze structure, as shown in Figure 2 .

[0067] Specifically, in step (6), after packaging each component of the sensor, a gas gap layer is formed between the coil layer and the piezoresistive layer for realizing capacitive sensing of the sensor, due to the height difference between the inner cavity of the support frame and the piezoresistive layer.

[0068] It should be noted that the planar complementary maze structure design of the coil layer and the gas gap layer structure design can simultaneously expand the sensing distance of the proximity and the sensing range of the force touch, and the specific reasons are as follows:

[0069] On the one hand, the capacitive electrode structure in the complementary maze structure can greatly increase the area of the electrode edge in a limited space, release more internal fields to the outside of the electrode plate plane through the edge, obtain a more dense and wider distributed edge electric field, and thus obtain a farther proximity sensing distance and improve the proximity sensing sensitivity, as shown in Figure 3 , 4 .

[0070] On the other hand, in the initial stage of contact between the object and the sensor, although the contact pressure from the object makes the flexible sensor begin to produce compression deformation, since the gas gap layer exists between the coil layer and the piezoresistive layer, the coil layer does not directly contact the piezoresistive layer, at this time, the sensor is still in the capacitive working mode, in this stage, the greater the contact force, the closer the coil layer to the piezoresistive layer, and the coil layer capacitance also increases, after the capacitive change is converted into an electric signal, the pressure of the system in the initial process of the object contacting the sensor can be calculated, that is, the pressure-capacitance effect of the sensor, wherein the response working principle of the sensor in the initial stage of contacting the object is as shown in Figure 5As shown, it can be seen that the planar complementary labyrinth structure design of the coil layer can also expand the sensing range of the sensor force tactile.

[0071] It should be noted that, in order to balance the diffusion range and intensity of the edge field of the coil layer capacitor electrode, it is necessary to limit the ratio of the width of the coil layer plate to the spacing between adjacent electrode plates.

[0072] More specifically, in step (1), the ratio of the width of the coil layer plate to the spacing between adjacent electrode plates is limited to the range of 5:1-1:1. The higher the ratio of the width of the electrode plate to the spacing between adjacent electrode plates, the higher the edge electric field intensity. However, too high a ratio will cause the edge electric field to be concentrated near the coil, affecting the expansion of the sensor's proximity sensing distance.

[0073] According to some preferred embodiments of the present application, the ratio of the width of the coil layer plate to the spacing between adjacent electrode plates can be any value in the range of 5:1-1:1, such as 5:1, 4:1, 3:1, 2:1, 1:1.

[0074] It should be noted that, in the case of improving the performance of the dual-mode sensor through structural and material design, the present application needs to realize the preparation of the sensor through a new preparation method.

[0075] Notably, in order to improve the proximity sensing distance and force tactile sensing range of the dual-mode sensor while ensuring the softness and deformability of the sensor and meeting the design of the homogeneity of the sensor, the present application uses mold casting to prepare the packaging layer and functional layer of the sensor.

[0076] Specifically, in order to simplify the preparation and packaging process and save costs, in step (2), the present application first obtains a mold for preparing the coil layer substrate according to the planar complementary labyrinth structure design of the coil layer through 3D printing technology, and then performs raw material pouring and solidification molding to obtain a patterned coil layer substrate. The patterned coil layer substrate obtained by the present application in step (2) not only simplifies the subsequent preparation process of the coil layer, but also simplifies the subsequent packaging process of the sensor. In addition, it is beneficial to reduce the preparation difficulty of the homogeneity of the sensor, improve the preparation efficiency, and reduce the cost.

[0077] More specifically, in step (2), the raw material for preparing the coil layer substrate is a mixture of a PDMS prepolymer and a curing agent. The PDMS prepolymer can be at least one of hydroxyl-terminated polydimethylsiloxane (HO-PDMS-OH), vinyl-terminated polydimethylsiloxane (Vi-PDMS-Vi), and hydrogen-containing terminated polydimethylsiloxane (H-PDMS-H). The curing agent contains hydrogen-containing silicone oil crosslinking agent and platinum gold catalyst.

[0078] It should be noted that in order to enable the PDMS prepolymer for preparing the coil layer substrate to be fully cured and to enable the coil layer substrate after curing to have good flexibility and deformability, the present application needs to limit the ratio of the PDMS prepolymer to the curing agent.

[0079] More specifically, in step (2), the mass ratio of the PDMS prepolymer for preparing the coil layer substrate to the curing agent is 5:1-20:1, which can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1; if the content of the curing agent is too low, it is easy to cause the PDMS prepolymer to be insufficiently cured, and the obtained coil layer substrate is too soft, has high viscosity, low elastic modulus, and decreased tear resistance and hardness, which is not conducive to being used as a coil substrate or a support frame; if the content of the curing agent is too high, it is easy to make the cured PDMS have too high hardness and too high brittleness, and the softness and deformability are reduced, which is prone to cracking and reduces the sensitivity, thereby affecting the application of the sensor in the fields of intelligent robots and smart homes.

[0080] More specifically, in step (2), the temperature for curing the PDMS prepolymer-curing agent mixture for preparing the coil layer substrate after pouring is 40-60℃, and the time is 70-100min; if the curing temperature is too high, it may cause uneven curing and affect the stability of the PDMS structure; if the curing temperature is too low, the curing rate is reduced, the curing time is long, and even the curing degree of the PDMS prepolymer is affected, thereby affecting the mechanical strength of the material; if the curing time is insufficient, incomplete curing of the material may occur, and the mechanical strength of the material is reduced and is prone to deformation; if the curing time is too long, the cost is increased.

[0081] It should be noted that in order to simplify the preparation and packaging process, save costs, and meet the homogenization and integration design of the sensor of the present application, the present application directly prepares the coil layer on the patterned coil layer substrate.

[0082] Specifically, in step (3), the PDMS prepolymer mixed raw material for preparing the coil layer is filled and coated in the pattern of the coil layer substrate prepared in step (2), and the coil layer is obtained after curing.

[0083] It should be noted that since the mixed raw material for preparing the coil layer contains the same component PDMS prepolymer as the coil base raw material, the coil layer is firmly combined with the coil layer base after curing, and the two are embedded into one whole, and in the later packaging process, the coil layer and the coil base layer can be packaged together with other parts (such as the support layer), at this time, the coil base layer becomes part of the outer packaging layer; compared with the existing method of preparing capacitor electrodes by silk screen printing, mask, etc., this preparation method not only meets the design requirements of the homogenization structure of the application, but also simplifies the preparation process, improves the interface bonding force and stability.

[0084] Specifically, in step (3), the application adds conductive carbon particles in the form of PDMS prepolymer to meet the design of sensor homogenization, improve sensor sensing stability, ensure the conductivity of the functional layer, and improve the sensing distance and range of the sensor.

[0085] It should be noted that in order to make the coil layer with a planar complementary labyrinth structure not only have high conductivity and capacitance strength and range, but also have excellent mechanical properties, maintain the essential softness and deformability of the coil layer base, and meet the design of the sensor homogenization of the application, the application needs to control the ratio of each component in the coil layer preparation raw material to control the content of each component in the composite material constituting the coil layer of the functional layer.

[0086] Specifically, in step (3), the mass ratio of the conductive carbon in the coil layer preparation raw material to the polydimethylsiloxane prepolymer is limited to 1:10-1:25, and the coil layer of the functional layer is obtained after filling and curing in the pattern of the coil layer base. The content of conductive carbon in the composite material constituting the coil layer is 4-8% by weight. If the carbon content is too low, it is easy to make the conductivity of the composite material less than the percolation threshold, resulting in poor or even no conductivity of the coil layer, affecting the edge electric field strength and range; if the content is too high, on the one hand, it is easy to form stress concentration points in the rigid agglomeration of the composite material, reducing the electrical conductivity and material flexibility, on the other hand, too high CNT content will affect the PDMS curing reaction, and at the same time, it will form a dense network in the PDMS matrix, hindering the adhesion effect between the PDMS in the raw material and the coil layer base during the curing process.

[0087] According to some preferred embodiments of the application, the content of conductive carbon in the composite material constituting the coil layer can be any value within the range of 4-8%, such as 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, and 8%.

[0088] It should be noted that in order to improve the interface bonding force between the conductive carbon particles and the PDMS prepolymer, reduce the interface stress of the combination of the two, improve the dispersion uniformity of the conductive carbon particles in the cured PDMS, maintain the softness and deformability of the cured PDMS, prevent cracking, and improve the service life of the sensor, the preparation process conditions of the coil layer need to be limited in the present application.

[0089] Specifically, in step (3), in order to improve the dispersion degree of the conductive carbon particles in the cured PDMS, the conductive carbon particles and the PDMS prepolymer are mixed in a solvent. The solvent used in the present application needs to have good CNT dispersion ability, good compatibility with the PDMS prepolymer, and a relatively low boiling point. The solvent can be one of isopropyl alcohol (IPA), ethanol, acetone, toluene, etc. The mass ratio of the solvent to the conductive carbon is 60:1 to 30:1 (such as 50:1). If too little solvent is added, the conductive carbon particles and the PDMS prepolymer may not be mixed sufficiently, causing the aggregation of the conductive carbon particles, the increase of the bonding stress, and affecting the conductivity, softness and deformability of the coil layer.

[0090] More specifically, in step (3), the conductive carbon particles (such as CNTs) are first added to IPA, uniformly dispersed to form a conductive carbon particle suspension, and then the PDMS particles are added.

[0091] It should be noted that in step (3), in order to improve the dispersion of the nanoscale conductive carbon particles and improve their bonding capacity with the PDMS prepolymer, a surfactant (such as sodium dodecyl benzene sulfonate, SDBS) is added to the conductive carbon particle solution and ultrasonic treatment is performed to promote the dispersion of the nanoparticles.

[0092] More specifically, in step (3), when selecting the surfactant, the non-covalent adsorption capacity of the surfactant to CNTs, as well as the compatibility and residual properties of the surfactant with the PDMS curing system, should be considered. The addition amount of the surfactant in the present application is 4:1 to 2:1 (3:1) of the mass ratio of the conductive carbon particles. If the amount is too small, it will not be able to completely cover the surface of the CNTs, thereby affecting the uniformity of the dispersion of the CNTs, and further leading to uneven distribution of the conductive network and a decrease in the conductivity. If the amount is too large, it may cause a decrease in the mechanical strength of the PDMS, and excessive residual of the surfactant hinders the formation of the CNT conductive network.

[0093] More specifically, the intensity of the ultrasonic treatment is 20-60 kHz (e.g., 50 kHz). If the ultrasonic frequency is too low, the cavitation effect generated is too strong, the local energy is too high, the de-agglomeration ability is too strong, but the energy is too concentrated and intense, which is more likely to cause structural damage to the CNTs (such as pipe wall defects or breakage), and the length of the CNTs is excessively shortened, which will destroy the continuity of the CNT conductive path and reduce the electrical conductivity of the composite material. If the ultrasonic frequency is too high, the cavitation effect is more moderate and uniform, which reduces the damage to the structure of the CNTs and helps to maintain the length and integrity of the CNTs, but the de-agglomeration efficiency is relatively low, and a longer ultrasonic time may be required to achieve the desired dispersion effect.

[0094] More specifically, the ultrasonic treatment time is 20-60 min (30 min). If the ultrasonic time is insufficient, the van der Waals force is not completely overcome, and the CNT agglomerates remain, which will lead to poor electrical performance, incomplete conductive network, and possibly poor mechanical performance, resulting in a decrease in material strength. If the ultrasonic time is too long, it may cause the CNTs to break and the length to be significantly shortened, which will cause the long-range conductive path to be broken and the electrical conductivity to be reduced. At the same time, the defects caused by excessive breakage may affect the interface bonding between the CNTs and the PDMS, and the mechanical performance may be reduced.

[0095] It should be noted that, in order to avoid the re-agglomeration of the conductive carbon, the present application removes the solvent in the PDMS prepolymer mixed solution by mechanical stirring.

[0096] Specifically, in step (3), after the PDMS prepolymer is added to the suspension uniformly dispersed with the conductive carbon particles, the suspension is mixed at a temperature of 60-100°C (e.g., 80°C) and a stirring speed of 500-1500 rpm (1500 rpm). In the case of ensuring uniform dispersion of the PDMS prepolymer, the solvent in the solution is evaporated to obtain a prepolymer in which the conductive carbon particles and the PDMS prepolymer are uniformly dispersed and mixed. The temperature cannot be too high, otherwise the suspension will boil and splash, making it difficult to accurately control the mass ratio of PDMS and conductive carbon particles. The temperature also cannot be too low, otherwise the isopropyl alcohol may not be fully volatilized, and the residual isopropyl alcohol may generate bubbles during the curing stage, affecting the structural integrity. If the mechanical stirring speed is too low, the solvent evaporation efficiency is low, and the conductive carbon particles may re-agglomerate due to insufficient settling or Brownian motion in the high-viscosity PDMS, resulting in uneven dispersion of the conductive carbon particles. If the mechanical stirring speed is too fast, the conductive carbon particle suspension may splash, resulting in a loss of PDMS and conductive carbon particles, making it difficult to accurately control the mass ratio of PDMS and conductive carbon particles.

[0097] It should be noted that the conductive carbon will affect the curing reaction of the PDMS prepolymer under the action of the curing agent, and the curing temperature and curing time of the coil layer conductive carbon-PDMS prepolymer-curing agent mixture need to be adjusted in the preparation process.

[0098] More specifically, in step (3), the temperature for curing the coil layer conductive carbon-PDMS prepolymer-curing agent mixture after pouring is 80-120°C, and the time is 4-8h. If the curing temperature is too high, it may cause uneven curing and affect the stability of the coil layer; if the curing temperature is too low, the curing rate is reduced, the curing time is long, and even the curing degree of the PDMS prepolymer is affected, affecting the mechanical strength of the material; if the curing time is insufficient, incomplete curing may occur, the mechanical strength of the material is reduced, and the material is prone to deformation; if the curing time is too long, the cost will be increased.

[0099] It should be noted that in order to improve the sensitivity of the force touch of the sensor, the thickness of the coil layer needs to be limited.

[0100] More specifically, the thickness of the coil layer is 0.8-1.5mm, preferably 1-1.5mm. The thinner the thickness of the coil layer, the more sensitive the sensor is to the deformation caused by pressure, and the higher the sensitivity of the force touch of the sensor. However, considering the limitations of the existing preparation process and the mechanical properties, the thickness of the coil layer cannot be too low.

[0101] According to some preferred embodiments of the present application, the thickness of the coil layer is any value within the range of 0.8-1.5mm, such as 0.8mm, 0.9mm, 1mm, 1.2mm, 1.3mm, 1.4mm, and 1.5mm.

[0102] It should be noted that in order to meet the requirements of the homogeneous and integrated structure design of the sensor, the material constituting the piezoresistive layer of the sensor is also a composite material of conductive carbon particles and PDMS. In the preparation process of the piezoresistive layer, in addition to the addition of inorganic salt to obtain a porous piezoresistive layer, the preparation method of the piezoresistive layer is the same as the preparation method of the coil layer described above, and the limitations of each component, added substances and process conditions are the same. Therefore, they will not be described here; only the differences will be explained below.

[0103] It should be noted that in order to enable the pressure sensor to realize force touch under greater pressure through the resistance sensing mode after reaching the range of pressure capacity effect sensing, and to expand the range of force touch of the sensor, the present application provides a porous piezoresistive layer below the coil layer, which continues to detect the contact force information of the object through resistance response.

[0104] It should be noted that the piezoresistive layer has a porous structure, when the contact force of the object is increased, the deformation of the sensor causes the coil layer to be in full contact with the piezoresistive layer, the porous structure of the piezoresistive layer is deformed, causing the internal conductive circuit path to change, increasing the contact area of the conductive path, the resistance becomes smaller, and the resistance changes are converted into an electrical signal, so that the greater pressure received by the sensor can be calculated, that is, the piezoresistive effect; the principle of realizing the force tactile perception of the sensor by the piezoresistive response is as shown in Figure 6

[0105] It should be noted that in order to improve the sensitivity and increase the force tactile perception range, the porosity of the piezoresistive layer needs to be limited, and the porosity is determined by the amount of inorganic salt added during the preparation of the piezoresistive layer. The inorganic salt used to obtain the porosity of the piezoresistive layer is chemically inert to PDMS and conductive carbon (no reaction), has good thermal stability (does not change or react when solidified under heat), has good solubility, and can be uniformly dispersed in the suspension of the conductive carbon together with the PDMS prepolymer.

[0106] Specifically, in step (4), at least one of NaCl, KCl, glucose C6H 12 O6, and NaCl is preferably used in consideration of the fact that NaCl is easily soluble in water.

[0107] Specifically, in step (4), the mass ratio of the inorganic salt to the conductive carbon particles is controlled to be 20:1-250:1, and the porosity of the piezoresistive layer is limited to 45-80%; if the amount of inorganic salt added is too high, the porosity of the piezoresistive layer will be too high, and when the sensor is switched from capacitive sensing to resistive sensing, the object contact force required will be too small, which is not conducive to the expansion of the force tactile perception range of the sensor; if the amount of inorganic salt added is too high, the porosity of the piezoresistive layer will be too small, which can easily cause the sensor to reach the limit of the capacitive sensing range after being pressed, and the coil layer cannot be in full contact with the piezoresistive layer, that is, the seamless switching of the sensor from capacitive sensing to resistive sensing cannot be achieved.

[0108] According to some preferred embodiments of the present application, the mass ratio of the inorganic salt to the conductive carbon particles added is any value within the range of 20:1-250:1, such as 20:1, 40:1, 50:1, 80:1, 100:1, 130:1, 160:1, 190:1, 210:1, 235:1, and 250:1.

[0109] ​It should be noted that in order to obtain the porous piezoresistive layer, the present application needs to remove the inorganic salt doped in the piezoresistive layer after curing by means of solvent soaking, and in order to improve the efficiency, the inorganic salt in the piezoresistive layer can be dissolved by using a solvent with a certain temperature.

[0110] Specifically, in step (4), the present application uses the method of soaking in hot water (70-90℃) to dissolve the inorganic salt in the piezoresistive layer after curing. On the one hand, hot water can promote the solubility of inorganic salt in water, promote the complete dissolution of inorganic salt, ensure no residue, and improve the dissolution efficiency. If NaCl is not removed completely, the salt crystals remaining in the PDMS will block the pores, leading to a decrease in the connectivity of the pores, and thus reducing the elasticity of the sponge (pore compression is limited) and the conductivity (the conductive network is blocked by NaCl); on the other hand, the temperature of hot water will not affect the physicochemical properties of PDMS, which can generally withstand temperatures above 150℃ after curing.

[0111] It should be noted that in order to ensure that the inorganic salt in the piezoresistive layer after curing is completely dissolved, the temperature of the hot water needs to be explained, and in order to improve the sensitivity and accuracy of the sensor, the thickness of the porous piezoresistive layer needs to be limited.

[0112] Specifically, the thickness of the piezoresistive layer is 1-6mm, and if the thickness of the piezoresistive layer is too large, it will lead to a decrease in sensitivity and accuracy. Based on the limitations of the existing preparation process, the thickness of the piezoresistive layer of the present application will not be too small.

[0113] According to some preferred embodiments of the present application, the thickness of the piezoresistive layer of the present application can be any value within the range of 1-6mm, such as 1mm, 2mm, 3mm, 4mm, 5mm, 6mm.

[0114] It should be noted that in order to expand the range of the sensor resistance force touch, the present application sets the porous piezoresistive layer to be composed of multiple layers of porous sponge layers, wherein the porosity of the multiple layers of porous sponge layers is gradiently changed from top to bottom.

[0115] Specifically, in step (4), by using the above method to configure PDMS prepolymer mixed prepolymer with different inorganic salt contents, pouring in the mold for preparing the piezoresistive layer in turn, and after curing, a piezoresistive layer composed of multiple layers of porous sponge layers can be obtained.

[0116] More specifically, the piezoresistive layer includes multiple layers of porous sponge layers, and from top to bottom, i.e. in the direction of the contact object applying contact pressure to the sensor, the porosity of the porous sponge layers decreases in turn; preferably, the piezoresistive layer includes 1-6 layers of the porous sponge layers, more preferably 2-3 layers.

[0117] According to some preferred embodiments of the present application, the number of the porous sponge layers can be 1, 2, 3, 4, 5, 6, and the more the number of the porous sponge layers, the more conducive to expand the range of the force tactile sensor, but increasing the number of the porous sponge layers will increase the size of the sensor, which is not conducive to the practical application of the sensor.

[0118] It should be noted that, due to the large number of pores in the upper sponge layer constituting the piezoresistive layer, the conductive material forms an incomplete conductive network in the matrix material, and when subjected to slight pressure, the CNTs with a relatively large distance will contact each other, resulting in a significant change in resistance value, thereby achieving high sensitivity to slight pressure; the lower layer has fewer pores, and the conductive material forms a relatively stable conductive network in the matrix material, and this network itself has a relatively low resistance value under low pressure, but because the slope of the resistance-pressure response curve is relatively small, it can withstand greater pressure without being quickly saturated, thereby enabling the sensor to perceive a larger pressure range.

[0119] It should be noted that, in order to maximize the range of force tactile perception while reducing the thickness of the piezoresistive layer, the present application needs to limit the thickness of each sponge layer.

[0120] Specifically, the thickness of the porous sponge layer is 1-2mm.

[0121] According to some preferred embodiments of the present application, the thickness of the porous sponge layer can be 1mm, 1.2mm, 1.5mm, 1.8mm, 2mm.

[0122] It should be noted that, in order to increase the range of force tactile perception, the present application needs to limit the difference in porosity between adjacent porous sponge layers, so that the air gap layer can enable the sensor to achieve seamless switching from capacitive sensing to resistive sensing while cooperating with the coil layer to achieve the range of force tactile sensor, thereby improving the reliability of sensor measurement, and the present application needs to limit the thickness of the air gap layer.

[0123] Specifically, the difference in porosity between adjacent porous sponge layers is 25-45%. If the difference in porosity is too large, it will cause the force tactile response interval of the piezoresistive layer to be discontinuous; if the porosity is too small, it will not significantly improve the sensitivity and the range of force tactile perception.

[0124] According to some preferred embodiments of the present application, the difference in porosity between adjacent porous sponge layers of the present application can be 25%, 27%, 30%, 32%, 35%, 38%, 40%, 42%, 45%.

[0125] It should be noted that in order to fix the piezoresistive layer in the subsequent packaging and provide an air gap layer between the coil layer and the piezoresistive layer, the structure and size of the support layer need to be defined.

[0126] Specifically, in step (5), according to the structure design of the piezoresistive layer and the size requirement of the air gap layer, a mold for preparing a support frame for placing the piezoresistive layer is obtained, pouring and curing to obtain the support frame, wherein the inner cavity size of the support frame is larger than the volume size of the piezoresistive layer, so as to be able to hold and fix the piezoresistive layer; the height difference constitutes the air gap layer of the sensor.

[0127] According to some preferred embodiments of the present application, the support frame has a square structure with an open top surface. In the subsequent packaging process of the sensor, after the piezoresistive layer is fixed on the bottom surface of the support frame by adhesive, the support frame and the coil layer substrate with the coil layer embedded are combined by adhesive, and the support frame and the coil layer substrate together constitute the packaging layer of the sensor.

[0128] According to some preferred embodiments of the present application, the support frame has a square structure with an open top surface and a ground surface. In the subsequent packaging process of the sensor, the support frame is first fixed on the bottom surface of the PDMS film (thickness about 300 μm) by adhesive, then the piezoresistive layer is fixed inside the support frame by adhesive, and finally the support frame and the coil layer substrate with the coil layer embedded are combined by adhesive, and the support frame, the coil layer substrate and the bottom surface of the film together constitute the packaging layer of the sensor.

[0129] It should be noted that the minimum thickness of the bottom surface of the support frame with an open top square structure can be 1 mm using the current pouring process. When a thinner PDMS film is used to replace the bottom surface of the support frame with an open top square structure, the sensor can be made lighter.

[0130] It should be noted that in order to make the air gap layer cooperate with the coil layer to realize the force tactile sensing range of the sensor, and at the same time enable the sensor to realize seamless switching from capacitive sensing to resistive sensing and improve the reliability of sensor measurement, the thickness of the air gap layer needs to be defined, that is, in the preparation process of the support frame, the difference between the height of the inner cavity of the support frame and the height of the piezoresistive layer is controlled by adjusting the structure size.

[0131] Specifically, in step (5), during the preparation of the support frame, the height of the inner cavity of the support frame is controlled to be higher than the height of the piezoresistive layer by 0.5mm < h < 1.5mm, that is, the thickness h of the air gap layer between the coil layer and the piezoresistive layer after packaging is 0.5mm < h < 1.5mm. The present application needs to make the coil layer fully contact the porous piezoresistive layer before the sensor reaches the range of the pressure-capacitance effect sensing, or at least when the sensor reaches the range of the pressure-capacitance effect sensing, so that the working mode of the sensor is converted to the piezoresistive mode, avoiding the discontinuity of the force tactile sensing of the sensor, and improving the reliability of the dual-mode sensor.

[0132] According to some preferred embodiments of the present application, the thickness h of the air gap layer can be any value in the range of 0.5mm < h < 1.5mm, such as 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm. If the thickness of the air gap layer is too low, on the one hand, contact may occur between the coil layer and the piezoresistive layer, and the electrodes may be conducted, so that the proximity and the pressure-capacitance modal force tactile sensing cannot be performed; on the other hand, when sensing the force tactile signal, the pressure-capacitance-piezoresistive modal conversion threshold is reduced, and the sensor is converted to the piezoresistive mode before reaching the limit of the pressure-capacitance force tactile sensing, resulting in a decrease in the overall range of the force tactile sensing. If the thickness of the air gap layer is too large, it may cause discontinuity of the force tactile range, because when the pressure-capacitance modal limit force tactile range is reached, the coil layer still does not fully contact the piezoresistive layer, which further causes discontinuity of the force tactile range, thereby affecting the measurement effect of the dual-mode sensor.

[0133] It should be noted that the piezoresistive sponge layer itself has a certain viscoelasticity, and the deformation and recovery process is not instantaneous during the loading and unloading of external force. This viscoelasticity causes the response speed of the piezoresistive sponge in force tactile response to be relatively slow (~200ms). The sensor designed in the present scheme is initially in the stage of small contact force (such as 0-60kPa) and realizes force tactile sensing through the relatively fast response speed (60ms) of the capacitance. In this stage, although the contact force from the outside causes the overall system to deform, the coil layer cannot contact the piezoresistive layer, and the external force applied to the sensor acts on the entire sensor, including the lower piezoresistive layer, so the piezoresistive sponge also deforms to a certain extent, which is the preloading process. When the contact pressure continues to rise to a certain degree (such as 60kPa or more), the piezoresistive sponge has been preloaded and no longer needs to go through the initial viscoelastic deformation process. Therefore, the sensor designed in the present scheme has a high response speed in the piezoresistive sensing stage of force tactile.

[0134] It should be noted that in order to meet the design of the homogeneous and integrated structure of the sensor, the present application uses semi-cured PDMS as the adhesive for bonding and packaging the parts of the sensor.

[0135] Specifically, in step (6), the same adhesive as the raw material of the coil layer and the support layer is used for encapsulation and curing; specifically: the support frame with a square structure with open top and bottom surfaces prepared in step (5) is adhered to the bottom surface of the encapsulation or a support frame with a square structure with an open top surface is directly used, and the piezoresistive layer is placed inside the support frame; the adhesive is applied to the top surface of the support frame, and the coil layer substrate is placed on the support frame, so that the side of the coil layer substrate filled with the coil layer is in contact with the support frame, and curing is performed to obtain the dual-mode sensor.

[0136] It should be noted that the coil layer substrate and the support frame combined by the adhesive constitute the encapsulation layer of the sensor of the present application; in addition, the coil layer, the piezoresistive layer and the pores (air gap layer) formed therebetween encapsulated in the encapsulation layer constitute the functional layer of the sensor of the present application; wherein the material of the encapsulation layer and the base body of the coil layer and the base body of the piezoresistive layer are the same, thereby realizing the structure design of the dual-mode sensor of the present application.

[0137] It should be noted that the semi-cured PDMS used to encapsulate the sensor needs to have a certain viscosity, which can be uniformly attached to the interface to be combined during the combination of the components of the sensor, and needs to have a certain bonding strength to ensure the stability and firmness of the combination and encapsulation.

[0138] Specifically, the method for preparing the semi-cured PDMS adhesive of the present application is: fully mixing PDMS prepolymer and curing agent in a certain mass ratio (such as 5:1-20:1), and pouring into a PLA mold after degassing in vacuum, and curing at a certain temperature of 60-90℃ (such as 80℃) for a period of 30-60min (such as 45min) to obtain the semi-cured PDMS.

[0139] The adhesive interface obtained by the semi-cured PDMS of the present application is compared with the adhesive interfaces obtained by the following three commercial adhesives: high vacuum grease (Dow Corning, HVG), Krazy Glue (3M CA40H), and Super Glue Gel (3M AD119); the results show that the shear strength and interface toughness of the PDMS interface obtained by the present application are 194.3kPa and 370.9J·m-2, respectively; the shear strengths obtained by HVG, Krazy Glue, and Super Glue Gel are 6kPa, 14.5kPa and 22.0kPa, respectively; the interface toughnesses are 20.6J·m -2 ,52.9J·m-2 and 81.0 J·m -2 ; for PDMS and porous PDMS / CNT sponge interface, the shear strength and interface toughness obtained by this scheme are 14.7 kPa and 40.0 J·m -2 , respectively, while the shear strength obtained by HVG, Krazy Glue, and Super Glue Gel are 3.9 kPa, 6.2 kPa and 6.9 kPa, respectively; the interface toughness are 4.0 J·m -2 , 10.5 J·m -2 , and 10.4 J·m -2 .

[0140] Need to be explained, the coil layer substrate and the support frame combined together by the adhesive constitute the packaging layer of the sensor of the application; in addition, the coil layer, the piezoresistive layer and the pores (air gap layer) formed between the two, which are packaged inside the packaging layer, constitute the functional layer of the sensor of the application; wherein the material of the packaging layer and the substrate of the coil layer and the substrate of the piezoresistive layer are the same, so as to realize the structure design of the homogenization of the dual-mode sensor of the application.

[0141] The application also provides a homogenized flexible dual-mode sensor prepared by the above method, and a structural diagram thereof is shown in Figure 7 The sensor comprises a packaging layer and a functional layer, and the functional layer is sealed inside the packaging layer; from top to bottom, the functional layer comprises a coil layer, an air gap layer and a piezoresistive layer in sequence, and the packaging layer comprises a coil layer substrate and a support frame bonded in sequence.

[0142] The application also provides a homogenized flexible dual-mode sensor prepared by the above method, and the sensor comprises a packaging layer and a functional layer, and the functional layer is sealed inside the packaging layer; from top to bottom, the functional layer comprises a coil layer, an air gap layer and a piezoresistive layer in sequence, and the packaging layer comprises a coil layer substrate, a support frame and a packaging bottom surface bonded in sequence.

[0143] Specifically, the coil layer and the coil layer substrate are mutually embedded and have a plane complementary labyrinth structure, which is used to provide an edge field capacitance to sense a close object and form a capacitive proximity sense of the sensor.

[0144] Specifically, the air gap layer is provided by the support frame, which is used to provide a space for the deformation of the coil layer when it is pressed, so as to sense a contact object by using the inter-plate capacitance of the coil layer and form a capacitive force touch of the sensor.

[0145] Specifically, the piezoresistive layer is fixed inside the support frame and has a porous structure, which is used to provide a resistance to sense a contact object and form a resistive force touch of the sensor.

[0146] Specifically, the material of the encapsulation layer is the same as the base material of the functional layer.

[0147] Compared with the prior art, the flexible bimodal sensor is improved in overall material and structure composition: on the one hand, the coil layer is designed as a planar complementary labyrinth structure, the piezoresistive layer is designed as a multi-layer sponge layer containing a gradient porosity, and an air gap layer is added in the sensor structure, so that the sensor proximity sensing distance is expanded, the force touch sensing range is expanded, and the response speed and sensitivity of the resistance force touch are improved; on the other hand, the material of the encapsulation layer is the same as the base material of the functional layer, the stability of the interface between the parts of the sensor is improved, and the sensor has high robustness and durability.

[0148] The thickness of the coil layer is adjusted to improve the sensitivity of the sensor to the deformation caused by pressure, so as to improve the accuracy of measuring the contact force of the object by the change of capacitance, wherein the thinner the thickness of the coil layer, the more sensitive the sensor to the deformation caused by pressure, and the adjustment of the thickness of the coil layer should also consider the mechanical properties of the coil layer, so that the structure and performance of the coil layer can be kept intact when the sensor is deformed by pressure, and the accuracy of the measurement result of the sensor is avoided.

[0149] The ratio of the width to the spacing of the coil layer is adjusted to balance the strength and range of the edge field generated by the coil layer, so as to ensure the accuracy of measuring the proximity distance or position of the object by the change of the edge field of the coil layer, and expand the proximity sensing distance of the sensor.

[0150] The piezoresistive layer is designed as a multi-layer porous sponge layer, and the porosity of the multi-layer sponge layer decreases from top to bottom, so as to improve the force touch sensing distance of the sensor and improve the accuracy of measuring the pressure of the sensor.

[0151] The air gap layer arranged between the coil layer and the piezoresistive layer not only enables the sensor to accurately perceive the contact force of the object by the change of capacitance, widens the range of force touch of the sensor, but also preloads the piezoresistive layer when the sensor is pressed, improves the response speed and accuracy of the piezoresistive layer in sensing pressure. At the same time, considering the whole sensor, the thickness of the air gap layer is adjusted to enable the sensor to successfully switch between the capacitive sensing mode and the resistance sensing mode, avoid the discontinuity of the force touch sensing of the sensor caused by the fact that the object does not fully contact the piezoresistive sponge after the sensor is pressed to the range of capacitive sensing, and truly expand the range of force touch of the sensor.

[0152] The flexible sensor prepared by the method of the application can realize bimodal response of proximity sense and force sense, Figure 8 The result graph of the proximity sense response of the flexible sensor prepared for the embodiment 1 of the application; Figure 9 The result graph of the force sense response of the sensor designed for the embodiment 1 of the application in the capacitance mode and the resistance mode, from Figure 9 It can be seen that when the contact force increases to 60kPa, the mode of the sensor for force sense perception is switched from the capacitance mode to the resistance mode. The sensor designed by the application has a far proximity sense response range and a wide force sense response range, and has good piecewise linearity in the range.

[0153] The sensing distance of the proximity sense of the sensor prepared by the method of the application can reach 250mm, such as 225-250mm; the range of the force sense of the sensor can reach 200kPa, such as 160-200kPa, and the response time of the force sense of the piezoresistive layer can reach 166ms, such as 160-240ms.

[0154] The following embodiments and comparative examples are used to further explain the technical solutions of the application.

[0155] The type of the PDMS prepolymer used in the embodiment is Sylgard 184.

[0156] Embodiment 1

[0157] The method for preparing a flexible proximity sense-force sense sensor with homogeneity and integration, specifically comprising the following steps:

[0158] (1) Designing a coil layer with a planar complementary square maze structure;

[0159] (2) According to the planar complementary square maze structure of the sensor coil layer, obtaining a polylactic acid (PLA) mold of the capacitance coil layer substrate by 3D printing technology, mixing the PDMS prepolymer and the PDMS curing agent at a mass ratio of 10:1, degassing in vacuum, and then pouring into the PLA mold, and curing at 50℃ for 80min to obtain the patterned coil layer substrate, wherein the thickness of the coil layer is 1mm, and the ratio between the electrode width and the electrode spacing of the planar complementary square maze structure is 3:1;

[0160] (3) CNT powder is added to isopropyl alcohol (IPA) at a mass ratio of 50:1, a small amount of surfactant sodium dodecyl benzene sulfonate (SDBS) is added (for example, CNT:SDBS mass ratio is 3:1), and ultrasonic treatment is performed for 30 min to form a suspension; then, PDMS prepolymer (23:2 with the content of CNT powder) is added to the suspension, and mechanical stirring is performed at a speed of 1500 rpm and a temperature of 80°C until the IPA in the mixture is completely volatilized; after sufficient cooling, PDMS curing agent (containing hydrogen silicone oil (crosslinking agent) and platinum gold catalyst) is added at a mass ratio of PDMS prepolymer: curing agent = 10:1 and stirred thoroughly to obtain a CNT / PDMS composite containing 8wt% CNT, and the mixture is filled into the pattern of the prepared coil layer substrate; curing is performed at a temperature of 120°C for 8h to obtain a coil layer; wherein the coil layer is embedded into the prepared coil layer substrate;

[0161] (4) Inorganic salt NaCl, PDMS prepolymer and CNT powder are added to an appropriate amount of IPA at a mass ratio of 20:10:0.8, ultrasonic oscillation is performed for 30 min, and mechanical stirring is performed at a temperature of 80°C and a speed of 1200 rpm until the IPA in the mixture is completely volatilized; after cooling, PDMS curing agent is added at a mass ratio of PDMS prepolymer: curing agent = 10:1 and stirred thoroughly to obtain a CNT / PDMS / NaCl composite containing 2 times inorganic salt and 8wt% CNT; then, the composite is injected into a customized PTFE mold, and a first sponge layer is obtained by pressure coating;

[0162] Inorganic salt NaCl, PDMS prepolymer and CNT powder are added to an appropriate amount of IPA at a mass ratio different from that for preparing the first layer of sponge layer, i.e. 100:10:0.8, and the above process is repeated to obtain a CNT / PDMS / NaCl composite containing 10 times inorganic salt and 8wt% CNT, which is pressure coated on the first layer of sponge layer to obtain a second layer of sponge layer;

[0163] Curing is performed at 80°C for 4h, and the piezoresistive sponge layer is repeatedly immersed in hot water (90°C) to dissolve the inorganic salt NaCl therein, thereby obtaining a piezoresistive layer composed of the second layer of sponge layer and the first layer of sponge layer, which have a gradient decreasing porosity from top to bottom, wherein the thickness of the second layer of sponge layer is 1mm and the porosity is 80%; the thickness of the first layer of sponge layer is 1mm and the porosity is 45%;

[0164] (5) A PLA mold for preparing a support frame is obtained by 3D printing, PDMS prepolymer and curing agent are thoroughly mixed at a mass ratio of 10:1, degassed in vacuum, and then poured into the PLA mold, and curing is performed at a temperature of 50°C for 80 min to obtain a support frame, wherein the support frame is 1mm thicker than the piezoresistive layer (i.e. the thickness of the air gap layer in the prepared sensor after packaging);

[0165] (6) Take a PDMS film with a thickness of 300 μm, apply semi-cured PDMS prepolymer on the film, and place the support frame prepared in step (3) on the film; place the piezoresistive layer prepared in step (2) in the reserved area of the support layer; apply semi-cured PDMS prepolymer on the top surface of the support frame, and place the coil layer substrate with the embedded coil layer prepared in step (1) on the support frame, and cure at 80°C for 1 h to obtain a flexible force tactile and proximity sensor 1.

[0166] Example 2

[0167] The same method as in Example 1 was used, except that in step (3), the prepared piezoresistive layer only included one sponge layer, and the mass ratio of raw materials inorganic salt NaCl, PDMS prepolymer and CNT powder was 100:10:0.8, and the thickness of the piezoresistive layer after curing was 1 mm and the porosity was 80%, and finally a flexible force tactile and proximity sensor 2 was obtained.

[0168] Example 3

[0169] The same method as in Example 1 was used, except that in step (3), the prepared piezoresistive layer included three sponge layers, and the mass ratio of raw materials inorganic salt NaCl, PDMS prepolymer and CNT powder was 100:10:0.8, 50:10:0.8 and 20:10:0.8, respectively, to obtain a piezoresistive layer composed of a third sponge layer, a second sponge layer and a first sponge layer from top to bottom, with a gradient decrease in porosity, wherein the thickness of the third sponge layer was 1 mm and the porosity was 80%; the thickness of the second sponge layer was 1 mm and the porosity was 70%; and the thickness of the first sponge layer was 1 mm and the porosity was 45%, and finally a flexible force tactile and proximity sensor 3 was obtained.

[0170] Example 4

[0171] The same method as in Example 1 was used, except that in step (1), the ratio between the electrode width and the electrode spacing of the electrode with a planar complementary square maze structure was 5:1, and finally a flexible force tactile and proximity sensor 4 was obtained.

[0172] Example 5

[0173] The same method as in Example 1 was used, except that in step (1), the ratio between the electrode width and the electrode spacing of the electrode with a planar complementary square maze structure was 1:1, and finally a flexible force tactile and proximity sensor 5 was obtained.

[0174] Example 6

[0175] The same method as in Example 1 was adopted, except that in step (5), the thickness of the supporting frame was 0.55 mm (i.e. the thickness of the air gap layer in the sensor after packaging), and finally a flexible force tactile sensor 6 with homogeneous integration was obtained.

[0176] Example 7

[0177] The same method as in Example 1 was adopted, except that in step (5), the thickness of the supporting frame was 1.45 mm (i.e. the thickness of the air gap layer in the sensor after packaging), and finally a flexible force tactile sensor 7 with homogeneous integration was obtained.

[0178] Comparative Example 1

[0179] The same method as in Example 1 was adopted, except that in step (1), the sensor coil layer adopted an interdigital electrode structure, and finally a flexible force tactile sensor 8 with homogeneous integration was obtained.

[0180] Comparative Example 2

[0181] The same method as in Example 1 was adopted, except that steps (4) and (5) were not included, and finally a flexible force tactile sensor 11 with homogeneous integration was obtained.

[0182] Comparative Example 3

[0183] The same method as in Example 1 was adopted, except that the mass ratio of the PDMS prepolymer to the CNT powder was 10:0.1, and finally a flexible force tactile sensor 9 with homogeneous integration was obtained.

[0184] Comparative Example 4

[0185] The same method as in Example 1 was adopted, except that in step (5), the thickness of the supporting frame was 1.55 mm (i.e. the thickness of the air gap layer in the sensor after packaging), and finally a flexible force tactile sensor 10 with homogeneous integration was obtained.

[0186] The structural parameters of the sensors obtained in the above examples and comparative examples are shown in Table 1:

[0187]

[0188]

[0189]

[0190] Test Example

[0191] The sensors 1-11 obtained in the examples and comparative examples were tested, and the results are as follows:

[0192] First, the sensor to be tested is placed directly below the Mark-10 F105 metal pressure head, and the metal pressure head is moved from 300 mm to 0 mm at a speed of 200 mm / min. The Keysight E4980 is used to collect the capacitance signal of the sensor to be tested during this process, and the Mark-10 F105 is used to record the distance signal to obtain the proximity response of the sensor to be tested.

[0193] Then, the metal pressure head is moved downward at a speed of 3 mm / min, and the sensor to be tested is subjected to pressure. The Keysight E4980 and Keithley 2450 are used to record the capacitance signal and resistance signal of the sensor to be tested during the pressure, respectively. The Mark-10 F105 is used to record the pressure signal to obtain the force tactile response of the sensor to be tested.

[0194] The results obtained after testing the sensors prepared in the examples and comparative examples are shown in Table 1.

[0195] Table 2 is the performance parameters of the sensors prepared in the examples and comparative examples

[0196]

[0197] The above description is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed by the present application can be easily thought by those skilled in the art, and should be covered within the protection scope of the present application.

Claims

1. A method for preparing a homogenously integrated bimodal sensor, characterized in that, The method comprises: (1) designing a coil layer with a planar complementary labyrinth structure; (2) obtaining a mold for preparing the coil layer substrate according to the structure of the coil layer, pouring, and curing to obtain a patterned coil layer substrate; (3) filling the pattern of the coil layer substrate and curing to obtain the coil layer, wherein the coil layer and the coil layer substrate are mutually embedded into one whole; (4) obtaining a mold for preparing the piezoresistive layer according to the structure design of the piezoresistive layer, pouring, and curing to obtain the piezoresistive layer; (5) obtaining a mold for preparing a support frame for placing the piezoresistive layer according to the structure design of the piezoresistive layer, pouring, and curing to obtain the support frame, wherein the support frame has a square structure with an open top surface or a square structure with open top and bottom surfaces, and the inner cavity size of the support frame is greater than the volume size of the piezoresistive layer, and the height difference constitutes the air gap layer of the sensor after packaging; (6) packaging: bonding the square structure support frame with open top and bottom surfaces prepared in step (5) on the packaging bottom surface or directly using the square structure support frame with an open top surface, placing the piezoresistive layer inside the support frame; applying the adhesive on the top surface of the support frame, placing the coil layer substrate on the support frame, and making the side of the coil layer substrate filled with the coil layer contact the support frame, and curing to obtain the dual-mode sensor, wherein the coil layer substrate and the support frame bonded together jointly constitute the packaging layer of the sensor, and the coil layer, the piezoresistive layer, and the air gap layer therebetween jointly constitute the functional layer of the sensor; wherein the packaging layer and the matrix of the coil layer and the matrix of the piezoresistive layer are made of the same material.

2. The method of claim 1, wherein, In steps (2) and (5), polydimethylsiloxane prepolymer is used for pouring.

3. The method of claim 2, wherein, The pouring temperature is 40-60°C, and the time is 70-100 min.

4. The method of claim 1, wherein, In step (3), a mixture containing conductive carbon and polydimethylsiloxane prepolymer is used for pouring.

5. The method of claim 4, wherein, In the mixture, the mass ratio of conductive carbon to polydimethylsiloxane prepolymer is 1:10-1:

25.

6. The method of claim 4, wherein, The mixture also contains a surfactant.

7. The method of claim 1, wherein, In step (4), a mixture containing conductive carbon, polydimethylsiloxane prepolymer, and inorganic salt is used for pouring.

8. The method of claim 7, wherein, The mass ratio of inorganic salt, conductive carbon, and polydimethylsiloxane prepolymer is 20-250:1:10-25.

9. The method of claim 1, wherein, In step (5), the height difference between the inner cavity of the support frame and the piezoresistive layer is 0.55-1.45 mm. And / or, the support frame has a square structure with an open top surface or a square structure with open top and bottom surfaces.

10. A homogenously integrated dual modality sensor, characterized in that, The sensor is prepared by the method of any one of claims 1-9, the sensor comprises a packaging layer and a functional layer, the functional layer is sealed inside the packaging layer; from top to bottom, the functional layer comprises a coil layer, an air gap layer, and a piezoresistive layer in sequence, and the packaging layer comprises a coil layer substrate, a support frame, and a packaging bottom surface bonded in sequence: The coil layer and the coil layer substrate are mutually embedded and have a planar complementary labyrinth structure for providing an edge field capacitance to sense a close object and form a capacitive proximity sense of the sensor. The air gap layer is provided by the support frame to provide a space for the deformation of the coil layer when pressed to sense a contact object by the capacitance between the coil layer electrodes and form a capacitive force touch sense of the sensor. The piezoresistance layer is fixed inside the support frame and has a porous structure to provide a resistance to sense a contact object and form a resistive force touch sense of the sensor. The material of the packaging layer is the same as that of the substrate of the functional layer.

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