Flexible electronic skin and preparation method thereof

Abstract

The invention discloses a flexible electronic skin and a preparation method thereof, and the flexible electronic skin comprises a flexible substrate and a conductive layer deposited on the flexible substrate; the resistance threshold of the flexible substrate is different from the resistance threshold of the conductive layer. According to the invention, a double-layer structure design is adopted, and a high-sensitivity sensor is formed by using the difference of resistance thresholds of two layers of materials. The sensor can generate a stable resistance waveform with a remarkable identification degree when receiving small deformation.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible skin, and in particular to a flexible skin and a preparation method thereof. Background Art

[0002] Flexible electronic skin is a cutting-edge concept born in recent years from the cross-integration of materials science, computer technology and human-computer interaction. This innovative technology breaks through the limitations of traditional rigid sensors and can collect human motion signals in a more sensitive and lasting way. Flexible electronic skin shows great application potential in medical monitoring and rehabilitation therapy. Due to its unique softness and ductility, this electronic skin can seamlessly fit with human skin, greatly improving the wearing comfort. This feature allows it to monitor various physiological parameters such as heart rate, blood pressure, body temperature, etc. for a long time and continuously without affecting the patient's daily life.

[0003] However, existing flexible electronic skins are not sensitive enough to strain.

[0004] Therefore, the prior art needs to be further improved and enhanced. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a flexible electronic skin and a preparation method thereof, aiming to solve the problem that the existing flexible electronic skin is not sensitive enough to strain.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0007] In a first aspect, a flexible electronic skin comprises: a flexible substrate and a conductive layer deposited on the flexible substrate; a resistance threshold of the flexible substrate is different from a resistance threshold of the conductive layer.

[0008] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0009] As a preferred technical solution, in the flexible electronic skin, the material of the flexible substrate is polydimethylsiloxane or aliphatic aromatic copolyester or SEBS.

[0010] As a preferred technical solution, in the flexible electronic skin, the thickness of the conductive layer is 0.1-0.300 μm.

[0011] As a preferred technical solution, the flexible electronic skin, wherein the thickness of the flexible substrate is 100-300 00 μm.

[0012] As a preferred technical solution, the flexible electronic skin, wherein the flexible substrate is filled with conductive fillers; the conductive fillers include carbon-based conductive materials, metal nanomaterials and conductive polymers.

[0013] As a preferred technical solution, in the flexible electronic skin, the filling mass fraction of the conductive filler is 2%-5%.

[0014] As a preferred technical solution, in the flexible electronic skin, the carbon-based conductive material is selected from one or more of carbon nanotubes, graphene and carbon black; and the metal nanomaterial is silver nanowire or gold nanowire.

[0015] In a second aspect, a method for preparing the flexible electronic skin according to the first aspect, comprising:

[0016] preparing a flexible substrate material into a film;

[0017] heat-treating the film to obtain a semi-cured film;

[0018] A conductive layer is deposited on the surface of the semi-cured film to obtain the flexible electronic skin.

[0019] As a preferred technical solution, the method for preparing the flexible electronic skin, wherein the step of preparing the flexible substrate material into a film specifically comprises:

[0020] The flexible base material and the cross-linking agent are mixed to obtain a mixed solution; the mass ratio of the flexible base material to the cross-linking agent is 10-30:1;

[0021] The mixed solution is applied to form a film.

[0022] As a preferred technical solution, the method for preparing the flexible electronic skin, wherein the film is heat-treated to obtain a semi-cured film, specifically comprises: placing the film in a baking device for baking, the baking temperature is 60-80°C, the baking time is 20-30 minutes, to obtain a semi-cured film.

[0023] Beneficial effects: Compared with the prior art, the present invention adopts a double-layer structure design and utilizes the difference in resistance thresholds of the two layers of materials to form a highly sensitive sensor. The sensor can generate a stable and recognizable resistance waveform when receiving a small deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the structure of the flexible electronic skin provided by the present invention;

[0025] Figure 2is a schematic diagram of the structure of the flexible electronic skin provided by an embodiment of the present invention;

[0026] Figure 3 The present invention implements the waveform of the flexible electronic skin cyclically stretched to about 150% (i.e. stretched from an original length of 5 cm to about 7.5 cm, with a cycle time of about 1.5 seconds);

[0027] Figure 4 yes Figure 3 A zoomed-in view of the first 100 points area. DETAILED DESCRIPTION

[0028] The present invention provides a flexible electronic skin and a method for preparing the same. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] It will be understood by those skilled in the art that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations. It should be understood that the term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0030] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as here.

[0031] It should be understood that the sequence number and size of each step in this embodiment do not mean the order of execution, and the execution order of each process is determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of this application. All instruments used are commercially available products.

[0032] Combination Figure 1The flexible electronic skin provided by the present invention comprises: a flexible substrate 10 and a conductive layer 20 deposited on the flexible substrate; the resistance threshold of the flexible substrate 10 is different from the resistance threshold of the conductive layer 20. In other words, the flexible electronic skin has a double-layer structure, and the resistance thresholds of the two layers are different. It is precisely because of the difference in the resistance thresholds of the two layers that it can generate a stable and recognizable resistance waveform when receiving a slight deformation, and the measurement result can be obtained by processing the waveform. In other words, the sensor formed by the flexible electronic skin has a high sensitivity.

[0033] In one implementation of the present invention, the material of the flexible substrate is polydimethylsiloxane or aliphatic aromatic copolyester (Ecoflex is an aliphatic aromatic copolyester, as a room temperature curing silicone polymer, it has high stretchability and ductility, and is easy to manufacture into complex shapes), SEBS (a linear three-block copolymer with polystyrene as the terminal segment and ethylene-butylene copolymer obtained by hydrogenation of polybutadiene as the middle elastic block, the full English name is Styrene Ethylene Butylene Styrene, referred to as SEBS). Among them, polydimethylsiloxane (Polydimethylsiloxane, PDMS). PDMS is a viscous liquid in liquid state, commonly known as "dimethicone", which belongs to silicone oil substances. It is a mixture of organosiloxanes composed of chain structures with different polymerization degrees, and its end groups and side groups are all hydrocarbon groups (such as methyl, ethyl, phenyl, etc.). In general, silicone oil presents the characteristics of colorless, odorless, non-toxic, and low-volatility liquid. When PDMS cures, it transforms into a unique silicone that is non-toxic, hydrophobic, chemically inert, non-flammable, transparent, and elastic.

[0034] PDMS as the base material for flexible electronic skin has the following characteristics: simple and fast preparation process, material cost is much lower than traditional silicon wafers, excellent light transmittance, outstanding biocompatibility, easy bonding with a variety of materials at room temperature, and high structural flexibility due to its low Young's modulus.

[0035] In one implementation of the present invention, Figure 2 The flexible substrate is filled with conductive fillers; the conductive fillers include carbon-based conductive materials, metal nanomaterials and conductive polymers. By filling the flexible substrate with conductive fillers, the flexible substrate layer can have a kΩ level of conductivity per square unit at room temperature.

[0036] In the present invention, the carbon-based conductive material is selected from one or more of carbon nanotubes, graphene and carbon black; the metal nanomaterial is silver nanowire or gold nanowire; the conductive polymer is polyaniline, two-dimensional metal carbide, two-dimensional metal nitride or two-dimensional metal carbonitride. Among them, carbon nanotubes have better conductivity than other carbon-based conductive materials at the same filling amount, are simpler to prepare than other types of materials, have better thermal stability and mechanical stability, and are easier to disperse in flexible substrates. The filling mass fraction of the conductive filler is 2%-5%, such as 2%, 3%, 4%, 5%. When it is below 2%, the concentration of carbon nanotubes is too low, resulting in the conductivity of the lower layer being not ideal. When it is above 5%, the conductivity will be improved, but the improvement will slow down, and the dispersion time will be longer.

[0037] In the present invention, the conductive layer 20 includes a connecting layer 21 and a conductive layer 22, wherein the conductive layer 22 performs the conductive function, and the connecting layer mainly performs the fixing and connecting functions. The conductive layer is made of Ag, and the connecting layer is made of Ti, or of course, Cr.

[0038] In the present invention, when the flexible electronic skin is subjected to horizontal tensile strain, the nanosilver layer on the surface will produce microcracks, causing its conductivity to drop sharply, and at this time the CNT network in the PDMS begins to play a major conductive role. This unique mechanism enables the sensor to generate a characteristic waveform with significant resistance changes in a time series. Through this dual-mode resistance change, we can obtain more resistance waveforms with unique characteristics, providing a rich data foundation for the subsequent intelligent process, thereby greatly improving the accuracy and sensitivity of action recognition.

[0039] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned flexible electronic skin, comprising:

[0040] S10, preparing the flexible base material into a film.

[0041] Specifically, dimethyl silicone oil and a cross-linking agent are mixed in a ratio of 10-30:1 (such as 10:1) to obtain a mixed solution, and the mixed solution is coated to prepare a thin film. Among them, when the proportion of the cross-linking agent is lower, the coagulation time of PDMS will be longer, and the adhesion of the surface after coagulation will also be stronger, and the subsequent metal deposition plated thereon will be unsatisfactory. However, reducing the proportion of the cross-linking agent is not conducive to controlling the semi-cured state during coagulation, so it is preferred to use a ratio of 10:1 for production. A mass ratio of PDMS to cross-linking agent of 10:1 is adopted. This ratio ensures that the cured PDMS maintains good elasticity and has a certain degree of adhesion, while ensuring excellent biocompatibility.

[0042] For example, the prepared flexible substrate mixed liquid is evenly coated into a thin film using a precision scraper with a thickness of 400 μm.

[0043] S20, heat-treating the film to obtain a semi-cured film.

[0044] Specifically, the film prepared in step S10 is placed in a precisely temperature-controlled baking device such as an oven, and dried at 60-80°C for 20 to 30 minutes to reach a semi-cured state. The semi-cured state refers to a state in which the PDMS has a rubber-like appearance, does not change shape immediately when squeezed, and does not flow like a liquid, but has not yet reached a completely cured state.

[0045] It should be noted that in the related research on mixing PDMS and cross-linking agent in a ratio of 10:1, the inventors have explored the relationship between the curing time and mechanical strength of PDMS and the temperature at curing temperatures from room temperature to above 150 degrees Celsius. The corresponding relationship between the complete curing time and mechanical strength of PDMS and the curing temperature is approximately:

[0046] At room temperature (about 25°C): 24-48 hours (Khanafer et al., 2009; Palchesko et al., 2012); Young's modulus: about 1.32-2.05 MPa (Johnston et al., 2014); Elastic modulus: about 0.5 MPa (Palchesko et al., 2012).

[0047] At 65°C: 4 hours (Mata et al., 2005); elastic modulus: about 1.5 MPa (Palchesko et al., 2012).

[0048] At 75°C: 2 hours (optimal temperature suggested by Liu et al., 2009); Young's modulus: about 1.82 MPa; tensile strength: about 3.51 MPa; elongation at break: about 160% (Johnston et al. (2014)).

[0049] At 80°C: 2 hours (Lee et al., 2003); Young's modulus: about 2.05 MPa; tensile strength: about 3.9 MPa; elongation at break: about 153% (Wang et al. (2014)).

[0050] At 100°C: 1-2 hours (Johnston et al., 2014) / 1 hour (Palchesko et al., 2012); Young's modulus: about 2.05-2.46 MPa (Johnston et al., 2014); Elastic modulus: about 2.5 MPa (Palchesko et al., 2012).

[0051] At 150°C: 10 minutes (Johnston et al., 2014) / 20 minutes (Schneider et al., 2009); Young's modulus: about 2.46 MPa; tensile strength: about 7.65 MPa; elongation at break: about 126% (Johnston et al. (2014)).

[0052] According to other studies, the Young's modulus of PDMS will continue to rise and the tensile strength will continue to decrease after exceeding 150°C. Therefore, considering the mechanical properties and semi-curing needs, it is better to use a temperature not exceeding 80°C.

[0053] It is easy to understand that: because it is difficult to control the time point of semi-curing at too high a temperature, in most cases, the temperature above 80°C is not used for experiments, but it can be used in theory. And if the semi-curing step is not required, then directly using a higher temperature will make the flexible substrate solidify faster, but there is a possibility that its flexibility will decrease, that is, it will become brittle and easy to break.

[0054] S30, depositing an Ag conductive layer and Ti on the surface of the semi-cured film for connection to obtain the flexible electronic skin.

[0055] Specifically, the semi-cured film was transferred to a thermal evaporation vacuum coating machine for Ti / Ag (10nm / 200nm) double-layer metal film deposition at a deposition rate of 10 / s, which helped to form a more uniform and dense film structure. This deposition process in a semi-cured state allows part of the metal to penetrate into the lower PDMS layer, forming a unique and stable double-layer structure.

[0056] The flexible electronic skin of the present invention is further explained below through specific preparation examples.

[0057] Example 1

[0058] PDMS and its corresponding cross-linking agent (generally composed of a hydrosilane compound and a catalyst) are mixed in a mass ratio of 10:1 to obtain a flexible substrate mixed liquid. The prepared flexible substrate mixed liquid is evenly coated into a thin film using a precision scraper with a thickness of 400μm. The prepared film is placed in a precisely temperature-controlled oven and dried at 70°C for 30 minutes to reach a semi-cured state. The obtained semi-cured film is transferred to a thermal evaporation vacuum coating machine for Ti / Ag (10nm / 200nm) double-layer metal film deposition at a deposition rate of 10 / s to obtain a high-performance flexible electronic skin with a nano-scale silver layer on the surface and PDMS on the lower layer.

[0059] Example 2

[0060] PDMS and its corresponding cross-linking agent (generally composed of a hydrosilane compound and a catalyst) are mixed in a mass ratio of 20:1 to obtain a flexible substrate mixed liquid. The prepared flexible substrate mixed liquid is evenly coated into a thin film using a precision scraper with a thickness of 400μm. The prepared film is placed in a precisely temperature-controlled oven and dried at 80°C for 25 minutes to reach a semi-cured state. The obtained semi-cured film is transferred to a thermal evaporation vacuum coating machine for Ti / Ag (10nm / 200nm) double-layer metal film deposition at a deposition rate of 10 / s to obtain a high-performance flexible electronic skin with a nano-scale silver layer on the surface and PDMS on the lower layer.

[0061] Example 3

[0062] PDMS and its corresponding cross-linking agent (generally composed of a hydrosilane compound and a catalyst) are mixed in a mass ratio of 30:1 to obtain a flexible substrate mixed liquid. The prepared flexible substrate mixed liquid is evenly coated into a thin film using a precision scraper with a thickness of 400μm. The prepared film is placed in a precisely temperature-controlled oven and dried at 120°C for 20 minutes to reach a semi-cured state. The obtained semi-cured film is transferred to a thermal evaporation vacuum coating machine for Ti / Ag (10nm / 200nm) double-layer metal film deposition at a deposition rate of 10 / s to obtain a high-performance flexible electronic skin with a nano-scale silver layer on the surface and PDMS on the lower layer.

[0063] Example 4

[0064] PDMS mixed with 4% carbon nanotubes and its corresponding crosslinker (generally composed of hydrosilane compounds and catalysts) are mixed in a mass ratio of 10:1 to obtain a flexible substrate mixed liquid. The prepared flexible substrate mixed liquid is evenly coated into a thin film using a precision scraper with a thickness of 400μm. The prepared film is placed in a precisely temperature-controlled oven and dried at 80°C for 25 minutes to reach a semi-cured state. The obtained semi-cured film is transferred to a thermal evaporation vacuum coating machine for Ti / Ag (10nm / 200nm) double-layer metal film deposition at a deposition rate of 10 / s to obtain a high-performance flexible electronic skin with a nano-scale silver layer on the surface and PDMS on the lower layer.

[0065] Example 5

[0066] PDMS and its corresponding crosslinker (generally composed of a hydrosilane compound and a catalyst) are mixed in a mass ratio of 10:1 to obtain a flexible substrate mixed liquid. The prepared flexible substrate mixed liquid is evenly coated into a thin film using a precision scraper with a thickness of 400μm. The prepared film is placed in a precisely temperature-controlled oven and dried at 80°C for 20 minutes to reach a semi-cured state. The obtained semi-cured film is transferred to a thermal evaporation vacuum coating machine for Ti / Ag (10nm / 200nm) double-layer metal film deposition at a deposition rate of 10 / s to obtain a high-performance flexible electronic skin with a nano-scale silver layer on the surface and PDMS on the lower layer.

[0067] The flexible electronic skin prepared in Example 4 was subjected to a cyclic stretch test. The test results are as follows: Figure 3 As shown, it can be seen that even when stretched to 200%, the waveform still does not undergo obvious deformation, indicating that the flexible electronic skin has high stability and flexibility.

[0068] In the specific application process, in terms of signal processing, wavelet transform technology can be used to reduce noise and extract features from the original resistance time series, effectively capturing signal features at different time scales. Dynamic time warping algorithm can be used to process differences in action execution speed and improve recognition stability.

[0069] To improve feature recognition, principal component analysis and independent component analysis can be used in combination to reduce data dimensions and extract representative independent features. In the selection of machine learning models, the integrated learning method of long short-term memory network and convolutional neural network can be considered, while using time series information and local pattern features.

[0070] To adapt to new action types, the concepts of transfer learning and incremental learning can be introduced to enable the system to quickly adapt to new actions and continuously optimize the model. In addition, data enhancement techniques such as adding noise and time axis scaling can be used to improve the robustness and generalization ability of the model.

[0071] The combined application of these signal processing and machine learning methods can give full play to the unique resistance response characteristics of this flexible electronic skin, and is expected to achieve significant improvements in motion recognition accuracy and system performance, opening up new possibilities for applications in the field of human-computer interaction.

[0072] Exemplarily, the data processing process is as follows:

[0073] 1. Data reading and initialization

[0074] oConvert timestamp to datetime format;

[0075] oSet up a time index and ensure data is sorted by time;

[0076] oDelete missing values ​​to ensure data integrity;

[0077] 2. Sliding window feature extraction;

[0078] o Use a fixed-size sliding window to traverse the entire time series;

[0079] o Perform the following feature extraction on each window: a) Fast Fourier Transform (FFT) Calculate the FFT of the data in the window; extract the main frequencies (the frequencies with the largest amplitude); calculate the mean and standard deviation of the FFT values;

[0080] b) Power Spectral Density (PSD) Analysis

[0081] Calculate PSD using Welch's method; extract the main frequencies (frequencies with the highest power) and calculate the mean and standard deviation of the PSD values; c) Symbol Aggregation Approximation (SAX); convert the data within the window into a sequence of symbols; use a fixed number of segments and alphabet size; 0 extract the symbol value of each segment as a feature;

[0082] d) Basic statistical characteristics

[0083] Calculate the average value of the data in the window (as resistance characteristic);

[0084] 3. Feature Normalization

[0085] o Use Min-Max Scaling to normalize all features to the range [0,1];

[0086] o Ensure that features of different dimensions can be compared on the same scale;

[0087] 4. Time window sequence creation

[0088] oCreate input sequences using fixed-length time windows;

[0089] oEach sequence contains all features at multiple time steps;

[0090] oThe corresponding target value is the resistance value of the next time step after the sequence;

[0091] The advantages of this method are: 0. It can capture the dynamic characteristics of time series data and combine the information of time domain and frequency domain. 0. It provides symbolic representation of signals through SAX. The sliding window approach allows real-time or near real-time feature extraction; normalization processing ensures the comparability of different features; the generated features and sequences are suitable for input into various machine learning models, especially deep learning models.

[0092] This method can also be subsequently adjusted, such as changing the window size, step size, SAX parameters or adding other feature extraction techniques.

[0093] In summary, the present invention provides a flexible electronic skin and a preparation method thereof, comprising: a flexible substrate and a conductive layer deposited on the flexible substrate; the resistance threshold of the flexible substrate is different from the resistance threshold of the conductive layer. The material of the flexible substrate can be polydimethylsiloxane (PDMS) or Ecoflex or SEBS. In addition, the flexible substrate contains a certain amount of carbon nanotubes. In the present invention, when the flexible electronic skin is subjected to horizontal tensile strain, microcracks will be generated on the surface of the nanosilver layer, causing its conductive performance to drop sharply, and at this time the CNTs network in the PDMS begins to play a major conductive role. This unique mechanism enables the sensor to generate a characteristic waveform with significant resistance changes in a time series. Through this dual-mode resistance change, we can obtain more resistance waveforms with unique characteristics, providing a rich data basis for the subsequent intelligent process, thereby greatly improving the accuracy and sensitivity of action recognition.

[0094] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A flexible electronic skin, It is characterized in that include: a flexible substrate and a conductive layer deposited on the flexible substrate; The resistance threshold of the flexible substrate is different from the resistance threshold of the conductive layer.

2. The flexible electronic skin according to claim 1, It is characterized in that The material of the flexible substrate is polydimethylsiloxane or aliphatic aromatic copolyester or SEBS.

3. The flexible electronic skin according to claim 1, It is characterized in that The thickness of the conductive layer is 0.1-0.30 μm.

4. The flexible electronic skin according to claim 3, It is characterized in that The thickness of the flexible substrate is 100-3000 μm.

5. The flexible electronic skin according to claim 1, It is characterized in that The flexible substrate is filled with conductive fillers; the conductive fillers include carbon-based conductive materials and metal nanomaterials.

6. The flexible electronic skin according to claim 5, It is characterized in that The filling mass fraction of the conductive filler is 2%-5%.

7. The flexible electronic skin according to claim 5, It is characterized in that The carbon-based conductive material is selected from one or more of carbon nanotubes, graphene and carbon black; and the metal nanomaterial is silver nanowire or gold nanowire.

8. A method for preparing the flexible electronic skin according to claim 1, It is characterized in that include: preparing a flexible substrate material into a film; heat-treating the film to obtain a semi-cured film; A conductive layer is deposited on the surface of the semi-cured film to obtain the flexible electronic skin.

9. The method for preparing the flexible electronic skin according to claim 8, It is characterized in that The step of preparing the flexible substrate material into a film specifically comprises: The flexible base material and the cross-linking agent are mixed to obtain a mixed solution; the mass ratio of the flexible base material to the cross-linking agent is 10-30:1; The mixed solution is applied to form a film.

10. The method for preparing the flexible electronic skin according to claim 8, It is characterized in that The heat treatment of the film to obtain a semi-cured film specifically includes: placing the film in a baking device for baking at a temperature of 60-80° C. for a baking time of 20-30 minutes to obtain a semi-cured film.

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