Flexible skin structure integrating exterior and interior perception and preparation method thereof

Abstract

The invention discloses a flexible skin structure fused with exterior and interior perception and a preparation method thereof.The flexible skin structure fused with exterior and interior perception comprises an elastic substrate, a plurality of layers of channel structures are arranged in the elastic substrate, and liquid metal is injected into the channel structures; the liquid metal forms a liquid metal network in the channel structure of the elastic substrate, and the liquid metal network serves as a sensing system and comprises an SSPP unit and piezoresistive channel structures arranged on the periphery of the SSPP unit in parallel; the cable comprises a flexible flat cable connected with the piezoresistive channel structure and a coaxial line connected with the SSPP unit. The invention discloses a flexible skin structure integrated with exterior and interior perception and a preparation method thereof. The flexible skin structure is compact in structure, high in function integration level and simple and convenient in preparation process. Cooperative perception and processing of surface layer and deep layer information are achieved through multi-mode flexible electronic skin. Surface layer pressure sensing and deep layer medium sensing can be achieved, and a multi-mode sensing function is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible electronic devices, and in particular to a flexible multimodal sensing electronic skin based on liquid metal microchannels that integrates surface tactile perception and inner layer penetrating medium perception, and a preparation method thereof. Background Art

[0002] With the rapid development of flexible electronic devices, wearable sensors, and human-computer interaction systems, flexible electronic skin, as a key carrier, has shown broad application prospects in the fields of intelligent medical monitoring, artificial intelligence, and robotic perception. Currently, common flexible electronic skins mostly use mechanisms such as piezoresistive, piezoelectric, and capacitive to acquire surface physical signals such as touch, strain, and temperature. However, existing technologies mostly focus on surface signal perception and are unable to simultaneously achieve "penetrating" information detection inside the target or deep tissue, limiting their functional expansion and information dimensionality in complex application scenarios.

[0003] To achieve higher levels of human-computer interaction and environmental perception, existing technologies are beginning to attempt to integrate multimodal sensing into the same flexible device. On the one hand, liquid metal, due to its excellent conductivity, flexibility, and stretchability, is an ideal material for realizing flexible conductive pathways and channel structures, and is widely used in flexible piezoresistive sensors. On the other hand, artificial surface plasmons (SSPPs), as artificial electromagnetic structures at the subwavelength scale, possess characteristics such as localized enhancement of electromagnetic waves, tunable frequency response, and medium sensitivity, providing a new path for non-contact deep medium sensing.

[0004] Although existing technologies have made certain progress in flexible pressure sensing and electromagnetic wave penetration detection, there is still a lack of an ultra-thin electronic skin that can efficiently integrate liquid metal microchannels with SSPP structures, which not only meets the requirements of flexible and highly sensitive tactile perception, but also has the ability to non-invasively detect changes in the target's internal medium. Summary of the Invention

[0005] The present invention overcomes the shortcomings of the existing technology and provides a flexible skin structure and its preparation method that integrates surface and inside perception with a compact structure, high functional integration, and simple preparation process. It realizes the coordinated perception and processing of surface and deep information through multimodal flexible electronic skin; it can realize surface pressure perception and deep medium perception, and has multimodal sensing function.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a flexible skin structure that integrates internal and external perception, including: an elastic substrate, several layers of channel structures are arranged in the elastic substrate, liquid metal is injected into the channel structure, and the liquid metal forms a liquid metal network in the channel structure of the elastic substrate. The liquid metal network serves as a perception system, including: an SSPP unit, and a piezoresistive channel structure arranged in parallel on the periphery of the SSPP unit; the cable includes a soft cable connected to the piezoresistive channel structure, and a coaxial cable connected to the SSPP unit.

[0007] In a preferred embodiment of the present invention, the piezoresistive channel structures are arranged in parallel on both sides of the SSPP unit to form a dual-channel sensing system.

[0008] In a preferred embodiment of the present invention, the elastic base includes a base layer, a flexible membrane with through holes, and a flexible membrane with channels stacked in sequence; a channel structure is formed in the middle of the flexible membrane with channels and the flexible membrane with through holes after being matched together, and a through groove is also provided on the flexible membrane with channels, and the through groove is connected to the through holes on the flexible membrane with through holes accordingly.

[0009] In a preferred embodiment of the present invention, one end of the flexible flat cable and the coaxial cable connected to the liquid metal network is embedded between the base layer and the flexible membrane with through holes, and the one end of the flexible flat cable and the coaxial cable connected to the liquid metal network corresponds to the through hole on the flexible membrane with through holes.

[0010] In a preferred embodiment of the present invention, the through holes of the flexible membrane with through holes and the through grooves on the flexible membrane with channels are blocked by the base layer and the packaging film respectively, so that the liquid metal is confined in the channel structure of the elastic base.

[0011] In a preferred embodiment of the present invention, an electromagnetic shielding layer is further provided on the elastic substrate; the elastic substrate is an elastic substrate made of PDMS material, PDMS being polydimethylsiloxane; the liquid metal is an indium-tin alloy having a melting point of 6° C., a density of 6.03 g / cm 3 , and a purity of 99%; Liquid metal is a conductive medium.

[0012] In a preferred embodiment of the present invention, a method for preparing a flexible skin structure integrating internal and external sensing includes the following steps: Obtaining a base layer, a flexible film with through holes, a flexible film with channels, liquid metal, a flexible flat cable, a coaxial cable, a packaging film, and an electromagnetic shielding layer; The flexible membrane with a channel, on which a channel structure is provided, is aligned with the flexible membrane with a through hole, forming a channel structure between the flexible membrane with a channel and the flexible membrane with a through hole; the other side of the flexible membrane with a through hole is aligned with the base layer, and one end of a coaxial line and a flexible flat cable are respectively embedded between the flexible membrane with a through hole and the base layer; the contact end of the coaxial line corresponds to the SSPP unit in the channel structure and contacts through the hole position on the flexible membrane with a through hole to transmit radio frequency signals; the contact end of the flexible flat cable contacts the corresponding piezoresistive channel structure in the channel structure to conduct piezoresistive signals; liquid metal is injected into the through hole on the flexible membrane with a through hole, and the liquid metal enters the channel structure to form a liquid metal network; Covering the encapsulation film on the through-holes of the flexible film with channels and injecting the liquid metal, so as to confine the liquid metal in the channel structure of the elastic substrate; The electromagnetic shielding layer is arranged on the outside of the base layer or the flexible film with the channel (it can cover the outside of the base layer or the flexible film with the channel, but only one can be covered).

[0013] In a preferred embodiment of the present invention, the method for preparing the base layer, the flexible film with through holes, and the encapsulation film comprises: A polydimethylsiloxane prepolymer and a curing agent were weighed and mixed in a mass ratio of 10:1 to obtain a PDMS solution; the mixture was degassed in a vacuum degassing chamber; the PDMS solution was spin-coated on a culture dish to form a PDMS liquid film; the PDMS liquid film was degassed and then step-cured and cross-linked in a constant temperature oven to obtain a flexible substrate film.

[0014] In a preferred embodiment of the present invention, the method for preparing a flexible membrane with channels comprises: Step S1, using a cleaning liquid combined with an ultrasonic cleaning process to perform surface treatment on the glass substrate; using high-purity nitrogen to purge and remove residual liquid on the surface of the substrate; obtaining a clean and dry surface of the glass substrate; Step S2, designing a photolithography mask based on a preset channel pattern, adopting a spiral topology configuration to obtain a photolithography mask with a channel pattern; Step S3: Based on the pre-treated surface of the glass substrate, a photosensitive dry film is evenly covered on the substrate surface through a precision film lamination process, and a hot pressing composite device is used to achieve close lamination between the dry film and the substrate under set temperature and pressure parameters to form a photosensitive dry film layer, thereby obtaining a coated substrate with a uniform photosensitive layer; Step S4, patterning the film-coated substrate using a contact photolithography method, so that the channel structure pattern on the mask is completely transferred to the photosensitive dry film layer; Step S5, using a sodium carbonate solution to wash away the unexposed portion of the DuPont photosensitive dry film on the dry film glass substrate to obtain a dry film glass substrate containing a channel structure; Step S6: Before implementing the PDMS casting process, the dry film glass substrate with the channel structure needs to be surface modified to obtain a silanized dry film glass substrate; Step S7, preparing a flexible structural film on the surface of the modified substrate using a prepolymer casting process to obtain a flexible film with channels; In a preferred embodiment of the present invention, the side of the flexible membrane with the channel provided with the channel is aligned with the flexible membrane with the through hole, and the step of forming the channel structure between the flexible membrane with the channel and the flexible membrane with the through hole comprises: First, a low-viscosity cleaning tape is used to remove particulate contaminants from the surface of the flexible membrane with through holes and the flexible membrane with channels. The flexible membrane with channels and the flexible membrane with through holes to be bonded are then placed in a plasma treatment device and subjected to surface activation treatment for 120±5s under 10±1W RF power and 8-10 NI / h oxygen flow rate to form hydroxyl active groups on the contact surface. The treated flexible membrane with channels and the flexible membrane with through holes are aligned and bonded with the activated surfaces facing each other. A pressing force of 0.01-0.05MPa is applied and the membrane is allowed to stand for 10-15 minutes to promote initial intermolecular bonding. Finally, the assembly is transferred to a constant temperature heating platform at 65±5°C for step-by-step bonding curing. The temperature is maintained at 50±2°C for the first 30 minutes to allow sufficient diffusion of the interface molecules, and then the temperature is raised to 70±2°C for 90 minutes to complete the covalent bonding. The through hole of the flexible membrane with through holes is provided with a flow guiding structure which is coaxially aligned with the through groove on the flexible membrane with channels for injecting liquid metal.

[0015] The steps of covering the encapsulation film on the through-holes of the flexible film with through-holes and injecting the liquid metal, and confining the liquid metal in the channel structure of the elastic substrate include: The film is processed into a packaging film by cutting, with a coverage area exceeding the edge of the liquid metal injection port by 1.0±0.2mm; Sil-Poxy silicone adhesive is selected to be coated on the periphery of the injection port with a uniform thickness of 25±5μm, and after optical alignment, a bonding pressure of 0.05±0.01MPa is applied; to eliminate thermally induced interfacial stress, the packaging film is completed in a constant temperature environment of 23±2℃ during the packaging process, and a static time of 30±2min is maintained during the curing stage to allow the adhesive to achieve molecular-level penetration without generating a thermal resistance layer.

[0016] Specifically, the steps for securing the flexible cable and coaxial line to the piezoresistive network and SSPP unit include: Using an 8-pin FPC cable as the flexible cable, aligning the cable's silver copper core with the through-holes on the flexible film with through-holes, forming a closed loop with the liquid alloy in the piezoresistive network. The coaxial line connects to the flexible film with forked solder tails. Its signal line connects to the SSPP unit in the liquid metal network through polygonal through-holes on either side of the film with through-holes. A ground line is sandwiched between the flexible film with through-holes and the flexible substrate.

[0017] Sil-Poxy silicone adhesive is applied between the flexible film with through holes and the flexible substrate with a uniform thickness of 25±5μm, and a bonding pressure of 0.05±0.01MPa is applied to complete the packaging process in a constant temperature environment of 23±2℃.

[0018] Specifically, the packaging film is a flexible PDMS packaging film with a thickness of 500±50 μm.

[0019] The present invention solves the defects existing in the technical background, and the beneficial technical effects of the present invention are: The present invention discloses a flexible skin structure and a preparation method thereof that integrates surface and interior perception, which has a compact structure, high functional integration, and a simple preparation process. The structure realizes the coordinated perception and processing of surface and deep information through multimodal flexible electronic skin; it can realize surface pressure perception and deep medium perception, and has multimodal sensing function.

[0020] This invention describes a flexible, multimodal sensing electronic skin based on liquid metal microchannels, integrating surface tactile perception with underlying penetrating media sensing, and its preparation method. The device integrates a piezoresistive sensing module and an artificial surface plasmon sensing module, achieving simultaneous perception of multimodal physical signals while maintaining the overall structural flexibility, thinness, and miniaturization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings and examples.

[0022] Figure 1 Schematic diagram of the flexible multimodal sensing electronic skin structure of the preferred embodiment of the present invention Figure 1 ; Figure 2 Schematic diagram of the flexible multimodal sensing electronic skin structure of the preferred embodiment of the present invention Figure 2 ; Figure 3 Schematic diagram of the structure of the liquid alloy sensor network according to a preferred embodiment of the present invention; Figure 4 Schematic diagram of the preparation process of a flexible membrane with channels according to a preferred embodiment of the present invention; Figure 5 Schematic diagram of the structure of the SSPP unit of a preferred embodiment of the present invention; Figure 6 A schematic diagram of a pressure sensing signal acquisition and processing circuit according to a preferred embodiment of the present invention; Figure 7 The dispersion relation simulation of the SSPP unit of the present invention based on HFSS Figure 1 ; Figure 8The present invention uses high-frequency electromagnetic simulation software to perform a system simulation of the S11 parameters of the artificial surface plasmon (SSPP) structure; Figure 9 The electric field intensity cloud distribution of the SSPP unit of the present invention; Figure 10 The distribution diagram of the electric field vector simulation results of the SSPP unit of the present invention in the xy plane; Figure 11 The distribution diagram of the electric field vector simulation results of the SSPP unit of the present invention in the xz plane; Figure 12 : is the magnetic field vector distribution diagram of the SSPP unit of the present invention in the xy plane; Among them, 1. Electromagnetic shielding layer; 2. Encapsulation film; 3. Flexible membrane with channels; 4. Liquid metal network; 51. Flexible membrane with through holes; 52. Base layer; 6. Flexible flat cable; 7. Coaxial cable; 8. Piezoresistive channel structure; 9. SSPP unit, 91. Transition section; 92. Surface waveguide section. DETAILED DESCRIPTION

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. These drawings are simplified schematic diagrams that only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0024] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, bottom, top, etc.), the directional indications are only used to explain the relative positional relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly. The terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Unless otherwise clearly specified and defined, the terms "set", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be a communication between the internal parts of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Example 1, as Figures 1-6As shown, a flexible skin structure that integrates both internal and external sensing features comprises an elastic base with several layers of channel structures. Liquid metal is injected into the channel structures, forming a liquid metal network 4 within the elastic base's channel structures. This network 4 is in electrical contact with the cable. An electromagnetic shielding layer 1 is also provided on the elastic base. In this embodiment, the elastic base is made of PDMS (polydimethylsiloxane). The liquid metal is an indium-tin alloy with a melting point of 6°C, a density of 6.03 g / cm3, and a purity of 99%. The liquid metal serves as a conductive medium. Electromagnetic shielding layer 1 is made of copper foil.

[0026] Specifically, the elastic base includes a base layer 52, a flexible membrane with through holes 51, and a flexible membrane with a channel, which are stacked in sequence; after the flexible membrane with a channel 3 and the flexible membrane with through holes 51 are matched, a channel structure is formed in the middle, and a through groove is also provided on the flexible membrane with a channel, and the through groove is connected to the through hole on the flexible membrane with through holes 51.

[0027] Specifically, the liquid metal network 4, serving as a sensing system, includes: SSPP units 9 and piezoresistive channel structures 8 arranged in parallel around the periphery of the SSPP units 9; the cables include a flexible flat cable 6 connected to the piezoresistive channel structures 8, and a coaxial cable 7 connected to the SSPP units 9. Furthermore, in this embodiment, the piezoresistive channel structures 8 are arranged in parallel on both sides of the SSPP units 9, forming a dual-channel sensing system.

[0028] Specifically, one end of the flexible flat cable 6 and the coaxial cable 7 connected to the liquid metal network 4 is embedded between the base layer 52 and the flexible membrane 51 with through holes, and one end of the flexible flat cable 6 and the coaxial cable 7 connected to the liquid metal network 4 corresponds to the through hole on the flexible membrane 51 with through holes.

[0029] Specifically, the through holes of the flexible membrane with through holes 51 and the through grooves on the flexible membrane with channels 3 are blocked by the base layer 52 and the packaging film 2 respectively, so that the liquid metal is confined in the channel structure of the elastic base.

[0030] In the second embodiment, a flexible skin structure integrating internal and external sensing realizes multimodal signal processing according to the first embodiment, comprising the following steps: 1. Piezoresistive acquisition: The spiral topology design achieves dual optimization of sensing performance, specifically: According to the law of resistance R = ρl / S , the electrode channel length l is maximized in the limited area of ​​20mm², so that the initial resistance RThe resistance of the channel is increased from 0 to 50-100Ω (preferably 75±5Ω), which significantly improves the detection signal-to-noise ratio of the resistance change (increased by 8-10 times) compared with the linear channel design (usually 5-10Ω); the spiral configuration allows a single pressure point to simultaneously trigger the coordinated deformation of 3-5 adjacent channels.

[0031] According to Δ R / R 0=2Δ S / S 0 sensitivity formula, the effective sensing area change rate Δ S / S 0 magnified to 3.2-4.8 times of the linear type.

[0032] The general circuit for collecting piezoresistive signals collects piezoresistive signals by connecting a resistor of appropriate resistance in series and reading the voltage change in the circuit. Figure 6 As shown in the figure, this circuit also uses the LM324 operational amplifier with a 21x gain. It is powered by the development board's 5V power connector and grounded with the board. The sensor's internal power is supplied by the board's 3.3V power connector, and the voltage divider resistor is 1kΩ.

[0033] SSPP signal analysis: The SSPP structure channel of SSPP unit 9 in the flexible electronic skin is connected to the SDR module (radio module), and the 1MHz signal f0 is transmitted through the 5.9GHz carrier f D The transmitter is connected to the SSPP module in the flexible electronic skin via coaxial cable 7, with a normalized output gain of 0.5. The RX port receives the signal, filters it through a low-pass filter (2MHz cutoff frequency, 0.5MHz bandwidth) to remove high-frequency noise, and then resamples it, storing 100 data points per second. The signal amplitude is then calculated in a Python module. This Python module was built using Gnuradio. When the concentration or properties of the ambient medium change, the dielectric constant of the surface material of the SSPP unit 9 and the piezoresistive channel structure 8 surrounding the SSPP unit 9 changes, affecting the resonance characteristics and transmission efficiency (S parameters) of the microwave signal on the SSPP unit 9. The amplitude of the received signal is calculated to determine the ambient medium outside the flexible electronic skin.

[0034] Embodiment 3, based on embodiment 1 or embodiment 2, a signal processing system implemented by a flexible skin structure integrating internal and external perception includes: An integrated platform for deep-layer medium identification and surface (piezoresistive contact identification) detection has been constructed, enabling simultaneous sensing and wireless remote transmission of multimodal signals. The system integrates a flexible skin structure (flexible SSPP sensor) with an embedded SDR module (radio module) for real-time acquisition and spectrum analysis of electromagnetic signals. For deep-layer material identification, the flexible skin structure (flexible SSPP sensor) incorporates an electromagnetic shielding layer 1 (copper foil) and an impedance matching circuit (transition section 91), significantly improving the system's anti-interference capabilities and spectral response sensitivity.

[0035] Example 4, a method for preparing a flexible skin structure integrating internal and external sensing, for preparing a flexible skin structure integrating internal and external sensing, comprising the following steps: Obtaining a base layer 52, a flexible film with through holes 51, a flexible film with channels 3, liquid metal, a flexible flat cable 6, a coaxial line 7, a packaging film 2, and an electromagnetic shielding layer 1; One side of the flexible membrane with a channel, 3, on which a microchannel is provided, aligns with the flexible membrane with a through-hole, 51, forming a channel structure between the flexible membrane with a channel, 3, and the flexible membrane with a through-hole, 51. The other side of the flexible membrane with a channel aligns with the base layer, 52, and one end of a coaxial line 7 and a flexible flat cable 6 are respectively embedded between the flexible membrane with a channel, 3, and the base layer, 52. The contact end of the coaxial line 7 corresponds to the SSPP unit 9 in the channel structure and contacts through the hole in the flexible membrane with a through-hole, 51, to transmit radio frequency signals. The contact end of the flexible flat cable 6 contacts the piezoresistive channel structure 8 in the channel structure to conduct piezoresistive signals. Liquid metal is injected into the through-holes of the flexible membrane with a through-hole, and the liquid metal enters the channel structure to form a liquid metal network 4. Covering the packaging film 2 on the through-holes of the flexible film 51 with through-holes and injecting the liquid metal, confining the liquid metal in the channel structure of the elastic substrate; The electromagnetic shielding layer 1 is arranged on the outside of the substrate layer 52 and / or the flexible membrane with channels 3 .

[0036] Example 5, a method for preparing a flexible skin structure integrating internal and external sensing, for preparing a flexible skin structure integrating internal and external sensing, comprising the following steps: Step 1: Obtain a base layer 52 , a flexible film with through holes 51 , a flexible film with channels 3 , liquid metal, a flexible flat cable 6 , a coaxial line 7 , a packaging film 2 , and an electromagnetic shielding layer 1 .

[0037] In this embodiment, the method for preparing the base layer 52, the flexible film with through holes 51, and the encapsulation film 2 includes: A polydimethylsiloxane prepolymer and a curing agent are weighed and mixed in a mass ratio of 10:1 to obtain a PDMS solution; the mixture is degassed in a vacuum degassing chamber; the PDMS solution is spin-coated on a culture dish to form a PDMS liquid film, and the PDMS liquid film is degassed and then cured by stepwise curing and cross-linking in a constant temperature oven to obtain a flexible substrate film. Several pieces of the flexible substrate film are used as a base layer 52, a flexible film with through holes 51, and an encapsulation film 2, respectively. More specifically, the polydimethylsiloxane prepolymer and the curing agent are accurately weighed and mixed in a mass ratio of 10:1, and stirred at a low speed of 300-500 rpm for 5 minutes to form a homogeneous mixed liquid; degassing is carried out in a vacuum degassing box for 30 minutes; 2.5 g of the mixed liquid is placed in a flat-bottomed culture dish treated with plasma, and a programmed spin coating process is used to spin coat at a speed of 550 r / min for 18 seconds to complete preliminary flattening, and then spin coat at a speed of 900 r / min for 9 seconds to achieve thickness uniformity; the spin-coated culture dish is placed in a vacuum environment of -0.1 MPa for degassing for 25 minutes; finally, the mixture is step-cured in a constant temperature oven at 55°C for 110 minutes, wherein the first 30 minutes are maintained at 48°C to promote molecular diffusion, and the temperature is raised to 68°C for the next 90 minutes to complete cross-linking and curing, thereby obtaining a functional flexible substrate film with a thickness uniformity deviation of ≤5%.

[0038] In this embodiment, the method for preparing the flexible membrane 3 with channels includes: Step S1, using a cleaning liquid combined with an ultrasonic cleaning process to perform surface treatment on the glass substrate; using high-purity nitrogen to purge and remove residual liquid on the surface of the substrate; obtaining a clean and dry surface of the glass substrate; specifically, placing the substrate on a heating platform at 115°C or in a vacuum heating chamber for heat treatment for 15 minutes to completely remove surface adsorbed water molecules and obtain a clean and dry surface of the glass substrate.

[0039] In step S2, a photolithography mask is designed based on the preset microchannel pattern. A spiral topology is used to obtain a photolithography mask with a microchannel pattern. Specifically, the microchannel line width is set to 50 μm. Under the design constraint of minimizing the area of ​​a single sensing unit (target value of approximately 20 mm²), the microchannel length is maximized by optimizing the spiral path. At the same time, the spacing of the spiral lines is compressed while ensuring that there is no signal crosstalk between adjacent channels and meeting the requirements of the subsequent bonding process. The size of the SSPP unit 9 is d =6mm, a =3mm, w =0.7mm, thickness t = 0.6mm, h = 0.7mm; the cutoff frequency is about 6.5GHz, and a transition section 91 and a surface waveguide section 92 are also provided at both ends of the SSPP unit 9 to reduce energy reflection and realize RF energy input and output. The SSPP unit 9 is as Figure 4As shown, the dispersion coefficient can be obtained by the following formula: ,in, k 0 is the free space wave vector, ε d is the dielectric constant of the dielectric, ε m is the equivalent dielectric constant of the metal structure; the drawn microchannel image is transferred to a PET polyester film to obtain a photolithography mask.

[0040] Step S3, as Figure 4 As shown, based on the pre-treated glass substrate surface, the photosensitive dry film is evenly covered on the substrate surface through a precision film lamination process, and a hot pressing composite device is used to achieve close bonding between the dry film and the substrate under set temperature and pressure parameters to form a photosensitive dry film layer, thereby obtaining a laminated substrate with a uniform photosensitive layer. Specifically, the thickness of the photosensitive dry film layer is 35µm, and the thickness tolerance of the dry film layer is controlled within the range of ±5%, thereby finally obtaining a laminated substrate with a uniform photosensitive layer.

[0041] Step S4: Patterning the film-coated substrate using a contact photolithography method to completely transfer the microchannel pattern on the mask to the photosensitive dry film layer. The contact photolithography method includes: tightly laminating a glass substrate coated with a DuPont series photosensitive dry film to a prefabricated photolithography mask with the film surface and the mask ink layer facing each other, applying a uniform clamping pressure of 0.1 MPa using a dedicated fixture to ensure seamless contact at the interface, and performing pattern transfer under a 365 nm wavelength UV light source with a precise exposure time of 5.5 seconds. The exposure process is carried out under an illumination of 15 mW / cm² to completely transfer the microchannel pattern on the mask to the photosensitive dry film layer.

[0042] Step S5: Using a sodium carbonate solution to wash away the unexposed portion of the DuPont photosensitive dry film on the dry film glass substrate, thereby obtaining a dry film glass substrate containing a channel structure. Specifically, a negative photolithography process is used to develop the exposed substrate, using a DuPont series negative photoresist as the photosensitive medium. A cross-linking reaction occurs in the UV-exposed area to form a channel structure, and the unexposed area is selectively dissolved by a 1.4% by mass sodium carbonate solution. The specific implementation process includes: placing the exposed substrate in a clean culture dish, injecting a 21° C. developer, and then oscillating at a frequency of 55 times / minute for 110 seconds to complete pattern development. Subsequently, pulse rinsing is performed with 18.2 MΩ·cm deionized water (5 seconds / time, repeated 3 times), and then curing in a 49° C. precision oven after purging with 0.4 MPa high-purity nitrogen for 28 minutes to obtain a dry film glass substrate containing a channel structure.

[0043] Step S6: Before implementing the PDMS casting process, the dry film glass substrate with the channel structure needs to be surface modified to obtain a dry film glass substrate after silanization treatment; specifically, a vapor-phase silanization agent is used to perform molecular self-assembly modification on the substrate surface in a closed reaction chamber to form a monolayer demolding interface, specifically including: placing the patterned substrate in a vacuum drying oven, introducing 1H,1H,2H,2H-perfluorooctyltriethoxysilane vapor, and reacting at 75°C for 28 minutes to form a hydrophobic fluorosilane molecular layer with a thickness of 1 nm, thereby obtaining a dry film glass substrate after silanization treatment.

[0044] In step S7, a flexible microstructured film was prepared on the modified substrate surface using a prepolymer casting process to obtain a flexible membrane with channels 3. Specifically, a polydimethylsiloxane (PDMS) prepolymer and a curing agent were mixed in a mass ratio of 10:1. The mixture was vacuum degassing treated (-0.095 MPa for 28 minutes) and spin-coated at 1500 rpm onto the silanized substrate surface to form a 450 μm thick liquid film. The film was then cured at 78°C for 115 minutes, ultimately obtaining an elastic PDMS film with a precisely replicated channel structure, i.e., a flexible microchannel film. A hole punch was used to punch holes at the reserved injection ports on both sides of each set of electrode channels.

[0045] In step 2, the side of the flexible membrane with channels 3 provided with microchannels is aligned with the flexible membrane with through holes 51 to form a channel structure between the flexible membrane with channels 3 and the flexible membrane with through holes 51.

[0046] In this embodiment, the side of the flexible membrane with a channel 3 on which the microchannel is provided is aligned with the flexible membrane with a through hole 51. The steps of forming a channel structure between the flexible membrane with a channel 3 and the flexible membrane with a through hole 51 include: first, using a low-viscosity cleaning tape to remove particulate contaminants on the surfaces of the flexible membrane with a through hole 51 and the flexible membrane with a channel 3; then placing the flexible membrane with a channel 3 and the flexible membrane with a through hole to be bonded in a plasma treatment device, and performing a surface activation treatment for 115 seconds under the conditions of 9W radio frequency power and 8NI / h oxygen flow rate to form hydroxyl active groups on the contact surface. The treated flexible membrane with a channel 3 and the flexible membrane with a through hole 51 are aligned and bonded with the activated surfaces facing each other, and a pressing force of 0.01 MPa is applied and the mixture is left to stand for 10 minutes to promote the initial bonding between molecules. Finally, the assembly is transferred to a constant temperature heating platform at 60°C for step-by-step bonding curing. The temperature is maintained at 48°C for the first 30 minutes to allow the interface molecules to fully diffuse, and then the temperature is raised to 68°C for 90 minutes to complete the covalent bonding. The through hole of the flexible membrane with a through hole 51 is provided with a guide structure coaxially aligned with the through groove on the flexible membrane with a channel for injecting liquid metal. Specifically, the position accuracy deviation is ≤50 μ m, to ensure reliable electrical connection between the subsequent flexible flat cable 6 and the microchannel electrode.

[0047] The other side of the channeled flexible membrane 3 is aligned with the base layer 52, forming an elastic base with microchannels. One end of a coaxial cable 7 and a flexible flat cable 6 are respectively embedded between the channeled flexible membrane 3 and the base layer 52. The elastic base with microchannels is connected to the prefabricated flexible flat cable 6, which is an FPC. The surface waveguide segments 92 at both ends of the SSPP unit 9 are connected to the coaxial cable 7, resulting in a thin film structure with a regular appearance. Liquid metal is injected into the microchannels of the thin film structure through the injection port of the through-holes in the flexible membrane 51. The liquid metal enters the channel structure, including the piezoresistive channel structure 8 and the SSPP unit 9, forming a liquid metal network 4. The contact end of the coaxial cable 7 corresponds to the SSPP unit 9 in the channel structure and contacts through the holes in the flexible membrane 51 to transmit radio frequency signals. The contact end of the flexible flat cable 6 contacts the piezoresistive channel structure 8 in the channel structure to conduct the piezoresistive signal.

[0048] Step 3: Cover the encapsulation film 2 over the through-holes in the flexible film 51 with through-holes, where the liquid metal is injected, confining the liquid metal within the channel structure of the elastic substrate. The specific steps include: cutting the film 2 to a coverage area 0.8 mm beyond the edge of the liquid metal injection port; applying a Sil-Poxy silicone adhesive to a uniform thickness of 20 μm around the injection port, and applying a bonding pressure of 0.04 MPa after optical alignment; to eliminate thermally induced interfacial stress, the encapsulation film 2 is placed in a constant temperature environment at 21°C during the encapsulation process. The curing phase is maintained for 28 minutes to allow the adhesive to penetrate the molecular level without forming a thermal resistance layer. Encapsulation film 2 is made of a 450 μm thick flexible PDMS encapsulation film.

[0049] Step 4: Dispose the electromagnetic shielding layer 1 on the outside of the base layer 52 and / or the flexible film with channels 3. The electromagnetic shielding layer 1 is made of copper foil, which is cut into rectangular films according to the size of the SSPP unit 9 and attached to the flexible film with channels 3 and the encapsulation film 2 using an adhesive.

[0050] Example 6. A method for preparing a flexible skin structure integrating internal and external sensing, for preparing a flexible skin structure integrating internal and external sensing, comprising the following steps: Step 1: Obtain a base layer 52 , a flexible film with through holes 51 , a flexible film with channels 3 , liquid metal, a flexible flat cable 6 , a coaxial line 7 , a packaging film 2 , and an electromagnetic shielding layer 1 .

[0051] In this embodiment, the method for preparing the base layer 52, the flexible film with through holes 51, and the encapsulation film 2 includes: A polydimethylsiloxane prepolymer and a curing agent are weighed and mixed in a mass ratio of 10:1 to obtain a PDMS solution; the mixture is degassed in a vacuum degassing chamber; the PDMS solution is spin-coated on a culture dish to form a PDMS liquid film, and the PDMS liquid film is degassed and then cured in a constant temperature oven in a stepwise manner and cross-linked to obtain a flexible substrate film. Several pieces of the flexible substrate film are used as a base layer 52, a flexible film with through holes 51, and an encapsulation film 2, respectively. Specifically, the polydimethylsiloxane prepolymer and the curing agent are accurately weighed and mixed in a mass ratio of 10:1, and stirred at a low speed of 400 rpm for 7 minutes to form a homogeneous mixed liquid; degassing is carried out in a vacuum degassing box for 30 minutes; 3.0 g of the mixed liquid is placed in a flat-bottomed culture dish treated with plasma, and a programmed spin coating process is used to spin coat at a speed of 600 r / min for 20±2 seconds to complete preliminary flattening, and then spin coat at a speed of 1000 r / min for 10 seconds to achieve thickness uniformity; the spin-coated culture dish is placed in a vacuum environment of -0.1 MPa for degassing for 30 minutes; finally, the mixture is step-cured in a constant temperature oven at 60°C for 120 minutes, wherein the first 30 minutes are maintained at 50°C to promote molecular diffusion, and the temperature is raised to 70°C for the next 90 minutes to complete cross-linking and curing, thereby obtaining a functional flexible substrate film with a thickness uniformity deviation of ≤5%.

[0052] In this embodiment, the method for preparing the flexible membrane 3 with channels includes: Step S1, using a cleaning liquid combined with an ultrasonic cleaning process to perform surface treatment on the glass substrate; using high-purity nitrogen to purge and remove residual liquid on the surface of the substrate; obtaining a clean and dry surface of the glass substrate; specifically, placing the substrate on a heating platform at 120°C or in a vacuum heating chamber for heat treatment for 20 minutes to completely remove surface adsorbed water molecules and obtain a clean and dry surface of the glass substrate.

[0053] In step S2, a photolithography mask is designed based on the preset microchannel pattern. A spiral topology is used to obtain a photolithography mask with a microchannel pattern. Specifically, the microchannel line width is set to 50μm. Under the design constraint of minimizing the area of ​​a single sensing unit (target value of approximately 20mm²), the microchannel length is maximized through spiral path optimization. At the same time, the spacing of the spiral lines is compressed while ensuring that there is no signal crosstalk between adjacent channels and meeting the requirements of the subsequent bonding process. The size of the SSPP is d =6mm, a =3mm, w =0.7mm, thickness t = 0.6mm, h = 0.7mm; the cutoff frequency is about 6.5GHz, and both ends include a transition section 91 and a surface waveguide section 92 to reduce energy reflection and realize RF energy input and output. The SSPP unit 9 is as follows Figure 4 As shown, the dispersion coefficient can be obtained by the following formula: ,in k 0 is the free space wave vector, ε d is the dielectric constant of the dielectric, ε m is the equivalent dielectric constant of the metal structure; the drawn microchannel image is transferred to a PET polyester film to obtain a photolithography mask.

[0054] In step S3, based on the pretreated surface of the glass substrate, a photosensitive dry film is evenly covered on the surface of the substrate through a precision film lamination process, and a hot pressing composite device is used to achieve close bonding between the dry film and the substrate under set temperature and pressure parameters to form a photosensitive dry film layer, thereby obtaining a laminated substrate having a uniform photosensitive layer. Specifically, the thickness of the photosensitive dry film layer is 37µm, and the thickness tolerance of the dry film layer is controlled within the range of ±5%, thereby finally obtaining a laminated substrate having a uniform photosensitive layer.

[0055] Step S4: Patterning the film-coated substrate using a contact photolithography method to completely transfer the microchannel pattern on the mask to the photosensitive dry film layer. The contact photolithography method includes: tightly laminating a glass substrate coated with a DuPont series photosensitive dry film to a prefabricated photolithography mask with the film surface and the mask ink layer facing each other, applying a uniform clamping pressure of 0.1-0.3MPa using a dedicated fixture to ensure seamless contact at the interface, and performing pattern transfer under a 365nm wavelength UV light source with a precise exposure time of 6s. The exposure process is carried out under an illumination of 17.5mW / cm² to completely transfer the microchannel pattern on the mask to the photosensitive dry film layer.

[0056] Step S5: Using a sodium carbonate solution to wash away the unexposed portion of the DuPont photosensitive dry film on the dry film glass substrate, thereby obtaining a dry film glass substrate containing a channel structure. Specifically, a negative photolithography process is used to develop the exposed substrate, and a DuPont series negative photoresist is selected as the photosensitive medium. A cross-linking reaction occurs in the UV-exposed area to form a channel structure, and the unexposed area is selectively dissolved by a 1.5% by mass sodium carbonate solution. The specific implementation process includes: placing the exposed substrate in a clean culture dish, injecting a 23° C. developer, and then oscillating at a frequency of 60 times / minute for 120 seconds to complete pattern development. Subsequently, pulse rinsing is performed with 18.2 MΩ·cm deionized water (5 seconds / time, repeated 3 times), and then purging with 0.4 MPa high-purity nitrogen gas in a 50° C. precision oven for curing for 30 minutes to obtain a dry film glass substrate containing a channel structure.

[0057] Step S6: Before implementing the PDMS casting process, the dry film glass substrate with the channel structure needs to be surface modified to obtain a dry film glass substrate after silanization treatment; specifically, a vapor-phase silanization agent is used to perform molecular self-assembly modification on the substrate surface in a closed reaction chamber to form a monolayer demolding interface, specifically comprising: placing the patterned substrate in a vacuum drying oven, introducing 1H,1H,2H,2H-perfluorooctyltriethoxysilane vapor, and reacting at 80°C for 30 minutes to form a hydrophobic fluorosilane molecular layer with a thickness of 1.5 nm, thereby obtaining a dry film glass substrate after silanization treatment.

[0058] In step S7, a flexible microstructured film is prepared on the modified substrate surface using a prepolymer casting process to obtain a flexible membrane with channels 3. Specifically, a polydimethylsiloxane (PDMS) prepolymer and a curing agent are mixed in a mass ratio of 10:1. The mixture is vacuum degassing treated (-0.097 MPa, 30 minutes), and then spin-coated at 2000 rpm onto the silanized substrate surface to form a 500 μm thick liquid film layer. The film is then cured at 80°C for 120 minutes, ultimately obtaining an elastic PDMS film with a precisely replicated channel structure, i.e., a flexible microchannel film. A hole punch is used to punch holes at the reserved injection ports on both sides of each set of electrode channels.

[0059] In step 2, the side of the flexible membrane with channels 3 provided with microchannels is aligned with the flexible membrane with through holes 51 to form a channel structure between the flexible membrane with channels 3 and the flexible membrane with through holes 51.

[0060] In this embodiment, the side of the flexible membrane with a channel 3 on which the microchannel is provided is aligned with the flexible membrane with a through hole 51. The steps of forming a channel structure between the flexible membrane with a channel 3 and the flexible membrane with a through hole 51 include: first, using a low-viscosity cleaning tape to remove particulate contaminants on the surfaces of the flexible membrane with a through hole 51 and the flexible membrane with a channel 3; then placing the flexible membrane with a channel 3 and the flexible membrane with a through hole to be bonded in a plasma treatment device, and performing a surface activation treatment for 120 seconds under the conditions of 10W radio frequency power and 9NI / h oxygen flow rate to form hydroxyl active groups on the contact surface. The treated flexible membrane with a channel 3 and the flexible membrane with a through hole 51 are aligned and bonded with the activated surfaces facing each other, and a pressing force of 0.03MPa is applied and the mixture is left to stand for 12.5min to promote the initial bonding between molecules. Finally, the assembly is transferred to a constant temperature heating platform at 65±5℃ for step-by-step bonding curing. The temperature is maintained at 50℃ for the first 30min to allow the interface molecules to fully diffuse, and then the temperature is raised to 70℃ for 90min to complete the covalent bonding. The through hole of the flexible membrane with a through hole 51 is provided with a guide structure coaxially aligned with the through groove on the flexible membrane with a channel for injecting liquid metal. Specifically, the position accuracy deviation is ≤50 μ m, to ensure reliable electrical connection between the subsequent flexible flat cable 6 and the microchannel electrode.

[0061] The other side of the channeled flexible membrane 3 is aligned with the base layer 52, forming an elastic base with microchannels. One end of a coaxial cable 7 and a flexible flat cable 6 are respectively embedded between the channeled flexible membrane 3 and the base layer 52. The elastic base with microchannels is connected to the prefabricated flexible flat cable 6, which is an FPC. The surface waveguide segments 92 at both ends of the SSPP unit 9 are connected to the coaxial cable 7, resulting in a thin film structure with a regular appearance. Liquid metal is injected into the microchannels of the thin film structure through the injection port of the through-holes in the flexible membrane 51. The liquid metal enters the channel structure, including the piezoresistive channel structure 8 and the SSPP unit 9, forming a liquid metal network 4. The contact end of the coaxial cable 7 corresponds to the SSPP unit 9 in the channel structure and contacts through the holes in the flexible membrane 51 to transmit radio frequency signals. The contact end of the flexible flat cable 6 contacts the piezoresistive channel structure 8 in the channel structure to conduct the piezoresistive signal.

[0062] Step 3: Cover the encapsulation film 2 over the through-holes in the flexible film 51 with through-holes for injecting liquid metal, confining the liquid metal within the channel structure of the elastic substrate. The specific steps include: cutting the film to form an encapsulation film 2 with a coverage area extending 1.0 mm beyond the edge of the liquid metal injection port; applying a Sil-Poxy silicone adhesive to a uniform thickness of 25 μm around the injection port, and applying a bonding pressure of 0.05 MPa after optical alignment; to eliminate thermally induced interfacial stress, the encapsulation film 2 is placed in a constant temperature environment of 23°C during the encapsulation process. The curing phase is maintained for 30 minutes to allow the adhesive to penetrate the molecular level without forming a thermal resistance layer. Encapsulation film 2 is a 500 μm thick flexible PDMS encapsulation film.

[0063] Step 4: Dispose the electromagnetic shielding layer 1 on the outside of the base layer 52 and / or the flexible film with channels 3. The electromagnetic shielding layer 1 is made of copper foil, which is cut into rectangular films according to the size of the SSPP unit 9 and attached to the flexible film with channels 3 and the encapsulation film 2 using an adhesive.

[0064] Example 7, a method for preparing a flexible skin structure integrating internal and external sensing, for preparing a flexible skin structure integrating internal and external sensing, comprising the following steps: Step 1: Obtain a base layer 52 , a flexible film with through holes 51 , a flexible film with channels 3 , liquid metal, a flexible flat cable 6 , a coaxial line 7 , a packaging film 2 , and an electromagnetic shielding layer 1 .

[0065] In this embodiment, the method for preparing the base layer 52, the flexible film with through holes 51, and the encapsulation film 2 includes: A polydimethylsiloxane prepolymer and a curing agent are weighed and mixed in a mass ratio of 10:1 to obtain a PDMS solution; the mixture is degassed in a vacuum degassing chamber; the PDMS solution is spin-coated on a culture dish to form a PDMS liquid film, and the PDMS liquid film is degassed and then cured in a constant temperature oven in a stepwise manner and cross-linked to obtain a flexible substrate film. Several pieces of the flexible substrate film are used as a base layer 52, a flexible film with through holes 51, and an encapsulation film 2, respectively. Specifically, the polydimethylsiloxane prepolymer and the curing agent are accurately weighed and mixed in a mass ratio of 10:1, and stirred at a low speed of 500 rpm for 10 minutes to form a homogeneous mixed liquid; degassing is carried out in a vacuum degassing box for 30 minutes; 3.5 g of the mixed liquid is placed in a flat-bottomed culture dish treated with plasma, and a programmed spin coating process is used to spin coat at a speed of 650 r / min for 22 seconds to complete preliminary flattening, and then spin coat at a speed of 1100 r / min for 11 seconds to achieve thickness uniformity; the spin-coated culture dish is placed in a vacuum environment of -0.1 MPa for degassing for 35 minutes; finally, the mixture is step-cured in a constant temperature oven at 65°C for 130 minutes, wherein the first 30 minutes are maintained at 52°C to promote molecular diffusion, and the temperature is raised to 72°C for the next 90 minutes to complete cross-linking and curing, thereby obtaining a functional flexible substrate film with a thickness uniformity deviation of ≤5%.

[0066] In this embodiment, the method for preparing the flexible membrane 3 with channels includes: Step S1, using a cleaning liquid combined with an ultrasonic cleaning process to perform surface treatment on the glass substrate; using high-purity nitrogen to purge and remove residual liquid on the surface of the substrate; obtaining a clean and dry surface of the glass substrate; specifically, placing the glass substrate on a heating platform or in a vacuum heating chamber at 125°C for heat treatment for 30 minutes to completely remove surface adsorbed water molecules and obtain a clean and dry surface of the glass substrate.

[0067] Step S2: Design a photolithography mask based on the preset microchannel pattern, using a spiral topology configuration to obtain a photolithography mask with a microchannel pattern; specifically, the microchannel line width is set to 50μm. Under the design constraint of minimizing the area of ​​a single sensing unit (target value of approximately 20mm²), the microchannel length is maximized through spiral path optimization. At the same time, while ensuring that there is no signal crosstalk between adjacent channels and meeting the requirements of the subsequent bonding process, the spacing of the spiral lines is compressed. Figure 5 As shown, the size of SSPP unit 9 is d =6mm, a =3mm, w =0.7mm, thickness t= 0.6mm, h = 0.7mm; the cutoff frequency is about 6.5GHz, and a transition section 91 and a surface waveguide section 92 are also provided at both ends of the SSPP unit 9 to reduce energy reflection and realize RF energy input and output. The SSPP unit 9 is as Figure 4 As shown, the dispersion coefficient can be obtained by the following formula: ,in k 0 is the free space wave vector, ε d is the dielectric constant of the dielectric, ε m is the equivalent dielectric constant of the metal structure; the drawn microchannel image is transferred to a PET polyester film to obtain a photolithography mask.

[0068] In step S3, based on the pre-treated surface of the glass substrate, a photosensitive dry film is evenly covered on the surface of the substrate through a precision film lamination process, and a hot pressing composite device is used to achieve close adhesion between the dry film and the substrate under set temperature and pressure parameters to form a photosensitive dry film layer, thereby obtaining a laminated substrate with a uniform photosensitive layer. Specifically, the thickness of the photosensitive dry film layer is 39µm, and the thickness tolerance of the dry film layer is controlled within the range of ±5%, thereby finally obtaining a laminated substrate with a uniform photosensitive layer.

[0069] Step S4: Patterning the film-coated substrate using a contact photolithography method to completely transfer the microchannel pattern on the mask to the photosensitive dry film layer. The contact photolithography method includes: tightly laminating a glass substrate coated with a DuPont series photosensitive dry film to a prefabricated photolithography mask with the film surface and the mask ink layer facing each other, applying a uniform clamping pressure of 0.3MPa using a dedicated fixture to ensure seamless contact at the interface, and performing pattern transfer under a 365nm wavelength UV light source with a precise exposure time of 6.5s. The exposure process is carried out under an illumination of 20mW / cm² to completely transfer the microchannel pattern on the mask to the photosensitive dry film layer.

[0070] Step S5: Using a sodium carbonate solution to wash away the unexposed portion of the DuPont photosensitive dry film on the dry film glass substrate, thereby obtaining a dry film glass substrate containing a channel structure. Specifically, a negative photolithography process is used to develop the exposed substrate, and a DuPont series negative photoresist is selected as the photosensitive medium. A cross-linking reaction occurs in the UV-exposed area to form a channel structure, and the unexposed area is selectively dissolved by a 1.6% by mass sodium carbonate solution. The specific implementation process includes: placing the exposed substrate in a clean culture dish, injecting a 25°C developer, and then oscillating at a frequency of 65 times / minute for 130 seconds to complete pattern development. Subsequently, pulse rinsing is performed with 18.2 MΩ·cm deionized water (5 seconds / time, repeated 3 times), and then curing in a 51°C precision oven for 32 minutes after purging with 0.4 MPa high-purity nitrogen gas, thereby obtaining a dry film glass substrate containing a channel structure.

[0071] Step S6: Before implementing the PDMS casting process, the dry film glass substrate with the channel structure needs to be surface modified to obtain a dry film glass substrate after silanization treatment; specifically, a vapor-phase silanization agent is used to perform molecular self-assembly modification on the substrate surface in a closed reaction chamber to form a monolayer demolding interface, specifically comprising: placing the patterned substrate in a vacuum drying oven, introducing 1H,1H,2H,2H-perfluorooctyltriethoxysilane vapor, and reacting at 85°C for 32 minutes to form a hydrophobic fluorosilane molecular layer with a thickness of 2 nm, thereby obtaining a dry film glass substrate after silanization treatment.

[0072] In step S7, a flexible microstructured film was prepared on the modified substrate surface using a prepolymer casting process to obtain a flexible membrane with channels 3. Specifically, a polydimethylsiloxane (PDMS) prepolymer and a curing agent were mixed in a mass ratio of 10:1. The mixture was vacuum degassing (-0.1 MPa, 32 minutes) and spin-coated at 2500 rpm onto the silanized substrate surface to form a 550 μm thick liquid film layer. The film was then cured at 82°C for 125 minutes, ultimately obtaining an elastic PDMS film with a precisely replicated channel structure, i.e., a flexible microchannel film. A hole punch was used to punch holes at the reserved injection ports on both sides of each set of electrode channels.

[0073] In step 2, the side of the flexible membrane with channels 3 provided with microchannels is aligned with the flexible membrane with through holes 51 to form a channel structure between the flexible membrane with channels 3 and the flexible membrane with through holes 51.

[0074] In this embodiment, the side of the flexible membrane with a channel 3 on which the microchannel is provided is aligned with the flexible membrane with a through hole 51. The steps of forming a channel structure between the flexible membrane with a channel 3 and the flexible membrane with a through hole 51 include: first, using a low-viscosity cleaning tape to remove particulate contaminants on the surfaces of the flexible membrane with a through hole 51 and the flexible membrane with a channel 3; then placing the flexible membrane with a channel 3 and the flexible membrane with a through hole to be bonded in a plasma treatment device, and heating the flexible membrane with a channel 3 at an RF power of 11 W and a power of 10 W. A surface activation treatment is performed for 125 seconds under NI / h oxygen flow conditions to form hydroxyl active groups on the contact surface; the treated flexible membrane with channels 3 and the flexible membrane with through holes 51 are aligned and bonded with the activated surfaces facing each other, a pressing force of 0.05MPa is applied and the membrane is left to stand for 15 minutes to promote initial bonding between molecules; finally, the assembly is transferred to a 70°C constant temperature heating platform for step-by-step bonding curing, the first 30 minutes are kept at 52°C to allow the interface molecules to fully diffuse, and then the temperature is raised to 72°C for 90 minutes to complete the covalent bonding; the through hole of the flexible membrane with through holes 51 is provided with a guide structure coaxially aligned with the through groove on the flexible membrane with channels 3 for injecting liquid metal. Specifically, its position accuracy deviation is ≤50 μm, to ensure reliable electrical connection between the subsequent flexible flat cable 6 and the microchannel electrode.

[0075] The other side of the channeled flexible membrane 3 is aligned with the base layer 52, forming an elastic base with microchannels. One end of a coaxial cable 7 and a flexible flat cable 6 are respectively embedded between the channeled flexible membrane 3 and the base layer 52. The elastic base with microchannels is connected to the prefabricated flexible flat cable 6, which is an FPC. The surface waveguide segments 92 at both ends of the SSPP unit 9 are connected to the coaxial cable 7, resulting in a thin film structure with a regular appearance. Liquid metal is injected into the microchannels of the thin film structure through the injection port of the through-holes in the flexible membrane 51. The liquid metal enters the channel structure, including the piezoresistive channel structure 8 and the SSPP unit 9, forming a liquid metal network 4. The contact end of the coaxial cable 7 corresponds to the SSPP unit 9 in the channel structure and contacts through the holes in the flexible membrane 51 to transmit radio frequency signals. The contact end of the flexible flat cable 6 contacts the piezoresistive channel structure 8 in the channel structure to conduct the piezoresistive signal.

[0076] Step 3: Cover the encapsulation film 2 over the through-holes in the flexible film 51 with through-holes for injecting liquid metal, confining the liquid metal within the channel structure of the elastic substrate. The specific steps include: cutting the film 2 to a coverage area 1.2 mm beyond the edge of the liquid metal injection port; applying a Sil-Poxy silicone adhesive to a uniform thickness of 30 μm around the injection port, and applying a bonding pressure of 0.06 MPa after optical alignment; to eliminate thermally induced interfacial stress, the encapsulation film 2 is placed in a constant temperature environment of 25°C during the encapsulation process. The curing phase is maintained for 32 minutes to allow the adhesive to penetrate the molecular level without forming a thermal resistance layer. Encapsulation film 2 is made of a 550 μm thick flexible PDMS encapsulation film.

[0077] Step 4: Dispose the electromagnetic shielding layer 1 on the outside of the base layer 52 and / or the flexible film with channels 3. The electromagnetic shielding layer 1 is made of copper foil, which is cut into rectangular films according to the size of the SSPP unit 9 and attached to the flexible film with channels 3 and the encapsulation film 2 using an adhesive.

[0078] Example 8: Based on Example 5, the SSPP unit 9 and the piezoresistive channel structure 8 around the SSPP unit 9 (SSPP is an artificial surface plasmon) in the present invention were subjected to a systematic electromagnetic characteristic simulation analysis using high-frequency structure simulation software (HFSS). The simulation results are as follows: Figure 7-12 shown. Figure 7The dispersion relation curve of SSPP unit 9 is displayed. Simulation data show that when the operating frequency is lower than 5 GHz, the structure does not exhibit obvious wavelength compression characteristics. However, when the frequency rises above 6 GHz, the dispersion curve shows good smoothness. Based on this frequency characteristic analysis, the present invention prefers 5-6 GHz as the optimal operating frequency band.

[0079] The present invention performs a systematic simulation analysis on the S11 parameters of the SSPP unit 9 and the piezoresistive channel structure 8 around the SSPP unit 9 by using high-frequency electromagnetic simulation software. Figure 8 The simulation curves displayed show that in the frequency range of 1-10GHz, the S11 parameter exhibits obvious frequency selection characteristics, among which two significant resonance valleys appear near 2.3GHz and 3.5GHz, and the S11 parameter reaches extreme values ​​of -40dB and -35dB respectively, indicating that these two frequency points have excellent energy coupling efficiency; in the operating frequency band of 5-6GHz, the S11 parameter is stably maintained in the range of -20dB to -25dB, showing good signal transmission performance; when the frequency exceeds 7GHz, the S11 parameter rapidly deteriorates to above -10dB, indicating that the structure has a natural suppression effect on high-frequency signals. It is particularly noteworthy that there is a transition region near 4.2GHz, where the S11 parameter rises rapidly from -30dB to -15dB. This characteristic provides a clear demarcation basis for frequency band selection. By analyzing the changing trend of the S11 parameter curve, it can be confirmed that the SSPP structure has good signal transmission efficiency (S11 <-20dB) and a moderate quality factor in the 5-6GHz frequency band. This feature makes it particularly suitable as the core sensitive unit of microwave sensors, providing an optimized frequency band selection scheme for achieving high-sensitivity material detection. At the same time, the multi-resonance point characteristics of the S11 parameter curve also provide potential possibilities for realizing multi-band composite sensing.

[0080] like Figure 9As shown in FIG, a cloud map distribution of the electric field intensity of the SSPP unit 9 is provided. The electric field distribution characteristics of the SSPP unit 9 in the present invention are analyzed in detail by high-frequency electromagnetic simulation software. The electric field cloud map clearly shows the electromagnetic field distribution characteristics of the SSPP unit 9 at a specific operating frequency, wherein the electric field intensity shows an obvious local enhancement effect at the edge of the groove of the periodic structure of the SSPP unit 9. This enhancement effect decays rapidly with increasing distance from the surface of the structure, which is consistent with the typical field distribution law of surface plasmons. It can be observed from the cloud map that the electric field energy is mainly concentrated in the metal-dielectric interface region of the SSPP unit 9, and exhibits an exponential decay distribution on the cross section perpendicular to the propagation direction, while on the longitudinal section along the propagation direction, it appears as a periodic wave. dynamic characteristics; it is particularly noteworthy that obvious electric field hotspots are formed at the key structural dimensions of the SSPP unit 9 (such as the groove depth and period length), and the electric field intensity in these areas reaches the maximum value, verifying the structure's efficient binding ability for the electromagnetic field; at the same time, the simulation results show that within the operating frequency band of 5-6 GHz, the electric field distribution has excellent stability and no obvious energy leakage. This feature is crucial for achieving high-sensitivity material detection; by quantitatively analyzing the intensity distribution of the electric field cloud map, the structural parameters of the SSPP unit 9 can be accurately optimized to ensure that it can achieve the best interaction effect between the electromagnetic field and the substance to be measured in sensing applications, providing a reliable simulation basis for subsequent sensor performance improvement.

[0081] Figure 10 and Figure 11 The electric field vector simulation results of the SSPP unit 9 in the xy plane and the xz plane are respectively shown. The electric field vector distribution of the SSPP unit 9 is obtained by high-frequency electromagnetic simulation in the present invention. The simulation results clearly show the vector characteristics of the electromagnetic field in the 5 GHz working frequency band. The electric field vector mainly shows a strong orientation along the propagation direction of the SSPP structure (z-axis), forming an obvious vector aggregation effect at the edge of the metal groove, and its field intensity amplitude reaches the maximum; in the xy cross-section, it can be seen that the electric field vector propagates in the form of surface waves at the dielectric-metal interface, and the vector direction shows a periodic oscillation characteristic, and shows an exponential decay law with increasing distance from the surface; it is particularly noteworthy that at the point where the groove depth of SSPP unit 9 suddenly changes, the electric field vector is significantly deflected and forms a local vortex structure. This characteristic field distribution pattern effectively enhances the interaction strength between the electromagnetic field and the substance to be measured; in the xz cross-section, the electric field vector forms an alternating distribution pattern along the propagation direction, and the vector phase difference between adjacent periodic units is π / 2, which is consistent with the typical propagation characteristics of surface plasmons; by quantitatively analyzing the distribution law of the vector diagram, it can be confirmed that the SSPP unit 9 has excellent field confinement ability in the 5GHz frequency band.

[0082] Figure 12The magnetic field vector distribution diagram in the xy plane is further given, and the simulation results clearly show that the magnetic field vector is mainly oriented along the Y direction. The above series of simulation results not only verify the excellent electromagnetic field binding ability and signal transmission characteristics of SSPP unit 9 in the 5-6GHz frequency band, but also provide an important theoretical basis for the structural optimization of the sensor. By setting the geometric parameters of SSPP unit 9, selective response to microwave signals in a specific frequency band is successfully achieved, which lays a solid foundation for subsequent sensor performance testing and application implementation.

[0083] Example 9, based on Example 8, Figure 6 As shown, the piezoresistive signal of the piezoresistive channel structure 8 outside the SSPP unit 9 is collected through a piezoresistive signal acquisition circuit. The piezoresistive signal acquisition circuit uses a high-precision analog switch chip ADG333ABRSZ to implement intelligent switching control of the 8-way piezoresistive sensor (i.e., the piezoresistive channel structure 8); when the ADG333 switch is switched to the Vref (2.5V) reference voltage terminal, the potential of the non-inverting input terminal and the inverting input terminal of the operational amplifier LMV321IDBVR are equal, forming a virtual short state. At this time, no current flows through the piezoresistive channel, and the system is in a test state; when the switch is switched to ground potential, a constant potential difference of 2.5V is formed across the piezoresistive channel, which is in direct contact with the feedback resistor R f Together they form a common-mode amplifier circuit. By measuring the voltage change at the output, the resistance of the path can be accurately calculated. The output voltage of the spiral piezoresistive network follows the formula: ; Among them, R f R is the feedback resistor between the inverting input and output of the amplifier (resistance 1kΩ±1%), i It is a dynamic resistor of the spiral piezoresistive network; the liquid alloy spiral piezoresistive path (i.e., the piezoresistive channel structure 8) presents a reference resistance of 10Ω±5% in the unpressurized state. When subjected to external pressure, the cross-sectional area of ​​its internal microchannel changes, causing the resistance value to linearly increase to about 20Ω. This change is digitally acquired by a 24-bit Σ-Δ ADC; the reference voltage is provided by the low-dropout linear regulator AMS1117-2.5 chip, which stably converts the 5V input voltage into a precise reference voltage of 2.5V; the circuit output terminals P1-P8 adopt a push-pull drive design and can output two states: 2.5V high level and ground level. The digital control terminals D2-D9 control the state switching of the 8 groups of single-pole double-throw switches of the ADG333 chip through the timing signal generated by the FPGA; the cyclic detection of the 8-channel piezoresistive signal is achieved through time division multiplexing to meet the application requirements of tactile sensing. By controlling the switch of the ADG333 chip, the voltage values ​​of the 8 piezoresistive spirals (i.e., the piezoresistive channel structure 8) are scanned and measured. In this embodiment, R f The resistance is 10Ω, R iThe variation range is 10-20Ω; therefore, the variation range of the measured voltage is 2.5-5V, but is not limited thereto. In other embodiments, the specific parameter settings can be adjusted according to actual usage requirements.

[0084] Working principle: This invention describes a flexible multimodal sensing electronic skin based on liquid metal microchannels that integrates surface tactile perception with underlying penetrating media sensing, and its preparation method. This multimodal flexible electronic skin achieves coordinated sensing and processing of surface and deep-layer information, enabling both surface pressure sensing and deep-layer media sensing, possessing multimodal sensing capabilities. The device integrates a piezoresistive sensing module and an artificial surface plasmon sensing module, achieving simultaneous sensing of multimodal physical signals while maintaining the overall structural flexibility, thinness, and miniaturization.

[0085] The present invention provides a flexible multimodal sensing electronic skin based on liquid metal microchannels that integrates surface tactile perception with underlying penetrating media sensing, and a method for fabricating the same. The process includes: fabricating a flexible membrane 3 with channels using soft lithography, based on preset microchannel dimensions and functional requirements, and integrating periodically slotted SSPP units 9 and a piezoresistive channel structure 8 within the membrane; preparing a flexible substrate 52 using a polydimethylsiloxane (PDMS) casting method, and bonding it to a microchannel film through plasma surface treatment to form an elastic composite substrate with microchannels. The resulting flexible substrate 52 is connected to the side of a flexible printed circuit board (FPC) with a flexible flat cable 6, and a flexible membrane 51 with through-holes is laminated to the other side of the FPC, thereby forming a complete piezoresistive sensing unit structure. The microchannel portion embedded with the artificial surface plasmon structure is connected to a radio frequency signal interface via an IPEX connector to construct an SSPP detection module with electromagnetic wave responsiveness. Liquid metal (such as eutectic gallium indium or Galinstan) is injected into the channel structure through a reserved injection port, forming a liquid metal electrode network with excellent conductive properties. Finally, a flexible encapsulation film 2 is used to seal the injection port, resulting in an integrated, ultra-thin, multimodal electronic skin device. By integrating the SSPP unit 9 with the liquid metal piezoresistive channel structure 8, this invention achieves the coupling and synergy of surface tactile perception and deep-layer media response while maintaining the device's flexibility and miniaturization. This provides an innovative technical approach for multimodal, highly sensitive, and non-invasive human body signal detection.

[0086] This invention utilizes soft lithography micro-nanofabrication techniques to construct a multilayer channel structure on an elastic substrate. Combined with the excellent flexibility of PDMS (polydimethylsiloxane), this method creates a microchannel array with excellent mechanical compliance and optical transmittance. After channel formation, liquid metal is injected as a conductive medium, achieving a highly conductive and stretchable sensing network. Simultaneously, plasma bonding technology is used to securely integrate the microchannel membrane with the upper and lower substrates, forming a highly stable and airtight microstructure platform. This manufacturing process does not require high temperatures or complex equipment, and is therefore highly scalable and cost-effective.

[0087] The above specific implementation methods are specific support for the scheme ideas proposed in the present invention, and cannot be used to limit the scope of protection of the present invention. Any equivalent changes or equivalent modifications made on the basis of this technical scheme in accordance with the technical ideas proposed in the present invention still fall within the scope of protection of the technical scheme of the present invention.

Claims

1. A flexible skin structure integrating internal and external sensing, characterized in that: include: An elastic substrate is provided with several layers of channel structures, and liquid metal is injected into the channel structures. The liquid metal forms a liquid metal network in the channel structures of the elastic substrate. The liquid metal network serves as a sensing system and includes: an SSPP unit and a piezoresistive channel structure arranged in parallel around the SSPP unit; the cable includes a flexible cable connected to the piezoresistive channel structure and a coaxial cable connected to the SSPP unit.

2. The flexible skin structure integrating internal and external sensing according to claim 1, characterized in that: include: The piezoresistive channel structures are arranged in parallel on both sides of the SSPP unit to form a dual-channel sensing system.

3. The flexible skin structure integrating internal and external sensing according to claim 2, characterized in that: The elastic base includes a base layer, a flexible membrane with through holes, and a flexible membrane with channels stacked in sequence; a channel structure is formed in the middle of the flexible membrane with channels and the flexible membrane with through holes when the flexible membrane with channels and the flexible membrane with through holes are matched; a through groove is also provided on the flexible membrane with channels, and the through groove is correspondingly connected to the through holes on the flexible membrane with through holes.

4. The flexible skin structure integrating internal and external sensing according to claim 3, characterized in that: One end of the flexible cable and coaxial line connected to the liquid metal network is embedded between the base layer and the flexible membrane with through holes, and the other end of the flexible cable and coaxial line connected to the liquid metal network corresponds to the through hole on the flexible membrane with through holes.

5. The flexible skin structure integrating internal and external sensing according to claim 4, characterized in that: The through holes of the flexible film with through holes and the through grooves on the flexible film with channels are respectively blocked by the base layer and the packaging film, so that the liquid metal is confined in the channel structure of the elastic base.

6. The flexible skin structure integrating internal and external sensing according to claim 5, characterized in that: An electromagnetic shielding layer is also provided on the elastic base; The elastic substrate is made of PDMS material, and the PDMS is polydimethylsiloxane; The liquid metal is an indium-tin alloy with a melting point of 6°C, a density of 6.03 g / cm3, and a purity of 99%. The liquid metal is a conductive medium.

7. A method for preparing a flexible skin structure integrating internal and external sensing, characterized by: The method for preparing the flexible skin structure capable of integrating internal and external sensing according to any one of claims 1 to 6 comprises the following steps: Obtaining a base layer, a flexible film with through holes, a flexible film with channels, liquid metal, a flexible flat cable, a coaxial cable, a packaging film, and an electromagnetic shielding layer; The flexible membrane with a channel, on which a microchannel is provided, is aligned with the flexible membrane with a through-hole, forming a channel structure between the flexible membrane with a channel and the flexible membrane with a through-hole; the other side of the flexible membrane with a through-hole is aligned with the base layer, and one end of a coaxial line and a flexible flat cable are respectively embedded between the flexible membrane with a through-hole and the base layer; the contact end of the coaxial line corresponds to the SSPP unit in the channel structure and contacts through the hole position on the flexible membrane with a through-hole to transmit radio frequency signals; the contact end of the flexible flat cable contacts the corresponding piezoresistive channel structure in the channel structure to conduct piezoresistive signals; liquid metal is injected into the through-hole on the flexible membrane with a channel, and the liquid metal enters the channel structure to form a liquid metal network; Covering the encapsulation film on the through-holes of the flexible film with channels and injecting the liquid metal, so as to confine the liquid metal in the channel structure of the elastic substrate; The electromagnetic shielding layer is arranged on the outside of the base layer or the flexible film with channels.

8. The method for preparing a flexible skin structure integrating internal and external sensing according to claim 7, characterized in that: The preparation method of the base layer, the flexible film with through holes, and the encapsulation film comprises: A polydimethylsiloxane prepolymer and a curing agent were weighed and mixed in a mass ratio of 10:1 to obtain a PDMS solution; the mixture was degassed in a vacuum degassing chamber; the PDMS solution was spin-coated on a culture dish to form a PDMS liquid film; the PDMS liquid film was degassed and then step-cured and cross-linked in a constant temperature oven to obtain a flexible substrate film.

9. The method for preparing a flexible skin structure integrating internal and external sensing according to claim 7, characterized in that: A method for preparing a flexible membrane with channels, comprising: Step S1, using a cleaning liquid combined with an ultrasonic cleaning process to perform surface treatment on the glass substrate; and removing residual liquid on the surface of the substrate; to obtain a clean and dry surface of the glass substrate; Step S2, manufacturing a photolithography mask based on a preset microchannel pattern, adopting a spiral topological configuration to obtain a photolithography mask with a channel pattern; Step S3: Based on the pre-treated surface of the glass substrate, a photosensitive dry film is evenly covered on the substrate surface through a precision film lamination process, and a hot pressing composite device is used to achieve close lamination between the dry film and the substrate under set temperature and pressure parameters to form a photosensitive dry film layer, thereby obtaining a coated substrate with a uniform photosensitive layer; Step S4, patterning the film-coated substrate using a contact photolithography method, so that the microchannel pattern on the mask is completely transferred to the photosensitive dry film layer; Step S5, using a sodium carbonate solution to wash away the unexposed portion of the DuPont photosensitive dry film on the dry film glass substrate to obtain a dry film glass substrate containing a channel structure; Step S6: Before implementing the PDMS casting process, the dry film glass substrate having the channel structure needs to be surface modified to obtain a dry film glass substrate after silanization treatment; Step S7: preparing a flexible microstructured film on the surface of the modified substrate by using a prepolymer casting process to obtain a flexible film with channels.

10. The method for preparing a flexible skin structure integrating internal and external sensing according to claim 7, characterized in that: The side of the flexible membrane with the channel having the channel structure is aligned with the flexible membrane with the through hole, and the steps of forming the channel structure between the flexible membrane with the channel and the flexible membrane with the through hole include: First, a low-viscosity cleaning tape is used to remove particulate contaminants from the surface of the flexible membrane with through holes and the flexible membrane with channels. The flexible membrane with channels and the flexible membrane with through holes to be bonded are then placed in a plasma treatment device and subjected to surface activation treatment for 120±5s under 10±1W RF power and 8-10 NI / h oxygen flow rate to form hydroxyl active groups on the contact surface. The treated flexible membrane with channels and the flexible membrane with through holes are aligned and bonded with the activated surfaces facing each other. A pressing force of 0.01-0.05MPa is applied and the membrane is allowed to stand for 10-15 minutes to promote initial intermolecular bonding. Finally, the assembly is transferred to a constant temperature heating platform at 65±5°C for step-by-step bonding curing. The temperature is maintained at 50±2°C for the first 30 minutes to allow sufficient diffusion of the interface molecules, and then the temperature is raised to 70±2°C for 90 minutes to complete the covalent bonding. The through hole of the flexible membrane with through holes is provided with a flow guiding structure coaxially aligned with the through groove on the flexible membrane with channels for injecting liquid metal; The steps of covering the encapsulation film on the through-holes of the flexible film with micro-channels and injecting the liquid metal, and confining the liquid metal in the channel structure of the elastic substrate include: The film was cut into an encapsulation film with a coverage area extending 1.0±0.2mm beyond the edge of the liquid metal injection port. Sil-Poxy silicone adhesive was applied to the periphery of the injection port at a uniform thickness of 25±5μm. After optical alignment, a bonding pressure of 0.05±0.01MPa was applied. To eliminate thermally induced interfacial stress, the encapsulation film was packaged at a constant temperature of 23±2°C during the encapsulation process. During the curing phase, a static time of 30±2min was maintained to allow the adhesive to penetrate the film at the molecular level without forming a thermal resistance layer. The encapsulation film is a flexible PDMS encapsulation film with a thickness of 500±50μm.

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