Magnetic control semi-filled microsphere flexible sensor and preparation method thereof

Abstract

The application discloses a kind of magnetically controlled semi-filled microsphere flexible sensors and preparation method thereof, belong to sensor technical field, sensor includes flexible dielectric layer and electrode layer, flexible dielectric layer includes flexible matrix and internal core-shell structure magnetically controlled semi-filled microsphere;Magnetic control semi-filled microsphere includes rigid insulating shell and inner cavity's magnetic conductive powder.It is first prepared and the inner core of polymer microsphere containing magnetic conductive powder is coated with silica shell layer on the surface of microsphere;Subsequently, high-temperature heat treatment is carried out under protective atmosphere to form porous structure;The obtained functional microspheres are dispersed in flexible matrix precursor and solidified into shape.The application constructs unique core-shell structure and porous microstructure, uses external magnetic field to control the distribution of powder inside microsphere, changes the effective compressible volume and support stiffness of microsphere in pressure direction, solves the problem that traditional magnetic conductive material is poor in dispersibility, easy to agglomerate and weak in interface bonding force in flexible matrix, realizes the adjustable control of sensor sensitivity and range.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a magnetically controlled semi-filled microsphere flexible sensor and its fabrication method. Background Technology

[0002] With the increasing application of flexible electronics technology in soft robotics, intelligent prosthetics, health monitoring, and human-computer interaction, flexible capacitive tactile sensors, as core sensing components, face increasingly stringent performance requirements. However, existing technologies still have significant shortcomings in the synergistic improvement of multi-dimensional sensing performance and intelligent adaptive capabilities when facing complex, unstructured dynamic environments. These shortcomings are mainly reflected in the following three interrelated technical bottlenecks:

[0003] First, there is an inherent trade-off between sensitivity and detection range, making it difficult to achieve both simultaneously. Specifically, there is a natural inversion between sensor sensitivity and detection range. Traditional methods often improve sensitivity by introducing microporous foaming or surface microstructures to reduce the initial modulus of the dielectric layer. However, this leads to structural densification under minute pressures, causing the capacitive response to saturate rapidly in the low-pressure range, making it impossible to maintain high linearity across a wide pressure range. This makes it difficult for a single-structure sensor to simultaneously meet the needs of soft robots performing multimodal tasks such as "precision manipulation" and "heavy-duty grasping."

[0004] Secondly, the microstructure and electromechanical response characteristics of sensors are fixed once fabricated, lacking dynamic adjustability. Whether it's the random pores formed by physical foaming or the array structure constructed by molding, once the sensor is solidified, its internal micromorphology and electromechanical response characteristics are locked, exhibiting static features. This means that the device's sensitivity curve, range, and mechanical stiffness are locked after molding, making it impossible to adjust its mechanical stiffness or sensitivity curve in real time according to actual operating conditions, thus limiting the level of intelligent application of sensors.

[0005] Third, the long-term stability and interface reliability of functional fillers are prominent issues. To introduce external field response characteristics such as magnetic and electrical properties, metallic magnetic powders or conductive fillers are often directly blended with flexible polymer matrices. This direct doping method not only makes the filler susceptible to oxidation, leading to electromagnetic performance degradation, but also, due to the significant modulus difference between the rigid filler and the flexible matrix, stress concentration easily occurs at the interface under cyclic deformation, causing filler detachment or interface peeling, severely affecting sensor signal drift or complete failure, and impacting its cyclic stability and service life.

[0006] In summary, existing flexible capacitive sensor technology is limited by its static, fixed microstructure design, making it difficult to overcome the performance trade-off between sensitivity and wide measurement range. Furthermore, it lacks the ability to dynamically reconstruct performance through external stimuli. Therefore, this paper proposes a magnetically controlled semi-filled microsphere flexible sensor and its fabrication method. Summary of the Invention

[0007] The purpose of this invention is to provide a magnetically controlled semi-filled microsphere flexible sensor and its fabrication method to solve the problems in the background art.

[0008] To achieve the above objectives, the present invention provides a magnetically controlled semi-filled microsphere flexible sensor, comprising a flexible dielectric layer and electrode layers disposed on both sides of the flexible dielectric layer, wherein the flexible dielectric layer comprises a flexible substrate and magnetically controlled semi-filled microspheres with a core-shell structure dispersed within the flexible substrate;

[0009] The magnetron semi-filled microspheres comprise a rigid insulating shell and magnetically conductive powder encapsulated within the cavity of the rigid insulating shell.

[0010] Preferably, the flexible matrix is ​​one of polydimethylsiloxane, polyurethane or silicone rubber, and the volume fraction of the magnetron semi-filled microspheres in the flexible matrix is ​​20~30 vol.

[0011] Preferably, the rigid insulating shell has a shell thickness of 500 nm to 1 μm and is made of silicon dioxide;

[0012] The magnetically conductive powder is an iron-nickel alloy powder, carbonyl iron powder, or ferrite powder, with an average particle size of 100~200nm.

[0013] Preferably, the magnetic conductive powder is an iron-nickel alloy powder, with a nickel mass fraction of 78-82%.

[0014] Preferably, the magnetically conductive powder is spherical nano-permalloy powder.

[0015] Preferably, in the magnetron-controlled semi-filled microspheres, the volume filling rate of the magnetic conductive powder is 40-60%.

[0016] Preferably, the magnetron-controlled semi-filled microsphere flexible sensor has the following two operating modes based on the direction of the external magnetic field:

[0017] High sensitivity mode: Under the action of a horizontal magnetic field parallel to the sensor surface, magnetic conductive powder is attracted by magnetic force and gathers on one side of the inner wall of the microsphere, so that the microsphere forms a structure in which the powder gathering area and the pure air cavity area coexist. The pure air cavity area has a large effective compressible stroke in the vertical force direction, so that the microsphere can produce a large longitudinal deformation when subjected to vertical pressure.

[0018] Wide range and high linearity mode: Under the action of a vertical magnetic field perpendicular to the sensor surface, the magnetic conductive powder is attracted by the magnetic force and gathers on the top or bottom inner wall of the microsphere. This causes the magnetic conductive powder to occupy part of the space of the microsphere in the vertical force direction, reducing the effective compressible stroke in the vertical direction, thereby limiting the longitudinal deformation of the microsphere under unit pressure.

[0019] This invention also provides a method for fabricating the above-mentioned magnetically controlled semi-filled microsphere flexible sensor, comprising the following steps:

[0020] S1. Preparation of magnetic polymer composite microspheres: Magnetic conductive powder is dispersed in a polymer solution, and solid polymer microspheres containing magnetic conductive powder are obtained through dispersion, emulsification and curing processes.

[0021] S2. Encapsulating a rigid insulating shell: The surface of the polymer solid microspheres is modified, and a rigid insulating material is coated on the surface of the modified polymer solid microspheres using an in-situ growth method to form core-shell structured microspheres.

[0022] S3. High-temperature pyrolysis pore formation and in-situ encapsulation: Under a protective atmosphere, the core-shell structured microspheres are subjected to staged high-temperature heat treatment to remove the polymer by pyrolysis and retain the magnetic conductive powder in the shell layer to obtain magnetron semi-filled microspheres.

[0023] S4. Flexible sensor molding and packaging: Magnetic semi-filled microspheres are dispersed in a flexible substrate precursor and cured in an environment without an external magnetic field to form a flexible dielectric layer. Then, electrode layers are integrated on the upper and lower surfaces of the flexible dielectric layer to obtain a flexible sensor.

[0024] Preferably, in S1, the mass ratio of magnetic conductive powder to polymer is (6~9):1; the polymer is polymethyl methacrylate or polystyrene.

[0025] Preferably, in step S2, the surface modification process uses a cationic surfactant; the in-situ growth process uses tetraethyl orthosilicate or methyl orthosilicate as the silicon source, and hydrolyzes and condenses under ammonia catalysis to generate a silica shell.

[0026] Preferably, the cationic surfactant is hexadecyltrimethylammonium bromide.

[0027] Preferably, in step S3, the protective atmosphere is a mixture of hydrogen and an inert gas, wherein the volume content of hydrogen is 1-10%.

[0028] Preferably, the inert gas is argon.

[0029] Preferably, in step S3, the staged high-temperature heat treatment process includes: first, heating to 200-300℃ at a heating rate of 1-5℃ / min and holding at that temperature for 20-60min; then heating to 400-550℃ at a heating rate of 0.2-2℃ / min and holding at that temperature for 2-6h.

[0030] Preferably, in step S3, the staged high-temperature heat treatment process includes: first, heating to 250°C at a heating rate of 2°C / min and holding at that temperature for 30 min; then heating to 450°C at a heating rate of 0.5°C / min and holding at that temperature for 4 h.

[0031] Preferably, in step S4, the flexible matrix precursor is a mixture of liquid polydimethylsiloxane prepolymer and curing agent.

[0032] Therefore, the magnetically controlled semi-filled microsphere flexible sensor and its fabrication method of the present invention have the following beneficial effects:

[0033] (1) The present invention achieves in-situ encapsulation of metal powder through the physical barrier of the SiO2 microsphere shell by the semi-filled hollow microsphere structure, effectively isolating external oxygen and moisture, and solving the problem of performance degradation caused by easy oxidation and rusting of nano iron powder; and uses external magnetic field to control the distribution state of magnetic conductive powder inside the microsphere, changing the structural stiffness of the microsphere in the direction of force; this stiffness adjustment mechanism based on magnetic control successfully solves the inherent contradiction between sensitivity and range.

[0034] (2) The present invention selects Fe-Ni alloy powder with high nickel content as the functional core. Its coercivity characteristics make it almost non-residual magnetism after the magnetic field is removed, avoiding magnetic agglomeration between powders and ensuring that the powder has excellent fluidity in the microsphere cavity. It can respond and recombine rapidly in milliseconds to changes in the external magnetic field. Combined with the high temperature pyrolysis process under reducing atmosphere, the high purity and high conductivity of the metal powder are ensured.

[0035] (3) The present invention uses a rigid SiO2 microsphere shell as an intermediate layer. On the one hand, it forms a strong chemical bond with the flexible substrate through surface modification, avoiding the interface stress concentration and delamination caused by direct doping of metal powder. On the other hand, the shell undertakes the main structural support and stress transmission functions, protecting the internal powder from direct shear damage. At the same time, the SiO2 insulating shell physically isolates the internal conductive powder from the external electrode, completely eliminating the risk of short circuit caused by conductive powder piercing the dielectric layer under large deformation, and greatly improving the durability and safety of the sensor.

[0036] (4) The preparation method of the present invention combines emulsion polymerization, sol-gel coating and high-temperature pyrolysis pore-forming technology. The pyrolysis of the polymer sacrificial core naturally forms a "cage-in-a-sphere" semi-filled structure, without relying on expensive photolithography equipment or complex micro-nano processing technology. Moreover, the magnetic powder is encapsulated in situ inside the microsphere, and the dispersion is good when it is subsequently combined with the flexible matrix. The process is easy to control and suitable for large-scale mass production.

[0037] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating the preparation process of an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the orientation of magnetically guided nano-permalloy (Fe-Ni) particles according to an embodiment of the present invention, wherein (a) is the vertical direction and (b) is the horizontal direction;

[0040] Figure 3 This is a schematic diagram of the deformation of a high-sensitivity mode sensor under pressure according to an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of the deformation of the wide-range / high linearity mode sensor under pressure according to an embodiment of the present invention;

[0042] Figure 5 This is a cross-sectional SEM image of the dielectric layer of the magnetically controlled semi-filled microsphere flexible sensor according to an embodiment of the present invention.

[0043] Figure 6 This is a pressure-capacitance response curve in the high-sensitivity mode of an embodiment of the present invention;

[0044] Figure 7 This is a pressure-capacitance response curve in the wide range / high linearity mode of an embodiment of the present invention. Detailed Implementation

[0045] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0047] This invention provides a method for fabricating a magnetically controlled semi-filled microsphere flexible sensor, such as... Figure 1 As shown, it includes the following steps:

[0048] S1. Preparation of magnetic polymer composite microspheres, specifically:

[0049] First, a polymer solution is prepared by dissolving the polymer in an organic solvent to obtain a polymer solution with a mass fraction of 5 wt%. The magnetic conductive powder is dispersed in the polymer solution according to a mass ratio of (6~9):1. A dispersant is added for high-power ultrasonic dispersion to prevent the agglomeration of high-concentration metal powder. The resulting suspension is added dropwise to an aqueous phase containing 1 wt% emulsifier and emulsified by high-speed shearing and stirring to form an emulsion. Then, it is placed in a water bath for continuous stirring to solidify, so as to slowly evaporate the organic solvent, causing the polymer to shrink and tightly encapsulate the magnetic conductive powder. After centrifugation, washing, and drying, solid polymer microspheres containing magnetic conductive powder are formed.

[0050] S2. Coating with a rigid insulating shell: The polymer solid microspheres obtained in step S1 are surface modified and dispersed in deionized water. The cationic surfactant hexadecyltrimethylammonium bromide is added and stirred at room temperature to make the surface of the microspheres positively charged, which is conducive to the subsequent adsorption of silicon source.

[0051] Subsequently, a rigid insulating material was coated onto the surface of the modified polymer solid microspheres using an in-situ growth method. Specifically, the modified polymer solid microspheres were transferred to a mixed solution of ethanol / deionized water / ammonia and stirred. Tetraethyl or methyl orthosilicate was added dropwise to the mixed solution at a rate of 1-5 mL / h as a silicon source, and the reaction time was controlled to be 6 h. Under the catalysis of ammonia, tetraethyl orthosilicate hydrolyzed and condensed to generate silica nanoparticles, which were adsorbed and grown on the surface of the polymer solid microspheres through electrostatic interaction to form a continuous and dense SiO2 shell, thus obtaining core-shell structured microspheres. The thickness of the SiO2 shell was 500 nm to 1 μm.

[0052] S3. High-temperature pyrolysis pore formation and in-situ encapsulation: Under a protective atmosphere, the core-shell structured microspheres are subjected to staged high-temperature heat treatment. Specifically, the core-shell structured microspheres are placed in a tube furnace, and after vacuuming, a mixture of hydrogen and inert gas is introduced. The volume content of hydrogen is 1~10%, and the gas flow rate is controlled at 100 sccm to prevent the magnetic conductive powder from oxidizing at high temperature and to reduce any trace oxides that may exist on the powder surface, ensuring its high conductivity and high permeability.

[0053] A phased high-temperature heat treatment is performed. First, the temperature is increased to 200-300℃ at a heating rate of 1-5℃ / min and held for 20-60min to remove solvent residue. Then, the temperature is increased to 400-550℃ at a heating rate of 0.2-2℃ / min and held for 2-6h. During this stage, the polymer depolymerizes and vaporizes. The low heating rate ensures that the gas slowly permeates through the micropores of the SiO2 shell, preventing excessive internal pressure from causing explosion and ensuring complete decomposition of the polymer without residue.

[0054] The above process removes the polymer through pyrolysis and retains the magnetically conductive powder within the shell, resulting in magnetron-controlled semi-filled microspheres.

[0055] S4. Flexible sensor molding and packaging: Liquid polydimethylsiloxane prepolymer and curing agent are mixed at a mass ratio of 10:1 to obtain a flexible matrix precursor; a small amount of reduced graphene oxide modified with silane coupling agent can be added as needed to optimize dielectric properties.

[0056] Magnetic semi-filled microspheres were dispersed in a flexible matrix precursor at a volume fraction of 20-30 vol%. The mixture was gently stirred to ensure uniform dispersion and vacuum degassing. The resulting slurry was then poured into a mold and cured at 80°C for 2 hours in an environment without an external magnetic field to form a flexible dielectric layer. The curing without a magnetic field ensured that the magnetic powder inside the microspheres was in a random and loose initial state and did not undergo directional aggregation.

[0057] Subsequently, flexible conductive materials (such as silver paste) are coated onto the upper and lower surfaces of the flexible dielectric layer using screen printing or mask spraying processes to form electrode layers. Finally, a flexible protective film is encapsulated on the outer layer of the device to obtain a magnetron-controlled semi-filled microsphere flexible sensor. The flexible protective film is a PDMS or PET film.

[0058] The operating mode of the magnetically controlled semi-filled microsphere flexible sensor prepared above is as follows:

[0059] 1) High-sensitivity mode (lateral magnetic induction): Under the action of a horizontal magnetic field, powder accumulates on the sidewall of the microsphere (e.g., the left side), while the cavity inside the microsphere is mainly distributed on the other side (e.g., the right side). In the vertical direction where the sensor is mainly subjected to force, its vertical compressible area is large, and its compressive stiffness is significantly reduced, thus producing large deformation under small pressure, achieving high-sensitivity capture of weak signals.

[0060] 2) Wide range / high linearity mode (vertical magnetic induction): Under the influence of a vertical magnetic field, powder accumulates at the bottom (or top) of the microsphere along the magnetic field direction, forming a series structure of "cavity-powder layer" in the vertical direction. In this case, the densely packed powder layer acts as a rigid base, occupying part of the vertical force path, resulting in a significant reduction in the effective compressible space in this direction. The equivalent elastic modulus of the microsphere is thus increased, enabling it to withstand greater loads without easily collapsing, thus achieving the "wide range / high linearity mode".

[0061] Its core mechanism lies in: utilizing the positional distribution of flowing magnetic powder inside the microsphere to change the "effective compressible stroke" of the microsphere in the vertical force direction, thereby controlling the macroscopic compressive modulus of the dielectric layer.

[0062] The preparation method described above will be further explained below with reference to specific embodiments.

[0063] Example 1

[0064] This embodiment prepares a flexible capacitive sensor, specifically including the following steps:

[0065] S1. Prepare magnetic polymer composite microspheres (sacrificial cores) to obtain solid polymer microspheres with uniformly dispersed magnetic conductive powder inside, which will serve as sacrificial templates for subsequent construction of hollow structures, as detailed below:

[0066] 1) Raw material preparation: Spherical nano-permalloy (Fe-Ni) powder with an average particle size of 100~200nm was selected as the magnetic functional filler, wherein the mass fraction of nickel (Ni) was preferably 80%. This alloy has high magnetic permeability, low coercivity, and excellent resistance to oxidation and corrosion. Polymethyl methacrylate (PMMA) was selected as the sacrificial core matrix, taking advantage of its characteristics of complete decomposition at high temperature and low residual carbon.

[0067] 2) Composite Microsphere Molding: PMMA was dissolved in dichloromethane to prepare a 5wt% polymer solution. To achieve a final microsphere volume filling rate of approximately 50%, nano-permalloy powder was added to the polymer solution at a mass ratio of m(Fe-Ni):m(PMMA) = 7.5:1. 0.5wt% oleic acid was added as a dispersant, and the mixture was subjected to high-power ultrasonic dispersion for 45 min to prevent agglomeration of the high-concentration metal powder. Subsequently, the resulting suspension was dropwise added to an aqueous phase containing 1wt% polyvinyl alcohol (PVA), and emulsified by stirring at a shear rate of 1000 rpm to form an emulsion.

[0068] The mixture was then solidified by continuous stirring in a 40°C water bath for 6 hours to slowly evaporate the dichloromethane, causing the PMMA to shrink and tightly encapsulate the metal powder, forming high-density Fe-Ni / PMMA composite microspheres with a particle size of 30~50μm. After centrifugation, washing, and drying, the microspheres were ready for use.

[0069] S2. Coating with a rigid insulating shell: A dense and controllable thickness rigid insulating layer is grown in situ on the surface of the above-mentioned magnetic polymer composite microspheres to form a core-shell structured microsphere, as detailed below:

[0070] 1) Surface modification: The magnetic polymer composite microspheres prepared by S1 were dispersed in deionized water, and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) was added. The mixture was stirred at room temperature for 1 hour to make the surface of the microspheres positively charged, which would facilitate the subsequent adsorption of silicon source.

[0071] 2) In-situ coating: A modified Stöber method was used. The modified composite microspheres were transferred to a mixed solution of ethanol / deionized water / ammonia and stirred. Tetraethyl orthosilicate (TEOS) was slowly added dropwise to the mixed solution at a rate of 2.5 mL / h, with the reaction time controlled at 6 h. Under the catalysis of ammonia, the silica (SiO2) nanoparticles generated by the hydrolysis and condensation of TEOS were adsorbed and grown on the surface of the composite microspheres through electrostatic interaction, forming a continuous and dense SiO2 shell. The thickness of the SiO2 shell was controlled between 500 nm and 1 μm. This thickness design ensured the structural integrity in subsequent processes and endowed the microsphere shell with the mechanical property of elastic buckling under pressure.

[0072] S3. High-Temperature Pyrolysis Pore Formation and In-Situ Encapsulation of Functional Fillers: This is the core step. High-temperature pyrolysis removes the polymer sacrificial core, constructing a "semi-filled hollow microsphere" structure containing loose magnetic powder, as detailed below:

[0073] 1) Heat treatment environment setup: The core-shell structured microspheres prepared by S2 were placed in a tube furnace, and after evacuation, a 5% H2 / 95% Ar mixed gas was introduced. The gas flow rate was controlled at 100 sccm to prevent the nano-permalloy from oxidizing at high temperature and to reduce any trace oxides that may exist on the powder surface, thus ensuring its high conductivity and high magnetic permeability.

[0074] 2) Pyrolysis and structural reconstruction: First stage: Increase the temperature to 250℃ at 2℃ / min, hold for 30 minutes, and remove solvent residue.

[0075] The second stage involves heating from 250°C to 450°C at an extremely low rate of 0.5°C / min. During this stage, PMMA undergoes depolymerization and gasification. The low heating rate ensures that the gas slowly permeates through the micropores of the SiO2 shell, preventing excessive internal pressure from causing an explosion.

[0076] The third stage: keep at 450℃ for 4 hours to ensure that the polymer is completely decomposed without any residue.

[0077] After the heat treatment was completed, the furnace was allowed to cool naturally to room temperature, with a protective atmosphere maintained during this period to prevent oxidation of the metal powder at high temperatures and shell cracking due to thermal shock. The final product was SiO2 hollow microspheres filled with approximately 50 vol% loose nano-permalloy alloy powder.

[0078] S4. Forming and Packaging of Flexible Sensors: The prepared semi-filled hollow microspheres are combined with a flexible substrate, and electrodes are integrated to obtain the final flexible sensor, as detailed below:

[0079] 1) Preparation of dielectric layer slurry: Liquid polydimethylsiloxane (PDMS) prepolymer and curing agent were mixed at a mass ratio of 10:1. A small amount (0.1wt%) of silane coupling agent-modified reduced graphene oxide (rGO) was added to optimize the dielectric properties.

[0080] 2) Composite and Curing: The semi-filled hollow microspheres prepared by S3 were added to the PDMS matrix at a volume fraction of 20-30 vol%, gently stirred to disperse evenly, and then degassed under vacuum. The slurry was poured into a mold and cured at 80°C for 2 hours in a magnetic field-free environment. Magnet field-free curing ensured that the magnetic powder inside the microspheres remained in a randomly loose initial state, without directional aggregation.

[0081] 3) Electrode Integration: Flexible conductive material (silver paste) is coated onto the upper and lower surfaces of the cured microsphere-containing PDMS dielectric layer using screen printing or mask spraying to form electrode layers. Finally, a flexible protective film (PDMS film) is encapsulated on the outer layer of the device to obtain a magnetron-controlled semi-filled microsphere flexible sensor.

[0082] Example 2

[0083] This embodiment is prepared in the same way as in Example 1, except that polymethyl methacrylate in S1 is replaced with polystyrene; tetraethyl orthosilicate in S2 is replaced with methyl orthosilicate; and the flexible matrix polydimethylsiloxane in S4 is replaced with polyurethane.

[0084] Example 3

[0085] This embodiment uses the same raw materials and preparation steps as Embodiment 1. The only difference is that in step S3, the high-temperature treatment process of the decomposition section is modified as follows: first, the temperature is raised to 200°C at a heating rate of 1°C / min and held for 20 min; then, the temperature is raised to 400°C at a heating rate of 0.2°C / min and held for 2 h.

[0086] Example 4

[0087] This embodiment uses the same raw materials and preparation steps as Embodiment 1. The only difference is that in step S3, the high-temperature treatment process of the decomposition section is modified as follows: first, the temperature is increased to 300°C at a heating rate of 5°C / min and held for 60 min; then, the temperature is increased to 550°C at a heating rate of 2°C / min and held for 6 h.

[0088] The flexible sensor obtained in Example 1 was tested, such as... Figures 2-7 As shown.

[0089] Figure 2 The study demonstrates the directional distribution and reconstruction mechanism of nano-permalloy (Fe-Ni) particles inside magnetron-controlled semi-filled microspheres under the influence of external magnetic fields in different directions. Figure 2(a) characterizes the magnetic field control mode in the vertical direction. Taking the downward magnetic force guidance direction as an example, when an external magnetic field is applied to the sensor along its thickness direction (i.e., perpendicular to the sensor surface), the loose nano-permalloy particles inside the microsphere are subjected to magnetic force, overcome gravity and interparticle friction, and migrate and gather in the top or bottom hemisphere region of the microsphere cavity.

[0090] In the vertical magnetic field control mode, whether the magnetic field is applied from above or below the sensor, the purpose is to induce the internal magnetic particles to align or accumulate along the vertical axis, thereby forming a hemispherical powder accumulation layer in the direction of pressure on the microsphere. Although there are still cavities inside the microsphere, their effective cavity height along the vertical axis is shortened by the powder layer. This distribution corresponds to the sensor's subsequent "wide range / high linearity mode".

[0091] Figure 2 (b) characterizes the horizontal / lateral magnetic field control mode. Taking the left-side magnetic guidance as an example, when an external magnetic field parallel to the sensor's surface (i.e., horizontal) is applied, the nano-permalloy particles inside the microsphere are attracted by the lateral magnetic field force, rapidly migrate, and are all adsorbed onto one side (such as the left, right, front, or rear) of the microsphere's inner cavity along the magnetic field direction. In the horizontal / lateral magnetic field control mode, regardless of whether the magnetic field is applied to the sensor from the front, back, left, or right, the effect is to concentrate the magnetic particles in one direction, forming a hemispherical particle accumulation area and a hemispherical cavity area. Since this cavity is a vertically oriented hemispherical structure, it provides a huge deformation space along the vertical pressure path. This distribution corresponds to the sensor's subsequent "high sensitivity mode".

[0092] Figure 3 and Figure 4 The dielectric response mechanism of magnetron semi-filled microspheres under different magnetic field distributions is demonstrated based on the difference in internal effective compressible stroke.

[0093] Figure 3 The image clearly demonstrates the sensor's state in high-sensitivity operating mode. In this mode, a horizontal lateral magnetic field attracts magnetically conductive powder to one side of the microsphere's inner wall (e.g., the left side). The microsphere's interior exhibits an asymmetrical distribution: powder on the left and a pure air cavity on the right. The pure air cavity on the right side has no solid filler in the vertical direction, possessing a complete vertical compressibility. Since the compressibility modulus of gas is much smaller than that of solid powder, this pure air cavity region exhibits a very high vertical compressibility ratio under vertical pressure. The overall compressive deformation of the microsphere is mainly contributed by this highly compressible cavity region, resulting in a significant change in the electrode spacing with pressure, thus achieving extremely high sensitivity.

[0094] Figure 4This demonstrates the sensor's state when operating in a wide-range and high-linearity mode. In this mode, a vertical magnetic field attracts the magnetically conductive powder to the top or bottom of the microsphere (near the point of force). The flowing powder directly accumulates along the vertical force path, occupying part of the vertical travel that would otherwise belong to the air. The microsphere's vertical structure then becomes a series structure of "silica shell - magnetic powder layer - air - silica shell". Because the magnetic powder layer is relatively incompressible, the effective compressible travel of the microsphere in the vertical direction is significantly shortened. This is analogous to replacing a spring with a rigid cylinder plus a short spring, resulting in a decrease in the overall compressibility in the vertical direction. This structure increases the equivalent stiffness of the dielectric layer, allowing the sensor to withstand greater pressure without easily saturating, thus achieving wide-range detection.

[0095] The cross-section of the dielectric layer of the magnetron-controlled semi-filled microsphere flexible sensor prepared in the above embodiments was examined using scanning electron microscopy, such as... Figure 5 As shown, the microspheres dispersed in the matrix maintain a highly regular spherical geometry without obvious collapse or cracking, demonstrating that the rigid insulating shell of silica (SiO2) possesses good structural strength and thermal stability, capable of withstanding the impact of high-temperature pyrolysis (450℃) during preparation and subsequent curing processes. This SiO2 shell exhibits a clear thin-walled characteristic, with uniform thickness at the submicron scale. This ultrathin and dense inorganic shell structure not only achieves physical isolation and protection of the internal functional materials but also provides the necessary mechanical basis for the elastic buckling deformation of the microspheres under pressure.

[0096] By observing the cross-section or translucent imaging area at the damaged part of the microsphere, it can be confirmed that the original solid polymer (PMMA) core inside the microsphere has completely disappeared, forming a clear internal cavity structure. This feature strongly confirms the effectiveness of step S3 (high-temperature pyrolysis pore formation) in this embodiment, that is, the polymer sacrificial core has been vaporized through pyrolysis and completely escaped through the shell micropores, successfully constructing a "sphere in a cage" hollow structure. A large number of nanoscale particles, namely nano-permalloy (Fe-Ni) powder, can be observed inside the microsphere's internal cavity. These magnetically conductive powders are not solidified and encapsulated by the polymer matrix, but rather exhibit a random, loosely packed state, with a volume filling rate of approximately 50% inside the microsphere (i.e., a "semi-filled" state). This loose physical state preserves the freedom of the powder particles within the cavity, providing the necessary spatial conditions for directional migration, adsorption (high sensitivity mode), or accumulation (wide range mode) under the influence of an external magnetic field. Meanwhile, the particle surface morphology was clear, and no obvious oxide layer thickening was observed, indicating that the heat treatment process under a reducing atmosphere effectively maintained the physicochemical properties of the metal filler.

[0097] From a macroscopic perspective, the aforementioned magnetronically controlled semi-filled microspheres are uniformly dispersed within a flexible polydimethylsiloxane (PDMS) matrix, with no obvious agglomeration observed. The outer wall of the microspheres maintains close contact with the PDMS matrix, exhibiting good interfacial bonding without significant microcracks or peeling voids. This is attributed to the surface modification treatment of the SiO2 shell and the in-situ growth process. The excellent interfacial compatibility facilitates the uniform transmission of stress within the dielectric layer, thereby ensuring the stability of the overall mechanical properties of the sensor. SEM characterization results fully verify that this invention successfully fabricated magnetronically controlled semi-filled microspheres with a unique structure of "rigid insulating shell - loose magnetic core," and that these microspheres achieve excellent structural preservation and uniform dispersion within the flexible dielectric layer, laying the microstructural foundation for the sensor to achieve magnetronically controlled tunable electromechanical response characteristics.

[0098] The sensor prepared in this embodiment was characterized in terms of performance. Its pressure response characteristics under horizontal lateral magnetic field guidance (i.e., high sensitivity mode) and vertical magnetic field guidance (i.e., wide range / high linearity mode) are as follows: Figure 6 , Figure 7 As shown.

[0099] Figure 6 The curve exhibits a clear bilinear segment characteristic, as detailed below:

[0100] In the low-pressure range (0~1.4 kPa), the sensor exhibits extremely high sensitivity. The data shows that when the pressure increases only to 1.4 kPa, the relative capacitance change rate ( The C / C ratio has rapidly climbed to 43.13%. This is because, in this mode, the magnetic powder inside the microsphere is adsorbed onto the sidewall. Since the vertical hemispherical cavity can cause significant deformation of the thin-walled shell under small pressure, it causes a dramatic change in capacitance, which is very suitable for capturing weak tactile signals.

[0101] In the high-pressure range (1.4–5 kPa), the capacitance change rate linearly increases from 43.13% to 65.67% (at 5 kPa) with further pressure increases. Although the sensitivity (curve slope) in this stage is lower than that in the 0–1.4 kPa range, it still maintains a good linear response. This indicates that after the sensor undergoes initial large deformation, the structural stiffness increases slightly, but signal saturation does not occur, and it still possesses continuous pressure resolution capability. Overall, the sensor exhibits ultra-high sensitivity in the low-pressure range under this mode, verifying the enhancing effect of lateral magnetic field arrangement on the sensing of minute forces.

[0102] and Figure 6 Compared to the high-sensitivity mode, Figure 7 The curve showed a single and stable linear growth trend throughout the entire test range of 0~5kPa, without any obvious sensitivity segmentation.

[0103] Specifically, as the pressure increases from 0 kPa to 5 kPa, the rate of change of relative capacitance ( The C / C ratio increased uniformly from 0% to 50.50%. Although its overall sensitivity (i.e., the change in capacitance per unit pressure) was lower than... Figure 6 The low-pressure section (e.g., at 1.4 kPa) Figure 7 The response value is approximately 13.23%, far lower than... Figure 6 While the overall sensitivity is relatively stable (43.13%), it exhibits excellent linearity (high R² value). This characteristic is attributed to the limited compressible area of ​​the magnetic powder in the direction of force on the microspheres under the action of a vertical magnetic field. This effectively suppresses excessive collapse of the microspheres in the initial stage of compression, providing stable compressive stiffness. This allows the sensor to withstand greater loads and output highly linear electrical signals, verifying the significant effect of the vertical magnetic field arrangement on improving the sensor's range and linearity.

[0104] The aforementioned mechanism, which uses an external magnetic field to non-contactly control the distribution of the internal microstructure, successfully enables a single flexible sensor to switch between two distinct working modes: "high-sensitivity detection" and "wide-range linear measurement." This effectively breaks the inherent bottleneck of the mutual constraint between the sensitivity and detection range of traditional flexible sensors, providing a novel solution for intelligent tactile perception in complex unstructured environments.

[0105] Therefore, this invention provides a magnetically controlled semi-filled microsphere flexible sensor and its fabrication method. By constructing a "semi-filled hollow microsphere" structure containing magnetic conductive powder, and utilizing the high permeability and low coercivity of the magnetic powder, the solid-gas two-phase distribution inside the microsphere is reconstructed under the action of an external magnetic field, thereby actively adjusting the equivalent mechanical modulus and electrical response characteristics of the dielectric layer. It not only achieves on-demand switching between high-sensitivity detection mode and wide-range measurement mode on a single device, but also significantly improves the device's oxidation resistance and interface bonding stability through in-situ encapsulation technology.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A magnetically controlled semi-filled microsphere flexible sensor, characterized in that: It includes a flexible dielectric layer and electrode layers disposed on both sides of the flexible dielectric layer. The flexible dielectric layer includes a flexible matrix and magnetron-controlled semi-filled microspheres with a core-shell structure dispersed in the flexible matrix. The magnetron-controlled semi-filled microspheres comprise a rigid insulating shell and magnetically conductive powder encapsulated within the cavity of the rigid insulating shell; the magnetically conductive powder is an iron-nickel alloy powder with a nickel mass fraction of 78-82%; the volumetric filling rate of the magnetically conductive powder in the magnetron-controlled semi-filled microspheres is 40-60%. The fabrication method of this magnetically controlled semi-filled microsphere flexible sensor includes the following steps: S1. Preparation of magnetic polymer composite microspheres: Magnetic conductive powder is dispersed in a polymer solution, and solid polymer microspheres containing magnetic conductive powder are obtained through dispersion, emulsification, and curing processes; the mass ratio of magnetic conductive powder to polymer is (6~9):1; the polymer is polymethyl methacrylate or polystyrene; S2. Encapsulating a rigid insulating shell: The surface of the polymer solid microspheres is modified, and a rigid insulating material is coated on the surface of the modified polymer solid microspheres using an in-situ growth method to form core-shell structured microspheres. S3. High-Temperature Pyrolysis for Pore Formation and In-Situ Encapsulation: Under a protective atmosphere, core-shell structured microspheres undergo staged high-temperature heat treatment to pyrolyze away the polymer while retaining the magnetically conductive powder within the shell, resulting in magnetronically controlled semi-filled microspheres. The staged high-temperature heat treatment process includes: first, heating to 200-300℃ at a rate of 1-5℃ / min and holding for 20-60min to remove solvent residue; then heating to 400-550℃ at a rate of 0.2-2℃ / min and holding for 2-6h; during this stage, the polymer depolymerizes and vaporizes. The low heating rate ensures that the gas slowly permeates through the micropores of the SiO2 shell, preventing excessive internal pressure from causing explosion and ensuring complete polymer decomposition without residue. The above process removes the polymer through pyrolysis while retaining the magnetically conductive powder within the shell, resulting in magnetronically controlled semi-filled microspheres. S4. Flexible sensor molding and packaging: Magnetic semi-filled microspheres are dispersed in a flexible substrate precursor and cured in an environment without an external magnetic field to form a flexible dielectric layer. Then, electrode layers are integrated on the upper and lower surfaces of the flexible dielectric layer to obtain a flexible sensor. The magnetically controlled semi-filled microsphere flexible sensor prepared above has the following two operating modes based on the direction of the external magnetic field: High sensitivity mode: Under the action of a horizontal magnetic field parallel to the sensor surface, magnetic conductive powder is attracted by magnetic force and gathers on one side of the inner wall of the microsphere, so that the microsphere forms a structure in which the powder gathering area and the pure air cavity area coexist. The pure air cavity area has a large effective compressible stroke in the vertical force direction, so that the microsphere can produce a large longitudinal deformation when subjected to vertical pressure. Wide range and high linearity mode: Under the action of a vertical magnetic field perpendicular to the sensor surface, the magnetic conductive powder is attracted by the magnetic force and gathers on the top or bottom inner wall of the microsphere. This causes the magnetic conductive powder to occupy part of the space of the microsphere in the vertical force direction, reducing the effective compressible stroke in the vertical direction, thereby limiting the longitudinal deformation of the microsphere under unit pressure. Its core mechanism lies in: utilizing the positional distribution of flowing magnetic powder inside the microsphere to change the "effective compressible stroke" of the microsphere in the vertical force direction, thereby controlling the macroscopic compressive modulus of the dielectric layer.

2. The magnetically controlled semi-filled microsphere flexible sensor according to claim 1, characterized in that: The flexible matrix is ​​one of polydimethylsiloxane, polyurethane or silicone rubber, and the volume fraction of the magnetron semi-filled microspheres in the flexible matrix is ​​20~30 vol.

3. The magnetically controlled semi-filled microsphere flexible sensor according to claim 1, characterized in that: The rigid insulating shell has a shell thickness of 500nm~1μm and is made of silicon dioxide. The average particle size of the magnetic conductive powder is 100~200nm.

4. The magnetically controlled semi-filled microsphere flexible sensor according to claim 1, characterized in that: In S2, the surface modification process uses a cationic surfactant; the in-situ growth process uses tetraethyl orthosilicate or methyl orthosilicate as the silicon source, and hydrolyzes and condenses under the catalysis of ammonia to generate a silica shell.

5. The magnetically controlled semi-filled microsphere flexible sensor according to claim 1, characterized in that: In step S3, the protective atmosphere is a mixture of hydrogen and an inert gas, wherein the volume content of hydrogen is 1-10%.

6. The magnetically controlled semi-filled microsphere flexible sensor according to claim 1, characterized in that: In S4, the flexible matrix precursor is a mixture of liquid polydimethylsiloxane prepolymer and curing agent.

Images