A flexible coil and its preparation method and application

Abstract

The present invention provides a flexible coil, a preparation method thereof and an application. The preparation method comprises the following steps: preparing an insulating polymer film and a sacrificial wire; wrapping the insulating polymer film on the surface of the sacrificial wire and forming a preset coil shape to obtain a sacrificial coil; encapsulating the sacrificial coil with a flexible matrix material and leaving an opening to obtain an encapsulated sacrificial coil; heating the encapsulated sacrificial coil to melt and remove the sacrificial wire to obtain a flexible matrix with a cavity channel inside; injecting a conductive material into the cavity channel in the flexible matrix, connecting leads at both ends and sealing the opening to obtain the flexible coil. The preparation method provided by the present invention can realize the preparation of flexible coils with high density and complex shapes, overcoming the problems that the existing process can only prepare flexible coils with simple structures such as planar and single-layer, and the prepared flexible coils have a large thickness of the insulating layer and a small coil density.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic coils, and particularly relates to a flexible coil, a preparation method thereof, and an application thereof. Background Art

[0002] In the past few decades, due to their excellent safety features and adaptability to environmental conditions, flexible robots have shown significant potential in various application scenarios. Their biological-like systems, with the ability to sense the environment, have self-awareness, and perform controlled movements, have always been the goal pursued by researchers. Generally speaking, advanced flexible robots need to have the capabilities of high precision, large working range, multi-physical sensing, and high response speed, high power density, and strong driving force. However, it is difficult to find a single unit that can integrate both sensing and driving functions simultaneously. Usually, multiple units need to work together to achieve these capabilities.

[0003] Currently, flexible pressure and temperature sensors usually lack the ability to move, while flexible actuators such as dielectric elastomers, pneumatic or hydraulic muscles usually do not have sensing functions. This inevitably leads to a bulky robot structure. Fortunately, among various types of sensors and actuators, flexible actuators using electromagnetic force driving mechanisms have greater integration potential.

[0004] Such flexible actuators using electromagnetic force driving mechanisms include a flexible coil that generates a force in the presence of an external magnetic field, thereby triggering the movement of the robot. Thanks to the latest progress in liquid metal technology, such electromagnetic actuators can seamlessly transition from copper coils to liquid metal coils (LMCs). High-power electromagnetic actuators not only exhibit excellent flexibility but also possess excellent sensing capabilities. For example, applying pressure will cause a change in its resistance, thereby enabling the detection of external forces. Compared with actuators such as dielectric elastomers, ion electroactive actuators, hydraulic muscles, and liquid crystal elastomers, robots equipped with flexible electromagnetic actuators usually show a better combination in terms of response speed, movement displacement, and force output capabilities. Therefore, they can be effectively used to develop flexible grippers, land walking robots, and underwater swimming robots. In addition, precise motion control can be achieved by adjusting the input electrical signal, allowing for programmable operations. The low operating voltage of the actuator enables seamless integration with smaller batteries.

[0005] However, different from the rigid coils wound with copper wires, the manufacture of liquid metal flexible coils faces significant challenges. Due to the fluidity and high surface tension of the material, the formation of something similar to liquid metal wires is not feasible. Instead, it can be injected into a flexible silicone tube with a spiral structure to generate a coil, but the liquid state of the flexible silicone material before curing poses challenges for the formation of channels. Therefore, most current research on liquid metal coils focuses on single-layer two-dimensional planar coils. However, these coils not only face difficulties in achieving curved surfaces, but also have a relatively large width of the insulating layer between channels, greatly affecting the utilization of flexible electromagnetic elastomers in flexible robots.

[0006] In summary, aiming at the problem of difficult preparation of current flexible electromagnetic coils, there is an urgent need to seek a new technology to meet the manufacture of flexible coils with higher performance. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a flexible coil and its preparation method and application. The preparation method provided by the present invention can realize the preparation of flexible coils with high density and complex shapes, overcoming the problems that the existing processes can only prepare flexible coils with simple structures such as planar and single-layer, and the prepared flexible coils have a relatively large thickness of the insulating layer and a small coil density.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a preparation method of a flexible coil, and the preparation method includes the following steps:

[0010] Prepare an insulating polymer film;

[0011] Prepare the sacrificial material into sacrificial wire;

[0012] Wrap the insulating polymer film on the surface of the sacrificial wire;

[0013] Make the sacrificial wire wrapped with the insulating polymer film into a preset coil shape to obtain a sacrificial coil;

[0014] Package the sacrificial coil with a flexible matrix material and leave an opening to obtain a packaged sacrificial coil;

[0015] Heat the packaged sacrificial coil to melt and remove the sacrificial wire, obtaining a flexible matrix with a cavity channel inside;

[0016] Inject a conductive material into the cavity channel in the flexible matrix, connect leads at both ends and seal the opening to obtain the flexible coil.

[0017] The flexible coil prepared in the present invention includes a coil body (constituted by a conductive material filled in a cavity channel, that is, a conductive core) and a flexible matrix wrapping the coil body.

[0018] It is easy for those skilled in the art to understand that the shape of the sacrificial wire in the sacrificial coil is the same as that of the conductive core in the flexible coil. In the present invention, there is no special limitation on the method of forming the sacrificial wire wrapped with an insulating polymer film into a preset coil shape. Exemplarily, it can be carried out by physical bending, winding, etc. After forming the basic preset coil shape, it is preferably pressed to make the wires in close contact with each other to increase the density of the coil.

[0019] In the flexible coil prepared by the preparation method provided by the present invention, the wire diameter of the conductive core can be controlled by adjusting the diameter of the sacrificial wire; the thickness of the insulating layer (that is, the distance between adjacent wires) can be controlled by adjusting the thickness of the insulating polymer film wrapped on the surface of the sacrificial wire; the shape of the conductive core can be realized by preparing a sacrificial coil of this shape. Theoretically, a conductive core of any shape can be created in the flexible matrix. Therefore, the preparation method provided by the present invention can not only realize the preparation of flexible coils with low density and simple structure, but also realize the preparation of flexible coils with high density and complex shapes (such as three-dimensional, multi-layer, curved surface, etc.), overcoming the problems that the existing process can only prepare flexible coils with simple structures such as planar and single-layer, and the prepared flexible coils have a large thickness of the insulating layer and a small coil density.

[0020] In some embodiments of the present invention, the material of the insulating polymer film includes one or more of silicone rubber, polyimide, and polytetrafluoroethylene, preferably including silicone rubber. However, the present invention is not limited thereto, and other insulating polymers suitable for film formation can also be applied to the present invention.

[0021] In some embodiments of the present invention, the step of preparing the insulating polymer film includes: applying an insulating polymer or a precursor of the insulating polymer on a substrate, forming a liquid film by spin coating, and forming an insulating polymer film after curing. However, the present invention is not limited thereto, and other methods capable of preparing an insulating polymer film with the required thickness can also be applied to the present invention.

[0022] It is easy for those skilled in the art to understand that since the sacrificial wire needs to be melted and removed when heating and encapsulating the sacrificial coil, its melting point should not be too high to avoid softening and deformation of the flexible matrix material when the sacrificial wire melts. As a preferred embodiment, the melting point of the sacrificial material is lower than the melting temperature of the flexible matrix material. In addition, since the sacrificial wire needs to exist in a solid form, its melting point is preferably greater than room temperature, and more preferably above 35°C.

[0023] In some embodiments of the present invention, the sacrificial material includes one or more of metal alloys, paraffin wax, and polyvinyl alcohol. However, the present invention is not limited thereto, and other materials that meet the above requirements for melting point and can be used to prepare the sacrificial coil are also applicable to the present invention.

[0024] In some embodiments of the present invention, the metal alloy includes Bi 32 In 51 Sn 17 (with a melting point of about 60.5 °C, and a composition of Bi: 32 wt%, In: 51 wt%, Sn: 17 wt%).

[0025] In some embodiments of the present invention, the step of preparing the sacrificial material into a sacrificial wire includes: melting the sacrificial material and injecting it into a mold, and demolding after the sacrificial material solidifies to obtain the sacrificial wire. However, the present invention is not limited thereto, and other methods capable of making the sacrificial material into a wire are also applicable to the present invention.

[0026] In some embodiments of the present invention, the total thickness of the insulating polymer film wrapped on the surface of the sacrificial wire is 20 - 500 μm, for example, it can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, or 500 μm, etc.

[0027] When the total thickness of the wrapped insulating polymer film is within this range, it helps to ensure sufficient insulation between the wires and enables the flexible coil to have a high density. However, the present invention is not limited thereto, and those skilled in the art can also select a thickness outside this range according to needs.

[0028] In some embodiments of the present invention, the flexible matrix material includes silicone rubber and / or epoxy resin. However, the present invention is not limited thereto, and other flexible polymer materials suitable for encapsulation are also applicable to the present invention.

[0029] In the present invention, no special limitation is imposed on the type of the silicone rubber. As a non-limiting example, it can be polydimethylsiloxane (PDMS), Ecoflex, 705RTV silicone rubber, human silicone, etc.

[0030] In some embodiments of the present invention, the preparation step of the encapsulated sacrificial coil includes: placing the sacrificial coil in a mold, injecting the flexible matrix material or the precursor of the flexible matrix material into the mold to submerge the sacrificial coil, leaving an opening, and demolding after curing to obtain the encapsulated sacrificial coil.

[0031] In some embodiments of the present invention, the conductive material includes one or more of liquid metal, ionic liquid, and graphite, preferably liquid metal.

[0032] In some embodiments of the present invention, the liquid metal includes eutectic gallium indium (EGaIn) or gallium indium tin alloy. However, the present invention is not limited thereto, and other liquid metals suitable for use as conductive materials can also be applied to the present invention.

[0033] In a second aspect, the present invention provides a flexible coil prepared by the preparation method described in the first aspect.

[0034] The flexible coil provided by the present invention includes a coil body (formed by a conductive material filled in a cavity channel, that is, a conductive core) and a flexible matrix wrapping the coil body.

[0035] The flexible coil provided by the present invention can achieve high density and complex shapes (such as three-dimensional, multi-layer, curved surfaces, etc.), not only ensuring the electrical insulation performance of the coil, but also ensuring the safety and reliability of the coil in a high-density structure. The flexible coil provided by the present invention not only has good mechanical flexibility, but also can achieve multiple functions, including but not limited to precise pressure sensing, temperature sensing, non-contact distance sensing, near-field communication, etc.

[0036] In a third aspect, the present invention provides an application of the flexible coil described in the second aspect in flexible electronic devices, flexible robots, medical devices, near-field communication devices, intelligent systems, and automation devices.

[0037] Among them, as a non-limiting example, the flexible electronic device can be a flexible display, a flexible sensor (including but not limited to a temperature sensor, a pressure sensor, a distance sensor), a flexible battery, etc. The high-density and multi-functional integration characteristics of the flexible coil provided by the present invention can significantly improve the performance and application value of these devices.

[0038] The flexible robot includes but is not limited to a flexible gripper, a bionic robot, a soft robot, etc. The excellent electromagnetic performance and multi-functional integration characteristics of the flexible coil provided by the present invention can achieve precise motion control and environmental perception.

[0039] The medical device includes but is not limited to a wearable health monitoring device, a flexible endoscope, an implantable sensor, etc. The flexibility and high-density characteristics of the flexible coil provided by the present invention can improve the comfort and performance of these instruments.

[0040] The near-field communication (NFC) device can realize non-contact information exchange and communication functions. The high-density and multi-functional characteristics of the flexible coil provided by the present invention can improve the transmission efficiency and stability of the NFC device.

[0041] The intelligent systems and automated devices include, but are not limited to, smart home, industrial automation, intelligent transportation, etc. The multi-functional integration and high-density characteristics of the flexible coil provided by the present invention can improve the intelligence level and working efficiency of these systems.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The preparation method provided by the present invention can not only realize the preparation of flexible coils with low density and simple structure, but also realize the preparation of flexible coils with high density and complex shapes (such as three-dimensional, multi-layer, curved surface, etc.), overcoming the problems that the existing process can only prepare flexible coils with simple structures such as planar and single-layer, and the prepared flexible coils have a large thickness of the insulating layer and a small coil density.

[0044] 2. The preparation method provided by the present invention can create a conductive core with any shape in a flexible matrix, and the shape and size of the conductive core can be designed according to the space limitation and performance requirements of specific application scenarios, expanding the application range of the flexible coil.

[0045] 3. The preparation method provided by the present invention can precisely control the diameter of the wire in the flexible coil. This flexibility enables the flexible coil to select a suitable wire diameter according to specific application requirements, optimizing the electromagnetic performance.

[0046] 4. The preparation method provided by the present invention can precisely control the thickness of the insulating layer in the flexible coil. This precise control not only improves the electrical insulation performance of the coil, but also ensures the safety and reliability of the coil in a high-density structure.

[0047] 5. By controlling the wire diameter and the thickness of the insulating layer, the preparation method provided by the present invention can realize the preparation of high-density flexible coils, and the ratio (k value) of the wire diameter to the thickness of the insulating layer can reach more than 10, which is equivalent to that of enameled wires, exceeding the density of the currently reported liquid metal coils (the highest is 1.25) or liquid metal wires (the highest is 5.75).

[0048] 6. The flexible coil provided by the present invention has good mechanical flexibility and can withstand a certain degree of stretching, compression, twisting and bending without damage.

[0049] 7. The flexible coil provided by the present invention can realize multiple functions, including precise pressure sensing, temperature sensing, non-contact distance sensing, and near-field communication. This characteristic of multi-functional integration significantly improves the application value of flexible electronic devices, and has broad application prospects especially in flexible robots, sensors and communication devices.

[0050] 8. The flexible coil provided by the present invention shows significant performance improvement in electromagnetic drives, enabling precise control and driving of bionic robots and achieving efficient motion control. Its high power density gives it obvious advantages in flexible drive applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a flowchart of the preparation method of the flexible coil provided by the embodiment of the present invention;

[0052] Figure 2a It is a schematic structural diagram of HD-LMC provided by the embodiment of the present invention;

[0053] Figure 2b It is the cross-sectional optical image and partial SEM image of the flexible matrix prepared in the embodiment of the present invention;

[0054] Figure 2c It is the optical image of HD-LMC provided by the embodiment of the present invention being stretched, compressed, twisted and bent;

[0055] Figure 3a It is the physical diagram of the sacrificial coil, flexible matrix and HD-LMC of the 3D multi-layer conical structure;

[0056] Figure 3b It is the physical diagram of the sacrificial coil, flexible matrix and HD-LMC of the 3D multi-layer planar structure;

[0057] Figure 4a It is the conceptual diagram of the pressure sensor using HD-LMC;

[0058] Figure 4b It is the inductance change rate - pressure curve graph of HD-LMC provided by the embodiment of the present invention;

[0059] Figure 4c It is the inductance change rate curve graph of HD-LMC provided by the embodiment of the present invention undergoing 100 cycle tests under a pressure of 214.29 kPa;

[0060] Figure 4d It is the inductance change rate curve graph of HD-LMC provided by the embodiment of the present invention within one pressure cycle during 100 cycle tests under a pressure of 214.29 kPa;

[0061] Figure 4e It is the conceptual diagram of the temperature sensor using HD-LMC;

[0062] Figure 4f It is the inductance change rate - temperature curve graph of HD-LMC provided by the embodiment of the present invention;

[0063] Figure 4gInductance change rate curve of HD-LMC provided by the embodiment of the present invention when the temperature rises with time;

[0064] Figure 4h Inductance change rate curve of HD-LMC provided by the embodiment of the present invention when the temperature changes cyclically with time;

[0065] Figure 4i Conceptual diagram of HD-LMC for non-contact induction of the distance of the metal surface;

[0066] Figure 4j Inductance change rate - distance curve of HD-LMC for different high-permeability metal plates;

[0067] Figure 4k Inductance change rate - distance curve of HD-LMC for different low-permeability metal plates;

[0068] Figure 4l Schematic diagram of the principle of non-contact eddy current detection;

[0069] Figure 4m Schematic diagram of HD-LMC for near-field communication;

[0070] Figure 4n Echo loss curve of NFC antenna under different quality factor Q values;

[0071] Figure 4o Impedance characteristic diagram of NFC antenna under different quality factor Q values;

[0072] Figure 4p Schematic diagram of the application scenario of NFC antenna using HD-LMC;

[0073] Figure 5a Schematic diagram of the structure of the HD-LMC integrated high-speed rotating robot;

[0074] Figure 5b HD-LMC drive principle diagram of the HD-LMC high-speed rotating robot;

[0075] Figure 5c Ideal current waveform diagram for driving the movement of the HD-LMC high-speed rotating robot;

[0076] Figure 5d Magnetic field distribution diagram of the HD-LMC high-speed rotating robot;

[0077] Figure 5e Image of the HD-LMC high-speed rotating robot performing in-situ high-speed rotation;

[0078] Figure 5fIt is a graph showing the relationship between the current drive frequency and the rotational speed of the HD-LMC high-speed rotating robot;

[0079] Figure 5g It is a graph of the maximum torque data generated by the HD-LMC high-speed rotating robot under different drive currents;

[0080] Figure 5h It is a motion diagram of the HD-LMC high-speed rotating robot under exciting currents of different frequencies;

[0081] Figure 5i It is a displacement-time relationship graph of the HD-LMC high-speed rotating robot under exciting currents of different frequencies;

[0082] Figure 5j It is a frequency-rotational speed curve graph of the inductance waveform of the HD-LMC high-speed rotating robot;

[0083] Figure 5k It is a graph of the inductance change rate-rotation angle of the HD-LMC high-speed rotating robot. Specific implementation manners

[0084] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation manners. Those skilled in the art should understand that the specific implementation manners are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0085] Example 1

[0086] This example provides a flexible coil and its preparation method. Among them, the flow chart of the preparation method is as Figure 1 shown and includes the following steps:

[0087] (1) Uniformly mix the prepolymer A of PDMS (Sylgard 184 Silicone Elastomer of Dow Corning, including prepolymer A and crosslinking agent B) and crosslinking agent B at a weight ratio of 10:1, ensure thorough stirring and vacuum pumping to remove air bubbles. Uniformly coat the mixed PDMS solution on the substrate, and form a film with a thickness of 50 microns by spin coating. The spin coating parameters are set to 2000 revolutions per minute for 60 seconds. Put the spin-coated PDMS film into an oven, heat it to 80 °C and keep it for 30 minutes to make it completely cured, and obtain the PDMS film.

[0088] (2) Use Bi 32 In 51 Sn 17 alloy (Bi: 32 wt%, In: 51 wt%, Sn: 17 wt%) as the sacrificial material. Heat the alloy to its melting point (about 60.5 °C) to ensure it is completely melted. The melted Bi32 In 51 Sn 17 The Sn-Sn alloy is poured into silica gel tubes with inner diameters of 0.68 mm, 1.2 mm, and 1.7 mm respectively, and sacrificial wire materials are formed after cooling. The cooled and solidified sacrificial wire materials are peeled off from the silica gel tubes to ensure that the surfaces of the sacrificial wire materials are smooth, without large defects and fractures.

[0089] (3) Wrap a layer of PDMS film on the surface of the sacrificial wire material, and then place the sacrificial wire material wrapped with the PDMS film in a mold and press it into the required coil shape to obtain a sacrificial coil. The design of the mold ensures that the geometric shape and size of the coil meet the expectations.

[0090] (4) Place the sacrificial coil in a cavity mold, add the PDMS glue solution described in step (1), with both ends of the sacrificial wire material exposed, fully evacuate to remove air bubbles, and heat to 55 °C to fully cure the glue solution to form a packaged sacrificial coil.

[0091] (5) Place the packaged sacrificial coil in an 80 °C water bath for 5 minutes to wash away the Bi-Sn sacrificial wire material, and obtain a flexible matrix with a cavity channel inside. 32 In 51 Sn 17 sacrificial wire material to obtain a flexible matrix with a cavity channel inside.

[0092] (6) Use liquid metal EGaIn (Ga: 75.5 wt%, In: 24.5 wt%) as the conductive core material, and ensure its purity and no impurities. Inject the liquid metal EGaIn into the cavity channel inside the flexible matrix to form a conductive core. After ensuring that the liquid metal EGaIn completely fills the channel, insert wires at both ends of the EGaIn conductive core as leads, and seal the opening part with 705RTV silicone rubber to prevent the leakage of liquid metal, and obtain a high-density liquid metal flexible coil (HD-LMC).

[0093] 1. Basic characteristics of HD-LMC

[0094] The structural schematic diagram of the HD-LMC provided in this embodiment is as Figure 2a shown, and it can generate a magnetic field when powered on. The cross-sectional optical image and local SEM image of the flexible matrix prepared in this embodiment are as Figure 2b shown. The optical images of the HD-LMC provided in this embodiment being stretched, compressed, twisted, and bent are as Figure 2c shown.

[0095] It can be seen from Figure 2a that the HD-LMC provided in this embodiment is a three-layer coil structure with a curved surface. It can be seen from Figure 2bIt can be seen that the diameter of the cavity channels in the flexible matrix prepared in this embodiment is approximately equal to the diameter of the sacrificial wire, and the thickness of the insulating layer (i.e., the distance between two adjacent cavity channels) is approximately twice the thickness of the PDMS film, both of which are consistent with the designed dimensions. From Figure 2c It can be seen that the HD-LMC provided in this embodiment is not damaged after being stretched, compressed, twisted, and bent, indicating that it has good mechanical flexibility.

[0096] 2. HD-LMCs with other structures

[0097] Figure 3a The physical pictures of a 3D multi-layered conical structure BiInSn sacrificial coil prepared by the method of Example 1, the flexible matrix (without liquid metal) formed after sacrificing BiInSn, and the HD-LMC (with liquid metal). Figure 3b The physical pictures of a 3D multi-layered planar structure BiInSn sacrificial coil prepared by the method of Example 1, the flexible matrix (without liquid metal) formed after sacrificing BiInSn, and the HD-LMC (with liquid metal).

[0098] Figure 3a and Figure 3b It shows that the preparation method provided by the present invention has universality and is applicable to the preparation of various high-density and complex-shaped flexible coils.

[0099] 3. Applications of HD-LMC units in pressure and temperature sensing, distance sensing, and near-field communication

[0100] 3.1. Pressure sensing of HD-LMC

[0101] HD-LMC (taking the structure with a wire diameter of 0.68 mm as an example) has the characteristic of flexibility. After being pressed, the structural deformation will greatly change its own inductance value. Use a universal mechanical testing machine to apply pressure to it, and use an LCR meter (precision inductance, capacitance, and resistance meter) to measure the inductance (AC voltage 1 V, frequency 100 kHz), and record the mechanical and inductance changes to calibrate the signal. This device has excellent potential for the function of a pressure sensor.

[0102] Among them, Figure 4a is the conceptual diagram of the pressure sensor using HD-LMC.

[0103] Figure 4b is the inductance change rate - pressure curve graph of HD-LMC. From Figure 4b it can be seen that the inductance change value of HD-LMC shows a linear relationship within a wide range of applied pressures (35.71 - 357.14 kPa, corresponding to 5 - 50 N).

[0104] Figure 4cInductance change rate curve of HD-LMC under 100 cycle tests at a relatively high pressure (214.29 kPa, corresponding to 30 N).

[0105] Figure 4d Inductance change rate curve of HD-LMC within one pressure cycle. From Figure 4c and Figure 4d it can be seen that the induction signal of HD-LMC responds to pressure relatively fast.

[0106] 3.2 Temperature perception of HD-LMC

[0107] HD-LMC (taking the structure with a wire diameter of 0.68 mm as an example) also has the function of temperature perception. Due to its flexible characteristics, the thermal stress caused by temperature difference can easily change the spatial position of its coil structure, thus triggering the change of inductance signal. Placing it and a standard thermocouple in a forced-air drying oven with temperature control for heating and recording the changes of temperature and inductance signal can realize the calibration of temperature. Therefore, it also has great potential application prospects as a temperature sensor.

[0108] Among them, Figure 4e is the conceptual diagram of the temperature sensor using HD-LMC.

[0109] Figure 4f Inductance change rate - temperature curve of HD-LMC. From Figure 4f it can be seen that within the temperature range from room temperature of 27 °C to 100 °C, there is a strong linear relationship between the inductance signal and temperature.

[0110] Figure 4g Inductance change rate curve of HD-LMC when the temperature rises with time (rising 5 °C every 30 minutes). From Figure 4g it can be seen that the inductance signal of HD-LMC shows a stable stepped shape, and the inductance change is relatively consistent with the temperature change.

[0111] Figure 4h Inductance change rate curve of HD-LMC when the temperature changes cyclically with time (heating in an 80 °C water bath from room temperature of 27 °C for 3 minutes and then cooling in a 27 °C water bath for 3 minutes, cycling). From Figure 4h it can be seen that HD-LMC shows good cycling stability.

[0112] 3.3 Distance perception of HD-LMC

[0113] The eddy current effect between HD-LMC (taking the structure with a wire diameter of 0.68 mm as an example) and the conductive material can be used to achieve non-contact distance sensing of an object. By using a stepper motor to control the distance between the metal sheet and HD-LMC and recording the relationship between the inductance signal and the distance, the calibration of non-contact distance sensing can be achieved.

[0114] Among them, Figure 4i is a conceptual diagram of HD-LMC for non-contact induction of the distance to the metal surface.

[0115] Figure 4j is the inductance change rate-distance curve graph of HD-LMC for different high-permeability metal plates (1j85 (nickel-iron-based soft magnetic alloy), iron, nickel, cobalt). From Figure 4j it can be seen that the inductance of HD-LMC changes with the distance from the metal plate, and the metal plate with higher permeability has an enhancing effect on the inductance signal, and different metals show different signal curves. This indicates that HD-LMC can not only achieve non-contact distance sensing but also has the function of measuring permeability and metal types to a certain extent.

[0116] Figure 4k is the inductance change rate-distance curve graph of HD-LMC for different low-permeability metal plates (304 stainless steel, aluminum, molybdenum, lead, copper, tin). From Figure 4k it can be seen that the distance positional relationship between the metal plate and HD-LMC can be characterized by the inductance signal, thus realizing the non-contact sensing function.

[0117] Figure 4l is a schematic diagram of the non-contact eddy current detection principle.

[0118] 3.4. HD-LMC for Near Field Communication (NFC)

[0119] After impedance matching between HD-LMC (taking the structure with a wire diameter of 0.68 mm as an example) and resistive and capacitive components, an NFC antenna is formed, which can achieve signal transmission at a frequency of 13.56 MHz. Its return loss and impedance can be detected using a vector network analyzer.

[0120] Among them, Figure 4m is a schematic diagram of HD-LMC for near field communication (NFC).

[0121] Figure 4n is the return loss (S11) curve graph of the NFC antenna under different quality factor Q values. From Figure 4n it can be seen that the smaller Q can lead to lower return loss and wider bandwidth.

[0122] Figure 4oImpedance characteristic diagrams of NFC antennas for different quality factor Q values. From Figure 4o it can be seen that smaller Q values have smaller real - part impedances, and the imaginary - part impedances of multiple Q values are zero at 13.56 MHz.

[0123] Figure 4p Schematic diagram of application scenarios of NFC antennas using HD - LMC, including receiving text messages, sending text messages, creating new contacts, making phone calls, opening emails, obtaining location information, accessing WiFi, browsing websites, etc.

[0124] 4. High - precision HD - LMC high - speed rotating robot with position recognition and speed feedback Figure 5a Schematic diagram of the structure of an integrated HD - LMC high - speed rotating robot.

[0125] Figure 5b Schematic diagram of the HD - LMC drive principle of the HD - LMC high - speed rotating robot.

[0126] Figure 5c Ideal current waveform diagram for driving the movement of the HD - LMC high - speed rotating robot. The current phase difference between the three groups of coils is 120°.

[0127] Figure 5d Magnetic field distribution diagram of the HD - LMC high - speed rotating robot. From Figure 5d it can be seen that the driving force of this robot comes from the interaction between the excited electromagnetic field and the background magnetic field.

[0128] Figure 5e Image of the HD - LMC high - speed rotating robot performing in - situ high - speed rotation.

[0129] Figure 5f Relationship diagram between the current drive frequency and the rotation speed of the HD - LMC high - speed rotating robot, including experimental and theoretical results. From Figure 5f it can be seen that when the HD - LMC high - speed rotating robot rotates in - situ, the rotation speed is basically consistent with the drive frequency, and the experimental results are in good agreement with the simulation results.

[0130] Figure 5g Diagram of the maximum torque data generated by the HD - LMC high - speed rotating robot under different drive currents. From Figure 5g it can be seen that the greater the current, the stronger the driving force.

[0131] Figure 5h Movement diagrams of the HD - LMC high - speed rotating robot under excitation currents of different frequencies (2 Hz, 3 Hz, 4 Hz, and 5 Hz). From Figure 5h it can be seen that the higher the frequency of the excitation current, the faster the movement speed of this robot.

[0132] Figure 5i The displacement-time relationship diagram of the HD-LMC high-speed rotating robot under the exciting currents with different frequencies (2 Hz, 3 Hz, 4 Hz, and 5 Hz). From Figure 5i it can be seen that higher-frequency exciting currents will make the robot move faster.

[0133] Figure 5j The frequency-rotation speed curve diagram of the inductance waveform of the HD-LMC high-speed rotating robot. From Figure 5j it can be seen that the actual rotation speed can be monitored by monitoring the waveform frequency of the inductance, and the two match.

[0134] Figure 5k The inductance change rate-angle curve diagram of the HD-LMC high-speed rotating robot. From Figure 5k it can be seen that different angles of the HD-LMC high-speed rotating robot correspond to different inductance signals, so the perception of its own position can be realized.

[0135] The above are only specific embodiments of the present disclosure, enabling those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to these embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a flexible coil, characterized in that, The preparation method includes the following steps: Prepare an insulating polymer film; Prepare the sacrificial material into sacrificial wire; Wrap the insulating polymer film on the surface of the sacrificial wire; Form the sacrificial wire wrapped with the insulating polymer film into a preset coil shape to obtain a sacrificial coil; Encapsulate the sacrificial coil with a flexible matrix material and leave an opening to obtain an encapsulated sacrificial coil; Heat the encapsulated sacrificial coil to melt and remove the sacrificial wire, obtaining a flexible matrix with a cavity channel inside; Inject a conductive material into the cavity channel in the flexible matrix, connect leads at both ends and seal the opening to obtain the flexible coil.

2. The preparation method according to claim 1, characterized in that, The material of the insulating polymer film includes one or more of silicone rubber, polyimide, and polytetrafluoroethylene.

3. The preparation method according to claim 1, characterized in that, The step of preparing the insulating polymer film includes: applying an insulating polymer or a precursor of the insulating polymer on a substrate, forming a liquid film by spin coating, and forming an insulating polymer film after curing.

4. The preparation method according to claim 1, characterized in that, The melting point of the sacrificial material is lower than the melting temperature of the flexible matrix material.

5. The preparation method according to claim 1 or 4, characterized in that The sacrificial material includes one or more of metal alloy, paraffin, and polyvinyl alcohol.

6. The preparation method according to claim 5, characterized in that, The metal alloy includes Bi 32 In 51 Sn 17 .

7. The preparation method according to claim 1, wherein The step of preparing the sacrificial material into sacrificial wire includes: melting the sacrificial material and injecting it into a mold, and demolding after the sacrificial material solidifies to obtain the sacrificial wire.

8. The preparation method according to claim 1, wherein, The total thickness of the insulating polymer film wrapped on the surface of the sacrificial wire is 20 - 500 μm.

9. The preparation method according to claim 1, characterized in that, The flexible matrix material includes silicone rubber and / or epoxy resin.

10. The preparation method according to claim 1, characterized in that, The step of preparing the encapsulated sacrificial coil includes: placing the sacrificial coil in a mold, injecting a flexible matrix material or a precursor of the flexible matrix material into the mold to submerge the sacrificial coil, leaving an opening, and demolding after curing to obtain the encapsulated sacrificial coil.

11. The preparation method according to claim 1, characterized in that, The conductive material includes one or more of liquid metal, ionic liquid, and graphite.

12. The preparation method according to claim 11, characterized in that, The liquid metal includes eutectic gallium indium or gallium indium tin alloy.

13. A flexible coil, characterized in that, The flexible coil is prepared by the preparation method according to any one of claims 1 - 12.

14. Application of the flexible coil according to claim 13 in flexible electronic devices, flexible robots, medical devices, near - field communication devices, intelligent systems, and automation devices.

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