WO2023137615A1 - 一种具有负热膨胀性的拓扑绝缘器件 - Google Patents

一种具有负热膨胀性的拓扑绝缘器件 Download PDF

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WO2023137615A1
WO2023137615A1 PCT/CN2022/072679 CN2022072679W WO2023137615A1 WO 2023137615 A1 WO2023137615 A1 WO 2023137615A1 CN 2022072679 W CN2022072679 W CN 2022072679W WO 2023137615 A1 WO2023137615 A1 WO 2023137615A1
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thermal expansion
component
rod
rod segment
topological
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PCT/CN2022/072679
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English (en)
French (fr)
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李鹰
王栋
蒋超然
沈翔瀛
黄吉平
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浙江大学
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Priority to PCT/CN2022/072679 priority Critical patent/WO2023137615A1/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B17/00—Insulators or insulating bodies characterised by their form
    • H01B17/56—Insulating bodies
    • H01B17/60—Composite insulating bodies

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  • the invention belongs to the field of thermal functional devices, in particular to a topological insulation device with negative thermal expansion.
  • Metamaterials are a class of artificially designed structures that do not exist naturally in nature but are composed of natural materials. Typically, metamaterials are assembled from artificially designed building blocks that endow metamaterials with often counterintuitive physical properties that exceed those of the natural materials that make up the structure.
  • topological materials have attracted extensive attention due to their non-trivial topological properties induced by topological phase transitions.
  • the most typical and well-known example is a topological insulator.
  • a topological insulator is a material whose energy band structure is an insulator when electrons are inside, but whose surface contains a series of specific conductive states, which means that electrons can only move along the surface of the material, thus showing the singularity of internal insulation and surface conductivity.
  • topological materials Similar to metamaterials, the scope of topological materials has also been extended from naturally occurring topological insulator materials to electromagnetic and acoustic materials composed of artificial units, but the design and application of topological materials are still limited to wave systems.
  • the macroscopic heat transfer process its physical law is described by the diffusion equation rather than the wave equation, so it is generally believed that there is no topological property in the macroscopic heat transfer process.
  • an unconventional topological insulator can be realized in the macroscopic heat transfer process, it will provide new ideas and feasibility for further research on the topological properties of diffusion systems.
  • the purpose of the invention is to solve the defect that the macroscopic heat transfer process in the traditional device cannot realize the topological property, and provide a topological insulation device with negative thermal expansion.
  • the surface of the device has the ability to conduct heat, but the interior cannot conduct heat, thus realizing the edge state and topological protection properties similar to the electrical topological insulator in the macroscopic heat conduction process, thus providing new ideas and feasibility for further research on the topological properties of the diffusion system.
  • a topological insulating device with negative thermal expansion which includes a first assembly, a second assembly, a third assembly and a heat-insulating substrate, and the three assemblies are all composed of different numbers of assembly units;
  • Each of the component units is a zigzag structure formed by connecting the first rod segment, the second rod segment, the third rod segment and the fourth rod segment in sequence, and the four rod segments all have positive thermal expansion characteristics of heated elongation and have the same linear expansion coefficient; wherein one end of the first rod segment is a free end, the other end of the first rod segment is connected to one end of the second rod segment through a first joint point, the other end of the second rod segment is connected to one end of the third rod end through a second joint point, and the other end of the third rod end is connected to one end of the fourth rod end through a third joint point.
  • the other end of the fourth rod end is a free end; in the non-working state, the first rod segment and the second rod segment are mirror images of the third rod segment and the fourth rod segment respectively, and the free end of the first rod segment, the second connection point, and the free ends of the fourth rod segment are respectively located on three corner points of a square, and the first rod segment and the fourth rod segment are respectively located on two adjacent sides of the same square;
  • the first assembly is composed of four assembly units spliced into a centrally symmetrical structure, wherein the first rod section of any one assembly unit overlaps and is connected with the fourth rod section of an adjacent assembly unit as a negative thermal expansion section;
  • the second assembly is spliced into a mirror-symmetrical structure by two assembly units, wherein the first rod section of one assembly unit overlaps and is connected with the fourth rod section of an adjacent assembly unit as a negative thermal expansion section, and the unconnected first and fourth rod sections of the two assembly units are both used as positive thermal expansion sections;
  • the third assembly is composed of a single assembly unit, wherein both the first rod section and the fourth rod section serve as positive thermal expansion sections;
  • the three components are assembled on the substrate to form a thermal conduction outer ring and a thermal insulation area wrapped by the thermal conduction outer ring;
  • the thermal conduction outer ring is sequentially spliced into a ring by several second components and several third components, and the thermal insulation area is formed by a number of the first components arranged in a periodic array;
  • the second joint points of all components in the thermal conduction outer ring and the thermal insulation area are fixed on the substrate and cannot move, while the first joint point and the third joint point can move freely;
  • any two adjacent components are passed through The respective positive thermal expansion sections are butted collinearly or in parallel;
  • in the thermal insulation area any two adjacent first components are collinearly butted only through a respective negative thermal expansion section; and the first component located on the edge of the thermal insulation area and the components corresponding to the thermal conduction outer ring are also butted collinearly through a respective negative thermal expansion section;
  • a third assembly is provided at the corner position for connection, while the remaining straight sections are connected with the second assembly.
  • the surfaces of the first rod segment, the second rod segment, the third rod segment and the fourth rod segment are all conductive, and each rod segment will generate Joule heat after conduction; the substrate is non-conductive.
  • first rod segment, the second rod segment, the third rod segment and the fourth rod segment are all made of multi-layer composite material, and the composite material uses a thermal expansion material as a skeleton and wraps a conductive layer outside the skeleton.
  • thermal expansion material is nickel alloy, copper alloy or nylon.
  • the conductive layer is a graphene paint coated on the skeleton and/or a conductive tape wound on the skeleton.
  • the first component, the second component and the third component are all formed through integrated processing, and the first rod segment and the fourth rod segment in the negative thermal expansion segment are non-spliced integrated rod segments.
  • first component, the second component and the third component are all processed by 3D printing technology.
  • the distance between any two components connected collinearly through the negative thermal expansion section is controlled based on the temperature threshold.
  • the collinear connection of the two negative thermal expansion sections is in a thermal conduction state.
  • the two negative thermal expansion sections that were originally collinearly connected are separated and are in a thermal disconnection state.
  • the temperature threshold is room temperature.
  • the present invention has the following beneficial effects:
  • the present invention designs a topological insulation device based on the negative thermal expansion structure through the design idea of the negative thermal expansion structure.
  • this topological insulation device three components with different properties are constructed by using component units with special geometric structures, and then assembled by different components to form a thermal conduction outer ring and a thermal insulation area wrapped by the thermal conduction outer ring, so that the device has the characteristics of surface thermal conduction and internal thermal insulation, and realizes edge states and topological protection properties similar to electrical topological insulators in the macroscopic thermal conduction process.
  • the electrical topological insulation device further designed in the present invention combines the thermal expansion phenomenon with the thermal effect of the resistor body, realizes the topological edge state of heat flow and direct current, and reflects the unconventional properties of electrical insulation in the body and electrical conduction on the surface.
  • Fig. 1 is a structural schematic diagram of a component unit in a topological insulating device
  • Figure 2 is the structural diagram of different types of components and the schematic diagram of the thermal deformation effect; where (a) and (c) are the schematic diagrams of the first component and the second component respectively, and (b) and (d) are the schematic diagrams of the arrow-shaped structure and the deformation of the second component before and after heating.
  • Fig. 3 is the display diagram of the local results of the topological insulating device under the finite element simulation in the present invention
  • (a) is the schematic diagram of the local device simulation structure of the boundary position
  • (b) represents the expansion situation of the second component and the first component when heated, the hollow part is the original shape, the black part is the shape after deformation
  • (c) is the temperature distribution situation after the high temperature is applied to the surface and interior of the device
  • (d) is the stress distribution situation after the high temperature is applied to the surface and interior of the device.
  • Fig. 4 is the corresponding relation and result display figure of device structure of the present invention and SSH model; Wherein (a) is the corresponding relation of structure of the present invention and SSH model; (b) is the SSH model schematic diagram; (c) is the energy band structure of the corresponding SSH model full-period structure of the present invention; (d) is the energy band structure of the corresponding SSH model half-period structure of the present invention.
  • Fig. 5 is a schematic diagram of a topological insulating device sample designed in an example of the present invention.
  • Fig. 6 is a test effect diagram of a topological insulation device sample in an example of the present invention; wherein (a) is the temperature distribution presented by applying a heat source to the surface of the device; (b) is the temperature distribution presented by applying a heat source to the inside of the device.
  • first and second are only used for the purpose of distinction and description, and cannot be interpreted as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features.
  • the features defined as “first” and “second” may explicitly or implicitly include at least one of these features.
  • a topological insulation device with negative thermal expansion includes a first component, a second component, a third component, and a thermally insulated substrate, wherein the substrate is used as the installation basis for the three components, and there can be multiple first components, second components, and third components installed on the substrate, which are combined and spliced into corresponding device planar shapes.
  • the three types of components are composed of different numbers of component units, so the specific structure and principle of a single component unit will be described in detail below.
  • the positive thermal expansion mentioned in the present invention is the normal thermal expansion characteristic, which is characterized by the volume expansion of the material after being heated.
  • its macro performance is mainly the increase of the diameter of the rod segment and the elongation of the length.
  • the important use of the present invention is the thermal expansion property of the length elongation of the rod segment after being heated.
  • the negative thermal expansion mentioned in the present invention refers to that when the temperature changes, the change of the length of each rod section of the component unit will cause the geometric change of the structure of the whole component unit, which is manifested as a phenomenon that the volume or area of the whole unit is reduced by the movement of some positions to the center of the unit macroscopically, that is, the phenomenon of thermal contraction. This phenomenon of heat shrinkage is opposite to conventional thermal expansion, so it is called negative thermal expansion.
  • FIG. 1 it is a schematic diagram of the structure of a single assembly unit.
  • a single assembly unit is a broken-line structure formed by sequentially connecting the first section, the second section, the third section and the fourth section.
  • the four rod sections all have positive thermal expansion characteristics, the so-called positive thermal expansion characteristics are the normal thermal expansion characteristics that the length of the rod sections becomes longer after being heated.
  • the linear expansion coefficients of the four rod segments are the same, and the linear expansion coefficient refers to the corresponding elongation of the rod segment per unit length when the temperature rises by 1 degree Celsius.
  • one end of the first pole section is a free end; the other end of the first pole section is connected with one end of the second pole section, and the joint point is called the first joint point, so the other end of the first pole section is connected with one end of the second pole section through the first joint point; similarly, the other end of the second pole section is connected with one end of the third pole end, and the joint point is called the second joint point, so the other end of the second pole section is connected with one end of the third pole end through the second joint point; the other end of the third pole end is connected with one end of the fourth pole end Connection, this connection point is called the third connection point, so the other end of the third rod end is connected to one end of the fourth rod end through the third connection point; the other end of the fourth rod end is a free end.
  • the materials used for the four kinds of rod segments in the assembly unit in the present invention are not limited, as long as they have a certain linear expansion coefficient.
  • the larger the linear expansion coefficient of the rod segment the more sensitive the response. It can be considered to use materials with larger linear expansion coefficients such as alloys or composite materials to process different rod segments.
  • the material of the substrate in the present invention is not limited, as long as it has the property of heat insulation.
  • the initial state where the component unit is not heated is referred to as a non-operating state, and the initial state not heated may generally be a state when the component unit is at room temperature.
  • the first pole section and the second pole section are mirror images of the third pole section and the fourth pole section respectively, and the free ends of the first pole section, the second connection point, and the free ends of the fourth pole section are respectively located on three corner points of a square, while the first pole section and the fourth pole section are respectively located on two adjacent sides of the same square.
  • the angle between the first pole segment and the second pole segment is recorded as Then the angle between the third segment and the fourth segment is also Record the angle between the second segment and the third segment as but and satisfy At the same time, the lengths of the first section and the fourth section are both recorded as t 2 , and the lengths of the second section and the third section are both recorded as t 1 , then t 1 and t 2 satisfy
  • the first component Based on the single component unit shown in FIG. 1 above, three different components can be formed: the first component, the second component, and the third component.
  • the structures of these three components will be described in detail below.
  • the first component is spliced into a centrally symmetrical structure by four component units, where the small square dotted line box in the upper left corner shows a single component unit, while the overall large square dotted line box shows the first component spliced by four component units.
  • the included angle They all face the center point of the first assembly, and the first section of any assembly unit overlaps with the fourth section of the adjacent assembly unit and is connected as one, and the connected first section and fourth section form a negative thermal expansion section.
  • the entire first component finally presents a two-dimensional shape composed of a four-pointed star and four negative thermal expansion segments.
  • the four corners of the four-pointed star are located at the four corners of a square, and the four negative thermal expansion segments face four different directions.
  • the two-dimensional shape may also be referred to as a square-star structure in the present invention.
  • overlapping of two pole sections in the present invention may mean that the two pole sections fit side by side, or completely overlap in space, as long as the two pole sections of the same length can be connected into an integrated pole section that still maintains the same length.
  • the second component is spliced into a mirror-symmetrical structure by two component units, in which the first segment of one component unit overlaps and connects with the fourth segment of the adjacent component unit as a negative thermal expansion segment, while the unconnected first segment and fourth segment of the two component units both serve as positive thermal expansion segments.
  • the mirror symmetry plane of the second component is exactly the negative thermal expansion segment therein.
  • the third assembly is composed of a single assembly unit, that is, as shown in FIG. 1 , in which both the first rod segment and the fourth rod segment serve as positive thermal expansion segments.
  • the so-called negative thermal expansion section in the present invention refers to the functional rod section that exhibits the aforementioned "negative thermal expansion”, that is, the negative thermal expansion section of the entire device will move toward the center of the component when it is heated, thereby causing the area or volume of the component to decrease, showing the macroscopic characteristics of thermal contraction.
  • the so-called positive thermal expansion section in the present invention refers to the functional rod section that exhibits the aforementioned "positive thermal expansion”, that is, the positive thermal expansion section of the entire device will be far away from the center of the component when it is heated, resulting in an increase in the area or volume of the component, showing the macroscopic characteristics of thermal expansion.
  • the local structure shown by the solid line rectangle on the right side in Fig. 2(a) is regarded as an arrow-shaped structure, and the effective thermal expansion coefficient is derived based on the arrow-shaped structure.
  • the maximum span of the arrow-shaped structure is recorded as the side length L, and the angle ⁇ ADB of the square-star structure is set to ⁇ , and the influence of the thickness of the arrow-shaped structure is ignored to simplify the derivation.
  • the deformation of the geometry of the arrow-shaped structure is shown before and after the temperature is increased.
  • ⁇ is the linear expansion coefficient of the rod section
  • ⁇ T is the increase in temperature
  • L original is the original size of the solid material without expansion
  • ⁇ L is the elongation of the material when the temperature change is ⁇ T.
  • the rod segment CG and the rod segment DM can freely expand along the direction of the rod segment when points C and D are restricted by fixed constraints, point G moves to the position of point H, and point M also moves symmetrically, both of which show positive thermal expansion.
  • rod segment GI and rod segment MN also exhibit positive thermal expansion, point I moves to point J, and point N also moves symmetrically.
  • the midpoints I and II of the structure in Figure 2(c) will expand freely along the x-axis direction when the temperature rises, so the structure will show normal thermal expansion characteristics in the x-direction, so the rod segment GI and rod segment MN are both positive thermal expansion segments.
  • rod segment CE and rod segment DE will jointly push rod segment AB to move upward in the y-axis direction after being heated.
  • Point A moves to point E
  • point B moves to point F. Therefore, the local structure will exhibit abnormal negative thermal expansion in the y direction
  • rod segment AB is a negative thermal expansion segment.
  • the third component does not have the special spatial geometric constraints of the first component and the second component, so both free ends exhibit positive thermal expansion, and the third component only has a positive thermal expansion section.
  • the three different components, the first component, the second component, and the third component have different thermal expansion characteristics, so they can be used for assembly on a substrate to form corresponding topological insulating devices.
  • the topological insulation device utilizes negative thermal expansion, and through the special design of the structure, the surface of the device has thermal conductivity, but the interior cannot conduct heat, that is, it meets the surface thermal conduction and the internal thermal insulation, thereby achieving edge states and topological protection properties similar to electrical topological insulators in the macroscopic heat conduction process.
  • the assembly form of the three components of the topological insulating device is described below:
  • the three components are assembled on the substrate to form two different types of areas, one is the thermal conduction outer ring, and the other is the thermal insulation area wrapped by the thermal conduction outer ring.
  • the outer ring of thermal conduction is equivalent to the surface of the device, while the thermally insulating region is equivalent to the interior of the device.
  • the thermal conduction outer ring is sequentially spliced into a ring by several second assemblies and several third assemblies, and the thermal insulation area is formed by several first assemblies arranged in a periodic array.
  • the specific numbers of the first component, the second component and the third component can be determined according to the actual surface shape of the device, which is not limited.
  • the second joint points of all components in the thermal conduction outer ring and thermal insulation area are fixed on the substrate and cannot move, while the first joint point and the third joint point can move freely, so as to meet the space constraints of the joint points required by each negative thermal expansion section and positive thermal expansion section.
  • the thermal conduction outer ring and the thermal insulation region also need to meet the constraints of the rod segment connection state, that is, in the thermal conduction outer ring, any two adjacent components are collinearly or parallel-connected through their respective positive thermal expansion segments; while in the thermal insulation region, any two adjacent first components are collinearly connected only through their respective negative thermal expansion segments; The components at the corresponding positions of the thermal conduction outer ring are also collinearly connected through a respective negative thermal expansion section.
  • collinear butt joint means that two rod segments are on the same straight line and their ends are butted and contacted to form thermal conduction, while parallel butt joint means that the two rod segments overlap.
  • parallel butt joint means that the two rod segments overlap.
  • the two adjacent components in the thermal conduction outer ring may be that the second component is adjacent to the third component, or that the second component is adjacent to the second component, or that the third component is adjacent to the third component.
  • any two adjacent components are collinear or parallel butted through their respective positive thermal expansion sections.
  • the specific collinear butt or parallel butt connection depends on the actual component form. Generally speaking, collinear butt joints are used for non-corner positions, while collinear butt joints may be used for corner positions, or parallel butt joints may be used.
  • the thermal conduction outer ring of the topological insulation device is a regular rectangle
  • the corner of the thermal conduction outer ring is connected by a third component
  • the remaining straight sections are connected by the second component
  • any two adjacent components in the entire thermal conduction outer ring are collinearly connected through their respective positive thermal expansion sections.
  • the thermal conduction outer ring of the topological insulation device is not a regular rectangle, but a special-shaped polygon with negative corners
  • the corner position of the thermal conduction outer ring is connected by the second component or the third component, and the rest of the straight lines are connected by the second component.
  • the two adjacent components in the corner position of the entire thermal conduction outer ring are collinearly or parallelly connected through their respective positive thermal expansion sections.
  • the characteristic verification of the topological insulating device is carried out through finite element simulation.
  • Fig. 3 the simulation results of partial surface positions and internal regions in the whole topological insulating device are shown.
  • Figure 3(a) the second connection points of all component units in the entire device are fixed by adiabatic anchor points, and the surface of the device is used to simulate the interface formed between the device and the external vacuum, showing the second component with five positive thermal expansion segments collinearly connected, but not showing the third component at the corner, while the internal area of the device shows the first component arranged in a 5 ⁇ 4 rectangular array.
  • the positive thermal expansion section of the second component that was originally collinearly connected remains in the butt-conduction state, so heat can be conducted on the surface unit of the device, but the negative thermal expansion section of the second component is heated and shrinks toward the center of the second component, and is out of contact with the negative thermal expansion section of the first component, forming a thermal disconnection state, causing the heat on the surface of the device to be unable to conduct internally;
  • the negative thermal expansion sections of the strips are heated and shrink toward the center of the first component, thereby breaking away from the negative thermal expansion sections of the surrounding first components, and the heat input thereby will be localized to the first component itself to which the temperature is applied, forming a thermal insulation effect.
  • topological insulating device of the present invention so that the structurally complete first component terminates at the device surface and is replaced by the structurally incomplete second or third component.
  • Such topological insulating devices can be compared to crystals, where the first component is an ideal complete unit cell, while the second and third components are defective unit cells.
  • Figure 3(a) due to the sudden termination of the periodicity of the lattice on the surface, the surface structure expands in the x-axis direction due to the increase in temperature, making the adjacent units on the surface contact each other, so it is in a thermal conduction state.
  • the periodic arrangement of unit cells makes all unit cell structures in a state of negative thermal expansion. This will cause any cell to thermally shrink in size when a high temperature source is applied to it, thereby breaking contact with adjacent cells.
  • the temperature will not diffuse inside, that is, the inside of the crystal is insulating for heat conduction, and the structure with this property is called a topological insulator based on a negative thermal expansion structure in the present invention.
  • the Su-Schrieffer-Heeger (SSH) model is used to explain the non-trivial topology in this two-dimensional structured system.
  • Figure 4(a) shows the corresponding relationship between different combinations of component units and the SSH model, where the component unit shown in i can be regarded as an “atom”, and the new unit structure shown in iv can be obtained by combining it through four 90° rotations.
  • the structures shown in ii and iii show the atomic bond strengths in the unit and between the units, respectively. It should be noted that the unit in the present invention is slightly different from the typical SSH model used to describe the two-dimensional lattice.
  • the bond strength between adjacent "atoms” in the corresponding unit will vary depending on whether the "atoms" are at the bulk boundary. As shown in Figure 4(b), the bond strength when the adjacent "atoms" in the unit are all located at the boundary is w 1 , and the bond strength when it is not at the boundary is w 2 , while in the structure, the bond strength between adjacent "atoms" in different units is uniformly set to v.
  • a, b, c, and d represent the four adjacent "atoms" in the unit, and i and j represent the unit located in the i-th row and j-th column in the entire structure, the symbol is "Dagger", which means the conjugate transpose operation, and hc means the contribution of the external field to the model Hamiltonian.
  • the first term can be written as:
  • k represents the wave vector in the SSH model
  • k x and ky represent the components of the wave vector in the x and y directions
  • the corresponding energy band can be calculated using Matlab software.
  • the calculated energy band diagram is shown in Fig. 4(c).
  • the semi-periodic crystal energy band diagram can be obtained by using the same algorithm as the crystal with completely periodic boundary conditions, as shown in Fig. 4(d). This result shows that boundary states appear in the energy band, and two edge state energy levels that do not appear in the full-cycle case appear in the figure.
  • the above-mentioned topological insulation device with negative thermal expansion has the thermal topological insulation characteristic of thermal conduction on the surface and thermal insulation inside, and the conduction and insulation characteristics are relative to heat.
  • the above-mentioned topological insulating device with respect to heat can be converted into an electrical topological insulating device.
  • This electrical topological insulation device also has the thermal topological insulation characteristic of surface thermal conduction and internal thermal insulation, and also has electrical topological insulation characteristics, that is, the surface of the device is conductive and the internal electrical insulation.
  • the structural form of this electrical topological insulation device is basically the same as the aforementioned topological insulation device, only need to adjust the material of the first rod segment, the second rod segment, the third rod segment and the fourth rod segment.
  • the surfaces of the first rod segment, the second rod segment, the third rod segment and the fourth rod segment are all conductive, and after conduction, each rod segment will generate Joule heat.
  • the Joule heat generated by the thermal effect of the current is used, and the Joule heat generated by the current will cause the geometry of the structure to respond now, thereby realizing the thermal topological insulation characteristics, and at the same time generating the electrical topological insulation characteristics in a chain.
  • the temperature increase caused by Joule heat will allow the current to be easily transferred on the surface of the device and exhibit an insulating state in the device body. Therefore, the present invention can couple temperature and direct current together, because they will have the same effect on the topological insulation characteristics of the device.
  • the materials used in the first rod segment, the second rod segment, the third rod segment and the fourth rod segment should be electrically conductive on the surface, and should have sufficient linear expansion coefficient at the same time, and whether the inside of the rod segment is conductive or not is not limited.
  • the first rod segment, the second rod segment, the third rod segment and the fourth rod segment are all made of multi-layer composite material, wherein the composite material uses a thermal expansion material as a skeleton and wraps a conductive layer outside the skeleton.
  • the thermal expansion material and the material of the conductive layer are not limited.
  • the thermal expansion material can be nickel alloy, copper alloy or nylon, etc., preferably nylon with a larger linear expansion coefficient.
  • the conductive layer on the surface of the skeleton is a graphene coating coated on the skeleton, or a conductive tape wound on the skeleton, or a combination of graphene coating and conductive tape, that is, spray a layer of graphene coating first, and then wrap the conductive tape outside.
  • the first component, the second component and the third component are described in the form of combinations of different component units, this is only for the convenience of description, and it does not limit that the corresponding components must first process independent component units and then assemble the component units into corresponding components.
  • the first component, the second component and the third component can all be formed through integrated processing, in which case the first rod segment and the fourth rod segment in the negative thermal expansion segment are non-spliced integrated rod segments.
  • the first component, the second component and the third component are all preferably processed by 3D printing technology.
  • first component, the second component and the third component may also adopt the method of first processing independent component units and then assembling the component units, which is not limited.
  • thermal topological insulation properties and electrical topological insulation properties of the above-mentioned electrical topological insulation device of the present invention will be verified through experiments in specific examples in combination with the aforementioned theoretical derivation and finite element simulation results.
  • the material of the rod segment required by the present invention is required to have a high thermal expansion rate, and at the same time, the material used to prepare the rod segment must also be electrically conductive due to the need to utilize the Joule heating effect.
  • materials with higher thermal expansion coefficients such as various high molecular polymers, are usually insulating.
  • nylon is selected as the skeleton material, and the thermal expansion coefficient of nylon is an order of magnitude larger than that of copper alloys with larger expansion coefficients in metals.
  • nylon materials are not suitable for processing by ordinary machining methods, but thanks to the vigorous development of 3D printing technology in recent years, a large number of nylon material skeletons can be obtained relatively easily. Further, in order to solve the non-conductive problem of the nylon material, the nylon skeleton is sprayed with a graphene coating.
  • a first internal component was selected and a current of 1A was applied to it, and the temperature diffusion was observed.
  • the results are shown in Fig. 6(b). It can be found that the temperature of the first component to which the current is applied increases significantly, but the temperature and current do not spread to the adjacent first component, but are localized on the first component.
  • thermomechanical superstructured topological insulator of the present invention has related properties similar to that of the electrical topological insulator.
  • the above-mentioned topological insulation devices can be set with corresponding operating temperatures according to actual application scenarios.
  • the working temperature is equivalent to a temperature threshold.
  • the temperature threshold can be set at room temperature, so that the device has the property of thermal topological insulation as long as it is manufactured, and can be used in industry to realize thermal insulation protection for heat-sensitive devices.
  • the electrical topological insulation device in the present invention has the advantages of reconfigurability and controllable local conduction, and can provide a unified integrated solution for industrially variable circuit layouts

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Abstract

提供了一种具有负热膨胀性的拓扑绝缘器件，属于热功能器件领域。在拓扑绝缘器件中，利用特殊几何结构的组件单元构建了三种不同性质的组件，进而由不同的组件组装形成热导通外环和由热导通外环包裹的热绝缘区域，从而使器件具有表面热导通而内部热绝缘的特性，在宏观热传导过程中实现与电学拓扑绝缘体相类似的边缘态和拓扑保护性质。

Description

一种具有负热膨胀性的拓扑绝缘器件 技术领域
本发明属于热功能器件领域，具体涉及一种具有负热膨胀性的拓扑绝缘器件。
背景技术
超构材料是一类并不在自然界天然存在，但是由天然材料构成的经过人为设计的结构。通常，超构材料是由经过人为设计的基础单元组合而成，这些基础单元使超构材料通常具有超出构成结构的天然材料性质的、反直觉的物理性质。
近年来，拓扑材料由于其具有拓扑相变导致的非平凡的拓扑性质，引发了人们的广泛专注。最典型和广为人知的例子就是拓扑绝缘体，拓扑绝缘体是一种电子在其内部时，能带结构为绝缘体，但其表面包含一系列特定的导电态的材料，这意味着电子只能沿着该材料的表面移动，从而呈现出内部绝缘，表面导电的奇异性质。
与超构材料相类似，拓扑材料的范围也已经从天然存在的拓扑绝缘体材料拓展到由人造单元构成的电磁和声学材料，但拓扑材料的设计和应用仍然局限在波动系统中。对于宏观热传递过程，其物理规律由扩散方程而非波动方程来描述，因此一般认为在宏观热传递过程中是不存在拓扑性质的。但是如果能够在宏观热传递过程中实现一种非常规的拓扑绝缘体，将为进一步研究扩散系统的拓扑性质提供新思路和可行性。
发明内容
本发明的目的在于解决传统器件中宏观热传递过程无法实现拓扑性质的缺陷，并提供一种具有负热膨胀性的拓扑绝缘器件。该拓扑绝缘器件通过特殊的结构设计，使器件表面具有热传导能力，但内部无法传导热量，由此在宏观热传导过程中实现与电学拓扑绝缘体相类似的边缘态和拓扑保护性质，从而为进一步研究扩散系统的拓扑性质提供新思路和可行性。
为实现上述发明目的，本发明拟采用的具体技术方案如下：
一种具有负热膨胀性的拓扑绝缘器件，其包括第一组件、第二组件、第三组 件以及隔热的基板，三种组件均由不同数量的组件单元构成；
每个所述组件单元为由第一杆段、第二杆段、第三杆段和第四杆段顺序连接而成的折线形结构，四条杆段均具有受热伸长的正热膨胀特性且线性膨胀系数相同；其中第一杆段的一端为自由端，第一杆段的另一端与第二杆段的一端通过第一联结点连接，第二杆段的另一端与第三杆端的一端通过第二联结点连接，第三杆端的另一端与第四杆端的一端通过第三联结点连接，第四杆端的另一端为自由端；在非工作状态下，第一杆段、第二杆段分别与第三杆段和第四杆段镜像对称，且第一杆段的自由端、第二联结点、第四杆段的自由端分别位于一个正方形的三个角点上，而第一杆段和第四杆段分别位于同一正方形的两条邻边上；
所述第一组件由四个组件单元拼接成中心对称结构，其中任意一个组件单元的第一杆段与相邻组件单元的第四杆段重合并联结为一体，作为负热膨胀段；
所述第二组件由两个组件单元拼接成镜像对称结构，其中一个组件单元的第一杆段与相邻组件单元的第四杆段重合并联结为一体，作为负热膨胀段，两个组件单元中未联结的第一杆段和第四杆段均作为正热膨胀段；
所述第三组件由单个组件单元组成，其中的第一杆段和第四杆段均作为正热膨胀段；
三种组件在所述基板上组装形成热导通外环和由热导通外环包裹的热绝缘区域；所述热导通外环由若干第二组件和若干第三组件顺次拼接成环形，所述热绝缘区域由若干所述第一组件呈周期性阵列形式排布而成；热导通外环和热绝缘区域中所有组件的第二联结点均在基板上位置固定无法移动，而第一联结点和第三联结点均能够自由移动；所述热导通外环中，任意两个相邻组件之间均通过各自的正热膨胀段共线对接或者并线对接；所述热绝缘区域中，任意两个相邻第一组件之间的仅通过各自的一条负热膨胀段共线对接；且位于热绝缘区域边缘的第一组件与所述热导通外环对应位置的组件也通过各自的一条负热膨胀段共线对接；
作为优选，所述热导通外环中，拐角位置设置第三组件进行连接，而其余直线段均采用第二组件进行连接。
作为优选，所述第一杆段、第二杆段、第三杆段和第四杆段的表面均导电，且导电后各杆段均会产生焦耳热；所述基板不导电。
进一步的，所述第一杆段、第二杆段、第三杆段和第四杆段均采用多层复合材料，所述复合材料以热膨胀材料为骨架，并在骨架外部包裹导电层。
进一步的，所述热膨胀材料为镍合金、铜合金或尼龙。
进一步的，所述导电层为涂覆在骨架上的石墨烯涂料和/或缠绕在骨架上的导电胶带。
作为优选，所述第一组件、第二组件和第三组件均通过一体化加工成型，所述负热膨胀段中的第一杆段和第四杆段为非拼接的一体化杆段。
进一步的，所述第一组件、第二组件和第三组件均采用3D打印工艺加工而成。
作为优选，所述热导通外环和热绝缘区域中，任意两个通过负热膨胀段共线对接的组件之间的间距均基于温度阈值进行导通控制，当两个组件的自身温度不高于所述温度阈值时，两条负热膨胀段共线对接处于热导通状态，当两个组件的自身温度高于所述温度阈值时，原本共线对接的两条负热膨胀段脱离处于热断开状态。
进一步的，所述温度阈值为室温。
本发明相对于现有技术而言，具有以下有益效果：
本发明通过负热膨胀结构的设计思路，设计了一种基于负热膨胀结构的拓扑绝缘器件。在该拓扑绝缘器件中，利用特殊几何结构的组件单元构建了三种不同性质的组件，进而由不同的组件组装形成热导通外环和由热导通外环包裹的热绝缘区域，从而使器件具有表面热导通而内部热绝缘的特性，在宏观热传导过程中实现与电学拓扑绝缘体相类似的边缘态和拓扑保护性质。另外，本发明中进一步设计的电学拓扑绝缘器件将热膨胀现象与电阻体的热效应相结合，实现了热流和直流电的拓扑边缘状态，体现出体内电绝缘，表面电导通的非常规性质。
附图说明
图1为拓扑绝缘器件中的组件单元结构示意图；
图2为不同类型组件的结构图与受热形变效果示意图；其中(a)、(c)分别为第一组件和第二组件的示意图，(b)、(d)分别为箭型结构和第二组件在受热前后形变的示意图。
图3为本发明中的有限元模拟下的拓扑绝缘器件局部结果展示图；其中(a) 为边界位置的局部器件模拟结构示意图；(b)表示第二组件和第一组件在受热时的膨胀情况，空心部分为原始形状，黑色部分为形变后的形状，(c)为对器件表面和内部施加高温后的温度分布情况，(d)为对器件表面和内部施加高温后的应力分布情况。
图4为本发明的器件结构与SSH模型的对应关系和结果展示图；其中(a)为本发明的结构与SSH模型的对应关系；(b)为SSH模型示意图；(c)为本发明所对应的SSH模型全周期结构的能带结构；(d)为本发明所对应的SSH模型半周期结构的能带结构。
图5本发明中的一个实例设计的拓扑绝缘器件样品示意图。
图6为本发明中的一个实例中拓扑绝缘器件样品的测试效果图；其中(a)为对器件表面施加热源所呈现的温度分布；(b)为对器件内部施加热源所呈现的温度分布。
具体实施方式
为使本发明的上述目的、特征和优点能够更加明显易懂，下面结合附图对本发明的具体实施方式做详细的说明。在下面的描述中阐述了很多具体细节以便于充分理解本发明。但是本发明能够以很多不同于在此描述的其它方式来实施，本领域技术人员可以在不违背本发明内涵的情况下做类似改进，因此本发明不受下面公开的具体实施例的限制。本发明各个实施例中的技术特征在没有相互冲突的前提下，均可进行相应组合。
在本发明的描述中，需要理解的是，术语“第一”、“第二”仅用于区分描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括至少一个该特征。
在本发明的一个较佳实施例中，提供了一种具有负热膨胀性的拓扑绝缘器件，组成该拓扑绝缘器件的核心部件包括第一组件、第二组件、第三组件以及隔热的基板，其中基板作为三种组件的安装基础，而基板上安装的第一组件、第二组件、第三组件均可以具有多个，组合拼接成相应的器件平面形状。
在本发明中，三种组件均由不同数量的组件单元构成，因此下面先对单个组件单元的具体结构和原理进行详细描述。
需要说明的是，本发明中所说的正热膨胀性即正常的热膨胀特性，表现为材料受热后体积膨胀的特点。对于杆件而言，其宏观表现主要为杆段直径的增大以及长度的伸长，本发明重要用到的是杆段受热后长度伸长的热膨胀性质。而本发明中所说的负热膨胀性，是指在温度发生变化时，组件单元的各杆段长度改变会导致整个组件单元的结构发生几何变化，在宏观上表现为部分位置向单元中心移动导致整个单元的体积或面积减小，即发送受热收缩的现象。这种受热收缩的现象，与常规的热膨胀性相反，因此称为负热膨胀性。
如图1所示，为单个组件单元拼的结构示意图，单个组件单元为由第一杆段、第二杆段、第三杆段和第四杆段顺序连接而成的折线形结构。而且四条杆段均具有正热膨胀特性，所谓正热膨胀特性即杆段受热后长度会变长的正常热膨胀特性。另外，四条杆段的线性膨胀系数相同，线性膨胀系数是指单位长度的杆段在温度每升高1摄氏度时对应的伸长量。其中，第一杆段的一端为自由端；第一杆段的另一端与第二杆段的一端联结，将该联结点称为第一联结点，因此第一杆段的另一端与第二杆段的一端通过第一联结点连接；同样的，第二杆段的另一端与第三杆端的一端联结，将该联结点称为第二联结点，因此第二杆段的另一端与第三杆端的一端通过第二联结点连接；第三杆端的另一端与第四杆端的一端联结，将该联结点称为第三联结点，因此第三杆端的另一端与第四杆端的一端通过第三联结点连接；第四杆端的另一端为自由端。
需要说明的是，本发明中组件单元中的四种杆段，其具体所用的材质不限，只要具有一定的线性膨胀系数即可。总体而言，杆段的线性膨胀系数越大其反应越灵敏，可考虑采用合金或者复合材料等具有较大线性膨胀系数的材质来加工制成不同的杆段。
另外，需要说明的是，本发明中的基板材质不限，只要具有隔热的特性即可。
为了便于描述，将组件单元处于不受热的初始状态称为非工作状态，而该不受热的初始状态一般可以是组件单元处于室温时的状态。
继续参见图1所示，在非工作状态下，第一杆段、第二杆段分别与第三杆段和第四杆段镜像对称，且第一杆段的自由端、第二联结点、第四杆段的自由端分别位于一个正方形的三个角点上，而第一杆段和第四杆段分别位于同一正方形的两条邻边上。因此，根据几何关系可知，将第一杆段和第二杆段的夹角记为
Figure PCTCN2022072679-appb-000001
则第三杆段和第四杆段的夹角也为
Figure PCTCN2022072679-appb-000002
将第二杆段与第三杆段的夹角记为
Figure PCTCN2022072679-appb-000003
则
Figure PCTCN2022072679-appb-000004
和
Figure PCTCN2022072679-appb-000005
满足
Figure PCTCN2022072679-appb-000006
同时，将第一杆段和第四杆段的长度均记为t 2，第二杆段和第三杆段的长度均记为t 1，则t 1和t 2满足
Figure PCTCN2022072679-appb-000007
基于上述图1所示的单个组件单元，可以组成第一组件、第二组件、第三组件三种不同的组件，下面分别对这三种组件的结构进行详细描述。
如图2(a)所示，第一组件由四个组件单元拼接成中心对称结构，其中左上角的小正方形虚线框示出的是单个组件单元，而整体的大正方形虚线框示出的是四个组件单元拼接成的第一组件。其中，四个组件单元在拼接时，其夹角
Figure PCTCN2022072679-appb-000008
均朝向第一组件的中心点，且任意一个组件单元的第一杆段与相邻组件单元的第四杆段重合并联结为一体，而联结为一体的第一杆段和第四杆段则组成了一条负热膨胀段。整个第一组件最终呈现出一个四角星型和四条负热膨胀段组成的二维形状，四角星型的四个角点位于一个正方形的四个角点位置，而四条负热膨胀段分别朝向四个不同的方向。为了便于叙述，本发明中亦可将该二维形状称为正方形-星型结构。
需要说明的是，本发明中两条杆段重合，可以是指两条杆段并排贴合，或者在空间上完全重合，只要能够使两条相同长度的杆段联结为与依然保持相同长度的一体化杆段即可。
如图2(c)所示，第二组件由两个组件单元拼接成镜像对称结构，其中一个组件单元的第一杆段与相邻组件单元的第四杆段重合并联结为一体，作为负热膨胀段，而两个组件单元中未联结的第一杆段和第四杆段均作为正热膨胀段。第二组件的镜像对称面正是其中的负热膨胀段。
而第三组件由单个组件单元组成，即如图1所示，其中的第一杆段和第四杆段均作为正热膨胀段。
需要说明的是，本发明中所谓的负热膨胀段，是指实现表现出前述“负热膨胀性”的功能杆段，即整个器件在受热时负热膨胀段会向所在组件的中心，从而导致所在组件的面积或体积减小，呈现受热收缩的宏观特性。另外，本发明中所谓的正热膨胀段，是指表现出前述“正热膨胀性”的功能杆段，即整个器件在受热时正热膨胀段会远离所在组件的中心，从而导致所在组件的面积或体积增大，呈现受热膨胀的宏观特性。
下面，对上述负热膨胀段和正热膨胀段的具体原理进行展开描述，以便于理解其本质。
如图2(a)所示，由于本发明中的所有杆段都具有一定的线性膨胀系数，杆段受热后长度会变长，单一杆段表现为正常的热膨胀特性。但是在第一组件中，各杆段之间是相互联结的，在特定的几何关系下，杆段的膨胀会导致的整个组件结构发生旋转或弯曲，进而表现出局部的负热膨胀性。具体而言，对于图2(a)所示的第一组件，如果限制该第一组件的四个第二联结点(图中分别标记为点1,2,3和4)被固定，即四个角在温度发生变化时在基板上均不会发生任何位移。满足上述固定约束条件后，将第一组件视为是一个整体结构，下面即可类比普通材料的热膨胀系数，推导出该第一组件的有效热膨胀系数。
推导过程中，将图2(a)中右侧的实线矩形框示出的局部结构视为一个箭型结构，以该箭型结构为基础来推导有效热膨胀系数。如图2(b)所示，将箭型结构的最大跨度记为边长L，同时将正方形-星型结构的角∠ADB设为θ，并且忽略箭型结构的厚度影响以简化推导。在图2(b)中，展示了当温度升高前后，箭型结构的几何形状所发生的形变。由于点C和D在空间上被锁定，则杆段AC和杆段AD无法自由地沿着原本的方向伸长，只能共同迫使点A向左位移至E点以释放由温度升高所产生的伸长量。由此，杆段AB的长度会变为L BF：
Figure PCTCN2022072679-appb-000009
式中，α是杆段的线性膨胀系数，ΔT是温度的增加量。
同时，由于点E在杆段CE和DE的对称作用下向左平移，因此箭型结构的顶点与底边缘之间的距离由L AB变为L EB。L EB的表达式应该为：
Figure PCTCN2022072679-appb-000010
由此可以得知点B在温度升高时，向左侧平移的距离为L BF：
Figure PCTCN2022072679-appb-000011
根据材料热膨胀系数的定义：
Figure PCTCN2022072679-appb-000012
式中：L original是固体材料在没有发生膨胀时的原始尺寸，ΔL是材料在温度变化量为ΔT时的伸长量。
由此，根据前述公式(4)给出的材料热膨胀系数的定义，可以得出箭型结构的等效热膨胀系数为：
α′＝-α·cot 2θ   (5)
这说明该箭型结构在温度升高时，对外表现出负热膨胀性质，即对于第一组件而言当温度升高时其中的负热膨胀段会向组件中心移动，表现为受热收缩现象。
同理，对于如图2(c)所示的第二组件，其相对于第一组件而言存在部分结构缺失。这种情况下，如图2(d)所示，由于上半部分两个组件单元缺失，仅由剩余两个组件单元构成了第二组件，导致点G和点N失去原来由上半部分结构在y方向上所提供的应力。当第二组件受热时，如图2(c)所示的构将发生形变，图2(d)中展示了形变前后的几何形状。图中可见，杆段CG和杆段DM在点C和D受到固定约束条件限制的情况下，可以自由沿着杆段自身方向自由膨胀，点G移动至点H位置，而点M也对称移动，两者均表现为正热膨胀性。同样的，杆段GI和杆段MN也表现出正热膨胀性，点I移动至点J位置，点N也对称移动。图2(c)的结构中点I和II在温度上升时将沿着x轴方向自由膨胀，因此该结构在x方向上会表现出正常的热膨胀特性，因此杆段GI和杆段MN均为正热膨胀段。与第一组件类似，由于点3和4的依旧维持着对称的固定约束条件，因此杆段CE和杆段DE受热后会共同推动杆段AB在y轴方向上向上移动，是点A移动至点E位置，点B移动至点F位置，因此该局部结构在y方向上会表现出反常的负热膨胀性，杆段AB为负热膨胀段。
另外对于第三组件而言，其不具备第一组件和第二组件中特殊的空间几何约束，因此两个自由端均表现出正热膨胀性，第三组件仅具有正热膨胀段。
综上，第一组件、第二组件、第三组件这三种不同的组件具有不同的热膨胀特性，因此可用于在基板上进行组装，形成相应的拓扑绝缘器件。该拓扑绝缘器件利用了负热膨胀性，通过结构的特殊设计，使器件表面具有热传导能力，但内部无法传导热量，即满足表面热导通而内部热绝缘，由此在宏观热传导过程中实现与电学拓扑绝缘体相类似的边缘态和拓扑保护性质。下面对该拓扑绝缘器件种三种组件的组装形式进行展开描述：
三种组件在基板上组装形成两类不同的区域，其一是热导通外环，其二是由热导通外环包裹的热绝缘区域。对于拓扑绝缘器件而言，热导通外环相当于器件 表面，而热绝缘区域则相当于器件内部。热导通外环由若干第二组件和若干第三组件顺次拼接成环形，而热绝缘区域由若干第一组件呈周期性阵列形式排布而成。第一组件、第二组件和第三组件的具体数量均可以根据实际的器件表面形状进行确定，对此不作限定。如前所述，为了实现部分组件的负热膨胀性，热导通外环和热绝缘区域中所有组件的第二联结点均在基板上位置固定无法移动，而第一联结点和第三联结点均能够自由移动，以此满足各负热膨胀段和正热膨胀段所需的联结点空间约束。另外，除了上述联结点的空间约束之外，为了实现拓扑绝缘器件表面热导通内部热绝缘的热学拓扑绝缘特性，热导通外环和热绝缘区域还需要满足杆段连接状态约束，即满足：在热导通外环中，任意两个相邻组件之间均通过各自的正热膨胀段共线对接或者并线对接；而在热绝缘区域中，任意两个相邻第一组件之间的仅通过各自的一条负热膨胀段共线对接；且位于热绝缘区域边缘的第一组件与所述热导通外环对应位置的组件也通过各自的一条负热膨胀段共线对接。
需要说明的是，本发明中所说的共线对接是指两条杆段处于同一直线上其端部对接接触形成热导通，而并线对接则是指两条杆段重合。此处重合的定义如前所述，不再赘述。
在上述杆段连接状态约束中，热导通外环中两个相邻组件可能是第二组件与第三组件相邻，也可能是第二组件与第二组件相邻，也可能是第三组件与第三组件相邻。但不论是哪种相邻情况，任意两个相邻组件之间均通过各自的正热膨胀段共线对接或者并线对接，具体采用共线对接还是并线对接需要根据实际的组件形式而定。一般而言，非拐角位置都采用共线对接，而拐角位置可能采用共线对接，也可能采用并线对接。
在本发明中，如果拓扑绝缘器件的热导通外环是规则的矩形，那么该热导通外环的拐角位置设置第三组件进行连接，而其余直线段均采用第二组件进行连接，整个热导通外环中任意两个相邻组件之间均通过各自的正热膨胀段共线对接。但是如果拓扑绝缘器件的热导通外环不是规则的矩形，而是存在阴角的异形多边形，那么该热导通外环的拐角位置设置第二组件或者第三组件进行连接，而其余直线段均采用第二组件进行连接，整个热导通外环中拐角位置两个相邻组件之间均通过各自的正热膨胀段共线对接或者并线对接，具体以可实现的对接形式而定，但 是非拐角位置都采用共线对接。
为了验证本发明中拓扑绝缘器件表面热导通内部热绝缘的热学拓扑绝缘特性，通过有限元模拟对拓扑绝缘器件进行了特性验证。如图3所示，展示了整个拓扑绝缘器件中部分表面位置和内部区域的模拟结果。如图3(a)所示，整个器件中所有组件单元的第二联结点被绝热锚点所固定，器件的表面用以模拟器件与外部真空形成的界面，示出了5个正热膨胀段共线对接的第二组件，但未示出拐角的第三组件，而器件的内部区域示出了5×4个矩形阵列排布的第一组件。通过有限元模拟软件COMSOL，此处模拟了温度升高时第一组件和第二组件的变形结果，如图3(b)所示。其结果于前述的理论分析的结果一致，即：由于缺乏对称的上半部分结构，第二组件在x轴方向上表现为正热膨胀性，而第一组件由于是完整的结构，四个角点均为限位，所以表现出负的热膨胀特性，膨胀系数与公式(5)所表示的等效热膨胀系数一致。需要说明的是，为了视觉上的直观性，图3(b)中的形变程度通过软件调整放大到真实形变量的50倍，以展示其结构的受热收缩特性。
另外，在图3(c)和图3(d)中，还展示了当高于初始温度的热源被施加到没有晶格缺陷的晶体的表面和晶体内某一晶胞时，晶胞温度分布的情况和应力分布情况，此处用应力分布来表征结构的形变程度。根据有限元模拟结果可知，当高于初始温度的热源被施加到器件表面时，原本共线对接的第二组件的正热膨胀段依然保持对接导通状态，因此热量可以在器件的表面单元进行传导，但第二组件的负热膨胀段则受热向第二组件中心收缩，与第一组件的负热膨胀段脱离接触，形成热断开状态，造成器件表面的热量无法向内部进行传导；而当高于初始温度的热源被施加到器件内部的第一组件上时，该第一组件的四条负热膨胀段均受热向第一组件中心收缩，从而与周边第一组件的负热膨胀段脱离接触，由此输入的热量则会被局域于被施加温度的第一组件本身，形成热绝缘效应。
由此可见，在本发明的拓扑绝缘器件表面会出现边界，使得结构完整的第一组件在器件表面处终止，被结构不完整的第二组件或第三组件代替。这种拓扑绝缘器件可以类比为晶体，其中的第一组件为理想的完整晶胞，而第二组件和第三组件则为存在缺陷的晶胞。以图3(a)所表示的结构类比于晶体为例，由于晶格在表面的周期性突然终止，表面结构由于在x轴方向上因温度升高而引起的膨胀， 使表面相邻的单元相互接触，因此处于热导通状态。而在晶体内部，由于没有缺陷以及对称性的缺失，导致周期排列的晶胞使所有的晶胞结构都处于负热膨胀状态。这将会导致当一个高温源施加在任意晶胞上时，该晶胞的结构尺寸会出现受热收缩，从而与相邻单元断开接触。这意味着在晶体内部，温度将不会在内部扩散，即晶体内部对于热传导而言是绝缘的，具有这种性质的结构在本发明中被称为基于负热膨胀结构的拓扑绝缘体。
进一步的，本发明对上述拓扑绝缘性质进行了理论上的解释和说明：
首先，使用Su-Schrieffer-Heeger(SSH)模型来解释此二维结构系统中的非平凡拓扑性。图4(a)分别展示了组件单元的不同组合方式与SSH模型的对应关系，其中i所示组件单元可以视为一个“原子”，将其通过4次90°的旋转组合可以得到如iv所示的中心对称的新单元结构，ii和iii所示结构分别展示了单元内和单元间的原子键键强。需要说明的是，本发明中的单元，与典型的用于描述二维晶格的SSH模型有些许不同。由于本发明中的负热膨胀结构将在边界处恢复正常的热膨胀特性，因此对应的单元内，相邻“原子”之间键强将随着“原子”是否处于体边界处而有所不同。如图4(b)所示，单元内相邻“原子”都位于边界时的键强为w 1，在非边界处时的键强为w 2，而在结构内，处于不同单元的相邻“原子”之间的键强统一设为v。
当结构是完全周期性的时，这个SSH模型的哈密顿量为：
Figure PCTCN2022072679-appb-000013
其中，a,b,c,d分别代表单元内相邻的四个“原子”，并用i和j表示在整个结构中，位于第i行第j列的单元，符号
Figure PCTCN2022072679-appb-000014
为“Dagger”，表示共轭转置操作，h.c表示外场对模型哈密顿量的贡献。
然后，分别对各项进行计算：
第一项可以写作：
Figure PCTCN2022072679-appb-000015
其中，k表示SSH模型中的波矢，k x和k y表示波矢在x方向和y方向的分量
计算第二项可得：
Figure PCTCN2022072679-appb-000016
通过字母代换，并且经过傅里叶变换后，哈密顿量的形式可以化简为：
Figure PCTCN2022072679-appb-000017
对于上述形式哈密顿量，将其转化成矩阵形式：
Figure PCTCN2022072679-appb-000018
根据矩阵形式的哈密顿量，可以使用Matlab软件计算出其所对应的能带。计算得到的能带图如图4(c)所示,在该能带的计算中，设键强w 2＝0.1,v＝1。
进一步，假设该晶体在x轴方向上有有限个原胞，但是在y方向上则依旧满足周期性边界条件，于是哈密顿量被改写为：
Figure PCTCN2022072679-appb-000019
其中：
Figure PCTCN2022072679-appb-000020
Figure PCTCN2022072679-appb-000021
需要说明的是，由于在本发明中的晶体中，处于表面的晶胞键强分布是不均匀的，所以当考虑晶体在x方向上有n＝10个晶胞时，在上下边界处的矩阵A 1和A 10的形式应改写为：
Figure PCTCN2022072679-appb-000022
Figure PCTCN2022072679-appb-000023
做出这种处理后，利用和完全周期性边界条件的晶体相同的算法，可以得到半周期性的晶体能带图，如图4(d)所示。此结果表明，在能带中出现了边界态，而且图中出现了两条在全周期情况下没有出现的边缘态能级。
需要说明的是，上述有限元模拟和理论解释均是为了更好的说明本发明的具有负热膨胀性的拓扑绝缘器件的原理和性质，但其中的举例均是为了便于叙述，不能理解为对本发明的限制。
另外，上述具有负热膨胀性的拓扑绝缘器件具有表面热导通而内部热绝缘的热学拓扑绝缘特性，这种导通和绝缘特性都是相对于热量而言的。但在本发明的一个较佳实施例中，可以将上述相对于热量而言的拓扑绝缘器件转换为电学拓扑绝缘器件。这种电学拓扑绝缘器件同样具有表面热导通而内部热绝缘的热学拓扑绝缘特性，同时也具有电学拓扑绝缘特性，即使得该器件的表面导电而内部电绝缘。这种电学拓扑绝缘器件的结构形式与前述的拓扑绝缘器件基本相同，仅需要调整第一杆段、第二杆段、第三杆段和第四杆段的材质即可，具体而言，第一杆段、第二杆段、第三杆段和第四杆段的表面均导电，且导电后各杆段均会产生焦耳热，同时应当保证基板除了不导热之外还应当不导电。在这种电学拓扑绝缘器件中，使用由电流的热效应产生的焦耳热，电流产生的焦耳热会导致结构的几何现在出现响应，进而实现热学拓扑绝缘特性，同时连锁产生电学拓扑绝缘特性。显然，由焦耳热引起的温度升高，将使电流可以很容易地在器件表面传递并在器件体内表现出绝缘状态。所以，本发明可以将温度和直流电耦合在一起，因为它们会对器件的拓扑绝缘特性产生相同的影响。
由此，上述电学拓扑绝缘器件中，第一杆段、第二杆段、第三杆段和第四杆段所用的材料应当表面导电，同时还应当具有足够的线性膨胀系数，而杆段内部是否导电不作限定。在本发明的一个优选实例中，第一杆段、第二杆段、第三杆段和第四杆段均采用多层复合材料，其中复合材料以热膨胀材料为骨架，并在骨 架外部包裹导电层。其中，热膨胀材料和导电层的材质不限。本发明中，热膨胀材料可以为镍合金、铜合金或尼龙等，优选为具有较大线性膨胀系数的尼龙。而骨架表面的导电层为涂覆在骨架上的石墨烯涂料，也可以是缠绕在骨架上的导电胶带，当然也可以是石墨烯涂料和导电胶带的组合，即先喷涂一层石墨烯涂料，再在外部包裹导电胶带。
另外，需要说明的是，上述各拓扑绝缘器件中，第一组件、第二组件和第三组件虽然采用了不同组件单元组合的形式来描述，但是这仅仅是为了描述方便，并非限定相应的组件必须先加工独立的组件单元再将组件单元拼装成相应的组件。实际上，第一组件、第二组件和第三组件可以均通过一体化加工成型，这种做法下负热膨胀段中的第一杆段和第四杆段为非拼接的一体化杆段。考虑到加工工艺的可实现性，第一组件、第二组件和第三组件均优选采用3D打印工艺加工而成。
当然，第一组件、第二组件和第三组件也可以采用先加工独立的组件单元再将组件单元拼装的做法，对此不作限定。
下面将结合前述的理论推导和有限元模拟的结果，通过具体实例中的试验来验证本发明的上述电学拓扑绝缘器件的热学拓扑绝缘特性和电学拓扑绝缘特性。在该具体实例中，首先对杆段材质进行选择。根据之前的理论推导和有限元模拟结果，本发明需要的杆段材料要求具有较高的热膨胀率，同时由于需要利用焦耳热效应，因此用于制备杆段的材料还必须导电。在易于加工的各种天然材料中，具有较高热膨胀系数的材料，例如各种高分子聚合物，通常是绝缘的。而在导电材料中，各种合金材料(镍合金，铜合金等)相比各种有机材料而言的线性膨胀系数相对较小。因此为了获得比较明显的实验效果，本实例选择使用不同种类的材料复合构成所需的杆段。其中骨架材料选择使用尼龙，尼龙的热膨胀系数比金属中膨胀系数较大的铜合金要大一个数量级。通常，尼龙材料是不适合采用普通的机加工方法进行加工的，但是得益于近年来蓬勃发展的3D打印技术，可以相对轻松的获得大量的尼龙材质骨架。进一步，为了解决尼龙材料不导电的问题，使用石墨烯涂料对尼龙骨架进行喷涂处理，由于石墨烯材料具有良好的导电性，因此附着了石墨烯涂层的尼龙骨架的表面具有良好的导电性。由此，我们获得了既有较大热膨胀系数，又有良好导电性的复合材料杆段用以制备拓扑绝缘器件。 整个拓扑绝缘器件样品的结构如图5所示，该器件构造了一个凹字型的边界，用以更加明显的展示其传热/导电的边界态。
接下来将恒流源电极连接至图5拓扑绝缘器件样品的热导通外环左上角及右上角单元，并施加1A的电流。之后，使用Fotric公司生产的348型红外热成像仪对整个样品的温度变化情况进行观测，得到结果如图6(a)，可以很显而易见的发现，样品的边界处的温度明显高于背景以及样品内部的温度，热量和电流都仅局限于器件表面，而没有传导至器件内部。
为了证实样品拓扑绝缘器件内部热绝缘区域的各第一组件之间表现出绝缘体性质，选取了内部一个第一组件并对其施加1A的电流，并观察温度的扩散情况。结果如图6(b)所示，可以发现，被施加电流的第一组件温度明显上升，但是温度和电流并没有向相邻第一组件扩散，而是被局域在该第一组件上。
以上结果证明了本发明的热机械超构拓扑绝缘体的设计具有类似电学拓扑绝缘体的相关性质。
需要注意的是，上述各拓扑绝缘器件可以根据实际的应用场景设置相应的工作温度。当器件所处的温度不高于工作温度时，处于非工作状态，而当器件所处的温度高于工作温度时，即可进入工作状态。因此，该工作温度相当于一个温度阈值，对于热导通外环和热绝缘区域，任意两个通过负热膨胀段共线对接的组件之间的间距均基于温度阈值进行导通控制，当两个组件的自身温度不高于温度阈值时，两条负热膨胀段共线对接处于热导通状态，当两个组件的自身温度高于温度阈值时，原本共线对接的两条负热膨胀段脱离处于热断开状态。作为一种优选实现方式，可以把这个温度阈值设定为室温，这样该器件只要制作出来就有热学拓扑绝缘的性质，可以在工业中用于实现对热敏感器件的隔热保护。
另外，本发明中的电学拓扑绝缘器件，具有可重构性，局部导电可控的优点，可为工业上多变的电路排布提供统一的一体化解决方案
以上所述的实施例只是本发明的一种较佳的方案，然其并非用以限制本发明。有关技术领域的普通技术人员，在不脱离本发明的精神和范围的情况下，还可以做出各种变化和变型。因此凡采取等同替换或等效变换的方式所获得的技术方案，均落在本发明的保护范围内。

Claims (10)

  1. 一种具有负热膨胀性的拓扑绝缘器件，其特征在于，包括第一组件、第二组件、第三组件以及隔热的基板，三种组件均由不同数量的组件单元构成；
    每个所述组件单元为由第一杆段、第二杆段、第三杆段和第四杆段顺序连接而成的折线形结构，四条杆段均具有受热伸长的正热膨胀特性且线性膨胀系数相同；其中第一杆段的一端为自由端，第一杆段的另一端与第二杆段的一端通过第一联结点连接，第二杆段的另一端与第三杆端的一端通过第二联结点连接，第三杆端的另一端与第四杆端的一端通过第三联结点连接，第四杆端的另一端为自由端；在非工作状态下，第一杆段、第二杆段分别与第三杆段和第四杆段镜像对称，且第一杆段的自由端、第二联结点、第四杆段的自由端分别位于一个正方形的三个角点上，而第一杆段和第四杆段分别位于同一正方形的两条邻边上；
    所述第一组件由四个组件单元拼接成中心对称结构，其中任意一个组件单元的第一杆段与相邻组件单元的第四杆段重合并联结为一体，作为负热膨胀段；
    所述第二组件由两个组件单元拼接成镜像对称结构，其中一个组件单元的第一杆段与相邻组件单元的第四杆段重合并联结为一体，作为负热膨胀段，两个组件单元中未联结的第一杆段和第四杆段均作为正热膨胀段；
    所述第三组件由单个组件单元组成，其中的第一杆段和第四杆段均作为正热膨胀段；
    三种组件在所述基板上组装形成热导通外环和由热导通外环包裹的热绝缘区域；所述热导通外环由若干第二组件和若干第三组件顺次拼接成环形，所述热绝缘区域由若干所述第一组件呈周期性阵列形式排布而成；热导通外环和热绝缘区域中所有组件的第二联结点均在基板上位置固定无法移动，而第一联结点和第三联结点均能够自由移动；所述热导通外环中，任意两个相邻组件之间均通过各自的正热膨胀段共线对接或者并线对接；所述热绝缘区域中，任意两个相邻第一组件之间的仅通过各自的一条负热膨胀段共线对接；且位于热绝缘区域边缘的第一组件与所述热导通外环对应位置的组件也通过各自的一条负热膨胀段共线对接；
  2. 如权利要求1所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述热导通外环中，拐角位置设置第三组件进行连接，而其余直线段均采用第二组 件进行连接。
  3. 如权利要求1所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述第一杆段、第二杆段、第三杆段和第四杆段的表面均导电，且导电后各杆段均会产生焦耳热；所述基板不导电。
  4. 如权利要求3所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述第一杆段、第二杆段、第三杆段和第四杆段均采用多层复合材料，所述复合材料以热膨胀材料为骨架，并在骨架外部包裹导电层。
  5. 如权利要求4所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述热膨胀材料为镍合金、铜合金或尼龙。
  6. 如权利要求4所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述导电层为涂覆在骨架上的石墨烯涂料和/或缠绕在骨架上的导电胶带。
  7. 如权利要求1所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述第一组件、第二组件和第三组件均通过一体化加工成型，所述负热膨胀段中的第一杆段和第四杆段为非拼接的一体化杆段。
  8. 如权利要求7所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述第一组件、第二组件和第三组件均采用3D打印工艺加工而成。
  9. 如权利要求1～8任一所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述热导通外环和热绝缘区域中，任意两个通过负热膨胀段共线对接的组件之间的间距均基于温度阈值进行导通控制，当两个组件的自身温度不高于所述温度阈值时，两条负热膨胀段共线对接处于热导通状态，当两个组件的自身温度高于所述温度阈值时，原本共线对接的两条负热膨胀段脱离处于热断开状态。
  10. 如权利要求9所述的具有负热膨胀性的拓扑绝缘器件，其特征在于，所述温度阈值为室温。
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