Subgrid method and system based on electromagnetic thermal coupling

Abstract

The invention discloses a sub-grid method and system based on electromagnetic thermal coupling, and the method comprises the steps: introducing a time domain finite difference sub-grid algorithm in the field of an electromagnetic algorithm into a multi-physical field, and delimiting a sub-grid region based on a simulation model; calculating an electric field value in the coarse grid, and updating the electric field value of the coarse grid at the grid interface; introducing the electric field value of the coarse grid into the sub-grid, and carrying out updating calculation on the electromagnetic field value in the sub-grid; an electromagnetic loss equation is used as a heat source, a thermal field is updated and calculated, and a coarse grid thermal field value at the interface is corrected; according to the corresponding linear interpolation, linking the coarse grid thermal field value into the sub-grid; calculating the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space, and updating the current conductivity value into the electromagnetic field parameters; and repeating the above steps until the set simulation time is satisfied, and finally obtaining the electromagnetic field distribution and the thermal field distribution when the simulation is finished, and the instantaneous change of the electromagnetic field and the temperature field of each point.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-physics field numerical simulation of electromagnetism and thermodynamics, and in particular relates to a sub-grid method and system based on electromagnetic-thermal coupling. Background Art

[0002] With the continuous progress of modern microelectronics technology, electronic information systems are gradually evolving towards multifunctionality, miniaturization and low cost. With the miniaturization of electronic devices such as chips, according to the principle of proportional reduction, the smaller the device feature size, the better the comprehensive performance of the chip (including speed, power consumption, reliability, etc.). In order to achieve the purpose of such chip miniaturization, a system-level packaging technology with complex structure and high packaging and interconnection integration density is adopted. In particular, when the chip adopts three-dimensional stacking technology, the power consumption density will be greatly increased, resulting in a sharp increase in heat and an increase in system temperature, thereby generating serious thermal effect problems. On the other hand, as the system temperature increases, the parameters with temperature-dependent characteristics in the system, such as the electrothermal parameters of the packaging material and the resistance parameters of the interconnection line, will change greatly with the increase in temperature, thereby affecting the electrical characteristics of the circuit, and then affecting the performance and reliability of the entire system. As a precision structure in the system-level packaging technology, TSV is in a high-density stacked chip. When the chip is in working state, the thermal effect generated by electricity has an influence on it that cannot be ignored. Therefore, it is very important and necessary to perform multi-physics field numerical simulation of electrothermal coupling and use it to guide the corresponding system-level packaging design.

[0003] For numerical simulation of complex structures, especially those with curved boundaries, if the traditional finite-difference time-domain algorithm is used for numerical simulation, in order to ensure the accuracy of numerical simulation, extremely fine meshing is required. However, when the meshing is fine, the computational efficiency will be greatly reduced. If the efficiency of simulation calculation is to be guaranteed, the simulation accuracy will be low.

[0004] Therefore, how to solve the multi-physics field simulation problem of electrothermal coupling in the precise and complex structures of chip packaging has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a subgrid method and system based on electromagnetic thermal coupling, which introduces the subgrid algorithm of finite difference time domain in the field of electromagnetic algorithm into multi-physics field, and constructs the part of the simulation model that needs fine grid division, that is, the complex and precise structure or the structure with arc-shaped boundary in the model with finer grid to improve the accuracy of the numerical simulation calculation of the algorithm, and the rest of the part adopts relatively coarse grid division to ensure the calculation efficiency of the algorithm. Thus, the algorithm accuracy is guaranteed while maintaining the calculation efficiency of the algorithm.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A subgrid method based on electromagnetic-thermal coupling includes the following steps:

[0008] S1: Introduce the subgrid algorithm of finite difference time domain in the field of electromagnetic algorithm into multi-physics field, and define the subgrid area based on the simulation model;

[0009] S2: Calculate the electric field value in the coarse grid and update the coarse grid electric field value at the grid interface;

[0010] S3: The electric field value of the coarse grid is introduced into the sub-grid by a linear interpolation algorithm, and the electromagnetic field value in the sub-grid is updated and calculated;

[0011] S4: Using the electromagnetic loss equation as the heat source, the thermal field is updated and calculated, and the coarse grid thermal field value at the interface is corrected;

[0012] S5: Connect the thermal field value of the coarse grid to the sub-grid according to the corresponding linear interpolation;

[0013] S6: Calculate the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space, and update it to the electromagnetic field parameters;

[0014] S7: loop S2-S6 until the set simulation time is met, and finally obtain the electromagnetic field distribution and thermal field distribution at the end of the simulation, as well as the instantaneous changes of the electromagnetic field and temperature field at each point.

[0015] Preferably, the electric field value in the coarse grid is calculated, and the electric field value of the coarse grid at the grid interface is updated; the electric field value of the coarse grid is introduced into the sub-grid by a linear interpolation algorithm, and the method for updating and calculating the electromagnetic field value in the sub-grid includes:

[0016] The electric field components in the coarse grid are obtained by iterative calculation through the FDTD algorithm. The electric field components of the coarse grid at the interface between the coarse grid and the sub-grid are updated by interpolation calculation.

[0017] By using linear interpolation, the coarse grid electric field component at the grid interface is introduced into the sub-grid to correct the interface electric field.

[0018] Based on the modified interface electric field, the sub-grid electromagnetic field values ​​and the magnetic field components in the coarse grid are iteratively calculated according to the FDTD algorithm.

[0019] Preferably, the method of using the electromagnetic loss equation as a heat source, updating and calculating the thermal field, and correcting the coarse grid thermal field value at the interface includes:

[0020] Update heat source Q = σ | E 2 |, and substitute it into the heat conduction equation;

[0021] According to the heat conduction equation, the FDTD form of the heat conduction equation is derived;

[0022] Based on the FDTD form of the heat conduction equation, the numerical simulation of the thermal field is started by using the sub-grid area division during the electromagnetic field calculation to obtain the coarse grid thermal field value at the interface;

[0023] The thermal field is processed by linear interpolation, and the coarse grid thermal field value at the interface is introduced into the sub-grid to update the fine grid thermal field value.

[0024] Preferably, the method of using the electromagnetic loss equation as a heat source, updating and calculating the thermal field, and correcting the coarse grid thermal field value at the interface includes:

[0025] Using the FDTD form of the heat conduction equation, calculate the coarse grid thermal field value, i.e., temperature T;

[0026] After iteratively calculating the thermal field value of the coarse grid once, a differential calculation is performed based on the thermal field values ​​of the coarse grid and the sub-grid near the interface between the coarse and sub-grid to correct the thermal field value of the coarse grid at the interface.

[0027] The specific calculation formula is:

[0028]

[0029] Where y as a subscript indicates the direction along the y direction; i, j, and k represent the i-th grid point in the x-direction, the j-th grid point in the y-direction, and the k-th grid point in the z-direction, respectively; κ is the thermal conductivity, ρ is the medium density, and C ρ is the specific heat capacity of the medium, Δt is the time step of each iteration, ΔX is the coarse grid spatial step in the X direction, that is, the distance between two adjacent grid points in the X direction, ΔY and ΔZ are similar to ΔX, which are the coarse grid spatial steps in the Y and Z directions respectively, T n The coarse grid temperature field value at the nth time step, Δy is the sub-grid spatial step length in the Y direction, is the grid interface, the nth time step in the Y direction and T n (i, j, k) are the temperature field values ​​of the adjacent sub-grids, and Q(·) is the heat source.

[0030] Preferably, the method of linking the coarse grid thermal field value to the sub-grid according to the corresponding linear interpolation includes:

[0031] t1=T1

[0032]

[0033] Among them, t1, t2, t3, t4, t5, t6, t7, t8, and t9 are the temperature values ​​of each point in the sub-grid, and T1, T2, T3, and T4 are the temperature values ​​of each point in the coarse grid.

[0034] Preferably, the method for calculating the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space includes:

[0035] σ=σ0÷(1+α·T),

[0036] Among them, σ0 is the conductivity of the dielectric material when the temperature T is zero, and α is the temperature coefficient of the dielectric material.

[0037] The present invention also provides a subgrid system based on electromagnetic thermal coupling, which is used to implement any of the subgrid methods based on electromagnetic thermal coupling, comprising: a simulation module, a coarse grid calculation module, a subgrid calculation module, a correction module, a correlation module, a conductivity calculation module and a circulation module;

[0038] The simulation module is used to introduce the sub-grid algorithm of the finite difference time domain in the field of electromagnetic algorithms into the multi-physics field, and to define the sub-grid area based on the simulation model;

[0039] The coarse grid calculation module is used to calculate the electric field value within the coarse grid and update the coarse grid electric field value at the grid interface;

[0040] The sub-grid calculation module is used to introduce the coarse grid electric field value into the sub-grid by a linear interpolation algorithm, and to update and calculate the electromagnetic field value in the sub-grid;

[0041] The correction module is used to use the electromagnetic loss equation as a heat source, update the thermal field calculation, and correct the coarse grid thermal field value at the interface;

[0042] The association module is used to associate the coarse grid thermal field value with the sub-grid according to the corresponding linear interpolation;

[0043] The conductivity calculation module is used to calculate the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space, and update it into the electromagnetic field parameters;

[0044] The circulation module is used to circulate the coarse grid calculation module-conductivity calculation module until the set simulation time is met, and finally obtain the electromagnetic field distribution and thermal field distribution at the end of the simulation, as well as the instantaneous changes of the electromagnetic field and temperature field at each point.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] Compared with the prior art, the present invention is mainly that in the electromagnetic-thermal coupling simulation of irregular complex structures, the simulation grid of the complex structure part is further refined and divided, and the remaining part is still simulated with a coarser grid, and then certain processing is performed at the interface to keep the internal and external field values ​​consistent, so that the calculation efficiency can be greatly improved while maintaining the simulation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0048] Figure 1 A schematic flow chart of a sub-grid method based on electromagnetic thermal coupling according to an embodiment of the present invention;

[0049] Figure 2 Schematic diagram of the electromagnetic sub-grid interface of an embodiment of the present invention (two-dimensional);

[0050] Figure 3 Schematic diagram of the thermal field sub-grid interface of an embodiment of the present invention (two-dimensional);

[0051] Figure 4 A two-dimensional schematic diagram of a simulation structure of an embodiment of the present invention;

[0052] Figure 5 A three-dimensional schematic diagram of a simulation structure according to an embodiment of the present invention;

[0053] Figure 6 A schematic diagram showing a comparison of time domain sampling of electric field values ​​between a sub-grid and a traditional fine grid according to an embodiment of the present invention;

[0054] Figure 7 Schematic diagram of time domain sampling comparison of thermal field values ​​between a sub-grid and a traditional fine grid according to an embodiment of the present invention. DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] Embodiment 1

[0058] like Figure 1 As shown, the present invention provides a sub-grid method based on electromagnetic thermal coupling, comprising the following steps:

[0059] S1: Introduce the subgrid algorithm of finite difference time domain in the field of electromagnetic algorithm into multi-physics field, and define the subgrid area based on the simulation model;

[0060] S2: Calculate the electric field value within the coarse grid and update the coarse grid electric field value at the grid interface, sacrificing a certain degree of accuracy to maintain the stability of the algorithm;

[0061] S3: The electric field value of the coarse grid is introduced into the sub-grid by a linear interpolation algorithm, and the electromagnetic field value in the sub-grid is updated and calculated;

[0062] S4: Using the electromagnetic loss equation as the heat source, the thermal field is updated and calculated, and the coarse grid thermal field value at the interface is corrected;

[0063] S5: Connect the thermal field value of the coarse grid to the sub-grid according to the corresponding linear interpolation;

[0064] S6: Calculate the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space, and update it to the electromagnetic field parameters;

[0065] S7: loop S2-S6 until the set simulation time is met, and finally obtain the electromagnetic field distribution and thermal field distribution at the end of the simulation, as well as the instantaneous changes of the electromagnetic field and temperature field at each point.

[0066] In this embodiment, based on the simulation model, the sub-grid area is delineated, and various field quantities and numerical simulation parameters are initialized. First, the electric field component in the coarse grid is iteratively calculated by the FDTD algorithm. At the interface between the coarse grid and the sub-grid, the electric field component E y As an example, we use the formula interpolation calculation to update the coarse grid electric field component at the interface:

[0067] where c i , d i is the weight of each magnetic field component, ε is the dielectric constant, σ is the conductivity, and Δt is the time step of the calculation; is the electric field value in the Y direction at the nth time step; n means the nth time step; y and x are used as subscripts to indicate the direction along the y or x direction; i, j, k respectively represent the i-th grid point in the X direction, the j-th grid point in the Y direction, and the k-th grid point in the Z direction; h xi 、h zi represents the subgrid magnetic field around the electric field; c i d iare the weights of the corresponding sub-grid magnetic fields; are the coarse grid magnetic field values ​​at the n+1 / 2 time step in the X and Z directions, respectively. This step, on the one hand, links the field value changes in the coarse grid with the sub-grid field value changes to ensure the integrity of the sub-grid algorithm, and on the other hand, maintains the accuracy of the algorithm results through such field value transfer. Then, using linear interpolation, the coarse grid electric field component at the grid interface is introduced into the sub-grid, referring to Figure 2 , the linear interpolation formula is as follows:

[0068]

[0069] e y2 =E y2

[0070]

[0071] Among them, E y1 、E y2 、E y3 、E y4 、E y5 、E y6 They are Figure 2 The electric field value in the Y direction at each point of the medium-coarse grid, e y1 、e y2 、e y3 、e y4 、e y5 、e y6 、e y7 、e y8 、e y9 They are Figure 2 The electric field value in the Y direction at each point of the Central Asian grid.

[0072] The mutual link between the sub-grid and coarse-grid field values ​​achieved through the above two steps ensures the continuity and integrity of the field values. Next, the sub-grid electromagnetic field values ​​and the magnetic field components in the coarse grid are iteratively calculated according to the FDTD algorithm. Specifically:

[0073] Take the iterative formula of the coarse grid electric field value in the Y direction as an example:

[0074]

[0075] Take the iterative formula of the sub-grid electric field value in the Y direction as an example:

[0076]

[0077] Each time the electromagnetic field is iterated, the thermal field is simulated and iterated. First, the heat source Q = σ|E is updated. 2 |, and substitute it into the heat conduction equation:

[0078]

[0079] Where κ is the thermal conductivity, ρ is the medium density, Cρ is the specific heat capacity of the medium, Δt is the time step of each iteration, and T is the symbol for temperature. Here is the Hamiltonian operator, a method of expressing a computational formula.

[0080] According to the above heat conduction equation, its FDTD form is derived:

[0081]

[0082] Among them, ΔX is the coarse grid spatial step in the X direction, that is, the distance between two adjacent grid points in the X direction. ΔY and ΔZ are similar to ΔX, which are the coarse grid spatial step in the Y and Z directions respectively. T n The coarse grid temperature field value at the nth time step.

[0083] According to the sub-grid area division during electromagnetic field calculation, the numerical simulation of the thermal field begins. The FDTD form of the heat conduction equation is used to calculate the coarse grid thermal field value, that is, the temperature T. After iteratively calculating the coarse grid thermal field value once, a differential calculation is performed based on the coarse grid and sub-grid thermal field values ​​near the coarse-subgrid interface to correct the coarse grid thermal field value at the interface, such as Figure 3 shown.

[0084]

[0085] Where Δy is the subgrid space step in the Y direction, is the grid interface, the nth time step in the Y direction and T n (i,j,k) The adjacent sub-grid temperature field values.

[0086] Taking the coarse subgrid ratio equal to 3 as an example, that is, ΔY = 3*Δy, the above formula can be simplified to obtain the following difference formula:

[0087]

[0088] For different positions on the interface, the formula has different forms. This formula is used to feed back the thermal field value in the sub-grid to the coarse grid, thereby synchronizing the field value changes from the sub-grid to the coarse grid. Secondly, we also use linear interpolation to process the thermal field and introduce the coarse grid thermal field value at the interface into the sub-grid, such as Figure 2 As shown, the specific formula is as follows:

[0089] l1=T1

[0090]

[0091] Among them, Figure 3 As shown, t1, t2, t3, t4, t5, t6, t7, t8, and t9 are the temperature values ​​of each point in the sub-grid, and T1, T2, T3, and T4 are the temperature values ​​of each point in the coarse grid.

[0092] The above linear interpolation formula realizes the introduction of the coarse grid thermal field value into the sub-grid. Combined with the differential calculation of the corrected interface field value in the previous article, the internal and external exchange of the coarse sub-grid field value is realized, and the continuity and unification of the thermal field value at the interface is achieved, forming an overall simulation calculation to ensure the accuracy of the thermal field simulation calculation.

[0093] After completing the above iterative calculation of the thermal field, the temperature value T at the current moment is obtained, and then the conductivity σ of the dielectric material at the current temperature is calculated according to the temperature change characteristics of the dielectric material, as shown in the following formula:

[0094] σ=σ0÷(1+α·T)

[0095] Where σ0 is the conductivity of the dielectric material when the temperature T is zero, and α is the temperature coefficient of the dielectric material. Then substitute the obtained conductivity back into the calculation of the electromagnetic field to calculate the electromagnetic field distribution and thermal field distribution at the next moment. Repeat the above steps until the required numerical simulation time is met.

[0096] Embodiment 2

[0097] In order to verify the correctness and efficiency of the proposed electromagnetic thermal coupling subgrid scheme, a three-dimensional numerical simulation was carried out. The two-dimensional and three-dimensional schematic diagrams are shown in Figure 4 , Figure 5 .

[0098] In the subgrid algorithm, the coarse grid of the entire simulation area occupies 27×27×27 Yee cells, and the unit size is 2um. The radius of the sphere is 11um, and the subgrid replaces the 14×14×14 Yee cells in the coarse grid. The coarse and fine grid ratio is selected as 3:1, and the subgrid has a total of 45×45×45 grids. The results produced by the subgrid algorithm are compared with the traditional FDTD uniform fine grid. The material parameters of the sphere are shown in the table, and the rest is filled with air.

[0099] Set a Gaussian pulse source at a point inside the sphere, as shown below:

[0100] E z (i,j,k,t)=-3×10 10 *exp(-4*π((t-5000*dt) / (2800*dt)) 2 )

[0101] Sphere structure material parameter table 1:

[0102] Table 1

[0103]

[0104] During the simulation, electromagnetic waves propagate in the medium. Due to the electromagnetic loss of the medium, heat is continuously generated, causing the temperature of the medium to change. The temperature change causes the conductivity of the medium to change, completing the entire simulation calculation process. Figure 6 , Figure 7 It can be seen from Table 2 that the simulation results obtained by the proposed three-dimensional electromagnetic thermal coupling sub-grid method are consistent with the fine grid simulation results of the traditional FDTD method.

[0105] Table 2

[0106]

[0107] It is not difficult to conclude that the proposed method has a much lower CPU time and a relatively lower memory cost than the traditional FDTD method. In this case, the CPU time is reduced by 88.7% and the memory cost is reduced by 13.9%.

[0108] Embodiment 3

[0109] The present invention also provides a subgrid system based on electromagnetic thermal coupling, which is used to implement the subgrid method based on electromagnetic thermal coupling, including: a simulation module, a coarse grid calculation module, a subgrid calculation module, a correction module, a correlation module, a conductivity calculation module and a circulation module;

[0110] The simulation module is used to introduce the sub-grid algorithm of the finite difference time domain in the field of electromagnetic algorithms into the multi-physics field, and to define the sub-grid area based on the simulation model;

[0111] The coarse grid calculation module is used to calculate the electric field value within the coarse grid and update the coarse grid electric field value at the grid interface;

[0112] The sub-grid calculation module is used to introduce the coarse grid electric field value into the sub-grid by a linear interpolation algorithm, and to update and calculate the electromagnetic field value in the sub-grid;

[0113] The correction module is used to use the electromagnetic loss equation as a heat source, update the thermal field calculation, and correct the coarse grid thermal field value at the interface;

[0114] The association module is used to associate the coarse grid thermal field value with the sub-grid according to the corresponding linear interpolation;

[0115] The conductivity calculation module is used to calculate the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space, and update it into the electromagnetic field parameters;

[0116] The circulation module is used to circulate the coarse grid calculation module-conductivity calculation module until the set simulation time is met, and finally obtain the electromagnetic field distribution and thermal field distribution at the end of the simulation, as well as the instantaneous changes of the electromagnetic field and temperature field at each point.

[0117] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A subgrid method based on electromagnetic thermal coupling, characterized in that: The following steps are involved: S1: Introduce the subgrid algorithm of finite difference time domain in the field of electromagnetic algorithm into multi-physics field, and define the subgrid area based on the simulation model; S2: Calculate the electric field value in the coarse grid and update the coarse grid electric field value at the grid interface; S3: The electric field value of the coarse grid is introduced into the sub-grid by a linear interpolation algorithm, and the electromagnetic field value in the sub-grid is updated and calculated; S4: Using the electromagnetic loss equation as the heat source, the thermal field is updated and calculated, and the coarse grid thermal field value at the interface is corrected; S5: Connect the thermal field value of the coarse grid to the sub-grid according to the corresponding linear interpolation; S6: Calculate the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space, and update it to the electromagnetic field parameters; S7: loop S2-S6 until the set simulation time is met, and finally obtain the electromagnetic field distribution and thermal field distribution at the end of the simulation, as well as the instantaneous changes of the electromagnetic field and temperature field at each point.

2. The subgrid method based on electromagnetic thermal coupling according to claim 1, characterized in that: Calculate the electric field value in the coarse grid and update the coarse grid electric field value at the grid interface; The method of introducing the coarse grid electric field value into the sub-grid by a linear interpolation algorithm and updating the electromagnetic field value in the sub-grid includes: The electric field components in the coarse grid are obtained by iterative calculation through the FDTD algorithm. The electric field components of the coarse grid at the interface between the coarse grid and the sub-grid are updated by interpolation calculation. By using linear interpolation, the coarse grid electric field component at the grid interface is introduced into the sub-grid to correct the interface electric field. Based on the modified interface electric field, the sub-grid electromagnetic field values ​​and the magnetic field components in the coarse grid are iteratively calculated according to the FDTD algorithm.

3. The subgrid method based on electromagnetic thermal coupling according to claim 2, characterized in that: The method of using the electromagnetic loss equation as a heat source, updating the thermal field, and correcting the coarse grid thermal field value at the interface includes: Update heat source Q = σ | E 2 |, and substitute it into the heat conduction equation; According to the heat conduction equation, the FDTD form of the heat conduction equation is derived; Based on the FDTD form of the heat conduction equation, the numerical simulation of the thermal field is started by using the sub-grid area division during the electromagnetic field calculation to obtain the coarse grid thermal field value at the interface; The thermal field is processed by linear interpolation, and the coarse grid thermal field value at the interface is introduced into the sub-grid to update the fine grid thermal field value.

4. The subgrid method based on electromagnetic thermal coupling according to claim 3, characterized in that: The method of using the electromagnetic loss equation as a heat source, updating the thermal field, and correcting the coarse grid thermal field value at the interface includes: Using the FDTD form of the heat conduction equation, calculate the coarse grid thermal field value, i.e., temperature T; After iteratively calculating the thermal field value of the coarse grid once, a differential calculation is performed based on the thermal field values ​​of the coarse grid and the sub-grid near the interface between the coarse and sub-grid to correct the thermal field value of the coarse grid at the interface. The specific calculation formula is: Where y as a subscript indicates the direction along the y direction; i, j, and k represent the i-th grid point in the x-direction, the j-th grid point in the y-direction, and the k-th grid point in the z-direction, respectively; κ is the thermal conductivity, ρ is the medium density, and C ρ is the specific heat capacity of the medium, Δt is the time step of each iteration, ΔX is the coarse grid spatial step in the X direction, that is, the distance between two adjacent grid points in the X direction, ΔY and ΔZ are similar to ΔX, which are the coarse grid spatial steps in the Y and Z directions respectively, T n The coarse grid temperature field value at the nth time step, Δy is the sub-grid spatial step length in the Y direction, is the grid interface, the nth time step in the Y direction and T n (i, j, k) are the temperature field values ​​of the adjacent subgrids, and Q(·) is the heat source.

5. The subgrid method based on electromagnetic thermal coupling according to claim 3, characterized in that: Methods for linking the coarse grid thermal field values ​​to the sub-grids based on the corresponding linear interpolation include: t1=T1 Among them, t1, t2, t3, t4, t5, t6, t7, t8, and t9 are the temperature values ​​of each point in the sub-grid, and T1, T2, T3, and T4 are the temperature values ​​of each point in the coarse grid.

6. The subgrid method based on electromagnetic thermal coupling according to claim 1, characterized in that: Methods for calculating the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space include: σ=σ0÷(1+α · T), Among them, σ0 is the conductivity of the dielectric material when the temperature T is zero, and α is the temperature coefficient of the dielectric material.

7. A sub-grid system based on electromagnetic thermal coupling, characterized in that: A subgrid method based on electromagnetic thermal coupling for implementing any one of claims 1 to 6, comprising: a simulation module, a coarse grid calculation module, a subgrid calculation module, a correction module, a correlation module, a conductivity calculation module and a circulation module; The simulation module is used to introduce the sub-grid algorithm of the finite difference time domain in the field of electromagnetic algorithms into the multi-physics field, and to define the sub-grid area based on the simulation model; The coarse grid calculation module is used to calculate the electric field value within the coarse grid and update the coarse grid electric field value at the grid interface; The sub-grid calculation module is used to introduce the coarse grid electric field value into the sub-grid by a linear interpolation algorithm, and to update and calculate the electromagnetic field value in the sub-grid; The correction module is used to use the electromagnetic loss equation as a heat source, update the thermal field calculation, and correct the coarse grid thermal field value at the interface; The association module is used to associate the coarse grid thermal field value with the sub-grid according to the corresponding linear interpolation; The conductivity calculation module is used to calculate the current conductivity value of the corresponding dielectric material according to the current temperature of each point in the current space, and update it into the electromagnetic field parameters; The circulation module is used to circulate the coarse grid calculation module-conductivity calculation module until the set simulation time is met, and finally obtain the electromagnetic field distribution and thermal field distribution at the end of the simulation, as well as the instantaneous changes of the electromagnetic field and temperature field at each point.

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