Design method of tunable electromagnetic metamaterials for wireless charging of power devices

Abstract

The present invention discloses a design method for an adjustable electromagnetic metamaterial for wireless charging of power equipment, comprising the following steps: (1) evaluating the maximum size of a square spiral structure according to requirements, determining the side length a of a metamaterial unit lattice and the maximum side length b of a square spiral coil in the unit; determining the coil wire width w and the turn spacing s according to the actual manufacturing process; (2) optimizing the number of turns of the square spiral structure; (3) determining the resonant frequency based on finite element simulation and verifying the negative magnetic permeability characteristics; (4) adding magnetorheological fluids of different concentrations or particle sizes; (5) evaluating the effects of concentration and particle size on the resonant frequency; (6) meeting the actual size requirements of the system and realizing dynamic adjustment of the resonant frequency within the frequency drift range. The design method of the present invention positions the resonant frequency in the kHz-MHz frequency band, which is universal for wireless charging application scenarios; realizing dynamic adjustment of the resonant frequency, while taking into account low-frequency and miniaturized design, and improving the integration and compactness of the system structure.

Description

Technical Field

[0001] The present invention relates to the field of metamaterials, and in particular to a design method of an adjustable electromagnetic metamaterial for wireless charging of power equipment. Background Art

[0002] Wireless charging technology supports load devices to obtain electrical energy in a non-contact manner and has been widely used in the field of power supply for power equipment. Magnetic coupling resonant wireless charging technology has attracted widespread attention as a new energy storage and transmission technology due to its advantages of high energy transfer efficiency, large transmission power, long energy transfer distance, and no strict directionality. It provides a new solution for power supply for power equipment and has broad engineering application prospects, such as wireless charging of substation inspection robots, wireless charging of SF6 gas-insulated fully enclosed switchgear (GIS), wireless charging of high-voltage primary equipment RF power amplifier power supply, and wireless charging of online monitoring systems for medium and high voltage electrical equipment.

[0003] In practical engineering applications, high efficiency, long distance, and miniaturization are still key issues that need to be overcome in the field of wireless charging technology. The negative magnetic permeability characteristics of electromagnetic metamaterials can regulate the magnetic field, providing a possibility for breaking through the bottleneck of existing wireless charging technology.

[0004] At present, the research on wireless charging technology based on electromagnetic metamaterials is based on fixed frequency design. After the electromagnetic metamaterial is made, the resonant frequency point cannot be adjusted. The wireless power transmission system is very sensitive to the change of resonant frequency. The temperature rise, internal resistance, parasitic parameters and load changes of the circuit, as well as the axial distance, radial displacement and angular deflection between coils will affect the resonant frequency and cause frequency drift. Its resonant frequency changes in line with the resonant frequency of the wireless power transmission system.

[0005] The unique electromagnetic properties of electromagnetic metamaterials come from the electromagnetic resonance of the metamaterials, which is generated by the inductance and capacitance of the elementary structure. At present, the research and application of electromagnetic metamaterials are mainly concentrated in the GHz high-frequency field, such as microwave engineering and optics. In the field of high-frequency electromagnetic metamaterial design, the most classic electromagnetic metamaterial structure is the open resonant ring. If this structure is directly applied to the electromagnetic metamaterial in the wireless charging system of power equipment with a resonant frequency band distributed in kHz-MHz, the system size is large and difficult to apply in actual engineering. Therefore, it is necessary to design electromagnetic metamaterials that take into account both low frequency and miniaturization. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and, in view of the actual working conditions of frequency drift, propose an adjustable electromagnetic metamaterial design method for wireless charging of power equipment. The method is an electromagnetic metamaterial design method with dynamically adjustable resonant frequency. The electromagnetic metamaterial design method of the present invention can be applied to wireless power transmission systems, can reduce magnetic leakage in wireless charging systems, increase transmission efficiency and distance, and open up a new direction for promoting the development and application of wireless charging technology.

[0007] The electromagnetic metamaterial design method of the present invention is based on a planar spiral structure electromagnetic metamaterial based on printed circuit board technology, and proposes an electromagnetic metamaterial design based on magnetorheological fluid to achieve dynamic adjustment of resonant frequency while taking into account low frequency and miniaturization.

[0008] The present invention adopts the following technical solution:

[0009] The method for designing an adjustable electromagnetic metamaterial for wireless charging of power devices comprises the following steps:

[0010] (1) determining the side length of the electromagnetic metamaterial unit lattice and the maximum side length of the square spiral coil in the electromagnetic metamaterial unit;

[0011] (2) Optimizing the number of turns of the square spiral coil;

[0012] (3) Determine the resonant frequency of electromagnetic metamaterials and verify the negative magnetic permeability characteristics based on finite element simulation;

[0013] (4) Using magnetorheological fluids of different concentrations and / or magnetorheological fluids of magnetic nanoparticles of different particle sizes to control the relative magnetic permeability of electromagnetic metamaterials;

[0014] (5) Evaluate the effect of magnetorheological fluid concentration and / or magnetic nanoparticle size in the magnetorheological fluid on the resonant frequency of electromagnetic metamaterials.

[0015] Furthermore, in step (1), the square spiral structure is a planar spiral structure based on printed circuit board technology.

[0016] Furthermore, in step (1), the side length of the electromagnetic metamaterial unit lattice and the maximum side length of the square spiral coil in the electromagnetic metamaterial unit are determined according to formula (1); the formula (1) is as follows:

[0017]

[0018] Where ω0 is the resonant frequency of the electromagnetic metamaterial, in rad / s; L eff is the equivalent inductance value, the unit is H; C is the electromagnetic metamaterial capacitance value, the unit is F.

[0019] Furthermore, in step (2), the number of turns of the square spiral structure is optimized and designed according to the calculation formula of the equivalent magnetic permeability of the resonator unit of the square spiral coil; the calculation formula of the equivalent magnetic permeability of the resonator unit of the square spiral coil is:

[0020]

[0021]

[0022] Where a is the side length of the electromagnetic metamaterial unit lattice, and b is the maximum side length of the square spiral coil in the electromagnetic metamaterial unit. The number of turns of the square spiral coil is calculated according to formula (2) and formula (3). ω is the operating frequency of the electromagnetic metamaterial; σ is the conductivity of the coil material, i is the imaginary unit, σi represents a pure imaginary number with a modulus of σ; the units of a and b are both m; σ is the conductivity of the coil material, in S / m; μ0 is the vacuum magnetic permeability, in H / m; ω0 is the resonant frequency of the electromagnetic metamaterial, in rad / s; ε0 represents the vacuum dielectric constant, in F / m; C is the capacitance value of the electromagnetic metamaterial, in F; N is the number of turns of the square spiral coil, in turns; s is the turn spacing of the square spiral coil, in m.

[0023] Furthermore, in step (3), after the electromagnetic metamaterial structural parameters are determined, the resonant frequency of the electromagnetic metamaterial is determined according to finite element simulation; the structural parameters are: the side length a of the electromagnetic metamaterial unit lattice (i.e., the side length a of the lattice where the coil is located); the maximum side length b of the square spiral coil in the electromagnetic metamaterial unit (i.e., the outer side length b of the coil); the wire width w in the coil and the coil turn spacing s.

[0024] Further, in step (3), the resonant frequency of the electromagnetic metamaterial is determined based on finite element simulation and the negative magnetic permeability characteristics are verified according to formulas (2) and (3), and the formulas (2) and (3) are as follows:

[0025]

[0026]

[0027] Wherein, a is the side length of the metamaterial unit lattice, in m; b is the maximum side length of the square spiral coil in the electromagnetic metamaterial unit, in m; σ is the conductivity of the coil material, in S / m, i is the imaginary unit, σi represents a pure imaginary number with a modulus of σ; μ0 is the vacuum magnetic permeability, in H / m; ω is the operating frequency of the electromagnetic metamaterial; ε0 represents the vacuum dielectric constant, in F / m; C is the capacitance value of the electromagnetic metamaterial, in F; N is the number of turns of the coil, and s is the coil turn spacing, in m.

[0028] Furthermore, in step (3), the resonant frequency calculation formula of the electromagnetic metamaterial is:

[0029]

[0030] Where ω0 is the resonant frequency of the electromagnetic metamaterial, L eff is the equivalent inductance, C is the capacitance of the electromagnetic metamaterial; ω0 is in rad / s; L eff The unit is H; the unit of C is F.

[0031] Furthermore, in step (4), when the concentration and the particle size of the magnetic nanoparticles are different, the magnetic permeability of the magnetorheological fluid is also changing. The change in magnetic permeability will change the magnetic resistance distribution, and then change the equivalent inductance value of the electromagnetic metamaterial, thereby achieving dynamic regulation of the resonant frequency.

[0032] Furthermore, in step (5), the evaluation of the influence of the concentration and particle size of the magnetorheological fluid on the resonant frequency is performed as follows: the relationship between the characteristic parameters of the magnetorheological fluid and its own BH curve is established, and the BH curve is used to perform numerical modeling analysis of the magnetorheological fluid and the electromagnetic metamaterial, and the calculation formula used is as follows:

[0033] B=μ0(1+X)H (4)

[0034]

[0035] M0=N×m0 (6)

[0036]

[0037]

[0038] Among them, N is related to the concentration of magnetorheological fluid and the particle size of magnetic nanoparticles, m o Related to the particle size of magnetic nanoparticles. B represents magnetic induction intensity, the unit is T; H represents magnetic field intensity, the unit is A / m; μ0 vacuum permeability, the unit is H / m; X represents magnetic susceptibility, the unit is m^3·kg -1 ; M0 is the maximum magnetization intensity of magnetic nanoparticles per unit volume, in A / m; N is the number of magnetic nanoparticles per unit volume; m o It is equal to the product of the magnetic domain magnetization intensity and the volume of the magnetic nanoparticle, and its unit is A*m^2; Ms is the saturation magnetization intensity, and its unit is A / m; M d is the magnetization intensity of the magnetic domain, the unit is A / m; M is the magnetization intensity, the unit is A / m; V M is the volume of the magnetic nanoparticle, in m^3; K is the Boltzmann constant, a physical constant, dimensionless; T is the absolute temperature, in °C; L(ξ) is the Langevin function, ξ is the magnetization intensity of the magnetic domain M d , magnetic field intensity H, magnetic nanoparticle volume VM , Boltzmann constant K, and absolute temperature T are variables represented by no practical meaning.

[0039] Furthermore, the design method also includes: step (6) obtaining different BH curves by changing the concentration of magnetorheological fluid and the particle size of magnetic nanoparticles, and different BH curves can reduce magnetic resistance or increase inductance values ​​differently, thereby obtaining the resonant frequency points of the electromagnetic metamaterial under the action of different magnetorheological fluid concentrations and particle sizes, meeting the actual size requirements of the wireless charging system and realizing dynamic adjustment of the resonant frequency within the frequency drift range.

[0040] Furthermore, when the concentration of the magnetorheological fluid is fixed, the resonant frequency points shift to the left as the particle size increases.

[0041] Furthermore, when the particle size of the magnetic nanoparticles is fixed, the resonant frequency points shift to the left as the particle size increases.

[0042] Specifically, 1. Design method of square spiral structure electromagnetic metamaterial based on printed circuit board technology:

[0043] The resonant frequency expression of the electromagnetic metamaterial is as shown in Equation 1, where ω0 is the resonant frequency of the electromagnetic metamaterial, L eff is the equivalent inductance value, and C is the capacitance value of the electromagnetic metamaterial. Increasing the size of the electromagnetic metamaterial can obtain greater capacitance and inductance to achieve a lower resonant frequency, but this is obviously not conducive to engineering applications. In order to design low-frequency electromagnetic metamaterials without significantly increasing the size of the electromagnetic metamaterial, a planar spiral structure based on printed circuit board technology can be used. The spiral structure has a larger inductance, and each two turns of the spiral can also provide a larger capacitance, so the spiral structure element has a lower resonant frequency. Compared with the circular spiral structure, the electromagnetic metamaterial with a square spiral structure can increase the volume share of the resonator unit, thereby reducing the resonant frequency.

[0044]

[0045] By adopting the physical open circuit method, the continuity of current is achieved through the inter-turn capacitance, and reverse charges are accumulated on the outer and inner circles. By using the conservation of electromotive force, the equivalent magnetic permeability of the resonator unit of the square spiral coil can be obtained as follows:

[0046]

[0047]

[0048] Among them, a is the side length of the metamaterial unit lattice, b is the maximum side length of the square spiral coil in the metamaterial unit, σ is the conductivity of the coil material, μ0 is the vacuum magnetic permeability, ω0 is the resonant frequency, ε0 ​​represents the vacuum dielectric constant, C is the material capacitance value, N is the number of coil turns, and s is the turn spacing.

[0049] From the analysis, we can see that the vacuum magnetic permeability μ0 and the vacuum dielectric constant ε0 are both constant values. In actual design, the size of the square spiral structure electromagnetic metamaterial can be determined according to the actual size requirements of the system, that is, the side length a of the metamaterial unit lattice and the maximum side length b of the square spiral coil can be determined. Based on the above considerations, when the number of coil turns N is different, each number of coil turns N corresponds to a unique resonant frequency ω0.

[0050] Assuming that the maximum size of the square coil actually required is a=100mm, b=96mm, the actual manufacturing process of the PCB metamaterial board determines the coil wire width w=0.5mm and the turn spacing s=0.5mm. Keeping the above parameters unchanged, the number of turns of the square spiral coil is optimized. When the number of turns N changes from 13 turns to 25 turns, the resonant frequency of the square spiral structure electromagnetic metamaterial first decreases and then increases. Due to the influence of the series and parallel inter-turn capacitances, the resonant frequency of the resonator unit does not change monotonically with the change of the number of turns. When N=19, the resonator unit obtains the minimum resonant frequency of 7.36MHz.

[0051] Table 1 shows the structural parameters of the square spiral structure electromagnetic metamaterial obtained by optimization design, and Table 2 shows the parameter description corresponding to the structural parameters of the square spiral structure electromagnetic metamaterial.

[0052] Table 1 Parameters of square coil electromagnetic metamaterial

[0053]

[0054] Table 2 Parameters of square coil electromagnetic metamaterial

[0055]

[0056] After the structural parameters of the square helical structure electromagnetic metamaterial are determined, the resonant frequency of the electromagnetic metamaterial can be determined according to finite element simulation. The simulation calculation results show that the resonant frequency of the electromagnetic metamaterial element is 7.36MHz, and when the frequency is in the range of 7MHz-7.4MHz, the equivalent magnetic permeability is greater than zero, and when it is in the range of 7.4MHz-12MHz, the equivalent magnetic permeability is less than zero.

[0057] The square spiral structure electromagnetic metamaterial structure is placed in a magnetic field in the z-axis direction only. The magnetic field frequency is 8MHz and the intensity is Hz=1A / m. A reverse magnetic field appears inside the coil. The magnetic field intensity outside the coil is 1A / m, and a -2A / m magnetic field appears inside the coil. The equivalent magnetic permeability of the square spiral structure electromagnetic metamaterial structure is negative, which can realize the regulation of the magnetic field of the wireless charging system.

[0058] In summary, the designed planar square spiral structure electromagnetic metamaterial has a resonant frequency of 7.36 MHz, which is within the common frequency band of the resonant frequency of the wireless charging system of power equipment. Its size is only 10 cm × 10 cm, which meets the miniaturization requirements of the wireless charging system for electromagnetic metamaterials.

[0059] 2. Design method of electromagnetic metamaterial with dynamically adjustable resonant frequency based on magnetorheological fluid

[0060] The relative magnetic permeability of electromagnetic metamaterials can be regulated by using magnetorheological fluids of different concentrations or magnetorheological fluids of magnetic nanoparticles of different particle sizes, thereby achieving dynamic adjustment of the resonant frequency of electromagnetic metamaterials. The principle is that when the concentration and particle size of magnetic nanoparticles are different, the magnetic permeability of the magnetorheological fluid is also changing. The change in magnetic permeability will change the magnetic resistance distribution, thereby changing the equivalent inductance of the electromagnetic metamaterial, thereby achieving dynamic regulation of the resonant frequency.

[0061] The Langevin equation can establish the relationship between the characteristic parameters of magnetorheological fluid and its own BH curve. The BH curve provides a basis for the numerical modeling and analysis of magnetorheological fluid and electromagnetic metamaterials.

[0062] B=μ0(1+X)H (4)

[0063]

[0064] M0=N×m0 (6)

[0065]

[0066]

[0067] N is the number of magnetic nanoparticles per unit volume, M0 is the maximum magnetization intensity of magnetic nanoparticles per unit volume, M d is the domain magnetization, Ms is the saturation magnetization, K is the Boltzmann constant, T is the absolute temperature, m o It is equal to the product of the magnetic domain magnetization intensity and the volume of the magnetic nanoparticles. Among them, N is related to the concentration of the magnetorheological fluid and the particle size of the magnetic nanoparticles. o It is related to the particle size of the magnetic nanoparticles. Therefore, different BH curves can be obtained by changing the concentration of the magnetorheological fluid and the particle size of the magnetic nanoparticles. Different BH curves can reduce the magnetic resistance or increase the inductance value differently, so the resonant frequency point of the electromagnetic metamaterial under the action of different magnetorheological fluid concentrations and particle sizes can be obtained.

[0068] The resonant frequency of the electromagnetic metamaterial is 7.36MHz when no magnetorheological fluid is added. When the concentration of the magnetorheological fluid is 100mg / ml, 200mg / ml, 300mg / ml, and 400mg / ml, the resonant frequency is 4.2MHz, 3.2MHz, 2.7MHz, and 2.4MHz, respectively. As the concentration of the magnetorheological fluid increases, the resonant frequency shifts to the left. The effect of magnetorheological fluid on reducing the resonant frequency from nothing to something is extremely significant. When the concentration of the magnetorheological fluid is continuously increased, the effect of reducing the resonant frequency is becoming less and less obvious. Similarly, when the concentration of the magnetorheological fluid is reduced, the resonant frequency increases.

[0069] When studying the effect of magnetorheological fluid concentration on the resonant frequency point, the particle size of the magnetic nanoparticles was fixed at 8nm. In addition to the influence of concentration, the particle size of the magnetic nanoparticles is also an important characteristic parameter of the magnetorheological fluid. When the concentration of the magnetorheological fluid is fixed at 400mg / ml, when the particle size of the magnetic nanoparticles is 8nm, 12nm, 16nm and 20nm, the resonant frequency points all shift to the left as the particle size increases. When the particle size is increased to 20nm, four resonant frequency points appear, and the smallest resonant frequency point can be reduced to 0.8MHz.

[0070] Increasing the concentration of magnetorheological fluid or increasing the particle size of magnetic nanoparticles can increase the inductance of electromagnetic metamaterials. From formula (1), it can be seen that the resonant frequency of electromagnetic metamaterials always decreases with the increase of inductance. Therefore, increasing the concentration of magnetorheological fluid or increasing the particle size of magnetic nanoparticles can reduce the resonant frequency of electromagnetic metamaterials. Similarly, reducing the concentration of magnetorheological fluid or reducing the particle size of magnetic nanoparticles can also reduce the inductance and increase the resonant frequency, thereby realizing dynamic regulation of the resonant frequency by magnetorheological fluid concentration or magnetic nanoparticle size.

[0071] The beneficial effects of the present invention are as follows:

[0072] The electromagnetic metamaterial design method of the present invention locates the resonant frequency in the kHz-MHz frequency band, which is universal for wireless charging application scenarios;

[0073] The electromagnetic metamaterial design method of the present invention is dedicated to realizing dynamic adjustment of the resonant frequency, which can effectively solve the problem of resonant frequency drift in the wireless charging system and thus lead to a decrease in transmission performance;

[0074] The electromagnetic metamaterial design method of the present invention aims to achieve adjustable resonant frequency while taking into account low-frequency and miniaturized design, thereby improving the integration and compactness of the system structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 It is an electromagnetic metamaterial with a square spiral structure, where a is the maximum side length of the metamaterial unit lattice, b is the maximum side length of the square spiral coil in the unit, w is the coil wire width, and s is the turn spacing.

[0076] Figure 2 shows the curve of equivalent magnetic permeability changing with the number of turns. Figure 2a It is the variation curve of equivalent magnetic permeability when the number of turns N changes from 13 turns to 19 turns; Figure 2b This is the changing curve of equivalent magnetic permeability when the number of turns N changes from 19 turns to 25 turns.

[0077] Figure 3 This is the curve of the equivalent magnetic permeability of the square coil electromagnetic metamaterial changing with the resonant frequency.

[0078] Figure 4 It is the magnetic field distribution of the square coil electromagnetic metamaterial in the z-axis direction.

[0079] Figure 5a The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the magnetic nanoparticle size is set to 8nm and the concentration of the magnetorheological fluid is 100mg / ml; Figure 5b The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the magnetic nanoparticle size is set to 8nm and the concentration of the magnetorheological fluid is 200mg / ml; Figure 5c The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the magnetic nanoparticle size is set to 8nm and the magnetorheological fluid concentration is 300mg / ml; Figure 5d The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the magnetic nanoparticle size is set to 8nm and the magnetorheological fluid concentration is 400mg / ml.

[0080] Figure 6a The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the concentration of the magnetorheological fluid is 400 mg / ml and the diameter of the magnetic nanoparticles is 8 nm; Figure 6b The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the concentration of the magnetorheological fluid is 400 mg / ml and the diameter of the magnetic nanoparticles is 12 nm; Figure 6c The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the concentration of the magnetorheological fluid is 400 mg / ml and the diameter of the magnetic nanoparticles is 16 nm; Figure 6d The real and imaginary distributions of the equivalent magnetic permeability of the electromagnetic metamaterial when the concentration of the magnetorheological fluid is 400 mg / ml and the diameter of the magnetic nanoparticles is 20 nm.

[0081] Figure 7 Schematic diagram of the method steps for designing dynamically tunable electromagnetic metamaterials. DETAILED DESCRIPTION

[0082] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. However, the following embodiments are limited to explaining the present invention, and the protection scope of the present invention should include the entire contents of the claims, and through the description of the following embodiments, those skilled in the art can fully implement the entire contents of the claims of the present invention.

[0083] The invention provides a design method of an adjustable electromagnetic metamaterial for wireless charging of power equipment. Figure 7 A flowchart of the method steps for designing dynamically tunable electromagnetic metamaterials. Figure 7 As shown, the design method of adjustable electromagnetic metamaterial for wireless charging of power devices includes the following steps:

[0084] (1) Evaluate the maximum size of the square spiral structure according to the requirements, determine the side length a of the metamaterial unit lattice and the maximum side length b of the square spiral coil in the unit; determine the coil wire width w and the turn spacing s according to the actual manufacturing process;

[0085] (2) Optimize the number of turns of the square spiral structure;

[0086] (3) Determine the resonant frequency and verify the negative permeability characteristics based on finite element simulation;

[0087] (4) adding magnetorheological fluid of different concentrations or particle sizes;

[0088] (5) Evaluate the effect of concentration and particle size on the resonant frequency;

[0089] (6) Meet the actual size requirements of the system and realize dynamic adjustment of the resonant frequency within the frequency drift range.

[0090] According to the actual working conditions of the wireless charging application scenario of power equipment where the resonant frequency is distributed in the kHz-MHz frequency band and combined with the actual size requirements of the system, the following design method is given.

[0091] The resonant frequency expression of the electromagnetic metamaterial is as shown in Equation 1, where ω0 is the resonant frequency of the electromagnetic metamaterial, L eff is the equivalent inductance value, and C is the capacitance value of the electromagnetic metamaterial. Increasing the size of the electromagnetic metamaterial can obtain greater capacitance and inductance to achieve a lower resonant frequency, but it is obviously not conducive to engineering applications. In order to design low-frequency electromagnetic metamaterials without significantly increasing the size of the electromagnetic metamaterial, a planar spiral structure based on printed circuit board technology can be used. The spiral structure has a larger inductance, and each two turns of the spiral can also provide a larger capacitance, so the spiral structure element has a lower resonant frequency. Compared with the circular spiral structure, the electromagnetic metamaterial with a square spiral structure can increase the volume share of the resonator unit, thereby reducing the resonant frequency. Taking the above factors into consideration, the design of an adjustable electromagnetic metamaterial for wireless charging of power equipment will be based on a planar square spiral structure. Figure 1 Figure 1 is a structural diagram of a square spiral electromagnetic metamaterial, where a is the side length of the metamaterial unit lattice, b is the maximum side length of the square spiral coil in the unit, w is the coil wire width, and s is the turn spacing.

[0092]

[0093] By adopting the physical open circuit method, the continuity of current is achieved through the inter-turn capacitance, and reverse charges are accumulated on the outer and inner circles. By using the conservation of electromotive force, the equivalent magnetic permeability of the resonator unit of the square spiral coil can be obtained as follows:

[0094]

[0095]

[0096] Among them, a is the side length of the metamaterial unit lattice, b is the maximum side length of the square spiral coil in the unit, σ is the conductivity of the coil material, μ0 is the vacuum magnetic permeability, ω0 is the resonant frequency, ε0 ​​represents the vacuum dielectric constant, C is the material capacitance, N is the number of coil turns, and s is the turn spacing. The above formula establishes the relationship between the electromagnetic metamaterial structural parameters, the resonant frequency, and the negative magnetic permeability characteristics of the electromagnetic metamaterial, which can provide a basis for the optimization design of the electromagnetic metamaterial structure.

[0097] First, the size of the square spiral coil is determined according to the actual requirements of the system, that is, the side length a of the metamaterial unit lattice and the maximum side length b of the square spiral coil are determined.

[0098] a and b are constants, and the vacuum magnetic permeability μ0 and vacuum dielectric constant ε0 are known. When the number of coil turns N is different, each number of coil turns N corresponds to a unique resonant frequency ω0. To expand the resonant frequency band to kHz, it is necessary to obtain the lowest resonant frequency when the values ​​of a and b are determined. Based on this, each set of a and b values ​​corresponds to a set of optimal coil turns.

[0099] Assuming that the maximum size of the square coil actually required is a = 100mm, b = 96mm, the actual manufacturing process of the PCB metamaterial board determines the coil wire width w = 0.5mm and the turn spacing s = 0.5mm. Keeping the above parameters unchanged, the number of turns of the square spiral coil is optimized. The optimization results are as follows: Figure 2a and Figure 2b As shown in the figure. When the number of turns N changes from 13 turns to 25 turns, the resonant frequency of the square spiral structure electromagnetic metamaterial first decreases and then increases. Due to the influence of the series and parallel inter-turn capacitances, the resonant frequency of the resonator unit does not change monotonically with the change of the number of turns. When N = 19, the square spiral structure electromagnetic metamaterial obtains the minimum resonant frequency.

[0100] Table 1 shows the structural parameters of the square spiral structure electromagnetic metamaterial obtained by optimization design, and Table 2 shows the parameter description corresponding to the structural parameters of the square spiral structure electromagnetic metamaterial.

[0101] Table 1 Parameters of square coil electromagnetic metamaterial

[0102]

[0103] Table 2 Parameters of square coil electromagnetic metamaterial

[0104]

[0105]

[0106] After the structural parameters of the square spiral structure electromagnetic metamaterial are determined, the resonant frequency of the electromagnetic metamaterial can be determined based on finite element simulation. The simulation results are shown in Figure 3 The resonant frequency of the electromagnetic metamaterial element is 7.36 MHz, and when the frequency is in the range of 7 MHz to 7.4 MHz, the equivalent magnetic permeability is greater than zero, and when the frequency is in the range of 7.4 MHz to 12 MHz, the equivalent magnetic permeability is less than zero.

[0107] The square spiral structure electromagnetic metamaterial structure is placed in a magnetic field in the z-axis direction only. The magnetic field frequency is 8MHz and the intensity is Hz=1A / m. The simulation results are as follows: Figure 4 As shown in the figure, a reverse magnetic field appears inside the coil, the magnetic field strength outside the coil is 1A / m, and a magnetic field of -2A / m appears inside the coil. The equivalent magnetic permeability of the square spiral structure electromagnetic metamaterial structure is negative, which can realize the regulation of the magnetic field of the wireless charging system.

[0108] The designed planar square spiral structure electromagnetic metamaterial has a resonant frequency of 7.36MHz, which is within the common frequency band of the resonant frequency of the wireless charging system of power equipment. It is only 10cm×10cm in size, meeting the miniaturization requirements of the wireless charging system for electromagnetic metamaterials.

[0109] The above provides an optimization design method for the square spiral structure electromagnetic metamaterial structure in response to the low-frequency and miniaturized application requirements of electromagnetic metamaterials. The following is a design method for achieving dynamic adjustment of the resonant frequency.

[0110] The relative magnetic permeability of electromagnetic metamaterials can be regulated by using magnetorheological fluids of different concentrations or magnetorheological fluids of magnetic nanoparticles of different particle sizes, thereby achieving dynamic adjustment of the resonant frequency of electromagnetic metamaterials. The principle is that when the concentration and particle size of magnetic nanoparticles are different, the magnetic permeability of the magnetorheological fluid is also changing. The change in magnetic permeability will change the magnetic resistance distribution, thereby changing the equivalent inductance of the electromagnetic metamaterial, thereby achieving dynamic regulation of the resonant frequency.

[0111] The Langevin equation can establish the relationship between the characteristic parameters of magnetorheological fluid and its own BH curve. The BH curve provides a basis for the numerical modeling and analysis of magnetorheological fluid and electromagnetic metamaterials.

[0112] B=μ0(1+X)H (4)

[0113]

[0114] M0=N×m0 (6)

[0115]

[0116]

[0117] N is the number of magnetic nanoparticles per unit volume, M0 is the maximum magnetization intensity of magnetic nanoparticles per unit volume, M d is the magnetic domain magnetization, Ms is the saturation magnetization, K is the Boltzmann constant, T is the absolute temperature, m o It is equal to the product of the magnetic domain magnetization intensity and the volume of the magnetic nanoparticles. Among them, N is related to the concentration of the magnetorheological fluid and the particle size of the magnetic nanoparticles. o It is related to the particle size of the magnetic nanoparticles. Therefore, different BH curves can be obtained by changing the concentration of the magnetorheological fluid and the particle size of the magnetic nanoparticles. Different BH curves can reduce the magnetic resistance or increase the inductance value differently, so the resonant frequency point of the electromagnetic metamaterial under the action of different magnetorheological fluid concentrations and particle sizes can be obtained.

[0118] Based on finite element numerical calculation, the effect of magnetorheological fluid concentration on the resonant frequency can be obtained. The calculation results are as follows: Figure 5a-5d As shown. When no magnetorheological fluid is added, the resonant frequency point of the electromagnetic metamaterial is 7.36MHz. When the concentration of the added magnetorheological fluid is 100mg / ml, 200mg / ml, 300mg / ml, and 400mg / ml, the resonant frequency points are 4.2MHz, 3.2MHz, 2.7MHz, and 2.4MHz, respectively. As the concentration of the magnetorheological fluid increases, the resonant frequency point shifts to the left. The effect of magnetorheological fluid on reducing the resonant frequency point from nothing to something is extremely significant. When the concentration of the magnetorheological fluid is continuously increased, the effect of reducing the resonant frequency point becomes less and less obvious. Similarly, when the concentration of the magnetorheological fluid is reduced, the resonant frequency point increases.

[0119] When studying the effect of magnetorheological fluid concentration on the resonant frequency point, the particle size of the magnetic nanoparticles was fixed at 8nm. In addition to the concentration effect, the particle size of the magnetic nanoparticles is also an important characteristic parameter of the magnetorheological fluid. Based on finite element numerical calculations, the effect of the magnetic nanoparticle size on the resonant frequency can be obtained. The calculation results are as follows: Figure 6a-6d As shown. When the concentration of the magnetorheological fluid is fixed at 400 mg / ml, and the particle size of the magnetic nanoparticles is 8 nm, 12 nm, 16 nm and 20 nm, the resonant frequency points all shift to the left as the particle size increases. When the particle size is increased to 20 nm, four resonant frequency points appear, and the smallest resonant frequency point can be reduced to 0.8 MHz.

[0120] Increasing the concentration of magnetorheological fluid or increasing the particle size of magnetic nanoparticles can increase the inductance of electromagnetic metamaterials. From formula (1), it can be seen that the resonant frequency of electromagnetic metamaterials always decreases with the increase of inductance. Therefore, increasing the concentration of magnetorheological fluid or increasing the particle size of magnetic nanoparticles can reduce the resonant frequency of electromagnetic metamaterials. Similarly, reducing the concentration of magnetorheological fluid or reducing the particle size of magnetic nanoparticles can also reduce the inductance and increase the resonant frequency, thereby realizing dynamic regulation of the resonant frequency by magnetorheological fluid concentration or magnetic nanoparticle size.

[0121] The present invention does not elaborate on some of the common technologies of those skilled in the art. The above-described embodiments are only descriptions of preferred implementations of the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementations described. Without departing from the design spirit of the present invention, various modifications and improvements made by ordinary technicians in this field to the technical solution of the present invention should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A design method for an adjustable electromagnetic metamaterial for wireless charging of power equipment, characterized in that: The following steps are involved: (1) determining the side length of the electromagnetic metamaterial unit lattice and the maximum side length of the square spiral coil in the electromagnetic metamaterial unit; (2) The number of turns of the square spiral structure is optimized according to the calculation formula of the equivalent magnetic permeability of the resonator unit of the square spiral coil; the calculation formula of the equivalent magnetic permeability of the resonator unit of the square spiral coil is: (2) (3) Where a is the side length of the metamaterial unit lattice, in m; b is the maximum side length of the square spiral coil in the electromagnetic metamaterial unit, in m; σ is the conductivity of the coil material, in S / m, i is the imaginary unit, σi represents a pure imaginary number with a modulus of σ; μ0 is the vacuum permeability, in H / m; ω is the operating frequency of the electromagnetic metamaterial; ε0 represents the vacuum dielectric constant, in F / m; C is the material capacitance, in F; N is the number of coil turns, s is the coil turn spacing, in m; the number of turns of the square spiral coil is calculated according to formula (2) and formula (3); (3) Determine the resonant frequency of electromagnetic metamaterials and verify the negative magnetic permeability characteristics based on finite element simulation; (4) Using magnetorheological fluids of different concentrations and / or magnetorheological fluids with magnetic nanoparticles of different particle sizes to control the relative magnetic permeability of electromagnetic metamaterials; (5) Evaluating the effect of the concentration of magnetorheological fluid and / or the particle size of magnetic nanoparticles in the magnetorheological fluid on the resonant frequency of the electromagnetic metamaterial; the evaluation of the effect of the concentration of magnetorheological fluid and / or the particle size of magnetic nanoparticles in the magnetorheological fluid on the resonant frequency of the electromagnetic metamaterial is performed as follows: establishing a relationship between the characteristic parameters of the magnetorheological fluid and the BH curve of the magnetorheological fluid, using the BH curve to perform numerical modeling analysis of the magnetorheological fluid and the electromagnetic metamaterial, and the calculation formula used is as follows: (4) (5) (6) (7) (8) B represents magnetic induction intensity, the unit is T; H represents magnetic field intensity, the unit is A / m; μ0 vacuum permeability, the unit is H / m; X represents magnetic susceptibility, the unit is m^3·kg -1 ; M0 is the maximum magnetization intensity of magnetic nanoparticles per unit volume, in A / m; N is the number of magnetic nanoparticles per unit volume; m o It is equal to the product of the magnetic domain magnetization intensity and the volume of the magnetic nanoparticle, and the unit is A. m^2; Ms is the saturation magnetization, the unit is A / m; M d is the magnetization intensity of the magnetic domain, the unit is A / m; M is the magnetization intensity, the unit is A / m; V M is the volume of the magnetic nanoparticle, in m^3; K is the Boltzmann constant, a physical constant, dimensionless; T is the absolute temperature, in °C; L(ξ) is the Langevin function, ξ is the magnetization intensity of the magnetic domain M d , magnetic field intensity H, magnetic nanoparticle volume V M , Boltzmann constant K, and absolute temperature T are variables represented by no practical meaning.

2. The design method according to claim 1, characterized in that: In step (1), the square spiral coil is a planar spiral structure.

3. The design method according to claim 1, characterized in that: In step (1), the maximum side length of the square spiral coil in the unit is determined according to formula (1); the formula (1) is as follows: (1) Where ω0 is the resonant frequency of the electromagnetic metamaterial, in rad / s; L eff is the equivalent inductance value, the unit is H; C is the electromagnetic metamaterial capacitance value, the unit is F.

4. The design method according to claim 1, characterized in that: In step (3), after the electromagnetic metamaterial structural parameters are determined, the resonant frequency of the electromagnetic metamaterial is determined according to finite element simulation; the structural parameters are: the side length a of the electromagnetic metamaterial unit lattice; The maximum side length b of the square spiral coil in the electromagnetic metamaterial unit; the wire width w in the coil and the coil turn spacing s.

5. The design method according to claim 1, characterized in that: In step (4), when the concentration and the particle size of the magnetic nanoparticles are different, the magnetic permeability of the magnetorheological fluid is also changing. The change in magnetic permeability will change the magnetic resistance distribution, and then change the equivalent inductance value of the electromagnetic metamaterial, thereby realizing dynamic regulation of the resonant frequency.

6. The design method according to claim 1, characterized in that: The design method further includes: step (6) obtaining different BH curves by changing the concentration of magnetorheological fluid and the particle size of magnetic nanoparticles. Different BH curves can reduce magnetic resistance or increase inductance values ​​in different ways, thereby obtaining the resonant frequency points of the electromagnetic metamaterial under the action of different magnetorheological fluid concentrations and particle sizes, thereby meeting the actual size requirements of the wireless charging system and realizing dynamic adjustment of the resonant frequency within the frequency drift range.

7. The design method according to claim 1, characterized in that: In step (5), the concentration of the magnetorheological fluid is fixed, and the resonant frequency points shift to the left as the particle size increases.

8. The design method according to claim 1, characterized in that: In step (5), the particle size of the magnetic nanoparticles is fixed, and as the particle size increases, the resonant frequency points shift to the left.

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