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Regulation of spatial fields in wireless power transfer with artificial magnetic conductor

Shi Tai-Xia Dong Li-Juan Chen Yong-Qiang Liu Yan-Hong Liu Li-Xiang Shi Yun-Long

Regulation of spatial fields in wireless power transfer with artificial magnetic conductor

Shi Tai-Xia, Dong Li-Juan, Chen Yong-Qiang, Liu Yan-Hong, Liu Li-Xiang, Shi Yun-Long
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  • In order to improve the efficiency of wireless power transfer (WPT) system, the spatial fields are regulated on a two-non-resonant-coil WPT system by hexagon artificial magnetic conductors (AMC). In our configuration, the AMC is located by the side of the two-non-resonant-coil WPT system and close to the transmitter coil. The AMC structure consists of small hexagon copper patches periodically arranged on the dielectric substrate. Each patch is grounded by a via passing through its center hole. Chip capacitors are soldered in the gaps between the adjacent patches. We can design the working frequency of WPT system through the capacitance of these chip capacitors. The results show that the electromagnetic fields are changed between the transmitter coil and the receiver coil in WPT system due to the introducing of the AMC structure. There are two main reasons. First, many resonant modes are excited by near magnetic fields on the AMC structure. Second, near magnetic fields are shielded by the AMC structure. The variation of space electromagnetic field improves the transmission efficiency of WPT system. When the working frequency is 27 MHz and the transmission distance is 3 cm, the experiment verifies that the transmission efficiency increases by 22% in the WPT system with the AMC structure compared with the WPT system without the AMC structure. Simultaneously, the transmission efficiency is raised by 25% at different transmission distances. The simulation results are almost consistent with the experimental results. There is a little difference that the number of resonant modes is different between the simulation and the experiment due to the resistance loss of the chip capacitors in experiment. Therefore, we correct the simulation results under consideration of resistive loss. In addition, the excited multiple resonant modes can supply multiple and adjustable working frequencies in the WPT system with the AMC structure. In practical applications, AMC is low in cost and easy to implement.
      Corresponding author: Dong Li-Juan, donglijuan_2012@163.com
    [1]

    Ejaz W, Naeem M, Shahid A, Anpalagan A, Jo M 2017 IEEE Commun. Mag. 55 84

    [2]

    Lu X, Wang P, Niyato D, Kim D I, Han Z 2016 IEEE Commun. Surv. Tut. 18 1413

    [3]

    RamRakhyani A K, Mirabbasi S, Chiao M 2011 IEEE Trans. Biomed. Circ. S. 5 48

    [4]

    Hoang H, Lee S, Kim Y, Choi Y, Bien F 2012 IEEE Trans. Consum. Electr. 58 327

    [5]

    Li S, Mi C C 2015 IEEE J. Em. Sel.Top. P. 3 4

    [6]

    Xie L, Shi Y, Hou Y T, Sherali H D 2012 IEEE Acm. Trans. Netw. 20 1748

    [7]

    Tesla N 1914 U. S. Patent 1 119 732

    [8]

    Brown W C 1984 IEEE Trans. Microw. Theory 32 1230

    [9]

    Kurs A, Karalis A, Moffatt R, Joannopoulos J D, Fisher P, Soljacic M 2007 Science 317 83

    [10]

    Song M, Belov P, Kapitanova P 2017 Appl. Phys. Rev. 4 021102

    [11]

    Wang B, Teo K H, Nishino T, Yerazunis W, Barnwell J, Zhang J 2011 Appl. Phys. Lett. 98 254101

    [12]

    Sun K, Fan R, Zhang X, Zhang Z, Shi Z, Wang N, Xie P, Wang Z, Fan G, Liu H, Liu C, Li T, Yan C, Guo Z 2018 J. Mater. Chem. C 6 2925

    [13]

    Urzhumov Y, Smith D R 2011 Phys. Rev. B 83 205114

    [14]

    Wang B, Yerazunis W, Teo K H 2013 Proc. IEEE 101 1359

    [15]

    Lipworth G, Ensworth J, Seetharam K, Huang D, Lee J S, Schmalenberg P, Nomura T, Reynolds M S, Smith D R, Urzhumov Y 2014 Sci. Rep. 4 3642

    [16]

    Huang D, Urzhumov Y, Smith D R, Teo K H, Zhang J 2012 J. Appl. Phys. 111 064902

    [17]

    Ranaweera A L A K, Thuc Phi D, Lee J W 2014 J. Appl. Phys. 116 043914

    [18]

    Glybovski S B, Tretyakov S A, Belov P A, Kivshar Y S, Simovski C R 2016 Phys. Rep. 634 1

    [19]

    Lapine M, Tretyakov S 2007 IET Microw. Antenn. P. 1 3

    [20]

    Sievenpiper D, Zhang L J, Broas R F J, Alexopolous N G, Yablonovitch E 1999 IEEE Trans. Microw. Theory 47 2059

    [21]

    Radi Y, Simovski C R, Tretyakov S A 2015 Phys. Rev. Appl. 3 037001

    [22]

    Costa F, Monorchio A, Manara G 2010 IEEE Trans. Antenn. Propag. 58 1551

    [23]

    Luukkonen O, Simovski C, Granet G, Goussetis G, Lioubtchenko D, Raisanen A V, Tretyakov S A 2008 IEEE Trans. Antenn. Propag. 56 1624

    [24]

    赵一, 曹祥玉, 高军, 姚旭, 马嘉俊, 李思佳, 杨欢欢 2013 物理学报 62 154204

    Zhao Y, Cao X Y, Gao J, Yao X, Ma J J, Li S J, Yang H H 2013 Acta Phys. Sin. 62 154204

    [25]

    Wu J, Wang B, Yerazunis W S, Teo K H 2013 2013 IEEE Wireless Power Transfer Conference Perugia, Italy, May 15-16, 2013 p155

    [26]

    Lawson J, Yates D C, Mitcheson P D 2015 2015 IEEE Wireless Power Transfer Conference Boulder, USA, May 13−15, 2015 p1

  • 图 1  (a) WPT结构示意图; (b) AMC单元结构示意图

    Figure 1.  (a) Schematic of the WPT structure; (b) schematic of the AMC unit cell structure.

    图 2  AMC结构的等效电路模型

    Figure 2.  Equivalent circuit model of the AMC structure.

    图 3  仿真的效率图

    Figure 3.  S21 plot from the simulation.

    图 4  仿真效率随距离的变化

    Figure 4.  S21 as a function of distance from the coil obtained from the simulation.

    图 5  (a)−(e)分别对应图3中的5个共振频率处的磁场侧面分布图; (f)对应无AMC结构时磁场侧面的分布图

    Figure 5.  (a)−(e) Side distribution of the magnetic field associated with the five resonance frequencies shown in Figure 3; (f) the side distribution of the magnetic field in the absence of an AMC structure.

    图 6  实验配置图

    Figure 6.  Experimental configuration.

    图 7  实验的传输效率图

    Figure 7.  S21 plot from the coil obtained from the experiments.

    图 8  实验效率随距离的变化

    Figure 8.  Change in S21 as a function of distance from the coil obtained from the experiments.

    图 9  贴片电容与电阻串联时的仿真效率

    Figure 9.  S21 plot from the simulation of each chip capacitor with a resistor in series.

  • [1]

    Ejaz W, Naeem M, Shahid A, Anpalagan A, Jo M 2017 IEEE Commun. Mag. 55 84

    [2]

    Lu X, Wang P, Niyato D, Kim D I, Han Z 2016 IEEE Commun. Surv. Tut. 18 1413

    [3]

    RamRakhyani A K, Mirabbasi S, Chiao M 2011 IEEE Trans. Biomed. Circ. S. 5 48

    [4]

    Hoang H, Lee S, Kim Y, Choi Y, Bien F 2012 IEEE Trans. Consum. Electr. 58 327

    [5]

    Li S, Mi C C 2015 IEEE J. Em. Sel.Top. P. 3 4

    [6]

    Xie L, Shi Y, Hou Y T, Sherali H D 2012 IEEE Acm. Trans. Netw. 20 1748

    [7]

    Tesla N 1914 U. S. Patent 1 119 732

    [8]

    Brown W C 1984 IEEE Trans. Microw. Theory 32 1230

    [9]

    Kurs A, Karalis A, Moffatt R, Joannopoulos J D, Fisher P, Soljacic M 2007 Science 317 83

    [10]

    Song M, Belov P, Kapitanova P 2017 Appl. Phys. Rev. 4 021102

    [11]

    Wang B, Teo K H, Nishino T, Yerazunis W, Barnwell J, Zhang J 2011 Appl. Phys. Lett. 98 254101

    [12]

    Sun K, Fan R, Zhang X, Zhang Z, Shi Z, Wang N, Xie P, Wang Z, Fan G, Liu H, Liu C, Li T, Yan C, Guo Z 2018 J. Mater. Chem. C 6 2925

    [13]

    Urzhumov Y, Smith D R 2011 Phys. Rev. B 83 205114

    [14]

    Wang B, Yerazunis W, Teo K H 2013 Proc. IEEE 101 1359

    [15]

    Lipworth G, Ensworth J, Seetharam K, Huang D, Lee J S, Schmalenberg P, Nomura T, Reynolds M S, Smith D R, Urzhumov Y 2014 Sci. Rep. 4 3642

    [16]

    Huang D, Urzhumov Y, Smith D R, Teo K H, Zhang J 2012 J. Appl. Phys. 111 064902

    [17]

    Ranaweera A L A K, Thuc Phi D, Lee J W 2014 J. Appl. Phys. 116 043914

    [18]

    Glybovski S B, Tretyakov S A, Belov P A, Kivshar Y S, Simovski C R 2016 Phys. Rep. 634 1

    [19]

    Lapine M, Tretyakov S 2007 IET Microw. Antenn. P. 1 3

    [20]

    Sievenpiper D, Zhang L J, Broas R F J, Alexopolous N G, Yablonovitch E 1999 IEEE Trans. Microw. Theory 47 2059

    [21]

    Radi Y, Simovski C R, Tretyakov S A 2015 Phys. Rev. Appl. 3 037001

    [22]

    Costa F, Monorchio A, Manara G 2010 IEEE Trans. Antenn. Propag. 58 1551

    [23]

    Luukkonen O, Simovski C, Granet G, Goussetis G, Lioubtchenko D, Raisanen A V, Tretyakov S A 2008 IEEE Trans. Antenn. Propag. 56 1624

    [24]

    赵一, 曹祥玉, 高军, 姚旭, 马嘉俊, 李思佳, 杨欢欢 2013 物理学报 62 154204

    Zhao Y, Cao X Y, Gao J, Yao X, Ma J J, Li S J, Yang H H 2013 Acta Phys. Sin. 62 154204

    [25]

    Wu J, Wang B, Yerazunis W S, Teo K H 2013 2013 IEEE Wireless Power Transfer Conference Perugia, Italy, May 15-16, 2013 p155

    [26]

    Lawson J, Yates D C, Mitcheson P D 2015 2015 IEEE Wireless Power Transfer Conference Boulder, USA, May 13−15, 2015 p1

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  • Received Date:  02 June 2019
  • Accepted Date:  07 August 2019
  • Available Online:  26 November 2019
  • Published Online:  01 November 2019

Regulation of spatial fields in wireless power transfer with artificial magnetic conductor

    Corresponding author: Dong Li-Juan, donglijuan_2012@163.com
  • 1. Institute of Solid State Physics, Shanxi Datong University, Datong 037009, China
  • 2. Shanxi Provincial Key Laboratory of Electromagnetic Functional Materials for Microstructure, Datong 037009, China
  • 3. School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China

Abstract: In order to improve the efficiency of wireless power transfer (WPT) system, the spatial fields are regulated on a two-non-resonant-coil WPT system by hexagon artificial magnetic conductors (AMC). In our configuration, the AMC is located by the side of the two-non-resonant-coil WPT system and close to the transmitter coil. The AMC structure consists of small hexagon copper patches periodically arranged on the dielectric substrate. Each patch is grounded by a via passing through its center hole. Chip capacitors are soldered in the gaps between the adjacent patches. We can design the working frequency of WPT system through the capacitance of these chip capacitors. The results show that the electromagnetic fields are changed between the transmitter coil and the receiver coil in WPT system due to the introducing of the AMC structure. There are two main reasons. First, many resonant modes are excited by near magnetic fields on the AMC structure. Second, near magnetic fields are shielded by the AMC structure. The variation of space electromagnetic field improves the transmission efficiency of WPT system. When the working frequency is 27 MHz and the transmission distance is 3 cm, the experiment verifies that the transmission efficiency increases by 22% in the WPT system with the AMC structure compared with the WPT system without the AMC structure. Simultaneously, the transmission efficiency is raised by 25% at different transmission distances. The simulation results are almost consistent with the experimental results. There is a little difference that the number of resonant modes is different between the simulation and the experiment due to the resistance loss of the chip capacitors in experiment. Therefore, we correct the simulation results under consideration of resistive loss. In addition, the excited multiple resonant modes can supply multiple and adjustable working frequencies in the WPT system with the AMC structure. In practical applications, AMC is low in cost and easy to implement.

    • 家居、城市、交通和太空智能等物联网器件[1]的在线, 需要灵活实时的能量供应, 这类能量供应的需求迅速增加和扩大了对无线能量传输(wireless power transfer, WPT)技术的应用需求和范围. 例如, 无线充电技术[2]已经被应用在生物医学植入[3]、消费电子产品[4]、电动汽车[5]、无线传感器网络[6]等领域.

      1914年, Tesla[7]提出WPT的最初设想; 1963年, Brown[8]实现了微波远场的WPT; 2007年, Kurs等[9]验证了磁谐振耦合感应式WPT, 其可以适用于近距离和中距离的能量传输; 随后有多种谐振子和传输路径设计方案被用来提高WPT的传输效率[10]. 2011年, Wang等[11]将人工微结构材料引入WPT系统中, 利用超材料(metamaterials)构造的特异表面结构放置在发射线圈和接收线圈的中间, 放大电磁场传输过程中的倏逝波, 从而增强了WPT系统的传输效率. 为了提高WPT的传输效率, 有多种微结构材料被应用在WPT系统[1217], 进行近电磁场调控.

      人工磁导体(artificial magnetic conductors, AMC)是由人工设计的特异表面结构[1824], 通过覆铜板刻蚀后实现, 同时也是一种高阻抗表面结构. 该结构被应用于天线, 由于高阻抗表面有抑制表面波和零相位反射的性质, 很大程度地提高了天线的方向增益性, 同时有利于天线体积微型化[2224]. 2013年, Wu等[25]提出将理想磁导体作为反射面用在WPT系统中, 仿真计算得到了传输效率增强的结果. 2015年, Lawson等[26]将加载了电容的AMC应用于磁感应式WPT系统中, 证实AMC结构具有电磁屏蔽的效果.

      本文将加载贴片电容的正六边形AMC结构引入到WPT系统中, 通过仿真和实验相结合的方式, 研究了WPT的传输效率, 得到了效率增强的结果, 并从物理上解释其原因. 相较于文献[25, 26], 我们不仅在实验上验证了效率的提升, 同时分析了引入AMC结构后空间电磁场的变化, 找到了WPT效率增强的物理原因.

    2.   结构设计
    • 文中采用的WPT系统结构设计如图1(a)所示, 从上而下依次是接收线圈、发射线圈和AMC, 两个线圈的直径相同, 且AMC的表面与线圈平行放置. 线圈的线直径是2 mm, 环直径是150 mm. AMC结构属于蘑菇型结构, 是由介质基板上周期排列的正六边形小贴片组成, 每个小贴片在其中心均通过镀铜过孔接地, 并在相邻单元的间隙焊接贴片电容. 取横向周期数为8, 在倾斜方向取两个单元为一个复式单元, 在纵向此复式单元的周期数为5; 正六边形铜贴片的边长为20 mm, 相邻贴片间的缝隙宽度为1 mm; 贴片电容的电容值均为4.7 nF; 镀铜过孔直径是1 mm; 电路板(printed circuit board, PCB)所用介质为介电常数4.4的FR4, 厚度为3 mm, 如图1(b)所示. 这里需要强调一点, PCB介质的介电常数对该结构在此应用的性能影响很小, 所以可以选择成本最低的材料.

      Figure 1.  (a) Schematic of the WPT structure; (b) schematic of the AMC unit cell structure.

      图1(a)还可以看到, AMC结构放置在发射线圈的一侧, 而接收线圈则被安排在另一侧, 这样放置的好处在于可以把发射线圈和AMC结构集成在一起, 而发射线圈和接收线圈中间没有任何遮挡物, 这样的结构在实际产品中比较容易实现.

    3.   仿真计算
    • 仿真软件采用基于时域有限差分法的CST MWS (computer simulation technology microwave studio)三维电磁仿真软件. 发射线圈的开口处为离散源端口, 接收线圈的开口处为离散负载端口. 当离散源端口通电, 发射线圈会产生磁场, 其中一部分磁场能量由于电磁感应被接收线圈所接收, 另一部分磁场能量作用于发射线圈一侧的AMC结构. AMC结构中横纵方向都有多个单元, 每个单元由介质、贴片电容、铜片、镀铜孔和底铜构成, 如图2所示, 其中贴片电容的电容值为C, 连接贴片与接地板的过孔则提供等效电感L, 这样每个单元就形成了LC等效电路, 即每个单元相当于一个谐振子. 由于AMC并非无限大, 导致它的不同位置谐振子的谐振频率略有差别, 部分谐振频率相同的谐振子则有能级分裂的情况, 同时各谐振子之间会相互耦合, 最终导致AMC整体结构有多个共振频率和多种耦合模式.

      Figure 2.  Equivalent circuit model of the AMC structure.

      图3图4均为仿真结果图, 实线对应有AMC结构, 点划线对应无AMC结构. 图3给出了发射线圈和接收线圈在有AMC结构和无AMC结构时效率曲线变化情况的对比图, 其中对应的发射线圈和接收线圈之间距离为30 mm. 从图3可以看到, 共振频率27.67 MHz处出现了最高峰值, S21达到了60%, 与无AMC结构时的S21相比提高了40%. 图4给出了发射线圈和接收线圈在有AMC结构和无AMC结构时S21随距离变化的情况, 可以看到, 有AMC结构时的S21比无AMC结构时的S21整体都提高了40%左右, 在发射线圈和接收线圈距离10 mm处, S21达到了74%. 另外, 从图3还可以看到, 由于近磁场激发了AMC结构中的多个谐振模式, 所以出现了多个峰值. 因此, 加入AMC结构的WPT系统, 可以进行多频率能量传输. 同时, AMC结构中的谐振频率可以通过结构参数来调节, 主要由贴片电容的容值、相邻贴片的缝隙宽度、镀铜孔的高度决定, 其中贴片电容的容值是对谐振频率影响最大的参数, 其他参数则可以进行微调.

      Figure 3.  S21 plot from the simulation.

      Figure 4.  S21 as a function of distance from the coil obtained from the simulation.

      为了更好地说明效率提升的物理原因, 图5(a)—(e) 5幅图分别给出了图3中标注的5个峰所对应频率的磁场侧面分布图, 图5(f)给出了无AMC结构时磁场侧面分布图. 从图5(f)可以看到, 非共振双线圈WPT系统中, 无AMC结构时, 能量有很大一部分分布在发射线圈的另一侧, 到达接收线圈的能量很有限. 然而, 当加入AMC结构时, 近磁场不同程度地被该结构屏蔽, 但是磁场屏蔽并不是传输效率提升的根本原因, 而是由于AMC结构使附近空间的磁场分布发生了变化, 如图5(a)图5(f)所示. 从图5(a)—(e)还可以看到, 对应不同的共振频率处, 对近磁场的屏蔽程度不同, 而且5个模式分布对应着正六边形AMC结构的不同阶模式, 所以传输效率不同. 值得一提的是, AMC结构有屏蔽MHz频段磁场的功能, 而传统磁材料一般低于1 MHz, 且现有的MHz磁屏蔽材料造价昂贵.

      Figure 5.  (a)−(e) Side distribution of the magnetic field associated with the five resonance frequencies shown in Figure 3; (f) the side distribution of the magnetic field in the absence of an AMC structure.

    4.   实验结果
    • 实验配置如图6所示, 实验测试所用仪器为矢量网络分析仪, 型号为Keysight E5063A, 发射和接收的线圈用漆包圆铜线制成, 线圈端口焊接SMA头, 然后通过同轴线连接到矢量网络分析仪.

      Figure 6.  Experimental configuration.

      图7图8均为实验结果图, 实线对应有AMC结构, 虚线对应无AMC结构. 图7给出了发射线圈和接收线圈在有AMC结构和无AMC结构时曲线变化情况的对比图, 其中发射线圈和接收线圈之间距离为30 mm. 从图7可以看到, 共振频率27 MHz处出现了最高峰值, S21达到了39%, 与无AMC结构时的S21相比提高了22%. 图8给出了发射线圈和接收线圈在有AMC结构和无AMC结构时S21随距离变化的情况, 可以看到, 有AMC结构时的S21比无AMC结构时的S21整体都提高了25%左右, 在发射线圈和接收线圈距离10 mm处, S21达到了56%. 另外, 从图7也可以看到出现了多个峰值; 与图3相比其峰值数量减少, 第2个和第3个峰融合; 30—35 MHz内, 峰的数量大量减少, 曲线走势趋于平缓.

      Figure 7.  S21 plot from the coil obtained from the experiments.

      Figure 8.  Change in S21 as a function of distance from the coil obtained from the experiments.

      实验仿真所用AMC的单元较多, 同时各谐振单元之间会相互耦合, 从而会存在多个谐振频率. 实验中峰的个数减少主要是因为焊接贴片电容时产生的串联电阻, 串联电阻会影响各谐振单元之间的耦合, 导致一些峰值大幅降低甚至消失, 峰值最受影响的是AMC边角位置数量较少的谐振单元对应的频率较高的模式. 对CST仿真计入损耗进行修正, 在加载AMC的WPT的系统中, 给AMC中的每个贴片电容串联一个电阻, 当电阻值较小时, 可以得到S21峰的数量减少、峰值降低的结果, 当电阻值较大时, AMC的作用将会消失. 加电阻进行修正的仿真结果如图9所示, 当加载电阻为0.01 Ω时, 其S21曲线与实验所得S21曲线非常相近; 当加载电阻为3 Ω时, AMC的作用不再显现.

      Figure 9.  S21 plot from the simulation of each chip capacitor with a resistor in series.

    5.   结 论
    • 本文通过仿真和实验手段研究了AMC结构应用在WPT系统中的效率增强特性. 研究结果表明, 由于AMC结构的介入, 多个谐振模式被激发, 同时达到磁屏蔽效果, 得到了效率增强的多模式工作方式. AMC结构的共振频率, 可以通过贴片电容的电容值来调节, 工作频率范围可以根据需求去设置. 同时, 由于AMC结构处于发射端的一侧, 比附加结构在发射端和接收端中间的情况更容易实现.

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