Figures (11)  Tables (3)

    • Figure 1. 

      Free-positioning for multiple-receivers WPT system.

    • Figure 2. 

      (a) Proposed HCS-Tx coil: l = 116 mm, w = 116 mm, and h = 116 mm. (b)−(d) Magnetic field distribution on Oxy, Oxz, and Oyz planes.

    • Figure 3. 

      Schematic illustration of the free-positioning WPT system.

    • Figure 4. 

      (a) Multiple-receivers WPT equivalent circuit. (b) Structural diagram of Multiple-receivers WPT.

    • Figure 5. 

      (a) Fabricated HCS-Tx coil, (b) rectangular Rx coil, and (c) circular Rx coil.

    • Figure 6. 

      Mutual inductance between the HCS-Tx coil and rectangular Rx coil.

    • Figure 7. 

      (a) Single receiver WPT system measurement. (b) S-parameter results.

    • Figure 8. 

      Coil-to-coil power transfer efficiency.

    • Figure 9. 

      (a) Schematic diagram of Rx circuit: Cr1 = 150 pF, Lr1 = 3.3 μH, Cr2 = 130 pF, Cr3 = 1 F, RLoad = 1.3 kΩ. (b) Experimental setup for the multiple-receivers wireless charging system with the positions of Rx coil represented by dxr = 82 mm, dyr = 14 mm, dzr = 65 mm, φxr = φyr = φzr = 0°, dxc = 80 mm, dyc = 40 mm, dzc = 5 mm, φxc = φyc = φzc = 0°.

    • Figure 10. 

      Performance comparison of wireless power transfer (WPT) systems operating at 6.78 MHz with multiple receivers.

    • Figure 11. 

      Waveform diagram to illustrate the relationship between electrical parameters.

    • FP HCS Tx Rectangular Rx Circular Rx
      Parameter Value Parameter Value Parameter Value
      L1t 25.56 μH L11 6 μH L12 1.07 μH
      R1t 36 Ω R11 2.36 Ω R12 0.67 Ω
      Lpt 8.2 μH C11 100 pF C12 655 pF
      C1t 85 pF C21 1 nF C22 2.4 nF
      C2t 1 pF RL1 50 Ω RL2 50 Ω
      RS 50 Ω

      Table 1. 

      Extracted lumped element values.

    • Rectangular Rx Circular Rx Overall PTE
      Coordinate (mm) Angle (°) PTE Coordinate (mm) Angle (°) PTE
      dxr dyr dzr φxr φyr φzr dxc dyc dzr φxc φyc φzc
      82 26 60 65 0 0 74.13% 35 85 5 0 0 0 20.42% 94.55%
      82 26 60 65 0 0 73.79% 5 35 35 0 90 0 22.35% 96.14%
      82 26 60 65 0 0 74.64% 5 80 80 0 90 0 20.42% 95.06%
      82 14 65 70 0 0 65.77% 80 40 5 0 0 0 20.42% 86.19%
      82 14 65 70 0 0 70.79% 80 40 5 0 0 0 22.38% 93.18%

      Table 2. 

      Summary of measured power transfer efficiency of multiple-receivers WPT system.

    • WPT method Resonant
      frequency (MHz)      		 Coil-to-coil transmission efficiency System efficiency Ref.
      Single Rx Multiple Rx
      Planar Tx coil with switchable IMNs 6.78 82.1% 93% NG [11]
      Class E amplifier with multiple receivers 6.78 NG 71.7% NG [29]
      WPT system for multiple receivers operating at Inductive and Resonant Operating Modes 6.78 NG 83% 66% [30]
      WPT system for a dual-mode transmitter, along with two receivers 6.78 NG 78% NG [31]
      Printed spiral half-cube shaped Tx structure 6.78 76.74% 96.14% 64% This work

      Table 3. 

      Performance Comparison of wireless power transfer (WPT) systems operating at 6.78 MHz with multiple receivers.