# A New Technique for Reducing Size of a WPT System Using Two-Loop Strongly-Resonant Inductors

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## Abstract

**:**

## 1. Introduction

## 2. Theoretical Analysis of Strongly-Coupled WPT Systems

## 3. Numerical Analysis

#### 3.1. High Q Coil System Specifications

#### 3.2. Low Q Coil System Specifications without Additional Inductor

#### 3.3. Effect of the Additional Coil Resistance on the System Efficiency

## 4. Experimental Setup

#### 4.1. System Design and Measurements

#### 4.2. System Maximum Efficiency

## 5. Results

## 6. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 1.**Electromagnetic field between the transmitter and receiver loops, which occurs due to changing polarity of the current flow.

**Figure 2.**(

**a**) A comparison between the conventional WPT system with a single set of coils ; and (

**b**) the proposed technique with an additional coil.

**Figure 3.**The circuit diagram of the proposed two-loop resonant WPT system with additional inductor. ${I}_{IN}$, ${I}_{2}$, ${I}_{3}$, ${I}_{4}$, ${I}_{5}$ and ${I}_{6}$ represent the currents in each branch, while the ${Z}_{T1}$, ${Z}_{T2}$, ${Z}_{R}$ and ${Z}_{R2}$ represent impedance of the inductors.

**Figure 4.**Calculated efficiency of the system with high Q of the transmitter and receiver coils, built based on the value of the elements from Table 1.

**Figure 5.**Efficiency of the system with low Q factor of the coil without additional inductor, calculated with advanced design system (ADS) software. A coupling factor at which maximum efficiency appears is much higher than that for the system with high Q.

**Figure 6.**Comparison between the coupling factor needed for the maximum efficiency to appear for the system with low Q and high Q of the coils.

**Figure 7.**The effect of the different values of additional inductors on the coupling factor needed to reach maximum efficiency. The coupling factor needed to reach maximum efficiency drops with the decrease of the value of additional inductor.

**Figure 8.**Comparison of the maximum distance between the ${T}_{X}$ and ${R}_{X}$ loops of the system with low Q design, with and without additional inductors and a system with high Q coil design.

**Figure 9.**Calculated efficiency of the proposed system with low Q of the coils with two additional inductors. The coupling factor at which maximum efficiency is much smaller than that for the low Q design without additional coils.

**Figure 10.**Effect of different resistance of added coils on the systems efficiency. The smaller the resistance, the higher the efficiency and vice-versa.

0.48 | 0.48 |

(a) b | (b) b |

**Figure 12.**Comparison between the measured and calculated maximum efficiency and frequency pattern for the modified circuit with additional coils. The results show close similarity of calculated and measured results.

**Figure 13.**Comparison between the measured and calculated maximum efficiency and frequency pattern of the conventional system with a high Q of the coil. A designed system shows close similarities with the calculations.

**Figure 14.**A comparison between the measured and calculated maximum distances between the low Q design coil with and without added inductor at frequency of 9.23 MHz. The system with an additional coils shows an increase in the distance between ${T}_{X}$ and ${R}_{X}$ at which mximum efficiency occurs.

**Figure 15.**Comparison between measured and calculated maximum distances between the ${T}_{X}$ and ${R}_{X}$ coil between the system with high Q coils and the system with added inductor. The results show a similar distance of transmission that can be achieved with both systems.

**Table 1.**Calculated elements of two-loop strongly coupled WPT system with high Q of coils, used to build a practical system.

Capacitance | Inductance | Resistance | Resistance |
---|---|---|---|

${C}_{1}$ = 1.6 pF | ${L}_{1}$ = 186.6 $\mathsf{\mu}$H | ${R}_{L1}$ = 0.15Ω | ${R}_{S}$ = 50Ω |

${C}_{2}$ = 1.3 pF | ${L}_{2}$ = 229.6 $\mathsf{\mu}$H | ${R}_{L1}$ = 0.15Ω | ${R}_{L}$ = 50Ω |

**Table 2.**Calculated base model of two-loop loosely coupled WPT system. The specification will be later used to built a practical model.

Capacitance | Inductance | Resistance | Resistance |
---|---|---|---|

${C}_{1}$ = 18 pF | ${L}_{1}$ = 16.37 $\mathsf{\mu}$H | ${R}_{L1}$ = 0.15Ω | ${R}_{S}$ = 50Ω |

${C}_{2}$ = 15 pF | ${L}_{2}$ = 19.65 $\mathsf{\mu}$H | ${R}_{L1}$ = 0.15Ω | ${R}_{L}$ = 50Ω |

**Table 3.**Calculated values of the elements used in the proposed model with two loop loosely coupled WPT system with a low Q of the coils and two additional inductors.

Capacitance | Inductance | Resistance | Resistance |
---|---|---|---|

${C}_{TX}$ = 18 pF | ${L}_{T2}$ = 16.37 $\mathsf{\mu}$H | ${R}_{L2}$ = 0.15Ω | ${R}_{L}$ = 50Ω |

${C}_{RX}$ = 15 pF | ${L}_{T1}$ = 0.2105 $\mathsf{\mu}$H | ${R}_{T1}$ = 0.15Ω | ${R}_{L}$ = 50Ω |

${L}_{R1}$ = 19.65 $\mathsf{\mu}$H | ${R}_{R1}$ = 0.15Ω | ||

${L}_{R2}$ = 0.2359 $\mathsf{\mu}$H | ${R}_{R2}$ = 0.15Ω |

**Table 4.**Comparison of the physical parameters of the conventional and modified systems. Proposed system shows a great improvement towards the conventional design.

Conv. ${\mathit{L}}_{\mathbf{TX}}$ | Mod. ${\mathit{L}}_{\mathbf{TX}}$ | Diff. % | Conv. ${\mathit{L}}_{\mathbf{RX}}$ | Mod. ${\mathit{L}}_{\mathbf{RX}}$ | Diff. % | |
---|---|---|---|---|---|---|

Length | 15 mm | 3 mm | 80% | 20 mm | 4 mm | 80% |

Weight | 7.37 g | 1.58 g | 78.6% | 8.63 g | 1.78 g | 79.4% |

Turns | 41 | 8 | 80.5% | 48 | 48 | 81% |

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## Share and Cite

**MDPI and ACS Style**

Rozman, M.; Fernando, M.; Adebisi, B.; Rabie, K.M.; Collins, T.; Kharel, R.; Ikpehai, A.
A New Technique for Reducing Size of a WPT System Using Two-Loop Strongly-Resonant Inductors. *Energies* **2017**, *10*, 1614.
https://doi.org/10.3390/en10101614

**AMA Style**

Rozman M, Fernando M, Adebisi B, Rabie KM, Collins T, Kharel R, Ikpehai A.
A New Technique for Reducing Size of a WPT System Using Two-Loop Strongly-Resonant Inductors. *Energies*. 2017; 10(10):1614.
https://doi.org/10.3390/en10101614

**Chicago/Turabian Style**

Rozman, Matjaz, Michael Fernando, Bamidele Adebisi, Khaled M. Rabie, Tim Collins, Rupak Kharel, and Augustine Ikpehai.
2017. "A New Technique for Reducing Size of a WPT System Using Two-Loop Strongly-Resonant Inductors" *Energies* 10, no. 10: 1614.
https://doi.org/10.3390/en10101614