# Single-Tube and Multi-Turn Coil Near-Field Wireless Power Transfer for Low-Power Home Appliances

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## Abstract

**:**

## 1. Introduction

- (i.)
- Two new systems (STLC and MTCWC) are designed and implemented, based on a parallel to parallel compensation capacitors topology.
- (ii.)
- The performance metrics of the two systems are explored in terms of transfer distance, output power, transfer efficiency, output voltage, and operating frequency.
- (iii.)
- A comparison between the two proposed systems is conducted in terms of performance metrics, with and without different resistive loads.
- (iv.)
- The battery-charging function of a mobile device is confirmed using the two systems.
- (v.)
- The proposed systems outperform the other methods in the literature, in terms of transfer distance, output power, and efficiency, according to the comparative results.

## 2. Related Works

- (i.)
- Without shield, which had simulated and measured transfer efficiencies of 98.3% and 96.2%, respectively;
- (ii.)
- Active shield, which had simulated and measured transfer efficiencies of 79.3% and 75.1%, respectively;
- (iii.)
- Non-resonator shield, which had simulated and measured transfer efficiencies of 97.1% and 95%, respectively; and
- (iv.)
- Prop-resonator reactive shield, which had simulated and measured transfer efficiencies of 93.6% and 90.2%, respectively, under a 6.78-MHz frequency and 10-W input power.

^{2}. Consequently, the total efficiency of 78.1% can be achieved, with a maximum output power of 2.7 W, at an air gap of 23 mm and frequency of 6.78 MHz.

## 3. Inductive Power Transfer for Low Power Home Appliances

- (i.)
- Users of smartphones, portable media players, digital cameras, tablets, and wearable devices request easy-to-use solutions, increased freedom of positioning, and reduced charging times. These applications typically require 2–15 W and prefer multi-standard interoperability. Wireless charging can coexist with near-field communication (NFC) and Bluetooth, thereby allowing for innovative solutions. For example, paired phones can charge one another when placed back-to-back, after the appropriate host and client have negotiated.
- (ii.)
- Accessories, such as headsets, wireless speakers, mice, and keyboards, can benefit from WPT. Plugging charging cables into the tiny connectors of small devices is an impediment to robust design. For example, Bluetooth headsets must be sweat-proof to survive in gyms, and only wireless charging can make this characteristic possible.
- (iii.)
- Public-access charging terminals, where charging pads (transmitters) are deployed in the public domain, require safe and secure systems. However, smart charging systems can offer considerably more than stand-alone charging solutions, thereby enabling quick network connectivity and creating billable charging stations when desired. Many coffee shops, airport kiosks, and hotels support these scenarios. Furniture manufacturers also incorporate discreet wireless power transmitters into their end and side tables.
- (iv.)
- Computer systems, such as laptops, notebooks, ultra-books, and tablet PCs, are all candidates for wireless charging, as either hosts or clients. The possibilities are endless.
- (v.)
- In cabin automotive applications, a wireless charger is ideal for charging mobile phones and key fobs. Such chargers can be placed either on the dash or in the center console of the car, without inconvenient wires protruding from cigarette lighter sockets. Moreover, combining NFC with wireless charging not only enables users to charge their phones but also automatically connects these devices to the Wi-Fi and Bluetooth networks of their cars, without undergoing any specific setup process. Bluetooth and Wi-Fi require authentication to connect phones to car electronics.
- (vi.)
- In miscellaneous applications, wireless chargers are now used for devices with batteries, such as game consoles and TV remotes, cordless power tools, cordless vacuum cleaners, soap dispensers, hearing aids, and pacemakers. Wireless chargers are also capable of charging super capacitors or any device that is traditionally powered by a low-voltage power cable [22].
- (vii.)
- Wireless charging can be used to charge WSNs and drones, which are used for different applications [4].

## 4. Methodology

#### 4.1. Proposed STLC and MTCWC System

- (i.)
- In series coupling capacitors, the effect of the parasitic shunt capacitance of the coil is negligible because it has a small value, whereas the effect should be considered in a parallel connection because parallel coupling capacitors cancel the effect of the small value of the parasitic shunt capacitance [9];
- (ii.)
- To obtain a more flexible technique (i.e., resonant frequency control technique), a discrete tuning variable parallel capacitor or parallel inductor with a receiver coil can be used [26];
- (iii.)
- The output transfer voltage, with a parallel coupling capacitor in the secondary coil, is considerably higher than that with a series coupling capacitor [27];
- (iv.)
- The transfer efficiency of the parallel topology is better than the series topology [28], where the transfer efficiency is 95% at 100 Ω load resistance;
- (v.)
- The parallel topology has a higher voltage boosting property than the series topology [26];
- (vi.)

#### 4.2. Proposed Systems Analysis

_{o}) [33].

_{s}and L

_{r}are the inductances of the source and the receiver, and C

_{s}and C

_{r}are the capacities of the source and the receiver, respectively.

_{s}, L

_{r}, C

_{s}, and C

_{r}(Table 1) yield a resonant frequency of approximately 1 MHz.

_{C}resonator circuit is used in the source and the receiver (Figure 5). Based on the circuit shown in Figure 5, the steady-state equations for the current and voltage can be computed for each branch and node in the source and receiver circuits. Kirchhoff’s voltage law can be applied to this circuit. Consequently, the transfer efficiency (η) can be calculated as follows [28]:

_{L}) is greater than (f

_{o}L

_{r}), and the resonant frequencies f

_{o}

_{1}and f

_{o}

_{2}of the two tanks are equal, as in our case, where the adopted resistive load is R

_{L}= 100 Ω and f

_{o}

_{1}= f

_{o}

_{2}= 1 MHz, then the adopted resistive load is clearly greater than the multiplication of f

_{o}L

_{r}, which is equal to 95. Then, Equation (2) of the efficiency of the STLC and MTCWC circuits at the tuned frequency is simplified as follows [28]:

_{sr}), the resonant frequency (f

_{o}), the self-inductance of the receiver coil (L

_{r}), the resistors of the source and receiver coils (i.e., R

_{LS}and R

_{Lr}), and the load resistor (R

_{L}). The self-inductance of the receiver coil, resonant frequency, and mutual inductance between the two coils should be increased to achieve a high transfer efficiency, while the resistor value of the coils (i.e., R

_{LS}and R

_{Lr}) should be decreased.

#### 4.3. Conjugate Image Impedance

_{S}is connected in parallel with the inductor Ls, and the capacitor Cr is connected in parallel with the inductor Lr (Figure 5).

_{pp}) can be expressed for the two port networks (i.e., port 1 and port 2), based on [34], as follows:

_{1}and Q

_{2}are the quality factors of the source and receiver coils, respectively; k is the coupling coefficient, where $k={M}_{sr}/\sqrt{{L}_{S}{L}_{r}}$; the other variables are based on [35]; and n is the transformer ratio, where $n=\sqrt{{L}_{S}/{L}_{r}}$. Thus, the expression of the conjugate image impedances is

_{o}is the input impedance.

## 5. STLC and MTCWC Experiment Topology

## 6. Experimental Results and Discussion

#### 6.1. STLC Results

#### 6.2. MTCWC Results

## 7. Comparison with the Literature

## 8. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 9.**Waveform and frequency spectra of (

**a**) a source circuit measured at the source coil; (

**b**) measured signals at the receiver coil for the system with a resistive load of 100 Ω at 6 cm; and (

**c**) measured signals at the receiver coil for the system with a resistive load of 100 Ω at 15 cm.

**Figure 11.**The relationship between transfer efficiency and transfer distance, with and without a load.

**Figure 12.**The relationship between output power and transfer efficiency versus distance with the following loads: (

**a**) 20 Ω; (

**b**) 50 Ω; and (

**c**) 100 Ω.

**Figure 13.**Measured voltage signals and frequency spectra at the receiver coil when the system is loaded with resistive loads of 100 Ω at (

**a**) 6 cm and (

**b**) 15 cm.

**Figure 15.**The relationship between transfer efficiency and transfer distance, with and without load.

**Figure 16.**The relationship between output power and transfer efficiency versus distance with the following loads: (

**a**) 20 Ω; (

**b**) 50 Ω; and (

**c**) 100 Ω.

Parameters | Value |
---|---|

Input voltage (E/Volt) | 12 |

Operating frequency (f/MHz) | 1 |

Inductance of transmitter coil (RFC1/µH) | 100 |

Inductance of transmitter coil (RFC2/µH) | 100 |

Compensating capacitor of transmitter coil (Cs/pf) | 300 |

Compensating capacitor of receiver coil (Cr/pf) | 300 |

Load resistance (RL/$\mathsf{\Omega}$) | 20, 50, 100 |

Resistances (Rs1/$\mathsf{\Omega}$) | 50 |

Resistances (Rs2/$\mathsf{\Omega}$) | 50 |

Specification | Source and Receiver Coils |
---|---|

Number of turns | Single loop |

Diameter of turn (cm) | 30 |

Thickness of coil (cm) | 0.1 |

Diameter of metal conductor | 0.958 |

Air gap between coils (cm) | 1–30 |

Specification | MTCWC |
---|---|

Number of turns | 45 |

Diameter of coil (cm) | 5.7 |

Diameter of wire | 0.8 |

Inductance (µH) | 95 |

Air gap between (cm) | 1–30 |

Ref. | Frequency (kHz) | Transfer Distance (cm) | ${\mathit{P}}_{\mathit{i}\mathit{n}}\left(\mathbf{W}\right)$ | ${\mathit{P}}_{\mathit{o}\mathit{u}\mathit{t}}\left(\mathbf{W}\right)(\mathbf{with}\mathbf{Load})$ | ${\mathit{\eta}}_{}(\%)(\mathbf{with}\mathbf{Load})$ | Type of Coils |
---|---|---|---|---|---|---|

[43]/2012 | 1.300 | 4.4 | 1.05 | 0.475 | 45.01 | Copper wire coil |

[13]/2013 | 29–32 | 1.5 | 1.25 | 0.5 | 40 | Copper wire coil |

[49]/2013 | 500 | 13 | 0.03 | 1.2 | 40 | Copper wire coil |

[44]/2014 | 3800 | 5 | 0.14 | 0.042 | 30 | Single tube loop coil |

[5]/2014 | 1000 | 10 | 0.056 | 3 | 53 | Copper wire coil |

[48]/2014 | 0.1–0.2 | 0.5 | 7.14 | 5–120 | 70 | Copper wire coil |

[47]/2015 | 97.56 | N/A | 6.92 | 4.5 | 65 | Copper wire coil |

[16]/2015 | 6.78 | 1.04 | 0.3 | 0.1 | 30 | Copper wire coil |

[45]/2016 | 0.097 | 0.06 | 6 | 3.1 | 48.2–51.2 | Copper wire coil |

[46]/2017 | 13.56 | 2.25 | 6.7 | 2.8 | 41.7 | Copper wire coil |

STLC (this work) | 1000 | 2, 6 and 15 | 6 | 4.84 @ 2 cm | 80.66 @ 2 cm | Single tube loop coil |

4 @ 6 cm | 66.66 @ 6 cm | |||||

2.82 @ 15 cm | 47.04 @ 15 cm | |||||

MTCWC (this work) | 1000 | 2, 6 and 15 | 6 | 2.37 @ 2 cm | 39.52 @ 2 cm | Multi turn copper wire coil |

2 @ 6 cm | 33.6 @ 6 cm | |||||

0.908 @ 15 cm | 15.13 @ 15 cm |

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## Share and Cite

**MDPI and ACS Style**

Jawad, A.M.; Nordin, R.; Gharghan, S.K.; Jawad, H.M.; Ismail, M.; Abu-AlShaeer, M.J.
Single-Tube and Multi-Turn Coil Near-Field Wireless Power Transfer for Low-Power Home Appliances. *Energies* **2018**, *11*, 1969.
https://doi.org/10.3390/en11081969

**AMA Style**

Jawad AM, Nordin R, Gharghan SK, Jawad HM, Ismail M, Abu-AlShaeer MJ.
Single-Tube and Multi-Turn Coil Near-Field Wireless Power Transfer for Low-Power Home Appliances. *Energies*. 2018; 11(8):1969.
https://doi.org/10.3390/en11081969

**Chicago/Turabian Style**

Jawad, Aqeel Mahmood, Rosdiadee Nordin, Sadik Kamel Gharghan, Haider Mahmood Jawad, Mahamod Ismail, and Mahmood Jawad Abu-AlShaeer.
2018. "Single-Tube and Multi-Turn Coil Near-Field Wireless Power Transfer for Low-Power Home Appliances" *Energies* 11, no. 8: 1969.
https://doi.org/10.3390/en11081969