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Wireless Power Transfer: Survey and Roadmap

Xiaolin Mou, Hongjian Sun

arXiv:1502.04727v1cs.ITmath.IT

TL;DR

Open research challenges are described as hindering public acceptance of WPT. This paper surveys WPT technologies and research themes, and reports that their power-transfer efficiency is lower than wired transfer while research focuses on efficiency, distance, and multiple-device charging.

  • Problem

    The paper identifies open WPT research challenges that hinder public acceptance of the technologies.

    Source: §I · p. 2

  • Method

    The paper surveys state-of-the-art WPT technologies and organizes research themes around efficiency, distance, and multiple transmitters or receivers.

    Source: §I · p. 2, §III · p. 5

  • Results

    The three WPT approaches differ in principle but share lower power-transfer efficiency than wired power transfer; research focuses on improving efficiency and distance and enabling multiple-device charging.

    Source: §VI · p. 11

  • Takeaways & Limitations

    The paper presents open challenges and a potential roadmap as part of its outlook on WPT research.

    Source: §I · p. 2

Abstract

from arXiv · show

Wireless power transfer (WPT) technologies have been widely used in many areas, e.g., the charging of electric toothbrush, mobile phones, and electric vehicles. This paper introduces fundamental principles of three WPT technologies, i.e., inductive coupling-based WPT, magnetic resonant coupling-based WPT, and electromagnetic radiation-based WPT, together with discussions of their strengths and weaknesses. Main research themes are then presented, i.e., improving the transmission efficiency and distance, and designing multiple transmitters/receivers. The state-of-the-art techniques are reviewed and categorised. Several WPT applications are described. Open research challenges are then presented with a brief discussion of potential roadmap.

I. INTRODUCTION

Wireless power transfer may make energy transfer wireless, but open challenges are described as hindering public acceptance. The paper surveys WPT technologies, research themes, applications, and challenges, then discusses a potential roadmap.

I. INTRODUCTION

  • WPT is presented as a technology that may make energy transfer wireless, with everyday uses including charging mobile devices.Source: §I · pp. 1–2
  • The paper groups WPT into inductive, magnetic-resonant, and electromagnetic-radiation approaches, which have different advantages and disadvantages.Inductive WPT uses magnetic-field induction; resonant coupling uses the same resonant frequency on both sides; electromagnetic radiation uses microwave frequencies.Source: §I · p. 2
  • Research themes include improving transmission efficiency and distance and designing systems with multiple transmitters or receivers.Source: §I · p. 2
  • The introduction says open research challenges hinder public acceptance of WPT technologies.It calls for addressing these challenges in support of WPT applications.Source: §I · p. 2
  • The paper surveys state-of-the-art WPT technologies and presents open research challenges and a potential roadmap.It outlines the paper's coverage of fundamental principles, research themes, applications, and challenges.Source: §I · p. 2

II. FUNDAMENTAL PRINCIPLES

The paper distinguishes inductive coupling, magnetic resonant coupling, and electromagnetic radiation as three WPT approaches. For inductive coupling, it describes magnetic-field induction and induced voltage, alongside short-range and alignment-related limitations.

II. FUNDAMENTAL PRINCIPLES

  • WPT has three categories: inductive coupling, magnetic resonant coupling, and electromagnetic radiation.Source: §II · p. 2

A. Inductive Coupling Approach

  • Inductive coupling uses magnetic-field induction, with Biot-Savart’s Law calculating the field from current and Faraday’s Law calculating induced receiver-coil voltage.The paper describes the field produced by a current distribution and the induced voltage as the rate of change of magnetic field through an effective surface area.Source: A. Inductive Coupling Approach · pp. 2–3
  • State-of-the-art inductive coupling supports transmission over millimetres or centimetres, and poor coil alignment significantly reduces PTE.Source: A. Inductive Coupling Approach · p. 3
  • Despite these limitations, inductive coupling is described as simple, safe, and used in applications including toothbrushes, laptops, mobile phones, and medical implants.Source: A. Inductive Coupling Approach · p. 3

B. Magnetic Resonant Coupling Approach

Magnetic resonant coupling uses resonant transmitter and receiver subsystems, with transfer efficiency shaped by resonator quality and mutual coupling. It can transfer power farther than inductive coupling without radiation or line of sight, but remains sensitive to misalignment and is difficult to tune for multiple devices.

B. Magnetic Resonant Coupling Approach

C. Electromagnetic Radiation Approach

Electromagnetic radiation WPT uses a microwave source, waveguide, and transmitting and receiving antennas to convert transmitted energy into direct current. The paper identifies efficiency and distance improvements, alongside multiple-transmitter/receiver design, as central research themes.

C. Electromagnetic Radiation Approach

  • A microwave source sends energy through a waveguide to a transmitting antenna, while a receiving antenna collects microwave energy and converts it to direct current.The described receiver uses a silicon-controlled rectifier diode.Source: C. Electromagnetic Radiation Approach · p. 5
  • Electromagnetic radiation WPT offers high power transmission efficiency over long distances, but raises radiation concerns and requires line of sight.Source: C. Electromagnetic Radiation Approach · p. 5

III. MAIN RESEARCH THEMES

  • The paper identifies improving transmission efficiency and distance as a main research theme.Source: §III · p. 5
  • Designing systems with multiple transmitters and receivers is the other main research theme.Source: §III · p. 5

A. Improving the transmission efficiency and distance

The paper reviews factors and techniques related to transmission efficiency and distance, with coil design as one focus. It reports efficiency gains from high-Q planar-Litz coils and from operating at specified coil-diameter-to-air-gap ratios.

A. Improving the transmission efficiency and distance

1) Coil Design:

  • Coil material and geometry are among the discussed design considerations, alongside coil size relative to transmission distance.The text notes magnetoplated wire, multilayer multi-turn tubular coils, and spiral, flat, square, and circular geometries.Source: 1) Coil Design · pp. 6–7
  • Using a high-Q planar-Litz coil can improve efficiency by almost 20% [11].Source: 1) Coil Design · p. 6
  • If the air gap is less than half the coil diameter (L/A < 0.5), transmission efficiency exceeds 80%; if L/A < 0.25, it can reach 90%.These conditions assume a constant Q-factor.Source: 1) Coil Design · p. 7

2) Coil Alignment:

The alignment discussion distinguishes lateral and angular misalignment and identifies a gap because existing work generally analyzes them separately. Circuit-design approaches include frequency tracking and a compensating mixed-resonant circuit, while excessive operating frequency can increase winding resistance.

2) Coil Alignment:

  • An ANSYS model was used to simulate transfer efficiency against lateral misalignment distance and determine a high-efficiency misalignment range [17].Source: 2) Coil Alignment · p. 7
  • Existing studies tend to analyze lateral and angular coil misalignment separately, although both may occur together, leaving a research gap.The text describes lateral offsets for parallel coils and angular misalignment when their centers are aligned.Source: 2) Coil Alignment · p. 7

3) Circuit Design:

  • Frequency tracking has been proposed to find the possible maximum PTE, but operating frequency should not be too high because skin and proximity effects increase winding resistance.Source: 3) Circuit Design · p. 7
  • A serious-shunt mixed-resonant compensating circuit was proposed to improve PTE, resulting in high transmission efficiency over long distance.Source: 3) Circuit Design · p. 7

4) The Environmental Analysis:

Environmental factors and coil design can affect power-transfer efficiency (PTE), while multi-transmitter/receiver systems raise challenges in frequency matching, power distribution, and efficiency. Reviewed approaches include receiver-coil additions and repeaters, with outcomes depending on system conditions.

4) The Environmental Analysis:

  • Some semiconductors are temperature-sensitive, and the environmental analysis identifies this as a factor affecting PTE.Source: 4) The Environmental Analysis · p. 7
  • A ferrite core can increase magnetic flux, while an intermediate coil can raise the apparent coupling coefficient through increased inductances.The intermediate coil boosts effective self-inductance and magnetizing inductance in the primary coil.Source: 4) The Environmental Analysis · pp. 7–8

B. Multiple transmitters/receivers design

IV. APPLICATIONS

The applications section describes WPT for home electronics, medical implants, and electric vehicles. Reported examples include TV charging, avoidance of implant-battery replacement surgery, and roadway-powered vehicle charging.

A. Home Electronics:

  • The cited text describes three self-resonators for charging a 47 inch LED TV and reports PTE up to 80%, but does not establish that efficiency for the TV system.Source: A. Home Electronics · p. 8

B. Medical Implants:

  • An external transmitter and an implanted receiver can avoid surgeries to replace batteries in medical implants.Source: B. Medical Implants · p. 9

C. Electric Vehicles:

  • 100 kW output at 80% PTE is reported at a 26 cm transmitter/receiver distance; series compensation is reported with high tolerance to lateral misalignment.Source: C. Electric Vehicles · p. 9

D. Wireless ‘Grid’:

The roadmap describes a prospective wireless electricity grid and identifies adaptive transmitter/receiver settings as research challenges. It highlights real-time response to misalignment and flexible coil design as areas requiring further work.

D. Wireless ‘Grid’:

  • A WPT-based grid could eliminate wired transmission grids, with future prospects including remote renewable sources and ambient micro-power harvesting,,.Source: D. Wireless ‘Grid’ · p. 9

A. Self-adaptation to Misalignment

  • Misalignment motivates mutual adaptation of transmitter and receiver parameters to pursue PTE and transmission distance; one proposed approach tracks receiver load power and adjusts receiver settings.Source: A. Self-adaptation to Misalignment · pp. 9–10
  • The challenge is adjusting lateral and angular alignment and operating frequency in real time while guaranteeing globally optimal power output; receiver feedback, including a Zigbee link, is another proposed approach.Source: A. Self-adaptation to Misalignment · pp. 9–10

B. Self-adaptation to Coil Length and Geomery

C. Small Animal Protection

The paper identifies small-animal protection during WPT charging as a research need and concludes that efficiency, distance, and multi-device charging remain central themes. It also notes lower PTE than wired transfer and the challenge of adapting systems to misalignment.

C. Small Animal Protection

VI. CONCLUSION

  • Inductive and magnetic resonant coupling are near-field techniques, while electromagnetic radiation-based WPT is far-field; the three suit different scenarios.Source: §VI · p. 10
  • The paper identifies lower PTE than wired transfer as common across WPT technologies and lists efficiency, distance, and multi-device charging as research focuses.Source: §VI · p. 11
  • Adapting transmitter or receiver parameters, including coil length and geometry, is identified as a challenge in addressing misalignment.Source: §VI · p. 11
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