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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "F: Electrical Engineering".

Deadline for manuscript submissions: closed (20 February 2022) | Viewed by 28694

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Special Issue Editor

Dr. Young-Jin Park

E-Mail Website
Guest Editor

Korea Electrotechnology Research Institute, An-San 15588, Republic of Korea
Interests: magnetic coupled WPT; beam-type WPT; coil design and system optimization; applications of WPT for mobile devices; medical devices; IoT sensors

Special Issue Information

Dear Colleagues,

The Guest Editor invites you to submit a manuscript to a Special Issue on “Next-Generation Wireless Charging Systems for Mobile Devices” in Energies.

The aim of this Special Issue is to publish technical papers reflecting the most recent research and application results in the area of the next-generation WPT for mobile devices and wearable devices.

It is expected that valuable research results and cutting-edge technologies for the next generation wireless power transfer for mobile devices, IoT sensors, and wearable devices will be submitted.

Topics of interest for publication include but are not limited to:

Coils, coil array, modeling, simulation, and design;
Free-positioning wireless charging/device-to-devices wireless charging/multiple device charging;
Topologies, components, integrated circuits, and packaging;
Power management and power electronics;
EMI/EMC/EMF issues for charging mobile devices;
Beam forming techniques and magnetic field shaping;
Applications of wireless power transfer (mobile devices, wearable devices, IoT sensors etc.);
Other topics related to devices and systems for wireless charging of mobile devices.

Dr. Young-Jin Park
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Free-positioning
Wireless charging
Magnetic coupling
EMI/EMC
Power control
Beam forming
Coil
Mobile devices
Wearable devices
IoT sensors
Resonator
Wireless power transfer

Published Papers (13 papers)

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Editorial

Jump to: Research

4 pages, 171 KiB

Open AccessEditorial

Next-Generation Wireless Charging Systems for Mobile Devices

by Young-Jin Park

Energies 2022, 15(9), 3119; https://doi.org/10.3390/en15093119 - 25 Apr 2022

Cited by 10 | Viewed by 2068

Abstract

Wireless power transfer (WPT) is currently sparking more attention towards the application of wireless charging for mobile devices and electric vehicles [...] Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

Research

Jump to: Editorial

11 pages, 1495 KiB

Open AccessArticle

Position Estimation of Multiple Receiving Coils and Power Transmission Control for WPT without Feedback

by Jun Heo, Sang-Won Kim, In-Kui Cho and Yong Bae Park

Energies 2022, 15(22), 8621; https://doi.org/10.3390/en15228621 - 17 Nov 2022

Viewed by 937

Abstract

It is important to determine the position of the receiver (Rx) coils in wireless power transfer (WPT) system, and to control the power transmitted to the Rx coil based on this result. In particular, in a situation where there is no feedback between the primary side and the secondary side, it is difficult to control the received power because the information is limited. In this paper, a method for determining the position of the Rx coils and controlling the received power using limited parameters in a feedback-free WPT system is proposed. The proposed method is verified by constructing a

4 \times 2

WPT system, and it is validated that the simulation result and the experimental result are consistent well. Furthermore, arbitrary power can be transmitted to the Rx coil based on the result of the position of the Rx coil. The experiment is conducted by transmitting about

1 W

to Rx 1 and Rx 2, and the efficiency for Rx 1 is about

32.93 %

, Rx 2 is

25.03 %

, and the overall efficiency is confirmed to be

57.96 %

. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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12 pages, 5499 KiB

Open AccessCommunication

Design of Moiré-Inspired Metasurface Lens for Focusing Electromagnetic Power in Fresnel Near-Field Region

by Tae-Heung Lim, Hyunsoo Kim, Chulhun Seo and Hosung Choo

Energies 2022, 15(11), 3911; https://doi.org/10.3390/en15113911 - 25 May 2022

Viewed by 1723

Abstract

This paper proposes a Moiré-inspired metasurface lens system to focus electromagnetic power in the Fresnel near-field region. The proposed metasurface lens (MSL) system is composed of two MSLs and a square patch antenna source. The MSLs are modeled based on the transmit phase distributions of Moiré lens theory, and each unit cell structure (patch shape and Jerusalem cross slot shape) is determined to fit the calculated transmit phase distributions at each location. When changing the unit cell structure, phase and transmittance variations are achieved over 330° and −3 dB. The square patch antenna source is then designed to excite the field to the MSLs. The measured reflection coefficients are below −10 dB at 5.8 GHz while rotating the second MSL. The focal length can be adjusted from a minimum of 38 cm to a maximum of 110 cm according to the rotation angle of the second MSL. The proposed MSL system can be employed for wireless power transmission applications to focus electromagnetic power at various locations in the near-field region. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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Graphical abstract

9 pages, 2213 KiB

Open AccessArticle

Maximum Efficiency Conditions Satisfying Power Regulation Constraints in Multiple-Receivers Wireless Power Transfer

by Won Lee, Woochan Lee and Dukju Ahn

Energies 2022, 15(10), 3840; https://doi.org/10.3390/en15103840 - 23 May 2022

Cited by 1 | Viewed by 1307

Abstract

We propose the conditions for maximum overall efficiency at the constraint of satisfying asymmetric load power requirements for each receiver, for multiple-receivers wireless power transfer. Previously, the limitation of multiple-receiver analysis was that only the efficiency was maximized, whereas the requirements of load power were neglected. In many cases, conventional efficiency maximization assigns insufficient power to receivers far from the transmitter, while supplying excessive power to receivers near the transmitter. To resolve this limitation, we maximize the efficiency at the constraints of specified load power for each receiver. The proposed closed-form equation provides an optimum TX coil current amplitude, and the optimum load resistances of each receiver, to achieve the maximum efficiency at the load power regulation. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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16 pages, 30389 KiB

Open AccessArticle

Charging Mobile Devices in Indoor Environments

by Diogo Matos, Ricardo A. M. Pereira, Helena Ribeiro, Bernardo Mendes, Daniel Belo, Arnaldo Oliveira and Nuno Borges Carvalho

Energies 2022, 15(9), 3450; https://doi.org/10.3390/en15093450 - 09 May 2022

Cited by 4 | Viewed by 1849

Abstract

Wireless power transfer promises to revolutionize the way in which we use and power mobile devices. However, low transfer efficiencies prevent this technology from seeing wide scale real-world adoption. The aim of this work is to use quasioptics to develop a system composed of a dielectric lens fed by a phased array to reduce spillover losses, increasing the beam efficiency, while working on the antenna system’s Fresnel zone. The DC-RF electronics, digital beamforming and beam-steering by an FPGA, and radiating 4 × 4 microstrip patch phased array have been developed and experimented upon, while the lens has been designed and simulated. This paper details these preliminary results, where the phased array radiation pattern was measured, showing that the beam is being generated and steered as expected, prompting the lens construction for the complete system experimentation. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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15 pages, 9677 KiB

Open AccessArticle

Shielding Sensor Coil to Reduce the Leakage Magnetic Field and Detect the Receiver Position in Wireless Power Transfer System for Electric Vehicle

by Seokhyeon Son, Seongho Woo, Haerim Kim, Jangyong Ahn, Sungryul Huh, Sanguk Lee and Seungyoung Ahn

Energies 2022, 15(7), 2493; https://doi.org/10.3390/en15072493 - 28 Mar 2022

Cited by 4 | Viewed by 2518

Abstract

This paper proposes a shielding sensor (SS) coil to solve the misalignment issue and the leakage magnetic field issue of the wireless power transfer (WPT) system for electric vehicles (EVs). The misalignment issue and leakage magnetic field issue must be solved because they can cause problems with power transfer efficiency reduction and electronic device malfunction. To solve these problems, the proposed SS coils are located over the Tx coil. The newly created mutual inductance between the Tx coil and the SS coil is used to detect the misalignment of the receiver in the Tx coil. In addition, the current phase of the SS coil is adjusted through impedance control of the SS coil to reduce the leakage magnetic field. The proposed SS coils were applied to the standard SAE J2954 model for the wireless charging of an EV. The WPT3/Z2 model of SAE J2954 with output power of 10 kW was simulated to compare the shielding effect according to the power transfer efficiency, and it was confirmed that a shielding effect of 76% was shown under the condition of a 3% reduction in the power transfer efficiency. In addition, the occurrence and direction of the misalignment between the receiver and the Tx coil were confirmed by using the tendency of mutual inductance between each SS coil and the Tx coil. In addition, as in the simulation result, the shielding effect and tendency were confirmed in an experiment conducted with the output power downscaled to 500 W. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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14 pages, 18571 KiB

Open AccessEditor’s ChoiceArticle

A Study on Automatically Target-Chasing Microwave Power Transfer Systems in Multipath Environments

by Naoki Shinohara and Taichi Sasaki

Energies 2022, 15(7), 2343; https://doi.org/10.3390/en15072343 - 23 Mar 2022

Cited by 1 | Viewed by 1814

Abstract

In this paper, we propose novel retrodirective systems to improve the efficiency and safety of microwave power transmission (MPT) systems in multipath environments. The retrodirective system consists of an array antenna with phased conjugation circuits and it sends back the phase-conjugate signal toward the pilot signal transmitted from the receiver. It is usually applied for one receiver MPT system, however, Ossia corp. develops the new retrodirective system in multipath environments named ‘Cota’. We simulated the detail of the Cota system, e.g., one receiver in multipath circumstance, one receiver with obstacle in the multipath circumstance, and multi receiver. Furthermore, we revised the retrodirective system with phase information as well as the amplitude information of the pilot signal to improve the MPT efficiency. We also find effect of the MPT efficiency by phase difference between two pilot signal sources. At last, we carried out the experiments of the retrodirective system in multipath circumstance to prove the simulation results. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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15 pages, 4364 KiB

Open AccessArticle

Wireless Power Transfer between Two Self-Resonant Coils over Medium Distance Supporting Optimal Impedance Matching Using Ferrite Core Transformers

by Jinwook Kim, Do-Hyeon Kim, Jieun Kim and Young-Jin Park

Energies 2021, 14(24), 8540; https://doi.org/10.3390/en14248540 - 17 Dec 2021

Cited by 4 | Viewed by 3159

Abstract

An efficient wireless power transfer (WPT) system is proposed using two self-resonant coils with a high-quality factor (Q-factor) over medium distance via an adaptive impedance matching network using ferrite core transformers. An equivalent circuit of the proposed WPT system is presented, and the system is analyzed based on circuit theory. The design and characterization methods for the transformer are also provided. Using the equivalent circuit, the appropriate relation between turn ratio and optimal impedance matching conditions for maximum power transfer efficiency is derived. The optimal impedance matching conditions for maximum power transfer efficiency according to distance are satisfied simply by changing the turn ratio of the transformers. The proposed WPT system maintains effective power transfer efficiency with little Q-factor degradation because of the ferrite core transformer. The proposed system is verified through experiments at 257 kHz. Two WPT systems with coupling efficiencies higher than 50% at 1 m are made. One uses transformers at both Tx and Rx; the other uses a transformer at Tx only while a low-loss coupling coil is applied at Rx. Using the system with transformers at both Tx and Rx, a wireless power transfer of 100 watts (100-watt light bulb) is achieved. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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10 pages, 1694 KiB

Open AccessArticle

Control of WPT Transmitter Coils for Power Distribution to Two Receiver Coils without Feedback

by Jun Heo, Sungyeal Park, Sang-Won Kim, In-Kui Cho, Songnam Hong and Yong Bae Park

Energies 2021, 14(20), 6828; https://doi.org/10.3390/en14206828 - 19 Oct 2021

Cited by 2 | Viewed by 1792

Abstract

This paper proposes the algorithm to control the current ratio of the transmitting (Tx) coils for proper power distribution to the two receiving (Rx) coils in wireless power transfer (WPT) system. The proposed algorithm assumes that each Rx coil appears at different times to consider the situation where multiple users request power transmission as practically as possible. That is, suppose the second Rx coil enters the charging space later than the first Rx coil. When each coil enters the charging space, only the Tx coil is used to obtain the value required for calculation. Using the obtained result, the optimized Tx coil current is calculated by the proposed algorithm and proper power distribution to both Rx coils is achieved. Three Tx coils and two Rx coils are constructed using the ANSYS MAXWELL simulation tool. As a result of applying the proposed algorithm, it was confirmed that a similar level of power was transmitted between 40∼60%, respectively. The sum of the power transmitted to the two Rx coils also appeared as more than 75%. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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Graphical abstract

19 pages, 6817 KiB

Open AccessArticle

Optimization and Analysis of Multilayer Planar Spiral Coils for the Application of Magnetic Resonance Wireless Power Transfer to Wearable Devices

by Young-Jin Park, Ji-Eun Kim, Kyung-Min Na, Ki-Dong Yang and Kyung-Hwan Cho

Energies 2021, 14(16), 5113; https://doi.org/10.3390/en14165113 - 19 Aug 2021

Cited by 6 | Viewed by 1968

Abstract

In this study, small multilayer planar spiral coils were analyzed and optimized to wirelessly charge an in-ear wearable bio-signal monitoring device in a wine-glass-shaped transmitter (Tx) based on magnetic resonance wireless power transfer (MR-WPT). For analysis of these coils, a volume filament model (VFM) was used, and an equivalent circuit formulation for the VFM was proposed. The proposed method was applied to design effective multilayer coils with a diameter and height of 6 and 3.8 mm, respectively, in the wearable device. For the coils, a printed circuit board having a 0.6 mm thick dielectric substrate and a 2 oz thick copper metal was used. Moreover, the coils on each layer were connected in series. The dimensions of the double-, four-, and eight-layer coils were optimized for the maximum quality factor (Q-factor) and coupling efficiency. The operating frequency was 6.78 MHz. The optimal dimensions for the maximum Q-factor varied depending on the number of coil layers, pattern width, and turn number. For verification, the designed coils were fabricated and measured. For the four-layer coil, the coupling efficiency and Q-factor using the measured resistance and mutual inductance were 58.1% and 32.19, respectively. Calculations showed that the maximum Q-factor for the four-layer coil was 40.8 and the maximum coupling efficiency was 60.1%. The calculations and measurement were in good agreement. Finally, the entire system of the in-ear wearable bio-signal monitoring device, comprising a wine-glass-shaped transmitter, the designed receiving coil, and a monitoring circuit, was fabricated. The measured dc-dc efficiency of the MR-WPT system was 16.08%. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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17 pages, 6263 KiB

Open AccessArticle

Dual-Band RF Wireless Power Transfer System with a Shared-Aperture Dual-Band Tx Array Antenna

by Chan-Mi Song, Hong-Jun Lim, Son Trinh-Van, Kang-Yoon Lee, Youngoo Yang and Keum-Cheol Hwang

Energies 2021, 14(13), 3803; https://doi.org/10.3390/en14133803 - 24 Jun 2021

Cited by 5 | Viewed by 2331

Abstract

In this paper, a dual-band RF wireless power transfer (WPT) system with a shared-aperture dual-band Tx array antenna for 2.4 and 5.8 GHz is proposed. The final configuration of the Tx array, which is made up of 2.4 GHz right-handed circular polarization (RHCP) patches and 5.8 GHz RHCP patches, is derived from the optimization of 2.4 and 5.8 GHz thinned arrays, ultimately to achieve high transmission efficiency for various WPT scenarios. The dual-band RF WPT Tx system including the Tx array antenna and a Tx module is implemented, and Rx antennas with a 2.4 GHz patch, a 5.8 GHz patch, and a dual-band (2.4 and 5.8 GHz) patch are developed. To validate the proposed dual-band RF WPT system, WPT experiments using a single band and dual bands were conducted. When transmitting RF wireless power on a single frequency (either 2.482 GHz or 5.73 GHz), the received power according to the distance between the Tx and Rx and the position of the Rx was measured. When the distance was varied from 1 m to 3.9 m and the transmitted power was 40 dBm, the received power value at 2.482 GHz and 5.73 GHz were measured and found to be 24.75–13.5 dBm (WPT efficiency = 2.985–0.224%) and 19.25–6.8 dBm (WPT efficiency = 0.841–0.050%), respectively. The measured results were in good agreement with the calculated results, and it is revealed that the transmission efficiency when wireless power is transmitted via beam-focusing increases more than that with conventional beam-forming. Furthermore, the dual-band WPT experiment proves that 2.482 GHz beam and 5.73 GHz beams can be formed individually and that their wireless power can be transmitted to a dual-band Rx or two different Rx. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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14 pages, 5765 KiB

Open AccessArticle

A Wirelessly Rechargeable AA Battery Using Electrodynamic Wireless Power Transmission

by Spencer E. Smith, Miah A. Halim, Stasiu T. Chyczewski, Adrian A. Rendon-Hernandez and David P. Arnold

Energies 2021, 14(9), 2368; https://doi.org/10.3390/en14092368 - 22 Apr 2021

Cited by 2 | Viewed by 3050

Abstract

We report the design, fabrication, and characterization of a prototype that meets the form, fit, and function of a household 1.5 V AA battery, but which can be wirelessly recharged without removal from the host device. The prototype system comprises a low-frequency electrodynamic wireless power transmission (EWPT) receiver, a lithium polymer energy storage cell, and a power management circuit (PMC), all contained within a 3D-printed package. The EWPT receiver and overall system are experimentally characterized using a 238 Hz sinusoidal magnetic charging field and either a 1000 µF electrolytic capacitor or a lithium polymer (LiPo) cell as the storage cell. The system demonstrates a minimal operating field as low as 50 µT_rms (similar in magnitude to Earth’s magnetic field). At this minimum charging field, the prototype transfers a maximum dc current of 50 µA to the capacitor, corresponding to a power delivery of 118 µW. The power effectiveness of the power management system is approximately 49%; with power effectiveness defined as the ratio between actual output power and the maximum possible power the EWPT receiver can transfer to a pure resistive load at a given field strength. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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13 pages, 11017 KiB

Open AccessArticle

Efficient, Load Independent and Self-Regulated Wireless Power Transfer with Multiple Loads for Long Distance IoT Applications

by Najam ul Hassan, Woochan Lee and Byunghun Lee

Energies 2021, 14(4), 1035; https://doi.org/10.3390/en14041035 - 16 Feb 2021

Cited by 7 | Viewed by 2207

Abstract

This paper proposes a wireless power transfer (WPT) system by placing repeater coils to transfer power to multiple loads for the internet of things (IoT) devices and sensors in smart grid applications. The proposed system intermediate resonators (repeaters) not only function as power relays to enhance the transfer distance but also supplies power to its load attached to them. Equal power distribution and load-independent characteristics were obtained without efficiency degradation when any one of the loads was changed during system operation. Identical high-quality factor coils were designed using Litz-wire to reduce the skin effect. The coil size was 15.5 cm × 15.5 cm and the four relays achieved total efficiency of 51.7%, delivering 2 W power and output voltage of 5 V to each load with a total power transfer distance of 62 cm. Full article

(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)

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