Tailored WIREless power transFeR Systems for mobile Electronic Equipments – WIREFREE

The project WIREFREE is organized into 4 main work packages (WP) (total duration: 36 months):
- WP1 deals with the coordination, valorization and dissemination of all activities of the project.
- WP2 provides the analysis tool for tailored WPT systems. A Method of Moments (MoM) code will be developed for the analysis and design of tailored WPT systems. At the same time, a fast numerical tool will be created for power budget link evaluation and novel circuit description of WPT systems based on network theory techniques.
- WP3 deals with the feeding network development. The condition for maximum power transfer for tailored WPT systems will be derived and used to define the best matching technique and corresponding feeding network.
- WP4 consists of the prototyping and experimental validation of tailored WPT systems. The exposure of the human body to magnetic and electric fields will be also considered. Numerical analysis will be validated by power and dosimetric measurements. Power, field and dosimetric measurements will be used to validate the complying by the systems to the safety guidelines ICNIRP 1998 and IEEE C95.1-1999 for the general public.

The main achievements during the first 18 months of activity of WIREFREE are:
1. In-house MoM code able to synthetize a required near-field profile for WPT systems operating in MHz range;
2. Fast numerical tool for the evaluation of the power budget and the circuital description of tailored WPT systems.
3. Analysis and design of efficient matching networks for WPT systems.
4. Development and testing of a self-matched resonant WPT system in PCB technology based on resonant coils driven by high Q-factor loops. The systems has an efficiency better than 40% for a separation distance of 1m at 10 MHz.

In the future WIREFREE will focus on:
- Evaluation of the human exposure of human bodies to WPT systems. This is key for the future deployment of such systems.
- Definition of a prototype with a tailored near field.
- Definition of a prototype with a tailored radiated field in the Fresnel zone. This prototype will show the benefit of the proposed approach in a larger area of operation.
- Definition of attractive solutions for far-field WPT systems; These systems are becoming more and more attractive for WPT for their longer operating range. The challenges are the location of the users over a large field of view and the efficiency of the system.

1. M. Koohestani, M. Zhadobov, and M. Ettorre,” Design Methodology of a Printed WPT System for HF-Band Mid-Range Applications Considering Human Safety Regulations,” in IEEE Transactions on Microwave Theory and Techniques, Vol. 65, No. 1, pp. 270 - 279, Jan. 2017.
2. M. Ettorre, W. A. Alomar, and A. Grbic,”2D VanAtta Array of Wideband,Wideangle Slots for Radiative Wireless Power Transfer Systems,”submitted to IEEE Transactions on Antennas and Propagation.
3. M. Koohestani, M. Zhadobov, and M. Ettorre,”Wireless Power Transfer in Presence of a Body,” 2016 IEEE AP-S Symposium, June 26 - July 1, 2016, Fajardo, Puerto Rico.
4. M. Koohestani, M. Ettorre, and M. Zhadobov, ”Wireless Power Transfer: Are Children More Exposed Than Adults? ,” EuCAP 2017, Paris, France, 19-24 March 2017.
5. M. Koohestani, M. Zhadobov, and M. Ettorre, ”Systèmes de transfert d'énergie sans fils en bande HF : étude dosimétrique,” 20èmes Journées Nationales Micro-Ondes, 16-19 mai 2017 à Saint-Malo.

Wireless power transfer (WPT) systems are electromagnetic devices able to transfer wirelessly energy over the distance. The current implementation of WPT systems is generally based on magnetic resonators interacting within each other’s reactive near-field zones. These systems respond to the widespread proliferation of portable rechargeable electronic devices and current limitations of battery charges and wire-based distribution networks. The social impact will be important since WPT systems are seen as the last frontier for the complete mobility of people. The revenue of the wireless power industry market is estimated to $1 billion with a very strong increasing rate in the coming years. The main research effort on WPT systems is registered in USA. The WPT system proposed by the Massachusetts Institute of Technology (MIT, USA) is still the state of the art for WPT systems. It presents a power efficiency of 40% over 2 m distance. During the years, new adaptive networks or cumbersome relay systems have been proposed to improve the performances of such system. No attempt as be done to date to define and investigate new operation schemes.
For the first time here, we propose to tailor the near-field of WPT systems (tailored WPT systems) to improve both the power efficiency and distance range and go much beyond the current state of the art. The innovative idea is to tailor the near field of the system to reduce the decay ratio of the magnetic field over the distance without radiating in free space. Indeed we are aiming to design super slowly-evanescent localized fields. The radiation resistance is kept small as for current systems, but the tails of the near field are enhanced by properly loading the structure. In other words, the equivalent impedance supporting the required near field is created on the aperture of the system. The system can be also electrically larger without radiating thanks to the imposed small radiation resistance. In this way the available space of domestic or industrial environment may be used to enhance the performances of the system by using larger transmitting systems. The overall system will be analyzed with an in-house code able to define an electromagnetic device from a given near-field profile. The developed code will be unique for the present state of the art of simulator tools. The proposed WPT systems may open new opportunities and possible technology transfers for many daily life applications.
WIREFREE is a 36-month JCJC (Jeunes Chercheurs - Jeunes Chercheuses) ANR project coordinated by IETR.