When dedication to research leads to innovation
In his second year of doctoral studies at the University of Savoie Mont Blanc (USMB), Rémi Recoquillé is conducting his research at CEA-Leti, where he began with an end-of-studies internship. Prior to that, he completed his first research internship at the École Technologique Supérieure de Montréal (Canada). Passionate about research, he naturally chose to continue in this field after five years at the University of Technology of Compiègne, where he pursued a generalist education in mechanical engineering, with a focus on mechatronics.
His decision to pursue his thesis at Leti was based on the institute's academic reputation and its renown in the field of applied research:
“I was looking for a research environment close to the academic world, which made CEA-Leti a very good choice."
The paper presented at JRNSE,
“Frequency-up Electrodynamic Receiver for Extremely-Low Frequency Wireless Power Transfer for Implanted Devices,"
lies at the intersection of mechanics and electronics. Supported by a collaboration between CEA-Leti and USMB, Rémi's goal is to develop a new way to power a wireless device. Similar to the widely used wireless phone charging stations, it would use a different frequency range, applied to power instrumented medical prostheses.
Exploring low frequency wireless power transmission
Most wireless power transmission systems currently operate at high frequencies, typically ranging from hundreds of kHz to GHz. However, these waves cannot pass through conductive materials such as metal or salt water, which act as barriers and block transmission. Rémi is investigating the use of extremely low frequencies, in the Hz range, which are capable of passing through metal while delivering sufficient power to supply autonomous sensor nodes.
“The range of power I'm working with, up to tens of milliwatts, is more than enough to power everything at the scale of small sensor nodes," he explains.
From a technical standpoint, the system developed is based on a transmitter coil and a magnet set in motion remotely at the receiver, similar to how a motor works. Rémi focused particularly on designing the receiver, which is the heart of his prototype. The device therefore incorporates a moving magnet whose movement generates the changes in field strength needed to transmit energy. This is known as electrodynamic wireless power transmission. He studied various modes of operation, such as oscillating the magnet or performing complete rotations.
The key innovation lies in a hybrid system combining two magnet movements: tilting of the magnet followed by oscillations around an equilibrium position. This approach takes advantage of the “frequency-up" principle, which involves the receiving magnet oscillating at a higher frequency than the transmitter. This generates sufficient voltage despite the transmitter's very low frequency, ensuring good power density and efficient energy transmission.
From experimental prototype to initial applications
At the JRNSE conference, Rémi presented a working prototype illustrating this approach. He demonstrated the feasibility of a very low frequency transmission system capable of passing through metal while complying with magnetic field exposure standards, a promising result for many industrial and biomedical applications.
As part of his experiments, he focused on biomedical applications, testing his system inside instrumented metal prostheses. Tests were carried out under real conditions on a human knee specimen at Brest University Hospital, as part of the ANR-funded PiezoKnee project. This is the first time that an electrodynamic power transfer system has been implemented and tested in a medical device on such a specimen.
The results presented open up interesting prospects for the wireless power supply of implanted medical devices: the lower the frequency, the more permissive the recommendations concerning limits on human exposure to magnetic fields.