Magnetic field non-contact optical sensor

In the field of the automobile and electric car of the future, research is focused on the induction charging of vehicle batteries.

The inductive charging coils operate at a single frequency which is in the 40 to 160 kHz band, depending on the technological choice of the various automotive consortia. Their typical power is about 2 kW (at 10 A). It is important to check that the magnetic field radiated around the inductors is compatible with safety standards.

For this, as part of the MOVEOTREV project in partnership with ADEME. We are developing a new non-contact type sensor capable of measuring magnetic fields over high dynamics, and at frequencies up to 200 kHz.

For this we use the well-known Faraday effect, which changes the polarization of light from a laser passing through a crystal with a high Verdet constant. This sensor then detects the change in polarization and, using on-board electronics, calculates the magnetic field along the axis of the crystal.

Secondly, we will map the magnetic field around the inductors using a robotic arm. The repeatability of the positioning of the measurement points is of the order of 1/10 of a millimeter. In the end, the sensor moved by the robotic arm will be able to observe the field inside a car and in its surroundings.

Impacts on application fields

This type of non-contact sensor , with high bandwidth and high dynamic range (a few µT to several hundred mT, or even 1T) can then be used to measure strong magnetic fields where the combination of bandwidth and high dynamic range is often prohibitive (use several types of sensor to overcome this problem).The rapidly expanding field of electric vehicles should be able to demonstrate the feasibility and integration of the system.