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Technology

The quantum technology embedded within MAG4Health OPM-MEG system was first developed for Space applications in 2013 to map the Earth magnetic field; our sensors are still working after 11 years!

Read more :
Swarm mission
Swarm Absolute Scalar Magnetometers first in-orbit results

The sensitive element of the sensor is a Helium gas cell in which a plasma allows the excitation of billions of atoms which behave as small magnets. A laser and radiofrequency fields impose a synchronized behavior to these magnets such that they all contribute to a global signal which allow a measurement of the tiny magnetic fields emitted by the brain (femto Tesla magnitude).

16 up to 96 sensors are deployed within the helmet offering adaptability to any head morphology. Once installed, the sensors automatically localize themselves with respect to each other, taking advantage of their capability to create and measure magnetic fields to compute their relative distances and orientations.

Helium-based magnetometers
A glimpse of Hardware and Physics

In the MAG4Health sensor the sensitive element is a gas of Helium (4He) atoms in their 23S1 metastable state. Helium is a noble gas, very stable over time, and has demonstrated its robustness and lifetime in Space magnetometry.

The size of the cell containing the 4He gas atoms is cylindrical with a 1 cm internal diameter and 1 cm internal height. The bottom of the sensor is surrounded by small 3-axis Helmholtz coils, which are used to apply both the RF fields and the compensation fields.

  • First, we apply a high frequency (HF) discharge that brings 4He atoms from the ground state to their 23S1 metastable state which is a spin-one state, sensitive to the magnetic field.
  • Then a alignment polarization is created by optically pumping the metastable state at 1083.2 nm wavelength with linearly polarized light.
  • Two radio-frequency fields at different frequencies (9 and 40 kHz) allow exciting parametric resonances. The measurement of the three components of the magnetic field 𝐵0⃗⃗⃗⃗ is obtained from the measurement of the compensation currents.

More details on our sensors can be found in our 2021 paper (Fourcault et al., https://doi.org/10.1364/OE.420031)

A brief on MAG4Health OPM technology

Room Temperature operation

The integration of non-cryogenic helium-4 sensors within the MAG4Health OPM system ensures operational efficiency without the need for heating or cooling within the sensor unit:

  • more stable measurement, 
  • no downtime between experiments.
  • strategic sensor placement directly on the scalp, boasting a cell offset of 1-3 mm (Zahran et al. 2022) and, enabling a larger magnitude of measured magnetic field vectors of 5 (Gutteling et al. 2023).


Large bandwidth

The large bandwidth of He OPM sensors makes possible to record all biomagnetic activities such as

  • spine activity (including motoneuronal firing)
  • muscle activity (including motor unit firing)
  • peripheral nerves
  • heart


High dynamic range (up to 200nT)

It reduces the specification for shielding and makes the system particularly well-suited for studies involving children or individuals with movement disorders.


Helmet and system design

Distance matters ! our sensors are placed directly on the scalp to avoid any loss of signal.

The system’s design minimizes installation constraints, requiring only lightweight shielding and eliminating the need for a cryogenic cooling chamber. This results in reduced overall installation costs, a smaller operational space requirement, and enhanced flexibility in deployment.

Sustainable Operation

The 4He OPM system’s low-maintenance profile, with no routine gas refills due to no heating or cooling, significantly reduces the potential for sensor damage and minimizes the likelihood of replacement or maintenance needs. This characteristic ensures continuous operational readiness (no downtime between uses).

Helium versus Alkali Optically-Pumped Magnetometers

MAG4Health Helium OPM Alkali OPM
Power dissipated
in the helmet		 1 W for a 50 sensors array 35 W for a 50 sensors array, causing a significant heating
Sensors dimensions 21 x 21 x 54 mm
(21 x 21 x 88 mm with the cable guide)		 16,6 x 20 x 27 mm
Cell offset from the scalp 4 mm 5 – 7 mm
Bandwidth -3 dB DC – >1000 Hz 1 – 130 Hz
Bandwidth for losing 5% of the signal DC – 1000 Hz Hz
Linear range of operation (so called dynamic range) Up to 200 nT, with linearity error better than 2/1000 8 nT (open-loop)
150 nT (closed-loop)
Maximum magnetic field recommended for biomagnetic measurement <50 nT to avoid large artifacts due to subject movements <50 nT to avoid large artifacts due to subject movements
Intrinsic noise on two main axes 30 fT/rtHz typically
40 fT/rtHz always		 20 fT/rtHz
Mechanisms implemented to limit measurement imperfections Closed loop operation on 3 axes, no lightshifts, better than 2/1000 linearity error Depending on brands: closed loop operation possible for some of them on some axes. Every axes not operating in closed loop causes cross-axis projection error (CAPE) on the others and has a high non-linearity
Helmet and Sensors localisation Flexible Helmet
Sensors 3D auto localisation
4 HPI coils for head localisation		 Rigid helmet providing guides for sliding the sensors
Sensors localized along the direction of the guide
HPI available
Reliability and lifespan Only inert gas in the cells, >10 years lifespan evaluated by accelerated ageing tests Limitations due to embedded-heater, laser source and alkali atoms reactivity

Interested in learning more about our OPM-MEG system? Willing to join the adventure?

Contact us!