Device for sensing ultra-low magnetic fields
Introduction
A device for sensing tiny magnetic fields, i.e. those generated by biological sources, working at 77K and with an all-optical readout, robust to external DC and pulsed applied fields. Our sensor is a good candidate for a multichannel system to image brain activity and connectivity with high spatial and temporal resolution, combining magnetoencephalography with magnetic resonance imaging and transcranial magnetic stimulation in the same system.
Technical features
The external magnetic field Hext, produced by brain or muscle activity or magnetized tissues, is transduced into a supercurrent I, circulating in the superconducting pick-up loop, which generates an amplified and strongly non-uniform internal magnetic field Hint at the nanoconstriction. The magnetic mechanical resonator is coupled to Hint, changing its mechanical resonance frequency. A transducer, preferentially optical, detects and measures such resonance frequency variation.
The device can be realized by surface micromachining and multistep deposition processes or by flip chip/wafer bonding. In a standalone configuration, the device operates in a vacuum chamber made of non-magnetic, thermally conductive material. The resonator is coupled to an optical fiber, which enters in the sensor housing through a feedthrough. The expected responsivity is few units of Hz/T and the limit of detection is about 10 fT/sqrt(Hz) on a 10 kHz bandwidth.
The project leading to this device has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement No. 828784.
Possible Applications
- Ultra-low magnetic field detection;
- Biomagnetic signals detection;
- Diagnostic imaging;
- Electromagnetic pollution detection.
Advantages
- Robustness to external magnetic fields;
- Scalability (small factor form);
- All-optical readout (by optical fibres);
- Multimodal imaging / multiple channels
- High signal to noise ratio;
- Bandwidth near DC- 10 kHz;
- No interference, no cross-talk, no ground loops or eddy currents;
- Versatile integration with other techniques and reproducibility with standard fabrication technologies.