High Sensitivity Magnetic Sensor Developed by Scuola Normale Superiore and Aalto University Researchers

Researchers from Scuola Normale Superiore and Aalto University have developed a highly sensitive magnetic field sensor.

Benefits of the sensor include modifiability for various ranges of measurement, less dissipation of power, and simple measurement.

This novel transducer is closely associated to the traditional Superconducting Quantum Interference Device (SQUID) used, for instance, in brain imaging applications. A superconducting loop forms the core of the sensor.  A normal metal detector constitutes a part of the core. The ordinary detector becomes a weak superconductor when it is in contact with a superconductor, due to proximity effect.

According to Professor Jukka Pekola, researchers had earlier intended to examine the effect of  superconducting proximity upon the flow of heat between lattice vibrations and electrons in normal metals. However, it was later found that the structure could also act as a tunable and sensitive sensor of the magnetic field.

The structure, known as Superconducting Quantum Interference Proximity Transistor (SQUIPT), integrates the tunnel junctions’ electric transport properties with the adjustability feature due to the superconducting proximity effect. Different materials and metal wires of varying lengths can be used to increase the device’s operating range.

The device consumes less power since measurements are carried out using weak direct current. This sensor structure is ideally suited for low temperature applications, where the sensitivity and performance of the device are good and the level of noise is comparatively low.

The initial experiments as well as theoretical analysis carried out with the device appear promising. Simplicity is the unique feature of this sensor. The device is fed with a direct current input, an external magnetic field is applied to the loop, and the resulting voltage is monitored. Pekola clarified that this type of direct voltage measurement allows the measurement of even minute magnetic fields.

So far, experiments have been mostly carried out at a temperature that was one-tenth of a degree over the absolute zero. Nevertheless, the device also functions at higher liquid helium temperatures, namely, at -269 °C or around 4 K, provided the suitable superconducting material is selected. This aspect is crucial for practical applications.

The next task for the research group is to optimize the device parameters that confirm the sensitivity in measurement the device can acquire and also find out how small are the fields that can be measured using the device.

At this juncture, Pekola is cautious about the judgment of future applications of the sensor. Pekola has said that developing an actual product from a prototype is a long process involving several years. However, the research team had initial discussions with the VTT regarding developing and manufacturing the sensor in the future. At best, this sensor is likely to substitute the traditional SQUID magnetometer for unique applications, according to Pekola.

Micronova Centre for Micro and Nanotechnology, run jointly by VTT and the Aalto University School of Science and Technology, created the sensor structure.