Magnetometers
Magnetometers based on SQUID are very sensitive low-frequency magnetic field sensors, reaching a spectral density noise of a few fT/Hz1/2 referred to a capture area of about 1 cm2. Due to their unique properties, SQUID devices are widely used in several applications, the largest demand for SQUID sensors being for applications in biomedical imaging. In particular, the interest is mainly focused on multichannel system for magnetocardiography and magnetoencephalography, which provide useful information on heart diseases or brain functionality. In order to increase the magnetic field sensitivity, a SQUID magnetometer includes an integrated superconducting flux transformer working as a magnetic flux pickup which determines the chip size.
Fully integrated magnetometer
We have developed a fully integrated dc-SQUID magnetometer based on niobium technology including a feedback coil design which allow us to reduce the mutual inductance between neighbor sensors and to increase the coupling with the pickup coil of the SQUID itself. In such a way, it is possible to reduce cross talk due to both the feedback coil and wires. This feature is very useful when a large number of channel are located close each to other. The experimental measurements performed in liquid helium and by using a low noise readout electronics specifically designed for large multichannel SQUID-based instruments have been demonstrated a substantial reduction of cross talk between neighboring sensors with respect to a traditional feedback coil. Furthermore, the new feedback coil system does not introduce any noise degradation.
Performance
Design
Main references:
Improved superconducting quantum interference device magnetometer for low cross talk operation
C. Granata, A. Vettoliere, and M. Russo
Applied Physics Letters 88, 212506 (2006)
Superconducting quantum interference magnetometer for large multichannel systems with low crosstalk level
A. Vettoliere, C. Granata, B. Ruggiero and M. Russo
International Journal of Modern Physics B 23, No. 31 (2009) 5759–5767
Miniaturized magnetometer
Main references:
Improved superconducting quantum interference device magnetometer for low cross talk operation
C. Granata, A. Vettoliere, and M. Russo
Applied Physics Letters 88, 212506 (2006)
Superconducting quantum interference magnetometer for large multichannel systems with low crosstalk level
A. Vettoliere, C. Granata, B. Ruggiero and M. Russo
International Journal of Modern Physics B 23, No. 31 (2009) 5759–5767
Miniaturized magnetometer
We have also developed a miniaturised dc-SQUID magnetometer designed for high magnetic field sensitivity applications with a sensing coil consisting of an integrated square superconducting coil with a length of 3 mm, involving a device area much smaller with respect to the typical SQUID magnetometers with a comparable magnetic field sensitivity; so it allows increasing the spatial resolution keeping the magnetic field sensitivity unaltered. Furthermore, a small pickup coil minimizes its antenna gain, reducing the radio frequency interference. At T=4.2 K, the sensors have shown smooth and resonance free V-Φ characteristics and an intrinsic white magnetic field noise spectral density of a few fT/Hz1/2, measured in flux locked loop configuration. The good agreement with the theoretical predictions guarantees the reliability and the controllability of the sensors. Due to their compactness and good characteristic parameters, such sensors are suitable for large multichannel systems used in biomagnetic imaging.
Performance
Design
Main references:
Miniaturized superconducting quantum interference magnetometers for high sensitivity applications
C. Granata, A. Vettoliere, and M. Russo
Applied physiscs letters 101 (12), 122601 (2012)
Performances of compact magnetometer for high sensitivity applications
C. Granata, A. Vettoliere, S. Rombetto, C. Nappi, and M. Russo