Demodulation effect of SQUID magnetometer to magnetic signal outside frequency bandwidth

Abstract

Event Abstract Back to Event Demodulation effect of SQUID magnetometer to magnetic signal outside frequency bandwidth Daisuke Oyama1*, Masanori Higuchi1, Jun Kawai1, Yoshiaki Adachi1, Gen Uehara1 and Hisashi Kado1 1 Kanazawa Institute of Technology, Japan OBJECTIVE: We proposed a new method to image magnetic particles or electric currents by detecting magnetic signal modulated by sounds, like ultrasound. This method is a combination of sonography and magnetometry, so we named it “sonomagnetometry”. It can observe spatial distribution and time shift of magnetic source simultaneously. We have developed a sonomagnetometry system using a SQUID magnetometer and an ultrasonic device. In this case, the SQUID magnetometer has to detect MHz signal, though its bandwidth is about 10 kHz in SQUID magnetometers that are generally used for biomagnetic measurements. Recently, bandwidths up to MHz were demonstrated by some groups [1][2]. In contrast to them, we also propose a method to detect MHz signal by narrow-bandwidth basic type SQUID magnetometer system. METHODS AND RESULTS: We used a SQUID magnetometer with 8 kHz bandwidth. It was normally used for MEG system. When 1 MHz magnetic signal to which amplitude is modulated by 500 Hz signal was impressed to the SQUID, voltage output of 500 Hz was observed. The shape of demodulated signal is very similar to modulation 500 Hz signal. These results demonstrate that SQUID magnetometers have demodulation effect [3] to magnetic signals of the frequency outside their bandwidth. This effect can be applied to sonomagnetometry by measuring time delay of output voltage from ultrasonic excitation and capturing the shape of demodulated signal. CONCLUSION : We examined behavior in a SQUID magnetometer to magnetic signal outside its bandwidth. The demodulation effect can be applied to sonomagnetometry.