Abstract
AbstractWe have developed a common-mode magnetic field rejection-type magneto-impedance (MI) gradiometer to reduce the common magnetic field applied to the sensing- and reference-type MI elements. Compared with a general-type MI gradiometer, the magnetic noise spectral density was lower and the noise at 60 Hz related to the power source line was reduced by 1/8. Using the developed sensor, we successfully detected a microscopic 5 nT magnetic signal in a common-mode magnetic field that was 14 times larger. We expect this will lead to a simpler method of detecting microscopic magnetic signals such as biomagnetism without the need for magnetic shielding.
Highlights
Magneto-impedance (MI) sensors can detect microscopic magnetic fields by utilizing the MI effect [1,2,3]
We have developed a CMMFR-type MI gradiometer and confirmed that it is robust against external magnetic noise
When the HCMMF was applied to the sensor head, the first-order-type MI gradiometer outputs the difference in the output of the sensing- and reference-type MI elements as noise because the outputs of both MI elements increased by a factor of 1167 with the differential amplifiers
Summary
Magneto-impedance (MI) sensors can detect microscopic magnetic fields by utilizing the MI effect [1,2,3]. A complementary metal–oxide–s emiconductor (CMOS)-MI sensor that can discriminate magnetic poles by measuring the voltage induced in a pickup coil wound around an amorphous wire was developed in 2002 [4]. MI sensors have a high magnetic resolution and can operate stably under geomagnetism This type of sensor can be used to reduce a spatially uniform magnetic noise by implementing it in a differential output circuit (i.e. gradiometer). We have been developing a first-order MI gradiometer using sensing- and reference-type MI elements [8,9]. We have confirmed the inhibitory effects of this new type of MI gradiometer against external magnetic noise
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