(Color online) Equivalent circuit diagram DROS second-order gradiometer (a), and photograph of a fabricated DROS second-order gradiometer (b). All parts of DROS second-order gradiometer except the pick-up coil are wrapped with a superconducting shield.
(Color online) Fabricated Josephson junction array (a), overall image of the Josephson junction array and the DROS (b). Two parts are superconductively connected with Nb wire and covered with a Pb of 99.9% purity.
(Color online) The orientation of the pickup coil, pre-polarization coil, measurement coil, gradient coil, and sample for the ULF-MRI system (a). The pulse sequence for a pre-polarization MRI system (b). The DROS second-order gradiometer is switched to the FLL state after turning-off the Bp; its delay time (tFLL) is 5 ms.
Noise spectrum of a DROS second-order gradiometer in a magnetically shielded room.
(Color online) Current limiting characteristics of a current limiter. Slowly-varying wave of (a) and (b) are DROS flux-to-voltage modulation curves in the response to an AC magnetic field of 0.5 Hz without and with the Josephson junction array, respectively. (c) shows the change in the dc magnetic field. The DROS modulation is suppressed by the Josephson junction array in the high magnetic field (∼6 mT) region.
(Color online) The single-scanned 1H NMR FID signal measured with a DROS second-order gradiometer (a). The FFT spectrum derived from 1H NMR FID signal (b). The FFT was performed after the zero-filling to enhance spectral resolution.
(Color online) The single-scanned FID signal under a magnetic field gradient (a), one-dimensional MR image of the water sample, which is separated by a rubber partition (b).
(Color online) The NMR spectrum derived from the single-scanned 1H NMR signal, which was wrapped with aluminum foil and paper.
(Color online) The single-scan FID signal of trimethylphosphate measured in a field of 5.4 µT (a), the NMR spectrum derived from the FID signal of trimethylphosphate (b). A heteronuclear J-coupling between 1H and 31P of trimethylphosphate, which splits the NMR line as a doublet.
Noise spectrum of dc-SQUID second-order gradiometer in magnetically shielded room.
(Color online) The single-scanned 1H NMR FID signal measured with a DROS based ULF-NMR system (a) and with a dc-SQUID based ULF-NMR system (b). The insets in (a) and (b) are FFT spectrum derived from each 1H FID signal.
Important parameters of DROS second-order gradiometer.
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