Type-I superconductor pick-up coil in superconducting quantum interference device-based ultra-low field nuclear magnetic resonance

Abstract

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“…Both of these type-II superconductors trap magnetic flux during the pre-polarization time and generate flux jumps during the subsequent measurement time. This significantly increases the low-frequency noise with a typical 1/f-shaped spectrum [4,5]. We have observed significant 1/f noise below 6 kHz after niobium gradiometers were exposed to a 0.1 T field [6].…”

A cryogen-free ultralow-field superconducting quantum interference device magnetic resonance imaging system

“…The SNR at higher fields could also be degraded because the critical field (H c1 ) of the PbSn solder (a type-II superconductor) coating used in our gradiometer is relatively low (80-200 mT). 14 In their recent work, Hwang et al 16 observed that the gradiometers made of type-II superconducting materials showed worse performance when operated above H c1 .…”

Dynamic nuclear polarization in the hyperfine-field-dominant region

“…The NMR signal is, thus, proportional to B p , which is electrically switched on and off. A stronger B p is, of course, advantageous for obtaining a stronger signal; however, it also creates unwanted side effects, such as the induction of eddy currents on the walls of a magnetically shielded room (MSR) [15][16][17] and flux trapping in superconducting pickup coils [24]. Both effects generate a temporally varying field, which broadens the NMR linewidth and distorts the MR image.…”