Figure 12.

Unshielded OPM-MRX measurements of a BNF-MNP dilution series. The excitation coil was switched off a few $\mathsf{\mu }\mathrm{s}$ before the timestamp $0 \mathrm{s}$. The gradiometric data were averaged 100-times and an averaged empty measurement was subtracted. Individual FPGA-data-points are indicated by crosses, solid lines are the corresponding exponential fits (compare Table 1). (a) FPGA data. (b) FPGA data and instantaneous magnetic field obtained via Hilbert transform of 1:20 BNF sample; top: logarithmical time axis, bottom: linear time-axis.