Corrections for sinusoidal background and non-orthogonality of signal channels in sinusoidal rapid magnetic field scans.

The rapidly-changing magnetic field of sinusoidal rapid scans creates background signals that are dominated by oscillations at the scan frequency. The background oscillations can be removed without acquiring off-resonance data. For data acquired in quadrature, up-field and down-field scan signals can be separated in the frequency domain. For each scan direction, the background oscillation can be calculated by fitting to the half cycle that does not contain the EPR signal. The extrapolated fit function is then subtracted from the half cycle that contains the EPR signal. By zeroing the array for the half cycles that do not contain the EPR signal, the signal-to-noise is improved and the data are corrected for non-orthogonality of the quadrature channels.