Cross-grating and along-grating motionless electromagnetic phase stepping (EPS) in a Talbot–Lau Interferometer. (a) In cross-grating EPS, the x-ray focal spot is shifted by a magnetic field B along the X axis, so that the spot moves along the Y axis, perpendicular to the grating lines. The moiré fringe lines on the detector are horizontal. The sample projection is shifted vertically across the fringe lines. (b) In along-grating EPS, the x-ray focal spot is stepped along the X axis in the direction parrallel to the grating lines. Slight rotations of G0 and G2 about the Z axis result in vertical moiré fringes, and the sample projection is moved horizontally across the fringes.