Active shims are commonly used in high-field, superconducting NMR magnets to improve the magnetic field homogeneity. However, shimming EPR magnets is less common nowadays. With the increased interest in low-frequency ODNP spectroscopy, active shims can greatly increase the sensitivity. Especially when recording the un-enhanced (off) signal.
The Bridge12 active shims for EPR magnets can easily be installed by the user between the magnet poles, and fit most commercially available EPR magnet. Commonly they are fitted with Z1, Z2, X, and Y coils. Higher order terms are available upon request. The shims are designed for a pole distance of 53 mm. Shims for other pole distances upon request.
Halbach magnet arrays have notoriously low magnetic field homogeneity resulting in broad NMR lines. With active shims the resolution and sensitivity can be dramatically increased and linewidths of < 10 Hz (< 0.7 ppm at 0.35 T) can be achieved. In addition, a B0 sweep coil can be added to the shim system to adjust the magnetic field strength. This is crucial in low-field ODNP experiments.