A Magnetic Compensation System Based on Spatial Constraint Coil With Large Uniform Region and High Uniformity

A large uniform region of magnetic field-free space is of great importance for magnetoencephalography (MEG) in a dynamic environment. Existing active compensation systems only compensate the magnetic field in a relatively small uniform region, the space utilization ratio (SUR) is low, as limited by the design theory. In this article, the design and the test of spatial constraint coil (SCC) are introduced. This type of coil maintains high uniformity in a relatively large region after special optimization, and the performance test results show that the SUR of the SCC can reach 12.5%, which is an improvement of about ten times compared with existing compensation coils. A magnetic field compensation system based on the SCC has been developed. After compensation, the residual magnetic field in our magnetic shielded room (MSR) is reduced to 0.5 nT in all three axes, which is 0.4% of the residual field before compensation, and the noise level is below 10 pT/Hz1/2 at 0.1–10 Hz. This method can greatly increase the uniform region while keeping high uniformity and compensation accuracy, which will provide a new solution for the creation of a large uniform region of magnetic field-free space in dynamic MEG measurement.