Planar Magnetic Shielding for Use With Electromagnetic Tracking Systems

This paper evaluates the use of planar magnetic shielding with electromagnetic (EM) tracking systems to prevent field distortion from ferromagnetic objects below a magnetic-field transmitter. A comparison of the shielding performance of MuMetal, ferrite, aluminum, and steel is presented over a frequency range of 1 Hz to 1 MHz. Both simulation and experimental results show the merits of each shield material. MuMetal and ferrite were found to give excellent shielding performance over a wide frequency range. The use of a ferrite and MuMetal shield is also demonstrated in a full 5 degree of freedom EM tracking system and is shown to successfully operate with position errors of 1.8 and 2.3 mm, respectively, in a volume of 25 cm × 25 cm × 25 cm. This is compared with a mean position error 67.3 mm without shielding. The orientation error for each shield was found to be 1.9° and 2.1° for the ferrite and MuMetal, respectively, in comparison with an error of 115.1° without shielding.