  Miniature magnetic tools have the potential to enable minimally invasive
surgical techniques to be applied to space-restricted surgical procedures in
areas such as neurosurgery. However, typical magnetic navigation systems, which
create the magnetic fields to drive such tools, either cannot generate large
enough fields, or surround the patient in a way that obstructs surgeon access
to the patient. This paper introduces the design of a magnetic navigation
system with eight electromagnets arranged completely under the operating table,
to endow the system with maximal workspace accessibility, which allows the
patient to lie down on the top surface of the system without any constraints.
The found optimal geometric layout of the electromagnets maximizes the field
strength and uniformity over a reasonable neurosurgical operating volume. The
system can generate non-uniform magnetic fields up to 38 mT along the x and y
axes and 47 mT along the z axis at a working distance of 120 mm away from the
actuation system workbench, deep enough to deploy magnetic microsurgical tools
in the brain. The forces which can be exerted on millimeter-scale magnets used
in prototype neurosurgical tools are validated experimentally. Due to its large
workspace, this system could be used to control milli-robots in a variety of
surgical applications.
