Optimization of multilayer cylindrical coils in a wireless localization system to track a capsule-shaped micro-device

A wireless electromagnetic localization method has been presented to track capsule-shaped micro-devices in the gastrointestinal tract. And a prototype for the novel localization system has been developed. In the localization method, cylindrical coils placed on the patient’s abdomen generate alternating electromagnetic fields one by one. The system of equations from the localization model has been established and then transformed into a nonlinear optimization problem. The localization method presents excellent anti-interference ability and high stability. In order to solve the magnetic inverse problem in the localization model, an analytical expression between the magnetic flux density and the position & orientation should be derived by superposition of the fields generated by the coil turns, which causes systematic errors. As a result, the geometry of the cylindrical coils is optimized to reduce the errors. A full factorial experiment with two factors has been carried out. The experiment shows that the optimal L/Dout ratio and Din/Dout ratio are 0.4 and 0.8, respectively. In this case, the mean error and the standard deviation are reduced to 0.89% and 0.77%, respectively, where the distance along the axis of the cylindrical coil from the coil’s center to a measured point is 30 mm. Furthermore, the experimental results also show that the imitation error decreases significantly with increased distance from the coil. The accuracy of the localization model can be further improved using the optimized coil.

► We develop a prototype of a novel wireless localization system with high stability.
► An analytical model is derived to solve the magnetic inverse problem.
► Excitation coils in localization are optimized to reduce imitation error.
► The imitation error decreases with increased inner-to-outer diameter ratio.
► The imitation error increases with increased length-to-diameter ratio.