Three-dimensional electromagnetic articulograph based on a nonparametric representation of the magnetic field

A measurement method of the three-dimensional electromagnetic articulograph system is presented to investigate the dynamic behavior of articulatory organs which can include lateral or rotational movements. To accurately represent the spatial pattern of the magnetic field, we use a multivariate B-spline function, which smoothly interpolates a given set of calibration data samples. The strength of the received signal is predicted based on the spline field function while considering the tilting effect of the receiver coil relative to the direction of the magnetic field. The position and orientation of the receiver coil are then estimated using an iterative procedure so that the difference between the measured and predicted signal strengths is minimized. Preliminary experiments showed that the mean estimation error of the receiver position is about 0.5 mm when the axis of the receiver coil is parallel with one of the axes of the coordinate system.