Wearable Joint-Angle Measurement with Modulated Magnetic Field from L/C Oscilators

We demonstrate how modulated magnetic field generated by an simple LC oscilator can be used to measure joint angles, which are a key element in posture recognition and many motion analysis applications. Our method uses the same physical principle as large stationary motion trackers, however it applies the principle in a way suitable for a small, low power wearable system. It has the potential to be more accurate while being smaller and cheaper then inertial tracking (MARG) approaches that today are state of the art in wearable motion tracking. The paper describes the principle behind our method, discusses the advantages and problems and presents our prototype implementation. On a large data set with an hour of recording, hundreds of motions and tens of thousands of measurement-points we demonstrate, that even with an initial crude system implementation reasonable accuracy (between 6 and 9 percent average error) can be achieved.