The design and development of a planar coil sensor for angular displacements

The increased prevalence of wearable sensing devices is accelerating the development of personalised medical devices for monitoring the human condition. The measurement of joint posture and kinematics is particularly relevant in areas of physiotherapy and in the management of diseases. Existing sensors for performing these tasks are however, either inaccurate or too technically complex and obtrusive. A novel approach has been taken to develop a new type of sensor for angular displacement sensing. This thesis describes the development of a series of novel inductive planar coil sensors for measuring angular displacement. The small profile of these sensors makes them ideal for integration into garments as part of wearable devices. The main objective of this work was to design a planar coil topology, based on an inductive methodology, suitable for measuring angular displacements typically observed in finger articulation. Finite Element Method software was initially employed to determine the feasibility of various coil topologies. The planar coils were subsequently manufactured on several types of substrate including rigid printed circuit boards and flexible polyester films incorporating an iron-based amorphous ribbon as the inductive element. A series of experimental investigations involving inductance and stray field measurements, were performed on a range of coil topologies and layered configurations. The resulting data provided information relating sensor performance to positioning of the amorphous element and its overall angular displacement. The main findings showed that inductance change was not frequency dependent in the range (20 – 100) kHz but decreased by up to 15% for large angular displacements when utilising a figure-of-eight coil design. The sensors developed in this work provide significantly better accuracy than current resistive-based flexible sensors. Further refinements to coil design and optimisation of the inductive element’s magnetic properties is expected to yield further improvements in sensor performance providing an excellent platform for future wearable technologies