Orthopaedic application of magnetic sensors

The purpose of this thesis is to propose a novel application of amorphous magnetic ribbons for use as knee force measurement sensors, without the need for secondary windings. This thesis demonstrates that the magnetic properties of amorphous ribbons are retained when embedded in Ultra-high molecular weight polyethylene (UHMWPE) tibial inserts, and these properties can be interrogated non-invasively. This is of importance, as it offers a viable solution for instrumented prosthesis which can be used for in-vivo monitoring. The research conducted also demonstrates that the tibiofemoral contact force on the instrumented tibial insert can be measured by observing the impedance changes in adjacent coils. Other conventional methods, though effective, require additional circuitry for non-invasive retrieval of measured data. The work contained herein eliminates this need, thereby reducing the structural modification of the implant required to accommodate the additional components. This research also shows that the variation in the coil impedance can be related to the permeability changes in the amorphous ribbons, and these can be quantified by tracking the resonant frequency of the coils. Amorphous ribbons have not been used in monitoring orthopaedic prosthesis before, and this work shows how the simplified measurement system can offer an alternative technique to knee implant monitoring