Characterization of a bone mimicking phantom by means of circumferential guided waves dispersion curves

Previous studies have evidenced the circumferential propagation of waves guided by the roughly cylindrical cortical shell of the femoral neck. We hypothesize that measuring the phase velocities of such waves could yield estimates of the cortical thickness and material properties, which could improve fracture risk prediction. The objective of this study is to test the ability of the DORT method, processing based on time reversal principle, to measure circumferential guided waves in a bone-mimicking tube. The tube has the typical dimensions of the mid-femoral neck. A focused array specifically designed for this study was used for emission and reception. To serve as a noise-free reference, the experiment was also simulated based on an analytical formulation. The DORT method was applied to experimentally recorded and simulated data to retrieve the guided waves dispersion curves. Five branches of modes were obtained. They were identified by comparison with the theoretical dispersion curves of a semi-immersed plate. Experimental branches can be used in an inverse scheme to obtain estimations of the shell properties. This study shows that measuring circumferential guided waves is feasible in a structure with dimensions and material properties (elasticity, attenuation) close to those of the cortical compartment of the femoral neck.