A 3D AIRBORNE ULTRASOUND SCANNER

This work investigates the feasibility of an ultrasound scanner design ed to reconstruct three-dimensional profiles of objects in air. There are many industrial applications in which it is important to obtain qu ickly and accurately the digital reconstruction of solid objects with contactless methods. The final aim of this project was the profile rec onstruction of shoe lasts in order to eliminate the mechanical tracers from the reproduction process of shoe prototypes. The feasibility of an ultrasonic scanner was investigated in laboratory conditions on woo den test objects with axial symmetry. A bistatic system based on five airborne polyvinylidenedifluoride (PVDF) transducers was mechanically moved to emulate a cylindrical array transducer that can host objects of maximum width and height 20 cm and 40 cm respectively. The object r econstruction was based on a simplified version of the synthetic apert ure focusing technique (SAFT): the time of flight (TOF) of the first i n time echo for each receiving transducer was taken into account, a co arse spatial sampling of the ultrasonic field reflected on the array t ransducer was delivered and the reconstruction algorithm was based on the ellipsoidal backprojection. Measurements on a wooden cone section provided submillimetre accuracy in a controlled environment.