A 3D airborne ultrasound scanner

This work investigates the feasibility of an ultrasounds canner designed to reconstruct three-dimensiona objects in air. There are many industrial applications in which it is important to obtain accurately the digital reconstruction of solid object with contactless methods.The final aim of this project was the profile reconstruction 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 wooden test objects with axial symmetry. A bistatic systém based on five airborne polyvinylidenedifluoride(PVDF) transducersw as 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 reconstruction was based on a simplified version of the synthetic aperture focusing technique (SAFT): the time of flight (TOF) of the first in time echo lor each receiving transducer was taken into account,a coarse spatial sampling of the ultrasonic fíeld reflected on the array transducer 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.