Fan-beam tomography of air flow in pipes using an electrostatic ultrasonic transducer array

A circular array of prototype divergent electrostatic ultrasonic transducer elements has been used to produce tomographic images of air flows in a pipe. The array formed part of a 100mm diameter pipe network through which air flows of up to 18 m/s could be achieved. Ultrasonic time of flight measurements in a fan beam geometry were used to reconstruct images of the disruption to air flows produced by various cylindrical bluff bodies with different diameters, using a filtered back-projection algorithm with a difference technique. The air flows through the pipe and array were modelled using FLOTRAN, and there was good agreement between the models and the reconstructed tomographic data.