In-situ ultrasonic imaging of dynamic process streams : system calibration and image processing

Ultrasonic imaging is a well-established technology that provides a safe method for imaging into optically opaque structures. These images can be generated by mechanically scanning a single transducer element, using tomography or by using a multiple-element transducer array, where the latter provides the most focussed images due to the precise positioning of the transmitting and receiving elements. An ultrasonic array comprises a number of individually addressable active piezoelectric elements and is controlled by a Phased Array Controller instrument to manipulate the ultrasonic pressure field within the load medium. Such arrays are typically used for sonar, medical diagnosis and non-destructive evaluation, however they have not yet been applied in the field of industrial process analysis. This paper aims to highlight how ultrasonic transducer arrays can be used to acquire in-situ images of dynamic process streams and how these images can provide valuable spatial information about the process, such as particle size distribution. The impact of this means that visualisation of a process stream will no-longer be limited to those systems that are optically transparent, therefore creating a greater breadth of spatial measurements within process analysis. This paper will be divided into two parts: image acquisition optimisation and image processing. The first part will outline the method used to determine the optimum number of array elements (active aperture) within the transducer array to acquire stable images of a dynamic system. For this work, the size of the active aperture will range from 16 to 128 elements, corresponding to an image region width of 11 to 90 mm. However, larger images require a longer data acquisition time and therefore produce a poorer image resolution when the target is dynamic in nature. The second part will show how relevant information about the process can be extracted from these ultrasonic images and how these measurements can be calibrated using a static system. The conclusion of this paper will discuss how an array ultrasonic image acquisition and processing system has the potential to become a new class of process analytical technology.