Design of a 2D sparse array transducer for integration into an ergonomic transcranial ultrasound system

Transcranial Doppler Ultrasound (TCD) is one of the techniques that have been used for stroke diagnosis. This paper compares the potential of three aperiodic sparse array configurations: random array; sunflower spiral array; and log spiral array for application to TCD. To cover the full temporal window, a 30mm diameter circular aperture is selected, with a 2MHz operating frequency to match current TCD instrumentation. A 2D model developed in MATLAB simulates the far field directivity function by applying the 2D FFT on an array's aperture function. Two evaluation criteria, Peak Side-lobe Level (PSL) and Integrated Side-lobe Ratio (ISLR), are used to assess the performance of each array configuration. Simulation results demonstrate that a compromise between PSL and ISLR is required to select a suitable transducer configuration for fabrication and further evaluation. These evaluation results demonstrate that the log spiral array configuration has desirably low PSL relative to the others, while the sunflower spiral array performs better in terms of ISLR. Considering this design evaluation, a prototype array based on a log spiral layout has been manufactured. Characterization of the prototype array show that it performs as predicted.