Design of sparse annular arrays for high-frequency imaging

The design of a 35 MHz sparse annular array is described The array -was designed to provide < 125 μm resolution over an 8 mm imaging depth, while suppressing the secondary lobes to more than 60 dB below the main beam. The array has 10 equal-area elements and a 5 mm outer diameter. The array was designed with 110 μm equals-width kerfs, resulting in only a 50% active aperture. The simulated performance of the array was compared to a 5 mm diameter, 10-element array operating with a 100% active aperture. The -6 dB beamwidths of the sparse and full arrays were found to increase smoothly from 61 microns at a depth of 6 mm to 125 microns at 14 mm. For the sparse array, secondary lobes were suppressed by more than 60 dB over the entire 8 mm region, whereas the fully active array produced secondary lobes that were suppressed to -60 dB lobes only at depths greater than 10 mm.