Ring array PSF synthesis by delay dithering

In this paper we examine synthetic aperture acoustic imaging for a forward-looking ring array. To investigate how the well-known Bessel sum approach using pulsed insonification in the nearfield works, we introduce an extension of the sum coarray. This coarray accounts for the dithering, or shot-to-shot variation in the transmit and receive delays that are added to any beamsteering and focusing delays to effect the synthesis. We observe that an arbitrary configuration of the extended coarray can always be implemented using N-squared data, but that the reconstruction algorithm from such data requires the addition of multiple, shifted versions of each transmit/receive element pair data record, which is an extension of the standard reconstruction approach. In order to produce a design that can be implemented as a small number of whole-array transmissions, we structure the array dither in a way that mimics the dither applied to produce Bessel beams, but with greater freedom in the configuration. This approach, with peak PSF sidelobes minimized by simulated annealing, is shown to produce lower sidelobe PSFs than Bessel synthesis designed by existing methods.