Daxsonics Affiliates at IEEE Ultrasonics: Real-time, 45 MHz, Split-Aperture Phased Array Beamformer with Efficient Sign Coherence Grating Lobe Suppression

Christopher A. Samson, Katherine Latham, and Jeremy A. Brown
School of Biomedical Engineering. Dalhousie University Halifax, Canada

Abstract—A digital variable sampling high-frequency beamformer implementing real-time grating lobe suppression is described. The system is tested using a semi-kerfed 64 element 45 MHz phased array with 1λ element pitch. The grating lobe suppression is facilitated with the sign coherence factor (SCF) and split-aperture transmit beamforming techniques. A new split-aperture transmit technique called “sub-aperture probing” (SAP) is described, experimentally validated, and compared to previously developed split-aperture techniques with respect to grating lobe suppression. Grating lobe levels were suppressed to be 49 and 60 dB below the main lobe when using 2 split-apertures with a SCF weighting factor of 1 and 2. These levels were further suppressed to 51 and 66 dB below the main lobe when splitting the aperture into 4 evenly sized apertures. When using SAP with 16 elements for the sub-aperture, grating lobes were suppressed to 49 and 64 dB below the main lobe. SAP with 8 elements yielded improved results compared to SAP with 16 elements; suppressing grating lobe levels to 49 and 65 dB below the main lobe for the associated SCF weighting coefficients. Finally the grating lobe suppression performance was tested on a wire target embedded in a tissue phantom and the signal to tissue speckle levels were characterized.