Low-Complexity Delay-Multiply-and-Sum (DMAS)beamforming Using Baseband Spatial Coherence

Conventional Delay-and-Sum (DAS)ultrasonic beamforming suffers from high lateral side lobe level. Different from DAS, Delay-Multiply-and-Sum (DMAS)imaging utilizes the spatial autocorrelation of receiving aperture to improve image resolution and contrast by multiplicative coupling of channel pairs. However, present DMAS imaging is based on the radio-frequency (RF)channel signals and thus requires large oversampling to avoid aliasing and additional band-pass (BP)filtering to isolate the corresponding spectral components for imaging. In this paper, a baseband version of DMAS beamforming (BB-DMAS)is proposed in this study using the baseband spatial coherence instead of the original RF multiplication of channel waveform. Note that the proposed approach does not suffer from the aforementioned requirement of oversampling and the additional band-pass filtering because no spectral up-shifting is expected in the multiplication of baseband channel data. Specifically, since the output of BB-DMAS beamforming remains at baseband, the same signal processing can be utilized in the proposed BB-DMAS beamforming as that in conventional baseband DAS beamforming.