Broadband Generalized Sidelobe Canceler Beamforming Applied to Ultrasonic Imaging

Abstract

A broadband generalized sidelobe canceler (Broadband-GSC) application for near-field beamforming is proposed. This approach is implemented in the wavelet domain. Broadband-GSC provides a set of complex, adapted apodization weights for each wavelet subband. The proposed method constrains interference and noise signal to improve the lateral resolution with only one single emission. Performance of the proposed beamforming is tested on simulated data obtained with Field II. Experiments have proved that the new beamforming can significantly increase the image quality compared with delay-and-sum (DAS) and synthetic aperture (SA). Imaging of scattering points show that Broadband-GSC improves the lateral resolution by 43.2% and 58.0% compared with SA and DAS, respectively. Meanwhile, Broadband-GSC reduces the peak sidelobe level by 11.6 dB and 26.4 dB compared with SA and DAS, respectively. Plane wave emission experiment indicates that Broadband-GSC can improve the lateral resolution by 44.2% compared with DAS. Furthermore, the new beamforming introduces the possibility for higher frame-rate and higher investigation depth with increased lateral resolution.Appl. Sci. 2020, 10, 1207 2 of 10 subband. However, how to appropriately divide the broadband signal into a set of narrowband signals based on sub-DFT needs more exploration. Appropriate division determines the quality of the system, thus sub-DFT beamforming is faceed with the problem of decreased robustness [12,13].This paper proposes an approach implemented in the wavelet domain. First, broadband echo signals are divided into a set of narrowband signals with discrete wavelet transform. Then, each wavelet subband is processed independently by a narrowband beamforming, generalized sidelobe canceler. Later, the processed subband responses are coalesced to provide the broadband beamforming output.The outline of this paper is as follows: Section 2 focuses on the traditional methodologies and its application to ultrasonic imaging. Section 3 looks into the principle and realization of the broadband generalized sidelobe canceler in detail. Section 4 presents the experiment results based on simulated data. Finally, the advantages of the proposed beamforming and its comparison with early proposed methodologies are discussed and concluded in Section 5. BackgroundThe diagram of the traditional ultrasonic imaging beamforming method is shown in Figure 1. First, one single element is excited to transmit the ultrasonic, and all elements receive the echo signal. Delay-and-sum (DAS) is introduced to obtain a receiving focused echo image, with low lateral resolution [14]. Then, exciting each element in turn, N's receiving focused images will be achieved. Later, N's receiving focused images are summed together to form the final beamforming output. Synthetic aperture (SA) is a passive process using fixed, data-independent apodization weights. The phase-shift can be implemented as time-delay and space-delay, therefore, SA achieves both receiving and transmitting focused [15,16]. The non-ad...

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