IEEE Trans Ultrason Ferroelectr Freq Control. 2010 Nov;57(11):2588-95. doi: 10.1109/TUFFC.2010.1725.
A small element-to-element pitch (~.5λ) is conventionally required for phased array ultrasound transducers to avoid large grating lobes. This constraint can introduce many fabrication difficulties, particularly in the development of highfrequency phased arrays at operating frequencies greater than 30 MHz. In this paper, a new transmit beamforming technique along with sign coherence factor (SCF) receive beamforming is proposed to suppress grating lobes in large-pitch phased-array transducers. It is based on splitting the transmit aperture (N elements) into N/K transmit elements and receive beamforming on all N elements to reduce the temporal length of the transmit grating lobe signal. Therefore, the use of synthetic aperture beamforming, which can introduce relative phase distortions between the echoes received over many transmit events, can be avoided. After each transmit-receive event, the received signals are weighted by the calculated SCF to suppress the grating lobes. After pulsing all sub-apertures, the RF signals are added to generate one line of the image. Simulated 2-way radiation patterns for different K values show that grating lobes can be suppressed significantly at different steering angles. Grating lobes can be suppressed by approximately 20 dB with K = 2 at steering angles greater than 25° and an element pitch greater than 0.75λ. A technique for determining the optimal transmit sub-apertures has been developed.
为了避免栅瓣的出现，相控阵超声换能器通常需要采用小的阵元间距（~0.5λ）。这一约束条件会给制造带来许多困难，尤其是在开发工作频率高于 30 MHz 的高频相控阵时。本文提出了一种新的发射波束形成技术和符号相干因子（SCF）接收波束形成技术，用于抑制大间距相控阵换能器中的栅瓣。它基于将发射孔径（N 个阵元）分为 N/K 个发射阵元和在所有 N 个阵元上进行接收波束形成，以减少发射栅瓣信号的时间长度。因此，可以避免使用合成孔径波束形成，因为这种方法可能会在多次发射事件中引入回波之间的相对相位失真。在每次发射-接收事件之后，根据计算出的 SCF 对接收信号进行加权，以抑制栅瓣。在脉冲激励所有子孔径后，将 RF 信号相加以生成图像的一行。不同 K 值的仿真 2 路辐射图表明，在不同的指向角下，可以显著抑制栅瓣。在大于 25°的指向角和大于 0.75λ的阵元间距下，通过 K=2 可以抑制约 20dB 的栅瓣。还开发了一种确定最佳发射子孔径的技术。
