Bavaro Vito, Caliano Giosuè, Pappalardo Massimo
Dipartimento di Ingegneria Elettronica, Università degli Studi Roma Tre, 00146 Roma, Italy.
IEEE Trans Ultrason Ferroelectr Freq Control. 2008 Feb;55(2):308-18. doi: 10.1109/TUFFC.2008.650.
Fully populated two-dimensional (2-D) arrays are needed to produce high quality ultrasonic volumetric images for real-time applications, but they present many challenges for their physical realization because of the large number of elements. In fact, lambda/2 and lambda minimum spacing between elements is required, respectively, for pyramidal and rectilinear scanning in order to avoid unwanted grating lobes (GLs). However, in past years, capacitive micromachined ultrasonic transducer (CMUT) technology has made possible the production of arrays with large flexibility in element shape and size. In this paper, this property is analyzed, and a new element shape, based on the concept of spatial interpenetration of adjacent elements, is proposed in order to design fully populated 2-D CMUT arrays with a low number of elements, whose beam characteristics are valid for volumetric imaging. Through the use of simulations, it is demonstrated that arrays with pitch larger than lambda (up to 3lambda) used for rectilinear scanning, have notably lower GLs than the equivalent standard arrays designed according to the classical squared element shape. As consequence, the proposed geometry has the advantage of reducing the number of elements (up to a factor of 9) and of enlarging the element size, implying an increase of the SNR relative to the single element. When beam steering is required, arrays can be designed with pitch equal to lambda, reducing the number of elements by a factor of 4 if the maximum steering angle is limited to +/-15 degrees .
要为实时应用生成高质量的超声容积图像，需要完全填充的二维（2-D）阵列，但由于元件数量众多，其物理实现面临诸多挑战。实际上，为避免出现不需要的栅瓣（GLs），金字塔扫描和直线扫描分别需要元件之间的间距为λ/2和λ最小值。然而，在过去几年中，电容式微机械超声换能器（CMUT）技术使得生产具有元件形状和尺寸高度灵活性的阵列成为可能。本文分析了这一特性，并基于相邻元件空间互穿的概念提出了一种新的元件形状，以设计元件数量少的完全填充二维CMUT阵列，其波束特性适用于容积成像。通过模拟表明，用于直线扫描的间距大于λ（最大可达3λ）的阵列，其栅瓣明显低于根据经典方形元件形状设计的等效标准阵列。因此，所提出的几何形状具有减少元件数量（最多可达9倍）和增大元件尺寸的优点，这意味着相对于单个元件，信噪比有所提高。当需要波束转向时，可设计间距等于λ的阵列，如果最大转向角限制在±15度，则元件数量可减少4倍。
