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《测试技术学报》2021,35(5)
为降低工程造价和系统复杂度,采用最小单元间距均大于一个波长的大间距阵列是较有效的措施,但阵列方向图会出现不期望的栅瓣.通过随机分布法对28×28个阵元的大间距非周期矩形栅格阵列进行优化.为抑制栅瓣,将均匀阵列划分为不同数量的子阵列,比较子阵列优化错位后的栅瓣抑制效果.然后,将阵列划分为4×4个和7×7个子阵,研究子阵(错位或均匀)和子阵内阵元(随机或均匀排布)的组合阵列,分析3种不同随机程度的组合阵列栅瓣抑制效果,并结合仿真图从栅瓣电平和平均副瓣电平角度对比说明各种排布的优劣.结果表明,子阵错位且子阵内阵元随机排布的栅瓣抑制效果最好,但平均副瓣电平会抬高,相比全随机排列阵列工程上更容易实现,且成本更低. 相似文献
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计算并分析了线阵、离散复合阵指向性,连续复合阵不同孔径函数透声窗的指向性以及孔径函数与旁瓣级的关系;并且通过实验验证了复合声学系统对指向性的改善,为实际布阵提供了重要的依据. 相似文献
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介绍西北工业大学开发的水声基阵波束分析与优化设计软件.该软件针对给定的基阵形式,可以设计期望的波束图,然后通过优化方法获得最优的波束形成权系数.同时软件还可以分析水声基阵的常规波束图和最优波束图,并计算波束图的主瓣宽度、旁瓣级、栅瓣位置、指向性指数等主要指标.软件中考虑的基阵形式主要有直线阵、圆阵、圆柱阵、平面阵、球阵、体积阵等.本软件的有效性通过波束优化设计与分析实例得到了验证. 相似文献
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介绍了一种小型化线列阵,阵结构与常规线列阵最大的不同在于阵元间距小于四分之一波长。通过理论分析和仿真计算优化了各阵元的最佳权系数,获得了良好的指向性,得到了实验的证明。小型化线列阵的指向性图具有四大特点:①单向性:仅在半空间出现一个轴对称的主波束,无栅瓣和次瓣。②端射特性:主波束出现在线阵的轴射方向。③超指向性:在阵的尺寸远小于二分之一波长条件下不仅可以获得良好的指向性图,并且波束宽度随阵元间距的减小而减小。④恒定束宽特性:在阵元间距小于八分之一波长条件下,波束宽度随频率变化非常平缓。这种小型化基阵也可用于大型基阵如拖曳阵和展开式体积阵的子基阵,进行低频宽带信号的检测。 相似文献
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Raju BI Hall CS Seip R 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2011,58(5):944-954
Ultrasound transducers designed for therapeutic purposes such as tissue ablation, histotripsy, or drug delivery require large apertures for adequate spatial localization while providing sufficient power and steerability without the presence of secondary grating lobes. In addition, it is highly preferred to minimize the total number of channels and to maintain simplicity in electrical matching network design. To this end, we propose array designs that are both space-filling and non-periodic in the placement of the elements. Such array designs can be generated using the mathematical concept of non-periodic or aperiodic tiling (tessellation) and can lead to reduced grating lobes while maintaining full surface area coverage to deliver maximum power. For illustration, we designed two 2-D space-filling therapeutic arrays with 128 elements arranged on a spherical shell. One was based on the two-shape Penrose rhombus tiling, and the other was based on a single rectangular shape arranged non-periodically. The steerability performance of these arrays was studied using acoustic field simulations. For comparison, we also studied two other arrays, one with circular elements distributed randomly, and the other a periodic array with square elements. Results showed that the two space-filling non-periodic arrays were able to steer to treat a volume of 16 x 16 x 20 mm while ensuring that the grating lobes were under -10 dB compared with the main lobe. The rectangular non-periodic array was able to generate two and half times higher power than the random circles array. The rectangular array was then fabricated by patterning the array using laser scribing methods and its steerability performance was validated using hydrophone measurements. This work demonstrates that the concept of space-filling aperiodic/non-periodic tiling can be used to generate therapy arrays that are able to provide higher power for the same total transducer area compared with random arrays while maintaining acceptable grating lobe levels. 相似文献
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Lu JY He S 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1999,46(6):1416-1421
Recently, a high frame rate imaging method has been developed to construct either 2-D or 3-D images (about 3750 frames or volumes/s at a depth of about 200 mm in biological soft tissues because only one transmission is needed). The signal-to-noise ratio (SNR) is high using this method because all array elements are used in transmission and the transmit beams do not diverge. In addition, imaging hardware with the new method can be greatly simplified. Theoretically, the element spacing (distance between the centers of two neighboring elements) of an array should be lambda/2, where lambda is the wavelength, to avoid grating lobes in imaging. This requires an array of a large number of elements, especially, for 3-D imaging in which a 2-D array is needed. In this paper, we study quantitatively the relationship between the quality of images constructed with the new method and the element spacing of array transducers. In the study, two linear arrays were used. One has an aperture of 18.288 mm, elevation dimension of 12.192 mm, a center frequency of 2.25 MHz, and 48 elements (element spacing is 0.381 mm or 0.591 lambda). The other has a dimension of 38.4 mmx10 mm, a center frequency of 2.5 MHz, and 64 elements (0.6 mm or 1.034 lambda element spacing). Effective larger element spacings were obtained by combining signals from adjacent elements. Experiments were performed with both the new and the conventional delay-and-sum methods. Results show that resolution of constructed images is not affected by the reduction of a number of elements, but the contrast of images is decreased dramatically when the element spacing is larger than about 2.365 lambda for objects that are not too close to the transducers. This suggests that an array of about 2.365 lambda spacing can be used with the new method. This may reduce the total number of elements of a fully sampled 128x128 array (0.5 lambda spacing) from 16384 to about 732 considering that the two perpendicular directions of a 2-D array are independent (ignoring the larger element spacing in diagonal directions of 2-D arrays). 相似文献
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Ullate LG Godoy G Martínez O Sánchez T 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(10):1944-1954
Two-dimensional (2-D) arrays of squared matrix have maximum periodicity in their main directions; consequently, they require half wavelength (lambda/2), interelement spacing to avoid grating lobes. This condition gives rise to well-known problems derived from the huge number of array elements and from their small size. In contrast, 2-D arrays with curvilinear configuration produce lower grating lobes and, therefore, allow the element size to be increased beyond lambda/2. Using larger elements, these arrays have the advantage of reducing the number of elements and of increasing the signal-to-noise ratio (SNR). In this paper, the beamforming properties of segmented annular phased arrays are theoretically analyzed and compared with the equivalent squared matrix array. In the first part, point-like elements are considered in order to facilitate the field analysis with respect to the array structure. Afterward, the effect of the element size on the steered beam properties also is presented. In the examples, it is shown that the segmented annular array has notably lower grating lobes than the equivalent squared matrix array and that it is possible to design segmented annular arrays with interelement distance higher than lambda whose beam characteristics are perfectly valid for volumetric imaging applications. 相似文献
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《IEEE sensors journal》2008,8(11):1755-1762
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Smith PR Cowell DM Raiton B Ky CV Freear S 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2012,59(1):40-49
Coarse time quantization of delay profiles within ultrasound array systems can produce undesirable side lobes in the radiated beam profile. The severity of these side lobes is dependent upon the magnitude of phase quantization error--the deviation from ideal delay profiles to the achievable quantized case. This paper describes a method to improve interchannel delay accuracy without increasing system clock frequency by utilizing embedded phase-locked loop (PLL) components within commercial field-programmable gate arrays (FPGAs). Precise delays are achieved by shifting the relative phases of embedded PLL output clocks in 208-ps steps. The described architecture can achieve the necessary interelement timing resolution required for driving ultrasound arrays up to 50 MHz. The applicability of the proposed method at higher frequencies is demonstrated by extrapolating experimental results obtained using a 5-MHz array transducer. Results indicate an increase in transmit dynamic range (TDR) when using accurate delay profiles generated by the embedded-PLL method described, as opposed to using delay profiles quantized to the system clock. 相似文献
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Ealo J.L. Camacho J.J. Fritsch C. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2009,56(4):848-858
In this work, a novel procedure that considerably simplifies the fabrication process of ferroelectret-based multi-element array transducers is proposed and evaluated. Also, the potential of ferroelectrets being used as active material for aircoupled ultrasonic transducer design is demonstrated. The new construction method of multi-element transducers introduces 2 distinctive improvements. First, active ferroelectret material is not discretized into elements, and second, the need of structuring upper and/or lower electrodes in advance of the permanent polarization of the film is removed. The aperture discretization and the mechanical connection are achieved in one step using a through-thickness conductive tape. To validate the procedure, 2 linear array prototypes of 32 elements, with a pitch of 3.43 mm and a wide usable frequency range from 30 to 300 kHz, were built and evaluated using a commercial phased-array system. A low crosstalk among elements, below -30 dB, was measured by interferometry. Likewise, a homogeneous response of the array elements, with a maximum deviation of plusmn1.8 dB, was obtained. Acoustic beam steering measurements were accomplished at different deflection angles using a calibrated microphone. The ultrasonic beam parameters, namely, lateral resolution, side lobe level, grating lobes, and focus depth, were congruent with theory. Acoustic images of a single reflector were obtained using one of the array elements as the receiver. Resulting images are also in accordance with numerical simulation, demonstrating the feasibility of using these arrays in pulse-echo mode. The proposed procedure simplifies the manufacturing of multidimensional arrays with arbitrary shape elements and not uniformly distributed. Furthermore, this concept can be extended to nonflat arrays as long as the transducer substrate conforms to a developable surface. 相似文献
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Nondiffracting beams are of interest for optical metrology applications because the size and shape of the beams do not change as the beams propagate. We have created a generating pattern consisting of a linear combination of two nondiffracting patterns. This pattern forms a nondiffracting interference pattern that appears as a circular array of nondiffracting spots. More complicated multiplexed arrays are also constructed that simultaneously yield two different nondiffracting patterns. We generate these Bessel function arrays with a programmable spatial light modulator. Such arrays would be useful for angular alignment and for optical interconnection applications. 相似文献
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Lu JY Greenleaf JF 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(5):724-739
The newly developed limited diffraction beams such as the Bessel beams and X waves have a large depth of field and approximate depth-independent property. They have possible applications in medical imaging, color Doppler imaging, tissue characterization, and nondestructive evaluation of materials, and in other wave related physical branches such as electromagnetics and optics. However, limited diffraction beams are currently produced with an annular array transducer that has to be steered mechanically. In this paper, we study the feasibility of steering these beams with a two-dimensional array, and show that there will be almost no distortion of beams if the effective aperture reduction of the array is properly compensated so that the beams have a constant transverse profile as they are steered. In addition, methods for reducing the complexity of the electronic multiplexing of the array elements are proposed. We also investigate the influences of the interelement distance and the size of array elements on the sidelobes and grating lobes of limited diffraction beams as the beams are steered. They are similar to those previously reported for conventional beams. 相似文献
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为了提高双线阵聚焦波束形成在阵元数少或频率低时的定位精度,文章研究了一种基于反卷积的双线阵聚焦波束形成被动定位方法。首先在测量区内对双线阵接收信号进行球面波补偿,给出噪声源分布的声图信息。然后根据阵型的参数,计算双线阵的指向性函数。最后利用一种适用于移变阵列的二维扩展R-L反卷积算法,对声图波束输出和双线阵的指向性函数做反卷积,求解基于反卷积波束形成的源的分布。该方法旁瓣更低,分辨力更高,有效提高双线阵聚焦波束形成的定位精度和左右舷分辨能力,为后续的减振降噪、噪声检测等工作提供了参考。 相似文献
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Stephens D Kruse D Qin S Ferrara K 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2011,58(8):1590-1602
As the applications of ultrasonic thermal therapies expand, the design of the high-intensity array must address both the energy delivery of the main beam and the character and relevance of off-target beam energy. We simulate the acoustic field performance of a selected set of circular arrays organized by array format, including flat versus curved arrays, periodic versus random arrays, and center void diameter variations. Performance metrics are based on the -3-dB focal main lobe (FML) positioning range, axial grating lobe (AGL) temperatures, and side lobe levels. Using finite-element analysis, we evaluate the relative heating of the FML and the AGLs. All arrays have a maximum diameter of 100λ, with element count ranging from 64 to 1024 and continuous wave frequency of 1.5 MHz. First, we show that a 50% spherical annulus produces focus beam side lobes which decay as a function of lateral distance at nearly 87% of the exponential rate of a full aperture. Second, for the arrays studied, the efficiency of power delivery over the -3-dB focus positioning range for spherical arrays is at least 2-fold greater than for flat arrays; the 256-element case shows a 5-fold advantage for the spherical array. Third, AGL heating can be significant as the focal target is moved to its distal half-intensity depth from the natural focus. Increasing the element count of a randomized array to 256 elements decreases the AGL-to-FML heating ratio to 0.12 at the distal half-intensity depth. Further increases in element count yield modest improvements. A 49% improvement in the AGL-to-peak heating ratio is predicted by using the Sumanaweera spiral element pattern with randomization. 相似文献