共查询到20条相似文献,搜索用时 15 毫秒
1.
A novel approach to the design of spatial arrays is presented. The hybrid array beamformer consists of a sparse array in which some of the elements are arranged periodically, thus creating a periodic sub-array. The outputs of the sparse and periodic arrays are then fused to create a beampattern with good resolution and low peak sidelobe levels. This approach is seen as matching the performance of standard periodic arrays but with a significant saving in terms of the required number of elements. Applications include sonar, radar and ultrasonic systems 相似文献
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针对水下成像时圆弧阵常规波束旁瓣级较高,当存在强干扰时容易带来较多虚警的缺点,提出一种基于二阶锥规划的稳健低旁瓣自适应波束形成方法。该方法通过对波束旁瓣进行优化设计,可以将波束旁瓣级进行严格控制,并进一步结合协方差矩阵重构法,使波束形成器的稳健性得到提高,最后将该波束优化问题转化为二阶锥规划问题进行求解。计算机仿真结果表明,相较于其他算法来说,文中算法在波束旁瓣级得到严格控制的同时,可以在存在各类失配的情况下获得更高的输出信干噪比,稳健性更高。水池实验进一步验证了该方法的有效性,该研究成果可以在声呐成像领域应用。 相似文献
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Zhu Q Steinberg BD 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1993,40(6):747-753
The quality of an imaging system is degraded by propagation anomalies that distort wavefronts propagating through the medium. Adaptive phase-deaberration algorithms compensate for phase errors in the wavefront. The algorithms suffer, however, when the wavefront is also significantly distorted. A theory which shows that the rise of image background level, which is the average sidelobe floor (ASF), in a single point-like source image is proportional to the amplitude distortion of the wavefront and inversely proportional to the effective number of array elements is derived. From the theory, the tolerance to the amplitude distortion, after the phasefront has been corrected by a deaberration algorithm, can be calculated based on the design requirement of the sidelobe floor for a given array. Computer simulations show good agreement with the theory. 相似文献
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Adaptive beamforming applied to medical ultrasound imaging 总被引:1,自引:0,他引:1
Synnevåg JF Austeng A Holm S 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(8):1606-1613
We have applied the minimum variance (MV) adaptive beamformer to medical ultrasound imaging and shown significant improvement in image quality compared to delay-and-sum (DAS). We demonstrate reduced mainlobe width and suppression of sidelobes on both simulated and experimental RF data of closely spaced wire targets, which gives potential contrast and resolution enhancement in medical images. The method is applied to experimental RF data from a heart phantom, in which we show increased resolution and improved definition of the ventricular walls. A potential weakness of adaptive beamformers is sensitivity to errors in the assumed wavefield parameters. We look at two ways to increase robustness of the proposed method; spatial smoothing and diagonal loading. We show that both are controlled by a single parameter that can move the performance from that of a MV beamformer to that of a DAS beamformer. We evaluate the sensitivity to velocity errors and show that reliable amplitude estimates are achieved while the mainlobe width and sidelobe levels are still significantly lower than for the conventional beamformer. 相似文献
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针对传统的最小方差无畸变响应(Minimum Variance Distortionless Response,MVDR)波束形成方法存在的旁瓣较高且抑制干扰性能不稳健的情况,提出一种旁瓣级可控的自适应波束形成算法。该算法在MVDR基础上进行峰值搜索,将获得的峰值点从大到小进行排序,取次大值作为最高旁瓣的值,将得到的最高旁瓣值与期望旁瓣值比较,在其方位添加虚拟干扰加以抑制,从而得到新的波束图。再对新的波束图进行峰值搜索,不断重复上述过程,经过有限次迭代以达到期望旁瓣值。计算机仿真结果表明在均匀线阵基础上该算法能够将旁瓣控制到期望旁瓣级以下且比较稳健。 相似文献
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The methods used to reduce the errors in the determination of the harmonic phase of periodic signals by means of digital techniques are considered. The authors first briefly review the theory of the discrete Fourier transform (DFT) in order to discuss the genesis of the phase errors. They then give evidence that this approach has no general validity. An original method to minimize these phase errors while keeping the computation burden comparable with the of the classic FFT algorithm is proposed. The results of some experimental work done to verify the proposed method are reported, showing that the phase errors can be reduced by up to two decades with respect to those of the usual methods 相似文献
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介绍了聚焦波束形成的基本原理,分析了一种基于半圆阵的相位补偿方法。通过Matlab仿真得出聚焦波束形成的波束图,相比远场方法,波束宽度减小,旁瓣得到抑制。设计了一种基于FPGA的数字聚焦波束形成器的实时处理结构,使用8组加权系数即可完成成像声呐近场范围内分辨力的改进。通过乒乓操作和并行结构提高处理速度,实时产生72个波束。实验结果表明,所设计的聚焦波束形成器使某型成像声呐近场分辨力得到了提高。 相似文献
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Holfort I.K. Gran F. Jensen J.A. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2009,56(2):314-325
A minimum variance (MV) approach for nearfield beamforming of broadband data is proposed. The approach is implemented in the frequency domain, and it provides a set of adapted, complex apodization weights for each frequency subband. The performance of the proposed MV beamformer is tested on simulated data obtained using Field II. The method is validated using synthetic aperture data and data obtained from a plane wave emission. Data for 13 point targets and a circular cyst with a radius of 5 mm are simulated. The performance of the MV beamformer is compared with delay-and-sum (DS) using boxcar weights and Hanning weights and is quantified by the full width at half maximum (FWHM) and the peak-side-lobe level (PSL). Single emission {DS boxcar, DS Hanning, MV} provide a PSL of {-16, -36, -49} dB and a FWHM of {0.79, 1.33, 0.08} mm. Using all 128 emissions, {DS boxcar, DS Hanning, MV} provides a PSL of {-32, -49, -65} dB, and a FWHM of {0.63, 0.97, 0.08} mm. The contrast of the beamformed single emission responses of the circular cyst was calculated as {-18, -37, -40} dB. The simulations have shown that the frequency subband MV beamformer provides a significant increase in lateral resolution compared with DS, even when using considerably fewer emissions. An increase in resolution is seen when using only one single emission. Furthermore, the effect of steering vector errors is investigated. The steering vector errors are investigated by applying an error of the sound speed estimate to the ultrasound data. As the error increases, it is seen that the MV beamformer is not as robust compared with the DS beamformer with boxcar and Hanning weights. Nevertheless, it is noted that the DS does not outperform the MV beamformer. For errors of 2% and 4% of the correct value, the FWHM are {0.81, 1.25, 0.34} mm and {0.89, 1.44, 0.46} mm, respectively. 相似文献
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We consider the ‘faint companion’ problem where substantial reduction of diffraction sidelobes is required in order to image a faint neighbour near a much brighter source. In addition to well-known pupil amplitude and shape apodization methods, we found that the required sidelobe reduction can be obtained by appropriate spatial phase modulations over an aperture. Here, our previous results on one-sided phase apodization in astronomical applications are extended in several ways. Specifically, (i) round and square pupil cases are examined via a simple computational approach based on Fourier iterations; (ii) finite target regions are considered in the image plane; (iii) the discrete (square pupil) phase functions are used to construct a segmented mirror. The mirror provides sidelobe reduction sufficient for imaging of extrasolar planets. 相似文献
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Amplitude Estimation by a Multipoint Interpolated DFT Approach 总被引:1,自引:0,他引:1
This paper focuses on the amplitude estimation by a multipoint interpolated discrete Fourier transform (DFT) method. Accurate results are obtained using the weighted multipoint interpolated DFT (WMIpDFT) method with maximum sidelobe decay windows. In addition, using the WMIpDFT method with maximum sidelobe decay windows, it is mathematically proven that the systematic errors affecting the amplitude estimation decrease as the number of interpolation points and/or the window order increases. Computer simulations confirm the accuracy of the derived expressions. Moreover, the influence of white Gaussian noise on the amplitude estimations has been analyzed by means of computer simulations. 相似文献
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Asl BM Mahloojifar A 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2011,58(4):858-867
In adaptive ultrasound imaging, accurate estimation of the array covariance matrix is of great importance, and biases the performance of the adaptive beamformer. The more accurately the covariance matrix can be estimated, the better the resolution and contrast can be achieved in the ultrasound image. To this end, in this paper, we have used the forward-backward spatial averaging for array covariance matrix estimation, which is then employed in minimum variance (MV) weights calculation. The performance of the proposed forward-backward MV (FBMV) beamformer is tested on simulated data obtained using Field II. Data for two closely located point targets surrounded by speckle pattern are simulated showing the higher amplitude resolution of the FBMV beamformer in comparison to the forward-only (F-only) MV beamformers, without the need for diagonal loading. A circular cyst with a diameter of 6 mm and a phantom containing wire targets and two cysts with different diameters of 8 mm and 6 mm are also simulated. The simulations show that the FBMV beamformer, in contrast to the F-only MV, could estimate the background speckle statistics without the need for temporal smoothing, resulting in higher contrast for the FBMV-resulted image in comparison to the MV images. In addition, the effect of steering vector errors is investigated by applying an error of the sound speed estimate to the ultrasound data. The simulations show that the proposed FBMV beamformer presents a satisfactory robustness against data misalignment resulted from steering vector errors, outperforming the regularized F-only MV beamformer. These improvements are achieved without compromising the good resolution of the MV beamformer and resulted from more accurate estimation of the covariance matrix and consequently, the more accurate setting of the MV weights. 相似文献
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Sparse 2-D arrays for 3-D phased array imaging--design methods 总被引:2,自引:0,他引:2
Austeng A Holm S 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(8):1073-1086
One of the most promising techniques for limiting complexity for real-time 3-D ultrasound systems is to use sparse 2-D layouts. For a given number of channels, optimization of performance is desirable to ensure high quality volume images. To find optimal layouts, several approaches have been followed with varying success. The most promising designs proposed are Vernier arrays, but also these suffer from high peaks in the sidelobe region compared with a dense array. In this work, we propose new methods based on the principles of suppression of grating lobes to form symmetric and non-symmetric regular sparse periodic and radially periodic designs. The proposed methods extend the concept of sparse periodic layouts by exploiting either an increased number of symmetry axes or radial symmetry. We also introduce two new strategies to form designs with nonoverlapping elements. The performance of the new layouts range from the performance of Vernier arrays to almost that of dense arrays. Our designs have simplicity in construction, flexibility in the number of active elements, and the possibility of trade off sidelobe peaks against sidelobe energy. 相似文献
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舷侧阵正常工作时,由于海洋环境比较复杂,以及每路水听器通道的传输特性不完全一致,使舷侧阵每一个水听器输出信号的相位和幅度叠加了一个随机误差。在作MVDR自适应波束形成时,该随机误差的存在将影响到基阵的阵增益,降低检测能力。仿真结果表明:幅度和相位误差的存在会降低MVDR波束形成器的阵增益,两类误差越大,阵增益就越小;输入信噪比越高,MVDR波数形成器的阵增益就越小。文中从统计学角度分析了随机相幅误差对协方差矩阵的影响,然后通过数值仿真得到阵增益的变化规律。 相似文献
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Zhu Q Steinberg BD Arenson RL 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1993,40(6):754-762
For part I, see ibid., vol.40, no.6, p.747-753 (1993). In vivo measurements of the rise of the sidelobe level in a single-source image obtained through the female breast as a function of the distortion of the wavefront amplitude are described. The measured sidelobe levels are the average sidelobe floor (ASF) and the peak sidelobe level (PSL). The ASF is shown to be proportional to the variance of the modulus of the wavefront normalized to the square of its mean value, with a proportionality constant close to the value predicted by theory. The PSL similarly increases linearly. The average ratio of PSL to ASF is 5 (7 dB). 相似文献
20.
Liu DL 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(9):1212-1221
The distortion effect of tissue on ultrasonic beamforming is simplified as a 2-D time-shifting screen placed against the array surface. The ideal correction of such distortion requires a 2-D array with infinitesimally small elements. However, elements of finite sizes must be utilized in practice, causing the so-called residual phase error (RPE). As element size is reduced, the magnitude of the RPE is reduced, and its spatial feature becomes finer. Analyses have been performed to reveal that the magnitude of the RPE is proportional to the imaging frequency, the rms magnitude of the original time-delay error, and the diagonal size of individual rectangular elements, and is inversely proportional to the correlation length of the original time-delay error. Simulations have been performed to study the peak sidelobe level caused by the RPE as the element sizes are reduced. The sidelobe is defined here as the difference between the ideal beam (with no phase error) and the beam obtained in the presence of the RPE. For a multi-row array in which a conventional 1-D array is divided into N rows of independent elements in the elevation direction, the peak sidelobe level is found to vary approximately as N/sup -1/ instead of the anticipated N/sup -2/. The reduction is caused by the reduced magnitude of the RPE, and the finer spatial feature of the RPE, although apparent in the reduced spatial correlation length, does not result in additional reduction of the sidelobe level. The reason for this has been analyzed. The results of this study provide guidance for designing multi-row arrays suitable for phase aberration correction. 相似文献