Elimination of scan blindness with compact defected ground structures in microstrip phased array

A compact H-shaped defected ground structure (DGS) is applied to reduce the mutual coupling between array elements and eliminate the scan blindness in a microstrip phased array design. The proposed DGS is inserted between the adjacent E-plane coupled elements in the array to suppress the pronounced surface waves. A two-element array is measured and the results show that a reduction in mutual coupling of 12 dB is obtained between elements at the operation frequency of the array. The scan properties of microstrip phased arrays with and without DGS are studied by the waveguide simulator method. The analysis indicates that the scan blindness of the microstrip phased array can be well eliminated because of the effect of the proposed DGS. Meanwhile, the active patterns of the array centre element in 7 x 3 element arrays with and without the H-shaped DGS are simulated, and the results agree with those obtained by the waveguide simulator method.     

智能天线系统中阵元间互耦的影响及盲校正方法

针对天线阵单元间互耦会导致智能天线性能下降这一问题,提出了一种盲校正方法.该方法基于均匀圆阵(UCA)互耦矩阵的特殊结构形式,利用子空间原理和拉格朗日乘子法,不需要任何辅助信号源就能同时完成阵列误差的校正和波达方向(DOA)的估计.在进行计算机仿真时,还提出了以空间响应相关系数(SRCC)为准则来详细地分析互耦对阵列性能的影响,并通过一些典型的例子证明了所提出的盲校正方法的可行性.     

A new decoupling method for phased arrays in magnetic resonance imaging: an experimental approach

A new decoupling method for magnetic resonance imaging (MRI) phased arrays is studied by experimental measurements. A laboratory measurement setup is built to characterise the signal coupling paths and their coupling strengths. A new concept, the receiving mutual impedance, is introduced to measure the coupled signals between the phased array elements. Measured values of the receiving mutual impedances for a typical two-element surface-coil array are obtained and used in other experiments to find the uncoupled voltages from the received voltages. Results show that the new decoupling method is both accurate and robust over a wide frequency range. Comparison of the uncoupled voltages with the actual ideal uncoupled voltages confirms that if the position of the signal source is known, almost error-free uncoupled voltages can be obtained. The errors resulted from a change of the position of the signal source are also measured and it is found that they generally increase with the deviation of the signal source from its position where the receiving mutual impedances are measured. The maximum % error of the uncoupled voltages is found to be below 10% when the signal source changes its position over a distance of half the length of a surface coil. Over this distance change, the signal isolation between the two surface coils is found to be at least 20 dB, whereas the maximum is more than 300 dB. The results demonstrate the effectiveness and the feasibility of the new decoupling method for use in MRI phased arrays.     

一种均匀线阵互耦校正算法

旋转不变子空间(Estimating Signal Parameters via Rotational Invariance Techniques,ESPRIT)算法是空间谱估计中的典型算法,但是阵列互耦会严重影响ESPRIT算法的测向性能。将均匀线阵划分为冗余阵元和有效中心阵元,对有效中心阵元利用ESPRIT算法估计出校正源方位角,结合冗余阵元信息估计出互耦系数阵。计算机仿真显示该算法在互耦自由度为2或3时均有效,算法还从仿真角度研究了幅度和相位误差对算法性能的影响。该算法校正时只需单个未知方位校正源,是一种操作简单的均匀线阵互耦校正算法。     

Shape calibration of a conformal ultrasound therapy array

A conformal ultrasound phased array prototype with 96 elements was previously calibrated for electronic steering and focusing in a water tank. The procedure for calibrating the shape of this 2D therapy array consists of two steps. First, a least squares triangulation algorithm determines the element coordinates from a 21×21 grid of time delays. The triangulation algorithm also requires temperature measurements to compensate for variations in the speed of sound. Second, a Rayleigh-Sommerfeld formulation of the acoustic radiation integral is aligned to a second grid of measured pressure amplitudes in a least squares sense. This shape calibration procedure, which is applicable to a wide variety of ultrasound phased arrays, was tested on a square array panel consisting of 7-×7-mm elements operating at 617 kHz. The simulated fields generated by an array of 96 equivalent elements are consistent with the measured data, even in the fine structure away from the primary focus and sidelobes. These two calibration steps are sufficient for the simulation model to predict successfully the pressure field generated by this conformal ultrasound phased array prototype     

基于时延冗余测量的阵形校准

海底柔性水平阵的阵形校准,可以利用两个校准声源测量阵元间的声传播时延差来求解得到。传统算法只利用了相邻阵元信号测量的时延差,但误差会随噪声增大而出现累积。在信噪比降低时,所提方法通过冗余时延测量有效地减少了误差累积,从而提高了阵形校准的精度与稳定性。数值仿真与实验结果都验证了该方法的有效性。     

Design and evaluation of a feedback based phased array system for ultrasound surgery

A driving system has been designed for phased array ultrasound applicators. The system is designed to-operate in the bandwidth 1.2 to 1.8 MHz, with independent channel power control up to 60 W (8 bit resolution) for each array element. To reduce power variation between elements, the system utilizes switching regulators in a feedback loop to automatically adjust the DC supply of a class D/E power converter. This feedback reduces the RF electrical power variation from 20% to 1% into a 16 element array. DC-to-RF efficiencies close to 70% for all power levels eliminates the need for large heat sinks. In addition to power control, each channel may be phase shifted 360 degrees with a minimum of 8 bit resolution. To ensure proper operation while driving ultrasound arrays with varying element sizes, each RF driving channel implements phase feedback such that proper phase of the driving signal is produced either at the amplifier output before the matching circuitry or after the matching circuitry at the transducer face. This feedback has been experimentally shown to increase the focal intensities by 20 to 25% of two tested phased arrays without array calibration using a hydrophone.     

辐射力天平法测量相控阵超声换能器的声功率

超声换能器相控阵已用于聚焦超声治疗的研究和应用已有20多年历史,但其声功率P的测量仍缺乏方便有效简易的测量方法。文章旨在提出一种基于凸球面吸收靶的辐射力天平（Radiation Force Balance,RFB）方法,测量其声功率。理论推导了这种RFB在各种阵元组合下的比值r=P/cF（c为水中声速,F为阵的声束轴方向的总辐射力）。论述了测量各种组合的发射声功率的实施方法和测量程序。为实际的测量系统设计和应用建立了良好的工作基础。     

声压基阵误差单辅助矢量水听器快速校准方法

针对方位依赖的声压基阵误差校正困难问题,提出了声压基阵误差单辅助矢量水听器快速校准方法。利用精确校正的单只矢量水听器,就可以对声源方位及方位依赖的声压基阵幅度相位误差,进行无模糊的联合估计。由于阵元位置误差、互耦及通道的幅度相位误差均可以等效为方位依赖的基阵幅度相位误差,所以可以对多种同时存在的基阵误差进行校正。该方法适用于任意的阵列结构,不存在参数联合估计的局部收敛问题,只需参数的一维搜索,运算量小可实时在线完成。通过计算机仿真实验验证了该方法的有效性。     

A parametric study of ultrasonic beam profiles for a linear phased array transducer

A numerical simulation model is presented to investigate the influences of design parameters of linear phased array transducers on beam focusing and steering performance. The characteristic of ultrasonic beam profiles has been simulated on the basis of the Huygen's superposition principle. For the simulation, a linear phased array is considered as the composition of finite number of elements separated by equidistance. Individual elements are considered as two-dimensional point sources. The waves generated from piezoelectric elements are considered as simplified transient ultrasonic waves that are constructed with the cosine function enveloped with a Hanning window. The characteristic of ultrasonic wave propagation into a medium from the phased array transducer is described. The effects of the number, the interelement spacing, steering angle, the focal length, and frequency bandwidth of the piezoelectric elements on beam directivity and ultrasonic pressure field in a linear phased array transducer are systematically discussed.     

Direction of arrival estimation for uniform circular array based on fourth-order cumulants in the presence of unknown mutual coupling

A direction of arrival (DOA) estimation algorithm in the presence of an unknown mutual coupling is presented for a uniform circular array. This algorithm is based on the fourth-order cumulants, and the DOA of signal sources can be accurately estimated without the need of any calibration source since the coupling is blindly compensated by the inherent mechanism of the proposed method. Because of the use of higher-order statistics, the number of sources that can be coped with may be larger than the number of sensors in the array, and the algorithm is insensitive to Gaussian noise. Comparing with existing calibration methods which use iterative approaches, this algorithm is computationally less expensive since it uses only a one-dimensional search. Validation and performance are illustrated by simulations.     

拉曼激光相位噪声对原子干涉重力仪测量分辨力的影响

为了保证相控阵雷达的性能,它的天线现场校准越来越受到重视。本文首先介绍相控阵雷达天线现场校准的现状, 提出目前存在的问题。然后分析光学电磁场探测技术优势,阐述基于光子技术的相控阵雷达天线现场校准实现的可行性,建立了现场校准装置。通过实验验证,该技术能实现对相控阵雷达天线现场校准,具有高精度,对天线的辐射场的影响较小,能满足相控阵雷达天线现场校准要求。     

Orientation dependence of electromechanical coupling factors in KNbO(3)

This paper is concerned with the electromechanical coupling factors for bulk waves in KNbO(3) crystal. The dependence of coupling factors on the orientation of vibrators for various types of vibration modes has been calculated. As a result, it has been found that most of these coupling factors are very large at certain orientations of vibrators. Especially, the maximum coupling factor of the thickness-extensional mode excited with a perpendicular field, k(t ), is as high as 69% for the rotated X-cut by an angle 49.5 degrees about the Y-axis; that of the thickness-shear mode, k(s), is 88% for the X-cut. To the best of our knowledge, these coupling factors are the highest among those of known piezoelectrics. It has also been found that the coupling factor of the width-extensional mode of a thin finite-width plate with electrodes on its edges, k(ww)', is 82% for the rotated Z-cut by an angle 43.5 degrees about the Y-axis. This vibrator would be promising as elements of phased array ultrasonic probes.     

精密水槽收缩段流场模拟与收缩曲线选型评估

通过求解RANS方程,数值模拟了精密水槽收缩段的流场特性。针对两种不同出口尺寸不同收缩比的收缩段,选取了三种不同的收缩曲线来进行选型评估。根据壁面是否分离、逆压梯度变化缓和程度、出口速度均匀度,来判断不同收缩曲线的优劣。研究表明:对于出口尺寸为250 mm×20 mm、收缩比为30的收缩段,双三次收缩曲线是最优的;对于出口尺寸为250 mm×10 mm、收缩比为60的收缩段,维氏收缩曲线是最优的。本次数值模拟计算的工作可为精密水槽收缩段优化设计工作提供借鉴。     

Performance analysis of multiple-input multiple-output orthogonal frequency division multiplexing systems under the influence of antenna mutual coupling effect

The effect of antenna mutual coupling on signal correlation and bit error rate (BER) of a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system has been modelled. A MIMOOFDM model with correlated channels is presented. The correlation matrices are determined with the antenna mutual coupling taken into account. The effect of antenna mutual coupling is characterised using the receiving and transmitting mutual impedances. A rigorous expression for the BER of the system employing quadrature phase-shift keying digital modulation is derived. A 2 x 2 MIMO-OFDM system using the Alamouti space?time block code for OFDM symbol transmission over 64 sub-channels spanning a 20 MHz band centred at 5.2 GHz is simulated. The simulated results show that the antenna mutual coupling has a significant effect on the BER performance, especially when the spacing between the antenna elements is small.     

Microstrip antenna array controlled with active phase shifter

Abstract

A two‐element microstrip antenna array controlled with active phase shifters has been fabricated and tested. The phase and amplitude of the active phase shifter output can be continuously changed by controlling the gate voltages of the dual gate FET. This array can be mounted on aircraft or missiles and be used in the direction finder or adaptive array systems.

The mutual couplings between microstrip patches are also experimentally studied. It is found that the self‐impedance and resonant frequencies depend highly on the separation if the patches are separated less than 0.4 wavelength and become constant as the separation is greater than 0.5 wavelength. The effect of mutual coupling in the E‐plane is less prominent than that in the H‐plane. In array patterns synthesis, the mutual coupling can be neglected if the separation is greater than 0.5 wavelength. However, if the separation becomes smaller, the mutual coupling must be considered such that the calculated patterns are in good agreement with the experimental results.     

Finite-difference time-domain simulation of a liquid-crystal optical phased array

Accurate modeling of a high-resolution, liquid-crystal-based, optical phased array (OPA) is demonstrated. The modeling method is extendable to cases where the array element size is close to the wavelength of light. This is accomplished through calculating an equilibrium liquid-crystal (LC) director field that takes into account the fringing electric fields in LC OPAs with small array elements and by calculating the light transmission with a finite-difference time-domain method that has been extended for use in birefringent materials. The diffraction efficiency for a test device is calculated and compared with the simulation.     

Application of metric tensors to conformal arrays

Using the metric tensor g ^{the author derives the scattering parameters appearing in the field equations of the uniform theory of diffraction (UTD). The method presented allows us to derive these field parameters in terms of tensors whose general form can be applied to high-frequency electromagnetic scattering problems or more specifically to the analysis of conformal arrays. All the parameters in the field solutions are related to the array manifold properties that are derived via the use of the metric tensor are shown. The expressions for the Frenet-field tensors and the generalised Fock parameter and the shortest path propagated by the fields along the array manifold using the metric tensor in the calculus of variations are determined. The method enables UTD mutual coupling calculations to be performed for various phased array manifolds.}     

延时分辨率对超声相控阵检测性能的影响

超声相控阵检测技术是近年发展起来的一种先进的无损探伤方法,阵元间的延时分辨率是决定超声相控阵检测系统性能的关键因素,通过研究延时分辨率对相控阵检测效果的影响,可以得到延时分辨率和相关性能参数之间的对应关系,从而提高超声相控阵系统的检测性能。