Element shape design of 2-D CMUT arrays for reducing grating lobes

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 .     

General synthesis method for linear phased antenna array

An efficient phase-only control method is presented to synthesise directive lobe and multilobe patterns, and create adaptive nulls in interference direction. The proposed method is based on iterative minimisation of a function that incorporates constraints imposed in each direction with respect to excitation phases. To verify the performances of the proposed technique, an eight-element array has been realised and tested for various types of beam configurations.     

Optical phased array configuration for an extremely large telescope

Extremely large telescopes are currently under consideration by several groups in several countries. Extrapolation of current technology up to 30 m indicates a cost of over dollars 1 billion. Innovative concepts are being explored to find significant cost reductions. We explore the concept of an Optical Phased Array (OPA) telescope. Each element of the OPA is a separate Cassegrain telescope. Collimated beams from the array are sent via an associated set of delay lines to a central beam combiner. This array of small telescope elements offers the possibility of starting with a low-cost array of a few rings of elements, adding structure and additional Cass elements until the desired diameter telescope is attained. We address the salient features of such an extremely large telescope and cost elements relative to more conventional options.     

A novel method for reducing the dimensionality in a sensor array

Specific types of gas sensors are normally produced by adding different dopants to a common substrate. The advancement of technology has made the fabrication of many dopants and consequently various sensors possible. As a result, in each family of gas sensors, one can find tens of different sensors which are only slightly different in the spectrum of response to various volatile compounds. The wide variety of available gas sensors creates a selection problem for any specific application. Sensor selection/reduction becomes even more important when cost and technology limitations are issues of concern. Accordingly, a methodology by which one can tailor a sensor array to a specific need is highly desirable. In this paper, a novel method is introduced to address this task using data from an electronic nose that uses polymer gas sensors. This method has been delineated based on the geometry of eigenvectors in Karhunen-Loeve expansion. The methodology is general and therefore suitable for many other feature selection problems     

一种相控阵雷达天线极化特征的外场测试方法

为了解决相控阵雷达天线极化特征的外场测量问题,研究了极化的幅相测量法和斜天线测试场的布局方法,设计了基于双通道接收技术的相控阵雷达天线极化特征的一种外场测试方法。给出了应用该种方法的测量装置、测量布局、测量内容、测量步骤,分析了测量误差。该种测试方法在相控阵雷达天线极化特征测试任务中得到成功应用,为某武器系统的研制提供了准确的测量数据和宝贵的研究资料。     

Diffraction efficiency of a grating coupler for an array illuminator

The diffraction efficiency of a grating coupler having a surface-relief grating is calculated by the use of coupled-wave theory. The grating couplers are fabricated to examine the validity of the calculated result. The dependence of the measured diffraction efficiency on the groove depth of the grating coupler agrees well with the calculated results. The array illuminator, which emits 10 and 20 beams with equal intensity, is designed and fabricated through the use of these numerical results. The uniformity error of the output beam caused by the error of the diffraction efficiency is also discussed.     

Sound field calculations for an ultrasonic linear phased array with a spherical liquid lens

Lenses are often used to provide focusing in the elevation dimension of ultrasonic linear phased-array transducers. The use of a liquid lens in this application adds a variable geometric focusing capability, determined by the radius of curvature of the lens surface and speed of sound in the liquid, to the electronic focusing produced by the linear phased array. An efficient method to calculate the sound field radiated from the linear phased-array transducer through the liquid lens is presented. It treats the lens surface as a secondary source distribution according to Huygens's principle, and employs a modified form of the rectangular radiator method to calculate the field. The appropriate phases for the array elements to focus and steer the beam are calculated by considering the refraction on the lens surface. Comparisons of computer simulations and experimental measurements of the field intensity distribution of a prototype linear array transducer with a liquid lens demonstrate the accuracy of the proposed method.     

Experimental demonstration of an optical phased array antenna for laser space communications

The feasibility of an optical phased array antenna applicable for spaceborne laser communications was experimentally demonstrated. Heterodyne optical phase-locked loops provide for a defined phase relationship between the collimated output beams of three single-mode fibers. In the far field the beams interfere with a measured efficiency of 99%. The main lobe of the interference pattern can be moved by phase shifting the subaperture output beams. The setup permitted agile beam steering within an angular range of 1 mr and a response time of 0.7 ms. We propose an operational optical phased array antenna fed by seven lasers, featuring high transmit power and redundance.     

A concentric-ring equivalent phased array method to model fields of large axisymmetric ultrasound transducers

An equivalent concentric-ring ultrasound phased array method was developed to estimate ultrasonic continuous wave fields generated by axisymmetric single-source transducers. The method models a given source as a concentric-ring phased array by mathematically segmenting it into many rings and subsequently finding the amplitude and phase for each ring that produces an acoustic field similar to the field of the single-source transducer. The excitation source of each ring was calculated using an inverse technique based on complex pressure measurements along a radial line close to the source. The predicting abilities of the method are evaluated by comparing measured and estimated ultrasound fields for six different transducers. The results show that the concentric-ring equivalent phased array method (CREPAM) is able to estimate quantitatively the ultrasound fields generated by large axisymmetric planar and focused transducers.     

Design and optimization of an OPFC ultrasonic linear phased array transducer

In contrast to piezoceramics, orthotropic piezoelectric fibre composites (OPFC) which can be used as actuator/sensor elements in damage detection show clear advantages because of their high sensitivity along the fibre direction and directivity. The focusing acoustic field distribution of the OPFC phased array transducer is analyzed by the finite element method together with directivity analysis in metallic materials. The optimal array parameters such as spacing, width and number of elements are obtained by studying the total displacement changes as various parameters change at the focus point. The feasibility of an OPFC ultrasonic phased array transducer for damage detection is validated.     

一种提高光栅投影轮廓术精度的方法

在光栅投影三维轮廓术中,直接条纹位移分析法存在着垂直条纹方向分辨率低的缺点。在分析产生低分辨率原因的基础上,提出移物法,该方法通过多次移动物体来提高测量的采样精度。测量结果表明,在不提高对光栅投影系统的要求的情况下,对物体移动N次分别进行测量,每次移动的距离为条纹宽度的1/(N 1),这样就可以使得测量精度提高N倍。     

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.     

采用光栅投影的三维测量方法

提出一种新的三维坐标测量方法,该方法基于光栅投影、相移和三角测量等测量方法。与传统的光学测量方法不同,测量系统采用两个CCD相机记录投影光栅,减小了测量误差,提高了测量精度。测量实验结果在各个坐标上的精度分别为?靘,?靘,?8.5靘,总体精度优于20靘,证明了该方法的先进性和可行性。     

一种高密度光栅结构光编码方法

针对光栅结构光传感器三维测量过程中光条识别问题,提出一种新的金字塔子光栅投射法结构光编码方法。该方法把高密度光栅逐级细分为若干个可容易识别的子光栅,用空间二分编码方法分别对每个子光栅进行编码,并详细介绍了确定光条点码值的方法。把该编码方法应用于光栅结构光传感器中,实现了维纳斯雕像的三维测量,并给出了三维重建结果。结果表明,该编码方法误码率仅为0.75%,特别适用于物体三维轮廓致密测量。     

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.     

基于模糊层次分析的相控阵无损检测仪器可靠性分配方法

层次分析法一定程度受到主观因素影响,该文综合层次分析法与三角模糊数方法提出一种基于模糊层次分析的相控阵无损检测仪器可靠性分配方法。通过引入模糊参数降低可靠性分配决策过程的主观性,以熵最小原则作为参数选择依据,使方法能够更充分、客观、综合地反映专家意见。应用表明,相控阵无损检测仪器主机可靠性分配结果有效、可行,具有一定的工程应用价值。     

基于阵列分解的星载相控阵天线波束成形网络设计

根据"子阵列"理论,对星载阵列相控阵多波束天线的阵元空间和波束空间进行子阵分割,分析天线阵元空间成形系数的复用情况,并结合分布式算法,在阵列分解基础上提出了一种波束成形网络的复用结构,节省了67%以上的资源。最后实现了波束成形网络的试验验证平台,并完成了算法的移植和验证。结果表明,该波束成形网络比常规方法节省了大量资源,并实现了多波束等通量覆盖的设计目标。