换能器组阵对声场指向性的影响

根据点声源的声场指向性函数,推导出了考虑换能器振动面积时单个超声波换能器的指向性函数和由其组成的矩形阵列的指向性函数,研究了单个超声波换能器和其组成阵列的指向性。计算分析了阵元面积、阵元间距及阵元数目对超声波换能器阵列指向性的影响,为高指向性噪声的控制和声武器对抗提供帮助。     

水平长线阵在浅海多途信道中的指向性分析

基于简正波模型研究了浅海多途环境下的水平长线阵的指向性。结果表明,由于接收信号中各阶简正波的相互干涉作用,偏离正横时,指向性图的主瓣略窄,而旁瓣丌高较多,从而使实际阵增益和作用距离减小。研究结果对线列阵声呐的探测性能预报具有一定的参考意义。     

一种简单的宽带基阵设计和处理方法

文章提供了一种简单的基阵设计和处理方法 ,这种方法利用 3个均匀子线阵 ,通过调整每个子阵的基本间距 ,来改变子阵的指向性函数 ,使得 1个子阵的指向性函数的栅瓣或旁瓣对应另 1个子阵指向性函数的零点 ,最后把 3个子阵的指向性函数相乘 ,得到总的指向性函数。由于 1个阵的指向性函数的零点抵消另 1个阵的指向性函数的栅瓣或旁瓣 ,这样可以得到比较好的指向性函数。因为 3个子阵的疏密程度不一 ,使得它们的栅瓣相互错开 ,因而特别适用于宽带信号     

复合声基阵指向性研究

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.     

小型化线列阵研究

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。     

点圆阵的矩阵变换对

针对点圆阵用常规方法不能有效压低旁瓣问题,从点圆阵指向性函数计算公式出发,导出指向性函数和权系数之间关系的点圆阵矩阵变换对,较好地解决了点圆阵指向性综合问题,有效压低点圆阵波束的旁瓣。该方法具有公式直观、使用方便、计算快捷的特点,适用于相控到任意方向和各种形状的波束综合;也适用于由多个同心点圆阵构成的体积阵指向性综合。     

星形立体传声器阵列设计与应用

研究了星形立体传声器阵列。利用粒子群优化算法对每条直线上的阵元进行优化排布,获得了具有较好指向性和较低旁瓣级的阵列阵型。基于优化得到的阵列阵型进行了星形立体传声器阵列的机械结构设计,设计的阵列主体能实现自如地折叠,便于包装和运输。研制了基于这种阵列阵型的声成像定位系统,通过数据仿真分析体现出优化设计阵型的优越性,同时通过实验验证了研制的声成像系统在声源定位中的有效性。     

单个矢量水听器空间处理增益分析

本文把单个矢量水听器看做传统意义上的一个声压阵,进行了常规波束形成和乘积波束形成.对照声压阵的阵增益形式,对单个矢量水听器的空间处理增益进行了理论上的分析.文中给出了白噪声背景下和球形各向同性噪声背景下单个矢量水听器的阵增益计算公式.理论分析表明,在一定的组合方式下,一个矢量水听器比一个声压水听器最大可有7.8dB的空间增益.可以形成单边指向性,克服水听器成阵后的左右模糊问题.这些都说明矢量水听器有极大的工程应用价值.     

多约束线性非均匀阵列天线的合成

为了提高线性非均匀阵列天线的优化效果,降低阵列天线设计的复杂性,本文提出了一种改进的蝙蝠算法来实现更低的峰值旁瓣电平(PSLL).改进的蝙蝠算法在阵列孔径约束和阵元上下界限的限制条件下,优化每个阵元位置来获得方向图峰值电平最低,实现全阵列最佳的阵元位置.本文分别对18个阵元和32个阵元阵列天线数值仿真,仿真结果达到了-20.081 dB和-22.656 dB.从而验证了提出方法的有效性和稳定性,并且实现了更高的优化效率.     

水下超声成像观察阵的随机尖峰旁瓣问题

本文叙述了相握线列阵（等加权和非等加权）用于水下超声成像观察阵时的波束特性。根据随机误差理论。本文给出了在阵元相位、振幅随机起伏时，相控线列阵的尖峰旁瓣的估计。 此外，本文对声图像点进行了模拟观察。并将某些计算机模拟到的随机旁瓣特性与通过随机误差理论估算获得的结果进行了比较，两者基本一致。本文还详细地研究了影响尖峰旁瓣特性的诸因素。并根据随机相位、振幅误差和阵元失灵，提出了相拴线列阵的设计指标。 本文可供设计其他超声成像阵列时参考。     

Grating lobe elimination in steerable parametric loudspeaker

In the past two decades, the majority of research on the parametric loudspeaker has concentrated on the nonlinear modeling of acoustic propagation and pre-processing techniques to reduce nonlinear distortion in sound reproduction. There are, however, very few studies on directivity control of the parametric loudspeaker. In this paper, we propose an equivalent circular Gaussian source array that approximates the directivity characteristics of the linear ultrasonic transducer array. By using this approximation, the directivity of the sound beam from the parametric loudspeaker can be predicted by the product directivity principle. New theoretical results, which are verified through measurements, are presented to show the effectiveness of the delay-and-sum beamsteering structure for the parametric loudspeaker. Unlike the conventional loudspeaker array, where the spacing between array elements must be less than half the wavelength to avoid spatial aliasing, the parametric loudspeaker can take advantage of grating lobe elimination to extend the spacing of ultrasonic transducer array to more than 1.5 wavelengths in a typical application.     

Generation of sinc wave by a one-dimensional array for applicationsin ultrasonic imaging

A new solution to the 2-D scalar wave equation is presented which describes an ultrasonic beam maintaining the lateral field response expressed by the sinc function over a finite depth of field. This new beam is realizable with a linear array transducer, and less subject to diffraction spreading than conventional focused beams, physically, it is a superposition of plane waves having the same wavelength, but traveling at different angles. It is shown by numerical simulation that the beam can provide more uniform lateral beamwidth and smoother on-axis field magnitude over a greater depth of field than the rectangular transducers and Gaussian apodized transmitters which have been used to increase the limited depth of field of conventional focused beams. Compared with currently developed limited diffraction beams which must be generated by 2-D array transducers, the beam has a wider lateral beamwidth but with lower sidelobe levels. In ultrasonic medical imaging, the beam enables one to obtain a line focus using a 1-D array transducer and to eliminate the diffraction correction required in some applications such as tissue characterization     

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.     

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.     

线阵相控换能器阵列参数对聚焦性能的影响分析

针对超声相控阵检测中广泛使用的一维线阵换能器,通过建立其声场数学模型和引入指向性函数,仿真分析了阵列参数对声束聚焦性能的影响,提出了改善换能器声场性能的措施。最后对优化参数的阵列换能器声场进行实验测试,测试结果表明其具有良好的声束聚焦性能,为超声相控阵缺陷检测中换能器的选择提供了参考。     

超指向性扬声器的系统设计与测试

超指向性扬声器是一种利用声波在空气中传播的非线性由不可听超声产生可听声的参量阵装置,这种声源相比相同大小的传统扬声器,可以产生非常强的指向性、像聚光灯光束一样的宽带可听声束.文章介绍了超指向性扬声器的基本原理,给出了一个基于模拟电路的系统实现方案,并着重介绍了基于所完成的工程样机所做的频率响应、总谐波失真和指向性测试及相关实验分析,还讨论了进一步工作的发展方向.     

宽带水声参量阵指向性设计与实验验证

利用宽带水声参量阵可产生高指向性宽带低频声束,推导了宽带水声参量阵生成低频声束的自解调理论模型,对其换能器指向性进行了分析与设计,并研制出了宽带水声参量阵样机。测试结果表明：该样机产成的2 kHz声束的-3 dB指向性锐角约为2.6°,具有很好的指向性,且旁瓣抑制效果好,能够产生无旁瓣的高指向性低频声束。这为解决浅海水声通信的多途干扰、远程水声保密通信等问题提供了一条新思路。     

Element size effect on phase aberration correction

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.     

A 100-MHz ultrasonic transducer array using ZnO thin films

A 100-MHz ultrasonic linear transducer array made from a piezoelectric zinc oxide thin film on a sapphire substrate was developed and evaluated. Epitaxial, high-acoustic quality 10-μm-thick ZnO film layers were produced by rf-magnetron sputter deposition onto a (111)-oriented gold film (with a chromium adhesion layer) that was vacuum-evaporated onto a (0001) sapphire surface. We found that, in well-oriented growth of gold, it is important to control the chromium sublayer thickness (less than 5 nm). An array was constructed by photolithography with an appropriate etch. V-shaped grooves between adjacent elements were formed by using an anisotropic etchant (HCl and HNO₃-based) that preferentially etched the c-plane of ZnO. Typical array elements were 90 μm wide, 3.2 mm long, and 10 μm thick, and the pitch of an array was typically 100 μm. Our fine uniform array resulted in uniform ultrasonic response of individual elements throughout the array. For a 32-element array, the ultrasound beam in the azimuth plane in water could be electronically focused in the 100 MHz range to obtain a half-amplitude width of 60 μm at the focal depth, agreeing well with theoretical predictions. Besides the use demonstrated with this present transducer, piezoelectric thin films should also lead to fabrication of various other kinds of ultrasonic transducers that can operate at high frequencies and should provide opportunities for miniaturizing transducers and making integrated ultrasonic devices     

Modeling of finite-amplitude sound beams: second order fields generated by a parametric loudspeaker

The nonlinear interaction of sound waves in air has been applied to sound reproduction for audio applications. A directional audible sound can be generated by amplitude-modulating the ultrasound carrier with an audio signal, then transmitting it from a parametric loudspeaker. This brings the need of a computationally efficient model to describe the propagation of finite-amplitude sound beams for the system design and optimization. A quasilinear analytical solution capable of fast numerical evaluation is presented for the second-order fields of the sum-, difference-frequency and second harmonic components. It is based on a virtual-complex-source approach, wherein the source field is treated as an aggregation of a set of complex virtual sources located in complex distance, then the corresponding fundamental sound field is reduced to the computation of sums of simple functions by exploiting the integrability of Gaussian functions. By this result, the five-dimensional integral expressions for the second-order sound fields are simplified to one-dimensional integrals. Furthermore, a substantial analytical reduction to sums of single integrals also is derived for an arbitrary source distribution when the basis functions are expressible as a sum of products of trigonometric functions. The validity of the proposed method is confirmed by a comparison of numerical results with experimental data previously published for the rectangular ultrasonic transducer.