共查询到20条相似文献,搜索用时 15 毫秒
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A Weyns 《Ultrasonics》1980,18(4):183-188
The exact equation to describe the propagation of ultrasonic pressure waves in a lossless, homogeneous medium was evaluated assuming pulse-excited radiators. Acoustical field patterns were studied using the dimensions and shape of the transducer, the ultrasonic frequency and number of cycles within the pulse as parameters. The results emphasize the influence of the number of cycles and piston shape on interference phenomena within the near-field and on beam-narrowing effects in the intermediate range between near- and far-field. The following transducer shapes are studied: planar circular, planar square and planar annular. 相似文献
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The unique features of radiation pattern formation in spherical mirror antennas are determined. It is shown that in antennas of this type there is a possibility of doubling directivity by placement of the feed at the paraxial focus. Equations are developed for calculation of the optimum feed placement, effective aperture radius, directional pattern width, and side lobe level. It is shown that side-lobe radiation from a spherical mirror antenna is formed by geometric optical reflection of the feed field on the peripheral portion of the mirror.Sevastopol Instrument Engineering Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 2, pp. 173–176, February, 1991. 相似文献
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This paper presents results from a theoretical model of the ultrasonic fields radiated by a 3x3 assembly of capacitive micromachined ultrasonic transducer (cMUT) sources on the same silicon substrate. These predictions have, for the first time, been compared directly to the fields measured experimentally using a scanned miniature detector. This work indicates that there is minimal cross-coupling between source elements, and demonstrates that it is possible to predict successfully the field characteristics of various geometries of such cMUT elements, with a view to the development of future imaging systems. 相似文献
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The so-called KLM-model for ultrasonic transducers is employed to optimize transducer design. Some new performance characteristics are defined which change monotonically with design parameters. These characteristics are based on the area of the envelope of the echo waveform produced by the transducer and of the corresponding amplitude spectrum. The efficiency of the transducer is defined by the round trip energy factor. The performance characteristics are used in a composite performance measure, which is then employed as a criterion in the optimization procedure. Two transducers are investigated: for medical imaging purposes and for spectral analysis of clinical echograms. The influence of electrical matching, backing impedance, matching layer impedance, bond line thickness and series induction on the optimized transducers is investigated. 相似文献
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Theoretical simulations of the pulse-echo beam forming of two-dimensional (2D) circular planar phase-array ultrasound transducers were conducted for the optimization of the effective architectures. These results were compared with equivalent linearly reticulated 2D phase-array transducer configurations. It is predicted that ultrasound imagers based on circular 2D phase-array transducers will out perform the other architectures for several medical applications. This study was motivated by the recent demonstration of micromachining of high-density circular as well as linear reticulated 2D phase-array transducers, to achieve real-time high-resolution completely electronic steerable volumetric medical noninvasive ultrasound imaging. 相似文献
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提出了一种新的类Quesne环状球谐振子势,应用二分量方法求解1/2-自旋粒子满足的Dirac方程, Dirac哈密顿量由标量和矢量类Quesne环状球谐振子势构成.在Σ=S(r)+V(r)=0的条件下,得到了Dirac旋量波函数下分量的束缚态解和能谱方程, 显示出类Quesne环状球谐振子势场中的赝自旋对称性.讨论了束缚态波函数和能谱方程的有关性质.
关键词:
类Quesne环状球谐振子势
Dirac方程
赝自旋对称性
束缚态 相似文献
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脉冲超声换能器是超声检测的关键部件,为了获取其声场特性参数,该文基于小球反射法,采用虚拟仪和单片机技术设计了工业用圆形晶片活塞声场测试系统。系统的程控交互界面采用美国国家仪器公司研制开发的图形化编程软件LabVIEW设计,通过调用动态链接库与系统核心硬件超声发射接收卡进行数据通信及对其功能进行设置,同时系统上位机通过RS232串口与下位机单片机通讯,实现对三轴扫查平台的多种扫查方式控制。该系统可实时显示脉冲换能器声压分布图像,并可通过对声压分布数据实现对换能器近场长度及扩散角等参数的测量。 相似文献
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The amplitude-frequency responses (AFRs) of ultrasonic oscillation transducers based on piezoelectric lithium iodate crystals of hexagonal modification and on magnetic soft ferrite powders are experimentally studied. The possibility to control the efficiency of magnetostriction powder transducers (MPTs) by variation in the value and orientation of the external magnetic field is shown. Results of measurements of the transformation efficiency for ferrites of various chemical compositions are presented. 相似文献
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超声相控阵技术在声悬浮中有十分重要的价值,相较于传统的一维单轴声悬浮装置,本文在凹球面双发射极超声阵列的基础上引入相控聚焦原理,产生了声悬浮能力较强的声场,重点研究了声场的仿真模拟与可视化验证.首先,介绍了自发设计的凹球面双发射极超声阵列结构,阐述了相控聚焦原理、超声驻波悬浮机理、声压与声辐射力等声学理论.然后,根据理论分析结果,借助COMSOL Multiphysics多物理场仿真软件,仿真模拟相控聚焦超声波场.产生该声场的各超声波换能器相位可单独控制,通过相位的实时变化,可使声场进行动态聚焦,实现微粒的悬浮与任意轨迹移动.最后,使用单反射纹影系统实现了该声场的实时可视化,与仿真结果进行比较,证实了凹球面双发射极超声波装置相控聚原理的准确性. 相似文献
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This paper presents the vibration characteristics of the radial mode in spherical piezoelectric transducers. The differential equations of piezoelectric radial motion have been derived in terms of radial displacement and electric potential. Applying mechanical and electrical boundary conditions yielded a characteristic equation for radial vibration. Theoretical calculations of the fundamental natural frequency have been compared with numerical and experimental results for transducers of several sizes, and have shown a good agreement. This paper discusses the dependence of natural frequencies on the radius and thickness of the piezoelectric spheres and the difference between piezoelectric and elastic resonances. From the results it has been concluded that the natural frequency was not affected for the first radial mode but was reduced by the piezoelectric phenomenon. It has also been concluded that the natural frequency of the first radial mode depended mostly on the radius rather than on the thickness of the sphere whereas the natural frequency of the second radial mode depended mostly on the thickness rather than the radius. 相似文献
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The relative performance of several types of ultrasonic transducer are assessed using reproducible acoustic transients generated from Q-switched Nd:YAG laser pulses incident on an aluminium alloy sample. A laser interferometer, a capacitance transducer, two types of electromagnetic acoustic transducers (EMATs), and a broad-band piezoelectric transducer are examined as detectors. The comparison includes a study of their rise-times, and typical signal-to-noise ratios. In the case of the interferometer and capacitance transducer, displacement measurements are shown to be highly consistent with theory. 相似文献
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In order to study the acoustic radiation from the spherical cap transducer,a theoretical model is used by solving the wave equation in spherical coordinates using the method of separation of variables,based on the spherical harmonic Fourier transform and boundary condition.The calculation formulas for the far field radiated pressure and directivity of spherical cap are derived.Some theoretical results are presented in the form of far-field directivity patterns of the spherical cap transducer for various polar angles of the spherical cap,radii of sphere baffle and operating frequencies.Both the diameter of the sphere baffle and the wavelength determine the directivity of acoustic radiation from a spherical cap.When the frequency is lower or the wavelength is longer than the diameter of the sphere baffle,the acoustic radiation from a spherical cap is omnidirectional.With the increase of the frequency or the diameter of the sphere baffle,the acoustic radiation from a spherical cap is more directional and the beamwidth more tends to spherical cap angle.Furthermore,the ripple in the beam is more obvious.The high frequency spherical cap transducer was fabricated and the directivity pattern was tested and the measurement data is shown to coincide with the theoretical results.This research can provide a guideline for designing the spherical cap transducers and arrays. 相似文献
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Wilfredo Montealegre Rubio Flávio Buiochi Julio Cezar Adamowski Emílio Carlos Nelli Silva 《Ultrasonics》2009,49(4-5):484-494
The application of functionally graded material (FGM) concept to piezoelectric transducers allows the design of composite transducers without interfaces, due to the continuous change of property values. Thus, large improvements can be achieved, as reduction of stress concentration, increasing of bonding strength, and bandwidth. This work proposes to design and to model FGM piezoelectric transducers and to compare their performance with non-FGM ones. Analytical and finite element (FE) modeling of FGM piezoelectric transducers radiating a plane pressure wave in fluid medium are developed and their results are compared. The ANSYS software is used for the FE modeling. The analytical model is based on FGM-equivalent acoustic transmission-line model, which is implemented using MATLAB software. Two cases are considered: (i) the transducer emits a pressure wave in water and it is composed of a graded piezoceramic disk, and backing and matching layers made of homogeneous materials; (ii) the transducer has no backing and matching layer; in this case, no external load is simulated. Time and frequency pressure responses are obtained through a transient analysis. The material properties are graded along thickness direction. Linear and exponential gradation functions are implemented to illustrate the influence of gradation on the transducer pressure response, electrical impedance, and resonance frequencies. 相似文献
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Caliano G Caronti A Baruzzi M Rubini A Iula A Carotenuto R Pappalardo M 《Ultrasonics》2002,40(1-8):449-455
Capacitive microfabricated ultrasonic transducers (cMUTs) are the newest and potentially the most promising devices to convert electrical into acoustic signals and vice-versa. These devices are based on the capacitance modulation of a microcondenser which is obtained by microfabrication onto a silicon substrate. The aim of this paper is to describe a PSpice model of the cMUT, based on an analytical distributed model previously reported (IEEE Trans. UFFC 49 (2) (2002) 159-168), which can be used to simulate the performances of a general ultrasound system, either in frequency or time domain. The PSpice model consists of a capacitor with a parallel resistor, which represent the static capacitance and the loss and bias resistances of the transducer, respectively, plus two quadrupoles (GLAPLACE) modeling the mechanical impedance of the membranes and the radiation impedance of the medium. The usefulness of a PSpice model is the possibility to simulate and optimize the cMUT transducers in transmission and reception, along with driving and receiving electronics, in a general ultrasound system. Experimental measurements on a 5 MHz cMUT operating in pulse-echo are in good agreement with model predictions. 相似文献
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开展了带楔块二维面阵脉冲超声相控阵辐射声场特性的研究。将安装在一定角度斜楔块上二维面阵相控阵换能器声场问题简化为液固界面情况进行讨论。以单阵元在液固平界面条件下的辐射声场为基础,推导了聚焦偏转法则,给出了带楔块二维面阵超声相控阵声场计算方法。以检测材料为钢板,安装在倾斜角为36°有机玻璃楔块上的频率为5 MHz、8×8二维面阵相控阵的辐射声场计算为例,分析了在不同偏转角和不同聚焦深度下检测材料中的辐射声场特性。计算结果表明该方法可有效的分析带楔块二维面阵超声相控阵声场特性并用于指导二维超声面阵角束探头的设计。 相似文献