A new algorithm for spatial impulse response of rectangular planar transducers

Previous solutions for spatial impulse responses of rectangular planar transducers require either approximations or complex geometrical considerations. This paper describes a new, simplified and exact solution using only trigonometric functions and simple set operations. This solution, which can be numerically implemented with a straightforward algorithm, is an exact implementation of the Rayleigh integral without any far field or paraxial approximation. Additionally, a nonlinear relationship was also established for spatial impulse responses from two field points which share the same projection point on the transducer surface plane. By incorporating this relationship in the algorithm, the computational efficiency of spatial impulse responses and continuous fields is improved about 20-folds and 14-folds, respectively. This algorithm has practical applications in designing l-D linear/phased arrays, 1.5-D arrays and 2-D arrays, as demonstrated through numerical simulations with array transducers. Experiments were also conducted to verify the new solution and results show that the algorithm is both accurate and efficient. The application of this method may include development of ultrasound imaging system for hard and soft tissue nondestructive assessment.     

A fast implementation for computing spatial impulse response of ultrasonic transducers

The spatial impulse response(SIR) method is often used as the 'gold standard5 in simulation of transient acoustic wave fields due to its high accuracy in the linear domain.However, a high sampling frequency is often required in order to achieve the high accuracy. As a result, a large amount of data has to be processed. In this paper a fast approach for computing spatial impulse response is proposed to reduce the computation burden. The proposed approach is developed by employing the relationship of SIRs at observed points and SIRs of the projection points on the transducer surface. Two critical parameters used in the proposed approach, the calculation sampling frequency and the interpolation sampling frequency, are then analyzed.Results show that for a 2.25 MHz rectangular transducer with the size of 5 mmxlO mm,a calculation sampling frequency of 1000 MHz and an interpolation sampling frequency of500 MHz can achieve superior performance while improving the computation efficiency 18 times than the direct solving.     

一种精确计算换能器空间脉冲响应的快速方法

空间脉冲响应被认为是最有效的瞬态声场计算方法,针对空间脉冲响应直接计算时需要很高的采样频率,导致数据量大、计算效率差的问题,推导了空间点与其在换能器平面的投影点脉冲响应之间的关系,提出了一种计算脉冲响应的快速算法,探讨了计算采样频率和插值采样频率对计算精度和计算效率的影响,研究发现,采用1000 MHz采样频率能够保证精度要求,采用500 MHz作为插值时的采样频率是较优的选择。该方法与直接求解相比,可提高计算效率18倍。     

一种精确计算换能器空间脉冲响应的快速方法

空间脉冲响应被认为是最有效的瞬态声场计算方法,针对空间脉冲响应直接计算时需要很高的采样频率,导致数据量大、计算效率差的问题,推导了空间点与其在换能器平面的投影点脉冲响应之间的关系,提出了一种计算脉冲响应的快速算法,探讨了计算采样频率和插值采样频率对计算精度和计算效率的影响,研究发现,采用1000 MHz采样频率能够保证精度要求,采用500 MHz作为插值时的采样频率是较优的选择。该方法与直接求解相比,可提高计算效率18倍。     

A new method for determining the energy independent effective interaction

A new algorithm for computing the effective-interaction is presented. Its convergence properties are tested in two solvable models and it is found to always converge and to be able to reproduce all the eigenvalues of the full Hamiltonian.     

Fluorescence method for determining laser parameters

This paper describes a method for determining some important laser parameters from the fluorescence changes of an excited media induced by a resonant laser pulse. The parameters measured include stimulated emission cross-section, metastable level population and spectral relaxation rate. Results are reported for Nd³⁺ in silicate and phosphite glasses and in solution in POCl₃ and SeOCl₂.     

A novel method for estimating the focal size of two confocal high-intensity focused ultrasound transducers

Estimating the focal size and position of a high-intensity focused ultrasound (HIFU) transducer remains a challenge since traditional methods, such as hydrophone scanning or schlieren imaging, cannot tolerate high pressures, are directional, or provide low resolution. The difficulties increase when dealing with the complex beam pattern of a multielement HIFU transducer array, e.g., two transducers facing each other. In the present study we show a novel approach to the visualization of the HIFU focus by using shockwave-generated bubbles and a diagnostic B-mode scanner. Bubbles were generated and pushed by shock waves toward the HIFU beam, and were trapped in its pressure valleys. These trapped bubbles moved along the pressure valleys and thereby delineated the shape and size of the HIFU beam. The main and sidelobes of 1.1- and 3.5 MHz HIFU beams were clearly visible, and could be measured with a millimeter resolution. The combined foci could also be visualized by observing the generation of sustained inertial cavitation and enhanced scattering. The results of this study further demonstrate the possibility of reducing the inertial cavitation threshold by the local introduction of shock wave-generated bubbles, which might be useful when bubble generation and cavitation-related bioeffects are intended within a small region in vivo.     

基于滑动峭度相关性准则的局部特征尺度分解分量筛选方法

轴承故障振动信号具有非平稳、非线性特征,且可视为多个调幅-调频分量的叠加,单分量的包络蕴含了轴承的故障特征。局部特征尺度分解可将振动信号准确分解为多个内禀尺度分量之和,某些分量能清晰反映轴承的运行状态,根据包络谱可进行故障诊断。为了准确筛选有用分量,提出了基于滑动峭度相关性准则的分量筛选方法。首先,对信号进行局部特征尺度分解,得到若干个内禀尺度分量;然后,对分量和原始信号分别计算滑动峭度,生成时间序列;最后,依据分量滑动峭度序列与原始信号滑动峭度序列的互相关系数筛选有用分量。通过轴承内圈故障数据分析发现：有用分量与非有用分量之间的滑动峭度互相关系数比互相关系数差异明显,区分度更大,有益于分量的分类、筛选。     

基于三元伪随机序列集的多声源房间脉冲响应测量方法*

在多输入多输出系统中,诸多情况下需并行测量任意输入输出之间的脉冲响应。虽然利用以Kasami序列集为代表的二元伪随机序列集良好的相关特性可以实现多声源并行测量,但是囿于其编解码信号相同且为二元信号的特点,使得其相关特性仍存在较大的可优化空间。该文提供了一种基于三元伪随机序列集的多声源房间脉冲响应测量方法,具有更好的相关特性,提高了测量准确度。仿真和实验验证了该测量方法的可行性和准确性。在封闭空间几何模型构建等领域中,可使用该方法提高测量效率并降低由于各通道不同步导致的误差。     

A comparison of two methods for determining ultrasonic intensity for medical transducers

The spatial and temporal average intensity (ISATA) is determined for four diagnostic ultrasound transducers by two methods: (a) direct measurements (beam profiling) with a miniature hydrophone, as described in the AIUM-NEMA standard, and (b) estimating from measurements of total power and assumptions about beam size. The latter method is frequently used by diagnostic ultrasound manufacturers when reporting output levels to users and regulatory agencies. However, due to the conventions for defining beam area, this method actually overestimates the spatial average intensity. For the four transducers tested, the estimated ISATA exceeds the measured ISATA by several hundred percent. The spatial peak, temporal average intensity (ISPTA) was also measured for the four transducers and is less than the estimated ISATA in every case.     

A new method for removing impulse noise based on noise space characteristic

This paper proposes a new method for eliminating impulse noise. Based on the space characteristic of object and noise, three kinds of basic noise patterns are introduced to describe noise and detect noise candidates. Correspondingly, noise removal operators are presented to remove the impulse noise. Extensive experiment results have shown that the proposed method is better than some of the state-of-the-art methods.     

重入式谐振腔特性参数的解析方法

 对于在速调管中广泛使用的重入式谐振腔以及内部无漂移管的盒形腔,在忽略漂移管壁厚的前提下,导出了能够准确求解其谐振频率的本征方程,并在此基础上进一步计算了腔体的特性阻抗和固有品质因数。针对具体算例的应用表明,由解析式确定的腔体特性参数与SUPERFISH的数值结果具有很好的一致性。     

Fast image method for impulse response calculations of box-shaped rooms

The image method has been used for calculating the impulse response of box-shaped rooms for over 25 years. While this method is functional, it can be inefficient because many of the commonly used mathematical operations are either redundant or unnecessary. This paper addresses these two inefficiencies by proposing both the use of look-up tables to prevent redundant calculations, and the use of a sorting method to allow the prevention of unnecessary calculations. Either technique, by itself, results in a large reduction in computation time. The greatest time reductions, however, can be achieved when both techniques are used together.     

A simple semi-empirical procedure for determining the parameters in the MO LCAO method

A simple method is described for evaluating the exchange and Coulomb integrals with account for the change in the properties of the atoms on entry into a molecule. Generalizations of Slater's rule permit the calculation of the ionization potentials of atoms in a molecule which make the main contribution to the Coulomb integrals. Analytical expressions are given for the Coulomb integrals in the -function approximation.I am indebted to N. A. Prilezhaeva and V. I. Danilova for their continuous interest in the work.     

A two-dimensional diffraction pattern sampling system for determining the optimum parameters of a matched spatial filter

The synthesis of a matched spatial filter based on holographic methods requires that the spatial frequency band in which the holographic fringe pattern with the best modulation is formed be tuned to the appropriate weighting at the Fourier transform plane of the spatial frequencies of the input object to be studied. For this purpose both the spectral intensity distribution of an input object at the Fourier transform plane and the intensity distribution of a reference beam at that plane must be accurately known beforehand. A two-dimensional diffraction pattern sampling system has been constructed which enables the Fourier spectral intensity distribution of the input object and the reference beam intensity distribution to be faithfully recorded. A preliminary experimental study shows the usefulness of this system.     

Complementary interference method for determining optical parameters of liquid crystals

ABSTRACT

Wedge cells of small apex angle, filled with liquid crystals, were used to determining optical characteristics as functions of temperature for three liquid crystalline mixtures recently produced and a reference nematic. The interference fringes appearing in polarised monochromatic light (of sodium yellow line) normally incident on the cell were exploited to measure the ordinary and extraordinary refractive indices in the reflection mode and birefringence in the transmission mode. The measurements were repeated using Abbe's refractometer for 6CHBT as the reference to verifying the precision. Additionally the order parameter was computed from birefringence as a function of temperature. The results confirm the usefulness of the method and provide the properties of two nematic liquid crystals of small and large birefringence and one smectic liquid crystal of medium birefringence, recently produced. The experimental systems served also to investigating phase transition between the liquid crystals and the isotropic liquid at near-clearing temperature.     

基于任意阵的最小方差无失真响应聚焦波束形成的被动定位方法

将最小方差无失真响应(MVDR)聚焦波束形成近场被动定位方法应用到平面任意结构阵列上,可以很好地解决线列阵由于阵长较长,在实际使用中存在布放困难、部分阵元失效影响定位性能等问题。本文首先分析了平面任意结构阵列的近场接收信号模型,推导出阵列流型,然后将MVDR聚焦波束形成技术应用到该模型中,得到了基于任意阵的MVDR聚焦波束形成近场被动定位方法。仿真验证了该方法的可行性和有效性。     

A multiple focused probe approach for high intensity focused ultrasound based surgery

To produce deep-seated surgical lesions using ultrasound requires high power and intensity levels at the target sites. Conventionally, large transducers are used which require big apertures and so are generally suitable only for extra-corporeal access. Such transducers also result in strong off-focus maxima, where the resulting hot spots can destroy normal tissue whilst deep-seated large tissue volumes are being ablated. This paper describes a new approach in which it is proposed that multiple probes are used simultaneously, each at a relatively low power, to result in an overlapping focused region of high temperature without strong off-focus hot spots. Robotic techniques could be used to move the individual probes in coordination to sweep out the desired region of tissue ablation. Simulation and planning are the key to quality prediction for high intensity focused ultrasound (HIFU). Simplified two-dimensional and three-dimensional models of HIFU probes have been developed to study the characteristics of various multi-probe configurations. Preliminary simulation results show that the multi-probe system can be arranged successfully to minimise off-focus hot spots. Experimental results are presented which validate the modality and confirm this positive finding. Further prediction studies and planning will be necessary to achieve the most appropriate desired treatment, by varying the pulse duration and spacing.