微机械薄膜变形镜的闭环校正模型

介绍了微机械薄膜变形镜(MMDM)面形影响函数的意义,并测量了Oko公司37通道MMDM的面形影响函数矩阵,实验验证了镜面形变和单个驱动电极电压平方之间的线性关系,分析了变形镜的校正能力,建立了自适应光学系统闭环校正的模型.搭建基于MMDM的自适应光学实验系统,采用人眼出射波前作为原始波前进行实验,结果表明,模型能快速有效的对动态畸变波前进行校正,为基于MMDM的自适应光学系统提供了算法支持.     

Application of eigenmode in the adaptive optics system based on a micromachined membrane deformable mirror

The construction process and characteristics of a deformable mirror eigenmode are introduced. The eigenmode of a 37-element micromachined membrane deformable mirror (MMDM) from OKO, Ltd. is analyzed. The Gaussian-Seidel low-order aberrations are fitted with eigenmodes as basic functions. An experimental adaptive optics (AO) system is constructed with the MMDM as the wavefront corrector, a deformable mirror eigenmode as the wavefront control algorithm, and a Shack-Hartmann wavefront sensor as the wavefront detector. The experimental results demonstrate that the deformable mirror eigenmode can act as the wavefront control algorithm for the AO system based on the MMDM.     

Adaptive control of a micromachined continuous-membrane deformable mirror for aberration compensation

The nonlinear response and strong coupling of control channels in micromachined membrane deformable mirror (MMDM) devices make it difficult for one to control the MMDM to obtain the desired mirror surface shapes. A closed-loop adaptive control algorithm is developed for a continuous-surface MMDM used for aberration compensation. The algorithm iteratively adjusts the control voltages of all electrodes to reduce the variance of the optical wave front measured with a Hartmann-Shack wave-front sensor. Zernike polynomials are used to represent the mirror surface shape as well as the optical wave front. An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels. The experimental results show that the algorithm can adaptively update control voltages to generate an optimum continuous mirror surface profile, compensating for the aberrations within the operating range of the deformable mirror.     

Comparative analysis of Zernike aberrations generation with deformable mirrors for ocular adaptive optics

The micromachined membrane deformable mirror (MMDM) and piezoelectric deformable mirror (PDM) are two types of cost-effective deformable mirrors (DMs) that are widely used in ocular adaptive optics. In the current study, a 59ch MMDM and a 37ch PDM are tested and compared in generation of Zernike aberrations which are the most dominant of the human eye. The results reveal that although PDM performs better in larger scope, both DMs have almost similar performance if the individual generation coefficient is within the range of ±1 µm.     

The influences of ambiguity phase aberration profiles on focusing quality in the very near field part II: dynamic range focusing on reception

For pt. I see ibid., vol. 49, no. 1, p. 57-71 (2002). The influences of ambiguity phase aberration profiles, including constant, tilted, and quadratic profiles, on focusing quality have been quantitatively analyzed with the very near field approximation for single range focusing on transmission. In this paper, their influences are analyzed in a very different situation: dynamic range focusing on reception, which is commonly used in medical ultrasound imaging for beam formation on reception. It is shown that the results for dynamic range focusing on reception are dramatically different from those for single range focusing on transmission. For example, constant phase aberration profiles are harmless to focusing quality for single range focusing on transmission but become harmful for dynamic range focusing on reception. The analysis also shows that, compared with single range focusing on transmission, dynamic range focusing on reception is much more sensitive to ambiguity phase aberration profiles, which have adverse effects on focusing quality even in the near field and far field. These significant differences are caused by the fundamental differences between single range focusing and dynamic range focusing as well as between transmission and reception. Numerical and simulation results are also derived to test the correctness and accuracy of the theoretical results     

用于OCT动态聚焦的液晶菲涅尔波带透镜研究

提出了利用液晶菲涅尔波带透镜实现光学相干层析成像(OCT)动态聚焦的方法.根据扭曲相液晶空间光调制器(TN-LCSLM)的光学特性,设计了适用于OCT动态聚焦的菲涅耳波带透镜.利用TN-LCSLM型菲涅耳波带透镜进行了变焦控制实验,焦距实测结果与设计值比较吻合.此外,本文讨论了采用TN-LCSLM型菲涅耳波带透镜实施动态聚焦涉及到的一些问题.     

Efficient dynamic focus control for three-dimensional imaging using two-dimensional arrays

An efficient dynamic focus control scheme for a delay-and-sum-based beamformer is proposed. The scheme simplifies dynamic focus control by exploiting the range-dependent characteristics of the focusing delay. Specifically, the overall delay is divided into a range-independent steering term and a range-dependent focusing term. Because the focusing term is inversely proportional to range, approximation can be made to simplify dynamic focus control significantly at the price of minimal degradation in focusing quality at shallow depths. In addition, the aperture growth controlled by a constant f//sub number/ can also be utilized to devise a nonuniform quantization scheme for the focusing delay values. Efficacy of the proposed scheme is demonstrated using simulated beam plots of a fully sampled, two-dimensional array. Design procedures are also described in detail. One design example shows that, with the proposed dynamic focus control scheme, a 4096-element array only requires 227 independent controllers for the range-dependent focusing term. Moreover, only 28 non-uniform quantization levels are required to achieve the same focusing quality as that of a conventional scheme with 784 uniform quantization levels. The beam plots of a fully sampled array show that sidelobes are slightly increased below the -30 dB level for imaging depths less than 3 cm. At greater depths, there is no observable degradation.     

On-line focusing of flavin derivatives using Dynamic pH junction-sweeping capillary electrophoresis with laser-induced fluorescence detection

Simple yet effective methods to enhance concentration sensitivity is needed for capillary electrophoresis (CE) to become a practical method to analyze trace levels of analytes in real samples. In this report, the development of a novel on-line preconcentration technique combining dynamic pH junction and sweeping modes of focusing is applied to the sensitive and selective analysis of three flavin derivatives: riboflavin, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Picomolar (pM) detectability of flavins by CE with laser-induced fluorescence (LIF) detection is demonstrated through effective focusing of large sample volumes (up to 22% capillary length) using a dual pH junction-sweeping focusing mode. This results in greater than a 1,200-fold improvement in sensitivity relative to conventional injection methods, giving a limit of detection (S/N = 3) of approximately 4.0 pM for FAD and FMN. Flavin focusing is examined in terms of analyte mobility dependence on buffer pH, borate complexation and SDS interaction. Dynamic pH junction-sweeping extends on-line focusing to both neutral (hydrophobic) and weakly acidic (hydrophilic) species and is considered useful in cases when either conventional sweeping or dynamic pH junction techniques used alone are less effective for certain classes of analytes. Enhanced focusing performance by this hyphenated method was demonstrated by greater than a 4-fold reduction in flavin bandwidth, as compared to either sweeping or dynamic pH junction, reflected by analyte detector bandwidths <0.20 cm. Novel on-line focusing strategies are required to improve sensitivity in CE, which may be applied toward more effective biochemical analysis methods for diverse types of analytes.     

Ultrasonic dynamic focusing using an analog FIFO and asynchronoussampling

A dynamic focusing method which employs an analog FIFO (AFIFO) for signal sampling and storage is proposed. The delay control on the ultrasound pulse echo at each array element for focusing delay compensation is achieved by the nonuniform sampling process, as suggested previously in a full digital beamforming system called Pipelined Sampled-Delay Focusing (PSDF). In the new focusing method, an analog sampling device, AFIFO, is used to sample and store values of the pulse echo as it arrives from each imaging point at each array element. Due to the first-in first-out operation of each AFIFO, all the samples for each imaging point along the axis of the beam are arranged at the same output position required on each channel and will be output simultaneously by a uniform output clock. Except for the nonuniform sampling control, all processing in the new dynamic beamforming method is carried out exactly the same as in conventional analog imaging systems. The advantages of the new system are that the sampling rate and hardware complexity for dynamic focusing can be greatly reduced by employing nonuniform sampling and analog signal processing. The performance and validity of the new method are verified experimentally     

Ultrasonic phased arrays with variable geometric focusing for hyperthermia applications

An ultrasonic applicator, which utilizes both electronic and variable geometric focusing, for deep-localized hyperthermia is investigated. The applicator is based around a linear phased array that furnishes its electronic focusing capability. The output of the array radiates through a spherical liquid-lens that provides the applicator a variable geometric focusing capability as well. A lens of this type adds dynamic focusing to the elevation dimension of the linear phased array. By controlling the volume of liquid in the lens (and thus the radius of curvature of its membrane), dynamic control of the geometrical focus can be achieved. Comparisons of computer simulations and experimental measurements of the field intensity distribution of a small-scale prototype applicator are presented. Important design parameters, such as the choice of the liquid for the lens and the size and number of array elements, are examined.     

双束投影管测试台中动态聚焦电路的研制

动态聚焦技术是为了改善显象管或投影管的边缘聚焦质量 ,动态的对屏幕中央及四周的聚焦差异进行补偿 ,从而达到提高整体分辨率的目的。作者针对双束投影管测试台的要求 ,设计了其中的动态聚焦电路。通过实验对比表明 ,用合适的聚焦电压 ,可以取得良好的聚焦效果     

A frequency domain model for generating B-mode images with array transducers

A frequency domain B-mode imaging model applicable to linear and phased array transducers was developed for simulating ultrasound images of random media. Computations are based on an approximation that is less restrictive than the Fresnel approximation. The model is compared with the exact time domain impulse response method, regarded as the "gold standard". In a typical application, errors in simulated rf waveforms are less than 1% regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1/150 of those using the exact method. This model takes into account the effects of frequency-dependent attenuation, backscattering, and dispersion. Modern beam-forming techniques such as apodization, dynamic aperture, elevational focusing, multiple transmit focusing and dynamic receiving focusing also can be simulated.     

Selective focusing of catecholamines and weakly acidic compounds by capillary electrophoresis using a dynamic pH junction

A systematic study of selective analyte focusing in a multisection electrolyte system by capillary electrophoresis (CE) is presented. It was found that a dynamic pH junction between sample and background electrolyte zones can be used to focus zwitterionic catecholamines and weakly acidic compounds without the use of special ampholytes. Differences in pH and concentration of complexing agents, such as borate, in the sample and background electrolyte zones were determined to cause focusing through changes in the local velocity of the analyte in two different segments of the capillary. Velocity-difference induced focusing (V-DIF) of analytes using a dynamic pH junction allowed the injection of large sample volumes and significantly improved the concentration sensitivity of CE. Under optimized conditions, the limit of detection for epinephrine was determined to be about 4 x 10(-8) M (the original sample) with conventional UV absorbance detection. Moreover, separation efficiencies greater than a million theoretical plates can be achieved by focusing such large sample volumes into narrow zones. Multisection electrolyte systems, which lead to the formation of a dynamic pH junction, can be tuned toward improving the concentration sensitivity of specific analytes if their chemical properties are known.     

应用模糊逻辑理论提高B型超声图像分辨力方法的探讨

本文介绍了利用模糊逻辑控制理论提高Ｂ型超声图像横向分辨力的方法,文章中介绍了变孔径技术,电子聚焦时原理及动态实时聚焦。     

一种用于相控阵B超成像的数字波束合成器的设计

本文介绍了一种能沿任意波束指向全程动态聚焦的数字波束合成器的设计，此合成器用于相控阵Ｂ超成像系统。回声信号的延时量分解为“指向延时”和“聚焦延时”两部分，分别用产生相控发射激励的时序逻辑电路和一个“动态聚焦延时量表”实现。通过对Ａ／Ｄ采样时钟的控制及对Ａ／Ｄ采样时钟、地址计数时钟和存储器写时钟的时序配合，实现了同相位数据点采样及无冗余数据的缓冲存储器。所设计的数字相控波束合成器只用廉价的高速数字电路即可实现，成本极低。实验结果验证了该方案的可行性。     

Energy focusing and the shapes of wave fronts in anisotropic fluid-saturated porous media

Summary The purpose of this paper is to investigate the energy focusing pattern evolution in the parameter space while the wave fronts propagate in the anisotropic fluid-saturated porous media. Firstly, the bifurcation conditions for a general anisotropic fluid-saturated porous material are deduced. Then, by choosing the material parameters as control variables, the influence of the anisotropy of the solid skeleton and pore fluid parameters on the development characteristics of energy focusing patterns is discussed, and the three-dimensional configurations for the focusing structures are explored. The results indicate that the energy focusing also exists on the wave fronts of the slow waves, which is a particular propagation characteristic for the slow waves in anisotropic fluid-saturated porous media. The distinct trends for the slow wave energy focusing are revealed. This has significant meaning in further understanding the roles of the fluid phase in the dynamic response of the fluid-saturated porous media.     

A study of synthetic-aperture imaging with virtual source elements in B-mode ultrasound imaging systems

We propose an all point transmit and receive focusing method based on transmit synthetic focusing combined with receive dynamic focusing in a linear array transducer. In the method, on transmit, a virtual source element is assumed to be located at the transmit focal depth of conventional B-mode imaging systems, and transmit synthetic focusing is used in two half planes, one before and the other after the transmit focal depth, using the RF data of each scanline, together with all other relevant RF scanline data previously stored. The proposed new method uses the same data acquisition scheme as the conventional focusing method while maintaining the same frame rate via high-speed signal processing, but it is not suitable for imaging moving objects. It improves upon the lateral resolution and sidelobe level at all imaging depths. Also, it increases the transmit power and image signal-to-noise ratio (SNR), due to transmit field synthesis, and extends the image penetration depth as well. Evaluations with simulation and experimental data show much improvement in resolution and SNR at all imaging depths.     

Multidepth synthetic aperture processing of ultrasonic data

The characterization of the size, shape, and location of subsurface discontinuities in metals using multidepth synthetic aperture processing of ultrasonic data is considered. A technique is proposed to increase the lateral resolution and signal-to-noise ratio when metals of large thickness are tested. The first technique to achieve multidepth was dynamic focusing. The aperture in the proposed technique is simultaneously focused at several depths by means of a computer program, thus avoiding the fixed hardware required in the dynamic focusing technique. Experimental evidence is presented to indicate the improvement in resolution, due to multidepth processing, over the single-focus technique.     

Dynamic isoelectric focusing for proteomics

Dynamic isoelectric focusing is a new technique that is related to capillary isoelectric focusing but uses additional high-voltage power supplies to provide control over the shape of the electric field within the capillary. Manipulation of the electric field changes the pH gradient, enabling both the location and width of the focused protein bands to be controlled. The proteins can be migrated to a designated sampling point while remaining focused, where they can be collected for further analysis. This ability to collect and isolate the protein bands while maintaining a high peak capacity demonstrates that dynamic isoelectric focusing has great potential as a first dimension in a multidimensional separation system. Dynamic isoelectric focusing can achieve a peak capacity of over 1000, as shown by both mass spectrometry analysis and direct imaging.