Determining Surface Potentials from Current Dipoles, with Application to Electrocardiography

This paper presents a method for determining the potentials over the surface of a three-dimensional volume due to internal current sources. The volume may be inhomogeneous and irregularly shaped. The method for determining the potentials uses N simultaneous equations which when solved produce the potentials at N different surface points. The N simultaneous equations are solved by an iterative technique on an IBM computer.     

Statistically Constrained Inverse Electrocardiography

This paper examines the feasibility of utilizing statistical constraints on the inverse potential model to determine the potential distribution over a 4 cm sphere surrounding the heart from perturbed torso potentials. These perturbed torso potentials reflect instrumentation, quadrature, electrode placement, and heart position uncertainties. This work is an extension of the authors' previous work which concluded that it is not feasible to determine this same potential distribution using unconstrained solutions. However, the results of the present work indicate that with the use of approximate signal and noise covariance matrices, it is possible to achieve estimates of this potential distribution with an average sum squared error of twenty-five percent. Further, the estimation of the signal and noise covariance matrices can be accomplished with a knowledge of heart geometry, torso geometry, The approximate measurement error, and a rough estimate of the time an average section of myocardium is depolarized, but without an a priori specification of the activation sequence.     

Quasi-Linearization and Inverse Electrocardiography

The feasibility of using quasi-linearization for obtaining solutions to the inverse problem in electrocardiography is investigated. Results suggest that convergence is unlikely when using real electrocardiographic data.     

Unconstrained Inverse Electrocardiography: Epicardial Potentials

The inverse problem in electrocardiography is attacked via the development of a model appropriate for the computation of epicardial potentials from a knowledge of heart and torso geometry as well as surface potentials. The model takes the form of an integral equation of the first kind in which the kernel is interpreted as a Green's function. A theoretical investigation of system independence in the presence of error is developed, and two techniques for the theoretical consideration of system independence are examined. Application of these two techniques to concentric spherical systems indicates that spheres with ratios of inner-to-outer radii less than 0.5 contain less than twenty independent parameters in the presence of realistic noise levels. The number of independent parameters deteriorates rapidly as this ratio falls below 0.5. These results suggest that it is not feasible to determine epicardial potentials from torso potentials by using unconstrained solutions.     

The Use of Time Dependent Models in Inverse Electrocardiography

This study investigates the feasibility of utilizing multiple dipole cardiac generators with time dependent dipole moments to obtain physiologically feasible inverse electrocardiographic solutions.     

Effect of Cardiac Motion on Solution of the Electrocardiography Inverse Problem

Previous studies of the ECG inverse problem often assumed that the heart was static during the cardiac cycle; consequently, a time-dependent geometrical error was thought to be unavoidably introduced. In this paper, cardiac motion is included in solutions to the electrocardiographic inverse problem. Cardiac dynamics are simulated based on a previously developed biventricular model that coupled the electrical and mechanical properties of the heart, and simulated the ventricular wall motion and deformation. In the forward computation, the heart surface source model method is employed to calculate the epicardial potentials from the action potentials, and then, the simulated epicardial potentials are used to calculate body surface potentials. With the inclusion of cardiac motion, the calculated body surface potentials are more reasonable than those in the case of static assumption. In the epicardial potential-based inverse studies, the Tikhonov regularization method is used to handle ill-posedness of the ECG inverse problem. The simulation results demonstrate that the solutions obtained from both the static ECG inverse problem and the dynamic ECG inverse problem approaches are approximately the same during the QRS complex period, due to the minimal deformation of the heart in this period. However, with the most obvious deformation occurring during the ST-T segment, the static assumption of heart always generates something akin to geometry noise in the ECG inverse problem causing the inverse solutions to have large errors. This study suggests that the inclusion of cardiac motion in solving the ECG inverse problem can lead to more accurate and acceptable inverse solutions.      

Theoretical Studies on the Inverse Problem in Electrocardiography and the Uniqueness of the Solution

This paper focuses on the theoretical formulation of the inverse problem in electrocardiography under a general inhomogeneous and anisotropic configuration of the torso conductor. The following points are especially considered: 1) derivation of the Fredholm integral equation of the first kind which relates epicardial to body surface potentials, 2) specification of the conditions which its kernel must satisfy, 3) general solution method for the inverse problem by using the vector space theory, taking into consideration the ill condition of this inverse problem, and 4) proof of the uniqueness of the epicardial potentials.     

Inverse Recovery of Two Moving Dipoles from Simulated Surface Potential Distributions on a Realistic Human Torso Model

We tested a procedure to recover two moving dipole (TMD) parameters from bidipolar potential distributions generated over the surface of a numerical human torso model, using 120 surface sampling points. The surface distributions were computed for either a finite homogeneous torso (T1), a finite torso with lungs (T2), or a finite torso with lungs and blood masses (T3). Inverse calculations were carried out to initially recover the multipole series components (15, 24, or 35 terms) using either a finite homogeneous torso (I1) or a finite torso with lungs (I2), and a least-squares difference procedure. Next, the TMD parameters were obtained by fitting these multipole series components (15 or 24 terms) to the multipole series components estimated from the Brody shift equations, using the Levenberg-Marquardt iterative algorithm and a series of initial estimates for the TMD solution. A simulation run involved 253 different input dipole-pair combinations and 20 initial estimates. The correct TMD solution almost always coincided with that yielding the minimum residue, which was also the solution obtained by the largest fraction of initial estimates. The lowest rms position error of 2.7 mm was obtained with a T1-I1 torso combination, and with 35 recovered multipole series components and 24 Brody shift equations. Larger errors were obtained using a lower number of recovered multipole series components and Brody shift equations, or pairs of parallel or antiparallel dipoles, or dipoles of unequal amplitude.     

Curtain Arrays of Horizontal Dipoles

The directivity patterns of a curtain array used in HF communication systems were calculated in the past on the assumption of sinusoidal current distribution. Since this assumption is not justified by the modern theory, there is a need to revise these calculations. Some experimental results which were not understood earlier also provide support for this view.     

感应电机自适应电流解耦逆控制

通过对感应电机状态方程的转换,将电机dq轴电流方程解耦,利用自适应逆控制思想,采用LMS(最小均方)算法,实现了对MIMO、多参量、强耦合感应电机的电流控制,电机长期运行会导致某些参数发生漂移,仿真验证了该算法对参数变化的鲁棒性.     

新型分形结构在印刷振子中的应用

为了设计小型化、多频化的印刷振子,采用递归法构造了一种新型的分形结构,并设计了单层分形印刷振子,利用Ansoft HFSS软件对天线进行仿真优化,结果表明:新型单层分形印刷振子尺寸缩减性优于Hilbert单层分形印刷振子.针对单层分形印刷振子频比固定的不足,提出了双层分形印刷振子模型,仿真结果表明:除具备单层分形印刷振子的所有特性外,双层分形印刷振子还具备频比可调特性,这将大大解决目前印刷振子所面临的小型化、多频化难题.     

CCD输出二极管反向漏电机理的研究

分析了CCD输出二极管反向漏电的机理,认为有三个途径造成CCD反向漏电：n^ 区通过SiO2漏电,n^ 区通过Si-SiO2表面漏电以及体内漏电。提出了解决漏电问题的方法,即控制好氧化、扩散、离子注入、光刻以及退火等工艺。     

An Artificial Dielectric Based on Conducting Dipoles

Journal of Communications Technology and Electronics - A structure of gratings consisting of conducting dipoles located in a dielectric layer is considered. The dispersion of the effective...     

A Principle for Solving a Class of Anisotropic Current Flow Problems and Applications to Electrocardiography

In studies of electrocardiographic lead performance, theoretical analyses of the influence of the anisotropic heart and skeletal muscle are particularly difficult. In this paper, the basic differential equations of static fields and steady current flow are arranged to emphasize the field and conductivity dependent charge distributions which arise in anisotropic media. The equations are applied to two types of problems of immediate interest. Firstly, the equations are used to explain how anisotropic media may be included in current digital computer studies of the heart-lead relation and to conclude that the techniques which made the computer studies possible tend to lose their advantage when applied to arbitrary anisotropic configurations. Secondly, the equations are used to develop a principle which permits exact solutions for the fields of numerous simple anisotropic configurations. Three such configurations useful for heart-lead studies are analyzed with the following results: the anisotropic skeletal muscle can be treated in special cases such as a head-foot heart-vector lead approximately as isotropic with resistivity of 280 ohm cm; the closed dipolar layer in an anisotropic, inhomogeneous heart produces the same null electric field as it does in homogeneous isotropic media; bounds on the influence of the heart's anisotropy on a heart-vector lead field are estimated at plus or minus 12 percent of the average lead field intensity.     

交叉振子平面反射阵列天线的分析

分析交叉振子平面反射阵列天线的移相特性和传输特性,针对FFS地板和交叉振子构成双层结构的阵列天线,采用整体建模并利用Floquent方法数值分析了其移相与传输特性.结果表明,相比单层结构分析方法,该实验结果更加准确,有助于反射阵列天线的精确设计.     

Wideband Dipoles on Electromagnetic Bandgap Ground Planes

The performance of broadband dipole antennas above electromagnetic bandgap (EBG) structures is investigated. Two different structures are examined. One is a diamond dipole over an EBG with square patch elements optimized by hand and the other an open sleeve dipole over an EBG optimized by a genetic algorithm (GA). Both configurations demonstrate that a low profile dipole antenna over an EBG can have a broad bandwidth. Careful design of both is required and in particular for best results, the antenna-EBG system should be optimized together, rather than as separate components. The performance is compared to an absorber backed wideband dipole antenna and it is found that the gain is significantly increased, whilst the bandwidth is reduced. In general, for the diamond dipole antenna return loss bandwidths of over 2:1 (67%) have been achieved, although radiation pattern control is difficult and reduces the bandwidth to the order of 1.4:1 (33%). The sleeve dipole over an EBG achieved a bandwidth of 1.28:1 (26%). The realized gain, which is power gain reduced by input match loss, of both structures are approximately the same. GA optimization and parametric studies seem to suggest that bandwidths significantly greater than these are difficult to achieve.     

A Circuit for Contact Monitoring in Electrocardiography

A circuit for contact impedance monitoring in ECG is presented. An ac current in the same frequency band as the ECG signal is used for the measurement. This makes the measurement independent of polarization potentials and gives the correct weight to the impedances in the skin-to-electrode junction. The measurement of the contact impedance is made continuously during ECG monitoring and causes no interference in the ECG signal.     

Coupling between Two Arbitrarily Oriented Dipoles through Multilayered Shields

The electromagnetic coupling between two arbitrarily oriented dipoles through planar multilayered shields is analyzed. The method of approach utilizes the plane-wave spectral representation of radiation fields [1] and the transformation matrices for multilayered media. Numerical results are found to be in good agreement with the experimental data for magnetic dipoles in the frequency range of 10 kHz to 1 MHz.     

A New Type of Circular Polarizer Using Crossed Dipoles

A method of obtaining a circularly-polaIized wave by use of two orthogonal dipoles driven in parallel by a common transmission line is shown. The lengths of the dipoles are so chosen that the real part of their input admittances are equal and the angle of the inpnt admittances differ by 90°. When these two conditions are met the resulting radiated wave in a normal direction will be circularly polarized. The method is applicable both to a circularly-polarized radiating antenna and to the problem of producing a circularly-polarized wave of the TE/sub 1/ mode in a round waveguide. For the first case, an analysis and a method of design are shown, and for the second case an experimentally developed example is given. The second case employs monopoles rather than dipoles for convenience in energizing from a coaxial line.