The Effects of Distant Cardiac Electrical Events on Local Activation in Unipolar Epicardial Electrograms

The effect of potentials generated during depolarization of the left ventricle on epicardial unipolar electrograms recorded from the right ventricle was studied using the right ventricular isolation procedure. This surgical technique disrupts electrical conduction and prevents activation wavefronts from propagating between the ventricles. Following the procedure, the ventricles were paced asynchronously with the left ventricle paced 100 ms before the right ventricle to geparate the electrogram into its local (due to depolarization of the right ventricle) and distant (due to depolarization of the left ventricle) components or with an interval of 20 ms or less between pacing the ventricles to mimic electrograms resulting from normal (synchronous) activration. Electrical activity in the left ventricle significantly affected the magnitude of the slope of the most rapid deflection and the timing of the maximum and minimum potentials of right ventricular unipolar electrograms. However, distant activity did not significantly alter the timing of the fastest 1 ms downstroke. No electrograms of distant components had negative slopes with magnitudes greater than 1.3 mV/ms, nor did any slopes of electrograms containing only local components have magnitudes less than 1.5 mV/ms. Simulated electrograms, calculated from the local and distant components, correlated well (r = 0.83 to 1.00, N = 48) with electrograms recorded during synchronous pacing.     

Four digital algorithms for activation detection from unipolarepicardial electrograms

The reproducibility of activation detection by each of four algorithms used to calculate maximum derivatives was tested on two sequential paced beats of right ventricular unipolar epicardial electrograms which represented either local activation of the right ventricle alone or synchronous activation of both ventricles. The methods were evaluated by comparing the shape of the two beats aligned on their selected activation times, i.e., the time at which the maximum negative deflection occurred, the differences in activation intervals for the two beats, and the effect on the activation time of superimposing distant events on local activation. The 17-point second-order data fit algorithm performed slightly better than the first-order difference, three-point Lagrange derivative, and five-point second-order data fit algorithms except that activation time selection by the 17-point technique was slightly, but significantly, delayed by the superposition of distant potentials. The 17-point second-order data fit technique is therefore recommended for use in detecting activation unless computation time is a major consideration. In that case, the five-point second-order data fit technique, which uses only four data values for each computation, can be used with only slight decreases in accuracy.     

A method for determining high-resolution activation time delays inunipolar cardiac mapping

Presents a method for determining activation time delays in unipolar cardiac mapping data to resolutions considerably smaller than the sample interval. The method involves taking two filtered, differentiated electrograms and computing the Hilbert transform of their cross correlation, which exhibits a negative-to-positive zero crossing at the delay time between the signals. Simultaneous endocardial/epicardial recordings of sinus rhythm were made in the swine right atrium using identical, precisely superpositioned electrode arrays. Data were amplified, lowpass filtered, and digitized at 1000 Hz. A window of data was chosen around each electrogram in an endocardial/epicardial electrogram pair. The windowed electrograms were differentiated and highpass filtered, and the Hilbert transform of the cross correlation between the electrograms was computed. The activation time delay was taken to be the first negative-to-positive zero crossing. Average activation time delays (±SD) were computed for 4-s sinus rhythm recordings from each endocardial/epicardial electrode pair. For a representative site, the average transmural activation time delay was 0.71±0.06 ms (n=10 electrograms). Time delays estimated using the Hilbert transform method were compared with time delays estimated using the maximum negative slope criterion. The Hilbert transform results exhibited much smaller standard deviations, indicating that the Hilbert transform method may produce more accurate time delay estimates than the maximum negative slope method     

基于AlGaN/GaN HEMT太赫兹探测器的340 GHz无线通信接收前端

利用天线耦合AlGaN/GaN HEMT太赫兹探测器的自混频和外差混频效应,分别设计并测试了340 GHz频段直接检波式和外差混频式接收机前端。通过接收机信噪比的测量和接收功率的定标,得到了两种接收机的等效噪声功率。直接检波模式下探测器的响应度约为20 mA/W,直接检波模式和外差混频模式下接收机的等效噪声功率分别约为?64.6 dBm/Hz1/2和?114.79 dBm/Hz。在相同的载波功率和接收信号带宽条件下,当本振太赫兹波功率大于?7 dBm时,外差混频接收的信噪比优于直接检波的信噪比。当本振功率大于0 dBm时,外差混频接收机表现出优良的解调特性,其信噪比高出直接检波接收机的信噪比10 dB以上。     

激光相干雷达中光单次下变频技术

在相干激光雷达远程测距中,为提高雷达的探测距离和距离分辨力,通常使用大时宽带宽积的信号如调频信号对光载波进行调制,并在接收端进行脉冲压缩处理,为降低接收端数字信号处理的数据量以提高运算的实时性,需要将接收信号下变频至合适的频段。传统的外差式雷达接收机需对光信号和电信号分别进行一次下变频,导致系统结构较复杂,且受器件非理想化的限制,下变频过程中会引入额外的噪声,此外还存在镜像频率噪声干扰的问题,导致解调信号信噪比降低。提出了一种将光信号直接下变频至脉冲压缩所需频段的方案,该方案使用正交解调的方式进行,能够简化系统结构同时抑制镜频噪声。首先将本振光进行频移并分为两束,通过控制相位使两本振光相互正交。将信号光分为两束并分别与两路本振光在光电探测器表面进行混频,接着对电信号进行采集,通过相关算法对幅相不平衡进行矫正。经仿真和实验,该方法能够在有效简化激光相干雷达接收机系统结构的同时避免镜频噪声干扰,在10 GSps采样率下,相较于外差式接收机,解调信号信噪比提高了约3 dB。     

基于局部检测统计量的分布式CFAR检测理论研究

本文系统研究了融合中心接收局部检测统计量的分布式CFAR检测技术。在假设局部检测器背景杂波功率水平相同以及不同传感器测试单元之间服从独立同分布的前提下,首先推导了局部采用单元平均（CA）检测器时融合中心的检测概率与虚警概率的解析表达式,在此基础上利用Laplace变换的频域微分性质,将其推广到局部采用其它检测器,获得了普适性的融合方法,可适用于局部采用任意数量、形式的均值（ML）类和有序统计量（OS）类CFAR检测器时的情形,避免了传统的融合中心采用MOS类方法时所需要的局部信杂比相同的假设,实验结果表明了算法的有效性。      

非均匀采样信号小波分析误差控制方法

标准的小波分析方法中,信号的低频能量和高频能量不能人为控制,因此在利用低频分量近似原信号时,在一些陡峭变化区域会存在较大偏差。针对这一问题,本文首先分析了小波分解各子带能量与采样频率的关系,发现增加采样频率可以降低高频能量,并给出了部分证明。以此为基础,提出了非均匀采样信号小波分析误差控制方法,考虑到小波分解的高频能量和低频能量存在互补关系,算法利用高频系数作为低频表示误差的判断指标,对误差超限位置处的数据增加采样,然后对修正后的数据进行低频分解;该方法使低频能量可根据误差门限人为进行调整。重构是分解的逆过程,可完全无误的恢复原始信号。实验表明算法对小波分析低频表示误差具有很好的控制能力。      

Self-heterodyne multiterminal system concepts for frequencydivision multiplexed fiber-optic communication

System structures are described that use a centralized optical source for supplying all optical power needs-signal generation and coherent detection. In the configurations described the following benefits occur. Functional systems can be implemented with already demonstrated, and in many cases readily available components. There is no need for local oscillator optical sources and there is no need to stabilize the local oscillators with respect to a remote transmitter frequency to achieve coherent detection. Increases selectivity against other signal frequencies and increased signal-to-noise result from the use of coherent detection. When configured to equalize reference and signal time delay paths, both slow and fast laser source phase and frequency jitter are compensated for. One may therefore efficiently implemented multiple-access frequency division multiplexed networks in which the individual communication bandwidths are small compared to the linewidth of the laser power source     

基于分段滤波的Prony算法在谐波检测中的应用

现代电力系统中的谐波与间谐波频率范围广,直接利用Prony算法辨识得到的结果往往不是很精确;随着信号中谐波含量的增多,模型阶数的变大,计算时间变得过于冗长。针对这些问题,文中提出一种基于分段滤波的Prony算法,首先根据谐波的频率范围进行频段划分,确定各频段的采样参数;然后由低频段到高频段依次进行Prony分析,在进行下一频段检测之前,将已辨识出的所有谐波含量从原始信号中滤除;最后综合各段分析结果,得出各频段谐波的模态参数。仿真试验和应用实例表明,对含量较多且复杂的谐波信号,改进后的方法能有效地提高计算速度和辨识精度。     

低维材料太赫兹探测器研究进展（特邀）

太赫兹技术在无损检测、生物医学、工业检查、环境监测、局域通信和国防安全等领域具有广阔的应用前景。太赫兹系统中太赫兹探测器是其核心器件,其性能决定了太赫兹系统的应用市场,是推动太赫兹技术进一步发展的重要研究方向之一。但是,太赫兹波段较低的光子能量使得实现高速、灵敏的太赫兹探测颇有挑战。随着纳米技术和新材料制备技术的进步,低维材料的高迁移率、宽响应频带等性能为太赫兹探测器提供了新的机遇,低维材料太赫兹探测器得到广泛关注,其主要优势是高灵敏度、宽频带和低噪声,在近年来取得了显著的研究进展。虽然太赫兹探测器已经取得突破性发展,但各类太赫兹探测器仍然存在一些问题。在此背景下,文中从太赫兹探测器的分类出发,简要介绍了测辐射热计、热释电探测器、等离子体共振探测器和热载流子调控探测器的物理机制以及最新研究进展,并展望了未来低维材料太赫兹探测器的发展方向。     

基于高频探测信号的金属探测器的研究

运用于食品领域,是金属探测器的一种新用途。与其他领域相比,在食品工业所使用的金属探测器需要有较高的灵敏度。文中从提高探测信号频率的角度,探讨了频率变化对于金属探测器探测灵敏度的影响,论证了采用高频探测信号是提高金属探测器性能的有效途径。     

Nonlinear adaptive noise compensation in electrogastrograms recorded from healthy dogs

Adaptive noise compensation is a popular method for improving signal-to-noise ratio in a variety of biomedical applications with its major disadvantage being the requirement for a reference channel containing noise strongly correlated to the noise in the primary channel. In many biomedical applications the utilization of a channel containing such noise without any representation of the information signal is difficult if not impossible. In this study we investigated the possibility of applying adaptive compensation in nonideal noise environments containing substantial presence of information signal in the reference channel. The signal in the reference channel was subjected to nonlinear manipulations for reducing the signal-to-noise ratio, thus diminishing the representation of information signal. The methodology was tested on canine electrogastrographic (EGG) signals of four unconscious dogs which underwent laparotomy and implantation of six pairs internal stainless steel electrodes in addition to the eight-channel abdominal EGG. Fourteen-channel (six internal and eight cutaneous) were obtained from each dog for 1/2 h. The signals were digitized and processed by computer. All internal signals showed regular and coupled gastric electrical activity with frequency of repetition in the normogastric range [3-9 cycles-per-minute (cpm)]. A single pair of primary and reference channels was selected from each cutaneous recording and exponential manipulators in the reference channels were introduced. The manipulators were tuned to maximize the percent distribution of spectral components in the canine normogastric range of each frequency spectrum calculated from the signal at the output of the adaptive compensator. Significant increment in the percent distributions in the normogastric range (p < 0.01) was noted after tuning the exponential manipulator, and in many frequency spectra the recovery of the genuine dominant frequency peak of gastric electrical activity as determined by the internal recordings was noted. This study indicated that low percent distributions registered by some EGG channels are related to external nonlinear factors, the impact of which can be partially compensated.     

分布式CFAR检测系统的最优门限求取新方法

针对并行分布式检测网络结构局部采用CFAR检测器的情形,提出了一种在融合规则给定时,局部CFAR检测器最优门限的求取方法。给出了在任意融合规则下融合中心的检测概率和虚警概率关于局部门限的一阶导数的数值计算公式,并利用Broyden方法求取最优的局部门限。该方法避免了传统方法需要计算二阶导数的复杂性,并且更容易推广到局部采用多类CFAR检测器的情形。实验分析表明了算法的有效性。     

Quasi-Optical Surface Waveguide and Other Components for the 100- to 300-Gc Region

Components and techniques for the generation, transmission, and detection of energy in the 100- to 300-Gc frequency region were investigated theoretically and experimentally. The design and construction of fundamental components, such as harmonic generators and detectors, were necessary since many items are not available commercially. A detailed theoretical analysis was performed for the propagation characteristics of single-conductor transmission lines, and attenuation calculations were made for several dielectric image lines. Experimental measurements were made at 105 and 140 Gc on these two types of surface waveguides. Attenuation of these lines is compared with that of dominant-mode rectangular waveguide. An analysis of phase-correcting Fresnel zone plates was carried out, and several zone plates were designed, constructed and successfully tested at frequencies of 140, 210, and 280 Gc. Zone plates were used at several frequencies to make relatively long path transmission measurements and were also used in a specially designed Michelson interferometer. The frequency stability of the source klystron and the dielectric properties of a number of plastic materials were determined by measurements made with the interferometer. A method of frequency filtering by focal isolation was demonstrated with this equipment.     

Narrowband heterodyne reception using unstabilized sources

Source power for laboratory-type experiments is often limited at millimeter and submillimeter wavelengths. This requires the use of sensitive receiving equipment. Cooled square-law detectors and narrowband heterodyne detectors are examples. We have developed a coherent mechanical frequency shifter, which makes possible narrowband heterodyne detection without the need for highly frequency stable sources. Identical frequency and phase fluctuations of the transmit and local oscillator signals derived from one source are eliminated at the intermediate frequency. The widely tunable frequency shifter, designed for a 637GHz scale-model radar, was tested in a 140GHz non-radar configuration. We investigated the receiver's minimum coherently resolvable bandwidth and its sensitivity. Several types of sources were compared for the effect of local oscillator amplitude noise on receiver sensitivity at low intermediate frequency.     

A comparison of four new time-domain techniques for discriminatingmonomorphic ventricular tachycardia from sinus rhythm using ventricularwaveform morphology

Electrical management of intractable tachycardia via implantable antitachycardia devices has become a major form of therapy. Newly advanced methods of ventricular tachycardia detection propose examination of changes in intraventricular electrogram morphology in addition to or in combination with earlier rate-based detection algorithms. Unfortunately, most of the proposed morphology analysis techniques have computational demands beyond the capabilities of present devices or may be adversely affected by amplitude and baseline fluctuations of the intraventricular electrogram. We have designed four new computationally efficient time-domain algorithms for distinguishing ventricular electrograms during monomorphic ventricular tachycardia (VT) from those during sinus rhythm using direct analysis of the ventricular electrogram morphology. All four techniques are independent of amplitude fluctuations and three of the four are independent of baseline changes. These new techniques were compared to correlation waveform analysis, a previously proposed method for distinction of VT from sinus rhythm. Evaluation of these four new algorithms was performed on data from 19 consecutive patients with 31 distinct monomorphic ventricular tachycardia morphologies. Three of the algorithms performed as well or better than correlation waveform analysis but with one-tenth to one-half the computational demands.     

Wavelet-based event detection in implantable cardiac rhythm management devices

This paper presents a novel event detector for implantable devices. The algorithm is based on a signal model which describes an event as a linear combination of basis functions. The linear combination involves two fundamental electrogram waveforms represented at different time scales. An efficient, low-complexity detector is developed using the dyadic wavelet transform with integer filter coefficients, and a generalized likelihood ratio test. The results show that reliable detection is obtained at an intermediate signal-to-noise ratio (SNR = 25 dB) for various common noise sources. In terms of probabilities of missed events and false alarms, an over-all performance of 0.7% and 0.1%, respectively, was achieved on electrograms corrupted by the different noise types at an intermediate SNR.     

Magnetic resonance driven electrical impedance tomography: a simulation study

Magnetic resonance electrical impedance tomography (MREIT) is a method for reconstructing a three-dimensional image of the conductivity distribution in a target volume using magnetic resonance (MR). In MREIT, currents are applied to the volume through surface electrodes and their effects on the MR induced magnetic fields are analyzed to produce the conductance image. However, current injection through surface electrodes poses technical problems such as the limitation on the safely applicable currents. In this paper, we present a new method called magnetic resonance driven electrical impedance tomography (MRDEIT), where the magnetic resonance in each voxel is used as the applied magnetic field source, and the resultant electromagnetic field is measured through surface electrodes or radio-frequency (RF) detectors placed near the surface. Because the applied magnetic field is at the RF frequency and eddy currents are the integral components in the method, a vector wave equation for the electric field is used as the basis of the analysis instead of a quasi-static approximation. Using computer simulations, it is shown that complex permittivity images can be reconstructed using MRDEIT, but that improvements in signal detection are necessary for detecting moderate complex permittivity changes.     

集中式O FDM-MIMO雷达自适应检测算法

针对频率分集条件下，集中式OFDM-MIMO雷达在未知杂波环境中的目标检测问题，首先分析了OFDM-MIMO雷达回波数据模型，由于OFDM-MIMO雷达的频率分集特性，不同频率通道回波数据相互独立，在此基础上，分别基于一步和两步广义最大似然比准则，给出了集中式OFDM-MIMO雷达GLRT和OFDM-MIMO雷达AMF两种检测器，并分析了这两种检测器的恒虚警特性。两种检测器有效利用集中式OFDM-MIMO雷达频率分集特性，提升目标检测性能，同时降低了矩阵求逆维数，以及参考单元数目的要求，并且具有恒虚警性能。计算机仿真验证了算法的有效性。     

Criteria for local myocardial electrical activation: effects ofelectrogram characteristics

The ability of several variables to distinguish unipolar deflections due to local activation from those due to nonlocal activity is studied. A model of polyphasic deflections based on atrial recordings during reentrant tachycardia was used to facilitate distinction of local and distant activity by methods independent of the test variables. The performances of variables were assessed by comparing areas under receiver operating characteristic curves. Optimal thresholds of test variables were identified by maximizing statistics which corrected for the pretest probability of local activation. It was found that the greatest negative first derivative of the unipolar potential discriminated between local and distant ventricular signals, but performed less well than the ratio of the first derivative to the potential for distinguishing between local atrial signals and distant ventricular signals. A linear combination of the potential and the ratio of the first derivative and the potential performed well for all groups of signals studied. Optimal criteria for detecting local activation are discussed