Amplitude spectrum compensation and phase spectrum correction of seismic data based on the generalized S transform

We propose a method for the compensation and phase correction of the amplitude spectrum based on the generalized S transform. The compensation of the amplitude spectrum within a reliable frequency range of the seismic record is performed in the S domain to restore the amplitude spectrum of reflection. We use spectral simulation methods to fit the time-dependent amplitude spectrum and compensate for the amplitude attenuation owing to absorption. We use phase scanning to select the time-, space-, and frequencydependent phases correction based on the parsimony criterion and eliminate the residual phase effect of the wavelet in the S domain. The method does not directly calculate the Q value; thus, it can be applied to the case of variable Q. The comparison of the theory model and field data verify that the proposed method can recover the amplitude spectrum of the strata reflectivity, while eliminating the effect of the residual phase of the wavelet. Thus, the wavelet approaches the zero-phase wavelet and, the seismic resolution is improved.

Phase aberration correction in ultrasonic phased array non-destructive testing systems

Phase aberration correction for medical ultrasound systems has attracted a great deal of attention. Since phased array techniques are now widely employed for industrial non-destructive testing （NDT） applications in various fields, the problem of phase aberrations in the process of NDT testing is considered. The technique of cross-covariance for phase aberration correction is presented. The performance of the technique for phase aberration correction is tested by means of echo signals obtained in practical non-destructive testing experiment. The results show that the technique has the better accuracy of phase correction.

Phase-sensitive fat suppression steady-state free procession sequence with phase correction

Robust and fast fat suppression is a challenge in balanced steady-state free precession （SSFP） magnetic resonance imaging. Although single-acquisition phase-sensitive SSFP can provide fat-suppressed images in short scan time, phase errors, especially spatially-dependent phase shift, caused by a variety of factors may result in misplacement of fat and water voxels. In this paper, a novel phase correction algorithm was used to calibrate those phase errors during image reconstruction. This algorithm corrects phase by region growing, employing both the magnitude and the phase information of image pixels. Phantom and in vivo imagings were performed to validate the technique. As a result, excellent fat-suppressed images were acquired by using single-acquisition phase-sensitive SSFP with phase correction.

θ Correction to the Analytical Expressions for Calculating Activities from Phase Diagrams Involving Intermediate Compounds

A set of correct expressions for calculating activities and activity coefficients from binary phase diagrams involving intermediate compounds are presented in this paper by the introduction of a correct parameter θ. The application of these expressions to system Mg-Sn shows that they are quite feasible.

Wavefront correction of Ti:sapphire terawatt laser with varying precision of phase conjugation between deformable mirror and wavefront sensor

The phase conjugation between the deformable mirror and the wavefront sensor in the aberration correction of a terawatt Ti：sapphire laser is studied experimentally and theoretically in this paper. At varying values of phase- conjugation precision, we focus the corresponding beams into spots of the same size of 5.1 μm × 5.3 μm with a f/4 parabola in the 32 TW/36 fs Ti：sapphire laser system. The results show that the precision of conjugation can induce an intensity modulation but does not significantly affect the wavefront correction.

Studies on absorption coefficients of dual-energy γ-rays and measur-ing error correction for multiphase fraction determination

In this article, principle and mathematical method of determining the phase fractions of multiphase flows by using a dual-energy γ -ray system have been described. The dual-energy γ -ray device is composed of radioactive isotopes of 241Am and 137Cs with γ -ray energies of 59.5 and 662 keV, respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The modified arithmetic is beneficial to removing the extra Compton scattering from the measured value. The result shows that the dual-energy γ -ray technique can be used in three-phase flow with average accuracy greater than 95%, which enables us to determine phase fractions almost independent of the flow regime. Improvement has been achieved on measurement accuracy of phase fractions.

PHASE CORRECTION AND BAND-PASS FILTERS IN CT IMAGING

This paper reports the use of the fast Fourier transform (FFT) in the direct Fourier transform method (DFM) in Computerized Tomography (CT) reconstruction. Phase corrections are needed in the CT reconstruction. In order to eliminate the image distortion from the basic DFM, Padding and band-pass filters are used in the improved DFM. Finally, some reconstructions from simulated projections and several experimental results are given.

A NOVEL ADAPTIVE ALGORITHM OF CPE CORRECTION FOR OFDM SYSTEMS

On the basis of the analysis of the effect of PHase Noise (PHN) and Common Phase Error (CPE) on Orthogonal Frequency Division Multiplexing (OFDM) systems, a cost function is constructed. By the cost function and the idea of Least-Mean-Square (LMS) adaptive algorithm, the adaptive algorithm for the correction of CPE is presented. The simulations have been performed to investigate the performance for tracking PHN and estimating CPE, the results show that the algorithm performs soundly.

Power Factor Correction Rectifier with a Variable Frequency Voltage Source in Vehicular Application

This paper presents a PFCVF (Power Factor Correction) rectifier that uses a variable frequency source for alternators for electric and hybrid vehicles application. In such application, the frequency of the signal in the alternator changes according to the vehicle speed, more over the loading effect on the alternator introduces harmonic currents and increases the alternator apparent power requirements. To overcome these problems and aiming more stability and better design of the alternator, a new third harmonic injection technique is proposed. This technique allows to preserve a good THD (Total Harmonic Distortion) of the input source at any frequency and to decrease losses in semiconductors switches, thereby allowing more stability and reducing the apparent power requirements. A comparative study between the standard and the new technique is made and highlights the effectiveness of the new design. A detailed analysis of the proposed topology is presented and simulations as well as experimental results are shown.

A Conceptual Design Study for the Error Field Correction Coil Power Supply in JT-60SA

This paper describes a conceptual design study for the circuit configuration of the Error Field Correction Coil （EFCC） power supply （PS） to maximize the expected performance with reasonable cost in JT-60SA. The EFCC consists of eighteen sector coils installed inside the vacuum vessel, six in the toroidal direction and three in the poloidal direction, each one rated for 30 kA-turn. As a result, star point connection is proposed for each group of six EFCC coils installed cyclically in the toroidal direction for decoupling with poloidal field coils. In addition~ a six phase inverter which is capable of controlling each phase current was chosen as PS topology to ensure higher flexibility of operation with reasonable cost.

融合长短基线的干涉图解缠错误自动改正

合成孔径雷达干涉测量(interferometric synthetic aperture radar,InSAR)技术因具有全天时、全天候、大范围的独特优势,已被广泛应用于地球科学研究、自然灾害监测和环境管理等领域。然而,受地表失相干、干涉条纹密集等因素影响,InSAR数据处理关键的步骤——干涉图相位解缠常出现错误,进而影响高程反演和地表形变监测精度。为此,文章提出了一种融合长短基线干涉相位闭合环的解缠错误自动探测与改正方法,并利用湖南省-江西省高植被覆盖区的Sentinel-1雷达影像开展了算法验证。实验结果表明,该方法可有效地改正干涉相位解缠错误,这对InSAR技术提升高程反演和形变监测精度具有重要意义。

一种基于相位误差校正技术的快速启动晶体振荡器

随着超低功耗(Ultra-Low Power,ULP)物联网(Internet of Things,IoT)系统的发展,采用能量注入技术的快速启动晶体振荡器因对IoT系统功耗影响巨大而逐渐成为研究热点.能量注入技术可以显著降低晶体振荡器的启动时间和启动能量,但是对注入源的精度要求苛刻.为了扩大注入频偏容限以及实现高注入效率,本文提出了一种基于延迟锁定环的相位误差校正技术.该技术将注入频偏容限扩大到2%,启动过程的非注入持续时间仅为4个周期,实现了高效注入.本文所述晶体振荡器采用40 nm CMOS工艺设计并流片.在1.0 V电源电压下采用24 MHz晶体进行测试,当注入频偏高达2%时,实现了7.2μs的启动时间,启动能量为5.1 nJ.相比同频偏下的传统注入方案,启动时间缩短了99.66%.

基于Blackman窗全相位FFT双谱线校正的同步宽频相量测量方法研究

为进一步分析电网电力电子化特征日益明显所带来的影响,电网运行状态监视向间谐波和高次谐波方向延伸,对同步宽频测量提出了更高要求。同步宽频测量广泛采用的加窗插值频谱分析方法存在频谱泄露,当基波频率发生偏移或信号中存在邻近信号时会导致较大误差。针对此问题,文中提出采用基于Blackman窗全相位FFT双谱线校正的改进宽频相量测量方法,结合全相位FFT和Blackman余弦窗对宽频信号进行频谱分析,并利用双峰谱线进行参数校正。文中方法可以有效提升频谱泄露的抑制效果,降低邻近频谱干扰,提升基波频偏或邻近频谱的复杂运行工况宽频信号参数测量精度。

多分量LFM干扰及动态环境下DBOC信号的捕获

针对双二进制偏移载波(double binary offset carrier,DBOC)信号在多分量线性调频(linear frequency modulation,LFM)干扰和动态环境下捕获算法缺乏的问题,提出布莱克曼窗预处理结合分数阶傅里叶变换(fractionalFouriertransform,FRFT)的干扰抑制算法以及离散多项式相位变换(discretepolynomial-phase transform,DPT)、部分匹配滤波器(partial matching filter,PMF)结合快速傅里叶变换(fast Fourier transform,FFT)加频谱校正的捕获算法。该算法首先对接收信号做布莱克曼窗预处理,抑制干扰谱线输出旁瓣,提高干扰汇聚的精确性;然后利用分级算法快速搜索信号的最优阶数,在保证精度量级的条件下减少了运算量;最后,在对应的最优阶数下做FRFT,结合干扰判断和轮询算法,逐个完成多分量LFM干扰的抑制。对干扰抑制后的信号首先利用定阶算法确定其动态阶数;然后通过DPT对动态信号做降阶处理,去除动态项;最后利用PMF-FFT加频谱校正完成DBOC信号的捕获。仿真结果表明,所提算法能够准确并完全地对三个LFM干扰分量进行逐个抑制,且抑制后的干扰分量不会对其他干扰分量的抑制造成影响。在检测概率达到1时,经过布莱克曼窗预处理后算法的信噪比比经过汉明窗预处理和经过凯塞窗预处理后算法的信噪比分别提升了4 dB和6.4 dB,比未经过预处理算法的信噪比提升了7.2 dB。此外,使用频谱校正可以突出捕获峰值,提高捕获精度。与未经频谱校正算法相比,经过频谱校正后算法的信噪比提升了1.6 dB,且能减少一定的捕获时间。

欠采样下的多频带通信信号高精度载频估计

为根本解决当前主流的基于调制宽带转化器(MWC)的欠采样频率估计方法存在的3个问题,即采样通道数目多、载频估计精度低、信源频带分布稀疏度条件高,该文提出基于互素谱相位差校正的通信信号载频估计方法。通过将两路互素欠采样取代多路调制宽带转化器欠采样,克服了其耗费欠采样通道数目多的缺陷;基于此,既推导出全景谱谱峰位置与两路互素输出IDFT支路序号对的映射关系,又推导出相邻快拍下该序号对的IDFT相位差与载频值的解析关系,从而克服了主流方法的载频估计精度低的缺陷;通过将最小尺寸全相位滤波器对半分解方法融入原型滤波器设计,构造出两路并行互素谱分析器,还彻底克服了对信源频带分布稀疏度条件高的依赖。仿真表明,相比于主流方法,该文方法仅需耗费不足其1/2的样本数量,载频估计的相对误差降至其1/20以下。

数字全息显微中相位像差校正技术综述

数字全息显微技术是数字全息技术与显微技术的结合,兼备两种技术的优点,为微纳领域的定量三维测量提供了一种无损、无标记、准确和近实时的测量手段。然而,由于元件缺陷和失调以及环境扰动等原因,会在数字全息显微测量结果中额外引入相位像差。为了获得准确的定量相位测量结果,必须对像差成因和主要成分进行分析,然后补偿和校正像差。这篇综述介绍了数字全息显微成像测量中主要的像差来源和影响,基于实现的方式对现有的像差校正方法进行了综述,并展望了未来像差校正领域的发展方向,为从事数字全息检测研究的研究者提供参考。

联合GNSS和GRACE数据分析华北平原地表垂直形变

为了分析华北平原陆地水储量变化等环境因素对GNSS非线性垂向时间序列产生的影响,结合GRACE数据和GNSS数据以水井水位数据为补充对华北平原进行研究。研究结果表明,华北平原地区GNSS垂向位移时间序列与GRACE负荷形变具有较好的相关性,改正后的GNSS观测与GRACE负荷形变的相关性有较大程度地减少。基于水井静水位资料对结果的可靠性进行了验证,扣除GRACE负荷形变影响后的GNSS垂向位移时间序列与水井静水位观测之间的相关系数相较于扣除前降低了40%~96.7%。将GRACE观测得到的负荷形变从GNSS时间序列中扣除,可以有效降低包括陆地水储量变化在内的环境因素导致的负荷形变对GNSS观测造成的非构造运动影响。研究结果为获取华北平原及其周边地区更为精确的垂向构造运动变形提供了科学参考。

能够校正相位误差的感应电机全阶磁链观测器

感应电机的传统全阶磁链观测器,采用预估校正法进行离散时转子磁链估计相位的误差较小。但是电机高速运行时,随着载波比的减小,估计相位误差会随之增大,进而引起电机控制性能下降。有鉴于此,通过分析磁链相位误差的影响以及电机控制变量之间的相互作用关系,推导出一种具有相位误差自校正功能的改进全阶磁链观测器。最后在感应电机实验平台上验证了改进全阶观测器的有效性。

基于修正电磁散射系数的距离频域脉冲相干法SAR回波仿真

针对传统合成孔径雷达(Synthetic Aperture Radar,SAR)回波仿真方法无法同时满足仿真精度高、速度快的缺点,设计了一种利用距离历程修正电磁散射系数的距离频域脉冲相干法(Range Frequency Domain Pulse Coherence,RFPC)目标回波仿真方案。该方案在离散方位采样点处采用物理光学法计算关于目标电磁散射特性的二维电磁散射系数,利用天线相位中心与目标间的距离历程修正电磁散射系数的相位,根据脉冲信号3 dB波束宽度修正电磁散射系数的幅度,利用RFPC在距离频域进行目标电磁散射系数与SAR发射信号的乘积处理,获取目标的二维回波信号,采用RD成像算法进行成像处理得到目标的SAR仿真图像。利用该方案分别对金属球和舰船模型进行了回波仿真试验,并与RaySAR的仿真结果进行对比,验证了该方案的精确性与高效性。

全相位FFT算法高精度谐波测量方法

针对电力系统精确测量谐波信号频谱特性这一技术问题,该文提出一种基于全相位FFT算法的高精度谐波测量方法。通过低漂移信号转换电路和程控滤波器对被测信号进行调理,再经高精度A/D转换器变换成数字量传至MCU进行全相位FFT变换,选择离散频谱中幅值最大的两根谱线进行校正得到信号精确测量结果。利用LTspice电路与Matlab算法协同仿真,结果表明:在输入信号为理想谐波、复杂谐波与间谐波、叠加白噪声信号的基波情况下,所提出的方法均可实现对信号频率和幅值的准确测量。在与传统FFT双谱线校正和加窗FFT双谱线校正相比,该文提出的测量方法精度更高、抗噪性更好,频谱泄漏抑制能力更强,适用于对电力信号的高精度测量。