Phase Delay Error Research Articles

Optimal wideband digital fractional-order differentiators using gradient based optimizer

In this paper, we propose a novel optimization approach to designing wideband infinite impulse response (IIR) digital fractional order differentiators (DFODs) with improved accuracy at low frequency bands. In the new method, the objective function is formulated as an optimization problem with two tuning parameters to control the error distribution over frequencies. The gradient based optimizer (GBO) is effectively employed on the proposed objective function. A wide range of design examples are presented to illustrate the effectiveness of the proposed approach. The proposed approximations are compared to those of recent literature in terms magnitude, phase, and group delay errors. The result reveal that our method can attain approximations have a favorable low frequency performance (with about 60% of relative magnitude error reduction) and maintain a comparable accuracy at most of the Nyquist band to those of the existing ones. Thus, our approximations can be attractive for low frequency applications.

The characterisation of a phase micro-stepper

The frequency steering of the local standard time is a common procedure for the timekeeping. The local radiofrequency reference output is modified by a phase and frequency offset generator to corresponds to the global timescales such as the International Atomic Time and Coordinated Universal Time timescales. The phase and frequency offset generator, also known as the phase micro-stepper, is used for such timescales for many years but it has not been very well characterized. It will be shown for a particular type of the phase micro-stepper that its phase delay error can exceed 10 ps and its frequency offset error can be relatively more than 10−16 of the reference frequency.

Calibration of Wideband LFM Radars Based on Sliding Window Algorithm

This paper addresses the challenges of wideband signal beamforming in radar systems and proposes a new calibration method. Due to operating conditions, the frequency-dependent characteristics of the system can be changed, and the amplitude, phase, and time delay error can be generated. The proposed method is based on the concept of the sliding window algorithm for linear frequency modulated (LFM) signals. To calibrate the frequency-dependent errors from the transceiver and the time delay error from the true time delay elements, the proposed method utilizes the characteristic of the LFM signal. The LFM signal changes its frequency linearly with time, and the frequency domain characteristics of the hardware are presented in time. Therefore, by applying a matched filter to a part of the LFM signal, the frequency-dependent characteristics can be monitored and calibrated. The proposed method is compared with the conventional matched filter-based calibration results and verified by simulation results and beampatterns. Since the proposed method utilizes LFM signal as the calibration tone, the proposed method can be applied to any beamforming systems, not limited to LFM radars.

Online Compensation of Phase Delay Error Based on P-F Characteristic for MEMS Vibratory Gyroscopes.

In this paper, an online compensation method of phase delay error based on a Phase-Frequency (P-F) characteristic has been proposed for MEMS Coriolis Vibratory Gyroscopes (CVGs). At first, the influences of phase delay were investigated in the drive and sense mode. The frequency response was acquired in the digital control system by collecting the demodulation value of drive displacement, which verified the existence and influence of the phase delay. In addition, based on the P-F characteristic, that is, when the phase shift of the nonresonant drive force through the resonator is almost 0° or 180°, the phase delay of the gyroscope is measured online by injecting a nonresonant reference signal into the drive-mode dynamics. After that, the phase delay is self-corrected by adjusting the demodulation phase angle without affecting the normal operation of the gyroscopes. The approach was validated with an MEMS dual-mass vibratory gyroscope under double-loop force-to-rebalance (in-phase FTR and quadrature FTR) closed-loop detection mode and implemented with FPGA. The measurement results showed that this scheme can detect and compensate phase delay to effectively eliminate the effect of the quadrature error. This technique reduces the zero rate output (ZRO) from −0.71°/s to −0.21°/s and bias stability (BS) from 23.30°/h to 4.49°/h, respectively. The temperature sensitivity of bias output from −20 °C to 40 °C has reached 0.003 °/s/°C.

A compact pulsatile simulator based on cam-follower mechanism for generating radial pulse waveforms

BackgroundThere exists a growing need for a cost-effective, reliable, and portable pulsation simulator that can generate a wide variety of pulses depending on age and cardiovascular disease. For constructing compact pulsation simulator, this study proposes to use a pneumatic actuator based on cam-follower mechanism controlled by a DC motor. The simulator is intended to generate pulse waveforms for a range of pulse pressures and heart beats that are realistic to human blood pulsations.MethodsThis study first performed in vivo testing of a healthy young man to collect his pulse waveforms using a robotic tonometry system (RTS). Based on the collected data a representative human radial pulse waveform is obtained by conducting a mathematical analysis. This standard pulse waveform is then used to design the cam profile. Upon fabrication of the cam, the pulsatile simulator, consisting of the pulse pressure generating component, pressure and heart rate adjusting units, and the real-time pulse display, is constructed. Using the RTS, a series of testing was performed on the prototype to collect its pulse waveforms by varying the pressure levels and heart rates. Followed by the testing, the pulse waveforms generated by the prototype are compared with the representative, in vivo, pulse waveform.ResultsThe radial Augmentation Index analysis results show that the percent error between the simulator data and human pulse profiles is sufficiently small, indicating that the first two peak pressures agree well. Moreover, the phase analysis results show that the phase delay errors between the pulse waveforms of the prototype and the representative waveform are adequately small, confirming that the prototype simulator is capable of simulating realistic human pulse waveforms.ConclusionsThis study demonstrated that a very accurate radial pressure waveform can be reproduced using the cam-based simulator. It can be concluded that the same testing and design methods can be used to generate pulse waveforms for other age groups or any target pulse waveforms. Such a simulator can make a contribution to the research efforts, such as development of wearable pressure sensors, standardization of pulse diagnosis in oriental medicine, and training medical professionals for pulse diagnosis techniques.

Phase delay error analysis of wave plate of division-of-amplitude full Stokes simultaneous polarization imaging system

The division-of-amplitude full Stokes simultaneous polarization imaging system has prominent merits, such as real time, high spatial resolution, high precision, etc. The development of the division-of-amplitude full Stokes simultaneous polarization imaging system has a high application value. The division-of-amplitude full Stokes simultaneous polarization imaging system uses polarization beam splitters, a half wave plate (HWP) and a quarter wave plate (QWP) to modulate the incident Stokes vector into four intensity images. Using the four intensity images, the incident Stokes vector can be analyzed. In the system, the phase delay errors of the HWP and the QWP have a direct influence on the measurement accuracy of the incident Stokes vector. A Stokes vector measurement error equation containing the phase delay errors of the HWP and the QWP is established. When there are the phase delay errors of the HWP and the QWP in the system, the Stokes vector measurement errors of the unpolarized light, 0° liner polarized light, 90° liner polarized light, 45° liner polarized light, 135° liner polarized light, right circularly polarized light and left circularly polarized light are analyzed. A method of solving the Stokes vector measurement error of incident light with any polarization state is given. When the Stokes vectors with different degrees of polarization (DOPs) are used as the incident light, the simulation results show that both the Stokes vector measurement error and the DOP measurement error increase with the DOP of incident light increasing. Therefore, we select the polarization measurement accuracy to evaluate the system when the DOP of incident light equals 1. To ensure that the polarization measurement accuracy of the system is within 2%, the phase delay error of the HWP should be within ±1.6° and the phase delay error of the QWP should be within ±0.5°. The analysis results of the phase delay errors of the HWP and the QWP are of great significance for improving the polarization measurement accuracy of the division-of-amplitude full Stokes simultaneous polarization imaging system, and also provide important theoretical guidance in designing and developing the system.

위상 배열 안테나 임피던스 부정합에 따른 실시간 지연회로의 위상 지연 오차 및 영향 분석

위상 배열 안테나 임피던스 부정합에 따른 실시간 지연회로의 위상 지연 오차 및 영향 분석

Deadbeat control based on a multipurpose disturbance observer for permanent magnet synchronous motors

Robustness against parameter mismatches and position-sensorless operation are two important research topics for permanent magnet synchronous motor (PMSM) drives. Usually, the existing observers are designed for achieving a specific function. While here, both the above two functions are integrated into the proposed sliding-mode disturbance observer: (i) if a position sensor is equipped, accurate current regulation can be achieved by deadbeat predictive current control despite mismatched motor parameters; (ii) if the position sensor is not equipped but with a good estimation of motor parameters, the observer can serve as a back electromotive force estimator. Then, the rotor position can be extracted for position-sensorless control. Usually, a low-pass filter is required to suppress high-frequency noises in the conventional sliding-mode observer. This inevitably leads to phase delay in the estimation. By comparison, a complex coefficient filter is inherently embedded in the proposed method, which can provide accurate estimation without phase delay or magnitude error. Experimental results obtained from a 2.4 kW PMSM drive platform indicate that high-performance current control can be achieved with good robustness for position sensor-based operation. Also, rotor position can be accurately estimated with good steady and dynamic performance for position-sensorless operation.

Performance Evaluation of Azimuth Offset Method for Mitigating the Ionospheric Effect on SAR Interferometry

Synthetic aperture radar (SAR) signals interact with the ionosphere layer when they propagate through the atmosphere, leading to the phase delay error for SAR interferometry (InSAR). To mitigate this error for SAR interferometry, azimuth offset method is proposed. However, the performance of it has not been fully investigated. In this situation, this study makes a comprehensive performance analysis of azimuth offset method through processing the simulated and real SAR data. The experimental result indicates that this method can effectively mitigate the ionospheric phase delay error, where the standard deviation of phase difference after correction (2.6 rad.) decreased by almost 2 times, compared to those before correction (5.3 rad.) for the real SAR data. However, it is also found that the method is affected by the random noise, which may induce the improper estimation of integral constants and consequently affect the ionospheric correction. Moreover, the severe deformation signals in the interferogram may lead to the estimation error of integral constants and scaling factor. Therefore, it should mask out the deformation signals when using the azimuth offsets method to correct the ionospheric error. This study may provide useful information when using azimuth offset method to mitigate the ionospheric phase delay error on InSAR.

Mitigation of ionospheric phase delay error for SAR interferometry: an application of FR-based and azimuth offset methods

ABSTRACTSynthetic aperture radar (SAR) signals interact with the ionosphere layer when they propagate through the atmosphere, leading to the phase delay error for SAR interferometry (InSAR). Although several methods have been proposed to mitigate the ionospheric phase delay, the application of these methods has not been fully investigated. In this study, an application of two ionospheric mitigating methods, azimuth offset and Faraday Rotation (FR), is investigated and analysed through processing two Phased Array type L-band Synthetic Aperture Radar onboard the Advanced Land Observing Satellite-1 full-polarimetric SAR images over Alaska. The result indicates that both methods can effectively mitigate the ionospheric phase delay error for SAR interferometry, where the standard deviations of the ionosphere-corrected result have decreased to 3.2 cm for FR-based method and 2.0 cm for azimuth offset method compared to those before correction (7.3 cm). However, it is also found that the FR-based method is easily contaminated by the noise, which may be a limitation in practical applications. Moreover, analysis of the residual ionospheric phase from azimuth offset method suggests that the residual phase contribution in the azimuth offset and interferometric phase images is a limitation when using the azimuth offset to mitigate the ionospheric effect on SAR interferometry. This study may provide useful information when using these two methods to mitigate the ionospheric phase delay error on InSAR.

Design and experimental evaluation of feedforward controller integrating filtered-x LMS algorithm with applications to electro-hydraulic force control systems

The control purpose of an electro-hydraulic force control (EHFC) system is to real time replicate the force exerted on a structure in laboratory so as to simulate loads that cannot otherwise be generated naturally. In contrast to electro-hydraulic position control system, the tracking performance of EHFC system is always limited. To enhance the force replication accuracy of EHFC systems, a feedforward inverse controller integrating filtered-x LMS adaptive algorithm is presented in this paper. The proposed controller comprises a feedforward inverse controller and an adaptive controller. The feedforward inverse controller working as an inner loop is firstly established by directly cascading the designed parametric inverse transfer function to the EHFC system with proportional integral controller and the inverse transfer function is obtained with the implementation of system identification and zero magnitude error tracking technology. Then, the adaptive controller employing the filtered-x LMS algorithm acting as an outer loop is further combined with the feedforward controller to deal with the error occurred in the inverse model design procedure. Therefore, the proposed controller is an easy-to-implement strategy and can effectively enhance the force replication performance for both phase delay errors and amplitude mismatch errors. Finally, a series of experiments are carried out on a real EHFC test rig by means of xPC target technology, and the experimental results indicate that the proposed controller has a relatively better tracking accuracy compared with the proportional integral controller and the feedforward controller. It is also worth noting that the proposed controller can also be extended to other servo control systems where high accuracy tracking performance is required.

최적화 기법을 이용한 두 개의 회전하는 사분파장판으로 구성된 타원편광분석기에서의 체계적인 오차 보정

두 개의 회전하는 사분파장판으로 구성된 타원편광분석기의 체계적인 오차를 보정하는 방법을 연구하고 이를 실증하였다. 두개의 사분파장판으로 구성된 타원편광분석기의 5가지 오차(두 개의 회전 사분파장판들의 회전 시작 각도 오차 및 상 지연 값의 오차, 그리고 편광 분석기의 정렬 각도 오차)를 근사 과정 없이 계산하기 위하여 시료가 없이 타원편광신호를 얻고 이로부터 25개의 퓨리에 성분을 추출하였다. 25개의 퓨리에 계수에서 관련된 11개의 성분만 이용하여 상호 비선형적으로 얽혀 있는 5개의 값을 비선형 최적화 방법으로 구할 수 있었다. 오차 보정 결과 회전광소자들의 정렬 각도 오차(<TEX>${\epsilon}_3$</TEX>, <TEX>${\epsilon}_4$</TEX>, <TEX>${\epsilon}_5$</TEX>)가 위상지연 오차(<TEX>${\epsilon}_1$</TEX>, <TEX>${\epsilon}_2$</TEX>)보다 더 중요하며, 모든 오차에서 0.05 rad 이하의 정밀도를 지니면 충분히 그 오차를 보정할 수 있다는 것을 확인할 수 있었다. 최종적으로는 이렇게 구한 광학계의 초기 정렬 오차 값을 미지의 광학 부품에 적용하여 미지의 광학부품의 위상 지연의 양과 빠른 축을 알 수 있었다. 오차 보정 검증을 위하여 미지의 샘플로 반파장판을 이용하였으며, 반파장판의 위상 지연 양과 빠른 축을 찾을 수 있었다. We have studied and demonstrated general, systematic error-correction methods for a dual rotating quarter-wave plate ellipsometer. To estimate and correct 5 systematic error sources (three offset angles and two unexpected retarder phase delays), we used 11 of the 25 Fourier components of the ellipsometry signal obtained in the absence of an optical sample. Using these 11 Fourier components, we can determine the errors from the 5 sources with nonlinear optimization methods. We found systematic errors <TEX>${\epsilon}_3$</TEX>, <TEX>${\epsilon}_4$</TEX>, <TEX>${\epsilon}_5$</TEX>) are more sensitive to the inverted Mueller matrix than retarder phase delay errors (<TEX>${\epsilon}_1$</TEX>, <TEX>${\epsilon}_2$</TEX>) because of their small condition numbers. To correct these systematic errors we have found that error of any variety must be less than 0.05 rad. Finally, we can use the magnitudes of these errors to correct the Mueller matrix of optical components. From our experimental ellipsometry signals, we can measure phase delay and the rotational angular position of its fast axis for a half-wave plate.

Baekdusan Volcano Time-Series Analysis from 1992 to 1998 Using Multi-Interferogram InSAR Processing

A multi-temporal SAR interferometry (InSAR) method was applied to a time-series analysis of the period from 1992-1998 to detect precursor volcanic activity at Baekdusan volcano, located on the border between China and North Korea. Permanent scatterers were selected for stable signal processing to monitor ground motion using the permanent scatterer InSAR (PSIn-SAR) technique, which generated a time-series surface deformation map using the refined small baseline subset (SBAS) InSAR method. The time-series analysis results were verified using a multi-track comparison technique for two different tracks (88/230 and 89/230). The time-series analysis of the two tracks represents an unaltered phase signal (mm scale) with time, except for periods with insufficient interferograms to make a precise time-series surface deformation map due to factors including atmospheric phase delay and other error effects (i.e., those that display a maximum value of the phase difference from -2.14 to +2.64 cm). These phase signals also have the Root Mean Square Error (RMSE) range from 0.32-2.56 cm. No surface deformation was detected from the Japanese Earth Resources Satellites (JERS-1) synthetic aperture radar (SAR) data collected between 1992-1998 at the Baekdusan volcano, as monitored using volcanic surface movements with dynamic magma activity. No volcanic eruption precursor signals were demonstrated during the inactive period (1992-1998) prior to the active period (2002-2006) of this volcano.

고차 구성의 개선된 직류 옵셋 제거 필터

Fault currents are expressed as a combination of harmonic components and exponentially decaying DC offset components, during the occurrence of fault in power system. The DC offset components are included, when the voltage phase angle of fault inception is closer to or . The digital protection relay should be detected quickly and accurately during the faults, despite of the distortions of relaying signal by these components. It is very important to implement the robust protection algorithm, that is not affected by DC offset and harmonic components, because most relaying algorithms extract the fundamental frequency component from distorted relaying signal. So, In order to high performance in relaying, advanced DC offset removal filter is required. In this paper, a new DC offset removal filter, which is no need to preset a time constant of power system and accurately estimate the DC offset components with one cycle of data, is proposed, and compared with the other filter. In order to verify performance of the filter, we used collecting the current signals after synchronous machine modeling by ATPDraw5.7p4 software. The results of simulation, the proposed DC offset removal filter do not need any prior information, the phase delay and gain error were not occurred.

Practical solutions for reliable triple probe measurements in magnetized plasmas

The triple probe method to obtain local, time-resolved measurements of density, electron temperature and plasma potential is investigated in detail. The difficulties in obtaining reliable measurements with this technique are discussed and overcome. These include phase delay errors, ion sheath expansion and limited bandwidth due to stray capacitance to ground. In particular, a relatively simple electronic circuit is described to strongly reduce stray capacitance. Measurements with the triple probe are presented in a plasma characterized by interchange-driven turbulence in the TORPEX device. The measured time-averaged and time-dependent, conditionally averaged parameters are cross-checked with other Langmuir probe based techniques, and show good agreement. Triple probe measurements show that electron temperature fluctuations are sufficiently large, such that the identification of plasma potential fluctuations with fluctuations of the floating potential is not a good approximation. Over a large radial region, the time-averaged fluctuation-induced particle flux can, however, be deduced from floating potential only. This is because the phase shift between density and electron temperature is close to zero there and temperature fluctuations do not give rise to a net radial particle transport.

New Demodulation Method for Efficient Phase-Rotation-Based Beamforming

In this paper, we present a new demodulation method to reduce hardware complexity in phase-rotation-based beamforming. Due to its low sensitivity to phase delay errors, quadrature demodulation, which consists of mixing and lowpass filtering, is commonly used in ultrasound machines. However, because it requires two lowpass filters for each channel to remove harmonics after mixing, the direct use of quadrature demodulation is computationally expensive. To alleviate the high computational requirement in quadrature demodulation, we have developed a two-stage demodulation technique in which dynamic receive focusing is performed on the mixed signal instead of the complex baseband signal. Harmonics then are suppressed by using only two lowpass filters. When the number of channels is 32, the proposed two-stage demodulation reduces the necessary number of multiplications and additions for phase-rotation beamforming by 82.7% and 88.2%, respectively, compared to using quadrature demodulation. We have found from simulation and phantom studies that the proposed method does not incur any significant degradation in image quality in terms of axial and lateral resolution. These preliminary results indicate that the proposed two-stage demodulation method could contribute to significantly reducing the hardware complexity in phase-rotation-based beamforming while providing comparable image quality.

New demodulation filter in digital phase rotation beamforming

In this paper, we present a new quadrature demodulation filter to reduce hardware complexity in digital phase rotation beamforming. Due to its low sensitivity to phase delay errors, digital quadrature demodulation is commonly used in ultrasound machines. However, since it requires two lowpass filters for each channel to remove harmonics, the direct use of conventional finite impulse response (FIR) filters in ultrasound machines is computationally expensive and burdensome. In our new method, an efficient multi-stage uniform coefficient (MSUC) filter is utilized to remove harmonic components in phase rotation beamforming. In comparison with the directly implemented FIR (DI-FIR) and the previously-proposed signed-power-of-two FIR (SPOT-FIR) lowpass filters, the proposed MSUC filter reduces the necessary hardware resources by 93.9% and 83.9%, respectively. In simulation, the MSUC filter shows a negligible degradation in image quality. The proposed method resulted in comparable spatial and contrast resolution to the DI-FIR approach in the phantom study. These preliminary results indicate that the proposed quadrature demodulation filtering method could significantly reduce the hardware complexity in phase rotation beamforming while maintaining comparable image quality.

A new improvement to the Powell and Chau linear phase IIR filters

An improvement to the realization of the linear-phase IIR filters is described. It is based on the rearrangement of the numerator polynomials of the IIR filter functions that are used in the real-time realizations proposed in literature. The new realization has better total harmonic distortion when a sine input is used, and it has smaller phase and group delay errors due to finite section length.

Correction of intensity-dependent phase delay in avalanche photodiodes for high-frequency modulation light

The output characteristics of an avalanche photodiode show an unwanted dependence on incident light intensity. For intensity modulated inputs, the corresponding signal delay in the diode output increases with decrease in the incident intensity. This characteristic leads to errors in distance measurements where the optical modulation method is employed. Such phase delay errors can be corrected by applying an optical dc bias into the modulated optical input. When the bias intensity is adjusted to make the mean diode output current constant at all times, the resultant phase value becomes independent of the intensity of modulated input.

A new scheme for Langmuir probe measurement of transport and electron temperature fluctuations

A new scheme to extend the triple Langmuir probe technique for the measurement of electron temperature fluctuations and the fluctuation-driven transport has been developed. The extension is aimed at reducing the phase delay error introduced by finite probe tip separations in standard triple-probe method. The modified triple-probe scheme provides a more reliable measurement of the temperature fluctuations for a proper interpretation of the density and potential fluctuations and the transport measurement from Langmuir probe data. New results on fluctuations have been obtained from Phaedrus-T and TEXT-U tokamaks.