Differential Phase Measurements Research Articles

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

Context. Young stellar objects are thought to accrete material from their circumstellar disks through their strong stellar magnetospheres. Aims. We aim to directly probe the magnetospheric accretion region on a scale of a few 0.01 au in a young stellar system using long-baseline optical interferometry. Methods. We observed the pre-transitional disk system DoAr 44 with VLTI/GRAVITY on two consecutive nights in the K-band. We computed interferometric visibilities and phases in the continuum and in the Brγ line in order to constrain the extent and geometry of the emitting regions. Results. We resolve the continuum emission of the inner dusty disk and measure a half-flux radius of 0.14 au. We derive the inclination and position angle of the inner disk, which provides direct evidence that the inner and outer disks are misaligned in this pre-transitional system. This may account for the shadows previously detected in the outer disk. We show that Brγ emission arises from an even more compact region than the inner disk, with an upper limit of 0.047 au (~5 R⋆). Differential phase measurements between the Brγ line and the continuum allow us to measure the astrometric displacement of the Brγ line-emitting region relative to the continuum on a scale of a few tens of microarcsec, corresponding to a fraction of the stellar radius. Conclusions. Our results can be accounted for by a simple geometric model where the Brγ line emission arises from a compact region interior to the inner disk edge, on a scale of a few stellar radii, fully consistent with the concept of magnetospheric accretion process in low-mass young stellar systems.

Neural magnetic field dependent fMRI toward direct functional connectivity measurements: A phantom study

Recently, the main issue in neuroscience has been the imaging of the functional connectivity in the brain. No modality that can measure functional connectivity directly, however, has been developed yet. Here, we show the novel MRI sequence, called the partial spinlock sequence toward direct measurements of functional connectivity. This study investigates a probable measurement of phase differences directly associated with functional connectivity. By employing partial spinlock imaging, the neural magnetic field might influence the magnetic resonance signals. Using simulation and phantom studies to model the neural magnetic fields, we showed that magnetic resonance signals vary depending on the phase of an externally applied oscillating magnetic field with non-right flip angles. These results suggest that the partial spinlock sequence is a promising modality for functional connectivity measurements.

Detecting Hazardous Spatial Gradients at Satellite Acquisition in GBAS

In this article, we develop a ground monitor capable of detecting anomalous signal-in-space spatial gradients for rising, newly acquired, and reacquired satellites in the ground-based augmentation system using either single or dual frequency. These gradients can be caused by satellite orbit ephemeris faults and ionospheric fronts. The monitor utilizes differential code and carrier phase measurements across multiple reference receiver antennas as the basis for detection. We show that the new monitor significantly improves performance over existing detection algorithms and is capable of meeting Category III precision approach and landing requirements.

A new sliding discrete Fourier transform phase difference measurement method for extreme frequency signals.

While there are many ultralow frequency signals and ultrahigh frequency signals in the vibration engineering field, the existing discrete Fourier transform (DFT) spectrum analysis methods bring about significant phase difference errors when measuring these extreme frequency signals. In order to improve the performance of these methods, a new sliding DFT phase difference measurement method for extreme frequency signals is proposed. First, the spectrum of extreme frequency signals is analyzed, which is used to illuminate the contribution of negative frequency. Then, the spectrum leakage is restrained by adopting rectangular self-convolution windows (RSCWs). Finally, the sliding recursive algorithm is introduced to reduce the computational load. The whole processes of formula derivation for phase difference measurement by adopting different RSCWs are described in detail. Simulations show that the proposed method obtains a better real time characteristic and a higher phase difference measurement precision than conventional DFT methods, which is suitable especially for extreme frequency vibration signals.

Air-writing via Receiver Array Based Ultrasonic Source Localization

Air-writing systems have recently been proposed as tools for human-machine interaction where instructions can be represented using letters or digits written in the air. Different technologies have been used to realize air-writing systems. In this article, we propose an air-writing system using acoustic waves. The proposed system consists of two components: a motion-tracking component and a text recognition component. For motion tracking, we utilize direction-of-arrival (DOA) information. An ultrasonic receiver array tracks the motion of a wearable ultrasonic transmitter by observing the change in the DOA of the signals. We propose a novel 2-D DOA estimation algorithm that can track the change in the direction of the transmitter using measured phase differences between the receiver array elements. The proposed phase-difference projection (PDP) algorithm can provide accurate tracking with a three-sensor receiver array. The motion-tracking information is passed next for text recognition. To this end, and in order to strike the desired balance between flexibility, processing speed, and accuracy, a training-free order-restricted matching (ORM) classifier is designed. The proposed air-writing system, which combines the proposed DOA estimation and text recognition algorithms, achieves a letter classification accuracy of 96.31%. The utility, processing time, and classification accuracy are compared with four training-free classifiers and two machine learning classifiers to demonstrate the efficiency of the proposed system.

Phase Difference Measurement of Under-Sampled Sinusoidal Signals for InSAR System Phase Error Calibration.

Phase difference measurement of sinusoidal signals can be used for phase error calibration of the spaceborne single-pass interferometric synthetic aperture radar (InSAR) system. However, there are currently very few papers devoted to the discussion of phase difference measurement of high-frequency internal calibration signals of the InSAR system, especially the discussion of sampling frequency selection and the corresponding measuring method when the high-frequency signals are sampled under the under-sampling condition. To solve this problem, a phase difference measurement method for high-frequency sinusoidal signals is proposed, and the corresponding sampling frequency selection criteria under the under-sampling condition is determined. First, according to the selection criteria, the appropriate under-sampling frequency was chosen to sample the two sinusoidal signals with the same frequency. Then, the sampled signals were filtered by limited recursive average filtering (LRAF) and coherently accumulated in the cycle of the baseband signal. Third, the filtered and accumulated signals were used to calculate the phase difference of the two sinusoidal signals using the discrete Fourier transform (DFT), digital correlation (DC), and Hilbert transform (HT)-based methods. Lastly, the measurement accuracy of the three methods were compared respectively by different simulation experiments. Theoretical analysis and experiments verified the effectiveness of the proposed method for the phase error calibration of the InSAR system.

Measurement for Phase Difference Rate without Phase Ambiguity

Firstly, the direction finding solution at the midpoint of a single base array is given for the purpose of this paper and the several functions relation between phase and frequency is also described. Then, the expression of phase difference rate is described based on the multichannel phase difference measurement. With stripping time difference item correspond to the baseline length from phase difference rate, a function is extracted which signifies the differential characteristics of wavelength integer and phase difference in a unit of length. Simulation calculation found that the variation of differential function of path difference in a unit of length is very regular. The corresponding corrected value can is determine directly by distinguishing the range of differential item of phase difference obtained by actual measurement. Thus, the function expression can be obtained that is equivalence with the quondam differential function of path difference and that is nothing to do with the difference item of wavelength integer. On this basic, several parameters are analyzed by using the method of phase difference measurement without phase ambiguity. The research results in this paper may provide a powerful technical support for engineering practical design related to the phase measuring.

An accurate ultrasonic wind speed and direction measuring method by combining time-difference and phase-difference measurement using coded pulses combination

In this paper, a high-precision and large-range wind speed and direction measuring method is proposed, which can solve the problem that traditional Time of Flight (ToF) method and phase detection method cannot simultaneously take into account measuring accuracy and measurement range. Firstly, based on the binary amplitude modulation and cross-correlation algorithms, the coded pulses combination is designed to measure time difference that the ultrasonic wave arrives different ultrasonic receivers. Because the coded pulses combination can obtain sharper correlation peaks, a more accurate time-difference measurement result can be gained, comparing with the traditional ToF method. Then, for further improving measuring accuracy and resolution of wind speed, a high-precision ±180° digital phase detection method based on double D flip-flops is proposed. Next, by combining time-difference and phase-difference measurement results, the measuring range of wind speed is extended and measuring accuracy is improved. Finally, a wind speed and direction measuring system is set up based on the proposed method. The experimental results show that the wind speed measuring accuracy is ±2%, the resolution is 0.05 m/s and the measurement range can theoretically reach several hundred meters per second; the wind direction measuring accuracy is ±5° and the resolution is 0.5°. At the same time, the standard deviations of the experimental results which are less than 10% demonstrate the stability of the system.

Extreme Probabilistic Characteristics of the Measurement Disambiguation in Multiscale Phase-Measuring Systems

We determine the upper limit on the correct measurement disambiguation probability in multiscale phase-measuring systems in which all scales are ambiguous. The measured value is estimated by the maximum likelihood method from the total of measured phase differences supplemented by an algorithm for rejecting (erasing) measurement results with anomalously large errors. Errors that exceed one-half of the main lobe of the likelihood function are considered anormalously large. The results are obtained by the methods of linear algebra with a geometric interpretation of the measurement disambiguation process in the space of total phase differences. The method was applied to phase direction finders, but can easily be adapted to other types of multiscale phase radio systems.

Direct digitalized phase comparison between signals with different nominal frequencies

In this paper, the direct digitalized phase comparison which has phase continuous and high resolution is proposed to measure the phase variation of the high-precision frequency standard with different nominal frequencies. During the least common multiple period, the phase difference between the two comparison signals is regular, therefore the phase comparison between arbitrary frequency signals is achieved directly through using a high-speed analog-to-digital converter as the counter and the equivalent phase-detecter. By experiments and analysis, it was shown that no-interval frequency measurement can be converted into the phase difference measurement and the frequency stability evaluated as the Allan deviation accords with the change law of 1/τ.

3-D Hemorrhage Imaging by Cambered Magnetic Induction Tomography

Magnetic induction tomography (MIT) is a promising imaging technique for hemorrhage detection due to the features of initial diagnosis and continuous monitoring. The dispersed nature of the electromagnetic field makes the MIT difficult to image the intraaxial hemorrhage. An open cambered MIT was proposed to improve the sensitivity of extraaxial hemorrhage which is located 14–20 mm below the scalp. Realistic head models with different hemorrhage volumes and positions are used for simulation. The imaging performance of the cambered MIT is compared with the cylindrical MIT based on the time-difference and frequency-difference imaging methods, respectively. Different levels of noise (standard deviation of phase difference at 0.5 and 0.75 m°) were added to the phase difference measurements of time difference at 1 MHz. 3-D images were reconstructed by the single-step Tikhonov regularization method. Two factors of correlation coefficient $r_{\mathrm{ pd}}$ and localization error $L_{e}$ are introduced to assess the quality of the images. The results show that the cambered MIT obtains a better imaging performance of extraaxial hemorrhage than cylindrical MIT. In particular, for the hemorrhage of 7 mL at the lower position by time-difference imaging, $r_{\mathrm{ pd}}$ of the cambered MIT is increased by 42.3% and $L_{e}$ is reduced by 37.7% relative to the cylindrical MIT. The cambered MIT obtained twice the signal-to-noise ratio of phase difference for the frequency-difference method than the cylindrical MIT. The cambered MIT improves the sensitivity of near-subsurface locations, which provides a high resolution and portable way to monitor the extraaxial hemorrhage.

A phase difference measurement method based on strong tracking filter for Coriolis mass flowmeter

In order to improve the measurement accuracy of Coriolis mass flowmeters, this paper investigates the possible application of a strong tracking filter during signal processing. Specifically, a novel phase difference measurement method, based on a strong tracking filter for Coriolis mass flowmeters, is proposed in order to overcome the problems associated with the extended Kalman filters, which cannot accurately track time-varying phase differences. Compared with the existing methods, the proposed method can continuously track phase difference variation with high precision. The proposed method is a parallel algorithm that does not need to predict signal frequency in advance; this can effectively eliminate the quadratic error associated with frequency estimation. The results of simulation and experiments verify the proposed method that has better estimation performance and enhances the anti-interference performance of phase difference estimation, which contributes to improving the measurement accuracy of Coriolis mass flowmeters.

A New Phase Difference Measurement System With Differential AC/Single-Ended DC Switching for One TVC

This paper describes a new phase difference measurement system based on the three-voltmeter method (3VM) by introducing differential ac/single-ended dc switching for a thermal voltage converter (TVC). The 3VM-based phase difference measurement system has been developed in consideration of the simulation results and the loading effects derived from the TVC. The expanded uncertainties of differential voltage and phase difference measurements have been estimated (e.g., $80~\mu \text{V}$ and 0.0073° at 10 V/1 V, 1 kHz, and 60°). The phase difference measurement uncertainties of two voltage conditions ( $V_{1} > V_{2}$ and $V_{1} = V_{2}$ ) have been focused and theoretically formulated. The phase difference measurements by the system have been made in the voltage range of 1 to 10 V at 1 kHz and 60°. The measurement results agree well with those obtained by a phase standard.

Simulation of optical vortex measurement for out-of-plane displacement by using fringe-based optical-flow

Fringe-based optical flow is a novel method for measuring the deformation of an object with a high sensitivity. When it is used for out-of-plane displacement measurement, there would be greatly error in low fringe-frequency area. To solve the problem, a new method is proposed, in which an optical vortex beam is used as the object light and a spherical wave as the reference light in double-optical-path interferometry. The interference system and principle are introduced. Some simulations are completed. The results show that there is an unmeasurable area with the circular closed fringe patterns formed by two plane waves. But with the non-closed circular fringe patterns formed by the OV object light and the spherical wave reference light, the measured phase differences are in good agreement with the standard values. And then the measurement errors would be decreased greatly. Besides, the method by using patterns obtained by the interference of an OV light and a spherical wave have a certain degree of anti-noise performance.

Uncertainty in Retrieving Raindrop Size Distribution from Polarimetric Radar Measurements

AbstractDrop size distribution (DSD) is a fundamental parameter in rain microphysics. Retrieving DSDs from polarimetric radar measurements extends the capabilities of rain microphysics research and quantitative precipitation estimation. In this study, issues in rain DSD retrieval were studied with simulated and measured data. It was found that a three-parameter gamma distribution model was not suitable for directly retrieving DSD from polarimetric radar measurements. A statistical constraint, such as the shape–slope relation used in the constrained-gamma (C-G) distribution model, helped to reduce the uncertainties and errors in the retrieval. The inclusion of specific differential phase (KDP) measurements resulted in more accurate DSD retrieval and rain physical parameter estimation if the measurement errors were properly characterized in the error minimization analysis (EMA), which was verified using two real precipitation events. The study demonstrated the potential of using full polarimetric radar measurements to improve rain DSD retrieval.

A Phase Difference Measurement Method Based on the Extended Kalman Filter for Coriolis Mass Flowmeters

Abstract According to the characteristics of stable single-phase flow, a phase difference measurement method based on the extended Kalman filter is proposed in this paper for use with Coriolis mass flowmeters. Firstly, the Mallat algorithm is applied to filter out interference signals. Then, the frequency and phase difference of the two reconstructed signals are detected through the extended Kalman filter. Compared with the sliding Goertzel algorithm or discrete time Fourier transform, the proposed method does not need to predict the signal frequency and avoids quadratic error. Simulations and experiments show that the proposed method has stronger anti-interference, higher measurement accuracy and lower relative error than the existing method based on the Hilbert transformation.

A new calibration implementation for Doppler Coherence Imaging Spectroscopy

A new widely tunable, continuous-wave laser named C-Wave enables direct calibration at the unshifted, center-of-mass wavelength for most plasma lines in the range between 450 and 650 nm for Doppler Coherence Imaging Spectroscopy. It also provides the ability to scan around each desired wavelength over a small range of ±50pm, thus enabling an easy way to translate the measured phase difference ΔΦ of the diagnostic to the desired Doppler line shift Δλ, that corresponds to the physical parameter of interest, the particle velocity of an observed plasma species.A first wavelength scan of the C-Wave laser ±50pm around a single plasma line of interest, C III at 464.881 nm, is presented and compared to a simulated wavelength scan. It demonstrates not only the C-Wave capability as a Doppler CIS calibration source, but also its potential to immensely simplify Doppler CIS analysis for nearly all visible plasma lines of interest.

Passive Localisation Using a Blind Interferometer on a Single UAV

This paper considers the problem of passive location using an interferometer on a single UAV. In conventional algorithm both measurements of baseline vector and initial phase difference are necessary to locate the target, which reduces the reliability of location system for the fact that the measurements may be polluted by noise or almost unavailable in practice. Therefore, a novel target location method without using the measurements of baseline vector and initial phase difference is proposed in this paper. Simulation results show that the proposed algorithm performs better than conventional algorithm when the measurements noise is relatively large.

On-Chip Static Phase Difference Measurement Circuit With Gain and Offset Calibration

A gain and offset-calibrated 3-state phase detector is proposed to accurately measure static phase difference. Forcing the phase detector to operate in two different modes provides the full-scalegain since the sum of the two results is ${2}{\pi }$ . Flipping the inputs and averaging the results cancels the offset. Proposed circuit enhancements realize a robust reset and a gain, independent of waveform rise/fall times. A $0.13-\boldsymbol {\mu }\text{m}$ CMOS prototype of the proposed enhanced phase detector has errors ≤ 0.5° for 2.4-GHz quadrature inputs. It consumes 3.6mA from 1.2V and occupies 0.0416 mm2. The proposed circuit can be used for on-chip measurement and calibration of multi-phase clock generators in radios and clocking circuits.

Development of a Miniaturized Frequency Standard Comparator Based on FPGA

Frequency standard comparison measurement has important practical significance for the rational use of frequency standard in engineering. This paper was devoted to the study of frequency standard comparison measurement based on classical dual mixing time difference method. However, in the actual system design and implementation, the commonly used counter was discarded and the phase difference was measured by a digital signal processing method based on Field Programmable Gate Array (FPGA). A miniaturized 10 MHz frequency standard comparator with good noise floor was successfully developed. The size of the prototype circuit board is only about 292.1 cm2. The experimental results showed that the noise floor of the frequency standard comparator was typically better than 7.50 × 10-12/s, and its relative error of phase difference measurement was less than 1.70 × 10-5.