Phase Difference Research Articles

Hybrid Coupler Used as Tunable Phase Shifter Based on Varactor Diodes

This paper describes the design of a hybrid coupler with a continuously variable output phase difference. This is achieved by using reconfigurable transmission lines with electrically tunable lengths controlled by two biasing voltages through varactor diodes placed across the coupler branches. The design of the coupler is based on the quadrature hybrid structure for the case where the output phase difference is 90° and on the asymmetric structure for the other cases. The proposed coupler can achieve a tunable output phase difference from 52° to 128°, while keeping a coupling coefficient of −3 dB (± 0.5 dB) over the entire desired frequency band. To validate the simulated results, a prototype working at 3.5 GHz was fabricated and tested. The measurement results show good correspondence with the simulation results, especially when the output phase difference is 90°, while a phase mismatch of less than 7° was observed for the other cases. The presented coupler would be a great asset for antenna feeding arrays, especially the Butler matrix.

Dynamics of the energy spectrum of solar-diural variations in the intensity of cosmic rays in 22–25 cycles of solar activity

Periodic 24-hour variations in the intensity of galactic cosmic rays, continuously observed by ground-based detectors, are called solar diurnal variations. The nature of these variations lies in the existence in the interplanetary medium of an anisotropic spatial distribution of galactic cosmic rays, which arises during the interaction of these particles with the heliosphere. It is believed that the physical factors responsible for the observed anisotropy of galactic cosmic rays are the processes of convection, diffusion and their drift. The combination of these factors determines the main parameters of solar diurnal variations, such as amplitude, phase and energy spectrum. To study the energy spectrum of solar-diurnal variations, we used measurement data from muon telescopes of the Yakutsk Cosmic Ray Spectrograph after A.I. Kuzmin and Nagoya stations (Japan). The research approach is based on the idea of the crossed telescope method, originally designed to take into account the temperature effect. Due to the difference in the receiving characteristics of the crossed northern and southern directions of the above muon telescopes, the intensity variations recorded by them are sensitive to changes in the energy spectrum of solar-diurnal variations. This property was used to assess the dynamics of the energy spectrum of solar-diurnal variations for 22–25 cycles of solar activity. Analysis of the data obtained showed that in the last minimum of solar activity in 2018-2021. An anomalously early phase of solar-diurnal variations was observed. To study this phenomenon, we simulated the ratio and phase difference of a pair of northern and southern crossed directions for both muon telescopes for different types and values of the energy spectrum of solar-diurnal variations. A comparison of model calculations and observational data has made it possible to establish that during periods of minimum solar activity in the positive polarity of the general magnetic field of the Sun, a significant softening of the energy spectrum of solar-diurnal variations is observed. The reasons for the discovered phenomenon are discussed.

Terahertz reflective metasurfaces realize wavefront modulation of circular polarization channels

The emergence of many efficient optical field modulation methods and planar optical devices is attributed to the continuous research of geometric phase. Nevertheless, conjugate symmetry of the geometric phase limits the multiplexing of metasurfaces. To overcome this limitation, integrating the propagation phase and the geometric phase to achieve self-decouped metasurfaces can effectively double channel capacity. Herein, a more in-depth derivation of Jones matrices is conducted, leveraging two degrees of freedom offered by the propagation phase and the geometric phase. This approach enables complete modulation in circular polarization channels. By designing the phase difference between a fast axis and a slow axis, energy allocation between different channels can be controlled. It means independent complex amplitude modulation is achieved. On this basis, the geometric phase is introduced to realize tri-channel multiplexing metasurfaces. To verify the feasibility of this method, two metasurfaces are designed, including a bifocal metasurface with adjustable energy allocation and a tri-channel multiplexing metasurface. The proposed multifunctional metasurface offers new insights into wavefront multiplexing for communication systems.

Photonic-assisted RF phase difference detector with full 0° to 360° phase detection capability

A microwave photonic structure for detecting the phase difference of two radio frequency (RF) signals is presented. It is capable of determining the RF signal phase difference unambiguously over the full 0° to 360° range, which overcomes the 0° to 180° phase detection range limitation in the reported structures. The proposed RF phase detector is designed to generate two DC voltages with amplitudes depending on the phase difference of the two input RF signals. An RF signal phase difference in the 0° to 360° range can be obtained from the ratio of the two system output DC voltages. The proposed RF phase detector has a wide operating frequency range, as it is free of microwave components. It overcomes the drawbacks of complex structures, large phase detection errors, limited phase detection range, and limited operating frequency range in the reported photonics-based RF phase detectors. Experimental results are presented that demonstrate 0° to 360° phase difference detection with errors below ±3∘ for different input RF signal frequencies.

Measurement insights and error analysis of electronic parameters for ultrasonic transducers

Abstract Piezoelectric ultrasonic transducers with the function of energy conversation, as well as their numerous advantages in high-power density, quick response, flexible design, and service reliability, are involved in wide applications of industrial processing, precision driving, smart sensing, and medical services. The electromechanical equivalent circuit and Kirchhoff’s law indicate that mechatronics parameters are essential for performance evaluation, reliability analysis, and fault diagnosis of ultrasonic transducers. Importantly, the ultrasonic transducer is a time-variant system, data of one single parameter collected from a certain test cannot match with the data of another single parameter acquired from a different test. So, a synchronous and precise online measurement of electronic parameters is encouraged for performance evaluation and optimization design of ultrasonic transducers. With the combination of virtual instrument technology, an asynchronous measurement system of electrical excitation parameters for the ultrasonic transducers of linear driving motors was established in this study. Furthermore, the systematic measurement methods and error theory were illustrated, including the calculation methods and measuring circuits of electric signals. Experimental results proved that the proposed system and methods for measuring the input electronic power of ultrasonic transducer (e.g. effective value method for voltage and current, energy moment method for frequency, and spectrum analysis method for phase difference) are highly precise, quickly responsive, robust, and reliable for ultrasonic transducers. The findings of this study provide valuable references and suggestions for efficient, accurate, and online performance evaluation of ultrasonic transducers, particularly for piezoelectric transducers utilizing ultrasonic high-voltage exciting signals.

Gender-related differences in kinematic parameters of the start and performance in a 50m breaststroke swimming

Introduction: In swimming, the competitions are divided by age categories, with each swimming event beginning at the start. For optimal improvements in swimming performance in the sprint events, the performance at the start and during swimming in each age category should be analyzed. Aim: The aim of our study is to show the differences in kinematic parameters of the start and performance in the sprint event of 50 m breaststroke from the perspective of gender in different age groups at international competitions organized in Slovakia. Materials and Methods: The females were categorized by age into K3 (2010-2011; n=36; 282 WA points), K2 (2008-2009; n=26; 409 WA points) and K1 (2007 and older; n=34; 503 WA points) groups. Males were categorized into K3 (2009-2010; n=27; 265 WA points), K2 (2007-2008; n=33; 372 WA points) and K1 (2006 and older; n=39; 207 WA points) groups. We used SwimPro cameras and Dartgish software to monitor kinematic parameters in the above-water, underwater, and swim phases. The parameters monitored were block time (BT), time (FT), and length (FD) of flight, time (UWT) and length (UWD) underwater, swim time (ST) and distance (SD) to 15 m, time to 15 m (T15), 25 m (T25), and 50 m (T50) distance. Data were tested by Shapiro-Wilk, Kruskal-Wallis ANOVA, and Mann-Whitney U test in Statistica software (version 13.5). Results: Statistically significant differences (p<0.01) in females were found in the above-water phase in BT, FT, and FD between K3 and K1. The underwater phase in UWT showed differences between K3 to K1, K2 to K1 whereas for UWD - between K3 and K2 and between K2 and K1. For T15 and T25, there were differences (p<0.01) between all categories, but in the final time (T50), the differences occurred between K3 and K2 and between K3 and K1. In males, there was a significant difference in the above-water phase between K3 and K1 and between K2 and K1. In UWD, ST, SD, T15, T25, and T50, there were significant differences between all categories. Differences (p>0.01) between males and females by category in the above-water phase were measured in FT (K1) and FD (K2, K1). In the underwater phase, the differences were found in UWT (K2) and UWD (K1). For T15, T25, and T50, significant differences were shown in all categories. Conclusions: The kinematic analysis revealed differences not only in the start phases and the 50 m breaststroke swimming in the male and female categories but also between genders. Differences in swimming performance may be due to performance at the start and therefore more attention should be paid to the start phases in the different categories of swimmers.

Fast phase retrieval without unwrapping for 3D measurement based on digital phase difference

Phase unwrapping is still a tough task for fringe projection profilometry (FPP), due to the heavy computation burden and slow rate of the existing phase unwrapping algorithms. To speed up the retrieval of the absolute phase, a fast phase retrieval algorithm without unwrapping for 3D measurement based on digital phase difference is presented in this paper. Firstly, 4-step phase-shifting profilometry is utilized to retrieve a complex-valued map, who contains the complete phase information of the measurement object in its phase part. Instead of extracting the phase map from the complex-valued map directly, a novel complex-valued map containing the differential phase is obtained by the division between the complex-valued map and its pixel-shifted version. Then, the differential phase can be extracted from the novel complex-valued map by regular phase extraction operation easily. Finally, the absolute phase can be retrieved by integrating the differential phase along the inverse pixel-shifted direction. This proposed algorithm can retrieve the absolute phase easily and fast, while the measurement object has continuous surface with the phase variation in the range of (−π, π]. Simulated and experimental results were demonstrated to present that this algorithm has faster phase retrieval rate than existing algorithms and has no obvious jump error, which allows fast and high-quality phase retrieval.

An integrated high precision absolute angular displacement sensor

Abstract This paper proposed a high precision absolute angular displacement time grating sensor, and was assembled into an integrated encoder. This absolute angle sensor contains two incremental sensors, namely, N1 measurement period fine measurement component and N2 measurement period coarse measurement component, N1 and N2 are mutually prime, and N1 > N2. The induction electrodes of the fine measurement component adopt differential design to minimize the effects of external electromagnetic interference and common mode interference between different sensing units so as to achieve high precision displacement measurement, the phase difference between two incremental sensor is used for absolute positioning. The reflecting ring design simplifies the structure of the encoder and facilitates sensor integration. The induction output signals of different components are cross connected through leads to the reflecting ring far away from the measurement component to the first harmonic error during the measurement period. The reading heads adopt a round, uniformly distributed design scheme, and the average effect of the whole circumference closed ring sampling scheme is beneficial for improving measurement accuracy and eliminating harmonic errors. A sensor prototype with a diameter of 83mm was manufactured and assembled into an integrated encoder. Experimental results show that the sensor achieve a precision of 12" over a full 360° measurement range and a resolution of 0.5", and it can realize absolute positioning.

Associations between circadian alignment and cognitive functioning in a nationally representative sample of older adults

Proper alignment of activity-rest and light–dark patterns allows for healthy bodily functions to occur at optimal times of the day. Disruptions to this alignment may cause poor sleep as well as physical, mental, and cognitive problems. The purpose of this cross-sectional study was to determine if poorer circadian alignment was associated with decreased cognitive functioning among older (> 60 years) participants in the National Health and Nutrition Examination Survey. We utilized actigraphy-based rest-activity and dark-light measurements to calculate phasor magnitude (strength of circadian alignment coupling) and phasor angle (phase difference between activity-rest and light–dark cycles). Multiple linear regression models were used to determine associations of phasor magnitude and angle with performance in various cognitive tests, including Digit Symbol Substitution Test score (DSSS), CERAD Savings Percentage (CSP), and Animal Fluency Test (AFT) score. The results showed that a lower phasor magnitude (which indicates decreased strength of alignment coupling between rest-activity and dark–light cycles) was significantly associated with decreased DSSS (indicating slower processing speed and poorer working memory) when controlling for many important sociodemographic factors. However, this association became non-significant when accounting for sleep duration and total physical activity. Phasor angle did not have a significant association with any of the cognitive scores. Overall, we provided evidence indicating that circadian alignment may be a predictor of cognitive performance. Future studies should investigate whether improving circadian alignment may improve cognitive function and prevent cognitive decline.

Leak detection and localization in underground water supply system using thermal imaging and geophone signals through machine learning

The underground water pipeline system is a crucial infrastructure that largely remains out of sight. However, it is the source of a clean and uninterrupted flow of water for our everyday lives. Various factors, including corrosion, material degradation, ground movement, and improper maintenance, cause pipe leaks, a silent crisis that causes an estimated 39 billion dollars of loss every year. Prompt leakage detection and localization can help reduce the loss. This research investigates the potential of two machine learning models as supporting tools for surveying extensive areas to identify and pinpoint the location of underground leaks. The presented combined approach ensures the speed and accuracy of the leakage survey. The first machine learning model is a hybrid ML model that employs thermal imaging to identify subterranean water leakage. It relies on detecting thermal anomalies and distinctive signatures associated with water leakage to identify and locate underground water leakage. The developed model can detect up to 750 mm underground leakage with 95.20 % accuracy. The second model uses binaural audio from geophones to localize the leakage position. The model utilizes interaural time difference and interaural phase difference for localization purposes, and the 1D-CNN network delivers an angle in twenty-degree increments with an accuracy of 88.19 %. Large-scale implementation of the proposed model could be a powerful catalyst to reduce water loss in the water supply system.

Transient spray combustion characteristics in a gas–liquid pintle rocket engine under acoustic excitation

In order to investigate the acoustic oscillation characteristics of gas–liquid pintle rocket engines and elucidate the path by which spray combustion process provides energy to the combustor pressure oscillation, a LOX/GCH4 pintle engine with rectangular combustor was designed. By adding transverse velocity disturbance for the first time, the acoustic response of spray combustion process was simulated, and the effect of excitation amplitude on acoustic response was researched. Numerical results show that the adopted transverse velocity disturbance can excite the first-order transverse acoustic oscillation with same excitation frequency in the engine combustor. The acoustic response maintenance mechanism under extrinsic excitation is summarized for pintle engines. Besides, the temperature distribution inside the engine combustor tends to be uniform, and the low-frequency oscillation caused by the flame transverse swing gradually disappears. The amplitude of combustor pressure oscillation is dominated by excitement amplitude and phase difference between the pressure and heat release in combustion reaction region. In addition, the time-averaged combustor pressure can be amplified mainly by transverse velocity disturbance. The research work can provide a reference for related fire tests on the acoustic response of a subscale gas–liquid pintle engine.

Kinematic Modeling and Experimental Study of a Rope-Driven Bionic Fish.

This paper presents a biomimetic fish robot featuring a flexible spine driven by cables, which integrates the cable-driven mechanism with a flexible spine. The drive system separates the body and tail fin drives for control, offering enhanced flexibility and ease in achieving phase difference control between the body and tail fin movements compared to the conventional servo motor cascaded structure. A prototype of the biomimetic fish robot was developed, accompanied by the establishment of a kinematic model. Based on this model, a control method for the biomimetic fish is proposed. Additionally, we introduce the concept of prestress to establish a numerical model for the biomimetic fish. Using multi-physical field simulation software, we simulate the two-dimensional autonomous swimming process of the biomimetic fish under different flapping frequencies and solve for its swimming characteristics as well as hydrodynamic properties. Both the simulation and experimental results validate the accuracy of our kinematic model.

Single-frame double-grating interferometry with two inherent-phase-shifted interferograms

In this work, we introduce a novel self-referencing, common-path, double-grating interferometry method for studying slowly varying phase samples. Two plane wave diffraction orders of the gratings, namely (0,+1) and (+1,0), with a certain phase difference, interfere with each other in a single frame. When a phase sample is applied in the middle of the impinging beam, two simultaneous inherent phase-shifted interferograms are generated on either side of the interference pattern. In one interferogram, the sample phase is added to (0,+1), while in the second one, the sample phase is added to (+1,0). Consequently, the phase of the first interferogram increases by the amount of the sample phase, while in the second interferogram, it decreases by the same amount. Without a phase sample, both interferograms have uniform intensity and value since the two interfering beams have the same phase difference in both patterns. We observe that the intensity changes in the two interferograms due to the phase sample, depending on the initial phase difference between the two interfering beams, can be equal or unequal, and in certain circumstances, they can be even complementary. We introduce a specific phase difference between the interfering orders by precisely controlling the separation between two diffraction gratings. This allows us to extract the sample's phase information from the resulting pair of interferograms. This setup enables us to obtain the sample phase without applying an additional phase shift(s) between the interfering beams. The method was applied to a thermal lens induced in a nonlinear liquid sample containing absorbent nanoparticles. The proposed method is characterized by its simplicity, accuracy, and insensitivity to vibrations, making it well-suited for analyzing dynamic samples with millimeter scales, such as nearly transparent organisms. The theory, simulations, and experimental results presented in this paper are found to be consistent. Unlike conventional methods, our approach does not necessarily require a reference interferogram. Additionally, when the absolute value of phase changes over the sample area and time is less than π, the raw phase pattern precisely matches the reconstructed phase pattern of the sample, eliminating the need for a phase-reconstructing algorithm. The phase pattern can be accurately calculated from the interferograms using an arcsine function without needing a fast Fourier transform. Compared to Fourier-based methods, the phase extraction process for each frame in our approach is 60 times faster. As a result, this technique operates in real-time for |φ(x, y;t) | < π.

Design and validation of a miniaturized reconfigurable power divider with arbitrary power split ratio and flexible output phase difference

This study introduces a microstrip line (ML) based reconfigurable 5-port power divider (PD) capable of manipulating power ratios at four output ports. The proposed PD offers two operational modes: unidirectional and bidirectional. In unidirectional transmission mode, the entire source power is directed to a particular output port, while in bidirectional transmission mode, the source power is equally distributed between two output ports. The selection of different transmission modes is accomplished by configuring six adaptive loads that are coupled to the PD structure, and the corresponding S-parameters of the proposed PD are derived by even–odd mode modeling. The resulting data is subsequently optimized by a numerical approach to identify the required design parameters that would ensure optimal performance. The proposed PD resonates at 1.06GHz and covers a frequency range spanning 0.9GHz to 1.2GHz, making it an excellent option for supplying regulated power to multi-port antennas or multiple input multiple output (MIMO) antennas proposed for aircraft navigation applications. The prototype has been developed to validate the notion of reconfigurable reactive loads utilizing varactor diodes and the recorded result is evaluated with the simulated results. The findings confirm excellent performance with regards to insertion loss (with a difference of <-2dB from the optimal values), reflection coefficient (≥-20dB), and isolation (≥-40dB) between the transmitting (input port) and non-transmitting or the remaining ports.

High-resolution, large field-of-view label-free imaging via aberration-corrected, closed-form complex field reconstruction

Computational imaging methods empower modern microscopes to produce high-resolution, large field-of-view, aberration-free images. Fourier ptychographic microscopy can increase the space-bandwidth product of conventional microscopy, but its iterative reconstruction methods are prone to parameter selection and tend to fail under excessive aberrations. Spatial Kramers–Kronig methods can analytically reconstruct complex fields, but is limited by aberration or providing extended resolution enhancement. Here, we present APIC, a closed-form method that weds the strengths of both methods while using only NA-matching and darkfield measurements. We establish an analytical phase retrieval framework which demonstrates the feasibility of analytically reconstructing the complex field associated with darkfield measurements. APIC can retrieve complex aberrations of an imaging system with no additional hardware and avoids iterative algorithms, requiring no human-designed convergence metrics while always obtaining a closed-form complex field solution. We experimentally demonstrate that APIC gives correct reconstruction results where Fourier ptychographic microscopy fails when constrained to the same number of measurements. APIC achieves 2.8 times faster computation using image tile size of 256 (length-wise), is robust against aberrations compared to Fourier ptychographic microscopy, and capable of addressing aberrations whose maximal phase difference exceeds 3.8π when using a NA 0.25 objective in experiment.

A novel approach to the FPIBSC strategy for an electric power steering system

The electric power steering system is used to improve comfort and steering feel for the user. In this article, we propose to use an integrated nonlinear control strategy for the electric steering system, which is described based on a complicated dynamic model. This work provides two new contributions. First, this control algorithm combines backstepping and proportional–integral (PI) techniques with parameters adjusted by a fuzzy algorithm, so it is called Fuzzy proportional–integral backstepping control (FPIBSC). The output of the PI algorithm is the input of the backstepping technique, while system stability is evaluated based on the Lyapunov function with virtual control variables. Second, road reaction torque is calculated based on a spatial dynamic model, which considers the influence of many other factors. Numerical simulation methods are used to evaluate the performance of the system. According to research findings, the value of the steering motor angle (controlled object) continuously tracks the desired value with negligible error. Under some specific conditions, the error between signals can be reduced to zero. In addition, other outputs that are obtained from the FPIBSC algorithm also tend to follow the reference signal with high accuracy. The phase difference phenomenon only occurs when using the conventional backstepping algorithm instead of FPIBSC. The assisted torque increases as speed decreases or the driver torque increases. In general, the system’s stability is always guaranteed under many different simulation conditions.

Generation of near-circularly polarized high-order harmonics in two-color cross-linearly polarized laser fields

We investigate theoretically the ellipticity of the high-order harmonic generation from the molecule by utilizing two-color cross-linearly polarized laser fields. A significant region of the large ellipticity can be achieved by adjusting the crossing angle and the relative phase between the two laser fields. By controlling the short trajectory, we can obtain the smoother harmonic spectrum. The minimum value observed in the plateau region can be attributed to the two-center interference of the molecule. Furthermore, we investigate the contribution of the two-center interference to the ellipticity of HHG. The underlying physical mechanisms of the ellipticity can be demonstrated by the phase difference and amplitude difference of the x and y components of the harmonics. As a result, we synthesized an isolated attosecond pulse with an ellipticity of 0.98.

A dual-band dual-sense circularly polarized patch antenna using hybrid capacitive-inductive proximity-coupling feed

This paper presents a new proximity-coupling mechanism between a rectangular patch and a microstrip line with an open circuit terminal. The patch is located to cover both adjacent maximum-voltage (capacitive coupling) and maximum-current (inductive coupling) points of the standing wave on the feedline, and consequently, two orthogonal resonant modes with 90° phase difference are excited on the patch for generating a circularly polarized (CP) radiation. Based on this feeding mechanism, a dual-band dual-sense CP antenna is designed, which is composed of two linear rectangular patch arrays coupled to an open-ending microstrip line. It is realized on a single-layer substrate and its CP rotating sense in each band is opposite to each other. For verification, the antenna operating at 5.0 and 8.0 GHz are designed, fabricated, and tested. Noting that the design concept can be easily implemented to other frequency bands. The measurements result in an impedance-matching bandwidth of 4.72 – 5.10 GHz and 7.50 – 8.20 GHz. The antenna is left-hand CP for the lower band and right-hand CP for the upper band. In addition, the prototype shows a 3-dB axial ratio bandwidth of 4.93 – 5.02 GHz and 7.40 – 8.10 GHz and peak gains of 11.4 and 12.7 dBic at the lower and upper bands, respectively.

Photovoltaic grid-connected monitoring technology considering power quality

Abstract With the continuous expansion of grid-connected photovoltaic power generation, monitoring the power quality fluctuations in intelligent photovoltaic grid-connected systems has become a key research direction. Addressing the issues of low accuracy in voltage and current monitoring, as well as insufficient monitoring of SOE events, a comprehensive power quality-oriented detection technology for photovoltaic grid integration is proposed. This technology enables automatic monitoring of power quality fluctuations by collecting signals such as voltage deviation and frequency deviation. The study compares techniques involving a determination of input voltage and current amplitudes, power, phase difference, and SOE event design. The results demonstrate that the power quality monitoring technology for photovoltaic grid integration proposed in this study exhibits high accuracy in monitoring the imbalance of three-phase voltage and current.

Soil moisture estimation using ground scatterometer and Sentinel-1 data

Soil moisture (SM) is a crucial criterion for agronomics and the management of water resources, particularly in areas where the socio-economic status and significant source of income depend upon agriculture and related sectors. This paper intends to estimate SM over the vegetative area using a generalized regression neural network (GRNN) and ground scatterometer and compare the results with SM retrieved using Sentinel-1 data. At the same time, random forest regression (RFR) and support vector regression (SVR) models are used for SM estimation. Correlation analysis results concluded that L-band HV-polarization at 300 incidence angle showed the highest correlation with the measured field parameters. This study investigated backscattering coefficients, VV/VH polarization ratio and polarization phase difference over wheat’s entire growth phase to estimate SM. The results indicate that the GRNN with backscattering coefficients and polarization ratio provided the highest accuracy compared to the random forest (RF) and SVR with the root mean square error of 0.093 over the Yavatmal District, Maharashtra, India.