Large Phase Difference Research Articles

Phase-shifted counterpropagating atmospheric pressure plasma jets: Characterization and interaction with materials

This study investigates the interaction between two counterpropagating atmospheric pressure plasma jets when their respective streamer ignition times are varied by introducing a phase difference between the AC waveforms used to generate them. When the plasma jets are driven in phase, the streamers form at approximately the same time, resulting in a dark region between the two jets. As the phase difference increases, this dark region shifts toward one of the electrodes. With a sufficiently large phase difference, this region vanishes, giving rise to a uniform plasma channel spanning the distance between the electrodes. High-speed imaging reveals that the interaction between the streamers within the channel reduces the streamer propagation length at intermediate phase differences. At large phase differences, the propagation distance of each streamer is enhanced due to the absence of the opposing streamer. Increasing the phase from 0° to 160° reduced the power consumption of the two jets by about 10%, while there was no significant change in the electron density or the N2 vibrational/rotational temperature. Finally, we show how phase-shifting enhances the interaction with three-dimensional objects located between the opposing jets, enabling the treatment of 3D substrates.

Exploiting the temporal characteristics of tidal stream power for green ammonia production

Green ammonia, a promising zero-carbon energy storage vector, has never been produced using solely tidal stream energy despite its predictable characteristics. Combining tidal stream sites with a phase difference (tidal phasing) facilitates anticorrelation between these sites’ power profiles, enabling a more consistent power output. Green ammonia production benefits from a steady and predictable power input. The objective of this paper is to determine if nearby tidal sites have a large enough phase difference (anticorrelation) to reduce the cost of ammonia production. Moreover, producing green ammonia from underutilized or unutilized remote and grid-constrained tidal stream sites may enable viability of these sites. This paper is the first analysis of green ammonia production using solely tidal stream energy and the first analysis of tidal phasing for green fuel production. Two UK case studies are presented in i) the North Channel of the Irish Sea and ii) Orkney. There are tidal sites in each which have a phase difference (e.g. the Mull of Kintyre/Sound of Islay, and Graemsay/North Ronaldsay with correlation coefficients of 0.17 and −0.02 respectively), utilising this phase difference reduces the levelized cost of ammonia by 8% in the Irish Sea and by 12% in Orkney.

Measuring tube structure optimization of coriolis mass flowmeter with liquid hydrogen

To improve the sensitivity of the Coriolis mass flowmeter (CMF) when measuring the mass flow rate of liquid hydrogen (LH2), this study investigates and compares the performance of measuring tubes with various shapes but identical lengths. The aim is to elucidate the mechanisms how the tube shapes affect the sensitivity of the CMF. An iterative fluid-structure interaction (FSI) calculation framework is developed on the ANSYS 2021R1 platform and validated using experimental results of water on a dual U-tube CMF. By employing the orthogonal test method in conjunction with numerical analysis, the tube structure is optimized. The variables considered for optimization include the length of the vertical and horizontal tubes, as well as the radius of the curved tube. Modal characteristics are analyzed, and their influence on the measurement performance of CMF is summarized. Additionally, the Coriolis force acting along the measuring tube, which is the primary factor causing the phase difference, is extracted to explore its impact. The results demonstrate that optimizing the measuring tube structure significantly increases measurement sensitivity, resulting in a larger phase difference. Furthermore, a dimensionless parameter is identified, exhibiting a strong correlation with measurement sensitivity. This parameter can serve as an approximation method for preliminary optimization of the measuring tube, effectively reducing the complexity of fluid-structure coupling calculations. More interestingly, the results of this research also indicated that the structural optimization results of the CMF with water and LH2 as the working fluids are the same.

Investigation of Low Order Parameters Affecting Tidal Stream Energy Resource Assessments

Tidal stream energy may have the potential to contribute to the baseline energy needs of the UK. There is a significant difference between the existing assessments of the UK’s resource, highlighting the need for a standardised model. The paper investigates some challenges of quantifying tidal stream energy. This study examines the sensitivity of resource assessments to low-order parameters, in order to inform higher order modelling and contribute to defining a standardised model. A combination of channel characteristics, turbine parameters and simulation settings formed the basis of 96+ cases to determine key parameters affecting resource assessments. Two 0-dimensional, idealised channels were modelled using 2-8 constituents from four UK sites spanning the semi-diurnal form factor range. Blockage-corrected blade element momentum theory was used to represent variable-speed, variable-pitch turbines. Three blockage designed rotors and one rotor designed for an unspecified blockage were simulated. Power capping and combined power and thrust capping were implemented.
 
 The study indicates dynamic balance is a key parameter affecting tidal dynamics when turbines are present in a channel. Variability of annual energy production due to the nodal cycle was most significant in the drag dominated channel with increasing blockage. Constituents with large amplitude and phase differences led to greater variability of the resource across the nodal cycle. Results indicate that the maximum deviation from the average annual energy production over the 18.6-year nodal cycle is +/- 8.8%. At a low form factor site, the difference between using 2 or 4 constituents was insignificant. However, for a higher form factor site, that is still semi-diurnal, the peak velocity increases by 0.32 m/s with 8 constituents compared to 2. Random Forest modelling indicates that the most important characteristic point on a variable-speed, variable-pitch turbine performance curve is the rated speed. Comparison of capping strategies highlights that combined power and thrust capping leads to an increase in energy per swept area. Combined capping decreased the variability of the resource over the nodal cycle, which is helpful to maintain a steady supply to the grid and sizing energy storage systems.

Bias-Voltage-SSHI Interface Circuit for Strong Coupling Piezoelectric Energy Systems

Compared with the standard extraction interface circuit (SEH), the harvested energy and harvested power of synchronized switching harvesting interface circuits (SSHI) and synchronous charge extraction interface circuit (SECE) cannot improve more effectively. This paper proposes a Bias-Voltage-SSHI Interface Circuit (BV-SSHI), consisting of a single peak voltage detection switch and a rectifier, to solve this problem. The proposed BV-SSHI improves the output voltage by biasing the voltage of the piezoelectric energy harvester and obtains similar harvested power as SSHI. Simulation results show that the BV-SSHI can obtain more harvested energy and harvested power than SEH under weak, medium, and strong coupling systems. Results show that the higher harvester's voltage and the larger phase difference cause the electrical restoring force (χV) to significantly weaken the vibration displacement, especially under strong coupling systems. Thus, the gain effect of the SSHI and SECE is weakened. The experimental results of the medium coupling systems show that the BV-SSHI can obtain 247.2% harvested energy and 121.2% maximum harvested power compared with SEH. The BV-SSHI can achieve at least 142.4% harvested energy and 100.3% maximum harvested power compared with what SSHI and SECE can achieve.

Diffractive liquid crystal device for privacy window with a low operating voltage

We demonstrate using a diffractive smart window with homogeneous-aligned (HA) liquid crystals (LCs) owing to the large spatial phase difference in all directions in the opaque state. The proposed grating cell had a high haze value (88.57%), which was 1.16 times higher than the previously reported vertically aligned (VA) grating cells because the proposed grating cell had a higher twist angle than what the VA grating cell had. Our proposed HA grating cell can be used in various smart window applications.

Formation, evolution and remove behavior of manganese-containing inclusions in medium/high manganese steels

The effect of manganese content, aluminium content, top slag and stirring on manganese-containing inclusions characteristics was investigated by laboratory thermal experiments and precipitation thermodynamics calculation. The results indicated that the types of manganese-containing inclusions in manganese steel were mainly single MnS, MnS–Al2O3, MnS–TiN and MnS–Al2O3–TiN complex inclusions. The morphology of manganese-containing inclusions was transformed from spherical and ellipsoidal to polyhedral as result of manganese content increased, which is attributed to large solidus-liquidus phase difference of high manganese steel, promoting the formation of type III MnS. It is also found that the manganese-containing inclusions shows irregular morphology with clear angularities after addition of aluminium, which was determined by both formation of flaky AlN and type III MnS with polygonal caused by increased of activity coefficient of S and the surface tension of molten steel. Furthermore, the manganese-containing inclusions in manganese steel is considered MnS–MnO type with top salg, in which patchy or multipoint shape MnS is embedded on the surface of oxide. The force field analysis in induction stirring demonstrated that the inclusion particles are removed by top slag and refractory adsorption under the action of strong electromagnetic force and buoyancy. This work provides an improved understanding for the controlling and removing of manganese-containing inclusions in high quality medium/high manganese steel.

Third harmonic potential distribution based stator ground fault accurate location method for large generators

The stator single-phase grounding fault location of large generator can provide guidance for rapid maintenance of faults. A third harmonic potential distribution based stator ground fault accurate location method is proposed. The current location methods mainly take coil as location unit and may have location error. However, accurate locate to the slot number is more meaningful for troubleshooting. In addition, the third harmonic potential induced by adjacent slots has larger phase difference, and has more distinct fault characteristics than the fundamental potential. In this paper, the fault location optimization model is constructed based on the analysis of the distribution characteristics of the third harmonic potential. The exhaustive solution of the location model is realized by artificially setting multiple reference points, and finally the reference point closest to the real fault point is obtained. The proposed method can accurately locate the fault slot number. PSCAD simulation verifies that the proposed method is robust against the transition resistance error and has higher accuracy than the existing methods.

Efficient mode (de)multiplexer with two cascaded horizontal polymer waveguide directional couplers.

In this paper, we present an efficient polymer two-mode (de)multiplexer with two cascaded horizontal waveguide asymmetric directional couplers (ADCs). Through extensive simulations, the optimized waveguide core dimensions were determined, and the distance L from the starting position of the first ADC to the cascaded position was 35300 µm. With the cascaded ADCs, the E21x mode of the wider waveguide was coupled into the E11x mode of the narrower waveguide with a coupling ratio of 96.73% at 1550 nm when the separation between the waveguide cores was 5 µm. The coupling ratio and extinction ratio of the fabricated (de)multiplexer reached a maximum of 96.12% and 14.21 dB at 1540 nm, respectively. The coupling ratios were greater than 90% in the wavelength range 1533-1565 nm with a minimum insertion loss of 9.75 dB. The influence of different cascaded positions on the mode coupling ratio, mainly caused by the large phase difference between the modes owing to the slowly varying envelope approximation, is analyzed theoretically and verified experimentally. The proposed cascaded two-mode (de)multiplexer can reduce the preparation process requirements and increase the channel capacity of optical communication systems.

A simulation of diffractive liquid crystal smart window for privacy application

Using a single substrate, we demonstrate a simple two-dimensional (2-D) phase grating cell with an octothorp electrode. Owing to the large spatial phase difference in any direction, the proposed grating cell has a high haze value in the opaque state (76.7%); Moreover, it has the advantages of a one-dimensional (1-D) phase grating cell, such as high fabricability, fast response time, and low operating voltage. Furthermore, the proposed grating cell has a faster response time than the 2-D grating cell (comparable to a 1-D grating cell). All the electro-optic parameters have been calculated using a commercial modeling tool. Consequently, we expect our proposed grating cell to find applications in virtual reality (VR)/augmented reality (AR) systems or window displays with fast response times.

Active phase control to enhance distance relay in converter-interfaced renewable energy systems

For the distance protection applied in converter-interfaced renewable energy systems, various AC fault ride-through strategies of converter-interfaced sources will cause a large phase difference between the operating current of the distance relay and the fault current, resulting in the mal-operation of the distance relay. To overcome this issue, this paper proposes an active phase control for the converter-interfaced renewable energy systems to enhance the reliability of the distance relay. This control scheme firstly calculates the phase difference between operating current and fault current by only using local measurements. Then, the phase difference is eliminated via phase angle adjustment. To verify the effectiveness of the proposed control scheme. The performance of the proposed method is tested in a radial three-terminal system and the IEEE 14-bus system in PSCAD/EMTDC.

Research on the Relationship between Stall Propagation and Flange Leakage of Mixed-Flow Pumps

In order to explore the internal relationship between stall core propagation and flange leakage flow in the rotating stall of a mixed-flow pump, based on the k-ε turbulence model, a SIMPLEC algorithm and hexahedral structured grid are used to simulate the internal flow field of the mixed-flow pump. By setting the flange clearance as 0.2 mm, 0.5 mm and 0.8 mm, the propagation characteristics of the rotating stall and the unsteady characteristics of flange leakage flow of the mixed-flow pump under the condition of near stall are studied, and the influence of the flange clearance on the pressure fluctuation characteristics of the mixed-flow pump under the condition of near stall is analyzed. The results show that the stall core is located at the outlet of the impeller and propagates from the leading edge of the adjacent blade along the opposite direction of blade rotation to the next flow channel. The pressure gradient in the stall channel and the energy loss are large. When the flange clearance is 0.5 mm and 0.8 mm, the stall core changes from one to two, and the propagation mechanism of the stall core tends to be complex in the two adjacent flow channels. When the flange clearance is 0.8 mm, the propagation period decreases. The variation law of leakage flow is consistent with the propagation law of stall core. When the flow passage changes from stall state to non-stall state, the leakage flow also changes from one state to another, so the leakage flow can be used as a form of apparent stall. Under the condition of near stall, the pressure fluctuation curve of the adjacent monitoring points has a large phase difference consistent with the propagation period of the stall core, and has a strong pressure drop. When the flange clearance is 0.5 mm and 0.8 mm, the time domain curve of pressure fluctuation has two wave troughs in one cycle. In the near stall condition, the main frequency of the pressure fluctuation at the monitoring point is the stall frequency, and the amplitude of the main frequency at the middle of the outlet is the largest. The characteristics of flange leakage flow and pressure fluctuation can better reflect the flow situation in the pump when rotating stall occurs. The research results can provide a basis for judging whether stall occurs in the flow passage of the pump.

Wideband diffusion metabsorber for perfect scattering field reduction

Both absorption and diffuse reflection can effectively suppress microwave backward reflection. However, the challenge of designing wideband absorptive elements with anti-phase reflection hinders the simultaneous working of the two principles. With aid of the wideband characteristic of bilateral complementary structure, we propose a strategy to design wideband absorptive elements with large reflection phase differences. For proof of concept, the proposed elements are arranged in a rectangular grid by optimizing scattering field distribution. The proposed diffusion metabsorber achieves over 20-dB scattering field reduction in the range of 8.5–20.3 GHz with good polarization stability and high angular insensitivity of up to ± 40 ° , which has been verified by real experiments. Furthermore, the proposed design strategy exhibits the potential to further reduce electromagnetic wave reflection, and the optical transparent characteristic is promising for window applications.

Effect of non-uniform magnetic field on radial oscillation of electron beam in a low-magnetic-field foilless diode

A theory regarding a non-uniform magnetic field with a parallel gradient is presented. The research results show that a proper non-uniform magnetic field can greatly reduce the transverse momentum of an electron beam and even eliminate its gyration motion, and it depends on the gradient of the magnetic field and the phases of electrons entering and leaving the local magnetic field region. Thus, a magnetic field that decreases along the axial direction is proposed to suppress the radial oscillation of the electron beam. However, in the drift tube, the suppression of the radial oscillation is not obvious, because the large phase differences among electrons lead to a mismatch between the electron beam and the non-uniform magnetic field. Further studies found that the non-uniform magnetic field applied in the anode-cathode gap can not only reduce the phase differences among electrons, but also effectively transform the transverse momentum of the electron beam into its axial momentum. The results obtained by PIC simulations and experiments consistently confirm that the non-uniform magnetic field can significantly suppress the radial oscillation of the electron beam in a low-magnetic-field foilless diode.

АНАЛИЗ ПЕРЕХОДНЫХ ПРОЦЕССОВ В СИНТЕЗАТОРАХ ЧАСТОТ С РАЗЛИЧНЫМИ ХАРАКТЕРИСТИКАМИ НЕЛИНЕЙНОГО ЗВЕНА В КОНТУРЕ ФАЗОВОЙ АВТОПОДСТРОЙКОЙ ЧАСТОТЫ

Phase-locked loop (PLL) frequency synthesizers that use phase detectors (PD) with variousnonlinear transfer characteristics have been considered. The goal of this work is comparative analysisof the frequency synthesizers operation speed depending on the type of the PD nonlinearity andmathematical description of the PD nonlinear characteristic which ensure the maximum operationspeed of the frequency synthesizer. In accordance with the present goal, the following problems aresolved in this work: the generalized model of the PLL frequency synthesizer is developed; mathematicalmodels of static characteristics of the PLL system nonlinear link are described when using varioustypes of known PDs and a modified PD with aperiodic characteristic; the analysis of the PLLsystem dynamics when changing the static characteristic of the nonlinear link is carried out. Themodified PD provides relay control of transient processes when a large phase difference occurs.Numerical evaluation of the PLL synthesizers operation speed depending on the initial frequencydeviation have been obtained when using known PDs and the modified PD. It is shown that the use ofthe modified PD allows to reduce frequency settling time about 1.5 times in comparison with the bestin operation speed conventional PD. Optimal values of the control signal ensuring the maximumoperation speed of the PLL synthesizer with the modified PD have been obtained for the specifiedfrequency deviations in the large disturbance mode. The results of this work are valid for PLL frequencysynthesizers of the UHF, L, S and C-bands (from 300 MHz to 8 GHz) which are used in wirelesscommunication systems of the fourth generation (4G) and the fifth generation (5G).

Effect of initial phase on the Rayleigh–Taylor instability of a finite-thickness fluid shell

Rayleigh–Taylor instability (RTI) of finite-thickness shell plays an important role in deep understanding the characteristics of shell deformation and material mixing. The RTI of a finite-thickness fluid layer is studied analytically considering an arbitrary perturbation phase difference on the two interfaces of the shell. The third-order weakly nonlinear (WN) solutions for RTI are derived. It is found the main feature (bubble-spike structure) of the interface is not affected by phase difference. However, the positions of bubble and spike are sensitive to the initial phase difference, especially for a thin shell (kd < 1), which will be detrimental to the integrity of the shell. Furthermore, the larger phase difference results in much more serious RTI growth, significant shell deformation can be obtained in the WN stage for perturbations with large phase difference. Therefore, it should be considered in applications where the interface coupling and perturbation phase effects are important, such as inertial confinement fusion.

Optically transparent and microwave diffusion coding metasurface by utilizing ultrathin silver films.

The past few years have witnessed the great success of artificial metamaterials with effective medium parameters to control electromagnetic waves. Herein, we present a scheme to achieve broadband microwave low specular reflection with uniform backward scattering by using a coding metasurface, which is composed of a rational layout of subwavelength coding elements, via an optimization method. We propose coding elements with high transparency based on ultrathin doped silver, which are capable of generating large phase differences (∼180°) over a wide frequency range by designing geometric structures. The electromagnetic diffusion of the coding metasurface originates from the destructive interference of the reflected waves in various directions. Numerical simulations and experimental results demonstrate that low reflection is achieved from 12 to 18 GHz with a high angular insensitivity of up to ±40° for both transverse electric and transverse magnetic polarizations. Furthermore, the excellent visible transparency of the encoding metasurface is promising for various microwave and optical applications such as electronic surveillance, electromagnetic interference shielding, and radar cross-section reduction.

Iterative parallel registration of strongly misaligned wavefront segments.

The paper presents an algorithm for the precise registration of multiple wavefront segments containing large misalignment and phase differences. The measurement of a wavefront with huge dynamics or a large aperture size can be carried out in multiple Shack-Hartmann sensor measurements of segments of the wavefront. The registration algorithm is flexible with respect to the shape of the wavefront and can reconstruct a plane as well as divergent wavefronts, making it suitable for freeform wavefronts. The algorithm enables parallel registration of the wavefront segments which is carried out in an iterative manner to compensate for large misalignment errors. A simulative analysis of the proposed algorithm compares its performance to a fast parallel registration (FPR) algorithm and the established iterative closest point (ICP) algorithm. For a sensor misalignment of up to 100 μm and 3 mrad the algorithm registers a plane and a divergent wavefront with a precision that is a factor 4 and 12 better than the registration precision of the FPR and ICP algorithm.

Broadband radar cross section reduction by an absorptive metasurface based on a magnetic absorbing material.

A highly feasible approach to achieve a broadband radar cross section (RCS) reduction using a simple magnetic metasurface is presented. A magnetic absorbing material (MAM) with high permittivity and magnetic loss is introduced into the metasurface design instead of the more common dielectric material to considerably reduce its thickness. The metasurface is composed of an optimized two-dimensional array of MAM meta-atoms and a metal plate in back. The meta-atoms share a simple square ring shape but with variable geometrical parameters, forming strong absorption in different frequency bands with large reflection phase differences. By hybridizing the absorption and phase-cancelation technique, a 10-dB RCS reduction from 3.4 to 18 GHz is achieved at a thickness of only 4 mm. Further experimental measurements are provided to evaluate the performance. Our work provides a promising way to broaden the bandwidth of RCS reduction with low density, reduced thickness, and stable performance, which can be utilized in harsh physical and chemical environments.

Compact Slow-Wave SIW H-Plane Horn Antenna With Increased Gain for Vehicular Millimeter Wave Communication

A substrate integrated waveguide (SIW) H-plane horn antenna with miniaturized longitudinal dimension and increased gain is proposed by loading slow-wave (SW) structures in the form of metallized blind via-holes inside the flare region of the horn for vehicular millimeter wave communications. The slow-wave structure can reduce the phase velocity around the center line of the broad wall and compensate the large phase difference between the center and edge of the aperture caused by reduction of longitudinal length of the horn. Compared with optimum horn with the same aperture width, the gain of miniaturized SIW horn is successfully increased, while the longitudinal dimension is decreased. A SW-SIW horn antenna which covers the 28 GHz band (27.5–28.35 GHz) allocated by Federal Communications Commission for the 5G millimeter wave communications is designed to verify the feasibility of the miniaturized SIW horn antenna facilitated by the proposed slow-wave structure. The SW-SIW horn realizes 53.83% reduction of longitudinal length compared with the optimum horn. The gain of the SW-SIW horn is improved by 1.1 dB on average over 27.5–28.5 GHz compared with optimum horn. A prototype of the proposed SW-SIW H-plane horn antenna is manufactured and measured. The measured results agree well with the simulations.