Smooth Phase Research Articles

An optimization-based design of a wideband, polarization-independent reflectarray antenna at terahertz frequencies

A broadband reflectarray antenna is proposed for operating at THz frequencies. An array of single-layer elements is composed of gold patches printed on a grounded cyclic olefin copolymer (COC) substrate. The elements are designed to have a smooth and linear phase reflection curve versus element positions. A random hill-climbing (RHC) optimization algorithm is applied to obtain the broadest bandwidth around the design frequency. The proposed antenna shows 3 dB relative bandwidth of 25% ranging from 0.9 to 1.15 THz, and it has a polarization-independent feature and low loss for better reflectarray performance.

A Novel Single Layer Wideband Reflectarray Design Using Two Degrees of Freedom Elements

A broadband linearly polarized single-layer reflectarray antenna constructed with element cells of spiral-dipoles is presented in this communication. The proposed method achieves the phase change requirements by continuously adjusting the two degrees of freedom (TDF) elements. Then, a linear and smooth phase response covering 360° is obtained by adjusting the TDF. Furthermore, by introducing four rectangular rings around the spiral-dipoles, a relatively slow phase change slope can be obtained and the maximum differences between the achieved phase acquired by element and ideal phase at 6.5 and 9.5 GHz are 20° and 58°, respectively, enlarging the operating bandwidth. A reflectarray prototype with a rectangular aperture of 300 mm in diameter is designed, fabricated, and experimentally verified. The results include a measured gain of 26.5 dBi at 8 GHz with an aperture efficiency of 55%; the 1 dB gain bandwidth can reach 35%. The proposed structure can be extrapolated to higher frequencies due to its single-layer performance. Its benefits include a reduction in manufacturing costs and the mitigation of alignment errors.

Core-shell Ni-rich NMC-Nanocarbon cathode from scalable solvent-free mechanofusion for high-performance 18650 Li-ion batteries

Although the Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode can store high electrical energy suitable for powering long-range electric vehicles, its poor cycling stability still hinders the practical application. Herein, a surface coating approach using a green scalable solvent-free mechanofusion process is introduced to prepare an infusing thin layer carbon nanosphere shell to improve the intrinsic drawbacks of NMC811 including poor electrical conductivity, Li+/Ni2+ cation mixing, parasitic reactions with electrolytes, and micro-crack formation. The in operando XRD of [email protected] [email protected] so-called NMC811cs reveals the smooth and fast phase transition through H1-H2-H3 with higher Li utilization and better stability even though it shows larger abrupt change in c lattice parameter compared to the pristine NMC811. In addition, the onset potential of CO2 and H2 evolution is found to be extended by the carbon coating as observed by an online Differential Electrochemical Mass Spectrometry. Finally, the practical application of the NMC811cs is demonstrated by the 18650 battery prototype which shows higher specific capacity and energy as well as excellent cycling stability compared to the pristine NMC811. This work provides both fundamental understanding and economical strategy towards highly stable and practical high-energy Li-ion batteries.

Light-shaping design by a fourier pair synthesis: the homeomorphic case.

From a physical-optics point of view, the far-field light-shaping problem mainly requires a Fourier pair synthesis. The Iterative Fourier Transform Algorithm (IFTA) is one of the algorithms capable of realizing this synthesis, however, it may lead to stagnation problems when the fields of the Fourier pair exhibit a homeomorphic behavior. To overcome this problem, we use a mapping-type relation for the Fourier pair synthesis. This approach results in a smooth phase response function in a single step, without requiring an iterative procedure. The algorithm is demonstrated with examples and the results are investigated via physical-optics modeling techniques.

Spectral evolution of long gamma-ray bursts observed with Konus-Wind

We present a preliminary analysis of spectral evolution of 35 long bright gamma-ray bursts (GRBs) detected by Konus-Wind instrument. From the temporal and spectral analyses of the sample, we investigate the evolution of parameters of the smoothly joined broken power-law spectral model (the Band “GRB” function), in particular, we analyse hardness-intensity correlation within a burst. We show that the bulk of bursts exhibit Ep ∝ F γ relation with the slope γ ∼ 0.3−0.5, where Ep is the vFv spectrum peak energy and F is the energy flux; while a number of events have the smooth initial phase with strong spectral evolution with γ ≳ 1. Finally, we discuss derived the Band function parameters and their evolution pattern in the framework of GRB emission models.

Manifold Learning and Clustering for Automated Phase Identification and Alignment in Data Driven Modeling of Batch Processes

Processing data that originates from uneven, multi-phase batches is a challenge in data-driven modeling. Training predictive and monitoring models requires the data to be in the right shape to be informative. Only then can a model learn meaningful features that describe the deterministic variability of the process. The presence of multiple phases in the data, which display different correlation patterns and have an uneven duration from batch to batch, reduces the performance of the data-driven modeling methods significantly. Therefore, phase identification and alignment is a critical step and can lead to an unsuccessful modeling exercise if not applied correctly. In this paper, a novel approach is proposed to perform unsupervised phase identification and alignment based on the correlation patterns found in the data. Phase identification is performed via manifold learning using t-Distributed Stochastic Neighbor Embedding (t-SNE), which is a state-of-the-art machine learning algorithm for non-linear dimensionality reduction. The application of t-SNE to a reduced cross-correlation matrix of every batch with respect to a reference batch results in data clustering in the embedded space. Models based on support vector machines (SVMs) are trained to, 1) reproduce the manifold learning obtained via t-SNE, and 2) determine the membership of the data points to a process phase. Compared to previously proposed clustering approaches for phase identification, this is an unsupervised, non-linear method. The perplexity parameter of the t-SNE algorithm can be interpreted as the estimated duration of the shortest phase in the process. The advantages of the proposed method are demonstrated through its application on an in-silico benchmark case study, and on real industrial data from two unit-operations in the large scale production of an active pharmaceutical ingredients (API). The efficacy and robustness of the method are evidenced in the successful phase identification and alignment obtained for these three distinct processes, displaying smooth, sudden and repetitive phase changes. Additionally, the low complexity of the method makes feasible its online implementation.

Graphene-based active metasurface with more than 330° phase tunability operating at mid-infrared spectrum

Metasurfaces composed of subwavelength optical antennas offer fruitful functionalities to manipulate the amplitude, phase and polarization of light. Sufficient phase tunability of metasurfaces has significant potential for dynamic beam steering, hologram and flat optics exhibiting tunable focusing. Here, we demonstrate a graphene based metasurface that gives rise to more than 330° smooth and continuous phase modulation at mid-infrared spectrum. The phase modulator model introduces multiple resonances including Split-Ring-resonator (SRR) resonance and inductance-capacitance (LC) resonance, leading to the outstanding sensitivity of the metasurface to tiny change of surrounding electromagnetic environment. Through adjusting the Fermi level of the monolayer graphene beneath the resonators, both scattered amplitude and phase can be efficiently modulated, so that the electrically programmable metasurface enables nearly arbitrary manipulation of scattered wavefront. Electro-optically tunable focusing and beam steering are numerally realized by constructing one dimensional discrete array element. The phased array design achieves an average efficiency up to 22% within 60° steering range. The reflective focusing lens with focal lengths of 10 μm, 15 μm and 20 μm are successfully demonstrated, respectively. The proposed metasurface has promising potential in optoelectronic applications such as imaging, sensing and focusing.

Effective Surface Texturing of Diamond-Wire-Sawn Multicrystalline Silicon Wafers Via Crystallization of the Native Surface Amorphous Layer

To increase the market shares of multicrystalline silicon (mc-Si) wafers obtained using diamond-wire sawing (DWS), it is necessary to develop efficient and cost-effective texturing methods. Surface texturing processes that increase light absorption are essential for manufacturing high-efficiency solar cells. The smooth surface, phase transformations, and amorphous silicon (a-Si) layer on mc-Si wafers manufactured via DWS hinder the effective texturing under conventional acidic conditions, which are typically used for multiwire slurry sawing (MWSS). To address this issue, this article focused on an efficient texturing process of DWS wafers by adapting a pre-thermal treatment (TT) process. We found that DWS mc-Si wafers could be effectively textured after the TT process by altering the surface roughness through the crystallization of surface amorphous silicon (a-Si) and phase transformation layers. For the DWS mc-Si wafers textured under conventional acidic etching conditions without TT, Rw was found to be 31.7%. The altered surface conditions achieved via the proposed TT method facilitate effective texturing on the DWS mc-Si wafer surface. Consequently, a weighted average reflectance (Rw) of 24.5% was obtained, which was comparable to that for MWSS mc-Si wafers subjected to conventional acidic etching (Rw = 24.4%). As a result of depositing a SiN x for surface passivation and antireflection coating in solar cell applications, Rw values of 8.1% and 8.3% were obtained for the thermal treated DWS mc-Si wafer and MWSS mc-Si wafer, respectively. The proposed texturing process for DWS mc-Si wafers can easily be applied to industrial inline processes using cost-effective existing acidic etching solutions.

Broadband single-layer reflectarray antenna loaded with meander-delay-lines for X-band applications

In this work, delay-lines loaded broadband reflectarray antenna is proposed for X-band applications. The array cells contain slotted square patch and quad meander delay-lines. The slotted square patch elements are combined with delay-lines to increase the reflection phase range. A smooth linear phase variation of 650° is realized through varying the length of delay-lines. The reflectarray unit element resonant behavior is observed through an equivalent circuit model approach. The reflectarray antenna is simulated and measured on a low-cost FR-4 substrate. A 23 × 23 elements reflectarray antenna is designed and simulated using a hybrid finite element boundary integral (FEBI) method. The proposed reflectarray antenna offers a measured gain of 25 dBi and 52.8% aperture efficiency for 10 GHz frequency band. The cross-polarization levels and side-lobe-levels and in E and H-plane are less than −35 dB and −22 dB respectively. Moreover, a measured 3-dB gain bandwidth of 29% and 1-dB gain of 19.5% is realized for the proposed reflectarray antenna.

Identification of Phase Fraction–Temperature Curves from Heat Capacity Data for Numerical Modeling of Heat Transfer in Commercial Paraffin Waxes

The area-proportional baseline method generates phase fraction–temperature curves from heat capacity data of phase change materials. The curves describe the continuous conversion from solid to liquid over an extended temperature range. They are consistent with the apparent heat capacity and enthalpy modeling approach for the numerical solution of heat transfer problems. However, the curves are non-smooth, discrete signals. They are affected by noise in the heat capacity data and should not be used as input to continuous simulation models. This contribution proposes an alternative method based on spline approximation for the generation of consistent and smooth phase fraction–temperature, apparent heat capacity–temperature and enthalpy–temperature curves. Applications are presented for two commercial paraffins from Rubitherm GmbH considering heat capacity data from Differential Scanning Calorimetry and 3-layer-calorimetry. Apparent heat capacity models are validated for melting experiments using a compact heat exchanger. The best fitting models and the most efficient numerical solutions are obtained for heat capacity data from 3-layer-calorimetry using the proposed spline approximation method. Because of these promising results, the method is applied to melting data of all 44 Rubitherm paraffins. The computer code of the corresponding phase transition models is provided in the Supplementary Information.

Lattice Evolution, Ordering Transformation and Microwave Dielectric Properties of Rock-Salt Li3 +xMg 2-2xNb 1-XTi 2xO6 Solid-Solution System: A Newly Developed Pseudo Ternary Phase Diagram

The new types of multi-component Li3+xMg2-2xNb1-xTi2xO6 (0≤x≤1) solid-solution ceramics were designed based on the Li2TiO3-Li3NbO4-MgO pseudo ternary phase diagram and studied for millimeter-wave applications. The ceramics showed a full range of solid solubility between the Li3Mg2NbO6 and Li2TiO3 endmembers. As the doping content (x) increased, we detected the phase transitions among the orthorhombic, cubic, and monoclinic phase driven by the compositional changes, as well as accompanied with an order-disorder-order transformation. Besides, the smooth orthorhombic-cubic phase transition interfaces were observed in the electron diffraction images for the sample with the low dopant concentration (x=0.2), and the reconstructed superlattices based on the orthorhombic or the cubic structure were both observed nearby the orthorhombic-cubic phase transition interface. The change of Q×f values showed a considerable increase with the emergence of the superlattices, and the enhancement of the Q×f values was related to the very small lattice vibrational anharmonicity in the structures that contain the reconstructed superlattices. Typically, when sintered at 1250 ℃ for 4 h, the ultra-low dielectric loss was achieved in the x=0.2 sample with the properties of er=16.1, Q×f=128,600 GHz (f=9.2 GHz) and τf=-30.4 ppm/℃, and the temperature stable properties were obtained in the x=0.9 sample with er=20.4, Q×f=90,300 GHz (f=7.9 GHz), and τf=2.9 ppm/℃.

Phase Transformation of Nickel‐Rich Phases in Al–Si Alloy Under Thermal Exposure

Al–11.5Si–xCu–yNi–Mg alloys with different Cu and Ni contents are prepared. The microstructure of the alloy and phase transformation of Al3CuNi are investigated by X‐ray diffraction (XRD), optical microscope, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy‐dispersive spectrometry (EDS). The nickel‐rich phase in Al–11.5Si–3Cu–2Ni–Mg alloy is only Al3CuNi phase. With the increase in Cu and Ni content, the Al3Ni phase and the Al7Cu4Ni phase appear, respectively. The alloys are subjected to thermal exposure treatment at 350 and 425 °C, respectively, and hardness tests are performed on alloys of different exposure times. The Brinell hardness of the alloy decreases with the extension of thermal exposure time. It is found that the microstructure of nickel‐rich phases dissolved and granulated after thermal exposure, and the decrease in the Brinell hardness of the alloy is related to the transformation of nickel‐rich phases. The changes of Al3CuNi during thermal exposure are studied by means of in situ follow‐up observation. A large number of serrated new phases are deposited on the smooth Al3CuNi phase interface during thermal exposure. In addition, the Al3CuNi phase break and granulates with time. TEM analysis shows that the new jagged phase formed at the interface of Al3CuNi phase is Al7Cu4Ni phase.

Robust tracking control in the inertia phase for generalised disturbance

To solve the problem of shift shock during the inertia phase caused by generalized disturbances in wheel loaders and other construction instruments, a robust double closed-loop tracking control method based on an improved disturbance observer (DOB) has been proposed. In this method, the inner loop robustly suppresses disturbance and the outer loop realizes trajectory tracking. The improved DOB based on a nominal disturbance value (NDV) can enhance the disturbance suppression ability of the inner loop when a large part of the generalized disturbance is determinable. The model matching method transforms the outer loop into a transfer function to meet the expected performance. A disturbance compensation controller eliminates the nominal disturbance in the system. A feedforward compensation controller eliminates the influence of reference inputs in the system. Considering the inertia phase of a fixed-axis automatic transmission of a wheel loader, the proposed method was applied to the driveline simulation platform of a specific type of wheel loader. Random loads under actual working conditions were considered as the input load of the simulation platform. The simulation results indicated that the DOB based on the NDV method has better disturbance suppression capability, more accurate tracking capability and smaller shift shock than the conventional DOB method. The proposed control method exhibits robustness under 10%, 50% and 90% of the maximum load. The highest shift shock is 4.94% of the manual shift shock and it is effectively reduced. Thus, robust and smooth inertia phase shift control of the automatic transmission can be realized. This study presents an effective method for solving robust disturbance suppression control problems and tracking control problem under large generalized disturbances.

Compression of laser pulses due to Raman amplification of plasma noises

The method of the laser pulse self-compression in the process of noise-seeded Raman scattering in a plasma created by a counterpropagating ionized pulse is considered. The sharpness of the ionization front ensures the formation of an output pulse close to the $\ensuremath{\pi}$-pulse solution with a sharp leading edge. The dependence of the gain increment on the transverse wave number leads to the formation of a smooth phase front of the output pulse. The energy efficiency in the output pulse reaches 28% of the total pump energy. A study of the influence of quasistatic inhomogeneities showed only a slight slowdown in the process, even in a plasma with 8% density modulation.

Quark-hadron phase transition in DGP including BD brane * * T. G. has been supported financially by Vice Chancellorship of Research and Technology, University of Kurdistan under research Project (98/11/2724). A. M. has been supported financially by Vice Chancellorship of Research and Technology, University of Kurdistan under research Project (98/10/34704)

A Dvali–Gabadadze–Porrati (DGP) brane-world model with perfect fluid brane matter including a Brans-Dicke (BD) scalar field on brane was utilized to investigate the problem of the quark-hadron phase (QHP) transition in early evolution of the Universe. The presence of the BD scalar field arises with several modified terms in the Friedmann equation. Because the behavior of the phase transition strongly depends on the basic evolution equations, even a small change in these relations might lead to interesting results about the time of transition. The phase transition is investigated in two scenarios, namely the first-order phase transition and smooth crossover phase transition. For the first-order scenario, which is used for the intermediate temperature regime, the evolution of the physical quantities, such as temperature and scale factor, are investigated before, during, and after the phase transition. The results show that the transition occurs in about a micro-second. In the following part, the phenomenon is studied by assuming a smooth crossover transition, where the lattice QCD data is utilized to obtain a realistic equation for the state of the matter. The investigation for this part is performed in the high and low-temperature regimes. Using the trace anomaly in the high-temperature regime specifies a simple equation of state, which states that the quark-gluon behaves like radiation. However, in the low-temperature regime, the trace anomaly is affected by discretization effects, and the hadron resonance gas model is utilized instead. Using this model, a more realistic equation of state is found in the low-temperature regime. The crossover phase transition in both regimes is considered. The results determine that the transition lasts around a few micro-seconds. Further, the transition in the low-temperature regime occurs after the transition in the high-temperature regime.

Design of a single-layer broadband reflectarray using circular microstrip patch loaded with two unequal slots

A linearly polarized single-layer single-resonator reflectarray, which is designed using a simple circular patch loaded with two unequal rectangular slots, is investigated for the first time. For the proposed design, the linearity and sensitivity of the phase curve (S-curve) can be easily optimized by adjusting the ratio of the two unequal slots changeable according to a simple design equation. Here, the patch radius serves as a phase-shifting geometrical parameter and it is able to achieve a wide phase range of more than 458° with low phase sensitivity and a low reflection loss of less than 0.5 dB. With the use of the optimized phase curve, an offset-fed 13 × 13 full-fledged reflectarray with a square aperture is designed, fabricated and measured. Measurement results show that a −1-dB gain bandwidth of 11.8% and an antenna gain of 23.4 dBi are realizable at the center frequency of 9.3 GHz. Also, the proposed reflectarray has an aperture efficiency of 42% and a radiation efficiency of 98%. The proposed reflectarray has a simple structure and it is able to achieve smooth phase curve, low cross-polarized radiation field and low sidelobes.

The Spectrum of Gravitational Waves, Their Overproduction in Quintessential Inflation and Its Influence in the Reheating Temperature

One of the most important issues in an inflationary theory as standard or quintessential inflation is the mechanism to reheat the universe after the end of the inflationary period in order to match with the Hot Big Bang universe. In quintessential inflation two mechanisms are frequently used, namely the reheating via gravitational particle production which is, as we will see, very efficient when the phase transition from the end of inflation to a kinetic regime (all the energy of the inflaton field is kinetic) is very abrupt, and the so-called instant preheating which is used for a very smooth phase transition because in that case the gravitational particle production is very inefficient. In the present work, a detailed study of these mechanisms is done, obtaining bounds for the reheating temperature and the range of the parameters involved in each reheating mechanism in order that the Gravitational Waves (GWs) produced at the beginning of kination do not disturb the Big Bang Nucleosynthesis (BBN) success.

Absolute phase measurement with four patterns based on variant shifting phases.

Fringe projection profilometry has been proverbially utilized for measuring the shapes of objects. A common challenge in those systems is to accurately obtain a smooth absolute phase. Many new methods have been proposed to address this challenge. In this paper, we discuss a technique based on variant shifting phases. This approach embeds codewords into the shifting phase and only needs four patterns. However, reliable measurement results are difficult to achieve with a large number of codewords because of the phase errors. To address this shortcoming, we present a robust coding method that embeds a specific code sequence into the shifting phase and can generate more than 36 periods. The fringe order is determined using unique three-adjacent-codes combining the current period and its neighbors. An error correction algorithm is also proposed to optimize the codewords. The proposed method is experimentally verified using an established measurement system. The result shows that the proposed method is robust and efficient.

Surface phase transitions and crystal habits of ice in the atmosphere.

With climate modeling predicting a raise of at least 2°C by year 2100, the fate of ice has become a serious concern, but we still do not understand how ice grows (or melts). In the atmosphere, crystal growth rates of basal and prism facets exhibit an enigmatic temperature dependence and crossover up to three times in a range between 0° and -40°. Here, we use large-scale computer simulations to characterize the ice surface and identify a sequence of previously unidentified phase transitions on the main facets of ice crystallites. Unexpectedly, we find that as temperature is increased, the crystal surface transforms from a disordered phase with proliferation of steps to a smooth phase with small step density. This causes the anomalous increase of step free energies and provides the long sought explanation for the enigmatic crossover of snow crystal growth rates found in the atmosphere.

Unsupervised phase learning and extraction from quasiperiodic multidimensional time-series data

Automatic phase extraction is commonly done by digital markers or handcrafted feature detection that are designed specifically for one particular type of signal. A few more generalized ways are to apply Hilbert transform or complex wavelet convolution. However, they are limited to single-dimensional signals, and they require the input window to cover multiple signal periods to extract a smooth phase sequence. In this work, we propose a learning-based phase extraction method for multi-dimensional signals, consuming only unlabeled signal examples for training. A neural network architecture is designed to map a window of signal directly to a phase value under a key constraint that encourages two consecutive phase values to progress forward. The concept has been generalized to a broad range of applications with an adjustable input window, a flexible phase progression penalty design, and better training stability. The proposed method consistently outperforms the complex wavelet convolution in three synthetic signals by reducing the phase extraction error by 63% while shortening the size of the observation window by over 90%. An experiment with an augmented electrocardiogram (ECG) signal also produces a clean phase sequence with an input window that is over thirty times smaller. A qualitative test on eleven-dimensional kinematic signals from three repetitive upper limb movements has shown that the method can also capture the fluctuation in phase progression. With the flexibility, the labelless training, the accuracy, and the short observation window, this technique has a potential to be used in a variety of applications that need instantaneous phase extraction.