Identical Amplitude Research Articles

Flexible substrate based wideband polarization converter with extremely high polarization conversion ratio

In this article an anticipated reflection-mode cross-polarization converters (CPCs) are designed on a polydimethylsiloxane (PDMS) based flexible substrate operating in the GHz region. The proposed CPC metasurface comprises three layers where a flexible substrate is endwise between the resonating layer and ground layers. The converter can convert linear to circular and circular to cross-polarized waves at the frequency range of 5–8 GHz, as evidenced by the identical amplitude of Rxx and Ryx and a phase difference of 90°. More than 99 % of the polarization conversion ratio (PCR) was performed between the 6.75 and 9.07 GHz frequency range, while more than 80 % of the PCR was performed between the 6.0 and 10.73 GHz frequency range. The highest PCR values show nearly flawless energy conversion from an x-polarized incident wave to a y-polarized reflected wave. The PCR ratio of 80 % is achieved by this ultra-wideband linear-to-cross- and circular-to-cross-polarization converter. The anticipated converter's spectrum for all incidence angles between 0◦ and 60°. The PCR remained higher than 99 % over a wide incidence angle range to 60° without much performance degradation. The bending stability of the PDMS-based flexible substrate is also investigated up to 60°. The structure is fabricated on a flexible substrate, and the measured performance is compared with simulated results. Radar, antenna, and communications systems, as well as other cross-polarization converters, can utilize the transmitted wave's very high polarization purity result.

Assessment of Thermal Management Using a Phase-Change Material Heat Sink under Cyclic Thermal Loads

Phase-change materials (PCMs) are widely used in the thermal management of electronic devices by effectively lowering the hot end temperature and increasing the energy conversion efficiency. In this article, numerical studies were performed to understand how temperature instability during the periodic utilization of electronic devices affects the heat-dissipation effectiveness of a phase-change material heat sink embedded in an electronic device. Firstly, three amplitudes of 10 °C, 15 °C, and 20 °C for fixed periods of time, namely, 10 min, 20 min, and 40 min, respectively, were performed to investigate the specific effect of amplitude on the PCM melting rate. Next, the amplitude was fixed, and the impact of the period on heat sink performance was evaluated. The results indicate that under the 40 min time period, the averaged melting rate of PCMs with amplitudes of 20 °C, 15 °C, and 10 °C reaches the highest at 19 min, which saves 14 min, 10 min, and 8 min, respectively, compared with the constant input of the same melting rate. At a fixed amplitude of 20 °C, the PCM with a period of 40 min, 20 min, and 10 min has the highest averaged melting rate at 6 min, 11 min, and 19 min, saving the heat dissipation time of 3 min, 8 min, and 14 min, respectively. Overall, it was observed that under identical amplitude conditions, the peak melting rate remains consistent, with longer periods resulting in a longer promotion of melting. On the other hand, under similar conditions, larger amplitude values result in faster melting rates. This is attributed to the fact that the period increases the heat flux output by extending the temperature rise, while the amplitude affects the heat flux by adjusting the temperature.

Experimental Study of Magnetron’s Power-Pulled Characteristic to Realize a Quasi-Dual-Frequency Microwave Output

This article presents experimental evidence demonstrating the feasibility of implementing a quasi-dual-frequency microwave signal generator using a 1 kW commercial magnetron. The injection-pulled magnetron may generate quasi-dual-frequency output with nearly identical amplitudes by injecting signal at specific powers and frequencies out of the Adler locking band. This generator offers the advantage of developing a large-power and tunable quasi-dual-frequency signal at low cost and with simple implementation. In the present study, a tunable quasi-dual-frequency signal with a frequency interval ranging from 0.48 MHz to 13.74 MHz is generated experimentally. Furthermore, the effects of anode voltage ripples on the dual-frequency outputs are experimentally investigated. An empirical relationship between the frequency interval and injection ratio is obtained and presented. In addition, neither the output power nor the efficiency of the magnetron in the dual-frequency mode decreases. This research is promising for improving microwave heating uniformity in large-scale industrial applications.

Measurement of Rubidium Vapor Density Based on Spin‐Exchange Rate

AbstractAn efficient method is proposed for quantifying rubidium vapor density by analyzing the spin‐exchange rate between alkali metals. This method effectively addresses two primary challenges in measuring alkali vapor density. First, it overcomes the limitation of absorption spectroscopy to measure vapor density under optically thick conditions, typically restricted to temperature higher than 420K, equivalent to alkali vapor density exceeding . Second, it mitigates the risk of disrupting shielding functionality due to the application of a strong magnetic field, often in the range of several tens of Gauss or higher, when employing the Faraday rotation for vapor‐density measurement. The spin‐exchange rate between atoms, inherently related to the vapor density, is evident in the electron‐paramagnetic‐resonance spectrum of spin‐polarized , thereby providing a possibility for measuring alkali vapor density. To eliminate overlap between two Lorentzian curves resulting from two decomposed components of an oscillating field, a small rotating magnetic field with identical amplitude and frequency but a 90‐degree phase shift along both the x and y axes is applied. This method is successfully employed to measure vapor density in the temperature range of 373–433 K, with the measured outcomes closely matching the saturation vapor curve.

Interaction of soliton gases in deep-water surface gravity waves.

Soliton gases represent large random soliton ensembles in physical systems that display integrable dynamics at leading order. We report hydrodynamic experiments in which we investigate the interaction between two beams or jets of soliton gases having nearly identical amplitudes but opposite velocities of the same magnitude. The space-time evolution of the two interacting soliton gas jets is recorded in a 140-m-long water tank where the dynamics is described at leading order by the focusing one-dimensional nonlinear Schrödinger equation. Varying the relative initial velocity of the two species of soliton gas, we change their interaction strength and we measure the macroscopic soliton gas density and velocity changes due to the interaction. Our experimental results are found to be in good quantitative agreement with predictions of the spectral kinetic theory of soliton gas despite the presence of perturbative higher-order effects that break the integrability of the wave dynamics.

Three-dimensional array of microbubbles sonoporation of cells in microfluidics.

Sonoporation is a popular membrane disruption technique widely applicable in various fields, including cell therapy, drug delivery, and biomanufacturing. In recent years, there has been significant progress in achieving controlled, high-viability, and high-efficiency cell sonoporation in microfluidics. If the microchannels are too small, especially when scaled down to the cellular level, it still remains a challenge to overcome microchannel clogging, and low throughput. Here, we presented a microfluidic device capable of modulating membrane permeability through oscillating three-dimensional array of microbubbles. Simulations were performed to analyze the effective range of action of the oscillating microbubbles to obtain the optimal microchannel size. Utilizing a high-precision light curing 3D printer to fabricate uniformly sized microstructures in a one-step on both the side walls and the top surface for the generation of microbubbles. These microbubbles oscillated with nearly identical amplitudes and frequencies, ensuring efficient and stable sonoporation within the system. Cells were captured and trapped on the bubble surface by the acoustic streaming and secondary acoustic radiation forces induced by the oscillating microbubbles. At a driving voltage of 30 Vpp, the sonoporation efficiency of cells reached 93.9% ± 2.4%.

Characteristics of a two-dimensional periodic wave energy converter array

This study concentrates on the hydrodynamics of wave energy converters (WECs) consisting of an array of periodic buoys. The interaction between the bodies and waves was solved by a precise analytical method. The intrinsic relationships between wave propagation, energy capture, and array response are analyzed. Bragg resonance was found not only in scattering waves but also in radiation waves. The radiation wave is affected by different power take-off (PTO) damping, which could lead to incoming waves travelling freely through the array or being prevented through the array. The results show that Bragg resonance reduces the extraction efficiency significantly, and each device is affected to a different degree. In addition, this study reveals that there is collective behavior in the periodic WECs, all bodies in the array oscillate with identical amplitude at the Bragg resonance frequencies. Furthermore, the parametric effects on the hydrodynamic performance are investigated. The result of the study may provide useful guidance for the practical design of the WEC array.

Uniform moduli characterization of asphalt mixtures under dynamic and static loading conditions

The modulus is a crucial material parameter reflecting stiffness characteristics of asphalt mixture in the elastic stage. Under specific conditions such as identical temperatures, loading velocities, and stress amplitudes, the moduli under the same stress state are theoretically identical. However, the moduli were artificially divided into dynamic moduli and static moduli based on loading methods during test, which brought uncertainties and disunity for estimating the stiffness performance of asphalt mixture. In this study, the dynamic and static moduli under distinct temperatures, loading velocities, and stress states were measured. The relationship between dynamic and static moduli was established by applying loading velocities as independent variable and moduli as the dependent variable. Through Sigmoidal function and WLF function fitting, the uniform characterization master curves of dynamic and static moduli under distinct temperatures, loading velocities, and stress states were established. The moduli of asphalt mixture under distinct test temperatures, loading velocities, and stress states can be obtained by the models, which provide material parameters for mechanical response analysis of asphalt pavements under distinct service environments. This resolves the issue of inconsistent moduli parameter selection.

A Compact Tri-Band Penta-Polarization Reconfigurable Planar Antenna for Interference Management in 5G Ultra-Dense Network Environment

Interference and multipath are the most common issues in the wireless domain due to the coexistence of a large number of wireless nodes operating within the constraint spectrum. A compact planar antenna with five reconfigurable polarization states in three distinct operating bands is presented in this article. A square patch is enclosed by a square outer ring in the design, and these antennas are coupled-decoupled successively using switching diodes to excite three distinct operating bands. Coplanar microstrip lines are used to feed the orthogonal edges of the antenna. The diagonal corners of the inner and outer ring patches are truncated to realize dual circular polarization (CP) states with proper biasing. Switching diodes are placed at the etched corners to realize vertical (VP) and horizontal (HP) polarization. Both the orthogonal feed lines are activated simultaneously with identical phase and amplitude to realize 45° linear polarization. A low-profile, single-feed, compact prototype reconfigurable microstrip antenna (MSA) is finally designed, fabricated, and measured at 1.8 GHz, 2.4 GHz, and 5.8 GHz bands, respectively. Each operating band shows five distinct operating states. The simulation results for all fifteen states are found to be consistent with the measurement.

Ultrawideband Compact Magnetoelectric Dipole Antenna/Array With Dual-Polarization

Design of ultra-wideband (UWB) dual-polarized antenna with compact size is presented in this communication, which is composed of a triple-layer magnetoelectric (ME) dipole, a pair of cross-placed Γ-shaped feeding structure and a box-shaped reflector. Three layers of the ME dipole cover low (around 1.5 GHz), middle (3.5 GHz) and high (4.5 GHz) bands respectively, leading to an ultra-wide operating band from 1 to 5 GHz. The total size of the design is 75mm (0.75λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) × 75mm (0.75λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) × 55mm (0.55λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ). An array that consists of 8 such antenna elements is designed, fabricated, and measured. Results show that the voltage standing wave ratio (VSWR) is less than two over the whole operating band for all ports. As for the radiation characteristics, boresight gain ranging from 5.3 to 8.8 dBi is achieved for each antenna element, when it comes to the array, a peak gain of 17.23 dBi occurs at 4 GHz when all the antenna elements are excited with identical amplitude and phase. Beam scanning is also realized in the whole operating band through phase disposing, the scanning range is up to ±45° from 1 to 2 GHz and ±30° from 2 to 5 GHz.

RELATIONSHIP INFORMATIONAL AND ORTHOGONAL COMPONENTS OF THE RECEIVING ANTENNA SCATTERING FIELD WITH ITS LOAD

Previously, we established that the total scattering field of the receiving antenna includes the information component of the total scattering field and the orthogonal component. Each of these components consists of a main and an additional component. Moreover, only the main information component of the total scattering field participates in the transfer of energy from a plane wave to the antenna load, despite the fact that both components of the total scattering field component have the same amplitude and phase characteristics and they differ from each other only in amplitudes. This work is devoted to the study of the connection between the components of the total scattering field component and the information component of the total scattering field of the receiving antenna with its load. It is shown that the currents that are created in the antenna load by the additional component of the total scattering field and the orthogonal component of the total scattering field cancel each other out, and the resulting current in the receiving antenna load is determined only by the main component of the total scattering field. This explains that, despite the identical amplitude and phase characteristics of the main and additional components of the total scattering field, only the main component is involved in the transmission of information from the plane wave to the antenna load.

A Low Detent Force DS-PMSLM Based on the Modulation of Cogging and End Forces

This article presents a low detent force double-sided permanent-magnet synchronous linear motor (DS-PMSLM), which contains two flat-type stators and a mover. The mover is constituted of a fiberglass support plate and Halbach array permanent magnets attached on both surfaces of this plate, which provides a large thrust force and low mover mass for high dynamic response. For the sake of reducing the thrust ripple, a modulation method of the cogging and end forces is proposed based on the destructive interference. The even-order harmonics in cogging and end forces are reduced by adjusting the width of the side slots and the lengths of end teeth, respectively. In order to reduce the odd-order harmonics of the detent force, the cogging force and end force are modulated to reverse phases and identical amplitudes by changing the equivalent lengths of four end teeth. An integrated subdomain analytical model considering the cogging and end effects is built to optimize five structural parameters of the stators for low detent force. Finally, the prototype and testing platforms are set up and the experimental results validate that the proposed DS-PMSLM can achieve a low thrust ripple of less than 1.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \%$</tex-math></inline-formula> .

Effect of pile orientation on the fatigue performance of jointless bridge H-piles subjected to cyclic flexural strains

This paper explores the effect of pile orientation on the low cycle fatigue (LCF) performance of steel H–piles (SPs) at jointless bridge (JB) abutments via experimental testing and finite element simulation. The experimental testing program includes 42 full scale SP specimens subjected to strong axis (SA) and weak axis (WA) bending. The SPs are tested under cyclic displacement reversals mimicking the thermal induced displacement cycles associated with the seasonal elongation and contraction of the JB in the summer and winter times. The magnitude of the axial load is also kept as a variable in the experimental testing program to investigate its effect on the cyclic performance of JB SPs. The test results are then verified via finite element simulation and a parametric numerical study is performed to further understand the cyclic behavior of SPs as a function of numerous parameters. The tests and numerical analyses results revealed that for identical cyclic flexural strain amplitudes, SPs oriented for WA bending generally demonstrate a superior performance in terms of LCF life in the presence of axial loads compared to those oriented for SA bending. Moreover, the research results showed that at large flexural strains, local buckling becomes more critical than the pile orientation for the LCF life of SPs in JBs.

Trapping wide-angle circularly polarized waves with giant circular dichroism using a single-channel coherent perfect graphene meta-surface absorber.

We propose a single-channel coherent perfect graphene meta-surface absorber to trap circularly polarized (CP) waves perfectly through cascading a polarization converting meta-array and a monolayer graphene sheet. To be more specific, the incident CP waves will be reflected into dual sets of orthogonally linearly polarized (LP) waves, where each group of the same polarized reflecting components can achieve identical amplitudes and a 180° phase difference at a certain frequency to have coherent absorption. In particular, we show that such a single-channel coherent perfect graphene meta-surface absorber possesses the merits of the wide-angular chiral absorbing capacity of CP waves with giant circular dichroism, thus should pave the way for building up more advanced coherent absorbers and offer more freedom to manipulate CP waves.

Multiservice transmissions in optical code-division multiple access networks of spectral amplitude coding based on hypothesis testing and multiple chip decoding

I propose a multiservice scheme in optical code-division multiple access (OCDMA) networks by adapting hypothesis testing to a receiver design of multiple chip decoding. Each transmitted bit of a single user is divided into several time-domain chips carrying an identical spectral amplitude coding (SAC) signature. Multiservice transmissions are achieved by assigning the users with different chip numbers based on the user classes. Hypothesis testing is employed to derive the required chip number supporting the desired bit-error rate (BER) performance. Numerical results have shown that efficient BER classifications are achieved among distinctive classes for multiple conditions of user numbers and power levels. The proposed multiservice scheme can be transparently applied to SAC-OCDMA systems with existing optical codes and various user class numbers.

Taming non-stationary chimera states in locally coupled oscillators

The imperfect traveling chimera (ITC) state is a novel non-stationary chimera pattern in which the incoherent domain of oscillators spreads into the coherent domain. We investigate the ITC state in locally coupled pendulum oscillators with heterogeneous driving forces. We introduce the heterogeneous phase value in the driving forces by two different ways, namely, the random phase from uniform distribution and random phase directions with identical amplitude. We discover two transition mechanisms from ITC to coherent state through traveling chimera-like state by taking the two different phase heterogeneity. The transition phenomena are investigated using cylindrical and polar coordinate phase spaces. In the numerical study, we propose a quantitative measurement named "spatiotemporal consistency" strength for distinguishing the ITC from the traveling one. Our research facilitates the exploration of potential applications of heterogeneous interactions in neuroscience.

Switchable Metasurface with Electromagnetically Induced Transparency and Absorption Simultaneously Realizing Circular Polarization‐Insensitive Circular‐to‐Linear Polarization Conversion

AbstractA metasurface (MS) with switching features from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) is theoretically investigated in the terahertz (THz) range by incorporating vanadium dioxide (VO2) when circular polarization‐insensitive circularly polarized waves are incidents, which can also simultaneously realize circular‐to‐linear polarization conversion well. While the VO2 ring is in an insulator state, two new transparent EIT windows both are gained between 0.97 THz and 1.16 THz because of destructive interference between the two metal rings that are seen as bright modes. Once the VO2 ring is tuned to the metallic state, a perfect EIA phenomenon is observed between 0.824 THz and 1.233 THz, achieving the transition from the EIT to EIA behavior well. The received electromagnetic waves are radiated to left‐handed circularly polarized (LCP) or right‐handed circularly polarized (RCP) waves with identical phases and amplitudes through the radiation patches when the LCP or RCP ones are incident. Whereby, a resultant linearly polarized wave is obtained between 0.9 THz and 1.2 THz, and relative bandwidth reaches 29%. The outcomes of maximal group index and group delay both are 1934 and 488 ps at 1.08 THz, and maximal absorption is 90.3% at 1.06 THz.

Memory in the relaxation of a polymer density modulation.

Using analytical considerations and particle-based simulations of a coarse-grained model, we study the relaxation of a density modulation in a polymer system without nonbonded interactions. We demonstrate that shallow density modulations with identical amplitudes and wavevectors that have been prepared by different processes exhibit different nonexponential decay behaviors. Thus, in contrast to the popular assumption of dynamic self-consistent field theory, the density alone does not suffice to characterize the configuration of the polymer system. We provide an analytic description within Linear-Response Theory (LRT) and the Rouse model that quantitatively agree with the results of the particle-based simulations. LRT is equivalent to a generalized model-B dynamics with an Onsager coefficient that is nonlocal in space and time. Alternatively, the Rouse description can be cast into a dynamic density-functional theory that uses the full probability distribution of single-chain configurations as a dynamic variable and yields a memory-free description of the dynamics that quantitatively accounts for the dependence on the preparation process. An approximate scheme that only considers the joint distribution of the first two Rouse modes-the ellipsoid model-is also explored.

Element-selective analysis of ultrafast demagnetization in Co/Pt multilayers exhibiting large perpendicular magnetic anisotropy

We use time-resolved resonant magnetic scattering experiments to investigate the laser induced demagnetization of Co/Pt multilayers with large perpendicular magnetic anisotropy. Our pump-probe approach, which relies on extreme ultraviolet pulses obtained via high-harmonic generation, allows us to monitor the temporal evolution of the system in an element-selective fashion, thus to disentangle the contributions from permanent and proximity-induced magnetic moments. By analyzing the data gathered at the Co M2,3 and Pt O3 edges, we are able to show that after femtosecond laser irradiation, both components display a very similar loss of magnetic order, with almost identical demagnetization amplitudes and characteristic times, but a small delay (10–20 fs) of the Pt magnetization quenching with respect to Co. Comparing our experiments with literature results, therefore, suggests that in these 3d–5d multilayers and alloys, the different constituents remain strongly coupled after optical excitation; no matter whether the thin films possess a preferred in-plane or out-of-plane easy magnetization direction.

Importance of seismic wave frequency in FEM-based dynamic stress and displacement calculations of the earth slope

Abstract Reliable assessment of earthen dams’ stability and tailing storage facilities widely used in the mining industry is challenging, particularly under seismic load conditions. In this paper, we propose to take into account the effect of the dominant frequency of seismic load on the stability assessment of tailing/earthen dams. The calculations are performed by finite element modelling (FEM) with the Mohr–Coulomb failure criteria. To separate the frequency content from other dynamic parameters describing the seismic wave, synthetic waveforms with identical amplitude and attenuation characteristics, but differing spectral characteristics have been used. The analysis has been performed for three different slope angles and two scenarios of seismic wave propagation. Consequently, the changes of total displacement and shear stresses depending on the frequencies have been determined and clearly show that lower frequencies cause higher stress levels and displacement. Finally, the response surface methodology has been applied to determine how different parameters affect the slope stability under dynamic load conditions. Overall, this study is a first step to improve the existing methods to assess slope stability when considering seismic load.