Accepted
, , Received Date: 2024-11-22
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, , Received Date: 2024-08-20
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Conformal metasurfaces with flexible structures can fit complicated platforms and have obvious advantages in moving platforms scattering manipulations. However, the far-field simulation of conformal metasurface is time-consuming and difficult to optimize, thereby making the its agile design difficult. Here, an efficient and intelligent scattering field calculation method is proposed based on transfer learning for conformal metasurfaces. Firstly, according to the consistency in physical mechanism between antenna theory and full wave simulation, an initial mapping model between phase distribution and far-field of metasurface is constructed and pre-trained based on a large quantity of theoretical data in source domain. Secondly, by pre-training, parameter freezing and model fine-tuning, the far-field prediction model for full wave simulation is transferred and achieved successfully, based on a small quantity of full wave simulation data in target domain. Finally, the transfer learning model for far-field prediction is transferred once again for conformal metasurfaces with different structures. Results indicate that the proposed method only consumes 0.1% of full wave simulation time for conformal metasurface far-field calculation. In fewer samples, the model with transfer learning can improve the average accuracy by 19.8%, and the training data account for only 42.9% for the models without transfer learning, which reduces the training data collection time by 50.1%. Moreover, our far-field calculation method demonstrates good transfer performance between conformal metasurfaces with different structures.
, , Received Date: 2024-09-10
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Low-frequency hysteresis flow and pulsating pressure caused by underwater explosion bubbles can cause overall damage to ships. The hydrodynamic and energy conversion of bubbles are very important to study underwater explosion bubbles. At present the study of bubble dynamics is based on ideal gas hypothesis, which is without thermal exchange and only suitable for bubbles of chemical detonating, but not for bubbles with higher temperature. The experimental study on the evolution of underwater explosion bubbles was carried out by underwater exploding wire. There is obvious thermal exchange during the evolution of bubbles, that is different from bubble behavior in chemical detonating underwater. Pulsating behavior and energy characteristic of bubbles are the focus of this study, as well as the difference from chemical detonating. The experimental facility is mainly composed of two parallel energy storage-discharge modules and a water tank. Each module is composed of two 20 μF capacitors and a gas switch located between the capacitors in series. A copper wire with a diameter of 0.9 mm and a length of 50 mm was used as the load. The experimental results show that the deposited energy density generated by electric explosion is almost equal to that of TNT. The wire plasma expansion produces an initial bubble with temperature radially spatial distribution. The times of bubble pulsation are less than 4. After energy exhaustion, bubbles collapse directly into water because the main component is metal vapor. By comparing the experimental data with the existing theoretical models, it is found that the vaporization of water in bubble expansion stage leads to certain energy loss, which makes difference on the motion trajectory of bubbles between the simulation and the experiment. This paper provides ideas and data support for the dynamic study of high temperature bubbles in underwater explosion.
, , Received Date: 2024-09-29
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Thermoreflectance techniques, particularly frequency-domain thermoreflectance (FDTR), play a crucial role in measuring the thermal properties of bulk and thin-film materials. These methods precisely measure thermal conductivity, specific heat capacity, and interfacial thermal conductance by analyzing the temperature-dependent reflectivity changes in materials. However, the complex interplay among parameters presents challenges in data analysis, where single-variable analysis often fails to accurately capture intra-layer and inter-layer interactions. In this work, the FDTR is used as a case study and the relationships between sensitivity coefficients of various parameters are systematically explored through singular value decomposition (SVD). Specifically, the SVD of sensitivity matrix S of the system's parameters is performed to identify smaller singular values and their corresponding right singular vectors, which are the basis vectors of the null space of matrix S . These vectors reveal the relationships among parameter sensitivities, and by contrast, these relationships reveal the most fundamental combination parameters that determine the thermoreflectance signal. This method not only clarifies the dependency relationship between variables but also determines the maximum number of parameters that can be experimentally extracted, and the parameters that must be known beforehand. To demonstrate the practical value of these combination parameters, this work conducts a detailed analysis of FDTR signals from an aluminum/sapphire sample. Unlike traditional FDTR experiments, which typically fit only thermal conductivity and interfacial thermal conductance of substrate, our sensitivity analysis reveals that it is possible to simultaneously determine the thermal conductivity of the metal film, substrate’s thermal conductivity, substrate’s specific heat capacity, and interfacial thermal conductance. The fitting results are consistent with reference values from the literature and measurements from other thermoreflectance techniques, thus validating the effectiveness and reliability of our method. This comprehensive analysis not only deepens the understanding of thermoreflectance phenomena but also provides strong support for the future development of thermal characterization technology and material research, showing the significant potential application of SVD in complex multi-parameter systems.
, , Received Date: 2024-09-17
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As one of the key design parameters of Hall thruster, magnetic field indirectly affects the macroscopic performance of the thruster by directly affecting electron transport, neutral atom ionization, plasma distribution and other microscopic behaviors. At present, the study on the influence of Hall thruster magnetic field focuses more on the size and distribution of the magnetic field in the discharge channel, while the little research on the influence of the plume magnetic field on the thruster. Based on this, the effect of plume region axial magnetic field profile on the performance of Hall thruster is studied by using two-dimensional hybrid simulation. The research results show that the axial magnetic field gradient in the plume region has a significant influence on the thruster performance, when the magnetic field characteristics (magnetic field topology and magnetic field intensity) in the discharge channel remain unchanged. The potential drop in the discharge channel decreases with the axial magnetic field gradient in the plume region decreasing. However，the electric field in the plume region and the peak ion number density in the discharge channel increase with the axial magnetic field gradient in the plume region decreasing. Overall, the performance of the thruster improvement by increasing the magnetic field strength in the plume region. More specifically, there is a critical value of axial magnetic field gradient in the plume region. When the axial magnetic field gradient in the plume region is greater than the critical value, the thrust increases with the axial magnetic field gradient decreasing. When the axial magnetic field gradient of the plume region is less than the critical value, the thrust decreases slightly with the axial magnetic field gradient decreasing. The comparison of plasma potential, electric field, ion number density and ionization rate distribution under different magnetic field distribution in the plume region shows that the effect of plume magnetic field on thrust is to affect the distribution of electric field in space by influencing the mobility of electrons, thus the thrust will change due to electric field. The results of this paper will provide theoretical support for the improvement performance of hall thrusters and the design of magnetic fields.
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The elastic collision cross-section is a key parameter in the study of inter-particle interactions, which helps to reveal the microscopic mechanism of gas insulation. For this reason, the elastic collision cross-sections of 24 gas molecules at 0-15 eV are calculated based on the R-matrix theory, and cross-section characteristic parameters of the lowest resonance state energy and its peak are extracted. Then the calculated and experimental values of SF6, CF2Cl2, and i-C3F7CN cross-sections are compared, and the low-energy cross-section data of i-C3F7CN at 0~1 eV are given for the first time. Furthermore the effects of Cl-substitution and carbon chain length on the cross-section parameters were analysed. Finally the correlation between cross-section characteristic parameters and insulation strength was investigated. The results show that the lowest shape resonance state energy for each molecule is in better agreement with the data from existing studies, with a mean square error of 0.181. F-substitution, the resonance energy gradually increases and the peak value gradually decreases; carbon chain extension is the opposite, the resonance state energy gradually decreases and the peak value gradually increases; The lowest resonance energy and peak value are strongly correlated with the insulation strength. The lower its lowest resonance energy and the larger the corresponding peak value, the higher the molecular insulation strength. Relevant data can theoretically complement existing experimental data. This study provides low energy cross-section properties of a wide range of insulating gas molecules, which can be useful for qualitatively evaluating the insulating properties of gas molecules, and thus for rapid screening of SF6 replacement gases.
, , Received Date: 2024-08-05
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A magnetic flux threading through magnetic atomic rings can induce topological superconductivity. It provides a novel approach to achieving low-dimensional (2D) topological superconductivity, which requires neither spin-orbit coupling nor helical magnetic order. In this paper, we introduce a topological superconductor model by depositing a ferromagnetic atomic ring on the surface of a 2D s-wave superconductor. When the moments of the magnetic atoms are perpendicular to the external magnetic field, a magnetic flux can induce topological superconductivity. Considering practical experiments, because the magnetic atomic chain breaks the inversion symmetry of the surface of the 2D substrate, the Rashba spin-orbit coupling (SOC) is introduced, leading to the appearance of helical magnetic order in the atomic chain. According to previous researches, this helical magnetic order ensures that the magnetic moments of the ring are perpendicular to the external magnetic field, and the patch angle of neighbor moment of the helical order is proportional to the strength of the SOC. However, the helical order or Rashba SOC may introduce topological superconductivity on their own. It is meaningful to investigate the influence of the effects of the Rashba SOC and helical magnetic order on the flux induced topological superconducting states. We find that the Rashba SOC has a disruptive effect on the existing topological state, while helical magnetic order merely shifts its transition position in the parameter space. Therefore, when selecting materials for experiment, it is recommended to choose materials with lower Rashba SOC strength.
, , Received Date: 2024-07-06
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In order to further study the nonlinear characteristics of the resonance magnetoelectric coefficient and vibration mode at the resonance frequency, three-layer magnetoelectric composite with length direction magnetization and thickness direction polarization is investigated in the article. Firstly, based on the Z-L model and the numerical solution characteristics of magnetization intensity, the magnetization intensity function was fitted, and the dynamic parameters of the giant magnetostrictive material, including dynamic piezomagnetic coefficient, dynamic elastic compliance coefficient, and dynamic magnetic permeability, were further derived. The effects of bias magnetic field and prestress on the corresponding composite were analyzed; Secondly, based on the nonlinear magnetostrictive constitutive equation, a symmetric magneto-elastic-electric equivalent circuit model of magnetoelectric laminate composite was established, and the expression of magnetoelectric coefficient was derived. The variation curve with bias magnetic field and prestress was analyzed, which is consistent with the conclusions of existing literature [8] and [9]; Finally, in order to compare with the theoretical results, the same parameters were set using COMSOL software, and the corresponding magnetoelectric coefficient frequency curve was plotted. The two results were in good agreement, and the maximum peak modal vibration shape was extracted, which can conveniently observe the vibration of the magneto electric laminate composite in the length direction. The results indicate that the theoretical model of this symmetric magneto-elastic-electric equivalent circuit and the numerical simulation method using COMSOL software are feasible, laying the foundation for further nonlinear analysis of magnetoelectric laminate composite and making it possible to design high-precision magnetoelectric micro devices.
, , Received Date: 2024-08-28
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In the measurement of pulsed neutrons in the MeV energy range, plastic scintillators are one of the most widely used materials, and their neutron energy spectrum response is the key data required for pulsed neutron energy spectrum measurement. Base on the time of flight (TOF) method, the neutron energy spectrum response of ST401 plastic scintillator with 5 different thicknesses from 0.5 to 10 mm were measured for the 0.5 to 100 MeV energy range on the white neutron source (WNS) beamline of the China Spallation Neutron Source (CSNS). The effects of in-beam gamma rays, the slow component of scintillators produced by the gamma flash and the pulse width of the neutron source on the measurement of neutron spectrum response were analyzed. Due to the boundary effect of the finite volume of the scintillator, the neutron energy spectrum response curves of ST401 with different thicknesses are approximately logarithmic, and proton escape is the main reason for the deviation of the curve from linearity. The thicker the scintillator, the higher neutron energy that deviates from linearity.
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Laser induced sintering, also known as laser enhanced contact optimization (LECO), can significantly reduce the contact resistance between metal electrodes and silicon in TOPCon solar cells, thereby improving its efficiency. This article first studied the effects of LECO process parameters such as reverse bias and laser intensity on the performance of TOPCon solar cells, and analyzed in detail their influencing mechanisms. In the LECO process, as the reverse bias voltage increases, the efficiency of the solar cell first increases and then decreases, while the contact resistivity first decreases and then increases. When the reverse bias voltage is high, the solar cell may be subjected to reverse breakdown. Once the solar cell is reverse breakdown, both the illuminated and non-illuminated areas are in a conducting state. Due to the current diversion effect, the local conducting current density in the illuminated area is much smaller compared to when the solar cell is not reverse broken down. Therefore, the Joule heating caused by this is also much smaller, and the contact resistance between the metal and silicon increases, resulting in a decrease in the efficiency of the solar cell.
Secondly, the influence of secondary high-temperature sintering and secondary LECO on the performance of TOPCon was studied. When the secondary sintering temperature increased from 280 0C to 680 0C, the efficiency of TOPCon sharply decreased from 26.35% to 1.3%. However, by subjecting the solar cells that have undergone secondary high-temperature sintering to secondary LECO treatment, the efficiency can be restored to the level before the secondary high-temperature sintering. Thirdly, TOPCon solar cells prepared using improved pure silver paste does not form effective metal-semiconductor contact between the silver electrode and silicon before LECO treatment, resulting in an average efficiency of only 0.02%. However, after LECO treatment, the efficiency of solar cells using pure silver paste increases to 26.35%, which is 0.41% higher than the reference solar cells using traditional silver aluminum paste. Fourthly, a physical model of LECO induced silver-silicon contact formation was proposed, providing a reasonable explanation for how secondary high-temperature sintering and secondary LECO treatment affect the performance of TOPCon. This is of great significance for further understanding and optimizing the application of LECO technology in TOPCon solar cells.
Secondly, the influence of secondary high-temperature sintering and secondary LECO on the performance of TOPCon was studied. When the secondary sintering temperature increased from 280 0C to 680 0C, the efficiency of TOPCon sharply decreased from 26.35% to 1.3%. However, by subjecting the solar cells that have undergone secondary high-temperature sintering to secondary LECO treatment, the efficiency can be restored to the level before the secondary high-temperature sintering. Thirdly, TOPCon solar cells prepared using improved pure silver paste does not form effective metal-semiconductor contact between the silver electrode and silicon before LECO treatment, resulting in an average efficiency of only 0.02%. However, after LECO treatment, the efficiency of solar cells using pure silver paste increases to 26.35%, which is 0.41% higher than the reference solar cells using traditional silver aluminum paste. Fourthly, a physical model of LECO induced silver-silicon contact formation was proposed, providing a reasonable explanation for how secondary high-temperature sintering and secondary LECO treatment affect the performance of TOPCon. This is of great significance for further understanding and optimizing the application of LECO technology in TOPCon solar cells.
Research on Electromagnetic Characteristics of Plasma Photon Crystal Array Structure Waveguide Model
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Photonic crystal with periodic dielectric constant distribution has become the focus of theoretical and applied research in recent years because of their bandgap structure similar to the electronic states in semiconductors. It is also a promising method for creating a stable low power microplasma. This area of research makes it possible to explore plasma science using microplasmas driven by millimeter wave bands. The dispersive and dissipative properties of plasma make plasma photonic crystals have properties that conventional dielectric photonic crystals do not have. The properties and parameters of plasma photonic crystal can be artificially controlled by changing the parameters of the plasma. To further investigate the influence of photonic crystals on electromagnetic wave transmission, a waveguide model with a plasma photonic crystal array structure was proposed in order to achieve modulation of electromagnetic wave transmission. This proposed model structure can achieve multiple frequency transmission points, making up for the shortcoming of single frequency point transmission in the W-band. Meanwhile, adding a plasma column to the center of defect vacancy in the gradient structure can limit the amplitude of electromagnetic waves and regulate the transmission of electromagnetic waves at different resonant frequencies. The results show that electromagnetic wave can achieve efficient transmission at multiple frequency points such as 85.2 GHz, 92.1 GHz, 98.5 GHz, 102.4 GHz, and 106 GHz without plasma interference, and transmission coefficients are greater than -0.42 dB. The construction of gradient structure can form different strong electric fields around the defect vacancy at the resonance frequency, resulting in gas breakdown and the generation of high-concentration microwave plasma, achieving effective control of the reflected power, transmitted power and absorbed power of electromagnetic wave. When the plasma concentration reaches the plasma frequency equivalent to the incident wave frequency, the electromagnetic wave can be transmitted with less loss during this period. When it reaches a considerable degree or higher, the electromagnetic wave will be rapidly absorbed or reflected by the high concentration plasma, and the transmission power will decrease rapidly, and finally stabilize at a low level. In addition, changing the size of the plasma column can further adjust the transmission characteristics of electromagnetic waves at different frequency points. This study can provide support for the transmission of high-frequency electromagnetic waves and the design of microwave devices.
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In the last decade, X-ray quantum optics has emerged as a new research field, driven by significant advancements in X-ray sources such as new generation synchrotron radiations and X-ray free electron lasers, as well as improvements in X-ray methodologies and sample fabrication. A very successful physical platform is the X-ray planar thin-film cavity, also known as the X-ray cavity QED setup, which represents a significant branch of X-ray quantum optics. So far, most X-ray cavity quantum optical studies are based on the Mössbauer nuclear resonances. However, the scope of the applications is limited by the few available nuclear isotope candidates and the lack of general applicability. Recently, X-ray cavity quantum control in atomic inner-shell transitions has been realized in experiments where the cavity effects simultaneously modify the transition energy and the core-hole lifetime. These pioneer works suggest that the X-ray cavity quantum optics with inner-shell transitions will become a new promising platform. Actually, the core-hole state is the fundamental concept in a variety of modern X-ray spectroscopic techniques. Therefore, integrating X-ray quantum optics with X-ray spectroscopies could lead to potential applications in core-level spectroscopies communities.
In this review, we introduce the experimental systems for the X-ray cavity quantum optics with inner-shell transitions, including the cavity structure, sample fabrications, and experimental methods. We explain that X-ray thin-film cavity samples require high flux, high energy resolution, small beam divergence, and precise angular control, necessitating synchrotron radiations. The grazing reflectivity and fluorescence measurements are shown in Fig.1, along with a brief introduction to resonant inelastic X-ray scattering. We also describe the theoretical simulation tools, including the classical Parratt's algorithm, semi-classical matrix formalism, quantum optical theory based on the Jaynes-Cummings model, and the quantum Green's function method. We discuss the similarities and characteristics of the electronic inner-shell transition compared to the nuclear resonance. Based on the observables, such as reflectivity and fluorescence spectra, we introduce several recent works, including cavity-induced energy shift, Fano interference, and core-hole lifetime control. In conclusion, we summarize the review and discuss several future directions. In particular, designing new cavity structures is essential to addressing current debates on the cavity effects with inner-shell transitions and discovering new quantum optical phenomena. Integrating modern X-ray spectroscopies with X-ray cavity quantum optics is a promising research area that could lead to valuable applications. Furthermore, X-ray free-electron lasers, which offer much higher pulse intensity and much shorter pulse duration, will advance X-ray cavity quantum optics studies from linear to multiphoton and nonlinear regimes.
In this review, we introduce the experimental systems for the X-ray cavity quantum optics with inner-shell transitions, including the cavity structure, sample fabrications, and experimental methods. We explain that X-ray thin-film cavity samples require high flux, high energy resolution, small beam divergence, and precise angular control, necessitating synchrotron radiations. The grazing reflectivity and fluorescence measurements are shown in Fig.1, along with a brief introduction to resonant inelastic X-ray scattering. We also describe the theoretical simulation tools, including the classical Parratt's algorithm, semi-classical matrix formalism, quantum optical theory based on the Jaynes-Cummings model, and the quantum Green's function method. We discuss the similarities and characteristics of the electronic inner-shell transition compared to the nuclear resonance. Based on the observables, such as reflectivity and fluorescence spectra, we introduce several recent works, including cavity-induced energy shift, Fano interference, and core-hole lifetime control. In conclusion, we summarize the review and discuss several future directions. In particular, designing new cavity structures is essential to addressing current debates on the cavity effects with inner-shell transitions and discovering new quantum optical phenomena. Integrating modern X-ray spectroscopies with X-ray cavity quantum optics is a promising research area that could lead to valuable applications. Furthermore, X-ray free-electron lasers, which offer much higher pulse intensity and much shorter pulse duration, will advance X-ray cavity quantum optics studies from linear to multiphoton and nonlinear regimes.
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