Shielding Structure Research Articles

Fabrication of dual-function conductive cellulose-based composites with layered conductive network structures for supercapacitors and electromagnetic shielding

In this work, a conductive TEMPO-cellulose nanofibers(TONF)/conductive carbon black(CCB)/ Vinasse activated carbon(VAC)(TCA) composite was constructed by electrostatic adsorption, freeze-drying, and hot pressing. In this composite, a conductive TONF composite with good electrical conducting properties was constructed by electrostatic adsorption between TONF and CCB. And the conductive TONF can be used as an ideal dispersant to effectively prevent accumulation between VACs. In addition, TONF imparts TCA composites with excellent mechanical properties. Due to the layered conductive network structure formed by the effective tight stacking between the highly conductive TONF layer and the VAC, the assembled supercapacitor exhibits a high specific capacitance of 263F g−1 (672 mF cm−2), energy density of 23.8 Wh kg−1, and power density of 5.7 KW kg−1. What's more, the assembled supercapacitor can exhibit excellent cycle stability after 12,000 cycles. In addition, An intelligent electromagnetic(EMI) shielding TCA-V composite material with shape memory function was prepared by introducing a dynamically cross-linked polymer Vitrimer. In summary, TCA composites have excellent integration properties, especially electrochemical properties with good stability performance and excellent EMI shielding properties. These remarkable features make nano cellulose/carbon-matrix composites have great attraction and potential in the field of supercapacitors and intelligent EMI shielding.

Effect of Determinants on Financial Leverage in FMCG Industry: An Empirical Study of Capital Structure Prior to COVID-19

FMCG stands for fast-moving consumer goods industry, also known as consumer packaged goods, which refers to an industry engaged in the production of packaged food, cosmetics, household goods and other readily consumable items. This industry’s main characteristics reveal frequent purchases by consumers, high inventory turnover and a short shelf life. The FMCG industry is the fourth-largest sector in the Indian economy. This study is aimed at understanding the capital structure financing and investigating the relationship between the capital structure determinants and financial leverage of NIFTY FMCG companies from the year 2000 to 2018, prior to the COVID-19 breakdown health emergency. It has been stated in the World Bank report for 2019 that India is the seventh largest consumer market in the world, which includes elements like private consumption, investments and exports, thus encouraging the study of the capital structure of FMCG companies to be conducted. It is postulated that the capital structure determinants are profitability, growth opportunity, size, risk, non-debt tax shield, liquidity and asset structure. It is believed that liquidity is expected to play an important role as a capital structure determinant. Thus, an approach is developed to investigate the impact of capital structure determinants on the debt ratio of FMCG firms in the light of capital structure theories.

Investigation on the Stress and Deformation Evolution Laws of Shield Tunnelling through a Mining Tunnel Structure

In the construction of a shield crossing an existing mined tunnel without load, it is imperative to develop corresponding design standards that reflect actual engineering force characteristics to ensure the successful completion of the tunnel construction. This study uses the MIDAS-GTS NX 2022 finite element software to facilitate the creation of a numerical model of a shield structure for an air-push-over mine tunnel project in Changsha, China while investigating the stress field’s evolution during shield construction and calculating the maximum positive and negative bending moments and maximum axial forces for different structures and other force states under various construction conditions. This study’s findings informed the design and construction optimisation of a shield tunnelling empty-push method. The outcomes of this numerical simulation led to several key findings: (1) The soil density exerted a significantly greater impact on the internal forces of the initial support structure than both the tunnel depth and soil Poisson’s ratio. Additionally, a sudden shift in internal forces occurred within the 300–350 mm range when the lining thickness was altered. (2) Factors such as the tunnel depth, soil density, soil Poisson’s ratio μ, and lining thickness similarly influenced the internal forces of the segment and the initial support. Notably, the backfill layer thickness significantly affected the segment’s maximum axial force, causing an abrupt change of approximately 300 mm. (3) It is essential to control the guide rail’s thickness under the shield machine equipment’s weight constraint to prevent it from becoming overly large.

Copper-nickel electroplating of 3D-printed acrylonitrile butadiene styrene for interference and radiation shielding applications

In this study, electromagnetic and radiation shielding structures were fabricated by 3D printing acrylonitrile butadiene styrene (ABS) structures via fused filament fabrication and electroplating with copper (Cu) and nickel (Ni) metals. Prior to electroplating, the printed ABS materials were made conductive by surface electrodepositon of polypyrrole (PPy). ABS adsorbs the pyrrole monomer, which subsequently polymerizes via oxidation forming conductive PPy layer on the printed structures. The successful anchoring of PPy layer can be attributed to its hydrogen bonding and electrostatic interactions with ABS. Thermal analysis, optical, and electron microscopy equipped with energy dispersive X-ray were employed to characterize the printed shielding structures, while the interference and radiation shielding effectiveness were evaluated using a spectrum analyzer and dosimeter, respectively. The interference shielding was found to be effective at 60 ± 5 dB over relatively small frequency range. Shielding was also apparent against gamma and X-ray ionizing rays, but more significantly effective against beta rays. Furthermore, the Cu/Ni coating was able to reduce any heat-induced dimensional changes for the 3D printed ABS substrate without compromising the mechanical integrity.

Eddy currents analysis methods for an MRI longitudinal gradient coil.

The rapid switching of the gradient fields induces eddy currents in neighboring metallic structures, causing undesirable effects. Numerical computations are thus required to understand eddy-currents effects for designing/implementing mitigation (involving passive shielding) and compensating techniques (using pre-emphasis). Previously, the network-analysis (NA) method was introduced to compute z-gradient eddy currents, although limited to a circularly symmetric and unconnected coil. Multi-layer integral method (MIM) method was recently introduced, modifying the circuit equation involving stream functions. We tailor MIM (TMIM) for a more general eddy-currents analysis in thin structures. Z-gradient eddy currents are analyzed and then compared using three methods (NA, TMIM, and Ansys). The analysis helps to evaluate the efficiency of passive shielding and to compensate eddy currents. NA and TMIM computational frameworks for harmonic and transient eddy-currents analysis were implemented and cross-validated against Ansys Maxwell. A pre-emphasis pulse was modeled for compensating eddy currents. Eddy-currents analysis of an unconnected z-gradient coil in both the passive shield and cryostat were computed, and results were comparable to the least computationally efficient Ansys simulations. Although NA computations are fast, TMIM is implemented with reasonable efficiency and applied to circularly unsymmetric geometries. TMIM computations were further validated against Ansys using a connected z-gradient. Our computations allowed the effective evaluation of the performance of three various passive-shielding configurations, non-capped, capped, and slitted (for the first time), and an effective pre-emphasis compensation model was computed. Three eddy-currents analysis methods were studied and compared. Computationally efficient TMIM allows both harmonic and transient eddy-currents analysis involving different/complex gradient configurations/situations as well as involved shielding structures. Eddy-currents pre-emphasis compensation was demonstrated.

Private Equity Leveraged Buyout Analysis: Evidence from Citrix Transaction

Evaluations of the leveraged buyout and the consideration of debt schedule are critical for private equity funds. Large amounts of debt can create value for a firm but increase the risk simultaneously. This paper describes the result of a specific transaction’s valuation based on the adjusted present value, the weighted average cost of capital method, and the equity cash flow valuation methods. The same results are presented by each method, but the interpretation can be quite different. Besides, the value creation to the firm through each variable in different methods and the validation steps are discussed. Furthermore, this paper presents the performance indicators: internal rate of return and cash on cash multiple. These results shed light on demonstrating the impact of tax shield and capital structure on the enterprise value, cost of equity, and cost of capital calculation.

A portable and monoenergetic 24 keV neutron source based on 124Sb-9Be photoneutrons and an iron filter

A portable monoenergetic 24 keV neutron source based on the 124Sb-9Be photoneutron reaction and an iron filter has been constructed and characterized. The coincidence of the neutron energy from SbBe and the low interaction cross-section with iron (mean free path up to 29 cm) makes pure iron specially suited to shield against gamma rays from 124Sb decays while letting through the neutrons. To increase the 124Sb activity and thus the neutron flux, a >1 GBq 124Sb source was produced by irradiating a natural Sb metal pellet with a high flux of thermal neutrons in a nuclear reactor. The design of the source shielding structure makes for easy transportation and deployment. A hydrogen gas proportional counter is used to characterize the neutrons emitted by the source and a NaI detector is used for gamma background characterization. At the exit opening of the neutron beam, the characterization determined the neutron flux in the energy range 20–25 keV to be 6.00±0.30 neutrons per cm2 per second and the total gamma flux to be 245±8 gammas per cm2 per second (numbers scaled to 1 GBq activity of the 124Sb source). A liquid scintillator detector is demonstrated to be sensitive to neutrons with incident kinetic energies from 8 to 17 keV, so it can be paired with the source as a backing detector for neutron scattering calibration experiments. This photoneutron source provides a good tool for in-situ low energy nuclear recoil calibration for dark matter experiments and coherent elastic neutrino-nucleus scattering experiments.

A numerical approach for assessing internal pressure capacity at liner failure in the expanded free-field of the prestressed concrete containment vessel

Since containment building is the major shielding structure to ensure safety of nuclear power plant, the structural behavior and ultimate pressure capacity of containments must be studied in depth. This paper addresses ambiguous issue of determining free-field position for liner failure by suggesting an expanded free-field region and comparing internal pressure capacities obtained by test data, conservative assumption and suggested free-field region. For this purpose, a practical approach to determine the free-field position for the evaluation of liner tearing is carried out. The maximum principal strain histories versus internal pressure capacities among different free-field positions at various azimuths and elevations are compared with those at the equipment hatch as a conservative assumption. The comparison shows that there are considerable differences in the internal pressure capacity at liner failure within the expanded free-field region compared to the vicinity of the equipment hatch. Additionally, this study proposes an approximate correlation with conservative factors by considering the expanded free-field ranges and material characteristics to determine realistic failure criteria for liner. The applicability of the proposed correlation is demonstrated by comparing the internal pressure capacities of full-scale containment buildings following liner failure criteria according to RG 1.216 and an approximate correlation.

Low-Loss Pogo Pin Probe Card with a Coupling Isolation Structure up to 50 GHz

A design for a millimeter wave RF probe card that removes resonance is proposed. The designed probe card optimizes the position of the ground surface and the signal pogo pins to resolve the resonance and signal loss issues that occur when connecting a dielectric socket and a PCB. At millimeter wave frequencies, the height of the dielectric socket and pogo pin matches the length of half a wavelength, allowing the socket to act as a resonator. When the leakage signal from the PCB line is coupled to the 2.9 mm high socket with pogo pins, resonance at a frequency of 28 GHz is generated. The probe card uses the ground plane as a shielding structure to minimize this resonance and radiation loss. The importance of the signal pin location is verified via measurements in order to address the discontinuity caused by field polarity switching. A probe card fabricated using the proposed technique exhibits an insertion loss performance of −8 dB up to 50 GHz and eliminates resonance. A signal with an insertion loss of −3.1 dB can be transmitted to a system-on-chip in a practical chip test.

Development of a 7T 1H/2H dual-tuned transceiver separation active decoupler MRI probe

Based on the current deuterium metabolism imaging (DMI) technology analysis, a design scheme of a dual-core imaging coil suitable for a 7T MRI system is proposed. The size and structure of the shield layer are optimized. Based on the single-layer shield structure, a double-layer shield structure is proposed to improve the stability of the probe. A detuning circuit is added to the 2H transmitting and receiving coils so that they can work in time for better decoupling. According to the design scheme, the 1H/2H dual-core imaging coil was fabricated and applied to the 7T magnetic resonance system. We performed imaging experiments on D2O samples and quantitatively compared the correlation performance (SNR) of a 1H/2H dual-tuned RF coil with the same size deuterium transceiving-receiving integrated surface coil. The results verified that deuterium metabolism imaging using 1H/2H dual-tuned transmit-receiving separation MRI probe can effectively improve the signal-to-noise ratio of the target region.

Analysis of Projectile Impact Resisting Characteristics of Hollow Triangular Matrix Structure

The numerical simulation of engineering structural elements and spatial combination form of the polarizing body using common engineering materials is carried out, and the triangular hole matrix space combination structure is proposed. The penetration depth and deflection angle of the projectile under different projectile velocities and incident positions are obtained by numerical simulation of the projectile impacting the composite structure under various working conditions. At the same time, through the comparative study of ordinary solid shell shielding structures, it is found that the higher the projectile velocity, the higher the shell shielding effectiveness of triangular hole matrix space composite structure.

Recent Developments of Shielding Effectiveness for Electronics and Information Devices

With the increase wireless communications, many wireless devices and equipment have been invented for special applications, resulting in mutual interference that might destroy the systems or distort signal in-transmission. One of the effective methods to reduce or eliminate interference is to devise a shielding to block the unwanted interference in between the approaching systems, circuits, devices, etc. Thus, shielding and estimation of its effectiveness are very important in order to protect the information devices from potential interference and to improve the performance of information equipment. In this survey, we present the recent developments of the shielding and shielding effectiveness techniques and methods, and give a design for an electromagnetic shielding structure.

Structure formation by electrostatic interactions in strongly coupled medium.

The formation of correlated structures is of importance in many diverse contexts such as strongly coupled plasmas, soft matter, and even biological mediums. In all these contexts the dynamics are mainly governed by electrostatic interactions and result in the formation of a variety of structures. In this study, the process of formation of structures is investigated with the help of molecular dynamics (MD) simulations in two and three dimensions. The overall medium has been modeled with an equal number of positive and negatively charged particles interacting via long-range pair Coulomb potential. A repulsive short-range Lennard-Jones (LJ) potential is added to take care of the blowing up of attractive Coulomb interaction between unlike charges. In the strongly coupled regime, a variety of classical bound states form. However, complete crystallization of the system, as typically observed in the context of one-component strongly coupled plasmas, does not occur. The influence of localized perturbation in the system has also been studied. The formation of a crystalline pattern of shielding clouds around this disturbance is observed. The spatial properties of the shielding structure have been analyzed using the radial distribution function and Voronoi diagram. The process of accumulation of oppositely charged particles around the disturbance triggers a lot of dynamic activity in the bulk of the medium. As a result of this, close encounters are possible even between those particles/clusters which were initially and/or at some point of time widely separated. This leads to the formation of a larger number of bigger clusters. There are, however, also instances when bound pairs break up and the electrons from bound pairs contribute to the shielding cloud, whereas ions bounce back into the bulk. A detailed discussion of these features has been provided in the manuscript.

Pankun: A New Generation of Broadband Ocean Bottom Seismograph.

This paper presents a new broadband ocean bottom seismograph (OBS) developed by the SUSTech OBS lab for passive-source seafloor seismic observations. This instrument, called Pankun, has several key features that set it apart from traditional OBS instruments. In addition to the seismometer-separated scheme, these features include a unique shielding structure to minimize current-induced noise, a compact gimbal for accurate leveling, and low power consumption for extended operation on the seafloor. The design and testing of Pankun's primary components are thoroughly described in this paper. The instrument has been successfully tested in the South China Sea, demonstrating its ability to record high-quality seismic data. The anti-current shielding structure of Pankun OBS has the potential to improve low-frequency signals, particularly on the horizontal components, in seafloor seismic data.

Graphene and Fe2O3 filled composites for mitigation of electromagnetic pollution and protection of electronic appliances

With extensive advancement and abundant availability of telecommunication and electronic devices, electromagnetic pollution has become a serious concern not only for human health but also for much sensitive electronic equipment which may fail or malfunction due to electromagnetic interference. Therefore, effective and lightweight electromagnetic interference (EMI) shielding structures are of vital importance for human protection as well as for safeguarding sensitive electronic equipment from interference. In this regard, carbon fiber reinforced composite structures (CFRCS) have proven as one of the best options due to their light weight, extraordinary mechanical properties, and excellent durability. This study explored the synergistic incorporation of graphene and ferric oxide nanoparticles in the CFRCS at various loading concentrations to enhance their electromagnetic shielding effectiveness (EMI SE). According to the results, maximum EMI shielding effectiveness of 95.57 dB was attained at a 4% loading concentration of graphene and a 6% loading concentration of ferric oxide, over a broader frequency range of 0.1 GHz–13.6 GHz. In light of these results, different EMI shielding structures can be developed, including EMI shielding rooms for better protection of humans as well as any sensitive electronic equipment from the harmful effect of electromagnetic radiation. The obtained results are outstanding and may be employed commercially for the protection of electronic equipment and human individuals.

Multi-coupled biomimetics for tire noise reduction

To explore ways of reducing tire noise, a 205/55R16 KR10 semi-steel radial tire was used as the research object. Vibration noise and aerodynamic noise were analyzed using the modal transfer vector method and the computational fluid dynamics method respectively. The cat’s paw pads can swivel left to right when walking, which dampens vibrations. The left-right pivoting characteristics of the cat’s paw pads are successfully transplanted into the tire by opening asymmetric bypass tube grooves in the tread to form a bionic tire. The results showed that the bionic tire can effectively decrease vibration noise. However, without considering the bypass tube’s resonant muffler acoustic noise reduction, the bionic tire increased aerodynamic noise. According to the multi-coupling bionic concept, the shark scale shield structure is coupled based on the bionic tire, and the shark-like structure is targeted at the sound source to form a multi-coupled bionic tire. Characterized by the left and right pendulum positive damping motion of the cat’s paw pad as well as the non-smooth damping structure of the shark scale shield, the multi-coupled bionic tire jointly reduced the tire vibration noise and aerodynamic noise.

Radiation Protection at Petawatt Laser-Driven Accelerator Facilities: The ELI Beamlines Case

ELI Beamlines is a newly constructed petawatt (PW) laser-based accelerator facility. Its flagship laser has a nominal peak power of 10 PW with a pulse duration of 150 fs. The radiation fields emerging from the laser-target interactions will be pulsed and made of mixed particles of high intensity and energy, thus posing new and daunting challenges compared to conventional radiation protection. The civil engineering constraints of a laser facility bring localized weaknesses to the shielding structures. The ultrashort pulses in conjunction with ultrahigh dose rates strain the capabilities of the commercially available radiation detectors. The complexity of modeling laser-target interactions and the resulting ionizing radiation complicates the radiation protection calculations. This paper is a review of the radiation protection challenges at ELI Beamlines, the adopted solutions, and the practices to minimize the harmful effects of ionizing radiation linked to its activities. Some of the presented solutions may have universal validity, while others are specific to this site and can only serve as an inspiration.

Study on leakage magnetic field and magnetic field shielding for transformers

This paper deals with the leakage magnetic field calculation and magnetic field shielding design of transformers. A large-capacity traction transformer is firstly established, and its magnetic flux density and eddy current loss of the transformer tank are calculated by the layered subdivision method and the surface impedance method. To reduce the eddy current loss of the tank, plate-shaped magnetic shielding and electromagnetic shielding are installed on the surface of the tank. And the simulation results show that plate-shaped magnetic shielding has better shielding effectiveness compared with electromagnetic shielding. Then based on the plate-shaped magnetic shielding, the tile-shaped magnetic shielding is proposed to further reduce the magnetic flux density and loss of the tank. By analyzing the shielding effect of tile-shaped shielding at different heights and widths, the tile-shaped shielding structure with the best shielding effect is obtained. Finally, the advantages of tile-shaped shielding are verified by magnetic-thermal coupling analysis.

Machine Learning Empowered Magnetic Substrate Coupled Broadband and Miniaturized Frequency Selective Surface

This works offers a polarization-insensitive, wide angular stable, and wideband electromagnetic interference shielding structure using an integration of frequency selective surface (FSS) with magnetic substrates. The equivalent circuit model (ECM) together with the analytical model is derived to figure out the physics of the shielding structure. The overall inductance of the shielding structure is increased using a magnetic ferrite sheet and magnetic silicon rubber sheet as substrates. Further, four different deep neural network configurations are investigated with inverse modeling to predict the shielding structure parameters within a fraction of seconds. The mse between expected and predicted output is only 2.92 × <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{-8}$</tex-math></inline-formula> . The entire X-band is shielded with a minimum 10-dB shielding effectiveness (SE) and with SE of 56 dB at resonance. The FSS unit cell size is only 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> × 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> . Furthermore, the proposed shielding structure shows stable transmission performance up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$75^{\circ}$</tex-math></inline-formula> angle of incidence for both perpendicular and parallel polarization. Finally, a prototype is fabricated and measured using nondestructive free space measurement. Good agreement among the simulated, ECM, analytical model, and measured results demonstrate the efficacy of the proposed technique for building an effective shielding structure.

An Electric Field Probe With High Immunity for SiC MOSFET Switching Voltage Measurement

Accurate measurement of switching voltage is the basis for evaluating the dynamic behavior of power devices. With the development of wide bandgap (WBG) devices, the high switching speed of the silicon carbide metal–oxide–semiconductor field-effect transistors (SiC MOSFETs) imposes high bandwidth and strong immunity requirements on the voltage probe. The electric field probe (EFP) based on the principle of electric field coupling has a naturally high bandwidth, which can be considered as a potential competitor. However, due to the noncontact suspended measurement method, the interference signal is easily coupled by the EFP and affects the measurement accuracy. Thus, this article proposes a high noise-immune structure for EFP to implement the measurement of SiC MOSFET switching voltage. The EFP is manufactured from the printed circuit board (PCB), which can provide a more accurate parameter design. Then, the shielded copper clad and via arrays structures are proposed, and the effectiveness of the shielding structure is verified by adding an interference source. Finally, through the double-pulse test, it is demonstrated that the performance of the proposed EFP is sufficient to measure the switching voltage of SiC MOSFETs.