High Frequency Properties Research Articles

Zn-Zr substituted M-type Sr-hexaferrites for effective electromagnetic wave absorptions in the 26.5–40 GHz range

This study explores the electromagnetic (EM) wave absorption properties of Zn-Zr substituted M-type Sr-hexaferrites (SrFe12–2xZnxZrxO19, x = 0.3, 0.4, 0.5, 0.6) integrated into polymer composites (10 wt%, epoxy or rubber). The hexaferrite powders were synthesized using solid-state reaction processes with and without the molten-salt (M-S) method. Compared to non-M-S samples, those processed with M-S exhibited larger grain sizes and more defined grain edge shapes without clustering. High-frequency characteristics (ε', ε", μ', and μ") and EM wave absorption properties, specifically reflection loss (RL), were evaluated over the frequency range of 26.5 ≤ f ≤ 40 GHz. Regardless of the M-S method application, hexaferrite-epoxy composites (10 wt%) demonstrated excellent EM wave absorption properties with RLmin < −40 dB and a shifting absorption band corresponding to variations in x, reflecting changes in the ferromagnetic resonance frequency (fFMR). For the x = 0.4 sample, flexible rubber binder (10 wt%) sheets dispersed with hexaferrite powder were fabricated, showing superior broadband absorption characteristics compared to epoxy composites. In rubber sheet form, M-S processed samples exhibited enhanced μ', μ" spectra and improved absorption performance compared to non-M-S samples. The M-S processed hexaferrite-rubber sheet demonstrated broad EM wave performance with RL < −10 dB across the entire frequency range, achieving RLmin = −61 dB at 32 GHz. This study underscores the potential of Zn-Zr-substituted SrM-polymer composites for robust EM wave absorption performance in the Ka-band (26.5–40 GHz), crucial for applications in 5 G communication frequencies.

Preparation of polyimide films with ultralow dielectric loss at high frequency by reducing intermolecular friction

Due to the rapid development of high frequency and high rate communication technology, polyimide (PI) films with ultra-low dielectric loss (Df) at high frequency, excellent thermal and mechanical properties are urgently needed. A series of PI films with ultra-low Df were prepared by introducing different mesogen units. Among them, one novel PI film with biphenyl liquid-crystal-like units (BAHQ-TFMB) achieve a recorded low Df of 0.00169 (10 GHz) which surpasses previous studies on pure PI bulk films. Importantly, the high degree of collinearity of the friction work (Wf) and Df of PI films (Pearson's r = 0.992) was confirmed, which indicate that Wf among PI macromolecules plays an important role in determining Df of PI films. To reveal underlying reason for reducing the Wf and Df of PI films, the contribution of the degree of orientation and crystallinity of PI films with or without liquid-crystal-like structures were comparative studied. Through a two-dimensional orientation determinant, it is found that increasing the crystallinity of liquid-crystal-like PI films is the main contribution to reducing Wf and corresponding Df of PI films while the orientation of PI films seems to have weak effect. Moreover, BAHQ-TFMB PI film exhibits excellent mechanical properties. The tensile strengths is 145.5 ± 12.0 MPa and Young's moduli is 4.76 ± 0.28 GPa.

Effect of divalent metal ions substitution on the magnetic properties of Ba3Co2-xMexFe24O41 (Me = Zn2+, Ni2+) hexagonal ferrites

With the high-frequency development of communication technology, traditional communication materials have been difficult to meet the application requirements. Z-type hexagonal ferrite materials are widely used as good magnetic dielectric materials in high-frequency communication applications due to their high cut-off frequency and magnetodielectric properties. However, the high-frequency magnetodielectric properties need to be further improved, so the magnetic properties of the divalent metal ion-substituted Co2Z hexagonal ferrite materials are studied, and the anisotropy is calculated according to its static magnetic properties in this paper. A series of the ferrites Ba3Co2-xMexFe24O41(Me = Zn2+, Ni2+, where x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were prepared by high-energy ball milling and sintering at 1260℃ for 3 h. The structural and magnetic properties of the samples were investigated using X-ray diffraction, vibrating sample magnetometer, and vector network analyzer. The studies indicated that the magnetic Ni2+ ions substitution increases the cutoff frequency, and the nonmagnetic Zn2+ ions substitution plays a positive role in increasing the magnetic permeability. Particularly, the Ba3Co1.6Ni0.4Fe24O41 and Ba3Co1.2Zn0.8Fe24O41 both have equal permeability and permittivity about 9 and 12, and their cutoff frequency exceed 2 GHz and 1 GHz, respectively. At the same time, these isomagnetic dielectric materials also have low loss, which will have great application potential in microstrip antennas.

Analysis of the Impact of Environmental Conditions on the Reliability in 5G PCB Assemblies

The designs of integrated systems are increasingly compact while the requirements of application, especially in the automotive sector, remain demanding. One main challenge is posed by the environmental conditions. In the present study, their impact on mmWave 5G PCB assemblies is evaluated with respect to both mechanical and highfrequency properties. To that end, material samples were stored at three temperatures for various durations in order to accelerate the ageing effects. Afterwards, the samples were tested by use of mechanical, dielectric and high-frequency test methods. Thermo-oxidative ageing processes were observed and lead to significant changes in mechanical and dielectric properties, with simultaneous changes of sample color. The combined approach of mechanical and high-frequency analysis allows for three innovative advantages: First, a correlation of the degradation in performance with other parameters, e.g. sample change of color, which is much easier to detect. Second, the definition of a Safe Area of Operation and a methodology to estimate the behaviour of a mmWave 5G PCB assembly over its lifetime. Finally, the study opens the pathway to a design for robustness of mmWave communication system in automotive applications.

High-frequency transmission properties of carbon nanofibers with carbonization temperature variations

Carbon nanofibers (CNFs) are promising materials in many fields because they can form multi-purpose matrices of carbon materials and have attractive electric conductivity, dielectric permittivity, thermal stability, and ultrahigh specific surface area. These properties of CNFs significantly depend on the carbonization temperature (CT). Thus, the effect of CT can be primarily crucial for zero- and high-frequency devices and circuits with CNFs. In this study, we report high-frequency transmission properties of the coplanar waveguide line (CPW line) with a CNF film synthesized at CTs of 700 °C, 800 °C, and 900 °C (denoted CNF-700, CNF-800, and CNF-900, respectively) in the frequency ranging from 0.5 to 10 GHz. For all samples, a bare CPW line, a CPW line with a tape, and a CPW line with three kinds of CNF films, the S11 magnitude (reflection coefficient) is less than −10 dB in the frequency range, and the S21 magnitude (transmission coefficient) significantly decreases linearly to −1.3 dB (CNF-700), −3.0 dB (CNF-800), and −5.5 dB (CNF-900) at 10 GHz. Furthermore, the effective permittivity (εeff) of CPW line with CNF films increases with CT, although εeff decreases with increasing frequency. Conversely, due to dielectric and conductive loss of CNF film, the attenuation constant (α) of CPW line with CNF film increases linearly with CTs and frequency. These results indicate that the CPW line with a CNF-900 (CPWCNF-900) shows lossier characteristic than the other CNF films because of finer three-dimensional network structure, higher conductivity, higher attenuation constant, higher shielding effectiveness, and larger effective permittivity. Furthermore, this study shows the possibility that thin CNF films with different CT variations can regulate signal transmission for high-frequency and high-speed circuit and device applications.

Enhanced resonance frequency in Co2FeAl thin film with different thicknesses grown on flexible graphene substrate

The flexible materials exhibit more favorable properties than most rigid substrates in flexibility, weight saving, mechanical reliability, and excellent environmental toughness. Particularly, flexible graphene film with unique mechanical properties was extensively explored in high frequency devices. Herein, we report the characteristics of structure and magnetic properties at high frequency of Co2FeAl thin film with different thicknesses grown on flexible graphene substrate at room temperature. The exciting finding for the columnar structure of Co2FeAl thin film lays the foundation for excellent high frequency property of Co2FeAl/flexible graphene structure. In-plane magnetic anisotropy field varying with increasing thickness of Co2FeAl thin film can be obtained by measurement of ferromagnetic resonance, which can be ascribed to the enhancement of crystallinity and the increase of grain size. Meanwhile, the resonance frequency which can be achieved by the measurement of vector network analyzer with the microstrip method increases with increasing thickness of Co2FeAl thin film. Moreover, in our case with graphene film, the resonance magnetic field is quite stable though folded for twenty cycles, which demonstrates that good flexibility of graphene film and the stability of high frequency magnetic property of Co2FeAl thin film grown on flexible graphene substrate. These results are promising for the design of microwave devices and wireless communication equipment.

High-frequency dielectric properties of K1-Li TaO3 ceramics compared to crystals

High-frequency dielectric properties of K1-Li TaO3 ceramics compared to crystals

High-frequency magnetic properties of FeB nanochains based soft magnetic composites for potential antenna applications up to GHz

Soft magnetic materials are a kind of promising materials for antenna substrates because their permeability and permittivity are both greater than unity. However, their magnetic properties would deteriorate dramatically as the frequency reaches 1 GHz owing to Snoek limit and domain wall resonance, thus limiting their application at high frequency. Here, we report a low-dimensional soft magnetic composite (SMC) prepared by FeB nanochains, achieving the optimized magnetic loss tangent (tanδμ) of 0.09 and the real part of permeability (μ′) of 3.3 at 1 GHz, which is more competitive than the conventional spherical FeB SMCs. Such an optimization is ascribed to the change in the dominant mechanism of the magnetization process from domain wall motion to magnetic moment precession, associated with the transition of the magnetic domain structure of the particles from multi- to mono-domain. The SMC proposed in this work provides a significantly potential candidate for high-frequency and miniaturized 5G antennas. Furthermore, the design concept and preparation method can be extended to other SMCs, providing a guidance for the development of high-performance antenna substrate materials.

High-Tc Josephson Junction Arrays for THz Applications

High-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductors (HTS) like yttrium barium copper oxide (YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> ) pave the way towards readily available and precise voltage standards at liquid nitrogen temperatures. They can be driven by terahertz radiation, thus achieving higher output voltages with a significantly reduced junction count. The reduced effort in cooling also simplifies the overall application. The use of a gallium focused ion beam (Ga-FIB) represents a promising method to tailor the geometry of Josephson junctions after conventional patterning of an array to tune the junction parameters individually. In this work, we present a Josephson junction array made from the HTS YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> based on grain-boundary Josephson junctions. The junction parameters are investigated and afterwards the influence of the Ga-FIB on the junctions is examined. This serves as an important step to show the suitability of this process for HTS voltage standards. Furthermore, the high frequency properties of the array and the associated Shapiro steps are characterized in the terahertz range. This technique represents an important step towards versatile HTS voltage standards.

High-frequency magnetic and dielectric properties of Ba1.5Sr1.5Co1Zn1Fe23O41 hexaferrites with Bi2O3 additives

Ba1.5Sr1.5Co1Zn1Fe23O41 hexaferrites added with x wt% Bi2O3 were successfully prepared, and their phase composition, microstructure, and high-frequency magnetic and dielectric properties were investigated. The results show that the Bi2O3 additive leads to the formation of the W-type ferrite phase and a subsequent increase in its proportion, which affects the magnetic and dielectric properties of Z-type hexaferrites. This effect can be explained by the effective medium theory. Furthermore, Bi2O3 additives improve the compactness and reduces the grain size. The permeability and permittivity of the samples decrease, but the magnetic and dielectric losses are successfully reduced. For x = 1.5 wt%, the samples have a similar permeability and permittivity, a large miniaturization factor (∼18), a cut-off frequency of about 0.9 GHz, and considerably reduced magnetic and dielectric losses. An appropriate amount of Bi2O3 additive improves numerous properties of the Ba1.5Sr1.5Co1Zn1Fe23O41 ferrite, making it a more suitable material for high-frequency miniaturized antennas.

As pessoas, a quasi-pronominal human impersonal construction in European Portuguese?

The grammaticalization of nouns meaning &amp;lsquo;man&amp;rsquo; or &amp;lsquo;person&amp;rsquo; into impersonal pronouns is a well-documented phenomenon found across the world. In Europe, such impersonal pronouns are characteristic of languages with obligatory subject expression like Germanic languages and French (Siewierska, 2011). However, European (EP) and Brazilian Portuguese (BP) also display impersonal uses of noun phrases with the lexeme pessoa &amp;lsquo;person&amp;rsquo; as recently discussed by Posio (2017, 2021) and Amaral and Mihatsch (2019, forthcoming). The present paper analyses the use of the plural form as pessoas &amp;lsquo;the people&amp;rsquo; in a sociolinguistic interview corpus of spoken EP, comparing it with similar data from Peninsular Spanish (Fern&amp;aacute;ndez Juncal, 2005) and with dialectal data from the CORDIAL-SIN corpus (Martins, 2000&amp;ndash;). In terms of frequency, as pessoas occurs over 30 times per 10,000 words in the EP interview data, in contrast to just over 3 occurrences in the CORDIAL-SIN and less than one occurrence of the cognate las personas in the Spanish data. In addition to discussing the high token frequency and other properties associated with grammaticalization, the paper examines the referential and quantificational properties of a gente and explores the hypothesis that as pessoas might be a sociolinguistically conditioned alternative for the impersonal pronoun a gente &amp;lsquo;people; us&amp;rsquo;, considered &amp;lsquo;popular&amp;rsquo; in normative EP. However, this hypothesis is not supported by the data: while sociolinguistic factors do affect the frequency of use of a gente and as pessoas, the two forms are functionally different in that a gente typically includes the speaker in its referential range and as pessoas implies a speaker-exclusive reading. &amp;nbsp;

Electronic and optical aspects of novel quinoxaline derivatives as electron donor materials for bulk heterojunction solar cells

In this paper, we design new forms of organic conjugated compounds-based quinoxaline derivatives. Specifically, we exploit density functional theory and time-dependent-density functional theory in order to study the structure, the optic, the electronic, the reorganization energy and the photovoltaic features of such new molecules. Particularly, all engineered compounds have a narrow band gap in the range of 0.696–0.721 eV, high oscillator frequency and good optical properties. Moreover, the PCBM is employed as an electron acceptor. Employing global reactivity descriptors, we demonstrate that the molecules can efficiently emit electrons into the PCBM and the electrons are attracted to PCBM from molecules. In addition, the results show an appropriate open circuit voltage in the range of 0.338–0.362 V. The proposed compounds exhibit excellent electron transport and charge conduction from the donor to the acceptor. These new molecules show potential properties to develop bulk heterojunction organic photovoltaic cells.

High-frequency magnetic properties of biphase Ce2Fe17N3/α-Fe microflakes with easy-plane anisotropy

Soft magnetic composites (SMCs) are effective as magnetic powder cores in an inductor. Due to high saturation magnetization, large magnetocrystalline anisotropy and high operating frequency of M (metal)-RE (rear earth) soft magnetic composites, it is possible to miniaturize inductor cores by reducing total loss, especially eddy current loss and excess loss at high frequencies. In this article, the characteristics of Ce2Fe17N3/α-Fe (CFN/F) loss per volume and effective permeability reaching a high frequency of 3 MHz are investigated. The biphase CFN/F composite exhibits a high permeability of 16 at 70 MHz, which is two times greater than that of pure Ce2Fe17N3 (CFN) powders. The total loss is as low as 545 mW/cm3 at 3 MHz and 6 mT. The direct current (DC)-bias properties have a percent of permeability exceeding 65% at H = 7960 A/m. This phenomenon indicates that our material has a higher working frequency and lower core loss than other materials; the biphase CFN/F structure is a promising and efficient approach for developing the miniaturized radio frequency (RF) inductor core.

The ferromagnetic resonance (FMR) of SrZ hexaferrite (Sr3Co2Fe24O41), and the tuning of FMR with an external magnetic field

The hexagonal Z-type ferrite Sr3Co2Fe24O41 (SrZ) was first synthesised in 2001 and reported as being a room temperature multiferroic material in 2010, with subsequent investigations into its multiferroic properties, but little into high frequency and microwave properties, and ferromagnetic resonance frequency (FMR), which determines its ability as an electromagnetic (EM) absorber and radar absorbing (RAM) stealth material. It was shown that SrZ existed as a majority or single phase after heating in a narrow temperature range between 1170 and 1190 °C using X-ray diffraction (XRD) and measurement of magnetic hysteresis loops, with the sample appearing to be single phase SrZ at 1190 °C. We measured complex permeability and permittivity of a single phase polycrystalline ceramic sample of SrZ between 500 MHz and 8 GHz (X-band). The sample had a relatively high permittivity >17 over this entire frequency range, and it showed a strong ferromagnetic resonance (FMR) at 2.3 GHz. This FMR could also be tuned by the effect of an external magnetic field, by moving a simple bar magnet progressively closer to a toroidal sample. This incurred a very slight shift in the peak up to 2.48 GHz at distances of 2.5–10 cm from the sample – a tuning of ∼5–6% with applied magnetic fields estimated to be 0.11–0.23 T, which is not insignificant. At a close distance of 0.5 mm we got a high degree of tuning of FMR to 3.4 GHz, a large change of 1.07 GHz (= 46% increase) with an applied magnetic field estimated to be 0.40 T. Despite this, the applied field had no significant effect on permittivity over 0.5–8 GHz. Such results have never been reported before, and are significant, as this would enable tuning of the FMR via simple physical/mechanical movement of a bulk alloy magnet, effectively creating a tuneable microwave filter or absorber.

Investigation on vibration induced fretting in degraded contact interface

Connectors are widely used in electrical systems and are subject to a variety of degradation mechanisms that can negatively impact electrical performance. One major cause of degradation is vibration induced fretting. While there has been considerable work on the effects of general connector degradation and defects on high frequency characteristics, there has been little focused work that specifically considers effects of vibration induced fretting in actual coaxial connector systems.Accordingly, in the present work, a detailed study of an example coaxial connector with a degraded contact surface was conducted, and the effects on vibration induced fretting are characterized using the high frequency results considering the parameters of resistance, capacitance, and inductance. The contact degradation process caused by the fretting was investigated using theoretical analysis, software simulation, and experimental tests. Simulations were performed to evaluate the high frequency behavior within a frequency range of 0.1 MHz to 1.0 GHz. An experimental investigation was conducted to investigate the effect of degraded contact surfaces on high frequency characteristics and provide validation for the model results. The simulation results were consistent with the measured results for both fresh and degraded connectors. Compared to the fresh condition, the S11 parameters and S21 parameters of the first and second degradation levels increased and decreased, respectively. These results indicate that contact damage due to fretting in the sample system generally results in the deterioration of high frequency properties and signal integrity.

High-frequency backscattering properties of quasi-omnidirectional corner reflector: The great-icosahedral-like reflector

The backscattering of perfectly conducting great-icosahedral-like reflectors is studied in the high-frequency domain. This particular faceted polyhedron, composed of 60 trihedral corner reflectors, is introduced to obtain closer omnidirectional backscattering. Due to the high cost of traditional methods, an estimation method for the full-polarized radar cross section is proposed, which is modified from the geometrical optics approximation method. The validity of the improved method is discussed, and its velocity is determined. The estimated results of the reflectors are studied, which lead to a conclusion that this complex structure has high-frequency properties of quasi-omnidirectivity and depolarization.

Biomimetic Synthesis of VOx@C Yolk‐Shell Nanospheres and Their Application in LiS Batteries

AbstractMany biological processes involve active transport where the desired substances can be transported against the concentration gradient with energy consumption. This feature is highly desirable for the synthesis of yolk‐shell structures using preformed capsules to efficiently encapsulate yolk materials. Here, the synthesis of VOx@C yolk‐shell nanospheres by biomimicking prey–predation of carnivorous Utricularia is reported. The high intrinsic frequency and superior mechanical properties of hollow mesoporous carbon spheres (HMCS) maintain their integrity during ultrasonication, making HMCS an ideal capsule. Numerical simulation elucidates that the encapsulation of the VOx nanoparticles is ascribed to the periodic change of pressure and the damping force generated from the relative motion between the mesoporous tunnel in the HMCS and VOx nanoparticles. The resulting VOx@C yolk‐shell nanospheres demonstrate promising application as a regenerative polysulfide‐scavenging layer (RSL) for high‐loading LiS batteries (≈5 mAh cm−2). As compared with the cells with a commercial Celgard polypropylene (PP) separator, those with a RSL present improved capacity retention from 467 to 860 mAh g−1 after 100 cycles, superior rate capability, and reduced impedance. This method provides an additional synthesis tool for yolk‐shell materials otherwise inaccessible by conventional methods with potential applications in energy storage and conversion devices.

Sr2+ Ion Substitution Enhanced Dielectric Properties of Co(2)Z Ferrites for VHF Antenna Substrate

The effect of Sr2+ ions on the microstructure and high frequency properties of 2.5 wt% Bi2O3 added to Co(2)Z hexaferrites (3Ba(1-x)SrxO•2CoO•12Fe2O3, x = 0.0, 0.2, 0.4 and 0.6) synthesised using the solid-state reaction method was investigated. Experimental results indicate that the dielectric properties were markedly enhanced with the increase in the content of Sr2+ ions, thereby increasing the miniaturisation factor, which enables a size reduction in a long frequency range. Slight changes to saturation magnetisation (Ms) and coercivity (Hc) were observed, i.e., the saturation magnetisation (Ms) decreased from 39.99 to 38.11 emu/g, and coercivity (Hc) increased from 59.05 to 65.21 Oe when x increased from 0.0 to 0.6. Meanwhile, ε′ increased from approximately 8 to 12, indicating the invariability in μ′. In addition, the processed materials exhibit relatively low magnetic loss and dielectric loss (magnetic loss tanδμ ≈ 0.08 and dielectric loss (tanδε ≈ 0.007)). These results indicate that the substituted CO(2)Z ferrites have excellent potential in high-frequency antenna applications.

High-frequency magnetic properties and micro-magnetic structure of Co2W-type ferrite with Bi2O3 addition for potential antenna applications

The development of 5G communication technology has launched a serious challenge to the research of communication antenna substrate materials. In this work, we prepared a high-quality Co2W-type ferrite with a near mono-domain structure by oxide addition. It possesses excellent magnetic properties with an operating frequency of up to 2.2 GHz and a permeability of 2.4, which exhibits a significant high frequency advantage over most existing antenna substrate materials. In addition, its high frequency magnetic properties and micro-magnetic structure were deeply investigated based on theoretical fitting and electron microscopy techniques. Such an excellent magnetic properties are credited to the change in magneto-moment dynamics due to the transition of the domain structure by oxide addition. More importantly, this present work not only reveals the effect of micro-magnetic structure on magnetic properties more intuitively, but also provides a promising candidate for high-performance antenna substrate.

High frequency properties of a planar ion trap fabricated on a chip.

We report on the measurement of the high frequency properties of a planar Penning ion trap fabricated on a chip. Two types of chips have been measured: the first manufactured by photolithographic metal deposition on a p-doped silicon substrate and the second made with printed circuit board technology on an alumina substrate. The input capacitances and the admittances between the different trap's electrodes play a critical role in the electronic detection of the trapped particles. The measured input capacitances of the photolithographic chip amount to 65-76 pF, while the values for the printed circuit board chips are in the range of 3-5 pF. The latter are small enough for detecting non-destructively a single trapped electron or ion with a specifically tuned LC resonator. We have also measured a mutual capacitance of ∼85 fF between two of the trap's electrodes in the printed circuit board chip. This enables the detection of single, or very few, trapped particles in a broader range of charge-to-mass ratios with a simple resistor on the chip. We provide analytic calculations of the capacitances and discuss their origin and possible further reduction.