Gigahertz Frequencies Research Articles

Bias field orientation driven reconfigurable magnonics and magnon−magnon coupling in triangular shaped Ni80Fe20 nanodot arrays

Reconfigurable magnonics have attracted intense interest due to their myriad advantages including energy efficiency, easy tunability and miniaturization of on-chip data communication and processing devices. Here, we demonstrate efficient reconfigurability of spin-wave (SW) dynamics as well as SW avoided crossing by varying bias magnetic field orientation in triangular shaped Ni80Fe20 nanodot arrays. In particular, for a range of in-plane angles of bias field, we achieve mutual coherence between two lower frequency modes leading to a drastic modification in the ferromagnetic resonance frequency. Significant modification in magnetic stray field distribution is observed at the avoided crossing regime due to anisotropic dipolar interaction between two neighbouring dots. Furthermore, using micromagnetic simulations we demonstrate that the hybrid SW modes propagate longer through an array as opposed to the non-interacting modes present in this system, indicating the possibility of coherent energy transfer of hybrid magnon modes. This result paves the way for the development of integrated on-chip magnonic devices operating in the gigahertz frequency regime.

Electrochemically modulated interaction of MXenes with microwaves.

Dynamic control of electromagnetic wave jamming is a notable technological challenge for protecting electronic devices working at gigahertz frequencies. Foam materials can adjust the reflection and absorption of microwaves, enabling a tunable electromagnetic interference shielding capability, but their thickness of several millimetres hinders their application in integrated electronics. Here we show a method for modulating the reflection and absorption of incident electromagnetic waves using various submicrometre-thick MXene thin films. The reversible tunability of electromagnetic interference shielding effectiveness is realized by electrochemically driven ion intercalation and de-intercalation; this results in charge transfer efficiency with different electrolytes, accompanied by expansion and shrinkage of the MXene layer spacing. We finally demonstrate an irreversible electromagnetic interference shielding alertor through electrochemical oxidation of MXene films. In contrast with static electromagnetic interference shielding, our method offers opportunities to achieve active modulation that can adapt to demanding environments.

Characterization of Transmission Lines in Microelectronic Circuits Using the ARTEMIS Solver

Modeling and characterization of electromagnetic wave interactions with microelectronic devices to derive network parameters has been a widely used practice in the electronic industry. However, as these devices become increasingly miniaturized with finer-scale geometric features, computational tools must make use of manycore/GPU architectures to efficiently resolve length and time scales of interest. This has been the focus of our open-source solver, ARTEMIS (Adaptive mesh Refinement Time-domain ElectrodynaMIcs Solver), which is performant on modern GPU-based supercomputing architectures while being amenable to additional physics coupling. This work demonstrates its use for characterizing network parameters of transmission lines using established techniques. A rigorous verification and validation of the workflow is carried out, followed by its application for analyzing a transmission line on a CMOS chip designed for a photon-detector application. Simulations are performed for millions of timesteps on state-of-the-art GPU resources to resolve nanoscale features at gigahertz frequencies. The network parameters are used to obtain phase delay and characteristic impedance that serve as inputs to SPICE models. The code is demonstrated to exhibit ideal weak scaling efficiency up to 1024 GPUs and 84% efficiency for 2048 GPUs, which underscores its use for network analysis of larger, more complex circuit devices in the future.

Управление свойствами магнитоупругих волн в слоистых антиферромагнитных гетероструктурах

In this work we present a model explaining the properties of magnetoelastic waves propagation in the heterostructure containing an antiferromagnetic layer on a non-magnetic elastic substate. The dispersion characteristic of magnetoelastic waves in such structure was obtained, and the effect of variation of the thickness of the antiferromagnetic layer and the external magnetic field on the frequency of the magnetoelastic resonance on the elastic structure was also studied. It was found that an increase in the magnetic field magnitude leads to the increase with pressure of the magnetoelastic resonance frequency, and, on the contrary, with an increase in the thickness of the AFM layer the magnitude of the magnetoelastic resonance frequency decreases. The results obtained can be used to create devices for generating and processing signals in the gigahertz and terahertz frequency ranges.

Evaluation of Viral Inactivation on Dry Surface by High Peak Power Microwave (HPPM) Exposure.

Previous research has shown that virus infectivity can be dramatically reduced by radio frequency exposure in the gigahertz (GHz) frequency range. Given the worldwide SARS-CoV-2 pandemic, which has caused over 1 million deaths and has had a profound global economic impact, there is a need for a noninvasive technology that can reduce the transmission of virus among humans. RF is a potential wide area-of-effect viral decontamination technology that could be used in hospital rooms where patients are expelling virus, in grocery and convenience stores where local populations mix, and in first responder settings where rapid medical response spans many potentially infected locations within hours. In this study, we used bovine coronavirus (BCoV) as a surrogate of SARS-CoV-2 and exposed it to high peak power microwave (HPPM) pulses at four narrowband frequencies: 2.8, 5.6, 8.5, and 9.3 GHz. Exposures consisted of 2 µs pulses delivered at 500 Hz, with pulse counts varied by decades between 1 and 10,000. The peak field intensities (i.e. the instantaneous power density of each pulse) ranged between 0.6 and 6.5 MW/m2 , depending on the microwave frequency. The HPPM exposures were delivered to plastic coverslips containing BCoV dried on the surface. Hemagglutination (HA) and cytopathic effect analyses were performed 6 days after inoculation of host cells to assess viral infectivity. No change in viral infectivity was seen with increasing dose (pulse number) across the tested frequencies. Under all conditions tested, exposure did not reduce infectivity more than 1.0 log10. For the conditions studied, high peak power pulsed RF exposures in the 2-10 GHz range appear ineffective as a virucidal approach for hard surface decontamination. © 2023 Bioelectromagnetics Society.

ECONOMIC EFFICIENCY OF VOLTAGE AND TEMPERATURE DRIFT COMPENSATION CIRCUIT FOR DIGITAL DELAY LINE

Nowadays when semiconductor devices sizes reached to the few nanometers, high-speed SERDES systems became less power-consuming, and systems operating frequen-cies reached dozens of gigahertz. Despite these advantages, devices became more vulne-rable against temperature-voltage drifts. Also, because of dozens of gigahertz frequency data transmission, it became more complicated to meet timing constraints in Serdes sys-tems. Therefore, it is important to have stable de-skew mechanisms, otherwise data loss and other timing issues can be observed. One of the commonly used circuits to over-come this problem is digital delay lines (DDL). Often integrated circuits (IC) being used in non-standard environments, so it is necessity to have voltage-temperature (VT) compensation circuit (VTDCC), otherwise DDL will lose its effectiveness. The development of the proposed of VTDCC has become an economically important condition, because VTDCC allows digital delay line (DDL) to work correctly in non-standard conditions, which increases the demand for DDL. Digital delay line with included compensation circuit has shown around 51% DDL delay range improvement during non-standard conditions VT drift compensation circuit requires an additional 37% area in DDL.

Anomalous diffusion, gigahertz, and terahertz spectroscopy of aliphatic ketones.

The experimental results of the complex dielectric permittivity of aliphatic ketones in dilute solutions of inert solvent cyclohexane in the gigahertz (GHz) and terahertz (THz) frequencies of the electromagnetic spectrum are examined in terms of the theory of inertial anomalous diffusion of polar molecules, considered as an assembly of molecules with interacting dipolar groups, in polar liquids. The theory is based on the generalization of the Debye rotational diffusion model of dielectric relaxation of polar molecules. The model comprises two interacting dipolar groups-one lighter and the other heavier; each has a finite moment of inertia and each experiences a finite friction with an extensive range of damping or drag coefficient and the dipole moment ratio of the two groups. The lighter group refers to the reference molecule, whereas the heavier group simulates the neighboring molecules, and the two groups interact with each other via the dipole-dipole interaction potential. The resulting approximate expression contains terms in both the Rocard form and the Сole-Сole form. The experimental data on aliphatic ketones are shown to fit extremely well with the theory, and parameters of the fit offer physical significance. An agreement of the plot of the experimental data on dielectric loss versus frequency to the formulas derived from the model offers a mathematical basis of the semiempirical equations used in the literature to fit the experimental data. Experimental results of the dielectric loss of neat polar liquid acetone in GHz and THz, as an example, are shown to fit the theory; however, the interaction potential parameter compared to its dilute solution counterpart is significantly increased, reflecting the increase in the dipole-dipole interaction energy.

Performance Analysis of MEMS Based Oscillator for High Frequency Wireless Communication Systems

The frequency oscillator is a basic component found in many electrical, electronic, and communications circuits and systems. Oscillators come in a variety of shapes and sizes, depending on the frequency range employed in a given application. Some applications need oscillators that generate low frequencies and other applications need oscillators that generate extremely high and high frequencies. As a result of the expansion and speed of modern technologies, new oscillators appeared that operating at extremely high frequencies. Most wireless communication systems are constrained in their performance by the accuracy and stability of the reference frequency. Because of its compatibility with silicon, micro-electro-mechanical system (MEMS) is the preferred technology for circuit integration and power reduction. MEMS are a rapidly evolving area of advanced microelectronics. The integration of electrical and mechanical components at the micro size is referred to as a MEMS. MEMS based oscillators have demonstrated tremendous high frequency application potential in recent years. This is owing to their great characteristics such as small size, integration of CMOS IC technology, high frequency-quality factor product, low power consumption, and cheap batch manufacturing cost. This paper's primary objective is to describe the performance of MEMS oscillator technology in high-frequency applications, as well as to discuss the challenges of developing a new MEMS oscillator capable of operating at gigahertz frequencies.

Low clock skew superconductor adiabatic quantum-flux-parametron logic circuits based on grid-distributed blocks

Adiabatic quantum-flux-parametron (AQFP) is a promising superconductor logic family exhibiting extremely low switching energy. Traditional excitation of AQFP circuits depends on a pair of ac sources (i.e., four-phase clocking), whose currents are propagated throughout the chip to excite and clock each gate sequentially. This scheme, however, produces a considerably large clock skew due to the long propagation of the current pair and will heavily limit the scalability of an AQFP circuit. In this work, a global clocking scheme for low skew AQFP circuits is proposed based on microwave H-tree excitation networks and grid-distributed blocks. The H-tree network starts with a single transmission line (TL) but is exponentially split to several levels of TLs by using passive splitters, creating multiple leaves at the final level. A large-scale AQFP circuit can thus be distributed into several local blocks and clocked synchronously by the split currents from these leaves. Therefore, the accumulation of clock skew is limited to a small value only within each local block. For validation, a test circuit comprising four blocks with data interconnections between each other, and a 1-to-4 H-tree excitation network is demonstrated, where we obtain correct operation and wide excitation margins at gigahertz frequencies. The proposed clocking scheme is advantageous for the realization of very large-scale adiabatic superconductor logic circuits in the future.

Electromagnetic Interference Shielding and Characterization of Ni2+ Substituted Cobalt Nanoferrites Prepared by Sol-Gel Auto Combustion Method

The structural, magnetic, and dielectric properties of a series of Ni2+ substituted cobalt nanoferrite particle samples with the composition Co1−xNixFe2O4 (where x = 0.0 ≤ x ≤ 1.0) synthesized by using the sol-gel auto combustion route are presented in this report. The electromagnetic interference shielding of Co1−xNixFe2O4/PVA nanocomposite films has been determined in the microwave X-band (8.2–12.4 GHz) frequencies. X-ray analysis revealed the single-phase formation of nickel-substituted cobalt nanoferrite samples. The decreasing trend of lattice parameters with Ni2+ substitution indicates the incorporation of Ni2+ into the crystal structure, obeying Vegard’s law. FTIR showed the absorption bands at 560–590 cm−1 ( v 1 ) and 390–400 cm−1 ( v 2 ) were attributed to (A-site) tetrahedral and (B-site) octahedral groups complex, respectively which confirm the spinel structure of the samples. Field emission scanning electron microscopy showed agglomerated grains of different sizes and shapes in the morphological observation. EDS reveals the chemical composition of the prepared samples. TEM analysis revealed that the synthesized particles were nearly monodisperse, show to be roughly spherical in shape, and have a polycrystalline nature. The dielectric constant and loss tangent (tanδ) is found to decrease with increasing frequency which shows normal behavior for ferrimagnetic materials. The magnetic properties determined using VSM have substantially changed with the substitution of Ni2+ ions. The saturation magnetization and the experimentally magnetic moment are observed to decrease with an increase in Ni2+ content x. A series of Co1−xNixFe2O4/PVA nanocomposite films are prepared by applying simple, rapid, and inexpensive methods for EMI shielding materials. The vector network analyzer data were used to evaluate the electromagnetic interference (EMI) shielding properties of the Co1−xNixFe2O4/PVA samples. At 9.2 GHz, a study of reflection loss showed a minimum reflection loss (RL) of −32.08 dB. Also, the synthesized Co1−xNixFe2O4/PVA nanocomposite samples show improved performance for EMI efficiency which proves the utility of this doping. With this low RL value, the results and techniques also promise a simple, effective approach to achieve light-weight Co1−xNixFe2O4/PVA nanocomposite films and make it excellent microwave absorbers, capable of working at gigahertz frequencies for application potentials in EMI shielding material, communication, radar stealth technology, and electronic warfare.

From MXene Trash to Ultraflexible Composites for Multifunctional Electromagnetic Interference Shielding.

The development of flexible composites based on the transition metal carbides/nitrides (MXenes) is gaining popularity because of MXenes' high application potentials for electromagnetic interference (EMI) shields. Here, we prepare a new type of ultraflexible composite films composed of "trashed" MXene sediment (MS) and waterborne polyurethane using a simple, facile solution casting approach. In addition to the outstanding mechanical strength and electrical conductivity, an extremely wide-range of MS contents can be achieved for the composites, resulting in EMI shielding effectiveness (SE) that may be controlled over a wide range. The X-band EMI SE of the flexible, low-density composites containing 70 wt % MS reaches 45.3 dB at a thickness of merely 0.51 mm. Moreover, the SE values of more than 34.5 dB in the ultrabroadband gigahertz frequency range including X-band, P-band, K-band, and R-band, are accomplished for the thin composites. Furthermore, the MS/WPU composite films show excellent electrothermal and photothermal performance, demonstrating the multifunctionalities of the MS-based EMI shields. Combined with the cost-efficient, sustainable, and scalable preparation approach, the ultraflexible, multifunctional composites from "trashed MXene" show great potentials for next-generation electronics. This work also opens a new avenue for the creation of innovative, high-performance, multifunctional flexible composites.

Optimizing magnetic/dielectric matching in permalloy/carbonized cotton fiber composites by strain-tunable ferromagnetic resonance and defect-induced dielectric polarization

• The ferromagnetic resonance modes could be tuned by stress caused by the shrinkage of the carbon fibers. • The ferromagnetic resonance frequency fr is proportional to the stress σ with the relationship of fr = 1.52 × σ + 9.38. • The simultaneous tunability of ferromagnetic resonance and dielectric polarization can be realized in permalloy/carbon fiber composites. Electromagnetic losses in composites could be synergistically controlled by permeability and permittivity, associated with multiple ferromagnetic resonances and dielectric polarization. However, it is still challenging for simultaneous tunability for both the terms in a magnetic/dielectric composite system. Here, we demonstrate the tunable ferromagnetic resonances and the enhanced dielectric losses at gigahertz frequencies in permalloy/carbonized cotton fiber composites with different annealing temperatures. It is theoretically confirmed that the stress field acting on the magnetic permalloy layer increases with increasing temperature because of the shrinkage of the dielectric carbonized cotton fibers, resulting in multiple ferromagnetic resonances, in which there is a linear relationship ( f r = 1.52 × σ + 9.38 ) between the resonance frequency ( f r ) and the stress ( σ ). The present work provides a fundamental insight into understanding the micromagnetic dynamics of the magnetic/dielectric composite system.

Recent progress in MXene and graphene based nanocomposites for microwave absorption and electromagnetic interference shielding

There is widespread use of telecommunication and microwave technology in modern society, and raised the electromagnetic interference (EMI) issue to alarming situation due to apprehensive demand and growth of 5G technology undesirably disturbing the human health. The two dimensional (2D) materials including graphene and MXenes are already been used for variety of electronic devices due to their exceptional electrical, mechanical, optical, chemical, and thermal properties. MXene is composed of metal carbides, in which mainly metals are the building blocks for dielectrics, semiconductors, or semimetals. However, the strong interfaces with electromagnetic waves (EM) are variable from terahertz (THz) to gigahertz (GHz) frequency levels and are widely used in EMI and Microwave absorption (MA) for mobile networks and communication technologies. The use of different organic materials with metal, organic, inorganic fillers, polymers nanocomposite and MXene as a novel material has been studied to address the recent advancement and challenges in the microwave absorption mechanism of 2D materials and their nanocomposites. In this concern, various techniques and materials has been reported for the improvement of shielding effectiveness (SE), and theoretical aspects of EMI shielding performance, as well stability of 2D materials particularly MXene, graphene and its nanocomposites. Consequently, various materials including polymers, conducting polymers, and metal–organic frameworks (MOF) have also been discussed by introducing various strategies for improved MA and control of EMI shieling. Here in this comprehensive review, we summarized the recent developments on material synthesis and fabrication of MXene based nanocomposites for EMI shielding and MA. This research work is a comprehensive review majorly focuses on the fundamentals of EMI/MA. The recent developments and challenges of the MXene and graphene based various structures with different polymeric composites are described in a broader perspective.

High efficiency fabrication of Co nanosheets deposited by SiO2 layer with controllable permittivity toward superior electromagnetic wave absorption

In this study, Co nanosheets covered by SiO2 nanoparticles were synthesized by employing microwave plasma assisted reduction (MPAR) technique, which was high-efficiency and energy-saving. The diagonal dimensions of the prepared nanosheets were in the range of 3–7 µm uniformly on a large scale. It was demonstrated that the flaky morphology with high aspect ratio could inherit well from self-sacrificing precursor, further benefitting for acquiring high complex permeability in the gigahertz frequency region. Meanwhile, the complex permittivity could be effectively engineered by adjusting the deposited amount of SiO2 nanoparticles, which could support sufficient dielectric loss to enhance the attenuation competence and improve the impedance matching. Consequently, the minimum reflection loss could reach up to −53 dB with only 1.5 mm thickness. Furthermore, a wide effective bandwidth from 2.6 to 18 GHz could be achieved by integrating the thickness from 1.0 ∼ 5.0 mm. Such excellent microwave absorption performances supplied the opportunity for applications in the fields of radar stealth and electromagnetic shielding. Besides, it is believed that the developed MPAR method provide new insights for the design and preparation of novel microwave absorption materials with desirable morphologies.

Construction of plate‐like magnetic heterostructure for synergistic microwave absorption

AbstractThe dramatically dropped permeability of magnetic materials at gigahertz frequencies, known as the Snoek's limit, has severely constrained the microwave absorbing performance of magnetic materials. To break the Snoek's limit at high frequencies, a plate‐like magnetic heterostructure composed of Ni‐Fe ferrite, nitride, and Permalloy is fabricated through nitridation of Ni‐Fe layered double hydroxide. It has been found that single‐phase magnetic flakes or the multi‐phase heterostructure with extraordinarily linked magnetic nanoplates can be obtained by simply adjusting the temperature of nitridation. Due to the highly anisotropic morphology and synergistic effect at abundant heterogeneous interfaces, the magnetic heterostructure shows enhanced imaginary permeability that is even higher than that of single‐phase Permalloy. Accordingly, the magnetic loss in C and X bands is improved, leading to significant enhancement of attenuation constant in this novel microwave absorber. Combined with the moderate permittivity, the impedance matching of the heterostructure is superior compared to every single component, as well as the mixture of these components. As a result, the minimum reflection loss of −59.30 dB at a thickness of 2.02 mm and effective absorption bandwidth (RL<−10 dB) of 2.44 GHz is realized. These findings provide a novel path to designing high‐performance microwave absorbers based on magnetic materials.

On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies

Liquid crystal elastomers that offer exceptional load-deformation response at low frequencies often require consideration of the mechanical anisotropy only along the two symmetry directions. However, emerging applications operating at high frequencies require all five true elastic constants. Here, we utilize Brillouin light spectroscopy to obtain the engineering moduli and probe the strain dependence of the elasticity anisotropy at gigahertz frequencies. The Young’s modulus anisotropy, E||/E⊥~2.6, is unexpectedly lower than that measured by tensile testing, suggesting disparity between the local mesogenic orientation and the larger scale orientation of the network strands. Unprecedented is the robustness of E||/E⊥ to uniaxial load that it does not comply with continuously transformable director orientation observed in the tensile testing. Likewise, the heat conductivity is directional, κ||/κ⊥~3.0 with κ⊥ = 0.16 Wm−1K−1. Conceptually, this work reveals the different length scales involved in the thermoelastic anisotropy and provides insights for programming liquid crystal elastomers on-demand for high-frequency applications.

Experimental Evidence of Radio Frequency Radiation From Staphylococcus aureus Biofilms

This paper reports the first successful detection of electromagnetic (EM) radiation from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Staphylococcus aureus</i> biofilms in the gigahertz (GHz) frequency range. Two novel sensing systems are deployed for the measurement. A very sensitive wideband near-zone radiative system specifically designed for this application is first used to search for signals in the 1–50 GHz frequency region. Notable radiation is observed in the 3–4 GHz band. Exposure to lethal doses of Zinc oxide nanopyramids (ZnO-NPY) is used to verify that the signals are indeed produced by living cells rather than material thermal emission. Afterwards, a spiral antenna system is exploited to further examine the band of interest in the near-field region. Radiation from 3 identical biofilm samples is monitored and recorded over 70 days. Two distinct frequency bands, namely the 3.18 GHz and the 3.45 GHz bands, are identified as potential “communication bands”. Furthermore, long-term and short-term cycles of the total radiation intensity within the band are observed over the course of the experiment. This work confirms the presence of EM radiation within bacterial communities, which is a key requirement to demonstrate EM signaling among bacterial cells. The insight could lead to breakthroughs in demystifying how cells communicate as well as advancement of important technologies in biology and communication systems.

Magnetic-Tunnel-Junction-Based True Random-Number Generator with Enhanced Generation Rate

True random-number generators (TRNGs) are crucial in modern information technology, especially in cryptographic systems. TRNGs can be realized via stochastic physical processes, such as the thermally activated magnetization switching in a magnetic tunnel junction (MTJ). The fluctuations in MTJ-based TRNGs are still too slow for many practical purposes, though. This study proposes that the simple application of a small magnetic field can increase the generation rate of a MTJ-TRNG by several orders of magnitude, up to gigahertz frequencies. This approach could turn commercialized MTJ-MRAM devices into fast TRNGs with minimal modification.

The integrated radio spectrum of G2.4+1.4

ABSTRACT The Galactic source G2.4+1.4 is an optical and radio nebula containing an extreme Wolf–Rayet star. At one time, this source was regarded as a supernova remnant, because of its apparent non-thermal radio spectrum, although this was based on limited observations. Subsequent observations instead supported a flat, optically thin thermal radio spectrum for G2.4+1.4, and it was identified as a photoionized, mass-loss bubble, not a supernova remnant. Recently, however, it has been claimed that this source has a non-thermal integrated radio spectrum. I discuss the integrated radio flux densities available for G2.4+1.4 from a variety of surveys, and show that it has a flat spectrum at gigahertz frequencies (with a spectral index α of 0.02 ± 0.08, where flux density S scales with frequency ν as S ∝ ν−α).

Single-mode and ultra-broadband gigahertz surface acoustic waveguides on AlN-on-SiC substrates

This paper proposes a class of high-performance surface acoustic wave (SAW) waveguides based on AlN-on-SiC substrates. Under the existing crystal growth and processing technology, these SAW waveguides offer excellent performance in single mode, low loss, ultra-broadband, operating at gigahertz frequencies. Quasi-Rayleigh SAWs can be excited by traditional interdigital transducers and guided freely with excellent efficiency. Based on these SAW waveguides, we further demonstrate SAW splitters and ring cavities with ultra-high qualities up to 107. These SAW components complement future integrated phononic circuits for high-frequency and compact acoustic manipulating, signal processing, sensing, computing, etc.