Microwave Frequency Range Research Articles

Study of structural, elastic, optical, dielectric, and magnetic properties of sol-gel synthesized Li0.2Co0.3Zn0.3Fe2.2O4 ferrite for optoelectronic and electrical applications

This work presents a detailed investigation of the structural, elastic, optical, dielectric, and magnetic properties of Li0.2Co0.3Zn0.3Fe2.2O4 ferrite synthesized through the sol-gel process. The experimental structural parameters closely match the theoretical values, confirming the proposed cation distribution of the prepared sample. The FTIR spectrum and ultrasonic pulse transmission method analysis showed that the sample has brittle mechanical properties. According to UV-Vis optical absorbance analyses and based on Tauc's law, the sample exhibits a direct optical transition, with the band gap energy (Eg) determined to be 2.51 eV. The study of electrical conductivity showed that the sample exhibited a reduced activation energy (Ea= 0.154 eV) and remarkable electrical resistivity at room temperature (ρdc ∼ 104 Ω.m), indicating the material's potential for microwave device applications. The conduction process of the sample aligns with the NSPT model. Additionally, the temperature coefficient of resistance (TCR) suggests that the sample is a promising candidate for infrared radiation detection. A low coercive field was also derived from the hysteresis loop, confirming the soft nature of the sample operating within a microwave frequency range of 8–9 GHz. Our results show that the Li0.2Co0.3Zn0.3Fe2.2O4 compound offers advantages over the undoped Li0.5Fe2.5O4 compound, including a lower band gap, reduced activation energy, and higher electrical resistivity. This suggests that substituting Co and Zn into Li0.5Fe2.5O4 ferrites improves their performance in electrical and optoelectronic applications.

Polarizing Magnetic Field Effect on Some Electrical Properties of a Ferrofluid in Microwave Field

The complex dielectric permittivity, ε (f, H) = ε′ (f, H) − i ε″ (f, H), in the microwave frequency range f, of (0.1–3) GHz and polarizing field values H, in the range of (0–135) kA/m, was measured for a kerosene-based ferrofluid with magnetite particles. A relaxation process attributed to interfacial type relaxation was highlighted, determining for the first time in the microwave field, the activation energy of the dielectric relaxation process in the presence of the magnetic field, EA(H), in relation to the activation energy in zero field, EA(H = 0). Based on the complex permittivity measurements and the Claussius–Mossotti equation, the dependencies on frequency (f), and magnetic field (H), of the polarizability (α) and electrical conductivity (σ), were determined. From the dependence of α(f,H), the electric dipolar moment, p, of the particles in the ferrofluid, was determined. The conductivity spectrum, σ(f,H), was found to be in agreement with Jonscher’s universal law and the electrical conduction mechanism in the ferrofluid was explained using both Mott’s VRH (variable range hopping) model and CBH (correlated barrier hopping) model. Based on these models and conductivity measurements, the hopping distance, Rh, of the charge carriers and the maximum barrier height, Wm, for the investigated ferrofluid was determined for the first time in the microwave field. Knowledge of these electrical properties of the ferrofluid in the microwave field is useful for explaining the mechanisms of polarization and control of electrical conductivity with an external magnetic field, in order to use ferrofluids in various technological applications in microwave field.

Extraction of two-magnon scattering and detection of inverse spin Hall effect up to 40 GHz in low-damping Fe65Co35/Pt bilayer thin film

Abstract We report an investigation of the inverse spin Hall effect (ISHE), as a measure of the pure spin current (J S ), induced by spin pumping in a Fe65Co35/Pt bilayer using coplanar waveguide ferromagnetic resonance (CPW-FMR) in the in-plane (IP) geometry over the broadband microwave frequency range of 8–40 GHz. From the IP-FMR measurements, the defect-induced two-magnon scattering (TMS) contribution is evaluated by analyzing the frequency dependence of FMR linewidth using Arias and Mills approach [Arias R and Mills D L (1999 Phys. Rev. B 60, 7395), Mills D L and Arias R (2006 Physica B 384 147–151)]. Here, we have determined a very low Gilbert damping constant (α G ) for Fe65Co35 bare film around 1.3 × 10−3, which is essential for the high spin current (>107 A/m2) generation. The enhanced value of α G ≈3.2 × 10−3 obtained for Fe65Co35/Pt bilayer film is due to spin pumping damping, α SP = 1.9 × 10−3, confirmed by the ISHE induced DC voltage (V DC ) signal measured across the edges of Pt layer. Out-of-plane (OP) angular ISHE measurements have been performed to disentangle spin pumping from spin rectification effects in the V DC signal. Further, we evaluated the effective spin-mixing conductance g eff ↑ ↓ = 3.33 × 1019 m−2, which is higher than the values reported in FeCo-alloy-based bilayer systems. The present study aims to detect the J S injected by low-damping Fe65Co35 thin films, leading to the realization of energy-efficient spintronic devices.

Thermal wave and Pennes’ models of bioheat transfer in human skin: A transient comparative analysis

The primary focus of this study is to analyze comparative heat transfer in a two-dimensional (2D) multilayered human skin using thermal waves and Pennes' bioheat transfer models. The model comprises the epidermis, dermis, hypodermis tissue, and inner cells, and aims to understand their response to microwave (MW) power and electromagnetic (EM) frequency. The system of equations involves EM wave frequency and bioheat equations and uses the finite element method (FEM) for solving. It encompasses a range of microwave power levels (4–16 W), frequencies (0.9–4 GHz), and exposure durations (0–180 s). It examines how MW power and frequency affect temperature predictions due to different relaxation times. The results are visually represented, illustrating microwave power dissipation, isothermal profiles within the skin tissue, temperature trends at several locations, relaxation times, specific absorption rate (SAR), and the mean surface temperature of the multilayered dermal cell. Thermal analysis shows that Pennes' equation predicts higher temperatures than the thermal wave model of bioheat transfer (TWMBT). A notable disparity in temperature evolution is observed between the two models, especially in high-frequency transient heating scenarios. The TWMBT forecasts a delay in heat transfer, offering valuable insights into the more realistic short-term thermal behavior that the classical Pennes' model fails to capture. This comparative study underscores the significance of selecting an appropriate bioheat transfer model for precise thermal analysis in biomedical applications, such as hyperthermia treatment and thermal diagnostics. The findings emphasize the potential of the TWMBT to enhance the accuracy of thermal treatments in clinical settings.

Development of Flexible Hydrophobic Polypropylene/SPCB/GNP Hybrid Nanocomposite Films With Excellent EMI Shielding and Mechanical Properties

ABSTRACTThe demand for effective electromagnetic interference (EMI) shielding materials has driven the development of novel and facile approach for fabrication of conductive polymer nanocomposites. In this study, a polypropylene (PP)‐based hybrid nanocomposite was prepared by incorporating Super P conductive carbon black (SPCB) and graphene nanoplatelets (GNP) via latex technology. A simplistic method of fabrication was adopted where the nanofillers were stirred into the PP latex at room temperature, ensuring the proper dispersion of fillers within the matrix. Hybridizing the nanocomposite by the usage of two different fillers has resulted in a substantial improvement in EMI shielding performance of the material along with its mechanical and thermal properties. The samples were fabricated and tested in three different thicknesses to ensure that EMI shielding effectiveness (EMI SE) is a thickness dependent property and also the studies were carried out over a broad range of microwave frequency. A high electrical conductivity of 7.6 S m−1 was obtained and exceptional EMI SE of 65 dB (X band), 69.76 dB (Ku band), and 72.38 dB (K band) was showcased by 2 mm thickness composites. The optical images of PP latex incorporated with the fillers gave a clear understanding about the formation of conducting networks within the polymer matrix at percolation threshold. The addition of SPCB and GNP also showed a significant increase in hardness and tensile strength of the composite and helped in protecting the polymer matrix against photo radiation. The fillers also aided in the enhancement of the hydrophobicity of the films. The thermal stability, crystallization temperature (TC) and melting temperature (TM) of the composites were also improved when compared to that of neat The works aims at fabricating a hydrophobic and low‐density polymer nanocomposite showing excellent absorption dominant EMI SE.

Design and development of low‐weight and high‐strength electromagnetic shielding nanocomposite in a microwave frequency range

AbstractIn this novel work, we fabricated the multiwalled carbon nanotubes (MWCNTs)/polypyrrole (PPy) nanocomposite by employing the novel ultrasonic dual mixing (UDM) method. Subsequently, the atomistics and structural characterizations of the fabricated MWCNT/PPy nanocomposite (PM) were performed using SEM, Raman, and XRD. Furthermore, we experimentally evaluated the mechanical properties of the fabricated PM by reinforcing the PPy matrix with MWCNTs at different wt.%. The experimental study of PM shows that the mechanical properties depend upon the amount and dispersion quality of MWCNTs in the PPy matrix. In order to validate the experimental outcomes, the conservative fully coupled finite element (FE) models were developed using the ANSYS Workbench and novel FEAST software. The electromagnetic interference (EMI) shielding effectiveness (SE) of developed PM was also calculated at different thicknesses of PM by taking the effect of SE due to absorption (SEA) and SE reflection (SER) in the microwave frequency range of the C‐band (5.37–8.2 GHz) into consideration. The total SE (SET), the cumulative sum of SEA and SER, is the strong function of the thickness of the PM. Additionally, our study's outcomes reveal that as the thickness of the PM increased, the SET also increased by dominating the SEA rather than the SER. The SET value of 75 dB was observed for a sample with a thickness of 3 mm, indicating a high level of shielding. Thus, material becomes a highly attractive option for achieving high‐performance EMI SE in the C‐band for satellite communications, Wi‐Fi devices, weather radar systems, surveillance, and cordless telephones. A complex permittivity and permeability were also studied using the Nicolson–Ross–Weir (NRW) method to understand the mechanism behind the EMI SE.Highlights Nanocomposite fabricated using the novel ultrasonic dual mixing method. FE models were developed to validate experimental results. The EC and EMI SE are improved with the increase in the sample thickness. Absorption, rather than reflection, dominated the shielding mechanism. SE was observed dB with good mechanical properties.

Dual Doping Strategy to Enhance Microwave Absorption Properties of LaFeO3

Microwave absorbing materials have the ability to absorb and dissipate electromagnetic radiation in the microwave frequency range, making them suitable for use in various applications. LaFeO3 has been recognized as a potential microwave absorbing material due to its unique structure and composition. In this paper, a dual doping strategy was adopted to modify the microwave absorption properties of LaFeO3. The results showed that F− doping into O-site is better than oxygen vacancies to enhance the microwave absorption properties for LaFeO3.

Microwave absorption properties of ytterbium substituted X-type ferrite in P-, L-, S-, and C-band

Ba1.5Sr0.5Zn2Fe28-xYbxO46 (x = 0.00, 0.07, 0.14, 0.21, and 0.28) hexaferrite were synthesized via sol-gel auto-combustion route to investigate the microwave absorption performance in different frequency bands. The structure has a single phase, and the variation in lattice parameter was observed due to Yb-content as host iron Fe3+ and substituted Yb3+ having different ionic radii. Microwave absorbing materials (MAMs) need to be lightweight, and the maximum crystallite size of prepared material is 41 nm. The physical properties vary with substitution, and the X-ray density value is higher than the bulk density, and the porosity of the prepared sample increases when the bulk density decreases. Micro-strain values are inverse to the crystallite size because Yb3+ has larger ionic radii than Fe3+. Rietveld refinement of the XRD patterns was conducted with a lower significance value. FTIR bands observed between 414 and 500 cm−1 are present due to iron-oxygen bond stretching and bending vibrations at octahedral and tetrahedral lattice sites. The cation distribution is highly responsible for the peak position of octahedral and tetrahedral sites—the dielectric constant increases with frequency because of dipole, interfacial, and electronic/atomic polarization. AC conductivity is very low, reflecting that the material can be used as a dielectric medium in the microwave frequency range's L, S, and C bands. The best MAM among all prepared materials is Ba1.5Sr0.5Zn2Fe27.72Yb0.28O46 which can be used for global positioning systems, weather radar, and satellite feeds as it has an excellent dielectric loss, remarkable tangential loss, and the reflection loss in P-, L-, S-, and C-bands. Other real-life application of all prepared materials are multi-layer chip inductor and longitudinal media recording.

Complex Permittivity Spectra of Granular Polymer Composites with Dispersed Ag-Coated Cu Flakes

Conductive particle-containing granular composites with tuneable negative permittivity are being studied to improve the performance of electromagnetic devices, such as shielding materials. In this study, we investigated the relative complex permittivity and electrical conductivity of granular composites of polyphenylene sulfide (PPS) resin and Ag-coated Cu flakes in the radio- to microwave-frequency range and compared them with those of PPS/bare Cu flake composites. Electrical conductivity measurements revealed that the PPS/Ag-coated Cu flake composites have a lower percolation threshold (φc) than the PPS/bare Cu flake composites, whereas the electrical conductivity of the PPS/Ag-coated Cu flake composites in the percolated particle state was higher at the same particle volume fraction. At particle contents above φc, a low-frequency plasmonic state of conduction electrons was achieved in the percolated particle chains in both composites, and negative permittivity spectra were obtained. The percolated PPS/Ag-coated Cu flake composites had a negative permittivity up to a higher frequency than the percolated PPS/bare Cu flake composites. Furthermore, the Drude model was used to analyze the negative permittivity spectra of the composites in the percolated particle state. The plasma frequency of the composites with percolated Ag-coated Cu flakes was higher than that of the composites with percolated bare Cu flakes. Thus, coating Ag on Cu particles improved the conductivity of the composite, leading to negative permittivity up to higher frequencies. This study contributes to the enhancement of the negative permittivity achieved by granular composites, which is useful for microwave technology applications.Graphical

Synthesis of new liquid crystal Schiff's bases bearing ester moiety, DFT calculation and mesomorphic studies

A new homologues series of liquid crystalline material (E)-4-(((3,4-dimethylphenyl) imino) methyl) phenyl4-n-alkoxybenzoate (SBn) synthesized. SBn compounds was subjected to analysis using infrared spectroscopy, proton magnetic resonance, 13C NMR, UV- visible and mass spectroscopy for characterization. The investigation of liquid crystalline phases and their transition enthalpies was carried out using a polarized optical microscope and differential scanning calorimetry, respectively. All compounds within the homologous series display mesogenic properties. The SB1 -SB7 homologues exhibit an enantiotropic nematic mesophase within the temperature range of 180–106 °C, while the SB14 -SB18 homologues show a smectic A mesophase at temperatures between 78 and 75 °C. Additionally, the SB8 -SB10 homologues exhibit a monotropic smectic A mesophase at 61–59 °C. The phase transitions observed in series SBn are compared with those of structurally related compounds to assess the influence of central linkage and lateral tail `substitution on their mesophase behavior. With the help of DFT; EHOMO and ELUMO energy gap were computed to be negative for all derivative molecules, indicating their stability and in the following order: SB4 > SB6 > SB8 > SB12. Dielectric through determined values of complex permittivity of the synthesised liquid crystal over a broad frequency range are reported. Determined static permittivity value of liquid crystal is 2.25, at room temperature. The compound SBn exhibited a relaxation peak in the dielectric loss spectra in the microwave frequency range, which may be assigned to the rotation of the end polar group of the molecule.

Influence of MXene Interlayer Spacing on the Interaction with Microwave Radiation

AbstractThe origin of MXene's excellent electromagnetic shielding performance is not fully understood. MXene films, despite being inhomogeneous at the nanometer scale, are often treated as if they are compared to bulk conductors. It is reasonable to wonder if the treatment of MXene as a homogeneous material remains valid at very small film thickness and if it depends on the interlayer spacing. The goal of the present work is to test if the homogeneous material model is applicable to nanometer‐thin Ti3C2Tx MXene films and, if so, to investigate how the model parameters may depend on variations in MXene interlayer spacings. MXene films containing flakes with interlayer spacing between 1.9 and 5.5 Å have been prepared using various intercalating agents. It is shown that modeling the films as being homogeneous agrees with experimental tests in the microwave frequency range. Microwave conductivity and dielectric constant parameters are estimated for the homogeneous film model by fitting measured results. The direct current (DC) conductivity matches the estimated microwave conductivity on the order of magnitude. A highly effective dielectric constant provides a good fit for the lower conductivity MXene films. Optical absorption agrees with the homogeneous material model of thin films as well.

Structure, thermal and microwave dielectric properties of cold-sintered Li2MoO4-Al2O3 ceramic

Dielectric ceramics are essential components in communication systems that operate within the microwave frequency range. In high-density packages, dielectric substrates ceramics must possess high thermal conductivity to efficiently dissipate heat. However, achieving adequate thermal conductivity (κ) in ceramics sintered at low temperatures is challenging. In this study, we employed the cold sintering process (CSP) to fabricate Li2MoO4-x%Al2O3 (0≤x≤80, in volume) ceramics under 200 MPa pressure at 150 °C. The Li2MoO4-40%Al2O3 composite exhibited significantly enhanced κ of 5.4 W·m–1·K–1, an 80% increase compared to pure Li2MoO4 ceramic with κ of 3 W·m–1·K–1. At 40% Al2O3 content, the Li2MoO4-Al2O3 ceramic demonstrated notable microwave properties (ε ∼ 6.67, Q×f ∼ 17,846 GHz, τf ∼ −105 ×10–6/°C). Additionally, simulation of a microstrip patch antenna for 5 GHz applications using Li2MoO4-20%Al2O3 ceramic as dielectric substrate via Finite Element Simulation software showed excellent performance, with radiation efficiency exceeding 99% and low return loss (S11 < −30 dB) at both 4.9 GHz and 28.0 GHz center frequencies. These findings underscore the suitability of Li2MoO4- Al2O3 ceramics for microwave dielectric substrate. KeynotesMicrowave dielectric ceramic, Thermal conductivity, Cold sintering process, Antenna

Enhancement of Microwave Absorption Properties of Crystal‐Engineered Perovskite Oxide Using Cobalt Ferrite

A multiferroic composite that comprises of a non‐ferromagnetic ferroelectric material with a high dielectric constant and a non‐ferroelectric ferromagnetic material with a high magnetostriction is of tremendous interest as microwave absorption material due to its applicability in tunable microwave phase shifters, resonators, filters, absorbers, etc. In the previous work, the solid solution of strontium titanate and sodium bismuth titanate (Sr0.5(Na0.5Bi0.5)0.5TiO3, SNBT50), which is observed to possess a very high dielectric constant at room temperature (Ferroelectrics, Vol 583, 252–263 [2021]), is successfully reported. Thus, in this work, a core–shell magnetoelectric composite is prepared by coating highly ferromagnetic and magnetostrictive cobalt ferrite onto a diamagnetic but strongly ferroelectric SNBT50 to enhance its magnetic properties and to investigate the modification in microwave absorption. Detailed characterization of electric and magnetic parameters in microwave frequency range (1–20 GHz) reports substantial enhancement in the magnetic permeabilities as well as the magnetic loss of the composite system, as opposed to bare SNBT50. This results in improved impedance matching in the system and enhanced microwave absorption, with a minimum reflection loss (RL) of −20.19 dB and an increased effective absorption bandwidth of 4.56 GHz at a mere 2.7 mm absorber length. Consequently, in this investigation, a promising pathway is established for the development of multiferroic composites with favorable magnetoelectric coupling at room temperature that possesses wide absorption bandwidth and suitable RL, making them highly suitable for use in multiferroic‐based microwave components.

Relationship between chemical bond characteristics and microwave dielectric properties of low temperature sintering CoO-V2O5 ceramics

The two most fundamental compositions within the CoO-V2O5 family, namely CoV2O6 and Co2V2O7 ceramics, were synthesized using the traditional solid-state method. The microwave dielectric properties of both ceramics were investigated for the first time. The P-V-L bond theory was used to analyze the correlation between their microwave dielectric properties and chemical bond characteristics. The CoV2O6 ceramic exhibits a γ phase (εr = 11.6, Q×f = 39,177 GHz, and τf = −15 ppm/°C) when sintered at 660 °C. However, it experiences a phase transformation from the γ phase to the α phase at 690 °C, which causes the dielectric properties to degrade. The Co2V2O7 ceramic demonstrates excellent dielectric characteristics (εr = 9.4, Q×f = 88,645 GHz, and τf = −37 ppm/°C) at 720 °C. Importantly, its sintering temperature can be lowered to 660 °C while still maintaining a good combination of microwave dielectric properties (εr = 7.7, Q×f = 75,887 GHz, and τf = −58 ppm/°C). It is found that Co2V2O7 exhibits a low dielectric loss due to relatively high lattice energy resulting from the contribution of Co–O bonds. CoV2O6, on the other hand, shows a lower sintering temperature because it contains more V2O5, which acts as an effective sintering aid. These two ceramics both exhibit good chemical compatibility with aluminum and are promising candidates for applications in low-temperature and ultra-low-temperature co-fired ceramics (LTCCs and ULTCCs) that operate in the microwave frequency range or higher.

Recent Progress of Iron-Based Magnetic Absorbers and Its Applications in Elastomers: A Review.

As a result of continuing scientific and technological progress, electromagnetic waves have become increasingly pervasive across a variety of domains, particularly within the microwave frequency range. These waves have found extensive applications in wireless communications, high-frequency electronic circuits, and several related fields. As a result, absorptive materials have become indispensable for dual-use applications across both the military and civilian domains because of their exceptional electromagnetic wave absorption properties. This paper, beginning with the operating mechanisms of absorptive materials, aims to provide an overview of the strategies that have been used to enhance the absorption performance of iron-based magnetic absorbers (IBMAs) and discuss the current research status of absorptive material components. The fabrication of a ferromagnetic absorber in terms of morphology, heterointerface coupling, and macrostructural enhancements and the effect of powder characteristics on their electromagnetic properties are discussed. Additionally, the application of IBMAs in elastomers is summarized. Finally, this paper summarizes the limitations of existing ferromagnetic absorber materials and offers a perspective on their potential future developments. The objective of the ongoing research is to fabricate absorptive components that have thin profiles, lightweight construction, wide absorption frequency ranges, and strong absorption capabilities.

Enhancing the magnetization, dielectric parameters and elastic parameters while simultaneously minimizing coercivity and dielectric loss in nickel-manganese-cobalt ferrite nanoparticles through Ce3+ doping assistance

This study focuses on examining how the rare-earth cerium incorporation affects the magnetic, dielectric, and mechanical characteristics of Ni0.5Mn0.25Co0.25CexFe2-xO4 spinel ferrite nanoparticles. (NMCCF). The nanoferrite Ni0.5Mn0.25Co0.25Ce0.04Fe1.96O4 acquires the lowest coercivity of 567 Oe and the highest saturation magnetization of 52.23 emu/g. All the NMCCFx nanoferrites exhibit a microwave frequency range of 9.47–11.55 GHz, suggesting potential applications in longitudinal recording media and microwave absorbance. Moreover, the nanoferrite Ni0.5Mn0.25Co0.25Ce0.1Fe1.9O4 demonstrates the highest dielectric value of 1871, with an enhancing ratio of 754 %, excellent conductivity at 3.12 μ(Ω.m)−1 along with a remarkably enhanced percentage of 369 %. Additionally, it shows a loss factor of 2.17, with a notable improvement percentage of 26 % compared to the pure NMCCF0 sample at 50 Hz and room temperature. The elastic moduli (longitudinal, shear, Young, and bulk) of the Ni0.5Mn0.25Co0.25Ce0.1Fe1.9O4 nanoferrite increased from 1.21 to 2.77 GPa, 0.25–0.76 GPa, 0.68–1.99 GPa, and 0.87–1.75 GPa, respectively. This study introduces a novel approach to Ni–Mn–Co–Ce spinel nanoferrites, highlighting their magnetic, electrical, and mechanical characteristics, which hold promise for electronic and high-frequency device applications.

Correlative Investigation on Dielectric-Mechanical-Morphological Characteristic for Kenaf-Glass-Hybrid Fibers Reinforced Epoxy Composite

In recent years, there are many applications where synthetic fibers and natural fibers are used as reinforcing materials in composites, such as the automotive and aerospace industries, the medical industry, and the construction industry. While these hybrid fibers effectively enhance mechanical and electrical properties, research into electrical characteristics remains inadequate and is an ongoing endeavor. In this work, synthetic woven glass fibers and natural woven kenaf fibers were used to fabricate composite materials by vacuum infusion technique. The dielectric properties of three different substrates, glass fibers, kenaf fibers and glass/kenaf fibers reinforced epoxy composites were investigated at 0° orientation. The ENA Network Analyzer was used to measure dielectric properties in a wide microwave frequency range. The substrates were single-joint overlapped with an adhesive and then mechanically tested. The shear strength of the joint as a function of strain, was tested using a Shimadzu universal testing machine. Visual inspections were performed to determine the failure modes of the composites. The dielectric constant and loss factor of the glass fiber composite were the highest, while the kenaf fiber composite had the lowest value. When a small amount of glass fibers is incorporated into kenaf fibers, which is called a hybrid composite, the polarization increases and the mechanical strength also increases compared to the kenaf fiber composite. Scanning electron microscopy (SEM) of the fractured tensile tests was performed to understand the nature of the interfaces between glass, kenaf and matrix. The kenaf/matrix interface was heterogeneous but exhibited voids, resulting in low dielectric properties and mechanical strength. By inserting a small amount of glass fibers, the hybrid with kenaf fibers improve the dielectric constant by 20.7% and the dielectric loss factor by 27% compared with the kenaf fiber composite. The results also show that the composites exhibit a correlation between the dielectric properties, tensile strength, and the morphological nature of the interfaces.

Generation of parabolic beam using an amplitude and phase modulated metasurface

In this work, non-diffraction parabolic beam is generated using a double-layer transmission metasurface in the microwave frequency range. A transmissive unit cell with bilayered substrates and three metallic layers is designed. By controlling the orientation angle and the opening angle of the intermediate ∈-shaped metallic layer, transmission amplitude from 0 to 1 and continuous phase shift from 0° to 360° can be modulated simultaneously. To experimentally verify the proposed concept and design, a transmissive metasurface is fabricated and measured at 20 GHz. The simulated and measured results are in good agreement with the theoretical results, and prove the generated parabolic beam still maintained non-diffraction and self-healing characteristics within the maximum non-diffraction distance of 40λ. The generated microwave parabolic beam with its properties can be applied to improving the distance and efficiency of WPT and near field modulation of complex EM waves.

Microwave gain-assisted optical limiter in molecular magnets.

We investigate the optical properties of a crystal of molecular magnets within the microwave frequency range. It is shown that in the presence of a static magnetic field and applying a coupling laser field in the microwave region, reverse saturable absorption in the microwave domain can be induced in molecular magnets. Notably, the intensity and detuning of the coupling laser field are shown to exert significant control over electromagnetically induced optical limiting (OL). Thus, the OL behavior can safeguard the active sensors in seekers against the saturation as they approach microwave sources. What we believe to be a novel optical limiting phenomenon is introduced, wherein the crystal amplifies noiselessly weak input microwave fields in the linear region of the optical limiter while attenuating intense input fields. Consequently, these findings suggest the potential for actively controlling radars or seekers by exploiting a gain-assisted optical limiter to detect microwave sources with weak signals. The static magnetic field, acting as a pivotal parameter, significantly influences the attainment of OL performance across a broad spectrum of microwave frequencies. We anticipate that the outcomes of this investigation could be applied in microwave photonics to enhance the ranging capabilities of missile seekers or radars via the identification of weak signal targets. Additionally, the research highlights the protective capabilities of microwave sensors against high-power microwave signals. Finally, the open aperture Z-scan technique is employed to confirm the induced gain-assisted optical limiting behavior in molecular magnets.

Dielectric properties of honey-water solutions over broad frequency range

The dielectric constant (ε′) and dielectric loss (ε″) of pure honey (PH) and honey-water mixtures have been measured over 20 Hz − 20 GHz frequency range, at 26 °C using a precision LCR meter and a Vector Network Analyzer. It has been observed that as water proportion in honey increases, ε′ and ε″ increases over the given frequency range. The dielectric relaxation peak of ε″ for honey-water mixture in the microwave frequency range shifts towards relaxation peak of water as amount of water in honey increases. The normalized ε′/ε′PH ratio is found to increase with increase in water content in Honey, reaching up to 1000 over 20 Hz to 2 kHz. In frequency range from 500 MHz to 5 GHz, ε′/ε′PH ratio approaches a value of 10 times at 750 mg/g. Over 20 Hz to 2 MHz frequency range, ε″/ε″PH ratio approaches 100 times that of PH, but over frequency range from 200 MHz to 600 MHz the ratio ε″/ε″PH is found to decrease anomalously with increase in water content in PH. Further, over the frequency range from 8.2 GHz to 20 GHz the ε″/ε″PH ratio continuously increases with increase in water content.