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In this paper, a comparison microwave method between Transmission and Reflection using a Coaxial Cable and complimentary double split ring resonator (CDSRR) for characterization of magneto-dielectric material is proposed. This method enables the determination of both relative permittivity and permeability of magneto-dielectric material. The CDSRR resonates at 3.46 GHz with a quality factor of 127 in unloaded condition. To determine the effects of permittivity and permeability on the shift of resonant frequency, the electric and magnetic fields are localized in two separate zones in the CDSRR sensor. Prediction formulas are proposed to extract the value of real permittivity and permeability from S21 parameter. For Transmission/Reflection Method, to extract the dielectric and magnetic properties, Nicolson-Ross-Weir (NRW) are used. The prototypes of proposed sensors are fabricated on a ROGERS 3003 and tested for validation of their functionality. A good agreement between the measured data using Transmission/Reflection Method and CDSRR sensor is observed. [ABSTRACT FROM AUTHOR]

A special medium-density fiberboard (MDF) has been fabricated in order to electromagnetic shielding composite by adding iron oxide nanoparticles (NF) to wood fiber (WF). The aim of this work was to study the panel properties with different loadings (1, 3, 5, 7, and 10 wt %) of Fe3O4 nanoparticles. The mechanical, physical, and Electromagnetic (EM) shielding properties of the produced fiberboard were analyzed. The maximum shielding effectiveness (SE) was 13.6 dB for the NF10 in the frequency range of 8.2–12.4 GHz and the absorption had the main contribution to the SE of the panels rather than the reflection. Internal bonding (IB) of the MDF panel was increased by 8.5% by adding 1% Fe3O4 nanoparticles. After that, the IB decreased compared to the control one. The modulus of rupture (MOR) and modulus of elasticity (MOE) of the MDF panels were less than the control panel. The MOR, MOE, IB, thickness swelling (TS), and water absorption (WA) of the panel with 10% Fe3O4 nanoparticles (NF10) panel showed 21.5, 2489, 0.56 MPa, 13.4%, and 61.4%, respectively. Generally, the fiberboard fabricated with 10% Fe3O4 nanoparticles indicated the ability for Electromagnetic shielding applications because of their acceptable properties according to the EN622-5 standard and appropriate EM shielding. [ABSTRACT FROM AUTHOR]

This research explores the application of an artificial intelligence (AI)-assisted approach to enhance the selectivity of microwave sensors used for liquid mixture sensing. We utilized a planar microwave sensor comprising two coupled rectangular complementary split-ring resonators operating at 2.45 GHz to establish a highly sensitive capacitive region. The sensor's quality factor was markedly improved from 70 to approximately 2700 through the incorporation of a regenerative amplifier to compensate for losses. A deep neural network (DNN) technique is employed to characterize mixtures of methanol, ethanol, and water, using the frequency, amplitude, and quality factor as inputs. However, the DNN approach is found to be effective solely for binary mixtures, with a maximum concentration error of 4.3%. To improve selectivity for ternary mixtures, we employed a more sophisticated machine learning algorithm, the convolutional neural network (CNN), using the entire transmission response as the 1-D input. This resulted in a significant improvement in selectivity, limiting the maximum percentage error to just 0.7% (≈6-fold accuracy enhancement). [ABSTRACT FROM AUTHOR]

The effect of different loading profiles of a conductive nanofiller on the electromagnetic absorption of a gradient nanocomposite (NC) absorber is studied. First, the relative permittivity of a polymer matrix loaded with different contents of the conductive nanofiller is obtained using a theoretical model and experimentally measured data. Then, gradient NCs in which the concentration of the filler and the intrinsic impedance modulus form linear, exponential, and triangular profiles are considered and their return loss, with backed metal plates, is calculated. It is found that the gradient NC with a triangular impedance profile provides the lowest reflection over the widest bandwidth. [ABSTRACT FROM AUTHOR]

This study explores the properties and potential of magneto-dielectric (MD) material Ni0.25Cu0.25Zn0.50Fe2O4–BaTiO3 as an antenna substrate for miniaturization and bandwidth enhancement. The MD material was synthesized using a solid-state method and different amounts of BaTiO3 (0, 5, 10, 15 and 20%) were added to improve its relative permittivity. Various investigations were carried out to analyze the crystallographic structure, microstructure, magnetic properties, permittivity, permeability, and losses of the samples at microwave frequencies. Results show that the MD composite with 5% BaTiO3 achieved a relative permittivity of 12.5 and a permeability of 2.9 at 0.7 GHz has enhanced the antenna's operating bandwidth with a fractional bandwidth of 61.1% and directivity of 3.1 dBi. The MD material with 20% BaTiO3 showed potential as an antenna substrate for miniaturization, with a relative permittivity and permeability of 17.1 and 1.9, respectively. It also displayed better gain (− 8.9 dBi) and radiation efficiency (8%) compared to the antenna with 5% BaTiO 3 (with a gain of − 14.4 dBi and radiation efficiency of 1.8%) as an antenna substrate. The findings of this study suggest that MD materials have significant potential as antenna substrates for miniaturization and bandwidth enhancement. [ABSTRACT FROM AUTHOR]

This work presents two approaches to design and implement three-dimensional (3D) graded index (GRIN) flat lenses consisting of concentric annular segments. Generally, the design of GRIN flat lenses calls for segments with very specific tailored permittivity which makes the realization of the lens challenging. To meet this challenge, each segment of the lens is replaced with a three-layer structure consisting of two materials with a high and a low dielectric constant in such a way that the high permittivity layer is sandwiched between two low permittivity layers. By treating the lens segments as transmission lines and taking the effect of multiple reflections into account, the layer thicknesses are adjusted in such a way that the rays passing through different segments interfere constructively at a focal point. To further improve the focusing performance, a practical design approach is introduced in which each segment of the lens is made of a symmetric seven-layer structure using only two materials (alternating in arrangement) with a high and a low dielectric constant. This design provides the following features: (1) almost all of the incident power passes the lens without considerable reflection, (2) the lens provides a constructive interference of the incident wave at a focal point, and (3) the lens has the potential to be manufactured using available material and technology. Numerical examples are provided in which silica and silicon are utilized as low and high permittivity materials, respectively. [ABSTRACT FROM AUTHOR]