In this study, we report on the electrical properties of multi-wall carbon nanotubes (MWCNT) composites functionalized with metal or metal alloy oxides and embedded in a polyurethane matrix to develop a lightweight material for microwave absorption and shielding. The CNT nanoparticles are functionalized with metallic oxides such as Cobalt oxide, Iron oxide, and Cobalt Iron oxide, at three different concentrations. Metallic oxides are used at 5%, 10%, and 20% concentration of the total CNT percentage weight. The resulting functionalized CNT is mixed with polyurethane polymer at 5% wt of the total composite weight. Three sets of cylindrical samples are developed, and each set contains three different metal oxide concentrations. The dielectric properties of the nine developed samples are obtained by measuring their permittivity spectra using an open-ended coaxial probe technique in the spectral range 5–50 GHz. The absorption efficiency of the composites is then obtained by calculating the reflection loss at normal incidence. The results show that the spectral range of absorption can be tuned by changing the CNT concentration, and the material thickness. Functionalized CNT with different alloyed metal oxides enhanced the absorption efficiency of the polyurethane/CNT composites. Such functionalized composites can be used to replace the common heavyweight materials used for microwave applications.
Plant diseases have a direct impact on agricultural food production. The time required to detect the pathogen plays a crucial role to minimize the fungal-induced disease damage in crops. Current microbial detection techniques take several days to identify the disease. Microwave detection techniques have proven to be a good candidate in identifying pathogens. Microwave dielectric characterization based on an open-ended coax technique is proposed to electrically characterize pathogens having potential applications in plant diseases. Seven common fungi growing on major crops in the United Arab Emirates were isolated and cultured in the lab. A microwave dielectric assessment kit, based on the open-ended coax technology, was used to obtain the dielectric properties of samples. Our data demonstrated a distinct variability between soil-and airborne pathogenic fungi. Thus, individual fungi can be identified based on their specific microwave dielectric signature. Factors such as conidial sporulation and hyphal growth and polarization of these fungi may attribute to these electric discrepancies. Dielectric spectroscopy modeling based on the Havriliak-Negami model was used to help to understand the molecular structure interaction with the high-frequency signal. This paper revealed a significant dielectric contrast behavior variation among all seven fungi. This paper also supported previous results obtained by other researchers, which classified fungi into two main groups, namely hydrophilic and hydrophobic. Nonetheless, the fungus Alternaria solani has different behavior from this classification. This research is the first to demonstrate the ability of dielectric microwave characterizations tests to facilitate rapid diagnosis and appropriate treatments of plant diseases. INDEX TERMS Dielectric spectroscopy, fungi, microwave characterization, open-ended coaxial probe, plant pathology.
This paper presents two new designs of MIMO dual band coplanar waveguide (CPW)-fed-slot antennas operating in the 5G frequency band (28 and 38 GHz). The first antenna is an XX MIMO antenna and the second antenna is an XY MIMO antenna. Simulated results for the S-parameters are presented for the two antennas using HFSS. Measured results are also presented for the return loss and gain with both results showing good agreement. The current distribution, group delay, envelope correlation coefficients (ECC), and diversity gain, are also presented for both antennas. The two antennas are fabricated on a substrate having dielectric constant ε
r
= 10.7 and substrate thickness 0.635 mm. The size of the antenna is 4.4 mm x 4.1 mm x 0.635 mm.
A multiband planar antenna designed and proposed with resonator slots is presented. The proposed antenna consists of a planar hexagonal patch composed of two pairs of resonator slots. The antenna is designed using Isola FR408 substrate (ε
r
= 3.68 and tanδ = 0.0092) with a compact dimension of 21 × 28 × 1.6 mm
3
. The designed antenna has good impedance matching and radiation characteristics for the desired multiband frequencies. Multibands are obtained by etching two pairs of modified mirror-imaged L-shaped resonator slots on the hexagonal planar patch. Simulated and measured results of the antennas' reflection coefficient are provided and there is good agreement between the simulation and measurement results. The antennas' measured peak gains are between 2 dB and 5 dB and measured efficiencies are between 40% and 80%. The proposed antenna, when compared to other antennas, exhibits multiband characteristic by using a single-feed structure and generates different combinations of isolated lower frequency bands in miniature size. The antenna has stable directional radiation patterns and has the potential to meet the requirements of wireless communications applications.
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