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A frequency reconfigurable microstrip patch antenna with a combination of an asymmetric armed U-slot and a reversed L-slot etched on a rectangular base patch of 6 GHz resonant frequency designed on an FR4 substrate (ɛ r = 4.4) is presented in this paper. Three RF PIN diodes are positioned at inimitable sites of these slots to achieve frequency reconfiguration. A DC bias circuitry, which includes DC blocking capacitors and RF blocking inductors, is integrated with the antenna structure for switching (ON/OFF) the PIN diodes. Six reconfigurable modes with resonant frequencies at 4.33, 4.63, 5.24, 5.87, 5.96, and 6.29 GHz is obtained with different ON-OFF combinations of these PIN diodes. These reconfigurable resonant frequencies cover two continuous bands from 4.21 to 5.43 GHz and 5.69 to 6.6 GHz and is considered to be useful for the applications like aeronautical radio navigation (4.3 GHz), sub-6-GHz 5G (4.4–5 GHz), WLAN (5.2 and 5.8 GHz) and Wi-Fi 6E (5.925–6.425 GHz). Measured gain of the antenna for all the modes varies between 5.86 dBi and 8.72 dBi. [ABSTRACT FROM AUTHOR]

Dielectric properties of nanosized Lithium Orthosilicate (Li4SiO4) and linear low-density polyethylene composite at X-Band frequencies are investigated, to realize its utility as a substrate for microwave devices. Solid state technique is used to synthesize nano Li4SiO4. To confirm the structural and morphological properties of the synthesized nano Li4SiO4, X-ray diffraction, Fourier transformed infrared spectroscopy and transmission electron microscopy are used. Composites of nano Li4SiO4 and linear low-density polyethylene matrix are synthesized with varying weight fraction of nano Li4SiO4 viz. 2%, 4% and 6%. The lateral portion of a fractured sample (composite) is examined using scanning electron microscope to confirm homogeneous dispersion of nano Li4SiO4 in linear low-density polyethylene matrix. Water absorption measurement of all the composites are carried out based on ASTM D570-98. Densities of the composites are measured via hydrostatic weighing by using Archimedes principle. Complex permittivity and permeability measurement of the composites are recorded by utilizing Nicholson-Ross approach. For all weight fraction of the nano inclusions, the real component of permittivity and dielectric loss tangent of the composites in the X-band are found to be in the range of 2.2 - 2.6 and 10-2 -10-4, respectively. Return losses for the composites are calculated from complex permittivity and permeability values to validate its applicability as substrate for various high frequency applications. [ABSTRACT FROM AUTHOR]

Dielectric properties of a magnesium silicate (MgSiO3) linear low-density polyethylene nanocomposite are studied in the X-band frequencies to realize its application as a substrate for high-frequency devices. MgSiO3 ceramics are synthesized by conventional solid state technique. Structural and morphological characteristics of MgSiO3 nanoparticles are confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. Transmission electron microscopy images reveal the average particle size to be ~100 nm. Composites are prepared by uniform dispersion of the nano-inclusions MgSiO3 in a linear low-density polyethylene matrix in three different wt.%, viz. 2%, 4% and 6%. The fractured lateral side of the composite is examined under a scanning electron microscope to ensure the uniform dispersion of the inclusions in the polymer. Water absorption measurement is carried out based on ASTM D570-98. Densities of the samples are measured by hydrostatic weighing by using Archimedes principle. Thermal conductivity of the composites is measured by modified hot plat method. Nicholson-Ross approach is used to investigate the dielectric characteristics of composites. The permittivity and dielectric loss tangent of the nano-composite in the X-band are found to be ~2.2–2.5 and 10−2–10−4 for all the inclusion concentration respectively. To see the applicability of the nanocomposite in the field of antenna, return losses are calculated from complex permittivity and complex permittivity data. [ABSTRACT FROM AUTHOR]

A pattern reconfigurable microstrip patch antenna with two parallel parasitic patches placed close to both sides of a rectangular driven patch is investigated and presented in this article. Four switchable shorting posts are used to enable the parasitic elements to act either as a reector or director for beam reconfiguration, based on the operating state of four associated PIN diode switches. To avoid large change in the dimension of both parasitic patch and ground plane, and minimize its effect on beam steerability and return loss, two PIN diodes are placed on the top face and the other two on the slots etched on the ground plane. Radiation pattern of the proposed antenna can be reconfigured into four distinct directions in the H-plane with radiation maximum at +40°, 0°, -40°, and ±45°. With overall compact dimension of (35 × 55)mm2 and acceptable return loss for all reconfigurable modes around 6.2 GHz frequency, the proposed antenna is a potential candidate for Wi-Fi 6E application. The measured peak gain varies between 3.9 dBi and 5.2 dBi with an average of 4.6 dBi for all beam tilt angles. Consistency between the simulated and experimental results validates the design theory and its promising application. [ABSTRACT FROM AUTHOR]

A frequency reconfigurable microstrip patch antenna with two asymmetric L-slots is proposed in this article. Two RF pin diodes inserted on the asymmetric L-slots are used to switch the operating frequency over the C band. Design and optimization of different physical parameters of the antenna viz. slot dimensions, feed location, notch size, and pin diode positions are carried out using High Frequency Structure Simulator Version 13.0. The design is implemented on an FR4 substrate (εr = 4.4) of dimension (35 × 40 × 1.6)mm³. DC bias circuitry for RF PIN diode activation is also integrated with the antenna. Switching combinations of two PIN diodes offer four reconfiguration modes of operation at 4.75, 5.05, 5.11, and 5.18GHz. In all the states, the -10 dB bandwidth shows minimal changes with average variations of 15.8% with respect to the state when both PIN diodes are OFF. The gains of the antenna for different modes of operation are found almost stable with an average of 6.64 dBi. [ABSTRACT FROM AUTHOR]

Power transformer is one of the most important high voltage apparatus in any power system network. The life span of such apparatus commonly relies upon its insulation condition. The primary reason for an insulation breakdown is partial discharge. Partial discharges (PDs) are electrical discharges that happen in the insulation system of the transformers. Occurrence of PDs results in deterioration of the transformer insulation system. Hence, measuring and detecting the PD at an initial stage is necessary to avoid complete breakdown of the transformer. Currently, various PD detection and measurement methods, such as, electrical, chemical, acoustic, UHF and optical methods are being used for PD monitoring in power transformers. The conventional PD monitoring techniques like electrical or chemical have some limitations. The optical Fiber Bragg Grating (FBG) Sensor has been used as a PD sensor for PD monitoring in the power transformer to overcome these issues. This paper presents a review of FBG sensors’ application as a sensor for PD monitoring in an oil-filled power transformer. The challenges and future prospects in this area are also discussed. [ABSTRACT FROM AUTHOR]

Composite substrates of linear low-density polyethylene with thermotropic liquid crystals as inclusions with three different weight fractions were synthesized. The dielectric characterizations of the composites in X band frequencies were studied to assess their applicability as substrates for microwave devices. Thermotropic liquid crystals, NN-(terephthalylidene)bis(4-n-butylaniline), NN-(terephthalylidene)bis(4-n-hexylaniline) and NN-(terephthalylidene)bis(4-n-decylbenzamine) were synthesized in the laboratory at room temperature. Structural characterization for synthesized thermotropic liquid crystals was done using nuclear magnetic resonance and Fourier transform infrared spectroscopy. To confirm the distribution of liquid crystal inclusions in the polymer matrix, scanning electron microscope images were used. Water absorbance test was carried out following Archimedes' principle. The real part of complex permittivity and the dielectric loss tangent at X band frequencies for all the weight fractions of the composite were found to be ~ 2.1–2.4 and ~ 10−2–10−4 respectively. The magnetic loss tangent was also measured for the substrates and showed values within the range of 10−1–10−2. To establish the suitability of the fabricated substrates for use in antennas, the return losses were calculated using the complex permittivity and permeability values. [ABSTRACT FROM AUTHOR]

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Partial discharge (PD) is the main cause of the insulation decay and hence periodical testing of the insulation condition of a distribution transformer is necessary. This paper presents a model of PD acoustic wave propagation, detection, and localization in an oil-filled distribution transformer using finite element method supported by COMSOL Multiphysics software. Using an acoustic module and AC/DC module of COMSOL Multiphysics software, oil filled distribution transformer, and the acoustic piezoelectric sensor are simulated to analyze and detect the PD inside the transformer. PD is numerically simulated in the transformer windings, core, and oil ducts that produce acoustic wave signal. The distribution of the acoustic pressure wave inside the model transformer is analyzed first. Next, the acoustic piezoelectric sensors are modelled at four different locations of the model transformer to detect the pressure acoustic wave signal induced due to PD in the transformer. Finally, using an artificial neural network (ANN), the localization, and identification of PD in various parts of the transformer have been analyzed. The results obtained for location and detection are quite encouraging. [ABSTRACT FROM AUTHOR]

Magnetodielectric substrate gives a new dimension for reducing the size of the planar antennas. In this article, the patch size is reduced by taking a substrate with nano-sized nickel ferrite inclusions in LDPE polymer matrix. The antenna is made to operate in X and Ku bands by engraving T slots along the resonant length of the patch. Structural modification of the substrate geometry as a step profile is incorporated along the slotted patch edges to enhance performance. The T-slots, along both the resonating lengths with the magnetodielectric stepped substrate show four resonant frequencies in both X- and Ku-bands with S11 < -15 dB and a maximum -10 dB bandwidth of 22.4%. A miniaturization factor of 2.97 is obtained. [ABSTRACT FROM AUTHOR]

A modification in the structure of a substrate has been carried out to reduce weight and improve the performance of microstrip patch antenna in X-band. A step profile is incorporated in the substrate along the radiating edges of the patch. The design is tested on both dielectric and magnetodielectric substrates. Return loss of antenna with varying step riser height and step tread length shows improvement in --10 dB bandwidth to 13.2% for the dielectric and to 12.3% for the magnetodielectric as compared to about 4.8% and 6.9% for unprofiled substrate geometry in dielectric and magnetodielectric respectively. As compared to the unprofiled planar antenna, maximum weight reduction for the stepped antenna on dielectric substrate is 54.75% and for the magnetodielectric is 58.9% is observed. An equivalent circuit modeling for the stepped structure is carried out for the proposed structure. [ABSTRACT FROM AUTHOR]

A modification in the structure of a substrate has been carried out to reduce weight and improve the performance of microstrip patch antenna in X-band. A step profile is incorporated in the substrate along the radiating edges of the patch. The design is tested on both dielectric and magnetodielectric substrates. Return loss of antenna with varying step riser height and step tread length shows improvement in -10 dB bandwidth to 13.2% for the dielectric and to 12.3% for the magnetodielectric as compared to about 4.8% and 6.9% for unprofiled substrate geometry in dielectric and magnetodielectric respectively. As compared to the unprofiled planar antenna, maximum weight reduction for the stepped antenna on dielectric substrate is 54.75 % and for the magnetodielectric is 58.9% is observed. An equivalent circuit modeling for the stepped structure is carried out for the proposed structure. [ABSTRACT FROM AUTHOR]

Magneto dielectric material using nano cobalt ferrite inclusions is prepared as potential substrate for microstrip antennas. Permittivity characterization at microwave frequency (8.7- 12.1 GHz) is conducted using an in touch superstrate method. Test set-up consists of microstrip antenna designed over glass epoxy substrate and loaded with the test samples of different volume fraction of inclusions. The real part of complex permittivity increases with volume fraction for different magneto dielectric material. The dielectric loss is found in the order of 10-3. Morphological characterizations like scanning electron microscopy and X-ray diffraction carried out on the test materials show homogeneous distribution of the inclusions in the composite and the size of the inclusions is found to be ˜ 10nm. With minor mathematical manipulations the method can be used to design antennas with dielectric cover at specific operating frequency. [ABSTRACT FROM AUTHOR]