Functional Properties of Donor (Al) and Acceptor (Cu) Codoped High Dielectric Constant ZnO Nanoparticles

In this work, we have synthesized donor-acceptor (Al-Cu) codoped ZnO nanoparticles with a doping concentration of 0%, 0.25%, 0.5%, and 0.75% by coprecipitation method. The synthesized samples were then annealed at 350°C and 600°C. All the samples showed wurtzite structure of ZnO with no secondary phase. The increase in doping concentration led to deterioration of crystalline quality, while improved crystallinity was observed at higher annealing temperature. The morphological study of these samples showed good grain-to-grain contact with less isolated pores. These samples were further characterized by impedance spectroscopy for analyzing dielectric properties. The values of the real part of dielectric constant and tangent loss showed decreasing trend with frequency. The appearance of semicircular arcs in the impedance complex plane plots indicates contribution of grains and grain boundaries and presence of different relaxation processes. 0.5% Al and Cu codoped ZnO showed the best dielectric response with a high value of dielectric constant and low tangent loss.

Insight into Structural and Optical Properties of Pristine and Sr2+ Doped La2NiMnO6

Double perovskites oxide (DPO) multiferroics La2-xSrxNiMnO6(x=0.0, 0.1, 0.2, 0.4, 0.6) are synthesized by sol-gel technique. The structural, optical and electrical (both DC and AC) properties of La2-xSrxNiMnO6 have been investigated by XRD and FTIR spectroscopy and two-probe resistivity and dielectric measurements as a function of temperature, respectively. The effect of doping of Strontium at A-site in double perovskites is discussed. XRD has revealed the formation of monoclinic structure of La2-xSrxNiMnO6 with space group P21 / n for x=0.0 and P21 for x=0.1, 0.2, 0.4, 0.6. The average crystallite size has been calculated to be in the range 31 to 46 nm as determined by Debye Scherrer equation. Infrared active optical phonons observed from reflectivity spectra have been analysed fitting the theoretical oscillators using Lorentz oscillator model. We have observed several well-resolved phonon modes in La2-xSrxNiMnO6 with increasing dopant concentration. Activation energy calculated using Arrhenius Plot is in the range of 0.31 to 0.18 eV, confirming the semiconducting nature of all samples. The dielectric constant and tangent loss as a function of temperature and frequency are also discussed for these multiferroics.

Second Iteration of Slotted Fractal Log Periodic Dipole Antenna for UHF Digital TV Band Application

This paper discusses the simulations and measurements of the antenna with and without slot implementation in terms of reflection coefficient (S11) and radiation pattern. The slot implementation on each of the radiating elements on the 2nd iteration log periodic fractal Koch antenna (LPFKA) was described in this paper. This method is utilised to reduce the antenna's size while also preventing the lower designated frequencies from shifting to the higher band as the iteration increases. The antenna is designed to test and observe performance in the Ultra High Frequency (UHF) band, which ranges from 0.5 GHz to 3.0 GHz. Computer Simulation Technology (CST) software is used to design and model the antenna, which was then built using the wet etching technique. The antenna's substrate is made of FR-4 laminated board with a dielectric constant of 4.6, tangent loss of 0.019, and a thickness of 1.6mm. The results demonstrate good agreement, with a steady radiation pattern over the operational bandwidth and a reflection coefficient of less than -10 dB for the frequency range of interest. The antenna is being tested with Digital TV decoder and the result is observed towards the picture of the Digital TV.

Effect of Structural Changes on the Electrical Properties of Sol-gel derived Iron Doped Barium Titanate

BaTi1-xFexO3 compositions for x = 0.0 - 0.5 were successfully synthesized using solgel method and the structural, dielectric, ferroelectric, and ferromagnetic properties of these compositions were studied. X-Ray diffraction patterns revealed a tetragonal phase in x=0.0 composition which changed to the hexagonal phase in x = 0.4 and 0.5 compositions. The co-existence of tetragonal and hexagonal phases was observed in iron doped samples up to x= 0.3. The difference in ionic radii of Ti and Fe ions was responsible for changing c/a ratio. Average grain size was found gradually increasing with Fe content in these compositions and was also observed in SEM micrographs. The dielectric constant and tangent loss were found decreasing with Fe concentration. The values of remnant and saturation polarizations decreased whereas that of saturation magnetization increased with an increasing content of Fe in barium titanate.

COMPARATIVE ANALYSIS ON DIFFERENT FEEDING TECHNIQUES OF TEXTILE ANTENNA FOR GPS-L1 APPLICATION

This paper presents a comparative analysis of textile antenna using different feeding techniques for Global Positioning System (GPS-L1) application. Textile materials which are commonly used in the wearable application has gained much attention due to the flexibility and conformability characteristic of the antenna. Nevertheless, the flexibility of this antenna will introduce the bending and stretching element to its physical structure that may degrades the performance. To ensure the maximum power transfer takes place takes place between the source and the antenna, a suitable feeding method must be identified. In this paper, the microstrip feedline technique and coaxial feeding technique will be studied comparatively using Felt textile material as the substrate with the relative permittivity, ?r of 1.098 and tangent loss, ? of 0.0395. It is attached to a copper tape which act as the conductive material with thickness of 0.035 mm. Using Computer Simulation Technology (CST) Microwave Studio software, the result will be analysed comparatively from the performance validation in return loss, gain, bandwidth, directivity and radiation pattern

Multiband Slotted Planar Inverted-F Antenna using Reactive Impedence Surface for Wireless Applicatios

This research work presents a low profile slotted planar invertedF antenna (PIFA) on a reactive impedance surface (RIS) for multiband. The quad-band frequency antenna for 2.4 GHz (WLAN), 4.2 GHz (C-band satellite downlink), 7.1 GHz (C-band satellite uplink), and 9 GHz (X-band )for wireless applications. The structure of the proposed PIFA has a compacted patch size of 23.33 mm × 2.66 mm × 1 mm placed on a dielectric substrate flame retardant 4(FR4) material, along with tangent loss = 0.02. The proposed antenna used two dielectric substrates whose heights are h1 = 1.59 mm and h2 = 1 mm . The rectangular slot is added in a radiating patch of the PIFA for multiband operations. The proposed antenna improves the parameters such as reduction scale, efficiency, narrow bandwidth, and gain enhancement. The slotted PIFA shows a quad-band with an S11 <-10 dB bandwidth of approximately 15.83% (2.24-2.62 GHz), 11.19% (3.93-4.4GHz), 12.67% (6.90-7.80GHz) and 10.55% (8.29-9.24GHz) under measurement. The proposed antenna design is excited by 50Ω microstrip line feed. The antenna exhibits radiation pattern, gain, and impedance matching across their operating bandwidths to demonstrate the benefits of multiple PIFA.

Carbon Nanotubes based composites for electromagnetic absorption- A review

: Radar is a delicate detection device and since its evolution different techniques for reducing electromagnetic reflections have been discovered. This paper provide concise review on fundamentals of absorption which reduces radar cross section from stealth target with which radar cross section has effects to survivability and mission capability. The reduction of radar cross section depend on dielectric and magnetic properties of material. The first section reviews the Radar Absorbing Material (RAM) in order to provide a background on fundamentals, various stealth techniques for absorption and its properties at microwave frequencies. The second section reviews the Multi-Walled Carbon Nanotubes and its different composites by encapsulation of other metals, polymers or epoxies into it and its microwave absorption properties were studies at microwave frequencies. Multi-Walled Carbon Nanotubes based composites for microwave absorption are reviewed on the basis of various factors; material composition, reflection loss performance, thickness, complex permittivity, complex permeability, dielectric tangent loss, magnetic tangent loss, bandwidth, and frequency band.

Effect of Sintering Temperature on the Physical Properties of Ba0.6Sr0.4TiO3 Prepared by Solid-State Reaction

Barium Strontium Titanate (BST) ceramic materials are widely used in electronic devices due to their stable operation at high temperatures, high tunability, low tangent loss, low DC leakage, and alterable curie temperatures. While pure BST materials are usually produced at high sintering temperatures (1250 °C), there are limited studies on the temperature and duration of the sintering process to produce pure BST, synthesised from micro or even nano-sized raw materials. This study aims to determine the effective sintering temperature for producing pure BST material using a mixture of raw materials with a mean particle size of 0.4 μm after milled for 58 hours. The BaCO3, SrCO3, and TiO2 materials as raw materials for Ba0.6Sr0.4TiO3 synthesis were milled for 58 hours to produce a homogeneous mixture with a mean particle size of 0.4 μm. Sintering was carried out in a temperature range of 500-1100 °C for 1 hour. This study investigates the impact of sintering temperature on the physical properties and the purity of Ba0.6Sr0.4TiO3 powder using the x-ray diffraction method. The results showed that the Ba0.6Sr0.4TiO3 phase was formed at a sintering temperature of 700 °C. Pure BST material was formed at the sintering temperature of 1000 °C with a crystallite size of 41 nm. Whereas at a higher sintering temperature (1100 °C), the pure BST material formed produced a larger crystallite, sized at 43 nm with cubic structure. The synthesis temperature and duration recorded in this research are lower than recorded in the BST material preparation using the solid-state method. The results of this study indicate that the sintering temperature greatly affects the purity, crystal system and crystallite size of the Ba0.6Sr0.4TiO3 material produced. The sintering temperature of 1100 °C produces Ba0.6Sr0.4TiO3 material with the best physical properties because it has a cubic-shaped crystal system and the largest crystal size.

Structural and Dielectric Properties of Calcium Bismuth Titanate (CaBi4Ti4O15) Ceramics

Calcium Bismuth Titanate (CaBi4Ti4O15) ceramics were prepared by conventional solid-state reaction method. X-ray diffraction patterns confirms the orthorhombic structure of CaBi4Ti4O15 and the lattice parameters were also determined. Bulk densities of the sintered ceramics were measured by the Archimedes method with xylene as the liquid media and found to be 97~98% of X-ray density. The surface morphology of CaBi4Ti4O15 is studied by Scanning Electron Microscope (SEM) attached with energy dispersive X-ray spectroscopy (EDS) inorder to determine the grain size as well as the chemical composition of CaBi4Ti4O15. The dielectric constant (k) and dielectric tangent loss (tan δ) of CaBi4Ti4O15 as a function of temperature were measured in the frequency range of 100 Hz-100 KHz. The dielectric constant, dielectric loss and ac conductivity of CaBi4Ti4O15 increases gradually with an increase in the temperature from 303 to 573 K. The ac conductivity of the prepared sample reveals that the conduction mechanism is electronic hoping

Circle Microstrip Antenna Simulation for Frequency 3.5 GHz

This research proposed microstrip circular patch antenna simulation at a working frequency 3500 MHz. The antenna has been designed using a Duroid RT5880 substrate with dielectric constant (εr) = 2.2, substrate thickness (h) = 1.575 mm, and tangent loss = 0.0009 with microstrip line feeding. The simulation result, return loss value obtained -26.385, VSWR value 1.09, gain value 7.64 dBi, total radiation efficiency value -0.6489 dB, and bandwidth value 72 MHz (3468.8 MHz – 3541.9 MHz).