Papers by Keyword: High Frequency

Abstract: TIG (Tungsten Inert Gas) welding has more and more application options. To always create new ways of optimization, a more in-depth study of the effects on the components subject to joining is necessary. The paper includes a study on the hardness resulting in the specific areas of the welded joint, using TIG welding with high frequency pulsed arc, applied to join some stainless-steel plates. The relative variation of the hardness was determined and analysed, in correlation with the process parameters. The study is part of the research on obtaining a good energy efficiency in the welding process, based on the requirements imposed on the quality of the joints.

Abstract: The magnetization process at elevated frequencies (up to 15 kHz) of ring-shaped binary Fe₈₁Ga₁₉ alloy was studied. Frequency and magnetic field dependences of coercive field and remanent induction were analyzed. Hysteresis loops and initial permeability were studied at low (200 Hz) and high (15 kHz) frequencies. The same measurements were made for FeGaRE alloys to establish the effect of rare-earth elements on dynamic magnetic properties.

Abstract: In this work, an AlGaN/GaN HEMT structure is grown on a 0.8 μm thick 3C-SiC layer on high resistivity Silicon substrate. The RF propagation losses are investigated and compared with the ones of epi-layers grown directly on Silicon and on 6H-SiC substrates. Short gate length transistors are fabricated using e-beam lithography. In spite of ohmic contact resistance of 0.6 Ω.mm, a saturated current density of 0.7 A/mm at a gate bias of +1V and a transconductance peak higher to 250 mS/mm for 75 nm T-shaped gate transistors are reached on structure with thick 3C-SiC template. Moreover, for the first time, transition frequencies f_T/f_max of 60/98 GHz are reported on such 3C-SiC template.

Abstract: Multilayer films exhibit high saturation magnetization, high permeability, and high cutoff frequency f_r, applying to magnetic inductors that satisfy both high frequency, miniaturization, and integration. In this work, we fabricate Fe/Ni₈₁Fe₁₉/Fe (t/100/t nm) multilayer films on Si (100) using electron beam evaporation, and investigate the Fe thickness dependence of surface morphology, saturation magnetization, coercivity, and ferromagnetic resonance f_r. The results demonstrate that Fe/Ni₈₁Fe₁₉/Fe (4/100/4 nm) multilayer film possess relatively high saturation magnetization (12.1 kGs), low coercivity (3.1 Oe), and high ferromagnetic resonance f_r (1.93 GHz).

Abstract: Graphene transistors are considered to be the successors’ of MOS transistors for the next generation of advanced integrated circuits. However, graphene suffers from the absence of energy band gap to experience a semiconductor like characteristics. In order to instigate a bandgap in graphene, several techniques and methods are introduced to beak its symmetry. The most common graphene form is the Graphene Nanoribbon (GNR) sheets. Few techniques have been used to grow GNR sheets. However, the main methods that gave better results are bottom-up techniques mainly based on nanotechnology principles. The present paper deals with the investigation of the bandgap engineering approach targeting an increase in graphene transistors switching characteristics leading to higher maximum frequencies applications. The GNR sheets are synthesized using bottom-up CVD based techniques yielding controlled electronics and physical characteristics. Results obtained on few GNR transistor samples compared to other forms of transistors showed good agreements and found to be close to that of standard silicon devices. Moreover, the GNRFETs frequency response is directly related to the bandgap of the material. It has been evidenced that gap modulation modulates the transistor frequency response. Whereas using other techniques, this cannot be achieved. We have found that small values of gap (100-300 meV) led to high mobility and frequencies of thousands of GHz. However, the edge quality limits the maximum frequencies as it induces traps in the graphene generated gap.

Abstract: As a key part of the RF PA system, VRM (Voltage-Regulate-Modulator), whose main role is to offer pulse voltage for RF power transistor, is often slighted. As a result, VRM has been a restraining factor now. In order to realize the needs of high speed and high frequency, a new method based on enhancement mode GaN HEMT of designing VRM is proposed in this paper. By using this method, the rise time and fall time of VRM could be as about 10ns with the peak voltage 75V and the peak current 150A, which is quite suitable for driving high voltage and high power GaN-based RF power transistor.

Abstract: Nowadays, the magnetic suspension is widely used in metallurgy for crucibleless melting of metals. We carry out the contactless suspension of metal under the inductor (a source of the high-frequency field), using the forces of interaction of the eddy currents, which are induced in the metal with a high-frequency magnetic field causing them. Besides, such a method of the suspension of metals allows to carry out simultaneously its heating and melting at the expense of the energy of the electromagnetic field of suspension

Abstract: Numerical analysis of distribution of resistive heat source in two-phase conducting medium (copper electrode – biological tissue) was carried out. Axisymmetric two-dimensional elliptic problem, with boundary conditions of the first and second kind was solved in the environment of MATLAB mathematical package, using the method of finite differences. Analysis results show that heat source concentration and other parameters are determined by skin effect. This fact should be taken into account in development of new effective methods of surgical treatment and respective instruments. This mathematical model can be applied in a wide frequency range for conducting materials with different conductivities.

Abstract: The dielectric properties of CCTO with addition Al₂O₃ prepared via solid state reaction investigated and reported at 1 GHz. With addition Al₂O₃ from 20 wt% to 80 wt%, secondary phase starts appear in XRD analysis such as copper dialuminium oxide (CuAl₂O₄), calcium titanate (CaTiO₃) and titanium oxide (TiO₂). These secondary phases show great influence on morphology and grain size of Al₂O₃/ CCTO composites. Hence, the addition of only 20 wt% Al₂O₃, the dielectric constant of CCTO reduce almost 50% and tangent loss is in between 0.0028 to 0.0630 which is very low and this characterization is suitable to use in electronic application in high frequency range.

Abstract: Li⁺ and Zr²⁺ codoped NiO ceramics was successfully prepared from the mixture of commercial Li₂CO₃, ZrO₂ and NiO using solid state reaction. The mixture of varies Li⁺ concentration (x = 0.01, 0.02, 0.03, 0.05 and 0.1), Zr²⁺ (y = 0.02) and NiO were ball milled for 24 hours. The samples were calcined at 1000oC for 2 hours, pressed into pellet shape at 250 MPa and sintered at 1280°C for 10 hours. The sintered pellets were subjected to XRD, SEM, density testing and Impedance analyzer. XRD result shows the single phase formation of Li_xNi_1-x-0.02Zr_0.02O. The grain becomes larger with the increament of Li⁺ mole %. The dielectric constant of Li_xNi_1-x-0.02Zr_0.02 decrease with the increasing frequency. The NiO codoped with Li⁺ and Zr²⁺ can be use excellently at high frequencies.Keywords: NiO doped Li⁺ and Zr²⁺, dielectric constant, high frequency