Search results for "Ave"
showing 10 items of 10362 documents
Guiding and splitting Lamb waves in coupled-resonator elastic waveguides
2018
Abstract We investigate experimentally Lamb wave propagation in coupled-resonator elastic waveguides (CREWs) formed by a chain of cavities in a two-dimensional phononic crystal slab with cross holes. Wide complete bandgaps, extending from 53 to 88 kHz, are first measured in a finite phononic crystal slab sample. A straight waveguide and a wave splitting circuit with 90° bends are then designed, fabricated and measured. Elastic Lamb waves are excited by a piezoelectric patch attached to one side of the phononic slab and detected using a scanning vibrometer. Strongly confined guiding and splitting at waveguide junctions are clearly observed for several guided waves. Numerical simulations are …
Determination of refractive index of submicron-thick films using resonance shift in a four-layer slab waveguide
2017
The measurement of refractive index of very thin films at the order of ten to hundred nanometers is cumbersome and usually requires employing sophisticated techniques such as the spectral ellipsometry. In this paper we describe a simple contact method for measuring the refractive index of thin films. Here we have used the prism-coupling technique for characterizing samples prepared as four-layer slab waveguides. The waveguide resonance condition can be calculated by solving simple analytic transcendental equations for the slab waveguide. Then the captured mode position as a function of cladding thickness is used for probing the refractive index of cladding layer. We used indium-tin-oxide la…
The effect of cavity tuning on oxygen beam currents of an A-ECR type 14 GHz electron cyclotron resonance ion source.
2016
The efficiency of the microwave-plasma coupling plays a significant role in the production of highly charged ion beams with electron cyclotron resonance ion sources (ECRISs). The coupling properties are affected by the mechanical design of the ion source plasma chamber and microwave launching system, as well as damping of the microwave electric field by the plasma. Several experiments attempting to optimize the microwave-plasma coupling characteristics by fine-tuning the frequency of the injected microwaves have been conducted with varying degrees of success. The inherent difficulty in interpretation of the frequency tuning results is that the effects of microwave coupling system and the ca…
New progress of high current gasdynamic ion source (invited).
2016
The experimental and theoretical research carried out at the Institute of Applied Physics resulted in development of a new type of electron cyclotron resonance ion sources (ECRISs)—the gasdynamic ECRIS. The gasdynamic ECRIS features a confinement mechanism in a magnetic trap that is different from Geller’s ECRIS confinement, i.e., the quasi-gasdynamic one similar to that in fusion mirror traps. Experimental studies of gasdynamic ECRIS were performed at Simple Mirror Ion Source (SMIS) 37 facility. The plasma was created by 37.5 and 75 GHz gyrotron radiation with power up to 100 kW. High frequency microwaves allowed to create and sustain plasma with significant density (up to 8 × 1013 cm−3 ) …
Study of the multipactor phenomenon using a full-wave integral equation technique
2017
Abstract Multipactor effect is a well-known phenomenon of RF breakdown in satellite payloads which degrades components, generates undesirable harmonics, contributes to power dissipation and increases noise in communications. Traditionally, multipactor has been investigated with the aim of obtaining the so-called multipactor threshold voltage, or to present different multipaction detection methods. However, very little attention has been focused on analysing this phenomenon using a multimodal approach. The main goal of this work is to analyse the interaction between a multipactor current and a realistic microwave cavity by means of a rigorous and accurate formulation. For the first time to t…
A New Multipactor Effect Model for Dielectric-Loaded Rectangular Waveguides
2019
Multipactor is an electron discharge that may appear in particle accelerators and microwave devices such as filters, multiplexers, and RF satellite payloads in satellite on-board equipment under vacuum conditions. When some resonance conditions are satisfied, secondary electrons get synchronized with the RF fields, and the electron population inside the device grows exponentially leading to a multipactor discharge. This multipactor discharge has some negative effects that degrade the device performance: increase of signal noise and reflected power, heating of the device walls, outgassing, detuning of resonant cavities, and even the partial or total destruction of the component. The main aim…
Study of the Secondary Electron Yield in Dielectrics Using Equivalent Circuital Models
2018
[EN] Secondary electron emission has an important role on the triggering of the multipactor effect; therefore, its study and characterization are essential in radio-frequency waveguide applications. In this paper, we propose a theoretical model, based on equivalent circuit models, to properly understand charging and discharging processes that occur in dielectric samples under electron irradiation for secondary electron emission characterization. Experimental results obtained for Pt, Si, GaS, and Teflon samples are presented to verify the accuracy of the proposed model. Good agreement between theory and experiments has been found.
Comparison of Single Event Transients Generated at Four Pulsed-Laser Test Facilities-NRL, IMS, EADS, JPL
2012
Four pulsed-laser single-event effects systems, differing in wavelength and pulse width, were used to generate single event transients in a large-area silicon photodiode and an operational amplifier (LM124) to determine how transient amplitude and charge collection varied among the different systems. The optical wavelength and the focused spot size are the primary factors influencing the resultant charge density profile. In the large-area photodiode the transients can be distorted by high charge-injection densities that occur for tightly focused, higher energy optical pulses. When the incident laser-pulse energies are corrected for reflection losses and photon efficiency, with collection de…
Microwave properties and structure of La–Ti–Si–B–O glass-ceramics for applications in GHz electronics
2017
Abstract A dielectric bulk glass-ceramic of the La 2 O 3 –TiO 2 –SiO 2 –B 2 O 3 system is developed which is able to fulfill the requirements for dielectric loading-based mobile communication technologies. It is shown that the given dielectric requirements can be fulfilled by glass-ceramic materials without being dependent on ceramic processing techniques. The material exhibited permittivity values of 20 ɛ r Qf τ f τ f material with a Qf value of 9500 GHz and ɛ r = 21.4 could be achieved at a ceramming temperature T cer = 870 °C. The material is aimed to provide an alternative to existing, commercially used sintered ceramic materials. Further focus is laid on the investigation of the dom…
Relaxation of polarization in (K0.5Na0.5)(Nb0.93Sb0.07)O3 ferroelectric ceramics modified by BaTiO3
2017
ABSTRACTA study of low-frequency relaxation of polarization in conventionally prepared ceramic compounds of (1-x)(K0.5Na0.5)(Nb0.93Sb0.07)O3+xBaTiO3+0.5mol.%MnO2 (x = 0.02, 0.04) examined over a wide temperature range is reported. Anomalous behavior of the temperature dependence of the coercive field Ec(T) is detected in the temperature range of the orthorhombic to tetragonal phase transition. The observed features of polarization are assigned to dynamics of the domain structure at the temperature range of phase coexistence.