RF Losses Research Articles

Studies on ac losses in Bi 2Sr 2CaCu 2O 8 single crystals

Using a novel technique of measuring absolute ac losses at radio frequencies, the temperature, magnetic field and angle dependence of rf losses in superconducting single crystals of Bi 2Sr 2CaCu 2O 8 is studied. An unexpected, larger than normal state ac loss is observed below T c. We provide an explanation for this observation in terms of the energy required to decouple the intrinsic Josephson junctions in the crystals. The studies are carried out both at zero magnetic field and at different values of magnetic fields applied at different angles θ between the field and the c-axis of the crystal. We observe two maxima in ac loss as a function of temperature. The amplitude, width and the position of the first maximum (peak A) change with the magnitude and orientation of the applied magnetic field. These results are discussed in terms of the critical current density of the Josephson junctions, which decreases with the increasing field and changes with the orientation. The second maximum (peak B) appears just below T c only in the presence of the magnetic field and has been attributed to the vortex motion. The amplitude of this peak as well changes with the magnetic field and with the angle of orientation. The analysis shows that the loss is due to pancake vortices.

Thermal and non-thermal particle interaction with the LHCD launchers in Tore Supra

The interaction between the lower hybrid current drive (LHCD) launchers and the plasma has been studied during long pulse, high power operation in the Tore Supra tokamak. The main diagnostics used for characterising the plasma–launcher interaction are calorimetry of the energy extracted by the launchers and infrared (IR) imaging of the launchers and their side limiters. The calorimetry has allowed to identify three different heat sources on the LHCD launchers, namely the RF losses in the waveguides, a fraction (∼0.8%) of the total injected energy and, finally, fast ion losses during ion cyclotron resonance heating (ICRH), accounting for ∼1% of the injected ICRH energy. The interaction by fast ions is identified by infrared imaging of the LHCD launchers as a localised hotspot on the ion drift side, below or at the mid-plane.

A novel packaging approach for RF MEMS switching functions on alumina substrate

This paper reports the design of a hermetic-compatible wafer-scale package for RF MEMS based components. The presented packaging concept consists in encapsulating the whole RF device or subsystem instead of encapsulating each MEMS component separately, which will reduce the device size and cost. This approach is based on the MEMS fabrication technology on ceramic substrate and the use of laser drilled vias hole techniques to realize full metallized vias in alumina substrates. These vias holes will allow a low loss RF signal transmission inside the package without breaking its hermeticity. Hence, several packaged switching networks prototypes, based on ohmic contact MEMS switches, have been designed following this approach and the packaging electromagnetic impact on these components has been especially studied to result on good performance devices.

Using low-E resonators to reduce RF heating in biological samples for static solid-state NMR up to 900 MHz

RF heating of solid-state biological samples is known to be a destabilizing factor in high-field NMR experiments that shortens the sample lifetime by continuous dehydration during the high-power cross-polarization and decoupling pulses. In this work, we describe specially designed, large volume, low-E 15N– 1H solid-state NMR probes developed for 600 and 900 MHz PISEMA studies of dilute membrane proteins oriented in hydrated and dielectrically lossy lipid bilayers. The probes use an orthogonal coil design in which separate resonators pursue their own aims at the respective frequencies, resulting in a simplified and more efficient matching network. Sample heating at the 1H frequency is minimized by a loop-gap resonator which produces a homogeneous magnetic field B 1 with low electric field E. Within the loop-gap resonator, a multi-turn solenoid closely matching the shape of the sample serves as an efficient observe coil. We compare power dissipation in a typical lossy bilayer sample in the new low-E probe and in a previously reported 15N– 1H probe which uses a double-tuned 4-turn solenoid. RF loss in the sample is measured in each probe by observing changes in the 1H 360° pulse lengths. For the same values of 1H B 1 field, sample heating in the new probe was found to be smaller by an order of magnitude. Applications of the low-E design to the PISEMA study of membrane proteins in their native hydrated bilayer environment are demonstrated at 600 and 900 MHz.

Monolithic microfabricated ion trap chip design for scaleable quantum processors

A design is proposed for a novel ion trap quantum processor chip, microfabricated using a process based on planar silica-on-silicon techniques. The trap electrodes are of gold-coated silica and are spaced by highly doped silicon in a monolithic structure. This design allows a unit aspect-ratio trap with an ion-electrode separation below 100 μm, when using current fabrication techniques. The trapping potential is modelled and the operating parameters required to achieve motional frequencies of a few MHz are calculated. RF loss and the resultant heating of the trap chip are not found to be a factor limiting the trap's operation. This monolithic unit aspect-ratio trap is therefore expected to exhibit a deep potential well, high trap efficiency, and a low RF loss, when compared to other microfabricated traps. This technological approach is in principle scaleable to complex devices, and may form the basis for large-scale ion trap quantum processors.

Commissioning of 3.7 GHz LHCD system on ADITYA tokamak and some initial results

To drive plasma current non-inductively, a lower hybrid current drive (LHCD) system has been designed, fabricated and successfully installed on ADITYA tokamak. The system is designed to launch 120 kW of RF power, at a frequency of 3.7 GHz. The system mainly consists of a high power CW klystron source, a long waveguide transmission line of about 100 m length, a UHV compatible modular waveguide line of about 2.65 m, and a conventional grill type antenna. Independent phase shifters, one each in the eight lines, are used to adjust the antenna phasing and also provides the flexibility to launch a composite spectrum. The antenna is designed to launch lower hybrid waves (LHW) with parallel refractive index ( N ||), in the range, 1 < N || < 4.5, by appropriately phasing the antenna. Antenna is positioned in the shadow of the poloidal limiter and is provided with 100 mm radial movement to achieve optimum coupling conditions. The complete system development includes design, fabrication and testing of number of waveguide components, modular waveguide lines and their integration. Different cost effective fabrication techniques are adopted to achieve good RF performance. Special attention is paid on the flanged joint seals in the long transmission line to minimize the RF losses. The entire LHCD system is calibrated, especially, in terms of phase, insertion loss and return loss measurements. After the successful integration of the system on ADITYA tokamak, some initial experiments have been carried out to assess the system commissioning and its performance. The experiments were done with a plasma (hydrogen) density of 2–5 × 10 12 cm −3 at a toroidal magnetic field of 0.8 T with 10–25 kA of plasma current. Initial results indicate that, good coupling is achieved in the presence of proper edge density. Measurements obtained from second harmonic electron cyclotron emission (ECE) and hard X-ray diagnostics suggest generation of suprathermal electrons in the presence of LH pulse. Plasma current pulse elongation with LH power is observed but needs further investigation to derive conclusions. This paper presents the design, fabrication, testing and integration of the waveguide lines, waveguide components and UHV compatible modular transmission lines of the LHCD system on ADITYA tokamak and discusses some of the initial results.

Cryogenic complex anisotropic permittivity of magnesium fluoride

The complex tensor permittivity of MgF 2 has been measured using whispering gallery mode and quasi TE 0np dielectric post resonator techniques as a function of frequency and temperature. MgF 2 exhibits uniaxial anisotropy. At room temperature permittivity component parallel to the anisotropy axis is 4.77 ± 0.2% and the component perpendicular to anisotropy axis is 5.49 ± 0.2%. Dielectric loss tangent component perpendicular to anisotropy axis is approximately 4 × 10 −5 and dielectric loss tangent component parallel to anisotropy axis is approximately 7 × 10 −5 at 39 GHz and room temperature. Losses at room temperature increase quasi-linearly with frequency. At the temperature of 15 K measured loss tangent values for both the components of the dielectric loss tangent were about 1 × 10 −6 at 39 GHz. The RF and microwave losses of magnesium fluoride (MgF 2) crystal are low as compared with other commonly used Fluorides. MgF 2 is hygroscopic and dielectric losses of this material vary with the contents of water.

Analysis of the surface resistance of the superconducting accelerating cavities of the S-DALINAC

The quality factors of the 20 cell, 3 GHz niobium cavities of the S-DALINAC are smaller by almost a factor of three compared to their design value. Combined with the limited cryogenic power of the helium refrigerator in use, this restricts the maximum electron energy of the S-DALINAC in continuous wave operation. Extensive studies to elaborate the origin of this degradation are presented. A 120 ∘ C baking combined with appropriate diagnostic tools for an attempt to improve the Q values has been applied to nine of the 11 cavities. The impact of this treatment on the BCS and residual resistance was evaluated and both were improved. Additionally, quality factor measurements of all modes of the TM 010 passband allowed to derive a spatial distribution of the mean surface resistance. The RF losses in the end cells are systematically higher compared to the inner cells. The studies presented in this article allowed to develop a model describing the Q degradation of the resonators and thereby identifying possible prospects to cure this limitation.

Study of thermal interaction between a 150 kW CW power coupler and a superconducting 704 MHz elliptical cavity

The power coupler needed for β = 0.65 SRF elliptical cavities dedicated to the driver of XADS (eXperimental Accelerator Driven System) should transmit a CW RF power of 150 kW to a 10 mA proton beam. The estimated average values of the RF losses in the coupler are 130 W (respectively 46 W) for the inner (respectively outer) conductor in SW mode. Due to such high values of the RF losses, it is necessary to very carefully design and optimize the cooling circuits of the coupler in order to efficiently remove the generated heat and to reduce the thermal load to the cavity operating at T = 2 K. An experiment simulating the thermal interaction between the power coupler and a 704 MHz SRF five cells cavity was performed in the CRYHOLAB test facility in order to determine the critical heat load that can be sustained by the cavity without degradation of its RF performance. Experimental data are compared to numerical simulation results obtained with the Finite Element Method code COSMOS/M. These data allow us also to perform in situ measurements of the thermal parameters needed in the thermal model of the coupler (thermal conductivity, thermal contact resistance). These data are used to validate numerical simulations.

Ku-band antenna array feed distribution network with ferroelectric phase shifters on silicon

This paper presents the design, fabrication, and experimental results of a 1 : 4 monolithic power distribution network for Ku-band array antenna applications. The network integrated on a high-resistivity silicon (HRS) substrate surface stabilized by polysilicon consists of three Wilkinson power dividers, four dc blocking filters, and four coplanar waveguide (CPW)-to-microstrip (MS) transitions. Each output ports are fed with a barium-strontium-titanate phase shifter. It is found that the introduction of the polysilicon layer between the oxide and HRS reduces RF losses significantly, which will enable the monolithic integration of high-power controller modules onto silicon because of the existence of the oxide layer, preventing any degradation of RF performances. The individual components show insertion losses ranging from 0.4 to 2.6 dB at 15 GHz, and the interconnecting CPW lines result in a loss of 0.064 dB/mm. This network was successfully integrated with MS patch antennas monolithically, showing good performance of 32-dB return loss at 14.85 GHz, and 10/spl deg/ beam-steering capability.

Micromachined wide-band lithium-niobate electrooptic Modulators

We present our detailed study of a micromachined substrate approach for a wide-band lithium-niobate modulator and other ultra-wideband RF interconnection applications. Resonant substrate mode coupling often results in large RF loss that affects the frequency performance in LiNbO/sub 3/ modulators. Using the micromachining approach, we demonstrated significantly reduced resonant mode coupling loss in LiNbO/sub 3/ modulator electrodes. In this paper, the effects of substrate geometry and material combination on microwave transmission are experimentally investigated. Our investigation showed that the RF launch of the coplanar-waveguide circuit is a major contributor to the resonant mode coupling. Micromachining the launch area allows us not only to suppress resonant couplings, but also to retain substrate mechanical strength for high-yield production. Two micromachined modulator die configurations were proposed and experimentally demonstrated.

Direct immersion gold (DIG) as a final finish

PurposeTo report on research on the alternative surface finish “direct gold on copper”, including reaction mechanism, methods of deposition and end uses.Design/methodology/approachExamines the deposition reaction of the electroless flash gold plating bath, and the effects of the copper surface roughness and deposition time on the deposit and solderability characteristics.FindingsDirect immersion gold is only partially immersion and mostly electroless in deposition mode. The surface is applicable to soldering for both leaded solder and lead‐free solders. The surface is also wire bondable.Originality/valueThe paper offers details of a new alternative surface finish for use in printed circuit board fabrication as well as in packaging applications. The paper shows the electroless deposition mode of the process. The finish is ideally suited where Rf losses must be minimized. It is suitable for soldering as well as for wire bonding.

ITER-like PAM launcher for Tore Supra's LHCD system

Abstract In the frame of the Tore Supra Composants d’Injection de Matiere et d’Energie Stationnaire (CIMES) Project, consisting in particle fuelling via a pellet injector and in energy powering using Lower-Hybrid Current Drive (LHCD) for pulses lasting 1000 s, complemented by the transmitter refurbishing, a new launcher, based on the Passive-Active Multijunction (PAM) concept already proposed for ITER, has been developed and is currently under realisation. It was designed for a power injection capability of 2.7 MW CW at 3.7 GHz, a power density of 25 MW/m 2 , to radiate a power spectrum peaked at N // = 1.7 with a maximum power directivity near the electron cut-off density and with very good coupling properties on a wide range of electron densities. In this paper, an overall description of the antenna as well as the foreseen manufacturing and assembling processes are given, followed by the results from studies and optimisations of its RF components, by a stress analysis of its thermo-mechanical behaviour, taking into account the plasma radiated flux at the mouth and the RF losses, and complemented with additional mechanical stresses due to the combined action of the eddy current induced in the launcher by disruptions and the residual toroidal magnetic field.

A high temperature superconductor tape RF receiver coil for a low field magneticresonance imaging system

High temperature superconductor (HTS) thin films have been applied in making alow loss RF receiver coil for improving magnetic resonance imaging imagequality. However, the application of these coils is severely limited by theirlimited field of view (FOV). Stringent fabrication environment requirements andhigh cost are further limitations. In this paper, we propose a simpler methodfor designing and fabricating HTS coils. Using industrial silver alloy sheathedBi(2−x)PbxSr2Ca2Cu3O10 (Bi-2223) HTS tapes, a five-inch single-turn HTS solenoid coil has been developed, andhuman wrist images have been acquired with this coil. The HTS tape coil hasdemonstrated an enhanced FOV over a six-inch YBCO thin film surface coil at 77 K withcomparable signal-to-noise ratio.

Two-stage ultrawide-band 5-W power amplifier using SiC MESFET

This paper describes a two-stage 5-W broad-band amplifier covering the frequency range from 10 MHz to 2.4 GHz. An SiC MESFET is used as the power stage. A large-signal table-based model has been developed and verified for the SiC device by comparison with measurements. A novel broad-band choke structure was developed to obtain high dc isolation and low RF loss over the full bandwidth. No impedance transformer was used at all. Broad-band input and output matching networks and shunt feedback topology were introduced to fulfill the bandwidth requirements. Typical values of 22-dB power gain, 37-dBm output power, 28% power-added efficiency, and 47-dBm third-order intercept points have been achieved in a two-stage design using a GaAs MESFET as driver stage. All power and linearity results were obtained over the whole frequency band. The design procedure is given in detail and the results are being discussed and compared with simulations.

Slit-patterned CoNbZr∕Nb∕CoNbZr magnetic film for rf noise suppressor

In this paper, we discuss the elimination of magnetic closure domains in a micropatterned film in order to have the desired loss generation profile against the operating frequency and describe a demonstration of the rf loss generation profile over a thin-film coplanar transmission line using micropatterned films with various slit designs. It was demonstrated that the micropatterned film causes loss in the transmission line in a narrow frequency band and the loss ratio in the other bands is smaller than in the nonpatterned film we measured. The peak frequency of loss generation is controllable according to the pattern dimension of the magnetic film. This technique is useful as a notch filter for integrated transmission lines.

A 24‐year follow‐up of root filled teeth and periapical health amongst middle aged and elderly women in Göteborg, Sweden

To describe the endodontic status amongst middle-aged and elderly women longitudinally and cross-sectionally over 24 years. A random sample of 1462 women 38, 46, 50, 54 and 60 years old, living in Göteborg, Sweden, were sampled in 1968 for medical and dental examinations with a participation rate of 90.1%. The same women were re-examined in 1980 and 1992 together with new 38- and 50-year-old women. The dental examination consisted of questionnaires, clinical and panoramic radiological survey (OPG). The number of teeth, number of root filled teeth (RF) and number of teeth with periapical radiolucencies (PA) were registered. The RF and PA ratios were calculated. Cross-sectional data were analysed by means of anova and longitudinal data by a general linear model for repeated measures. Sample prevalences were compared and statistical inferences were made with the chi-squared test. In all analysis, the confidence interval (CI) regarded mean difference between groups (95% CI). The RF and PA ratio decreased over time as well as the frequency of edentulous subjects. Cross-sectional analysis revealed a minor increase in frequency of RF and PA and loss of teeth with age. Longitudinally, loss of teeth was evident in all cohorts. In addition, there was a trend of lower number of teeth with PA, and the RF ratio increased with age. The prevalence of periapical disease did not increase with age, probably as a result of root canal treatment and extractions. Data showed that the prevalence of RF teeth and teeth with PA decreased for comparable age cohorts during the 24-year follow-up.

Self-assembled monolayers and chemical derivatization of Ba 0.5Sr 0.5TiO 3 thin films: Applications in phase shifter devices

Thin films of barium strontium titanate (Ba 1− x Sr x TiO 3 (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift °/dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9 eV, indicative of a possible S O interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780 cm −1, which is characteristic of an O S C stretching and reveals the modification of the BSTO thin film by the coupling of the O of the BSTO with the S of the mercapto compound. All the modification using mercapto compounds is through sulfur to the BSTO thin film. MHDA SAM on BSTO thin film was chemically derivatized using APS shown by XPS and FT-IR. The SAMs modified phase shifters showed an improvement in performance with respect to those phase shifters fabricated with standard methods.

A low loss RF MEMS Ku-band integrated switched filter bank

A switched Ku-band filter bank has been developed using two single-pole triple-throw (SP3T) microelectromechanical systems (MEMS) switching networks, and three fixed three-pole end-coupled bandpass filters. A tuning range of 17.7% from 14.9 to 17.8 GHz was achieved with a fractional bandwidth of 7.7 /spl plusmn/2.9%, and mid-band insertion loss ranging from 1.7 to 2.0 dB.

Stimulated Brillouin scattering for efficient improvement of radio-over-fiber systems

simple and efficient technique based on stimulated Brillouin scattering is proposed to reduce RF loss in radio-over-fiber systems. The modulation depth and RF signal gain increase with the power of the input modulated signal. A modulation depth of 100% can be easily attained at a lower input power. The experimental results are in good agreement with the theoretical predictions. Approximately 26 dB of RF signal gain in the band from 1 to 18 GHz is achieved in the experiment with this technique. Finally, the transmission experiment shows that this technique can effectively improve the performance of radio-over-fiber systems.