RF Losses Research Articles

Mechanical design of the second ICRF antenna for EAST

In order to satisfy the requirements of heating plasma on EAST project, 3MW ion cyclotron range of frequency (ICRF) heating system will be available at the second stage. Based on this requirement, the second ICRF antenna, has been designed for EAST. The antenna which is planned to operate with a frequency ranging from 30MHz to 110MHz, comprises four poloidal current straps. The antenna has many cooling channels inside the current straps, faraday shield and baffle to remove the dissipated RF loss power and incoming plasma heat loads. The antenna is supported via a cantilever support box to the external support structure. Its assembly is plugged in the port and fixed on the support box. External slideway and bellows allow the antenna to be able to move in the radial direction. The key components of the second ICRF antenna has been designed together with structural and thermal analysis presented.

Whole Body Screening Using High-Temperature Superconducting MR Volume Resonators: Mice Studies

High temperature superconducting (HTS) surface resonators have been used as a low loss RF receiver resonator for improving magnetic resonance imaging image quality. However, the application of HTS surface resonators is significantly limited by their filling factor. To maximize the filling factor, it is desirable to have the RF resonator wrapped around the sample so that more nuclear magnetic dipoles can contribute to the signal. In this study, a whole new Bi2Sr2Ca2Cu2O3 (Bi-2223) superconducting saddle resonator (width of 5 cm and length of 8 cm) was designed for the magnetic resonance image of a mouse's whole body in Bruker 3 T MRI system. The experiment was conducted with a professionally-made copper saddle resonator and a Bi-2223 saddle resonator to show the difference. Signal-to-noise ratio (SNR) with the HTS saddle resonator at 77 K was 2.1 and 2 folds higher than that of the copper saddle resonator at 300 K for a phantom and an in-vivo mice whole body imaging. Testing results were in accordance with predicted ones, and the difference between the predicted SNR gains and measured SNR gains were 2.4%∼2.7%. In summary, with this HTS saddle system, a mouse's whole body can be imaged in one scan and could reach a high SNR due to a 2 folds SNR gain over the professionally-made prototype of copper saddle resonator at 300 K. The use of HTS saddle resonator not only improves SNR but also enables a mouse's whole body screen in one scan.

A novel DMTL capacitive switch with electrostatic actuation MAM capacitors

A novel DMTL capacitive switch with electrostatic actuation metal–air–metal (MAM) capacitors is presented. The top board of MAM capacitors will be pulled down together with the switch bridge. It has higher isolation in down-state than DMTL capacitive switch and has lower insert loss and higher self-actuation RF power comparing with MEMS shunt capacitive switch. Two of the novel DMTL capacitive switches are designed for high isolation and high self-actuation RF power, respectively. The calculated result shows that both of the two novel switches have lower insert loss than the MEMS shunt capacitive switch. The self-actuation RF power of them are 4 and 2.4 times that of MEMS shunt capacitive switch, respectively, at the cost of −6.23 and −3.54 dB reduction in isolation (30 GHz).

GaN-on-Silicon Evaluation for High-Power MMIC Applications

Today microwave market has identified GaN-HEMT technology as a strategic enabling technology for next generation MMICs to be implemented in high performance RF sub-assemblies such as T/R Modules, Solid State Power Transmitters, Compact Receivers, High Speed Communications. To allow commercial market entry of GaN technology, a tradeoff between high RF performance and low cost is mandatory and a possible solution is represented by GaN-on-Silicon substrate. In this scenario the evaluation of FETs RF performance and losses of passive components are demanding to understand the feasibility of GaN MMIC on Si. Following such approach, in SELEX Sistemi Integrati a 4 inches GaN-on-Si wafer containing discrete active devices and passive components has been fabricated with the 50μm Si thickness. RF FETs performance demonstrates an output power of 4W/mm @ 3GHz, while passive components characterization exhibits similar behavior of GaN SiC passive elements up to C Band.

A Biocompatible SiC RF Antenna for In-Vivo Sensing Applications

ABSTRACTIn this study, we present a small-size implantable RF antenna (biosensor) which is made of fully biocompatible material, cubic silicon carbide. Silicon Carbide is one of the few semiconducting materials that combine biocompatibility and sensing potentiality. The hypothesis of a SiC based antenna, to be used for glucose monitoring, is that the changes in the medium surrounding the antenna affect the antenna properties such as input impedance and resonance frequency, and these changes can be used to estimate the patient’s plasma glucose level. An all-SiC patch antenna has been designed, simulated and fabricated with a target frequency of operation of 10 GHz. A Cu patch antenna was fabricated on SiC to serve as a reference antenna. The all-SiC antenna was realized by growing a poly-crystalline 3C-SiC film using CVD on a thick oxide layer that had been coated with poly-Si to serve as a growth template. A semi-insulating 4H-SiC substrate was used to minimize RF losses during operation.

Design of a Low Loss RF Mixer in Ku-Band (12 - 18 GHz)

The goal of this paper is to design and develop low conversion loss mixers at Ku Band (12 - 18 GHz) in microstrip line configuration. The Ku-band (Kurtz-under band) is primarily used for satellite Communications, particularly for editing and broadcasting satellite television. CAD tools (Agilent’s Advance Design System software) have been used for simulation and optimization of the circuits. 180 degree balanced mixer configuration has been adopted due to better RF to LO isolation requirement. The circuit is designed on microstrip line using RT Duroid (Dielectric Constant = 2.22). Initially a rat race coupler (180 degree hybrid) was designed and simulated and optimized for required performance successfully.

LDMOS-transistors on semi-insulating silicon-on-polycrystalline-silicon carbide substrates for improved RF and thermal properties

SOI enables reduced capacitive coupling in RF power technology but the thick oxide causes thermal problems. In this paper, the authors present a new type of substrate, where the oxide insulator and the silicon substrate in SOI, are replaced by silicon carbide (SiC). SiC has higher thermal conductivity and is semi-insulating which can improve the thermal and RF performance. Here, LDMOS-transistors are processed and characterized on 150mm silicon-on-polycrystalline-silicon carbide (Si-on-poly-SiC) substrates as well as on high power and RF optimized SOI reference substrates. The electrical performance for the Si-on-poly-SiC was improved or equal compared to the SOI reference and the device self-heating was reduced. The hybrid substrate had lower RF losses and the RF measurements on transistors were not ideal due to no isolation between the devices.

High-Performance Low-Leakage-Current AlN/GaN HEMTs Grown on Silicon Substrate

In this letter, ultrathin-barrier AlN/GaN high-electron mobility transistors (HEMTs) capped with in situ metal-organic-chemical-vapor-deposition-grown SiN have been successfully fabricated on 100-mm Si substrates. Output current density exceeding 2 A/mm has been reached, which represents, to the best of our knowledge, the highest value ever achieved for GaN-on-Si HEMTs. This results from the high 2DEG density of the optimized AlN/GaN heterostructure. Despite the ultrathin barrier of 6 nm, low gate and drain leakage currents of about 10 μA/mm are obtained without the use of a gate dielectric that generally induces reliability issues. Furthermore, the high aspect ratio (gate length <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> /gate-to-channel distance) and low RF losses (at the buffer/Si substrate interface) are reflected in excellent RF performances. The current gain extrinsic cutoff frequency <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and the maximum oscillation frequency <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> were 52 and 102 GHz with a 0.2- μm gate length, respectively, resulting in an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> · <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> product as high as the reported state-of-the-art GaN-on-Si HEMTs.

Demonstration of a Linearized Traveling Wave Y-Fed Directional Coupler Modulator Based on Electro-Optic Polymer

In this paper, we demonstrate a traveling wave linear modulator for high speed analog optical link applications. A two-section Y-fed directional coupler modulator based on electro-optic polymer is linearized with Δβ-reversal technique to suppress the third-order intermodulation distortions. A traveling wave electrode with low RF loss and excellent velocity matching is designed and demonstrated with the bandwidth-length product of 125 GHz ·cm. The 3-dB electrical bandwidth of 10 GHz and the spurious free dynamic range of 110 ±3 dB/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> over the modulation frequency of 2-8 GHz are measured form the fabricated device.

Novel instrumentation for measurement of relative intensity noise

Laser diode relative intensity noise (RIN) metrology capabilities have been developed and demonstrated, providing significantly improved sensitivity and accuracy compared with existing methods. The novel use of the demonstrated reference noise source has shown significant advantages, achieving improved sensitivity, reducing measurement accuracy as low as ±1 dB and simplifying the system calibration methodology, thus improving flexibility. Laser RINs of between 10 and 14 dB below the shot RIN have been shown (typically −170 dBm/Hz), which is a direct result of the improved system sensitivity. A neodinium yag 1319-nm ring laser provided a ‘cold’ reference source, in a similar manner to that used in RF electrical metrology. Application of the ‘flat’ low noise optical RF noise source from 10 MHz to 20 GHz has been demonstrated for the first time in optical RF metrology, providing a calculable reference traceable via the incident optical power received. Because of the simplistic nature of this approach, system calibration can be performed for each RIN measurement that is carried out, reducing measurement uncertainty associated with RF mismatch, system linearity and loss. High specification components have been assessed individually and in the combined system indicating an overall system noise figure of 2–3 dB over the 10 MHz to 20 GHz frequency range (−171 to −172 dBm), some 4–5 dB better than previously reported.

Abstract 5299: A new class of multifunctional magnetic nanoconstructs for imaging and thermal ablation in cancer

Abstract New paramagnetic nanoconstructs (nCS) are demonstrated with superior MRI and thermal ablation properties. The nCSs are generated by loading Gd-DTPA and ultra-short gadonanotubes (GNTs) within the nanoporous matrix of systemically injectable silicon nanoporous particles (SiNPs) [1]. Gd-DTPA is a Gd-based contrast agent currently used in clinical practice. The GNTs consist of Gd3+-ion clusters encapsulated within carbon nanotube capsules, which are 20-80 nm in length and 1.3 nm in diameter. Nanoporous discoidal SiNPs are fabricated by combining optical lithography and electrochemical etching. Two different particle sizes (small 600×200 nm and large 1000×400 nm) and particle surface configurations (untargeted and RGD-4C targeted) are considered in this study. The nCSs are characterized in terms of (i) biodistribution in tumor bearing mice; (ii) MRI longitudinal relaxivity r1 and (iii) thermal ablation efficiency. The nCS accumulation in 6 organs (liver, spleen, heart, lungs, kidneys and brain) and in tumors is quantified by elemental silicon analysis through inductively coupled plasma-optical emission spectrometer. Organ accumulation is observed to highly dependent on particle shape and size. In tumors, the larger discoidal particles are observed to accumulate more than the smaller particles, with a percentage of injected dose per gram organ of about 5% and 1.5%, respectively. For RGD-4C targeted particles, the tumor accumulation percentages grow up to about 10% and 8% of the injected dose / gram tumor, respectively. For MRI applications, the nCSs exhibit a relaxivity enhancement up to 3-4 times the values of the original Gd-based imaging agent loaded (either Gd-DTPA or GNT). In particular, for the GNT loaded SiNPs, longitudinal relaxivities up to 160 mM-1s-1 per Gd3+-ions are measured at 1.5T, which are two orders of magnitude higher than for clinically available MRI agents (r1 = 4 mM-1s-1 per Gd3+-ions at 1.5T). Eventually, the nCS thermal ablating properties are characterized upon excitation through externally applied electromagnetic fields. High quality-factor resonators (0.5-300 MHz) with separated radio frequency -electric (up to 200 V/m) and -magnetic (up to 5 mT) fields are used for non-invasive nCS stimulation and fiber optic temperature sensors are used to map the associated temperature increase. The nCSs have shown both magnetic and dielectric rf losses and significant heating at 120 MHz. Mechanisms and efficiency of heating are discussed in terms of both magnetic and electric fields excitation, the concentration of nCSs, loading of GNTs into nCSs, frequency and power of the external generator.The multifunctionality and superior biodistribution performance of these nCSs could be effectively used in cancer imaging and treatment through alternative physical-based approaches. [1] Ananta JS,…, Decuzzi P. Nat Nanotechnol. 2010;5:815-21 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5299. doi:10.1158/1538-7445.AM2011-5299

Capacitive-Sensor-Induced Losses in 900-, 1800-, and 1900-MHz Antennas

Capacitive sensors have been designed for use as user proximity sensors in mobile-phone antennas. Sensor-induced losses were measured in 900- and 1800-MHz capacitive coupling element antennas and a 1900-MHz planar inverted-F antenna (PIFA) and compared to the RF losses caused by an impedance-matching sensor. The lengths of the capacitance sensors varied from 1 to 43 mm, which induced antenna losses from 0.05 to 1.35 dB at 1 GHz. A pair of pad sensors induced 0.1-0.25-dB losses at 0.8-1.85 GHz. The loss of capacitive sensors in sizes below 5 mm2 was comparable to that of antenna-matching sensors. Total RF insertion losses due to the compared proximity sensors and loss compensation systems were 0.4 and 0.55 dB, respectively, across the 900- and 1900-MHz frequency bands.

Impact of neutron irradiation on the RF properties of oxidized high-resistivity silicon substrates with and without a trap-rich passivation layer

This work investigates the influence of high-energy neutrons on oxidized high-resistivity silicon substrates (HR-Si). Two oxide thicknesses as well as the presence of a trap-rich passivation layer are considered. The impact of neutron irradiation is directly related to the competition between the generation of interface traps added to the mobility and carrier lifetime degradation, which are beneficial to reduce parasitic surface conduction (PCS) into the Si substrate similarly to the passivation layer, and accumulation of radiation-induced positive charges in oxide, which would unfortunately increase PSC. It is shown that under neutron irradiation, RF losses are strongly reduced in the case of thin oxide ( t ox = 50 nm), while substrates with a polysilicon passivation layer are almost insensitive to the neutron irradiation.

Design of transmission line driven slot waveguide Mach-Zehnder interferometers and application to analog optical links

Slot waveguides allow joint confinement of the driving electrical radio frequency field and of the optical waveguide mode in a narrow slot, allowing for highly efficient polymer based interferometers. We show that the optical confinement can be simply explained by a perturbation theoretical approach taking into account the continuity of the electric displacement field. We design phase matched transmission lines and show that their impedance and RF losses can be modeled by an equivalent circuit and linked to slot waveguide properties by a simple set of equations, thus allowing optimization of the device without iterative simulations. We optimize the interferometers for analog optical links and predict record performance metrics (V(pi) = 200 mV @ 10 GHz in push-pull configuration) assuming a modest second order nonlinear coefficient (r(33) = 50 pm/V) and slot width (100 nm). Using high performance optical polymers (r(33) = 150 pm/V), noise figures of state of the art analog optical links can be matched while reducing optical power levels by approximately 30 times. With required optical laser power levels predicted at 50 mW, this could be a game changing improvement by bringing high performance optical analog link power requirements in the reach of laser diodes. A modified transmitter architecture allows shot noise limited performance, while reducing power levels in the slot waveguides and enhancing reliability.

Involvement of hydrogen-vacancy complexes in the baking effect of niobium cavities

Baking is necessary to improve high accelerating gradient performances of superconducting niobium cavities. Ten years after this discovery in 1998, the understanding of this effect still resists a lot of theoretical explanations. For the first time, positron annihilation spectroscopy performed on niobium samples reveals the increase after baking of positrons trapped under the Nb surface. Presence of hydrogen-vacancy complexes and their dissociation by baking could both explain rf losses observed at high fields (Q drop) and its cure (baking effect).

Improvement of the Performance of a Helix Slow-Wave Structure With a Copper-Embedded Barrel

The effect of a copper-embedded barrel on the performance of a helix slow-wave structure (SWS) has been studied theoretically and experimentally. The heat dissipation capability and cold-test characteristics of the SWSs with a monel barrel, a normal copper barrel, and a copper-embedded monel barrel have been analyzed and compared. With its combination of high mechanical strength and good thermal conductivity, the copper-embedded monel barrel enables better heat dissipation capability than the other barrel types and has low RF losses.

Single and repetitive short-pulse high-power microwave window breakdown

The mechanisms of high-power microwave breakdown for single and repetitive short pulses are analyzed. By calculation, multipactor saturation with electron density much higher than the critical plasma density is found not to result in microwave cutoff. It is local high pressure about Torr class that rapid plasma avalanche and final breakdown are realized in a 10–20 ns short pulse. It is found by calculation that the power deposited by saturated multipactor and the rf loss of protrusions are sufficient to induce vaporizing surface material and enhancing the ambient pressure in a single short pulse. For repetitive pulses, the accumulation of heat and plasma may respectively carbonize the surface material and lower the repetitive breakdown threshold.

High fieldQslope and the baking effect: Review of recent experimental results and new data on Nb heat treatments

The performance of superconducting radio-frequency (SRF) cavities made of bulk Nb at high fields (peak surface magnetic field greater than about 90 mT) is characterized by exponentially increasing rf losses (high-field $Q$ slope), in the absence of field emission, which are often mitigated by low-temperature ($100--140\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, 12--48 h) baking. In this contribution, recent experimental results and phenomenological models to explain this effect will be briefly reviewed. New experimental results on the high-field $Q$ slope will be presented for cavities that had been heat treated in a vacuum furnace at high temperature without subsequent chemical etching. These studies are aimed at understanding the role of hydrogen on the high-field $Q$ slope and at the passivation of the Nb surface during heat treatment. Improvement of the cavity performances, particularly of the cavities' quality factor, have been obtained following the high-temperature heat treatments, while secondary ion mass spectroscopy surface analysis measurements on Nb samples treated with the cavities revealed significantly lower hydrogen concentration than for samples that followed standard cavity treatments.

Development of multi-channel high power rectangular RF window for LHCD system employing high temperature vacuum brazing technique

A 3.7 GHz., 120 kW (pulsed), lower hybrid current drive (LHCD) system is employed to drive non-inductive plasma current in ADITYA tokamak. The rf power is coupled to the plasma through grill antenna and is placed in vacuum environment. A vacuum break between the pressurized transmission line and the grill antenna is achieved with the help of a multi (eight) channel rectangular RF vacuum window.The phasing between adjacent channels of 8-channel window (arranged in two rows) is important for launching lower hybrid waves and each channel should have independent vacuum window so that phase information is retained. The geometrical parameter of the grill antenna, like periodicity (9mm), channel dimensions (cross sectional dimension of 76mm × 7mm), etc. is to be maintained. These design constraint demanded a development of a multi channel rectangular RF vacuum window. To handle rf losses and thermal effects, high temperature vacuum brazing techniques is desired. Based on the above requirements we have successfully developed a multi channel rectangular rf vacuum window employing high temperature vacuum brazing technique. During the development process we could optimize the chemical processing parameters, brazing process parameters, jigs and fixtures for high temperature brazing and leak testing, etc. Finally the window is tested for low power rf performance using VNA. In this paper we would present the development of the said window in detail along with its mechanical, vacuum and rf performances.

Experimental test of a supercritical helium heat exchanger dedicated to EUROTRANS 150kW CW power coupler

The coaxial power coupler needed for beta = 0.65 superconducting RF cavities used in the high energy section of the EUROTRANS driver should transmit 150 kW (CW operation) RF power to the proton beam. The estimated RF losses on the power coupler outer conductor in standing wave mode operation are 46 W. To remove these heat loads, a full scale copper coil heat exchanger brazed around the outer conductor was designed and tested using supercritical helium at T = 6 K as a coolant. Our main objective was to minimise the heat loads to cold extremity of SRF cavity maintained at 2 K or 4.2 K. A dedicated test facility named SUPERCRYLOOP was developed and successfully operated in order to measure the performance of the cold heat exchanger. The test cell used reproduces the realistic thermal boundary conditions of the power coupler mounted on the cavity in the cryomodule. After a short introduction, a brief discussion about the problem of power coupler cooling systems in different machines is made. After that, we describe the experimental set-up and test apparatus. Then, a heat exchanger thermal model will be developed with FEM code COSMOS/M to estimate the different heat transfer coefficients by comparison between numerical simulation results and experimental data in order to validate the design. Finally, thermo-hydraulic behavior of supercritical helium has been investigated as function of different parameters (inlet pressure, flow rate, heat loads).