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In this paper, we illustrate the RF design and measurements of a C-band prototype structure for an Ultra High Dose Rate medical linac. (1) Background: FLASH Radiotherapy (RT) is a revolutionary new technique for cancer cure. It releases ultra-high radiation dose rates (above 100 Gy/s) in microsecond short pulses. In order to obtain a high dose in a very short time, accelerators with high-intensity currents (the order of 100 mA peak currents) have to be developed. In this contest, Sapienza University, in collaboration with SIT-Sordina IORT Technology spa, is developing a new C-band linac to achieve the FLASH regime. (2) Methods: We performed the RF electromagnetic design of the prototype of the C band linac using CST STUDIO Suite Code and the RF low power RF test at Sapienza University of Rome. The measurements of the field in the cavity have been done with the bead-pull technique. (3) Results: This device is a nine-cell structure operating on the π / 2 mode at 5.712 GHz (C-band). We report and discuss the test measurement results on a full-scale copper prototype, showing good agreement with CST RF simulations. A tuning procedure has been implemented in order to ensure proper operating frequency and to reach a field profile flatness of the order of a few percent. (4) Conclusions: The prototype of a C-band linac for FLASH applications was successfully tested with low RF power at Sapienza University. The fabrication and ad hoc tuning procedures have been optimized and discussed in the paper. [ABSTRACT FROM AUTHOR]

Velocity-selective (VS) excitation is a relatively new type of excitation that can be useful for generating image contrast based on spin's motion. This review aims to explain the principles of VS excitation and their utilization for clinical applications. We first review the generalized excitation k-space formalism, which reveals a Fourier relationship between sequence parameters and excitation profiles for spins with arbitrary spatial location, off-resonance, and velocity. Based on the k-space framework, we analyze practical VS excitation pulse sequences that yield sinusoidal or sincshaped velocity profiles. Then we demonstrate how these two types of VS excitation can be used as magnetization preparation for clinical applications, including saturation- or inversion-based arterial spin labeling and black- or bright-blood angiography. We also discuss practical considerations and issues for each application, including the determination of design parameters and the effects of MR system errors, such as magnetic field offsets and eddy currents. [ABSTRACT FROM AUTHOR]

In this paper, we illustrate the RF design and measurements of a C-band prototype structure for an Ultra High Dose Rate medical linac. (1) Background: FLASH Radiotherapy (RT) is a revolutionary new technique for cancer cure. It releases ultra-high radiation dose rates (above 100 Gy/s) in microsecond short pulses. In order to obtain a high dose in a very short time, accelerators with high-intensity currents (the order of 100 mA peak currents) have to be developed. In this contest, Sapienza University, in collaboration with SIT-Sordina IORT Technology spa, is developing a new C-band linac to achieve the FLASH regime. (2) Methods: We performed the RF electromagnetic design of the prototype of the C band linac using CST STUDIO Suite Code and the RF low power RF test at Sapienza University of Rome. The measurements of the field in the cavity have been done with the bead-pull technique. (3) Results: This device is a nine-cell structure operating on the π/2 mode at 5.712 GHz (C-band). We report and discuss the test measurement results on a full-scale copper prototype, showing good agreement with CST RF simulations. A tuning procedure has been implemented in order to ensure proper operating frequency and to reach a field profile flatness of the order of a few percent. (4) Conclusions: The prototype of a C-band linac for FLASH applications was successfully tested with low RF power at Sapienza University. The fabrication and ad hoc tuning procedures have been optimized and discussed in the paper.

Purpose: Phosphorus saturation‐transfer experiments can quantify metabolic fluxes noninvasively. Typically, the forward flux through the creatine kinase reaction is investigated by observing the decrease in phosphocreatine (PCr) after saturation of γ‐ATP. The quantification of total ATP utilization is currently underexplored, as it requires simultaneous saturation of inorganic phosphate (Pi) and PCr. This is challenging, as currently available saturation pulses reduce the already‐low γ‐ATP signal present. Methods: Using a hybrid optimal‐control and Shinnar‐Le Roux method, a quasi‐adiabatic RF pulse was designed for the dual saturation of PCr and Pi to enable determination of total ATP utilization. The pulses were evaluated in Bloch equation simulations, compared with a conventional hard‐cosine DANTE saturation sequence, before being applied to perfused rat hearts at 11.7 T. Results: The quasi‐adiabatic pulse was insensitive to a >2.5‐fold variation in B1, producing equivalent saturation with a 53% reduction in delivered pulse power and a 33‐fold reduction in spillover at the minimum effective B1. This enabled the complete quantification of the synthesis and degradation fluxes for ATP in 30‐45 minutes in the perfused rat heart. While the net synthesis flux (4.24 ± 0.8 mM/s, SEM) was not significantly different from degradation flux (6.88 ± 2 mM/s, P =.06) and both measures are consistent with prior work, nonlinear error analysis highlights uncertainties in the Pi‐to‐ATP measurement that may explain a trend suggesting a possible imbalance. Conclusions: This work demonstrates a novel quasi‐adiabatic dual‐saturation RF pulse with significantly improved performance that can be used to measure ATP turnover in the heart in vivo. [ABSTRACT FROM AUTHOR]

Advantage of non-brazing methods in manufacturing of cavities has been considered in high gradient studies because of the softening of copper by brazing cavities at high temperatures. Recent studies with hard copper cavities have been shown that the harder materials can reach larger accelerating gradients for the same breakdown rate. Shrinking, as a braze-free method for construction of the cavities, was used recently to fabricate and assemble acceleration cavities of an electron linear accelerator at the Institute for Research in Fundamental Science (IPM-Iran). Based on the results obtained in this project, this paper proposes the design of a 3-cell S-band standing wave structure operating at 2.9985 GHz for high gradient tests, considering shrink-fit construction method. The desired cavity consists of three cells so that the maximum gradient in the middle cell is about twice that of the surrounding cells. Simulation with Ansys-HFSS showed that maximum axial electric field 59 MV.m-1 achievable for 2 MW input power in middle cell. [ABSTRACT FROM AUTHOR]

Extracting the unknown frequency of a radar pulse has been one of the most challenging aspects of instantaneous frequency measurement (IFM) receivers. The conventional IFM receivers are limited in accurate frequency extraction by their design. In this article, a digital processing unit is added to the conventional IFM to extract the frequency with higher accuracy. A 2–4 GHz IFM has been designed combining the compact conventional RF section with the new digital processing unit using a novel efficient frequency extraction algorithm. The algorithm of minimum mean square error (MMSE) estimator is explored for use within the IFM, and it is proven that it can achieve much higher frequency accuracy. The novelty of this article includes both investigation and development of the algorithm to be a good fit for the frequency extraction in IFM receivers and also a digital implementation of the algorithm which meets the minimum requirements of an industrial IFM. The design has been implemented using microstrip filters on Rogers substrate and a Spartan-3E field-programmable gate array (FPGA) processor. The measurement results show promising achievements and verify the principle idea of digital processing for accurate frequency extraction in IFM receivers. The designed and fabricated receiver reaches 1.7 MHz rms frequency error in the frequency band of 2–4 GHz, which is at least $10\times $ improvement with respect to the state-of-the-art works. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a pyramidal horn antenna loaded with unit cell of metamaterial is proposed, designed and realized for L‐band that including terrestrial digital audio broadcasting T‐DAB, GPS, and GSM. The proposed antenna operates in the frequency range from 1.722 to 1.931 GHz. The metamaterial is fabricated on a printed circuit board as Capacitive Loaded Loop (CLL). The work aims to exhibit the advantage of metamaterial loaded inside the horn antenna in terms of the gain enhancement of the radiation pattern and the resonant frequency shift toward lower frequency. The retrieval technique used show that the constitutive parameters of the unit cell as CLL have a zero index metamaterial (ZIM) from 1.34 to 1.49 GHz and a near zero index of refraction from 1.495 GHz to 2 GHz, which is within the operating frequency of the horn antenna. The achieved results show that the total gain is improved over the frequency range. The simulation and the measurement are in good agreement. [ABSTRACT FROM AUTHOR]

ABSTRACT Nowadays, parametric macromodeling techniques are widely used to describe electromagnetic structures. In this contribution, the application of such parametric macromodeling techniques to the design of integrated inductors and radio-frequency circuit design is investigated. In order to allow such different operations, a new modeling methodology is proposed, which improves the modeling accuracy when compared to former techniques. The new methodology is tailored to the unique characteristics of the devices under study. The obtained parametric macromodel is then used in a synthesis methodology and in the design of a voltage controlled oscillator in a 0.35-μm CMOS technology. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1207-1212, 2017 [ABSTRACT FROM AUTHOR]

Tunnel field effect transistors (TFETs) have emerged as one of the most promising post‐CMOS technologies for digital, analogue and RF designs. However, it has been demonstrated by several researchers that TFET circuits face increased on‐state Miller capacitance effect, which leads to poor transient characteristics with large overshoots and undershoots. This would minimise the reliability of TFET circuits though energy efficient. This work gives more design insights (optimal sizing, number of stages, supply voltage) into TFET circuit reliability and proposes a TFET based circuit interaction design approach for ultra‐low power and reliable ring oscillator circuit design. It has been shown that TFET circuit designs without proper reliability enhancement techniques such as circuit interaction or co‐design approach exhibits very large undershoots/overshoots (∼20–50%). The proposed TFET circuit co‐design approach (i.e. differential topology based design in comparison with the complementary static TFET logic designs) enhances the TFET circuit reliability by minimising the undershoots/overshoots to less than 0.5% with a trade‐off in operating frequency and power consumption. [ABSTRACT FROM AUTHOR]

This paper presents a CMOS based LC tank VCO topology improving the tuning range linearity. The VCO tuning range is linearized with PMOS varactors which remain in the inversion region for an extended range of the control voltage. This is achieved with the design of the quiescent operating point in the VCO's output nodes with a value close to the voltage rails, letting the varactors to behave quasi linearly in the achievable VCO tuning range. The experimental results of a VCO in a CMOS 0.35 µm process show a linear tuning range improvement of 75% of the control voltage in the (1.43–1.55) GHz range, with a minimum VCO gain variation compared to similar architectures. The results show a phase noise improvement from −94 dBc/Hz to −124 dBc/Hz @600 kHz offset from the carrier with an overall reduced amplitude noise for the VCO. [ABSTRACT FROM AUTHOR]

Velocity-selective (VS) excitation is a relatively new type of excitation that can be useful for generating image contrast based on spin's motion. This review aims to explain the principles of VS excitation and their utilization for clinical applications. We first review the generalized excitation k-space formalism, which reveals a Fourier relationship between sequence parameters and excitation profiles for spins with arbitrary spatial location, off-resonance, and velocity. Based on the k-space framework, we analyze practical VS excitation pulse sequences that yield sinusoidal or sinc-shaped velocity profiles. Then we demonstrate how these two types of VS excitation can be used as magnetization preparation for clinical applications, including saturation- or inversion-based arterial spin labeling and black- or bright-blood angiography. We also discuss practical considerations and issues for each application, including the determination of design parameters and the effects of MR system errors, such as magnetic field offsets and eddy currents., (© 2022 John Wiley & Sons Ltd.)

Abstracts To match the beam from the Radio Frequency Quadrupole (RFQ) accelerator to the Superconducting Half-wave Resonator (HWR) Linac, two room temperature (RT) double-gap Quarter-wave Resonator (QWR) bunchers are designed to be located in the Medium Energy Beam Transport Line (MEBT) for the C-ADS Injector II at IMP. Both cavities work at 162.5 MHz, with β =0.067 and a beam aperture diameter of 40 mm. The effective voltage of these two cavities needs to reach 135 kV in Continuous Wave (CW) mode. In this paper, the RF design and thermal analysis of the cavities will be presented, along with the tuners and coupler consideration. The measured frequencies, R sh / Q 0 , Q 0 and voltage of the cavities agree well with the simulation result. Details of the RF test results including the full power tests of the cavities will be shown. [ABSTRACT FROM AUTHOR]

This letter describes the design and implementation of a wideband radio frequency-baseband multiplexer. This device makes it possible to superimpose radio frequency noise to a functional baseband signal with controlled and repeatable transfer characteristics. The baseband path has a measured dc—380 \mathrmM\mathrmHz bandwidth, while the radio frequency path (up to 1  \mathrmW) has a 150 \mathrmk \mathrmHz \text-5 \mathrmG\mathrmHz bandwidth. This multiplexer can be used for electromagnetic conducted immunity testing of digital and mixed-signal devices. [ABSTRACT FROM PUBLISHER]

RF design and implementation of ceramic‐filled resin‐based 3D printed millimetre‐wave bandpass filters (BPFs) using a new class of compact high‐quality‐factor hemispherical cavity resonators are addressed. Design concept of the hemispherical resonator is discussed for BPF applications in both X and Ka bands. For validation purpose, the Ka‐band fourth‐order BPF is fabricated with a high‐temperature‐resistant ceramic‐filled resin using a fast and low‐cost stereolithography‐based 3D printing technique, and its surface metallisation is realised by employing electroless copper/silver plating. The proposed BPF's geometrical configuration contributes to a significantly improved out‐of‐band rejection. The RF‐measured results demonstrate the Ka‐band BPF an insertion loss of 0.43−0.9 dB from 31.52 to 32.42 GHz, a passband return loss mostly better than 15 dB, and a small frequency shift of about 0.06%. [ABSTRACT FROM AUTHOR]

A four-vane continuous wave (CW) RFQ has been designed for the injector II LINAC of China ADS project. To acquire the experience of a CW RFQ on design, tuning, conditioning, running, etc., a 1-m-long RFQ accelerator prototype has been built. Working at 162.5 MHz, the RFQ prototype accelerates protons of 10 mA from 20 keV to 560 keV in one meter length with a low inter-vane voltage of 65 kV and a safe Kilpatric factor of 1.3. Conditioning and beam test of the accelerator prototype have been completed, and it shows the transmission efficiency can reach 90% with a 10 mA CW proton beam. Design, fabrication and tests of the RFQ prototype will be presented in detail in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Eight different reduced field-of-view (FOV) MRI techniques suitable for high field human imaging were implemented, optimized, and evaluated at 7T. These included selective Inner-Volume Imaging (IVI) based methods, and Outer-Volume Suppression (OVS) techniques, some of which were previously unexplored at ultra-high fields. Design considerations included use of selective composite excitation and adiabatic refocusing radio-frequency (RF) pulses to address B1 inhomogeneities, twice-refocused spin echo techniques, frequency-modulated pulses to sharply define suppressed regions, and pulse sequence designs to improve SNR in multi-slice scans. The different methods were quantitatively compared in phantoms and in vivo human brain images to provide measurements of relative signal to noise ratio (SNR), power deposition (specific absorption rate, SAR), suppression of signal, artifact strength and prevalence, and general image quality. Multi-slice signal losses in out-of-slice locations were simulated for IVI methods, and then measured experimentally across a range of slice numbers. Corrections for B1 nonuniformities demonstrated an improved SNR and a reduction in artifact power in the reduced-FOV, but produced an elevated SAR. Multi-slice sequences with reordering of pulses in traditional and twice-refocused IVI techniques demonstrated an improved SNR compared to conventional methods. The combined results provide a basis for use of reduced-FOV techniques for human imaging localized to a small FOV at 7T. [Copyright &y& Elsevier]

This paper presents a dual mode CMOS low noise amplifier (LNA) suitable for Worldwide Interoperability for Microwave Access applications, at 2.4 GHz. The design concept is based on body biasing. An off chip Digital to Analog Converter is used to generate the proper body bias voltage to control the LNA gain and linearity. Measurement results show that in the high gain mode, for V = 0.3 V, the cascode LNA, implemented in a 0.13 μm CMOS standard process, exhibits a 14 dB power gain, a 3.6 dB noise figure (NF) and −4.6 dBm of third order intercept point (IIP3) for a 4 mA current consumption under 1 V supply. Tuning V to −0.55 V, switches the LNA into the low gain mode. It achieves 8.6 dB power gain, 6.2 dB NF and 6 dBm IIP3 under a constrained power consumption of 1.7 mW. [ABSTRACT FROM AUTHOR]

Abstract: An INFN-LNF/UCLA/SAPIENZA collaboration is developing a hybrid photoinjector in X-band. A hybrid photoinjector is a novel high brightness electron source that couples a standing wave cell cavity (acting as an RF gun) directly to a multi-cell travelling-wave structure. This configuration offers a number of advantages over the split standing wave/travelling-wave system. Most notably the reflected RF transient is almost completely suppressed, thus eliminating the need for a circulator and the bunch lengthening effect that occurs in the drift section of the split system. These properties allow scaling of the device to higher field and frequencies, which should dramatically improve beam brightness. The RF coupling between the standing and the traveling wave sections is accomplished in the fourth cell encountered by the beam, with the SW section electrically coupled to it on-axis. This mode of coupling is particularly advantageous, as it is accompanied by a 90° phase shift in the accelerating field, resulting in strong velocity bunching effects on the beam that reverse the usual bunch lengthening induced after the gun exit in standard 1.6 cell photoinjectors. In this scenario, from the beam dynamics point of view, it is seen that device may produce ten''s of femtosecond beams at ∼3.5MeV and the emittance compensation dynamics remains manageable even in the presence of strong compression. We present here a survey of the device characteristics. In particular we show the results of the electromagnetic simulations, a beam dynamics analysis related to the temperature tuning of the SW and TW section, and a RF characterization using bead pull and scattering coefficient measurements of a device prototype. [Copyright &y& Elsevier]

Abstract: A single-cell, 1300-MHz, TM110-like mode vertically deflecting cavity is designed and built for beam slice emittance measurements, and to study the temporal response of negative electron affinity photocathodes in the ERL injector at Cornell University. We describe the cavity shape optimization procedure, RF and mechanical design, its performance with beam. [Copyright &y& Elsevier]

The RF design of stub‐loaded‐based wide‐band bandpass filters (BPFs) with multiple tunable rejection bands in their transmission range is presented. The proposed concept exploits the replacement of the short‐circuited resonant stubs of the stub‐loaded‐based BPF with multi‐band bandstop (BS) sections. Each multi‐frequency BS section is formed by several in‐parallel‐cascaded 90°‐long stubs that are terminated by frequency‐agile resonators so that each of them results in an independently‐controlled transmission zero. In this manner, a plurality of high‐order reflective‐type rejection bands can be created and arbitrarily controlled. Further operational characteristics include: (i) scalability to any number of rejection bands and degree of selectivity, (ii) independent tuning of each notch without any influence on the remaining ones, and (iii) spectral‐merging of multiple stopbands to increase their bandwidth (BW) and enable controllability of the number of active notches in the passband. The aforementioned principles are experimentally validated through a prototype that exhibits a wide‐band (fractional BW: 68%), low‐loss (<0.7 dB) passband at 1000 MHz and two high‐attenuation (>60 dB) notches that can be independently tuned within the 870–1150 MHz range. [ABSTRACT FROM AUTHOR]

A three-cell 1.3 GHz, Normal Conducting (NC) buncher is designed for a possible future upgrade of the European X-ray Free Electron Laser (Eu-XFEL) to operate in a continuous-wave (CW)/ long pulse (LP) mode. The RF geometry of the buncher is optimized for high shunt impedance, large mode separation as well as multipacting free in the operation range. The nominal buncher voltage is 400 kV with an RF power dissipation of 14 kW, and its shunt impedance is ∼ 50% higher than existing CW bunchers. The RF power coupler cell is optimized for field symmetry to minimize coupler kick effect on beam dynamics. The thermal load due to RF power dissipation is analyzed using Multiphysics simulations in CSTMWS and a cooling scheme is designed. [ABSTRACT FROM AUTHOR]

A lumped scalable model of silicon integrated inductors for RF IC design is presented. It was validated up to 20 GHz using measured performance parameters of more than 70 single-ended and differentially driven spirals covering 0.2- to 8.3 nH inductance values. Excellent accuracy, full geometrical scalability, compactness and high capability for implementation in circuit simulators promote the proposed model as a reliable time-saving design tool. Two circuital example, i.e., 5-GHz down-converter and 10-GHz VCO, are also presented to demonstrate its use in practical cases. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009. [ABSTRACT FROM AUTHOR]

Abstract: We present an analytic solution for the B1 field produced in a gapped toroidal cavity resonator designed as a probe for high field MRI. This resonator supports standing TEM waves, so its electric and magnetic fields are identical to those produced by a stationary planar current source with the same (constant) cross-section multiplied by a complex exponential propagation factor. An explicit expression for the field may therefore be found by solving Laplace’s equation for the static potential, which is accomplished with a two-dimensional logarithmic conformal transformation algorithm. The equipotential curves are also the contours of the field strength B, and the B (vector) field at any point is directed along the contour passing through that point. With this information, we construct the solution by computing the angle made by the equipotential curve with the horizontal axis at each point, using this angle to analyze the B field into its x and y components, and adding the contributions from the current sources to obtain the magnitude and direction of B at each point in the region of interest. Some proposed extensions of this algorithm are also discussed. [Copyright &y& Elsevier]

A non-50-Ω interstage matching technique has been used for designing multistage microwave power amplifiers. The technique is especially relevant to cases where the final stage uses an LDMOS device whose dynamic input impedance is extremely low and is best matched directly (without first translating to 50 Ω) to the output of the previous stage. A specific example is presented. The concept, however, is quite general and will be of interest to the RF design community at large. [ABSTRACT FROM PUBLISHER]

650 MHz 2-cell superconducting cavities are proposed for the main ring of the Circular Electron–Positron Collider (CEPC). The cavity is designed with two detachable double-notch higher order mode (HOM) couplers to suppress the fundamental mode and extracted the HOM power. The present paper describes the design, fabrication, surface treatment and vertical tests of the cavities and HOM couplers. The performances of the cavity at 2 K is not affected after the installation of the HOM coupler. The maximum intrinsic quality factor Q 0 of the cavity dressed with the HOM coupler reached 3. 1 × 1 0 10 at operation accelerating gradient. The vertical tests results showed that the fundamental mode external quality factor Q e of all HOM couplers is an order of magnitude larger than Q 0 of the cavity. The HOM damping results for the 650 MHz 2-cell cavity were also measured at cryogenic temperature and compared with the simulated and measured results at room temperature. Two 650 MHz 2-cell cavities each with two HOM couplers will be assembled in the CEPC 650 MHz test cryomodule after helium vessel dressing. [ABSTRACT FROM AUTHOR]

There are many benefits in using time division duplex (TDD) instead of frequency division duplex (FDD) schemes in fixed wireless cellular systems. To name a few; channel reciprocity for the single carrier frequency used on both up and downlinks will allow easy access to channel state information, reduced complexity of RF design, much higher flexibility in handling dynamic traffic, simpler frequency plan, etc. However, there exists a serious limiting factor in using dynamic-TDD (D-TDD) in cellular systems. This is due to a steady interference on uplinks in a cell, caused by downlink transmissions of other cells. Simulation results show in D-TDD cellular systems, performance is unacceptable, when omni-directional antennas are used at base stations. Simulation results have also demonstrated a great potential for smart antennas in fixed D-TDD bandwidth-on-demand wireless systems [ABSTRACT FROM PUBLISHER]