Simple RF Research Articles

Intrapulse frequency stability of a magnetron frequency-locked through a wave reflected from an accelerating cavity

A laboratory-size Free Electron Laser (FEL) driven by a classical S-band microtron fed by a 2.5 MW magnetron generates terahertz radiation tunable in a wide range. The FEL provides output pulse power of ∼50 W in the wavelength range of 100–300 μm with a pulse duration of 2–4 μs. The FEL parameters are available due to stabilization of the accelerated beam current and the magnetron frequency. The latter is stabilized by the frequency locking in the magnetron through a wave reflected from the microtron accelerating cavity, which also serves as an external stabilizing resonator, providing the RF reference signal for the magnetron. The simple RF stabilizing scheme provides the r.m.s. magnetron frequency instability, δf≈10–13 kHz relative to the reference frequency at the frequency pulling bandwidth of 0.43–0.85 MHz and at the initial power of the reflected wave ≈30 kW. The developed stabilization provided stable and reliable operation of the FEL for more than 10 years. Measured and simulated results are described in this paper.

Fast production of largeNa23Bose-Einstein condensates in an optically plugged magnetic quadrupole trap

We demonstrate a fast production of large $^{23}\mathrm{Na}$ Bose-Einstein condensates in an optically plugged magnetic quadrupole trap. A single global minimum of the trapping potential is generated by slightly displacing the plug beam from the center of the quadrupole field. With a dark magneto-optical trap and a simple rf evaporation, our system produces a condensate with $N\ensuremath{\approx}{10}^{7}$ atoms every 17 s. The Majorana loss rates and the resultant heating rates for various temperatures are measured with and without plugging. The average energy of a spin-flipped atom is almost linearly proportional to temperature and determined to be about $60%$ of the average energy of a trapped atom. We present a numerical study of the evaporation dynamics in a plugged linear trap.

Electron Optics System of a 100-MW S-Band Klystron

This paper presents the design and experimental results of the electron optics system for use in an S-band 100-MW high-peak-power klystron. The gun operating voltage is 415 kV with a beam current of 535 A. For the design of the gun, special emphasis is placed on the geometric layout of the electrodes to ensure a moderate voltage gradient, reasonable cathode loading, and accurate beam perveance. The beam-focusing system is a space-charge balanced flow type with a solenoidal magnet structure. The magnetic field at the center of the cathode is 60 G, and the longitudinal magnetic field in the interaction region is in the range of 1.0-1.38 kG. The electron optics system design was accomplished with SUPERFISH, EGUN, and a Particle-in-Cell (PIC) code. Simulation results indicate that the gun has a voltage gradient lower than 220 kV/cm and excellent beam transport characteristics with a beam-to-tunnel radial fill factor of less than 0.75. The focusing beam trajectories simulated by EGUN and the PIC code both have good laminarity. Two prototypes based on a simplified RF design (not intended to achieve full RF power) were fabricated in order to demonstrate the beam optics, and the measured beam transport is in agreement with predictions made by simulation codes. RF circuit simulation designs with the 1-D large-signal code KLY_12 and the PIC code are also presented.

Comparison of radiofrequency applied to the total inferior choncha with application to its anterior third

Objective To compare radiofrequency application to the anterior 1/3 of the inferior choncha with application to the whole of the inferior choncha. Material and method 40 patients with nasal obstruction due to isolated inferior choncha hypertrophy were evaluated. RF was applied in the first group only to the anterior 1/3 of the choncha, whereas in the second group the whole choncha was ablated. Anterior rhinomanometry measurements were obtained both before and 6 weeks after surgery along with visual analog scales. Complete data was used to compare the efficacy of both techniques. Results The combined nasal resistance showed a significant decrease in both groups. VAS scores were also substantial for both groups. Both groups showed similar data proving the two techniques to have similar efficacy. Conclusion Application to the anterior 1/3 compared with application to the whole of the choncha show no significant differences. Simple RF application here not only provides adequate control but also is safer as there is less risk of interruption of continuity of the nasal mucosa.

Thermally Actuated Latching RF MEMS Switch and Its Characteristics

Here, a new thermally actuated latching wideband RF microelectromechanical systems (MEMS) switch is presented. The switch employs two thermal actuators connected to two thin metal arms which serve as signal lines of coplanar waveguide switch. The actuators pull the thin arms sequentially, and latch the switch. The switch can be actuated on and off by using either short voltage or current pulses. Using a dielectric bridge (nitride) as an interface between the actuators and the thin arms, the RF circuitry is separated from DC actuators, allowing wide-band operation. The switch demonstrates an excellent wideband RF performance with an insertion loss of better than 0.3 dB up to 20 GHz and better than 0.8 dB up to 40 GHz. The return loss and isolation of the switch is better than 20 dB for the entire frequency band. The switch also has a very satisfactory repeatability with better than 0.1-dB variation in insertion loss and less than 1-dB variation in return loss and isolation at 30-dB level up to 6000 times switching cycles. The switch has been also successfully tested for RF power handling capability up to 40 dBm. The proposed switch has very simple RF structure which makes it an ideal candidate to be integrated in the form of more complex circuitry. An application of the proposed switch for a band selection network which is used in multiband transceivers has been presented here.

Vibration-induced PM and AM noise in microwave components

The performance of microwave components is sensitive to vibrations to some extent. Aside from the resonator, microwave cables, and connectors, bandpass filters, mechanical phase shifters, and some nonlinear components are the most sensitive. The local oscillator is one of the prime performance-limiting components in microwave systems ranging from simple RF receivers to advanced radars. The increasing present and future demand for low acceleration sensitive oscillators, approaching 10(-13)/g, requires a reexamination of sensitivities of basic nonoscillatory building-block components under vibration. The purpose of this paper is to study the phase-modulation (PM) noise performance of an assortment of oscillatory and nonoscillatory microwave components under vibration at 10 GHz. We point out some challenges and provide suggestions for the accurate measurement of vibration sensitivity of these components. We also study the effect of vibration on the amplitude-modulation (AM) noise.

Writing simple RF electronic devices on paper with carbon nanotube ink

This paper shows that we can print on paper simple high-frequency electronic devicessuch as resistances, capacitances or inductances, with values that can be changedin a controllable manner by an applied dc voltage. This tunability is achievedwith the help of an ink containing functionalized carbon nanotubes and water.After the water is evaporated from the paper, the nanotubes remain steadilyimprinted on paper, showing a semiconducting behavior and tunable electricalproperties.

Role of bias frequency in a dual electron cyclotron resonance-radio-frequency hybrid plasma

The effects of an rf-bias on the Ar plasma in the dual ECR-rf plasma reactor were investigated both experimentally and numerically. It is demonstrated that the application of 13.56-MHz rf bias significantly modifies the characteristics of bulk plasma based on Langnuir probe measurements, which is attributed to the oscillation of rf sheath. Under the rf bias of 400 kHz, there exists negligible reaction between the ECR plasma and the low-frequency bias. By using a hybrid model with simplified rf sheath as the boundary condition, the characteristic of the dual ECR-rf plasma was simulated. Modeling results are consistent qualitatively with experimental measurements.

Simple RF design for human functional and morphological cardiac imaging at 7 tesla

Morphological and functional cardiac MRI can potentially benefit greatly from the recent advent of commercial high-field (7tesla and above) MRI systems. However, conventional hardware configurations at lower field using a body-coil for homogeneous transmission are not available at these field strengths. Sophisticated multiple-transmit-channel systems have been shown to be able to image the human heart at 7tesla but such systems are currently not widely available. In this paper, we empirically optimize the design of a simple quadrature coil for cardiac imaging at 7tesla. The size, geometry, and position have been chosen to produce a B1 field with no tissue-induced signal voids within the heart. Standard navigator echoes for gating were adapted for operation at the heart/lung interface, directly along the head–foot direction. Using this setup, conventional and high-resolution cine functional imaging have been successfully performed, as has morphological imaging of the right coronary artery.

X-band rf structure with integrated alignment monitors

We present the electrical design for an $X$-band traveling wave accelerator structure with integrated alignment monitors to measure the transverse wake, which will be used as part of the PSI-XFEL project and in the CLIC structure testing program. At PSI, it will compensate nonlinearities in the longitudinal phase space at the injector prototype of the PSI-XFEL. At CLIC it will be tested for breakdown limits and rates in the high gradient regime. The prolonged operation of such a structure in the PSI-XFEL injector, albeit not for the CLIC parameter regime, will constitute a good quality test of the manufacturing procedures employed. The operation in the PSI-XFEL injector will be at a relatively modest beam energy of 250 MeV, at which transverse wakes can easily destroy the beam emittance. For this reason, the layout chosen employs a large iris, $5\ensuremath{\pi}/6$ phase advance geometry, which minimizes transverse wakefield effects while still retaining a good efficiency. As a second important feature, the design includes two wakefield monitors coupling to the transverse higher order modes, which allow steering the beam to the structure axis, potentially facilitating a higher precision than mechanical alignment strategies. Of special interest is the time domain envelope of these monitor signals. Local offsets due to bends or tilts have individual signatures in the frequency spectrum, which in turn are correlated with different delays in the signal envelope. By taking advantage of this combined with the single bunch mode at the PSI-XFEL, the use of a relatively simple detector-type rf front end should be possible, which will not only show beam offsets but also higher order misalignments such as tilts in the structure. The resolution of these monitors is determined by the tolerance of the random cell-to-cell misalignment leading to a spurious signal in the monitors.

Cryogenic ion trapping systems with surface-electrode traps

We present two simple cryogenic rf ion trap systems in which cryogenic temperatures and ultra high vacuum pressures can be reached in as little as 12 h. The ion traps are operated either in a liquid helium bath cryostat or in a low vibration closed cycle cryostat. The fast turn around time and availability of buffer gas cooling made the systems ideal for testing surface-electrode ion traps. The vibration amplitude of the closed cycled cryostat was found to be below 106 nm. We evaluated the systems by loading surface-electrode ion traps with (88)Sr(+) ions using laser ablation, which is compatible with the cryogenic environment. Using Doppler cooling we observed small ion crystals in which optically resolved ions have a trapped lifetime over 2500 min.

スピンを伴う飛翔体に搭載可能なGPS受信機の開発

This paper describes the design and development of a dedicated GPS receiver for spin stabilized launch vehicles. The receiver is built around a commercially available low cost GPS chip set and operates an enhanced firmware specifically adapted for high dynamics applications. In order to keep tracking a sufficient number of GPS signals even during the spinning motion, we use multiple GPS patch antennas and space them equally apart each other around the cylindrical launcher body. A new signal combining scheme was developed to avoid deep fading in antenna gain pattern. This technique requires phase control to keep signals received on multiple antennas in phase with each other. A dualantenna GPS receiver was developed to evaluate the proposed signal combining algorithm. The result showed that the proposed algorithm was capable of providing stable and continuous signal tracking under a high-rate spinning motion while simple RF combining through a power combiner was failed.

SD-MAC: Design and Synthesis of a Hardware-Efficient Collision-Free QoS-Aware MAC Protocol for Wireless Network-on-Chip

To bridge the widening gap between computation requirements and communication efficiency faced by gigascale heterogeneous SoCs in the upcoming ubiquitous era, a new on-chip communication system, dubbed Wireless Network-on-Chip (WNoC), is introduced by using the recently developed CMOS UWB wireless interconnection technology. In this paper, a synchronous and distributed medium access control (SD-MAC) protocol is designed and implemented. Tailored for WNoC, SD-MAC employs a binary countdown approach to resolve channel contention between RF nodes. The receiver_select_sender mechanism and hidden terminal elimination scheme are proposed to increase the throughput and channel utilization of the system. Our simulation study shows the promising performance of SD-MAC in terms of throughput, latency, and network utilization. We further propose a QoS-aware SD-MAC to ensure the serviceability of the entire system and to improve the bandwidth utilization. As a major component of simple and compact RF node design, a MAC unit implements the proposed SD-MAC that guarantees correct operation of synchronized frames while keeping overhead low. The synthesis results demonstrate several attractive features such as high speed, low power consumption, nice scalability and low area cost.

An Automatic Antenna Tuning System Using Only RF Signal Amplitudes

The operating environment of mobile phones fluctuates continuously, due to changing handling conditions and nearby objects. The resulting fluctuations in antenna impedance cause both a decrease in link quality and a higher standing wave ratio, that requires more robust and hence less efficient power amplifier implementations. In this paper, an automatic antenna tuner system for handheld applications is presented that uses two series reactances combined with three simple RF peak detectors to sense both reactive and real impedance mismatches. The control loop only requires low-frequency electronics which makes it low cost, low power and relatively easy to integrate. Measurements on a demonstrator system show correct behaviour for voltage standing-wave ratio up to 10.

Growth of p-type Si nanotubes by catalytic plasma treatments

We have demonstrated a new technique to transform bulk materials intoone-dimensional nanostructures. We have shown that p-type Si nanotubes (SiNTs)can be grown by a simple dual RF plasma treatment of p-type Si substrates at500 °C. These SiNTs havediameters of ∼50–80 nm withtubular wall thickness of ∼10–15 nm. The use of Cu vapor and reactive plasma has enabled the growth of these SiNTsinstead of Si nanowires.

Lightning: A Hard Real-Time, Fast, and Lightweight Low-End Wireless Sensor Election Protocol for Acoustic Event Localization

We present the Lightning Protocol, a hard real-time, fast, and lightweight protocol to elect the sensor closest to an impulsive sound source. This protocol can serve proximity-based localization or leader election for sensor collaboration. It utilizes the fact that electromagnetic waves propagate much faster than acoustic waves to efficiently reduce the number of contending sensors in the election. With simple RF bursts, most basic comparison operations, no need of clock synchronization, and a memory footprint as small as 5,330 bytes of ROM and 187 bytes of RAM, the protocol incurs O(1) transmissions, irrespective of the sensor density, and guarantees hard real-time (O(1)) localization time cost. Experiment results using UC Berkeley Motes in a common office environment demonstrate that the time delay for the Lightning Protocol is on the order of milliseconds. The simplicity of the protocol reduces memory cost, computation complexity, and programming difficulty, making it desirable for low-end wireless sensors.

Rf-microwave switches based on reversible semiconductor-metal transition of VO2 thin films synthesized by pulsed-laser deposition

Microwave switching devices based on the semiconductor-metal transition of VO2 thin films were developped on two types of substrates (C-plane sapphire and SiO2∕Si), and in both shunt and series configurations. Under thermal activation, the switches achieved up to 30–40dB average isolation of the radio-frequency (rf) signal on 500MHz–35GHz frequency band with weak insertion losses. These VO2-based switches can be electrically activated with commutation times less than 100ns, which make them promising candidates for realizing efficient and simple rf switches.

Selective control of the states of a three-level quadrupole nucleus by means of nonselective RF pulses

The scheme for obtaining the composite operator of the selective rotation from nonselective RF pulses separated by intervals of free evolution has been proposed for quadrupole nuclei. Using the example of three levels, it has been shown that the rotation by this operator is performed with an accuracy comparable with the accuracy of a simple selective RF pulse but in a shorter amount of time.

Simplified RF noise de-embedding method for on-wafer CMOS FET

A simplified RF noise de-embedding method for an on-wafer CMOS device using only one dummy structure for simplicity and area reduction is presented. The method describes the use of a 'thru' test structure to subtract completely the parasitic effects of pads and in/out interconnections from the device under test. A comparison of the de-embedding results among the simplified method and existing de-embedding methods is given, which proves that the new method is effective, accurate and time efficient.

An easily constructed, tuning free, ultra-broadband probe for NMR

We have developed an easy to construct, non-resonant wideband NMR probe. The probe is of the saddle coil geometry and is designed such that the coil itself forms a transmission line. The probe thus requires no tuning or matching elements. We use the probe with a spectrometer whose duplexer circuitry employs a simple RF switch instead of the more common λ/4 lines, so the entire probe and spectrometer perform in an essentially frequency-independent manner. Despite being designed with electro- and magnetostatic formulas, the probe performs well at frequencies up to 150 MHz and beyond. We expect that with additional design effort, the probe could be modified for use at significantly higher frequencies. Because our construction method relies on commercial circuit fabrication techniques, identical probes can be easily and accurately produced.