Radio Frequency Measurements Research Articles

Computational Fluid Dynamics (CFD) Simulations and Experimental Measurements in an Inductively-Coupled Plasma Generator Operating at Atmospheric Pressure: Performance Analysis and Parametric Study

In this article, electrical characteristics of a high-power inductively-coupled plasma (ICP) torch operating at 3 MHz are determined by direct measurement of radio-frequency (RF) current and voltage together with energy balance in the system. The variation of impedance with two parameters, namely the input power and the sheath gas flow rate for a 50 kW ICP is studied. The ICP torch system is operated at near atmospheric pressure with argon as plasma gas. It is observed that the plasma resistance increases with an increase in the RF-power. Further, the torch inductance decreases with an increase in the RF-power. In addition, plasma resistance and torch inductance decrease with an increase in the sheath gas flow rate. The oscillator efficiency of the ICP system ranges from 40% to 80% with the variation of the Direct current (DC) powers. ICP has also been numerically simulated using Computational Fluid Dynamics (CFD) to predict the impedance profile. A good agreement was found between the CFD predictions and the impedance experimental data published in the literature.

Evaluation of Low-Temperature Saturation Velocity in <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-(AlxGa1–x)2O3/Ga2O3 Modulation-Doped Field-Effect Transistors

We report on the high-field transport characteristics and saturation velocity in a modulation-doped β-(Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> heterostructure. The formation of a 2-D electron gas (2DEG) in the modulation-doped structure was confirmed from the Hall measurements, and the 2DEG channel mobility increased from 143 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s at room temperature to 1520 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s at 50 K. The high electron mobility at 50 K made it feasible to achieve velocity saturation inside the channel. The saturation velocity was estimated based on both pulsed current-voltage measurements and smallsignal radio frequency (RF) measurements. The measured velocity-field profile suggested a saturation velocity above 1.1 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s at 50 K. The small-signal RF characteristics were measured for the fabricated modulation-doped field-effect transistors with a Pt-based Schottky contact. The current gain cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) and maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) showed significant increases from 4.0/11.8GHz at room temperature to 17.4/40.8GHz at 50 K for the device with gate length of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> = 0.61 μm. The analysis of the low temperature f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> based on device simulations indicated a peak velocity of 1.2 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s. The three-terminal off-state breakdown measurement further suggested an average breakdown field of 3.22 MV/cm. The high saturation velocity and high breakdown field in β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> make it a promising candidate for high-power and high-frequency device applications.

Detuning radio-frequency electrometry using Rydberg atoms in a room-temperature vapor cell

Traceable radio-frequency electric field measurements with high sensitivity have been demonstrated from the centimeter wave to the millimeter wave using room-temperature Rydberg atoms. Here, we investigate the splitting spectra of electromagnetically induced transparency induced by a radio-frequency electric field, which is detuned from the resonant frequency of transitions between two Rydberg states, 47D5/2 ↔ 48P3/2. By varying the detuning of the radio-frequency electric field, we measure the separation between the two peaks, and in particular their relative height. The resulting measured resonant transition frequency between two Rydberg states is found to exhibit a visible change when the power of the radio-frequency electric field is varied, thus causing uncertainty in the traceable radio-frequency electric field measurement. Further, the effect of detuning of the probe light on the radio-frequency electric field measurement is presented.

High-speed photo detection at two-micron-wavelength: technology enablement by GeSn/Ge multiple-quantum-well photodiode on 300 mm Si substrate.

We report high-speed photo detection at two-micron-wavelength achieved by a GeSn/Ge multiple-quantum-well (MQW) p-i-n photodiode, exhibiting a 3-dB bandwidth (f3-dB) above 10 GHz for the first time. The epitaxy of device layer stacks was performed on a standard (001)-oriented 300 mm Si substrate by using reduced pressure chemical vapor deposition (RPCVD). The results showed promise for large-scale manufacturing. To our knowledge, this is also the first photodiodes-on-Si with direct radio-frequency (RF) measurement to quantitatively confirm high-speed functionality with tens of GHz f3-dB at 2 µm, which is considered as a promising candidate for the next data communication window. This work illustrates the potential for using GeSn to extend the utility of Si photonics in 2 µm band integrated optical transceivers for communication applications.

Compressive Sensing Based Radio Tomographic Imaging with Spatial Diversity.

Radio tomographic imaging (RTI) has emerged as a promising device-free localization technology for locating the targets with no devices attached. RTI deduces the location information from the reconstructed attenuation image characterizing target-induced spatial loss of radio frequency measurements in the sensing area. In cluttered indoor environments, RF measurements of wireless links are corrupted by multipath effects and thus less robust to achieve a high localization accuracy for RTI. This paper proposes to improve the quality of measurements by using spatial diversity. The key insight is that, with multiple antennae equipped, due to small-scale multipath fading, RF measurement variation of each antenna pair behaves differently. Therefore, spatial diversity can provide more reliable and strong measurements in terms of link quality. Moreover, to estimate the location from the image more precisely and make the image more identifiable, we propose using a new reconstruction regularization linearly combining the sparsity and correlation inherent in the image. The proposed reconstruction method can remarkably reduce the image noise and enhance the imaging accuracy especially in the case of a few available measurements. Indoor experimental results demonstrate that compared to existing RTI improvement methods, our RTI solution can reduce the root-mean-square localization error at least 47% while also improving the imaging performance.

Radio frequency measurement and tuning of a 13 MeV Alvarez-type drift tube linac for a compact pulsed hadron source.

This paper describes the radio frequency (RF) measurement and tuning result of a 13 MeV Alvarez-type drift tube linac (DTL) for a compact pulsed hadron source (CPHS) at Tsinghua University. The design, machining, assembly, and alignment of the DTL are presented for integrity. The CPHS project consists of a high-current proton linac (13 MeV, 16 kW, peak current of 50 mA, 0.5 ms pulse width at 50 Hz), a neutron target station, a small-angle neutron scattering instrument, and a neutron imaging/radiology station. The linac contains an electron cyclotron resonance ion source, a low energy beam transport line, a four-vane radio frequency quadrupole (RFQ) accelerator, an Alvarez-type DTL, a high energy beam transport line, and a RF power supply and distributor. Construction on the CPHS started in June 2009, and the CPHS has provided 2000 h since 2013 to users with the neutrons produced by the 3 MeV proton beam from the radio frequency quadrupole bombarding on the beryllium target as an achievement of its mid-term objective. Presently, the tuning of the assembled DTL cavity has been completed successfully. The 4.3-m-long DTL consists of 40 accelerating cells, among which 39 full-length drift tubes (DTs) are suspended inside the cavity, and two half-length DTs are mounted inside the two end flanges of the cavity. Each DT contains a permanent magnet quadrupole. Thirteen post couplers and nine tuners are available for the tuning of the field. The relative error of the field after tuning is within ±1.6%, with a tilt sensitivity within ±33%/MHz in all cells. The beam energy will reach its designed value of 13 MeV after the DTL is installed in the beam line downstream the 3 MeV RFQ accelerator.

Plasma heating and innovative microwave launching in ECRIS: models and experiments

Microwave-to-plasma coupling in ECRIS has been based on the classic scheme of waveguide-to-cylindrical plasma cavity matching. Optimization has been often obtained by empirical adjustments leading to an oversimplified model, though obtaining satisfactory performances. In order to overcome the ECR-heating paradigm, on-purpose design of launchers' setup and adequate diagnostics are going to be developed at INFN. This paper describes three-dimensional numerical simulations and Radio Frequency (RF) measurements of wave propagation in the microwave-heated magnetized plasmas of ion sources. Moreover, driven by an increasing demand of high frequency ECR ion sources, innovative ideas for the geometry for both the plasma chamber and the related RF launching system—in a microwave absorption-oriented scenario—are presented. Finally, the design of optimized launchers enabling “single-pass” power deposition, not affected by cavity walls effects, are described.

Radio frequency nonionizing radiation exposure burdens to the population at major market centers in Ibadan metropolis, Nigeria

There has been proliferation of mobile phone base station towers in recent years due to an expansion of mobile telephone networks. This has been accompanied by an increase in the community concern about possible radiation exposure due to the radio frequency (RF) radiation emissions from antennae mounted on the base station towers. This work presents RF measurements and information on the levels at selected markets in Ibadan, Nigeria. The highest RF power density of 499.6 μW/m2 obtained at Global System for Mobile Communication (GSM) 1800 band occurred at Apete market. The lowest RF power density of 0.1 μW/m2 was also obtained at Alesinloye for GSM 1800, Dugbe, and Ogunpa for GSM 900; at this point of measurement, the base transceiver station was not in the line of sight. The measured RF levels were compared with the maximum permissible limit for nonoccupational exposure with respect to the Radiocommunications (Electromagnetic Radiation – Human Exposure) Standard 1999 which specifies a maximum nonoccupational exposure limit of 2 W/m2 (equivalent to 200 μW/cm2) at relevant base station frequencies. The results showed that the RF exposure levels were several orders of magnitude below the maximum permissible limits around the environments of the major markets in the city of Ibadan.

Radiofrequency method for measurement of liquefied petroleum gas mass in the tank of a gas tank truck

Radiofrequency method for measurement of liquefied petroleum gas mass under overload from gas tank trucks into tanks of automotive gas-filling stations and gas-holders is considered. Experience of application of radiofrequency measurement system SU-5D-MASS for mass measurement of various liquids and gas condensates under their storage in reservoirs and pumping through pipelines is taken into account. Optimization of measurement system is suggested implying equipment of 1–2 gas tank-cars by Coriolis flow-meters and radiofrequency sensor of liquefied petroleum gas mass in the tank of a gas tank-car while other gas tank-cars are equipped only such a mass sensor. New approach of calibration of tanks of gas tank trucks and automotive gas-filling stations is suggested.

Study on Thermionic RF Electron Gun after Retuning Process

Relativistic femtosecond electron bunches can be produced from the electron accelerator system at the PBP-CMU Electron Linac Laboratory of the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University (CMU). A thermionic radio-frequency (RF) gun is used as an electron source for this accelerator. The RF gun has a 1.6-cell standing-wave structure with side-coupling cavity. The 2856 MHz RF wave is transmitted from the klystron to the gun through a waveguide system. So far, two RF guns have been used at our laboratory. The first gun was designed and constructed mostly in Thailand. The second one was constructed at the National Synchrotron Radiation Research Center (NSRRC), Taiwan, R.O.C. It was then transported from the NSRRC to our laboratory and was tested after the cavity retuning process. The low-level and high-level RF measurements were conducted. This gun has a resonant frequency of 2855.68 MHz at 26.2°C with a quality factor of 12264. The high-power RF measurements showed that an optimal operating temperature of the gun was 34°C. The electromagnetic (EM) field distribution inside the gun was simulated by using the 3D-model created with program CST Microwave Studio 2012@. Study of electron beam dynamics in the gun using program PARMELA was done to estimate the beam properties at the gun exit. Moreover, measurements of the beam properties were performed. The results showed that at optimal conditions the RF gun could produce the beam of ∼2 μs (FWHM) pulse width with a charge of 850.1 ± 34.7 nC. The major fraction of the beam has an energy in the range of 1.5-2.5 MeV.

95-GHz Front-End Receiving Multichip Module on Multilayer LCP Substrate for Passive Millimeter-Wave Imaging

In this paper, directional filters (DFs) are first proposed to improve the stability of multichip modules (MCMs), and a new integration approach between microstrip line on liquid crystal polymer (LCP) substrate and electrooptic (EO) modulator on lithium niobate substrate is presented, together enabling an EO front-end receiving MCM at 95 GHz for passive millimeter-wave (mmW) imaging with large distributed aperture. The DFs can efficiently pick the spectrum of interest with low reflection and drop the undesired out-of-band power to the additional ports, thus reducing the possibility of oscillation. With the above and some other integration and packaging technologies, the multilayer LCP-based MCM achieves a high gain of more than 63 dB, a 3-dB bandwidth of 4.7 GHz centered at 95 GHz, and a low noise figure of less than 6 dB within this spectrum, which was characterized using both radio frequency and optical measurement approaches. The packaged MCM has been successfully utilized in passive mmW imaging and may find lots of applications in other wireless systems.

DC and RF characteristics optimization of AlGaN/GaN/BGaN/GaN/Si HEMT for microwave-power and high temperature application

Abstract AlGaN/GaN/Si high electron mobility transistors (HEMTs) developed by molecular beam epitaxy (MBE) are studied with several methods for characterization, the most utilized are direct-current and radio-frequency measurements, to see power and microwave performance of components. The increase in these parameters is not based just with on improvement technological for example, decrease of length gate (Lg) and passivation. For sure, another very important point is to reduce the thickness of barrier while keeping the reduction in the length of gate, in order to reduce the transit time (τ), and consequently access to highest cut-off frequency (FT). For this situation, it’s appears a harmful phenomenon of type “punch-through”, because of the weak confinement of electrons in the channel. In this paper, the main objective is to show how to reduce this effect.

Editorial Special Issue on Advances in Integrated Microwave Photonics

The field of integrated microwave photonics explores the incorporation of photonic integration technology for the generation, processing, and measurement of radio-frequency and microwave signals and is one of the fastest growing fields in signal processing. The last 10 years have seen a strong trend towards integration of microwave photonics functionalities on a single chip, with the scope to reduce size, weight, power, and cost.

Using radiation pressure to develop a radio-frequency power measurement technique traceable to the redefined SI

We discuss a power-measurement technique traceable to the International System of Units (SI) based on radiation pressure (or radiation force) inherent in an electromagnetic wave. A measurement of radiation pressure offers the possibility for a power measurement traceable to the kilogram and to Planck's constant through the redefined SI. Towards this goal, we performed measurements of the radiation pressure in a radio-frequency (RF) electromagnetic field at three frequencies (26.5 GHz, 32.5 GHz, and 40.0 GHz) and power levels ranging from 2 W to 25 W using a commercially available mass scale. We show comparisons between the RF power obtained with this technique and those obtained with a conventional power meter. The results in this paper represent the first step towards the realization of a more direct link to RF power within the newly redefined SI.

In2Se3 saturable absorber for generating tunable Q-switched outputs from a bismuth–erbium doped fiber laser

An Indium–selenide based saturable absorber is proposed and demonstrated for the passive generation of Q-switched pulses in a C- to L-band fiber laser. The proposed laser uses a 21 cm long bismuth–erbium doped fiber (Bi-EDF) as the linear gain medium, and is capable of generating passively Q-switched outputs that can be tuned over a bandwidth of 40 nm from 1533 nm to 1573 nm. The generated pulses have a maximum repetition rate of 52 kHz and a minimum pulse width of 2.2 μs at the maximum available pump power of 134 mW. Similarly, a maximum pulse energy and average output power of 13.5 nJ and 0.7 mW respectively are obtained at the same pump power. Radio frequency measurement indicates a stable pulse obtained with a high signal-to-noise ratio of 42.8 dB and with no other frequency peaks observed, indicating that only the fundamental mode is present. The proposed tunable Q-switched Bi-EDF laser would have significant potential for applications requiring tunable, high energy pulses such as spectroscopy and medicine in the C- and L-band regions.

A 300 THz tabletop radar range system with sub-micron distance accuracy

We are presenting a compact radar range system with a scale factor of 105. Replacing the radio frequency (RF) by optical wavelength (300 THz), the system easily fit on a tabletop. We used interferometric time-of-flight to reproduce radar ranging measurements. Sub-micron range accuracy was achieved with a 100 fs laser pulse, which correspond to 3 cm for a s-band (3 GHz) radar. We demonstrated the system potential on a simple target, and compared the results with radio frequency measurement using a vector network analyzer. We also present measurement with a more realistic model, a 3D printed reproduction of the USS Arizona battleship, for which a 3D model is extracted from the ranging data. Together with our previous demonstration of radar cross section measurement with a similar system, this report further validates our proposal to use optics to simulate radar properties of complex radio frequency systems.

Tunnel diode resonator for precision magnetic susceptibility measurements in a mK temperature range and large DC magnetic fields.

Precision radio-frequency measurements of the magnetic susceptibility using the tunnel diode resonator (TDR) technique are used to study the delicate effects in magnetic and superconducting materials. High resolution (in ppb range) measurements are particularly important for studies of the London and Campbell penetration depths in a superconductor and for the investigation of magnetic transitions in (anti)ferromagnets. Due to the small rf magnetic-excitation in a mOe range, the TDR is especially useful at low-temperatures in a mK range, if Joule heating generated in the TDR circuitry is efficiently removed and the circuit is stabilized with sub-mK precision. Unfortunately, the circuit has significant magnetic field dependence, and therefore, most of the precision TDR measurements at low-temperatures were conducted in zero magnetic field. In this work, we describe the design of a setup for precision TDR measurements in a dilution refrigerator down to ∼40 mK with a 14 T superconducting magnet. The key features of our design are the separated electronics components and the placement of the most field sensitive parts in the field-compensated zone far from the center of solenoid as well as the heat-sinking at a higher temperature stage. The performance of the working setup is demonstrated using several superconductors.

Antenna Configuration Method for RF Measurement Based on DOPs in Satellite Formation Flying

Radio frequency (RF) measurement technology provides a relative navigation solution that can be of great importance to have significant potential for application to the satellite groups. With the development of the RF relative measurement sensors, it is found that the antenna configuration of the sensors affects the precision of relative position and attitude measurement. This study proposes improvements to the precision of the sensors by the virtue of the optimal antenna configuration. Furthermore, the concept of dilution of precision (DOP) is extended to the RF relative measurement sensors, and a new dilution called IDOP is proposed as a benchmark to determine the precision of relative position and attitude measurement in engineering applications of the space mission. In order to select the optimal antenna configuration in real time in a scene where the intersatellite position and attitude change dynamically, this study presents an optimal antenna configuration selection strategy and models the antenna configuration selection as a combinatorial optimization problem. Furthermore, the genetic algorithm (GA) with two encoding mechanisms is proposed to solve this problem. Finally, numerical results are presented to verify the robustness.

A quantum-based power standard: Using Rydberg atoms for a SI-traceable radio-frequency power measurement technique in rectangular waveguides

In this work, we demonstrate an approach for determining radio-frequency (RF) power using electromagnetically induced transparency (EIT) in a Rydberg atomic vapor. This is accomplished by placing alkali atomic vapor in a rectangular waveguide and measuring the electric (E) field strength (utilizing EIT and Autler-Townes splitting) for a wave propagating down the waveguide. The RF power carried by the wave is then related to this measured E-field, which leads to a direct International System of Units measurement of RF power. To demonstrate this approach, we first measure the field distribution of the fundamental mode in the waveguide and then determine the power carried by the wave at both 19.629 GHz and 26.526 GHz from the measured E-field. We show comparisons between the RF power obtained with this technique and those obtained with a conventional power meter.

Efficient B-Mode Ultrasound Image Reconstruction From Sub-Sampled RF Data Using Deep Learning

In portable, 3-D, and ultra-fast ultrasound imaging systems, there is an increasing demand for the reconstruction of high-quality images from a limited number of radio-frequency (RF) measurements due to receiver (Rx) or transmit (Xmit) event sub-sampling. However, due to the presence of side lobe artifacts from RF sub-sampling, the standard beamformer often produces blurry images with less contrast, which are unsuitable for diagnostic purposes. Existing compressed sensing approaches often require either hardware changes or computationally expensive algorithms, but their quality improvements are limited. To address this problem, in this paper, we propose a novel deep learning approach that directly interpolates the missing RF data by utilizing redundancy in the Rx-Xmit plane. Our extensive experimental results using sub-sampled RF data from a multi-line acquisition B-mode system confirm that the proposed method can effectively reduce the data rate without sacrificing the image quality.