Low Radio Frequency Research Articles

Hydrogen barrier performance of sputtered La2O3 films for InGaZnO thin-film transistor

We report the hydrogen barrier performance of sputtered La2O3 thin films for the device stability of amorphous indium–gallium–zinc–oxide (a-IGZO) thin-film transistors (TFTs). Hydrogen acts as a shallow donor in a-IGZO films, which makes TFTs conductive, resulting in degradation of their on/off properties. Since hydrogen can be easily incorporated by external environments or post-processing, an appropriate hydrogen barrier is essential for enhancing device stability. La2O3, with its extreme electronegativity, can provide excellent hygroscopic characteristics. Because hydrogen exists in the form of –OH groups inside a-IGZO films, La2O3 is expected to be a promising barrier material for preventing hydrogen incorporation. Therefore, we investigate the growth characteristics of sputtered La2O3 thin films as hydrogen barrier layers, focusing on variations in growth rate, refractive index, and film stress, which depend on various process parameters, such as radio-frequency (RF) power, O2 partial pressure, and substrate temperature during reactive magnetron sputtering. The effects of these parameters on hydrogen barrier properties are systematically investigated and correlated with the microstructures of La2O3 films. The results demonstrate that La2O3 films grown with low RF power and low O2 partial pressure have an amorphous phase and provide excellent hydrogen barrier performance. We anticipate that these experimental results will help improve the environmental stability of a-IGZO TFTs.

Design and optimization of a low voltage RF switch MEMS capacitance using genetic algorithm and Taguchi method

Purpose This paper aims to design, optimize and simulate the Radio Frequency (RF) micro electromechanical system (MEMS) Switch which is stimulated by electrostatically voltage. Design/methodology/approach The geometric structure of the switch was extracted based on the design of Taguchi-based experiment using the mathematical programming and obtaining objective function by the genetic meta-heuristic algorithm. Findings The RF parameters of the switch were calculated for the design of Taguchi-based S11 = −5.649 dB and S21 = −46.428 dB at the working frequency of 40 GHz. The pull-in voltage of the switch was 2.8 V and the axial residual stress of the proposed design was obtained 28 MPa and the design of Taguchi-based S11 = −4.422 dB and S21 = −48.705dB at the working frequency of 40 GHz. The pull-in voltage of the switch was 2.5 V and the axial residual stress of the proposed design was obtained 25 MPa. Originality/value A novel complex strategy in the design and optimization of capacitive RF switch MEMS modeling is proposed.

A Silicon Photonic RF Phase Shifter With Linear Phase Response and Low RF Power Variation

We propose and experimentally demonstrate a microwave photonic phase shifter based on a tunable silicon photonic interleaver. This device consists of a microring resonator, a tunable interleaver, and a $2\,\times \,1$ multimode interferometer (MMI). By thermally tuning the interleaver, a linear phase shift of 188° is realized with a linearity of 0.08 and a radio-frequency (RF) power variation within 1 dB for a 40-GHz signal.

A unified heteronuclear decoupling picture in solid-state NMR under low radio-frequency amplitude and fast magic-angle-spinning frequency regime.

Heteronuclear spin decoupling is a highly important component of solid-state NMR experiments to remove undesired coupling interactions between unlike spins for spectral resolution. Recently, experiments using a unification strategy of standard decoupling schemes were presented for high radio-frequency (RF) amplitudes and slow-intermediate magic-angle-spinning (MAS) frequencies, in the pursuit of deeper understanding of spin decoupling under phase-modulated RF irradiation [A. Equbal et al., J. Chem. Phys. 142, 184201 (2015)]. The approach, unified two-pulse heteronuclear decoupling (UTPD), incorporates the simultaneous time- and phase-modulation strategies, commonly used in solid-state NMR. Here, the UTPD based decoupling scheme is extended to the experimentally increasingly important regime of low RF amplitudes and fast MAS frequencies. The unified decoupling approach becomes increasingly effective in identifying the deleterious dipole-dipole and, in particular, J recoupling conditions which become critical for the low-amplitude RF regime. This is because J coupling is isotropic and therefore not averaged out by sample spinning unlike the anisotropic dipole-dipole coupling. Numerical simulations and analytic theory are used to understand the effects of various nuclear spin interactions on the decoupling performance of UTPD, in particular, the crucial difference between the low-phase and high-phase UTPD conditions with respect to J coupling. In the UTPD scheme, when the cycle-frequency of the pulse-sequence is comparable to the RF nutation frequency, the existence of a non-zero effective rotation in the basic two-pulse scheme becomes an essential feature for the efficient and robust averaging out of the scalar J coupling. This broad viewpoint is expected to bring different optimum low-power decoupling pulse schemes under a common footing.

Comparative study of 3.4 micron band features from carbon dust analogues obtained in pulsed plasmas

AbstractSyntheses of carbon dust analogues are key experiments in laboratory astrophysics, as an approach to study some chemical and topological features of interplanetary and interstellar carbon dust. We report a comparative experimental study for carbon dust analogues obtained in (1) an atmospheric pressure dielectric barrier discharge (DBD), fed with helium – saturated hydrocarbons gas mixtures, (2) a low pressure radio frequency (RF) discharge and (3) a pulsed laser deposition (PLD) experiment with a Nd:YAG laser and a graphite target. The aliphatic –C–H stretching band, known as the 3.4 micron feature, as well as the CH2/CH3 ratio, the H/C ratio value and the physical appearance at microscopic scale, show a variability that is influenced by the synthesis method and the experimental parameters of each specific technique.

A Holistic Experimental Static Bias Point Identification Method for Low Power Wireless RF Amplifier

A holistic and effective experimental method of optimum static gate bias identification is presented here for a modern wireless Radio Frequency (RF) power amplifier operating in 1900 MHz band. The amplifier is targeted for low complexity, high efficiency and low power Base Station (BS) having RF conducted power of less than 1 watt at its output load. Through the measured results, it is shown that out of various other static gate bias points obtained, the optimum gate bias condition is achieved at 2.4 volts. At this bias point setting, the PA delivers a modulated output power of +24 dBm in a standalone mode and with external RF linearization circuits added, the channel power enhanced upto +26 dBm and the Adjacent Channel Power Ratio (ACPR) is improved by 5.3 dB. At linear back-off power level, the achieved efficiency is 13.2%.

Combination of Resection and Ablative Treatment for Hepatocellular Carcinoma: Usefulness of Complementary Radiofrequency Ablation

Aim/Background: In HCC patients with multiple tumors in separate segments, monotherapy with surgical resection is often difficult when the estimated residual liver volume after surgery is thought to be inadequate. We evaluated the usefulness of resection combined with low invasive radiofrequency ablation (RFA) for treatment of such cases. Materials/Methods: We analyzed 115 HCC patients with countable multiple tumors (≤5) without vascular invasion and/or extrahepatic metastasis, and treated solely with resection (SR group: n = 82), or with both resection and RFA (Comb group: n = 33) from January 2000 to December 2017. Clinical characteristics, overall survival rate (OSR), and disease-free survival rate (DFSR) were analyzed in a retrospective manner. Results: There were 88 males (76.5%) and the average age of all patients was 67.8 ± 8.9 years. The average number of tumors and average maximum tumor size were 2.4 ± 0.7 and 4.1 ± 2.1 cm, respectively. Forty-two (36.5%) patients were classified as beyond up-to-7 criteria. The 3- and 5-year OSRs in the SR group were 82.0 and 67.0%, respectively, and in the Comb group were 75.2 and 65.6%, respectively (p = 0.244), while the 3- and 5-year DFSRs in the SR group were 45.2 and 28.0%, respectively, and those in the Comb group were 37.3 and 23.3%, respectively (p = 0.257). Conclusion: The combination of surgical resection and complementary RFA may be an effective strategy for treating HCC patients with countable multiple tumors, who are otherwise difficult to treat with surgical resection or RFA alone.

Adaptive Body Biasing Circuit for Reliability and Variability Compensation of a Low Power RF Amplifier

This paper presents a simple compensation biasing circuit to enhance the reliability and variability of the low-power radio-frequency (RF) amplifier. The compensation function is achieved through a threshold voltage adjustment, which is realized by an adaptive varying body voltage of power amplifier transistors. The proposed circuit effectively preserves the power amplifier performance over a wide level range of output power under threshold voltage shift and electron mobility degradation. At the 0.63 dBm output power level, the sensitivity of the normalized efficiency of the power amplifier with the proposed compensation circuit under 0.16% threshold voltage shift and 0.16% mobility variations decreases as nearly 6.7 times and 2 times compared to the power amplifier without the compensation circuit, respectively. The operational principle of this structure is studied by deriving the analytical equations. The post-layout simulation results in the 180-nm RF complementary metal–oxide–semiconductor process are obtained and verify the proposed circuit effectiveness.

Baryon Acoustic Oscillations from Integrated Neutral Gas Observations: Radio Frequency Interference Measurements and Telescope Site Selection

The Baryon acoustic oscillations from Integrated Neutral Gas Observations (BINGO) telescope is a new 40[Formula: see text]m class radio telescope to measure the large-angular-scale intensity of H i emission at 980–1260[Formula: see text]MHz to constrain dark energy parameters. As it needs to measure faint cosmological signals at the milliKelvin level, it requires a site that has very low radio frequency interference (RFI) at frequencies around 1[Formula: see text]GHz. We report on measurement campaigns across Uruguay and Brazil to find a suitable site, which looked at the strength of the mobile phone signals and other radio transmissions, the location of wind turbines, and also included mapping airplane flight paths. The site chosen for the BINGO telescope is a valley at Serra do Urubu, a remote part of Paraíba in North-East Brazil, which has sheltering terrain. During our measurements with a portable receiver, we did not detect any RFI in or near the BINGO band, given the sensitivity of the equipment. A radio quiet zone around the selected site has been requested from the Brazilian authorities ahead of the telescope construction.

A prospective, non-randomized evaluation of a novel low energy radiofrequency treatment for nasal obstruction and snoring

BackgroundWeak or inward-bent cartilage of the nasal sidewall at the level of the internal nasal valve (INV) can produce narrowness or collapse of the nasal valve. This is a common cause of impaired nasal breathing during daily activities and there is also an established connection between nasal obstruction and snoring. The condition is often difficult to treat, although even a small enlargement of the lumen at the nasal valve can lead to a significant improvement in the ease of nasal breathing.MethodsThe primary objective of this prospective study was to evaluate the safety and efficacy of the Vivaer system for the treatment of narrowed nasal valves and to measure changes in the symptoms of nasal obstruction and snoring. The Vivaer system uses low energy radiofrequency to remodel the nasal sidewall in order to improve airflow.ResultsThe study involved 31 patients presenting from 1st September 2017 to 1st May 2018 with symptoms of nasal obstruction and snoring. In all patients, an improvement was observed in nasal breathing measured by NOSE score, sleep quality by SOS questionnaire and quality of life as measured by EQ-5D and SNOT-22.ConclusionVivaer intranasal remodeling can provide a durable and well-tolerated non-invasive treatment for those patients who are suffering congestion due to narrowness or collapse of the INV.

GMRT survey of Cygnus OB2 region

A good fraction of very high energy (VHE; > 100 GeV) sources do not have confirmed counterparts at any of the other branches of electromagnetic spectrum. In the extra-galactic sky, most of the VHE sources with counter-parts are blazars, a sub-class of active galactic nuclei. However, VHE sources with identified counterparts in our Galaxy do have a wide range of categories, ranging such as supernovae remnants, colliding wind binaries, pulsar wind nebulae, micro-quasars, etc. The VHE emission and radio emission due to synchrotron process do occur from the same population of relativistic electrons in several type of sources, so the radio band is the first band to search for possible counterparts to unidentified VHE sources. In addition, the radio spectral index also gives important constraints on compactness and energetics of the electron population. In this work we present a two-frequency radio survey, at frequencies 325 MHz and 610 MHz, of the Cygnus OB2 region with the Giant Metrewave Radio Telescope (GMRT) in order to address several astrophysical problems. The survey covers a wide area (~ 5 square degrees) at sub-mJy sensitivity which helps to discover faint radio sources to several objects for the first time. Also this is the first deep wide area radio survey of the region below 1.4 GHz, and the low radio frequency will preferentially pickup more non-thermal radio sources as compared to high radio frequencies. Here, we present the early results from this survey.

A single-chip integrated transceiver for high field NMR magnetometry.

We present the design and performance of a broad-band single-chip integrated transceiver specifically conceived for nuclear magnetic resonance magnetometry. The single-chip transceiver is realized using a standard silicon complementary metal-oxide-semiconductor integrated circuit technology. A radio-frequency (RF) transmit amplifier, a transmit/receive switch, a low noise RF receive amplifier, a quadrature (IQ)-mixer, and two intermediate frequency amplifiers are integrated on a single silicon chip of 1.8 mm2. The advantages and problematic aspects with respect to conventional discrete electronic approaches are discussed. We show the results of magnetic field measurements performed at 1.4 and 7.05 T, using solid and liquid samples having volumes from 40 μl down to 100 pl. Particular attention is devoted to the comparison of the experimentally measured magnetic field standard deviation with respect to the Cramer-Rao lower bound value. With a sample of distilled water (T1 ≅ T2 ≅ 3 s, T2 *≅ 20 ms) having a volume of 40 μl, a standard deviation of 2.5 nT at 7.05 T (i.e., 0.5 ppb) in 1 s of averaging time is achieved, with a projected Cramer-Rao lower bond of 8 pT (i.e., 1.1 ppt).

A Cosmic Microscope to Probe the Universe from Present to Cosmic Dawn:Dual-element Low-frequency Space VLBI Observatory

A space-based very long baseline interferometry (VLBI) programme, named as the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space working together with giant ground-based telescopes (e.g., Square Kilometre Array, FAST, Arecibo) to image the low radio frequency Universe with the purpose of unraveling the compact structure of cosmic constituents including supermassive black holes and binaries, pulsars, astronomical masers and the underlying source, and exoplanets amongst others. The operational frequency bands are 30, 74, 330 and 1670 MHz, supporting broad science areas. The mission plans to launch two 30-m-diameter radio telescopes into 2,000 km x 90,000 km elliptical orbits. The two telescopes can work in flexibly diverse modes: (i) space-ground VLBI. The maximum space-ground baseline length is about 100,000 km; it provides a high-dynamic-range imaging capacity with unprecedented high resolutions at low frequencies (0.4 mas at 1.67 GHz and 20 mas at 30 MHz) enabling studies of exoplanets and supermassive black hole binaries (which emit nanoHz gravitational waves); (ii) space-space single-baseline VLBI. This unique baseline enables the detection of flaring hydroxyl masers, and more precise position measurement of pulsars and radio transients at milli-arcsecond level; (iii) single dish mode, where each telescope can be used to monitor transient bursts and rapidly trigger follow-up VLBI observations. The large space telescope will also contribute in measuring and constraining the total angular power spectrum from the Epoch of Reionization. In short, the Cosmic Microscope offers astronomers the opportunity to conduct novel, frontier science.

Filterless frequency octupling circuit using dual stage cascaded polarization modulators

ABSTRACTThis paper demonstrates the photonic generation of millimetre-wave carriers by frequency octupling of a radio frequency (RF) carrier using a circuit with two parallel arms each containing two polarization modulators in series. The low RF drive power required and the absence of optical filters make this architecture suitable for generating highly stable and tunable optical millimetre-waves. A transfer function representation is used to analyse the operation and a simulation using Virtual Photonic Inc. software package is presented as a proof of concept. The simulation results show very high unwanted optical and electrical side harmonic suppression ratio for a wide range of modulation index compared to the prior art. Further, considering the practical scenario, operating tolerance against the imbalances in the key parameters is established. The unwanted RF sidebands are more than 19 dB and 30 dB below the desired signal power even when a deviation of ±3° is considered in individual RF phase and polarizer angle respectively.

262. Assessment of occupational exposure to electromagnetic field around 1.5 T and 3.0 T MRI scanners

Purpose MRI uses a combination of strong Static Magnetic Field ( B 0 , 0 Hz), which is constantly present inside and around the MRI facility, switching gradient fields oscillating in the Very Low Frequency range (VLF, 0.3–3 KHz) and radiofrequency pulses in the Very High Frequency range (VHF, 30–300 MHz). Staff entering an MRI scanner room may experience instantaneous SMF exposure, as well as time-varying magnetic field exposure (dB/dt) at extremely low frequency, when they move through the non-uniform static magnetic field nearby the scanner. In some situations MRI staff are present inside the scanner room during image acquisition, implying the exposure to the different Electromagnetic Field (EMF). In this study we investigated the compliance of occupational exposure to MRI-related EMF with the 2013/35/EU Directive. Methods The personnel exposure to both dB/dt and B0 during work activity were evaluated on 1.5 T and 3.0 T clinical whole body MRI scanner by using a portable electronic dosimeter for static magnetic field (Talete® Tecnorad, Italy). The dosimeters was capable of measuring B0 at 18 Hz sampling rate. The estimated values were compared with the Exposure Limit Values (ELVs) established from 2013/35/EU Directive. The electric field and magnetic field associated with VLF and VHF were measured at different positions inside the scanner room for three different acquisition technique. The measured values were compared with the Action Levels (ALs) given in 2013/35/EU Directive. For f Results The ALs and the ELVs set by the 2013/35/EU Directive were not exceeded. Conclusion The assessment of occupational exposure to electromagnetic field around 1.5 T and 3.0 T MRI scanners is difficult because of many different EMF. Furthermore many signals and modulations are present in to VHF and VLF emission spectra, besides the use into clinical practice of different equipment and acquisition techniques. In the routine daily work activities, the respect of ALs and ELVs given by 2013/35/EU Directive is demonstrated.

Tunable Silicon Photonic RF Phase Shifter With Low RF Power Variation Based on Constructive Interference of an Add-Drop Ring Resonator

We propose and experimentally demonstrate a tunable silicon photonic radio frequency (RF) phase shifter with low power variation based on constructive interference of an add-drop ring resonator. The thermal nonlinear effect of the add-drop ring resonator is used to realize a nearly 2π-phase shift, and the RF power variation is minimized by allowing two lights at the outputs of the add-drop ring resonator to combine at a directional coupler to achieve constructive interference. By thermally tuning the add-drop ring resonator, a nearly 2π-phase shift is realized and the operation is verified by an experiment. Experimental results show that a 0-5.2-rad phase-shift range with an RF power variation within 0.2 dB for a frequency range of a 40-GHz signal is achieved by thermally tuning the ring resonator. A phase shift up to 4.1 rad over a frequency range of 20-40 GHz is also realized.

Exposure and health risks perception of extremely low frequency and radiofrequency electromagnetic fields and the effect of providing information

Given that regardless of actual exposure levels, high-risk perceptions of electromagnetic fields of non-ionizing radiation (EMF-NIR) may cause health effects, it is important to understand the mechanisms behind perceptions in the general population. The aims of this study were to assess perceptions of both exposure and health-risk among mothers of the INMA (Environment and childhood)-Gipuzkoa child cohort; to explore possible determinants that explain such perceptions; and to evaluate whether providing information on exposure levels has any effect on perceptions. Overall, 387 mothers completed a questionnaire composed of four questions on perceived exposure and perceived health-risk of exposure to extremely low frequency (ELF) and radiofrequency (RF) fields answered on a Likert-type scale from 0 to 10. Later, measurements of ELF and RF fields were conducted in the houses of a subsample of 104 participants. All measured levels were far below the levels established by the European Council recommendation. This was explained in the individual reports sent to the families. After reading the results, mothers completed the aforementioned questionnaire a second time, plus two additional questions regarding the role of public health bodies in risk communication.The association between perceived and measured levels as categorical variables was assessed with a chi-square test. Multiple linear regressions were conducted for each of the questions related to perceived exposure and health-risk perceptions. Wilcoxon signed-rank test was conducted to assess the effect of receiving information.Both exposure and health risk were perceived to be very high for both ELF and RF fields, with mean and medians of 7 on a 10-point scale. Reporting higher perception levels was not associated with higher levels of exposure measured at home. Variables that were repeatedly associated with higher perceptions included: manual social class, not having the feeling of living in a good neighborhood, difficulty getting by financially, not having a television antenna within 600 m, being younger and having fewer devices at home. Providing information on EMF-NIR exposure levels at home did not alter health-risk perceptions, but mean perceived RF exposure decreased significantly (by 0.7 points). Most of the participants claimed to have received no or insufficient information regarding exposure and health-risks of EMF-NIR from public bodies and considered it very important that they should.

Bonding, structural properties and thermal stability of low damage RF (N2) plasma treated diamond (100) surfaces studied by XPS, LEED, and TPD

In this work, we investigate the interaction of N2 radio frequency (RF) plasma with single crystal diamond (100) surface. This study shows that a low-level damaged nitrogen terminated diamond (100) surface may be produced using a bent plasma source and a grounded mesh electrode placed at the source exit. Optical emission spectroscopy (OES) was used to characterize the species present in the plasma. The chemical, structural and thermal stability of the N-terminated diamond (100) surface were investigated in-situ by X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and low energy electron diffraction (LEED). OES showed that increasing the flow rate and operating pressure could decrease the ratio of charged-to-neutral nitrogen particles. From XPS results it is determined that the adsorbed nitrogen to the diamond surface may occupy a number of bonding configurations and that the damage to the surface upon nitridation, as reflected in the C(1s) peak shape analysis, can be minimized. From annealing experiments, it was found that some of the incorporated nitrogen onto the diamond surface is stable upon annealing to 1000 °C. LEED results show that upon a short RF (N2) plasma exposure time a (1 × 1) pattern was observed which was preserved upon annealing to 1000 °C suggesting that a thermally stable and ordered nitrogen terminated surface was formed. The TPD spectrum shows two low-temperature N2 desorption peaks that are associated to weakly bonded nitrogen chemisorbed species to the diamond surface at 210 and 560 °C.

Grafting of amine functions on cellulose acetate fibers by plasma processing

The aim of this study was to graft the amine functions on the surface of cellulose acetate (CA) fibers by two kind of plasma processing; namely, inductively coupled plasma (ICP) and radiofrequency plasma, using either NH3/He or mixture of N2/H2 gases. Optical emission spectroscopy was used to examine the various chemical species of the N2/H2 ICP system. Due to the entangled morphology of the CA fibers, only X-ray photoelectron spectroscopy (XPS) was used to characterize the surface. The effects of the different experimental conditions on the grafting efficiency have been studied. The results showed that in all cases NH2 groups were successfully grafted onto the surface of the CA fibers, and it seems that the ICP process is more effective for the amine grafting than low pressure radiofrequency plasma. Ageing tests carried out under laboratory conditions on the plasma-treated CA tow showed that the density of grafted amines was almost stable over a period of 60 days.

RFID Enabled Framework for Substation Maintenance Management

Objectives: Effective substation maintenance management based on low cost and reliable Radio Frequency Identification (RFID) enabled implementation framework. Methods/Statistical Analysis: Economical operation of substation by minimizing the equipment maintenance cost is the prime concern for all the power distribution utilities. Number of maintenance management strategies has been developed for optimizing the substation equipment maintenance cost. Effectiveness of these optimized maintenance strategies lies on the actual implementation in the field. Currently equipment maintenance activities are carried out with off-line association with equipment. Also, equipment maintenance data is acquired and populated manually into host computer which is running maintenance cost optimization applications. Inherently manual process suffers from various drawbacks and results in poor maintenance management. RFID based technology along with embedded system is identified for making the above off-line process into an on-line process with data integrity. Findings: Present paper proposes a Radio Frequency Identification (RFID) enabled implementation framework to perform the maintenance with on-line association with equipment. This allows on-line access with the equipment and eliminates the manual process of acquiring data from equipment at the substation level. Also, ensures the on-line update of pre-maintenance and postmaintenance information of equipment in the Computerised Maintenance Management System (CMMS). Conventional RFID readers which are based on multi-purpose hand-held computers are driven by high level operating systems and programming languages. Due to high level system software on handheld readers, the network latency increases and data refresh rate decreases. This paper proposes a low cost microcontroller based RFID reader with up-stream data interface using low level network programming to address the above issues. Host computer data interface is implemented using a TCP/IP protocol which assures the data integrity. The low level programming at the host computer for network communication minimizes the network latency in the data transfer and improves the data refresh rate. Maintenance process with RFID framework is designed and explained. Application/Improvements: Maintenance management strategies can be implemented effectively using the proposed RFID enabled framework with customized RLU along with low level network interface to CMMS. Present implementation based on Ethernet interface over TCP/IP can be extended seamlessly for wireless (Wi-Fi) as well. Keywords: JSP, Maintenance, RFID, Substation, TCP/IP