Radio Frequency Range Research Articles

Vertical pillar nanoantenna for emission enhancement and redirection

Designing efficient metallic nanostructures can help in realizing bright single photon emission in the visible and near-infrared ranges. We propose a novel nanostructure design that combines the benefits of plasmonic hot spot generation in the near-field and the concept of antennas developed in the radio-frequency range. The antenna is formed by a vertical stack of metallic and dielectric nanocylinders. When used for controlling the far-field emission of a localized source, its key features are moderate losses in the metal, relatively large Purcell factors, as well as a low sensibility to the lateral position of the emitter. A redirection process necessary for these vertical structures is proposed, based on the versatility of the vertical geometry, and allows an efficient redirection of the emitted light even for antennas on dielectric substrates.

An Analysis of Dielectric Parameters and Penetration Depth of Tomato Sauces

The dielectric constant and dielectric loss of the Tomato Sauce have been measured at different moisture levels in the radio frequency range i.e. 100 kHz to 1 MHz. The measurements were carried out in the temperature 25°C to 50°C. The dielectric properties show remarkable changes as the moisture levels i.e. salt content vary. The dielectric properties have also been used to determine the penetration depth. The penetration depth was found to be quite high in radio frequency range in comparison to penetration depth for microwaves.

Fiber-Optic Acceleration Sensor on Duplex Fiber Bragg Structures

We propose an assessment of the possibility to use narrow-band fiber Bragg structures as the basis of a measuring system for an acceleration sensor (accelerometer). The assessment of applicability is carried out on the basis of mathematical and computer simulation and analytical assessments of the model's working capacity. We propose to solve the problem by transferring a signal from the optical (THz) to the radio frequency (GHz) range of measurements due to the theory and technology of radiophoton methods. The result is a significant increase in the signal-to-noise ratio. We suggest to use the measuring system based on two narrow-band fiber Bragg gratings with the following two properties: central frequencies are in the optical range, and a difference of central frequencies is in the radio frequency range of the spectrum. The optical signal obtained in the optoelectronic circuit is fed to a photodetector. An analysis of the resulting electrical signal allows to make a conclusion on the magnitude and direction of the force acting along the axis of the sensor sensitivity. The magnitude of the effective inertia force is directly related to the acceleration acting on the measuring system. We propose an approach to determine the magnitude of the effective force. The approach does not require measurement of the intermediate radio frequency, and determines the dependence of the effective force on the magnitude of the dual-frequency beats modulation factor. We propose to implement the design of the sensor in such a way as to minimize the effect of temperature deviations on the measuring system as a whole.

Optical and dielectric investigations of nano crystalline scheelite A0.5B0.5MoO4 (A=B=Ba, Sr and Ca)

The synthesis of nanocrystalline A0.5B0.5MoO4 by an auto-igniting combustion technique is reported. The structural characterization done by X-ray diffraction, Fourier transform Raman spectroscopy and infrared spectroscopy reveals that the as-prepared powder itself is phase pure with tetragonal structure. The particle size determined from Transmission electron microscopy are in the range 23–25 nm. The optical band gap determined show that the compounds are wide bandgap semiconductors. The photoluminescence spectrum of A0.5B0.5MoO4 shows green emission, associated with the perfect order and crystallinity of the sample. All the samples are sintered at a temperature less than 875°C. The dielectric constant and loss factor of the samples are measured at radiofrequency range and its variation with temperature is also studied. The effect of change in composition of A2+ site of scheelite AMO4 compounds comparative are also presented. The experimental results show that nano A0.5B0.5MoO4 is an excellent luminescent material and also a promising ‘Low temperature Co-fired Ceramic. Also it is inferred that we can fine tune both optical and dielectric properties to desired values according to our requirements by adjusting the cationic stoichiometric ratio in [AO8] octahedron.

Magneto-dielectric properties studies of the matrix composite [SrFe12O19(SFO)1-X – BiFeO3(BFO)X

The effects of different BiFeO3 (BFO) additions (0, 20, 40, 60 and 80 wt%) on the SrFe12O19 hexaferrite ceramic matrix (SFO) have been studied by Complex Impedance Spectroscopy (CIS), Mössbauer spectroscopy, magnetic hysteresis and X-Ray Diffraction (XRD) analysis. The solid state reaction method was used for the production of the SFO and BFO, the phase formation was confirmed by the XRD and Rietveld refinement, where the obtained fitting presented an effective refinement. The diffractogram for BFO-SFO composites presented all peaks in agreement with the BFO and SFO phases. The thermo-activated process was studied by the CIS and the Arrhenius equation in the composite series of BFO-SFO with SFO presenting higher values of activation energy between the analyzed samples and the frequency and temperature range studied was 1–10 MHz and 160 °C to 300 °C, respectively. The addition of BFO in the SFO ceramic matrix lead to an improvement of the thermal-stability of the composite, where a signal inversion of Temperature Coefficient of Capacitance (TCC), in the composites, was observed. The Nyquist plots showed the presence of a semicircle that was fitted by an equivalent circuit model using R - CPE association, showing the same profile in all samples. The Mössbauer spectrum of the composites demonstrate the typical five Fe3+ site for M-type hexagonal ferrites even after the addition of BFO in a ceramic matrix. The addition of BFO in the formation of composites, with SFO, showed interesting results in the radio frequency range and presented magnetic properties that can be explored in applications in the area of telecommunications, medicine and military industry.

Electromagnetic Emission from Electric Propulsions under Ground Conditions

Analysis and methodological generalization of available methods used for determining characteristics of intrinsic emission from electric propulsions (EP) in a radio-frequency range that can be the interference for the “Earth-spacecraft (SC)” channel of the space communication system are the subjects of this paper. Intrinsic emission from the electric propulsion in a radio-frequency range is examined in detail by the example of a measuring complex developed in RIAME MAI and the measurement results are presented. The electric field intensity distribution in a radio-frequency range for the vertical and horizontal polarizations of the received emission is considered as the main characteristics. Measurements performed for the EP intrinsic emission by using the developed complex and measurements performed in metal vacuum chambers are compared and comparative results are presented in the paper.

Frequency-Oriented Subsampling by Photonic Fourier Transform and I/Q Demodulation

Subsampling can directly acquire a passband within a broad radio frequency (RF) range, avoiding down-conversion and low-phase-noise tunable local oscillation. However, subsampling suffers from band folding and self-image interference. In this paper, we propose a frequency-oriented subsampling to solve those two problems. With ultrashort optical pulse and a pair of chromatic dispersions, the broadband RF signal is first short-time Fourier-transformed to a spectrum-spread pulse. Then, a time slot, corresponding to the target spectrum slice, is coherently optical-sampled by in-phase/quadrature (I/Q) demodulation. We demonstrate the novel bandpass sampling by a numerical example, which shows the desired uneven intensity response, i.e., prefiltering, to avoid the band folding. We show in theory that appropriate time-stretch capacity from dispersion can result in prefiltering bandwidth less than sampling rate. Image rejection due to I/Q sampling is also analyzed. A proof-of-concept experiment, which is based on a time-lens sampling source and chirped fiber Bragg gratings, shows the center-frequency-tunable prefiltered subsampling with bandwidth of 6 GHz around, as well as imaging rejection larger than 26 dB. Our technique may benefit future broadband RF receivers for frequency-agile Radar or channelization.

New triple band electromagnetic band gap microstrip patch antenna with two shaped parasitic elements

This paper presents a triple band microstrip electromagnetic band gap (EBG) patch antenna with two shaped parasitic elements used for 2nd and 3rd mode excitation, permitting multiple band resonance and control of the resonance frequencies. Simulation and measurement results show triple-band (S/C/X-band) antenna applications that can effectively cover three separate bandwidths: 3.79 GHz for moderate range surveillance, terminal air traffic control, long-range weather, marine radar; 7.5 GHz that satisfy the requirements of the C-band applications specific for long-distance radio telecommunications; 11.8 GHz that satisfy the requirements for X-band applications destined for satellite communications, radar, terrestrial broadband, space communications, amateur radio, molecular rotational spectroscopy. The main characteristics of the proposal is its ability to increase the gain, directivity, return loss and the total efficiency of the antenna without affecting the geometric parameters, which makes the designed antenna applicable for a wide range of radio frequency devices operating at the chosen resonance frequencies. The simulated results using computer simulation technology 2014 compared to experiment have demonstrated attractive performance such good impedance matching, compact features (light weight, small sized, low cost), and rigidness compared to other classic antennas.

Performance and Characterization of a Wide IF SIS-Mixer-Preamplifier Module Employing High-J c SIS Junctions

This paper reports the simulation, performance, and detailed characterization of a low-noise heterodyne module with very wide intermediate frequency (IF) bandwidth in the 385-500-GHz radio frequency (RF) range. The module integrates a superconductor-insulator-superconductor (SIS) mixer with a 3- 21-GHz cryogenic low-noise preamplifier (CLNA). The utilization of high current density SIS junctions offers wide RF bandwidth and facilitates better matching between SIS junctions and the CLNA. Based on an equivalent circuit of the SIS mixer chip, we calculate the IF output impedance and simulate how different matching conditions affect the performance of the CLNA. Simulations predict that low-noise module performance can be obtained over a 3-18GHz IF range, limited mainly by parasitic elements in theSIS mixer chip. The measurement results of the heterodyne module demonstrate flat gain and a typical noise temperature of 70-80 K over the 3-18-GHz IF range, at local oscillator frequencies of 400-480 GHz. Mixer chip output impedance and CLNA input impedance have been directly measured by recording S-parameters at cryogenic temperatures. The results enabled us to quantify the contribution of various parasitic elements in the mixer IF circuitry. Calculations based on our model are in good agreement with measurements.

Epitaxial Gd2O3 on GaN and AlGaN: a potential candidate for metal oxide semiconductor based transistors on Si for high power application

We report structural and electrical properties of hexagonal Gd2O3 grown epitaxially on GaN/Si (1 1 1) and AlGaN/GaN/Si(1 1 1) virtual substrates. GaN and AlGaN/GaN heterostructures were grown on Si(1 1 1) substrates by plasma assisted molecular beam epitaxy (PA-MBE), whereas the Gd2O3 layer was grown by the pulsed laser ablation (PLA) technique. Initial structural characterizations show that Gd2O3 grown on III-nitride layers by PLA, exhibit a hexagonal structure with an epitaxial relationship as and . X-ray photoelectron measurements of the valence bands revealed that Gd2O3 exhibits band offsets of 0.97 eV and 0.4 eV, for GaN and Al0.3Ga0.7N, respectively. Electrical measurements such as capacitance–voltage and leakage current characteristics further confirm that epi-Gd2O3 on III-nitrides could be a potential candidate for future metal-oxide-semiconductor (MOS)-based transistors also for high power applications in radio frequency range.

Strategy of adjusting negative permittivity with invariant permeability property in metallic granular percolating composites

The electromagnetic properties including ac conductivity, reactance, permittivity, and permeability of percolating Fe/Epoxy composites are investigated at radio-frequency range. Percolating behavior is observed in the composites. Below percolation threshold, ac conductivity spectra follows the Jonscher’s power law indicating the weakened trend of hopping conductive behavior, while the skin effect is dominant above percolation threshold. Plasma-type negative permittivity is attributed to the low frequency plasmonic state explained by Drude model. The frequency region and value of negative permittivity are effectively adjusted by SiO2-coated iron particles’ controlling percolating network, while permeability property could be almost kept invariant. Invariant permeability property is attributed to suppressing current loops by SiO2 layers. This strategy with tunable permittivity and invariant permeability provides a method of suppressing the strong electromagnetic coupling effect in intrinsic metamaterials, and can facilitate applications of negative permittivity materials.

Multi-harmonic quantum dot optomechanics in fused LiNbO3–(Al)GaAs hybrids

We fabricated an acousto-optic semiconductor hybrid device for strong optomechanical coupling of individual quantum emitters and a surface acoustic wave. Our device comprises of a surface acoustic wave chip made from highly piezoelectric LiNbO3 and a GaAs-based semiconductor membrane with an embedded layer of quantum dots. Employing multi-harmonic transducers, we generated sound waves on LiNbO3 over a wide range of radio frequencies. We monitored their coupling to and propagation across the semiconductor membrane, both in the electrical and optical domain. We demonstrate the enhanced optomechanical tuning of the embedded quantum dots with increasing frequencies. This effect was verified by finite element modelling of our device geometry and attributed to an increased localization of the acoustic field within the semiconductor membrane. For moderately high acoustic frequencies, our simulations predict strong optomechanical coupling, making our hybrid device ideally suited for applications in semiconductor based quantum acoustics.

Heuristics for the optimized deployment of small cells in next-generation networks

Heterogeneous Networks (HetNets) have been introduced as an alternative means of improving the overall network capacity. However, HetNets increase the complexity and cost of transport due to the large number of smallcells (SCs) that have to be connected, and hence, it is essential to investigate the best way to plan the joint deployment of radio and transport resources. For this reason, some planning strategies have been put forward in the literature with the aim of reducing both the number of SCs and amount of transport. These systems are generally based on OFDM (Orthogonal Frequency Division Multiplexing) which uses a radio frequency range from 2 to 20 GHz. However, those papers do not evaluate path loss, which is a major component in the analysis or how to design the link budget of a telecommunication system. In this paper, we examine a heuristic for the joint planning of radio (i.e., SCs) and transport resources (i.e., point-to-point fiber links) by using suitable propagation models for next generation networks. Through the proposed heuristics, it is possible to save up to 12% of the total costs of the network deployment incurred by other systems found in the literature.

Pulsar science at the Sardinia Radio Telescope

AbstractThe Sardinia Radio Telescope (SRT) is a modern, fully-steerable 64-m dish located in San Basilio, Sardinia (Italy). It is characterized by an active surface that allows it to cover a wide range of radio frequencies (300 MHz to 100 GHz). During SRT’s commissioning phase, we installed the hardware and software needed for pulsar observations. Since then, SRT has taken part in Large European Array for Pulsars and European Pulsar Timing Array observations for the purpose of gravitational wave detection. We have installed a new S-band receiver that will allow us to search for pulsars in the Galactic Center. We also plan to combine our efforts to search for Extraterrestrial Intelligence (SETI) with the search for pulsars and Fast Radio Bursts.

Electrical Properties Tomography Based on $B_{{1}}$ Maps in MRI: Principles, Applications, and Challenges.

Electrical properties (EPs), including conductivity and permittivity, are closely related to many fundamental properties of tissue and its pathological conditions. Noninvasively measuring the in vivo EPs of tissue can have an important impact on biomedical research and clinical applications. Among approaches developed for EP quantification and imaging, electrical properties tomography (EPT) is a promising technology that reconstructs EPs based on the B1 field distribution that can be measured in the radiofrequency range using an MRI device. In this article, we review the basic principle of EPT, reconstruction methods, biomedical applications including tumor imaging, and existing challenges. As an important application of EPT, the estimation of specific absorption rate (SAR) and its current development are discussed.

Cancellation of interference for emission measurement in open area test site

This paper proposes a technique for implementing the concept of a virtual chamber for radiation emission measurements in time domain. At present measurements for electromagnetic emissions are carried out either with FFT based analyzers or with a conventional-hybrid spectrum analyzer based on heterodyning where interested band of frequencies is swept in the radio frequency range in an anechoic chamber. This method requires a large measurement time especially for wide band frequency measurements; therefore such methods cannot guarantee reliable results in open area. The difficulty lies in the interference cancellation from random sources for prolonged measurement duration.In this paper time domain measurement technique for electromagnetic emissions at open area test site has been proposed, designed, implemented and tested in a laboratory environment. The proposed technique captures multichannel signal from interference sources and equipment under test (EUT) simultaneously on different antenna ports. The continuous signal streams sampled at a very high rate before being fed to the stochastic gradient based adaptive filter. This materializes the cancelation of interference generated by various electronic sources using advanced digital processing techniques. The factors influencing the exactness in estimating interference are discussed in detail and cancelation of interference over the range of frequency (DC-1GHz) has been simulated. The simulation results exhibit how the proposed technique can revoke different kinds of interferences like continuous or transient, narrow or broad band. The performance evaluation of this method is verified through experiments conducted on real electronic appliances in open space environment and cross validated in an anechoic chamber up to 1GHz. The outcome of the research demonstrates the cancellation of both generated as well as naturally existing random interfering signals in an urban site polluted with electrical noise. The results substantiate the accuracy and usefulness of this new method for the measurement of radiation emissions and electromagnetic compatibility in accordance with CISPR standards. Pre-compliance electromagnetic compatibility testing is realized with this work without the need of an expensive anechoic chamber and with a reduced measurement time compared to the conventional measurement system.

Nanometric alternating magnetic field generator

In this work we introduce an alternating magnetic field generator in a cylindrical nanostructure. This field appears due to the rotation of a magnetic domain wall located at some position, generating a magnetic region that varies its direction of magnetization alternately, thus inducing an alternating magnetic flux in its vicinity. This phenomenon occurs due to the competition between a spin-polarized current and a magnetic field, which allows to control both the angular velocity and the pinning position of the domain wall. As proof of concept, we study the particular case of a diameter-modulated nanowire with a spin-polarized current along its axis and the demagnetizing field produced by its modulation. This inhomogeneous field allows one to control the angular velocity of the domain wall as a function of its position along the nanowire allowing frequencies in the GHz range to be achieved. This generator could be used in telecommunications for devices in the range of radiofrequencies or, following Faraday’s induction law, could also induce an electromotive force and be used as a movable alternate voltage source in future nanodevices.

Complex Permittivity and Permeability Spectra of Nickel/Polyphenylene Sulfide Composite in Radio Frequency Range

Due to the distinct electromagnetic properties, double negative materials have bright application prospect in many areas in the future. The nickel (Ni)/polyphenylene sulfide (PPS) composites were prepared by hot pressing Ni and PPS powders mixture. Microstructures, dielectric properties, and magnetic performances of the resulted composites were studied in detail. Once Ni contents exceeded the percolation threshold, the conductive networks would form and the conduction mechanism would change from hopping conduction to metal-like conduction. Due to the plasma oscillation of the free electrons within the conductive networks, negative permittivity appeared. Interestingly, circuit loops in the connected Ni particles induced by external electric field resulted in a diamagnetic phenomenon under high frequency for the composite with ferromagnetic Ni particles.

Electromagnetic shielding of polypyrrole–sawdust composites: polypyrrole globules and nanotubes

Economic and efficient materials for the shielding of electromagnetic interference are required by many applications. Electrically conducting composite materials based on wood sawdust modified by polypyrrole (PPy) with different morphology, globular and nanotubular, were prepared through in-situ polymerization of pyrrole with the use of iron (III) chloride as an oxidant. The effect of PPy morphology and content in composite with sawdust on the DC conductivity and shielding effectiveness (SE) were investigated. Composites of sawdust with globular PPy demonstrated higher DC conductivity as compared to those with PPy nanotubes as long as PPy content was less or equal to 18 vol.%. Above this concentration the opposite trend was observed. The SE of composites was evaluated theoretically in the radio-frequency range, and measured by waveguide method in the frequency range 5.85–8.2 GHz. The SE increased with increase in DC conductivity, and good agreement between the theoretically calculated SE and experimental results was achieved. The SE of the composites extended over 20 dB level above 18 vol.% PPy at the thickness of the order of 10 μm. Polypyrrole nanotubes perfomed better than globular PPy at high conducting polymer content. The composites are good candidates for the application as shielding materials in the microwave band.

Optimization of AZO films for integrating optically transparent antennas with photovoltaics

The importance of having an optimal material for fabricating Optically Transparent Antennas (OTAs) is crucial for designing highly efficient antennas that can be integrated with photovoltaics. Transparent Conductor Oxides are promising for OTA fabrication due to their capability of being simultaneously transparent at optical frequencies and conductive within the radio frequency (RF) range. Here in this study, thin aluminum and zinc oxide layers were co-sputtered onto Si and a polycrystalline photovoltaic cell and then annealed between 350 °C and 450 °C for 24 and 48 h in a N2 ambient. The annealing process ensured the formation of Aluminum Zinc Oxide (AZO) with low resistivity ≈10−5 Ω cm and a transparency of 86% between 350 and 750 nm. The material was tested by performing RF characterization and by fabricating and testing two different OTAs. The results of the optimization process and characterization show that the AZO material is feasible for OTA fabrication.