Broad Frequency Spectrum Research Articles

Space Charge Wave with Broad Frequency Spectrum Formation in Transit Section of Klystron-type Two-stream FEL with Helical Electron Beam

Space Charge Wave with Broad Frequency Spectrum Formation in Transit Section of Klystron-type Two-stream FEL with Helical Electron Beam

High Performance Reversible Direct Data Synthesizer for Radio Frequency Applications

Design of Reversible logic gate enabled Reconfigurable Direct digital synthesizer is evaluated here. The need for Direct Digital Synthesizers (DDS) inherently finds application in the area of radio frequency communication. DDS is a method of producing an analog waveform—usually a sine wave—by generating a time-varying signal in digital form and then performing a digital-to-analog conversion. The proposed design presents an important analysis based on Reversible logic gates for the application of DDS which is a powerful device employed to produce standard signal sweeps from lowest frequency to highest frequency. The sweeps of DDS frequency depends on the configurable frequency words produced by high speed Field Programmable Gate Array (FPGA) platforms. Because operations within DDS devices are primarily digital, it can offer fast switching between output frequencies, fine frequency resolution, and operation over a broad spectrum of frequencies. With advances in design and process technology, today’s DDS devices are very compact and draw little power. Here the proposed system focuses on development of DDS through Artificial Intelligence (AI) with Field Programmable Gate Array (FPGA) devices. The primary need for FPGA and AI combination provides the replacement of analog Phase Locked Loop (PLL) in traditional DDS circuits. The fully digital architecture enable the system able to configure the digital PLL developed inside the FPGA core. Low noise and Low power factor is being achieved through low power techniques utilized in the architecture development part. The proposed system increase the sweep frequency resolution, Reverse fluctuations through leakage voltage etc.

Prospects for the Detection of Electronic Preturbulence in Graphene

Based on extensive numerical simulations, accounting for electrostatic interactions and dissipative electron-phonon scattering, we propose experimentally realizable geometries capable of sustaining electronic preturbulence in graphene samples. In particular, preturbulence is predicted to occur at experimentally attainable values of the Reynolds number between 10 and 50, over a broad spectrum of frequencies between 10 and 100GHz.

Ultrafast response of spray-on nanocomposite piezoresistive sensors to broadband ultrasound

We present a nano-engineered thin-film-type piezoresistive sensor, coatable or sprayable on a medium surface for in-situ acquisition of broadband ultrasound up to 1.4 MHz – a trait of nanocomposite-based piezoresistive sensing devices that has until now not been discovered and explored. With polyvinylidene fluoride as the matrix, fabrication of the spray-on sensor is attempted in a comparative manner, with multiscale nanofillers ranging from zero-dimensional carbon black, through one-dimensional multiwalled carbon nanotubes, to two-dimensional graphene nanoparticles. With a morphologically optimal nano-architecture, the quantum tunneling effect can be triggered in the percolating nanofiller network when ultrasound signals traverse the sensor, inducing dynamic alteration in the piezoresistivity manifested by the sensor. In-situ morphological analysis and experiment reveal high fidelity, ultrafast responses, and high sensitivity of the sensor to dynamic disturbance, from static strain to ultrasound in a regime of megahertz yet with an ultralow magnitude (of the order of microstrain or nanostrain). These findings are remarkable as no other investigation has probed the response of nanocomposite piezoresistive sensors over such a broad frequency spectrum.

A Compact Reconfigurable Multi-mode Resonator-based Multi-band Band Pass Filter for Intelligent Transportation Systems Applications

A compact wide band reconfigurable bandpass filter (BPF) which utilises a hemi-circular flower shaped multimode resonator (MMR) is presented. The proposed MMR provides three resonant modes which fall within the broad frequency spectra. Among these, two modes are even and one is odd. These modes are optimised by varying the dimensions so as to obtain the desired frequency response. The fractional bandwidth is more than 96 per cent. The filter can be operated as multi-band BPF. In OFF condition of ‘Pin’ diode, the centre frequencies are 2.43 GHz, 3.5 GHz, and 5.9 GHz in ON condition of ‘Pin’ diode centre frequencies are 2.43 GHz, 3.5 GHz, 5.9 GHz, 6.5 GHz, and 8.8 GHz which are used for vehicular, WiMAX, intelligent transportation systems and satellite communication respectively. Microstrip filter structures are integrated with ‘Pin’ diodes. Appropriate biasing has been provided by choosing lumped components with precise values. The insertion loss in OFF condition are 0.5 dB, 0.67 dB, and 0.8 dB and in ON condition 0.5 dB, 0.7 dB, 1.2 dB, and 1.9 dB. The measured results agree well with the full-wave simulated results.

Hybrid simulation approaches for induction machine calculation

PurposeInduction machines for traction applications are operated at working points of high ferromagnetic saturation. Depending on the working point, a broad spectrum of harmonic frequencies appears in the magnetic flux density of induction machines. Detailed loss analysis therefore requires local and temporal highly resolved nonlinear field computation. This loss analysis can be performed in the post processing of nonlinear transient finite element simulations of the magnetic circuit. However, it takes a large number of transient simulation time steps to build up the rotor flux of the machine.Design/methodology/approachIn this paper, hybrid simulation approaches that couple static FEA, transient FEA and analytic formulations to significantly decrease the number of simulation time steps to calculate the magnetic field in steady state are discussed, analyzed and compared.FindingsThe proposed hybrid simulation approaches drastically decrease the simulation time by shortening the transient build-up of the rotor flux. Depending on the maximum error of the rotor flux linkage amplitude compared to the steady state value, a reduction of simulation time steps in the range of 55.5 to 98 per cent is found.Originality/valueThe presented hybrid simulation approaches allow efficient performing of the transient FE magnetic field simulations of induction machines operated as traction drives.

Pressure and stress tensor of complex anharmonic crystals within the stochastic self-consistent harmonic approximation

The self-consisted harmonic approximation (SCHA) allows the computation of free energy of anharmonic crystals considering both quantum and thermal fluctuations. Recently, a stochastic implementation of the SCHA has been developed, tailored for applications that use total energy and forces computed from first principles. In this work, we extend the applicability of the stochastic SCHA to complex crystals with many degrees of freedom, with the optimisation of both the lattice vectors and the atomic positions. To this goal, we provide an expression for the evaluation of the pressure and stress tensor within the stochastic SCHA formalism. Moreover, we develop a more robust free energy minimisation algorithm, which allows us to perform the SCHA variational minimisation very efficiently in systems having a broad spectrum of phonon frequencies and many degrees of freedom. We test and illustrate the new approach with an application to the phase XI of water ice using density-functional theory. We find that the SCHA reproduces extremely well the experimental thermal expansion of ice in the whole temperature range between 0 K and 270 K, in contrast with the results obtained within the quasi-harmonic approximation, that underestimates the effect by about 25 %.

MULTIPLE THREE-WAWE RESONANCES IN TWO-STREAM FREE-ELECTRON LASER WITH A HELICAL ELECTRON BEAM

Background. A powerful terahertz radiation sources creation is one of the perspective tendencies in relativistic plasma electronics. Nowadays there are few devices able to create powerful radiation in millimeter-infrared waveband (even in the part of this band). Therefore, theoretical research of novel powerful terahertz radiation sources, that are also characterized by broad frequency spectrum, is an actual problem.Objective. The aim of the paper is a study of the influence of multiple three-wave resonant interactions in the klystron type two-stream superheterodyne free-electron laser (TSFEL) with helical electron beam on the forming effectiveness of the powerful waves with broad frequency spectrum.Methods. In order to theoretically analyze multiple resonances of wave harmonics, as initial, we use quasihydrodynamic equation, the continuity equation and Maxwell’s equations. We apply the hierarchic approach to the theory of oscillations and waves to the equations of motion and continuity, Maxwell’s equations are solved by means of the slowly varying amplitudemethod. As a result, we derive a system of differential equations for complex amplitudes of SCW electric field strength harmonics which we analyze by standard methods.Results. It was shown that in the two-stream superheterodyne FELs, utilizing the two-stream instability in helical electron beams as an additional electromagnetic wave amplification mechanism, the powerful multiharmonic space charge wavewith broad frequency spectrum forms due to multiple resonant interactions. The spectrum width of such wave is larger compared to the spectrum width in TSFELs utilizing straight electron beams. It is also found out that amplification rates in such TSFELs are higher.Conclusions. An application of helical electron beams in multiharmonic TSFELs using multiple resonant interactions leads to the improvement of their amplification characteristics, frequency spectrum widening in multiharmonic signal generation mode, and to overall geometric dimensions decreasing compared to TSFELs utilizing straight beams.Keywords: two-stream superheterodyne free-electron laser; two-stream instability; helical electron beams; three-wave resonances.

In-vivo Measurements of Tissue Impeditivity by Electrical Impedance Spectroscopy.

The electrical properties of biological tissues differ depending on their structural characteristics. In literature, a lot of study have been carried out with the intent of taking advantage of bioimpedance analysis. Unfortunately, many apparatuses used during these evaluations were not always designed for measurements on living tissues. As a consequence, data could be affected by electrode polarization. In 2016, we presented a new impedance meter, developed for measurements on living tissues. Initially, it was tested only on ex-vivo rabbit's tissues with promising results. As a continuation, this device has been tested on in-vivo samples by placing a needle-probe into 3 tissues (liver, spleen, ovary) of 2 female dogs. Furthermore, was evaluated also the bioimpedance signal of the ovary explanted, comparing it with the in-vivo data. Bioimpedance was analyzed in terms of modulus and phase along a broad spectrum of frequencies (10Hz - 10kHz).Data obtained confirm the possibility of discriminating among the 3 tested tissues, at high frequencies for modulus and at low for phase. Confirmation that values on in-vivo and exvivo tissues are comparable if detected within few minutes after the explant, is also reported. We conclude that this clinical evaluation confirmed, also in-vivo, the good performance of the device previously tested on ex-vivo tissues, and provide more information about the tissue properties and characteristics.

Investigating the V2V Millimeter-Wave Channel Near a Vehicular Headlight in an Engine Bay

In this letter, the first public millimeter-wave channel measurements near a vehicular headlight in an engine bay are presented, providing detailed information about the typical excess loss and root-mean-square delay spread that are experienced in this exemplary vehicle-to-vehicle communication channel, providing at least 140° field of view. The measurements cover a broad frequency spectrum, ranging from bands considered for future general wireless access to those that are specifically considered for automotive radar applications. The results show that, unless blocked by the vehicle’s coachwork, typical excess loss is at least 10 dB, typically 20 dB, and a maximum delay spread of 4 ns is observed. Through the provision of these new real-world measurements, this letter contributes further to the community by accelerating the development of high-fidelity channel models.

Towards simulating natural transition in hypersonic boundary layers via random inflow disturbances

A random forcing approach was implemented into a high-order accurate finite-difference code in order to investigate ‘natural’ laminar–turbulent transition in hypersonic boundary layers. In hypersonic transition wind-tunnel experiments, transition is caused ‘naturally’, by free-stream disturbances even when so-called quiet tunnels are employed such as the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University. The nature and composition of the free-stream disturbance environment in high-speed transition experiments is difficult to assess and therefore largely unknown. Consequently, in the direct numerical simulations (DNS) presented here, the free-stream disturbance environment is simply modelled by random pressure (acoustic) disturbances with a broad spectrum of frequencies and a wide range of azimuthal wavenumbers. Results of a high-resolution DNS for a flared cone at Mach 6, using the random forcing approach, are presented and compared to a fundamental breakdown simulation using a ‘controlled’ disturbance input (with a specified frequency and azimuthal wavenumber). The DNS results with random forcing clearly exhibit the ‘primary’ and ‘secondary’ streak pattern, which has previously been observed in our ‘controlled’ breakdown simulations and the experiments in the BAM6QT. In particular, the spanwise spacing of the ‘primary’ streaks for the random forcing case is identical to the spacing obtained from the ‘controlled’ fundamental breakdown simulation. A comparison of the wall pressure disturbance signals between the random forcing DNS and experimental data shows remarkable agreement. The random forcing approach seems to be a promising strategy to investigate nonlinear breakdown in hypersonic boundary layers without introducing any bias towards a distinct nonlinear breakdown mechanism and/or the selection of specific frequencies or wavenumbers that is required in the ‘controlled’ breakdown simulations.

Optimized design of adaptable vibrations suppressors in semi-active control of circular plate vibrations

Due to flexibility of thin plates, high amplitude vibrations are observed when they are subjected to severe dynamic loads. Due to the extensive application of circular plates in industry, attenuating the undesired vibrations is of foremost importance. In this paper, adaptable vibration suppressors (AVSs) as a semi-active control approach, are utilized to suppress the vibrations in a free circular plate; under the concentrative harmonic excitation. Using mode summation method, mathematical model of the hybrid system, including the plate and an arbitrary number of vibration suppressors is analyzed. By developing a complex multiple-loops algorithm, optimum values for the AVSs’ parameters (stiffness and position) are achieved such that the plate deflection is comprehensively minimized. According to the results, AVSs act efficiently in suppressing the vibrations in resonance/non-resonance conditions. It is also observed that optimum AVSs reduce the plate deflection over a broad spectrum of excitation frequencies. Finally, since the algorithm is developed in a general user friendly style, AVSs’ design can be extended to other shapes of plates with various boundary conditions and excitations.

Coherence Volume of an Optical Wave Field with Broad Frequency and Angular Spectra

We consider the sizes of a region in a three-dimensional space in which an optical wave field excites mutually coherent perturbations. We discuss the conditions under which the length of this region along the direction of propagation of the wave field and, correspondingly, its volume are determined either by the width of the frequency spectrum of the field or by the width of its angular spectrum, or by the parameters of these spectra simultaneously. We obtain expressions for estimating extremely small values of the coherence volume of the fields with a broad frequency spectrum and an extremely broad angular spectrum. Using the notion of instantaneous speckle-modulation of the wave field, we give a physical interpretation to the occurrence of a limited coherence volume of the field. The length of the spatiotemporal coherence region in which mutually coherent perturbations occur at different times is determined. The coherence volume of a wave field that illuminates an object in high-resolution microscopy with frequency broadband light is considered. The conditions for the dominant influence of the angular or frequency spectra on the longitudinal length of the coherence region are given, and the conditions for the influence of the frequency spectrum width on the transverse coherence of the wave field are examined. We show that, when using fields with broad and ultrabroad spectra in high-resolution microscopy, this influence should be taken into account.

Novel optimization parameters of power quality disturbances using novel bio-inspired algorithms: A comparative approach

Abstract Automatic classification of Power Quality Disturbances (PQDs) is a challenging concern for both the utility and industry. In this paper, a novel technique for automatic classification of single and hybrid PQDs is proposed. The proposed algorithm consists of the Discrete Wavelet Transform (DWT) and Probabilistic Neural Network based BAT (PNN-BAT) optimal feature selection of PQDs. DWT with Multi-Resolution Analysis (MRA) is used for the feature extraction of the disturbances. The power quality disturbances are in the form of signals like voltage sag, voltage swell, voltage transients, flicker, voltage imbalance, and harmonics. Such disturbance signals cover a broad frequency spectrum because of its high sampling rate and produce megabytes of data which leads to the requirement of high storage space. In this paper, discrete wavelet transform is used to analyze the power quality disturbance signals and to reduce the storage space required. The PNN classifier is used as an effective classifier for the classification of the PQDs. However, the two critical concerns such as the selection of the optimal features and the spread constant value might affect the performance of the classifier. Hence, these two issues are addressed using a novel technique PNN-BAT based optimal feature selection and parameter optimization for improving the performance of the classification system. The BAT algorithm is used to select optimal features from a large feature set and the optimal value of the PNN spread constantly. The optimal feature selection method retains the useful features and discards the redundant features.

Influence of two-stream relativistic electron beam parameters on the space-charge wave with broad frequency spectrum formation

We developed a cubic non-linear theory describing the dynamics of the multiharmonic space-charge wave (SCW), with harmonics frequencies smaller than the two-stream instability critical frequency, with different relativistic electron beam (REB) parameters. The self-consistent differential equation system for multiharmonic SCW harmonic amplitudes was elaborated in a cubic non-linear approximation. This system considers plural three-wave parametric resonant interactions between wave harmonics and the two-stream instability effect. Different REB parameters such as the input angle with respect to focusing magnetic field, the average relativistic factor value, difference of partial relativistic factors, and plasma frequency of partial beams were investigated regarding their influence on the frequency spectrum width and multiharmonic SCW saturation levels. We suggested ways in which the multiharmonic SCW frequency spectrum widths could be increased in order to use them in multiharmonic two-stream superheterodyne free-electron lasers, with the main purpose of forming a powerful multiharmonic electromagnetic wave.

Fully-digital transmitter architectures and circuits for the next generation of wireless communications

The rapidly evolving trend for increased data rates in today’s and future cellular communication systems poses extreme difficulties for developers of cellular transceivers. A multitude of standards ranging from legacy 2G to the upcoming, yet to be defined, 5G needs to be supported across a broad but fragmented frequency spectrum. Higher data throughput necessitates higher bandwidths, increased number of aggregated carriers, and more complex of modulation schemes. Capable transmitters must exhibit highest in-band performance, e.g. linearity and error vector magnitude. Simultaneously, out-of-band performance, like noise and spurious emissions, is crucial to co-exist with other wireless channels, such as the transceiver’s receivers and other participants. While a “more of everything” is expected, competitive solutions for the wireless market require a constant decrease in silicon area, bill of materials, and especially power consumption. This paper presents the evolution of integrated transmitter architectures facing the above challenges: From conventional analog direct conversion transmitters to fully-digital direct modulation RF transmitters, challenges and benefits are highlighted, presenting modern architectures that benefit from the most advanced technology nodes while supporting upcoming 5G cellular wireless communications.

Diverse dynamical characteristics across the frequency spectrum of wind speed fluctuations

Wind speed oscillations are known to exhibit varying characteristics at different time scales. Our recent analysis has shown that a collection of autoregressive models fitted separately on the frequency components of wind speed data can significantly increase the prediction accuracy. In this paper, we report the results of the investigation of dynamical behaviour across a broad frequency spectrum of wind speed measurements. The results show the existence of diverse characteristics such as stochastic, deterministic and chaotic behaviour apart from the variation of the dimensionality of underlying dynamics as well as the degree of fluctuations. It is also demonstrated that a cluster of deterministic models built upon separate frequency components of a wind speed time series can enhance the prediction accuracy by as much as 80%, on the average, consistently for predictions up to 12 h. The comparison shows the definite advantage of deterministic prediction models over autoregressive models. The f-index introduced in this paper to measure the fluctuations of wind speed over a period indicates that the observed seasonal variations of prediction errors can be correlated with changes in the f-index of the component series contributed mostly by the lower scales of decomposition.

Flexible graphene sound device based on laser reduced graphene

Existing thermoacoustic devices are based on a complicated fabrication process, which extremely limits their practical applications. In this paper, we realize a flexible graphene sound device based on laser reduced graphene. The graphene oxide is converted into graphene by a 450 nm laser with a one-step process. The performance of the graphene sound device is affected by the laser power, the scanning speed, and the substrate thickness. The experimental results match well with the theoretical results. Besides, the sound device has the advantages of excellent flexibility, broad frequency spectrum (0–40 kHz), fast fabrication process, and low cost, which will become a promising alternative in the flexible electronic systems in the future.

A Modified Plane Wave Model for Fast and Accurate Characterization of Layered Media

The accuracy and computational speed of ground penetrating radar (GPR) largely rely on the inverse model implemented. In most cases, both accuracy and processing speed cannot be achieved together because of the inherent limitation of modeling GPR signal in complex media. Full wave models (FWMs) are most promising approaches to characterize multilayered media. However, they are inefficient due to the requirement of significant time for integration over singularity. In this paper, a modified plane wave model (MPWM) is proposed to achieve accuracy and better computational speed. The model is derived based on the analytical solution of an FWM. It is versatile for finding response due to multilayered media. The rigorous analysis has shown the similarity between the proposed model and FWMs with cross-correlation value close to unity across a broad frequency spectrum and large ranges of media parameters. Model inversion is achieved by a novel layer stripping technique followed by a gradient-based method. Testing of layered media in laboratory environment demonstrates that the proposed MPWM has significant advantage over FWMs.

Decoupling Frequencies, Amplitudes and Phases in Nonlinear Optics

In linear optics, light fields do not mutually interact in a medium. However, they do mix when their field strength becomes comparable to electron binding energies in the so-called nonlinear optical regime. Such high fields are typically achieved with ultra-short laser pulses containing very broad frequency spectra where their amplitudes and phases are mutually coupled in a convolution process. Here, we describe a regime of nonlinear interactions without mixing of different frequencies. We demonstrate both in theory and experiment how frequency domain nonlinear optics overcomes the shortcomings arising from the convolution in conventional time domain interactions. We generate light fields with previously inaccessible properties by avoiding these uncontrolled couplings. Consequently, arbitrary phase functions are transferred linearly to other frequencies while preserving the general shape of the input spectrum. As a powerful application, we introduce deep UV phase control at 207 nm by using a conventional NIR pulse shaper.