Frequency Modulation Parameters Research Articles

Field-free orientation of 7LiH steered by a few-cycle nonlinearly chirped pulse

We demonstrate theoretically that an efficient field-free molecular orientation of 7LiH molecule steered by a few-cycle nonlinearly chirped laser pulse with frequency in the terahertz regime can be achieved. The frequency modulation parameter β plays an important role in the molecular orientation, the maximum molecular orientation |〈cosθ〉|max is 0.848 and the orientation duration is 150 fs when β=7.25. In the range of electric-field peak intensity E0=[0.1,4.0] MV/cm, we can find the maximum orientation degree in both positive and negative directions. Compared to the scheme steered by a normal laser pulse, we can find that a more efficient molecular orientation and a smaller difference in population between the adjacent states can be realized by using the nonlinearly chirped laser pulse under the same near-single-period conditions. In addition, at the same temperature, a higher molecular orientation and a smaller decrease rate of orientation with temperature can be obtained by the nonlinearly chirped laser pulse.

Enhancing Quantum Temporal Steering via Frequency Modulation

Abstract Various strategies have been proposed to harness and protect space-like quantum correlations in different models under decoherence. However, little attention has been given to temporal-like correlations, such as quantum temporal steering (TS), in this context. In this work, we investigate TS in a frequency-modulated two-level system coupled to a zero-temperature reservoir in both the weak and strong coupling regimes. We analyze the impact of various frequency-modulated parameters on the behavior of TS and non-Markovian. The results demonstrate that appropriate frequency-modulated parameters can enhance the TS of the two-level system, regardless of whether the system is experiencing Markovian or non-Markovian dynamics. Furthermore, a suitable ratio between modulation strength and frequency (i.e., all zeroes of the 0th Bessel function J 0(δ/Ω)) can significantly enhance TS in the strong coupling regime. These findings indicate that efficient and effective manipulation of quantum TS can be achieved through a frequency-modulated approach.

Principle of signal-to-noise ratio direct measurement

The sensitivity of radio receivers and other systems used in all fields of practical applications of electronics is carried out at certain signal-to-noise ratio value. Examples of systems, for which this ratio is one of the important qualitative indicators, are given. The aim of the investigation is to solve the actual problem of signal-to-noise ratio measurement in a wide range of frequencies, simplify instruments and improve their technical and metrological parameters. A principle of signal-to-noise ratio measurement has been proposed, its theoretical foundation has been given. Precise relationship between the signal-to-noise ratio and the parameters of noise amplitude, phase and frequency modulation has been established, thus modulation meters can measure signal-to-noise ratio. There are three options for implementing the developed measurement principle. All of them use one existing industrial modulation meter and provide direct signal-to-noise ratio. For two options there are no restrictions on the origin and type of noise, it may be arbitrary. A pilot test of the measurement principle was conducted, and three implementation options were actually tested. Their discrepancies with the original data of the signal and noise generator lie within error limits of the instrumentation of the former. Mathematical modeling of the principle of signal-to-noise ratio measurement in Mathcad software package was also carried out. Recommendations on the use of the principle are given. The fundamental advantages of the developed principle consist of simple implementation by a single industrial instrument and solving the problem of metrological ensuring of signal-to-noise measuring instruments using the existing state verification plans. The main technical and metrological characteristics obtained by using the principle are determined by parameters of existing modulation meters and are proven to be high, the frequency range is till 26,5 GHz and the measurement error is as low as 8 %.

Estimation of LFM signal parameters using RD compressed sampling and the DFRFT dictionary

In this paper, a method combining random demodulator (RD) and discrete fractional Fourier transform (DFRFT) dictionary is suggested to directly estimate the parameters of linear frequency modulation (LFM) signals from compressed sampling data. First, the RD system parameters are modified in accordance with the characteristics of the LFM signal to produce effective compressed sampling data. Next, a DFRFT dictionary is built using the fractional Fourier transform theory, and sparse representation coefficients are obtained by reconstructing the compressed sampling data using the recovery algorithm and DFRFT dictionary. The signal exhibits characteristics that make it pulse under the best fractional transform order, so the problem of signal parameter estimation can be reduced to searching for the location of the maximum value of sparse representation coefficients. The location is determined by a parameter optimization algorithm, and from there, the initial frequency and Chirp rate of the LFM signal can be estimated. Lastly, simulation and real data tests are performed to confirm that the suggested method can directly be utilized to estimate the parameter of LFM signals using compressed sampling data in addition to having high sparse representation ability for LFM signals.

Adaptive Fast Chirplet Transform and Its Application Into Rolling Bearing Fault Diagnosis Under Time-Varying Speed Condition

Tacholess order tracking is a commonly-used technique for the fault diagnosis of bearing with time-varying speed, in which time-frequency analysis (TFA) is a key step for estimating the rotation frequency. The current TFA methods are either weak in energy concentration or have high computational complexity. To this end, an adaptive fast chirplet transform (AFCT) based on the adaptive optimal search angle band is proposed in this paper. The proposed method uses the modulation operator of synchrosqueezed transform to adaptively optimize the search band of the frequency modulation parameters, which overcomes the problem of low computational efficiency in chirplet transform (CT) and its variants. Moreover, a novel time-frequency energy concentration evaluation index mean-energy-to-peak-ration (MEPR) is proposed. The simulation result shows that the proposed method has both good time-frequency concentration performance and low computational complexity. Especially, its calculation speed is much faster than other TFA methods with high time-frequency resolution. The proposed method is successfully applied to estimate the rotation frequencies from the fault vibration signals from a test rig and a civil aircraft engine. The comparative results verify the comprehensive advantage of the proposed method in ridge extraction accuracy and computational efficiency compared to the existing classical TFA methods. With the proposed method, the fault features of rolling bearings under time-varying speed can be effectively extracted.

Research on Frequency Response Modeling and Frequency Modulation Parameters of the Power System Highly Penetrated by Wind Power

Renewable energy units led by wind power participate in diversified control primary frequency modulation, making the frequency response modes and the setting of frequency modulation parameters more complex. This paper proposes a frequency response model of the power system which is highly penetrated by wind power based on the two mainstream control strategies of wind power that participate in primary frequency modulation. The model considers the influence of wind capture devices, maximum power point tracking (MPPT), and other complex control strategies on system frequency response. Based on this model, the calculation formulas of the maximum change rate of dynamic frequency, the lowest point of dynamic frequency, and the maximum steady-state frequency deviation of the system after fault disturbance are derived in the frequency domain. The influences of wind power permeability and two typical frequency response control strategies on system frequency stability are analyzed. On the one hand, it is found that the proposed model can fit the system frequency response better than the traditional system frequency response model. Beyond that, two control strategies are mainly aimed at the different frequency stability requirements. On the other hand, under the condition of meeting the system’s stability requirements, the paper calculates the control parameters of frequency response of the doubly-fed induction generator (DFIG). The time-domain simulation model of the improved IEEE three-machine nine-node system and IEEE 39-node system with high permeability of wind power are built. Through the different fault scenarios, the simulation results verify the effectiveness of the proposed model and the accuracy of control strategy parameter calculation.

Tuned in to communication sounds: Neuronal sensitivity in the túngara frog midbrain to frequency modulated signals

For complex communication signals, it is often difficult to identify the information-bearing elements and their parameters necessary to elicit functional behavior. Consequently, it may be difficult to design stimuli that test how neurons contribute to communicative processing. For túngara frogs (Physalaemus pustulosus), however, previous behavioral testing with numerous stimuli showed that a particular frequency modulated (FM) transition in the male call is required to elicit phonotaxis and vocal responses. Modeled on such behavioral experiments, we used awake in vivo recordings of single units in the midbrain to determine if their excitation was biased to behaviorally important FM parameters. Comparisons of stimulus driven action potentials revealed greatest excitation to the behaviorally important FM transition: a downward FM sweep or step that crosses ~600 Hz. Previous studies using long-duration acoustic exposure found immediate early gene expression in many midbrain neurons to be most sensitive to similar FM. However, those data could not determine if FM coding was accomplished by the population and/or individual neurons. Our data suggest both coding schemes could operate, as 1) individual neurons are more sensitive to the behaviorally significant FM transition and 2) when single unit recordings are analytically combined across cells, the combined code can produce high stimulus discrimination (FM vs. noise driven excitation), approaching that found in behavioral discrimination of call vs. noise.

Suppression of Radiated Emissions from Inductive-Resonant Wireless Power Transfer Systems by Using Spread-Spectrum Technique

Inductive-resonant wireless power transfer systems are often used for wireless transfer of electric power. However, they are significant sources of radiated electromagnetic emissions. The effect of spread-spectrum approach based on classical switching frequency modulation of inductive-resonant wireless power transfer system inverter operating frequency and multi-frequency technique on the radiated emissions and efficiency is studied experimentally in detail. The influence of the classical frequency modulation and multi-frequency technique parameters on the peak radiated emission levels and the efficiency of the inductive-resonant wireless power transfer system are investigated more comprehensively. It is shown in the paper that the spread-spectrum approaches can lead to an appreciable radiated emissions reduction with small or large impact on the system’s efficiency. Some useful recommendations on how to choose parameters of the periodic switching frequency modulation or the multi-frequency technique considering a trade-off between the radiated emissions reduction and the efficiency are also proposed.

Characteristic Parameter Optimization of Wireless Flaw Sensing System Based on Active Interference Suppression Algorithm

Based on the active interference suppression algorithm, this study combines the radar working mode and the interference type and realizes the effective detection of the flaw detection signal by successively processing the radar receiving signal and the filtering processing. Firstly, this article builds a simulation platform similar to the actual situation to verify the existing conventional active interference suppression algorithms. Secondly, for the detection of chirp active deception jamming signals entering from the main lobe, a radar active deception jamming detection method based on the characteristic parameter matching of the harmonic components of active deception jamming signals is proposed. After that, the spectral characteristics of the harmonic components of the deception interference signal are analyzed, and the center frequency and the tuning frequency of the real target echo are obtained. Finally, by establishing a frequency modulation parameter library for possible interference harmonic signal components, the acquisition phase of the radar gate by the jammer matched analysis with the preestablished frequency modulation parameter library is implemented to achieve active deception interference detection. This method can effectively detect active deception jamming signals in a complex tunnel environment. The interference suppression algorithms verified by simulation include noise FM interference suppression algorithm based on cancellation and distance false target interference suppression algorithm based on LFM radar summary processing. Through actual measurement data processing and analysis, the effectiveness of the method is verified and the idea of interference suppression is expanded. The construction of the simulation platform is obtained by appropriately modifying the actual parameters, a certain type of suppression jammer, and a certain type of deception jammer used in a certain countermeasure field test at a radar station.

Non-Invasive Monitoring of the Technical Condition of Power Units Using the FAM-C and FDM-A Electrical Methods

This article presents the selected results of analytical and structural work conducted at the Air Force Institute of Technology (pl. ITWL) in the field of building a measuring apparatus for non-invasive monitoring of the technical condition of aircraft power units. Presented innovative FAM-C and FDM-A methods allow for observation of frequency modulation parameters as well as identification and diagnostic classification of particular mechanical subassemblies supplying the on-board generator and thus enable non-invasive monitoring of technical condition of the aircraft power unit and the aircraft propulsion system. The main purpose of this article is to present the measurement apparatus errors that occur in the signal conditioning system in the FAM-C and FDM-A methods. In spite of the fact that the measuring instrument was built on the basis of digital technology and that it uses typical solutions of electronic frequency measurement, due to the specificity of the applied diagnostic method there occur specific measuring errors which are presented in this article.

ANALYSIS OF THE VIBRATION STATE OF ROLLING BEARINGS WITH THE DEFECT "WEAR OF THE INNER BEARING CAGE"

In this paper, the issues that need to be taken into account when analyzing the vibration state of rolling bearings with the defect "wear of the inner bearing cage" are touched upon. A design diagram of rolling bearings and a diagram of the forces acting on the bearings during their operation in a screw compressor are presented. Studies of the vibration state of rolling bearings on an operating screw compressor at a real industrial facility have been carried out. Vibration measurements were carried out when the compressor was operating with new bearings and with workers on whom there was obvious wear of the inner cage. The effect of wear of the inner bearing cage on the vibration state of the screw compressor is shown. It is established that for this type of bearing defect, in relation to the object un-der study, when analyzing the vibration state, the use of direct autospectral parameters is ineffective. For the case under consideration, the most effec-tive are the parameters of amplitude and frequency modulation.

Autodyne Sensor Signals with Amplitude-Frequency Modulation of Radiation.

A mathematical model of an autodyne oscillator with a combined amplitude-frequency modulation, which is under the influence of its own radiation reflected from the target, is developed. The main relations are obtained for analyzing the autodyne response of a single-circuit oscillator depending on the delay time of the radiation reflected from the target with an arbitrary law of simultaneous amplitude and frequency modulation. The characteristics of the amplitude selection of signals, as well as their temporal and spectral characteristics, are calculated for harmonic amplitude-frequency modulation. The features of signal formation are established for various values of the amplitude and frequency modulation parameters and the feedback parameter of the “oscillator—target” autoparametric system. The results of experimental studies, performed on a Tigel-0.8M hybrid-integrated Ka-band oscillator module with a Gann mesa-planar diode, confirmed the findings of the theoretical analysis.

Cyber-Enabled Intelligence Control and Security Optimization for Complex Microgrid Networks Transient Frequency Stability Analysis of Power Systems considering Photovoltaic Grid Connection

In view of the photovoltaic grid-connected power system, the transient frequency stability of the system is analyzed in this paper. First, the photovoltaic grid-connected power system was modeled and analyzed. On this basis, the maximum frequency deviation is used as the index to determine the interval in which the system accommodates the maximum photovoltaic capacity, and the influence of frequency stability of the high-permeability photovoltaic high disturbance system is studied. Second, the evaluation and prediction methods of frequency dynamic characteristics of photovoltaic access nodes based on surface fitting are proposed, and the critical values of high penetration photovoltaic access for different grid points are given. Finally, an improvement measure based on the optimization of the frequency modulation parameters of large-capacity units is proposed, and the effectiveness of the proposed method in improving the transient frequency stability of the system after photovoltaic access is verified by the IEEE 39-standard system.

Adaptive data-driven nonlinear synchro squeezed transform with single class radial basis function kernel support vector machine applied to wind turbine planetary gearbox fault diagnostics

Planetary stage gears operated at low rotational speed and varying wind speed result variation in load. Variable speed and variable load induce nonstationary operating conditions. Vibration signal measured from Wind power gear transmission systems are embedded with multiple sources of vibration and attenuated considerably as it travels from source of vibration to measuring point. Efficacious multi-component decomposition without mode mixing ensures the accurate fault signature recognition. Synchro squeezing transform is the promising tool that represents the ridges with high resolution in time as well as in frequency axis. An efficient vibration analysis technique, short windowed Fourier synchro squeezing transform with nonlinear radial basis function kernel support vector machine is proposed to detect the mechanical faults in low speed planetary stage of wind turbines. Raw vibration is modeled in time–frequency plane to extract fault pattern signatures effectively with high resolution by adapting an empirical nonlinear tool synchro squeezing transforms. Amplitude modulation and frequency modulation parameters are sculpted from instantaneous amplitude and instantaneous phase, frequency. Hybrid feature space with signal attributes, statistical moments, and randomness measures are extricated from amplitude modulation-frequency modulation components. Single class radial basis function support vector machine is trained with hybrid features. The fault detection accuracy of the proposed method is compared with the standard variants of empirical mode decomposition. The proposed short windowed Fourier synchro squeezing transform-radial basis function kernel support vector machine shows 98.2% accuracy, 98% sensitivity, and 98% specificity.

Radar-Assisted UAV Detection and Identification Based on 5G in the Internet of Things

Unmanned aerial vehicles (UAVs) have broad application potential for the Internet of Things (IoT) due to their small size, low cost, and flexible control. At present, the main positioning method for UAVs is the use of GPS. However, GPS positioning may be affected by stronger electromagnetic signals from spoofing attacks. In this study, a radar-assisted positioning method based on 5G millimeter waves is proposed. In 5G end-to-end network slices, the rotors of UAVs can be detected and identified by deploying 5G millimeter wave radar. High-resolution range profile (HRRP) is used to obtain the UAV location in the detection zone. Micro-Doppler characteristics are used to identify the UAVs and the cepstrum method is used to extract the number and speed information of the UAV rotor. The sinusoidal frequency modulation (SFM) parameter optimization method is used to separate multiple UAVs. The proposed method provides information on the number of UAVs, the position of the UAV, the number of rotors, and the rotation speed of each rotor. The simulation results show that the proposed radar detection method is well suited for UAV detection and identification and provides a valid GPS-independent method for UAV tracking.

Passive harmonic mode-locking in an erbium-doped fibre laser

We report an all-fibre erbium laser operating in the regime of passive harmonic mode-locking based on the effect of nonlinear polarisation rotation. The generation of the 67th harmonic with a pulse repetition rate of 5.62 GHz and a duration of 1.8 ps is demonstrated. It is shown that as the harmonic number increases, both the frequency modulation parameters and the pulse duration change.

Spin-dressed relaxation and frequency shifts from field imperfections

Critical dressing, the simultaneous dressing of two spin species to the same effective Larmor frequency, is a technique that can, in principle, improve the sensitivity to small frequency shifts. The benefits of spin dressing and thus critical dressing are achieved at the expense of generating a large (relative to the holding field $B_{0}$,) homogeneous oscillating field. Due to inevitable imperfections of the fields generated, the benefits of spin dressing may be lost from the additional relaxation and noise generated by the dressing field imperfections. In this analysis the subject of relaxation and frequency shifts are approached with simulations and theory. Analytical predictions are made from a new quasi-quantum model that includes gradients in the holding field $B_{0}=\omega _{0}/\gamma $ and dressing field $B_{1}=\omega _{1}/\gamma $ where $B_{1}$ is oscillating at frequency $\omega $. The results are compared with a Monte Carlo simulation coupled with a 5$^{\text{th}}$ order Runge-Kutta integrator. Comparisons of the two methods are presented as well as a set of optimized parameters that produce stable critical dressing at a range for oscillating frequencies $\omega ,$ as well as pulsed frequency modulation parameters for maximum sensitivity.

Laser Frequency Analysis Aided by Electronic Frequency Dividers

Conventional laser spectral analysis relies on direct measurement of power spectral density (PSD), which is not able to distinguish certain types of phase and frequency modulations without ambiguity. In this paper, we propose and demonstrate a modified scheme aimed at improving the specificity in laser frequency analysis. Our method is based on PSD measurement of the downshifted laser spectrum in the radio-frequency range but introduces an electronic frequency divider (EFD) prior to the spectrum analyzer. By monitoring the spectral changes caused by the EFD, we show, both theoretically and experimentally, that common scenarios of phase and frequency modulations, such as wideband frequency modulation (FM) and broadband phase modulation, can be differentiated without ambiguity. Moreover, the new method allows for quantitative assessment of wideband FM parameters such as modulation frequency, modulation index, and frequency deviation, which is not possible with any conventional spectral analysis methods. This technique may find potential applications in laser frequency metrology, microwave photonics, optical sensing, and radar/lidar technologies.

Parameter Estimation of Hybrid Linear Frequency Modulation-Sinusoidal Frequency Modulation Signal

In this letter, a novel method which employs the Radon transform (RT) and inverse Radon transform is proposed to estimate the parameters of the hybrid linear frequency modulation (LFM)-sinusoidal frequency modulation (SFM) signal. By adding a parameter called width, we extend the original RT to a three-parameter transform, which we named as extended Radon transform (ERT). Compared with the original RT, the ERT has shown more capacities, such as estimating the parameters of a strip in a plane. As the time–frequency representations (TFRs) of the hybrid LFM-SFM signal is a strip where there is a sinusoidal pattern embedded, the parameters of the signal are related to the strip; herein, we employ the ERT to estimate several parameters of the signal. With the estimated parameters values, the signal can be dechirped to be a SFM signal, whose parameters can be estimated by some existing methods. As it is based on the TFRs, the proposed method has strong robustness under low signal-to-noise ratios. Numerical results and analysis are provided to demonstrate the effectiveness of the proposed method.

Spatial mapping of correlation profile in Brillouin optical correlation domain analysis

We report an approach to spatially map the correlation profile along the sensing fiber in Brillouin optical correlation domain analysis by pulsing the pump radiation. Simulations are carried out to demonstrate the influence of frequency modulation parameters of a narrow linewidth source on the width of the correlation profile and its peak position. The simulation results are validated through controlled experiments. The correlation profile is mapped over 1 km long fiber with spatial resolution of 1 m, limited only by the finite lifetime of acoustic phonons in the silica fiber.