Time-domain Waveform Research Articles

Concurrent performance and security enhancement of ultrahigh-order DSM signals via null subcarriers.

In this paper, we propose leveraging null subcarriers in discrete multi-tone modulation (DMT) to process the DMT signal in both time and frequency domains. Additionally, we employ discrete memory enhanced chaos (DMEC) to scramble the signal in the frequency domain, thereby achieving physical layer signal encryption while ensuring a more uniform power distribution in the time-domain waveform. In our experimental demonstration, we achieved high-security transmission of a DSM-based 65536-QAM signal at a data rate of 16.01 Gb/s over a 25 km single-mode fiber (SMF) in an intensity-modulation direct-detection (IMDD) system. Additionally, in the transmission experiments for 13684-QAM and 65536-QAM signals, the proposed method demonstrated a receiver sensitivity gain of over 0.5 dB compared to the traditional DSM-based ultrahigh-order transmission.

Firing patterns and fast–slow dynamics in an N-type LAM-based FitzHugh–Nagumo circuit

The diversity of firing patterns and their bifurcation mechanisms of a neuron circuit are crucial for exploiting bionic applications. This paper constructs an N-type locally active memristor (LAM)-based FitzHugh–Nagumo (FHN) circuit by replacing the tunnel-diode in the original FHN circuit. Numerical simulations and hardware measurements reveal that the N-type LAM-based FHN circuit can reproduce rich neuromorphic firing patterns of quasi-periodic/periodic bursting behaviors and chaotic/periodic spiking behaviors. The bursting and spiking behaviors are triggered by a low-frequency stimulus and a high-frequency one, respectively. Besides, the fold and Hopf bifurcation sets are depicted. Then, the bifurcation mechanisms for the quasi-periodic and periodic bursting behaviors via Hopf/Hopf and Hopf/fold bifurcations are theoretically deduced by time-domain waveform and equilibrium trajectory. The numerical results and hardware experiments exhibit the effectiveness of the proposed memristive FHN circuit in reproducing abundant firing patterns of bursting and spiking behaviors.

Spinning waveforms from the Kosower-Maybee-O’Connell formalism at leading order

We provide the analytic waveform in time domain for the scattering of two Kerr black holes at leading order in the post-Minkowskian (weak field, but generic velocity) expansion and up to fourth order in both spins. The result is obtained by the generalization of the Kosower-Maybee-O’Connell formalism to radiative observables, combined with the analytic continuation of the five-point scattering amplitude to complex kinematics. We use analyticity arguments to express the waveform directly in terms of the three-point coupling of the graviton to the spinning particles and the gravitational Compton amplitudes, completely bypassing the need to compute and integrate the five-point amplitude. In particular, this allows us to easily include higher-order spin contributions for any spinning compact body. Finally, in the spinless case, we find a new compact and gauge-invariant representation of the Kovacs-Thorne waveform. Published by the American Physical Society 2024

Diagnostics on Power Electronics Converters by Means of Autoregressive Modelling

Power conversion systems for wireless power transfer (WPT) applications have demanding requirements for continuity of service, besides being operated with stressing environmental conditions. Diagnostic and prognostic programs are thus quite useful and this work shows a novel approach based on the analysis of spectra of an autoregressive (AR) model to recognize a wide range of faulty devices, including incipient faults, when deviations from nominal parameters begin to manifest. AR modeling provides cleaner and easier to interpret spectra, where only the salient features remain, and they are more sensitive to variations in the corresponding time domain waveforms. A log spectral distance is calculated that successfully separates healthy and faulty states of the feeding single-phase inverter, even in challenging scenarios of poor signal-to-noise ratio.

Clipping Noise in Visible Light Communication Systems with OFDM and PAPR Reduction

This paper presents an analytical study of signal clipping that leads to the noise/distortion in the waveform of DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM)-based visible light communication (VLC) systems. The pilot-assisted (PA) technique is used to reduce the high peak-to-average power ratio (PAPR) of the time-domain waveform of the DCO-OFDM system. The bit error rate (BER) performance of the PA DCO-OFDM system is investigated analytically at three different clipping levels as well as without any clipping. The analytical BER performance is verified through simulation and then compared to that of the conventional DCO-OFDM without PAPR reduction at the selected clipping levels. The PA DCO-OFDM system shows improved BER performance at all three clipping levels.

Phase-resolved measurement and control of ultrafast dynamics in terahertz electronic oscillators

As a key component for next-generation wireless communications (6 G and beyond), terahertz (THz) electronic oscillators are being actively developed. Precise and dynamic phase control of ultrafast THz waveforms is essential for high-speed beam steering and high-capacity data transmission. However, measurement and control of such ultrafast dynamic process is beyond the scope of electronics due to the limited bandwidth of the electronic equipment. Here we surpass this limit by applying photonic technology. Using a femtosecond laser, we generate offset-free THz pulses to phase-lock the electronic oscillators based on resonant tunneling diode. This enables us to perform phase-resolved measurement of the emitted THz electric field waveform in time-domain with sub-cycle time resolution. Ultrafast dynamic response such as anti-phase locking behaviour is observed, which is distinct from in-phase stimulated emission observed in laser oscillators. We also show that the dynamics follows the universal synchronization theory for limit cycle oscillators. This provides a basic guideline for dynamic phase control of THz electronic oscillators, enabling many key performance indicators to be achieved in the new era of 6 G and beyond.

Generation and autocorrelation traces investigation of Nyquist pulse sequences

We propose a novel approach for generating Nyquist pulse sequences using a dual parallel Mach-Zehnder modulator (DPMZM) and a phase modulator (PM). The generated Nyquist pulse sequence achieves a repetition frequency of 10 GHz and a full width at half maximum (FWHM) of 4.22 ps. The time-domain waveforms of these sequences are retrieved using the phase and intensity from cross-correlation and spectrum only (PICASO) method. Further investigation into the autocorrelation traces reveals a pulse width conversion factor of approximately 0.75 between the Nyquist pulse sequences and their autocorrelation traces. Our work offers an alternative approach to generating and measuring Nyquist pulse sequences.

A novel method for stress measurement utilizing the Rayleigh wave virtual superimposed interference spectrum

This study presents a novel stress measurement method utilizing the Rayleigh waves virtual superimposed interference spectrum (RW-VSIS). This method achieves stress measurements by exploiting the effect of stress on the superimposed interference spectrum of two beams of Rayleigh waves. Firstly, the effect of stress on Rayleigh wave velocity is theoretically investigated by partial wave theory and matrix solving algorithm. The theoretical results show that the Rayleigh wave propagation direction versus the stress direction will affect the wave velocity and the time of flight (TOF). Then, a theoretical model of RW-VSIS under pre-stress is derived. It's found that the stress will dominate the first characteristic frequency (FCF). The regulation effects of propagation distance and angle on FCF are discussed. Finally, the feasibility of stress measurement based on the FCF is validated through experiments. The impact of stress on TOF and FCF is comparatively analyzed. The results show a significant improvement of stress measurement by FCF in the superimposed interference spectrum, compared to the TOF in time domain waveform. With a calibration and verification test for the unknow coefficient of an aluminum specimen, the experimental examination of the stress shows a maximum error of less than 4 MPa indicating good measurement accuracy.

A Time-Domain Doppler Estimation and Waveform Recovery Approach with Iterative and Ensemble Techniques for Bi-Phase Code in Radar Systems

This paper presents a novel, cost-effective technique for estimating the Doppler effect in the time domain using a single pulse and subsequently leveraging the precise Doppler value to recover the radar waveform. The proposed system offers several key advantages over existing techniques, including the ability to calculate the target speed without any frequency ambiguity and the ability to detect a wide range of target speeds. These two features are not available in any existing techniques, including the conventional moving target detection (MTD) processor. To ensure improved accuracy and robust estimation, the system employs ensemble and iterative techniques by recursively and efficiently reducing the Doppler residues from the signal. Furthermore, the proposed system demonstrates effective signal recovery of a well-known bi-phase code shape at low signal-to-noise ratios in just a few iterations. The performance evaluation of the new algorithm demonstrates its practicability and its superiority over traditional radar systems. Implementation on software-defined radio (SDR) reveals that the proposed system excels in Doppler estimation and signal recovery at low SNRs, demonstrating promising results.

Numerical and experimental investigation on the whirling vibration characteristic of ship propulsion shafting under multi-source uncertainty

Conventional numerical models struggle to accurately capture the whirling vibration characteristics of ship propulsion shafting due to the influence of multi-source uncertainties and gyroscopic effects. Hence, this study develops nonparametric modelling to incorporate multi-source uncertainties into the dynamic equations for shafting. Based on random matrix theory, these uncertainties are represented by random matrices for mass, damping, gyroscopic moment, and stiffness. The whirling frequency under different uncertainties is analysed, revealing that stiffness significantly influences on whirling frequency, followed by mass. Conversely, the gyroscopic moment has the most negligible impact. The range of the first four-order whirling frequencies is estimated accurately using confidence intervals. Additionally, the bearing vibration response is calculated by considering gravity, unbalanced force, and misalignment force. The findings suggest that the time-domain waveform fluctuates within a defined range when considering uncertainty, and unbalance and misalignment are exacerbated, leading to poor stability. Finally, a vibration signal acquisition experiment and modal testing are conducted using a test bench. The experimental results further confirm the effectiveness of nonparametric modelling that considers multi-source uncertainties and gyroscopic effects as more accurate.

Processing and analysis of friction vibration signal of diamond-like carbon film microtextured dry gas seal rings

PurposeThis paper aims to analyze the characteristics of friction vibration signals and identify the vibration excitation source at the start and stop stage of microtextured end face of dry gas seals.Design/methodology/approachThe friction pair consists of a diamond-like carbon (DLC) film microtextured seal ring and a spiral groove seal ring. Friction vibration signal feature extraction method based on harmonic wavelet packet and spectrum analysis was proposed. Signals were collected using acceleration sensor, acquisition card and LabVIEW software. Vibration acceleration signal was decomposed into 32 frequency bands using MATLAB wavelet packet transformation. The 32nd band coefficient was extracted for reconstruction, time-domain and spectral waveforms were obtained and spectra before/after denoising were compared.FindingsThe end face of the DLC film microtextured seal ring generates a good dynamic pressure effect, and the friction and vibration reduction effects are obvious. The harmonic wavelet packet can decompose the vibration signal conveniently and precisely. In the case of this experiment, the frequency of vibration of the seal ring is 7500 HZ.Originality/valueThe results show that the method is effective for the processing of friction vibration signal and the identification of vibration excitation source. The findings will provide ideas for the frictional vibration signal processing and basis for further research in the field of tribology of dry gas seal ring.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0084/

Analysis of a new three-dimensional jerk chaotic system with transient chaos and its adaptive backstepping synchronous control

A new three-dimensional Jerk chaotic system with line equilibrium points is proposed. The system is researched in detail by the Lyapunov exponent graph, bifurcation diagram, phase diagram, and time domain waveform diagram, which show that the system has rich dynamical behaviors, such as eight types of coexisting attractors, extreme multistability of four different attractor states, and offset boosting in two directions. In addition, the system also has six types of transient chaos, which greatly increase the complexity of the system. We study the variation of the spectral entropy (SE) and C0 complexity when the system takes different initial values. Also, in this paper, the initial conditions under which the system is in a synchronized state are determined by initial values with higher complexity. The correctness of the theoretical analysis and numerical simulation is verified by circuit simulation and hardware experiments. Finally, the new system achieves synchronization control utilizing a designed adaptive backstepping controller, laying the foundation for its subsequent use in secure communications.

Study on magnetostrictive properties of oriented silicon steel sheet under different working conditions

Accurate measurement of magnetostriction is the basis for calculating the vibration of silicon steel laminated core. In this paper, a laser magnetostriction measurement system (MST500) is used to study the magnetostriction characteristics of silicon steel under sinusoidal, third harmonic, and DC bias magnetization. The magnetostrictive butterfly curves, time domain waveforms, and spectrum diagrams of silicon steel sheets under different excitations are compared and analyzed. The effects of different operating conditions on the magnetostrictive properties of silicon steel sheets were studied and analyzed, mainly including amplitude and spectrum analysis. Finally, the magnetostrictive peak to peak curves under different operating conditions were extracted, providing a data basis for the core vibration of power equipment.

A vibration model of a flexible multiple shaft gear system with the tip relief modification

The fixed-shaft gear system (FSGS) is one critical part in gear transmission systems (GTSs), whose vibrations can significantly influence performances of GTSs. To reduce the vibrations of rigid FSGS caused by installation and manufacture errors, the tooth profile modifications without the shaft deformation were widely introduced. This paper establishes a flexible multiple shaft gear system (FMSGS) model of an unmanned underwater vehicle, which can obtain vibrations of rotor at different axial positions. However, the previous rigid FSGS model cannot obtain those vibrations. In the FMSGS model, the Timoshenko beam elements are applied to the establishment of shaft segments considering flexibility. The meshing stiffness for helical gears with different ranges of tooth profile modification are quantitatively expressed by a gear slicing method. Based on the kinetic relationship between the gear pairs, shaft segment, and bearings, the dynamic equations of FMSGS are derived. By comparing the time-domain waveforms and spectra of FMSGS, the effects of the tooth profile modification amounts and lengths on the vibrations of FMSGS are revealed. The proposed FMSGS model is validated by an experiment. This study extends the dynamic methods of FSGSs, and some suggestions on the vibration control of FSGSs are given.

Research on Leakage Current Waveform Spectrum Characteristics of Artificial Pollution Composite Insulator

In order to know about the change features of leakage current during the pollution flashover process of composite insulators, the study of the pollution flashover test on composite insulator under the pollutional condition is presented in the artificial fog cabinet. The characteristics of leakage current waveforms in time-domain and frequency-domain are measured and analyzed during the test. The analysis results show that there is a strong correlation among the fundamental harmonic, the third harmonic and fifth harmonic. The characteristics of leakage current spectrum are represented by the maximum value of leakage current (Im), total harmonic distortion (THD), and phase difference of fundamental leakage current (θ). During a near-flash event, the leakage current exhibits high amplitude, low harmonic content, and small phase difference between the fundamental leakage current and voltage. The research findings provide a basis for establishing a pollution flash warning system based on leakage current characteristic quantities.

Research on axial nonlinear vibration characteristics of ball screw feed system considering segmented restoring force

Taking the ball screw feed system as the research object, the two degree of freedom axial dynamic model of the system is constructed firstly. Based on Hertz contact theory, when the ball screw pair adopts variable lead self-preloading to eliminate the assembly clearance between the ball and raceway, considering the nonlinear segmented axial elastic recovery force generated by the uneven contact deformation between the ball and raceway under the action of external excitation force, further derive the nonlinear dynamic equation group of the system. Next, the fourth-order Runge-Kutta method was used to numerically solve the equation system, obtaining the system’s two and three-dimensional phase diagrams, Poincaré sections, time-domain waveform diagrams, frequency spectra, and bifurcation diagrams. Then, the effects of damping constant, initial contact angle between ball and raceway in ball screw pairs, and number of balls on the system’s response characteristics were analyzed, and the influence of external excitation forces on system stability was further studied. Finally, it was verified through experiments that the axial vibration of the system is indeed nonlinear vibration, providing a theoretical basis for the study of the dynamic characteristics of the ball screw feed system.

Generation and analysis of the chaos phenomenon in the molecular-distillation-Navier–Stokes (MDNS) nonlinear system

Introduction: For the Navier-Stokes equation, one of the most essential tasks should be to study its completeness of the complex nonlinear systems. Also, its nature and physical practical applications would be depth explored. Moreover, as one of the routes to chaos, this equation with an external force has been investigated numerically in 1989. Recently, some information is worth noting that when the high symmetry was imposed on the velocity field, the complex nonlinear motions should occur even lead to the chaos phenomenon. However, most of the published papers are based on theoretical studies and rarely deal with the above results, which lost of the match between them and the integrity of the scientific system.Methods: This study analyzed the molecular distillation process in detail based on the basic theory of nonlinear chaotic systems. Then, the mathematical model for the process of molecular distillation with one brushless DC motor (BLDCM) is built and named the Molecular-Distillation-Navier-Stokes (MDNS) equation. Also, its complex and potentially chaotic behaviors and chaotic processes are first discovered and demonstrated, such as chaotic attractors, chaotic co-attractors, phase portraits, time-domain waveforms, Lyapunov exponent spectrums, Poincare maps, the bifurcation diagrams, and so on.Results: The good agreement among theoretical analysis, simulation and experimental results verifies the practicability and flexibility of the configured model.Discussion: The related conclusions have supplemented and improved the theoretical system for the Navier Stokes equations. Also, it reflects the significance in molecular distillation processes. Meanwhile, the novel research direction for the fields of the chaotic nonlinear and complex industrial systems have been explored and discovered.

Enhancing Demodulation Performance of DCM Algorithm in φ-OTDR System Through Temporal Spline Interpolation

For expanding the amplitude-frequency response range of the differential cross-phase multiply (DCM) algorithm in the φ-OTDR system, a temporal spline interpolation (TSI) method is proposed to pre-process Rayleigh backscattering (RBS) signals. Through the TSI method, the discrete temporal signals characterizing RBS traces are subjected to interpolation, facilitating a reduction in differential approximation errors. This, in turn, establishes a heightened level of precision in phase demodulation, especially relevant across extensive sensing distances. By comparing the recovered time-domain waveforms and the corresponding power spectral densities without and with the TSI, the above improvement effect has been experimentally validated by utilizing the TSI. The results show that, with the TSI, the amplitude-frequency response range of the DCM algorithm is enlarged by 2.78 times, and the new relationship among fpulse, f, and D under the root mean square error (RMSE) tolerance less than 0.1 can be expressed as 1.9(D+1)f ≤ fpulse. This contribution underscores a substantial advancement in the capabilities of the DCM algorithm, holding promise for refined performance in optical fiber sensing applications.

Temporal light modulation: A phantom array visibility measure

At temporal light modulation (TLM) frequencies between 80 Hz and 20 000 Hz observers may perceive a series of repeated images called the phantom array effect (PAE) when they move their eyes in large saccades across a modulating light source or across a scene lit by the modulating light source. To date, there is no well-established measure for quantifying PAE visibility, but there is growing awareness of the need for one among design professionals and sensitive populations. This paper documents a new measure, the phantom array visibility measure (PAVM), which is based on the results of recent human factors experiments. The measure follows the mathematical underpinning used by the flicker visibility measure and the stroboscopic visibility measure, where the time-domain TLM waveform is converted into its Fourier frequency components; each component is evaluated through a threshold curve of modulation depth, then summed through an equation employing a Minkowski exponent. This scales the PAVM so that a value of 1 indicates a waveform at a threshold visibility in the conditions of the underlying experiment.

Nonlinear vibration characteristics of an aeroengine cantilever flexible rotor considering interference fit and unbalance

Aeroengine power turbine rotor is a typical nonlinear rotor system, in which the interference connection between long shaft and short shaft has a prominent influence on the coupling vibration of the system, especially at high speed, the nonlinear stiffness change of interference contact is more obvious. Therefore, the paper considers the change of the contact characteristics of the long shaft and the short shaft of the turbine rotor, and the nonlinear restoring force of the bearing to analyze the dynamic characteristics of the rotor. Firstly, according to the theory of elasticity, the contact parameters under different speed states are calculated, the contact stiffness model under interference fit is established, and the relationship between contact stiffness and speed is analyzed. Secondly, according to the Hertz contact theory, a bearing nonlinear restoring force model considering time-varying characteristics is established. Finally, the dynamic model of the bearing-flexible rotor coupling considering interference contact is established. The influence of contact parameters and unbalance parameters on the nonlinear vibration characteristics of the rotor is analyzed by amplitude-frequency curve, bifurcation diagram, time-domain waveform, spectrum diagram, trajectory diagram and Poincaré diagram. In addition, the simulation results are compared with the experiment results of the rotor test rig to verify the accuracy of the established dynamic model. By analyzing the influence of different parameters such as interference magnitude, unbalance position, unbalance magnitude and unbalance couple on the nonlinear vibration of the rotor, the basis for the design and vibration control of the cantilever turbine rotor is provided.