Sideband Frequency Research Articles

Localization of a Breathing Delamination Using Nonlinear Lamb Wave Mixing

Abstract A guided wave-based method for localization of breathing delamination is presented in this investigation. The proposed technique utilizes one-way mixing of a dual-frequency fundamental antisymmetric Lamb modes with judiciously selected central frequencies. The dual-frequency interrogation signal, upon interacting with a breathing delamination, leads to additional frequency sidebands in the frequency response spectrum, strength of which is quantified in terms of the combination tone index. The numerical predictions of these sidebands are validated using an in-house experimentation. It is further exposited that the combination tone index depends strongly on the extent of the temporal overlap that the two constituent wave envelopes have as they propagate through the breathing delamination. Accordingly, for a synchronous passage (with 100% temporal overlap), the combination tone index is maximum while it reduces with the decreasing temporal overlap. By utilizing the dispersive nature of the chosen Lamb mode, a relation is then developed correlating the temporal separation of the wave envelopes at the location of the actuator, the group speeds, and the distance between the actuator and the delamination. Based on these inferences, a technique for localizing a breathing delamination is proposed, which involves interrogating the component by systematically altering the temporal overlap in the input waveform and monitoring the combination tone index for its maxima. The efficacy of the localization technique (close to 90%) is demonstrated through an illustrative case analyzed numerically as well as experimentally.

General Multi-Frequency Small-Signal Model for Resonant Converters

AbstractResonant converters are periodic time-varying system, one of whose distinctive features is the sideband effect. To be specific, when a small-signal perturbation is injected into the converter, a series of sideband frequency components will occur. The two sideband frequency components around the switching frequency determine the small-signal response of the resonant tank if it has sufficient band-pass filtering. Using complex Fourier series, the relationship between different frequency components can be described with a series of gains. This paper derives all the necessary transfer functions between different frequencies for resonant converters. Combining them together forms a general small-signal model of resonant converters. There are multiple frequency components, i.e., the perturbation frequency and two sideband frequencies in this model, hence the name multi-frequency model. Two kinds of inverters, i.e., the full-bridge and half-bridge structure, and three modulation methods, i.e., the switching frequency control, the duty-cycle control, and the input voltage control are considered in this paper. The experimental results verify the validity of the proposed model.

Simulating acoustic waves in acoustic black hole analogues

We present a physical model and a numerical method to simulate nonlinear acoustic waves emitted from moving boundaries in a moving background flow field with transition from subsonic to supersonic flow speeds. The physical model is based on a convective form of the Westervelt equation and accounts for the motion of the background medium and the progressive distortion of a finite amplitude acoustic wave. A suitable coordinate transformation in physical space allows us to accommodate the motion of the wave emitting boundary, while solving the governing equation in a fixed computational domain using standard finite difference techniques. We present the case of an oscillating spherical wave emitting boundary with an induced spherical flow as a prototypical example of an acoustic black hole analogue, where the acoustic waves cannot escape from the horizon of sonic flow speed during the contraction phase. It is demonstrated that the accelerating motion of the wave emitting boundary gives rise to frequency sidebands and amplitude modulations of the acoustic wave. The influence of the background flow speed on this nonlinear Doppler effect is investigated with the present methodology, thus contributing to an improved understanding of the acoustic wave behavior in the proximity of a sonic horizon.

Comparison of Eccentricity Impact on Electromagnetic Forces in Internal- and External-Rotor Permanent Magnet Synchronous Motors

The influence of static eccentricity (SE) and dynamic eccentricity (DE) on the electromagnetic forces in internal- and external-rotor permanent magnet synchronous motors (PMSMs) is investigated in this article. First, the analytical model of the electromagnetic force is derived. By introducing the eccentricity coefficient, the influence of eccentricity on the electromagnetic force is then analyzed. The results show that SE changes the spatial component of the electromagnetic force in internal-rotor motors, while the frequency remains unchanged. While for the external-rotor motors, both the spatial order and frequency of electromagnetic force are affected by SE. Contrary to SE, DE introduces additional spatial components and sideband frequency harmonics to the electromagnetic force of internal-rotor motors. For external-rotor motors, only the spatial order is changed. In addition, axial-flux PMSMs suffer from the extra unbalanced bending moment (UBM), which is a unique feature that differs from traditional radial-flux PMSMs. The expression of UBM caused by eccentricity is further derived. Finally, the theoretical analysis is validated by the simulation and test results, respectively. This study will benefit the researchers and designers in terms of source identification and reduction of acoustic noise in PMSMs.

Impact of Random Grain Structure on Spin-Hall Nano-Oscillator Modal Stability

Spin-Hall nano-oscillators are a promising class of microwave spintronic devices with potential applications in RF/microwave communication and neuromorphic computing. The nano-constriction spin-Hall nano-oscillators (NC-SHNO) have relatively high power, narrow linewidth, and low drive current. Several synchronization schemes e.g. arrays of spin-wave coupled oscillators have been proposed for more stable operation and higher output power. For such arrays, it is crucial to have good oscillator stability and small device-to-device variability. Here, a micromagnetic simulation technique is proposed that includes realistic material properties and hence enables variability and modal stability to be investigated. It is demonstrated, using both measurements and simulation, that the presence of physical grains in the free magnetic layer can induce multiple oscillation modes or frequency sidebands. Our investigation could help in the development of more stable NC-SHNOs that would enable oscillator arrays with stronger synchronization.

Photonics-Assisted Frequency Conversion and Self-Interference Cancellation for In-Band Full-Duplex Communication

A photonics-assisted frequency conversion and self-interference cancellation approach is proposed and experimentally demonstrated for in-band full-duplex (IBFD) communication. Carrier suppressed single sidebands (CS-SSB) of the intermediate frequency (IF) signal and the local oscillator (LO) signal are simultaneously obtained through the X-DPMZM in a dual-polarization dual-parallel Mach-Zehnder (DP-DPMZM) modulator. A transmit signal with high purity is produced, and a shared LO optical sideband is also provided for the subsequent downconversion. The carrier suppressed double sideband (CS-DSB) modulation for the signal of interest (SOI) is achieved via the Y-DPMZM. The self-interference signal is suppressed by adjusting the bias voltage of its main MZM. An optical bandpass filter (OBPF) is combined to realize frequency downconversion. The experimental results show that the spurious-free dynamic range (SFDR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) is 102.6 dB/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> for frequency upconversion, a cancellation depth of more than 50 dB for single-frequency self-interference cancellation (SIC), and more than 22 dB for wideband SIC. The proposed link has superiority in multifunctionality, including in-band transmission, reception, and self-interference cancellation, with a shared LO.

Adaptive Scheme for Detecting Induction Motor Incipient Broken Bar Faults at Various Load and Inertia Conditions.

This paper introduces a novel online adaptive protection scheme to detect and diagnose broken bar faults (BBFs) in induction motors during steady-state conditions based on an analytical approach. The proposed scheme can detect precisely adjacent and non-adjacent BBFs in their incipient phases under different inertia, variable loading conditions, and noisy environments. The main idea of the proposed scheme is monitoring the variation in the phase angle of the main sideband frequency components by applying Fast Fourier Transform to only one phase of the stator current. The scheme does not need any predetermined settings but only one of the stator current signals during the commissioning phase. The threshold value is calculated adaptively to discriminate between healthy and faulty cases. Besides, an index is proposed to designate the fault severity. The performance of this scheme is verified using two simulated motors with different designs by applying the finite element method in addition to a real experimental dataset. The results show that the proposed scheme can effectively detect half, one, two, or three broken bars in adjacent/non-adjacent versions and also estimate their severity under different operating conditions and in a noisy environment, with accuracy reaching 100% independently from motor parameters.

Forced response vibration analysis of induction motor stators induced by electromagnetic forces

There is an increasing demand for efficient electric motors in various industrial fields, such as electric vehicles. When developing electric motors, it is inevitable to consider electromagnetic noise and vibration generated by electric motors. Electric motors in general consists of a stator and a rotor that generates torque as a resultant of distributed electromagnetic force generated between the rotor and the stator. Since this force is oscillatory and noisy, it causes structural vibration of the stators. In this paper, forced response vibration analysis of induction motors under operating conditions is presented. The finite element methods are applied for the electromagnetic and structural dynamics analyses. The results are compared with measurements. It is revealed that the vibration response contains frequency components that are related to the mechanical rotational frequency and the side-band frequencies of the carrier frequency.

Modeling Techniques and Stability Analysis Tools for Grid-Connected Converters

Large-scale integration of renewable generation interfaced to the network through power electronic converters has led to drastic changes in power system dynamics. In islanded microgrids or weak grids, different control concepts for the synchronization of converters have been proposed to provide virtual inertia and improve their resilience against transient events, ensuring safe operation without heavy redundant design. The complexity of these power-related control algorithms and their interaction with the inner control loops causes problems in frequency components above the range of traditional studies which calls on modeling techniques with a wider bandwidth. This work aims to provide an outline of modeling methods for grid-connected converter dynamics from subsynchronous to switching sideband frequency range and relevant analyzing tools. The major contributions of this work are: 1. Theoretical foundations and the derivation processes are discussed for each of the modeling methods within the time domain, frequency domain and harmonic domain. 2. Similarities and differences between these methods are highlighted and recommendations are given regarding different grid situations. 3. A case study with an active front end converter is shown and the analysis results are validated by simulation and Hardware-in-the-Loop (HiL) test, illustrating the effectiveness of these methods.

Photonic Filter-Free Scheme for D-Band mm-Wave Signal Generation with Frequency 12-Tupling Only via One Integrated In-Phase and Quadrature Modulator

In this work, we have proposed a new scheme of generating continuously tunable and filter-less D-band millimeter-wave (mm-wave) signal with frequency 12-tupling only via one integrated in-phase and quadrature (I/Q) modulator. The two sub-MZMs in the I/Q modulator, biased at peak point, are applied to eliminate odd order optical tones. By controlling the phase and amplitude of RF driving signals, I/Q modulator bias point, and the optical phase shifter embed in the lower arm of I/Q modulator, a frequency 12-tupling signal can be obtained through the beat frequency in the photodetector. Employing 10 GHz RF drive signal, 120 GHz millimeter wave signal can be realized by detailed mathematical formula derivation and simulation, and optical sideband suppression ratio (OSSR) can reach 37.65 dB and radio frequency sideband suppression ratio (RFSSR) can reach 32.08 dB.

A using remodulation filterless scheme of generating frequency 32-tupling millimeter-wave based on two DPMZMs

In this paper, we introduce a filterless system for generating frequency 32-tupling millimeter waves (mm waves) by using two dual-parallel MZMs (DPMZM). A 5 GHz RF signal is used to modulate DPMZM-1. After the first beat, a 20 GHz signal for remodulating DPMZM-2 is generated. Unnecessary sidebands are suppressed by the following methods in the structure of DPMZM-2. Firstly, the ±(4n-2)th-order optical sidebands are suppressed by controlling the phase difference between two Mach-Zehnder modulators (MZMs). Then, the 0th-order sideband is offset by adjusting the value of optical attenuator (OA) and optical phase shifter (OPS). Finally, the 1st and 7th-order optical sidebands nearly disappear by adjusting the modulation index of DPMZM-2 is 3.94. Remaining sidebands enter the photodetector beat frequency to obtain frequency 32-tupling mm waves. Simulation results show that its optical sideband suppression ratio (OSSR) is 27.7 dB and radio frequency sideband suppression ratio (RFSSR) is 27.96 dB, which is consistent with the theory. Using 5 GHz RF signal to drive the DPMZM-1, 160 GHz mm-wave signal was obtained. Furthermore, analyzes the effects of modulation index, optical power and attenuator value on the system performance, optimize the system performance to the best state.

A New and Simple Frequency Quadrupling Millimeter-Wave Signal Generation Enabled by a Single Mach-Zehnder Modulator Without Optical Filter

In this work, we have designed and proposed a new optical method to realize the generating of frequency quadrupling millimeter-wave (mm-wave) only employing one Mach-Zehnder modulator (MZM), and no any optical filter is needed. Compared with the previously reported quadruple frequency scheme, this work greatly simplifies the structure of the system, and makes the performance better and the cost lower. In the scheme, the MZM is operated at peak bias point, which is applied to retain the even order optical sidebands and wipe off the odd order optical harmonics. By tuning-up the optical shifter and optical attenuator (OATT) to control the zeroth order optical carrier returns zero, only ±2nd order optical tones are generated. We demonstrated and discussed the presented scheme feasibility based on the detailed mathematical formula derivation and numerical simulation, the simulation results of which show that employing a sinusoidal radio frequency (RF) source with frequency at 10 GHz to drive a push-pull MZM, a 40 GHz millimeter-wave (mm-wave) signal can be obtained. In the work, the performance of the generated quadrupling signal is that the optical sideband suppression ratio (OSSR) is 34.8 dB and the radio frequency sideband suppression ratio (RFSSR) can reach 27.2 dB.

Squeezed light at 2128 nm for future gravitational-wave observatories

All gravitational-wave observatories (GWOs) have been using the laser wavelength of 1064 nm. Ultra-stable laser devices are at the sites of GEO 600, Kagra, LIGO, and Virgo. Since 2019, not only GEO 600, but also LIGO and Virgo have been using separate devices for squeezing the uncertainty of the light, so-called squeeze lasers. The sensitivities of future GWOs will strongly gain from reducing the thermal noise of the suspended mirrors, which involves shifting the wavelength into the 2 µm region. This Letter aims to reuse the existing high-performance lasers at 1064 nm. Here we report the realization of a squeeze laser at 2128 nm that uses pump light at 1064 nm. We achieve the direct observation of 7.2 dB of squeezing as the first step at megahertz sideband frequencies. The squeeze factor achieved is mainly limited by the photodiode's quantum efficiency, which we estimated to (92±3)%. Reaching larger squeeze factors seems feasible also in the required audio and sub-audio sideband, provided photo diodes with sufficiently low dark noise will be available. Our result promotes 2128 nm as the new, to the best of our knowledge, cost-efficient wavelength of GWOs.

Sensitivity to Envelope Interaural Time Differences: Modeling Auditory Modulation Filtering.

For amplitude-modulated sound, the envelope interaural time difference (ITDENV) is a potential cue for sound-source location. ITDENV is encoded in the lateral superior olive (LSO) of the auditory brainstem, by excitatory-inhibitory (EI) neurons receiving ipsilateral excitation and contralateral inhibition. Between human listeners, sensitivity to ITDENV varies considerably, but ultimately decreases with increasing stimulus carrier frequency, and decreases more strongly with increasing modulation rate. Mechanisms underlying the variation in behavioral sensitivity remain unclear. Here, with increasing carrier frequency (4-10kHz), as we phenomenologically model the associated decrease in ITDENV sensitivity using arbitrarily fewer neurons consistent across populations, we computationally model the variable sensitivity across human listeners and modulation rates (32-800Hz) as the decreasing range of membrane frequency responses in LSO neurons. Transposed tones stimulate a bilateral auditory-periphery model, driving model EI neurons where electrical membrane impedance filters the frequency content of inputs driven by amplitude-modulated sound, evoking modulation filtering. Calculated from Fisher information in spike-rate functions of ITDENV, for model EI neuronal populations distinctly reflecting the LSO range in membrane frequency responses, just-noticeable differences in ITDENV collectively reproduce the largest variation in ITDENV sensitivity across human listeners. These slow to fast model populations each generally match the best human ITDENV sensitivity at a progressively higher modulation rate, by membrane-filtering and spike-generation properties producing realistically less than Poisson variance. Non-resonant model EI neurons are also sensitive to interaural intensity differences. With peripheral filters centered between carrier frequency and modulation sideband, fast resonant model EI neurons extend ITDENV sensitivity above 500-Hz modulation.

A filterless frequency 32-tupling photonic scheme to generate Sub-Terahertz wave signal enabled by optical polarization modulators

A scheme based on polarization modulators to generate Sub-Terahertz (Sub-THz) wave signal with frequency 32-tupling is proposed. The system consists of two subsystems in cascade, and each subsystem consists of 4 paralleled polarization modulators. In this scheme, by properly controlling two subsystems, an optical signal with optical carrier and ±16th-order optical sidebands is achieved. Next, by adjusting the optical attenuator and optical phase shifter, the optical carrier can be canceled. Finally, the Sub-THz wave with frequency 32-tupling can be obtained after beaten in the photodetector. The results show the ±16th-order optical sideband suppression ratio is 53.38 dB and the radio frequency sideband suppression ratio of the 32-tupling Sub-THz wave is 42 dB, which are consistent with the theoretical analysis very well. Meanwhile, the effects of phase offset, modulation index, and attenuator deviation on suppression ratio are analyzed.

Large Tunable 16-Tupled Millimeter Wave Generation Utilizing Optical Carrier Suppression With a Tunable Sideband Suppression Ratio

Coping up with the rising bandwidth demands for 5G ultra-high speed applications, utilizing millimeter (MM) wave spectrum for data transmission over the radio over a fiber-based system is the ideal approach. In this study, a highly conversant and spectrally pure photonic generation of a 16-tupled MM wave signal using a series-connected DD-MZM with a lower modulation index, a splitting ratio, and a wider tunable range is presented. A 160-GHz MM wave is generated through a double sideband optical carrier suppression technique having an optical sideband suppression ratio (OSSR) of 69 dB and a radio frequency sideband suppression ratio (RSSR) of 40 dB. However, the OSSR and the RSSR are tunable with values greater than 15 dB when the modulation index (M.I.) varies from 2.778 to 2.873, ±8° phase drift, and a 15-dB enhancement in the OSSR with a wider nonideal parameter variation range giving acceptable performance can be seen in the model as compared with previous research works.

Coherent structures in a compressible turbulent plane jet

Coherent structures represented by proper orthogonal decomposition (POD) modes from large-eddy simulation of a compressible plane jet are analyzed. The leading POD modes of the fluctuating velocity components u′, v′, and w′, and the pressure fluctuation p′ are considered. Spatial and temporal features of these modes are analyzed by the modes and the spectra of the temporal coefficients, respectively. Interactions between leading modes of u′, v′, and w′ and the relationship between the modes of u′, v′, and w′ and of the p′ are discussed. The results show that the leading mode of u′ is in the shape of longitudinal stripes, and the mode is dominated by the jet column frequency Stc. For spanwise fluctuation w′, the leading modes are a pair of modes in the shape of a train of ridges along streamwise, and they are dominated by the fundamental frequency St0. The leading modes for v′ are a pair of modes in a row of ribs. For the dominant frequencies of the v′ modes, suppression of subharmonic frequency at St0/2 and formation of sideband frequencies around (St0 ± Stc)/2 are observed. These spatiotemporal features suggest the mode of v′ is modulated by the modes of u′ and w′. Both the leading modes of p′ and of v′ are in the shape of puffs outside the averaged shear layer. These puff modes are related as an oscillation system, which is confirmed by the spectral-POD modes.

A detection method of gear micro-cracks based on tuned resonance

Detection of micro-cracks before assembling has always been a challenge in gear defect detection. A mature detection method of micro-cracks is not available. Due to the complex detection environment and large production of gears, it’s urgent to develop a rapid and accurate detection method of gear micro-cracks. It’s the key to separate and extract weak vibration signals accurately under complex disturbances in gear defect detection. In this study, vibration characteristics of gear defects under resonance conditions were firstly explored and a detection method of gear micro-cracks was proposed based on tuned resonance. Based on the amplification effect of tuned resonance on the peak frequency spectrum of gear vibration, meshing frequency and sideband frequency characteristics of the gear defect signal spectrum were experimentally investigated. The amplitudes of gear meshing frequency and its harmonic meshing frequency in the signal frequency domain diagram were higher and the surrounding sideband frequency components were clearer.

Research on resonance splitting under sinusoidal modulation in resonant optic fiber gyro

In this study, the sinusoidal phase modulation and demodulation principle in resonant fiber optic gyro (RFOG) are introduced. The RFOG simulation system is established, through which the relationship between resonance splitting and modulation frequency of dual-frequency sawtooth and sinusoidal signal is obtained. The resonance splitting is then explained based on sideband spectrum theory. The experimental device is built and the results show that there are obvious resonance splitting and distortion in linear region of demodulation output, when the sinusoidal frequency is higher than FWHM/2. Finally, the feasibility of the sideband frequency locking technology is verified by resonance splitting based on sideband spectrum theory, providing theoretical support for this novel technology, which can suppress backscattering noise effectively.

Phase-sensitive amplification in dispersion oscillating fibers

The modulation of the dispersion along the fiber length is responsible for the emergence of multiple resonant sidebands, which arise due to modulation instability. We propose to use modulation instability (MI) sidebands for phase-sensitive amplification (PSA). An accurate analytical treatment of the PSA process in dispersion oscillating fibers is provided. The analytical model agrees well with results of numerical calculations. The phase-to-phase and phase-to-amplitude transfer functions are demonstrated. We find that the gain depends both on the modulation phase of the fiber dispersion and the individual phases of interacting waves. The effect of the pump depletion on the shift of resonant frequencies of MI sidebands is described. We show that MI sidebands can be used for the squeezing of the phase and amplitude of the signal wave. We demonstrate that parametric amplification in dispersion oscillation fibers accompanies a reduction of the stimulated Brillouin scattering.