High Frequency Oscillations Research Articles

Noise Influence on Characteristics of Current, Flowing through Semiconductor Superlattice, in High Frequency Oscillation Mode

Noise Influence on Characteristics of Current, Flowing through Semiconductor Superlattice, in High Frequency Oscillation Mode

A Switching Oscillation Event-Triggered Switch Fault Detection Method for SiC DC–DC Converter

Switch fault detection is critical for the safety and reliability of a SiC dc–dc converter, which is however difficult by directly comparing the PWM voltage and the gate signal due to the harsh electromagnetic environment and ultrahigh switching frequency. To address the challenges, a novel method is proposed to detect and diagnose the switch fault using the converter PWM high-frequency (HF) switching oscillation. First, the switching event status in a SiC dc–dc converter is captured from the HF switching oscillation current in a noncontact way. Then, the switch fault is detected and diagnosed by checking the signal integrity of the switching events with no need for a gate signal. Finally, a switching oscillation event-triggered switch fault detection system is developed including the HF oscillation sensor, switching event capture circuit, and switch fault detection and diagnosis unit. Experimental work is carried out and the results demonstrate the performance of the method with high safety up to MHz.

AC Series Arc Fault Detection Based on RLC Arc Model and Convolutional Neural Network

AC series arc faults in the power system can lead to electrical fires. However, the generalization performance of the determined detection method would be affected under unknown loads, as current features vary with loads. To address this issue, this paper presents a series arc fault detection method based on a high-frequency (HF) RLC arc model and one-dimensional convolutional neural network (1DCNN). By the current transformer used for receiving differential HF features (D-HFCT), current with complex features is firstly simplified and divided into different oscillation-signal types. Since the types of real D-HFCT data are limited, the RLC arc model is used to generate D-HFCT data with various types of oscillation features by adjusting load types, initial phase angles and Bernoulli-sequence frequencies. Then, the simulated data are adopted to train the 1DCNN model. Finally, the trained 1DCNN model can detect series arc faults under different types of real loads. Compared with the 1DCNN method driven by the limited types of real-current data, the presented method shows good generalization ability and achieves 99.33% average detection accuracy under nine types of unknown loads, which benefits from the training of simulated D-HFCT data with abundant HF oscillation features.

Epileptic seizure detection combining power spectral density and high-frequency oscillations

Detection of pre-seizure signs in epileptic signals may help patients to survive the seizure with minimal damage. This study aims to detect epileptic seizure patterns using EEG datasets of five patients. The signals' maximum power spectral density (PSD) and high-frequency oscillations (HFOs) signals are investigated. The PSDs of all patients' signals are calculated, and the subbands of the maximum PSD are examined. It is observed that 95%, 85%, 85%, 75%, and 80% of the channels of the five patients are in the sum of delta and theta subbands of the maximum PSD, respectively. All patients' maximum power frequency subbands of F4 and T3 channels included only delta and theta subbands. Furthermore, frequency increase rates of pre-ictal and ictal signals are investigated, and increasing PSDs of ripples and fast ripples are then calculated. A much higher-frequency ripple follows the low-frequency ripple in 75%, 75%, 65%, 85%, and 75% of the channels of the first, second, third, fourth, and fifth patients, respectively. For the pre-ictal data, a much higher frequency ripple is not seen, followed by a low-frequency ripple in 90%, 85%, 75%, 90%, and 90% of all channels of five patients, respectively. In addition, in this study, the frequency of signals is observed to be 80 Hz and above in the Fp2, C4, P4, O2, and Pz channels, which are common to all patients. Consequently, examining PSD and HFO signals ensures the detection of the differences between the data sets and detects the epileptic seizure patterns in all five patients.

High-frequency oscillations in a spin-torque nano-oscillator due to bilinear coupling

High-frequency oscillations in a spin-torque nano-oscillator due to bilinear coupling

High-Frequency Oscillation Suppression Strategy for Flexible DC Transmission Systems Based on Additional Joint Damping

Flexible DC transmission systems experience negative damping characteristics in the high-frequency range due to the delay in the system control link. This can lead to interactions between the impedance of modular multilevel converters (MMCs) and AC transmission lines, resulting in high-frequency oscillation (HFO) issues. To resolve this problem, a simplified MMC control model was developed, taking into account the current inner loop control link. The Sobol method was employed to analyze the factors influencing the impedance characteristics of MMC. Additionally, a combined approach involving a virtual passive filtering method and an equivalent current sampling method was proposed to provide additional damping. The study compared and analyzed the impact of additional damping control on the impedance characteristics and system stability of MMCs. Lastly, a flexible direct current grid connection simulation model was constructed using PSCAD to validate the effectiveness of the proposed additional damping control strategy.

The role of superficial and deep layers in the generation of high frequency oscillations and interictal epileptiform discharges in the human cortex

Describing intracortical laminar organization of interictal epileptiform discharges (IED) and high frequency oscillations (HFOs), also known as ripples. Defining the frequency limits of slow and fast ripples. We recorded potential gradients with laminar multielectrode arrays (LME) for current source density (CSD) and multi-unit activity (MUA) analysis of interictal epileptiform discharges IEDs and HFOs in the neocortex and mesial temporal lobe of focal epilepsy patients. IEDs were observed in 20/29, while ripples only in 9/29 patients. Ripples were all detected within the seizure onset zone (SOZ). Compared to hippocampal HFOs, neocortical ripples proved to be longer, lower in frequency and amplitude, and presented non-uniform cycles. A subset of ripples (≈ 50%) co-occurred with IEDs, while IEDs were shown to contain variable high-frequency activity, even below HFO detection threshold. The limit between slow and fast ripples was defined at 150 Hz, while IEDs’ high frequency components form clusters separated at 185 Hz. CSD analysis of IEDs and ripples revealed an alternating sink-source pair in the supragranular cortical layers, although fast ripple CSD appeared lower and engaged a wider cortical domain than slow ripples MUA analysis suggested a possible role of infragranularly located neural populations in ripple and IED generation. Laminar distribution of peak frequencies derived from HFOs and IEDs, respectively, showed that supragranular layers were dominated by slower (< 150 Hz) components. Our findings suggest that cortical slow ripples are generated primarily in upper layers while fast ripples and associated MUA in deeper layers. The dissociation of macro- and microdomains suggests that microelectrode recordings may be more selective for SOZ-linked ripples. We found a complex interplay between neural activity in the neocortical laminae during ripple and IED formation. We observed a potential leading role of cortical neurons in deeper layers, suggesting a refined utilization of LMEs in SOZ localization.

High-frequency oscillation mechanism analysis of wind farm-side MMC station considering converter transformer stray capacitance

High-frequency oscillation is one of the critical issues threatening the stability of modular multilevel converter (MMC) based high-voltage direct current (HVDC) system. A new 2 kHz high-frequency oscillation has occurred in the wind farm-side MMC station of Rudong wind farm integrated MMC-HVDC project of China during no-load charging process. The mechanism of this high-frequency oscillation is different to previous ones. Apart from the time delay of MMC, the stray capacitance of converter transformer makes a significant contribution to the high-frequency oscillation. This paper investigates the high-frequency oscillation mechanism of wind farm-side MMC station during no-load charging process. First, the harmonic state space (HSS) model of a wind farm-side MMC station is established. In addition to the leakage inductance, the stray capacitance is considered in the converter transformer model. To reveal the significance of the converter transformer stray capacitance in this new high-frequency oscillation, the root loci of the system are calculated with varying stray capacitance. Then, the state variables with high degree of participation in the high-frequency oscillation modes are determined by the participation factor analysis. A reduced-order model suitable for the high-frequency oscillation analysis is further established based on the participation factor analysis results. Next, the high-frequency oscillation mechanism is revealed by impedance analysis. Finally, the effects of system parameters are analyzed by the combination of eigenvalue analysis and impedance analysis. The analysis results are validated by electromagnetic transient simulations.

High-Frequency Oscillation Mechanism Analysis and Suppression Strategy of Grid-Forming Control MMC-HVDC

Recently, several high-frequency oscillation (HFO) events have occurred in the modular multilevel converter (MMC) based HVDC (MMC-HVDC) projects, threatening the safety and reliability of power systems. Existing studies only focus on the HFO of MMC-HVDC with grid-following control (GFWC) but less on the HFO of MMC-HVDC with grid-forming control (GFMC). Therefore, this paper establishes the small-signal model of MMC-HVDC with GFMC through the dynamic phasor method. Then, the impact of different parameters on the HFO is discussed. Unlike MMC-HVDC with GFWC, the outer loop control of MMC-HVDC with GFMC has a great influence on HFO. Meanwhile, the existing HFO suppression strategies by adding a low-pass filter (LPF) to feedforward control of terminal voltage for MMC-HVDC with GFWC will increase the HFO risk of MMC-HVDC with GFMC. Further, the HFO suppression strategies suitable for MMC-HVDC with GFMC are proposed based on the mechanism analysis results. Finally, the obtained results are verified by the time-domain simulation of the studied system in RT-LAB.

Characteristics of nano-PMMA dust explosion through the vented tube

The explosion venting experiments of 150 nm polymethyl methacrylate (PMMA) dust with different lengths (L) and diameters (D) of the vent tube are conducted. The effect of tube size on overpressure and flame propagation behavior is explored. High-frequency and low-frequency Helmholtz oscillations are observed on the overpressure curves in the chamber. The (dP/dt)max in the chamber is increased with high-frequency oscillations, while the maximum flame width is also visible with low-frequency Helmholtz oscillations. As the L increases from 0 m to 2 m, the Pred,max increases by 29.2–145.1% and the (dP/dt)max increases by 38.4% − 127.7%. With the increase of the D, the Pred,max in the chamber and vent tube decreases, and the flame transforms from an under-expansion jet flame to a subsonic jet flame. Due to the interaction between the external flow field and the concentration of unburned particles, the maximum external overpressure increases alongside with the incease of the tube length and diameter. In addition, the maximum calculation error of EN14491 is 1100%, while NFPA68 seriously underestimates the explosion venting pressure. A modified prediction model is established to provide a design method for a safe vent through the vent tube of the nano-dust explosion.

Generation of super high frequencies by graphene on piezoelectric buffer layer upon applied nanosecond electrical pulse

An unforeseen phenomenon occurred when measuring the current–voltage (I–U) characteristics of graphene samples in the pulsed regime. The graphene monolayer of the samples was grown by chemical vapor deposition and transferred onto 50 nm buffer HfO2 and AlO3 layers. Bilayer graphene was obtained from epitaxial graphene grown on SiC and was transferred onto 100 nm SiO2. The distance between contacts varied from 5 to 25 µm. The measurements were performed employing cables of 50 Ω impedance to transmit the pulses and a 0–12 GHz bandwidth sampling scope was used to register them. The transmitted registered pulses through graphene/HfO2 and graphene/SiO2 samples were superposed with super high frequency (SHF) oscillations. The wave packet oscillations of about 2 ns in duration appeared on the pulses passed through graphene/HfO2. On the passed-through graphene/SiO2 pulses, the appearing wave packet turns into continuous generation along the pulse length. Spectral decomposition reveals that the base frequency of the oscillations is about 10 GHz; however, bisected frequencies are also present in the spectra. Preliminary analysis of the SHF oscillations occurrence shows that the wave packets appear as an inverse piezoelectric response to a rapidly rising voltage of the pulses. It is proposed that due to acoustic–electronic interaction, the oscillating wave packet in graphene/SiO2 turns into the continued generation, which consumes three-quarters of the pulse energy. These results show that the coupling between graphene and the piezoelectric buffer layer combined with acoustic–electronic interaction brings forth novel effects that are in demand for practical applications.

Uncooled 100-GBaud Directly Modulated Membrane Lasers on SiC Substrate

We investigate the temperature dependence of the dynamic characteristics of a 1.3-μm InGaAlAs-based directly modulated membrane laser on a SiC substrate. The laser is fabricated by combining direct wafer bonding of SiC and InP substrates using a very thin (∼10 nm) oxide layer and epitaxial regrowth of a membrane InP layer on the InP/SiC template. The membrane laser structure on SiC with a high thermal conductivity (490 Wm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) and a moderate refractive index (∼2.6) ensures both high thermal dissipation and a large optical confinement factor in the active region, which are ideal for increasing the relaxation oscillation frequency even at high operating temperatures. We further leverage the optical feedback effect from the output facet of a waveguide to enhance the bandwidth and enable signal modulation at 100 GBaud and beyond. Owing to the high relaxation oscillation frequency and the photon-photon resonance effect, it is possible to obtain a flat frequency response at temperatures ranging from 25 to 85°C. The fabricated membrane laser on SiC with an active-region length of 50 μm exhibits 3dB bandwidths of >110, 97, and 74 GHz at 25, 55, and 85°C, respectively. We successfully demonstrate 2-km transmissions of 100-Gbit/s NRZ signals under uncooled conditions (25 to 85°C). Furthermore, the laser is capable of 112-Gbit/s NRZ modulation at 85°C.

Pulse sequences for manipulating the spin states of molecular radical-pair-based electron spin qubit systems for quantum information applications.

Molecular qubits are an emerging platform in quantum information science due to the unmatched structural control that chemical design and synthesis provide compared to other leading qubit technologies. This theoretical study investigates pulse sequence protocols for spin-correlated radical pairs, which are important molecular spin qubit pair (SQP) candidates. Here, we introduce improved microwave pulse protocols for enhancing the execution times of quantum logic gates based on SQPs. Significantly, this study demonstrates that the proposed pulse sequences effectively remove certain contributions from nuclear spin effects on spin dynamics, which are a common source of decoherence. Additionally, we have analyzed the factors that control the fidelity of the SQP spin state, following the application of the controlled-NOT gate. It was found that higher magnetic fields introduce a high frequency oscillation in the fidelity. Thereupon, it is suggested that further research should be geared toward executing quantum gates at lower magnetic field values. In addition, an absolute bound of the fidelity outcome due to decoherence is determined, which clearly identifies the important factors that control gate execution. Finally, examples of the application of these pulse sequences to SQPs are described.

High-frequency chest wall oscillation multiple times daily can better reduce the loss of pulmonary surfactant and improve lung compliance in mechanically ventilated patients

BackgroundHigh-frequency chest wall oscillation (HFCWO) has been widely recognized for its airway secretion clearance effectiveness in critically ill ICU patients. ObjectivesThe purpose of this randomized controlled trial is to validate and compare the effects of different frequencies of HFCWO on oxygenation, lung compliance, and pulmonary surfactant proteins (SPs) in critically ill patients admitted to the intensive care unit (ICU). MethodsSixty patients with severe craniocerebral injury treated with a tracheostomy and mechanical ventilation were randomized into three groups (20 patients in each group): a single group (treated with 30 minutes of HFCWO once daily) and a double group (treated with 30 minutes of HFCWO twice daily), and a blank group (treated without HFCWO). Primary outcome measures included results on several specific proteins (SP-A, SP-B, SP-C, and SP-D) in serum and alveolar lavage fluid. Secondary outcome measures were lung static compliance test and oxygenation. ResultsPatients in both the single and double groups exhibited significant oxygenation and static compliance improvement. Similar results were observed in changes in SPs concentrations in the alveolar lavage fluid. However, a significant reduction of SPs levels was observed in the serum. In the group comparison analysis for the same variables between the single and double group, twice daily HFCWO treatments showed a significantly better result. ConclusionCompared with HFCWO once daily, HFCWO twice daily is advantageous in patients with tracheostomy and prolonged ventilation, which demonstrated significantly greater effectiveness in improving oxygenation and lung static compliance linked to the increase of and SPs contents in the airways as well as a reduction of SPs shift from airways to the blood.

A Nonlinear Impact-Driven Triboelectric Vibration Energy Harvester for Frequency Up-Conversion.

Energy harvesting effectively powers micro-sensors and wireless applications. However, higher frequency oscillations do not overlap with ambient vibrations, and low power can be harvested. This paper utilizes vibro-impact triboelectric energy harvesting for frequency up-conversion. Two magnetically coupled cantilever beams with low and high natural frequencies are used. The two beams have identical tip magnets at the same polarity. A triboelectric energy harvester is integrated with the high-frequency beam to generate an electrical signal via contact-separation impact motion between the triboelectric layers. An electrical signal is generated at the low-frequency beam range achieving frequency up-converter. The two degrees of freedom (2DOF) lumped-parameter model system is used to investigate the system's dynamic behavior and the corresponding voltage signal. The static analysis of the system revealed a threshold distance of 15 mm that divides the system into monostable and bistable regimes. In the monostable and bistable regimes, softening and hardening behaviors were observed at low frequencies. Additionally, the threshold voltage generated was increased by 1117% in comparison with the monostable regime. The simulation findings were experimentally validated. The study demonstrates the potential of using triboelectric energy harvesting in frequency up-converting applications.

Interactive interface for spatio-temporal mapping of epileptic human brain using characteristics of high frequency oscillations (HFOs)

Spontaneous High Frequency Oscillations (HFOs) have been considered as emerging specific biomarkers of the epileptogenic region. As a first issue, a significant difference in the implementation of automatic HFOs detection methods can sometimes occur between researchers. In addition, clinicians are not even particularly familiar with the concept of signal and image processing, and programming skills. To overcome these limitations, we propose a plug-and-play interactive Graphical User Interface (GUI) that incorporates an amalgamation of six validated methods used for detecting and quantifying of HFOs events. As a second issue, the most automated HFOs detection methods to date have a high false detection rate and low specificity, ranging, in some cases up to 80% and below 37% respectively. Therefore, the eventual utilization of HFOs detection algorithms in clinical settings requires a checking step to save clinically relevant HFOs and remove spurious oscillations from the detection results. As a last issue addressed in the present study, the major previous HFOs studies have been limited only to the detection and classification of HFOs, but only a few studies have been conducted to efficiently follow the neural dynamics of epileptic focus by studying HFOs characteristics through different brain regions and clinical stages. Therefore, in our software, the brain mapping of HFOs characteristics is done based on the duration, the inter-duration, the average frequency, and the power of HFOs. The present developed software may be considered helpful for understanding the functional significance of HFOs and also to reduce the interaction gap between fundamental research and applied clinical practice related to HFOs.

Flexible, high-resolution cortical arrays with large coverage capture microscale high-frequency oscillations in patients with epilepsy.

Effective surgical treatment of drug-resistant epilepsy depends on accurate localization of the epileptogenic zone (EZ). High-frequency oscillations (HFOs) are potential biomarkers of the EZ. Previous research has shown that HFOs often occur within submillimeter areas of brain tissue and that the coarse spatial sampling of clinical intracranial electrode arrays may limit the accurate capture of HFO activity. In this study, we sought to characterize microscale HFO activity captured on thin, flexible microelectrocorticographic (μECoG) arrays, which provide high spatial resolution over large cortical surface areas. We used novel liquid crystal polymer thin-film μECoG arrays (.76-1.72-mm intercontact spacing) to capture HFOs in eight intraoperative recordings from seven patients with epilepsy. We identified ripple (80-250 Hz) and fast ripple (250-600 Hz) HFOs using a common energy thresholding detection algorithm along with two stages of artifact rejection. We visualized microscale subregions of HFO activity using spatial maps of HFO rate, signal-to-noise ratio, and mean peak frequency. We quantified the spatial extent of HFO events by measuring covariance between detected HFOs and surrounding activity. We also compared HFO detection rates on microcontacts to simulated macrocontacts by spatially averaging data. We found visually delineable subregions of elevated HFO activity within each μECoG recording. Forty-seven percent of HFOs occurred on single 200-μm-diameter recording contacts, with minimal high-frequency activity on surrounding contacts. Other HFO events occurred across multiple contacts simultaneously, with covarying activity most often limited to a .95-mm radius. Through spatial averaging, we estimated that macrocontacts with 2-3-mm diameter would only capture 44% of the HFOs detected in our μECoG recordings. These results demonstrate that thin-film microcontact surface arrays with both highresolution and large coverage accurately capture microscale HFO activity and may improve the utility of HFOs to localize the EZ for treatment of drug-resistant epilepsy.

N°142 – Phase-amplitude coupling between beta power and high frequency oscillations as a clinically usefull biomarker for deep brain stimulation therapy

N°142 – Phase-amplitude coupling between beta power and high frequency oscillations as a clinically usefull biomarker for deep brain stimulation therapy

Correlation between scalp high-frequency oscillations and prognosis in patients with benign epilepsy of childhood with centrotemporal spikes.

The study aimed to explore whether high-frequency oscillations (HFOs) can predict seizure risk and atypical manifestations of benign epilepsy of childhood with centrotemporal spikes (BECTS). We recruited 60 patients and divided them into three groups: (1)seizure-free BECTS, (2) active typical BECTS, and (3) active atypical forms of BECTS. Electroencephalogram was used to record the number, location, average amplitude, and duration of spikes, and spike ripples were analyzed using time-frequency technology. Multivariable logistic regression analysis was used to investigate independent predictive factors for prognosis. The number of sleep spike ripples, rather than spikes, was an independent risk factor for the active period of the disease (odds ratio [OR] = 4.714, p = 0.003) and atypical forms of BECTS (OR = 1.455, p = 0.049); the optimal thresholds for the spike ripple rate were >0 (area under the curve [AUC] = 0.885, sensitivity = 96.15%, specificity = 73.33%) and >0.6/min (AUC = 0.936, sensitivity = 84.21%, specificity = 96.15%), respectively. Furthermore, in typical BECTS, the spike ripple rate showed significant negative correlations with time since the last seizure (ρ = -0.409, p = 0.009) and age (ρ = -0.379, p = 0.016), while the spike rate did not. Spike ripple was a marker for distinguishing typical and atypical forms of BECTS and reflected the risk of seizure recurrence better than the spike alone. The present findings might assist clinicians in BECTS treatment.

Thermoelastic damping in high frequency resonators using higher-order shear deformation theories

Thermoelastic damping (TED) in high frequency oscillators shifts their natural frequencies and attenuates the vibration amplitude. The amount of damping depends upon the temperature of the environment in which the device is operating. Here, we model the oscillator as a simply-supported beam of rectangular cross-section undergoing infinitesimal deformations. We consider three (the Levinson, the Timoshenko and a sinusoidal) through-the-thickness shear strain distributions, both translational and rotational inertia, and heat conduction to analytically delineate their effects on the shift in frequencies and the attenuation of their amplitudes for the lowest three vibration modes. The shear deformation distribution function multiplied by the Poisson ratio appears in the volumetric strain. The TED in the Timoshenko, the Levinson and a beam with sinusoidal variation of shear stresses is related to that in the Euler beam to recover the famous Lifshitz–Roukes formula. Various results are presented to qualitatively and quantitatively illustrate the dependence of the TED upon the lowest three frequencies and the resonator thickness. The analytical solutions presented here can be used as benchmark solutions for checking the numerical solutions.