High Frequency Band Research Articles

Simulated investigation of a ku-band relativistic magnetron with modified all-cavity axial extraction at a low magnetic field

Since its invention in 1921 by Hull, magnetrons have undergone rapid development, transitioning from low-power devices to high-power relativistic magnetrons (RMs). However, research on RMs has been predominantly confined to L-X bands until now. To explore the potential of RM in higher frequency bands and align with the trend toward miniaturization of high-power microwave sources, a Ku-band RM has been investigated in this paper. Theoretical analysis dictates the selection of 24 cavities for optimal performance at a low magnetic field. Utilizing a three-dimensional particle-in-cell simulation platform, we demonstrate that the RM can generate a microwave power of 116 MW at a resonant frequency of 13.717 GHz with an electron beam of 126 kV and 2.0 kA, under a magnetic field of 0.22 T, corresponding to a power conversion efficiency of 46%. The integration of a modified all-cavity axial extraction structure in the Ku-band RM allows for a minimized inner radius of the magnetic field system to approximately 25 mm, while maintaining a high-power microwave output.

The performance evaluation of hybrid roller bearings under lubricant contamination conditions

Purpose This paper aims to evaluate the dynamic performance of hybrid roller bearings under lubricant contamination. Design/methodology/approach Some steel rollers in traditional cylindrical thrust roller bearings were replaced with ceramic rollers to assemble hybrid roller bearings. Friction experiments were conducted under lubricant contamination using alumina as the contaminant, and simultaneous vibration acceleration signals from the bearings were collected to evaluate their tribological and dynamic performance. Findings Under lubricant contamination, hybrid roller bearings with a sufficient number of ceramic rollers exhibit greater wear resistance compared to traditional all-steel bearings. There is a noticeable suppression of energy in both tangential and normal frequency bands of the bearings, with more pronounced suppression observed in higher frequency bands. Originality/value This study provides valuable insights for the development of hybrid ceramic bearings. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2024-0291/

Investigation and estimation of structural and dielectric properties of chromium-doped cobalt ferrites nano particles

Abstract Nano ferrite materials are of critical importance in meeting the global demand for microwave and electronic devices, as spinel ferrites possess remarkable morphological, structural, and dielectric characteristics. This study investigates chromium-doped ferrite nanoparticles with the chemical composition CoCrxFe2-xO4 (x = 0.00, 0.30, 0.60, and 0.90), synthesize using the sol–gel technique and subjected to annealing at 900 °C. Energy Dispersive x-ray Analysis EDAX patterns confirmed compositional stoichiometry. X- Ray Diffraction analysis reveals that all samples exhibit a cubic crystal structure. Replacing some of the ions with chromium (Cr3+) led to a decrease in the x-ray density form (5.329–5.324). The average crystallite size in the fabricated samples ranged from 46.07 to 31.84 nm, and the lattice parameters decrease from 8.382 to 8.364 Å as the chromium content increase. Infrared spectra show that lower frequency band (ν2) at around 479.69-392 .60 cm–1 and a higher frequency band (ν1) within a range from 611.05–57661 cm–1 a clear indication of spinel structure characteristics. The examination using FE-SEM indicates that the produced materials exhibit porosity and amorphous characteristics. The significant tangent loss observe at lower frequencies suggests that these materials may have potential applications in medium-frequency devices. Consequently, spinel nanoferrites can offer advantages for advanced electronic and microwave technologies.

Abnormal Autonomic Nervous Regulation in Patients with Globus Pharyngeus.

Globus pharyngeus could be described as a benign sensation of lump or foreign object in the throat. The etiology of the globus as a solitary syndrome is still unknown, but it is proposed that stress could have an important role in symptom emergence. To evaluate the autonomic nervous regulation in patients with globus compared to healthy controls in reaction to stress. Patients included in the study were diagnosed based on ROME IV criteria for Disorders of Gut Brain Interaction. Besides globus, the patients did not suffer any other substantial medical condition. As a control group, measurement of healthy volunteers was performed. Both groups underwent the same stress protocol assessment in the same laboratory settings. The protocol consist of two types of stressors: cold pressor test and mental arithmetic test to test different types of autonomic reactivity. Baroreflex sensitivity was significantly decreased in patients compared to controls in all phases of the protocol. Low-frequency band of systolic blood pressure variability was significantly increasedduring both stress phases in patients compared to controls. High-frequency band of heart rate variability was significantly decreased in patients compared to controls during the both of the stress phases. The results of this study shows discrete abnormalities in complex autonomic reflex control which are predominantly manifested in response to stressful stimuli indicating altered neurocardiac regulation as a reaction to stress associated with globus pharynegus. This fact could have an important role in the personalized management of globus patients such as biofeedback.

Single layer dual wideband linear to circular polarisation converter with integrated parasitic elements

This paper presents a novel single-layer, single-sided, dual-wideband linear-to-circular (LTC) polarsation converter. The unit cell of the polarisation converter comprises two identical diagonally oriented C-shaped metallic strips arranged symmetrically and integrated with four outwardly extending diagonal parasitic strips. The LTC polarisation converter is placed on the top side of an ultra-thin substrate layer with a profile size of 0.020 λo at 11.9 GHz and 0.05 λo at 30.7 GHz. The inclusion of parasitic strips in the unit cell design is pivotal, inducing a 90º phase shift between the orthogonal wave components, thus enhancing LTC polarisation conversion. The design achieved near-equal transmission amplitudes and maintained a stable phase difference of nearly 90° across two distinct frequency bands, enabling right-hand circular polarisation in the lower frequency band and left-hand circular polarisation in the higher frequency band. Numerical and experimental results showed that the polariser can realise a wideband LTC polarisation conversion for both x- and y-polarised electromagnetic wave incidences at two distinct frequency bands of 6.78–17.08 GHz (fractional bandwidth of 86.3%) and 25.09–36.40 GHz (36.8%). The converter maintained consistent polarisation conversion performance across a broad range of incidence angles and exhibited high and uniform total transmittance in both operational frequency bands.

Design of a high power combiner in HF band

Power combiners are commonly used in power amplifiers to achieve high power, especially in long-range and medium-range wireless communication device transmission systems. This paper proposes designing and implementing a high-power two-way power combiner operating in the HF (High Frequency) band, aiming to achieve an output power of over 1 kW. The power combiner is designed, implemented, and tested in the laboratory with the following achieved parameters: insertion loss between output and input better than 3.4 dB and isolation between inputs better than 26 dB. The experimental results showed that the proposed power combiner had better performance than existing combiners on the market. Mainly, power combining efficiency is over 88%, the standing wave ratio at ports is less than 1.25, and the operating temperature of the power combiner is less than 50 °C, meeting the set requirements.

A novel ultra-wideband rasorber based on triple lossy layers

Abstract By surpassing the limitations of transmission efficiency found in traditional double-lossy-layers rasorbers, a novel rasorber with three distinct lossy absorption layers is presented, offering low insertion loss and ultra-wideband bandwidth. Compared to conventional rasorbers which have non-negligible insertion loss and large thickness, our design extends the bandwidth in the higher frequency band without increasing thickness, while maintaining high transmission efficiency. To further broaden the absorption band, an additional lossy layer resonating at lower frequency band, with high transmission above the resonance frequency was incorporated into the previous design. The composite structure is developed by the equivalent circuit model (ECM) whose results are in accord well with the simulation results. The simulated results demonstrate that an insertion loss of 0.37 dB at 10 GHz, and a 159.5% 10 dB reflection reduction bandwidth from 2.04 to 18.05 GHz are attained under normal incidence. A manufactured specimen of the proposed structure is measured to validate our design.

Intracranial EEG-Based Directed Functional Connectivity in Alpha to Gamma Frequency Range Reflects Local Circuits of the Human Mesiotemporal Network.

To date, it is largely unknown how frequency range of neural oscillations measured with EEG is related to functional connectivity. To address this question, we investigated frequency-dependent directed functional connectivity among the structures of mesial and anterior temporal network including amygdala, hippocampus, temporal pole and parahippocampal gyrus in the living human brain. Intracranial EEG recording was obtained from 19 consecutive epilepsy patients with normal anterior mesial temporal MR imaging undergoing intracranial presurgical epilepsy diagnostics with multiple depth electrodes. We assessed intratemporal bidirectional functional connectivity using several causality measures such as Granger causality (GC), directed transfer function (DTF) and partial directed coherence (PDC) in a frequency-specific way. In order to verify the obtained results, we compared the spontaneous functional networks with intratemporal effective connectivity evaluated by means of SPES (single pulse electrical stimulation) method. The overlap with the evoked network was found for the functional connectivity assessed by the GC method, most prominent in the higher frequency bands (alpha, beta and low gamma), yet vanishing in the lower frequencies. Functional connectivity assessed by means of DTF and PCD obtained a similar directionality pattern with the exception of connectivity between hippocampus and parahippocampal gyrus which showed opposite directionality of predominant information flow. Whereas previous connectivity studies reported significant divergence between spontaneous and evoked networks, our data show the role of frequency bands for the consistency of functional and evoked intratemporal directed connectivity. This has implications for the suitability of functional connectivity methods in characterizing local brain circuits.

Relationship Between High Frequency Component of Heart Rate Variability and Delta EEG Power During Sleep in Women With Irritable Bowel Syndrome Compared to Healthy Women.

To explore the relationship between the high frequency (HF) heart rate variability (HRV) and electroencephalogram (EEG) delta band power in women with irritable bowel syndrome (IBS) versus healthy control women. Twenty women with IBS and twenty healthy controls were studied over three consecutive nights using polysomnography in a sleep laboratory. To avoid the first night effect, only second-night data were analyzed. Power spectral analysis was applied to HRV and EEG recordings. The linear system coherence/phase analysis assessed the relationship between normalized HF power of HRV and normalized delta band power of EEG during the first four NREM-REM sleep cycles. Women with IBS exhibited a significantly higher percentage of NREM sleep, higher normalized HF, lower normalized low frequency (LF) and decreased LF/HF ratio of HRV in the first four NREM-REM sleep cycles compared to controls. Additionally, their normalized delta band power was significantly lower in these sleep cycles and over the whole night. The phase shift between HF and delta band power was significantly longer in the IBS group. While the coherence between normalized HF and normalized delta band power was lower in the IBS group, the difference was not statistically significant. The coherence/phase analysis showed a dysregulated interaction between autonomic and central nervous systems in women with IBS, manifested by increased lag time between cardiac and EEG delta band power compared to healthy controls. Whether this dysregulation contributes to the pathophysiology of IBS remains to be determined.

Adaptive Matching of Discrete Antenna Tuning Units of High Frequency Band to Varying Load Impedance

The issue of matching the antenna with thetransmitter-receiverplays a primary role in radio communications. The matching problem is relevant for different ranges and is solved in many ways. In the high frequency wave range, matching has a number of features when using an antenna coupler based on discrete elements consisting of capacitance and inductance boxes. The article discusses the concept of fast matching of high-frequency amplifying paths ofdecametric wavestransceivers with non-stationary loads using discrete antenna couplers. An innovative approach has been developed to the tuning process when changing the operating frequency and ensuring self-adaptation of the antenna coupler when changing the impedance, based on methods for quickly searching for the geometric proximity of points. A quick method for configuring the antenna coupler is proposed, eliminating the procedure for recalculating the input impedance based on the results of measuring the input impedance of the antenna coupler. When using it, the speed of setting the antenna coupler at the current operating frequency is limited only by the time of a single state change of the discrete power circuit, which in the case of electromagnetic relays is numerically equal to their switching time. The configuration of the antenna coupler using the method of fast search for the geometric proximity of points is based on a set of frequency cards with settings options. Such cards can be recalculated for the reference plane between the generator and the antenna coupler input for all combinations of discrete elements in accordance with the known matrix model of a discrete power circuit. This eliminates the complicated procedure of recalculating the input impedance of the antenna using complex numbers. The technical result of the proposed innovative method of antenna coupler configuringis simplification, tracking of systematic errors of the impedance meter, elimination of time-consuming calculations with complex numbers, expansion of the method functionality, reduction of the tuning duration and improvement its quality. The practical significance lies in the fact that the implementation of the proposed technical solutions in the high frequency range communications means can significantly (about 100 times) limit the duration of preparation for a radio communication session, eliminate the procedure for recalculating the antenna input impedance and reduce the resource requirements of switching elements.

Theoretical investigation of new composite based on metamaterial able to strongly attenuate heat and noise propagation for civil engineering

New design in civil engineering need reduction of cost of material. Engineers and researcher are focused on material parameter to improve proposed alternatives. In this work we are developed theoretical tool based on finite element method to evaluate transmission noise and heat transfer along composite wall for civil engineering. In this work, composite based metamaterial is used for wall elaboration. At first Time noise level in broad band high frequency level was extracted using frequency acoustic finite element method, and using advection, diffusion model heat transfer distribution was also extracted. Finally, combination of constitutive model with metaheuristic optimization enabled us optimal parameters of the material composite, for specific condition. Constitutive resulted and discussion will have detailed in the paper. Keywords: frequency acoustic analysis, advection diffusion, genetic algorithm, civil engineering, material science, metamaterial

Analysis of broadband linear polarization-converting meta-materials and their sensing and detection functions

In this paper, we present a broadband perfect-reflective linear polarization-converting metamaterial, which achieves perfect-reflective linear polarization conversion over a broadband frequency range of 28.15 GHz–60.80 GHz, and the narrow-band perfect-polarization-converting peaks appearing at the high frequency of 67.121 GHz can be used for microwave solution concentration detection. The design consists of a surface metal resonator structure, a Roggers 5880 dielectric layer and a copper metal backing. The surface metal resonator is a combination of a circular open ring, a square open ring, and a centrally located cross-metal cross ring nested in a modified, highly anisotropic structure. The perfect polarization transition peak at the high frequency band can be used for the solution detection function, which can detect the concentration of salt solution, glucose solution, and alcohol solution. When the refractive index of the solution sample to be tested changes gradually from 1.0 to 1.4, the polarization conversion peak shows obvious frequency shift, and the peak polarization conversion rate is always kept above 99%. The polarization principle was analyzed using surface electromagnetic field distribution and related theories, and the sample structure was processed and tested. The designed super-surface polarization conversion structure has potential applications in the field of microwave detection and microwave communication.

Compact and low‐loss IPD bandpass filter using 3D glass‐based redistribution layer technology

AbstractA low‐loss miniaturized bandpass filter is presented using 3D glass‐based RDL packaging technology. A new topology consisting of one modified Pi‐section and one modified T‐section is introduced to generate three transmission zeros which can achieve the high out‐of‐band rejection. A combination of 2D planar inductors and high‐Q 3D inductors is used to achieve low insertion loss and minimize the filter size. In addition, one grounded resonator at input terminal is introduced to generate an extra transmission zero in the low end. The proposed bandpass filter covering 3.3–4.2 GHz is fabricated with a compact size of 1.6 mm × 0.8 mm × 0.25 mm. It exhibits an insertion loss of less than 1.0 dB at a center frequency of 3.75GHz and a return loss of better than 14 dB. The proposed design has a 3 dB fractional bandwidth of 37.6%. Its out‐of‐band rejection is better than 20 dB at the low frequency band from DC to 2.0 GHz and better than 19 dB at the high frequency band from 5.0 to 9.0 GHz. The simulated and measured results of the proposed BPF are in reasonably good agreement.

Analysis of noise and its characteristics in avalanche photodiode

Avalanche photodiodes (APDs) produce noise during operation, which affects the device performance. However, the previous research on its noise is mainly theoretical analysis and is only reflected as optical noise. Therefore, according to the characteristics of APD material and the mechanism of noise generation, the main noise of the device is analyzed in this paper. First, the test method of noise in APDs is established, including testing of dark noise, optical noise, and multiplication noise in high frequency bands. The main noises in APDs are 1/f noise, thermal noise, shot noise, generation recombination noise, and multiplication shot noise, and shot noise is suppressed by Fermi–Dirac distribution and Coulomb action. Second, the reliability of APDs is evaluated by measuring and analyzing the noise parameters of the device through thermal aging experiments. It is concluded that the defects introduced by thermal aging can be reflected by the change in noise, which is consistent with the results in the literature. This method can comprehensively obtain the noise in APDs, which is helpful to improve the working efficiency, life, and reliability of the device.

Four-port dual-band textile MIMO antenna for biomedical health monitoring systems: on-body mutual coupling reduction characterization

The paper outlines a methodology to diminish mutual coupling in 4-port dual-band MIMO textile antenna for biomedical applications. This antenna leverages MIMO technology and Wireless Body Area Network (WBAN) for operation in two distinct frequency bands at (3.5 & 2.45 GHz). The antenna is made up of four octagonal patch antennas, each having a bar and a split-ring (SR) slot with 47.2 × 31 mm2 dimensions for each patch. A hybrid mutual coupling (MC) approach was investigated with closely spaced patches (up to 0.05λ). Various bending setups have been selected along with flat case to examine the antennas’ resilience which demonstrate such agreement between measured and simulated findings. Furthermore, the MC is only −20 dB, the envelope correlation coefficient (ECC) is 0.001, and maximum peak measured gain of 5.2 dBi is achieved with lowest peak specific absorption rate (SAR) value. Even when bent at a 60° angle along with y-axis and x-axis, the antenna retains a decent gain of 1.861 dBi in the low frequency region and 5.479 dBi at high frequency band. Surprisingly, the antenna outperforms the attenuation produced by the lossy effects of the human body, indicating a favorable alignment between the modelled and observed findings.

CONCERTO at APEX On-sky performance in continuum

Context. CarbON CII line in post-rEionisation and ReionisaTiOn epoch (CONCERTO) instrument is a low-resolution mapping spectrometer based on lumped element kinetic inductance detector (LEKIDs) technology, operating at 130-310 GHz. It was installed on the 12-metre APEX telescope in Chile in April 2021 and was in operation until May 2023. CONCERTO’s main goals were the observation of [CII]-emission line fluctuations at high redshift and of the Sunyaev–Zel’dovich (SZ) signal from galaxy clusters. Aims. We present the data processing algorithms and the performance of CONCERTO in continuum by analysing the data from the commissioning and scientific observations. Methods. We developed a standard data processing pipeline to proceed from the raw data to continuum maps. Using a large dataset of calibrators (Uranus, Mars, and quasars) acquired in 2021 and 2022 at the APEX telescope across a wide range of atmospheric conditions, we measured the CONCERTO continuum performance and tested its stability against observing conditions. Further, using observations on the COSMOS field and observations targeting a distant sub-millimetre galaxy in the UDS field, we assessed the robustness of the CONCERTO performance on faint sources and compared our measurements with expectations. Results. The beam pattern is characterised by an effective full width at half maximum (FWHM) of 31.9 ± 0.6″ and 34.4 ± 1.0″ for high-frequency (HF) and low-frequency (LF) bands, respectively. The main beam is slightly elongated with a mean eccentricity of 0.46. Two error beams of ~65″ and ~130″ are characterised, allowing us to estimate a main beam efficiency of ~0.52. The field of view is accurately reconstructed and presents coherent distortions between the HF and LF arrays. LEKID parameters were robustly determined for 80% of the read tones. Cross-talks between LEKIDs are the first cause of flagging, followed by an excess of eccentricity for ~10% of the LEKIDs, all located in a given region of the field of view. Of the 44 scans of Uranus selected for the absolute photometric calibration, 72.5% and 78.2% of the LEKIDs were selected as valid detectors with a probability >70%. By comparing the Uranus measurements with a model, we obtain calibration factors of 19.5±0.6 Hz Jy−1 and 25.6±0.9 Hz Jy−1 for HF and LF, respectively. The point-source continuum measurement uncertainties are 3.0% and 3.4% for the HF and LF bands, ignoring the uncertainty in the model (which is <2%). This demonstrates the accuracy of the methods we deployed to process the data. Finally, the RMS of CONCERTO maps is verified to evolve as proportional to the inverse square root of the integration time. The measured noise-equivalent flux densities (NEFDs) for HF and LF are 115±2 mJy beam−1 s1/2 and 95±1 mJy beam−1 s1/2, respectively, obtained using CONCERTO data on the COSMOS field for a mean precipitable water vapour (pwv) and elevation of 0.81 mm and 55.7 deg. Conclusions. CONCERTO has unique capabilities in fast dual-band spectral mapping at ~30 arcsec resolution and with a ~18.5 arcmin instantaneous field of view. CONCERTO’s performance in continuum is perfectly in line with expectations.

From the latin "re-cordis, passing through the heart": autonomic modulation differentiates migraineurs from controls when recounting a significant life event.

The literature on clinical psychophysiology highlights the possibility of using Heart Rate Variability (HRV) as an index of psychophysical balance and resilience to stress. This study investigates the differences in stress reactivity and subsequent recovery between a group of migraineurs and healthy controls. Socio-demographic (i.e., sex, age, profession, marital status, and level of education) and psychophysiological (HR and HRV) measures of a group of thirty subjects with migraine (26 migraineurs without aura (86.7%), 2 migraineurs with aura (6.7%), and 2 migraineurs with and without aura (6.7%)) and from thirty healthy control subjects were collected. In particular, HRV was analyzed through frequency-domain parameters, including Low-Frequency (LF; 0.04-0.15 Hz) and High-Frequency (HF; 0.15-0.4 Hz) bands as well as LF/HF ratio during a Psychophysiological Stress Profile (PSP) structured in seven phases: (1) Baseline, (2) Objective stressor 1 (Stroop Test), (3) Rest 1, (4) Objective stressor 2 (Mental Arithmetic Task), (5) Rest 2, (6) Subjective stressor (recount a significant life event), and (7) Rest 3. The LF, HF, and LF/HF ratio values were transformed into a logarithmic scale (i.e., log-LF, log-HF, and log LF/HF ratio). Additionally, LF and HF were converted into normalized units (0-100) (i.e., LF% and HF%) which, in turn, were used to obtain reactivity and recovery to stress through delta values (Δ) calculation. Subjects with migraine reported greater ΔLF% levels of reactivity and recovery to subjective stressor, demonstrating a prevalence of sympathetic activity while recounting a personal life event. At the same time, a lowering of the same values was found in the subjects of the group control. Our results underline the importance of conducting a psychophysiological assessment in patients with headaches because reduced stress management skills could influence the clinical manifestations of the disease, considering stress as one of the most common triggers for migraine patients.

Near-Ground wind field characteristics of tracking photovoltaic systems based on field measurements

The study conducts field measurements at a tracking photovoltaic power station in Zhongwei City, Ningxia Hui Autonomous Region, investigating near-ground incoming wind characteristics, spatial coherence, and their impact on the flow field of the tracking photovoltaic system. Actual measurements indicate a low dispersion degree in the roughness index of this area, with an average roughness index of α = 0.1228, which is consistent with the characteristics of open land and desert areas. The incoming wind speed profile largely complies with European wind load specifications, with turbulence intensity measured at different heights exceeding other wind load specifications, primarily due to increased sand movement contributing to turbulence in desert areas. Additionally, this study proposes calculation formulas for measured turbulence intensity, integration scale, and gust factor, offering valuable insights into the incoming wind field characteristics in this region. Furthermore, the investigation into spatial coherence and decay parameters revealed the superior performance of the Krenk model in high frequency bands and over long distances. Lastly, the tracking photovoltaic array induces noticeable shading effects, altering flow field characteristics significantly, with a diminished impact on wind flow velocity as the tilt angle of the photovoltaic panel decreases. These studies serve as a valuable reference for gaining a deeper understanding of wind field characteristics, wind load calculation, and the optimal design of tracking photovoltaic systems.

Virtual reality-brain computer interface hand function enhancement rehabilitation system incorporating multi-sensory stimulation

Stroke is an acute cerebrovascular disease in which sudden interruption of blood supply to the brain or rupture of cerebral blood vessels cause damage to brain cells and consequently impair the patient's motor and cognitive abilities. A novel rehabilitation training model integrating brain-computer interface (BCI) and virtual reality (VR) not only promotes the functional activation of brain networks, but also provides immersive and interesting contextual feedback for patients. In this paper, we designed a hand rehabilitation training system integrating multi-sensory stimulation feedback, BCI and VR, which guides patients' motor imaginations through the tasks of the virtual scene, acquires patients' motor intentions, and then carries out human-computer interactions under the virtual scene. At the same time, haptic feedback is incorporated to further increase the patients' proprioceptive sensations, so as to realize the hand function rehabilitation training based on the multi-sensory stimulation feedback of vision, hearing, and haptic senses. In this study, we compared and analyzed the differences in power spectral density of different frequency bands within the EEG signal data before and after the incorporation of haptic feedback, and found that the motor brain area was significantly activated after the incorporation of haptic feedback, and the power spectral density of the motor brain area was significantly increased in the high gamma frequency band. The results of this study indicate that the rehabilitation training of patients with the VR-BCI hand function enhancement rehabilitation system incorporating multi-sensory stimulation can accelerate the two-way facilitation of sensory and motor conduction pathways, thus accelerating the rehabilitation process.

Integrative role of attention networks in frequency-dependent modular organization of human brain.

Despite converging evidence of hierarchical organization in the cerebral cortex, with sensory-motor and association regions at opposite ends, the mechanism of such hierarchical interactions remains elusive. This organization was primarily investigated regarding the spatiotemporal dynamics of intrinsic connectivity networks (ICNs). However, more effort is needed to investigate network dynamics in the frequency domain. We aimed to examine the integrative role of brain regions in the frequency domain with graph metrics. Phase-based connectivity estimation was performed in three frequency bands (0.011-0.038, 0.043-0.071, and 0.076-0.103Hz) in the BOLD signal during rest. We applied modularity analysis to connectivity matrices and investigated those areas, which we called integrative regions, that showed frequency-domain flexibility. Integrative regions, mostly belonging to attention networks, were densely connected to higher-order cognitive ICNs in lower frequency bands but to sensory-motor ICNs in higher frequency bands. We compared the normalized participation coefficient (Pnorm) values of integrative and core regions with respect to their relation to higher-order cognition using a permutation-based t-test for multiple linear regression. Regression parameters of integrative regions in relation to three cognitive scores in executive functions, and working memory were significantly larger than those of core regions (Pfdr < 0.05) for salience ventral attention network. Parameters of integrative regions in relation to intelligence scores were significantly larger than those with core regions (Pfdr < 0.05) in dorsal attention network. Larger parameters of neuropsychological test scores in relation to these flexible parcels further indicate their essential role at an intermediate level in behavior. Results emphasize the importance of frequency-band analysis of brain networks.