Frequency Band Research Articles

Suprathermal Electron Scattering by Narrowband Whistler Waves and Broadband Electrostatic Waves: Parker Solar Probe Observations

Abstract We utilize Parker Solar Probe measurements from the first nine perihelia to investigate suprathermal electron scattering near the Sun. We employ a normalized isotropy parameter to identify pitch-angle scattering (PAS) regions in the inner heliosphere, and compare the plasma conditions during these periods to the background (BG) solar wind. Suprathermal electron scattering also commonly occurs during full/partial current sheet (PCS) heliospheric current sheet (HCS) crossings, as identified in previous work. We find slightly higher electron collisional ages in the PAS and PCS/HCS regions than in BG regions, but conclude that Coulomb collisions alone likely cannot explain the observed suprathermal scattering. We investigate plasma wave-modes that could play a role in suprathermal electron scattering, and identify trends in the wave occurrence in BG, PAS, and PCS/HCS regions. We find higher occurrence rates of narrowband whistler-mode waves with frequencies of 0.04–0.19 f/f ce, and a higher occurrence of larger magnetic field wave power in this frequency band, in the PAS and PCS/HCS regions. These observations support the hypothesis that whistler-mode waves play a role in suprathermal electron scattering at moderate distances. However, closer to the Sun, narrowband whistlers are more rarely observed. Instead, we find higher occurrence rates of broadband electrostatic waves with frequencies of 0.1–4.4 f/f lh, and a higher occurrence of larger electric wave power in this band, in the near-Sun PAS and PCS/HCS regions. These observations suggest a role for broadband electrostatic waves in suprathermal electron scattering closer to the Sun.

An omnidirectional hinge antenna integrated for laptops with full metal housing operating at 2.4/5/6 GHz frequency bands

An omnidirectional hinge antenna integrated for laptops with full metal housing operating at 2.4/5/6 GHz frequency bands

Neural Oscillations and Tinnitus: A Review of Pathogenesis and Therapy

ABSTRACTTinnitus is a prevalent auditory perceptual disorder, characterized by a subjective sensation of sound without any external acoustic signals. This disorder significantly impacts the quality of daily life of patients. The pathogenesis of tinnitus is complex and generally associated with auditory system damage and abnormal neural activity. Much evidence from individuals with tinnitus indicates that alterations in the rhythmic oscillatory activity of cortical neurons correlate with tinnitus perception. Here, we review the role of neural oscillations across various frequency bands in auditory processing and the pathogenesis of tinnitus. The thalamocortical dysrhythmia (TCD) model proposes that deafferentation leads to altered auditory thalamocortical oscillations, where resting‐state alpha activity is replaced by theta–gamma cross‐frequency coupling. Additionally, altered oscillatory neural network connectivity in patients with tinnitus suggests modified interactions between various brain regions including auditory and nonauditory areas. We also summarize neural oscillation‐based therapeutic approaches, emphasizing precision medicine in tinnitus treatment. This review focuses on the relationship between neural oscillations and tinnitus and related pathogenesis. Targeting neural modulation within specific frequency bands may open up new avenues for tinnitus therapy in clinical practice.

Delta and Theta Band Power Alterations During Face and Face Pareidolia Perception in Children with Autism Spectrum Disorder: An Electroencephalographic Analysis

Background and Objectives: Autism Spectrum Disorder (ASD) is characterized by a range of deficits across cognitive, sensory, motor, emotional, language, and social domains, which can significantly hinder daily functioning and social interactions. This study explores the differences in brain activity between children with ASD and typically developing peers, focusing on their responses to face and face pareidolia stimuli. Materials and Methods: A group comprising ten typically developing children (four males, six females), aged between 6 and 16 years, alongside eleven children diagnosed with ASD (three males, eight females), whose ages ranged from 6 to 15 years, were engaged in the pilot study. We recorded brain electrical activity using electroencephalography (EEG) while participants viewed images of face and face pareidolia images. Following face and pareidolia stimulus presentation, delta and theta powers in the 0.5–4 Hz and 4–6 Hz frequency ranges and within the 140–190 ms time window were analyzed for both typically developing children and children with ASD. Results: The research result reveals that children with ASD show lower amplitude and delayed latency in their EEG responses, particularly in the theta and delta frequency bands, when processing images that evoke face pareidolia. Conclusions: The findings suggest that while children with ASD face challenges in recognizing faces, they may still possess some perceptual abilities that could be harnessed for therapeutic interventions. Moreover, this research highlights the potential of the face pareidolia paradigm to provide insights that could inform future strategies aimed at enhancing social attention and interaction skills in children with ASD. Despite the limitations of the current sample size, this study provides a valuable foundation for future investigations. Expanding the participant pool will be crucial for confirming and generalizing these findings.

Maternal and paternal infant directed speech is modulated by the child’s age in in two and three person interactions

Prosody in infant-directed speech (IDS) serves important functions for the infant’s attention, regulation, and emotional expression. However, how the structural characteristics of this vocal signal are influenced by the presence or absence of one or two parents at different infant ages remains under-investigated. This study aimed to identify the acoustic characteristics of parental vocalizations in 69 families during specific phases of the Lausanne Trilogue Play (LTP) setting. Vocalizations were analyzed in both two-person contexts (mother-baby or father-baby interacting with the infant individually) and three-person contexts (mother-baby or father-baby interactions in the presence of the other parent) at three time points: when the infant was 3, 9, and 18 months old. Videos of interactions were coded, and the parental vocalizations were extracted. Five components of acoustic features related to the prosodic aspects of speech were extracted for subsequent analysis: intensity and its variability, pitch and pitch variability, formant amplitude, the intensity of specific speech frequency bands affecting sound timbre, and the rate of voiced and unvoiced segments per second. The study demonstrated a main effect of infant age on parental acoustic prosodic characteristics, along with significant interactions between infant age and interaction context (two- versus three-person) and between infant age and parental role (mother versus father). Across contexts and parental roles, intensity, pitch, and their variability consistently increased from 3 to 9 months. By 9 months, distinct prosodic patterns emerged, including a reduced syllable rate and formant amplitude, along with an increase in pauses. The mother’s voice exhibited a steady increase in intensity, as well as in pitch and intensity variability. Interestingly, when comparing parents across the two contexts, IDS in the three-person context is characterized by a higher rate of syllables and fewer pauses, with the most pronounced changes observed at 9 months of age. The development of prosodic characteristics in IDS is not constant across age and it is influenced by the complex interactions between age phases, parental gender, and contextual factors, with a dynamic adaptation of the communication strategies in three-person contexts. The current study underscores the importance of taking a comprehensive perspective in analyzing infant-directed speech within an interactive context involving both fathers and mothers in two- and three-person settings.

A shared aperture multiport antenna for rural wireless communication and safety monitoring using TVWS, ISM, and 5G mmWave bands

To accommodate the antenna demand for rural communication and safety monitoring a shared aperture muti-port antenna sensor is presented for three different operating frequencies covering both Sub- 6 GHz and 5G millimeter-wave bands. The antenna sensor is designed on a single substrate, while different ports are connected to different radiating elements to achieve multiple frequency responses. The simulated and measured findings show that the presented antenna can cover TV-white-space (TVWS) frequency band, 5.8 GHz ISM band, and the 5G millimeter-wave frequency band. At the TVWS band, the antenna yields an omnidirectional radiation pattern with a peak gain of 3.14 dBi. While the antenna provides a unidirectional radiation pattern at the 5.8 GHz ISM and 5G millimeter-wave band with a peak gain of 6.76 dBi and 7.68 dBi, respectively. Moreover, all the antenna ports offer a radiation efficiency of more than 92%. Additionally, the 2-port MIMO configuration at the 5G millimeter-wave band shows excellent MIMO diversity performances by utilizing the proposed novel decoupling structure, which consists of metallic stub and cavity vias. Overall performance of the proposed antenna, especially the three operating frequency band including the TVWS band, makes it a viable solution for the sensing and communication in rural areas.

Anatomically resolved oscillatory bursts reveal dynamic motifs of thalamocortical activity during naturalistic stimulus viewing.

Anatomically resolved oscillatory bursts reveal dynamic motifs of thalamocortical activity during naturalistic stimulus viewing.

Event-related dynamic phase-amplitude coupling analysis reveals facial emotional processing deficits in patients with major depressive disorder: a cross-sectional study

BackgroundPhase-amplitude coupling (PAC) measures the interaction between neural oscillations in different frequency bands and reflects brain functional network coordination in psychiatric patients. The event-related dynamic changes in PAC characteristics and their association with the neural physiological mechanisms under emotional stimulation in major depressive disorder (MDD) remain poorly understood.MethodsWe proposed a cross-sectional study that investigated three PAC methods using simulated data and selected the Gaussian-Copula Event-Related PAC (GC-ERPAC) method for dynamic analysis of 128-channel electroencephalogram data from 53 participants, including 24 patients with MDD and 29 healthy controls (HCs). Participants were exposed to three emotional stimuli (fearful, happy, and sad). The correlation between PAC strengths and clinical scales was then analyzed in each condition.ResultsThe MDD group exhibited abnormal PAC patterns. With happy stimuli, the strengths of delta-gamma coupling (DGC), theta-gamma coupling (TGC), and alpha-gamma coupling (AGC) in the frontal-parietal regions of the MDD group were lower compared to HCs. With fearful stimuli, the strength of AGC in the occipital region was higher in the MDD group. The correlation between TGC and AGC was weaker for couplings among different frequencies in the MDD group. Additionally, AGC was negatively correlated with the clinical scale in MDD but positively correlated with HCs.Clinical trial numberNot applicable.ConclusionsThis study confirmed that GC-ERPAC was an effective method for revealing emotion recognition features in MDD. We provided novel evidence of abnormal spatiotemporal PAC patterns linked to emotional processing deficits. Reduced DGC and TGC, along with increased AGC, suggest potential biomarkers in MDD.

Pump-induced stimulated superradiant Smith-Purcell radiation with ultra-narrow linewidth

Lasers with the gain medium of gas, liquid, semiconductor, and solid could generate coherent light with rather narrow spectral linewidth, which play an important role in the fields of communication, measurement, sensing, and so on. Although free electron lasers have been realized with their unique advantages, they face challenges in narrowing the spectral linewidth, owing to electron energy fluctuation, Coulomb effect, and other mechanism. Here we demonstrate the superradiant Smith-Purcell radiation (S-SPR) in terahertz frequency band with ultra-narrow and continuously tunable linewidth in a compact device. By proposing a new effect of pump-induced stimulated S-SPR (PIS-SPR), the spectral linewidth could be reduced to 0.3 kHz @ 291.7 GHz, which is about two–six orders of magnitude narrower compared with those obtained by accelerators and other electron devices. Meanwhile, the wide range of continuously tunable spectral linewidth spanning 0.3–900 kHz is observed for the first time. This work provides a way to greatly narrow the spectral linewidth of free electron radiation and to achieve high-order harmonic of S-SPR in a compact device, and offers a platform to study the interaction between free electron bunches and different micro-&nano-structures.

High-Frequency Oscillation Suppression Strategy for Renewable Energy Integration via Modular Multilevel Converter—High-Voltage Direct Current Transmission System Under Weak Grid Conditions

To address the high-frequency resonance issues in renewable energy systems integrated via MMC-HVDC transmission under weak grid conditions, this paper establishes a wide-frequency sequence impedance model for renewable energy grid-side converters and MMC-HVDC sending-end converters. The impedance characteristics of the MMC-HVDC transmission system under two distinct control modes are compared, and the constant power control mode is selected for detailed analysis to better evaluate the effectiveness of suppression strategies. Based on this framework, the superposition theorem is employed to analyze the interaction mechanism between the impedance characteristics of the MMC-HVDC sending-end converter and the renewable energy grid-connected system. Since the aim of this study is to propose suppression strategies for the MMC-HVDC transmission system, a sensitivity analysis of its control parameters is conducted. The results identify the current loop and voltage feedforward control as the dominant factors influencing high-frequency oscillations. Accordingly, a coordinated control strategy combining current loop regulation and voltage feedforward compensation is proposed. An electromagnetic transient simulation model is developed in MATLAB/Simulink. The simulations demonstrate that the proposed strategy effectively suppresses oscillations in the MMC-HVDC system across high-frequency ranges. Furthermore, it avoids negative damping characteristics within a broad frequency band, significantly enhancing the steady-state performance of renewable energy systems integrated via MMC-HVDC transmission.

Cross brain reshaping in congenital visual or hearing impairment: triple-network dysfunction

Abstract This research examines how congenital visual or hearing impairment reshapes brain function using EEG. The study involved 40 children with congenital visual impairment, 40 with hearing impairment, and 42 age and gender-matched normal children as controls. The investigation included assessments of visual and auditory abilities, along with comprehensive EEG evaluations. Techniques such as source localization, functional connectivity, and cross-frequency coupling were used to analyze variations in brain activity. Machine learning methods, specifically support vector machines, were utilized to identify key reshaping characteristics associated with congenital impairments. Results showed reduced activation in the visual cortex for visually impaired children and decreased activation in the auditory cortex for hearing-impaired children compared to the control group. Both impairment groups demonstrated significant reductions in functional connectivity across various brain regions, including the visual and auditory cortices, insula, parahippocampal gyrus, posterior cingulate gyrus, and frontal cortex. The machine learning model highlighted aberrant connectivity between the visual/auditory cortex and the right insula, the medial prefrontal cortex and dorsolateral prefrontal cortex, and the visual and auditory cortex in children with these impairments in the alpha frequency band. Spatially similar patterns of cross-frequency coupling of rhythmic activity were also observed. The study concludes that congenital visual and hearing impairments significantly impact brain development, identifying distinct functional characteristics and shared reshaping patterns. The consistent presence of dysrhythmic activity and reduced functional connectivity suggest the existence of a triple network anomaly.

Terahertz broadband achromatic focusing vortices

In this paper, we propose to combine an achromatic lens phase and a spiral phase in the metadevice phase profile to achieve terahertz (THz) broadband achromatic focusing vortices in the frequency range from 0.8 THz to 1.3 THz. The designed metadevices are composed of elliptical high-resistivity silicon pillars with different sizes to cover the propagation phase from −π to π. The particle swarm optimization (PSO) algorithm is implemented to search for the most suitable metaatoms in the structure library to achieve the THz broadband achromatic focusing vortices. The lens phase and spiral phase are simultaneously considered in the PSO algorithm to determine the reference phase values, which can optimize the achromatic characteristics of focusing vortices. The broadband achromatic characteristics are confirmed at design and non-design frequencies, demonstrating the implementation of broadband achromatic focusing vortices across the entire design THz frequency band. Our design enables broadband THz focusing vortices to be detected in the same area, which has great application prospects in THz communication systems and THz information processing.

Natural fabric wearable high isolation fractal MIMO antenna for wireless communication and 5G uses

The integration of material science into wireless communication has facilitated the development of textile-based antennas, particularly for wearable 5 G and next-generation communication systems, including military Défense applications. This paper presents a multi-band, natural fabric-based MIMO antenna featuring a Lorentz-shaped fractal structure with elliptical radiating elements. The antenna is fabricated using natural cotton fabric (εr=1.6) as the substrate, ensuring flexibility, lightweight properties, and suitability for wearable applications. It is created and modelled with the use of CST Microwave Studio Suite, resonating at 5.1, 8.7, 10.3, 10.6, 13.8, 18.3, 20.7, and 22.3 GHz, which makes it perfect for 5 G and advanced wireless networks. The antenna employs microstrip line feeding and maintains robust MIMO functionality, with an envelope correlation coefficient (ECC) of ≤ 0.0027, ensuring minimal signal interference. Additionally, the diversity gain (DG) exceeds 9.99 dB (9.9946 dB), and the antenna achieves strong isolation of ≤ − 37 dB. Unlike conventional rigid antennas, the proposed design does not incorporate a defected ground structure (DGS), yet it ensures stable gain and consistent performance across multiple frequency bands. A comparative analysis with various textile-based antennas highlights its superior compactness, flexibility, and isolation performance. These features establish the antenna as an optimistic candidate for wearable, rapid pace of data, and energy-efficient communication systems for 5 G and beyond.

State of the Art of Low-Frequency Acoustic Modulation: Intensity Enhancement and Directional Control.

High-intensity low-frequency acoustic sources with directivity play a significant role in various fields such as medical treatment, underwater communication, and environmental monitoring. However, the long wavelengths, strong penetration, and their tendency to easily diffract of low-frequency acoustic waves make it challenging to achieve directional control and intensity enhancement. Thanks to the development of acoustic metamaterials, acoustic devices can now effectively manipulate low-frequency acoustic waves at subwavelength scales with excellent acoustic performance. Currently, the directional control and intensity enhancement of low-frequency acoustic waves mainly concentrate on source design and the modulation of propagation processes. These techniques employ acoustic resonance, focusing, and other phase control methods to achieve energy concentration and directional control of low-frequency acoustic waves. Nevertheless, existing low-frequency acoustic wave control techniques still face issues such as low energy efficiency, poor directional control, and limited controllable bandwidth. This paper systematically reviews methods for achieving high-intensity emission and directional control of low-frequency acoustic waves, comprehensively compares the advantages and disadvantages of various technologies, and discusses how to extend these methods to lower acoustic frequency bands, aiming to provide new insights for the development of miniaturized, efficient, and accurately directional ultra-low frequency acoustic devices.

Multifunctional Hierarchical Metamaterials: Synergizing Visible-Laser-Infrared Camouflage with Thermal Management

With the rapid development of multispectral detection technology, realizing the synergistic camouflage and thermal management of materials in multi-band has become a major challenge. In this paper, a multifunctional radiation-selective hierarchical metamaterial (RSHM) is designed to realize the modulation of optical properties in a wide spectral range through the delicate design of microstructures and nanostructures. In the atmospheric windows of 3–5 μm and 8–14 μm, the emissivity of the material is as low as 0.14 and 0.25, which can effectively suppress the radiation characteristics of the target in the infrared band, thus realizing efficient infrared stealth. Simultaneously, it exhibits high emissivity in the 2.5–3 μm (up to 0.80) and 5–8 μm (up to 0.98) bands, significantly improving thermal radiation efficiency and enabling active thermal management. Notably, RSHM achieves low reflectivity at 1.06 μm (0.13) and 1.55 μm (0.005) laser wavelengths, as well as in the 8–14 μm (0.06) band, substantially improving laser stealth performances. Additionally, it maintains high transmittance in the visible light range, ensuring excellent visual camouflage effects. Furthermore, the RSHM demonstrates exceptional incident angle and polarization stability, maintaining robust performances even under complex detection conditions. This design is easy to expand relative to other frequency bands of the electromagnetic spectrum and holds significant potential for applications in military camouflage, energy-efficient buildings, and optical devices.

Seismic Response Analysis of Buried Nuclear Power Plant Structures in Non-Bedrock Sites

In this paper, a refined 3D direct finite element model including nuclear power plant structures and soil is developed. The wave input method, including free-field loads and a viscous spring artificial boundary, is used. The effects of structural burial depths on the seismic response of power plant structures are studied. Research shows that the seismic response of this new nuclear power structure is influenced by structural burial depths. The seismic response of the acceleration response and relative floor displacement decreases significantly with increasing structural burial depths. The floor spectrum in the low-frequency region is less influenced by different burial depths. The region of the frequency band corresponding to the peak floor spectrum is significantly influenced by different burial depths. The frequencies corresponding to the peak of the floor spectrum shift towards the lower-frequency bands. The higher-frequency bands of the floor spectrum are less influenced by different burial depths.

Acoustic Features of Airway Protective Maneuvers as Biomarkers of Radiation-Associated Dysphagia and Penetration/Aspiration in Head and Neck Cancer Patients.

This study aimed at identifying acoustic features of airway protective maneuvers as biomarkers of radiation-associated dysphagia, involving penetration/aspiration and pharyngeal residue. Temporal and spectral acoustical analyses were carried out on voluntary coughs, voluntary throat clearings, and reflexive coughs. Head and neck cancer patients with and without penetration/aspiration were compared. The same was done for patients and healthy controls. A decreased convexity of the amplitude contour and decreased salience of periodicity in the frequency band 0-400 Hz were observed in induced reflexive coughs of patients compared to healthy controls. A longer length and a less steep slope of the amplitude contour of voluntary throat clearings were observed in patients with penetration/aspiration versus those without. Acoustic features of induced reflexive cough discriminate between patients and healthy controls, but do not relate to penetration/aspiration. However, acoustic features of voluntary throat clearing are associated with penetration/aspiration in head and neck cancer patients.

Attempts at Pseudo-Inverse Vibro-Acoustics by Means of SLDV-Based Full-Field Mobilities

Lightweight components can have structural integrity and reliability concerns, coming from dynamic airborne pressure fields. Hardly tuned numerical structural models may enter into vibro-acoustic simulations of the pressure fields radiated by vibrating plates, potentially masking the forecast of severe outputs. Instead, this paper proposes—for the direct and inverse vibro-acoustic approaches—to characterise the broad frequency band structural dynamics of radiating surfaces by means of experiment-based full-field contactless techniques, with increased spatial resolution, but without the inertia-related distortions of traditional measurement transducers. The SLDV-based mobilities bring the real-life behaviour of the component into the vibro-acoustic simulations, with the actual realisation-related complete structural dynamics and broad frequency band excitation. The paper aims at assessing the procedure for the estimation, in the whole spectrum, of the airborne force, which can be transmitted by an airborne pressure field to known structural locations. The simulation tools revisit the simple Rayleigh integral approximation of sound radiation from a vibrating surface, a real thin flat plate, describable by SLDV-based complex-valued full-field mobilities. Airborne pressure fields and excitation forces concern the early attempts of direct and pseudo-inverse vibro-acoustics. Details, examples and considerations about the whole procedures are thoroughly provided: on the simulation of the vibro-acoustic transfer matrix and of the radiated sound pressures with given excitation forces; on the retrieval of the airborne forces in restraining locations, together with the assessment of the numerical precision of the retrieving procedure.

Tailored Multi-Band Microwave Absorption Performance via Entropy Engineering in Spinel Ferrite/Carbon Nanofiber Composites.

The development of electromagnetic microwave absorption (EMA) materials with broad frequency compatibility remains a great challenge, as most of the conventional materials fail to deliver effective microwave attenuation across multiple frequency bands owing to the inferior balance between dielectric and magnetic components. To address this, a novel entropy engineering strategy is presented to fabricate spinel ferrites/carbon composite nanofibers through a combined electrospinning and heat-treatment method as versatile candidates for microwave absorption. Distinct from the traditional spinel oxides, the customized atomic species in MNZCFO/C nanofibers offer superior control over electromagnetic attenuation in specific frequency bands, enabling enhanced multi-band absorption properties. Notably, (Mn0.05Ni0.45Zn0.05Co0.45)Fe2O4/C (MNZCFO/C-3) nanofibers exhibit an optimal reflection loss (RL) value of -54.62dB with a matching thickness of 2.03mm and a maximum effective absorption bandwidth (EAB) of 7.28GHz with low filling ratio of 15wt.%. Additionally, (Mn0.25Ni0.25Zn0.25Co0.25)Fe2O4/C (MNZCFO/C-2) nanofibers display tunable multi-band absorption characteristics, with effective absorption behaviors shifting across a wide frequency range (3.84-18GHz). This work presents an innovative strategy for tailoring multi-band EMA materials with flexible and tunable absorption capabilities.

Оценка параметров модели подводного аппарата на основе расчета характеристик рассеяния нестационарного сигнала

The results of a numerical solution of the problem of scattering an unsteady sound signal on a finite isotropic cylindrical shell located in an infinite liquid medium are obtained. The shell has hemispherical tips and is considered as a model of the hull of an uninhabited underwater vehicle. Incident pulses from a rectangular envelope and frequency-modulated pulse signals at different angles of the model location are considered. The solution of the problem involves decomposing the Fourier images of the pressures and potentials of the shell material into series according to the eigenfunctions of the Helmholtz equation for a given surface shape. Using the spectrum of the scattered signal in the frequency band, the shape and duration of the scattered pulse are found. To calculate the latter, the values of the angular scattering characteristics of stationary sound were used, obtained based on the numerical solution of the boundary integral equation at nodal points on the shell surface. The temporal and spectral scattering characteristics for different shell thicknesses and materials for the reverse, specular, and shadow directions are calculated and analyzed.