Frequency Bands Of Spectrum Research Articles

Development and Characterization of a Flexible Soundproofing Metapanel for Noise Reduction

This study addresses the critical challenge of developing lightweight, flexible soundproofing materials for contemporary applications by introducing an innovative Flexible Soundproofing Metapanel (FSM). The FSM represents a significant advancement in acoustic metamaterial design, engineered to attenuate noise within the 2000–5000 Hz range—a frequency band associated with significant human auditory discomfort. The FSM’s novel structure, comprising a box-shaped frame and vibrating membrane, was optimized through rigorous finite element analysis and subsequently validated via comprehensive open field tests for enclosure-type soundproofing. Our results demonstrate that the FSM, featuring an optimized configuration of urethane rubber (Young’s modulus 6.5 MPa) and precisely tuned unit cell dimensions, significantly outperforms conventional mass-law-based materials in sound insulation efficacy across target frequencies. The FSM exhibited superior soundproofing performance across a broad spectrum of frequency bands, with particularly remarkable results in the crucial 2000–5000 Hz range. Its inherent flexibility enables applications to diverse surface geometries, substantially enhancing its practical utility. This research contributes substantially to the rapidly evolving field of acoustic metamaterials, offering a promising solution for noise control in applications where weight and spatial constraints are critical factors.

Radiation Behavior of Synthesized LiTi Ferrite Based Microstrip Antenna in X Band

The paper comprehensively explores the development, characteristics, and antenna applications of lithium titanium (LiTi) ferrite. Utilising a solid-state reaction technique, the study examines the substrate’s electrical, magnetic, and structural properties in detail. Additionally, it assesses the far-field radiation patterns of a magnetically-biased LiTi ferrite-based antenna. Key findings point to a noticeable reduction in mutual coupling and radiated power, along with an isotropic redistribution of minor side lobes. Comparative analysis with RT-duroid substrates in X band frequency spectrum highlights the LiTi ferrite-based antenna’s remarkable 62.85 % miniaturization and consistent directivity, along with a superior quality factor. These findings emphasise LiTi ferrite’s potential for compact, high-performance applications in demanding environments. LiTi ferrite’s advantages in miniaturisation and stability position it for specific applications, despite trade-offs in bandwidth, gain, and impedance compared to RT-duroid substrates.

Synthesis and characterization of flexible CaCoAlFe2O4 based microwave substrate for triband polarization-insensitive metamaterial absorber

This study investigated CaxCo(0.90-x)Al.01Fe2O4 nanoparticle synthesized using the sol–gel synthesis method to achieve a flexible substrate with a high dielectric constant value. The XRD, FESEM, and dielectric characteristic is analyzed to explore the performance of the suggested Ox Wheels-shaped (OWS) metamaterial absorber unit cell. The X-ray diffraction (XRD) analysis found significant peaks at 30° (318), 33° (176), 35° (794), 43° (232), 53° (116), 57° (256), 62° (304), and 74° (126) planes. The dielectric constant values of the prepared nanomaterial materials are 4.52 (X = 90 %), 4.73 (X = 60 %), and 5.07 (X = 30 %) due to the deviations in raw material compositions. The prepared, flexible substrate is used in the anticipated OWS metamaterial absorber unit cell, and analysis has been widely considered and continuously concerned due to their excellent ultra-thin thickness, lightweight, and high absorbance resonance features. The predicted structure reached S21 response at 3.47 GHz, 7.05 GHz, and 10.76 GHz with the magnitude of −24.11 dB, −17.07 dB, and −19.19 dB, respectively, using CST simulation software. The absorber prototype is measured for further investigation within the frequency range of 2.25–2.76, 5.84–6.15 GHz, and 9.63–9.76 GHz, where maximum magnitude is achieved at 2.50 GHz, 6.02 GHz, and 9.70 GHz, respectively. This specific resonance frequency reached the highest 99.61 %, 98.03 %, and 98.79 % absorption, which covers the S, C, and X band frequency spectrum. Various electrical, magnetic, mechanical, and multi-parameter responses are examined to achieve almost perfect absorption (PA). The enormous range of possible uses of metamaterial, such as absorber wave modification, infrared imaging, radiative cooling, energy harvesting, and chemical detection, makes it appreciated. The CaCoAlFe2O4 ferrite-based flexible metamaterial absorber structure has ultra-thin, flexible, and non-corrosive advantages.

A finite element framework for fluid–structure interaction of turbulent cavitating flows with flexible structures

We present a finite element framework for the numerical prediction of cavitating turbulent flows interacting with flexible structures. The vapor–fluid phases are captured through a homogeneous mixture model, with a scalar transport equation governing the spatio-temporal evolution of cavitation dynamics. High-density gradients in the two-phase cavitating flow motivate the use of a positivity-preserving Petrov–Galerkin stabilization method in the variational framework. A mass transfer source term introduces local compressibility effects arising as a consequence of phase change. The turbulent fluid flow is modeled through a dynamic subgrid-scale method for large eddy simulations. The flexible structure is represented by a set of eigenmodes, obtained through a modal decomposition of the linear elasticity equations. While a partitioned iterative approach is adopted to couple the structural dynamics and cavitating fluid flow, the deforming flow domain is described by an arbitrary Lagrangian–Eulerian frame of reference. We establish the fidelity of the proposed framework by comparing it against experimental and numerical studies for both rigid and flexible hydrofoils in cavitating flows. Under unstable partial cavitating conditions, we identify specific vortical structures leading to cloud cavity collapse. We further explore features of cavitating flow past a rigid body such as re-entrant jet and turbulence-cavity interactions during cloud cavity collapse. Based on the validation study conducted over a flexible NACA66 rectangular hydrofoil, we elucidate the role of cavity and vortex shedding in governing the structural dynamics. Subsequently, we identify a broad spectrum frequency band whose central peak does not correlate to the frequency content of the cavitation dynamics or the natural frequencies of the structure, indicating the induction of unsteady flow patterns around the hydrofoil. Finally, we discuss the coupled fluid–structure dynamics during a cavitation cycle and the underlying mechanism associated with the promotion and mitigation of cavitation.

Time-Series Signals of Affect and Neural Dynamics with Technology to Identify Depression Risk

Despite extensive research documenting the impact of depression on basic human developmental parameters (employment, health, education, social roles, and overall quality of life), multiple individual and systemic barriers limit accessibility to clinical assistance among vulnerable populations. Research-backed digital interventions, such as smartphone applications, may serve as convenient and reliable tools for detecting and monitoring depressive symptoms and attenuate the increasing pressure on conventional mental health resources. This review evaluates the significance of key time-series signals of affect dynamics (average levels, granularity, variability, instability, inertia) and electroencephalographic (EEG) patterns (power spectrum of frequency bands, alpha asymmetry) in predicting critical transitions in depressive symptom severity. An evidence-based prototype for a smartphone application that can reliably integrate multivariate time-series signals of affect dynamics and neural oscillations is proposed, to prospectively anticipate and detect affective abnormalities with greater accuracy in individuals susceptible to depression.

IoT Frequency Band Canalization in Indonesia as a Recomendation For Preparation Machine-to-Machine Communication in The 5G Era

The development of cellular technology in Indonesia is accompanied by the widespread use of cellular com-munication in various aspects, one of which is its use in machine-to-machine(M2M) communication and con-necting to the Internet, often called the Internet of Things (IoT). 5G Enables large in-text connections with ex-tremely low power consumption and costs, which will drive the development of IoT technology and enable "everything connectivity." because the use of IoT is starting to grow and helping humans in all aspects, it is possible to change its name to the Internet of Everything (IoE). However, the absence of special regulations regarding the use of the IoT frequency spectrum in Indonesia allows for interference or other disturbances if there is massive use of IoT technology in the future. This research was conducted by studying primary and secondary data to provide rec-ommendations related to special frequency band canalization for IoT in Indonesia. The author classifies fre-quency canalization for IoT into 2 classes, namely class A (for short-distance transmission) in the 433 MHz spectrum and class B (for long-distance transmission) in the 915 MHz spectrum. We also hope that the Indone-sian government decides to serve a new unlicensed spectrum frequency band in the range of 915-921 MHz. This is a good step towards global harmonization of unlicensed spectrum that can grow LPWAN-based IoT.

Double Band MIMO Antenna Design for WLAN, IoT and LTE Applications

This paper presents a double band multiple-input multi-output (MIMO) antenna design for UWB applications, WLAN 2.4 GHz, WiMAX 3.3 – 3.6 GHz, Internet of Things (IoT) and LTE 9/24 38/41 48/52 bands. Two circular patches form the MIMO antenna array with an “I” shaped EBG structure inserted between the patch antennas to improve the isolation between elements. The The low frequency band spectrum is from 1.03 GHz to 5.03 GHz, and the high frequency band spectrum is from 6.13 GHz to 11.62 GHz. The maximum isolation between ports at 3.8 GHz and 6.9 GHz are 7 dB and 8 dB, respectively. The antenna gain at 7 GHz reaches 4.05 dB.

Bicontrollable all dielectric metasurface absorber for chemical and biosensing applications

A bi-controllable all dielectric metasurface structure is designed at terahertz, which consists of an InAs micro-cylindrical array on the gold ground plane. The maximum absorptance frequency is tunable with the help of an external magnetic field and also by geometrical rotation of the metasurface as InAs is a gyrotropic material whose property depends on the magnitude and direction of an external magnetic field. Simulation results indicate that the proposed metasurface can achieve an absorptance of more than 99 % at 9.756 THz as well as it can provide a high tunability rate of around 2.55 THz T−1 in lower band and 3.33 THz T−1 in the upper band frequency spectrum with the application of the magnetic field. Additionally, the metasurface also acts as polarization insensitive when no external magnetic field is applied. Furthermore, the maximum absorptance frequency shows sensitivity towards the change in the refractive index value of the surrounding medium, thus the metasurface can be used for chemical and biosensing applications. It shows high chemical sensitivity of around 2727 GHz/RIU for the detection of different chemicals and bio sensitivity of 787 GHz/RIU for the detection of various viruses.

10-Hz tACS up-regulates a visual attention network and down-regulates the rich club

Abstract Synchronization of oscillatory brain activity may play a critical role in linking distributed neuronal populations into transient functional networks, with up-regulation of engaged networks during task performance accompanied by down-regulation of less salient networks. Can tACS be used to elicit network-specific changes in brain function, given that the distributed nodes of a network may experience varying amplitudes of exogenous current flow? We utilized MEG to characterize brain dynamics following bilateral parietal 10-Hz tACS during a visual attention task (8 healthy adults; 1 mA, verum/sham 20 min/30 s). Regions of interest included a cortico-cerebellar sensory processing network (SP: frontal, parietal, temporal cortex, hippocampus, cerebellum) and the Rich Club (bilateral superior parietal and frontal cortex, precuneus, hippocampus). Persistent changes in local oscillatory dynamics were seen in the SP network across a broad spectrum of frequency bands. Changes in alpha-band activity extended before, during, and after presentation of global/local letter images, consistent with a tonic influence of the 10-Hz tACS on alpha-band dynamics. Up-regulation of alpha and down-regulation of theta throughout the SP network was consistent with results seen in previous working memory studies. Moreover, increases in alpha were accompanied by increased gamma-band activity, consistent with a cross-frequency relationship between these rhythms. In contrast, down-regulation of alpha was characteristic of regions in Rich Club, with the exception of up-regulation in superior parietal cortex. Interestingly, despite a lack of consistency of a reciprocal relationship between alpha and theta in the Rich Club, the stimulation also reduced both theta and gamma-band activity, suggesting a role for theta-gamma coupling in the Rich Club. Our results suggest that tACS may provide a method for identifying and up-/down- regulating individual brain networks. Importantly, identifying tACS parameters that maximize changes to specific networks may be critical to increase efficacy and reduce potential negative side-effects of tACS. Research Category and Technology and Methods Basic Research: 8. Transcranial Alternating Current Stimulation (tACS) Keywords: tACS, MEG, Network, Visual Attention

Subjective time is predicted by local and early visual processing

Time is as pervasive as it is elusive to study, and how the brain keeps track of millisecond time is still unclear. Here we addressed the mechanisms underlying duration perception by looking for a neural signature of subjective time distortion induced by motion adaptation. We recorded electroencephalographic signals in human participants while they were asked to discriminate the duration of visual stimuli after different types of translational motion adaptation. Our results show that perceived duration can be predicted by the amplitude of the N200 event-related potential evoked by the adapted stimulus. Moreover, we show that the distortion of subjective time can be predicted by the activity in the Beta band frequency spectrum, at the offset of the adaptor and during the presentation of the subsequent adapted stimulus. Both effects were observed from posterior electrodes contralateral to the adapted stimulus. Overall, our findings suggest that local and low-level perceptual processes are involved in generating a subjective sense of time.

Estimation Based on Chirp Modulation for Desired and Interference Power and Channel Occupancy Ratio in LoRa.

In terms of low power consumption and long-range communication—low-power wide-area networks (LPWAN) are suitable for wireless sensor networks. Long-range (LoRa) wireless communication is one of the standards of LPWAN. LoRa shares common frequency spectrum bands with both multiple transmitters, which are the sensors in the LoRa system (and those in the other system). Therefore, co-channel interference (CCI) degrades the packet delivery rate. To avoid CCI, the CCI power and the occurrence probability of CCI in the target channel are estimated, then the sensor decides whether to use the channel and where the occurrence probability of CCI is defined as the channel occupancy ratio (COR). If a large signal power is obtained at the receiver, the received signal can be demodulated because of the capture effect. The desired signal power must also be estimated for the capture effect. In this study, we propose an estimation scheme based on chirp modulation of LoRa under spectrum sharing among other systems. The proposed scheme estimates the desired signal power, CCI power, and COR. From the computer simulation results, we clarify the advantages of the proposed scheme in terms of estimation accuracy and packet delivery rate.

Laser Vibration Characteristics of Marble Specimens and Failure Criterion

Rock failure and instability usually lead to significant engineering disasters. This paper aims to establish an experimental failure criterion to predict rock failure via testing the laser vibration characteristics of marble specimens. Uniaxial compression tests and Brazilian tests were carried out on marble specimens coupled with acoustic emission technology and laser Doppler vibrometry measurement technology. The whole laser vibration waveform of the marble specimen was divided into elastic stage, plastic stage, and failure stage. Although different frequency spectrum characteristics were identified in different waveform phases, a wide frequency spectrum was always present prior to rock failure. Furthermore, the wide frequency band frequency spectra characteristics took place 30.9 s and 21.3 s earlier than the rapid increase of the acoustic emission counts in the uniaxial compression test and Brazilian test, respectively. Taking the wide frequency spectrum as a failure criterion for the failure of loaded marble is quick, convenient, and reasonable. Using laser Doppler vibrometry measurement has the advantages of being remote, non-contacting, and earlier warning. This research can provide a reference for the further study of forecasting rock failure.

Fiber-optic temperature sensor based on beat frequency and neural network algorithm

A multi-longitudinal mode fiber laser sensor (MLMFLS) system based on neural network (NN) algorithm is proposed. Gaussian process regression (GPR) is used to denoise the beat frequency signal (BFS). The frequency change of BFS has a linear relationship with the applied external temperature change. Neural network algorithm is used to fit the linear relationship between the frequency of BFS and external temperature change. Processing and analysis of experimental data showed that the method fitted very well with the relationship between the beat frequency signal and external temperature change. The MATLAB App Designer tool is used to display the wide band frequency spectrum, frequency of BFS and corresponding temperature change. The sensitivity of single beat frequency is 5.204 kHz/℃, the maximum absolute error is ± 0.15 ℃ and the average error is 0.072 ℃. The five beat frequencies sensitivity is 5.206 kHz/℃, the maximum absolute error is ± 0.09 ℃ and the average error is 0.055 °C. Through the combination of neural network algorithm and beat frequency sensing system, simple, fast and real time temperature sensing is realized.

Sensing and analysis of spectrum holes in ISM band using USRP testbed

The spectrum frequency in the wireless communication industry is getting great attention due to the internet of things (IoT) technology's growth. However, the radio spectrum's frequency band use is limited because the primary user for specific services can cause spectrum interference as multiple users use the same spectrum frequency. Meanwhile, at each spectrum frequency, the number of users and utilization time are distinct. These will create vacancies for spectrum frequency assigned to the primary user. A new alternative in using the cognitive radio (CR) spectrum is accessible to these vacancies. This paper analyzed the frequency spectrum in the industrial, scientific and medical (ISM) band and identified spectrum holes for transmission by the secondary users. This work employed a realistic approach by measuring the spectrum using Universal Software Radio Peripheral (USRP) devices. Thus, the spectrum holes in the frequency spectrum had distinguished by using an energy detection technique. In the energy detection technique, the threshold energy level is set and then compared with the energy detector output to identify the primary user's existence (PU). The result indicates that 0.61% of spectrum holes have been detected in the 2.43-2.44 GHz range. This range is sufficient for home appliances, radio frequency peripherals (RF), and bluetooth devices.

What drives spectrum prices in multi-band spectrum markets? An empirical analysis of 4G and 5G auctions in Europe

ABSTRACT Spectrum auctions have recently experienced increased sophistication in the allocation of multi-band frequencies, with efficiency issues becoming much more complex in such scenarios. This empirical analysis seeks to identify the drivers of auction prices associated with 4G and 5G technologies in seven European countries during the period 2008–2019. This study draws on a purpose-built dataset including auction design, spectrum frequency bands at auction, bandwidth supplied to mobile operators, and characteristics of the market structure. We use panel data techniques to identify the main determinants of European spectrum auction prices in the presence of substitutability and complementarities exhibited by the preferences in multi-band spectrum markets. In this regard, we find that mobile operators pay lower auction prices if there are alternative frequency bands used for previous mobile standards and that operators perceive as substitutes. Furthermore, auction prices are higher in more concentrated markets, when more licenses are auctioned and when the CCA format is used (possibly due to the existence of complementarities).

Wideband miniaturized patch radiator for Sub-6 GHz 5G devices

In this article, the compact wideband elliptically slotted semi-circular patch radiator with the defected ground structure for sub-6 GHz applications is designed and developed. The proposed miniaturized patch radiator offers flexibility in adjusting the band of operation by varying the slot dimensions. The effective size reduction is achieved by comparing different iterations in the process of designing and the size of the regular circular-shaped radiator is reduced into the semi-circular radiating patch. The impact of the variation of effective radius of the semi-circular patch, major-axis radius of the elliptical slot, ground plane length, and feed line width is investigated. The size of the proposed radiator is 23.885 × 23.885 × 1.405 mm3. This compact structure manifests the wide bandwidth of 2140 MHz (3.2 GHz–5.34 GHz) with 50% of fractional bandwidth (FBW). The measured results show good agreement with the simulated results. The various parameters validate the utility of the radiator in the C band of super-high frequency (SHF) spectrum and n77 (3.3 GHz–4.2 GHz), n78 (3.3 GHz–3.8 GHz), and n79 (4.4 GHz–5 GHz) bands of the frequency range 1 (FR1) of the sub-6 GHz 5G spectrum.

Overlay dynamic spectrum sharing in cognitive radio for 4G and 5G using FBMC

Dynamic spectrum sharing allows the 4G-LTE and 5G-NR to use the same frequency spectrum band for communication and the spectrum allocator allocates the spectrum to the users based on their demands. In this paper we have analyzed existing OFDM (orthogonal Frequency division multiplexing) Technique in the physical layer for the spectrum sharing and proposed a FBMC (Filter Bank Multi Carrier) technique with Long duration Pulse Shaping filter and designed a Sequence Based Spectrum Allocator for designing a high spectral efficient network. Results were validated based on the parameters like Secondary User Score and Primary User Satisfaction Ratio and Secondary user throughput for overlay spectrum sharing mode in cognitive radio.

Notched Integrated Planar Antenna for UWB Application

A new ultra-wideband antenna (UWB) with band notch characteristics has been studies in this work. The propose structure has constructed using air gap between two layer, defected ground structure (DGS) and shorting post. The structure covers frequency ranges from 4.61 GHz to 9.85 GHz. The radiation pattern is quite stable throughout the whole operating range. The antenna operates in C band of frequency spectrum and provides wide impedance bandwidth of 72%. 5.5GHz frequency has been notched and an average gain around 5.8 dBi has been achieved which is very useful for enormous data handle in modern wireless communication. All the simulation has been carried out using High Frequency Structural Simulator (HFSS) software.

On generation of a stochastic GW background by the scattering on relic wormholes

We study collective features of the scattering of gravitational waves on relic wormholes and normal matter objects. We derive and solve the GW energy transport equation and show that the scattered signal lies in the same frequency spectrum bands as the basic signal. The scattering forms long living tails which always accompany the basic signal and have a universal form. The scattering on normal matter objects forms tails which have always the retarded character, while wormholes lead to advanced tails as well. In addition, wormholes may produce considerably stronger effect when the total energy in tails detected on the Earth exceeds that in the incident direct wave. In both cases the retarding tails have a long living character when the mean amplitude behaves with time as hsim 1/sqrt{t+R/c}. For a single GW event the echo tails give only a tiny contribution to the mean amplitude. However such tails accumulate with events and form a stochastic GW background which may be observed by the contribution to the noise.

Fundamental research on surface electromyography analysis using discrete wavelet transform-an analysis of the central nervous system factors affecting muscle strength.

[Purpose] We aimed to investigate the central nervous system factors that affect muscle strength based on the differences in load and time using the discrete wavelet transform, which is capable of a time-frequency-potential analysis. [Participants and Methods] Surface electromyography (EMG) of the right upper bicep muscle in 16 healthy adult males were measured at 10% MVC (maximum voluntary isometric contraction), 30%, 50%, 70%, and 80% to 100% MVC. We used a discrete wavelet transform for the electromyographic analysis and calculated the median instantaneous frequency spectrum (MDF) and frequency band component content rate (FCR) at 1-ms intervals as well as their spectrum integrated values (I-EMG). [Results] MDF and FCR tended to be high throughout the measurements. Specifically, the high-frequency band component content rate was high at the time of low muscle strength; fast-twitch muscle fibers may be involved during these muscle contractions. We found significant changes in the I-EMG as the muscle strength increased from 10% MVC to 100% MVC. [Conclusion] Analyzing the surface electromyograph using discrete wavelet transform enabled us to assess the central nervous system factors that increase in the EMG amplitude integrated values and change in the median instantaneous frequency spectrum and in the frequency band component content rate.