Spectra In Frequency Range Research Articles

Energy-Efficient User Association in mmWave/THz Ultra-Dense Network via Multi-Agent Deep Reinforcement Learning

As a key enabler for 5G and 6G wireless communications, millimeter-wave (mmWave) and terahertz (THz) ultra-dense network (UDN) has received a great deal of attention recently. The mmWave/THz UDN can greatly improve the capacity of cellular network by exploiting the reduced path loss of densified network and the wide range of frequency spectrum. In order to maximize the capacity gain of UDN, the associations between small base stations (SBSs) and users should be designed deliberately. However, since computational complexity and signaling overhead increase exponentially with the numbers of SBSs and users, it is very difficult to apply the conventional centralized approaches in the UDN. In this paper, we propose a decentralized user association technique based on multi-agent actor-critic (AC) to maximize the energy efficiency of UDN. In our technique, actor network determines the user association of the SBS using the local observation and critic network informs the energy-efficient user association decision to the actor network. In doing so, the DRL agent in each SBS can find out the user association decision maximizing the network energy efficiency. From the extensive simulations, we demonstrate that the proposed scheme achieves more than 50 % average energy efficiency gain over the conventional user association techniques.

Design of Microstrip Antennas Array for Wireless Applications by Using HFSS

The modern wireless communication desires high gain, wide bandwidth and minimal size antennas that are efficient to provide improved performance over a wide range of frequency spectrum. This requirement leads to the design of microstrip patch antenna. This paper presents the design of compact 1X2 microstrip patch antenna array which uses the corporate feed technique for excitation. The proposed antenna is designed on FR-4 substrate with dielectric constant 4.4 and thickness 1.6mm. Dielectric constant and parameters like Return Loss, Gain and Radiation pattern are calculated using high frequency simulation software. The fabricated antennas results are to be compared with Simulation results. The antenna has been designed for the range 2.4 GHz. Keywords: Microstrip antenna, corporate feed, FR-4 substrate, Microstrip antenna array

Analysis of the Impact of Vibrations on a Micro-Hydraulic Valve Using a Modified Induction Algorithm

This paper addresses the impact of mechanical vibrations of different frequencies on a particular type of valve. It has been shown that a neural network can be used to compress measurement data and determine the frequency range that is most important in describing the impact of mechanical vibrations on a micro-hydraulic overflow valve. Later, induction decision trees were used for the generated areas, determining key measurement points. The most important areas of dependence are determined using inductive decision trees in induction. The entropy measure is used to determine the most significant attribute. A modified induction algorithm was used for the comprehensive analyses. The analysis carried out in the paper identified the intervals in which the flow rate plays a decisive role for the entire amplitude and frequency spectrum. An analysis was performed for the 200…900 [Hz] frequency interval of the external driving force, with a harmonic step of 10 [Hz]. The analysis was performed while considering these main valve parameters: the pressure of the overflow valve opening p = 10 [MPa]; flow rate in the valve: 0.6, 0.8 and 1 [dm3/min]; stiffness of valve spring c = 7.49 [N/mm]. Plots were presented and for each plot, the most important four intervals were determined. They are hierarchically ordered in the interval range of the whole frequency spectrum range: (coefficient IV)—the most important; (coefficient III)—important; (coefficient II)—less important; (coefficient I)—least important. A test rig and the results of a study on the effect of mechanical vibration on changes in the amplitude-frequency spectrum of pressure pulsations of a micro-hydraulic system, in which a micro-hydraulic relief valve was subjected to mechanical vibration, are presented.

Development of robust ultra-high-performance carbon nanofiber aggregates (UHPCNFAs) for structural health monitoring

Ultra-high-performance concrete (UHPC) is rapidly implemented to build robust, durable, and sustainable structures. This study presents the development of a robust self-sensing sensor with the motivation to monitor structures with high-performance construction material, such as UHPC. The ultra-high-performance carbon nanofiber aggregates (UHPCNFAs) are carbon nanofibers (CNFs) and UHPC-based smart aggregates. The newly developed UHPCNFAs are experimentally investigated in uniaxial compression. Sweep-frequency and fixed-frequency tests are adopted in alternating current measurements for determining the electrical behavior of the UHPCNFAs. UHPCNFAs are compressed in parallel and perpendicular loading orientations to understand the difference in the sensor's electrical sensitivity and mechanical behavior in each case. In addition, the robustness of the UHPCFNA is examined to the point of failure in both orientations. The relationship between stress, strain, and electrical impedance variation is established for eight different frequencies. Furthermore, the UHPCNFAs are compressed at a fixed frequency to verify the repeatable behavior. This paper examines the effect of loading orientations on electrical and mechanical response, robustness, and sensitivity of UHPCNFA in a wide range of frequency spectrum to check its suitability in real-time structural health monitoring.

Dynamic Downlink Interference Management in LEO Satellite Networks Without Direct Communications

We investigate effective interference management for Low Earth Orbit (LEO) satellite networks that provide downlink services to ground users and share the same frequency spectrum range. Since there are multi-group LEO satellites with different constellation orbits, the ground users will experience time-varying interference due to the overlapping of main/side lobes of the satellite beams, which becomes even challenging when the interfering satellites cannot communicate directly. To address the problem, we consider two LEO satellite groups that provide communication service in the same ground area, while competing for communication resources. We develop solutions that maximize the throughput and manage the time-varying interference under a certain level, without explicit message exchanges between the satellite groups. By exploiting statistical learning and deep reinforcement learning techniques, we develop learning-based resource allocation schemes and evaluate their performance through extensive simulations. We show their effectiveness under different reward settings and different interference managements, and demonstrate that a Deep Q-Network (DQN)-based scheme can achieve the close-to-optimal performance.

Downlink spectrum sharing of heterogeneous communication systems in LEO satellite networks

We study downlink spectrum sharing in low earth orbit (LEO) satellite networks, where wide beam coverage and side lobe beam make it hard to manage mutual interference between satellites. As a first step, we consider a two-satellite system of control satellite and interference satellite, which share the same frequency spectrum range and are located close enough to have interference each other. We investigate resource allocation strategy for the control satellite to maximize its throughput performance while satisfying interference constraints. Assuming that the control satellite has no prior knowledge about the behavior of the interference satellite, we develop online frequency allocation algorithms that successfully manage the interference by employing a learning-based design with UCB index. Under the proposed algorithms, we can maximize throughput of the control satellite while constraining interference at the interference satellite as well as at the control satellite, without any direct information exchange with the interference satellite. Through simulations, we demonstrate that the proposed schemes achieve high throughput performance satisfying interference constraints.

Related Reviews: Multiband Planar Inverted Antenna for Mobile Communication

Research in the field of planar inverted antennas with multiband frequencies is currently being developed. Due to the hugely increased number of mobile users, at least every time a new generation is released, a mobile communication system is released with additional features. All additional features of a mobile communication system require an antenna that resonates over a specific frequency spectrum range, meaning multiple antennas are required in a single mobile device to function across all generations for all frequency spectrums. To reduce the number of antennas on a mobile communication system device, it is necessary to design a new type of antenna that operates in a different frequency range. The inverted planar multiband antenna is designed to have changing sizes, shapes, and material properties. Types of inverted planar antennas include planar inverted-L antennas (PILA) and planar inverted-F antennas (PIFA). After analysis, the antenna designed by Juan Zhang et al. is the best solution for mobile communication systems. The designed antenna has compact antenna dimensions and four frequency bands that can be applied to N1/N78/N79 5G and 5.8 GHz WLAN. The antenna has a high gain of almost 5dB in the 5.60–7.00 GHz frequency range. They also claim that the antenna has a beam efficiency of four very high-frequency antenna points and a small side lobe that appears only at the top at the highest frequency point. But unfortunately, the antenna cannot cover the entire frequency range that must exist in a mobile communication system

Microstrip patch antenna design for wireless network applications

Advances in communication systems involve the promotion of low cost, low weight, light weight and low profile antennas has been improved over last few years. It has capable of maintaining higher performance over a large range of frequency spectrum. This technological trend has focused a great deal of effort on growing of micro strip patch antennas due to its unalienable characteristics. It meets the requirement of modern communication devices. In this work, the inset feed technique was used to present the design and simulation of a compact rectangular slot patch antenna for double frequency operation at 5.27 GHz. The simulation of the built antenna was performed using the 2019 studio suite of computer simulation technology (CST) and MATLAB which will be used to measure the parameters. The substrate used for the proposed antenna is the four flame-resistant (FR-4) with a dielectric constant of 4.3 and a loss tangent of 0.023. The antenna proposed could find applications in Wireless Local Area (Wi-Fi) and Bluetooth technology.

The influence of diatomite rock on humus substances of sod-podsolic soil in conditions of agro ecosystems and physical-chemical mechanism of their interaction

The paper provides an assessment of physical and chemical changes of humus substances in the sludge-colloidal fraction, isolated from the sod-podsolic sandy loamy soil, during its interaction with the diatomite rock of the Inzen deposit in conditions of agro ecosystem of the Nizhny Novgorod Region. The experience was a 3-year (2015-2017) microfield experiment, laid down on one of the fields of Elitkhoz. The diatomite was added to soil once during the summer season of 2014 in doses of 3, 6 and 12 t/ha, on which winter wheat, barley and peas were subsequently grown (varieties are zoned in the Volga-Viatskiy Region). Each year, upon completion of crop cultivation, a silo-colloidal fraction was isolated from selected soil samples by the Kachinsky gravimetric method and analyzed on an IR-Fourier-spectrometer, determining absorption spectra in frequency range of 4000-400 cm-. In soil samples the content of specific organic substance (humus) was also determined by the Thurin method with spectrophotometric termination. The studies revealed that interaction of diatomite with the organic soil matrix resulted in organosilanes RnSiH4-n (930 cm-), organosilanes oxygen-free Si-CH3 (1253 cm-) and oxygen-containing compounds Si-O-CH3 (1110 cm-), as well as siloxane bonds of Si-O-Si (570 cm-). The obtained facts directly indicate formation of silicon-containing organo-mineral complexes in sludge-colloidal fraction and participation of silicon in their formation. It is evident that an active diatomite represented by various silicon acids (HnSiOm) was involved in formation of these bonds. The use of diatomite has helped to maintain content of humus substances in soil at the control level, which can also confirm effects of interaction of silicon substances with organic part and, as a result, prevent its degradation. Based on the obtained results and analysis of scientific literature, a mechanism is proposed for possible physical-chemical interaction of active silicon substances with an organic component of the sludge-colloidal fraction of the sod-podsolic soil, which consists in polymerization of silicon on organo-mineral complexes (bonds -Si-O-Si-), as well as in interaction of the hydrolyzed part of humus substances with silicon with subsequent formation of organosilanes, which are subsequently connected with an organic Si-O-CH3 matrix. Due to the fact that organic matter of soils is involved in the formation of ecological stability of soil cover the established effects make it possible to speak about the increase of agro ecological stability of humus substances in sod-podsolic soil due to the use of diatomite rocks.

An Experimental Investigation of Enclosure’s Effect on Noise Reduction in Portable Generators (Technical Note)

The portable generators are the main means of compensating the shortage of national electricity power as in Iraq. However, their noise causes a huge disturbance, uncomforting and loss of concentration of the nearby resident. This problem requires a solution because most shops and residential houses use generators. Covering method is a simple and relatively low cost one for reduction of generators noise. In the present study, an experimental investigation is conducted for evaluating the effect of using an enclosure on noise reduction of portable generators. The enclosure is made from some available and traditional materials such as foam and plywood. The sound transmission loss due to the use of enclosure is estimated for a wide range of frequency spectrum and the results showed that used enclosure helps in reduction of noise effectively. Furthermore, it was found that the generator temperature was not affected much by the use of the present enclosure. The present study is intended to be a step stone for a development of a low cost and effective commercial enclosure of portable generator.

Rumination recognition method of dairy cows based on the change of noseband pressure

Rumination is closely related to ruminant's health and welfare, so it is very important to monitor rumination. Rumination monitoring equipment based on chewing and swallowing audio is easy to be affected by ambient noise, equipment based on acceleration sensor is not easy to monitor number of cuds and other information, equipment based on video monitoring has high cost and is easy to be affected by weather and other cows, while equipment based on chewing pressure can accurately record the chewing pressure of dairy cows, and use related processing technology to obtain the number of cuds and other information. In the related research, the peak value and interval of masticatory pressure peak in time domain were used to identify rumination. In view of the problem that the standard of pressure peak was not well defined due to the different head size and masticatory strength of different age and different breed cows, this paper proposed a method to identify the number of rumination, duration of rumination and number of cuds of cows by using standard deviation and noseband pressure signal frequency spectrum. The accurate and stable frequency spectrum range of rumination noseband pressure signal was obtained by frequency spectrum analysis, and the interference of feeding noseband pressure signal to rumination noseband pressure signal was eliminated by using standard deviation. Compared with the direct observation, the results showed that the recognition accuracy of the method proposed in this paper were 100%, 94.2% and 94.45% for the number of rumination, duration of rumination and number of cuds respectively, and the average absolute errors were 0, 2.0029% and 2.5623% respectively, which showed that the method can accurately identify the rumination information of dairy cows.

The role of mid-gap phonon modes in thermal transport of transition metal dichalcogenides**Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish

We present a comprehensive theoretical study on thermal transport in monolayer transition metal dichalcogenides MX2 (M: Mo, W; X: S, Se) with various sample sizes. An unusually high anharmonic scattering strength is found in MoSe2 compared to the other three family members, which arises from its unique phonon band dispersion, specifically the mid-frequency phonon branches associated with the vibrations of Se atoms of MoSe2. The mid-frequency modes almost completely span the gap that exists between the high-frequency phonon branches and the acoustic ones, allowing the former to readily decay into the latter. The resultant high anharmonic scattering gives rise to a short mean free path which makes the room temperature in-plane thermal conductivity in MoSe2 even lower than WSe2 when the sample length is larger than 51.5 nm. With varying sample sizes, the ordering of thermal conductivity among the four materials changes as phonon transport transits from the ballistic to diffusive regime, driven by the competition between the phonon frequency spectrum range and the scattering strength. Our work provides a microscopic picture of phonon transport in TMDs and guidance to tailor their thermal conductivities for electronic and thermoelectric applications.

An Ultra-Wideband Measurement Method for the Dielectric Property of Rocks

Dielectric properties of rocks are the important indicators of subsurface formations when electromagnetic sensing methods are applied. Interpreting those in situ measurements relies on characterizing the dielectric permittivity of rock samples in the laboratory. For solid phase samples, the parallel-plate capacitance method (PCM) serves as one of the most accurate and feasible methods for charactering electrical properties. Low-frequency (~kilohertz) PCM measurements are most common; extending the PCM to an ultra-wideband measurement will establish a general framework for measuring both low-frequency and high-frequency (~gigahertz) properties (e.g., permittivity and conductivity). Major challenges of ultra-wideband measurements using the PCM are: 1) at high frequency, the measurement apparatus may introduce errors due to reflection and dissipation of the electromagnetic waves and 2) resonance caused by impedance mismatching in the apparatus design can occur at higher frequency, which will significantly compromise the accuracy of this method. Thus, the optimization and modification of the method is needed. In this letter, we: 1) show the validity and accuracy of the PCM for permittivity measurement by comparing numerical simulation and experiments; 2) propose a practical geometric parameter to conduct system-level optimization under giving constrains; 3) perform the optimization for the sample holder to increment the measurement accuracy at higher frequency without downsizing the sample. The results show that a satisfactory accuracy and stability can be achieved in an ultra-wide range of frequency spectrum from 100 kHz to 1.5 GHz with the improved PCM apparatus design.

Irradiation effect on infrared spectra of LiF:OH crystals: Theoretical modeling

First-principles simulations of LiF:OH crystal infrared absorption spectra were performed using density functional calculations with periodic boundary conditions to explain the yet unclear nature of experimentally observed irradiation-induced absorption bands in infrared spectra in frequency range 1900–2200 and 1000–1300cm−1. To model the irradiation effect, various defect structures were explored. Simulations demonstrated that a new type of defect should be taken into consideration to explain the infrared spectra features. Specific new defect is formed by one fluorine atom displaced from the lattice site into the interstitial position due to irradiation. At the same time, hydrogen atom, produced by of hydroxyl group radiolysis decay, occupies position between fluorine atoms in anionic (Fa) and interstitial (Fi) positions forming covalently bonded negatively charged defect, referred to as F-H-F complex. Asymmetrical stretching oscillation of this defect complex is responsible for infrared absorption band near 2200cm−1. Features in the infrared spectra observed near 1000cm−1 originate from two types of vibrations: bending vibrations of proposed new defect complex and oscillations of hydrogen ions in the anionic positions. Defect formed by negatively charged hydrogen ion in interstitial position results infrared absorption band at 1288cm−1. The experimentally observed decrease of the oscillation frequency near 2200cm−1 under further irradiation is associated with increase of negative charge value on the proposed defect complex caused by F-centers creation.

Numerical aperture influences on image speckle fields near a random surface

In order to reveal influences of numerical aperture on image speckle fields near a random surface, we adopt a convenient and practical method to make it. We choose an interference pattern of a reference light and an image speckle field, and then obtain its first-order frequency spectrum by Fourier transform. In inverse Fourier transform, we change the range of the frequency spectrum, and different distributions of speckle intensities, phase and phase vortices are presented. In addition, their statistical properties are also given. It is shown that with a decrease of range of the first-order frequency spectrum, equivalent to numerical aperture reduced, image speckle fields take on different features. Moreover, their statistical properties are distinct from each other. This paper is significant to understand influences caused by numerical aperture on image speckle fields and helpful for applications of speckle fields near a random surface.

Stabilizing derma collagen structure with modified dispersions of montmorillonite

The article reviews structural changes of derma collagen resulting from processing with modified montmorillonite dispersions. The infrared spectroscopic studies of gelatin as a simulated collagen established chemical interaction of chromium modified montmorillonite dispersions with reactive groups of the native protein. The derma collagen structure is stabilized through formation of hydrogen bonds with the surface hydroxyl groups of montmorillonite of Si-O... H-C and Si-O- H...O-C type. The formation of hydrogen bond between the nitrogen atoms of amino groups of collagen and the water proton in the interlayer space of MMT with cations in the exchange complex is possible. The formation of hydrogen bonds of Si-O....H-C type between the functional groups of chromium modified montmorillonite with CH- groups of protein, as well as Si-O....H-N with NH - groups of protein in the low- frequency spectrum range is also very likely. The efficiency of stabilizing collagen with chromium modified montmorillonite dispersions is proven by an increase of the gelatin melting temperature with mineral consumption of 3-4% of protein weight and chromium compounds (III) for the modification of the mineral around 10% of montmorillonite weight.

Investigation of underwater sound scattering on a cylindrical shell coated with anechoic coatings by the finite element method based on an equivalent parameter inversion

Anechoic coating attached to the surface of an underwater object is used for absorbing sound wave thereby reducing the reflection. The anechoic coating is often made of viscoelastic materials embedded with designed acoustic substructures, such as air cavities. The prediction of sound scattering on underwater object coated with such materials can be challenging due to the complex geometry of the anechoic coating, and it has been a research subject of interest in underwater acoustics. In this paper, we study the sound scattering on an infinite cylindrical shell coated with anechoic coating. Two types of coatings are considered: one is a layer of homogeneous isotropic material, and the other is a layer of homogeneous isotropic material with periodically embedded cylindrical air cavities. We use an equivalent method, in which the anechoic coating with air-filled cavities is regarded as a homogeneous isotropic material with equivalent material properties. The key point of the equivalent method is to ignore the internal structure of the anechoic coating, and the anechoic coating is considered as a homogeneous isotropic layer with the same complex reflection coefficient. These equivalent material properties are acquired based on the data of complex reflection coefficient obtained from either the physical experiment using water-filled impedance tube or the numerical experiment using the finite element method with COMSOL Mutiphysics software. Then a genetic algorithm is developed to inversely calculate the equivalent Young's modulus, Poisson's ratio, and damping loss factor of the coating which has the same reflection coefficient as the original coating. The results of the equivalent material properties show that 1) the three properties are all frequency dependent; 2) in general, equivalent Young's modulus increases with the increase of frequency, meanwhile the equivalent damping loss factor tends to decrease; 3) there is a wide variation in the results of equivalent Poisson's ratio. Despite that, the reflection coefficient of the equivalent homogeneous isotropic coating accords well with that of the original coating.Based on the above, the sound scattering on the infinite cylindrical shell coated with the equivalent coating is calculated by using the finite element method based on COMSOL Mutiphysics software. In order to verify the accuracy of the equivalent model, we use COMSOL Mutiphysics software to build up the full geometrical model of the coated shell to calculate the sound scattering. This can be considered as the benchmark. The results of morphic function show that the scattering calculated using equivalent material properties accords well with that obtained from the full finite element model with a mean error of about 1 dB in all frequency spectrum range.

A continuous wavelet transform approach for harmonic parameters estimation in the presence of impulsive noise

Impulsive noise caused by some random events has the main character of short rise-time and wide frequency spectrum range, so it has the potential to degrade the performance and reliability of the harmonic estimation. This paper focuses on the harmonic estimation procedure based on continuous wavelet transform (CWT) when the analyzed signal is corrupted by the impulsive noise. The digital CWT of both the time-varying sinusoidal signal and the impulsive noise are analyzed, and there are two cross ridges in the time–frequency plane of CWT, which are generated by the signal and the noise separately. In consideration of the amplitude of the noise and the number of the spike event, two inequalities are derived to provide limitations on the wavelet parameters. Based on the amplitude distribution of the noise, the optimal wavelet parameters determined by solving these inequalities are used to suppress the contamination of the noise, as well as increase the amplitude of the ridge corresponding to the signal, so the parameters of each harmonic component can be estimated accurately. The proposed procedure is applied to a numerical simulation and a bone vibration signal test giving satisfactory results of stationary and time-varying harmonic parameter estimation.

Low-frequency linear vibrations of single-walled carbon nanotubes: Analytical and numerical models

Abstract Low-frequency vibrations of single-walled carbon nanotubes with various boundary conditions are considered in the framework of the Sanders–Koiter thin shell theory. Two methods of analysis are proposed. The first approach is based on the Rayleigh–Ritz method, a double series expansion in terms of Chebyshev polynomials and harmonic functions is considered for the displacement fields; free and clamped edges are analysed. This approach is partially numerical. The second approach is based on the same thin shell theory, but the goal is to obtain an analytical solution useful for future developments in nonlinear fields; the Sanders–Koiter equations are strongly simplified neglecting in-plane circumferential normal strains and tangential shear strains. The model is fully validated by means of comparisons with experiments, molecular dynamics data and finite element analyses obtained from the literature. Several types of nanotubes are considered in detail by varying aspect ratio, chirality and boundary conditions. The analyses are carried out for a wide range of frequency spectrum. The strength and weakness of the proposed approaches are shown; in particular, the model shows great accuracy even though it requires minimal computational effort.

Optical characterization of GaAs photoconductive antennas for efficient generation and detection of Terahertz radiation

We report the optical characterization of low temperature (LT)-GaAs and Semi Insulating (SI)-GaAs based dipole types Photoconductive (PC) antennas with gap of 5μm for the generation and detection of Terahertz (THz) signals. We have used tunable 140femto-seconds laser pulses at 80MHz repetition rate of different power and biasing voltage to evaluate the performance of our antennas as a THz generator and detector. Interestingly, we found that LT-GaAs and SI-GaAs have high photocurrent (density of charge carriers) response at some specific laser wavelengths such as 840nm and 880nm, respectively. We have employed these selected wavelengths for the generation and detection of THz radiation from these materials made PC antennas. The comparative study shows that the intensity of THz radiation in case of SI-GaAs is higher than the LT-GaAs made PC antennas. The THz frequency spectrum range of LT-GaAs and SI-GaAs antennas are extended up to 3.6THz and 2.5THz respectively. Finally, we have cross verified the reliability of our antennas to detect the THz radiation generated from ZnTe crystal.