Medium Frequency Band Research Articles

Optimal Design and Dynamic Control of an ISD Vehicle Suspension Based on an ADD Positive Real Network

As a two-terminal mass element, an inerter makes up for the lack of mass impedance in a traditional vehicle suspension system. A passive Inerter-Spring-Damper (ISD) suspension can significantly improve vibration isolation performance in a low frequency range, while the impact is not obvious in other frequency bands. To isolate a wider frequency of vibrations in a vehicle suspension system on the basis of an ISD suspension, this paper combines the concepts of using an Acceleration-Driven-Damping (ADD) approach, which can effectively suppress vibrations in medium and high frequency bands, and an ISD passive network, which is superior in low frequency bands. First, an ideal model optimization design method of an ISD vehicle suspension based on an ADD positive real network is proposed, and a second-order model is built. The parameters are optimized by means of the artificial fish swarm algorithm considering both positive real constraints and suspension performance constraints. Then, on the basis of the optimal ideal model, a radial basis function sliding mode controller is designed to control the ISD vehicle suspension system using a mechatronic inerter. Finally, simulations and experiments are carried out to verify the dynamic performance of the proposed ISD suspension. The results show that a controllable ISD suspension system based on an ADD positive real network can improve the suspension performance effectively and isolate a wide range of frequency vibrations. This research provides theoretical evidence and methodological guidance for further enriching the design and dynamic control of ISD suspension systems.

Double-Solenoid Ferrite Coils for Magnetic-Field Amplification in LF and MF Bands

A design method to amplify the magnetic fields in the high-frequency (HF) band by a planar double-loop coil is known. We applied the design method to double-solenoid ferrite coils for amplifying magnetic fields in the low-frequency (LF) and medium-frequency (MF) bands. It was demonstrated that the design method can be applied to the ferrite coils operating in the LF and MF bands. Hence, the design method is applicable to magnetic field amplification without increasing the power consumption in the frequency range from the LF to HF bands. This feature is useful for reducing power consumption of short-range wireless applications such as radio frequency identification (RFID) and wireless power transmission (WPT).

The Study of Ocean Ambient Noise Reconstruction in Low and Medium Frequency Bands

Ocean ambient noise is the general background of the sea, the sources of which is highly variable, the generated noise signal is random, it changes with time and space. It is usually considered that ocean ambient noise is a special random process with certain power spectrum, so the broadband stationary random process can be used for fitting the continuous spectral noise. This paper carried out statistical analysis on sample data obtained by continuous observation in one day, and then the statistic characteristics of ambient noise frequency spectrum in low and medium frequency bands can be calculated. Generating filter with specific frequency response based on the probability density function of sound pressure level in each frequency randomly, and ocean ambient noise is reconstructed effectively by Gaussian white noise passing the filter above. The simulation results have important implication for low and medium frequency underwater acoustic signal analysis in lab conditions, and it is helpful to test the performance of platform in the oceanic background.

Broadband longwave radio remote sensing instrumentation.

We present the performance characteristics of a high-sensitivity radio receiver for the frequency band 0.5-470 kHz, known as the Low Frequency Atmospheric Weather Electromagnetic System for Observation, Modeling, and Education, or LF AWESOME. The receiver is an upgraded version of the VLF AWESOME, completed in 2004, which provided high sensitivity broadband radio measurements of natural lightning emissions, transmitting beacons, and radio emissions from the near-Earth space environment. It has been deployed at many locations worldwide and used as the basis for dozens of scientific studies. We present here a significant upgrade to the AWESOME, in which the frequency range has been extended to include the LF and part of the medium frequency (MF) bands, the sensitivity improved by 10-25 dB to be as low as 0.03 fT/ , depending on the frequency, and timing error reduced to 15-20 ns range. The expanded capabilities allow detection of radio atmospherics from lightning strokes at global distances and multiple traverses around the world. It also allows monitoring of transmitting beacons in the LF/MF band at thousands of km distance. We detail the specification of the LF AWESOME and demonstrate a number of scientific applications. We also describe and characterize a new algorithm for minimum shift keying demodulation for VLF/LF transmitters for ionospheric remote sensing applications.

H∞ Optimal Performance Design of an Unstable Plant under Bode Integral Constraint

This paper proposed the H∞ state feedback and H∞ output feedback design methods for unstable plants, which improved the original H∞ state feedback and H∞ output feedback. For the H∞ state feedback design of unstable plants, it presents the complete robustness constraint which is based on solving Riccati equation and Bode integral. For the H∞ output feedback design of unstable plants, the medium‐frequency band should be considered in particular. Besides, this paper presents the method to select weight function or coefficients in the H∞ design, which employs Bode integral to optimize the H∞ design. It takes a magnetic levitation system as an example. The simulation results demonstrate that the optimal performance of perturbation suppression is obtained with the design of robustness constraint. The presented method is of benefit to the general H∞ design.

A Novel Multidimensional Frequency Band Energy Ratio Analysis Method for the Pressure Fluctuation of Francis Turbine

The pressure fluctuation has multiple influence on the steady operation of Francis turbine, and the impact degree varies with the operation condition. In this paper, for the analysis of pressure fluctuation in the Francis turbine, a novel feature extraction method of multidimensional frequency bands energy ratio is proposed based on Hilbert Huang Transform (HHT). Firstly, the pressure fluctuation signal is decomposed into intrinsic mode functions (IMFs) by EEMD. Secondly, the Hilbert marginal spectrum is utilized to analyze the frequency characteristics of IMFs. Then, according to the inner frequency of IMFs, each of them is divided into high, medium, or low frequency band which are constructed based on the frequency characteristic of the pressure fluctuations in the Francis turbine. Afterward, the energy ratio of each frequency band to the original signal is calculated, which is to realize the feature extraction of multidimensional frequency band energy ratio. Actual applications verify that this method not only can extract the time-frequency characteristics but also can analyze the condition feature of the pressure fluctuation. It is a novel method for extracting the feature of pressure fluctuation in the Francis turbine.

Delay-Time-Compensated Peak Detector for Medium-Frequency Band

Loop delay degrades the accuracy of the traditional peak detectors and limits operational frequency to 1 MHz or less. This paper proposes a delay time compensation scheme boosting operational frequency to 20 MHz while delivering high-accuracy measurements of the peak voltage. The proposed peak detector is implemented using TSMC 0.18 \(\upmu \)m CMOS process requiring only 1.05363 mm\(^2\). The new approach doubles measured performance over standard peak detectors.

A survey on ambient energy sources and harvesting methods for structural health monitoring applications

Structural health monitoring is widely used for maintaining and monitoring various structures in different areas. In general, the structural health monitoring system life span depends on the capability of the batteries, but it can be increased by energy harvesting approaches to autonomously produce power. These autonomously powered structural health monitoring systems have received increasing attention over the past decades. This article reviews recent developments in the ambient energy sources and energy harvesting methods for structural health monitoring applications. First, the earliest and most common method of harvesting energy from sunlight and wind is discussed. Then, vibration and thermal gradient energy harvesting methods are reviewed together with their feasibilities. Finally, radio frequency energy harvesting, a unique method developed in recent years, is highlighted. A double-resonant coil ferrite rod antenna for radio frequency energy harvesting in medium frequency band is proposed. Simulation results indicate that the proposed double-resonant coil ferrite rod antenna can increase the gain by 2.8 dBi and the receiving voltage by 25.77% compared with a conventional single-resonant coil ferrite rod antenna.

WSN-Based Vibration Characteristic Research for Various Railway Track Structures for Pattern Classification

To effectively study vibration characteristics of tracks under different track structures, wavelet transforms of the vibration data are used for pattern classification of vibration feature. First, acceleration data of the track are collected with running speed of 150[Formula: see text]km/h at 26 positions respectively on a slab tangent track, ballast tangent track and ballast curve track by a wireless sensor network (WSN). Then they are analyzed using the power spectral densities (PSDs) and wavelet-based energy spectrum analysis. The paper elaborates on the reasons for the differences of vibration energy and excitation frequencies due to the mechanism of different frequency bands and the corresponding track structures. Based on these, the instantaneous frequencies, vibration energies and durations in the low, medium, and high frequency bands are selected as the features for three track structures. A function curve representing the features is proposed to detect the abnormal track structure by a correlation analysis. Finally, the proposed method of pattern classification has been validated by experimental testings.

Multi-Scale Topography Analysis of Multi-Axis Machined Surfaces Based on Dual-Tree Complex Wavelet Transform

Multi-axis ball end milling experiments of H13 die steel have been conducted with four different cutter postures, and the 3D topographies of machined surfaces are acquired by optical profiler. The multi-scale analysis is carried out on the machined surfaces based on 2D dual-tree complex wavelet transform (2D DT-CWT). The topographies are decomposed into different frequency bands, and the roughness in every frequency band is calculated. The results reveal that the roughnesses of the machined surfaces under different cutter postures are quite different, the roughness is the lowest when the lead angle is 12° and the tilt angle is-22°. The roughnesses under different cutter postures exhibit similar changing trend with the variation of frequency bands: the roughnesses in the high and low frequency bands are relatively lower, the roughnesses in the medium frequency bands are higher. The 2D DT-CWT provides an ideal comprehensive topography analysis method for performance evaluation of machined surfaces.

MECHANISMS OF INTERACTION BETWEEN THE CIRCADIAN SYSTEM, EEG RHYTHMS AND REGULATION OF VEGETATIVE PROCESSES

Aim - to investigate the dynamics of EEG rhythms and vegetative responses in human on a short-term exposure of the retina to the blue light in the spectrum of maximum sensitivity of circadian photoreceptors during daytime wake. Materials and methods. EEG parameters (BP-010302 BrainАmp Standart128), blood pressure and heart rate variability (HRV) were recorded at 22 volunteer students aged 18-20 years before, after and during the 2-5 minute stimulation of circadian retinal receptors by blue light with maximum wavelength of 480 nm. Results. The stimulation of the photoreceptors of the circadian system correlates with the dynamics of the following neurovegetative processes: desynchronization in beta2- and gamma EEG rhythms, synchronization in teta2- and alpha1-frequency bands; increase in the duration of RR interval and power of low-frequency component of HRV, decrease in the percentage of high-frequency oscillation spectrum of HRV and decrease in systolic blood pressure. Termination of the stimulation of circadian system photoreceptors causes the transformation of EEG rhythms response with predominance of synchronization in low (teta1, teta 2), medium (alpha 1, alpha 2, alfa 3) and high frequency (beta 2) bands. Conclusion. The paper shows the possibility of quick correction of human vegetative background by controlling the circadian system. The human circadian clock is likely to control functional brain activity involving beta 2- and gamma-quantization.

Analysis of muscle fatigue conditions using time-frequency images and GLCM features

Abstract In this work, an attempt has been made to differentiate muscle non-fatigue and fatigue conditions using sEMG signals and texture representation of the time-frequency images. The sEMG signals are recorded from the biceps brachii muscle of 25 healthy adult volunteers during dynamic fatiguing contraction. The first and last curls of these signals are considered as the non-fatigue and fatigue zones, respectively. These signals are preprocessed and the time-frequency spectrum is computed using short time fourier transform (STFT). Gray-Level Co-occurrence Matrix (GLCM) is extracted from low (15–45 Hz), medium (46–95 Hz) and high (96–150 Hz) frequency bands of the time-frequency images. Further, the features such as contrast, correlation, energy and homogeneity are calculated from the resultant matrices. The results show that the high frequency band based features are able to differentiate non-fatigue and fatigue conditions. The features such as correlation, contrast and homogeneity extracted at angles 0°, 45°, 90°, and 135° are found to be distinct with high statistical significance (p < 0.0001). Hence, this framework can be used for analysis of neuromuscular disorders.

Effects on deep ocean ambient noise caused by typhoon

Sea-surface wind speed has significant impacts on ocean ambient noise at medium and low frequency bands. When a typhoon comes close, sea-surface wind speed increases sharply, which results in the surge of the ambient noise level. By analyzing the sound data collected by a vertical array in deep ocean environment during two typhoon periods, both the wind speed and frequency dependencies of ambient noise are established. Noise field at receivers is calculated via numerical simulations with combination of the source intensity model of wind generated noise and the typhoon generated noise intensity model. Simulated noise intensity is fitted with the experimental data by least square method, through which the exponent of the wind speed and frequency in the source intensity model is determined. Our result indicate that the variations of wind speed caused by typhoon heavily impact on the noise at frequency band higher than 200 Hz. And specifically, the ambient noise intensity is approximately proportional to the 3rd power of the wind speed, where the exponent of frequency is around - 0.85.

Technical Overview of Frequency Assignment For Radio Broadcasting In Nigeria

In Nigeria, the VHF and UHF frequency bands of the electromagnetic spectrum are mainly occupied by television services, while radio broadcasting is transmitted in the low frequency, medium frequency and high frequency bands. Therefore, it is important to manage the allocated spectrum for these services to ensure that radio stations, cellular network and television broadcast stations do not interfere in signal transmission . The governance of spectrum use on a global basis is a core responsibility of the International Telecommunication Union (ITU) and in particular, its Radio communication Sector (ITU-R).At the national level, the Radio Frequency Spectrum is managed by the following organs of government which include Ministry of Information and Communications (MoIC); National Frequency Management Council (NFMC); Nigerian Communications Commission (NCC) and National Broadcasting Commission (NBC).Frequency assignment and management is less stringent with good planning and monitoring. Radio wave propagation are affected by transmission impairment , if not well planned will results in signal degradations on the system. Hence, this paper reviews the technicalities involved in frequency assignment taking a holistic view at the existing spectrum management. Keyword: Frequency assignment, ITU, MoIC, NFMC, NCC, NBC, ISM, RF.

Surface electromyography based muscle fatigue progression analysis using modified B distribution time–frequency features

Abstract In this work, an attempt has been made to analyze the progression of muscle fatigue using surface electromyography (sEMG) signals and modified B distribution (MBD) based time–frequency analysis. For this purpose, signals are recorded from biceps brachii muscles of fifty healthy adult volunteers during dynamic contractions. The recorded signals are preprocessed and then subjected to MBD based time–frequency distribution (TFD). The instantaneous median frequency (IMDF) is extracted from the time–frequency matrix for different values of kernel parameter. The linear regression technique is used to model the temporal variations of IMDF. Correlation coefficient is computed in order to select the appropriate value for kernel parameter of MBD based TFD. Further, extended version of frequency domain features namely instantaneous spectral ratio (InstSPR) at low frequency band (LFB), medium frequency band (MFB) and high frequency band (HFB) are extracted from the time–frequency spectrum. In addition to these features, IMDF and instantaneous mean frequency (IMNF) are also calculated. The least square error based linear regression technique is used to track the slope variations of these features. The results show that MBD based time–frequency spectrum is able to provide the instantaneous variations of frequency components associated with fatiguing contractions. The values of InstSPR at MFB and HFB regions, IMDF and IMNF show a decreasing trend during the progression of muscle fatigue. However, an increasing trend is observed in LFB regions. Further the coefficient of variation is calculated for all the features. It is found that the values of IMDF, IMNF and InstSPR in LFB region have lowest variability across different subjects in comparison with other two features. It appears that this method could be useful in analyzing various neuromuscular activities in normal and abnormal conditions.

Time–frequency featured co-movement between the stock and prices of crude oil and gold

The nonlinear relationships among variables caused by the hidden frequency information complicate the time series analysis. To shed more light on this nonlinear issue, we examine their relationships in joint time–frequency domain with multivariate framework, and the analyses in the time domain and frequency domain serve as comparisons. The daily Brent oil prices, London gold fixing price and Shanghai Composite index from January 1991 to September 2014 are adopted as example. First, they have long-term cointegration relationship in time domain from holistic perspective. Second, the Granger causality tests in different frequency bands are heterogeneous. Finally, the comparison between results from wavelet coherence and multiple wavelet coherence in the joint time–frequency domain indicates that in the high (1–14 days) and medium frequency (14–128 days) bands, the combination of Brent and gold prices has stronger correlation with the stock. In the low frequency band (256–512 days), year 2003 is the structure broken point before which Brent and oil are ideal choice for hedging the risk of the stock market. Thus, this paper offers more details between the Chinese stock market and the commodities markets of crude oil and gold, which suggests that the decisions for different time and frequencies should consider the corresponding benchmark information.

Acoustic Characterization of Sugarcane Bagasse Particleboard Panels (Saccharum officinarum L)

The use of sugarcane bagasse minimizes the environmental impact and contributes to the creation of a new product with low density, good sound absorption capacity and can improve the acoustic conditions of buildings. The goal of this study aims to determine the intensity response of sugarcane bagasse particleboard panels’ sound absorption and compare them with particleboard panels of the species Pinus sp. and Eucalyptus sp. To accomplish this, the sound pressure levels in different frequency bands were analyzed. The results showed higher sound absorption between the low and high frequency bands for the three types of panels, with an absorption peak in 315 Hz identifying the characteristic frequency of resonance from these materials. However, the sugarcane bagasse panel presented differently than the others, with a greater retention of sound energy in the medium frequency band between 630 Hz and 1,000 Hz with a maximum absorption at 55 dB at the frequency of 800 Hz. Keywords: sugarcane bagasse, particleboard, sound absorption, acoustics

Comparison about parametric effects on wave propagation characteristics

The frequency effects on the velocities and attenuations of the bulk waves in a saturated porous medium are numerically studied in the cases of considering and neglecting the compressibility of solid grain, respectively. The results show that the whole frequency can be divided into three parts, i.e., low frequency band, medium frequency band, and high frequency band, according to the variation curves and the characteristic frequency. The compressibility of the solid grain affects the P 1 wave distinctively, the S wave tiny, and the P 2 wave little. The effects of the porosity and Poisson’s ratio on the bulk waves are numerically analyzed. It is found that both the porosity and Poisson’s ratio have obvious effects on the bulk waves. Compared with the results in the case of neglecting the porosity-moduli relation, the results in the case of considering the porosity-moduli relation are more reasonable. The results in the case of considering the porosity-moduli relation can be degenerated into the results of elastic solid and pure fluid, while the results in the case of neglecting the porosity-moduli relation cannot be degenerated into the results of elastic solid and pure fluid. Therefore, the porosity-moduli relation must be considered in the parametric study for a certain porous medium.

Resonant Frequency Estimation of Reradiation Interference at MF from Power Transmission Lines Based on Generalized Resonance Theory

The resonant mechanism of reradiation interference (RRI) over 1.7MHz from power transmission lines cannot be obtained from IEEE standards, which are based on researches of field intensity. Hence, the resonance is ignored in National Standards of protecting distance between UHV power lines and radio stations in China, which would result in an excessive redundancy of protecting distance. Therefore, based on the generalized resonance theory, we proposed the idea of applying model-based parameter estimation (MBPE) to estimate the generalized resonance frequency of electrically large scattering objects. We also deduced equation expressions of the generalized resonance frequency and its quality factor Q in a lossy open electromagnetic system, i.e. an antennatransmission line system in this paper. Taking the frequency band studied by IEEE and the frequency band over 1.7 MHz as object, we established three models of the RRI from transmission lines, namely the simplified line model, the tower line model considering cross arms and the line-surface mixed model. With the models, we calculated the scattering field of sampling points with equal intervals using method of moments, and then inferred expressions of Pade rational function. After calculating the zero-pole points of the Pade rational function, we eventually got the estimation of the RRI’s generalized resonant frequency. Our case studies indicate that the proposed estimation method is effective for predicting the generalized resonant frequency of RRI in medium frequency (MF, 0.3~3 MHz) band over 1.7 MHz, which expands the frequency band studied by IEEE.

The electromagnetic shielding of textured steel yarn based woven fabrics used for clothing

The electromagnetic shielding effectiveness (EMSE) of herringbone, whipcord, barathea, and crêpe woven fabrics, which are twill and sateen derivatives, woven with textured steel yarns has not been investigated so far. Therefore, in this research, textured stainless steel yarn, which has soft feeling and flexibility, required properties for clothing fabrics, was selected as a conductive yarn to produce conductive fabrics whose weaves are twill, twill and sateen derivatives. The EMSE of these common clothing fabrics woven with different conductive yarn densities were measured by free space measurement technique with different antenna polarizations, because of the possibility to obtain measurements for a large bandwidth. It was observed that all conductive clothing woven fabric samples shielded well in medium and high frequency bands, which contain 900 MHz GSM, 1800 MHz GSM, 2100 MHz 3G, and 2400 MHz Wi-Fi bands. Most of the samples give acceptable EMSE values up to 40 dB at certain frequencies. The EMSE of fabric samples would remain almost the same, although conductive yarn density changed, because of diagonally or symmetrically arranged conductive yarn floats in fabric structures. The EMSE characteristics of different weave types are investigated and it is seen that when the yarn floats arrangement is changed the EMSE characteristic changes. And also, it is observed that measurements of fabrics, positioned so that the weft yarns were parallel to the antenna polarization are similar to those of fabrics, positioned so that the weft yarns were vertical to the antenna polarization.