Frequency Filtering Research Articles

Serial digital QAM-modem based on complex band-pass IIR filters with LF-prototypes of Bessel

The article is devoted to the development and implementation of algorithms for the single-channel sequential quadrature amplitude modulation and demodulation based on digital complex band-pass IIR filters with LF-prototypes of Bessel. The use of complex IIR filters of Bessel allows to obtain orthogonal carrier signals which are close in shape to symmetric signals with practical non-overlapping spectra. The procedure for calculating the 4th-order digital low-pass Bessel filter using the generalized bilinear transformation method, which is used in the theory of digital signal processing to convert a continuous-time system into a discrete-time system, is considered. The variants of implementing the digital complex bandpass filters with a sequential structure using the complex delay method are considered, which allows to obtain the block diagrams of complex bandpass filters without additional calculations and to realize the restructuring of the central frequency without changing the frequency response shape by changing only two coefficients in complex delays. The procedure for obtaining of the expression of the impulse response of digital complex band-pass IIR filters of Bessel is considered. With the help of circuit modeling, the amplitude-frequency response and impulse response of such filter are determined. If the IIR filters are used in the modulator, the pulse characteristics of which are infinite and asymmetric, then it is necessary to use digital complex FIR filters consistent with the truncated pulse characteristic in the demodulator. But as an exception, the Bessel digital IIR filter has a phase-frequency response similar in shape closely to the linear one and, accordingly, a pulse response close to the symmetric one. In this case, the same recursive complex Bessel filters, similar to the filter in the modulator, can be used as matched filters in the demodulator. Therefore, the serial block diagram of the modem contains the same complex band-pass IIR filters with LF-prototypes of Bessel. The choice of the central frequency of the channel digital complex bandpass IIR filter is carried out by setting two coefficients. The results of circuit modeling of the data transmission system with the quadrature amplitude modulation (QAM-16) in the Microcap environment are presented, confirming the operability of the proposed option.

Custom hearing protection devices: Are they better?

When hazardous noise is unavoidable, hearing protection devices (HPDs) are used to reduce the risk of noise-induced hearing injuries. The question of which HPD is appropriate or “the best” is often a subject of debate. Appropriateness may be dictated by environmental factors, such as noise exposure type and level, mission requirements such as communication needs, compatibility with other personal protective equipment, or even personal preference. Regardless of the type used, properly fitting hearing protection is paramount to prevent or reduce hazardous noise entering the auditory system. Custom HPDs are designed to fit the specific anatomy of an individual and, when made and fit properly, may be appropriate for many applications and missions (e.g., band members, certain aviators). In addition to being tailor-made to each individual, custom HPDs may be designed to couple with communication devices, frequency or level-specific filters, and/or may incorporate electronics to provide capabilities such as amplification or reduction of ambient noise. Attenuation performance of custom HPDs coupled to a communication earplug (CEP) was measured and compared to traditional foam HPDs coupled to the CEP. This discussion will include custom HPD fabrication options, performance characteristics, benefits, drawbacks, and finally their potential real-world application.

Fiber-optic temperature sensor based on glass Fabry – Perot interferometer

In this work, analytical expressions are obtained that allow one to determine the shift of the central wavelength of a four-component addressable fiber Bragg structure (FAFBS). The computer simulation of the use of CHAVBS in the problems of measuring the temperature of the windings of power transformers has been carried out. Simulation showed that more accurate temperature measurement results are obtained when the circuit operates in reflection, i.e. at an additional address frequency. With the use of FAFBS, there is no need to install additional frequency filters. It is not required to use address component recovery schemes compared to the three-component AFBS option. This fact is a significant difference between the developed systems based on AFBS and systems based on two- and three-component AFBS.

Design of satellite mobile synchronization system based on OFDM code

In the 5G era, satellite communication has been widely applied in more scenarios. Orthogonal Frequency Division Multiplexing (OFDM) has been adopted to the 3GPP standard and is the primary sync encoding method for satellite communication. However, the OFDM-based system is extremely susceptible to carrier frequency offset (CFO), and Doppler shift make a major impact on the CFO. Therefore, the traditional methods of synchronization based on OFDM cannot meet the requirement of satellite communication with large frequency offset and delay. There are many studies focus on improving the methods of CFO estimation and compensation to adapt the technologies of synchronization based on OFDM to the satellite communication system. In this paper, ZC based and matrix-vector multiplication method, multi-symbol merging method and preamble and PSS symbols based and filter frequency locked loop-based method of synchronization of OFDM-based satellite communication will be introduced. The accuracy and complexity of these methods both meet the requirement of 5G satellite communication system. Future researchers may focus on reducing complexity and expanding application scenarios.

Dynamic Parameter Optimization of High-Speed Pantograph Based on Swarm Intelligence and Machine Learning

Good pantograph–catenary interaction quality is a fundamental premise for ensuring stable and reliable current collection of high-speed trains, and the optimization of dynamic parameters of high-speed pantographs provides an effective approach to improve the current collection quality of the pantograph–catenary system. In this paper, with the objective of minimizing the standard deviation of the pantograph–catenary contact force, the multi-parameter joint optimization for pantograph at different filtering frequencies and running speeds was carried out by using swarm intelligence optimization algorithm and artificial neural network method. First, the selection operator in genetic algorithm (GA) was introduced into crow search algorithm (CSA), and the selective CSA was proposed, which can effectively improve the solution accuracy and convergence rate of multi-parameter optimization. Second, a radial basis function (RBF) neural network was used to construct a surrogate model of the standard deviation of contact force with respect to the running speed and pantograph dynamic parameters, and a method for optimizing the upper limit of mapping interval of the decision variables by the selective crow search algorithm (SCSA) was proposed, which effectively improves the generalization ability of the surrogate model. Finally, by combining the surrogate model and SCSA, optimization iterations for a total of 630 combined conditions such as cut-off frequency, running speed and pantograph dynamic parameters were conducted, and an optimization method for high-speed pantograph dynamic parameters with universal applicability was proposed.

High-order Harmonics of a Kink Wave and a Narrow Quasiperiodic Fast-propagating Wave Train Excited Simultaneously in a Plasma Resonator

We present the observations of multimode kink waves and a narrow quasiperiodic fast-propagating (QFP) wave train in association with a jet on 2011 December 11. The jet impinged on a loop, which excited a propagating kink mode transitioning into a standing kink mode and also excited a QFP wave train away from the jet. Motion magnification is used to fit the higher harmonic standing wave oscillation profile with three periods at three different spatial locations. The periods have the ratio 6:3:2. The ratio of the fundamental mode to the second harmonic of the standing wave is about 1.95, suggesting that the magnetic field strength variation effect is strong enough to cancel out the density stratification. The differential emission measure is used to estimate the loop’s plasma property at these three points, and it found the density and the temperature are roughly constant. The magnetic field strength, B = 51 ± 16 G, is derived by the coronal seismology using the fundamental kink mode. It is striking to find that the the ratio of the second harmonic to the third harmonic of the kink wave coincides with that of the periods of the QFP wave train, and the ratio of periods is about 1.5 in both cases. We propose that the excitation of the high-order harmonics and the QFP wave train could be the nonlinear response of the steep density-gradient plasma interacting with electromagnetic field in the southwest foot region. This region, like a resonator, might play an important role in energy reservoir capture and act as a frequency filter to generate propagating waves of particular frequencies.

An embedded feature selection approach for depression classification using short text sequences

Depression has become a serious mental health issue worldwide, particularly due to the rise of the Global Pandemic. Identifying depression of an individual from short texts shared in social media is a challenging task. The present work aims to select the optimal feature subset for classifying short texts for depression detection. By performing feature selection, it is possible to eliminate redundant and noisy features in high-dimensional datasets with small sample sizes. This can prevent the ”curse of dimensionality” and enhance the effectiveness of classification algorithms. However, current feature selection methods often focus on optimizing classification or clustering performance, while neglecting the stability of the selected features. This can lead to unstable results and make it challenging to identify meaningful and interpretable features. This paper introduces a novel embedded feature selection approach named Statistical Relevance Class Frequency based on Whale Optimization Algorithm (SRCF-WOA) for selecting feature subsets from short texts in social media. The proposed methodology extracts both the unigram features and composite features to capture the semantic and structural information. χ2.rcf (Chi-squared relevance class frequency) filter approach is applied to rank the extracted features to signify the importance of the features. WOA is adapted to retrieve the optimal subset of features with low-dimensional space using its high exploration and high exploitation capability. In the evaluation process, four benchmark short text datasets and two classifiers are used. The comparison shows that the proposed embedded feature selection method outperforms other algorithms in terms of accuracy and Fβ scores(β=0.5,1, and 2). The sensitivity analysis is carried out to check the robustness and stability of the proposed method. The findings indicate that the SRCF-WOA surpasses other methods on the majority of datasets, achieving the maximum classification accuracy while utilizing the minimal features. The statistical importance of these findings is further supported by the Analysis of Variance (ANOVA) F-test. Moreover, the proposed method strikes the optimal balance between classification accuracy and feature stability.

Nucleation control of high crystal quality heteroepitaxial Sc0.4Al0.6N grown by molecular beam epitaxy

High ScN fraction ScxAl1−xN has promise in important application areas including wide bandwidth RF resonators and filters, and ferroelectric devices such as non-volatile memory, but demands high crystal quality. In this work, the role of the nucleation layer (NL), ScxAl1−xN growth temperature, and strain management to preserve the wurtzite crystal structure are investigated to maximize both acoustoelectric and ferroelectric material properties for high ScN fraction ScxAl1−xN grown on SiC substrates. A 5 nm AlN nucleation layer reduces the x-ray diffraction 0002 reflection full width at half maximum (FWHM) for a Sc0.32Al0.68N film by almost a factor of 2, and reducing the growth temperature to 430 °C enables a Sc0.40Al0.60N film with a FWHM of 4100 arcsec (1.1°) while being only 150 nm thick. Grading the initial ScxAl1−xN layer from x = 0.32 to 0.40 suppresses the formation of rock-salt grain nucleation at the Sc0.40Al0.60N lower interface and reduces the anomalously oriented grain density by an order of magnitude. Increasing the total ScxAl1−xN growth thickness to 500 nm produces an average x = 0.39 ScxAl1−xN layer with a FWHM of 3190 arcsec (0.89°) and an anomalously oriented grain areal fill factor of 1.0%. These methods enable the lowest heteroepitaxial ScxAl1−xN FWHM reported for x ∼ 0.4, with layer thicknesses and defect densities appropriate for high frequency (>10 GHz) filter applications.

SAW Filters on LiNbO3/SiC Heterostructure for 5G n77 and n78 Band Applications.

The 5G communication system has experienced a substantial expansion of the spectrum, which poses higher requirements to radio frequency (RF) filters in enhancing their operating frequencies and bandwidths. To this end, this work focused on solving the filtering scheme for challenging 5G n77 and n78 bands and successfully implemented the corresponding spurious-free surface acoustic wave (SAW) filters exploiting large-coupling shear horizontal (SH) modes based on X-cut LiNbO3 (LN)/silicon carbide (SiC) heterostructure. Here, we initially investigated the suppression methods for spurious modes theoretically and experimentally and summarized an effective normalized LN thickness ( [Formula: see text] range of 0.15-0.30 for mitigating Rayleigh modes and higher order modes, as well as tilted interdigital transducers (IDT) by about 24° for eliminating transverse modes. Resonators with wavelengths ( λ) from 0.95 to [Formula: see text] were also fabricated, showing a scalable resonance from 2.48 to 4.21 GHz without any in-band ripple. Two filters completely meeting 5G n77 and n78 full bands were finally constructed, showing center frequencies ( fc) of 3763 and 3560 MHz, 3-dB fractional bandwidths (FBW) of 24.8% and 15.6%, and out-of-band (OoB) rejections of 18.7 and 28.1 dB, respectively. This work reveals that X-LN/SiC heterostructure is a promising underpinning material for SAW filters in 5G commercial applications.

Post stack seismic data processing for enhancing subsurface reservoir mapping in the Shushan basin, Western Desert, Egypt

ABSTRACT Reprocessing of seismic reflection data over Nader field in the Egyptian Western Desert, improved the images of the surface structural framework. The appearance of seismic data can be affected by various factors apart from subsurface structure, including data acquisition problems and processing artefacts. Different post-stack processing steps were tested and compared to the original seismic data determine the enhancement of data quality and improvements on imaging the subsurface. The applied post-stack processing sequence increased the seismic data resolution through increasing the signal-to-noise ratio, enhancing faults detection, and reflectors sharpness and continuity. The Time Variant Frequency Filter (TVF) application is found to be better than applying the filter in one time window and provided more detailed frequency contents and in turn better reflectors identification. The Frequency/Wave Number (F/K) filter removed lot of the existing linear noises resulted in more clear images. The Frequency/Distance (F/X) Deconvolution enhanced the data coherency by removing the existing random noises. The Spiking Deconvolution showed remarkable enhancement in compressing the reflectors and increasing their continuity. The reprocessed data interpretation of Abu Roash C member in Nader Filed, Shushan basin, North Western Desert, Egypt, comparing to the original, showed better mapping and faults detection, which highlighted new potential structures that could act as hydrocarbon traps.

A laterally excited bulk acoustic resonator with scattering vias in electrodes

Laterally excited bulk acoustic resonators (XBARs) using interdigital electrodes are currently limited in potential 5G applications due to the accompanied spurious modes and small capacitance. This Letter presents an XBAR with scattering vias in electrodes, named SV-BAR. The non-parallel boundaries thoroughly disrupt the coherent formation of standing waves in the lateral direction, thereby suppressing the higher-order spurious modes. The duty factor of SV-BAR is optimized as 0.5 using COMSOL Multiphysics finite element analysis for the 50 Ω impedance matching. The SV-BAR is fabricated using a 390 nm Z-cut LiNbO3 on an insulator substrate and exhibits an impressive ratio of Zp/Zs near 64.5 dB, a Kt2 of 21.80% at 4.762 GHz, as well as a large value f · Bode_Qmax · Kt2 (3.43 × 1011). The measured temperature coefficient of frequency is −69.8 ppm/°C, which can be compensated using SiO2 thin films. The SV-BAR provides an effective solution for high-performance radio frequency filters for 5G communication.

Model-free idealization: Adaptive integrated approach for idealization of ion-channel currents

Single-channel electrophysiological recordings provide insights into transmembrane ion permeation and channel gating mechanisms. The first step in the analysis of the recorded currents involves an "idealization" process, in which noisy raw data are classified into two discrete levels corresponding to the open and closed states of channels. This provides valuable information on the gating kinetics of ion channels. However, the idealization step is often challenging in cases of currents with poor signal-to-noise ratios and baseline drifts, especially when the gating model of the target channel is not identified. We report herein on a highly robust model-free idealization method for achieving this goal. The algorithm, called adaptive integrated approach for idealization of ion-channel currents (AI2), is composed of Kalman filter and Gaussian mixture model clustering and functions without user input. AI2 automatically determines the noise reduction setting based on the degree of separation between the open and closed levels. We validated the method on pseudo-channel-current datasets that contain either computed or experimentally recorded noise. We also investigated the relationship between the noise reduction parameter of the Kalman filter and the cutoff frequency of the low-pass filter. The AI2 algorithm was then tested on actual experimental data for biological channels including gramicidin A, a voltage-gated sodium channel, and other unidentified channels. We compared the idealization results with those obtained by the conventional methods, including the 50%-threshold-crossing method.

A study of the long term changes in the electromagnetic environment using data from continuous monitoring sensors in Greece

Owing to the advancement of wireless technologies, there is a strong public perception of increasing exposure to Radiofrequency (RF) electromagnetic fields (EMF). The aim of this study is to determine the evolution of EMF in the environment, and consequently, human exposure to them, over a period of about two decades, spanning from the end of 2003 until February 2022. The study is based on data collected by two non-ionizing radiation monitoring networks in Greece. The networks consist of fixed EMF sensors that register the RMS electric field value every 6 min, on a 24 h basis. We used the Seasonal–Trend decomposition method using (LOESS), known as the STL method to decompose the time series into trend, seasonal, and noise components. Additionally, since the sensors include frequency filters for separating the cellular frequencies, the recorded data were used to identify the exposure contribution by cellular networks in comparison to other EMF sources. The study indicates that RF-EMF do not explicitly decrease or increase but rather fluctuate over time. Similarly, the contribution of mobile cellular networks to the total field change over time.

Cascaded Inverters Increasing the Number of Levels and Effective Switching Frequency in Output Using Coupled Inductors

In this paper, a new coupled-inductor based modular multilevel cascaded inverter using a new phase-shift control is presented. The proposed inverter can generate a high output ac voltage using standard low voltage rating devices. The number of levels in the output pulse width modulation (PWM) voltage and the effective switching frequency of the output filter are increased using coupled inductors and phase-shift control. The switching signals of the cascaded units in the proposed inverter are phase-shifted by 360°/4n, where n is the number of cascaded units. The proposed phase-shift control results in (4n+1) levels in the output PWM voltage of the proposed inverter and increases the effective switching frequency of the output filter by 4n times of the actual switching frequency fsw. As a result, the output waveforms can be generated with better quality and less distortion. In addition, the output filter can be decreased dramatically in size. Besides, fewer coupled inductors are used to reduce the footprints, the number of inductors, and magnetic volume. Moreover, the proposed inverter is exceptionally reliable due to no short-circuit risk in the circuit.

Tunable locking of calcite narrow frequency filters through modulation switching.

Generating pairs of Raman beams for gravimetry with fiber phase modulators is quite convenient but generates additional frequencies that must be filtered. The frequency filtering could be achieved by using a long (dispersive) birefringent calcite crystal followed by a polarizer that blocks the transmission of certain laser frequencies, as has been shown before. Here, we present a method to tune such a filter to the desired frequency position. The correction signal for the feedback is obtained by comparing (subtracting) the transmission through the filter when sending light that has been phase modulated or not, taking advantage of the fiber modulator that is already installed in the system. The method allows for continuously alternating between using the modulator for monitoring the filter position and other uses, an important characteristic for the operation of a complete gravimetric sequence.

A Reconfigurable Multi-band Resonator and Its Application to Band-pass Filter

A reconfigurable tri/quad-band resonator and the application to tri/quad-band band-pass filter have been demonstrated. By changing the switching state of the PIN diodes, the filter can work in tri-band mode or quad-band mode. Correspondingly, the resonant frequencies of the band-pass filter are 1.21 GHz, 2.0 GHz, 3.23 GHz, 1.27 GHz, 2.0 GHz, 2.61 GHz, and 3.41 GHz, respectively. Especially, the filter has a combined structure of lumped capacitors and some transmission lines and achieves a small mechanical size of 0.14 λg × 0.09 λg , where λg denotes the wavelength on the substrate of the filter at the first central frequency. The measurement results of the fabricated filter agree with the electromagnetic simulation data.

Circulating Current Suppression Scheme for Interleaved Active Neutral Point Clamped Nine-Level Inverter

The interleaved active neutral point clamped nine-level (ANPC-9L) inverter can be used in 1500V photovoltaic power generation because of its advantages of low voltage stress, high equivalent switching frequency and small filter size. Circulating current between sub modules is a key problem for ANPC-9L. A simple scheme to realize circulating current suppression for ANPC-9L inverter is presented in this paper. The operation of the ANPC-9L is briefly discussed, and the model of coupled inductor is given. Analysis shows that the redundant working states of the inverter with same output voltage can be used to suppress the circulating current. Another objective is to analyze circulating current imbalance at the band transition when using phase disposition pulse width modulation (PD SPWM) strategy. A solution is proposed to cancel current imbalance. Simulation and experiment verify the effectiveness of the proposed strategy.

Bandpass filter induced by imaginary resistance in the low-pass discrete electrical transmission lattice

We examine a discrete low-pass electrical line in presence of imaginary resistance. The linear lattice is analyzed both from direct Kirchhoff law and classical points of view. The direct Kirchhoff law allows obtaining a linear Schrödinger equation which mimics quantum physics. From this point of view, it has been found that the imaginary resistance transforms the non-hermitian Hamiltonian due to the loss of pseudo-hermitian ones. The energy spectrum shifts from the low to the passband. The angular frequency is identical to the energy spectrum of the direct Kirchhoff law. The full integration of the lattice confirms the phase shift of the dispersion relation due to the imaginary resistance with the localization of the wave with a frequency equal to the cutoff frequency of the low pass filter and the propagation of the nonlinear voltage with the same frequency for different values of imaginary resistance.

Enhancing Audio Signal Quality and Learning Experience with Integrated Covariance Weiner Filtering in College Music Education

In recent years, computer music technology has become increasingly prevalent in college music education, offering new possibilities for creative expression and pedagogical approaches. This paper concentrated on the music education in the colleges with the application of integrated time and frequency filtering (ITFF) with Kalman integrated covariance Weiner filtering in college music education. The ITFF technique combines time and frequency domain analysis to enhance the quality and clarity of audio signals. By integrating the Kalman integrated covariance Weiner filtering, the ITFF method provides robust noise reduction and improved signal representation. This integrated approach enables music educators to effectively analyze and manipulate audio signals in real-time, fostering a more immersive and engaging learning environment for students. The findings of this study highlight the benefits and potential applications of ITFF with Kalman-integrated covariance Weiner filtering in college music education, including audio signal enhancement, sound synthesis, and interactive performance systems. The integration of computer music technology with advanced filtering techniques presents new opportunities for exploring sound, composition, and music production within an educational context.

Robust discrete sliding mode controller design for a single-phase onboard integrated electric vehicle charger with disturbance estimation

A new sliding mode controller (SMC) design is proposed for a single-phase current source rectifier (CSR) integrated into onboard electric vehicle (EV) chargers. The controller's design aims to reduce the impact of varying grid impedance on the CSR's performance by using a disturbance estimator. The proposed method utilizes the Lagrange extrapolation technique for disturbance estimation, which accurately estimates disturbances caused by changes in the grid impedance. The precise state-space equation provided by the disturbance estimator is essential for designing the SMC, which can effectively handle mismatched disturbances. To mitigate the impact of the capacitor inductance filter's resonance frequency, a virtual parallel resistance with the capacitor is used, reducing the resonance amplitude. The proposed controller also controls the power factor to ensure the capacitor voltage and grid current are in phase. Simulation and experimental results demonstrate that the proposed method achieves stability and meets the harmonic content limitations of the IEC61000–3–2 standard. The total harmonic distortion (THD) is also kept below 5% despite changes in the grid impedance, demonstrating the effectiveness of the proposed method in handling varying grid conditions.