Behavior Of Filter Research Articles

A linearly constrained framework for the analysis of the deficient length least-mean square algorithm

Most adaptive system identification analyses assume the length of the adaptive filter to match the length of the unknown system response. This assumption tends to be unrealistic, and its conclusions may not apply to some practical applications. The behavior of deficient length adaptive filters has been studied using different approaches. This work formulates the deficient length adaptive system problem using a Linearly Constrained Minimum Mean Squared Error (LCMMSE) framework. This new formulation leads to a very interesting interpretation that allows the utilization of results from the study of constrained adaptive filters to understand the behavior of the deficient length LMS adaptive filter. The reduced number of coefficients is formulated as a linear optimization constraint that defines a projection onto the feasible space for the adaptive weight vector. We derive analytical models for the mean and mean-square behavior of the adaptive weights. In addition, we derive an analytical model for the variance of the steady-state squared estimation error which provides important design information. Simulation results show excellent matching between theory and actual algorithm behavior.

On the Behavior of a Non-Linear Bandpass Filter with Self Voltage-Controlled Resistors

In this work, we explore the behavior of a classical RLC resonance-based bandpass filter, which includes two resistors (one of which is associated with a non-ideal inductor), when either of these resistors is self voltage-controlled. In particular, self-feedback control is achieved by using the voltage developed across the inductor or the capacitor to dynamically change the value of the controlled resistor. This results in a multiplication-type non-linearity, which transforms the linear filter into a non-linear filter described by a set of non-linear differential equations. When gradually increasing the strength of the non-linearity, a notch-like behavior is observed at twice the resonance frequency. However, the non-linear filter can lose its stability with excessive feedback. Simulations and experimental results are provided to support the theory.

Stray Light in 3D Porous Nanostructures of Single‐Crystalline Copper Film

In the design of optical devices and components, geometric structures and optical properties of materials, such as absorption, refraction, reflection, diffraction, scattering, and trapping, have been utilized. Finding the ideal material with certain optical and geometric characteristics is essential for a customized application. Herein, unoxidizable achromatic copper films (ACFs) are fabricated on Al2O3 substrates utilizing an atomic sputtering epitaxy apparatus. ACFs are made up of two regions vertically: a comparatively flat layer region and a 3D porous nanostructured region on top of the flat region. The measured specular reflectance displays low‐pass filter behavior with a sharp cutoff frequency in the infrared spectrum. Furthermore, the measured diffusive reflectance spectra show light‐trapping behavior in the spectral region above the cutoff frequency, where there are no known absorption mechanisms, such as phonons and interband transitions. A focused ion beam scanning electron microscope is utilized to study the thin film's nanostructured region through 3D tomographic analysis in order to comprehend the phenomena that are observed. This work will shed fresh light on the design and optimization of optical filters and light‐trapping employing porous nanostructured metallic thin films.

Series active filter using seven level packed U cell converter for power quality enhancement

In a low-voltage electrical grid, harmonics can have devastating effects on electrical equipment, leading to premature aging, reduced lifespan, and increased maintenance costs. To mitigate these issues, the control of a PUC-type multi-level converter series active filter is investigated in this study, with the primary objective of improving energy quality and reducing disturbed electrical voltage. The proposed filter utilizes a PUC-type voltage inverter controlled by PWM (Pulse Width Modulation) and employs two methods for identifying disruptive voltages: the instantaneous power (P-Q) method for harmonic compensation and the SRF (Synchronous Reference Frame) method. The simulation models are built using the MATLAB-Simulink software platform, which allows for accurate and efficient modeling of the filter's behavior under various operating conditions. The simulation results demonstrate the effectiveness of the series active filter in mitigating harmonics and voltage disturbances, highlighting its potential for real-world applications. The results show that the filter is able to significantly reduce the total harmonic distortion (THD) of the output voltage, improving the overall power quality. Furthermore, the simulation results also demonstrate the ability of the filter to quickly respond to changes in the grid voltage, making it an effective solution for addressing voltage disturbances. The study's findings suggest that the PUC-type multi-level converter series active filter has great potential for real-world applications in low-voltage electrical grids, particularly in systems that require high-quality power supply and efficient harmonic compensation. The proposed filter's ability to improve power quality and reduce harmonic distortion makes it a promising solution for mitigating the negative effects of harmonics on electrical equipment in low-voltage electrical grids.

Geotextile filters: from idealization to real behaviour (Giroud Lecture 2023)

Geotextiles have been used as filters in geotechnical and geoenvironmental works for decades. Despite their broad utilization, these filters still find obstacles to the expansion of their application in larger projects and under complex soil and flow conditions. However, environmental issues are increasingly pressing for a greater use of geotextile filters in substitution to natural granular materials. Even though many important studies in the literature have improved the understanding of soil-fluid-geotextile filter interaction, some issues still require thorough investigation aiming at a better understanding of the behaviour of geotextile filters and the development of better design methodologies. This paper discusses how geotextiles filters are expected to behave in the field and some contradictions between idealized and real behaviour. Concerns regarding the use of geotextile filters under severe and critical conditions and how filter malfunction can be avoided or minimised are also addressed as well as approaches available to predict filter behaviour. A broad investigation on geotextile filter behaviour under severe and critical conditions was carried out and shows that these filters have been very successful, particularly bearing in mind the small number of failures in comparison with the huge number of applications of geotextile filters.

Study of soot dynamic behavior and catalytic regeneration in diesel particulate filters

Catalytic diesel particulate filters (CDPFs) are key technologies for controlling particulate matter emissions. Nevertheless, it is challenging to experimentally observe the internal working states of the CDPF, which hinders comprehensive research on the flow, capture, and regeneration characteristics. In this study, we utilized quartet structure generation set to generate two-dimensional porous walls, lattice Boltzmann method to simulate CDPF flow and diffusion, cellular automata to simulate soot motion, and global reaction kinetics to simulate soot oxidation. The accuracy of the model is validated through flow, combustion, and pressure drop experiments. We propose a new concept of local porosity, where the porosity of a partially porous wall is used to represent the filtering parameters of that part. These findings indicate that porosity dominates filtering. A higher local porosity results in increased near-wall velocity and greater deposition of soot particles. Similarly, alterations in local porosity and deposition mutually influence each other. The velocity distribution and pressure difference at the inlet and outlet are directly influenced by the upstream velocity. Compared with velocity and porosity, particle diameter has less effect on deposition location, but more effect on deposition efficiency. Active regeneration (800 K) occurs approximately 31.17 times more quickly than passive regeneration (600 K) in the absence of a catalyst. The platinum-based catalyst significantly enhanced the soot oxidation rate by oxidizing NO to NO2, resulting in a 3.62-fold increase in passive regeneration and an estimated 1.17-fold increase in active regeneration. These findings are crucial for developing efficient CDPF systems and for reducing particulate emissions.

Functional bio-foam filters: An effective barrier for microplastic and other emerging pollutant containment

This research focuses on designing functional biopolymer-based foam filter comprising composites of biopolymers, chitosan (CS), and Agar (Ar), in an optimized ratio. These filters are further enhanced by incorporating Al and Zr oxide/oxyhydroxide functional-composites (AZ-FCs) as fillers, with an optimized concentration for improved performance. Comprehensive characterization of the filters' physicochemical properties and structural mechanisms is conducted using advanced analytical techniques, including FE-SEM, XRD, IR, XPS, and Zeta potential analysis. Furthermore, the adsorption behaviour of the bio matrix filters is investigated for emerging pollutants, namely Ciprofloxacin (Cf), Paracetamol (Pr), and Fluoride (F−), wherein the optimized AC (0.5AZ) filter demonstrates exceptional adsorption capacities with maximum values of 308.38 mg g⁻1 for Cf, 67.58 mg g⁻1 for Pr, and 81.3 mg g⁻1 for F−, respectively. The practical applicability of the AC (0.5AZ) filters is evaluated in a continuous flow filtration system operating at 1 bar pressure for large-scale removal of these contaminants. The filters exhibit an impressive flux rate of approximately 618 ± 12 L m⁻2 h⁻1, indicating high filtration efficiency and suitability for high-volume applications. Furthermore, the AC (0.5AZ) filters are also assessed for the removal of microplastics (MPs) of varying sizes within the same filtration module, where they have achieved a rejection rate of around 92%, demonstrating their effectiveness in addressing the pressing issue of micro-plastic pollution.

Scale up validation tests for Buckingham Pi theorem applied to leaf test experiments for iron ore slurry

Bench tests were conducted on ore slurry filtration using the leaf test method, varying scales, pressures, and water/solids ratios. These results were compared with analytical outcomes derived from applying the dimensionless Buckingham pi method to the general equation of slurry filtration with incompressible cakes under constant pressure. The aim was to validate the tests by corroborating experimental findings with calculated parameters for scale-up purposes. Vacuum pressure was employed to facilitate slurry dewatering, forming a cake comprising solids from the slurry. This cake’s thickness evolved over time, introducing specific resistivity that impeded filtering efficiency. Parameters such as cake resistance and filter media resistance were computed. Filtrate volume was measured over time to determine the filtration rate. These values were then adjusted using factors obtained through dimensional analysis. These factors facilitated comparisons to validate the feasibility of employing the Buckingham pi method for predicting slurry filtration results at larger scales. The results indicated lower errors when analyzing the filtrate rate over time with a solids/water ratio of 20/80%. When evaluating cake resistance, the method yielded lower errors at a ratio of 70/30%, while results for medium resistance were inconclusive. It’s important to consider the ratio and associated errors when predicting the behavior of an industrial filter based on bench test results, aiming to achieve theoretical scaled filtration rates and cake resistances. However, it’s not advisable to rely on the Buckingham pi method for scale-up purposes when evaluating medium resistance.

The Behavior of Phobic and Philip Oil Mist Filters Under High Pressure

The Behavior of Phobic and Philip Oil Mist Filters Under High Pressure

Federated Learning for Microwave Filter Behavior Prediction

Federated Learning for Microwave Filter Behavior Prediction

Power-Law Negative Group Delay Filters

A study of the behavior of the power-law negative group delay filters, accompanied by a comparison with their integer-order counterparts, is performed in this work. Employing a curve-fitting based approximation technique, the resulting integer-order rational transfer function is versatile in the sense that it has the same form independent of the order and/or the type of the filter. Its implementation is performed by following three alternative approaches, each one offering different advantages. The findings of this work are supported by simulation and experimental results using suitable platforms.

Flame transfer function analysis of hydrogen diffusion swirl flames

This paper investigates the first Flame Transfer Functions (FTFs) of hydrogen diffusion swirl flames, which are crucial for predicting and mitigating thermoacoustic instabilities. Given the need to develop new combustion technologies for hydrogen, it is therefore essential to accurately measure and analyze these FTFs. Employing acoustic and optical methods, we obtained the FTFs over a wide frequency range from 50 to 1000 Hz. Using the acoustic method, the FTFs are deduced from the flame transfer matrices. The FTFs exhibit a low-pass filter behavior with gains decreasing significantly above 150 Hz. Strouhal number normalization effectively collapses the FTFs across various thermal powers, bulk mass flow rates and global equivalence ratios. This result suggests that a generic flame response to acoustic perturbations exists and that the FTF can be interpolated over a range of operating conditions. This study identifies two dominant combustion modes in these hydrogen diffusion swirl flames: a diffusion-mode thin reaction layer near the nozzle and a partially premixed thicker reaction layer downstream. Phase-averaged OH* and OH-PLIF imaging revealed non-uniform transversal oscillations of the reaction zone, offering key insights into the complex swirling flow and the convective wavelength of the coherent heat release rate oscillations along these turbulent hydrogen diffusion swirl flames.

Designing Multi-Layer electret filters via numerical simulation

The deposition of neutral and charged particles inside an electrostatically charged filter can affect its performance by decreasing its ability to capture additional particles and by increasing its pressure drop. The particle-loaded behavior of a composite filter comprised of three fibrous layers is studied in this paper using a macroscale simulation approach. Each of these fibrous layers were assumed to have fibers with the same amount of charge but different charge polarities of only unipolar positive, only unipolar negative, or only bipolar. The charged layers were stacked on top of one another in three different configurations with respect to the flow direction and their filtration efficiency and pressure drop were compared during particle loading with neutralized particles (having the Boltzmann equilibrium charge distribution), singly-charged particles, and neutral particles. Our simulations revealed that placing the bipolarly-charged layer downstream of the unipolarly charged layers helps to lower the negative impact of particle deposition on pressure drop and filtration efficiency of the resulting composite filter. This study introduces a design tool which can be used to optimize the configuration of a composite filter for enhanced particle capture efficiency and reduced pressure drop increase.

Modulation of spin and charge currents through functionalized 2D diamond devices

In this study, we explore the potential of functionalized two-dimensional (2D) diamond for spin-dependent electronic devices using first-principles calculations. Specifically, we investigate functionalizations with either hydroxyl (−OH) or fluorine (−F) groups. In the case of an isolated layer, we observe that the quantity and distribution of (−OH) or (−F) on the 2D diamond surface significantly influence the sp 2/sp 3 ratio of the carbon atoms in the layer. As the coverage is reduced, both the band gap and magnetic moment decrease. When the 2D diamond is placed between gold contacts and functionalized with (−OH), it results in a device with lower resistance compared to the (−F) functionalization. We predict that the maximum current achieved in the device increases with decreasing (−OH) surface coverage, while the opposite behavior occurs for (−F). Additionally, the surface coverage alone can alter the direction of current rectification in (−F) functionalized 2D diamonds. For all studied systems, a single spin component contributes to the total current for certain values of applied bias, indicating a spin filter behavior.

Graph-Time Convolutional Neural Networks: Architecture and Theoretical Analysis.

Devising and analysing learning models for spatiotemporal network data is of importance for tasks including forecasting, anomaly detection, and multi-agent coordination, among others. Graph Convolutional Neural Networks (GCNNs) are an established approach to learn from time-invariant network data. The graph convolution operation offers a principled approach to aggregate multi-resolution information in each layer and offers some degree of mathematical analysis by exploring tools from graph signal processing. This analysis provides insights on the equivariance properties of GCNNs; spectral behaviour of the learned filters; and the stability to perturbations in the graph topology, which arises because of support perturbations or uncertainties. However, extending the convolution-principled learning and respective analysis to the spatiotemporal domain is challenging because spatiotemporal data have more intrinsic dependencies. Hence, a higher flexibility to capture jointly the spatial and the temporal dependencies is required to learn meaningful higher-order representations. Here, we leverage product graphs to represent the spatiotemporal dependencies in the data and introduce Graph-Time Convolutional Neural Networks (GTCNNs) as a principled architecture to aid learning. The proposed approach can work with any type of product graph and we also introduce a parametric product graph to learn also the spatiotemporal coupling. The convolution principle further allows a similar mathematical tractability as for GCNNs. In particular, the stability result shows GTCNNs are stable to spatial perturbations but there is an implicit trade-off between discriminability and robustness; i.e., the more complex the model, the less stable. Extensive numerical results on benchmark datasets corroborate our findings and show the GTCNN compares favourably with state-of-the-art solutions. We anticipate the GTCNN to be a starting point for more sophisticated models that achieve good performance but are also fundamentally grounded.

Polarization-Insensitive and Oblique Incident Angle Stable Miniaturized Conformal FSS for 28/38 GHz mm-Wave Band 5G EMI Shielding Applications

This letter presents a miniaturized conformal dual-band mm-wave frequency selective surface (FSS) for fifth-generation (5G) electromagnetic interference (EMI) shielding applications. Two back-to-back resonators are separated with a 0.254 mm thin dielectric substrate. The proposed FSS exhibits two wide stopbands (S21<-10 dB) in the mm-wave 5G frequency spectrum. The stopband bandwidths (BW) are 42.8% at 28 GHz and 24.2% at 38 GHz. The periodicity of the unit cell is 0.26 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength of the lower stopband. The key features of the proposed FSS include a miniaturized unit cell structure for 28 GHz and 38 GHz frequency bands with a high oblique incident angle (OIA) stable filter behavior up to 60°. The proposed FSS also features polarization insensitivity and conformality. The simulated and measured results show good agreement for EMI shielding applications.

Experimental and numerical investigations of forced response of multi-element lean-premixed hydrogen flames

Understanding the distinctive thermoacoustic properties of multi-element lean-premixed hydrogen flames is crucial for the development of hydrogen-capable gas turbines. Extending our earlier investigations of the self-excited dynamics of a cluster of lean-premixed pure hydrogen-air flames, here we explore the dynamic response to harmonic velocity perturbations, using an integrative approach combining loudspeaker-forced direct measurements and LES-based numerical simulations. Electronically-excited OH intensity distribution, generally assumed to be equivalent to the flame's heat release rate, shows an anchored conical reaction zone. Numerical simulations of heat release rate contours, however, reveal the formation of a more concentrated thin annulus region resembling an inverted V shaped layer, created by preferential diffusion of hydrogen molecules. This difference between OH-intensity distribution and heat release rate contours suggests consequential uncertainties in surrogate-dependent flame transfer function evaluations; the transfer function gains from measured data are well defined by a fast-decaying low-pass filter behavior, but the simulation result exhibits slowly-decaying large gain with slight overshoot over the entire range of frequency. Because the systematic uncertainties associated with the estimation of the flame's heat release rate cannot be accurately quantified, we rely on a reduced-order network modeling framework combined with direct measurement to test the accuracy of the prediction of the growth of self-sustained pressure fluctuations. We demonstrate that LES-based transfer functions predict the system's stability more accurately, and this suggests that the calculated heat release rate data are closer to the hydrogen flame's true heat release response than the wavelength-specific light intensity measurement. This assessment enables us to identify structurally simple moderate transverse oscillations of local regions containing atypically concentrated energy as pivotal processes controlling high-frequency hydrogen combustion dynamics.

Titania Nanoparticle-Stimulated Ultralow Frequency Detection and High-Pass Filter Behavior of a Flexible Piezoelectric Nanogenerator: A Self-Sustaining Energy Harvester for Active Motion Tracking.

A significant driving force for the fabrication of IoT-compatible smart health gear integrated with multifunctional sensors is the growing trend in fitness and the overall wellness of the human body. In this work, we present an autonomous motion and activity-sensing device based on the efficacious nucleation of the polar β-phase in an electroactive polymer. Representatively, we investigate the nucleating effect of TiO2 nanoparticles on weight-modulated PVDF-HFP films (PT-5, PT-10, and PT-15) and subsequently prototype a sensing device with the film that demonstrates superior β-phase nucleation. The PT-10 film, with an optimal polar β-phase, shows the highest remnant polarization (2Pr) and energy density of 0.36 μC/cm2 and 22.3 mJ/cm3, respectively, at 60 kV/cm. The films mimic a high pass filter at frequencies above 10 KHz with very low impedance and high ac conductivity values. The frequency-dependent impedance studies reveal an effective interfacial polarization between TiO2 nanoparticles and PVDF-HFP, explicitly observed in the low-frequency region. Consequently, the sensor fabricated with PT-10 as the sensing layer exhibits ultralow frequency detection (25 Hz) resulting from the blood flow muscle oxygenation. The device successfully senses voluntary joint movements of the human body and actively tracks a range of motions, from brisk walking to running. Additionally, through repetitive human finger-tapping motion, the nanogenerator lights up multiple light-emitting diodes in series and charges capacitors of varying magnitudes under 50 s. The real-time human motion sensing and movement tracking modalities of the sensor hold promise in the arena of smart wearables, sports biomechanics, and contact-based medical devices.

Field Programmable Analog Array Based Non-Integer Filter Designs

The approximation of the frequency behavior of fractional-order, power-law, and double-order filters can be performed by the same rational integer-order transfer function. This can be achieved through the utilization of a curve fitting based approximation. Moreover, their implementation can be performed by the same core, by only changing the corresponding time constants and scaling factors. The aforementioned findings are experimentally verified using a Field Programmable Analog Array device.

Dynamic Response of a Light-Modulated Magnetometer to Time-Dependent Fields

The dynamic response of a Bell-and-Bloom magnetometer to a parallel (to the bias field) time-dependent field is studied by means of a model that goes beyond the commonly assumed quasi-static regime. The findings unveil features that are related to the parametric nature of the considered system. It is shown that for low-amplitude time-dependent fields, different operating conditions are possible and that, besides the commonly reported low-pass filter behavior, a band-pass response emerges. Moreover, we show that a larger amplitude of the time-dependent field makes the parametric nature of the system appear more clearly in the output signal. A harmonic analysis of the latter is numerically performed to highlight and characterize these emerging features.