Frequency Response Research Articles

This paper presents the design and analysis of a low-cost all-metal frequency-selective surface (AM-FSS). The proposed structure is manufactured using a laser cutting method on a 0.6 mm thick stainless steel sheet. The unit cell consists of a square ring with four stubs positioned off-center toward the middle of the structure. The AM-FSS functions as a bandpass filter, with measured resonance 5.91 GHz, a fractional bandwidth of 38.9 % , and an insertion loss of less than 1.0 dB. The design is remarkably thin, measuring just 0.011 λ 0 , where λ 0 is the free-space wavelength and has compact dimensions of 0.3 λ 0 × 0.3 λ 0 , making it suitable for miniaturized microwave applications. The proposed design is polarization-insensitive, exhibiting steady angular performance in both TE and TM modes, with a steady response for incidence angles up to 45 ∘ . An equivalent circuit model was utilized to evaluate the frequency response. A prototype of the design has been fabricated, and experimental results closely match the simulations, confirming the validity of the proposed design. The all-metal construction eliminates the need for commercial laminates, ensuring durability, high power handling capabilities, and cost efficiency. This makes the AM-FSS ideal for applications in microwave filtering and radar systems.

The β3-agonist vibegron is available for treatment of storage symptoms, but in vitro data in human tissues are not yet available. Based on findings with mirabegron, mechanisms other than inhibition of voiding contractions in the detrusor may account for symptom improvements, and off-target effects in the prostate and bladder appear possible. Here, we examined vibegron effects in human detrusor and prostate tissues. Detrusor and prostate tissues were obtained from radical cystectomy, radical prostatectomy and laser enucleation. Concentration response curves for agonists and frequence response curves for electric field stimulation (EFS) were examined in organ baths with 0.01, 0.1, 1 and 10µM vibegron or vehicle control. In detrusor tissues, 10µM vibegron reduced EFS-induced contractions by half, while no biologically relevant inhibitions occurred with lower concentrations or with carbachol- or methacholine-induced contractions. Pretensions before contractions were relaxed > 20% by 0.1-10µM vibegron. EFS-induced contractions were halved by 10µM vibegron in prostatectomized tissues, but unaffected by lower concentrations and in laser-enucleated prostate tissues. Additionally, 10µM vibegron right-shifted concentration response curves and increased the EC50 values for noradrenaline, phenylephrine and methoxamine in prostatectomized and laser-enucleated prostate tissues, while lower concentrations had no consistent effect. Similar to mirabegron, improvements of storage symptoms by vibegron involve mechanisms beyond inhibition of voiding contractions. Off-target effects occur with 10µM, and include inhibition of neurogenic contractions and antagonism of prostatic α1A-adrenoceptors. Vibegron effects in the prostate may differ between patients with low BPH progression, and patients needing surgery for BPH.

The decoupling properties and low-inertia characteristics of large-scale wind power have heightened concerns regarding power grid frequency stability, particularly as modern power systems impose stringent frequency regulation requirements on wind integration, leading to an increased complexity of frequency response characteristics under fault conditions. To address this challenge in high-wind-penetration grids, this paper proposes a post-fault frequency dynamics analysis method capable of concurrently accommodating multi-wind-speed scenarios through three key innovations: the linearization of traditional AC system components (including network equations, composite load models, and generator prime mover-governor systems) to establish nodal power increment equations; the development of wind turbine frequency regulation models under diverse wind conditions using small-signal analysis, incorporating regional operational disparities and refined by information entropy-based reliability quantification for adaptive parameter adjustment; and the derivation of the system state equation for post-fault frequency response using wide-area measurement system (WAMS) data, yielding an analytical model that captures region-specific regulation characteristic disparities for physically faithful frequency analysis. Validation via tailored IEEE 39-node simulations convincingly demonstrates the method’s effectiveness and superiority in handling fault-induced transients and wind variability.

Efficacy and tolerability of magnesium sulfate in children with infantile epileptic spasms syndrome: A systematic review and meta-analysis.

Deep Reinforcement Learning Based Control of Wind Turbines for Fast Frequency Response

Generic Low-Order Primary Frequency Response Model for Frequency Nadir Prediction

In this Letter, we propose and demonstrate a channel-response-aware delta-sigma modulator (CRA-DSM) optimized by a genetic algorithm for low-resolution digital-to-analog converter (DAC)-based pre-equalization systems. CRA-DSM adaptively shapes the noise distribution to match the channel frequency response, flattening and improving signal-to-noise ratio (SNR) without additional hardware complexity. Transmission of a 32 Gb/s 16-quadrature amplitude modulation (QAM) discrete multi-tone (DMT) signal over a low-pass channel and a 15.2 Gb/s 16-QAM orthogonal frequency division multiplexing (OFDM) signal over a 5.5 GHz bandpass channel is experimentally demonstrated. The results show that CRA-DSM outperforms traditional DSM, achieving 1.6 dB and 1.2 dB SNR gains in the two channels, respectively. These results verify CRA-DSM as a practical solution for bandwidth-limited mobile fronthaul systems.

Highly sensitive and wide frequency response fiber-optic accelerometer array with switchable resonance frequency

The dielectric electroactive polymers gain a high interest as materials for the construction of actuators and sensors. Further, the requirements of practical use require high repeatability and also techniques to identify the inaccuracy of the devices. This study examines the problem of preparation, identification, and analysis of dielectric electroactive polymers with magnetorheological bias. The core innovation lies in utilizing passive magnetic fields to precondition and enhance the actuation response of the DEA without the need for active magnetic sources. A detailed investigation is conducted on how the MRE, when mechanically coupled to the DEA, influences its performance in terms of dynamic behavior. This novel type of actuator gives a response with high level amplitude in comparison to typical actuators. The main goal of this research is to analyze the parameters of the actuators and its correlation to varying conditions. We systematically analyze how variations in magnet position - both vertical and radial - affect actuator performance under electrical excitation. Four actuators were fabricated and tested using step and chirp voltage signals across different voltage levels and biasing configurations. Key dynamic parameters such as displacement amplitude, frequency response, and model gains were extracted using system identification methods. Statistical analysis and classification techniques reveal that selected parameter combinations, such as displacement amplitude and static gain, enable effective differentiation of actuator responses under varying conditions. These findings provide new insights into the design and tunability of DEA-MRE actuators for applications in soft robotics and adaptive systems.

Low-light image enhancement in architectural scenes presents a considerable challenge for computer vision applications in construction engineering. Images captured in architectural settings during nighttime or under inadequate illumination often suffer from noise interference, low-light blurring, and obscured structural features. Although low-light image enhancement and deblurring are intrinsically linked when emphasizing architectural defects, conventional image restoration methods generally treat these tasks as separate entities. This paper introduces an efficient and robust Frequency-Space Recovery Network (FSRNet), specifically designed for low-light image enhancement in architectural contexts, tailored to the unique characteristics of such scenes. The encoder utilizes a Feature Refinement Feedforward Network (FRFN) to achieve precise enhancement of defect features while dynamically mitigating background redundancy. Coupled with a Frequency Response Module, it modifies the amplitude spectrum to amplify high-frequency components of defects and ensure balanced global illumination. The decoder utilizes InceptionDWConv2d modules to capture multi-directional and multi-scale features of cracks. When combined with a gating mechanism, it dynamically suppresses noise, restores the spatial continuity of defects, and eliminates blurring. This method also reduces computational costs in terms of parameters and MAC operations. To assess the effectiveness of the proposed approach in architectural contexts, this paper conducts a comprehensive study using low-light defect images from indoor concrete walls as a representative case. Experimental results indicate that FSRNet not only achieves state-of-the-art PSNR performance of 27.58 dB but also enhances the mAP of the downstream YOLOv8 detection model by 7.1%, while utilizing only 3.75 M parameters and 8.8 GMACs. These findings fully validate the superiority and practicality of the proposed method for low-light image enhancement tasks in architectural settings.

ABSTRACT Acoustic metamaterials have garnered significant research interest due to their unique wave-manipulation capabilities, with potential applications spanning noise control, subwavelength imaging, and non-destructive testing. However, conventional design paradigms rely on trial-and-error experimentation, biomimetic inspiration, and finite element analysis (FEA). These approaches suffer from three critical limitations, namely prohibitive experimental costs, serendipity-driven biological analogies, and computationally intensive simulation cycles. To address these challenges, this study proposes a surrogate model-driven framework for rapid optimal design and performance prediction of gradient acoustic metamaterials (GAM). Specifically, a bidirectional mapping between structural parameters and frequency response characteristics is established through three key innovations: 1) Systematic construction of parameter domains via rigorous screening of structural and frequency-response descriptors; 2) Implementation of Gaussian process regression to quantify nonlinear relationships between design variables and acoustic performance metrics while generating probabilistic predictions with error bounds; 3) Development of an uncertainty-aware prediction model that simultaneously outputs predicted values and confidence intervals, effectively bypassing computationally expensive FEA iterations. Experimental validation demonstrates exceptional accuracy and computational efficiency. Notably, the dual-output capability enhances engineering decision-making by quantifying design reliability, while maintaining physical interpretability through explicit parameter-performance correlations. This paradigm-shifting approach establishes a data-driven design framework for acoustic metamaterials, with methodological innovations readily generalisable to multifunctional metamaterial systems requiring performance predictability and design interpretability.

Marathi saint literature is very rich in all aspects. When it comes to maintaining mental health, the poems, ovis and abhangas of saints act as medicine. Just reciting the poems or abhangas uplifts the mind. During the time of Saint Dnyaneshwar and Saint Namdev, there was a Manu kingdom of hardworking Brahmins. They were scholars who interpreted the scriptures according to their convenience. State administration, religious administration and justice were concentrated in one place, so living in that time was unbearable. Dnyaneshwari was created under immense mental stress. Saint Muktabai's Tati Abhangs testify to this. The time of Saint Tukaram was a time of fierce attacks by the sword. The Muslim rule was controlling everything with the edge of the sword. At such a time, the gift of Shri Sant Tukaram Gatha was received. Today's time is of the Indian Constitution. The scourge of materialism is hitting the youth. Huge mental stress is arising from this. For today's youth, the literature of saints provides relief from terrible mental stress, invisible fear, the constant feeling that something bad will happen, something bad will always happen to me, feelings of inferiority, shocking events from the past, etc. If recited, it uplifts the mind. In this research, the intensity of sound is measured using a stopwatch method. Its unit is dB. Generally, the intensity of the sound produced is converted into Hz and recorded in a table. There is no direct relationship between sound and the human brain. Brain waves are a different matter. The method of measuring that frequency is different. Anxiety and mood swings are prevalent in the new generation. The intensity of sound in the sacred literature becomes a medicine for such mental illnesses because the frequency responses of the brain such as delta, theta, alpha, beta, gamma rhythm responses which match the sacred, Marathi Saint literature.

ABSTRACT The main aim of this study is to numerically investigate the influence of a baffle on reducing earthquake-induced swirling sloshing waves in rectangular fluid storage tanks. To achieve this, the study utilized the Navier–Stokes equations (RANS) and the Volume of Fluid (VOF) method, alongside the General Moving Object (GMO) technique, to perform numerical solutions. Initially, a numerical simulation was performed on a baseline model, with validation conducted by comparing the results to existing data. Following this, the frequency response of the concrete rectangular tank was analyzed by modeling it under a broad spectrum of harmonic excitations. The results demonstrated that resonant frequencies generated swirling waves within the tank, indicating that the sloshing phenomenon was multidirectional rather than unidirectional. To manage rotational sloshing, the study examined the effect of a perpendicular plate on the water surface, aiming to diminish the seismic response of tanks subjected to harmonic excitation at various frequencies. The findings showed that the plate effectively mitigated oscillation intensification by modifying the tank’s vibrational frequency and preventing the onset of rotational sloshing. Additionally, it significantly enhanced the tank’s seismic response, leading to reductions in base shear and overturning moments.

Abstract An integrated microsystem for trace gas detection based on multi-pass radial-resonant photoacoustic spectroscopy (MR-PAS) has been proposed. A polished photoacoustic cavity is specifically designed to facilitate incident laser light coupling, enable multi-pass reflection, and resonantly amplify the photoacoustic (PA) pressure. Finite element analysis (FEA) is employed to simulate the acoustic field distribution, frequency response, and ray tracing behavior.Simulation results reveal that the designed cavity achieves 771-fold excitation of the incident laser and amplifies PA pressure by operating in the first-order radial resonant mode. To validate the performance of the MR-PAS, a CO₂ detection system is constructed. Experimental results demonstrate that the MR-PAS achieves an impressive minimum detection limit (MDL) of 12.4 ppb with a 274 s integration time, according to the normalized noise-equivalent absorption coefficient of 1.71×10⁻⁸ cm⁻¹•W•Hz⁻¹/². The compact photoacoustic cavity (1.1 mL) enables rapid response, with gas replacement and stabilization completed within ~180 s at a flow rate of 50 sccm.

This study aims to design and analyze a third-order active analog low-pass filter using the Butterworth approach and the Sallen-Key topology. This filter functions to filter unwanted high-frequency signals, with a flat frequency response characteristic in the passband and a sharp drop after the cutoff frequency. The circuit was designed through simulations in Proteus and further analyzed using MATLAB, then physically realized in the Electronics and Instrumentation Laboratory of the Faculty of Mathematics and Natural Sciences, UNY. The testing process includes analysis of the output amplitude, the phase difference between the input and output signals, and the response to a square signal. The results show that the filter successfully reduces the signal amplitude at high frequencies and produces a phase response that matches the theory. In addition, when given a square signal, the circuit shows stable low-pass characteristics. This study demonstrates that the third-order Butterworth design with the Sallen-Key topology can be effectively implemented as a low-frequency analog signal filtering system.

This paper considers cylindrical composite sandwich shells that consist of two thin outer layers and one thick honeycomb filler. The outer layers are made of a composite orthotropic material, for example, carbon-reinforced plastic. The honeycomb filler is made of an orthotropic plastic, for example, PLA, using additive technologies. To obtain a mathematical model of nonlinear structural vibrations, the honeycomb core is homogenized into a uniform orthotropic solid layer using a finite-element simulation in ANSYS. Parametric vibrations of the cylindrical shell under the action of a longitudinal load are considered. Each layer of the structure is described by a higher-order shear theory, which uses five generalized displacements (three displacements projections onto the axes and two rotation angles of the middle surface normal). The displacement projections are continuous at the layer interfaces. The assumed mode method is used to obtain a system of nonlinear ordinary differential equations in the generalized coordinates. The method uses the kinetic and the potential energy of the structure. The shooting technique and the parameter continuation method are used jointly to analyze nonlinear vibrations, their stability and bifurcations. The multipliers are calculated to estimate the vibration stability. The stability and bifurcations of periodic oscillations are shown in the frequency responses, which describe the structure dynamics in the principal parametric resonances. As shown by the numerical analysis, standing waves are observed in the cylindrical shell. As a result of the bifurcations, the standing waves are transformed into travelling ones, which are described by a loop in the frequency response.

Investigation into complex neural circuits necessitates interfaces capable of high channel count recording and stimulation. However, existing commercial neural headstages often have limited scalability, restrictive proprietary designs, and constrained bidirectional capabilities, which worsens accessibility challenges and compels researchers to reinvent tools rather than build on a shared foundation. Here, we present two open-source, 128 channel headstages-Iris 128B and Iris 128S-designed for integration with microelectrode arrays. The Iris 128B enables fully bidirectional interfacing, with stimulation or recording across all 128 electrode channels, while the Iris 128S provides recording on 128 channels and stimulation on 16 simultaneous channels, which can be assigned to any 16 of the 32 available stimulation channels. Both designs use Intan Technologies' RHS and RHD series ICs for amplification, filtering, digitization and stimulation. The headstages were validated through benchtop impedance, noise, and frequency response measurements, as well as acute in vivo recordings in an anesthetized rat. Results demonstrate low noise levels and reliable signal acquisition across all channels. By releasing fully documented printed circuit board designs for headstages, this work aims to take a step towards broader adoption of bidirectional recording and stimulation systems while increasing channel counts. Future iterations will focus on miniaturization and wireless integration to improve usability in chronic and freely moving small animal experiments.

Abstract According to the characteristics of multi-variable control object in small modular reactors control system, a design method of control system is presented in this paper. Firstly, the nonlinear differential equations of the system are constructed according to the principle of mechanism modeling, and then the transfer function of the system is obtained by linearization. Then, the coupling characteristics of the system are analyzed by using Gershgorin Circle Theorem in modern frequency domain analysis method. On this basis, the inverse Nyquist array method is used to decouple the two key channels of reaction-exit temperature channel and feed-water valve-steam pressure in small modular reactors. Then the PI correction network is designed by frequency response method. In order to fully verify the performance of the decoupling controller, the system is verified based on linear model and nonlinear model respectively, and the pre-compensation matrix processing strategy under variable load conditions is proposed. Simulation results show that this method can significantly reduce the coupling degree between the two channels, and the performance of the control system after decoupling is significantly improved compared with that before decoupling.

The nose is a resonator, the acoustic properties of which are determined by its shape. Due to its complex anatomy and hence intricate acoustical response the identification of universal acoustic characteristics of nasalized vowels and consonants is challenging. The purpose of this investigation was to 1) elucidate acoustic properties of the nasal resonator, 2) document how the paranasal sinuses affect it, and 3) examine if 3D-replicas of anatomical specimens provide reliable data for acoustic analysis. In this experimental study the resonance properties of the nasal tract were analyzed in ex-vivo specimens as well as in their 3-D replicas. Their sound transfer characteristics were recorded by sending a sinewave, gliding from low to high frequency from an earphone airtightly sealed into the velopharyngeal port. The response was picked up at a nostril. The acoustical influence of the sinuses was reversibly eliminated by occlusion of the sinus ostia. Response curves of the nasal tract were found to possess two main resonances, one in the vicinity of 600-750 Hz and one in the 2500 - 3500 Hz range. Comparison of the acoustical responses obtained while including and excluding the influence of the paranasal cavities showed a great inter-individual variation in the response curve morphology. The cavities were found to introduce V-shaped sound level minima in the response curves. When the influence of the paranasal cavities is eliminated, the nasal cavity presents two main resonances, which are determined mainly by its anatomical length. The resonances of the paranasal cavities introduce minima and maxima in the frequency response of the nasal tract at frequencies with substantial inter-individual variation. Replicas of anatomical specimens provide reliable data for acoustic analysis.

Abstract Partial discharge (PD) detection is critical for evaluating insulation degradation in high‐voltage power cables. Flexible piezoelectric acoustic sensors offer a compelling solution owing to their conformability to curved surfaces and strong immunity to electromagnetic interference. However, conventional piezoelectric thin films typically suffer from low sensitivity due to the intrinsic trade‐off between piezoelectric coefficient (d 33 ) and dielectric constant (ε r ). In this work, a TiO 2 buffer layer is introduced to engineer Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) thin films with significantly enhanced performance. The 266 nm TiO 2 buffer layer is prepared by the sol‐gel method. The TiO 2 layer reduces ε r from 650 to 150 at the frequency of ≈100 kHz, promotes refined grain, a self‐poled state, and strong (100) texture, and increases d 3 3 from 45 to 160 pm V −1 , resulting in an estimated ultrahigh piezoelectric voltage constant g 3 3 of 124 mV·m·N −1 . The fabricated flexible sensor exhibits a wide frequency response up to 600 kHz with an average sensitivity of 65 dB and peak sensitivity exceeding 70 dB. It captures high‐resolution acoustic signals of PD events in a 110 kV power cable, outperforming both unmodified PZT and commercial PVDF sensors. Long‐term and thermal stability evaluations confirm excellent durability. This study presents a robust strategy for tuning piezoelectric thin‐film properties via interface engineering and demonstrates the potential of TiO 2 ‐buffered PZT sensors for advanced acoustic sensing in power equipment insulation health monitoring applications.