Frequency Response Research Articles

Theoretical and experimental modal analysis of polymeric hybrid lap joint structure with and without damage

AbstractThis research reported the eigenvalue responses of delaminated hybrid (adhesive and bolted) polymeric joint components using a simulation model via ABAQUS. First, a simulation model is developed into by combining two different eight‐noded elements for the glass‐fiber‐reinforced polymeric adherents (quadrilateral in‐plane general‐purpose continuum shell element, SC8R) and the adhesives (linear brick) for the discretization of the component. The necessary end boundary conditions are now adopted to compute the desired eigenvalues using Lanchzo's solution steps. Further, the model validity, including the element‐sensitive analysis, is performed by computing a few examples. In this regard, the responses are initially compared with numerical results available in the published domain and further verified with in‐house experimentation (intact and damaged). The frequency response of the developed model deviates from the published data by a maximum of 15%. Similarly, the numerical frequency response deviates from the experimental findings, ranging from a minimum of 1.13% to a maximum of 18.5%. Based on the model's accuracy and consistency, the simulation model of the hybrid polymeric joint structure is extended further to evaluate the influences of geometrical parameters and delamination. Finally, a set of recommendations is illustrated from the numerical experimentation of the intact/damaged hybrid lap joint structure. The fiber layup orientation, boundary condition, and aspect ratio significantly impact the natural frequency response of adhesively bonded joints.Highlights The hybrid joint modal responses are investigated numerically, including delamination. Two types of joints (adhesive and anchored with bolt) are utilized for the component fabrication. The simulated frequency values are verified with in‐house experimentation. The effect of delamination on hybrid joint frequency is computed via numerical experimentation.

Pattern Optimization to Minimize Dynamic Impacts of Wrapping Cables in Plate-Like Space Structures: Experimental Validation

Abstract In lightweight space structures, incorporating power and control signal transmission cables significantly impacts the dynamics of the host structures. This study presents an experimental effort to provide proof of concept for the mathematical modeling techniques developed for the ideal cable placement to preserve the dynamic properties of host plate structures. By assuming a periodic cable wrapping pattern, the cable-harnessed structure is modeled using repeating fundamental elements. This periodicity enables the application of an energy-equivalence homogenization method, leading to partial differential equations that describe the out-of-plane vibrations of the cable-harnessed plate system. The presented test results further validate several optimal wrapping designs for host plate structures. The frequency response functions for the optimal cable pattern from the analytical model are compared against the test results, demonstrating excellent agreement.

Takagi–Sugeno Fuzzy Nonlinear Control System for Optical Interferometry

The Takagi-Sugeno (T-S) fuzzy control is a nonlinear method that uses a combination of linear controllers as its control law. This method has been applied in various fields of scientific research: buck converters, biomedicine, civil engineering, etc. To the best of the authors’ knowledge, although works on traditional fuzzy control and optical interferometry have already been published, this is the first time that T-S fuzzy (specifically) is applied to demodulate interferometry signals. Through a proof-of-concept experiment, the paper describes the fusion of an open-loop interferometer with an external closed-loop digital observer based on T-S fuzzy (both simple and inexpensive), which actuates like a closed-loop interferometer (but without its drawbacks). The observer design is based on stability conditions using linear matrix inequalities (LMIs) solutions. The system is maintained at the optimal 90∘ operation point (compensating for environmental drifts) and enables the demodulation of optical phase signals with low modulation index. Simulations and measurements were performed by using a Michelson interferometer, verifying that the method demodulates signals up to π/2 rad amplitudes and higher than 100 Hz frequencies (with maximum error of 0.45%). When compared to the important arc tangent method, both presented the same frequency response for the test PZT actuator.

Barium titanate and lithium niobate permittivity and Pockels coefficients from megahertz to sub-terahertz frequencies

Abstract The Pockels effect is essential for controlling optical signals at the highest speeds, particularly for electro-optic modulators in photonic integrated circuits. Lithium niobate (LN) and barium titanate (BTO) are two excellent Pockels materials to this end. Here we measure the Pockels coefficients and permittivity in LN and BTO over a continuous frequency range from 100 MHz to 330 GHz. These properties are constant across this frequency range in LN, but have a strong frequency dependence in BTO. Still, our measurements show that BTO has remarkable electro-optic properties compared with LN. Furthermore, we show how BTO devices can be designed with a flat electro-optic frequency response despite the Pockels coefficient dispersion. Finally, we expound our method for broadband characterization of these vital electro-optic properties, utilizing specialized integrated electro-optic phase shifters. Altogether, this work empowers the design of high-speed BTO devices and the development of new electro-optic materials.

Multi-objective optimization of flexible positioning platform considering displacement frequency and dynamic stiffness responses

In order to study the impact of periodic loads on the vibration performance of the flexible positioning platform in the key mechanisms of the ultra-high acceleration macro–micro motion platform, and to improve the performance and stability of the platform, this paper combined SolidWorks and ANSYS Workbench to conduct modal analysis and harmonic response of the flexible positioning platform. Analysis to obtain its inherent characteristics. The piezoelectric actuator provides the driving force of the micro-motion platform and achieves precise micro-motion displacement positioning, which is used to study the frequency response results of simple harmonic excitation. By analyzing the node displacement frequency response, the dynamic stiffness response characteristics of the hinge and micro-motion platform of the flexible positioning platform under actual loads were determined, and potential dangerous areas were identified. Finally, both response surface optimization and direct optimization methods were used to optimize the design of the hazard zones for the flexible positioning platform, and the results of both optimization models were validated. The findings indicate that the direct optimization results validate the accuracy of the response surface optimization. After response surface optimization, the first-order natural frequency of the flexible positioning platform increased by 3.28%, and the mass decreased by 1.84%. The maximum deformation and response peak of the first-order vibration mode decrease, and the dynamic stiffness increases. This research provides valuable reference for the structural design and vibration performance optimization of positioning platforms containing flexible hinges.

A Signal-Harmonizing Hybrid Neural Pathway Enabled by Bipolar-Chemo-Synapse Spiking Interneuron.

To realize human-machine fusion, a hybrid neural pathway operating in the same modality with biological systems becomes imperative, which requires an interneuron unit to encode information in biorecognizable spike sequences and tune the frequency upon excitatory and inhibitory neurotransmitters. Existing artificial interneurons cannot encode information upon different neurotransmitters, and the activation threshold and frequency responsivity do not align with those of biological counterparts, leading to limited success in constructing a signal-harmonizing hybrid neural pathway for neuroprosthetics, neurorehabilitation, and other neuroelectronic applications. Herein, we develop a bipolar-chemosynapse interneuron to encode the spike frequency in a highly bionic paradigm. Bipolar synapses dynamically respond to excitatory and inhibitory neurotransmitters and translate time-series chemical signals into the spike sequence, achieving the lowest activation threshold (6.25 μM) and the highest frequency responsivity (0.55 Hz μM-1) to date, close to the biological counterpart. A signal-harmonizing hybrid sensorimotor pathway mediated by excitatory and inhibitory neurotransmitters is constructed for the first time, which encodes upstream mechanical stimuli, modulates the downstream leg swing frequency of a mouse, and balances neural activity accordingly.

Evaluation of the information transmission of treatment with dental aligners in social media: empathetic language versus non-empathetic language

BackgroundInformation presented in audiovisual format, is more effective in the retention of information by patients than traditional written methods. On the other hand, empathy in the transmission of information is a crucial element in the relationship between health professionals and patients. This study aimed to determine whether the presentation of information in audiovisual format in an affective and empathetic way, as is done in social networks, improves the knowledge acquired by orthodontic patients treated with aligners.Methods60 participants, which were equally randomized in 2 groups, took part in this pilot study. Two videos were created that delivered the same informative content about treatment with dental aligners. One video used non-technical and empathetic language, for the level of understanding of patients (empathic video: EG), and the other used technical (similar to that used in clinical practice) but non-empathetic language (non-empathetic video: N-EG). Thirty randomized participants watched the empathic video and another thirty watched the non-empathetic video, and then completed the same questionnaire to compare the information acquired. The relative frequencies of correct responses in each group, were analysed by means of cross-tabulations. The significance of the differences between the results of the two groups was calculated with the Chi-square test.ResultsThe questionnaire confirmed that 70% of the participants had no prior knowledge of aligners. The 66.7% of patients, had no relatives or close friends or family who had been previously treated with aligners. Also 75% of them, stated that they had not previously searched for information about aligners on the Internet. After viewing the videos, all patients were able to respond adequately to most of the questions asked, regardless of whether they had viewed the empathic (EG) or non-empathetic (N-EG) video. Significant differences (p < 0,05) were recorded in 2 questions classified as technical difficulty, in which the EG obtained better results in terms of knowledge acquired than the N-EG.ConclusionsShowing audiovisual format information to patients, improves patients’ understanding of orthodontic treatment with dental aligners. Empathy enhances acquired knowledge for unusual and unknown information.

Investigating Cognitive Load and Autonomic Arousal During Voice Production and Vocal Auditory-Motor Adaptation.

Cognitive load and autonomic arousal are hypothesized to affect voice production, yet the nature of these relationships is unclear. The purpose of this study was to assess how cognitive load and autonomic arousal differentially affect voice production and vocal motor control. Physiological measures of autonomic arousal were recorded from 30 adults under different cognitive loads elicited by a Stroop task. In Experiment 1, voice acoustic measures were measured during speech production. In Experiment 2, fundamental frequency (fo) responses to predictably altered auditory feedback (sensorimotor adaptation) were measured. Mixed linear-effects models assessed relationships between variables. Changes between cognitive loads were compared among the two experiments. In Experiment 1, increased cognitive load was associated with increases in sound pressure level, whereas increases in autonomic arousal measures (i.e., decreases in skin conductance rise time, pulse amplitude, and period) were related to decreases in cepstral peak prominence. Increased autonomic arousal (i.e., decreased pulse amplitude) was related to increased adaptation in Experiment 2. Participants who responded to increased cognitive load by decreasing fo during Experiment 1 showed more adaptation in Experiment 2. Differential effects of cognitive load and autonomic arousal emphasize the importance of individual physiological variability when assessing how stress affects the voice.

RMS Modeling and Control of a Grid-Forming E-STATCOM for Power System Stability in Isolated Grids

This paper presents a comprehensive RMS-based phasorial model of an E-STATCOM with grid-forming (GFM) control, designed to improve power system stability in isolated grids. Unlike previous approaches, this model integrates a governor with an internal power system stabilizer (PSS) and an active current limiter (ACL) to enhance frequency regulation and mitigate oscillations. Additionally, an exciter with a nonlinear modulation function is introduced to optimize voltage regulation and reactive power support. A detailed conventional supercapacitor (SC) model is also incorporated, enabling dynamic DC-voltage control based on active power variations, improving frequency stability. The proposed E-STATCOM RMS model includes algebraic equations, dynamic governor and exciter models, supercapacitor-based energy storage control, and an advanced current-limiting strategy. Simulations are conducted on the Fuerteventura–Lanzarote (Canary Islands, Spain) power system, comparing the E-STATCOM with a synchronous condenser (SynCon) in frequency response, voltage regulation, and fault performance. The results show that the E-STATCOM improves frequency stabilization and energy efficiency while complying with grid codes. This study introduces a novel RMS-based modeling approach for GFM E-STATCOMs, bridging the gap between theoretical phasorial analysis and real-world applications. The findings confirm that E-STATCOMs are a viable alternative to SynCons, enhancing grid stability in high-renewable-penetration systems.

A Novel Multi-Dynamic Coupled Neural Mass Model of SSVEP

Steady-state visual evoked potential (SSVEP)-based brain—computer interfaces (BCIs) leverage high-speed neural synchronization to visual flicker stimuli for efficient device control. While SSVEP-BCIs minimize user training requirements, their dependence on physical EEG recordings introduces challenges, such as inter-subject variability, signal instability, and experimental complexity. To overcome these limitations, this study proposes a novel neural mass model for SSVEP simulation by integrating frequency response characteristics with dual-region coupling mechanisms. Specific parallel linear transformation functions were designed based on SSVEP frequency responses, and weight coefficient matrices were determined according to the frequency band energy distribution under different visual stimulation frequencies in the pre-recorded SSVEP signals. A coupled neural mass model was constructed by establishing connections between occipital and parietal regions, with parameters optimized through particle swarm optimization to accommodate individual differences and neuronal density variations. Experimental results demonstrate that the model achieved a high-precision simulation of real SSVEP signals across multiple stimulation frequencies (10 Hz, 11 Hz, and 12 Hz), with maximum errors decreasing from 2.2861 to 0.8430 as frequency increased. The effectiveness of the model was further validated through the real-time control of an Arduino car, where simulated SSVEP signals were successfully classified by the advanced FPF-net model and mapped to control commands. This research not only advances our understanding of SSVEP neural mechanisms but also releases the user from the brain-controlled coupling system, thus providing a practical framework for developing more efficient and reliable BCI-based systems.

Age-related differences in the relationship between confidence and false memory in a mnemonic discrimination task

In addition to episodic memory loss there is an increase in false remembering in ageing especially when the discrimination between studied and new items is difficult in a recognition memory task. The aim of this study was to identify the underlying psychological mechanisms of this behavior, specifically, the possible role of false recollection. We used the Mnemonic Similarity Task, a widely used task in neuroscience research developed to assess the behavioral manifestation of hippocampal computations, pattern separation and pattern completion. First, older and young adults (n = 39 and 44, respectively) were presented with images of everyday objects. Then, on a surprise recognition test, they saw old (studied) and new (non-studied) items as well as visually similar lures of the images seen in the study phase. Instead of using the original Old/New test format, we asked participants to make confidence judgments. Our response frequency and ROC (receiver operating characteristics) analyses revealed overconfidence in false memories for the lures in the group of older adults suggesting false recollection. Such overconfidence was not observed for the completely new stimuli. Our results imply that older adults tend not to acknowledge some memory problems as a consequence of very high confidence in false memories.

The Impact of Squeeze Film Damper and Support Nonlinear Forces on the Dynamic Response of High-Speed Flexible Rotors

To investigate the nonlinear dynamic response of rotor systems, a finite element model of the squeeze film damper-rotor system was established. With the Euler–Bernoulli beam rotor model, the nonlinear oil film forces of the squeeze film damper (SFD) and the nonlinear restoring forces of the supports are applied as external loads to the support nodes using the finite element method. The Newmark Beta method was used to solve it, and the nonlinear dynamic response of the rotor was analyzed using frequency–response curves, time-domain response diagrams, and shaft centerline trajectory diagrams. The effects of different oil film gaps and support restoring force coefficients on the rotor response were examined. The results show that the coupling effect of the two nonlinear forces is the superposition of their individual effects; the two nonlinear forces have a significant impact on the rotor response amplitude, and appropriate parameter selection and installation positions can reduce the amplitude by 19%; and finally, among the two nonlinear forces, the SFD nonlinear oil film force mainly affects the amplitude, while the support nonlinear restoring force affects both the amplitude and frequency.

XDev: a mixed-signal, software-defined neurotechnology interface platform for accelerated system development

Objective.Advances in electronics and materials science have led to the development of sophisticated components for clinical and research neurotechnology systems. However, instrumentation to easily evaluate how these components function in a complete system does not yet exist. In this work, we set out to design and validate a software-defined mixed-signal routing fabric, 'xDev', that enables neurotechnology system designers to rapidly iterate, evaluate, and deploy advanced multi-component systems.Approach.We developed a set of system requirements for xDev, and implemented a design based on a 16 × 16 analog crosspoint multiplexer. We then tested the impedance and switching characteristics of the design, assessed signal gain and crosstalk attenuation across biological and high-speed digital signaling frequencies, and evaluated the ability of xDev to flexibly reroute microvolt-scale amplitude and high-speed signals. Finally, we conducted an intraoperativein vivodeployment of xDev to rapidly conduct neuromodulation experiments using diverse neurotechnology submodules.Main results.The xDev system impedance matching, crosstalk attenuation, and frequency response characteristics accurately transmitted signals over a broad range of frequencies, encapsulating features typical of biosignals and extending into high-speed digital ranges. Microvolt-scale biosignals and 600 Mbps Ethernet connections were accurately routed through the fabric. These performance characteristics culminated in anin vivodemonstration of the flexibility of the system via implanted spinal electrode arrays in an ovine model.Significance.xDev represents a first-of-its-kind, low-cost, software-defined neurotechnology development accelerator platform. Through the public, open-source distribution of our designs, we lower the obstacles facing the development of future neurotechnology systems.

Theoretical insights into 1:2 and 1:3 internal resonance for frequency stabilization in nonlinear micromechanical resonators

Abstract Micromechanical resonators are essential components in time-keeping and sensing devices due to their high frequency, high quality factor, and sensitivity. However, their extremely low damping can lead to various nonlinear phenomena that can compromise frequency stability. A major limiting factor is the Duffing hardening effect, which causes frequency drift through amplitude variations, known as the amplitude-frequency effect. Recently, internal resonance (InRes) has emerged as an effective approach to mitigate this issue and enhance frequency stabilization. In this study, we investigate the frequency stabilization mechanisms of 1:2 and 1:3 InRes using a generalized two-mode reduced-order model that includes Duffing nonlinearity and nonlinear modal coupling. By analyzing the frequency response curves and $$\pi /2$$ π / 2 –backbone curves, we demonstrate how different parameters affect the effectiveness of frequency stabilization. Our results identify two distinct regimes depending on the coupling strength relative to the stiffening effect as a key factor in determining the stabilization mechanism. For the regime of weak coupling, both 1:2 and 1:3 InRes achieve frequency stabilization through amplitude and frequency saturation over a range of forcing amplitudes. In contrast, strong coupling reduces the amplitude-frequency effect by forming an asymptote line for 1:2 InRes or a zero-dispersion point for 1:3 InRes. These insights offer valuable guidelines for designing micromechanical resonators with high-frequency stability, highlighting InRes as a robust tool for enhancing performance in practical applications.

Assessing Factors Influencing Drug Interactions: Insights from Healthcare Practitioners at a North Indian Tertiary Care Hospital

Background: Drug interactions (DIs) occur when a drug, herb, or food disrupts the activity of another drug, potentially causing beneficial or harmful effects. Understanding practitioners' ability to identify and manage these interactions is crucial for patient safety. This study aimed to evaluate the factors affecting common drug interactions by assessing practitioners' knowledge, attitude, and awareness in their daily practice. Methods: In a cross-sectional study conducted at a tertiary care hospital in Northern India, 300 doctors were randomly selected from 15 different specialties in the outpatient department. The study employed a validated questionnaire that included sections on demographic information, knowledge and practice related to drug interactions (DIs), and attitudes toward various sources of drug information. The frequency of response was calculated in percentage for the categorical variables. The chi-square test was used to examine the association between variables. P-value &lt;0.05 was considered as significant. Results: The study revealed a low level of knowledge among practitioners regarding drug interactions, with only half of the respondents correctly classifying drug pairs. Factors contributing to drug interactions included communication gaps between doctors and patients and insufficient counseling on drug-drug and drug-food interactions due to patient overload. Many practitioners expressed the need for interactive training sessions and the implementation of an electronic surveillance system to prevent harmful interactions. Conclusions: Regular training and collaboration between practitioners and pharmacologists are crucial to enhancing knowledge and expertise on drug interactions. This integration would enable appropriate patient counseling and improve treatment outcomes. Keywords: Drug interaction, Healthcare practitioners, Patient safety, Knowledge, Attitude, Awareness

Emergency Load-Shedding Strategy for Power System Frequency Stability Based on Disturbance Location Identification

With the evolution of modern power systems, the proportion of renewable energy generation in the grid continues to grow. At the same time, grid operation modes have become increasingly complex and dynamic, leading to heightened uncertainty in disturbance faults. Moreover, power electronic equipment exhibits relatively low-level immunity to disturbances. The issue of frequency stability in power systems is becoming increasingly severe. These factors make the pre-programmed control strategies based on strategy tables, which are widely used as the second line of defense for frequency stability in power systems, prone to mismatches. When a power disturbance occurs, it is crucial to adopt an appropriate emergency load-shedding strategy based on the characteristics of unbalanced power distribution and the network’s frequency profile. In this paper, for a simplified multi-zone equivalent system, the coupling relationship between different load-shedding locations and the system’s frequency response after a disturbance is analyzed. This analysis integrates the power distribution characteristics after the disturbance, a system frequency response (SFR) model, and the frequency distribution law in the network. It is demonstrated that under identical load-shedding amounts and action times, implementing load shedding closer in electrical distance to the disturbance location is more beneficial for stabilizing system frequency. A convolutional neural network (CNN) is employed to localize system faults, and combined with research on the emergency load-shedding amounts based on SFR model parameter identification, a rapid disturbance location-based emergency load-shedding strategy is proposed. This strategy enables prompt and accurate load-shedding actions to enhance the security and stability of the power system. Finally, the effectiveness of the proposed approach is validated using the CEPRI-LF standard arithmetic system.

Novel APD Array Configurations for Improved Detection Area and Frequency Response

This paper presents two novel avalanche photodiode (APD) array structures designed to significantly enhance both detection area and bandwidth, overcoming the common trade-off between these parameters in conventional photodetectors. The impact of various parameters on the bandwidths of the two distinct array structures was theoretically simulated. Experimental validation using the self-fabricated 2 × 2 array on PCB board confirmed the bandwidth enhancement realized through inductor integration, with one APD array demonstrating an increase to 780 MHz (1.41 times greater) and another showing an increase to 1.21 GHz (1.35 times greater). Unlike prior works where array bandwidth is often lower than single detectors, our structures maintain high bandwidth while expanding the detection area. Structure 2 is particularly recommended over Structure 1 because of its lower noise, better signal-to-noise ratio (SNR), and reduced power consumption.

Numerical and Experimental Investigation of rubbing Existence in the Context of a Rotating Machine Under Base excitation

Abstract This work presents an experimental investigation regarding the dynamic behavior of an onboard rotating machine in the case of disk-stator rubbing. The concept of onboard rotating machine has to do with the situation in which base excitations are considered in the mechanical modeling of the system. In the present study the system is composed of a disk mounted on a flexible shaft that is supported by rolling bearings at the ends of the shaft. The model is obtained from the classical Lagrange's equations and the finite element method, considering both the strain energy and kinetic energy of the shaft and the kinetic energies of the disk and the unbalance mass. The phenomenon of contact was included in the modeling of the onboard rotor. For this aim, two possible formulations for the contact effect were taken into consideration. The numerical results were compared with the experimental ones stemming from a test rig that was constructed to support the present research work. Different experimental tests were performed both in the frequency and the time domain, so that frequency response functions, orbits and unbalance responses were obtained. A good correspondence between numerical and experimental results was observed.

Nonlinear forced vibration analysis of FG-CNTRC sandwich beams with viscoelastic core under various boundary conditions

In this study, the nonlinear forced vibration response of sandwich beams with functionally graded face sheets reinforced with carbon nanotubes (FG-CNTRC) and a viscoelastic core is investigated. In the thickness direction, a functionally graded pattern can be followed or a uniform distribution of CNTs can be used throughout the face sheets. By using the higher order zig-zag theory, shear and normal deformations in the core layer are incorporated into the analytical formulation. Geometric nonlinearity is addressed using von Kármán’s strain-displacement relations. Based on Hamilton’s principle, the equations of motion and boundary conditions are developed. The final nonlinear frequency-amplitude equation contains complex parameters due to the damped core modulus. These parameters arise from the geometrically nonlinear coupling associated with the viscoelastic core layer. The technique of harmonic balance is considered. The damping and frequency response curves are analyzed for beams with different boundary conditions. Different support scenarios are analyzed. An extensive parametric analysis is conducted to investigate the impact of carbon nanotubes on the nonlinear vibration of sandwich beams. Results show that peak amplitude increases with higher core-to-skin thickness ratios and nanotube volume fractions, with the FGX-CNTRC beam exhibiting the highest peak amplitude.

The Frequency Response Characteristics of Ge-on-Si Photodetectors Under High Incident Power.

This study explores the mechanisms responsible for the bandwidth reduction observed in germanium photodetectors under high signal light power. We investigate the impact of the carrier-shielding effect on the bandwidth through simulations, and we mitigate this effect by increasing the applied bias voltage. The increase in the concentration of photogenerated carriers leads to a reduction in the carrier saturation drift velocity, which reduces the bandwidth of the germanium photodetector; this phenomenon is studied for the first time. The bandwidth is determined primarily by the carrier saturation drift velocity when the incident light power is below 2.5 mW. The decrease in bandwidth that is calculated based on the decrease in carrier saturation drift velocity is consistent with the experimental results. However, when the signal light power exceeds 3 mW, both the carrier-shielding effect and the reduction in the carrier saturation drift velocity contribute to the bandwidth reduction. This study provides good theoretical guidance for the design of high-power germanium photodetectors.