Low Frequency Domain Research Articles

A simplification of the time-domain equivalent circuit model for lithium-ion batteries based on low-frequency electrochemical impedance spectra

The traditional time-domain equivalent circuit model (ECM) for Li-ion batteries may achieve high accuracy by identifying model parameters through limited dynamic conditions. However, the traditional ECM (TECM) parameter matching techniques based on time-domain may have the problem of adaptability of working conditions. To solve the problem of dependence on time-domain working conditions and improve the stability of the full-cycle modeling of lithium batteries, it is critical to establish the ECM based on the principle of electrochemical impedance spectroscopy (EIS). However, the full-frequency domain ECM structures (FECM) and the corresponding parameters based on the whole frequency ranges of the EIS employ too many resources for on-line estimation. In this paper, we firstly analyze the frequency region of the standard operating conditions of electric vehicles and theoretically discuss the rationality of the Simplified ECM base on the low-frequency region of the EIS. The proposed low-frequency domain ECM (LECM) simplifies the elements that describe the medium-high frequency regions of the EIS. It only uses the low-frequency region of the EIS to identify the model parameters. The results show that the accuracy of the proposed LECM is almost the same as that of FECM, and saves an average of 40% of the calculation load.

The Case for Considering Polarization in the Interpretation of Electrical and Electromagnetic Measurements in the 3 kHz to 3 MHz Frequency Range

Usually, in situ electrical polarization measurements (in geophysical prospection referred to as induced polarization or spectral induced polarization (SIP)) are carried out at frequencies below 1 kHz. These techniques have mainly been used for mining exploration, followed by a larger panel of environmental applications. However, in this ultra low and extremely low-frequency domain, the duration of each individual measurement is long, i.e., typically several tens of minutes for a single full SIP spectrum down to the mHz range. This restriction makes it unrealistic to implement high-density measurement mapping campaigns over large areas, which would otherwise be possible at higher frequencies. In the intermediate frequency range [3 kHz–3 MHz], laboratory studies of soil and rock samples have shown that they can be strongly polarized notably in the presence of clays, and this property has been confirmed by several in situ mapping experiments using electromagnetic induction in the time and frequency domains (FDEM and TDEM), as well as by an electrostatic method (often named capacitive-coupled resistivity or CCR). The present paper recalls these results in an effort to promote polarization measurements at intermediate frequencies and to emphasize the importance of measuring this phenomenon.

Opioid effect on the autonomic nervous system in a fetal sheep model.

Opioid use during labour can interfere with cardiotocography patterns. Heart rate variability indirectly reflects a fluctuation in the autonomic nervous system and can be monitored through time and spectral analyses. This experimental study aimed to evaluate the impact of nalbuphine administration on the gasometric, cardiovascular, and autonomic nervous system responses in fetal sheep. This was an experimental study on chronically instrumented sheep fetuses (surgery at 128 ± 2days of gestational age, term = 145days). The model was based on a maternal intravenous bolus injection of nalbuphine, a semisynthetic opioid used as an analgesic during delivery. Fetal gasometric parameters (pH, pO2, pCO2, and lactates), hemodynamic parameters (fetal heart rate and mean arterial pressure), and autonomic nervous system tone (short-term and long-term variation, low-frequency domain, high-frequency domain, and fetal stress index) were recorded. Data obtained at 30-60min after nalbuphine injection were compared to those recorded at baseline. Eleven experiments were performed. Fetal heart rate, mean arterial pressure, and activities at low and high frequencies were stable after injection. Short-term variation decreased at T30 min (P = 0.02), and long-term variation decreased at T60 min (P = 0.02). Fetal stress index gradually increased and reached significance at T60 min (P = 0.02). Fetal gasometric parameters and lactate levels remained stable. Maternal nalbuphine use during labour may lead to fetal heart changes that are caused by the effect of opioid on the autonomic nervous system; these fluctuations do not reflect acidosis.

Longitudinal changes in the control mechanisms for blood pressure and cerebral blood flow in Alzheimer's disease: Secondary results of a randomized controlled trial.

Dynamic cerebral autoregulation (dCA) and baroreflex sensitivity (BRS) are key mechanisms involved in the homeostasis of blood pressure (BP) and cerebral blood flow. We assessed changes in these mechanisms in Alzheimer's disease (AD) during a 1.5 year follow-up. In this secondary analysis of a randomized controlled trial we measured beat-to-beat BP, heart rate, and cerebral blood flow velocity at baseline, 0.5 and 1.5 years, during: rest (spontaneous oscillations), repeated sit-stand maneuvers (induced oscillations), an orthostatic challenge, and hypo- and hypercapnia. dCA was estimated using transfer function analysis and the autoregulatory index on spontaneous and induced oscillations. BRS was estimated by calculating the heart rate response to BP changes during induced oscillations. Linear mixed models were used to assess changes over time. 56 patients were included (mean age:73±6 years, 57% female). BRS did not change over time. dCA parameters showed small changes after 0.5 years, suggestive of a reduction in efficiency (e.g. higher gain [linear mixed effect model: B=0.09, SE=0.03, P= 0.008] and lower phase [B=-9.7, SE= 3.2, P= 0.004] in the very low frequency domain, and lower autoregulatory index during induced oscillations [B=-0.69, SE=0.26, P= 0.010]). These changes did not show further progression after 1.5 years of follow-up. In this sample of patients with dementia due to AD we found no evidence that dCA or BRS become impaired during AD progression. This paves the way for further studies that investigate the safety and benefits of antihypertensive treatment in patients with AD.

Generalized Face Antispoofing by Learning to Fuse Features From High- and Low-Frequency Domains

In this article, we propose a face spoofing detection method by learning to fuse high-frequency (HF) and low-frequency (LF) features, in an effort to improve the generalization capability and fill up the domain gap between training and testing when the antispoofing is practically conducted in unseen scenarios. In particular, the proposed face antispoofing model consists of two streams that extract HF and LF components of a facial image with three high-pass and three low-pass filters. Moreover, considering the fact that spoofing features exist in different feature levels, we train our network with a novel multiscale triplet loss. The cross-frequency spatial attention module further enables the two streams to communicate and exchange information with each other. Finally, the outputs of the two streams are fused with a weighting strategy for final classification. Extensive experiments conducted on intra- and cross-database settings show the superiority of the proposed scheme.

Fault Estimation Filter Design for Two-Dimensional Fornasini-Marchesini Dynamical Systems in Low-Frequency Domain

This paper discusses the problem of fault estimation for two-dimensional (2-D) Fornasini-Marchesini (FM) dynamical systems. The objective of this paper is to design a fault estimation filter to reconstruct the characteristics of faults in low-frequency domain and satisfy different performance levels. Utilizing the generalized Kalman-Yakubovich-Popov (GKYP) lemma, this problem is transformed into a multi-objective optimization problem, which is non-convex in essence. On this basis, an optimization algorithm is proposed to solve the non-convex optimization problem. Sufficient conditions are derived for the proposed fault estimation filter. Finally, simulation results show the effectiveness of the theoretical results.

Dual-Rate Data-Driven Virtual Reference Feedback Tuning: Improvement in Fast-Tracking Performance and Ripple-Free Design

In this study, a data-driven design method is proposed for a dual-rate system, where the sampling interval of a plant output is restricted and is an integer multiple of the holding interval of a control input. In our proposed method, single-rate virtual reference feedback tuning (S-VRFT), where the holding interval is the same as the sampling interval, is extended to the dual-rate virtual reference feedback tuning (D-VRFT) system. In D-VRFT, a controller is decided using a set of input/output data used in S-VRFT, and it is easy to extend S-VRFT to D-VRFT and implement D-VRFT. In this study, intersample oscillations caused in such a dual-rate control system is prevented because a weighting filter is introduced for penalizing the control input deviation between the sampling instants. The filter is designed as an integrator for weighting the low-frequency domain. The improvement in fast-tracking performance as well as the ripple-free property are demonstrated through both the numerical and experimental results.

Position-rate control for the time delay control system of tip-tilt mirror

In the image-based tip-tilt mirror control system, the closed-loop performance and bandwidth of the system and are limited due to the influence of sensor sampling frequency and system delay. Under the condition of limited bandwidth, this paper proposes to use linear encoder to measure the position, and get the rate signal by differ-ence. The position-rate feedback control based on the image sensor system is realized to improve the error sup-pression ability of the tip-tilt mirror control system. Because of the addition of rate feedback, the control system has differential characteristics. When the rate feedback closed-loop is completed, the image position loop has integral characteristic. At this time, a PI controller is used to stabilize the system, which makes the system rise from zero type to two type system, and improves the error suppression ability of the system. Simulation and experiment show that this method can effectively improve the closed-loop performance of the tracking control system in low frequency domain.

Cyclical alteration in heart rate variability among young eumenorrheic women

Introduction: The female sex hormones are known to have a cardioprotective role in premenopausal women compared to postmenopausal women.1,2,5 The key hormone estrogen and progesterone shows a cyclical variation along the different phases of menstrual cycle. Parasympathetic activity via vagus is known to improve the cardiac function compared to sympathetic activity.3 Heart rate variability (HRV) is one of the sensitive and non-invasive method to record the cardiac autonomic activity.4 Thus we chose this study to assess how the female sex hormones affect autonomic activity on the heart during the phases of menstrual cycle. Aim: To assess the effect of cyclical alteration in female sex hormones on cardiac autonomic activity by HRV. Materials and Methods: After getting institutional ethics committee clearance, short term HRV (5 minutes) was recorded in fifty young female volunteers aged between 20-30 years within normal range of BMI and regular menstrual cycle in supine posture after 10 minutes rest using PHYSIO PAC PP4 Medicaid system Chandigarh in the autonomic function lab, Department of Physiology, Sri Venkateshwaraa Medical College Hospital and Research Center, Ariyur, Pondicherry. Statistical analysis was done using SPSS 17 version. Results: The sympathetic parameters like (low frequency domain) LF nu, LF/HF ratio was significantly increased in the premenstrual phase. The parasympathetic parameters like (high frequency domain) HF nu, TP (total power) were significantly increased in the proliferative phase of the menstrual cycle. Conclusion: Thus the cardioprotective role of female sex hormones in premenopausal women was more pronounced in the proliferative phase of menstrual cycle. Keywords: Heart rate variability, Cardioprotective, Premenstrual phase, Proliferative phase.

Numerical and experimental analysis on the vibration and radiated noise of the cylinder washing machine

The radiated noise of washing machines plays a pivotal role in user experience. Several studies have provided evidence that the low-frequency vibration of washing machine makes great contributions to its radiated noise. Unlike high-frequency noise, low-frequency noise decreases slowly and its wavelength is longer, so it can easily pass through obstacles and bring out a far-reaching impact on human health. Recently researchers pay intense attention to decease the low-frequency noise caused by household washing machines. The infinite element method (IFEM) is relatively simple and practical in simulating infinite region among numeric methods in acoustic computing with low frequency. Besides, IFEM could be coupled well with FEM and has high computational efficiency in low-frequency domain. Accordingly, our work introduces FE-IFEM into the prediction on the radiated noise of the washing machine. In this work, we analyze the dynamic characteristics and accurately estimate the radiated noise based on FE-IFEM. Firstly, the finite element model of washing machine is established and the natural frequency is measured to ensure the reliability of the model. Furthermore, the rigid-flexiblecoupling dynamic model is constructed to analyze the vibration and the vibration response test is carried out to verify the estimates of dynamic analysis. Finally, the radiated noise of the washing machine is calculated by using FE-IFEM and the noise experiment is performed. The simulation results are compared with the results obtained from the experiment and we conclude that the simulation estimates are in good agreement with the measured results. The maximum error obtained by this method is less than 6 dB. It indicates that FE-IFEM is an appropriate choice for predicting the radiated noise of washing machines in the low-frequency domain.

Local Electrochemical Impedance Spectroscopy: Towards an Improvement in the Low Frequency Domain

The ability to probe surface reactivity at the local scale has led to a new understanding of the electrochemical reactivity in relation to the surface microstructure. Among the various techniques developed in recent years, local electrochemical impedance spectroscopy (LEIS) takes advantage of using a transient approach to locally characterize a stationary electrochemical system without the need to add any redox mediator in solution. The principle of LEIS was pioneering by Isaacs et al. [1, 2]. The local current density, , is obtained from the local potential difference in solution, , measured with a probe which consisted in three reference microelectrodes positioned close to the interface of interest, as depicted in Fig. 1.Whatever the mode of operation, the spatial resolution of the technique is governed by the following parameters [3, 4]:- The diameter of each microelectrode used for sensing the local potential in solution;- The distance between the two potential microprobes (the smaller the distance, the smaller the potential difference) [5];- The distance between the dual probe and the substrate is an important parameter to be considered. Due to the potential distribution in the electrochemical cell, the difference in potential to be measured will be smaller if the probe is positioned far from the substrate. This may result in difficulties in measuring properly LEIS response in the low frequency domain, as regularly encounter, for instance, in coating degradation application.In the present work, we reported a new experimental setup that allows the measurement of local electrochemical impedance response of an interface in a wide frequency range, including the low frequency domain which is discussed. Proofs of concept with model systems, as well as passive materials and coatings are presented. Keywords:Local electrochemical impedance spectroscopy; low frequency measurements; electrochemical instrumentation; micro-electrochemistry.

Global dynamics of a non-smooth system with elastic and rigid impacts and dry friction

Global dynamics of a non-smooth dynamic model is discussed under the combined effects of three non-smooth factors of elastic impact, rigid impact and dry friction,which is a rarely discussed topic before.Six different basic phases, nine events and six segments of the system have been described. The stability of periodic motions in the system is analyzed theoretically. The motions distribution and the transition to the sticking-adhesion motions are studied. Influences of the sliding bifurcation and grazing bifurcation in the way to the transition to sticking-adhesion motions are demonstrated. The transition to sticking-adhesion motions composed of one or more of three basic routes is illustrated. The transition law of three kinds of fundamental periodic motions in the low-frequency and small-gap parameter domain is further analyzed so as to delineate the transition mechanism from fundamental periodic motions to sticking-adhesion motions. In high frequency region, the global motions distribution in the system is obtained through the global analysis method in parameter-state space. The transition and coexistence of the motions including stable and unstable periodic motions are further explored. In addition, the motions distribution and transition of large friction force versus forcing amplitude from the static state are discussed. The results will be beneficial for the motions control of the system.

Ashok chakra-structured meta-structure as a perfect sound absorber for broadband low-frequency sound

We present thin acoustic meta-structures with subwavelength dimensions through which almost perfect sound absorption is achieved in the low-frequency domain. Our overall strategy builds on the fact that the sound absorption capabilities of the meta-structures primarily depend on the geometric dimensions and can easily be reconfigured as per requirements through a change of geometry. To analyze various possibilities, we optimize the geometric structure through hybrid regression analysis using the genetic algorithm approach and finite element-based numerical simulations so that the geometry is tuned for high attenuation of acoustic signals over a broad range of frequencies. Both theoretical and experimental data show good parity and are able to establish the meta-structure nature of the assembly with respect to different frequency bands in the low frequency domain.

Axion-photon-dark photon oscillation and its implication for 21-cm observation

We examine the resonant conversion of axion-like particle (ALP) or dark photon to the electromagnetic photon in the early Universe, which takes place due to the ALP-photon-dark photon oscillations in background dark photon gauge fields. It is noted that the corresponding conversion probability can have an unusual spectral feature which allows strong conversion at low frequency domain, but has negligible conversion at high frequencies above certain critical frequency which is determined by the ALP coupling to dark photon and the strength of background dark photon gauge field. We apply this scheme to heat up the 21 cm photons without affecting the Cosmic Microwave Background, which can explain the tentative absorption signal of 21 cm photons detected recently by the EDGES experiment.

The effect of considering Pasternak elastic foundation on acoustic insulation of the finite doubly curved composite structures

This approach focuses on the acoustic characteristic of a simply supported doubly curved composite shell subjected to the Pasternak-type elastic foundation. To carry out the sound analysis of a finite shell, displacements and rotation terms and acoustic pressures are developed based on the infinite longitudinal and transversal modes. According to Hamilton's principle, the dynamic equations of the structure equipped with an elastic foundation are extracted. Subsequently, the construction is stimulated using an acoustic wave. Considering infinite modes, the necessity of terminating this process by applying a large number of modes is concerned. Therefore, in addition to the design of the convergence algorithm, some configurations against variations of dimensions and frequencies are proposed. Before presenting the numerical outcomes, the accuracy of the formulation is checked by either natural frequencies or sound transmission spectra. It is realized that although Winkler spring stiffness is impressive to improve the noise property at the low-frequency domain, the positive effects of Shear layer one are specified in the whole region. The outcomes also contain some 3D new shapes for variations of the Winkler spring and Shear layer stiffness.

Transient destabilisation in anisotropic vibrational properties of wood when changing humidity

Abstract Moisture changes cause transient effects in various polymeric materials. In wood, they are mainly documented in semi-static or low-frequency domains and could explain various anomalies in wood behaviour, including the so-called mechano-sorptive effect. This article aimed at exploring and quantifying transient effects in wood vibrational properties, evidenced but in few publications. A series of 65 experiments on spruce and maple, in longitudinal (L) and radial (R) directions, spanning many humidity trajectories, were monitored through time (1–7 weeks) after step-change in relative humidity (RH). Changes in dimensions and specific dynamic modulus of elasticity (E′/γ) closely followed change in moisture content (MC). But the damping coefficient (tanδ) always increased (whether MC increased or decreased) within first hours/days, before slowly re-decreasing. This was quantitatively analysed by subtracting equilibrium moisture content (EMC) dependence from the global changes in tanδ, which simultaneously expressed destabilisation, followed by physical ageing (a slow process towards approaching equilibrium). For small EMC steps, the amplitude of destabilisation in L tanδ exceeded changes due to EMC dependence. Destabilisation was of similar importance relative to L or to R tanδ, while R tanδ showed much (2−4×) stronger EMC dependence. Amplitude of destabilisation increased with wider RH/EMC-steps (and faster sorption rates). Within an experiment, maximum destabilisation occurred nearly concomitantly with maximum sorption rate. Equilibrium was usually reached in MC, even within one week, but seldom in tanδ, even after several weeks. Results suggested that: (i) drying caused similar amplitudes of destabilisation, but that occurred sooner, and recovered faster, than humidifying; (ii) small RH-steps caused relatively smaller amplitudes of destabilisation, but that occurred later, and spanned over longer time before recovering equilibrium, than wide RH-steps. Some possible hypotheses are introduced to explain the observed phenomena. These phenomena also have important practical consequences in real-life wood uses and, particularly, in the design of experimental protocols.

Negative Capacitance and Inverted Hysteresis: Matching Features in Perovskite Solar Cells.

Negative capacitance in the low-frequency domain and inverted hysteresis are familiar features in perovskite solar cells, which origin is still under discussion. Here we use impedance spectroscopy to analyze these responses in methylammonium lead bromide cells treated with lithium cations at the electron-selective layer/perovskite interface and in iodide devices exposed to different relative humidity conditions. Employing the surface polarization model, we obtain a time constant associated with the kinetics of the interaction of ions/vacancies with the surface, τkin, in the range of 100-102 s for all the cases exhibiting both features. These interactions lead to a decrease in the overall recombination resistance, modifying the low-frequency perovskite response and yielding a flattening of the cyclic voltammetry. As a consequence of these results we find that negative capacitance and inverted hysteresis lead to a decrease in the fill factor and photovoltage values.

Reliability, reproducibility and validity of dynamic cerebral autoregulation in a large cohort with transient ischaemic attack or minor stroke

Objective: Cerebral autoregulation (CA) is critical to maintenance of cerebral perfusion but its relevance to the risk of stroke and dementia has been under-studied due to small study sizes and a lack of consensus as to the optimal method of measurement. We determined the reliability and reproducibility of multiple CA indices and the effect of intensive data-processing in a large population with transient ischaemic attack or minor stroke. Approach: Consecutive, consenting patients in the population-based Oxford Vascular Study (OXVASC) Phenotyped cohort underwent up to 10-min supine continuous blood pressure monitoring (Finometer) with bilateral middle cerebral artery (MCA) transcranial ultrasound (DWL-Dopplerbox). Un-processed waveforms (Un-A) were median-filtered, systematically reviewed, artefacts corrected and their quality blindly graded (optimal (A) to worst (E)). CA metrics were derived in time-domain (autoregulatory index (ARI), Pearson’s Mx, Sx, Dx) and in very-low (VLF) and low-frequency (LF) domains (WPS-SI: wavelet phase synchronisation, transfer function analysis), stratified by recording quality. Reliability and reproducibility (Cronbach’s alpha) were determined comparing MCA sides and the first vs. second 5-min of monitoring. Main results: In 453 patients, following manual data-cleaning, there was good reliability of indices when comparing MCA sides (Mx: 0.77; WPS-SI-VLF: 0.85; WPS-SI-LF 0.84), or repeated five minute epochs (Mx: 0.57; WPS-SI-VLF: 0.69; WPS-SI-LF 0.90), with persistently good reliability between sides even in lower quality Groups (Group D: Mx: 0.79; WPS-SI-VLF: 0.92; WPS-SI-LF: 0.91). Reliability was greatest for Pearson’s Mx and wavelet synchronisation index, with reasonable reliability of transfer function analyses, but ARI was prone to occasional, potentially defective, extreme estimates (left vs right MCA: 0.68). Significance: Resting-state measures of CA were valid, reproducible and robust to moderate noise, but require careful data-processing. Mx and wavelet synchronisation index were the most reliable indices for determining the prognostic value of CA in large epidemiological cohorts and its potential as a treatment target.

Design of a Narrowband Adaptable Filter in Low-Frequency Domain

To improve the Signal to Noise Ratio and the precision of data acquisition systems in the condition of broad bandwidth, an adaptive narrow-band filter circuit has been designed for obtaining weak signals in low-frequency domain. And the problems of classic filter circuits, such as wave form distortion and suffering from non-linearity of varactors, can be solved by the novel design in replacing varactor with voltage control capacitor. Simultaneously, by improving LRC filter circuit, our designs also can increase quality factor in traditional RC filter circuit. Therefore, this design has great advantages over classic filter circuits for its narrow frequency band, high quality factor and low signal deformation. The above properties of this circuit can make it used widely in removing noise for modulation and acquisition circuits with high precision, and can be used to obtain accurate band-pass filtering in low frequency bands, which has been verified by experiments showing superior advantages of improving the SNR and filtering effects.

Development of sound pressure identification method to detect internal leak of safety relief valves in nuclear power plants

This article presents a sound pressure identification method to detect internal leak of safety relief valve (SRV) during the sealing surface damaged between valve disk and valve seat. An adjustable acoustical generator was designed to generate ultrasonic waves and detect internal leak. This approach was established by using computational fluid dynamics (CFD) with large eddy simulation (LES) to compute flow field and applying ACTRAN software with Lighthill’s acoustic analogy model to simulate acoustic field. The performance of the proposed method is evaluated by testing under the different leakage rates, as 0.5 L/min, 1 L/min to 5.5 L/min with every 0.5 L/min, respectively. Two microphone sensors were installed at external designed added device around the SRV to capture sound pressure level (SPL) of internal leakage signal. In order to ensure safety of the experiment, the high temperature dry saturated steam was replaced by compressed air as flow (10 MPa). The experimental results show that the proposed method can efficiently identify internal leakage rate higher than 1 L/min, and the sensitive frequency ranges from 7 kHz to 40 kHz. Hence, the acoustic signal of leakage can easily distinguish from noise because ambient noise focuses on low frequency domain. The study makes it possible to detect internal leak of SRV and prevent catastrophic failures in nuclear power plants.