Impedance Variation Research Articles

Highly Robust Active Damping Approach for Grid-Connected Current Feedback Using Phase-Lead Compensation

The grid-current-feedback active damping (GCFAD) strategy has been widely utilized in LCL-type cascaded H-bridge static var generator (SVG) systems. Although digital control in GCFAD enhances sampling accuracy, it introduces delays in the subsequent calculation and execution processes, thereby reducing the effective damping region and weakening the robustness of the LCL-type cascaded H-bridge SVG system under a broad domain of grid impedance changes. This paper expands the effective damping area from (0, fR) (fR ∈ (fs/6, fs/3)) to (0, 0.45fs) by introducing a phase-lead compensator into the active damping feedback loop to reduce the delay. This reduces the negative effect of the digital control on the system’s effective damping region and significantly enhances its robustness under an extensive domain of grid impedance variations. The improved GCFAD is employed to establish the system’s discrete domain model and the controller parameters are adjusted in conjunction with the mentioned model. Simulation outcomes indicate the efficiency of the presented approach.

Study on the mechanism and characteristics of pulsed corona discharge in water

Abstract Plasma pulse is a safe and environmentally friendly unconventional technology for enhancing
oil and gas production. However, during the pulsed discharge process, an abnormal discharge
phenomenon often occurs, which severely affects the performance of the equipment and is
referred to as corona discharge. This paper combines laboratory discharge test data to
theoretically analyze and validate through Comsol simulation the mechanism of corona
discharge generation under the same electrode gap distance. A comparative analysis with arc
discharge is also conducted to further examine its characteristics, and nonlinear regression
analysis is used to study the impedance variation of the plasma channel during corona
discharge. Results indicate that the decrease in switch breakdown voltage in the later stages of
continuous discharge leads to the generation of corona discharge. The impedance of the
plasma channel can be characterized by a time-varying resistance model based on a double
exponential function. Finally, validation through theoretical calculations and Simulink
simulations achieves a fitting rate of over 99%. The research provides significant guidance
for further analysis of corona discharge and the development of suppression methods in
plasma pulse technology, contributing to the optimization of the equipment and enhancing its
operational performance.

Study on Instability Mechanism and Compensation Strategy for Distributed Energy Storage Systems

Distributed energy storage systems (DESSs), which would become key components in a new power system, can flexibly deliver peak load shaving and demand management. With the popularization of distributed renewable energy generation in a distribution network, the grid impedance varies and DESSs thus have to face stability issues. In order to enhance the system’s stability, a compensation strategy is proposed for the inverter in a DESS. First, a stability analysis model is developed to show the main factors that affect system stability. Then, an improved compensation strategy is proposed for the phase-locked loop (PLL) in a DESS, in which control parameters are adaptively tuned on-line according to real-time conditions to improve the stability of a grid-tied DESS. Simulation and hardware-in-the-loop (HIL) experimental results are given to validate the effectiveness of the proposed strategy. Simulation and experimental results show that the proposed strategy significantly increases the system’s tolerance to grid impedance variations, maintains total harmonic distortion (THD) below 5% during normal operation, and effectively reduces low-order harmonic content caused by impedance fluctuations. Moreover, the strategy is demonstrated to enhance system stability under low state-of-charge (SOC) conditions, showcasing its robustness and adaptability across various operating scenarios.

Clinical Characteristics of Patients With Proton Pump Inhibitor-refractory Globus.

Globus is often linked with gastroesophageal reflux disease, which influences its treatment strategies. This study aimed to investigate clinical characteristics of patients with refractory proton pump inhibitor (PPI) globus to better understand its etiology. Between 2017 and 2023, 123 out of 592 patients with Globus from the Samsung medical center outpatient clinic who were unresponsive to eight weeks of PPI treatment were analyzed. Patients underwent 24-hour esophageal pH monitoring and highresolution manometry (HRM). They were divided into acid reflux, non-acid reflux, and no reflux groups, with basal impedance (BI) measurements taken at 3, 9, and 15 cm along the esophagus. These values were compared against data of healthy volunteers to identify significant differences across groups. The acid reflux group displayed a median impedance of 1152 Ω at 3 cm, which was significantly lower than the median impedance of the non-acid reflux group (2644 Ω) and the no-reflux group (3083 Ω), highlighting varying degrees of reflux impact (P = 0.015). Most patients in non-acid reflux and no-reflux groups showed higher impedance levels at both 3 cm and 15 cm compared to the first quartile of healthy individuals with significant differences (P = 0.032 and P = 0.029, respectively). There was no notable difference in the average impedance variation between 3 cm and 15 cm in the no-reflux group (P = 0.540). Reduced proximal BI values compared to distal BI values suggest increased permeability in globus patients. Further studies with a larger cohort of refractory PPI patients and healthy volunteers are needed to explore these findings and their implications on globus etiology.

Optimized PVA-(ZnO)x-(PANI)1−x nanocomposites: characterization and humidity sensing application

This work presents an effort to study the potential of ternary PVA/ZnO/PANI nanocomposite for humidity sensing applications. Easily-peeled-off films of the ternary system were formed by the solution casting method and characterized. FTIR manifested the uniformity of the synthesized films and the existence of both polyaniline and ZnO functional groups in the relevant PVA host matrix. Characteristic absorption bands of PVA were overlapped with some characteristic bands of polyaniline. XRD patterns show the typical semicrystalline peak for the pristine PVA. The XRD analysis did not demonstrate any crystalline peaks for ZnO due to the capping-off effect of the PVA macromolecule. Energy dispersive X-ray mapping analysis and SEM micrographs manifested a homogeneous distribution of ZnO and PANI particles and a smooth yet dense film appearance. A study of electronic transitions and band gap displayed that the value of the band gap varies based on component concentration with the lowest value for the film of equal concentration of both ZnO and polyaniline. The humidity sensing behavior of the films was explored at different frequencies. The most variation in impedance was reached at 500 Hz, while the impedance variation at 50 Hz is the best from the performance point of view, where the relation between the impedance and relative humidity is linear. Samples F3 [PVA (ZnO)0.7(PANI)0.3], and F4 [PVA (ZnO)0.5(PANI)0.5] revealed the highest sensitivity among other tested samples. The measured hysteresis for the F3 and F4 samples were 1.38E + 05 MΩ/RH and 1.55E + 05 MΩ/RH, respectively. Impedance and complex impedance spectroscopy measurements confirmed that the film F3 revealed the highest sensitivity among the other tested samples. The proposed structure of the sensor can be employed for real-life applications since it can be easily coupled with electronic read devices and its overall functionality.

Impedance for Assistance: Upper-Limb Assistive Soft Robotic Suit Using Linked-Layer Jamming Mechanisms.

Wearable robots, especially those composed of soft materials, are increasingly attracting interest due to their comfort, ease of donning and doffing, and their ability to provide assistance across various applications. In wearable robotics, striking a balance between ensuring low impedance for wearer comfort and providing sufficient assistive force is a notable design challenge. In this study, we propose exploiting impedance variation in accordance with the types of muscle contraction in the human body. Particularly in eccentric muscle contraction, the impedance can help reduce the muscular load, since it exerts force in the same direction as the muscles. To utilize the relation, we proposed a linked-layer jamming mechanism, which adjusts its impedance largely in various directions. This mechanism allows not only a broad variable range of impedance in multiple rotation directions but also directional torque design, even when equipped in human multi-degree-of-freedom (DoF) joints. By constructing a wearable robot prototype equipped with the proposed linked-layer jamming mechanisms, the effectiveness of this impedance-based assistance approach was confirmed through experiments. The findings from this study present new possibilities in wearable robot design, showing that suitably amplified impedance can assist human motion, potentially enhancing task efficiency and lowering injury risk. This work thus offers a new perspective for researchers in the field of wearable robots, demonstrating that impedance, often minimized in existing designs, can be utilized beneficially when properly amplified.

Robust Controller Design for a Grid-Connected VSI via an LCL Filter in the Presence of Unknown Grid Impedance

Inverters connected to the grid can become unstable under specific grid impedance conditions. In order to find a solution to this problem, it is possible to ensure system stability and their robustness to R-L type grid impedances by satisfying two conditions. The first condition is to ensure that the closed-loop poles of the system are in stable positions to variations in the grid impedance. The second condition is reliant on the admittance model of the equivalent circuit. Specifically, the product of this admittance and the grid impedance must adhere to the Nyquist stability criterion. In this work, the stability of the converter connected to the grid through an LCL filter is analysed. For this purpose, the output admittance is modelled in the Laplace domain taking into account the behaviour of the discrete controller. In addition, to ensure that the closed-loop poles are in stable positions, the system open-loop response is analysed. These two conditions are examined across scenarios where system states are partially or completely fed back, for different system parameter values. Consequently, a robust controller is designed for variations of the R-L type grid impedance.

High flow nasal cannula and low level continuous positive airway pressure have different physiological effects during de novo acute hypoxemic respiratory failure

BackgroundLarge tidal volumes during de novo acute hypoxemic respiratory failure (AHRF) may promote patient self-inflicted lung injury. Tidal volume assessment under high flow nasal cannula (HFNC) is not routinely feasible at the bedside. Our objective was to determine whether tidal volume during low-level continuous positive airway pressure (CPAP) could predict tidal volume during HFNC and to compare the physiological effects of HFNC and low-level CPAP.MethodsProspective, single-center study including 29 de novo AHRF patients treated with HFNC (50 to 60 L.min− 1). Patients were monitored using electrical impedance tomography during HFNC then CPAP at 4 cmH2O. Tidal volume during HFNC was calculated based on tidal impedance variation. The ability of tidal volume under low-level CPAP to predict tidal volume under HFNC was explored using Bland-Altman analysis. CPAP and HFNC were compared in terms of tidal volume, minute ventilation, respiratory comfort, dyspnea, oxygenation, ventilation distribution, end-expiratory lung volume, thoraco-abdominal asynchrony and recruitment.ResultsUnder HFNC, patients had a tidal volume of 6.6 (5.9–8.7) mL.kg− 1 PBW. 20 (69%) patients exhibited a tidal volume between 4 and 8 mL.kg− 1 PBW, while in 5 (17%) patients it exceeded 9 mL.kg− 1 PBW. Tidal volume under CPAP was higher (9.4 (8.3–11) mL.kg− 1 PBW, p < 0.001). Tidal volumes under CPAP and under HFNC were modestly correlated (Spearman r = 0.50, p = 0.005). Bland-Altman analysis showed a bias of 2.4 mL.kg− 1, with limits of agreement ranging from − 1.1 mL.kg− 1to 5.9 mL.kg− 1. Nevertheless, a larger (> 11.5 mL.kg− 1 PBW ) tidal volume under low-level CPAP predicted a larger (> 9 mL.kg− 1 PBW ) tidal volume under HFNC with 80% sensitivity and 96% specificity. Low-level CPAP was associated with increased minute ventilation, end-expiratory lung volume, and oxygenation as compared to HFNC. It decreased signs of respiratory distress in the most severe patients but was associated with lower comfort compared to HFNC.ConclusionAmong ICU patients with de novo AHRF, tidal volume under HFNC was mostly protective. Tidal volume during CPAP at 4 cmH2O did not predict tidal volume during HFNC. Such low-level CPAP was associated with increased tidal volume, minute ventilation, end-expiratory volume, and oxygenation.Trial registrationClinicalTrials.gov ID NCT03919331. Registration date: 2019-03-26.

Lithium Electrodeposition Process in Various Hydrogenated Electrolyte Solutions

Introduction: The lithium metal anode, which is attracting attention as a high-capacity next-generation anode material, is hindered in practical application by the formation of dendritic deposits known as lithium dendrites during charging (electrodeposition). One method to achieve dendrite-free electrodeposition of Li involves the addition of a small amount of water to an electrolyte containing LiPF6, leading to the formation of HF through hydrolysis. During electrodeposition, LiF precipitates along with lithium, resulting in the formation of columnar lithium, which is known to inhibit dendrite formation [1]. In this study, therefore, we investigated the influence of solvent properties on the columnar structure of lithium by adding a small amount of water to electrolytes containing LiPF6 in three different solvents with varying properties, comparing the mass changes on the electrode surface and the composition of the deposits during lithium electrodeposition.Experiment: Three solvents (pure dimethyl carbonate (DMC), a mixture of ethyl carbonate (EC) and DMC (v/v = 1:1), and a mixture of EC and diethyl carbonate (DEC) (wt/wt = 1:1)) were used for the experiments after adding 1 M LiPF6 and approximately 50 ppm water, ensuring sufficient progress of hydrolysis. Copper foil or copper-coated quartz crystal microbalance (QCM) electrodes were employed as the working electrode, and lithium foil was used as the counter electrode. Lithium electrodeposition was conducted at a constant current density of -0.5 mA cm-2 for 2 hours, during which the mass changes and impedance variations were monitored using QCM and electrochemical impedance spectroscopy (EIS), respectively. Additionally, composition analysis of the deposited lithium after electrodeposition was performed using X-ray photoelectron spectroscopy (XPS).Results and Discussion: The rate of hydrolysis of LiPF6 by the added water varied significantly depending on the solvent, with durations of 2 days for DMC alone, 8 days for EC/DMC, and 20 days for EC/DEC. This difference is seemed to be due to variations in the dissociation of LiPF6. When a current was passed through the copper electrode, a plateau region of cell voltage due to HF reduction was maintained for 10 to 20 seconds around 2 V, followed by a decrease in voltage and a constant voltage of ca. -0.2 V, indicating the onset of lithium deposition. The ratio of mass increase during lithium deposition (mass per electron; MPE) was in the reverse order of the rate of hydrolysis, with EC/DEC > EC/DMC > DMC. Additionally, the resonant resistance increased significantly in the order of DMC > EC/DMC > EC/DEC. Based on the mass changes and the morphology of the deposition mentioned later, it is highly probable that an increase in viscosity and density of the electrolyte due to side reactions, or an increase in surface area due to dendrite formation, occurred. In EC/DEC and EC/DMC, a characteristic blue-colored precipitate indicative of columnar lithium structures was observed, while in DMC, it was gray, showing lithium dendrite. XPS analysis revealed that LiF was dominant on the surface of the deposited lithium in all electrolytes, but there were significant differences in the amount of surface carbon, with EC/DEC > EC/DMC > EC/DEC. These results suggest that differences in EC content lead to variations in the dissociation and viscosity of the electrolyte, which in turn affect the morphology of the deposited lithium.

Estimating petrophysical properties using Geostatistical inversion and data-driven extreme gradient boosting: A case study of late Eocene McKee formation, Taranaki Basin, New Zealand

Estimation of petrophysical properties holds significant importance in evaluating the feasibility of hydrocarbon extraction and enhancing production efficiency. Therefore, theintegration of seismic data with well data for reservoir characterization has garnered significant attention in the oil and gas industry. This approach provides a comprehensive view of the lateral variations across the entire reservoir. In this study, our goal is to establish a relationship between seismic attributes and the petrophysical properties of the reservoir, enabling the prediction of property distribution across the entire reservoir. We employed geostatistical inversion to generate detailed P-impedance maps of the reservoir, capturing its spatial heterogeneity. A total of 100 realizations were produced and ranked into P10, P50, and P90 scenarios, representing different probabilistic outcomes. The P90 scenario, considered the most representative of the reservoir's average properties, was selected for interpretation, enabling a comprehensive analysis of reservoir heterogeneities and their distribution. Subsequently, we estimated porosity using various seismic attributes, employing a Data-driven Extreme Gradient Boosting (Xgboost) approach within the reservoir analysis. This method enabled us to estimate a high-resolution acoustic impedance and porosity with minimal root mean square error of 3.8 and r2score of 66 % across the spatial gap which ranges from 8468.84 to 9367.85(g/cc) *(m/s) and 10 to 45 % between wells, revealing the lateral variation of acoustic impedance and porosity within the reservoir interval of interest. The information provided was found to be of significant value in the identification of potential sweet spots and plays a pivotal role in the development of a reservoir management strategy for future hydrocarbon exploration.

Anodic Dissolution of Stainless Steel Covered with Oxide Thin Film in PEFC Simulated Environment

Stainless steels have been considered for the bipolar plate materials in fuel cell stack components to reduce the cost of the fuel cell vehicles (FCVs). However, the contact resistance between the gas diffusion layer (GDL) and bipolar plates fabricated by the stainless steels may show large values due to the formation of passive film on the stainless steels 1,2). Further, the anodic dissolution of stainless steels may occur in FC operation, leading to the increase of the contact resistance between the GDL and bipolar plates. In the present study, we developed the surface treatment method for bipolar plates fabricated by the stainless steels using oxide thin film. The dissolution behavior of stainless steels with oxide thin film was investigated in the polymer electrolyte fuel cell (PEFC) simulated environment. In addition, the contact resistance between the GDL and stainless steels with oxide thin film was evaluated before and after corrosion test. In the present study, the stainless steel sheets covered with oxide thin film were fabricated by the vacuum evaporation. The dissolution behavior of these samples was investigated by an electrochemical measurement by a three-electrode system. To simulate PEFC environment, the test solution containing 3 ppm NaF and 10 ppm NaCl was used as the electrolyte solution. The pH of the test solution was adjusted at pH 3. The stainless steel sheet or stainless steel sheet covered with oxide thin film was used as the working electrode. The platinum wire and the KCl-saturated Ag/AgCl electrode were used as the counter electrode and reference electrode, respectively. The potentiostanic polarization was performed at an arbitrary potential. The electrochemical impedance was measured under potentiostanic polarization. In this measurement, the AC potential amplitude was 10 mV and the frequency range was 100 kHz to 0.01 Hz at 5 frequencies per decade. The potentiostatic polarization of the stainless steel sheets and stainless steel sheet covered with oxide thin film was carried out at an arbitrary potential to evaluate the corrosion behavior of each sample. In the stainless steel sheet, the increase and the decrease in the current density were observed under potentiostatic polarization, implying the dissolution of Fe ions or the dissolution and repassivation of the passive film. The time variation of the current density for stainless steel sheet covered with oxide thin film under potentiostanic polarization suggested that the dissolution rate of Fe ions was small under potentiostatic polarization. Based on these results, we measured the impedance spectra of the stainless steel sheet covered with oxide thin film under potentiostanic polarization. In this case, the time variation of impedance was investigated by 3D plots of impedance to determine the instantaneous impedance at arbitrary measurement time 3,4). The charge transfer resistance of each sample, which was estimated by curve fitting using equivalent circuit, at arbitrary measurement time was discussed to examine the corrosion mechanisms. References (1) A.Miyazawa, T. Himeno, A. Nishikata, J. Power Sources, 220, 199 (2012).(2) A.Miyazawa, E Tada, A. Nishikata, J. Power Sources, 231, 226 (2013).(3) Z.B. Stoynov, B.S. Savova-Stoynov, J. Electroanal. Chem. 183, 133 (1985).(4) Y.Hoshi et al., Corros. Sci., 232, 112018 (2024). Acknowledgement This is based on results obtained from a project, JPNP20003, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).

Dynamic Impedance Model of Low-Voltage Electric Shock in Animals Considering the Influence of Water Electrolysis

This study aims to tackle the challenge of explaining the underlying mechanisms behind the time-varying impedance phenomenon in animals experiencing low-voltage electric shocks. A dynamic impedance model that considers the effect of water electrolysis (WEDI) has been developed. First, we conducted root cause analyses through progressive validation experiments, identifying water within the shocked body as the key factor influencing impedance variation. Monitoring hydrogen concentration above the electrodes and measuring mass changes in the shocked body revealed that the time-varying impedance is closely related to internal water electrolysis. Second, we quantitatively analyzed the impact of water molecule decomposition during electrolysis on the salt concentration and conductivity within the electrically shocked body. A mathematical relationship between the variable resistance within the body and time was derived. A dynamic impedance model for animal electric shock that considered the effects of water electrolysis was subsequently established, explaining the underlying mechanism behind the time-varying impedance phenomenon. Finally, the Mean Absolute Percentage Error (MAPE), Mean Absolute Error (MAE), and Root Mean Square Error (RMSE) between the electric shock current predicted by the WEDI model and actual measurements were 0.00357, 0.00350, and 0.00446. Compared to existing models, the WEDI model demonstrates superior accuracy and interpretability.

Effect of Dielectric Properties of Cochlea on Electrode Insertion Guidance Based on Impedance Variation

The cochlear neuromodulator provides substantial auditory perception to those with impaired hearing. The accurate insertion of electrodes into the cochlea is an important factor, as misplaced may lead to further damage. The impedance measurement may be used as a marker of the electrode insertion guidance. It is feasible to investigate the impact of the dielectric properties of the cochlea tissue layers on the electrode insertion guidance using sophisticated bio-computational methods that are impractical or impossible to perform in cochlear implant (CI) patients. Although previous modeling approaches of the cochlea argued that the capacitive impact of the tissue layer can be neglected using the quasi-static (QS) approximation method, it is widely accepted that tissue acts as a frequency filter. Thus, the QS method may not always be appropriate due to short-duration pulses. This study aimed to investigate the impact of the frequency-dependent dielectric properties of the cochlea tissue layers on the impedance variation by following a systematic approach. The volume conductor model of the cochlea layers was developed, the dielectric properties of each tissue layer were attained, and the cochlea neuromodulator settings were applied to obtain the results based on both QS and transient solution (TS) methods. The results based on the QS and TS methods were compared to define to what extent these parameters affect the outcome. It was suggested that the capacitive impact of the cochlea layers should be considered after a certain frequency level.

Microfluidic and impedance analysis of rosemary essential oil: implications for dental health

BackgroundOral health is closely linked to systemic conditions, particularly non-communicable diseases (NCDs), which can exacerbate oral issues. Essential oils (EOs) have emerged as potential alternatives for oral health due to their antibacterial, anti-inflammatory, and antioxidant properties. Among these, rosemary essential oil (REO) shows promise due to its various biological activities. This study investigates the potential of REO in dental applications using microfluidic devices and electrochemical impedance spectroscopy (EIS) to analyze the electrical properties of REO in artificial saliva (AS) mixtures.ResultsThe study demonstrated significant variations in impedance across different REO concentrations and their mixtures with AS. Higher impedance was observed in REO mixtures, particularly at lower frequencies, indicating distinct electrical properties compared to pure AS. The impedance of REO was influenced by its concentration, with a 1% REO solution showing higher impedance than a 4% solution, possibly due to micelle formation and changes in dielectric properties. Additionally, microfluidic devices enabled precise control over fluid interactions and real-time monitoring, offering valuable insights into REO's behavior in a simulated oral environment. The impedance data demonstrated significant differences in REO–AS mixtures, highlighting potential interactions critical for oral care applications.ConclusionsRosemary essential oil exhibits unique electrical properties, making it a promising candidate for dental applications, particularly in preventing and treating oral diseases. Microfluidic devices enhance the accuracy and reliability of studying REO's interactions with AS, providing a robust platform for future dental research. The findings suggest that REO could be effectively incorporated into oral care products, offering a natural alternative for combating oral pathogens, reducing inflammation, and protecting against oxidative stress. Future research should focus on clinical trials to validate these findings and explore the synergistic effects of REO with other essential oils.

Biocompatible dipeptide coated on Pt/PEDOT:PSS modified silicon probes for tissues rejection alleviation

The implantable neural probe is an indispensable tool to record the high-quality spike signals. However, the high interface impedance of electrode-tissue and severe tissue rejection degrade the signal quality and shorten the service life of neural probes in-vivo. Here, a Pt/PEDOT:PSS modified silicon probes with biocompatible dipeptide layer is proposed to avoid these issues. First, a bilayer Pt/PEDOT:PSS was electrochemically deposited on gold microelectrodes to reduce the impedance. Then, a layer of dipeptide was deposited on the modified probe by physical vapor deposition (PVD) to mitigate tissue rejection. The electrochemical results show that the electrode-tissue interface impedance can be reduced by two orders of magnitude by the Pt/PEDOT:PSS modification, with negligible impedance variation by the following dipeptide layer. From the in-vitro accelerated aging, it can be inferred that the Pt/PEDOT:PSS/dipeptide modified microelectrodes can survive for more than 10 weeks. In-vitro cytotoxicity experiments show that the dipeptide can help improve the biocompatibility. Lastly, in-vivo implantation further proves that dipeptide may contribute to the realization of lower tissues rejection and higher signal-to-noise ratio within 8 weeks of implantation. The widely used silicon neural probes with the Pt/PEDOT:PSS modification and overall dipeptide coating provide as a new solution for long-term biocompatibility and high-quality neural signals.

Analysis of Low-Frequency Sound Absorption Performance and Optimization of Structural Parameters for Acoustic Metamaterials for Spatial Double Helix Resonators

Low-frequency noise absorbers often require large structural dimensions, constraining their development in practical applications. In order to improve space utilization, an acoustic metamaterial with a spatial double helix, called a spatial double helix resonator (SDHR), is proposed in this paper. An analytical model of the spatial double-helix resonator is established and verified by numerical simulations and impedance tube experiments. By comparing the acoustic absorption coefficients of the spatial double-helix resonator, it is shown that the results of the analytical model, the numerical model, and the experiments are in good agreement, proving the accuracy of the theoretical model. The effects of different structural parameters on the peak sound absorption coefficient and resonance frequency are quantitatively revealed. The impedance variation law of the model is obtained, and the resistance and reactance distributions at the resonance frequency are analyzed. In the optimization model, the Back Propagation (BP) network is used to construct the mapping between the structural parameters and the resonance frequency and sound absorption coefficient, and this is used as the constraints of the equation, which is combined with Wild Horse Optimization (WHO) to establish the BP-WHO optimization model to minimize the volume of the spatial double helix resonator. The results show that, for a given noise frequency, the optimized structural parameters enhance the space utilization without affecting the performance of the space double helix resonator.

Investigating electrochemical impedance and performance variation in nanostructured Mn3O4/activated carbon/reduced graphene oxide asymmetric supercapacitors with different electrolytes

Investigating electrochemical impedance and performance variation in nanostructured Mn3O4/activated carbon/reduced graphene oxide asymmetric supercapacitors with different electrolytes

Acoustic black hole effect due to variation in duct wall impedance

This presentation explores the acoustic black hole (ABH) effect achieved through variation of duct wall impedance. Unlike the method of Mironov and Pislyakov, which utilizes tapered annular rings within the duct to achieve the ABH effect, this approach leverages mechanical impedance variation to create the desired acoustic behavior. By engineering the impedance profile along the duct wall, an axially decreasing local phase speed results that mimics the event horizon of a black hole, causing sound waves to be significantly attenuated and trapped. Governing equations are derived and solved using both the WKB approximation and numerical methods. The solutions reveal that specific impedance profiles can effectively decelerate and absorb acoustic waves, resulting in substantial reduction in sound transmission. Verification is performed using the fully coupled structural acoustic finite element algorithm Sierra/SD. This research further paves the way for the development of innovative acoustic materials and devices which utilize ABH principles to achieve enhanced noise control and acoustic wave manipulation. [Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-NA-0003525.]

A mollifier approach to seismic data representation

AbstractThe extension of the seismic bandwidth to lower frequencies enhances impedance contrasts that can be poorly represented by the broadband acquisition wavelet. Furthermore, long filters that are used to shape the wavelet of processed data can cause issues with noise, phase and interference between seismic events. In this paper, we use a mathematical technique known as mollification to resolve impedance variations with the highest detail allowed by the bandwidth of the data. The mollifier is integrated and windowed to match the low‐frequency content of the data to yield a convenient conversion to relative impedance. Synthetic data created from wedge models show that the windowed mollifier provides an improved representation of the impedance profile. This is replicated by application to an acoustic well log and a regular seismic dataset recorded in the Southern North Sea as well as a broadband dataset recorded in the North Sea.

Physiological definition for region of interest selection in electrical impedance tomography data: description and validation of a novel method

Objective. Geometrical region of interest (ROI) selection in electrical impedance tomography (EIT) monitoring may lack sensitivity to subtle changes in ventilation distribution. Therefore, we demonstrate a new physiological method for ROI definition. This is relevant when using ROIs to compute subsequent EIT-parameters, such as the ventral-to-dorsal ratio during a positive end-expiratory pressure (PEEP) trial.Approach.Our physiological approach divides an EIT image to ensure exactly 50% tidal impedance variation in the ventral and dorsal region. To demonstrate the effects of our new method, EIT measurements during a decremental PEEP trial in 49 mechanically ventilated ICU-patients were used. We compared the center of ventilation (CoV), a robust parameter for changes in ventro-dorsal ventilation distribution, to our physiological ROI selection method and different commonly used ROI selection methods. Moreover, we determined the impact of different ROI selection methods on the PEEP level corresponding to a ventral-to-dorsal ratio closest to 1.Main results.The division line separating the ventral and dorsal ROI was closer to the CoV for our new physiological method for ROI selection compared to geometrical ROI definition. Moreover, the PEEP level corresponding to a ventral-to-dorsal ratio of 1 is strongly influenced by the chosen ROI selection method, which could have a profound clinical impact; the within-subject range of PEEP level was 6.2 cmH2O depending on the chosen ROI selection method.Significance.Our novel physiological method for ROI definition is sensitive to subtle ventilation-induced changes in regional impedance (i.e. due to (de)recruitment) during mechanical ventilation, similar to the CoV.