Electrical Membrane Research Articles

Electrokinetic Enhancement of Membrane Techniques for Efficient Nanoparticle Separation and Preconcentration.

Efficient separation and preconcentration of nanoparticles are crucial in a wide range of biomedical applications, particularly as target substances continue to diminish in size. In this study, we introduce an electric field-assisted membrane system that synergistically combines oversized-pore membranes with an electrokinetic particle retention mechanism. Utilizing Ti/Au-coated poly(tetrafluoroethylene) (PTFE) membranes, our approach generates electrokinetic forces to effectively separate and retain charged nanoparticles even smaller than the pores, achieving a separation efficiency over 99% and a preconcentration factor of 1.76 within 10 min. Additionally, membrane fouling and transmembrane pressure are significantly reduced compared to conventional filtration techniques, offering advantages such as lower driving pressure and improved particle recovery. Rigorous experimental analysis and theoretical modeling reveal that this method establishes a critical balance between drag and electrokinetic forces acting on the nanoparticles, thereby enhancing separation and concentration efficiencies. Our research outcome paves the way for advanced particle manipulation techniques, potentially transforming biomolecule enrichment practices in diverse biomedical fields, including point-of-care diagnostics, highly sensitive biochemical detection, and bioprocessing applications.

Preparation and performance of MXene-based electric field-responsive separation membranes

Preparation and performance of MXene-based electric field-responsive separation membranes

Simplified Plasmodium falciparum membrane feeding assay using small Petri dishes and gel warmers

Studies on Plasmodium falciparum transmission require blood-feeding infectious gametocytes to mosquitoes using standard membrane-feeding assays (SMFAs). SMFAs are routinely performed using electric heating coils or glass membrane feeders connected to a circulatory water bath using tubing and clamps. Each of these approaches is expensive and requires a complex setup, hence restricting the number of assays that can be performed simultaneously. Furthermore, existing methods cannot be easily applied in low-resource field settings. This study presents a low-cost and simplified method for feeding mosquitoes with an infectious blood meal using 35 mm Petri dishes where temperature is maintained by using reusable gel warmers. The intensity and prevalence of infection in mosquitoes (Anopheles stephensi and Anopheles gambiae) fed via a Petri dish overlaid with gel warmers were comparable to mosquitoes fed using standard glass membrane feeders. The methodology described here can be easily applied in low-resource and field settings due to its low cost, ease of set up, and use of easily available supplies, such as Petri dishes, and reusable gel warmers. We believe a wide range of laboratories can easily adapt this method for P. falciparum transmission studies.

Real-Time Overpotential Evaluation and Control Method for PEMFC

Fuel cells have an important role in promoting decarbonization because they can generate electric power from a chemical reaction between hydrogen and oxygen and do not emit carbon dioxide. Fuel cells can generate electric power through a chemical reaction between hydrogen and oxygen, and since they do not emit carbon dioxide, they play an important role in promoting decarbonization. PEMFCs are used in vehicles and household cogeneration systems because of their low operating temperatures, high power density, compact size, and light weight.However, fuel cells decrease the output power depending on the internal conditions. Dry-out caused by drying electrolyte membranes and flooding due to the generated water remaining in the flow channels and catalysts. For the widespread use of fuel cells, it is necessary to detect these failures and immediately recover from the decreasing of power. Evaluation methods for diagnosing fuel cell failures are existed the individual calculation of overpotential and the Electrochemical Impedance Spectroscopy (EIS).Individual calculation of overpotential is to diagnose internal failure of fuel cells by determining the overpotential, which is the amount of decrease from the theoretical electromotive force, for each factor calculated from cell voltage, cell resistance, and load current by calculation using the least-squares method. This method has the characteristics of identifying the cause of voltage decrease. However, the overpotential evaluation by calculating with cell voltage, stack current, and cell temperature allows real-time evaluation while making measurements, however it depends on the accuracy of the calculating may cause false evaluation. The EIS is a method of diagnosing internal conditions by sweeping frequency from high to low frequency and calculating resistance by factor from the Cole-Cole plot, which is the impedance response. Although this method can diagnose the internal conditions of the electrolyte membrane and catalyst in detail, it can only measure under constant current conditions, and the measurement time is long. Therefore, it is useful for detailed cell analysis, however, difficult to apply for real-time control. Real-time and highly accurate evaluation of internal conditions is necessary to control fuel cells to maintain their output, which varied as the output decrease due to drying of the electrolyte membrane and remaining of generated water.The purpose of this study is to propose a method for highly accurate and real-time operational control. The study examined a diagnostic method that combines individual overpotential calculations and fixed-frequency impedance measurements. Fixed-frequency impedance measurement refers to measuring electrolyte membrane resistance by making impedance measurements at only a single fixed-frequency, unlike EIS. In other words, the method used in this study is to calculate the overpotential from real-time measurements by using the electrolyte membrane resistance obtained by fixed-frequency impedance measurements to calculate the individual calculation of overpotential. Electrolyte membrane resistance was calculated by applying only a constant high frequency (1 kHz) using the impedance measurement system ALDAS-F and each overpotential was evaluated by performing the individual calculation of overpotential using calculated electrolyte membrane resistance and the measured voltage and current. We found that with this method, the overpotential can be evaluated without calculation by the least-squares method while measuring in real time. To improves the stability and reliability of the fuel cell, this study controls the fuel cell operation using this real-time overpotential evaluation method and compare the results with the existing method.In the experiment using a 500 W PEMFC at 20 A, the real-time overpotential evaluation was compared with the overvoltage evaluation by the EIS, which showed a similar trend in the decrease in overpotential before and after warm-up operation for each method. The results of each method also showed similar overpotential characteristics when compared with the load current. The results show that the proposed method can evaluate the fuel cell’s overpotential as well as the EIS. Moreover, we evaluated the overpotential by applying a frequency of 1 kHz, and each overpotential could be evaluated respectively. For diffusion overpotential, the increasing diffusion overpotential along the voltage as observed in the low current. In the high current, the overpotential decreased as the voltage recovered due to hydrogen purging. The cell resistance increased, and the resistive overpotential also increased.These results imply that the overpotential evaluation is a referenceable metric in real-time control by operating the fuel cell with a constant frequency applied. Moreover, it was verified experimentally that the proposed method is not affected to calculate by least-squares method because it can measure the electric membrane resistance. This study made it possible to control the operation of fuel cells through real-time evaluation.

Performance of a novel annular electric field membrane bioreactor and its membrane fouling control in treating catering wastewater

This study aimed to investigate the effects of different voltage and aeration conditions on catering wastewater treatment and membrane fouling in a novel annular electric field membrane bioreactor (AEMBR). The results indicated that the synergistic effect of annular electric field and aeration promoted the degradation of wastewater and the alleviation of membrane fouling. The treatment effect was optimal under a micro electric field of 0.5 V, with removal rates for COD, NH4+-N, TP, and oil ranging from 96.85% to 99.36%, 80.43%–83.01%, 95.46%–97.79%, and 98.83%–99.15%, respectively. Additionally, the fluorescence intensity of macromolecular proteins and small molecular acids decreased. Simultaneously, the average growth rate of transmembrane pressure (TMP) reduced by approximately 0.4 kPa/d. The species abundance and diversity of activated sludge increased, promoting the growth of dominant bacteria, all while maintaining low energy consumption. The aeration intensity had relatively little impact on system operation, and the force of the annular electric field was greater than the force of aeration. This study verified the optimal benefits under micro electric field conditions and provided a basis for the optimization of future process design to achieve a more efficient and economical wastewater treatment system.

Electric Demulsification Membrane Technology for Confined Separation of Oil-Water Emulsions.

Demulsification technology for separation of oil-water (O/W) emulsions, especially those stabilized by surfactants, is urgently needed yet remains highly challenging due to their inherent stability characteristics. Electrocoalescence has emerged as a promising solution owing to its simplicity, efficacy, and versatility, yet hindered by substantial energy consumption (e.g., >50 kWh/m3) along with undesirable Faradic reactions. Herein, we propose an innovative electric demulsification technology that leverages conductive membrane microchannels to confine oil droplets from the oil-water emulsion for achieving high energy-efficient coalescence of oil droplets. The proposed system reduces the required voltage down to 12 V, 2 orders of magnitude lower than that of conventional electrocoalescence systems, while achieving a similar separation efficacy of 91.4 ± 3.0% at a low energy consumption (3 kWh/m3) and an ultrahigh permeability >3000 L/(m2·h·bar). In situ fluorescence microscopy combined with COMSOL simulations provided insight into the fundamental mechanistic steps of an electric demulsification process confined to membrane microchannels: (1) rapid electric-field redistribution of oil droplet surfactant molecules, (2) enhanced collision probability due to confined oil droplet concentration under dielectrophoretic forces, and (3) increased collision efficacy facilitated by the membrane pore structure. This strategy may revolutionize the next generation of demulsification and oil-water separation innovations.

Construction of multiple interpenetrati ng network electric field-assisted healing hydrogel composite damage-resistant membrane

Inspired by the intrinsic self-healing ability of organisms, this study proposes to incorporate healing properties into separation membranes that are susceptible to physical damage during installation, operation, maintenance, and cleaning. The polyacrylic acid (PAA) hydrogel-modified layer was first obtained by in situ cross-linking and free radical polymerization in this research. After that, the construction of multiple interpenetrating three-dimensional (3D) network hydrogel-modified layers was realized via inserting amininated carbon nanotubes (CNTs-NH2) and Fe3+. Under the external effect of the electric field, the reversible dynamic linkage bonded in the conductive network constructed by CNTs-NH2 and Fe3+ benefited the rearrangement and diffusion of PAA molecular chains at the fractured interface. The dye separation performance of the composite membrane was restored to ca. 90 % of the initial level without affecting the dynamic operation after damage. The hydrogel-modified layer can be structurally stabilized for as long as 100 days. The Fe3+/CNTs-NH2/PAA/PES hydrogel composite membrane maintained a pure water flux of as high as 124.66 L m−2 h−1∙bar−1. This coating also exhibited excellent electrical conductivity (714.33 Ω/sq), mechanical strength (4.31 Mpa), repair, and screening capabilities. It provides a theoretical basis for achieving industrial scale-up and demonstrates good application prospects and empowerment potential.

Beyond static: Tracking the dynamic nature of water absorption and Young's modulus in IPMC devices

AbstractIonomeric polymer‐metal composites (IPMC) are advanced materials designed to mimic biological systems. Their performance depends on various factors, including electrical stimulus intensity, membrane hydration, ionic migration, and Young's modulus. However, there is a lack of studies in the literature investigating how the water absorption capacity and elastic modulus change over time in IPMCs. Understanding the hydration level variation as a function of time is essential because as this parameter deviates, the ionic migration capacity and Young's modulus also change, altering the device's electromechanical efficiency over time. To address this research gap, Nafion/Pt‐based IPMC devices exchanged with four monovalent cations (H+, Li+, Na+, and K+) and one ionic liquid (1‐butyl‐3‐methylimidazolium—BMIM+) were prepared, and a comprehensive investigation on how the water absorption capacity and Young's modulus vary as a function of time, relative humidity (RH), and counterion size was performed. The results revealed that the water uptake capacity is significantly higher and occurs more rapidly at higher RH levels and when the counterion's ionic radius decreases. Consequently, the time required for the device to reach osmotic equilibrium can range from 40 to 270 min, depending on the RH and counterion used. Furthermore, it was observed that the first natural frequency and Young's modulus also exhibit time‐dependent behavior. Under constant RH conditions, the mechanical properties of the IPMC can vary by up to 50% in less than 60 min. Notably, the combined results from water uptake capacity, Young's modulus, electrochemical impedance spectroscopy, and electromechanical response analyses (including blocking force, displacement, displacement rate, current, coulombic efficiency, and voltage) suggest that a morphological transformation within the polymer is likely to occur once RH exceeds 60%. This finding strengthens the hypothesis that ion migration is mainly influenced by their movement through Nafion's ionomeric channels rather than the filling of ionic agglomerates.

Preparation and Characterization of Graphene/Carbon Nano-Cellulose/Polyvinylidene Fluoride Electric Heating Membrane

Preparation and Characterization of Graphene/Carbon Nano-Cellulose/Polyvinylidene Fluoride Electric Heating Membrane

Calculation and analysis of the design of a roll-type electric pressure membrane apparatus for separating of industrial solutions

The designs of electrochemical membrane devices are analyzed. Formulas are obtained for calculating the volume and mass of the elements of the electric membrane apparatus and the volume of the liquid being processed. A diagram of the apparatus is presented. Keywords:membrane, shell, permeate, retentate, anode, cathode sedoplatov2010@yandex.ru, sseedd@mail.ru

Dielectric barrier discharge plasma promotes disinfection-residual-bacteria inactivation via electric field and reactive species

Traditional disinfection processes face significant challenges such as health and ecological risks associated with disinfection-residual-bacteria due to their single mechanism of action. Development of new disinfection processes with composite mechanisms is therefore urgently needed. In this study, we employed liquid ground-electrode dielectric barrier discharge (lgDBD) to achieve synergistic sterilization through electric field electroporation and reactive species oxidation. At a voltage of 12 kV, Pseudomonas fluorescens (ultraviolet and ozone-resistant) and Bacillus subtilis (chlorine-resistant) were completely inactivated within 8 and 6 min, respectively, surpassing a 7.0-log reduction. The lgDBD process showed good disinfection performance across a wide range of pH values and different practical water samples. Staining experiments suggest that cellular membrane damage contributes to this inactivation. In addition, we used a two-dimensional parallel streamer solver with kinetics code to fashion a representative model of the basic discharge unit, and discovered the presence of a persistent electric field during the discharge process with a peak value of 2.86 × 106 V/m. Plasma discharge generates excited state species such as O(1D) and N2(C3Πu), and further forms reactive oxygen and nitrogen species at the gas-liquid interface. The physical process, which is driven by electric field-induced cell membrane electroporation, synergizes with the bactericidal effects of reactive oxygen and nitrogen species to provide effective disinfection. Adopting the lgDBD process enhances sterilization efficiency and adaptability, underscoring its potential to revolutionize physicochemical synergistic disinfection practices.

ИССЛЕДОВАНИЕ ЭЛЕКТРОДИФФУЗИОННОЙ ПРОНИЦАЕМОСТИ УЛЬТРА - И МИКРОФИЛЬТРАЦИОННЫХ МЕМБРАН В ВОДНЫХ ФОСФАТ-СОДЕРЖАЩИХ РАСТВОРАХ

More than 70% of process solutions from car wash stations are discharged contaminated and exceeding MAC standards. Current legislation prohibits the discharge of wastewater generated at a car wash into the environment, even onto the ground, without treating it. To solve the problem of pollution of the aquatic environment with synthetic surfactants, it is necessary to use special purification methods, for example, the use of adsorbents, flotation, electromembrane separation and other technologies. Modern wastewater treatment systems are designed with the ability to extract valuable components from separated aqueous solutions and return purified water to the enterprise water supply system. An analysis of the works of domestic and foreign authors in the field of technologies for purifying aqueous media from pollutants shows that the greatest economic and environmental efficiency can be achieved by using electric membrane separation methods, namely, ultra- and microfiltration. The technological scheme for purifying aqueous media using electric membrane units at the output produces filtrate in the amount of 97% of the volume of purified water and concentrate in the amount of 3% of the volume of purified water. To calculate the technological scheme for purification from specific pollutants, it is necessary to conduct experimental studies to determine the dependencies of the main kinetic characteristics of electric membrane separation. In the process of mass transfer of dissolved substances through membranes, the main contribution occurs due to electrodiffusion permeability. Therefore, the purpose of the presented work is to study the electrodiffusion permeability of ultra- and microfiltration membranes UFM-100, MFFC-2G, MMK 0.45 in aqueous phosphate-containing solutions. Analysis of the research results will allow us to propose an expression for a mathematical description of the coefficient of electrodiffusion permeability of membranes. The resulting expression takes into account the influence of the concentration of the initial solution, current density and temperature.

Experimental Research on the Influence of Ion Channels on the Healing of Skin Wounds in Rats

At the level of skin wounds, an electrical potential difference develops between the edges of the wound and the center of the wound, which favors the migration of cells in the process of their healing. Cells migrate in an electric field because they have a certain electrical membrane potential. This potential is due to differences in the transmembrane electrochemical gradient. The transmembrane electrochemical gradient is due to the migration of sodium, potassium, and calcium ions into the corresponding ion channels. If this is the case, the modification of the functionality of these ion channels should influence the membrane potential and, as a consequence, the wound healing process. In this experiment, we set out to investigate whether the chemical manipulation of ion channels by amiodarone influences the wound healing process. Amiodarone blocks several types of ion channels, but at different concentrations: at low concentrations, it blocks only potassium channels; at medium concentrations, potassium and calcium channels; and at high concentrations, it blocks potassium, calcium, and sodium channels. We worked on rats that were given experimental skin lesions and evaluated the influence of the healing of these lesions upon the topical administration of amiodarone in three concentrations, 200 nM, 2000 nM and 200,000 nM, compared to an untreated group and a group treated with benzyl alcohol, the amiodarone solvent. In our experimental conditions, low concentration amiodarone promoted wound healing both in terms of duration of healing and also in terms of speed of healing. This means that blocking some ions, possibly potassium channels, might promote wound healing.

Engineering of Multivalent Membrane-Anchored DNA Frameworks for Precise Profiling of Variable Membrane Permeability During Reversible Electroporation.

Electroporation techniques have emerged as attractive tools for intracellular delivery, rendering promising prospects towards clinical therapies. Transient disruption of membrane permeability is the critical process for efficient electroporation-based cargo delivery. However, smart nanotools for precise characterization of transient membrane changes induced by strong electric pulses are extremely limited. Herein, multivalent membrane-anchored fluorescent nanoprobes (MMFNPs) that take advantages of flexible functionalization and spatial arrangement of DNA frameworks are developed for in situ evaluation of electric field-induced membrane permeability during reversible electroporation . Single-molecule fluorescence imaging techniques are adopted to precisely verify the excellent analytical performance of the engineered MMFNPs. Benefited from tight membrane anchoring and sensitive adenosine triphosphate (ATP)profiling, varying degrees of membrane disturbances are visually exhibited under different intensities of the microsecond pulse electric field (µsPEF). Significantly, the dynamic process of membrane repair during reversible electroporation is well demonstrated via ATP fluctuations monitored by the designed MMFNPs. Furthermore, molecular dynamics (MD) simulations are performed for accurate verification of electroporation-driven dynamic cargo entry via membrane nanopores. This work provides an avenue for effectively capturing transient fluctuations of membrane permeability under external stimuli, offering valuable guidance for developing efficient and safe electroporation-driven delivery strategies for clinical diagnosis and therapeutics.

(Invited) Microwave Dielectric Relaxation Spectroscopy: A Technique to Inform Ion Transport in Hydrated Polymer Membranes

Providing sustainable supplies of purified water and energy is a critical global challenge for the future, and polymer membranes will play a key role in addressing these clear and pressing global needs for water and energy. Polymer membrane-based processes dominate the desalination market because they are more energy efficient than thermal desalination processes, and polymer membranes are crucial components in several rapidly developing power generation and energy storage applications that rely on membranes to control, selectively, rates of ion transport. Much remains unknown about the influence of polymer structure on basic intrinsic transport properties, and these relationships are important for designing next generation polymer membrane materials.Key to controlling ion transport in membranes for water purification and energy applications is engineering interactions between ions and the solvated polymer matrix. Microwave dielectric relaxation spectroscopy is a tool that enables study of hydrated polymer membranes because water molecule dipoles can be probed in the microwave frequency region. This technique can provide unique insight into hydrated polymer dielectric permittivity (or dielectric constant) properties, which are critical in emerging thermodynamic modeling of ion transport in hydrated polymers. This presentation discusses the use of microwave dielectric relaxation spectroscopy to uncover structure property relationships in hydrated polymers and, more broadly, presents an overview of research aimed at further understanding fundamental structure/property relationships that govern small molecule transport in polymeric materials considered for desalination and electric potential field-driven membrane applications that can help address global needs for clean water and energy.

Inflammasome Activation and IL-1β Release Triggered by Nanosecond Pulsed Electric Fields in Murine Innate Immune Cells and Skin.

Although electric field-induced cell membrane permeabilization (electroporation) is used in a wide range of clinical applications from cancer therapy to cardiac ablation, the cellular- and molecular-level details of the processes that determine the success or failure of these treatments are poorly understood. Nanosecond pulsed electric field (nsPEF)-based tumor therapies are known to have an immune component, but whether and how immune cells sense the electroporative damage and respond to it have not been demonstrated. Damage- and pathogen-associated stresses drive inflammation via activation of cytosolic multiprotein platforms known as inflammasomes. The assembly of inflammasome complexes triggers caspase-1-dependent secretion of IL-1β and in many settings a form of cell death called pyroptosis. In this study we tested the hypothesis that the nsPEF damage is sensed intracellularly by the NLRP3 inflammasome. We found that 200-ns PEFs induced aggregation of the inflammasome adaptor protein ASC, activation of caspase-1, and triggered IL-1β release in multiple innate immune cell types (J774A.1 macrophages, bone marrow-derived macrophages, and dendritic cells) and invivo in mouse skin. Efflux of potassium from the permeabilized cell plasma membrane was partially responsible for nsPEF-induced inflammasome activation. Based on results from experiments using both the NRLP3-specific inhibitor MCC950 and NLRP3 knockout cells, we propose that the damage created by nsPEFs generates a set of stimuli for the inflammasome and that more than one sensor can drive IL-1β release in response to electrical pulse stimulation. This study shows, to our knowledge, for the first time, that PEFs activate the inflammasome, suggesting that this pathway alarms the immune system after treatment.

Insights into the Mechanisms of Reuterin against Staphylococcus aureus Based on Membrane Damage and Untargeted Metabolomics.

Reuterin is a dynamic small-molecule complex produced through glycerol fermentation by Limosilactobacillus reuteri and has potential as a food biopreservative. Despite its broad-spectrum antimicrobial activity, the underlying mechanism of action of reuterin is still elusive. The present paper aimed to explore the antibacterial mechanism of reuterin and its effects on membrane damage and the intracellular metabolome of S. aureus. Our results showed that reuterin has a minimum inhibitory concentration of 18.25 mM against S. aureus, based on the 3-hydroxypropionaldehyde level. Key indicators such as extracellular electrical conductivity, membrane potential and permeability were significantly increased, while intracellular pH, ATP and DNA were markedly decreased, implying that reuterin causes a disruption to the structure of the cell membrane. The morphological damage to the cells was confirmed by scanning electron microscopy. Subsequent metabolomic analysis identified significant alterations in metabolites primarily involved in lipid, amino acid, carbohydrate metabolism and phosphotransferase system, which is crucial for cell membrane regulation and energy supply. Consequently, these findings indicated that the antibacterial mechanism of reuterin initially targets lipid and amino acid metabolism, leading to cell membrane damage, which subsequently results in energy metabolism disorder and, ultimately, cell death. This paper offers innovative perspectives on the antibacterial mechanism of reuterin, contributing to its potential application as a food preservative.

Investigation of filtration performance and phosphorus removal in an electric field controlled dynamic membrane bioreactor

Dynamic membrane bioreactor (DMBR) offers several advantages over traditional membrane bioreactor, including cheaper costs, less resistance, and easier cleaning. Membrane fouling and poor phosphate removal performance restrict the application of DMBR. To address it, this study creatively combined electric field with DMBR and investigated the mechanisms. The results showed that applying an electric field significantly decreased membrane fouling rate in electric dynamic membrane bioreactor with Ti anode (E-DMBR-Ti). The median membrane fouling rate of E-DMBR-Ti was 2.28 kPa/h, which was 48.99 % lower than that of control group (4.47 kPa/h) during stable operation period. However, hydrogen bubbles formed on the cathode blocked membrane during membrane formation period. The enrichment of electroactive and denitrifying microorganisms (e.g., Lactococcus, Hydrogenophaga) in E-DMBR-Ti, which consumed electrons that would flow to the hydrogen evolution reaction, alleviated the negative impact. To address the issue of poor phosphorus removal efficiency of DMBR, based on the previous research, we replaced the titanium mesh of the anode with aluminum plates, and innovatively using the electrocoagulation technology which named E-DMBR-Al. At 2.4 A/m2 current density, E-DMBR-Al showed the highest phosphorus removal efficiency, with a median of 94.69 %, which was 37.69 % higher than that of DMBR. Furthermore, the enrichment of electroactive microorganisms (e.g., Lactococcus) and polyphosphate-accumulating organisms (e.g., unclassified_f__Comamonadaceae) on membrane contributed to the excellent phosphorus removal performance of E-DMBR-Al.

Modeling a Fluid-Coupled Single Piezoelectric Micromachined Ultrasonic Transducer Using the Finite Difference Method.

A complete model was developed to simulate the behavior of a circular clamped axisymmetric fluid-coupled Piezoelectric Micromachined Ultrasonic Transducer (PMUT). Combining Finite Difference and Boundary Element Matrix (FD-BEM), this model is based on the discretization of the partial differential equation used to translate the mechanical behavior of a PMUT. In the model, both the axial and the transverse displacements are preserved in the equation of motion and used to properly define the neutral line position. To introduce fluid coupling, a Green's function dedicated to axisymmetric circular radiating sources is employed. The resolution of the behavioral equations is used to establish the equivalent electroacoustic circuit of a PMUT that preserves the average particular velocity, the mechanical power, and the acoustic power. Particular consideration is given to verifying the validity of certain assumptions that are usually made across various steps of previously reported analytical models. In this framework, the advantages of the membrane discretization performed in the FD-BEM model are highlighted through accurate simulations of the first vibration mode and especially the cutoff frequency that many other models do not predict. This high cutoff frequency corresponds to cases where the spatial average velocity of the plate is null and is of great importance for PMUT design because it defines the upper limit above which the device is considered to be mechanically blocked. These modeling results are compared with electrical and dynamic membrane displacement measurements of AlN-based (500 nm thick) PMUTs in air and fluid. The first resonance frequency confrontation showed a maximum relative error of 1.13% between the FD model and Finite Element Method (FEM). Moreover, the model perfectly predicts displacement amplitudes when PMUT vibrates in a fluid, with less than 5% relative error. Displacement amplitudes of 16 nm and 20 nm were measured for PMUT with 340 µm and 275 µm diameters, respectively. This complete PMUT model using the FD-BEM approach is shown to be very efficient in terms of computation time and accuracy.

Separation Performance of Lithium and Calcium from Synthetic Geothermal Brine Using Electric Field-assisted Membrane

Green low-carbon technology development has spurred an increased demand for lithium. Brine, including geothermal brine, is the world’s largest source of lithium. However, the low lithium content and the presence of other ions pose challenges in concentrating lithium. An electric field-assisted membrane is a separation approach combining nanofiltration membranes with an electric field as an additional driving force, effectively separating lithium from magnesium and strontium. This study was conducted to separate lithium and calcium from synthetic geothermal brine using an electric field-assisted membrane. The separation process is conducted for lithium (50 ppm) and calcium (300, 800, and 2,000 ppm) with variations in electrical voltage (0V, 2V, and 3V). The decrease in lithium rejection reaches up to 50% at an electrical voltage of 2V. Conversely, the increase in electrical voltage does not significantly impact calcium rejection (calcium rejection remains at 89% with an electrical voltage of 3V) and the permeate flux for lithium and calcium. The increasing calcium concentration affects permeate flux significantly but does not notably affect calcium rejection, with the rejection remaining above 85%. The findings suggest the feasibility of concentrating lithium through electric field application without compromising calcium rejection within a single salt solution system.