Electrical Resistivity Monitoring Research Articles

FFF print defect characterization through in-situ electrical resistance monitoring

Fused filament fabrication is a popular fabrication technique. Currently there is a need for in-situ monitoring modalities to gather real-time information on prints, both for quality control and closed-loop control. Despite current advancements, effective and affordable in-situ monitoring techniques for non-destructive defect detection of voids and bonding quality are still limited. This work demonstrates in-situ monitoring of fused filament fabrication through electrical resistance measurements as an alternative to thermal and optical methods. A new, easy-to-implement setup is demonstrated which measures the electrical resistance of a conductively doped filament between the nozzle and single or multi-electrodes on the bed. Defects can be located in an unprecedented way with the use of encoded axes in combination with the observed resistance variations throughout the part. A model of the anisotropic electrical conduction is used to interpret the measurements, which matches well with the data. Warping, inter-layer adhesion, under-extrusion and overhang sagging print defects can be observed in the measurements of parts with a complex geometry, which would be difficult to measure otherwise. Altogether in-situ electrical resistance monitoring offers a tool for optimising prints by online studying the influence of the print parameters for quality assessment and it opens up possibilities for closed-loop control.

A Review on Concrete Structural Properties and Damage Evolution Monitoring Techniques.

Concrete structures have emerged as some of the most extensively utilized materials in the construction industry due to their inherent plasticity and high-strength characteristics. However, due to the temperature fluctuations, humidity, and damage caused by human activities, challenges such as crack propagation and structural failures pose threats to the safety of people's lives and property. Meanwhile, conventional non-destructive testing methods are limited to defect detection and lack the capability to provide real-time monitoring and evaluating of concrete structural stability. Consequently, there is a growing emphasis on the development of effective techniques for monitoring the health of concrete structures, facilitating prompt repairs and mitigation of potential instabilities. This paper comprehensively presents traditional and novel methods for concrete structural properties and damage evolution monitoring, including emission techniques, electrical resistivity monitoring, electromagnetic radiation method, piezoelectric transducers, ultrasonic techniques, and the infrared thermography approach. Moreover, the fundamental principles, advantages, limitations, similarities and differences of each monitoring technique are extensively discussed, along with future research directions. Each method has its suitable monitoring scenarios, and in practical applications, several methods are often combined to achieve better monitoring results. The outcomes of this research provide valuable technical insights for future studies and advancements in the field of concrete structural health monitoring.

Rapid integration of screen-printed electrodes into thermoplastic organ-on-a-chip devices for real-time monitoring of trans-endothelial electrical resistance.

Trans-endothelial electrical resistance (TEER) is one of the most widely used indicators to quantify thebarrier integrity of endothelial layers. Over the last decade, the integration of TEER sensors into organ-on-a-chip (OOC) platforms has gained increasing interest for its efficient and effective measurement of TEERin OOCs. To date, microfabricated electrodes or direct insertion of wires has been used to integrate TEERsensors into OOCs, with each method having advantages and disadvantages. In this study, we developed aTEER-SPE chip consisting of carbon-based screen-printed electrodes (SPEs) embedded in a poly(methylmethacrylate) (PMMA)-based multi-layered microfluidic device with a porous poly(ethylene terephthalate)membrane in-between. As proof of concept, we demonstrated the successful cultures of hCMEC/D3 cellsand the formation of confluent monolayers in the TEER-SPE chip and obtained TEER measurements for 4days. Additionally, the TEER-SPE chip could detect changes in the barrier integrity due to shear stress oran inflammatory cytokine (i.e., tumor necrosis factor-α). The novel approach enables a low-cost and facilefabrication of carbon-based SPEs on PMMA substrates and the subsequent assembly of PMMA layers forrapid prototyping. Being cost-effective and cleanroom-free, our method lowers the existing logistical andtechnical barriers presenting itself as another step forward to the broader adoption of OOCs with TEERmeasurement capability.

Pit-mound microrelief on a forested slope drives infiltration and preferential flow after heavy rainfall – experiments with soil resistance monitoring and dye tracing

With the changing climate, short heavy rainfalls (SHRs) are becoming more frequent and intensive. The distribution of rainwater and subsurface runoff formation in forest soils can be strongly affected by soil disturbances and surface microrelief. Rainwater redistribution and the formation of preferential flow in response to natural and simulated SHRs were investigated in soil profiles on slopes forested by Norway spruce with a pit-mound microrelief formed by historical tree uprooting using two independent methods; soil electrical resistance monitoring and the application of dye tracer. In the deepest soil layers, resistance decreased in responses to natural SHRs on average by 46% in pits and by 11% on ‘smooth slope’ controls, reflecting the deeper redistribution of infiltrated water in pits. Dye tracing in the simulated rainfall revealed the formation of shallow biomat flow at the control plot. In contrast, the shallow lateral flow was focused by the pit and redirected into funnel flow underneath the pit bottom. The sum of medium and high dye concentration classes obtained with the support vector machine classification of profile photographs indicated a higher water entry into topsoil and subsoil layers in pit (44% and 31% of area, respectively) as compared to the control profile (16% and 8% of area, respectively). Leaving pit-mound microrelief as the natural legacy in forest soils can mitigate some of the negative hydrological effects of intensive forest management and may improve the water yields on forested slopes by redirecting shallow subsurface runoff and facilitating deep distribution of infiltrated water. Such beneficial effects of pit-mounds on the hydrology of forested slopes should be considered in future hydrological modelling and land management.

4D interpretation of time-lapse electrical resistivity monitoring data to identify preferential flow path in a landfill, South Korea.

Monitoring the leakage of leachate from a landfill is critical in preventing possible contamination in the surrounding area. Time-lapse (TL) electrical resistivity tomography (ERT) has been performed along eleven survey lines at four different time points in a landfill in Korea. The TL data sets were interpreted using an in-house 4D inversion algorithm. Changes in 4D inversion results were analyzed in order to interpret a leachate-contaminant region. Since the rainy season started during obtaining TL ERT data sets, the effects of precipitation on TL ERT data are also analyzed. Changes in electrical resistivity (ER) showed that precipitation increases ER of contaminant zones. As hydrogeochemical data offer contamination information in some areas where boreholes are located, these are helpful to interpret and compare with ERT inversion results to evaluate the extent of the contaminated plume. We also classified soil textures from particle size analysis on soil samples and analyzed electrical conductivity (EC) and dissolved oxygen (DO) using groundwater samples obtained from observation wells in the survey site. The information on soil structure as well as the results of 4D inversion provided insight into the location of a preferential flow path.

Organ-on-a-Chip Platform with an Integrated Screen-Printed Electrode Array for Real-Time Monitoring Trans-Epithelial Barrier and Bubble Formation.

Cellular tight junctions play a key role in establishing a barrier between different compartments of the body by regulating the selective passage of different solutes across epithelial and endothelial tissues. Over the past decade, significant efforts have been conducted to develop more clinically relevant "organ-on-a-chip" models with integrated trans-epithelial electrical resistance (TEER) monitoring systems to help better understand the fundamental underpinnings of epithelial tissue physiology upon exposure to different substances. However, most of these platforms require the use of high-cost and time-consuming photolithography processes, which limits their scalability and practical implementation in clinical research. To address this need, we have developed a low-cost microfluidic platform with an integrated electrode array that allows continuous real-time monitoring of TEER and the risk of bubble formation in the microfluidic system by using scalable manufacturing technologies such as screen printing and laser processing. The integrated printed electrode array exhibited excellent stability (with less than ∼0.02 Ω change in resistance) even after long-term exposure to a complex culture medium. As a proof of concept, the fully integrated platform was tested with HMT3522 S1 epithelial cells to evaluate the tight barrier junction formation through TEER measurement and validated with standard immunostaining procedures for Zonula occludens-1 protein. This platform could be regarded as a stepping stone for the fabrication of disposable and low-cost organ and tissue-on-a-chip models with integrated sensors to facilitate studying the dynamic response of epithelial tissues to different substances in more physiologically relevant conditions.

Novel TIM Evaluation Method With in Situ Electrical Monitoring

Thermal interface materials (TIMs) transfer heat between two surfaces in electronic assemblies. Specifically, a TIM 2 is a TIM used to transfer heat from a component’s lid to a heat sink. During use, TIM 2s experience thermal aging and mechanical stress (caused by board/component/heat sink expansion mismatches and warpage during heating/cooling). Understanding the response of TIMs to these stresses is critical for understanding TIM and product reliability. However, the responses of TIMs are complex and difficult to predict or model. TIMs are often polymeric materials heavily loaded with thermally conductive fillers and have time, temperature, and rate-dependent properties. Therefore, experimental studies are needed to address TIM reliability. However, monitoring TIM stability or performance while in situ is difficult. Electrical capacitance has been used to monitor the stability of dielectric TIM in situ, allowing for monitoring TIM stability and, indirectly, the TIM thermal performance, but electrically conductive TIMs cannot be used with capacitance measurements, so a new technique is needed. Monitoring a conductive TIM’s electrical resistance could give insight into a TIM’s stability, as both thermal and electrical resistances are affected by a TIM’s contact with surfaces, thickness, and area. This study examines four electrically conductive graphite pad TIMs on a test board, representing a large printed circuit board with a large shared heat sink, in an accelerated thermal cycle from 0 °C to 100 °C. The electrical resistance of the TIMs was monitored in situ, and after testing, postmortem failure analysis of the TIMs was done. The efficacy of electrical resistance monitoring for evaluating TIM stability was examined, and correlations with failure analysis results were made. Electrical resistance monitoring provided insight into the TIMs’ stability, failure time, and extent of failure.

Smart fiber orientation monitoring system in a mold via electrical route modeling

The orientation of unidirectional carbon fibers (UDCFs) in a manufacturing process is critical to the mechanical properties of carbon fiber reinforced plastics (CFRPs). This study presents a method to monitor the orientation of UDCFs on a mold using electrical resistance during the CFRP manufacturing process. An equivalent electrical model for UDCFs was proposed to develop an in situ sensor in a mold. The orientation of UDCFs during the CFRP manufacturing process is investigated in terms of its orthotropic electrical properties. The proposed technique can have strong implications on in situ monitoring of composite molding process where the fiber orientation is unseen by monitoring electrical resistance with Cu tapes as electrodes. • Fiber orientation and the corresponding electrical resistance was correlated. • Analogous 3D model for electrical route was proposed with empirical rationales. • Fiber orientation in a mold can be detected by electrical resistance monitoring. • Fiber orientation monitoring is available during the composite manufacturing.

Iron island films on sapphire grown by pulsed laser deposition with in situ electrical resistance monitoring

Iron island films were grown on sapphire by pulsed laser deposition with in situ electrical resistance control, which made it possible to precisely determine the percolation transition. Four growth stages can be distinguished: initial nucleation, independent island growth, ripening with channel formation, and island coalescence into a labyrinth structure. The morphology of the iron island films corresponded to these stages, depending on the time and deposition rate at a given temperature. At growth temperatures of T ≥ 350 °C, the percolation thickness exponentially depended on the temperature. The electrical response time τ of the system to a single pulse was<1 s, and the temperature dependence of 1/τ was linear in Arrhenius coordinates with a slope corresponding to an activation energy of 0.41 eV. The dependence of the film thickness and island diameter on the pulse frequency before the onset of the percolation transition reached a maximum, which can be explained by two competing factors: diffusion stimulation owing to the high kinetic energy of the incident particles and an increase in the number of initial nuclei in the substrate regions without islands.

Electrical resistivity monitoring of lower Rio Grande River-Groundwater intermittency

• Time-lapse electrical resistivity before, during, and after the intermittent river flooding. • Resistivity used to characterize the transient and spatial connectivity transitions. • Resistivity changes due to water saturation characterized connectivity transitions. • Resistivity changes after connection occurred were dominated by river temperature. • Resistivity sensitivity to temperature was also used to characterized infiltration. In the current era of rapid environmental changes, more rivers are projected to dry up and transition to disconnected systems in unprecedented duration and frequency. However, river-groundwater interactions, including connectivity, remain a challenge to characterize, especially for managed-ephemeral rivers such as the lower Rio Grande in southern New Mexico, where conjunctive use for irrigated agriculture is prevalent. This investigation used a noninvasive and spatially distributed geophysical method for mapping the disconnection/connection of groundwater with the Rio Grande River, which has been validated with ancillary data that includes river flow, water levels in the river and adjacent wells, and river and groundwater temperature and electrical conductivity. Time-lapse monitoring of electrical resistivity before, during, and after the river flooding season was used to characterize the transient and spatial connectivity of the water table with the Rio Grande, from disconnection to connection, and back to disconnection. The relationships between electrical conductivity from the geophysical analysis versus the large array of ancillary data helped to narrow down the driver of observed temporal changes in connectivity after the transition from disconnection to connection. The results convey that water temperature is potentially the main influence on the changing electrical conductivity after the connectivity transition. The surface water temperature showed a direct and strong correlation to the electrical conductivity of shallow sediments, which was similar to the river stage/groundwater elevation drivers of infiltration. Time-lapse electrical resistivity can be used to monitor river-groundwater connectivity throughout the intermittency cycle, due to its sensitivity to changes in both water saturation and temperature.

Advances in Trans-Epithelial Electrical Resistance (TEER) monitoring integration in an Intestinal Barrier-on-Chip (IBoC) platform with microbubbles-tolerant analytical method

Trans-epithelial resistance (TEER) is one of the most widely performed analysis in vitro methods for monitoring barrier tissue development, formation and functional maturation. It is a basic and important tool for the reproduction of an artificial human epithelium. However, in the design and construction of organ on chip devices, the reliable TEER measurements still remain a challenge, in spite of their efficacy in providing real time information on tissue integrity and function. The observed limitations often concern the nature of the selected electrodes, made with opaque or metal materials that prevent microscopic investigation, their correct and stable reposition that affect the impedance spectroscopy analysis and microbubbles interference. Here, we present a method to perform real time TEER analysis on an Intestinal Barrier-on-Chip (IBoC) using integrated transparent electrodes, by means of impedance spectroscopy analysis and supported by a microbubble-tolerant calculation method. The human Caco-2 cells were used as an in vitro model of the intestinal epithelial cell barrier. Measurements can be carried out even in presence of microbubbles during the analysis, thus allowing application of this analytical method in microfluidic organ on chip devices that must perform in continuum for a long time.

Development of knitted reinforced structures with self-diagnostic function for composite applications

The research aims the development of knitted reinforcement structures for inducing self-diagnostic properties into knitted reinforced composites for structural health monitoring. Conductive carbon fiber was used in knitted inlaid structures as inlay yarns, and l × 1 Rib knitted base fabric of polyester filament yarn was used for knitting. The reinforcement’s conductive nature induced self-diagnostic properties into composites using correlation of mechanical damages and changes in electrical resistance values. Single and double stimuli layers and inlay patterns of 3 × 1, 6 × 1 and 9 × 1 was used to check their impact on self-diagnostic properties. Mechanical testing and real-time electrical resistance monitoring proved knitted structures as a solution to induce self-diagnostic properties into composite materials. Composites having double stimuli (conductive) layers exhibited better self-diagnostic properties than single stimuli layer composites, and the self-diagnostic properties also improved as the inlay pattern of reinforcement moved from 9 × 1 to 6 × 1 and 3 × 1 inlay. Such knitted reinforced self-diagnostic composites could be practically used in structural health monitoring applications, e.g., complicated structures of large buildings infrastructures and machinery which require record of each minor happening with structures to keep smooth and successful running of the system.

Experimental and modeling investigations of the non-isothermal and isothermal precipitations in an Al-Cu-Mg-Zr alloy with various pre-precipitation microstructures

The complex precipitation evolutions of Al-Cu-Mg alloys during both non-isothermal and isothermal thermal processes have been found to work on their mechanical properties and electrical resistivity. Modeling of the precipitation kinetics, electrical resistivity and strength evolution is therefore essential for optimizing heat treatment and processing of these alloys. In this work, in situ electrical resistivity monitoring during both non-isothermal and isothermal thermal processes and microstructural characterizations were conducted on an Al-Cu-Mg-Zr alloy with different pre-precipitation microstructures to provide fundamental insights of precipitation behaviors. The results showed that precipitation behaviors of Al-Cu-Mg-Zr alloy, such as the dominant strengthening phase, were highly dependent on pre-precipitation microstructures and thermal history. A time–temperature-microstructure-properties map was established to unravel precipitation characteristics and their strengthening functions. The maximum hardness was indicated to be attributed to the combined presence of Guinier–Preston–Bagaryatsky (GPB) zones and fine S (Al2CuMg) phase. Further, in situ electrical resistivity was used as the main input data to develop an improved model based on the classical Kampmann and Wagner type numerical model (KWN model). This integrated model could not only reveal precipitation kinetics but also well predict hardness evolutions of the studied alloy during non-isothermal and isothermal processes.

In vitro 3D cocultured tumor-vascular barrier model based on alginate hydrogel and Transwell system for anti-cancer drug evaluation

The development of three-dimensional (3D) in vitro model to recapitulate the in vivo tumor tissue is essential for studying tumor biology, discovering anti-cancer drugs, and evaluating anti-cancer drug efficacy. However, most of the previous models lack the involvement of vascular barrier. Here, we proposed an in vitro 3D cocultured tumor-vascular barrier model by the combination of alginate hydrogels beads and Transwell system. PC-3 cells and NIH/3T3 cells were encapsulated in alginate hydrogel beads, which were cultured in the bottom chamber of Transwell, while human umbilical vein endothelial cells (HUVECs) were cultured on the porous membrane in the upper chamber to form vascular barrier. The effect of the concentration of alginate sodium on the morphology, diameter and swelling ratio of the beads was studied. The alginate sodium content and cell seeding density were further optimized according to cell proliferation ability. The formation of endothelial barrier was verified by immunostaining with tight junction protein VE-cadherin and transendothelial electrical resistance (TEER) monitoring. Finally, the drug response of 3D cocultured tumor-vascular barrier model to curcumin was evaluated. Compared with two-dimensional (2D) coculture model and 3D coculture spheroid model, 3D tumor-vascular barrier model showed the highest activity of cancer cells and the strongest drug resistance. The developed 3D cocultured tumor-vascular barrier model possesses great potential to be applied for in vitro evaluation of anti-tumor drugs.

Highly Precise, Continuous, Long-Term Monitoring of Skin Electrical Resistance by Nanomesh Electrodes.

The transepidermal water loss has been widely used as a method for directly evaluating the barrier function of the stratum corneum of the skin. However, transepidermal water loss could not be measured continuously for a long period of time, and there were no reports of continuous monitoring of skin barrier functions. Here, a method is reported to continuously monitor the skin electrical resistance by nanomesh electrodes for a long period of time while maintaining the natural skin condition that does not inhibit water evaporation. Simultaneous measurements of the skin electrical resistance by nanomesh electrodes and transepidermal water loss exhibits a linear fit with a high negative correlation. Furthermore, dynamics of skin physiological functions are successfully visualized by monitoring of the skin electrical resistance by nanomesh electrodes for 30 h in daily life.

Analysis of the Influence of Crystalline Admixtures at Early Age Performance of Cement-Based Mortar by Electrical Resistance Monitoring.

Crystalline admixtures are employed for waterproofing concrete. This type of admixtures can affect the early age performance of cement-based mixes. The electrical resistance properties of cement have been related to the initial setting time and to the hydration development. This paper proposes a system for remote monitoring of the initial setting time and the first days of the hardening of cement-based mortars to evaluate the effect of the incorporation of crystalline admixtures. The electrical resistance results have been confirmed by other characterization techniques such as thermogravimetric analysis and compressive strength measurements. From the electrical resistance monitoring it has been observed that the incorporation of crystalline admixtures causes a delay in the initial setting time and hydration processes. The measurements also allow to evaluate the influence of the amount of admixture used; thus, being very useful as a tool to define the optimum admixture dosage to be used.

In situ monitoring of electrical resistivity and plasma during pulsed laser deposition growth of ultra-thin silver films

Ultra-thin silver films of thicknesses of the order of 10 nm and less were prepared in different ambient conditions (vacuum, Ar, and N2) by pulsed laser deposition on glass and fused silica substrates. The in situ monitoring of electrical resistance of deposited films and optical emission spectroscopy of plasma were implemented as real-time analysis techniques. Change in the growth mechanism of the Ag layer in N2 ambient is expressed by an acceleration of the coalescence process, which shifts the percolation point toward lower mass thicknesses. The films prepared in vacuum and Ar ambient were found to be unstable for a final resistance in the range from 1 to 100 MΩ while the films deposited in N2 revealed stable electrical resistance. The percolation point was further lowered by introducing a sublayer of AgxOy for the film deposited in N2 gas. Based on data provided by AFM, SEM, and spectroscopic ellipsometry, different film formation mechanisms are discussed in relation to surface morphology and optical properties. Optical emission spectroscopy was used to monitor the deposition process and identify the species presented during the deposition process. The energy of the ejected particle is affected by the addition of ambient gas and depends on the properties of the working gas.

Development and evaluation of thin film electrical resistance sensors for monitoring CO2 top of the line corrosion

CO2 top of the line corrosion of carbon steel was studied using an in-house Electrical Resistance (ER) monitoring system. The system comprised a thin film ER sensor made of 50 μm thick carbon steel foil, and a high precision constant current circuit. Compensation for the variation in metal resistivity with temperature was achieved by the standard method of using two different circuit paths (corroding and reference). The offset-compensated ohms method using a switched relay circuit was found to effectively overcome thermoelectric junction potentials between the copper connecting wires and the steel sensor element, thus achieving reliable and reproducible top of the line corrosion rates at short time scales. The possible current short circuits by droplet or continuous thin film pathways through the condensate layer were modelled using finite element techniques and confirmed to be insignificant even for a fluid with an electrical conductivity equivalent to that of seawater, more than two orders of magnitude above that of the condensed fluid. The monitoring results successfully demonstrated the role of increasing gas temperature in accelerating top of the line corrosion. The accuracy and the reproducibility of the ER technique for the measurement of corrosion in low conductivity fluids are shown to be at least as good as other published results, and the ability to give a cumulative measurement of corrosion rather than an instantaneous rate is shown to allow the true long term total corrosion depth to be measured, unaffected by short term variations due to cyclic droplet formation.

Regularization Algorithms for Increasing the Stability of the Solution to the Inverse Problem in Precision Monitoring of Electrical Resistivity Using the VES Method

Regularization Algorithms for Increasing the Stability of the Solution to the Inverse Problem in Precision Monitoring of Electrical Resistivity Using the VES Method

Binding and neutralization of C. difficile toxins A and B by purified clinoptilolite-tuff.

Clostridioides difficile (C. difficile) infection is a major public health problem worldwide. The current treatment of C. difficile-associated diarrhea relies on the use of antibacterial agents. However, recurrences are frequent. The main virulence factors of C. difficile are two secreted cytotoxic proteins toxin A and toxin B. Alternative research exploring toxin binding by resins found a reduced rate of recurrence by administration of tolevamer. Hence, binding of exotoxins may be useful in preventing a relapse provided that the adsorbent is innocuous. Here, we examined the toxin binding capacity of G-PUR®, a purified version of natural clinoptilolite-tuff. Our observations showed that the purified clinoptilolite-tuff adsorbed clinically relevant amounts of C. difficile toxins A and B in vitro and neutralized their action in a Caco-2 intestinal model. This conclusion is based on four independent sets of findings: G-PUR® abrogated toxin-induced (i) RAC1 glucosylation, (ii) redistribution of occludin, (iii) rarefaction of the brush border as visualized by scanning electron microscopy and (iv) breakdown of the epithelial barrier recorded by transepithelial electrical resistance monitoring. Finally, we confirmed that the epithelial monolayer tolerated G-PUR® over a wide range of particle densities. Our findings justify the further exploration of purified clinoptilolite-tuff as a safe agent in the treatment and/or prevention of C. difficile-associated diarrhea.