Use Of Dielectric Spectroscopy Research Articles

Effect of soil compaction on the measurements of complex dielectric permittivity spectrum with an open-ended antenna probe and the coaxial cell system

The paper proposes the use of dielectric spectroscopy to measure changes in dielectric permittivity for soil subjected to compression. Density-dependent dielectric permittivity characteristics of soils for the entire range of obtained density, and thus for a significant parameter of soil properties corresponding with ideal conditions for plant growth as well as those inhibiting their growth were presented. Measurements were carried out for three soil types with different moisture content using an open-ended antenna probe (OE-A), operating in the frequency range of 20 MHz–1.2 GHz and a coaxial cell system in frequency range of 20 MHz–3 GHz. Experimental results showed that an increase in bulk density and volumetric water content of soil affects the complex dielectric permittivity spectrum – a model for this relationship was proposed. Soil dielectric permittivity as a parameter reflecting soil moisture and density can be useful in assessing soil quality.

Noninvasive Glucose Monitor Using Dielectric Spectroscopy

ObjectiveThe Alertgy noninvasive continuous glucose monitor (ANICGM) is a novel wristband device that reports glucose levels without entailing skin puncture. This study evaluated the performance of the ANICGM compared to a Food and Drug Administration-approved glucose meter in patients with type 2 diabetes. MethodsThe ANICGM device measures changes in the electromagnetic field generated by its sensor to produce a dielectric spectrum. The data contained within this spectrum are used in tandem with machine learning algorithms to estimate blood glucose levels. Values from the ANICGM were collected, sent to the Alertgy lab, formatted, and compared with fingerstick blood glucose levels, which were measured using the Accuchek Inform II glucometer. Fifteen patients completed three 120-minute sessions. The mean absolute relative difference (MARD) was calculated. ResultsMARD values were compared between study days 2 and 3. The MARD for day 2 was 18.5% (95% CI, 12.8-42.2%), and the MARD for day 3 was 15.3% (95% CI, 12.3-18.4%). The difference in the MARD between days 2 and 3 was not statistically significant (P = .210). ConclusionThe resulting MARDs suggest that further investigation into the use of dielectric spectroscopy for glucose monitoring should be explored.

Fast Dynamics of Inverse Wormlike Micelles Probed Using Mechanical and Dielectric Spectroscopy.

The rheology of wormlike micelle (WLM) solutions is tunable by engineering the micellar structure and topology. While much is known about how microscopic properties influence the rheological characteristics, questions remain regarding the quantification of fast relaxation processes, including Rouse and rotational modes. These fast processes are challenging to access using mechanical spectroscopy as bending modes dominate high-frequency mechanical measurements. In this work, we demonstrate the use of dielectric spectroscopy (DES) to directly interrogate these fast relaxation modes in solutions containing reverse WLMs. These consist of lecithin solutions in n-decane swollen with water. We develop an equivalent circuit model that separates the fast spectral features from the low-frequency processes and show that this relaxation feature is consistent with a combination of high-frequency Rouse and rotational modes. Further, we show that the low-frequency response is not determined by polymer dynamics alone. These findings demonstrate the potential of DES measurements to describe WLM behavior and pave the way toward in situ measurements under steady and transient shear flow.

On the Segmental Dynamics and the Glass Transition Behavior of Poly(2-vinylpyridine) in One- and Two-Dimensional Nanometric Confinement.

Geometric nanoconfinement, in one and two dimensions, has a fundamental influence on the segmental dynamics of polymer glass-formers and can be markedly different from that observed in the bulk state. In this work, with the use of dielectric spectroscopy, we have investigated the glass transition behavior of poly(2-vinylpyridine) (P2VP) confined within alumina nanopores and prepared as a thin film supported on a silicon substrate. P2VP is known to exhibit strong, attractive interactions with confining surfaces due to the ability to form hydrogen bonds. Obtained results show no changes in the temperature evolution of the α-relaxation time in nanopores down to 20 nm size and 24 nm thin film. There is also no evidence of an out-of-equilibrium behavior observed for other glass-forming systems confined at the nanoscale. Nevertheless, in both cases, the confinement effect is seen as a substantial broadening of the α-relaxation time distribution. We discussed the results in terms of the importance of the interfacial energy between the polymer and various substrates, the sensitivity of the glass-transition temperature to density fluctuations, and the density scaling concept.

Use of Dielectric Spectroscopy for the Study of Concentration of Glyphosate in Distilled Water

In this paper, the capability of sensing low concentrations of glyphosate in water of two interdigital capacitive transducers are analyzed using numerical simulations and measurements. Each microwave sensor is analyzed using the surface electric field produced at the resonance frequency. In addition, the reflection coefficient of each transducer submerged in water with glyphosate is measured and compared with distilled water. Prepared samples with concentrations of 1ppm/L (1 part per million over a liter of distilled water) are used for the experimental tests.

Dielectric Spectroscopy to Improve the Production of rAAV Used in Gene Therapy

The insect cell-baculovirus expression vector system is an established method for large scale recombinant adeno-associated virus (rAAV) production, largely due to its scalability and high volumetric productivities. During rAAV production it is critical to monitor process parameters such as Spodoptera frugiperda (Sf9) cell concentration, infection timing, and cell harvest viabilities since they can have a significant influence on rAAV productivity and product quality. Herein we developed the use of dielectric spectroscopy as a process analytical technology (PAT) tool used to continuously monitor the production of rAAV in 2 L stirred tank bioreactors, achieving enhanced control over the production process. This study resulted in improved manufacturing robustness through continuous monitoring of cell culture parameters, eliminating sampling needs, increasing the accuracy of infection timing, and reliably estimating the time of harvest. To increase the accuracy of baculovirus infection timing, the cell growth/permittivity model was coupled to a feedback loop with real-time monitoring. This system was able to predict baculovirus infection timing up to 24 h in advance for greatly improved accuracy of infection and ensuring consistent high rAAV productivities. Furthermore, predictive models were developed based on the dielectric measurements of the culture. These multiple linear regression-based models resulted in correlation coefficients (Q2) of 0.89 for viable cell concentration, 0.97 for viability, and 0.92 for cell diameter. Finally, models were developed to predict rAAV titer providing the capability to distinguish in real time between high and low titer production batches.

Thermodynamics Characterization of Lung Carcinoma, Entropic Study and Metabolic Correlations

In recent years, the use of dielectric spectroscopy as an investigation technique to determine the chemical–physical characteristics of biological materials has had a great increase. This study used the non-equilibrium thermodynamics with internal variables theory to test the potential pathological features of lung cancer. After a brief exploration of the dielectric polarization concept highlighting some aspects that were used, some thermodynamic functions were obtained as functions of the frequency, both for lung tumor cells and physiological ones. Variations in the intensity of values but not in the trend of the curves were observed and this was attributed to the perturbing field. The trend of this field explains the behavior of phenomena described by other functions, as related to the frequencies of the perturbing field. Compared to the physiological ones, the cancer cells appeared to be “more predisposed” to conserve their state as characterized by minor entropy production, probably because this helped cells to obtain the required adenosine triphosphate (ATP) from the minimum amount of nutrients.

Application of dielectric spectroscopy to unravel the physiological state of microorganisms: current state, prospects and limits.

Microbial physiology is an essential characteristic to be considered in the research and industrial use of microorganisms. Conventionally, the study of microbial physiology has been limited to carrying out qualitative and quantitative analysis of the role of individual components in global cell behaviour at a specific time and under certain growth conditions. In this framework, groups of observable cell physiological variables that remain over time define the physiological states. Recently, with advances in omics techniques, it has been possible to demonstrate that microbial physiology is a dynamic process and that, even with low variations in environmental culture conditions, physiological changes in the cell are provoked. However, the changes cannot be detected at a macroscopic level, and it is not possible to observe these changes in real time. As an alternative to solve this inconvenience, dielectric spectroscopy has been used as a complementary technique to monitor on-line cell physiology variations to avoid long waiting times during measurements. In this review, we discuss the state-of-the-art application of dielectric spectroscopy to unravel the physiological state of microorganisms, its current state, prospects and limitations during fermentation processes. Key points • Summary of the state of the art of several issues of dielectric spectroscopy. • Discussion of correlation among dielectric properties and cell physiological states. • View of the potential use of dielectric spectroscopy in monitoring bioprocesses.

Enabling new exploration opportunities on planetary surfaces: In situ geochemical characterization in soils by dielectric spectroscopy onboard the AXEL rover system

In the work, we present dielectric spectroscopy (DS) is an analytical method capable of characterizing and quantifying electrochemically active materials (water/ice, ions, etc.) in planetary regoliths. Detection of these materials occurs when a small amount of energy is applied to an in situ sample, causing perturbation in the form of potential kinetic energy and inducing polarization and/or relaxation processes in materials of interest. The frequency dispersion on the electrical properties of impendences, relative permittivity, and conductivity spectra represents chemical and physical properties in association with inherent material properties. Therefore, measuring these energetic states can provide a unique fingerprint of the materials, depending on the frequencies that are scanned. In the case of water content in soils, the Debye equivalent circuit model can accurately predict its electrical properties and provide excellent quantification of the water content in soils.Use of DS is enabled by miniaturization of the key components and the low power requirements. DS is therefore capable of offering substantial scientific returns as an in situ sampling and non-destructive measurement technique, making it ideally suitable for deployment onboard many smaller space exploratory platforms. This work reports the first deployment use of DS from a field test for geochemical characterization of in situ soils, specifically on the quantification of water onboard the AXEL mobility system in the Mojave Desert.Laboratory testing has confirmed the sensitivity of DS with respect to particle size (fine vs coarse) determination as well as water content (down to 0.01 ​wt%) under a wide range of environmental conditions. Water content associated with bound and bulk water was uniquely identified in the soil mixture. We also describe a field demonstration using DS using two distinct insertion dielectric probes specifically design for sub-surface measurements, verifying their mechanical robustness and chemical stability. The field measurements are in good agreement with laboratory data and effectively quantified water content at about 3.0 ​wt% and 8.0 ​wt% for field test sites #1 and #2, respectively.

Study on the effect of side-chain group on the segmental dynamics of selected methacrylate polymers at ambient and high pressures

In this work, we have investigated the effect of changes in the side groups within the polymer chain on the glass transition dynamics of selected methacrylate polymers. The relaxation dynamics of the studied polymers: poly (glycidyl methacrylate), poly (hydroxy-propyl methacrylate), poly (isopropyl methacrylate) and poly (n-propyl methacrylate), was investigated with the use of dielectric spectroscopy and differential scanning calorimetry. In addition to that, high-pressure dielectric measurements were performed to understand better the effect of density changes on the segmental dynamics within the studied family of compounds. A comparison of poly (isopropyl methacrylate) and poly (n-propyl methacrylate), that have the same chemical composition while differ only in the molecular orientation of the side-chain group, has revealed pronounced differences in the glass transition temperature of almost 26 K and sensitivity of the segmental dynamics to pressure changes.

Analysis of Apple Candying by Microwave Spectroscopy.

Process control in the industry requires fast, safe and easily applicable methods. In this sense, the use of dielectric spectroscopy in the microwave range can be a great opportunity to monitor processes in which the mobility and quantity of water is the main property to produce a quality and safety product. The candying of fruits is an operation in which the samples are first osmotically dehydrated and then exposed to a hot air-drying operation. This process produces changes in both the structure of the tissue and the relationships between water, the solid matrix and the added soluble solids. The aim of this paper is to develop a dielectric tool to predict the water/sucrose states throughout the candying of apple, by considering the complexity of the tissue and describing the different transport phenomena and the different transition processes of the sucrose inside the sample.

Study of Increasing Pressure and Nanopore Confinement Effect on the Segmental, Chain, and Secondary Dynamics of Poly(methylphenylsiloxane)

The effect of increasing pressure and two-dimensional (2D) confinement on the dynamics of glass-forming polymer poly(methylphenylsiloxane) (PMPS) was investigated with the use of dielectric spectroscopy. We demonstrate that the glass-forming polymer confined to nanoporous alumina might obey the density scaling relation similar to that in the bulk and that the same value of the scaling exponent is used to superimpose the α-relaxation time measured under different thermodynamic conditions. Our comprehensive analysis of the relaxation processes detected in the dielectric loss spectra of PMPS allows us to identify the Johari–Goldstein β-relaxation which for a bulk polymer shows up as a well-resolved peak while under 2D nanoconfinement only as an excess wing. In contrast to previous studies, we provide dielectric evidence of an additional α′-relaxation, slower than the segmental (α-) dynamics, which is related to the chain dynamics of PMPS.

Optimised use of dielectric spectroscopy at microwave frequencies for direct online monitoring of polymerisation reactions

This study reports the first use of dielectric spectroscopy over at a wide frequency range to monitor, in real time, the progress of a ring opening polymerisation. An open-ended coaxial line sensor was placed directly into the reaction medium of a polymerisation of ε-caprolactone and used to characterise the dielectric properties of the polymerisation mixture both ‘in-situ’ and with time at microwave frequencies. In addition to measurements obtained by the sensor, samples of the medium were extracted at various time points for off-line analysis, to confirm the level of conversion and polymer molecular weights that had been achieved. The results demonstrated that the dielectric properties values exhibited by the reaction medium with time could be correlated directly to the progress of the reaction. Thus, the experimental data allowed the construction of a calibration curve which could be used to predict the conversion of monomer to polymer at any given point of the reaction. The dielectric data permitted also the identification of key reaction parameters, such as the optimum point of termination for the reaction. Furthermore, the analysis of the dielectric data over a wide frequency spectrum enabled the identification of the most suitable frequencies for the practical operation of the sensor, in terms of linearity and sensitivity. This will enable the development of suitable instrumentation and an improved strategy for the online monitoring and control of a broad range of polymerisation reactions.

Determination of the oxidative stability of olive oil using an integrated system based on dielectric spectroscopy and computer vision

During storage, olive oil may suffer degradation leading to an inferior quality level when purchased and consumed. Oxidative stability is one of the most important parameters for maintaining the quality of olive oil, which affects its acceptability and market value. The current methods of predicting the oxidative stability of edible oils are costly and time-consuming. The aim of the present research is to demonstrate the use of dielectric spectroscopy integrated with computer vision for determining the oxidative stability index (OSI) of olive oil. The most effective features were selected from the extracted dielectric and visual features for each olive oil sample. Three machine learning techniques were employed to process the raw data to develop an oxidative stability prediction algorithm, including artificial neural network (ANN), support vector machine (SVM) and multiple linear regression (MLR). The predictive models showed a great agreement with the results obtained by the Rancimat instrument that was used as a reference method. The best result for modelling the oxidative stability of olive oil was obtained using SVM technique with the R-value of 0.979. It can be concluded that this new approach may be utilized as a perfect replacement for quicker and cheaper assessment of olive oil oxidation.

Investigation of the interfacial interactions in epoxy nano-composites filled with functionalized graphene based fillers

ABSTRACTThis work discusses the investigation of filler-matrix interfacial interactions in epoxy matrices filled with different loadings of graphene based fillers – graphene oxide (GO) and n-butylamine functionalized graphene oxide (GO-ButA). To probe whether the matrix cure reactivity has any influence on these interactions, two different curing agents have been used – a polyetheramine based and an aliphatic amine based to process the nano-composites. Interfacial interactions have been extensively investigated using rheology, DMA and fractographic analysis. As a complementary technique for a better understanding of these interactions, the use of dielectric spectroscopy has been explored. Rheology and dielectric spectroscopy confirm the fillers’ participation in the cure reaction. DMA and fractography show strong interfacial interaction signatures in the slow curing polyetheramine epoxies. The fast curing aliphatic amine epoxies are found to be less amenable in promoting these interactions. However, the filler dispersion quality is observed to be fairly impervious to the curing agent used. Besides surface functionalities of the fillers, the interfacial interactions are seen to be influenced by factors like cure reactivity of epoxy matrices too. Interestingly the thermal stability of the nano-composites is found to be influenced cumulatively by the interfacial interactions and the thermal stability of the fillers.

Development of a non-destructive detection system of Deep Pectoral Myopathy in poultry by dielectric spectroscopy

The trend in meat consumption has changed drastically in the last years, mainly due to the relationship of red and processed meats with cancer and cardiovascular diseases, which has caused a substantial growth in poultry meat consumption, 8% in 2016. Therefore, poultry production has suffered an intensification that has led to an increase in the incidence of internal malformations in chickens and turkeys for fattening, especially in the pectoral muscles, as Deep Pectoral Myopathy (DPM). Currently, industry is not able to detect DPM breasts when sold as whole carcasses. In this context, the use of dielectric spectroscopy, complemented by a deep study of the chemical, biochemical and microstructural transformations of the muscle and the effect that these changes have on the electrical dispersions in radiofrequency range, may become feasible for online DPM detection. For this paper, non-damaged and affected by DPM chicken breasts (pectoralis major and pectoralis minor) was analysed. Permittivity in radiofrequency and microwave ranges were measured in the different tissues: pectoralis minor, major and skin in order to characterize them. Moreover, proteins content, ion content and pH were measured. With this data, a sensor for measuring the permittivity of chicken whole carcass with skin was developed; it consists of two pairs of two flat plates sensor connected to an impedance Agilent analyzer 4294A and can measure the permittivity from 40 Hz to 1 MHz. The results demonstrated the feasibility of the permittivity in radiofrequency range as an potential identification technique of chicken breasts affected by DPM.

Study of polymeric nanocomposites prepared by inserting graphene and / or Ag, Au and ZnO nanoparticles in a TEGDA polymer matrix, by means of the use of dielectric spectroscopy

Polymeric nanocomposites were prepared by inserting graphene and/or Ag, Au and ZnO nanoparticles in a TEGDA (tetraethyleneglycol diacrylate) polymer matrix. The polymeric films were characterized in terms of their dielectric properties by electrochemical impedance spectroscopy. The impedance data were fitted by generalized relaxation functions in order to determine conductivity, dielectric response and molecular relaxation time of the nanocomposite films. In particular, a stretched exponential function, Kohlrausch-Williams-Watts function (KWW), was used to investigate polymer/graphene/metal nanocomposites.

On the use of dielectric spectroscopy for the real time assessment of the dispersion of carbon nanotubes in epoxy

We report the on line monitoring of the dispersion of carbon nanotubes in a typical aerospace epoxy system via dielectric spectroscopy.

Process analytical technology tools for perfusion cell culture

During cell cultivation processes for the production of biopharmaceuticals, good process performance and good product quality can be ensured by online monitoring of critical process parameters (e.g. temperature, pH, or dissolved oxygen). These data can be used in real‐time for process control, as suggested by the process analytical technology (PAT) initiative. Today, solutions for real‐time monitoring of parameters such as concentrations of cells, main nutrients, and metabolism by‐products are developing, but applications of these more complex tools in industrial settings are still limited. Here, we evaluated the use of dielectric spectroscopy (DS) and near‐infrared spectroscopy (NIRS) as PAT tools for a perfusion PER.C6® cultivation process. We showed that DS enabled predictions of viable cell density from the cultivation vessel, with a root mean square error of prediction (RMSEP) of 4.4% of the calibration range. Additionally, predictions of glucose and lactate concentrations from the cultivation vessel (RMSEP of 10 and 14%, respectively) and from the perfusion stream (RMSEP of 12 and 10%, respectively) were achieved with NIRS. We also showed that the perfusion stream offers great opportunities for noninvasive, yet frequent process monitoring. Accurate online monitoring of critical process parameters with PAT tools is the essential first step toward increased control of process output.

Water and ion transport in ultra-adsorbing porous magnesium carbonate studied by dielectric spectroscopy

Porous materials are used in application areas ranging from drug and vaccine delivery, medical implants, molecular sieves and cosmetics to catalysis and humidity control. In the present work, we employed an alternative approach to gain in-depth understanding about water interaction properties in such materials by the use of dielectric spectroscopy and thereby show that it is possible to obtain information that is not accessible from the more commonly employed water interaction analysis techniques. Specifically, the complex dielectric response of Upsalite, a novel, super-hydroscopic, high-surface area, porous magnesium carbonate material was measured in isothermal frequency scans between 10−3 and 106 Hz at controlled relative humidity (RH). We found the dielectric constant of the dry material to be 1.82. The ratio of bound to free water present in Upsalite after adsorption at room temperature was found to be high irrespective of the surrounding humidity with values ranging from ∼67% to ∼90%. We further found that OH− ions are the charge carriers responsible for the electrode polarization observed in the dielectric response and that the amount of these ions that are free to move in the material corresponds to a concentration of the order of 1–10 μmol l−1 independent of RH. Finally, the OH− diffusion coefficient displayed a drastic decrease with decreasing RH, typical of transport in unsaturated conditions. The presented results provide detailed insight about water interactions in the novel water adsorbing material under study and it is foreseen that the employed analysis methods can be used to evaluate other types of moisture adsorbing materials as well as the movement of functional species in the pores of inorganic drug delivery materials and materials tailored for adsorption of harmful charged species.