Permittivity Of Liquids Research Articles

Nonlocal electrostatics in ionic liquids: The key to an understanding of the screening decay length and screened interactions.

Screened electrostatic interactions in ionic liquids are investigated by means of exact statistical mechanical analysis combined with physical arguments that enhance the transparency and conceptual accessibility of the analysis and results. The constituent ions and immersed particles in the liquid can have arbitrary shapes and any internal charge distributions. The decay of the screened electrostatic potential and the free energy of interaction in ionic liquids can be exponentially damped oscillatory (like in molten simple salts) as well as plain exponential and long-ranged (like in dilute electrolyte solutions). Both behaviors are in agreement with the exact statistical mechanical analysis and reasons for their appearances are investigated. Exact but surprisingly simple expressions for the decay parameter κ of the screened electrostatics are obtained, which replace the classical expression for the Debye-Hückel parameter κDH (the reciprocal Debye length). The expressions are applicable both for cases with plain exponential and oscillatory behaviors. The key importance of nonlocal electrostatics is thereby demonstrated explicitly. Dielectric properties of ionic liquids and other electrolytes are investigated, in particular the static dielectric function ϵ̃(k) and some effective relative permittivities (Ereff and Er∗), which take roles that the dielectric constant εr has for polar liquids consisting of electroneutral molecules. The dielectric constant in the latter case, which is the limit of ϵ̃(k) when the wave number k → 0, can be expressed solely in terms of dipolar features of the molecules. In contrast to this, the effective dielectric permittivities of ionic liquids have contributions also from quadrupolar, octupolar, and higher multipolar features of the constituent ions. The "dielectric constant" of electrolytes does not exist since ϵ̃(k)→∞ when k → 0, a well-known effect of perfect screening. The effective relative permittivities, Ereff, and Er∗ of ionic liquids are obtained from the non-diverging part of ϵ̃(k), but not as a k → 0 limit. Influences of ion associations, especially pairing, are investigated for screened electrostatics and these permittivities. A general, multipolar expansion of ϵ̃(k) is derived and used to analyze dielectric properties of ionic liquids and other electrolytes.

On optimization of absorption–dispersion spectra

A modified approach to the analysis of spectra of the complex electric permittivity of liquids in the Infrared region is presented. These spectra are derived from experimental spectra of the complex refractive index. Subsequently they are used to determine important secondary quantities, e.g. spectra of complex molecular polarizabilities and an integral property – the molar vibrational polarization. The accuracy of these quantities depends essentially on the accuracy of both components of the complex electric permittivity spectrum.In the proposed procedure, the spectra of the complex electric permittivity are approximated using the Classical Damped Harmonic Oscillator (CDHO) model for the description of individual bandshapes. The CDHO model defines both the real and imaginary part of the complex permittivity. The fitting procedure includes a simultaneous optimization of both the real and imaginary parts of the complex permittivity spectrum. A comparison of absorption-only curve fitting and the novel absorption-dispersion double curve fitting is presented; advantages of the new approach in accuracy, reliability and convergence time are pointed out.Due to the complexity of the problem, the choice was restricted to non-gradient methods of optimization. The performance of several gradientless algorithms was tested. Among numerous procedures the Powell General Least Squares Method Without Derivatives was found to be the most efficient. The reliability of obtained results of the band separatiovn process was tested on several simulated spectra of increasing complexity.The applicability of the developed approach to the analysis of exemplary experimental data was evaluated and discussed.

Electrostatic Micro-Hydraulic Systems

MEMS micro-hydraulic structures for amplification of force or deflection are introduced. These structures are integrated with capacitances to form electrostatic micro-hydraulic actuators (EMA). Hydraulic amplification and liquid permittivity are used to create stand-alone, efficient, and large deflection, and high force actuators. Force is generated using electrostatics with no need for external pressure sources. Use of integrated electrostatic force significantly reduces the device size. Utilizing this concept, a micro-valve and two types of EMA micro-piston arrays (water-based and silicone oil-based) are fabricated and tested. The micro-valve can switch fluid flows with the pressure ranging from 10 to 50 kPa at a maximum flow conductance of 20.3 sccm at 10 kPa with an actuation voltage of 340 $V_{\mathrm{ DC}}$ or 120 $V_{\mathrm{ AC}}$ . The silicone oil based micro-hydraulic micro-piston array has shown a maximum out-of-plane deflection of about 100 $\mu \text{m}$ at 210 $V_{\mathrm{ DC}}$ , and a maximum bandwidth of about 5 Hz with a foot print size of 0.16 cm2 and a maximum power consumption of 20 $\mu \text{W}$ at 1 Hz. These devices are the smallest ever reported micro-hydraulic systems that include the actuation source. [2015–0257]

A spherical cavity model for quadrupolar dielectrics

The dielectric properties of a fluid composed of molecules possessing both dipole and quadrupole moments are studied based on a model of the Onsager type (molecule in the centre of a spherical cavity). The dielectric permittivity ε and the macroscopic quadrupole polarizability αQ of the fluid are related to the basic molecular characteristics (molecular dipole, polarizability, quadrupole, quadrupolarizability). The effect of αQ is to increase the reaction field, to bring forth reaction field gradient, to decrease the cavity field, and to bring forth cavity field gradient. The effects from the quadrupole terms are significant in the case of small cavity size in a non-polar liquid. The quadrupoles in the medium are shown to have a small but measurable effect on the dielectric permittivity of several liquids (Ar, Kr, Xe, CH4, N2, CO2, CS2, C6H6, H2O, CH3OH). The theory is used to calculate the macroscopic quadrupolarizabilities of these fluids as functions of pressure and temperature. The cavity radii are also determined for these liquids, and it is shown that they are functions of density only. This extension of Onsager's theory will be important for non-polar solutions (fuel, crude oil, liquid CO2), especially at increased pressures.

Three-Dimensional Numerical Simulation of Bubble Dynamics in Microgravity under the Influence of Nonuniform Electric Fields

A three-dimensional VOSET method is used along with the adaptive mesh refinement (AMR) method to simulate the behaviors of a bubble departing from the outside wall of a horizontal square-cross-section tube in microgravity under the influence of nonuniform electric fields. The effects of gravity, electric field intensity, fluid permittivity, and bubble initial position on the bubble detachment and rising are investigated and analyzed. Computational results show that the gravity and electric fields have significant influences on the bubble detachment and rising velocity and rising trajectory. Decrease in gravity results in the decrease in the buoyancy exerted on the bubble, considerably mitigating the rising capability of the bubble and delaying the bubble detachment. Imposing a nonuniform electric field, which exhibits physically the strongest intensity in regions near the tube wall, can supply an additional driving force as a replacement of the buoyancy to accelerate the bubble detachment and rising. It is also shown that a larger electric field intensity or larger ratio of liquid permittivity to gas permittivity leads to a larger deformation, easier detachment, and larger rising velocity, of the bubble. The nonuniformity of the electric fields can also affect the bubble motion trajectory and result in the asymmetric deformation of the bubble.

Complex Permittivity of Water-Based Liquids for Liquid Antennas

Liquid antennas have attracted increasing attention recently. In this letter, a promising candidate for liquid antennas, namely water with propylene glycol (PG), is investigated using both measurement and numerical simulation approaches. The nonlinear least-squares fitting routines are employed to derive new formulas for the approximation of the complex permittivity of the liquid. The permittivity of this liquid at various temperatures and substance concentration levels are investigated. The results are obtained and compared to the measurement. Good agreements are obtained, and new comprehensive knowledge is gained. In particular, the permittivity of water with PG at various conditions is reported for the first time. These results should be very useful for a range of applications such as liquid antenna designs.

A Novel Technology for Measurements of Dielectric Properties of Extremely Small Volumes of Liquids

A high sensitivity sensor for measurement radio frequency (RF) dielectric permittivity of liquids is described. Interference is used and parasitic effects are cancellation, which makes the sensor can catch weak signals caused by liquids with extremely small volumes. In addition, we present the relationship between transmission coefficient and permittivity of liquids under test (LUT). Using this sensor, quantitative measurements of the dielectric properties at 5.8 GHz are demonstrated of LUTs. Experiments show that the proposed method only requires the volume of 160 nanoliters for liquids. Therefore, the technology can be used for RF spectroscopic analysis of biological samples and extremely precious liquids.

Open-Ended Coaxial Dielectric Probe Effective Penetration Depth Determination.

We have performed a series of experiments which demonstrate the effect of open-ended coaxial diameter on the depth of penetration. We used a two layer configuration of a liquid and movable cylindrical piece of either Teflon or acrylic. The technique accurately demonstrates the depth in a sample for which a given probe diameter provides a reasonable measure of the bulk dielectric properties for a heterogeneous volume. In addition we have developed a technique for determining the effective depth for a given probe diameter size. Using a set of simulations mimicking four 50 Ω coaxial cable diameters, we demonstrate that the penetration depth in both water and saline has a clear dependence on probe diameter but is remarkably uniform over frequency and with respect to the intervening liquid permittivity. Two different 50 Ω commercial probes were similarly tested and confirm these observations. This result has significant implications to a range of dielectric measurements, most notably in the area of tissue property studies.

An SIW Resonator Sensor for Liquid Permittivity Measurements at C Band

This letter presents a novel substrate integrated waveguide (SIW) resonator sensor that is specifically designed to measure the complex permittivity of liquids. The resonant characteristics of the sensor are influenced by liquids through a slot opened on the top plane. The inverse problem of obtaining permittivity is solved with artificial neural network. Experiments were performed with an SIW resonator sensor designed at C band. Experimental data were reported and they agreed well to the reference values. The sensor is simple and low cost, which may be applied to permittivity measurements in applications at the industrial, scientific and medical (ISM) frequencies.

Electromagnetic properties of water on GHz frequencies for medicine tasks and metamaterial applications

In problems of modern radio physics and medicine it is important to know dielectric permittivity of liquids. Dispersion characteristics of water in UHF frequency band can be used to analyze the states of biological objects, and also to construct materials (metamanerials). The present work is intended to study the material properties of water in UHF frequency band based on two different techniques: Nicolson-Ross-Weir (NRW) [1] and the Active Nearfield Diagnostics [2].

A Practically Validated Adaptive Calibration Technique using Optimized Artificial Neural Network for Level Measurement by Capacitance Level Sensor

Design of an adaptive calibration technique using an optimized artificial neural network for liquid-level measurement is discussed in this paper. The objective of the present work is to design and validate an adaptive calibration technique so as (1) to extend the linearity range of measurement to 100% of full-scale input range and (2) to make the measurement technique adaptive of variations in tank diameter, permittivity of liquid, liquid temperature, and to achieve objectives (1) and (2) using an optimized neural network. An optimized artificial neural network is a network having least possible number of hidden layers to achieve minimum mean square error between outputs and targets by comparing various algorithms, schemes, and transfer functions of neuron. The output of capacitance level sensor is capacitance. A data conversion unit is used to convert it to voltage. A suitable optimized artificial neural network is designed and used in place of conventional calibration circuit. The proposed technique is tested with simulated data and validated with practical data. Results show that proposed technique has fulfilled the set objectives.

Dielectric anisotropy in polar solvents under external fields

We investigate dielectric saturation and increment in polar liquids under external fields. We couple a previously introduced dipolar solvent model to a uniform electric field and derive the electrostatic kernel of interacting dipoles. This procedure allows an unambiguous definition of the liquid dielectric permittivity embodying non-linear dielectric response and correlation effects. We find that the presence of the external field results in a dielectric anisotropy characterized by a two-component dielectric permittivity tensor. The increase of the electric field amplifies the permittivity component parallel to the field direction, i.e. dielectric increment is observed along the field. However, the perpendicular component is lowered below the physiological permittivity , indicating dielectric saturation perpendicular to the field. By comparison with Molecular Dynamics simulations from the literature, we show that the mean-field level dielectric response theory underestimates dielectric saturation. The inclusion of dipolar correlations at the weak-coupling level intensify the mean-field level dielectric saturation and improves the agreement with simulation data at weak electric fields. The correlation-corrected theory predicts as well the presence of a metastable configuration corresponding to the antiparallel alignment of dipoles with the field. This prediction can be verified by solvent-explicit simulations where solvent molecules are expected to be trapped transiently in this metastable state.

Calibrated Layer-Stripping Technique for Level and Permittivity Measurement With UWB Radar in Metallic Tanks

A method to measure liquid level and electrical properties based on ultra-wideband pulsed radar is developed in this paper. Current methods of material property measurement using free-space radar typically use computationally intensive frequency-domain analysis or finite time-domain methods. The method presented is modified from layer-stripping algorithms and includes several improvements over previous techniques, such as an antenna array that allows measurement in a metallic tank environment and a method of calibration that characterizes path-loss and near-field effects for accurate amplitude-distance prediction. The method presented here also estimates the material loss properties and uses accumulated power with noise compensation to predict reflected pulse power. The method extends the use of pulsed radar for liquid-level measurement in tanks to the evaluation of liquid permittivity and the estimation of liquid height in liquids consisting of multiple layers. The accuracy of the presented method is evaluated using a transmitting single antenna element, a four-element antenna array, and an eight-element antenna array for measurement in a metallic tank environment. Accuracy is improved with larger antenna arrays, but the calibration becomes more critical. The accuracy for varying layer heights and materials is investigated to demonstrate the method reliability.

Whispering-Gallery-Mode Resonator Technique With Microfluidic Channel for Permittivity Measurement of Liquids

Studies of biochemical liquids require precise determination of their complex permittivity. We developed a microwave characterization technique on the basis of a high-quality whispering-gallery mode (WGM) sapphire resonator with a microfluidic channel filled with the liquid under test. A novel approach allows obtaining the complex permittivity of biochemical liquids of sub-microliter/nanoliter volumes with high accuracy. The method is based on special procedure of analysis of the interaction of electromagnetic field with liquid in WGM microfluidic resonator and measurements of both the WGM resonance frequency shift and the change of the inverse quality factor. The approach is successfully applied to obtain the complex permittivity in the Ka band of glucose, albumin bovine serum, lactalbumin and cytochrome C aqueous solutions using the developed microwave technique.

An Accurate Radially Stratified Approach for Determining the Complex Permittivity of Liquids in a Cylindrical Microwave Cavity

A complex permittivity measurement method is introduced that is applicable to radially stratified resonant microwave cavities excited by a TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0m0</sub> eigenmode. This single-frequency approach is well suited to the measurement of the complex permittivity of liquids because it can accurately account for a supporting tube container. It can also be applied advantageously to solid rods or tubes. The frequency dependence, as well as the field configuration at the cavity walls are taken into account more accurately than in other approaches. Comparing our results with published measurements of well-known liquids validates this technique.

Calibration-independent measurement of complex permittivity of liquids using a coaxial transmission line.

In recent years, several calibration-independent transmission/reflection methods have been developed to determine the complex permittivity of liquid materials. However, these methods experience their own respective defects, such as the requirement of multi measurement cells, or the presence of air gap effect. To eliminate these drawbacks, a fast calibration-independent method is proposed in this paper. There are two main advantages of the present method over those in the literature. First, only one measurement cell is required. The cell is measured when it is empty and when it is filled with liquid. This avoids the air gap effect in the approach, in which the structure with two reference ports connected with each other is needed to be measured. Second, it eliminates the effects of uncalibrated coaxial cables, adaptors, and plug sections; systematic errors caused by the experimental setup are avoided by the wave cascading matrix manipulations. Using this method, three dielectric reference liquids, i.e., ethanol, ethanediol, and pure water, and low-loss transformer oil are measured over a wide frequency range to validate the proposed method. Their accuracy is assessed by comparing the results with those obtained from the other well known techniques. It is demonstrated that this proposed method can be used as a robust approach for fast complex permittivity determination of liquid materials.

Wireless Sensing of Complex Dielectric Permittivity of Liquids Based on the RFID

A wireless sensing system for the evaluation of the complex dielectric permittivity of solvent liquids is presented. Two sensing tags are proposed for testing of the samples. The first tag is based on a cavity resonator and the second makes use of the epsilon-near-zero effect. Both circuits are designed over the planar substrate-integrated-waveguide (SIW) technology, and operate at 4 GHz. A quartz capillary tube is used for the liquid measurements where only a small amount of sample volume is required. With the addition of planar antennas at the input and output of the sensors, the complete system is implemented for wireless sensing of the materials following the RF identification scheme. The cavity perturbation technique for SIW structures is applied for the dielectric liquid characterization. The proposed sensing tags and system have high potentials for low-cost wireless measurements and real-time monitoring applications.

Detection of Hazardous Liquids Using Microwaves.

We investigate the feasibility of using dielectric spectra to classify hazardous and nonhazardous liquids. The dielectric spectra of several liquids was obtained with a shielded-open coaxial fixture, and we present a new full-wave model for calculating the complex permittivity of liquids using this fixture. Using the measured complex permittivity for each liquid, we examine several classification methods for distinguishing between the hazardous and nonhazardous liquids and report on the error rates of each method.

Effects of Oxygen-Containing Functional Groups on Supercapacitor Performance

Molecular dynamics (MD) simulations of the interface between graphene and the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM OTf) were carried out to gain molecular-level insights into the performance of graphene-based supercapacitors and, in particular, determine the effects of the presence of oxygen-containing defects at the graphene surface on their integral capacitance. The MD simulations predict that increasing the surface coverage of hydroxyl groups negatively affects the integral capacitance, whereas the effect of the presence of epoxy groups is much less significant. The calculated variations in capacitance are found to be directly correlated to the interfacial structure. Indeed, hydrogen bonding between hydroxyl groups and SO3 moieties prevents BMIM(+) and OTf(-) ions from interacting favorably in the interfacial layer and restrains the orientation and mobility of OTf(-) ions, thereby reducing the interfacial permittivity of the ionic liquid. The results of the simulations can facilitate the rational design of electrode materials for supercapacitors.

Mesure de la permittivité complexe de liquides de référence pour la détermination du débit d’absorption spécifique (DAS)

This paper presents our work for the measurement of the complex permittivity of liquids, carried out in the framework of a European Metrology research project entitled “Traceable measurement of field strength and SAR for the Physical Agents Directive”. One of the aims of this project was to establish the traceability of the specific absorption rate measurements to the SI up to 10 GHz. We use a vector network analyser to measure the S 21 parameter of coaxial cells containing the liquid under test (a reference liquid or an equivalent tissue liquid). The method does not require the network analyser to be calibrated in terms of impedance. In fact, only the length of the coaxial cell and the working frequency need to be known.