Controlled Measurement Setup for Ultra-Wideband Dielectric Modeling of Muscle Tissue in 20–45 ∘C Temperature Range

In order to design electromagnetic applicators for diagnostic and therapeutic applications, an adequate dielectric tissue model is required. In addition, tissue temperature will heavily influence the dielectric properties and the dielectric model should, thus, be extended to incorporate this temperature dependence. Thus, this work has a dual purpose. Given the influence of temperature, dehydration, and probe-to-tissue contact pressure on dielectric measurements, this work will initially present the first setup to actively control and monitor the temperature of the sample, the dehydration rate of the investigated sample, and the applied probe-to-tissue contact pressure. Secondly, this work measured the dielectric properties of porcine muscle in the 0.5–40 GHz frequency range for temperatures from 20 ∘C to 45 ∘C. Following measurements, a single-pole Cole–Cole model is presented, in which the five Cole–Cole parameters (ϵ∞, σs, Δϵ, τ, and α) are given by a first order polynomial as function of tissue temperature. The dielectric model closely agrees with the limited dielectric models known in literature for muscle tissue at 37 ∘C, which makes it suited for the design of in vivo applicators. Furthermore, the dielectric data at 41–45 ∘C is of great importance for the design of hyperthermia applicators.

ABOUT THE PARAMETERS OF THE DIELECTRIC MODEL OF SOILS USED IN THE SMOS ALGORITHM

The features of the four-component refractive dielectric model of moist soils are considered. Typical values of the parameters of the Debye model of bound water obtained by processing experimental data using this model are given. The reasons why the parameters of the Debye model of free soil water in this model differ from the true values of these parameters are explained. It is shown that the excess of the static permeability and specific conductivity values relative to the true values is caused by the Maxwell – Wagner relaxation process with a relaxation time of sev-eral nanoseconds.

Application of Fractional Calculus to Modeling the Non-Linear Behaviors of Ferroelectric Polymer Composites: Viscoelasticity and Dielectricity

Ferroelectric polymer composites normally show non-linear mechanical and electrical behaviors due to the viscoelastic and dielectric relaxation of polymer matrixes. In this paper, a fractional calculus approach is used to describe the non-linear behavior of ferroelectric polymer composites from both viscoelastic and dielectric perspectives. The fractional elements for viscoelasticity and dielectricity are “spring-pot” and “cap-resistor”, which can capture the intermediate properties between spring and dashpot or capacitor and resistor, respectively. For modeling the viscoelastic deformation, the “spring-pot” equation is directly used as the fractional mechanical model. By contrast, for the dielectricity of ferroelectric polymer composites, which is usually characterized by dielectric constants and dielectric losses, the “cap-resistor” equation is further formulated into the frequency domain by Fourier transform to obtain the fractional order dielectric model. The comparisons with experimental results suggest that the proposed models can well describe the viscoelastic deformation as well as the frequency dependence of the dielectric constant and dielectric loss of ferroelectric polymer composites. It is noted that the fractional order dielectric model needs to be separated into two regions at low and high frequencies due to the polarization effect. Additionally, when the dipole relaxations occur at higher frequencies, the proposed model cannot describe the rise of the dielectric loss curve.

Experimental Study on the Dielectric Model of Common Asphalt Pavement Surface Materials Based on the L-R Model

The establishment of a dielectric model of the asphalt pavement surface material is the premise and key to applying the electromagnetic wave technology to asphalt pavement nondestructive testing. Asphalt pavement can be made of different materials, including various types of asphalt mixtures. Therefore, in order to study and analyze the dielectric properties of different types of asphalt mixtures and establish a dielectric model of the asphalt pavement surface material, this paper studies four types of asphalt mixtures commonly used in the asphalt pavement surface course. Based on the comparative analysis of three classical models, the complex refractive index method (CRIM), Brown, and Looyenga; based on the L-R model, the linear regression analysis was conducted on the test data. The dielectric models which are suitable for the interpretation of four types of asphalt mixtures were established, and the dielectric model database of asphalt pavement surface materials was extended, which provides theoretical and technical support for nondestructive testing of the asphalt pavement.

Mechanism Analysis of Dynamic On-State Resistance Degradation for a Commercial GaN HEMT Using Double Pulse Test

The dynamic on-resistance (RON) behavior of one commercial GaN HEMT device with p-GaN gate is investigated under hard-switching conditions. The non-monotonic performance of dynamic RON with off-state voltage ranging from 50 to 400 V is ascribed to the “leaky dielectric” model. The highest normalized RON value of 1.22 appears at 150 and 200 V. The gradual increase and following maximum of dynamic RON are found when the device is exposed to a stress voltage for an extended stress time under 100 and 200 V, which is due to a much longer trapping time compared to detrapping time related to deep acceptors and donors. No obvious RON degradation, thanks to the suppressed trapping effect, is observed at higher VDS. From the multi-pulse test, the dynamic RON is seen to be insensitive to the frequency. It is demonstrated that the leakage, especially under source and drain contact, is a key issue in the dynamic resistance degradation.

Numerical Analysis on the Stability Conditions of an Electrohydrodynamic Jet

The Taylor cone jet is a well-known electrohydrodynamic flow (EHD), usually produced by applying an external electric field to a capillary liquid. The generation of this kind of flow involves a multi-phase and a multi-physics process and its stability has a specific operation window. This operating window is intrinsically dependent on the flow rate and magnitude of the applied electric voltage. In case high voltages are applied to the jet it can atomize and produce an electrospray. Our work presents a numerical study of the process of atomization of a Taylor cone jet using computational fluid dynamics (CFD). The study intents to assess the limit conditions of operation and the applied voltage needed to stabilize an electrospray. The numerical model was implemented within OpenFOAM, where the multi-phase hydrodynamics equations are solved using a volume-of-fluid (VOF) approach. This method is coupled with the Maxwell equations governing an electrostatic field, in order to incorporate the electric body forces into the incompressible Navier-Stokes equations. The leaky-dielectric model is used and, therefore, the interface between the two phases is subject to the hydrodynamic surface tension and electric stress (Maxwell stress). This allows a leakage of charge though the phase due to ohmic conduction. Thus, the permittivity and conductivity of the phases are taken into consideration. A two-fluid system with relevant electric properties can be categorized as, dielectric-dielectric, dielectric-conducting, and conducting-conducting considering the electrical conductivity and permittivities of the participating phases. Due to the usage of the leaky-dielectric model, it is possible to simulate any of this physical situations. By increasing the applied voltage reaches a value where the cone instability is verified, allowing a discussion on this effect. It is demonstrated that to adequately model the process of atomization a fine grid refinement is needed. The validation of the numerical model is made by comparing against diverse experimental data, for the case of a stable jet. The diameter and velocity of the droplet and the electric current of the jet are the main variables that are compared with previous results. The tests were performed with Heptane. The cone and the jet are strongly affected by the flow rate. The dimensionless diameter, as a function of the dimensionless flow rate, agrees with the scaling laws. The model predicts accurate results over a wide range of flow rates with an accuracy of around 10%. The results are obtained using structured meshes.

Dielectric Model of Carbon Nanofiber Reinforced Concrete

The formula describing the relationship between the dielectric constant of a composite and the dielectric constants or volume rates of its components is called a dielectric model. The establishment of a cement concrete dielectric model is the basic and key technique for applying electromagnetic wave technology to concrete structure quality testing and internal damage detection. To construct the dielectric model of carbon nanofiber reinforced concrete, the carbon nanofiber reinforced concrete was measured by the transmission and reflection method for dielectric constant ε, and ε,, in the frequency range of 1.7~2.6 GHz as the fiber content was 0, 0.1%, 0.2%, 0.3% and 0.5%. Meanwhile, concrete was considered as a composite material composed of three phases, matrix (mortar), coarse aggregate (limestone gravel) and air, and the dielectric constants and volume rates of each component phase were tested. The Brown model, CRIM (Complex Refractive Index Model) model and Looyenga model commonly used in composite materials were modified based on the experimental data, suitable dielectric models of carbon nanofiber reinforced concrete were constructed, and a reliability check and error analysis of the modified models were carried out. The results showed that the goodness of fit between the calculated curves based on the three modified models and the measured curves was very high, the accuracy and applicability were very strong and the variation rule for the dielectric constant of carbon nanofiber concrete with the frequency of electromagnetic wave could be described accurately. For ε, and ε,,, the error between the dielectric constant calculated by the three modified models and the corresponding measured values was very small. For the dielectric constant ε,, the average error was maintained below 1.2%, and the minimum error was only 0.35%; for the dielectric constant ε,,, the average error was maintained below 3.55%.