Equivalent Permittivity Research Articles

Electrical Permittivity and Conductivity of a Graphene Nanoplatelet Contact in the Microwave Range.

This paper investigates the electrical properties in the microwave range of a contact made by graphene nanoplatelets. The final goal is that of estimating the range of values for the equivalent electrical complex permittivity of a contact obtained by integrating low-cost graphene in the form of nanoplatelets (GNPs) into a high-frequency electrical circuit. To this end, a microstrip-like circuit is designed and realized, where the graphene nanoplatelets are self-assembled into a gap between two copper electrodes. An experimental characterization is carried out, both to study the structural properties of the nanomaterials and of the realized devices, and to measure the electromagnetic scattering parameters in the microwave range by means of a microstrip technique. A full-wave electromagnetic model is also derived and used to investigate the relationship between the measured quantities and the physical and geometrical parameters. The combined use of the experimental and simulation results allows for retrieving the values of the equivalent complex permittivity. The equivalent electrical conductivity values are found to be well below the values expected for isolated graphene nanoplatelets. The real part of the electrical relative permittivity attains values comparable to those obtained with GNP nanocomposites.

Study of optical pumping influence on carbon nanotubes permittivity in THz frequency range

Equivalent complex permittivity of carbon nanotubes (CNT) was measured with/without light illumination at the frequency range of 0.2-1 THz. It was shown that we can tune the dispersion of the CNT complex conductivity during varying of optical pumping (wavelength of 980 nm). These results mean that CNT is perspective candidate for development of THz tunable attenuators and phase shifters.

MyDEP: A New Computational Tool for Dielectric Modeling of Particles and Cells

Dielectrophoresis (DEP) and electrorotation (ROT) are two electrokinetic phenomena exploiting nonuniform electric fields to exert a force or torque on biological particles suspended in liquid media. They are widely used in lab-on-chip devices for the manipulation, trapping, separation, and characterization of cells, microorganisms, and other particles. The DEP force and ROT torque depend on the respective polarizabilities of the particle and medium, which in turn depend on their dielectric properties and on the field frequency. In this work, we present a new software, MyDEP, which implements several particle models based on concentric shells with adjustable dielectric properties. This tool enables the study of the variation in DEP and ROT spectra according to different parameters, such as the field frequency and medium conductivity. Such predictions of particle behavior are very useful for choosing appropriate parameters in DEP experiments. The software also enables the study of the homogenized properties of spherical or ellipsoidal multishell particles and provides a database containing published cell properties. Equivalent electrical conductivity and relative permittivity of the cell alone and in suspension can be calculated. The software also offers the ability to create graphs of the evolution of the crossover frequencies with the electric field frequency. These graphs can be directly exported from the software.

Determination of multicomponent media permittivity by high-frequency method

The problem of determining the multicomponent media equivalent permittivity by a high-frequency dielectric method was considered. Analytic calculations of the medium equivalent permittivity by changing the frequency of the measuring high-frequency generator were presented. The variation of the volume ratio measurements results of the mixture components caused by the different components distribution in the volume was determined. The results of an experimental study in laboratory conditions of the dielectric permittivity measurer physical model were presented.

Built-in capacitance sensor for control rod position measurement in NHR-200 with PEEK material

The accurate control rod position measurement is crucial to ensure the reactor safety and reliability. Based on the variations of equivalent electrical permittivity with different control rod positions in NHR-200, the built-in capacitance control rod position measurement system (BCRMS) has been successfully used for the PEEK material control rod guide rod due to its advantages of non-invasion, low-cost, high reliability and non-radiation. And a novel method is proposed to calibrate the built-in capacitance control rod position sensor (BCRS) based on the grating linear displacement measuring probe. The BRCMS was experimentally tested on the horizontal test facilities. In addition, Capacitances obtained by the built electric theoretical model and FEM analysis were compared with experiment results to verify the built models. Meanwhile, measurement resolution of the newly designed BCRMS is as high as ±7.09 mm. Errors caused by the eccentricity and sensor end effects are analyzed to be in the reasonable range. The built models and newly designed BCRMS are proved to be an effective solution to measure the control rod position in NHR-200.

Off-axis core transmission characteristics of helically twisted photonic crystal fibers.

The transmission characteristics of helically twisted photonic crystal fibers (PCFs) having off-axis cores are theoretically investigated for the first time, to the best of our knowledge. Due to the modified equivalent permittivity and permeability tensors induced by helical twisting, the transmission characteristics of helically twisted PCFs depend on the core position. A beam propagation method developed for helically twisted waveguides, which qualitatively and quantitatively explained the reported transmission spectra of helically twisted PCFs, is used for the analysis. The loss is significantly increased for a shorter wavelength side, if the position of the core is far from the rotation axis, due to the coupling to twist-induced cladding modes. On the other hand, for a longer wavelength side, the loss of one of the components of circularly polarized light is increased; namely, input linearly polarized light becomes close to left- or right-circularly polarized light, depending on the rotation direction. These results indicate that helically twisted PCFs with off-axis cores can be used for core-position-dependent polarization controlling devices.

Single mode approach with versatile surface wave phase correction for the extraordinary optical transmission comprehension of 1D period nano-slits arrays

A simple semi-analytical model for the comprehension of the extraordinary optical transmission of a 1D array of periodic subwavelength slit is proposed. In this single mode model, the mono layer of the perforated metal film is considered as a homogeneous medium. Therefore, the electromagnetic response of this structure to a plane wave excitation is equivalent to that of a slab with homogeneous equivalent permittivity. A versatile phase correction is added to this model in order to handle the contribution of surface waves in the EOT phenomenon. The proposed model leads to a cavity-like dispersion relation that allows accurate prediction of the resonance frequencies of the 1D structure.

A Microwave Tomography Strategy for Underwater Imaging via Ground Penetrating Radar

Detection and monitoring of underwater structures is one of the most challenging applicative scenarios for remote sensing diagnostic techniques, among which ground penetrating radar (GPR). With this aim, an imaging strategy belonging to the family of microwave tomographic approaches is proposed herein. This strategy allows the imaging of objects located into a wet sand medium below a freshwater layer and it can find application in investigation of lakes, rivers, and hydraulic structures. The proposed strategy accounts for the layered structure of the scenario under test by exploiting a spatially variable equivalent permittivity in the inverse scattering model. This allows a reliable reconstruction of depth and horizontal size of underwater hidden objects. The imaging capabilities of the strategy are verified by processing experimental data referred to a laboratory environment reproducing a submerged archeological site at scale 1:1. The results are compared with those obtained by modelling the reference scenario as a homogeneous medium, in order to verify the effective improvement in terms of reconstruction accuracy.

A novel L-band slow wave structure for compact and high-efficiency relativistic Cerenkov oscillator

A novel L-band slow wave structure (SWS) for compact and high-efficiency relativistic Cerenkov oscillator is proposed. The SWS is composed of orthogonal array of two all-metal metamaterial units. Since the metamaterial used for constructing the SWS has a negative equivalent permittivity and permeability, the fundamental mode of the SWS has a negative dispersion and can work below cutoff frequency of circular waveguide with the same size, indicating that the structure has advantage of miniaturization. Analysis of high-frequency characteristics shows that interaction impedance of the fundamental mode (quasi TM01 mode) is greater than 70 Ω across operating frequency band, which indicates that this structure is expected to achieve the high efficiency of high power microwave sources. By adopting an orthogonal arrangement between metamaterial resonant units, the angular uniformity of electric field in SWS space is significantly improved, and the non-uniformity of electric field due to asymmetry of the metamaterial units is reduced. In addition, an L-band relativistic Cerenkov oscillator is constructed using this metamaterial SWS. In the acceleration voltage U = 550 kV, beam current I = 1.5 kA, and axial uniform magnetic field B = 1.5 T conditions, preliminary particle simulations show that the Cerenkov oscillator obtains a 240 MW average power at 1.405 GHz, with an efficiency of 29.1%, and axial length around one λ. This Cerenkov oscillator obtains a high power and efficiency in a miniature and compact microwave device.

Control rod position measurement with helix-electrode capacitance sensor in nuclear heating reactor

Capacitance sensors are frequently applied for dielectric objects measurements. However, the study on the ungrounded/grounded control rod position measurements with capacitance sensor is limited. In this connection, a system based on the helix-electrode capacitance sensor is applied to measure the rod position in NHR. Based on the variations of equivalent electrical permittivity with different control rod positions in NHR, the helix-electrode capacitance sensor has been successfully used for the ungrounded/grounded control rod position measurement due to its advantages of non-invasion, low-cost, high reliability and non-radiation. The finite element method is used to calculate the sensor capacitance and the sensor sensitivity is also presented. Then, the ungrounded/grounded control rod position experiment is carried out to measure the response of the helix-electrode capacitance sensor, in which a novel method is proposed to calibrate the helix-electrode capacitance sensor based on the grating linear displacement measuring probe. The capacitances obtained by simulations were compared with experiment results to verify the proposed models. The subsequent quantitative analyses on the data indicate the reliability and accuracy of the apparatus for monitoring control rod position. It is demonstrated that such a system shows promising applications for measurements of the control rod position in NHR.

Improvements of Interfacial and Electrical Properties for Ge MOS Capacitor with LaTaON Gate Dielectric by Optimizing Ta Content**Supported by the National Natural Science Foundation of China under Grant No 61274112.

The interfacial and electrical properties of high-k LaTaON gate dielectric Ge metal-oxide-semiconductor (MOS) capacitors with different tantalum (Ta) contents are investigated. Experimental results show that the Ge MOS capacitors with a Ta content of ∼30% exhibit the best interfacial and electrical properties, including low interface-state density (7.6 × 1011 cm−2 eV−1), small gate-leakage current (8.32 × 10−5 A/cm2) and large equivalent permittivity (22.46). The x-ray photoelectron spectroscopy results confirm that the least GeOx is formed at the Ge surface for the sample with a Ta content of ∼30% due to the effective blocking role of Ta against O diffusion and the greatly improved hygroscopicity of LaON.

Tuning rectangular microstrip antenna through scan and zoom algorithm

Microstrip antennas have been widely studied and can be applied to a large number of wide frequency domain in wireless communication. Microstrip antennas are featured with light weight, small volume, and low cost advantages. Planar or spatial structures could substantially affect the frequency reliability and sidelobe level of microstrip antennas. Designing high performance microstrip antennas requires the tuning of the length and width of microstrip patch, the equivalent permittivity, the feed position of the coaxial line, and so on. Although electromagnetic theory could provide a solution for antenna design, such solution is probably not optimal solution due to complex environment and the affection of multiple factors. This paper attempts to tuning the design of microstrip antennas by using scan and zoom algorithm. It does not require derivative information of antenna model. This algorithm consists of search space scan and search domain zoom stages. The effectiveness of the scan and zoom algorithm is firstly tested on mathematical functions. The algorithm is then verified on rectangular microstrip antenna design. Compared with theoretical solution, the novel algorithm attains better design solution. The algorithm can also be easily extended to tackle other antenna design problems.

Monodomain NiCuZn Ferrite With High Miniaturization Factor and Low Magnetic Loss at 200 MHz for Antenna Miniaturization

Monodomain NiCuZn ferrites were investigated for use in the design of a high-efficiency terrestrial digital multimedia broadcasting antenna with reduced physical dimensions. The results show that the reported monodomain design is effective. Specifically, monodomain ferrite with 1 wt% Co2O3 doping has a high miniaturization factor (~14) and very low loss factors (tan $\delta _{{\mu }} = 0.017$ and tan $\delta _{{\varepsilon }} = 0.012$ , respectively). It also reveals equivalent permeability and permittivity ( $\mu ^\prime = 14.05$ and $\varepsilon ^\prime = 14.12$ , respectively) at the frequency of 200 MHz, implicating the convenient impendence match in the antenna application and consequent miniaturization. The magnetic spectra of the monodomain samples were studied with a numerical fitting method to obtain guidelines for preparing high-quality materials. The results indicate that it is necessary to lower relaxation frequency $\omega _{{{\text{r}}}}$ and maintain the other dispersion parameters as moderate to achieve a high real part of permeability and low tan $\delta _{{\mu }}$ . Furthermore, we demonstrate that appropriate Co2O3 doping is a feasible way to adjust the dispersion parameters.

Equal permeability and permittivity in a low temperature co-fired In-doped Mg-Cd ferrite

A low-temperature co-fired In3+ ion doped Mg-Cd ferrite (Mg0.8Cd0.2Fe2−xInxO4 with 0 ≤ x ≤ 0.15) with a 3wt% Bi2O3 additive was synthesized using a solid-state reaction method. X-ray diffraction reveals that the samples contain both a spinel ferrite phase and a CdIn2O4 dielectric phase. Following In3+ ion doping, the saturation magnetization increases first but then decreases. Coercivity, on the other hand, decreases first before it increases. The combined effects of In doping together with the addition of Bi2O3 endowed the compound materials with excellent magnetic permeability and dielectric permittivity. Using 3wt% Bi2O3, the magnetic permeability increases first from 16 to 26.5, and then decreases to 15.6, while the dielectric permittivity increases from 19 to 32. The equivalent permeability and permittivity appears when x = 0.10. The real parts of both permeability and permittivity are about 26, and the material had low loss-tangents (both magnetic and dielectric). This indicates that this ferrite is an excellent material to be used in miniature antennas.

Tailoring optical pulling force on gain coated nanoparticles with nonlocal effective medium theory.

We study the optical scattering force on the coated nanoparticles with gain core and nonlocal plasmonic shell in the long-wavelength limit, and demonstrate negative optical force acting on the nanoparticles near the symmetric and/or antisymmetric surface plasmon resonances. To understand the optical force behavior, we propose nonlocal effective medium theory to derive the equivalent permittivity for the coated nanoparticles with nonlocality. We show that the imaginary part of the equivalent permittivity is negative near the surface resonant wavelength, resulting in the negative optical force. The introduction of nonlocality may shift the resonant wavelength of the optical force, and strengthen the negative optical force. Two examples of Fano-like resonant scattering in such coated nanoparticles are considered, and Fano resonance-induced negative optical force is found too. Our findings could have some potential applications in plasmonics, nano-optical manipulation, and optical selection.

A bandwidth enhanced metasurface antenna for wireless applications

AbstractThis article presents a two layer metasurface antenna in which the top layer is metasurface and the bottom layer is patch antenna. The metasurface enhances the bandwidth and gain of the patch antenna. The metasurface is composed of an array of radiating element which is arranged in 5 × 6 layout. Complementary split ring resonator is used as radiating element. The substrate used for metasurface and patch antenna is Rogers RO4350B having loss tangent of 0.0037, relative permittivity of 3.48 and thickness of 1.524 mm.The overall length and width of the total structure is 0.72λo × 0.95λo (38 × 50 mm2). The metasurface is acting as Double Negative material in which permeability and permittivity both are negative so as a result refractive index will also be negative. The waves coming out of the patch antenna is affected by the array of radiating element on the metasurface, which is above the patch antenna due to which equivalent relative permittivity and permeability of the structure changes and therefore there is change in the performance of the patch antenna. The proposed antenna resonates at 5.7 GHz with bandwidth enhancement from 150 to 260 MHz with gain of 5.8 dBi. The return loss bandwidth is found to be 2.83% (5.64–5.8 GHz) under simulation and 4.64% (5.62–5.78 GHz) under measurement at the resonating frequency when metasurface is used with patch antenna. Overall 39% increase in return loss bandwidth is achieved. The fractional bandwidth of 55.22% is achieved. The proposed antenna is useful for WiFi application.

Effects of humidity and temperature on the optical properties of wet sand

Prediction method for the effect of air humidity and temperature on the optical properties of wet aerosol particles is a key research point on the atmospheric science, earth science, and so on. This paper firstly discussed the effect of moisture, salinity, and temperature on the particle's dielectric constant, and then analyzed the effect of these parameters on the electromagnetic scattering properties of wet sand. The results showed that with the increasing of the temperature, the real part of the permittivity of sand decreased, but its imaginary part increased, and the variation on the real part was much smaller than the imaginary part. With the increasing of the humidity, the equivalent permittivity of wet sand increased, and the difference of permittivity between the sand covered by pure water and the saline sand became obvious. In addition, the extinction efficiency, the scattering efficiency, the back-scattering efficiency and the asymmetry factor of dry sand particle are smaller than those of the wet sand, and with the increasing of the wavelength of electromagnetic wave, the scattering efficiency, the back-scattering efficiency and the asymmetry factor of the dry and wet sand particle are all exponential increased, but the extinction efficiency showed a different changing rule.

Monodomain MgCuZn ferrite with equivalent permeability and permittivity for broad frequency band applications

In order for the miniaturization of a broadband antenna to be achieved, monodomain Mg0.78Cu0.2Zn0.02Fe1.96O3.94 ferrites with various microstructures were prepared by conventional solid-state reaction method. The effect of microstructure on the magnetic and dielectric properties was studied. The results displayed that monodomain MgCuZn ferrite is a potential magneto-dielectric material for broad frequency band applications. In addition, grain size and porosity apparently influenced the permeability and permittivity spectra of the monodomain ferrite. Specifically, densely sintered MgCuZn ferrites with an average grain size of 1.41µm displayed equivalent permeability and permittivity (such as μ' and ε'~13), as along with a low loss factor (such as tan δμ<0.02, tan δε<0.005) in a fairly wide frequency range extending from 10MHz to 100MHz.

Study on magnetocapacitance effect of magnetic particle polymer matrix composite system by finite element method

In this paper, the magnetocapacitance effect of magnetic particles Fe3O4 embedded in polymer insulating matrix polydimethylsiloxane is investigated using finite element method by commercial software Comsol Multiphysics. With this method, the process of the capacitance variation under different magnetic field is simulated, and the factors influencing magnetocapacitance effect are studied. In particular, we apply the micro-macro coupling method for simulation analysis due to a large amount of calculation in the actual model. First, a three-dimensional microscopic model is calculated to obtain the effect of the magnetic field on the equivalent permittivity of the composite. The relationship is then substituted into the material property of the macroscopic model to simulate the magnetocapacitance effect. The results show that the composite exhibits magnetocapacitance characteristics that are related to the magnetic field intensity, particle size, and particle concentration. The capacitance value increases with the magnetic field at certain particle size and particle volume fraction. Meanwhile, the capacitance value at the same magnetic field increases with the particle size and particle volume fraction. The numerical results are consistent with the experimental results. The simulation model can provide a reference for research on the magnetocapacitance effect involving similar composite systems composed of magnetic particles and polymer matrix.

Equivalent Permittivity Based on Debye Model of Blood and Its SAR

Dielectric parameters vary with frequencies are important properties of biological systems, which determine the absorption rates of electromagnetic radiation in human body. Two phase dielectric model is considered to investigate the dielectric properties of human blood in this paper. This paper systematically calculates the body's specific absorption rate of electromagnetic fields at low frequencies based on the dielectric properties obtained from the Debye model. This study could lay foundation not only for the theoretical basis for further study on electrical properties of biological tissue, but also for the exposure limits of health standard on electromagnetic radiation.