Dielectric resonance effect with negative permittivity in a La1.5Sr0.5NiO4+δ ceramic

Tran Dang Thanh,Nguyen Van Dang,Le Van Hong,The-Long Phan,Seong-Cho Yu 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.10

A polycrystalline sample of La1.5Sr0.5NiO4+δ was prepared by using a solid-state reaction. Xraydiffraction proved the sample to be a single phase with a tetragonal structure (space group:I4/mmm). By using an iodometric titration method to determine the non-stoichiometric oxygenconcentration (δ) in La1.5Sr0.5NiO4+δ, we found δ = −0.017, which corresponds to a doping level ofnh = x + 2δ = 0.466. Also, a strong increase of the magnetization in theM(T) curve at temperaturesbelow the spin-ordering temperature (TSO 100 K) was observed. The M(H) curves show verysmall magnetic moments, which proves the weak ferromagnetic nature of La1.5Sr0.5NiO4+δ. Thedependences of the dielectric constant on the frequency and the temperature, "(!, T) = "0(!, T) +i"00(!, T), was investigated in the frequency range of 1 − 13 MHz. At temperatures around roomtemperature, the maximum of the real part ("0) was higher than 105. Particularly, an abnormaldependence of the permittivity on frequency was observed. Depending on temperature, a dielectricresonance was observed at about 500 kHz or 8 MHz. Interestingly, we observed the dielectricresonanceeffect with a negative permittivity. Such a feature is very similar to that observed inleft-handed materials. The fitting of the experimental data for the dielectric constant at frequenciesaround the resonance frequency to the equations associated with an equivalent RLC series circuitproves that La1.5Sr0.5NiO4+δ belongs to the class of multiferroic materials.

Analysis of Longitudinal Porous Dielectric-Loaded Rectangular Waveguide

Kean Jeudy,Tuptim Angkaew 대한전자공학회 2017 대한전자공학회 학술대회 Vol.2017 No.1

The miniaturization of rectangular waveguide by loading with longitudinal porous dielectric material has been proposed. The porous dielectric is a kind of composite material which can be fabricated in practical. The finite element analysis of guided modes in longitudinal porous dielectric-loaded rectangular waveguide has been carried out to investigating dispersion characteristics. Numerous numerical experiments of modal analysis of rectangular waveguides loaded with different porosity have been conducted. The cutoff frequency of the fundamental mode and single mode operation bandwidth in porous dielectric-loaded waveguides depend on porosity or filling factor. It is found that the cutoff frequencies increase in accordance with the increasing of filling factor, which benefits to miniaturize the waveguide.

Reduced Recombination Losses with Enhanced Dielectric Permittivity of Donor Polymers in Polymer Solar Cells

Namchul Cho(조남철),Tae-Dong Kim(김태동),Alex K.-Y. Jen(알렉스 젠) 한국고분자학회 2018 폴리머 Vol.42 No.4

본 연구에서는 나이트릴 그룹을 작용기로 가지는 고분자에 전기장을 가해주어 고분자의 분극도를 높여 고분자의 유전상수를 증가시키는 연구를 진행하였다. 전자주게 고분자의 유전상수를 증가시켜 재결합에 의한 손실을 효과적으로 감소시킬 수 있었고 이로 인해 고분자 태양전지의 개방전압을 증가시킬 수 있음을 보고하였다. 이러한 결과로부터 고분자 태양전지에서 고분자의 유전상수가 가지는 중요성 및 외부 전기장에 의한 고분자의 배열을 이용한 응용분야에 대한 중요성을 밝혔다. In this work, we have demonstrated that the electric field assisted poling of the donor polymer possessing conformationally labile nitrile groups increases dipolar polarization and dielectric permittivity. We find that the enhanced dielectric permittivity of the donor polymer reduces non-geminate recombination losses in bulk-heterojunction (BHJ) solar cells (SCs), resulting in increased open circuit voltage (VOC) compared with unpoled devices. This result reveals the importance of dielectric permittivity of polymers and also signifies the promising applicability of electric field assisted poling for high dielectric polymers in BHJ SCs.

Tunability of Negative Permittivity and Permeability of Ag/Zr0.9Ni0.1Oy Nanocomposites with Morphology

Reza Gholipur,Ali Bahari 대한금속·재료학회 2017 ELECTRONIC MATERIALS LETTERS Vol.13 No.2

In this work, the effect of doping by Ag and stirring time on the structural,dielectrical and magnetical properties of Ag/Zr0.9Ni0.1Oy nanocomposite isconsidered. For all samples, the transmission electron microscopy (TEM)analyses show that doped Ag nanoparticles are dispersed randomly in thehost dielectric. The permittivity and permeability behaviors of sampleswere investigated. Also, by changing the size of Ag, variation ofpermittivity and permeability changes are introduced. It was found thatsamples with 45, 47 and 50 wt% Ag exhibit the double negative (DNG)properties. Simultaneous negative permittivity and negative permeabilitywere tunable in the Ag/Zr0.9Ni0.1Oy nanocomposites. We believe that thethis work will be useful to all those interested in preparation of randomnanocomposite DNG metamaterial.

Debye shielding of an electron in various plasma distributions

Lee Sunggeun,Lim Hankwon 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.2

A single test electron in a plasma experiences a force arising from its induced potential due to the shielding by charges around the test charge. This electric potential can be obtained by solving the Poisson equation or computing the dielectric permittivity. We obtain the length of a test electron’s shielding (or Debye length) for the various distribution functions in a plasma by calculating the dielectric permittivity. As the Maxwellian distribution function leads to a Yukawa-type potential, other distributions give the same potential type but with different damping distances. The results agreed with the formerly known results obtained by solving the Poisson equation. Distributions with twisted waves or orbital angular momentum may lead to a Coulomb potential in certain limits in the absence of ions.

强誘電體의 分極에 미치는 溫度의 影響

이충호 忠州大學校 2008 한국교통대학교 논문집 Vol.43 No.-

The electric properties of PbMg1/3Nb2/3O3(PMN), PbFe1/2Nb1/2O3(PFN) and PbLi1/4Nb3/4O3(PLN) of ferroelectric relaxor composition was studied which was capable of sintering in lower temperature and having superior characteristics to BT system. 0.7PMN-0.25PFN-0.05PLN was mixed and calcined and then the dielectric properties of samples were tested followed by sintering at 1000~1100[℃] during 1~3hrs. From D-E hysteresis curves, the role of dielectric polarizability and the resultant sequence of polar variants was discussed that it is most important profound influence on dielectric properties. The results are as follows; 1. As the sintering temperature was increased, dielectric permittivity was also increased, but dielectric loss factor was decreased. The dielectric permittivity and loss factor was saturated at above 1050[℃]. In the dielectric permittivity versus sintering temperature experiment, somewhat different result was induced. The saturation was occurred at above 1050[℃], dielectric permittivity was decreased, as sintering time was increased. 2. It is shown that the surrounded area of hysteresis loop is increased, as dielectric loss factor is also increased. The area means the energy flowed into the unit area of ferroelectrics and it was consumed by heat in ferroelectrics and became the dielectric loss. 3. The fact that the dielectric permittivity increased, as remained polarization increased and coercive electric field decreased was shown in experiments but not in sintered at 1050[℃] during 3hrs. The relationships between the dielectric permittivity and remained polarization and coercive field should be studied more seriously.

Frequency‐Independent and Colossal Dielectric Permittivity of Platy Alumina/Few‐Layer Graphene Multilayered Composites

최기범,이성민,황재열,윤대호,이규형,김종영 대한화학회 2018 Bulletin of the Korean Chemical Society Vol.39 No.4

In this work, we investigated the dielectric property of layer‐structured Al2O3/few‐layer graphene (FLG) composite by high temperature impedance spectroscopic analysis. The sintered composites have highly enhanced permittivity (ε = 17.3) compared to pure platy alumina (ε = 7.3) with low dielectric loss (tanδ ~ 10−3). Percolative permittivity of the composites exhibits almost frequency‐independent behavior at 1 Hz to 1 MHz even though the real permittivity was increased, compared to that of pure platy alumina. Such behavior can be explained by intervening dielectric interface between alumina and FLG based on multilayer filler model. After percolation threshold (FLG > 0.75 vol %), the permittivity is further enhanced up to ~260 (@1 kHz), which amounts to >35 fold increase, compared to pure platy alumina because of interfacial capacitance between FLG platelets and alumina. According to temperature‐dependent impedance analysis, a dielectric relaxation due to Al2O3/FLG interface is observed in the frequency range of 1 Hz to 1 kHz at high temperature (RT = 400°C) besides that due to Al2O3 grains (>10 MHz). Real permittivity increases up to >20 000 at 400°C at low frequency, whereas dielectric loss remains as tanδ ~ 3 × 10−4. High temperature impedance analysis shows that the effect of interface between Al2O3 and FLG is responsible for such dielectric relaxation at high temperature.

Electric double layers interactions under condition of variable dielectric permittivity

Payam, Amir Farrokh,Fathipour, Morteza Techno-Press 2010 Interaction and multiscale mechanics Vol.3 No.2

In this paper, a theoretical method has been developed for the electric double layer interaction under condition of the variable dielectric permittivity of water. Using Poisson-Boltzmann equation (PBE), for one plate and two plates having similar or dissimilar constant charge or constant potential, we have investigated the electric double layer potential, its gradient and the disjoining pressure as well as the effect of variation of dielectric permittivity on these parameters. It has been assumed that plates are separated by a specific distance and contain a liquid solution in between. It is shown that reduction of the dielectric permittivity near the interfaces results in compression of electric double layers and affects the potential and its gradient which leads to a decreased electrostatic repulsion. In addition, it is shown that variation of dielectric permittivity in the case of higher electrolyte concentration, leads to a greater change in potential distribution between two plates.

Radiation Characteristics of a Probe-Fed Microstrip Patch Antenna on a Finite Grounded High Permittivity Substrate

Eun-Hyuk Kwak,Young-Min Yoon,Boo-Gyoun Kim 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.4

Radiation characteristics of a probe-fed rectangular microstrip patch antenna printed on a finite grounded high permittivity substrate are investigated systematically for various square grounded dielectric substrate sizes with several thicknesses and dielectric constants by experiment and full wave simulation. The effect of the substrate size on the radiation characteristics of a rectangular patch antenna is mainly determined by the effective dielectric constant of surface waves on a grounded dielectric substrate. As the effective dielectric constant of surface waves increases, the substrate sizes for the maximum broadside gain and the required onset for a large magnitude of squint angle decrease, while the variations of the broadside gain, the front-to-back ratio, and the magnitude of squint angle versus the substrate size increase due to the increase of the power of the surface wave.

Microwave Dielectric Properties of Grain Using Free-Space Trasmission Method

Kim, Jong-Heon 광운대학교 신기술연구소 1997 신기술연구소논문집 Vol.26 No.-

X-밴드용 표준이득 혼안테나를 이용한 자유공간 전송방법에 의하여 벼 그리고 현미와 같은 젖은 곡물을 통과하는 마이크로파의 감쇠 및 위상변이를 측정하였다. 이때, 곡물의 함수율은 젖은 상태에서 11%에서 25%까지 변화시켰다. 젖은 곡물의 함수율에 대한 유전상수와 손실계수를 벡터 회로망 분석기를 이용하여 측정된 감쇠와 위상변이로 부터 얻었다. 또한, 곡물의 유전특성에 있어서 주요 인자중의 하나인 산물밀도에 따른 유전상수와 손실계수의 변화를 살펴보았다. 그리고 수분밀도의 함수로 표시되는 유전상수들의 측정치와 곡물의 유전상수를 예측하기 위한 예측 모델로 부터 얻은 계산치와 비교하였다. A free space transmission method using X-band standard gain horn antennas is applied to measure the attenuation and phase shift of a microwave signal through wetted grain such as rough rice and brown rice. The moisture content of grain varied from 11 to 25% based on its wetted condition. The dielectric constant and loss factor, which depend on the moisture content of the wetted grain, is calculated from the attenuation and phase shift measurement using vector network analyzer. The effect of density fluctuation, which is an important parameter governing the dielectric properties of grain, on the dielectric constant and loss factor is presented. The measured values of dielectric constants as a function of moisture density are compared with the values obtained using the predicted model for estimating dielectric constants of grain.