High Electric Permittivity Research Articles

Simulation and measurement of inset‐fed microstrip patch antennas on BiNbO4 substrates

AbstractThis work presents an experimental investigation of the properties of microstrip patch antennas on bismuth niobate ceramic substrates. The substrate fabrication process and characterization are described. Several prototypes were built and measured for wireless communication systems. A good agreement was observed between measured and simulated results. The very high electrical permittivity of the ceramic substrate provided a reduction of the antenna dimensions. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1034–1036, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25098

X-ray photoelectron spectroscopy energy band alignment of spin-on CoTiO3 high-k dielectric prepared by sol-gel spin coating method

The characteristics of CoTiO3 high-k dielectric prepared by sol-gel spin coating method had been demonstrated. High electrical permittivity (k∼40.2) of CoTiO3 dielectric was extracted via the transmission electron microscopy image and capacitance-voltage curves. In addition, the valence band offset between thermal SiO2 and spin-on CoTiO3 was about 4.0 eV, which was detected by x-ray photoelectron spectroscopy. The band gaps of thermal SiO2 and spin-on CoTiO3 were 9.0 and 2.2 eV, respectively. Energy band alignment of spin-on CoTiO3 directly with SiO2 and indirectly with Si was determined in this work.

Experimental study on bubble detachment under variable heat load and the action of electric field

This paper is aimed at studying single bubble growth and detachment in controlled conditions and under the action of an electric field. An experimental set-up was built, consisting mainly of a stainless steel lamina with a nucleation site etched in its center, facing the testing fluid. The required heating power was provided by an SMD microresistor, stuck by means of epoxy resin on the back side of the plate. A signal generator, connected to the resistor, allowed for heating power modulation and thus for variation of the bubble size. Two different fluids, FC-72 and HFE-7100 were tested. An external electrostatic field was applied by imposing up to 15 kV dc to a ring of 4 mm inner diameter suspended 3 mm above the plate: in this way, a very clear axisymmetric configuration was created, suitable for two-dimensional analyses. High speed images were taken by means of a high-speed camera, operated at 1000 frames per second with a resolution of about 100 pixel/mm. Images were treated with a dedicated image processing software to obtain bubble significant geometrical parameters. The preliminary results reported here show elongation of the detached bubble under the action of the electric field, confirming former results obtained with nitrogen bubbles originating from an orifice in the same liquids. The detachment volume under the action of the electric field either increases or decreases, for low and high electric permittivity fluid, respectively, evidencing the complex nature and role of the electric forces. First results under variable heat load evidence a reduction in detachment diameter. The dynamical forces outside the microlayer region seem to have a minor role, compared to the static ones, in vapor bubble growth.

Surface characterization of clay particles via dielectric spectroscopy

This work deals with the high frequency dielectric relaxation of clay (sodium montmorillonite, or NaMt) suspensions. By high frequency it is meant that the permittivity will be determined in the region where the Maxwell-Wagner-O’Konski relaxation takes place, roughly, the MHz frequency range. The applicability of dielectric determinations for the characterization of the electrical properties of these complex systems is demonstrated. In fact, standard electrophoresis measurements only allow to detect that the charge of the particles becomes slightly more negative upon increasing pH. Much more information is obtained from the high frequency electric permittivity for different concentrations of solids and pHs. From the characteristic frequencies of the relaxation it is possible to detect separate processes for parallel and perpendicular orientations of the clay platelets, modelled as oblate spheroids with a high aspect ratio. In addition, using a suitable model the surface conductivity of the clay particles can be estimated. Our data indicate that this quantity is minimum around pH 7, which is admitted as representative of the isoelectric point of the edges of the clay platelets. Data are also obtained on the amplitude (value of the relative permittivity at low frequency minus that at high frequency) of the relaxation, and it is found that it depends linearly on the volume fraction of solids, and that it is minimum at pH 5. These results are considered to be a manifestation of the fact that particle interactions do not affect the electric conduction inside the electric double layer, while the special behaviour at pH 5 is related to the existence of aggregates at pH 5, which increase the effective size of the particles and provoke a reduction of their effective conductivity.

Nitrogen analysis in high- k stack layers: a challenge

In order to increase performance in advanced MOS devices, alternative gate insulators with high electrical permittivity are investigated to replace SiO 2. Recent developments include the presence of nitrogen in or around the HfO 2 stack. It is thus important to be able to acquire knowledge of the depth distribution of the nitrogen in the layers with enough accuracy. This remains a real challenge for SIMS due to varying matrices in which the nitrogen is distributed. We first present results obtained with Xe and Cs profiling. We determined the “best to use” clusters in order to retrieve the maximum information of the data. In the second part, we investigate some less standard operational mode of SIMS profiling. For instance, it has also long been considered that the detection of MCs + clusters suffers from less matrix effect and could thus be advantageous for this kind of analysis, where the Cs surface concentration is reduced by the use of Xe–Cs co-sputtering. We also introduce a new method in order to increase the sensitivity to nitrogen by using a “carbon-based” flooding and using the CN − cluster detection.

The potential of fracture imaging using high‐frequency, single‐hole electromagnetic data

This paper presents an inversion scheme for high‐frequency electromagnetic (EM) data from a single borehole for detection and characterization of fluid‐filled fractures. Water in the fracture zone may be characterized by its high electrical permittivity and, if saline, by high electrical conductivity. High electrical conductivity results in increased attenuation of EM fields, whereas high electrical permittivity reduces the phase velocity of propagating EM fields. Taking advantage of these effects, we use high‐frequency EM fields to detect and characterize fluid‐filled fractures. To demonstrate the feasibility of single‐hole EM imaging, we develop a three‐step inversion scheme to map a fluid‐filled fracture near the borehole and to evaluate its electrical conductivity and permittivity.We assume that a fluid‐filled fracture can be simulated by a conductive thin sheet. To test our inversion scheme, we generated synthetic data using the thin‐sheet integral equation method. A vertical magnetic dipole was used as a source, and the resultant magnetic fields were inverted using a nonlinear least‐squares method. First, the background conductivity and permittivity were obtained using vertical magnetic field data from below and above the transition frequency, at which conduction and displacement current magnitudes are equal. Next, using the phase difference between EM fields at two neighboring frequencies in the wave propagation realm, both the vertical and dipping sheets were successfully mapped using NMO and migration techniques. Electrical properties of the sheet were well resolved by subsequent inversion after having fixed the location of the sheet and host electrical properties.This study shows the potential of imaging the fracture using high‐frequency EM data obtained from single‐hole surveys.

Localized and delocalized models in the theory of polarization: perovskite oxides

Possibilities of working out the theory of polarization in perovskite-type oxides in frameworks of localized and delocalized models are analysed. Born effective charges are used as a criterion of correlating these models. It is shown that taking into account gradients of effective electric fields on anions and high electric permittivity ensures the adequate description of polarization in these crystals by using the Slater localized (static) model. The results of our calculations in the framework of the Slater model are given and compared with ab initio calculation data.

A Barrier Discharge Reactor with Ferroelectric Electrodes I. Influence of thickness and surface area of electrodes

AbstractA study aimed at finding a way of scaling‐up a small laboratory reactor employing an electric discharge with a dielectric barrier was carried out. The dielectric used was ferroelectric ceramic material of a high permittivity (ϵ above 1000) comparing to glass (ϵ ≈︁ 3–10), which is generally used. The main component of the ceramics was BaTiO3. The advantage of using this type of ceramics is related to a considerable increase in power density without the need of increasing voltage which supplies the system.The influence of the thickness and surface of ferroelectric electrodes on the macroscopic characteristics of the discharge and efficiency of chemical process was investigated. Ozone synthesis from oxygen was the reaction under consideration.A new structure of the reactor was proposed comprising a series of parallelly spaced thin ceramic plates. High electric permittivity of the ferroelectric ceramics enables such „sandwich”︁ structure to be supplied by only two edge ceramic electrodes.

High electric field effects and permittivity changes in non-polar liquids

The change of the permittivity ΔIµ is measured in high electric fields E up to 107 V m–1 for n-hexane, n-heptane, cyclohexane, carbon tetrachloride, benzene, toluene and carbon disulphide at 25 °C. The effects are positive, vary linearly with E2 and do not depend on the frequency of the analysing field in the range 0.5–50 MHz. The amplitudes of the effects are similar to recent literature values, but differ when measured in cells of different design. ΔIµ is determined from the amplitude modulation of the output voltage of a resonant circuit to which an alternating high field is applied. The effect shows dispersion with the frequency of the high field in the kHz region. From this as well as from the linear dependence of most ΔIµ/E2 values on Iµ2 it is concluded that an important part of the effect is due to electrode movements. The corrected values are compatible with experimental Kerr constants. The best value for carbon disulphide is ΔIµ/E2=(1.25 ± 0.10)× 10–19 V–2 m2.

Design and development directions

The electromagnetic (EM) characteristics of the carbon nanotubes/carbonyl iron powders (CNTs/CIPs) complex absorbers synthesized by mixing CNTs with CIPs were studied at 2–18 GHz, for the aim of the absorbing coating with thinness, lightness, width, and strength. Compared with CIPs, the CNTs/CIPs composites had higher electrical conductivity, permittivity, and dielectric loss, which gradually increased with the increasing CNTs content (WCNTs). Among them, with WCNTs = 2.2 %, a reflection loss (RL) exceeding −20 dB was obtained in the frequency range of 6.4–14.8 GHz for a coating thickness of 1.2–2.5 mm. Particularly, a minimum RL of −33.3 dB was found at 11.2 GHz corresponding to a matching thickness of 1.5 mm. The excellent EM-wave absorption properties are a consequence of a proper EM matching and enhanced absorption abilities resulting from the addition of a small quantity of CNTs with high electrical conductivity, permittivity, and dielectric loss. Thus, CNTs/CIPs complex absorbers may be promising candidates for EM-wave-absorption materials with strong-absorption, thin-thickness, light-weight, and low-cost.