Showing papers on "Relative permittivity published in 1990"

Electrical Properties of Tissue

Abstract: This chapter discusses the electrical and dielectric properties of tissue, covering the frequency range from d.c. to over 10 GHz. The electrical character of tissues over a wide range of frequencies may be described by using the two properties relative permittivity, ∈′ (the charge) and conductivity, σ (current densities set up in response to an applied electric field of unit amplitude). From both of these, the complex relative permittivity, ∈*, can be defined by the equation ij , characterize the effect in terms of the charge generated for unit applied stress under short circuit conditions.

Broad-band simultaneous measurement of complex permittivity and permeability using a coaxial discontinuity

Abstract: A technique for simultaneously measuring the real and imaginary parts of both the permittivity and the permeability of a given material is discussed. A gap in a coaxial line is filled with the material under test. Complex permittivity and permeability are computed from the S-parameter (S/sub 11/ and S/sub 21/) measurement made on the gap, taking into account higher-order modes excited at the discontinuity. Measured epsilon /sub r/ and mu /sub r/ data for several materials are presented from 45 MHz up to 18 GHz. This technique shows good agreement between calculated and generally accepted values. >

Broadband complex permittivity measurements by time-domain spectroscopy

Abstract: The complex permittivity measurements of some materials, taken by using the time-domain reflectometry (TDR) method, are presented. As an example of the wide frequency measurement capability, both at the radio and microwave frequencies, the complex permittivity measurement of a liquid crystal is presented in the frequency range between 100 kHz and 1 GHz. The measurement of an ionic water-in-oil microemulsion system is given to describe the case of a conductive sample. From the measurement of this system, it is clear that the TDR technique can be used to measure the complex permittivity of a sample with high DC conductivity. Even if the sample has a small dielectric absorption hidden behind the high DC conductivity, the method should be able to distinguish between the two. Complex permittivity measurements of strongly polar liquids are presented to show the highest frequency attainable by the TDR system. The result indicates that the complex permittivity can be measured up to 25 GHz with sufficient accuracy if the cutoff frequency of the TDR system is higher than 25 GHz. This high-frequency limit is due to the limitation of the system given by the performance of the sampling system. >

Laser-induced chemical vapor deposition of aln films

Abstract: AlN intended for metal‐insulator‐semiconductor applications has been prepared by laser activated chemical vapor deposition from ammonia and trimethylaluminum precursors. The films are high‐density polycrystalline with 〈100〉 preferential orientation, and there is no evidence of the presence of Al2O3. A consistent band gap of 6.00±0.03 eV is obtained for film thickness in the range 0.3–1.2 μm. Conductivity is below 5×10−14 Ω−1 cm−1 at room temperature and is thermally activated with a range of excitation energies between 0.6 and 0.8 eV. The breakdown electric field is about 3×106 V/cm, while the relative permittivity varies between 7.8 and 8.2 in the frequency range 100 Hz–13 MHz.

Complex permittivity of a conductor-loaded dielectric

Abstract: The complex permittivity of a composite dielectric containing conducting inclusion is derived. The shape of the inclusions is described by their aspect ratio. The resultant equations describe the frequency dependence of the permittivity exactly, without recourse to empirically derived parameters.

Isothermal–isobaric molecular dynamics simulation of liquid water

Abstract: Results of the first isothermal–isobaric molecular dynamics simulation of water are reported. Water molecules are assumed to be flexible and to interact via a sum of pairwise interatomic potentials. Extensive runs for 256 molecules at 298 and 373 K and 1 bar give satisfactory agreement with observed properties of liquid water as diverse as density, internal energy, heat capacity, compressibility, pair correlation functions, diffusion coefficient, vibrational spectrum, relative permittivity, and dielectric relaxation spectra. The nonlinear dependence of the relative permittivity on the electric field is also computed by means of fluctuation–dissipation relations.

NMR radio frequency coil with dielectric loading for improved field homogeneity

Abstract: An RF coil assembly for an NMR instrument includes a cylindrical coil (10) surrounded by a cylindrical shield (11). The annular space (13) between the coil and the shield is filled with a dielectric material having a relative permittivity selected to improve the RF field homogeneity in the radial direction.

Measurement of static dielectric constants of supercritical fluid solvents and cosolvents: Carbon dioxide and argon, carbon dioxide, and methanol at 323 K and pressures to 25 MPa

Abstract: A new apparatus for the measurement of dielectric constants of high pressure gases has been constructed. The apparatus consists of a recirculating visual flow cell and a concentric cylinder dielectric constant flow cell. Measurement of the dielectric constant is made by a unique counter-oscillator circuit, in which the capacitance is determined by relaxation of a unijunction transistor oscillator circuit and counted by a crystal oscillator. Dielectric constants are reported for supercritical mixtures of carbon dioxide + argon and carbon dioxide + methanol at a temperature of 322.9 K and pressures to 25 MPa. The dielectric constant shows a sharp increase near the critical pressure. Dielectric constants were linear with densities calculated by the Suzuki equation-of-state. The dielectric constant for the methanol-carbon dioxide system was found to be less than a mole fraction average of the pure component dielectric constants.

Transport properties in lead phthalocyanine thin films for use in FET structures

Abstract: DC electrical measurements have been made for a wide lead phthalocyanine (PbPc) thickness range (d ~ 0.5–5.0 µm). Measurements of capacitance as a function of inverse thickness revealed a low frequency relative permittivity (∊ r ~ 3.9), slightly higher than in copper phthalocyanine. At low voltages Ohm's law was followed, with a thermally-activated hole concentration of (1 · 1–21) × 1016 m-3. Above a threshold voltage Vt, a power-law dependence of current density on applied voltage was observed, indicating space-charge-limited conductivity, Vt varied in the range 0.4–20 V and was approximately proportional to d2, providing further evidence for this effect. The results were accounted for in terms of an exponential distribution of traps of total concentration 2.8 × 1025 m−3 within the bandgap, as observed in similar organic materials.

Active matrix liquid crystal display device and method for production thereof

Abstract: Metal-insulator-metal devices having an insulation layer between two metal layers wherein the relative dielectric constant of the insulation layer is less than the relative dielectric constant of oxidized Ta, and C.sub.CF ×C.sub.LC /[(C.sub.CF +C.sub.LC)×C.sub.MIM ]>2 where CCF is the capacitance of the second substrate, CLC is the capacitance of the liquid crystal material, and CMIM is the capacitance of the metal-insulator-metal elements and an active matrix liquid crystal display panel including the metal-insulator-metal devices are provided. A method for producing such an active matrix liquid crystal display panel is also provided.

Millimeter wave complex refractive index, complex dielectric permittivity and loss tangent of high purity and compensated silicon

Abstract: Single-crystal high-resistivity (11000- Omega -cm) boron-doped silicon was found to exhibit the lowest absorption loss at room temperature (25 degrees C) in the entire millimeter-wave region. The millimeter-wave absorption coefficient values for the compensated silicon are at least one order of magnitude less than values obtained with undoped pure silicon. At 140 GHz, the loss tangent value of the compensated silicon is as low as 40 mu rad. The study of the dielectric properties of silicon as a function of resistivity reveals that the low-frequency free-carrier absorption present in all silicon (and other semiconductors) vanishes with increasing resistivity. The dispersive Fourier transform spectroscopic technique was utilized for the measurements. >

Determination of landau free-energy parameters by dielectric measurements in (ch3NH3)5Bi2CI11 crystals+

Abstract: The adiabatic dielectric permittivity in the biasing electric field and spontaneous polarization of (CH3NH5)5Bi2Cl11 crystals are measured near the high temperature phase transition. Coefficients of the dielectric state equation are determined.

Method of analyzing the alcohol content and/or the calorific value of fuels

Abstract: A method of determining the alcohol content and/or the calorific vaue of fuels by containing the fuel and measuring the electrically measurable values in a measurement cell to determine the relative permittivity of the mixture as the characteristic of the alcohol content of the calorific value. The relative permittivity is then determined by means of a computer or circuitry, independent of the influence of the conductivity of the fuel.

Complex permittivity of lanthanum aluminate in the 20 to 300 K temperature range from 26.5 TO 40.0 GHZ

Abstract: Dielectric constants of microwave substrates are required in the design of superconducting microwave circuits at various temperatures. In this paper, the results are reported of a study of the complex permittivity of the newly developed lanthanum aluminate (LaAlO3) substrate, in the 20 to 300 K temperature range at frequencies from 26.5 to 40.0 GHz. The value of the complex permittivity was obtained by measuring the sample scattering parameters using a microwave waveguide technique. It is observed that, while the dielectric constant did not change appreciably with frequency, its value decreased by approximately 14 percent from room temperature to 20 K.

Characterization of capacitive array for NDE applications

Abstract: We have developed a capacitive array sensor which responds to the complex dielectric constant of an interrogated material. The sensor requires only single-sided access and operates in a differential mode for detection of discontinuities in the relative dielectric constant, e r , or in the absolute mode where the interest is in absolute quantities. The device in general is noncontacting but can be fabricated as an embedded sensor. Various proof-of-concept studies have been performed to explore possible applications of the device. In the differential mode, small surface features (notches) were detected in a conductor; in dielectrics, both surface and subsurface features were detected. The probe was sensitive to change in impedance caused by a curing epoxy, viewed through a graphite-epoxy composite panel. A study was performed to assess the use of the probe for noncontact characterization of sintering of ceramics. In this (absolute) mode, the effects of liftoff and dielectric constant must be separa...

The dielectric properties of alumina substrates for microelectronic packaging

Abstract: The dielectric characterization of alumina substrate materials used in high-performance microelectronic packaging is described. These materials included both pure and impure polycrystalline substrates and, as a reference standard, pure and chromium-doped single crystals of alumina. For each material the permittivity (e′) and dielectric loss (e″) has been measured over a frequency range of 0.5 kHz to 10 MHz, at room temperature, and correlated with the structure and composition as determined by supplementary techniques. At room temperature the pure substrates show the frequency independence of both e′ and e″, characteristic of pure single-crystal material. The permittivity (e′= 10.1) agrees closely with the average of the anisotropic values for the single crystal but the dielectric loss is an order of magnitude higher than in the single crystal, giving tan σ ≈ 1.5 × 10−3. The impure substrates compared with the pure, show a small increase in e′ and a marked, frequency-dependent increase in dielectric loss. Measurements have also been made in both the high- and low-temperature ranges (i.e. 20 to 600 ° C and 77 to 293 K, respectively) in order to establish the variation of permittivity with temperature and frequency. At temperatures below 200 °C the temperature coefficient of permittivity, [(e′ −1)(e′ + 2)]−1 (∂e′/∂T) p is about 9 × 10−6 K−1 for the pure materials but this increases rapidly with impurity addition.

Pinning effect on microwave dielectric properties and soft mode in TlInS2 and TlGaSe2 ferroelectrics

Abstract: This paper presents the results of an investigation of microwave dielectric dispersion in the proper semiconductive ferroelectrics TIInS2 and TIGaSe2 with an incommensurate structure modulation. In these crystals there is a strongly overdamped soft ferroelectric mode, whose frequency in the vicinity of the phase transitions drops to the millimetre wave region and causes dielectric microwave dispersion plus a high contribution to the static dielectric permittivity. Within the incommensurate phase crystal defects, such as impurities, cause pinning of the soft mode. Because of this pinning effect the phason frequency increases. Pinning also changes the dynamical dielectric properties and the contribution of the phason and amplitudon to the static permittivity.

The Influence of Growth Rate on the Properties of Anodic Oxide Films on Titanium.

Abstract: ac Impedance measurements and photocurrent spectroscopy have been used to examine the dependence on growth rate of the solid state properties of thin (<20 nm) anodic oxide films on titanium. At room temperature, the relative permittivity and defect concentration profiles in the oxide were found to depend markedly on growth rate. The effects on the photocurrent of recombination and trapping were most pronounced when the films are grown rapidly. It was found that the high defect densities associated with rapidly grown oxide films could be decresed by growing or annealing the oxide films at higher temperatures.

Measurement of the dielectric properties of materials by using time domain reflectometry

Abstract: The authors present some TDR (time-domain-reflectometry) applications for complex permittivity measurements for strong polar liquid in the frequency range of 1 to 35 GHz, liquid crystal from 100 kHz to 1 GHz, and ionic microemulsion at frequencies between 30 MHz and 20 GHz. In each case, the necessary TDR techniques for optimal condition are given. The new TDR system (HP54120A+HP54121A) used has excellent stability compared with the earlier TDR system (HP181). It was found that, for methanol, the TDR system implemented can obtain information about the complex permittivity in the frequency range up to 25 GHz with sufficient accuracy and can possibly go up to 35 GHz using a bilinear correction. In the case of the liquid crystal, it is shown that the method is powerful not only in the microwave range but also in the radio frequency range. From the measurement of the ionic microemulsion system, it is clear that the TDR technique is applicable to the measurement of the complex permittivity of a sample with high DC conductivity. >

The dielectric response of a commercial polybutylene terephthalate

Abstract: Contour maps of complex relative permittivity within the range −170 to +175° C and 0.1 Hz to 3 MHz are presented for a commercial polybutylene terephthalate. The interdependence ofe′ ande″, as required by the Kramers-Kronig relations, is particularly apparent. Individual dispersion regions are attributed toα- andβ-relaxation processes and to Maxwell-Wagner-Sillars polarizations. Possible explanations are proposed for the structure which is apparent in theα-peak.

Electromagnetic scattering from a circular cylinder of homogeneous dielectric coated by a dielectric shell with a permittivity profile in the radial and azimuthal directions-even TM case

Abstract: Equations are formulated and numerical results presented for electromagnetic scattering from an infinitely long circular cylinder of homogeneous dielectric coated with a dielectric shell. The permittivity of the dielectric shell varies as rho /sup -2/ in the radial direction and as a weighted cosine in phi . Plane waves with an electric field parallel to the cylinder axis constitute the incident fields, restricting the analysis to the transverse magnetic (TM) case. This permittivity profile allows the unknown electric field in the dielectric region to be represented by a series of cosine-elliptic Mathieu functions of even integer orders with unknown expansion coefficients. The unknown expansion coefficients are determined by enforcing boundary conditions and using the orthogonal properties of the trigonometric functions and of the Mathieu functions. The far scattered field is then evaluated and numerical results for the scattered field versus different geometrical parameters are obtained and presented. >

RCS reduction of dielectric cylinders using a simulated annealing approach

Abstract: The reduction of RCSs (radar cross sections) of dielectric cylinders is of great interest from the point of view of enhancing the performance of antennas that use these cylinders as supports for radomes or feed systems. RCS reduction of dielectric cylinders under TM plane-wave illumination can be achieved by loading the cylinder with perfect electrically conducting narrow strips oriented parallel to the cylinder axis. For certain specific strip configurations and directions of radiation, it can be shown that the far fields radiated by the polarization currents are partially canceled by those produced by the conduction currents induced on the strips. This, in turn, has the effect of reducing the bistatic RCS of the isolated dielectric cylinder. The authors present a simulated annealing algorithm that simultaneously minimizes the bistatic RCS in different scattering angles, and/or frequencies, by searching for the optimal strip configuration. The scattering of a lossless dielectric cylinder measuring 1 by 0.2 wavelengths and characterized by a relative permittivity of 4 was minimized for a TM plane wave incident on the broad cylinder axis. >