Showing papers on "Relative permittivity published in 2007"

RFID Tag and RF Structures on a Paper Substrate Using Inkjet-Printing Technology

Abstract: In this paper, inkjet-printed UHF and microwave circuits fabricated on paper substrates are investigated for the first time as an approach that aims for a system-level solution for fast and ultra-low-cost mass production. First, the RF characteristics of the paper substrate are studied by using the microstrip ring resonator in order to characterize the relative permittivity (epsivr) and loss tangent (tan delta) of the substrate at the UHF band for the first time reported. A UHF RFID tag module is then developed with the inkjet-printing technology, proving this approach could function as an enabling technology for much simpler and faster fabrication on/in paper. Simulation and well-agreed measurement results, which show very good agreement, verify a good performance of the tag module. In addition, the possibility of multilayer RF structures on a paper substrate is explored, and a multilayer patch resonator bandpass filter demonstrates the feasibility of ultra-low-cost 3-D paper-on-paper RF/wireless structures.

Permittivity of pure water, at standard atmospheric pressure, over the frequency range 0-25 THz and the temperature range 0-100 °C

Abstract: All the currently available experimental permittivity data for pure water are used to derive an interpolation function that precisely represents e(ν,t,) at standard atmospheric pressure, for frequencies and temperatures in the ranges 0⩽ν⩽25THz and 0⩽t⩽100°C. The permittivity data is represented in terms of relaxations and resonances processes. There are three relaxations in the microwave region and two resonances in the far infrared. The temperature dependence of the relaxation and resonance parameters are determined. For example, at 25°C the three relaxation frequencies are 18.56GHz, 167.83GHz, 1.944THz and the two resonance frequencies are 4.03 and 14.48THz.

Electric energy density of dielectric nanocomposites

Abstract: Dielectric materials with large electric energy density are actively pursued for many applications. The authors analyze the effective permittivity, breakdown strength, and electric energy density of dielectric nanocomposites using an effective medium approximation, modeling the nanocomposite as a three-phase material by the double-inclusion method. The addition of nanoparticles enhances the permittivity but reduces the breakdown strength, making the potential gain in electric energy density small. In addition, the interfacial interaction shifts the “percolation” threshold toward lower volume fraction of nanoparticles. The analysis suggests that the microstructure of nanocomposites must be carefully controlled to maintain high dielectric strength and therefore realize enhanced electric energy density.

Capacitance wire-mesh sensor for fast measurement of phase fraction distributions

Abstract: We introduce a new wire-mesh sensor based on capacitance (permittivity) measurements. The sensor can be used to measure transient phase fraction distributions in a flow cross-section, such as in a pipe or other vessel, and is able to discriminate fluids having different relative permittivity (dielectric constant) values in a multiphase flow. We designed and manufactured a prototype sensor which comprises two planes of 16 wires each. The wires are evenly distributed across the measuring cross-section, and measurement is performed at the wire crossings. Time resolution of the prototype sensor is 625 frames per second. Sensor and measuring electronics were evaluated showing good stability and accuracy in the capacitance measurement. The wire-mesh sensor was tested in a silicone oil/water two-phase bubbly flow.

Complex permittivity of sodium chloride solutions at microwave frequencies

Abstract: The complex permittivity of aqueous solutions at 20 °C has been measured at concentrations between 0.001 and 5 mol/L and over a frequency range 0.13–20 GHz. The results were combined with literature values to derive empirical equations to predict the dielectric behavior of sodium chloride solutions between 0 and 5 mol/L and 5°C–35 °C. Bioelectromagnetics 28:264–274, 2007. © 2007 Wiley-Liss, Inc.

Significantly enhanced low-frequency dielectric permittivity in the BaTiO3/poly (vinylidene fluoride) nanocomposite

Abstract: To disclose an effect of ceramic particle size on dielectric properties of BaTiO3/ poly(vinylidene fluoride) (BT/PVDF) composites at low frequency, the dielectric properties of the BT/PVDF composites loaded with different diameter BT particles at the same volume concentration were studied at wide frequency ranges from 10−1to107Hz. A significant low-frequency dielectric permittivity increase in the BT/PVDF nanocomposite was noticed, which was not reported previously. The authors considered that the marked aggrandizement of interface and dipole polarization at low frequency is charged with the significant increase in dielectric permittivity.

Enhanced electromagnetic wave absorption properties of Fe nanowires in gigaherz range

Abstract: Fe nanowires with 70–200nm in diameter and 20–50μm in length were synthesized by a chemical vapor deposition method for electromagnetic wave absorption application. The frequency dependences of relative permittivity (er) and permeability (μr) were strongly dependent on the diameter of Fe wires. Compared with micrometer wires or flakelike samples, nanowires exhibited a magnetic resonance (μr″) peak in the range of 1–18GHz, suggesting that nanowires have significant effect for reducing the eddy current loss, therefore, the resin compacts of 29vol% Fe nanowires with thicknesses of 1.3–4.0mm provided good electromagnetic wave absorption performances in the range of 5.6–18GHz.

Reference liquids for the calibration of dielectric sensors and measurement instruments

Abstract: A comparative study of microwave complex dielectric permittivity data from different laboratories is provided for liquids. Four liquids—water, cyclohexane, methanol and dimethyl sulphoxide—are recommended as reference materials because their parameter sets from different measurements result in almost identical predictions of their dielectric properties in the frequency range up to 10 GHz. Within the limits of experimental error this agreement includes that of the extrapolated low frequency permittivity with the recently determined static permittivity of the liquids. Parameters for water are given for the frequency range 0–60 °C. For cyclohexane, which does not display relaxation behaviour up to the submillimetre frequency range, the frequency-independent permittivity is represented between 10 and 50 °C. Relaxation and static permittivity data for methanol and dimethyl sulphoxide are presented at 25 °C.

Dipolar correlations and the dielectric permittivity of water.

Abstract: The static dielectric properties of liquid and solid water are investigated within linear response theory in the context of ab initio molecular dynamics. Using maximally localized Wannier functions to treat the macroscopic polarization we formulate a first-principles, parameter-free, generalization of Kirkwood's phenomenological theory. Our calculated static permittivity is in good agreement with experiment. Two effects of the hydrogen bonds, i.e., a significant increase of the average local moment and a local alignment of the molecular dipoles, contribute in almost equal measure to the unusually large dielectric constant of water.

Dielectric properties of BST/polymer composite

Abstract: A composite of barium strontium titanate (BST) and thermoplastic cyclic olefin copolymer (COC) was investigated with different BST loadings using common and nanosize ceramic powders. The relative permittivity and loss tangent of the composites were measured as a function of loading at 1 GHz and as a function of temperature at 0.1 MHz. A relative permittivity of 6.0 and a loss tangent of 0.0009 at 1 GHz (room temperature) were obtained for a BSTc-COC composite with 25 vol.% loading using common-size particles of BST. The values for a BSTn-COC composite loaded with 25 vol.% of nanosize BST particles were 7.3 and 0.0023, respectively. A modified Lichtenecker logarithmic equation showed good correspondence with measured relative permittivity of the BSTc-COC composite, but especially at a higher loading level, the model failed with the BSTn-COC composite.

Higher permittivity rare earth doped HfO2 for sub-45-nm metal-insulator-semiconductor devices

Abstract: Rare earth (RE) doping (Gd, Er, Dy) of HfO2 reduces leakage current by three orders of magnitude compared with pure HfO2. The key to reducing HfO2 leakage current and equivalent oxide thickness (EOT) is stabilization of the higher permittivity tetragonal phase. RE doping of 10–20at.% stabilizes tetragonal HfO2 and increases permittivity. The maximum permittivity achieved for HfREOx is 28. The maximum permittivity for ZrREO is 32. HfGdO metal-insulator-semiconductor capacitors with EOT=1.93nm and leakage current <1×10−8A∕cm2 after 1070°C have been demonstrated.

Ultrawide range dielectric spectroscopy of BaTiO3-based perovskite dielectrics

Abstract: Ultrawide range dielectric spectra from the kilohertz to terahertz range of BaTiO3 (BT), Ba(Zr0.25Ti0.75)O3 (BZT), (Ba0.6Sr0.4)TiO3 (BST), and SrTiO3 ceramics were presented by analyzing dielectric permittivity and IR reflectivity data. It was found that the permittivity of the ST was determined only by the ionic polarization while that of the BT was determined by the ionic polarization as well as the dipole polarization due to the domain contribution. The high permittivity of the BZT ceramics was attributed to the dipole polarization of polar nanoregions in the relaxors. The dipole and ionic polarizations overlapped in the BST.

Dielectric properties of M-type barium hexaferrite prepared by co-precipitation

Abstract: Highly stoichiometric and phase pure barium hexaferrite has been synthesized by co-precipitation as well as a solid-state preparative method using high purity nitrates, oxides and carbonates of iron(III), barium(II) and ammonium hydroxide. The isochronal and isothermally measured complex permittivity and dielectric loss tangents over 1 MHz–1 GHz in frequency remained relatively stable until a sintering temperature between 1100 and 1300 °C. A high value of relative permittivity of 32 and low loss tangent of 0.0329 indicate suitable high frequency characteristics for barium hexaferrite. The measured apparent densities before and after each firing cycle showed a monotonic increase. The crystal structure determined from X-ray diffraction studies confirmed the presence of single phase belonging to the theoretical space group P63/mmc with calculated cell parameters of a = b = 5.895 A and c = 23.199 A. In addition the DTA hexaferrite formation temperature was found to be 1050 °C.

Tuning the effective properties of metamaterials by changing the substrate properties

Abstract: Tunable properties of materials are highly desirable in many applications. Metamaterials with negative properties (permittivity, permeability, or both) can have many applications if such properties can be made tunable or can be switched alternatively between positive and negative property behavior. This paper is a numerical study of the effect of substrate properties on the effective properties of a metamaterial slab. We present both simulation results and measurement data for a specific split-ring resonator structure for two different substrate thicknesses and demonstrate very good agreement. Then, using finite element simulation, varying the permittivity of the substrate from 1 to 14 while keeping its physical thickness fixed, we show that the resonance frequency drops from ∼16to∼6GHz. Alternately, when the physical thickness of the substrate is varied from 0.05to2mm, keeping its permittivity fixed, the resonance frequency decreases from ∼13.2to∼9.2GHz. In each case, the effective refractive index is re...

Preparation and electromagnetic wave absorption properties of Fe-doped zinc oxide coated barium ferrite composites

Abstract: Fe-doped zinc oxide (ZnO) coated barium ferrite composite particles were prepared by a heterogeneous precipitation and thermal treatment process The prepared composite particles were characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM) The complex relative permittivity and permeability of ZnO/barium ferrite composites were measured in the frequency range of 2–12 GHz The results show that the coverage of ZnO has a great influence on microwave response of barium ferrite particles The formation of a ZnO thin layer on the surface of a barium ferrite particle changes the character of the frequency dispersion of the complex relative permittivity and permeability By changing the thickness of ZnO coverage, the frequency dependence of the microwave electromagnetic and absorbing properties could be adjusted, which provides us an opportunity for the synthesis of tailored particles

High permittivity and low dielectric loss in ceramics with the nominal compositions of CaCu3−xLa2x∕3Ti4O12

Abstract: Ceramics with the nominal compositions of CaCu3−xLa2x∕3Ti4O12 were prepared by the conventional solid-state reaction technique. It was found that these ceramics have the properties of rather high dielectric permittivity and sufficiently low dielectric loss. In particular, CaCu2.9La0.2∕3Ti4O12 ceramics sintered at 1050°C for 20h showed the high dielectric permittivity of 7500 with weak frequency dependence below 1MHz, the low dielectric loss less than 0.05 in the wide frequency range of 120Hz–200kHz (with the minimum 0.012 at 20kHz), and the small temperature coefficient about ±15ppm∕°C between −80 and 125°C. From the analysis, it was suggested that CaTiO3 secondary phase due to Cu deficiency and La doping plays the important roles in the observed excellent dielectric properties in CaCu3−xLa2x∕3Ti4O12 ceramics. The results indicated that they are a very promising class of high-permittivity materials for practical applications.

Epitaxial Thin-Film Deposition and Dielectric Properties of the Perovskite Oxynitride BaTaO2N

Abstract: Pulsed-laser deposition was employed to grow epitaxial thin films of the oxynitride perovskite BaTaO2N on a conducting SrRuO3 buffer layer deposited on a 100-cut SrTiO3 single-crystal substrate. Phase purity and epitaxy were optimized at a substrate temperature of 760 °C in a mixed gas atmosphere of 100 mTorr N2/O2 (∼20:1). The dielectric permittivity, κ, of the BaTaO2N film was large, exhibiting a slight frequency dependence ranging from about 200 to 240 over the frequency range 1−100 kHz. Furthermore, over the temperature range 4−300 K the permittivity showed minimal variation as a function of temperature. The temperature coefficient of the dielectric constant, τκ, is estimated to be in the range of −50 to −100 ppm/K. The coexistence of high dielectric permittivity and weak temperature dependence is an unusual combination in a single-phase material.

A new structure and its analytical model for the electric field and breakdown voltage of SOI high voltage device with variable-k dielectric buried layer

Abstract: A new SOI high voltage device structure with variable- k (permittivity) dielectric buried layer (VK SOI) is proposed in this paper. In this structure, the buried layer is made of two dielectrics, one of which is the low- k dielectric. The breakdown voltage is enhanced due to the modulation effect of the variable- k buried layer on the electric fields in the buried layer and drift region. An analytical model for the electric field and breakdown voltage in VK SOI is presented taking the modulation effect into account, from which the RESURF condition is derived. The dependences of the electric field distribution and breakdown voltage on the device parameters for VK SOI are investigated. Compared with the conventional SOI, the electric field of the buried layer and breakdown voltage of VK SOI with relative permittivity k I2 = 2 of the low- k dielectric are enhanced by 81% and 56%, respectively. The analytical results are in good agreement with those of 2D simulations. Finally, the proposed model and RESURF condition can be well applied to the conventional SOI and also extended to VT SOI (variable thickness buried layer SOI) devices.

Active metamaterials: Sign of refractive index and gain-assisted dispersion management

Abstract: We derive an approach to determine the causal direction of wavevectors of modes in optical metamaterials, which, in turn, determines signs of refractive index and impedance as a function of real and imaginary parts of dielectric permittivity and magnetic permeability. We use the developed technique to demonstrate that the interplay between resonant response of constituents of metamaterials can be used to achieve efficient dispersion management. Finally, we demonstrate broadband dispersionless index and impedance matching in active nanowire-based negative index materials. Our work has a potential to open new practical applications of negative index composites for broadband lensing, imaging, and pulse routing.

Microwave absorbing property of Fe-filled carbon nanotubes synthesized by a practical route

Abstract: Fe-filled carbon nanotubes were prepared reliably and economically via pyrolyzing of ferrocene and activated carbon. The sample was characterized by high-resolution transmission electron microscopy, electron diffraction and fast Fourier transforms. The complex relative permittivity and permeability parameters were measured in a frequency range of 2–18 GHz and microwave absorbing behavior was investigated. The sample exhibits the maximum reflection loss and the widest bandwidth of below −5 dB is −11.29 dB and 4.13 GHz (matching thickness = 2.5 mm), respectively.

Frequency dependence of effective permittivity of carbon nanotube composites

Abstract: Dependence of the permittivity of single-walled and multiwalled carbon nanotube composites on frequency and concentration was investigated experimentally using the coaxial air-line method over 0.1–10 GHz. The results are in good agreement with that obtained using the impedance method. It is found that scaling law based on the percolation theory provides a good description of the frequency dependence of measured permittivity in carbon nanotube composites. Parameters of the scaling law and deviations from the percolation theory are also discussed.

Coupled dipole method to compute optical torque: Application to a micropropeller

Abstract: The coupled dipole method is a volume integral equation method which allows computation of the scattered field from an arbitrary object (shape and relative permittivity). This method has been extended to the computation of optical forces. In this article we further extend the coupled dipole method to the computation of optical torque. First, we establish the equation to obtain the optical torque using the coupled dipole method, stressing the importance of the radiative reaction term. Second, we compare our theory to existing models for validation. Third, we apply our method to the computation of optical torque, from a plane wave circularly polarized on a micropropeller. The influence of geometry and relative permittivity on the optical torque is studied.

Microstrip Resonator Technique for Measuring Dielectric Permittivity of Liquid Solvents and for Solution Sensing

Abstract: A simple planar circuit method has been applied for the first time to measure the dielectric permittivity of solvents in trace amounts (0.3mul to 5mul) at multiple frequencies. It has been shown that due to the high sensitivity of the device it can be used effectively to characterize the quantity of dissolved impurities in a given solution. For relative dielectric permittivity measurements a square ring resonator prototype has been fabricated. Three solvents have been used as standards to measure seven unknowns at 1GHz, 2GHz and 3GHz. The measured results show excellent agreement with theoretical. An open loop resonator has also been developed to characterize glucose-water solutions of various concentrations at 1GHz.

Maxwell–Wagner polarization mechanism in potassium and titanium doped nickel oxide showing giant dielectric permittivity

Abstract: KxTiyNi1−x−yO(x = 0.05–0.3, y = 0.02–0.25) ceramics (abbreviated as KTNO) have been synthesized showing high permittivity. All the KTNO samples of varying compositions exhibit high dielectric permittivity (~104) near room temperature, which is comparable to that of the recently discovered CaCu3Ti4O12 (CCTO) ceramic. The high dielectric constant of KTNO depends on both the K and Ti content and can be attributed to the Maxwell–Wagner polarization mechanism and to a thermally activated mechanism.

Structural and electrical characterization of xBiScO3–(1−x)BaTiO3 thin films

Abstract: Using a tolerance factor approach, it was predicted that xBiScO3–(1−x)BaTiO3 will have a morphotropic phase boundary that should enhance both the polarizability and permittivity, relative to the BiScO3 end member, near a composition of x=0.4. To verify this prediction, pulsed laser deposition was used to grow xBiScO3–(1−x)BaTiO3 thin films on (100) SrRuO3∕LaAlO3 and Pt-coated Si substrates. Typical growth conditions were 700°C and 100mTorr O2∕O3. The perovskite structure was found to be stable for compositions of x=0.2–0.6 in epitaxial films, with reduced stability in polycrystalline films. The temperature where the maximum permittivity occurs rises as BiScO3 is added to BaTiO3, and increasingly relaxorlike behavior is observed with increasing BiScO3 content. Room temperature permittivity values ranged from 200 to 400, with loss tangents of ∼0.1 at 10kHz. The experimental morphotropic phase boundary occurs near x=0.4. 0.4BiScO3–0.6BaTiO3 showed a broad permittivity maximum near 800 from 150–275°C. Films w...

Characterization of Al2O3 thin films prepared by spray pyrolysis method for humidity sensor

Abstract: $Al_2O_3$ thin films were deposited on silicon, steel and nickel substrates to fabricate MOS and MIM devices. The films were prepared by spray pyrolysis method using a spray solution of Aluminium acetyl acetonate dissolved in dimethyl formamide and this solution was sprayed on to the hot substrates at temperatures of 300 and $350^oC$. The films were amorphous in nature as detected by XRD. Capacitance versus voltage (C–V), current versus voltage (I–V) and capacitance versus frequency (C–f) measurements were taken for these films. MOS capacitor was used as a humidity sensor using the home made humidity sensor setup. ac capacitance and parallel resistance of the capacitor as a function of humidity were studied. It was found that the capacitance value increases from 0.537 to 2.073 nf with the increase in relative humidity (RH) from 0 to 90% and the resistance decreases from 153 to 93 $k\Omega$ with the increase in relative humidity from 20 to 87%. Relative dielectric constant versus temperature measurements were done for the MOS device to check its ferroelectric behavior and its critical temperature was found to be around $66^oC$. MIM device was also used as a humidity sensor by measuring capacitance as a function of time by keeping the sensor in a dessicator. The 555 timer circuits were used to check the sensor behavior of the MOS device. Volume resistivity and breakdown electric field of the film deposited on steel were measured and found to be $5\times10^{11} \Omega \hspace{2mm} cm \hspace{2mm} and\hspace{2mm} 5\hspace{2mm} MV/cm$, respectively.

Microwave dielectric properties of carbon black filled polymers under uniaxial tension

Abstract: Broadband microwave spectroscopy is commonly employed in the determination of the wave transport properties in mesostructured polymers with embedded carbon black particles. However, very little is known on how uniaxial stress affects the effective permittivity of these percolative materials. In this work we carry out a comprehensive study of the complex permittivity spectra of carbon black filled ethylene butylacrylate copolymer which is submitted to a tensile stress up to 45% over the 0.1−3 GHz frequency range and at room temperature. Permittivity measurements indicated large decreases in the real and imaginary parts of the effective permittivity of the axially elongated samples. This set of experiments illustrates that these microwave permittivity data scale as a power law in frequency, where the exponent is strongly sensitive to stress. In addition, we show that our effective permittivity measurements under stress can be explained in terms of the Gaussian molecular network model in the limit of low str...

Theoretical prediction and experimental study of dielectric properties in poly(vinylidene fluoride) matrix composites with micronanosize BaTiO3 filler

Abstract: Composites of micronanosize BaTiO3 (BT) particles embedded into a polyvinylidene fluoride matrix were prepared. They were studied with respect to the effect of nanosize particles on microstructure and dielectric properties. The results show that the dielectric permittivity of composites with nanosize BT is close to the predicted values calculated at high concentration of fillers, if the interactions among BT fillers and between BT fillers and polymer are included. The enhanced dielectric permittivity mainly originates from a noticeably increasing phase interfaces in the composites, which brings out the strong interfacial polarization effect at low frequencies.