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Showing papers on "Dielectric loss published in 1999"


Journal ArticleDOI
TL;DR: In this article, whispering gallery modes were used for very accurate permittivity and dielectric loss measurements of ultralow loss isotropic and uniaxially anisotropic single crystals.
Abstract: Whispering gallery modes were used for very accurate permittivity and dielectric loss measurements of ultralow loss isotropic and uniaxially anisotropic single crystals. Several materials including sapphire, YAG, quartz, and SrLaAlO4 were measured. The total absolute uncertainty in the real part of permittivity tensor components was estimated to be ±0.1%, limited principally by the uncertainty in sample dimensions. Imaginary parts of permittivities were measured with uncertainties of about 10%, limited by the accuracy of Q-factor measurements of whispering gallery modes. It has been observed that, for most crystals, dielectric losses can be approximated by a power function of absolute temperature only in limited temperature ranges. At temperatures between 4-50 K, losses are often affected by impurities, which are always present in real crystals.

319 citations


Journal ArticleDOI
TL;DR: In this paper, single phase thin films of Ba0.5Sr 0.5TiO3 (BST) have been deposited onto MgO and LaAlO3 substrates using pulsed laser deposition and the capacitance and dielectric Q (1/tan δ) of as-deposited and annealed films have been measured from 1 to 20 GHz as a function of electric field (0-80 kV/cm) at room temperature using interdigitated Ag electrodes.
Abstract: Oriented, single phase thin films (∼5000 A thick) of Ba0.5Sr0.5TiO3 (BST) have been deposited onto (100) MgO and (100) LaAlO3 (LAO) substrates using pulsed laser deposition. The capacitance and dielectric Q (1/tan δ) of as-deposited and annealed films have been measured from 1 to 20 GHz as a function of electric field (0–80 kV/cm) at room temperature using interdigitated Ag electrodes deposited on top of the film. For films deposited onto MgO, it is observed that, after a postdeposition anneal (1000–1200 °C), the dielectric constant decreases and the dielectric Q increases. For films deposited onto LAO, a postdeposition anneal (⩽ 1000 °C) resulted in a significant increase in the dielectric constant and a decrease in Q. The observed dielectric properties of the BST films are attributed to the changes in film stress, which affects the extent of ionic polarization.

260 citations


Journal ArticleDOI
TL;DR: In this paper, the relationship between resonant frequencies, dimensions of the resonant structure, and permittivity of the sample under test is calculated with a radial mode-matching technique.
Abstract: Whispering-gallery modes are used for very accurate permittivity, dielectric loss, and temperature coefficient of permittivity measurements for both isotropic and uniaxially anisotropic dielectric materials. The relationship between resonant frequencies, dimensions of the resonant structure, and permittivity of the sample under test is calculated with a radial mode-matching technique. The relative accuracy of these computations is better then 10/sup -4/. The influence of conductor losses on dielectric loss tangent determination is treated for both whispering-gallery-mode and TE/sub 01/spl delta//-mode dielectric-resonator techniques. Two permittivity tensor components of sapphire and their temperature dependence were measured from 4.2 to 300 K. The total uncertainty in permittivity when use is made of whispering-gallery modes was estimated to be less than 0.05%. The uncertainty was limited principally by uncertainty in sample dimensions. Experimental and calculated resonant frequencies of several whispering-gallery modes differed by no more than 0.01%. The dielectric loss tangent of sapphire parallel and perpendicular to its anisotropy axis was calculated to be less than 10/sup -9/ at 4.2 K. The permittivity and dielectric loss tangent of a commercially available low-loss high-permittivity ceramic material has also been measured at S- and C-band frequencies using a large number of whispering-gallery modes.

218 citations


Journal ArticleDOI
TL;DR: In this article, different compositions of NiZn ferrites prepared by the citrate precursor method and sintered in the temperature range 1100-1400°C were reported for different compositions.
Abstract: Dielectric properties such as dielectric constant, ϵ′ , and dielectric loss factor, tan δ ∈ , are reported for different compositions of NiZn ferrites prepared by the citrate precursor method and sintered in the temperature range 1100–1400°C. It is observed that ϵ′ and tan δ ∈ for samples prepared in the present work are much lower than those normally obtained for NiZn ferrites prepared by the conventional ceramic method. The low values are attributed to better compositional stoichiometry, single-phase spinel structure and uniform microstructure of the samples. The low dielectric loss makes these samples especially attractive for use at high frequencies.

206 citations


Journal ArticleDOI
A.M Abdeen1
TL;DR: In this article, the dielectric properties of Ni 1− x Zn x Fe 2 O 4 ferrite samples were studied as a function of temperature, frequency and composition.

188 citations


Journal ArticleDOI
TL;DR: In this article, Ba0.5Sr 0.5TiO3 thin films have been synthesized on (001) LaAlO3 substrates by pulsed laser ablation.
Abstract: Perovskite Ba0.5Sr0.5TiO3 thin films have been synthesized on (001) LaAlO3 substrates by pulsed laser ablation. Extensive x-ray diffraction, rocking curve, and pole-figure studies suggest that the films are c-axis oriented and exhibit good in-plane relationship of 〈100〉BSTO//〈100〉LAO. Rutherford backscattering spectrometry studies indicate that the epitaxial films have excellent crystalline quality with an ion beam minimum yield χmin of only 2.6%. The dielectric property measurements by the interdigital technique at 1 MHz show room-temperature values of the relative dielectric constant, er, and loss tangent, tan δ, of 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively. The obtained data suggest that the as-grown Ba0.5Sr0.5TiO3 films can be used for development of room-temperature tunable microwave elements.

172 citations


Journal ArticleDOI
TL;DR: Dielectric spectroscopy covering more than 18 decades of frequency has been performed on propylene carbonate in its liquid and supercooled-liquid state and finds evidence for additional processes in the crossover regime.
Abstract: Dielectric spectroscopy covering more than 18 decades of frequency has been performed on propylene carbonate in its liquid and supercooled-liquid state. Using quasioptic submillimeter and far-infrared spectroscopy, the dielectric response was investigated up to frequencies well into the microscopic regime. We discuss the alpha process whose characteristic time scale is observed over 14 decades of frequency and the excess wing showing up at frequencies some three decades above the peak frequency. Special attention is given to the high-frequency response of the dielectric loss in the crossover regime between alpha peak and boson peak. Similar to our previous results in other glass-forming materials, we find evidence for additional processes in the crossover regime. However, significant differences concerning the spectral form at high frequencies are found. We compare our results to the susceptibilities obtained from light scattering and to the predictions of various models of the glass transition.

168 citations


Journal ArticleDOI
TL;DR: In this paper, the compositional variation of DC resistivity and dielectric constant show the inverse trend with each other, while the dielectral constant increases slowly with temperature in the beginning and then abruptly at about 473 K and above.

162 citations


Journal ArticleDOI
TL;DR: In this paper, the dielectric and insulating properties of epitaxial SrTiO3 (STO) thin film capacitors were studied, and the capacitors revealed a large tunability, i.e., a nonlinear e(E) dependence with respect to voltage biasing.
Abstract: The dielectric and insulating properties of epitaxial SrTiO3(STO) thin film capacitors were studied. The films were grown by inverted cylindrical magnetron sputtering in the radio frequency mode on (100) STO substrates which were covered with a (001)-oriented YBa2Cu3O7−x (YBCO) layer as a ground electrode. As a top electrode we used YBCO or Au thin films. A high dielectric constant, e, of up to 5000 was observed at T=80 K. The capacitors revealed a large tunability, i.e., a nonlinear e(E) dependence, with respect to voltage biasing. By applying 3 V, e decreased to 1000 which was 20% of its maximum value. The frequency dependence of e, the temperature dependence of the dielectric loss factor, tan δ, and the direct currency conductivity reflected that variable range hopping via localized states was present and dominated the conduction process in the STO films at low temperatures. The field strength for the electrical breakdown amounted to 300 kV/cm even for rather thin films with a thickness of about 40 nm....

160 citations


Journal ArticleDOI
TL;DR: In this article, a model where the fringing fields are rigorously accounted for and the resonance condition is derived is presented, and a method for nondestructively measuring the complex permittivity of materials is examined.
Abstract: This paper presents a full-wave analysis of the split-cylinder resonator. We outline a model where the fringing fields are rigorously accounted for and the resonance condition is derived. Using this model, a method for nondestructively measuring the complex permittivity of materials is examined. Measurements of the complex permittivity for low-loss dielectric materials using the split-cylinder resonator agree well with measurements made in a cylindrical cavity. An uncertainty analysis for the complex permittivity is also provided.

154 citations


Journal ArticleDOI
TL;DR: In this article, the variation of the dielectric constants with composition, frequency and temperature is explained qualitatively, and an attempt is made to explain the possible mechanism of the possible variation.

Patent
15 Oct 1999
TL;DR: A tunable dielectric structure as discussed by the authors consists of a first layer, a second layer, and electrodes for applying a controllable voltage across the first layer of dielectrics, where at least one of the electrodes is positioned between the first and second layers.
Abstract: A tunable dielectric structure includes a first layer of dielectric material, a second layer of dielectric material positioned adjacent to the first layer of dielectric material, with the second layer of dielectric material having a dielectric constant that is less than the dielectric constant of the first layer of dielectric material, and electrodes for applying a controllable voltage across the first dielectric material, thereby controlling a dielectric constant of the first dielectric material, wherein at least one of the electrodes is positioned between the first and second layers of dielectric material. The dielectric materials can be formed in various shapes and assembled in various orientations with respect to each other. The tunable dielectric structure is used in various devices including coaxial cables, cavity antennas, microstrip lines, coplanar lines, and waveguides.

Journal ArticleDOI
TL;DR: In this article, an exhaustive collection of dielectric relaxation data of glassy, crystalline, and molten ionic conductors are analyzed to obtain the magnitudes of their constant losses and the dependencies on temperature, ion density, ion mass, dc conductivity activation energy, dcconductivity level, the nonexponential conductivity relaxation parameter β, the mixed alkali effect, and the decoupling index Rτ.
Abstract: A frequency independent or nearly frequency independent contribution to the dielectric loss is present in all ionic conductors independent of the chemical and physical structures. An exhaustive collection of dielectric relaxation data of glassy, crystalline, and molten ionic conductors are analyzed to obtain the magnitudes of their constant losses and the dependencies on temperature, ion density, ion mass, dc conductivity activation energy, dc conductivity level, the nonexponential conductivity relaxation parameter β, the mixed alkali effect, and the decoupling index Rτ. Trends of changes in the constant loss when modifying the structure of the glassy matrix or mixing two different alkali ions are also found. In a glass-forming molten salt, 0.4Ca(NO3)2⋅0.6KNO3, the constant loss turns out to have approximately the same temperature dependence as the mean square displacement of the ions obtained by elastic neutron scattering measurement. All dependencies and properties found indicate that the physical origin of the constant loss may be traced to the displacement of the ions in their local librational or vibrational motion, but anharmonicity is not a necessary ingredient.

Journal ArticleDOI
01 Jun 1999-EPL
TL;DR: In this article, the glass transition temperature Tg and the temperature Tα corresponding to the peak in the dielectric loss due to the α-process were simultaneously determined as functions of the film thickness d through dielectrics measurements for thin films of polystyrene.
Abstract: The glass transition temperature Tg and the temperature Tα corresponding to the peak in the dielectric loss due to the α-process have been simultaneously determined as functions of the film thickness d through dielectric measurements for thin films of polystyrene. A decrease of Tg was observed with decreasing film thickness, while Tα was found to remain almost constant for d > dc and decrease drastically for d < dc. Here, dc is a critical thickness dependent on molecular weight. The thickness dependence of Tg is related to the distribution of the relaxation times of the α-process, not to the relaxation time itself.

Journal ArticleDOI
TL;DR: In this paper, an analytical expression for the energy loss suffered by a fast electron passing near a homogeneous dielectric sphere is derived within a fully relativistic approach, and the variation of the energy-loss spectra with both the radius of the sphere and the impact parameter of the electron trajectory is studied in detail.
Abstract: An analytical expression for the energy loss suffered by a fast electron passing near a homogeneous dielectric sphere is derived within a fully relativistic approach. The sphere is described by a frequency-dependent dielectric function. The electromagnetic field induced by the passage of the electron is then obtained by expressing the solution of Maxwell’s equations for this geometry in terms of the scattering of the multipole expansion of the incoming electromagnetic field at the sphere. The energy loss is derived from the induced field acting back on the electron. The variation of the energy-loss spectra with both the radius of the sphere and the impact parameter of the electron trajectory is studied in detail. Part of the energy loss is transformed into radiation, which is also investigated. For spheres characterized by real dielectric functions, like those of ionic materials in the transparency-frequency region, it is shown that the entire energy loss is transformed into radiation. Examples of loss spectra and radiation emission spectra are given for a material described by a Drude-like dielectric function ~e.g., Al! and for SiO2 . @S0163-1829~99!12103-9#

Journal ArticleDOI
TL;DR: In this article, a modification to this measurement technique utilizing two dielectric plugs which are used to house the granular or liquid materials was described, where no approximation to the measurement apparatus is made while the presence of the plugs are fully accounted for in the derivations.
Abstract: There are numerous dielectric property characterization techniques available in the microwave regime each with its own uniqueness, advantages and disadvantages. The two-port completely-filled waveguide (transmission line) technique is a robust measurement approach which is well suited for solid dielectric materials. In this case, the dielectric material can be relatively easily machined to fit inside the waveguide and the subsequent measurement of the scattering parameters of this two-port device renders the dielectric properties of the material filling the waveguide. However, this technique is not well suited for measuring the dielectric properties of granular and liquid materials. These materials are used in the production of various composites which are increasingly replacing the use of metals in many environments. If this technique is directly applied to these types of materials, several approximations either in the measurement apparatus or the formulation must be made. To overcome this problem, this paper describes a modification to this measurement technique utilizing two dielectric plugs which are used to house the granular or the liquid dielectric material. In this approach no approximation to the measurement apparatus is made while the presence of the plugs are fully accounted for in the derivations. Using this technique, the dielectric properties of cement powder, corn oil, antifreeze solution and tap water, constituting low- and high-loss dielectric materials (granular and liquid) were measured. In addition, the important issue of measurement uncertainty associated with this technique is also fully addressed. The issue of optimal choice of various measurement parameters is also discussed as it relates to the measurement uncertainty.

Journal ArticleDOI
TL;DR: In this article, BaTiO3 thin films with perovskite structure were grown by sol-gel spin-on processing onto (111)Pt/Ti/SiO2/Si substrates.
Abstract: Ferroelectric BaTiO3 thin films with perovskite structure were grown by sol-gel spin-on processing onto (111)Pt/Ti/SiO2/Si substrates. In order to investigate the effects of space charge in BaTiO3 thin films, we measured the relative dielectric constant and the ac conductivity of the films as a function of frequency, ac oscillation amplitude, and temperature. Dielectric constant and dielectric loss were 147 and 0.03 at 100 kHz, respectively. Also, BaTiO3 thin films exhibited marked dielectric relaxation above the Curie temperature and in the low-frequency region below 100 Hz. This low-frequency dielectric relaxation is attributed to the ionized space-charge carriers such as oxygen vacancies and defects in BaTiO3 film and the interfacial polarization. The thermal activation energy for the relaxation process of the ionized space-charge carriers was 0.72 eV.

Journal ArticleDOI
TL;DR: In this article, the microwave properties of low-melting ZnO, BaO, and PbO were investigated using the parallel plate dielectric resonator rod method.
Abstract: The trend to fabricate mulitlayer structures of microwave dielectric ceramics cofired with low melting conductors results in the demand of additives for low temperature sintering. Low-melting glasses are good candidates for low temperature sintering aids. When the concentration of the added low-melting glasses reaches a high content of about 10–20 mol%, their microwave properties will certainly affect the performance of the final multilayer devices. It is the object of this study to investigate the microwave properties of low-melting ZnO–B 2 O 3 –SiO 2 , BaO–B 2 O 3 –SiO 2 , and PbO–B 2 O 3 –SiO 2 glasses. The parallel plate dielectric resonator rod method was employed for measurements of relative dielectric constants, quality factors, and temperature coefficients of frequency in the microwave frequency range. A thermo-mechanical analyzer was used to determine deformation temperatures of glasses. Properties of these three glass systems are chiefly determined by the amount of structural modifier oxides (ZnO, BaO, and PbO) and the ionic size of the modifying cations (Zn 2+ , Ba 2+ , Pb 2+ ). In contrast, the effect of the ratio of B 2 O 3 to SiO 2 is relatively small. The frequency constants of these three glass systems range from 500 to 3400, which are equivalent to tan δ of 0.02–0.003 at 10 GHz. The temperature coefficients of frequency range from −3 to −155 ppm/°C.

Journal ArticleDOI
TL;DR: In this paper, the microwave-sintered compacts produced much finer grain sizes at near theoretical density compared to conventional sintering, resulting in material properties such as flexure strength and breakdown strength.
Abstract: Microwave sintering behaviors of three kinds of ceramics with different dielectric loss [Al 2 O 3 , Ce–Y–ZrO 2 and lead-based relaxor ferroelectrics (PMZNT)] in 2·45 GHz microwave furnace were described. Measurement of sample densities showed an enhancement of the sintering processing for all materials studied. For PMZNT and Ce–Y–ZrO 2 with high dipolar loss or ionic conductive loss, the associated microstructure examined using scanning electron microscopy showed that microwave-sintered compacts produced much finer grain sizes at near theoretical density compared to conventional sintering. Resulting material properties, such as flexure strength and breakdown strength, were also increased due to developed microstructure in microwave processing. However, a comparable grain size and properties were observed for high pure Al 2 O 3 with low dielectric loss in microwave and conventional methods. ©

Journal ArticleDOI
TL;DR: In this article, X-ray diffraction was performed on Ln(Mg1/2Ti 1/2)O3 (Ln = Dy, La, Nd, Pr, Sm, Y) compositions and their pertinent properties for use as thin film substrates for YBa2Cu3Ox (YBCO) were measured.
Abstract: Ln(Mg1/2Ti1/2)O3 (Ln = Dy, La, Nd, Pr, Sm, Y) compositions have been prepared, and their pertinent properties for use as thin film substrates for YBa2Cu3Ox (YBCO) were measured. X-ray diffraction shows that Ln(Mg1/2Ti1/2)O3 compositions have noncubic symmetry and the GdFeO3-type structure. Dielectric constant measurements revealed values between 22 and 27, which are larger than those of the LnAlO3 family. Quality factor (=1/ tan δ) of the ceramic specimens measured at room temperature was larger than 3000 at 10 GHz. Among the compounds, La(Mg1/2Ti1/2)O3 exhibited the highest dielectric constant and the lowest dielectric loss. Chemical reaction was observed between Ln(Mg1/2Ti1/2)O3 (Ln = Dy, Sm, Y) and YBCO after annealing a 1 : 1 mixture at 950 °C. Considering dielectric and physical properties, La(Mg1/2Ti1/2)O3 and Sm(Mg1/2Ti1/2)O3 were determined to be suitable substrates for YBCO thin film used in microwave applications.

Journal ArticleDOI
M. A. El Hiti1
TL;DR: In this article, the effect of frequency, temperature and composition on the dielectric behavior was studied for MgxZn1−xFe2O4 ferrite samples prepared using the usual ceramic technique.

Journal ArticleDOI
TL;DR: In this article, the power law frequency response is accounted for well by the logarithmic mixing rule in 2D square networks with different proportions of resistors and capacitors.
Abstract: Simulations of the AC electrical characteristics of 2D square networks randomly filled with resistors or capacitors exhibit many features in common with experimental dielectric responses of solids. These include the `universal' fractional power law dispersions in permittivity and dielectric loss characterized by the Cole-Davidson response function. Simulations are presented of networks containing different proportions of resistors and capacitors which show that the power law frequency response is accounted for well by the logarithmic mixing rule. Limiting high and low frequency characteristics are found to be controlled by percolation paths of either resistors or capacitors. It is suggested that the power law response of a solid could be an indication that it is microscopically inhomogenous, containing an effective microscopic random network of conducting and dielectric insulating islands.

Journal ArticleDOI
TL;DR: The dielectric properties of layer perovskites in the Dion−Jacobson (KCa2Nb3O10, HCa2 Nb4O13, KLa 2NbTi2O10) and Ruddlesden−Poppper (K2La2Ti3O 10) series were investigated in this article.
Abstract: The dielectric properties of layer perovskites in the Dion−Jacobson (KCa2Nb3O10, HCa2Nb3O10, CsPb2Nb3O10, HPb2Nb3O10, KCa2NaNb4O13, KLa2NbTi2O10) and Ruddlesden−Poppper (K2La2Ti3O10) series, and of...

Journal ArticleDOI
TL;DR: Terahertz time-domain spectroscopy has been used to characterise the refractive index and absorption coefficient of samples fabricated using the negative photoresist SU-8, in the frequency range 0.1-1.6 THz.
Abstract: Terahertz time-domain spectroscopy has been used to characterise the refractive index and absorption coefficient of samples fabricated using the negative photoresist SU-8, in the frequency range 0.1-1.6 THz. At a frequency of 1 THz, the corresponding dielectric constant and dielectric loss tangent are 2.9 and 6.3/spl times/10/sup -6/, respectively.

Journal ArticleDOI
TL;DR: In this article, the temperature coefficient of permittivity of Ba6-3xR8+2xTi18O54 (R=La-Gd) solid solutions revealed a high degree of correlation with the ratio of mean radii (rA/rB) of A- and B-site ions.
Abstract: Studies of the temperature coefficient of permittivity of Ba6-3xR8+2xTi18O54 (R=La–Gd) solid solutions revealed a high degree of correlation with the ratio of mean radii (rA/rB) of A- and B-site ions. Single-crystal X-ray diffraction analyses of La, Sm and Pr analogues showed that rA/rB can be further correlated to tilting of the TiO6 octahedra in the network of the Ba6-3xR8+2xTi18O54 crystal structure. Changes in the tilting of the octahedra induce changes in the crystal field and subsequently, changes in the temperature coefficient of permittivity as well as dielectric loss. Variations in dielectric properties are limited by the flexibility of the crystal structure. Variations in the tilting of the octahedra resulting from changes in the composition are highly anisotropic, which explains the markedly high electrical anisotropy of Ba6-3xR8+2xTi18O54 solid solutions.

Journal ArticleDOI
TL;DR: In this paper, the performance of (Ba,Sr)TiO3 (BST) capacitors for ultralarge scale integration dynamic random access memories (DRAM) was investigated.
Abstract: Interfaces and hence electrodes determine the performance of (Ba,Sr)TiO3 (BST) capacitors for ultralarge scale integration dynamic random access memories. Electrode materials forming a rectifying contact on BST drastically reduce the dielectric constant and hence the capacitance and charge storage density of the capacitor, when the dielectric thickness is reduced. This can limit the role of Pt as an electrode material for gigabit dynamic random access memories (DRAM). The conducting oxide, La0.5Sr0.5CoO3 (LSCO) with its perovskite structure, has structural and chemical compatibility with BST. Our results in LSCO/BST/LSCO capacitor show that the mechanism of conduction is not interface limited but predominantly bulk limited. A 75 nm BST film with LSCO electrodes shows a leakage current density of 1×10−7 A/cm2 at 1 V, 85 °C. The dielectric constant at 1 V, 105 Hz is 350, making LSCO a potential contact electrode for DRAM memories.

Journal ArticleDOI
X.M. Chen1, J.S Yang1
TL;DR: In this article, the authors characterized the dielectric properties of tungsten-bronze ceramics in the BaO-NdTi 2 Ta 3 O 15 and Ba 5 NdTi 3 Ta 7 O 30 systems.
Abstract: Dielectric ceramics in the BaO–Nd 2 O 3 –TiO 2 –Ta 2 O 5 system were prepared and characterized. The ceramics with tungsten–bronze structure based on the compositions Ba 2 NdTi 2 Ta 3 O 15 and Ba 5 NdTi 3 Ta 7 O 30 had a high dielectric constant (>100) with a lower frequency-dependency when complete densification was achieved; a low dielectric loss was obtained in the former.

Journal ArticleDOI
TL;DR: Results show that both the aspect ratio and the volume have a significant effect on the heating rates, time to thaw and the non-uniformity of temperatures during thawing.
Abstract: Non-uniformity of temperatures in thawing of food and biological materials inside a microwave oven is affected by size, shape, and dielectric properties of the load (food) The objective of this study was to relate the time to thaw and the non-uniformity of heating to the shape, size, and the dielectric properties of the load The details of the heat transfer analysis, experimental measurement of thermal and dielectric properties, and temperature measurements are described in a companion paper Results show that both the aspect ratio and the volume have a significant effect on the heating rates, time to thaw and the non-uniformity of temperatures during thawing A "shield" develops from surface thawing and leads to reduced microwave penetration This "shield" develops more readily at higher dielectric loss, thereby effectively increasing the thawing time even more for a lossy material at higher power levels Thawing time increases linearly with volume As the load aspect ratio decreases (it is made flatter), it thaws faster since the energy decays relatively less in a thinner material These new results could provide a more rational and quantitative approach to development of frozen food products to be heated in a microwave oven

Journal ArticleDOI
TL;DR: In this article, two-dimensional (2D) photonic crystals (PCs) composed of lossy dielectric rods in air were constructed with a microwave bandgap between 4-8 GHz.
Abstract: Square and triangular lattice two-dimensional (2D) photonic crystals (PCs) composed of lossy dielectric rods in air were constructed with a microwave bandgap between 4-8 GHz. Fabry-Perot resonators of varying length were constructed from two of these PCs of adjustable thickness and reflectivity. The quality factor of cavity modes supported in the resonators was found to increase with increasing PC mirror thickness, but only to a point dictated by the lossiness of the dielectric rods. A 2-D periodic Green's function simulation was found to model the data accurately and quickly using physical parameters obtained in separate measurements. Simple rules are developed for designing optimal resonators in the presence of dielectric loss.

Journal ArticleDOI
TL;DR: In this article, the frequency dependence of a dielectric loss tangent (tan δ ) is found to be abnormal, giving a peak at a certain frequency for all the compositions.