Corrugated spherical antenna

The radiation characteristics of a corrugated metallic sphere with an azimuthal slot are studied. For the purpose of analysis, a dielectric coating equivalent to the corrugation on the surface is assumed. Expressions for the equivalent relative permittivity, input admittance, gain and radiated far field, based on the boundary-value approach, are presented. For a spherical antenna of k0a = 4.9087 with corrugation corresponding to an equivalent dielectric coating of relative permittivity 8.36, it is shown that the increase in gain over the uncorrugated antenna is 6.15 dB. The above antenna was fabricated and the experimental pattern obtained is compared with the theoretical result.     

An asymmetric multilayer pendry lens

The optical-band subwavelength imaging by a multilayer Pendry lens consisting of alternating layers of a metal with the permittivity ε _m < 0 and a dielectric with the permittivity ε _d = ?ε _m is considered. In the earlier papers by Pendry and Ramakrishna, it is shown that, in a nonideal case, i.e., for |ε _d | = |ε _m | ≠ 1, the image can be obtained only with the use of an asymmetric scheme, when the image is formed in a medium with a permittivity equal to ε _d , the source being located in vacuum. However, in this case, the image quality is impaired (the image spectrum is narrowed). This phenomenon is explained in this study.     

Calculation of attenuation of dielectric-rod waveguides

A method is suggested for calculating the attenuation constant of a dielectric waveguide when the dependence of the phase coefficient on the permittivity of the dielectric material is known. The relevant formula, in an obvious notation, is a = (?d?/d?) tan ?     

Determination of electrodynamical parameters of dielectric pipe-shaped materials using millimeter wave cavity

Employment ofE _0np modes of cylindrical cavity resonator for measurement of electrodynamical parameters of dielectric pipe-shaped materials in millimeter wavelength band is suggested. Dielectric permittivity ? and conductivity σ of a sample can be found by measuring the frequency shift and theQ-factor change of the resonator. Method of “mode basis” is used for the calculation of sample permittivity ? and conductivity σ. Measurements were carried out at 8mm wavelength and related calculations have demonstrated use and possibilities of the method in studying the dielectric properties of samples of cylindrical and other forms.     

Localized DC Field Produced by Diode Implanted in Isotropic Homogeneous Medium and Exposed to Uniform RF Field

Minimally invasive selective stimulation of biological tissue within the body can be achieved by implanting a small rectifying diode and then applying an RF field by means of electrodes or a coil on or near the surface of the body. A theoretical analysis of a simplified model consisting of a cylindrically symmetrical unit implanted in an isotropic homogeneous medium of conductivity ?and permittivity ? and exposed to a uniform RF field relates the dc component of electrode current to the detailed geometry of the electrodes of the implanted unit and to the amplitude of the applied field.     

Novel temperature-stable ceramics for microwave dielectric resonators and microstrip substrates

Ceramics comprising homogeneous single-phase zirconate solid solutions of suitable composition have very low temperature coefficients of permittivity, low-frequency permittivities of 30?40 and low losses. Dielectric resonators give Q values up to 4000 and permittivities of 28?35 at 4?5 GHz. The effective permittivity measured on a microstrip ring resonator on a calcium-zirconate substrate shows the dispersion predicted theoretically; the effective permittivity increases from 17 to 23 over the frequency range 1?12 GHz and gives 28.1 as the calculated real value of the permittivity of the substrate. The measured Q value of 200 indicates negligible dielectric losses compared with the I2R losses.     

Narrow-beam antennas using an artificial dielectric medium with permittivity less than unity

Radiation from a line source of electric current placed inside a slab of artificial dielectric medium with a permittivity less than unity has been studied. It is found that radiation patterns with single or multiple narrow beams may be obtained by the proper choice of parameters. In a typical case for ?r=0.1378, ?r=1.322, a beamwidth of about 1° is obtained when the thickness of artificial dielectric slab is about 2.33 times the wavelength.     

The Conical Antenna as a Sensor or Probe

The electrically small wide-angled spherically capped conical monopole is shown to have frequency-related properties closely resembling those of the electrically thin cylindrical dipole. It is frequency-independent when used to measure the time derivative of the electric field when it is connected to a matched load and kL = kl( 1 + ?0) ? 1. Here/is the radius of the conical surface and ?0 is half of the angle subtended by the cone. Graphs are shown for ?0 470° = 0.82 rad for which the characteristic impedance is 50 ?.     

Suppression of travelling high-field-domain mode oscillations in GaAs by dielectric surface loading

It is shown that travelling high-field-domain-mode oscillations in GaAs, with n0l > 1012cm?2, can be suppressed by attaching a dielectric material of high permittivity (BaTiO3) to the surfaces of the GaAs. Experimental results observed with a sampling oscilloscope are given.     

Zn位非化学计量对BaNb_(0.69)(Zn_(0.116)Co_(0.217))O_3微波介电性能的影响

采用传统固相反应法制备BaNb0.69[Zn0.116(1+0.025x)Co0.217]O3(BCZN)(x=0～4)微波介质陶瓷。研究了Zn位离子的微量添加对BCZN陶瓷性能的影响。结果表明:少量添加Zn,可以促进烧结致密化,改善BCZN陶瓷的介电性能。在1300℃下烧结3h,可以获得τf近零,介电常数εr为33、Q·f为51322 GHz的陶瓷。     

Some Effects of Field Perturbation Upon Cavity-Resonance and Dispersion Measurements on MIC Dielectrics

An analysis is presented of field perturbations in MIC resonators in order to examine the errors which occur in permittivity measurements made by cavity-resonance methods: Q factor, coupling effects, fringing fields, crystal misalignment (for anisotropic materials), changes in ambient temperature are all considered. Analysis of a cavity with mixed boundary conditions shows that the resonant-mode frequencies depend to the first order on that part of Q/sub 0/ associated with imperfect electric (metal) walls, but to the second order on that part associated with imperfect magnetic (open-circuit) walls. A new expression is given for the Q of an open-ended microstrip resonator when surface waves are excited in the dielectric, and it is shown that the unloaded Q (Q/sub 0/) can be dominated by this phenomenon. It is further shown that these Q-related effects, together with reactive perturbations arising from fringing, coupling structures, are the principal source of error in measurements for epsilon or epsilon/sub eff/. Such reactive effects may be treated semiquantitatively by applying Slater's perturbation theorem to the affected region. These procedures lead to the following revised values for the crystal permittivity of sapphire (monocrystalline Al/sub 2/0/sub 3/) in the microwave region: epsilon/sub ||/ (parallel to the c axis) = 11.6; epsilon/sub /spl perp// (base-plane) = 9.4.     

A model for the complex permittivity of ice at frequencies below 1 THz

Using empirical fits to published data, formulas are suggested for the complex permittivity of ice. The radio frequency may range from 0 to 1000 GHz, and the temperature from 0° to ?40°C. It then becomes apparent where additional data would be welcome.     

Theoretical and experimental results of guided wavelength of a slot on a low-permittivity substrate

In the letter theoretical results for the guided wavelength and characteristic impedance of different slots are given for a substrate of relative permittivity ?r = 2.17. A formula is given for the first parameter. A comparison of theory and experiment, according to a model of a transmission-line applied to the slot, is presented.     

Barrier-height determinations in thin-film tunnel junctions

Using the previously determined value of the internal electric field of tunnel diodes, the authors use the electric tunnel method for the evaluation of metal?dielectric barrier heights. Effective mass of electron and dielectric permittivity are constant for a range of thickness from 50 to 150 ?.     

TM and TE Mode Surface Waves on Grounded, Anisotropic, Inhomogeneous, Lossless, Dielectric Slabs (Correspondence)

J. H. Richmond has given the WKB solutions for the field distribution of surface waves on inhomogeneous, isotropic, plane layers. It is the purpose of this letter to extend his work to include a simple anistropy in the dielectric constant by considering a diagonalized relative permittivity tensor with components /spl epsi//sub x/(x), /spl epsi//sub y/(x), and /spl epsi//sub z/(x). The geometry is the same as before except that a perfectly conducting plane is now positioned at x = 0. For easy reference we have used the same notation as Richmond, except where specified otherwise. Compactness in notation has been achieved by expressing the integrations from 0 to x and by considering the x variations outside the slab to be exp {-a(x-a)}.     

Dielectric spectroscopy studies on (PVP + PVA) polyblend film

The thermal behavior of (PVP + PVA) polyblend film have been examined using differential scanning calorimetry and scanning electron microscopy. Capacitance and loss tangent values of polyvinyl pyrrolidone (PVP) + polyvinyl alcohol (PVA) polyblend film were measured in the frequency range 1-100 kHz and temperature range 298-423 K. Dielectric permittivity of real part (ε′) was obtained from capacitance data and dielectric permittivity of imaginary part (ε″) was obtained from real part of dielectric permittivity and loss tangent values. The decrease in dielectric permittivity was observed with increasing frequency and also observed increase in dielectric permittivity with increasing temperature. The complex dielectric constant (ε*) has been described by the electric modulus M* = (1/ε*) = M′ + iM″. The data of M* has been analysed by the stretched exponential decay of the electric field, Φ(t) = exp−(t/τ₀)^β.     

Two-frequency resonance scattering by finite thin metamaterial plates

A finite thin plate made from a metamaterial with negative values of permittivity ? and permeability ?? is considered. The 2D problem of excitation of the plate by a cylindrical wave is numerically investigated. It is found that the frequency dependence of the excited near field has two high-Q resonances closely spaced in frequency and that the constitutive parameters have values close to those that lead to triple (double) degeneration of a surface wave in an infinite plate. The near and far fields at the resonance frequencies are calculated.     

Synthesis procedure for, and characteristics of, one-port linear magnetoelastic dispersors

The necessity of an internal magnetic field with spatially constant gradient for a linear frequency?time delay property of ? = 0 magnetoelastic waves is demonstrated, and certain limitations on achievable time?bandwidth product are formulated. The internal-field configuration is approximated using a composite single-crystal/polycrystalline ferrimagnetic structure, and comparisons between theory and practice are drawn.     

Modes of a planar nonlinear-metamaterial waveguide

Modes of a planar dielectric waveguide are investigated. The waveguide is made from a nonlinear metamaterial with a negative permittivity and a negative permeability. The mode wavenumbers and field distributions are calculated for structures with parabolic permittivity and permeability profiles. It is shown that anomalously high field intensities can be observed in such a structure. The dependences of the mode propagation coefficients on the electric field are analyzed for the case of nonlinear media. The effect of nonlinearity saturation is considered.