Normalization factors for magnetic relaxation of small particle systems in non-zero magnetic field.

We critically discuss relaxation experiments in magnetic systems that can be characterized in terms of an energy barrier distribution, showing that proper normalization of the relaxation data is needed whenever curves corresponding to different temperatures are to be compared. We show how these normalization factors can be obtained from experimental data by using the Tln (t/t0) scaling method without making any assumptions about the nature of the energy barrier distribution. The validity of the procedure is tested using a ferrofluid of Fe3O4 particles.

Investigation of dielectric and elastic properties of selected dielectric ceramics and oxide glasses

The dielectric and elastic properties are of considerable significance to the science and technology of matter in the solid state. The study of these properties give information about the magnitude of the forces and nature of the bonding between the atoms. Our aim has been to investigate systematically the effect of doping of an appropriate element on the elastic and dielectric properties of selected dielectric ceramics and oxide glasses. These materials have got wide technological applications due to their interesting electrical, optical, thermal and elastic behaviour. Ultrasound propagation and capacitance measurement techniques have been employed for the systematic investigation of the elastic and dielectric properties of selected number of these materials. Details of the work done and results obtained are presented in this thesis.

Electrical properties and phase transitions insome ammonium containing ferroelectrics

The thesis aims to present the results of the experimental investigations on the electrical properties like electrical conductivity, dielectric constant and ionic thermo~ currents in certain ammonium containing ferroelectric crystals viz. LiNH4SO4, (NH4)2SO4 and (NH4)5H(SO4)2. Special attention has been paid in revealing the mechanisms of electrical conduction in the various phases of these crystals and those asso~ ciated with the different phase transitions occurring in them, by making studies on doped, quenched and deuterated crystals. The report on the observation of two new phase transitions in (NH4) S O2 and of a similar one in ( NH4 ) H (2SO4 ) are included. The relaxation mechanisms of the impurity-vacancy complexes and the space charge phenomena in pure and doped crystals of LiNH4SO4 and (NH4)2SO4 and the observation of a new type of ionic thermo-current viz. Protonic Thermo-Current (PTC) in these crystals are also presented here.

Investigations on the radiation characteristics of new hollow dielectric horn antennas

Investigations on the design and development of certain new hollow dielectric hom antennas of rectangular cross section have been carried out. The main shortcoming of the existing ordinary hollow dielectric hom antenna (HDH) is the abrupt discontinuity at the feed-end. A new launching technique using a dielectric rod is introduced to overcome this limitation. Also a strip loading technique is employed for further modification of the antenna. Radiation parameters of new I-IDH antennas of Eplane sectoral, H-plane sectoral and pyramidal types were studied and are found to be very attractive. Theoretical approach based on Marcatili’s principle and two aperture theory along with diffraction theory and image theory is used to support the experimental findings. The HDH is considered as solid horn of effective dielectric constant and the aperture field is evaluated. The antenna is excited by the open waveguide in the dominant TE1o mode and so the existence of any hybrid mode is mled-out. The theoretical results are observed to be in good agreement with the experimental results.

Investigations On A Microstrip Excited Rectangular Dielectric Resonator Antenna

The thesis relates to the investigations carried out on Rectangular Dielectric Resonator Antenna configurations suitable for Mobile Communication applications. The main objectives of the research are to: - numerically compute the radiation characteristics of a Rectangular DRA - identify the resonant modes - validate the numerically predicted data through simulation and experiment 0 ascertain the influence of the geometrical and material parameters upon the radiation behaviour of the antenna ° develop compact Rectangular DRA configurations suitable for Mobile Communication applications Although approximate methods exist to compute the resonant frequency of Rectangular DRA’s, no rigorous analysis techniques have been developed so far to evaluate the resonant modes. In this thesis a 3D-FDTD (Finite Difference Time Domain) Modeller is developed using MATLAB® for the numerical computation of the radiation characteristics of the Rectangular DRA. The F DTD method is a powerful yet simple algorithm that involves the discretimtion and solution of the derivative form of Maxwell’s curl equations in the time domain.

Rectangular Dielectric Resonator Antenna Configurations For Mobile Communication Applications

Experimental investigations on Microstrip line excited Dielectric Resonator Antenna configurations suitable for Mobile Communication applications are reported. High permittivity (εrd = 48) resonator samples with different aspect ratios are employed for the study. Theoretical analysis performed using FDTD method is also presented.

Characterization of low dielectric constant polyaniline thin film synthesized by ac plasma polymerization technique

Polyaniline thin films were prepared by ac plasma polymerization technique. Capacitance, dielectric loss, dielectric constant and ac conductivity of these films were investigated in the frequency range from 100 Hz to 1MHz and in the temperature range from 300 to 373 K. Capacitance and dielectric loss decreased with frequency and increased with temperature. This type of behaviour was found to be in good agreement with an existing model. The ac conductivity σ(ω) was found to vary as ωs with the index s 1. Annealing of polyaniline thin films in high vacuum at 373K for 1 h was found to reduce the dielectric loss. FTIR studies reveal that the aromatic ring is retained in the polyaniline thin films, which enhances the thermal stability of the polymer films

Evaluation of a.c. conductivity of rubber ferrite composites from dielectric measurements

The effect of frequency, composition and temperature on the a.c. electrical conductivity were studied for the ceramic, Ni1–xZnxFe2O4, as well as the filler (Ni1–xZnxFe2O4) incorporated rubber ferrite composites (RFCs). Ni1–xZnxFe2O4 (where x varies from 0 to 1 in steps of 0×2) were prepared by usual ceramic techniques. They were then incorporated into a butyl rubber matrix according to a specific recipe. The a.c. electrical conductivity (sa.c.) calculations were carried out by using the data available from dielectric measurements and by employing a simple relationship. The a.c. conductivity values were found to be of the order of 10–3 S/m. Analysis of the results shows that sa.c. increases with increase of frequency and the change is same for both ceramic Ni1–xZnxFe2O4 and RFCs. sa.c. increases initially with the increase of zinc content and then decreases with increase of zinc. Same behaviour is observed for RFCs too. The dependence of sa.c. on the volume fraction of the magnetic filler was also studied and it was found that the a.c. conductivity of RFCs increases with increase of volume fraction of the magnetic filler. Temperature dependence of conductivity was studied for both ceramic and rubber ferrite composites. Conductivity shows a linear dependence with temperature in the case of ceramic samples

Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites

Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties