Modern wireless telecommunication devices (GSM Mobile system) (cellular telephones and wireless modems on laptop computers) have the potential to interfere with implantable medical devices/prostheses and cause possible malfunction. An implant of resonant dimensions within a homogeneous dielectric lossy sphere can enhance local values of SAR (the specific absorption rate). Also antenna radiation pattern and other characteristics are significantly altered by the presence of the composite dielectric entities such as the human body. Besides, the current safety limits do not take into account the possible effect of hot spots arising from metallic implants resonant at mobile phone frequencies. Although considerable attention has been given to study and measurement of scattering from a dielectric sphere, no rigorous treatment using electromagnetic theory has been given to the implanted dielectric spherical head/cylindrical body. This thesis aims to deal with the scattering of a plane electromagnetic wave from a perfectly conducting or dielectric spherical/cylindrical implant of electrically small radius (of resonant length), embedded eccentrically into a dielectric spherical head model. The method of dyadic Green's function (DGF) for spherical vector wave functions is used. Analytical expressions for the scattered fields of both cylindrical and spherical implants as well as layered spherical head and cylindrical torso models are obtained separately in different chapters. The whole structure is assumed to be uniform along the propagation direction. To further check the accuracy of the proposed solution, the numerical results from the analytical expressions computed for the problem of implanted head/body are compared with the numerical results from the Finite-Difference Time-Domain (FDTD) method using the EMU-FDTD Electromagnetic simulator. Good agreement is observed between the numerical results based on the proposed method and the FDTD numerical technique. This research presents a new approach, away from simulation work, to the study of exact computation of EM fields in biological systems. Its salient characteristics are its simplicity, the saving in memory and CPU computational time and speed.

Thesis (Masters Diploma (Electrical Engineering) -- Cape Technikon, Cape Town,1991 / Communication in all its various forms, has always played an important role in both the business and social environments. The conventional telephone, taken more often than not for granted, is responsible for keeping over five million people in South Africa alone, in daily contact. For the deaf and mute society, of which their are approximately 300 000 in South Africa, the telephone, on its own, has remained a useless gadget. Without the aid of a personal computer or terminal and a modem, communication for the deaf via the PSTN (Public Switched Telephone Network) has been impossible. Use of computers may be one way of overcoming this obvious problem, but expense now becomes the more important issue. To analyse the situation, two issues had to be taken into consideration. The first is, what makes the above solution so expensive, and the secondly, is thi!t expensive equipment necessary to complete the relatively simple task of interactive communication. The technology built into todays personal computers is continuously changing and in order to keep up with these changes, regular upgrades to the computer are necessary if one intends being able to recover ones investment at a later stage. The cost of a modem, with its sophisticated error-eorrection routines and auto-dial software, can also increase the initial outlay considerably. Bearing these costs in mind, it must now be investigated how one can achieve the objective of communicating with only the bear essential. By replacing the PC's monitor with a Liquid Crystal Display, the powerful processor with a relatively simple one, eliminating the disk storage entirely, reducing the on-board ROM!RAM memory, and finally, substituting a single-chip low speed modem for the free standing modem, the cost can be drastically reduced. By combining all these components together and developing a program to control them, the result is the 'Voiceless Telephone".

Abstract The thesis describes electrically tunable microwave devices utilising low sintering temperature, screen printable Barium Strontium Titanate (BST) thick films. The work has been divided into two parts. In the first section, the fabrication and microwave characterisation of BST material based structures compatible with Low Temperature Cofired Ceramic technology (BST-LTCC) are presented. Three different fabrication techniques, namely: direct writing, screen printing and via filling techniques, were used for the realisation of the structures. A detailed description of these fabrication techniques is presented. The dielectric properties such as relative permittivity, static electric field dependent tunability and loss tangent of BST-LTCC structures at microwave frequencies were characterised using coplanar waveguide transmission line and capacitive element techniques. The measured dielectric properties of BST-LTCC structures realised with the different fabrication methods are presented, compared and discussed. The second section describes tunable microwave devices based on BST-LTCC structures. A frequency tunable folded slot antenna (FSA) with a screen printed, integrated BST varactor is presented. The resonant frequency of the FSA was tuned by 3.2% with the application of 200 V external bias voltage. The impact of the BST varactor on the total efficiency of the antenna was studied through comparison with a reference antenna not incorporating the BST varactor. A compact, frequency tunable ceramic planar inverted-F antenna (PIFA) utilising an integrated BST varactor for mobile terminal application is presented. The antenna's resonant frequency was tuned by 3% with an application of 200 V bias voltage. Frequency tunable antennas with a completely integrated electrically tunable BST varactor with silver metallisation are introduced in this work for the first time. The integration techniques which are described in this thesis have not been previously reported in scientific literature. The last part of the thesis presents a microwave delay line phase shifter operating at 3 GHz based on BST-LTCC structures. The figure of merit (FOM) of the phase shifter was measured to be 14.6 °/dB at 3 GHz and and the device employs a novel structure for its realisation that enabled the required bias voltage to be decreased, while still maintaining compliance with standard screen printing technology. The performance of the phase shifter is compared and discussed with other phase shifters realised with the BST thick film process. The applications of BST-LTCC structures were demonstrated through frequency tuning of antennas, varactors, and phase shifters. The low sintering temperature BST paste not only enables the use of highly conductive silver metallisation, but also makes the devices more compact and monolithic.

Abstract The thesis describes the development of a novel LTCC material system for RF and microwave telecommunication purposes. The work has been divided into three parts. In the first section, the compositional and firing properties of this novel LTCC dielectric have been studied as well as its thermomechanical and dielectric properties. The second section describes the multilayer component preparation procedure for the ceramic material including tape casting and lamination parameters and the selection of the conductor paste. In the last section, the novel LTCC material system has been used to demonstrate its properties in RF multilayer resonators and a bandpass filter. The dielectric material for the novel LTCC system was prepared using magnesium calcium titanate ceramic, the firing temperature of which was decreased to 900°C by the addition of a mixture of zinc oxide, silicon oxide and boron oxide. The powder was made without any prior glass preparation, which is an important process advantage of this composition. The fired microstructure was totally crystalline with high density (3.7 Mg m-3) and low porosity (0.5 %). The mechanical properties were virtually identical to the values of the commercial LTCCs, but the higher thermal expansivity makes it most compatible with alumina substrates. The dielectric values were also good. The permittivity was 8.5 and the dissipation factor (0.9·10-3 at 8 GHz) less than that of the commercial LTCCs. Furthermore, the temperature coefficient of the resonance frequency was demonstrated to be adjustable between the range of +8.8 ... -62 ppm/K with a simple compositional variation of titanium oxide. The slurry for the tape casting was prepared using poly(vinyl butyral) -base organic additives and the 110 μm thick tapes had a smooth surface (RA < 0.5 μm). The multilayer components were prepared using 20 MPa lamination pressure, 90°C temperature and 1 h dwell time. The most suitable conductor paste for this composition was found to be commercial silver paste (duPont 6160), which produced satisfactory inner and outer conductor patterns for multilayer components. Finally, resonators with a resonant frequency range of 1.7 ... 3.7 GHz were prepared together with a bandpass filter suitable for the next generation of telecommunication devices. This demonstration showed the potential of the developed novel LTCC material system at high RF frequencies.