Ungvichian, Vichate

This effort studies the implementation of a biocompatible Planar Inverted-F Antenna
(PIF A) for the Medical Instrument Communication System (MICS) frequency band of
402 to 405 MHz for RFID applications. The basic electromagnetic properties of human
tissues are investigated at 403 .5 MHz. Then, the radiation characteristics of submerged
wire antenna are evaluated in order to approximate the effects of multilayered media on a
PIFA's performance. The PIFA is assessed using Ansoft's Finite Element Method based
electromagnetic evaluation software, HFSS v.l 0. The electrical parameters of the
antenna in relation to the surrounding environment, notably air, silicone capsule, and a
three-layered bio-media, are presented. The analysis shows that the resonant frequency
as well as the electrical performance of the design is significantly affected by the physical
dimensions and the relative permittivity of the dielectric materials covering the antenna.

FAU's Office of Undergraduate Research and Inquiry hosts an annual symposium where students engaged in undergraduate research may present their findings either through a poster presentation or an oral presentation.

This thesis addresses the electromagnetic analyses of two structures. The first structure, a low frequency loop antenna recommended for use by national standards on electromagnetic compatibility (EMC), is incorrectly specified to have the same voltage to magnetic field conversion ratio (antenna factor) when used with a 50 ohm receiver in lieu of a high impedance type ($>$600 ohm). Two independent measurement sets were performed to demonstrate the prevailing discrepancy, and a corrected antenna factor is presented for use with a 50 ohm receiver. The second structure, a partial spiral "pancake" applicator used to generate high EM fields in its vicinity, was evaluated for its (induction) reactive near-field electromagnetic characteristics. Construction of an induction zone measurement system including the development of an electrically small electric field is described. Measured data on three dimensional EM field contours over the face of the applicator, are presented.

This thesis addresses pertinent studies concerning the use of electromagnetic composite media as EMI shielding materials. Specifically biphasic composites constituted by conducting and/or lossy inclusions dispersed in a dielectric host are considered. The effects of conductivity and/or dielectric loss, shape, size and volume fraction of the included component in deciding the shielding effectiveness of the composite material are ascertained over radio frequency spectrum. Theoretical studies in modeling the effective complex permittivity of the test composite are presented in the classical and state-of-the-art perspectives and hence the shielding effectiveness of the test composite is elucidated. The theoretical considerations also refer to two types of inclusions namely, conducting particulates (metallic particles, fibers and flakes), and lossy nonmetallic inclusions. In the first case the host-inclusions system refers to polemically opposite constituents and in the later case, it is simply a dielectric-dielectric mixture. Experimental studies to evaluate the shielding effectiveness of a set of test composite are presented. Relevant descriptions include details on the test composites synthesized, experimental arrangement and the test procedure followed. Particulars on test materials constituted by a host ceramic medium (such as TiO2) with conducting inclusions such as iron particles, copper rods and aluminum flakes are presented. Measured results on the shielding effectiveness of these materials over the frequency range (200 to 1500 MHz) are listed and compared with theoretical results. Conclusions and discussions as regard to pertinent applications of such materials are presented.

This thesis is concerned with the analysis of the current distributions in coplanar parallel microstripline structures, and the calculation of crosstalk in these structures. This is accomplished by using a Finite Element Method approach. Two parallel strips, a right angle bend junction, and a T junction are studied in order to gain an insight into the current distributions and the primary causes of crosstalk. The control of crosstalk is also investigated, with alternative geometries for microstrip designs. It is seen that the finite element method can yield results comparable with other accepted methods, and other perceivable physical models of the test structures. Also shown in the present study that crosstalk can be reduced by decreasing the trace-to-ground plane separation.

This thesis investigates the characteristics of varactors and crystals that affect Q and therefore the frequency stability of a voltage controlled oscillator (vco) when employed in a one MHz to three hundred MHz frequency synthesizer. A low noise VHF crystal oscillator, a low noise common base UHF oscillator, and a low noise test set-up are described, built, and tested.

This thesis describes two major research topics: (i) the design of an UWB LHCP low-profile microstrip antenna of Archimedean spiral version; (ii) Modification of the SAC of the Florida Atlantic University's EMI R&D Laboratory to a FAC to perform the required antenna characterizations for the designed UWB antenna. The microstrip spiral antenna is designed to operate in a traveling wave mode. It is constructed on a typical FR4 substrate and is center-fed through an SMA surface-mount connector. An RF chip-resistor located at the outer edge provides impedance matching. The UWB frequency performance of this antenna is among the widest reported in the microstrip antenna literature. The second study refers to a methodology to modify the EMC listed SAC to emulate a FAC. Several pyramidal RF absorbing cones are strategically placed on the reflecting ground surface. The validation between the frequency range 300 MHz to 1 GHz is investigated.

This dissertation is concerned with the studies on the frequency-dependent characteristics of microstrip line structures. Relevant considerations are applied to evaluate crosstalk in symmetric, coupled and lossy (dispersive) microstrip transmission lines. The technique adopted supplements the wide-range of semi-empirical expressions available in the literature on the frequency-dependent even- and odd-mode effective dielectric constants as well as the characteristic impedances of coupled microstrip lines. The accuracy of a crosstalk transfer function deduced is verified with theoretical and experimental results. The behavior of crosstalk versus line-spacing, dielectric substrate characteristics, and line-length is analyzed. This study is also extended to address the influence of temperature on crosstalk induced in microstrip lines. Further, analogous to relaxation considerations of Cole-Cole diagrams as applied to dielectric materials, a "reactive relaxation" concept is introduced to represent the frequency-dependent characteristics of lossless and lossy microstrips. The present algorithm depicting the dynamic permittivity of the microstrip structure (via Cole-Cole diagram) directly leads to a convenient and modified Smith chart representation. It includes the frequency-dependent influence of the fringing field and the lossy characteristics cohesively. Results based on the proposed model are compared with the available data in the literature in respect of a microstrip patch antenna. As far as the authors know of, this is the first attempt in depicting the dispersion characteristics of a microstrip line via Cole-Cole diagram format.

In printed circuits employing high-speed digital circuits, the interconnects can be considered as transmission lines. The dispersion effects in signals transmitted via such interconnects are of importance in crosstalk phenomena inasmuch as the amount of interline coupling (or crosstalk) in a symmetric, coupled microstrip version of interconnect depends on the difference between the frequency-dependent propagation constants pertinent to even and odd modes of lines. This dissertation is concerned with the studies on the distortion and coupling of transient signals propagating in a symmetric, coupled and lossy (dispersive) microstrip transmission lines. Both time as well as frequency domain characteristics are analyzed and relevant mathematical expressions are obtained vis-a-vis pulse signals on signal lines and coupling on sense lines. Fourier transform technique (FT) and spectral domain approach (SDA) are the methods used in the studies pursued. Specifically, an optimization technique to minimize crosstalk in multilayered, multitrace microstrip lines is developed. Typical simulation results are finished which indicate the feasibility of achieving a crosstalk reduction by 76% at a given distance of 40 mm from the source-end excited with a 25 picosecond gaussian pulse by optimization of the geometry of the structure appropriately. This technique is a new strategy for optimal design of high-speed, digital interconnections on a printed circuit board (PCB). The anomalous behavior of the crosstalk versus the pulse-width of a high-speed digital signal in a closely-spaced, parallel coupled microstrip line is presented. It is shown that depending on the pulse-width of a pulse signal, the space between two lines must be beyond a certain limit for a given strip-width (w) and strip-thickness (h) so that crosstalk can be reduced by spacing lines away. The relevant analysis indicates plausible reasons which cause the said anomalous characteristics of crosstalk. A transient signal propagating on a multilayered, coupled microstrip line with lossy substrates is characterized. Relevant computational algorithm is presented. The Cole-Cole diagrams depicting the odd and even mode complex permittivity versus frequency are evolved. The concept of Cole-Cole representation is applied to analyze crosstalk in a microstrip line. Typical simulations show some very interesting and useful results. This study is the first of its kind and has not been done earlier. Lastly, relevant to above research, logical inferences and conclusions are enumerated and the scope for future research is presented.

The research addressed refers to a study on the electromagnetic performance aspects of body-worn radio units operating in the presence of scatterers in close proximity, using analytical, numerical, and experimental methods. The application potentials of such methods include evaluating the integrity of radio units such as cell phones. Consistent with the scope of the study above, considered in this research are specific details on analytical and numerical modeling of the effects of a nearby conducting cylindrical object on the electromagnetic field near a human-model phantom. Calculations are performed using the Finite Difference Time Domain (FDTD) method. Considered are various separations of the body wearing the test radio unit from the proximal object and polarization of the incident wave. An anechoic chamber and the test setup used for the measurement of EM field amplitudes near a saline-water phantom are described. Within the anechoic chamber, a small shielded loop is used as a field measurement probe and is positioned near the test phantom. The field probe orientation was in the vertical plane for characterizing the prevailing electromagnetic field intensity. This study indicates that variations in the field amplitude near the phantom occur, which are responsive to phantom rotation and measurement distance from the phantom. The electromagnetic field amplitude decreases rapidly with increasing distance between the probe and the surface of the phantom. The analysis is also extended to examine the electromagnetic field distribution in the gap between a human body phantom model and a nearby conducting cylinder. An appropriate three-dimensional FDTD method is presented and applied to a near-field problem of analyzing the influence of proximal conductive objects on fields near a phantom wearing an RF unit.