Abstracts of some thesis papers

7/30/2019 Abstracts of some thesis papers

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Conformal multi-functional antennas and rectifying circuits for wirelesscommunication and microwave power beamingbyYang, Guangli, Ph.D., University of South Carolina, 2005 , 163 pages; AAT 3201372

Abstract (Summary)

Conformal multifunctional antennas are greatly desired for man-portable, vehicular, and wirelesssensor applications since they can support the functions of multiple antennas with the use of a single

aperture. This eliminates inter-antenna mutual coupling while reducing size, cost, and complexity.The most significant challenges in multifunctional antenna research are to achieve the requiredbandwidth, radiation pattern, gain, and polarization at each operating frequency band with a singleantenna aperture. Antennas must also be designed considering their mounting platforms, whichgreatly alter performance characteristics.

In this dissertation the concept of achieving multifunctional operation by antenna geometricaloptimization is studied first by developing full-wave three dimensional electromagnetic models of theantenna and its integrating platform, such as vehicles and wireless sensor circuit boards. Severalantennas and associated circuits are designed, fabricated, and tested to demonstrate multifunctionalperformance for applications ranging from land mobile radio to wireless sensors. The solutions

proposed in this category include linearly polarized antennas with omnidirectional and directionalpattern coverage at 225 and 450 MHz for vehicular application and miniature wideband circularlypolarized microstrip patch antennas for wireless sensor application.

In the second part of this dissertation a novel switched multifunctional antenna is introduced where awideband stacked microstrip patch is reconfigured for operation in two frequency bands to supportwireless power beaming and data communication to sensors. First, the principles of reconfiguration isillustrated by constructing full-wave simulation models followed by experimental measurements onworking prototypes switched with the help of high frequency PIN diodes. It is demonstrated that thereconfigurable antenna has excellent bandwidth, pattern, and gain characteristics to support adirectional high gain operation at 5.7 GHz and another nearly omnidirectional, moderate gain

operation at 2.45 GHz. This design is scalable in frequency and hence directly relevant to otherapplications, such as satellite handheld terminals and land mobile radio. Finally, the concept of usingour switched multifunctional antenna to beam wireless power to sensors is demonstrated bydesigning, developing, and testing a high-frequency rectifying circuit integrated with the antenna.Measured results indicate that power transmission conversion efficiency in excess of seventy percentcan be readily achieved at 5.7 GHz along with more than adequate high-speed data communicationbandwidth at 2.45 GHz.

Microwave detection of breast tumors using the finite difference time domain

methodbyYang, Peng, Ph.D., University of South Carolina, 2006 , 209 pages; AAT 3224487

Abstract (Summary)

With the development of modern computer technologies and techniques, a computational approachto accurately and analytically solving complicated electromagnetic problems becomes possible.Various numerical methods were developed to predict the characteristics of the electromagnetic fieldsin complicated structures. The Finite Difference Time Domain (FDTD) algorithm, introduced by K. S.Yee in 1996, is one of the most popular tools. FDTD begins with the general Maxwell's curl equationsin time domain; it applies to a large number of linear and nonlinear materials and various geometries.Numerous technologies are used to make the FDTD calculation more efficient and accurate, among


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these are conformal calculation, non uniform mesh and anisotropic perfect matched layers (APMLs)boundary conditions.

It is well known that early detection of tumors is key in reducing cancer mortality. Although X-raymammography is currently the most popular technology in breast cancer screening, about 10--30% ofearly cases are missed by the mammogram. It has been found that breast tumors' electricalproperties at microwave frequencies are significantly different from those of healthy breast tissues;thus, microwave technology is particularly promising for breast cancer detection. Over the past

several years, steady progress has been made towards realizing this dream. In this research, 2dimensional and 3 dimensional conformal non-uniform FDTD Maxwell's solvers are developed tosimulate the breast cancer early detection system. We apply a virtual-focus scanning method todetect a tumor inside a simplified breast model in which breast tissue, ribs, tumor and antennas aresimulated to resemble a real case. The tumor can be located very accurately. We believe that asimple method such as the one we propose in this research is needed in order to make a detectionsystem reliable and practical.

In addition, conformal calculations and APMLs boundary conditions are applied in the codes whichwill make the solution more accurate. Conformal calculations use the weighted electromagneticparameters of the media in the boundary between two objects in the computation domain. APML

shows better absorbing results than other absorbing boundary conditions.

This research shows that using FDTD to simulate microwave breast tumor detection system is anefficient way to solve the complex electromagnetic problems. Combined with the tumor's highreflections in the microwave band, we get a high signal to noise level. We conclude that FDTDsimulation will improve the real detection system which can detect breast cancer in the early stages.

Novel embedded antennas and engineered materials in wireless

communications and sensingbyShams, Khan Mohammed Ziaus, Ph.D., University of South Carolina, 2007 , 124 pages; AAT3296685

Abstract (Summary)

Recent years have seen a remarkable growth in wireless technology, e.g. mobile telephony, wirelesslocal area network (WLAN), Bluetooth, Global Positioning Systems (GPS), and radio frequencyidentification devices (RFIDs). Given that many of these technologies operating at disparatefrequency bands with different bandwidth, pattern, and polarization requirements are being packagedwithin a single wireless device created a tremendous need for miniature, wideband, highly efficientantennas. However, it is extremely difficult to overcome the challenges associated with achievingthese objectives using conventional antenna design methodologies since antenna performancecharacteristics are largely dependent on its electrical dimensions. In this work the prospects of

antenna miniaturization, bandwidth improvement and gain enhancement are studied by exploring anovel non-contact feeding scheme and the design and application of metamaterial loading.

A novel non-contact feeding technique to design two miniature embedded antennas is proposedfollowed by systematic studies on antenna design using metamaterial loading. A Method of Moments(MoM) analysis is performed on a finite length cylindrical dipole antenna enclosed by a homogenousDouble Negative (DNG) metamaterial. The dipole exhibits wide bandwidth characteristics due to therelative insensitivity of the impedance with frequency. The dipole also shows resonance at muchlower frequencies than its resonant frequency in free space. A new class of SRR (split ring resonator)geometry is introduced which by virtue of its increased inductance provides wider stopband


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bandwidth than existing SRRs available in the literature. A simple intuitive design methodology todesign metamaterial structures is introduced which utilizes easy to use algebraic equations to predictthe operating frequencies of such structures. Experimental prototypes are developed and tested tovalidate performance.

Several applications of metamaterials are investigated experimentally, such as, wireless powertransmission to a buried sensor rectenna in concrete, antenna bandwidth improvement, and near-field energy focusing. It is demonstrated that an SRR metamaterial when placed in front of the

transmit antenna helps increase the received power by a rectenna by a factor of three. Similarly, avertical array of DNG metamaterial when placed surrounding a monopole antenna increases theantenna bandwidth significantly. Finally, in a near-field energy focusing experiment a DNGmetamaterial placed between a transmit antenna and a rectenna resulted in a five-fold increase ofthe rectenna received power when the distance between the DNG and transmit antenna was onewavelength.

Designing electrically small antennas and the effects of their radiation on

humansbySayem, Abu Taher Mohammad, Ph.D., University of South Carolina, 2007 , 130 pages; AAT3296682

Abstract (Summary)

Wireless devices, such as mobile phones, personal digital assistants, and Bluetooth headsets emitelectromagnetic (EM) radiation. Such devices when used near a user result in EM energy absorptionin the head or body of the user. The effect of this absorption is thermal and non-ionizing and themetric that is used to characterize the extent of this absorption is called the specific absorption rate(SAR), which is a function of the electric field intensity emitted by the antenna. There are nationaland international standards organizations that have developed safe limits of SAR based on animalstudies, which ensure that the temperature rise in the user's head or body is small enough not tocause any harmful effects. Currently, in order to determine the SAR induced by a particular wireless

device measurements are performed in a head or body simulating dielectric liquid phantom using arobot and near-field probes. The process is very complicated and tedious. Reports on SARcomputation and modeling techniques are abound but they mostly focus on algorithm refinement orthe development of different types of head or body models. At present there is no simplestraightforward method to even distinguish the SAR induced by an extremely small RFID (radiofrequency identification device) antenna and that by a mobile phone primarily because of our lack ofunderstanding of the relationship between antenna performance characteristics (eg. bandwidth,directivity) and SAR. Yet such relationship can enable us to predict the SAR of an antenna moreeasily and quickly and for some antennas possibly eliminate the need for testing altogether if theyemit a power below a certain threshold. To achieve this goal, in this work, we start from the definitionof the fundamental limits ofantenna quality factor, design antennas of different types, shapes, and

sizes and investigate their performance characteristics and SAR over a wide frequency range bothnumerically and experimentally.

Our results on dipole antennas elucidate that a focusing factor can be defined forantennas near alossy dielectric object, such as the human head or body and that the smaller antennas focus moreenergy in the SAR averaging mass than the longer. We also conclude that among all classes,shapes, and sizes ofantennas investigated in this study, the dipole antennas generally inducehigher SAR compared to all otherantennas and that the antenna free-space bandwidth is stronglyrelated to the SAR. Based on these findings we develop a simple easy to use formula which can beused to estimate the threshold power that directly corresponds to the SAR induced by an antenna


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once the antenna free- space bandwidth is known. We also design, fabricate, and test twocompletely new antennas with unique performance characteristics and test our SAR estimationformula on them. The first is a new planar microstrip-fed dual-band Hilbert slot antenna which hastwo distinct patterns, end-fire and broad-side, at the low and high resonant frequencies, respectivelyand the second is a miniature spiral diversity antenna with high overall gain and low mutual couplingcharacteristics.

Antenna design using space filling curves and electromagnetic band gap

structuresbyAzad, Mohammed Ziaul, Ph.D., University of South Carolina, 2008 , 154 pages; AAT 3336562

Abstract (Summary)

At present there is a tremendous demand for small portable/wearable wireless devices that canaccommodate a variety of applications operating in different frequency bands and require differentbandwidth, radiation patterns, and polarizations. Miniaturization in the component level is the key tosuccessful device design. This is particularly important when it comes to designing the antennas forsuch devices. Similarly for base stations or WiMax type terminals that may support directional beamsantenna size reduction is essential. However, a systematic study is required to ensure that

miniaturization is not achieved at the cost of unsatisfactory bandwidth, pattern, and gaincharacteristics. The focus of this dissertation is to explore miniature antenna design using space-filling curves and electromagnetic bandgap (EBG) structures.

Under the first thrust, the Hilbert curve is used to study and design various platform integratedantennas for application in the mobile telephone, wireless local area network (WLAN), and globalpositioning system (GPS) frequency bands. The effects of miniaturization on antenna bandwidth,pattern, and gain are investigated in the presence of conductor and dielectric losses. A simple,intuitive, and easy to use method to design Hilbert inverted-F antennas (IFAs) is presented whichcan also be used to design diversity antennas that have superior performance in a fadingenvironment. The feasibility of using a miniaturized implanted GPS Hilbert antenna to track the

elderly with declining mental capacity, such as Alzheimer's disease is demonstrated. This was donefirst by performing numerical simulations of the implanted antenna in a representative block muscleand skin model as well as in an anatomically based human body model. Finally the validity of thedesign was demonstrated by performing experimental field tests where the antenna was immersed inan equivalent tissue simulating fluid.

Under the second thrust a new method is proposed using which wideband directional printed dipoleantennas can be designed for base stations or WiMax type terminals. The proposed design methodexploits the effects of the EBG reflection phase on the antenna impedance and thus generates areflection phase that results in a thin wideband design. Following this technique a novel widebanddirectional dipole antenna is fabricated and tested to validate performance from 1.75 GHz to 2.5

GHz.

Proximity coupled non-intrusive wireless sensors for monitoring and

diagnosticsbyBhuiyan, Rashed Hossain, Ph.D., University of South Carolina, 2010 , 199 pages; AAT 3433122

Abstract (Summary)

Automated wireless sensors to monitor infrastructure, such as power systems have drawn a greatdeal of attention in the research community recently. To ensure reliable and uninterrupted power


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supply, sensors can be developed which will probe the power cables non-intrusively, transmit the faultinformation wirelessly to a central control unit and harvest the required energy for the operation of thesensor. This work explores and develops new ideas to design and develop automated, self-sustainingwireless sensor patches that can be distributed on power transmission lines.

The primary thrusts of this dissertation are on (1) in-situ static electric field type sensor developmentwhich can be wrapped around power line cables in critical locations that are more prone to insulationdamage either due to high humidity and temperature, (2) a broadband conformal low-profile surface

wave exciter development which can be used to inject a broadband pulse to determine the location offaults using reflectometry principles such as time domain reflectometry, frequency domainreflectometry or joint time frequency domain reflectometry, (3) efficient 915 MHz antenna design withwide pattern and gain coverage to support the data telemetry functions of the sensor, and finally (4) aminiature energy harvester design and development using thin high permeability magnetic materials,which can charge the batteries needed to make the non-intrusive wireless sensor functional.

Electromagnetic exposure in a phantom in the near and far fields of wire and

planar antennasbyMazady, Md. Anas Boksh, M.S., University of South Carolina, 2010 , 102 pages; AAT 1483674

Abstract (Summary)

Due to the wide availability and usage of wireless devices and systems there have been and areconcerns regarding their effects on the human body. Respective regulatory agencies have developedsafety standards based on scientific research on electromagnetic (EM) exposure from wirelessdevices and antennas. The metric that quantifies the exposure level is called the Specific AbsorptionRate (SAR). Wireless devices must satisfy the regulatory standards before being marketed. In thepast, researchers have primarily focused on investigating the EM exposure from wireless devices thatare used very near to the user's head or body (less than 25 mm). But as time progressed many morewireless devices have become ubiquitous (vehicular wireless devices, laptop PCMCIA cards,Bluetooth dongles, wireless LAN routers, cordless phone base stations, and pico base stations are to

name a few) and are operated at distances greater than 25 mm yet smaller than 200 mm. Given thevariations in operating frequency, distance, and antenna size and type it is challenging to develop anapproach using which EM exposure from a wide variety of wireless devices can be evaluated. Theproblem becomes more involved owing to the difficulties in identifying the antenna zone boundaries,e.g. reactive near-field, radiating near-field, far-field etc. The focus of this thesis is to investigate alarge class of low and highly directive antennas and evaluate the EM exposure from them into alarge elliptical phantom. The objective is to be able to predict threshold power levels that meet theSAR limits imposed by the regulatory agencies. It was observed that among the low directivityantennas at close near-field distances, electrically small antennas induced distinguishably higherSAR than electrically largerantennas. But differences in SAR were small as the phantom moved intothe far-fields of the antennas. SAR induced by highly directive antennas were higher when the

phantom was in the far-field of the antennas and was facing the antenna frontal plane. The samewas not true when the phantom was in the near-field of the antennas. Finally, by analyzing thesimulation and measurement data threshold power formulas were developed for low directivityantennas using which power levels corresponding to the safe exposure limits independent of devicetype or geometry can be estimated.

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Abstracts of some thesis papers