İlhami Ünal

An experimental microwave imaging system for breast tumor detection on layered phantom model

In this paper, the microwave imaging system currently being developed and realized at the Scientific and Technological Research Council-BILGEM, is introduced. A stacked patch antenna has been designed, fabricated and tested in operation in the experimental setup consisting of a spectrum analyzer (with vector network analysis option) and a planarly layered breast phantom model with tumor. Images are successfully obtained by using scattering electromagnetic waves from the tumor (S11). In the future study, ultrawide-band (UWB) confocal microwave radar-based imaging system with right-handed circularly polarized (RHCP) and left-handed circularly polarized (LHCP) antennas located as an array on a section of a hemisphere, as well as improved and fast imaging algorithms, will be designed and developed in order to minimize mutual coupling between antenna elements, reflections from the skin and mechanical parts of the antenna system for getting better resolution results than similar recent developed microwave imaging systems.

Extracting the dielectric constant of materials using ABC-based ANNs and NRW algorithms

ABSTRACT Five different Nicolson–Ross–Weir (NRW) extracting techniques are used to extract the dielectric constants of Teflon, Rexolite, Glass (borosilicate and soda-lime), Paper, and Ultralam 3850HT from S-parameters. The results of these extraction techniques are used to train the Artificial Neural Networks. In order to improve the accuracy of the results, the weights of ANNs are calculated using artificial bee colony estimation method. The results are compared with that obtained using NRW, Newton–Raphson, and genetic algorithm. The obtained results indicate that the proposed model gives good extracted parameters as compared with the previously published results.

Materials classification by partial least squares using S-parameters

This paper presents a simple and usable algorithm, which is called Partial Least Squares, to classify the samples in different thicknesses and frequency range. This model employed to reconstruct the samples using S-parameters which are collected by Vector Network Analyzer in Free Space Measurement method. The relationship of between S-parameters is showed to classify the materials using proposed model. The Partial Least Squares algorithm has a good potential to classify the different samples with non-contactless and non-destructive measurement method. The classification process will be easy by using the proposed model, due to its practical and simple usage. In addition, the extraction techniques, which are Nicolson Ross Weir, Newton–Raphson, and Genetic Algorithm, are used in order to extract the dielectric constant of samples, in this study. The Newton–Raphson algorithm is selected to obtain the complex permittivity of samples since it gives best results than other extracting techniques and the results are used for classification.

Reduction of S-parameter errors using singular spectrum analysis

A free space measurement method, which consists of two horn antennas, a network analyzer, two frequency extenders, and a sample holder, is used to measure transmission (S21) coefficients in 75-110 GHz (W-Band) frequency range. Singular spectrum analysis method is presented to eliminate the error and noise of raw S21 data after calibration and measurement processes. The proposed model can be applied easily to remove the repeated calibration process for each sample measurement. Hence, smooth, reliable, and accurate data are obtained to determine the dielectric properties of materials. In addition, the dielectric constant of materials (paper, polyvinylchloride-PVC, Ultralam® 3850HT, and glass) is calculated by thin sheet approximation and Newton-Raphson extracting techniques using a filtered S21 transmission parameter.

ELECTROMAGNETIC MODELING OF RETINAL PHOTORECEPTORS

ELECTROMAGNETICMODELINGOFRETINALPHOTORECEPTORSC.Canbayand ˙I. Unal¨DepartmentofElectricalandElectronicsEngineeringYeditepeUniversity26A˘gustosYerle¸simi,Kayi¸sda˘gi,34755,Istanbul,Turkey˙Abstract—New electromagnetic models for the rods and conesthat are the photoreceptors at the back of the retina aredeveloped and simulated in order to explain the roles of dimension,geometricalstructure,directionalsensitivityandvisualpigmentsofthephotoreceptorsinthereceptionofvisiblelight. Therodsandconesaremodeled as uniform and quasi-tapered helical antennas, respectively.Theresultsofthemodelstudyshowthatifthemodelantennashavetheoriginalphotoreceptorcelldimensions,thefrequencyresponsesofthemodelantennasandthespectralsensitivitiesofthephotoreceptorswouldbeveryclosetoeachother. Inaddition,it’sobservedthatthespectralsensitivitiesof

ANALYSIS OF DISPERSIVE EFFECTS OF BREAST PHANTOM MODEL ON ULTRA WIDEBAND MICROWAVE IMAGING OF BREAST CANCER TUMOR

In this paper, effects of frequency dispersive dielectric properties of a half-spherical breast phantom model on breast cancer tumor detection capability of the microwave radar-based imaging system, currently being developed at the Scientific and Technological Research CouncilBILGEM-UEKAE, are investigated by simulation studies. An ultra wideband (UWB) bow-tie antenna array surrounding the breast has been designed in the presence of the breast phantom. The designed antenna operates efficiently across the band from 1 GHz to 8 GHz and it’s assumed to be immersed in a coupling medium to get a good impedance matching with the breast. Fidelity factor of the case with the dispersive breast phantom is found to be 4.14% less than the non-dispersive case, due to increasing pulse distortion in dispersive dielectric tissues. Images are formed by using delay-and-sum (DAS) algorithm for the detection of spherical tumor with 2 mm diameter. Imaging results of the case with the dispersive breast phantom present signal reduction of 0.628 dB in the tumor response level as well as faulty locating of the tumor in the image, as compared to the successful results of the non-dispersive case. A better imaging algorithm compensating the dispersive effects will be used in the future.

An analysis for the use of compressed sensing method in microwave imaging

One of the most important problems encountered in microwave imaging methods is intensive data processing traffic that occurs when high resolution and real time tracking is desired. Radar signals can be recovered without loss of data with a randomly selected subset of the measurement data by compression sensing (CS) method which has been popular in recent years. For this reason, in this study, the use and capabilities of the CS method were investigated for tracking moving human, and the target information was correctly determined for the data obtained much below the Nyquist sampling criterion. In this study, it was revealed that the CS method can be developed for target detection and tracking.

Experimental studies based on classification of explosive and non-explosive liquids

Nowadays, since the explosive liquids can easily be obtained by mixing simple substances, the electromagnetic methods developed for safety purposes have gained acceleration. In this study; liquids which may be explosive with chemical explosion, combustion and combination, as well as, non-explosive liquids which may be found inside baggages in airports are used to measure electromagnetic responses ranging from 1–50 GHz and complex dielectric permeability coefficients are calculated with commercial software. Explosive and non-explosive liquids are classified a with the help of three different algorithms such as PLS, PCA and K-Means.

A W band waveguide detector module using zero bias schowttky diode

In this paper, it is aimed to design and realize a broad W-band and high sensitive waveguide detector module using a zero-bias schottky diode. The commercial off-the-shelf GaAs detector diode Aeroflex / Metelics MZBD-9161 is adopted to build a zero-bias direct detector, along with full band antipodal finline transition, microstrip line with DC microstrip blocker and low pass filter. This structure is placed in a gold-plated brass box (input W band waveguide and output SMA female connector) to form a W-band detector module. Voltage sensitivity up to 700 mV/mW from 75 GHz to 110 GHz (full W-band) is achieved. The module is based on microstrip circuit and gold plated brass box and is therefore easy and cheap to fabricate, which satisfies the low-cost requirements of assembling radiometer and millimeter wave imagers.

Statistical modeling of propagation channels for Terahertz band

Digital revolution and recent advances in telecommunications technology enable to design communication systems which operate within the regions close to the theoretical capacity limits. Ever-increasing demand for wireless communications and emerging numerous high-capacity services and applications mandate providers to employ more bandwidth-oriented solutions to meet the requirements. Trend and predictions point out that marketplace targets data rates around 10Gbps or even more within the upcoming decade. It is clear that such rates could only be achieved by employing more bandwidth with the state-of-the-art technology. Considering the fact that bands in the range of 275GHz-3000GHz, which are known as Terahertz (THz) bands, are not allocated yet for specific active services around the globe, there is an enormous potential to achieve the desired data rates. Although THz bands look promising to achieve data rates on the order of several tens of Gbps, realization of fully operational THz communications systems obliges to carry out a multidisciplinary effort including statistical propagation and channel characterizations, adaptive transceiver designs, reconfigurable platforms, advanced signal processing algorithms and techniques along with upper layer protocols equipped with various security and privacy levels. Therefore, in this study, several important statistical parameters for line-of-sight (LOS) channels are measured. High resolution frequency domain measurements are carried out at single-sweep within a span of 60GHz. Impact of antenna misalignment under LOS conditions is also investigated. By validating exponential decay of the received power in both time and frequency domain, path loss exponent is examined for different frequencies along with the frequency-dependent path loss phenomenon. Furthermore, impact of humidity is also tested under LOS scenario. Measurement results are presented along with relevant discussions and future directions are provided as well.