Mehrdad Saviz

University of Tehran, Teheran, Tehrān, Iran

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Publications (17)17.46 Total impact

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    ABSTRACT: Especially in the THz region, little data is available regarding material properties based on measurements. It has been argued that the effective medium theory could provide a useful tool to estimate material data needed for electromagnetic field computations. In this paper, two numerical approaches are presented to test the applicability of the effective medium theory (EMT) with special regard to mm- and sub-mm-wavelengths. One approach is based on the well-known free-space method and the other one on a power loss evaluation scheme. Within the scope of application of the free-space method, the usability of the EMT is proven for two sets of dielectric tissue parameters on a longitudinally homogeneous and transversely structured sample. Moreover, power loss evaluation is a suitable method to show the applicability of the EMT. Analysis of layered models at 1–10 THz confirms that the EMT is a suitable tool to develop equivalent homogenized models with maximum errors for the dissipated powers of about 1%. In a more realistic example for a physiological fluid with spherical inclusions, the EMT yields an error of less than 1%.
    IEEE Transactions on Magnetics 03/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2361958 · 1.21 Impact Factor
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    ABSTRACT: Millimeter-wave reflectometry can be used as a non-invasive method for early detection of skin cancers. Less penetration and higher resolution are only some reasons to use mm-waves for skin cancer diagnosis. The dielectric parameters data of human skin at mm-wave frequencies are not widely addressed in the literature due to the expensive instruments and the complicated structure of human skin. Available dielectric properties of cancerous tissues in the literature are for other tissues rather than skin and are restricted to the frequencies below 20 GHz. In this paper, dielectric properties of healthy and malignant skin tissues were estimated in the range of 20–100 GHz by applying the effective medium theory. A stratified skin model and some skin tumors were presented. The possibility of mm-wave reflectometry for detection of skin cancers has also been studied. The results of this paper can be used as a theoretical basis for taking further steps in skin cancer research.
    The 22nd Iranian Conference on Electrical Engineering (ICEE 2014), Tehran, Iran; 05/2014
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    ABSTRACT: In this paper millimeter wave (mm-wave) reflectometry was studied as a potential non-invasive method for early detection of skin cancers. The reason of our choice was lower penetration, but higher resolution and technology maturity. Finite Difference Time Domain (FDTD) method was used to present a model for mm-wave reflectometry from the human skin. Due to the limited data regarding dielectric properties of human skin and lack of data for malignant skin lesions at mm-wave frequencies, extrapolated and measured dielectric properties of skin, fat and muscle tissues are used here. This could prevent obtaining accurate results due to the approximations. Two frequency ranges were studied; 20-26 GHz and 50-75 GHz. Simulated reflection values from normal, benign and malignant tissues were compared to each other and showed a considerable contrast between benign and malignant tissues. Reflection measurements on a novel skin-equivalent phantom mimicking a cancerous skin tissue showed a significant contrast between normal and cancerous sites.
    EuCAP 2014 - The 8th European Conference on Antennas and Propagation, The Hague, The Netherlands; 04/2014
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    ABSTRACT: Several phantoms have been fabricated for reflection measurements from human tissues in the range of 26.5–40 GHz. For the first time, a novel composition is introduced for fabrication of low-cost simple tissue-equivalent phantoms. The effective medium theory is applied to estimate the dielectric properties of phantoms consisting of polyethylene (PE) powder and the results are verified by dielectric properties measurement on the proposed phantoms. It is shown that mixing theory can estimate the dielectric properties of the PE-based phantoms with minimum error. Therefore, the amount of the ingredients can be estimated theoretically.
    Electronics Letters 04/2014; 50:618-620. DOI:10.1049/el.2014.0749 · 1.07 Impact Factor
  • M. Saviz, R. Faraji-Dana
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    ABSTRACT: In this paper we show why the poorly conducting cytoplasmic membranes have little effect on the overall impedance of the tissue above a certain frequency, and derive an estimate of this upper frequency. It is further shown that the induced transmembrane potentials at different sites over the membrane can be found through a simple formula for frequencies above the threshold, without the need to analytically or theoretically model the membranes directly. The findings are validated for an irregular cell shape through rigorous numerical modeling.
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    ABSTRACT: The dielectric properties of typical tris(hydroxymethyl)aminomethane (TRIS) solutions have been measured and modeled using a Cole-Cole model in the frequency range 200 MHz up to 20 GHz. The physics of the dielectric behavior of TRIS solutions have been discussed and the effect of TRIS molecules on the permittivity of the aqueous medium have been investigated by theoretical models. To facilitate reproduction and use of the data and to provide interpolated values at concentrations other than those used for measurements, closed form polynomial expressions have been developed for the Cole-Cole model parameters. The data can be useful in the design and analysis of experiments in bioelectromagnetics, where they can be used to more precisely theoretically estimate the field strength in the solutions under exposure.
    ICBEM 2013; 12/2013
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    ABSTRACT: We designed a rectangular waveguide exposure system to study the effects of mobile phone frequency (940 MHz) electromagnetic fields (EMF) on luciferase structure and activity. The luciferase activity of exposed samples was significantly higher than that of unexposed samples. Dynamic light scattering of the exposed samples showed smaller hydrodynamic radii compared to unexposed samples (20 nm vs. 47 nm ± 5%). The exposed samples also showed less tendency to form aggregates, monitored by turbidity measurements at λ = 360 nm. A microwave dielectric measurement was performed to study the hydration properties of luciferase solutions with a precision network analyzer over frequency ranges from 0.2 to 20 GHz before and after exposure. The change in the dielectric properties of the exposed luciferase solution was related to the disaggregation potency of the applied field. Together, our results suggested that direct interactions with luciferase molecules and its dipole moment were responsible for the reduced aggregation and enhanced luciferase activity upon exposure to the EMF. Bioelectromagnetics. 9999:XX-XX. © 2013 Wiley Periodicals, Inc.
    Bioelectromagnetics 09/2013; 34(6). DOI:10.1002/bem.21792 · 1.86 Impact Factor
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    ABSTRACT: The dielectric properties of biological tissues and their substructures at terahertz frequencies are needed for computational dosimetry, radiation safety regulation, and medical imaging, but experimental tissue data are only scarcely available for the terahertz band. Tissue properties can be theoretically predicted at terahertz frequencies if the tissue microstructure and composition, and the dielectric properties of several basic biological materials are known. This paper introduces a new open-source toolbox where a material database and many of the relevant formulas are implemented to facilitate related research. Several examples have been analyzed and successfully verified with experimental data from the literature.
    Journal of infrared, millimeter and terahertz waves 07/2013; 34(7-8):529-538. DOI:10.1007/s10762-013-9997-z · 1.89 Impact Factor
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    ABSTRACT: This paper contributes to the topic of radiation safety in the THz band by providing theoretical estimations of the permissible incident power densities over 100 GHz – 10 THz. Microthermal absorption has been characterized and a worstcase analysis has been done to provide thresholds for the tissueinternal electric field strength at THz frequencies. Dielectric models for the skin and the cornea of the eye as exposed surface tissues have been constructed and used to estimate the corresponding thresholds for incident power densities. The findings of this study shall be useful as a new theoretical framework for future studies related to THz radiation safety and regulation.
    IEEE Transactions on Terahertz Science and Technology 06/2013; 3(5):635-640. DOI:10.1109/TTHZ.2013.2264327 · 4.34 Impact Factor
  • Joint Meeting of The Bioelectromagnetics Society (BEMS) and the European BioElectromagnetics Association (EBEA) (BioEM 2013), Thessaloniki, Greece, 10.06.-14.06.2013; 01/2013
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    ABSTRACT: The number of current applications in the THz-frequency range (0.1-10 THz), e.g. full-body scanners or WLAN communication technologies, is rapidly rising. Accordingly, the need for methods to determine the risk for the general public and for employees due to electromagnetic exposure from such sources is growing. The currently available literature provides only information about dielectric material properties of biological tissues for frequencies below 100 GHz. For higher frequencies, the knowledge is sparse. The “effective medium theory” is applied here to estimate the required material data above 100 GHz, which are obviously needed for numerical dosimetry purposes in the THz range. These data are used subsequently for numerical computations of electromagnetic THz-fields in human tissues and resulting heat elevations.
    EMC Europe 2013, Brugge, Belgium, 02.-06.09.2013; 01/2013
  • Mehrdad Saviz, Reza Faraji-Dana
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    ABSTRACT: This paper presents a structured model of the dielectric properties of the corneal tissue at microwave frequencies, based on the fine structure and chemical composition of its constituents. This is accomplished by appropriately combining the known properties of tissue substructures using mixing rules, in order to obtain the effective macroscopic properties of the medium. The presented approach is multi-scale: it begins from the microscopic scale and derives the macroscopic properties after several scale-steps. The predictions of the model agree with the existing measured data in the literature. Verification and analysis of the model sensitivity to input parameters have been presented. The model is expected to find application in non-invasive medical sensing where it can relate dielectric response to pathological structural changes in the tissue. The model is also useful for the prediction of dielectric properties for high-frequency computational dosimetry, and for understanding the physical mechanisms behind the macroscopic dielectric behaviour in general.
    Progress In Electromagnetics Research 01/2013; 137:389-406. DOI:10.2528/PIER12112510 · 5.30 Impact Factor
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    ABSTRACT: In order to develop computational methods for determining the reaction of biological systems exposed to THz radiation, conventional approaches of numerical dosimetry have to be extended. The penetration depth of electromagnetic fields at THz frequencies is less than 1 mm and thus substantially smaller than for radio frequencies. In addition, the short wavelengths in this frequency range cause the necessity of high resolution models. Here, a selection of simulation models of the human skin and of the eye as well as of the excitation field are presented together with a proposal to assess the appropriate dielectric tissue parameters.
    International Symposium on Electromagnetic Compatibility (EMC Europe 2012), Rom, Italy, 17.-21.09.2012; 09/2012
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    ABSTRACT: We report a novel tilting exposure photolithography (TEL) technique where gradual pattern displacement is employed to achieve high-resolution features over large areas with reasonable exposure times. A linear array with features of the order of 100 nm has been realized using this technique with standard blue-light LED sources. TEL can be useful in the visible and ultraviolet spectra to create two-dimensional periodic structures. The created structures include the nanometric array of spots and lines. The proposed technique can be used as a writing method where complex features can be generated by moving the sample-holding leading to serpentine nanometric linear arrays.
    Applied Optics 06/2012; 51(16):3329-37. DOI:10.1364/AO.51.003329 · 1.78 Impact Factor
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    ABSTRACT: After discovering drawbacks of current similar methods of cell exposure, a new approach towards such setup was taken by examining the possibility of using a grounded Coplanar-Waveguide (C.P.W) with a different substrate to make the near-perfect line matching possible for intended frequencies. A considerable size reduction was also achieved and holes were considered for simultaneous microscopy. Specific Absorption Rate (SAR) and temperature change in the biological sample were then computed and compared with standards to investigate compatibility with bioelectromagnetic requirements. Finally, the radiated fields of such setup were measured and compared with safety standards to ensure operator safety.
    Electrical Engineering (ICEE), 2011 19th Iranian Conference on; 06/2011
  • Ali Molaei, Mehrdad Saviz, Reza Faraji-Dana
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    ABSTRACT: This paper presents the fine modeling and simulation of retinal rod cells under exposure to electromagnetic waves at power, Radio and microwave frequencies. The novelty lies in detailed modeling according to recent electron micrographs of the actual geometry of retinal cell. Local heat generation at different sites in the cell is shown for different frequencies.
    Electrical Engineering (ICEE), 2011 19th Iranian Conference on; 06/2011
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    ABSTRACT: The work disclosed herein investigates the edge conditions for a perfect electrically conducting wedge in a medium with negative permittivity. A typical structure has been assumed in accordance with previous works for ordinary media, and an optimization technique has been used to solve the problem numerically. Special cases of importance have been explored mathematically.
  • M. Saviz, R. Faraji-Dana
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    ABSTRACT: In this paper the reduction of the area allocated to the filtering functionality in planar circuit design is discussed. A space-saving structure has been considered, featuring several tunable parameters that are adjusted using particle swarm optimization. The results indicate the possibility of achieving the design goals while saving space for other circuit elements.