Mehrdad Saviz

University of Tehran, Teheran, Tehrān, Iran

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Publications (22)13.33 Total impact

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    ABSTRACT: The ongoing development of new applications in the terahertz (THz) frequency range, such as wireless communication systems, full-body scanners, or other imaging procedures for biological and medical techniques, rapidly increases the number of persons who are potentially exposed to the electromagnetic radiation of those devices. Studies of thermal effects in humans caused by electromagnetic (EM) exposure with frequencies in the THz frequency range can rarely be found in the literature. In this paper, a method for the numerical computation of a potential thermal response in human skin due to EM fields between 0.1 and 10 THz is introduced. The method starts with the development of adequate simulation models for EM fields with penetration depths less than 1 mm. In a further step, it covers the provision of absolutely needed dielectric tissue parameters with help of the “effective medium theory,” since material properties above 100 GHz are not listed in the commonly consulted databases. The absorbed power in EM exposed human skin models of different complexity is calculated and subsequently used as heat source for temperature simulations. Spatial and time-dependent temperature profiles in the tissue are analyzed for transient and continuous exposures.
    No preview · Article · Sep 2015 · IEEE Transactions on Terahertz Science and Technology
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    Reza Aminzadeh · Mehrdad Saviz · Amir Ahmad Shishegar
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    ABSTRACT: Several low-cost tissue mimicking materials were used to fabricate tissue-equivalent phantoms. The dielectric properties of each composition were measured in the range of 20- 40 GHz using an open-ended coaxial slim probe. The measured data are in good agreement with the available reported data in the literature as well as calculated theoretical values. In order to verify the accuracy of measurements, the dielectric properties of formamide at 30C were measured in the range of 1-40 GHz and compared to the literature data. Also some tests were performed regarding the calibration method for slim probes and the results are discussed.
    Full-text · Conference Paper · May 2015
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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%.
    No preview · Article · Mar 2015 · IEEE Transactions on Magnetics
  • M. Saviz · R. Faraji-Dana
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    ABSTRACT: This paper describes a new, open-source Matlab toolbox, which can be used to directly build realistic, complex geometrical models of irregular biological cell shapes and organelles based on user definitions on single two-dimensional micrographs. The main advantages are flexibility and versatility as needed for irregular cell shape modeling for computational bioelectrical and biomechanical studies, which are not met in conventional computer modeling tools. The algorithms, results and applications are briefly described. Specifically as shown, the software can be used to study the effects of cell shape on local absorption and microthermal effects under electrical stimulation.
    No preview · Article · Dec 2014
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    Reza Aminzadeh · Mehrdad Saviz · Amir Ahmad Shishegar
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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.
    Full-text · Conference Paper · May 2014
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    Mehrdad Saviz · Reza 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.
    Preview · Article · Apr 2014 · Journal of Electrical Bioimpedance
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    Reza Aminzadeh · Amir Ahmad Shishegar · Mehrdad Saviz
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    ABSTRACT: In this paper millimeter wave (mm-wave) reflectom-etry 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.
    Full-text · Conference Paper · Apr 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.
    No preview · Article · Apr 2014 · Electronics Letters
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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.
    Full-text · Conference Paper · Dec 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.
    Full-text · Article · Sep 2013 · Bioelectromagnetics
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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.
    No preview · Article · Jul 2013 · Journal of infrared, millimeter and terahertz waves
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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.
    No preview · Article · Jun 2013 · IEEE Transactions on Terahertz Science and Technology

  • No preview · Conference Paper · Jan 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.
    No preview · Conference Paper · Jan 2013
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    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.
    Preview · Article · Jan 2013 · Progress In Electromagnetics Research
  • M. Saviz · R. Faraji-Dana
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    ABSTRACT: A novel approach has been introduced to remedy the computational complexities of the recently introduced time domain periodic Green's functions in the 1D and 2D periodic case. Specifically, it has been shown that for a certain class of temporal basis functions, the computational cost of convolutions with temporal basis functions, which results in the band-limited GFs needed by most time domain integral equations solvers, can be considerably reduced, as compared to conventional methods that are currently in practice. It is also well known that the computational complexity of the Floquet-wave based Green's functions increases when the point of observation approaches a source. Robust forms have been obtained for both 1D and 2D periodic TDGFs for any source-observation distance, which are then further improved for high-efficiency numerical implementation.
    No preview · Article · Nov 2012
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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.
    No preview · Conference Paper · Sep 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.
    Full-text · Article · Jun 2012 · Applied Optics
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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.
    Full-text · Article · Aug 2011
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    N. Firoozy · M. Saviz · R. Faraji-Dana
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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.
    Full-text · Conference Paper · Jun 2011