Browsing by Author "Atanasova G."

Now showing 1 - 6 of 6
  • No Thumbnail Available
    Item
    A Flexible Miniature Antenna for Body-Worn Devices: Design and Transmission Performance
    (2023-03-01) Al-Sehemi A.; Al-Ghamdi A.; Dishovsky N.; Atanasov N.; Atanasova G.
    The last few years have seen a rapid increase in body-worn devices because these devices cover a broad spectrum of potential uses. Moreover, body-worn devices still require improvements in their flexibility, size, and weight that necessitate the development of flexible and miniature antennas. In this paper, we present a new flexible miniature antenna for body-worn devices. To ensure flexibility and comfort when the antenna is in contact with the human body, a substrate from natural rubber filled with TiO2 is developed. The miniaturization is achieved using the quadratic Koch curve. The antenna design, optimization, and characterization are performed on a human body model. The performance of the antenna is analyzed in two scenarios: (1) in- to on-body, and (2) on- to off-body wireless communications. The results show that the antenna realized the maximum telemetry range of more than 80 mm for in-body communications and more than 2 m for off-body communications. Moreover, the highest 10 g specific absorption rate value was 0.62 W/kg. These results, in addition to the antenna’s compact dimensions (12 mm × 26 mm × 2.5 mm) and the low manufacturing price, make the proposed antenna an ideal candidate for health telemetry applications.
  • No Thumbnail Available
    Item
    A flexible planar antenna on multilayer rubber composite for wearable devices
    (2017-01-01) Al-Sehemi A.; Al-Ghamdi A.; Dishovsky N.; Atanasova G.; Atanasov N.
    This paper presents the design of a flexible antenna using planar dipole with a reflector to achieve optimal radiation efficiency and low specific absorption rate (SAR) when the antenna is placed directly over the skin of body model. The antenna is designed for the 2.45GHz frequency band. The parametric analysis of the proposed antenna is carried out. The proposed antenna achieves stable onbody performance: |S11| varies from −16.05 dB (on skin) at 2.47 GHz resonant frequency to −16.40 dB (in free space) at 2.44 GHz resonant frequency. It was found that the maximum 1 g average SAR value is only 0.23W/kg for an input power of 100mW when the antenna is placed directly over the skin of a three-layer body model, and radiation efficiency is 20.5%. The measured results are presented to demonstrate the validity of the proposed antenna.
  • No Thumbnail Available
    Item
    Flexible polymer/fabric fractal monopole antenna for wideband applications
    (2021-01-01) Al-Sehemi A.; Al-Ghamdi A.; Dishovsky N.; Atanasova G.; Atanasov N.
    A novel flexible polymer/fabric fractal monopole antenna with a wideband performance is presented. A thin sheet of highly conductive fabric and a natural rubber-based composite have been used for conductive and non-conductive parts of the antenna, which allow keeping the antenna as flexible and thin as possible. The proposed antenna has been simulated, prototyped and tested. Results show that the antenna has a simulated impedance bandwidth of 3.8 GHz (2.2–6.0 GHz) and a measured impedance bandwidth of 3.7 GHz (2.3–6.0 GHz) to cover the most commonly used standards in wireless communication systems. The radiation efficiency of the antenna reaches over 93% throughout the operating frequency band with satisfactory radiation patterns and gain.
  • No Thumbnail Available
    Item
    On monitoring mechanical characteristics of rolled electrolytic copper
    (2016-01-01) Angelova D.; Yankova S.; Yordanova R.; Atanasova G.
    Rolling technology for producing high-electrical-conductivity-copper strips and their quality are under investigation. The technology is designed for and used in the Bulgarian Metallurgical Plant SOFIA MED SA, Sofia. The copper strips are produced in three different tempers - soft, half hard and hard - under different rolling and heat-treatment conditions. The copper strips from different tempers are subjected to specialized testing and their mechanical and high-electrical-conductivity characteristics analyzed. On the basis of mechanical rolled-strip parameters - yield strengths, R e , ultimate tensile strengths, R m , Vickers hardness, HV, and elongation after fracture, A, - some Stress-hardness and Stress-hardness-elongation spaces have been plotted. These Spaces can be used as an instrument for general evaluation of the applied rolling technology and for prediction of copper-strip mechanical behaviour under given exploitation conditions.
  • No Thumbnail Available
    Item
    Preparation and characterization of SnO2 films for sensing applications
    (2008-01-01) Stefanov P.; Atanasova G.; Manolov E.; Raicheva Z.; Lazarova V.
    SnO2 thin films for gas sensing applications were deposited by RF sputtering in a mixture of oxygen and argon. The morphology, structure and composition of the SnO2 films were analysed by XRD, SEM and XPS. SnO2 thin films showed a crystalline structure with a submicron particle size of 200 nm. The electronic structure of the film surface was elucidated by analysis of the photoelectron core level and valence band spectra of Sn.
  • No Thumbnail Available
    Item
    Selective adsorption of thiophene and its polyaromatic derivatives from fuels on pyrolyzed rice husks: A thermodynamic study
    (2019-01-01) Uzunova S.; Uzunov I.; Atanasova G.; Angelova D.; Ivanov I.
    This work presents the study of the adsorption affinity of biobased adsorbent prepared by pyrolysis of rice husks (PRH) toward thiophene (T), benzothiophene (BT) and dibenzothiophene (DBT) in single and mixed solutions in a batch mode using a model fuel and real diesel. A degree of desulfurization higher than 40 % is observed in case of an initial sulfur concentration in the fuel not higher than 1000 ppm. The adsorption selectivity of PRH from single solutions of the three aromatic sulfur heterocycles (ASHs) decreases following the line: T > BT > DBT. The theoretical equilibrium adsorption capacity of PRH in regard to the three sulfur compounds adsorption is determined using the adsorption isotherms of Langmuir, Freundlich, Dubinin-Radushkevich and Temkin. The calculated values of the thermodynamic parameters, such as the Gibbs energy, ΔG0, the entropy, ΔS0, and the enthalpy, ΔH0, indicate that the adsorption in PRH-ASHs-fuel system proceeds at normal and high temperature values through simultaneous physical and chemical interactions.