Browsing by Author "Atanasov N."

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    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.
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    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.
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    Effect of activated carbons on the dielectric and microwave properties of natural rubber based composites
    (2017-10-01) Al-Sehemi A.; Al-Ghamdi A.; Dishovsky N.; Nickolov R.; Atanasov N.; Manoilova L.
    The effect of six different types of activated carbons has been studied in view of their applicability as functional fillers upon the dielectric and microwave properties of natural rubber based composites. It is found that the textural characteristics of the studied active carbons exert influence both on the real part of dielectric permittivity and dielectric loss angle tangent, as well as on the microwave properties of the studied composites. The composite containing activated carbon on the basis of wooden material possesses the highest value of the total shielding effectiveness in comparison with the composites, containing another activated carbons. It has the lowest values of specific surface area, area and volume of micropores and the highest values of external surface area, volume of mesopores and average pore diameter. With gradually increasing the values of the indices in the first group and gradually decreasing the values of the indices in the second group, the value of total shielding effectiveness decreases. It is obvious that these indices have influence on the rubber matrix-filler particle interactions, such as multicontact chain adsorption to the surface of the filler. The spatial inhomogeneities formed give rise to polarization phenomena and to a frequency dependence of the dielectric properties.
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    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.