Ismahayati Adam
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Preferred name
Ismahayati Adam
Official Name
Adam, Ismahayati
Alternative Name
Adam, I.
Ismahayati, A.
Adam, Ismahayati
Main Affiliation
Scopus Author ID
26428028100
Researcher ID
K-7483-2019

Research Output

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  • Publication
    Development of cascaded voltage doubler rectifier for RF energy harvesting
    ( 2022-02-21)
    Ismahayati Adam
    ;
    Mohd Najib Mohd Yasin
    ;
    Ibrahim S.Z.
    ;
    Haris N.
    Radio Frequency (RF) energy harvesting is a process where RF energy from the ambient source is collected and converted into an electrical energy by using a rectifier circuit. However, the collected RF energy only supplies very low input power. Therefore, it is important to design a circuit that not only rectified the RF signal, but also with amplified characteristic to obtain a higher output voltage from a low input power. Driven by the increasing use of Internet of Things (IoT) devices operating in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band, the presented rectifier circuit in this paper is designed in the same band as well. Initially, the voltage doubler circuit is chosen as the primary rectifier circuit, afterward cascaded into several stages until the most optimized result is obtained. The optimization is investigated across-30 dBm to 0 dBm of RF input power by varying the value of capacitor and resistor at a single stage. Based on the topology analysis, Dickson topology yields slightly higher voltage compared to Villard. In turn, the optimized number of stages is 6 because higher stages resulted to less output power. The measured reflection coefficient of the fabricated prototype is better than 40 dB at the center frequency with 240 MHz bandwidth. The rectified voltage is 3.4 V with 0 dBm input power. When it is supplied by 5 dBm input power, the green LED that connected to rectifier circuit output is light-up, confirming the RF energy harvesting application.
  • Publication
    Higher-order-mode triple band circularly polarized rectangular dielectric resonator antenna
    ( 2021-04-02)
    Zambak M.F.
    ;
    Mohd Najib Mohd Yasin
    ;
    Ismahayati Adam
    ;
    Iqbal J.
    ;
    Osman M.N.
    The paper presents a triband circular polarized rectangular dielectric resonator antenna. A single coaxial cable feeds the DRA to a double stub strip on the DRA side. A patch strip coupled to the feed assists in widening the bandwidth of the proposed DRA. The degenerate mode pair TEx∂11 and higher-TEx∂23 has been excited to achieve CP and enhance the antenna gain. The higher-order mode has been excited using a low-cost simple excitation mechanism without compromising on the size and shape of the DRA. An impedance bandwidth of 48% with a gain ~6–9 dBic was achieved in all resonance frequencies. Additionally, the AR bandwidth of 5.5%, 4.2%, and 2.76% was obtained at three different frequencies. Note that the proposed DRA exhibits a wide beamwidth of 112o, which is good for better signal reception. A comparison between the measured with simulated results shows that the measured results are matched by the simulated result trends.
  • Publication
    Harvesting Systems for RF Energy: Trends, Challenges, Techniques, and Tradeoffs
    ( 2022-03-01)
    Muhammad S.
    ;
    Tiang J.J.
    ;
    Wong S.K.
    ;
    Rambe A.H.
    ;
    Ismahayati Adam
    ;
    Smida A.
    ;
    Waly M.I.
    ;
    Iqbal A.
    ;
    Abubakar A.S.
    ;
    Mohd Najib Mohd Yasin
    The RFEH design challenges can be broadly classified into overall radio frequency direct current (RF-to-DC) power conversion efficiency (PCE), form factor, operational bandwidth (BW), and compactness. A detailed overview of the essential components of an RFEH system is presented in this paper. Various design approaches have been proposed for the realization of compact RFEH circuits that contribute immensely to mm-wave rectenna design. Effective mechanisms for configuring the rectenna modules based on the recommended spectrums for the RFEH system were also outlined. This study featured a conceptual viewpoint on design tradeoffs, which were accompanied by profound EH solutions perspectives for wireless power communications. The work covers some challenges attributed to 5G EH in mm-wave rectenna: from a controlled source of communication signals to distributed ambient EH and system level design. Conversely, the primary targets of this work are to: (I) examine a wide range of ambient RF sources and their performance with various antennae and RF-rectifier layouts; (II) propose unique rectenna design techniques suitable for current trends in wireless technology; (III) explore numerous approaches for enhancing the rectenna or RF-rectifier efficiency in a low-power ambient environment; and (IV) present the findings of a comprehensive review of the exemplary research that has been investigated. These are aimed toward addressing the autonomous system’s energy challenges. Therefore, with the careful management of the reported designs, the rectenna systems described in this study would influence the upcoming advancement of the low-power RFEH module.
  • Publication
    5G Millimeter Wave Wearable Antenna: State-Of-the-Art and Current Challenges
    ( 2021-01-01)
    Hasliza A Rahim @ Samsuddin
    ;
    Mashagba H.A.
    ;
    Yahaya N.Z.
    ;
    Mohd Najib Mohd Yasin
    ;
    Jamaluddin M.H.
    ;
    Muzammil Jusoh
    ;
    Thennarasan Sabapathy
    ;
    Ismahayati Adam
    ;
    Abdulmalek M.
    Fifth Generation (5G) is the next evolution of mobile communication that will provide seamless and massive high speed connectivity to the society. Paralleled with the rise of 5G, it is foreseen that wearable devices particularly wearable antenna will be the significant end node for wearable devices in Millimeter Wave (mmWave) frequency bands. Thus, this paper discusses the new development of the 5G sub-6 GHz and mmWave wearable antenna, introduces the research results of the 5G mmWave wearable antenna in recent years, and addresses the key challenges in the development trend of the development trend of the 5G mmWave wearable antenna.
      1  6
  • Publication
    Analysis of Symmetric Two and Four-coil Magnetic Resonant Coupling Wireless Power Transfer
    ( 2022-04-01)
    Ali A.
    ;
    Mohd Najib Mohd Yasin
    ;
    Rambe A.H.
    ;
    Ismahayati Adam
    ;
    Ramli N.
    ;
    Hasliza A Rahim @ Samsuddin
    ;
    Thennarasan Sabapathy
    ;
    Mohd Natashah Norizan
    ;
    Sobri S.A.
    This study examined the efficiency of power transfer for two-coil and four-coil spiral magnetic resonant coupling wireless power transfer (WPT) using distance to coil diameter (D/dm) ratio and reflection coefficient, S21 value. Adding resonators reduced the total resistance in the two-coil WPT system while increasing the S21 values of the whole system. A same-size spiral coil was proposed for the system and simulated using computer simulation technology (CST). A prototype with similar specifications for a four-coil design was implemented for verification. The proposed method yielded an optimal efficiency of 76.3% in the four-coil system, while the two-coil WPT yielded a 23.2% efficiency with a 1.33 D/dm ratio.
      2  13