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
    Comparison of rectifier performance using different matching technique
    ( 2017-01-03)
    Ismahayati Adam
    ;
    Mohd Najib Mohd Yasin
    ;
    Mohammad Shahrazel Razalli
    This paper describes the design and implementation of the 4-stage Villard multiplier for RF energy harvesting. Each stage is a combination of two HSMS 2850 Schottky diodes and two capacitors for each stage. For ambient energy harvesting, the incident power is extremely small, thus an efficient rectifier is needed. The designed rectifier with the matching circuit is a good candidate since it is able to enhance the rectified output power up to 300% during -40dBm input power compared to the rectifier circuit alone.
  • 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
    Bending Assessment of Dual-band Split Ring-shaped and Bar Slotted All-Textile Antenna for Off-body WBAN/WLAN and 5G Applications
    ( 2020-09-28)
    Mashaghba H.A.
    ;
    Hasliza A Rahim @ Samsuddin
    ;
    Soh Ping Jack
    ;
    Abdulmalek M.
    ;
    Ismahayati Adam
    ;
    Muzammil Jusoh
    ;
    Thennarasan Sabapathy
    ;
    Mohd Najib Mohd Yasin
    ;
    Khairul Najmy Abdul Rani
    This paper presents a dual-band split ring-shaped and bar slotted textile antenna for potential WBAN/WLAN and 5G applications. The antenna is made using textiles and features a full ground plane to possibly alleviate coupling to the human body. The overall size of the antenna is 70 x 70 mm2, with a patch sized at 47.2 x 31 mm2 0.472 \lambda \times 0.031 \lambda. The antenna is made using ShieldIt Super as its conductive textile and felt as its substrate. To enable its dual-band resonance at 2.45 and 3.5 GHz a split ring-shaped and bar slots are integrated onto the patch. The proposed antenna is evaluated when bent under different radii and at different axes to estimate its performance in terms of reflection coefficient, bandwidth, efficiency and gain. A 10-dB impedance bandwidth of 57 % or 135 MHz (from 2.39 to 2.52 GHz) and 70 % or 240 MHz (from 3.45 to 3.56 GHz) are obtained when evaluated in the planar /bent configuration. The maximum realized gain is 6 dBi for at 3.5 GHz. These performances indicate that the antenna proposed in this work can be potentially improved for applications in WBAN/WLAN and 5G bands.
  • Publication
    Mitigating mutual coupling effects on circular polarization for improved bandwidth in MIMO systems: A novel approach
    ( 2024-03-30)
    Ali A.
    ;
    Mohd Najib Mohd Yasin
    ;
    Ismahayati Adam
    ;
    Ismail A.M.
    ;
    Soh Ping Jack
    ;
    Alghaihab A.
    ;
    Nor N.I.M.
    ;
    Rahman N.A.A.
    An improved mutual coupling compensation in circularly polarized (CP) multi-input multi-output (MIMO) dielectric resonator antenna (DRA) is presented in this paper. Using trimming approach, the mutual coupling (MC) between closely spaced DRA units at 0.3λ has been significantly reduced while axial ratio performance has been maintained. Mutual coupling reduction is obtained by trimming the DRA to ensure low mutual coupling below −20dB. The exclusive features of the proposed MIMO DRA include wide impedance matching bandwidth (BW), triple band circular polarization, and suppressed MC between the radiating elements. The impedance bandwidth matches perfectly with a triple band's 3 dB axial ratio (AR). It is designed with characteristic mode analysis with good agreement of the measurement that has been obtained. Using the probe feed method, the DRA and patch strip are coupled together to allow bandwidth widening of the pro-posed DRA. An impedance bandwidth of 34% at a lower frequency to around 2% at a higher frequency was achieved in all resonance frequencies. Thus, we refer to our newly designed DRA as a proposed method for effectively reducing the mutual coupling between DRAs. Additionally, the 3 dB AR bandwidth matched at 3.3 GHz, 4.6 GHz, and 6.3 GHz with a percentage of 11.66%, 3.04%, and 2.22% obtained at the three different frequencies. Note that the proposed DRA exhibits low mutual coupling (below −20 dB) at the targeted frequencies, which is suitable for better signal reception for MIMO applications. By computing, the metrics envelop correlation coefficient, diversity gain, channel capacity loss, and total active reflection coefficient, the MIMO performance of the proposed antenna is verified. The experiments show a close result between simulated and computed validation of the proposed DRA.
  • Publication
    Flexible UWB Compact Circular Split-Ring Slotted Wearable Textile Antenna for Off-Body Millimetre-Wave 5G Mobile Communication
    ( 2020-01-01)
    Lee H.W.
    ;
    Hasliza A Rahim @ Samsuddin
    ;
    Abdulmalek M.
    ;
    R Badlishah Ahmad
    ;
    Jamaluddin M.H.
    ;
    Muzammil Jusoh
    ;
    Mohsin D.A.
    ;
    Wee Fwen Hoon
    ;
    Ismahayati Adam
    ;
    Yahya N.Z.
    ;
    Khairul Najmy Abdul Rani
    A flexible ultra-wideband (UWB) compact circular split-ring slotted wearable textile antenna for off-body 28 GHz fifth-generation (5G) mobile communication is proposed. The proposed antenna is implemented using low-cost felt textile substrates and copper. The proposed 5G wearable antenna of compact circular split-ring slotted with enhanced bandwidth of 0.5% with the resonance frequency of 28 GHz is presented. The S11 for patch antenna with slot exhibited 43.4% more than the patch antenna without slot. The results also exhibited that the bending angle of 10° and 20° perform better return loss than in flat condition, up to 14% for patch antenna with slot against without the slot.
  • Publication
    Feasibility study on RF energy harvesting in Malaysia
    ( 2017-01-01)
    Ismahayati Adam
    ;
    Mohd Najib Mohd Yasin
    ;
    Mohd Fareq Abd Malek
    ;
    Hasliza A Rahim @ Samsuddin
    ;
    Shakhirul Mat Salleh
    ;
    Mohammad Shahrazel Razalli
    Worlds are looking for a renewable energy to replace current energy sources. Solar and wind renewable energy has been deployed for some years as one renewable energy in a few countries in a large scale. For a small scale renewable energy, the development of electromagnetic energy harvesting has good potential as one of the sources of renewable energy since the electromagnetic energy is available all the time and everywhere, unlike other renewable energy (e.g., solar, wind, thermal and ocean wave). First step of feasibility of scavenging an RF energy is investigated through power density measurement in urban and semi-urban area. An average power of −13.33 dBm (UMTS band) measured in urban environment.
  • 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
    Mutual Coupling Suppression in Wearable MIMO Antenna for On/Off-Body WBAN Applications
    ( 2021-03-01)
    Ismahayati Adam
    ;
    Hasliza A Rahim @ Samsuddin
    ;
    Mohd Najib Mohd Yasin
    ;
    Muhammad Nazrin Mohd Nasrol
    A 2x1 wearable multiple-input-multiple-output (MIMO) antenna with line patch as mutual coupling suppression is presented. The proposed MIMO antenna is based on a simple rectangular structure that works at 2.45 GHz frequency. The patches are designed using ShieldIt textiles and are placed to a very closed (0.1λ) gap. The results show that the suppression in the mutual coupling of 5 dB (from-20 dB to-25dB), reduced by 25% after the line patch is inserted in between patches. On a positive note, an improvement in the antenna gain, from 4.4 dB to 4.7dB is achieved. On top of that, the performance of the reflection coefficient (S11) and the antenna impedance bandwidth is preserved. Important diversity performance parameter for MIMO antenna such as ECC, diversity gain and MEG results are found to be in an acceptable limit.
      1
  • Publication
    A Comprehensive Review of Midrange Wireless Power Transfer Using Dielectric Resonators
    ( 2021-01-01)
    Azuwa Ali
    ;
    Mohd Najib Mohd Yasin
    ;
    Faiz Wan Ali W.F.
    ;
    Norsuria Mahmed
    ;
    Kamarudin M.R.
    ;
    Ismahayati Adam
    ;
    Muzammil Jusoh
    ;
    Hasliza A Rahim @ Samsuddin
    ;
    Khor Shing Fhan
    ;
    Nurulazlina Ramli
    ;
    Norshamsuri Ali @ Hasim
    Magnetic resonant coupling (MRC) is one of the techniques that are widely used in wireless power transfer (WPT) systems. The technique is commonly used for enhancing distance while maintaining power transfer efficiency (PTE). Many studies have investigated new technologies to extend the distance of MRC while maintaining high PTE values. The most promising technique to date in MRC is the addition of a resonator between the transmitter and the receiver coil. The implementation of the resonator varies based on different designs, sizes, and material types, although the outcomes remain unsatisfactory. By introducing dielectric material resonators, PTE can be improved by lowering the ohmic loss which becomes a problem on conventional resonators. This study presents a general overview on the use of dielectric material as a resonator in MRC WPT technology and its technological development. The basic operation of MRC WPT is summarized with up-to-date technical improvements related to dielectric material as a resonator in the field of WPT. An overview of the current limitations and challenges of this technique is also highlighted in this study.
      1