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

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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
    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.
  • Publication
    UWB Antenna with Artificial Magnetic Conductor (AMC) for 5G Applications
    ( 2020-01-01)
    Syuhaimi Kassim
    ;
    Hasliza A Rahim @ Samsuddin
    ;
    Abdulmalek M.
    ;
    R Badlishah Ahmad
    ;
    Jamaluddin M.H.
    ;
    Muzammil Jusoh
    ;
    Mohsin D.A.
    ;
    Yahya N.Z.
    ;
    Wee Fwen Hoon
    ;
    Ismahayati Adam
    ;
    Rani K.N.A.
    This paper presents the design of an ultra-wideband (UWB) antenna for Internet of Things (IoT) applications that operate within 5G operating frequencies. One of the IoT-based devices’ architecture is wireless body area networks (WBANs). WBAN allows computer device to communicate with human body signal by trading digital information like electrical conductivity. Fifth generation (5G) is the state-of-the-art generation mobile communication. A higher data speed it offers will improve data communication efficiency in WBAN system. One of the biggest challenges foreseen for the wearable UWB antenna is the antenna bandwidth. The challenge is to warrant a wideband performance throughout the operating frequency, and a trade-off with a high dielectric in proposed substrate is essential. This paper presents design and parametric analysis of an antenna using a typical industry-preferred Rogers material (RO4350B) substrate with wider bandwidth as compared to 5G frequencies, 10.125–10.225 GHz. This paper also exhibits bandwidth improvement with the presence of artificial magnetic conductor (AMC) as a metasurface. A typical UWB patch antenna was initially designed before being integrated with AMC through a parametric analysis. This paper analyzes the frequency, gain, directivity and antenna efficiency before and after optimization. This paper successfully demonstrates a slotted Y-shaped antenna design with coplanar waveguide (CPW) using a Rogers material (RO4350B) as a substrate and the bandwidth improvement by 15.6% with the AMC as a metasurface.
  • 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
    Ambient radio frequency energy harvesting featuring antenna with multistage rectifier
    ( 2018)
    Ismahayati Adam
    The work presented in this thesis focuses on a radio frequency (RF) energy harvesting approach which scavenging energy from RF electromagnetic radiation to generate electrical signal in a real environments. Compared to other alternative energy sources, such as solar and wind, RF energy is the only one that can provide continuous supply of energy regardless days or nights and not affected by bad weather conditions. One of the challenging problems of RF energy harvesting is the low power densities yielded from ambient RF energy. Thus, it is very crucial to design a highly efficient harvester operating at widespread use of RF spectrums. One of the novelty of this thesis is contributes by the investigation of the feasibility of RF energy harvesting in Malaysia, in advance of the harvester design. Through this power density measurements, the scavengeable ambient frequency sources with their associated available RF power level were identified. It is demonstrated that wireless communication systems of GSM 900 (860 – 960 MHz), GSM 1800 (1730 – 1866 MHz) and UMTS (2100 – 2200 MHz) bands provide optimal sources for power harvesting at both measured urban and semi-urban location in Malaysia. The antenna and rectifier circuit are then designed separately prior to their combination and performance assessment. Operated from 1800 MHz up to 2.5 GHz, the proposed RF energy harvester features a broadband antenna and a multistage rectifier in one integrated circuit. Furthermore, the harvester sensitivities are optimized between -30 to -20 dBm, based on the measured available power in the surroundings. The performance of the harvester is investigated by six combination of two rectifiers and three different antennas, tested in both indoor and outdoor environment for dedicated and non-dedicated RF power sources. To further demonstrate the relation between the rectenna polarizations with the capability to harvest the RF energy, a polarization study is conducted. To realize this measurement, a novel simple and broadband circular polarized antenna is proposed. The obtained measurement results are consistent with the power densities measured in power density measurement, where more dc output are obtained in urban areas compared to semi-urban areas. In an urban area, the measurement results indicate the system is capable of harvesting up to 1.8 V dc output from non-dedicated ambient RF energy sources. The dc generated in RF energy harvesting may be less than generated by solar and wind techniques, however it can be significant in the absence of other energy sources.
  • 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.