Zaiki Awang

Bio: Zaiki Awang is an academic researcher from Universiti Teknologi MARA. The author has contributed to research in topics: Microwave & Dielectric. The author has an hindex of 12, co-authored 129 publications receiving 645 citations. Previous affiliations of Zaiki Awang include University of Leeds.

Gas sensors: A review

Abstract: In this paper a review of different technologies for gas sensors is presented. The different types of gas sensors technologies including catalytic gas sensor, electrochemical gas sensors, thermal conductivity gas sensor, optical gas sensor and acoustic gas sensor are discussed together with their principle of operation. The Surface Acoustic Wave Gas Sensor technology is discussed in greater detail. The advantages and disadvantages of each sensor technology are also highlighted. All these technologies have been used for several decades for the development of highly sensitive and responsive gas sensors for the detection of flammable and hazardous gases. However, for improved sensitivity and selectivity for these sensors, future trends and outlook for researchers are suggested in the conclusion of this article. Copyright © 2014 IFSA Publishing, S. L.

A Study on Microwave Absorption Properties of Carbon Black and Ni0.6Zn0.4Fe2O4 Nanocomposites by Tuning the Matching-Absorbing Layer Structures.

Abstract: Microwave absorption properties were systematically studied for double-layer carbon black/epoxy resin (CB) and Ni0.6Zn0.4Fe2O4/epoxy resin (F) nanocomposites in the frequency range of 8 to 18 GHz. The Ni0.6Zn0.4Fe2O4 nanoparticles were synthesized via high energy ball milling with subsequent sintering while carbon black was commercially purchased. The materials were later incorporated into epoxy resin to fabricate double-layer composite structures with total thicknesses of 2 and 3 mm. The CB1/F1, in which carbon black as matching and ferrite as absorbing layer with each thickness of 1 mm, showed the highest microwave absorption of more than 99.9%, with minimum reflection loss of −33.8 dB but with an absorption bandwidth of only 2.7 GHz. Double layer absorbers with F1/CB1(ferrite as matching and carbon black as absorbing layer with each thickness of 1 mm) structure showed the best microwave absorption performance in which more than 99% microwave energy were absorbed, with promising minimum reflection loss of −24.0 dB, along with a wider bandwidth of 4.8 GHz and yet with a reduced thickness of only 2 mm.

Experimental Breast Tumor Detection Using Nn-Based UWB Imaging

Abstract: This paper presents a system with experimental comple-ment to a simulation work for early breast tumor detection. The ex-periments are conducted using commercial Ultrawide-Band (UWB) transceivers, Neural Network (NN) based Pattern Recognition (PR) software for imaging and proposed breast phantoms for homogenous and heterogeneous tissues. The proposed breast phantoms (homoge-neous and heterogeneous) and tumor are constructed using available low cost materials and their mixtures with minimal e®ort. A speci¯c glass is used as skin. All the materials and their mixtures are con-sidered according to the ratio of the dielectric properties of the breast tissues. Experiments to detect tumor are performed in regular noisy room environment. The UWB signals are transmitted from one side of the breast phantom (for both cases) and received from opposite side diagonally repeatedly. Using discrete cosine transform (DCT) of these received signals, a Neural Network (NN) module is developed, trained and tested. The tumor existence, size and location detection rates for both cases are highly satisfactory, which are approximately: (i) 100%,95.8% and 94.3% for homogeneous and (ii) 100%, 93.4% and 93.1% for heterogeneous cases respectively. This gives assurance of early de- tection and the practical usefulness of the developed system in near future.

A Free-Space Method for Complex Permittivity Measurement of Bulk and Thin Film Dielectrics at Microwave Frequencies

Abstract: A free-space, non-destructive method for measuring the complex permittivity of a double-layer bulk dielectrics and thin fllm oxide layers at microwave frequencies have been developed. The method utilizes a spot-focusing antenna system in conjunction with a vector network analyzer in the range of 18{26GHz. The bulk dielectric was measured using the Transmission Method and Metal-Backed Method, while the Metal-Backed Method was used to investigate the thin fllms. Both types of samples were sandwiched between two quarter-wavelength Te∞on plates to improve the mismatch at the frequencies of measurement. The thin fllm sample arrangement was backed by an additional metal plate. The double-layer bulk dielectric samples were Te∞on-PVC and Plexiglas-PVC, while the thin fllm samples consisted of SiO2 layers of difierent thicknesses grown on doped and undoped Si wafer substrates. The relative permittivity obtained for PVC ranged between 2.62 to 2.93, while those for Plexiglas exhibited values between 2.45 to 2.63. The relative permittivity of SiO2 deposited on these wafers was between 3.5 to 4.5. All these values are in good agreement with published data. The advantage of the method is its ability to measure the dielectric properties of the fllms at the mid- frequency band irrespective of the substrate type used. Simulations of the measurement setup were carried out using CST Microwave Studio and the simulation results agreed closely with the measurements.

Influence of different BFO filler content on microwave absorption performances in BiFeO3/epoxy resin composites

Abstract: Multiferroic BiFeO3 (BFO) has garnered interest in recent years due to its magneto-electric coupling between ferroelectric and magnetic ordering. This unique property offers some advantages when applied as electromagnetic (EM) wave absorbers. In work reported here, the microwave absorption properties of multiferroic BFO/epoxy resin composites with different weight percentage (wt%) of BFO fillers of various thicknesses were investigated. The BFO powders were synthesized using high energy ball milling (HEBM) and sintered at 775 °C in a furnace with an ambient air condition. The sintered BFO powders with different weight ratios (50 wt%, 60 wt% and 70 wt%) were mixed with epoxy resin as a matrix to form a composite with thicknesses of 1, 2 and 3 mm. Phase identification, grain size and morphology, magnetic and microwave absorption properties of prepared samples were characterized. The absorption performances of samples were measured in the frequency range of 8–18 GHz. As a result, the compressed BFO powders and BFO/epoxy resin composites with 50–70 wt% BFO filler showed dual-band microwave absorption resonance behavior. The best performances were demonstrated by a 3 mm thick BFO70 composite sample which exhibited a primary reflection loss (RL1) of −26.0 dB at 9.1 GHz and a secondary reflection loss (RL2) of −40.5 dB at 11.3 GHz, along with an associated −10 dB bandwidth of 1.31 GHz. The minimum reflection loss (RL) peaks were shifted to a lower frequency as the thicknesses were increased due to the λ 4 condition. Theoretical studies on the absorbing wave mechanism reveal a unique combination of dielectric loss relaxations and antiferromagnetic resonance effects in the BFO absorbers.

Fluorinated MOF platform for selective removal and sensing of SO2 from flue gas and air.

Abstract: Conventional SO2 scrubbing agents, namely calcium oxide and zeolites, are often used to remove SO2 using a strong or irreversible adsorption-based process. However, adsorbents capable of sensing and selectively capturing this toxic molecule in a reversible manner, with in-depth understanding of structure-property relationships, have been rarely explored. Here we report the selective removal and sensing of SO2 using recently unveiled fluorinated metal-organic frameworks (MOFs). Mixed gas adsorption experiments were performed at low concentrations ranging from 250 p.p.m. to 7% of SO2. Direct mixed gas column breakthrough and/or column desorption experiments revealed an unprecedented SO2 affinity for KAUST-7 (NbOFFIVE-1-Ni) and KAUST-8 (AlFFIVE-1-Ni) MOFs. Furthermore, MOF-coated quartz crystal microbalance transducers were used to develop sensors with the ability to detect SO2 at low concentrations ranging from 25 to 500 p.p.m.

Design and Application of the CSRR-Based Planar Sensor for Noninvasive Measurement of Complex Permittivity

Abstract: A novel microwave noninvasive planar sensor based on the complementary split ring resonator (CSRR) is proposed for an accurate measurement of the complex permittivity of materials. The CSRR is etched in the ground plane of the planar microstrip line. Two CSRRs of rectangular and circular cross-sections are chosen for the sensitivity analysis, where the later is found to possess higher sensitivity and hence appears to be more appropriate for the sensor design. At resonance, the electric field induced along the plane of CSRR is found to be quite sensitive for the characterization of specimen kept in contact with the sensor. A numerical model is developed here for the calculation of the complex permittivity as a function of resonant frequency and the quality factor data using the electromagnetic simulator, the Computer Simulation Technology. For practical applications, a detailed air gap analysis is carried out to consider the effect of any air gap present between the test sample and the CSRR. The designed sensor is fabricated and tested, and accordingly the numerically established relations are experimentally verified for various reference samples e.g., teflon, polyvinyl chloride, plexiglas, polyethylene, rubber, and wood. Experimentally, it is found that the permittivity measurement using the proposed sensor is possible with a typical error of 3%.

Recent Advances in Electrochemical Sensors for Detecting Toxic Gases: NO₂, SO₂ and H₂S.

Abstract: Toxic gases, such as NOx, SOx, H2S and other S-containing gases, cause numerous harmful effects on human health even at very low gas concentrations. Reliable detection of various gases in low concentration is mandatory in the fields such as industrial plants, environmental monitoring, air quality assurance, automotive technologies and so on. In this paper, the recent advances in electrochemical sensors for toxic gas detections were reviewed and summarized with a focus on NO2, SO2 and H2S gas sensors. The recent progress of the detection of each of these toxic gases was categorized by the highly explored sensing materials over the past few decades. The important sensing performance parameters like sensitivity/response, response and recovery times at certain gas concentration and operating temperature for different sensor materials and structures have been summarized and tabulated to provide a thorough performance comparison. A novel metric, sensitivity per ppm/response time ratio has been calculated for each sensor in order to compare the overall sensing performance on the same reference. It is found that hybrid materials-based sensors exhibit the highest average ratio for NO2 gas sensing, whereas GaN and metal-oxide based sensors possess the highest ratio for SO2 and H2S gas sensing, respectively. Recently, significant research efforts have been made exploring new sensor materials, such as graphene and its derivatives, transition metal dichalcogenides (TMDs), GaN, metal-metal oxide nanostructures, solid electrolytes and organic materials to detect the above-mentioned toxic gases. In addition, the contemporary progress in SO2 gas sensors based on zeolite and paper and H2S gas sensors based on colorimetric and metal-organic framework (MOF) structures have also been reviewed. Finally, this work reviewed the recent first principle studies on the interaction between gas molecules and novel promising materials like arsenene, borophene, blue phosphorene, GeSe monolayer and germanene. The goal is to understand the surface interaction mechanism.

SAW Sensors for Chemical Vapors and Gases.

Abstract: Surface acoustic wave (SAW) technology provides a sensitive platform for sensing chemicals in gaseous and fluidic states with the inherent advantages of passive and wireless operation. In this review, we provide a general overview on the fundamental aspects and some major advances of Rayleigh wave-based SAW sensors in sensing chemicals in a gaseous phase. In particular, we review the progress in general understanding of the SAW chemical sensing mechanism, optimization of the sensor characteristics, and the development of the sensors operational at different conditions. Based on previous publications, we suggest some appropriate sensing approaches for particular applications and identify new opportunities and needs for additional research in this area moving into the future.

Room-Temperature Gas Sensors Under Photoactivation: From Metal Oxides to 2D Materials

Abstract: Room-temperature gas sensors have aroused great attention in current gas sensor technology because of deemed demand of cheap, low power consumption and portable sensors for rapidly growing Internet of things applications. As an important approach, light illumination has been exploited for room-temperature operation with improving gas sensor’s attributes including sensitivity, speed and selectivity. This review provides an overview of the utilization of photoactivated nanomaterials in gas sensing field. First, recent advances in gas sensing of some exciting different nanostructures and hybrids of metal oxide semiconductors under light illumination are highlighted. Later, excellent gas sensing performance of emerging two-dimensional materials-based sensors under light illumination is discussed in details with proposed gas sensing mechanism. Originated impressive features from the interaction of photons with sensing materials are elucidated in the context of modulating sensing characteristics. Finally, the review concludes with key and constructive insights into current and future perspectives in the light-activated nanomaterials for optoelectronic gas sensor applications. Highlights: 1 Operations of metal oxide semiconductors gas sensors at room temperature under photoactivation are discussed.2 Emerging two-dimensional (2D) materials-based gas sensors under light illumination are summarized.3 The advantages and limitations of metal oxides and 2D-materials-based sensors in gas sensing at room temperature under photoactivation are highlighted.