In this paper, a compact planar ultrawideband (UWB) antenna and an antenna array setup for microwave breast imaging are presented. The proposed antenna is constructed with a slotted semicircular-shaped patch and partial trapezoidal ground. It is compact in dimension: 0.30λ × 0.31λ × 0.011λ, where λ is the wavelength of the lowest operating frequency. For design purposes, several parameters are assumed and optimized to achieve better performance. The prototype is applied in the breast imaging scheme over the UWB frequency range 3.10-10.60 GHz. However, the antenna achieves an operating bandwidth of 8.70 GHz (2.30-11.00 GHz) for the reflection coefficient under-10 dB with decent impedance matching, 5.80 dBi of maximum gain with steady radiation pattern. The antenna provides a fidelity factor (FF) of 82% and 81% for face-to-face and side-by-side setups, respectively, which specifies the directionality and minor variation of the received pulses. The antenna is fabricated and measured to evaluate the antenna characteristics. A 16-antenna array-based configuration is considered to measure the backscattering signal of the breast phantom where one antenna acts as transmitter, and 15 of them receive the scattered signals. The data is taken in both the configuration of the phantom with and without the tumor inside. Later, the Iteratively Corrected Delay and Sum (IC-DAS) image reconstructed algorithm was used to identify the tumor in the breast phantom. Finally, the reconstructed images from the analysis and processing of the backscattering signal by the algorithm are illustrated to verify the imaging performance.
Today, electromagnetic wave theory is commonly used in many engineering devices. However, such devices produce electromagnetic (EM) radiation, damaging people's health and the impact of other electronic device's operation. Therefore, Microwave Absorber has been widely used in anechoic chamber to measure equipment radiation and prevent unwanted radiation and electromagnetic interference. This research investigates the absorption performance of pyramidal absorbers with a slotted method design. This research used rectangular and triangular slotted on the hollow pyramidal absorber. There are six types of slotted: Design 1, Design 2, and Design 3
which have triangular shapes, and Design 4, Design 5, and Design 6, have rectangular shapes. The pyramidal absorber is produced using CST Microwave Studio Suite. Afterward, the fabrication process is performed using cardboard and coated with Powdered Activated Carbon (PAC). Measurement had been done successfully via far-field measurement using an arch method at 1 GHz to 12 GHz. The slotted pyramidal absorber's absorptivity was taken in each frequency band and was tabulated in figure 10. The result is compared with their maximum absorption in each of the four frequency bands. Comparison based on slot design, triangular and rectangular each had its own advantages at a certain frequency. However, small rectangular slot of Design 1 shows consistent absorption performance at all frequency band.
This paper aims to provide a review of the analytical extraction techniques for polycyclic aromatic hydrocarbons (PAHs) in soils. The extraction technologies described here include Soxhlet extraction, ultrasonic and mechanical agitation, accelerated solvent extraction, supercritical and subcritical fluid extraction, microwave-assisted extraction, solid phase extraction and microextraction, thermal desorption and flash pyrolysis, as well as fluidised-bed extraction. The influencing factors in the extraction of PAHs from soil such as temperature, type of solvent, soil moisture, and other soil characteristics are also discussed. The paper concludes with a review of the models used to describe the kinetics of PAH desorption from soils during solvent extraction.
Recent developments in the field of microwave planar sensors have led to a renewed interest in industrial, chemical, biological and medical applications that are capable of performing real-time and non-invasive measurement of material properties. Among the plausible advantages of microwave planar sensors is that they have a compact size, a low cost and the ease of fabrication and integration compared to prevailing sensors. However, some of their main drawbacks can be considered that restrict their usage and limit the range of applications such as their sensitivity and selectivity. The development of high-sensitivity microwave planar sensors is required for highly accurate complex permittivity measurements to monitor the small variations among different material samples. Therefore, the purpose of this paper is to review recent research on the development of microwave planar sensors and further challenges of their sensitivity and selectivity. Furthermore, the techniques of the complex permittivity extraction (real and imaginary parts) are discussed based on the different approaches of mathematical models. The outcomes of this review may facilitate improvements of and an alternative solution for the enhancement of microwave planar sensors' normalized sensitivity for material characterization, especially in biochemical and beverage industry applications.
The development of microwave absorbing materials based on recycled hematite (α-Fe2O3) nanoparticles and polycaprolactone (PCL) was the main focus of this study. α-Fe2O3 was recycled from mill scale and reduced to nanoparticles through high energy ball milling in order to improve its complex permittivity properties. Different compositions (5% wt., 10% wt., 15% wt. and 20% wt.) of the recycled α-Fe2O3 nanoparticles were melt-blended with PCL using a twin screw extruder to fabricate recycled α-Fe2O3/PCL nanocomposites. The samples were characterized for their microstructural properties through X - ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The complex permittivity and microwave absorption properties were respectively measured using the open ended coaxial (OEC) probe and a microstrip in connection with a vector network analyzer in the 1-4 GHz frequency range. An average α-Fe2O3 nanoparticle size of 16.2 nm was obtained with a maximum imaginary (ε") part of permittivity value of 0.54 at 4 GHz. The complex permittivity and power loss values of the nanocomposites increased with recycled α-Fe2O3 nanofiller content. At 2.4 GHz, the power loss (dB) values obtained for all the nanocomposites were between 13.3 dB and 14.4 dB and at 3.4 GHz, a maximum value of 16.37 dB was achieved for the 20 % wt. nanocomposite. The recycled α-Fe2O3/PCL nanocomposites have the potential for use in noise reduction applications in the 1-4 GHz range.
Wi-Fi is a wireless communication technology that uses specific electromagnetic frequencies. The increasing use of Wi-Fi has raised public concerns about the impact of electromagnetic radiation on the environment and human health. Since the exposure level of the electromagnetic field (EMF) radiation differs between different locations, it is important to measure the strength of the EMF at various locations under observation. This study aimed to obtain specific values related to the radiofrequency and microwave EMF which is described by four specific parameters, that are 1) the frequency of the wave, 2) the electric field strength E, 3) the magnetic field strength H, and 4) the power density S. This study was carried out at the first floor area of Hamdan Tahir Library, Universiti Sains Malaysia Health Campus. Mapping of Wi-Fi signal and measurement of Wi-Fi radiation level was performed at four specific locations, that are Laptop zone 1, Laptop zone 2, Computer lab, and Cozy corner. The average radiation level was compared with the ICNIRP standard limit for public user. It was observed that the Wi-Fi signal was highest in Laptop zone 2 followed by Laptop zone 1 which displayed a moderate signal strength. Whereas moderate but lower signal level was detected in Computer lab zone and Cozy corner. The electric and magnetic fields as well as power density were found highest in Laptop zone 1, followed by Laptop zone 2, Cozy corner, and Computer lab. Comparison with standard ICNIRP limit showed that the radiation level is still far below the ICNIRP limit, which is only 2% of exposure level. To conclude, Laptop zone 2 exhibited the strongest Wi-Fi signal whereas Laptop zone 1 displayed the highest radiation level. However, the strength of the electric and magnetic fields as well as power density is still far below the ICNIRP limit.
This paper investigates the optimum processing conditions of microwave assisted extraction (MAE) of anthraquinone (aloe emodin, AE) and flavonoids (kaempferol 3-gentiobioside, K3G and kaempferol, KA) from Senna alata (L.) Roxb. The kinetic study indicates that MAE showed a greater extraction rate, compared to ultrasonic-assisted and maceration, due to the enhanced power which altered the leaf microstructures. The optimisation was undertaken using one-factor-at-a-time, two-level factorial design and central composite design were used to maximise the yield of the target compounds. The optimum yield of K3G (4.27 mg/g DW), KA (8.54 mg/g DW) and AE (0.86 mg/g DW) was obtained at 90.5% ethanol, microwave power of 18.6 W/mL with a desirability of 0.82. In addition, the yield of K3G and KA is correlated positively with the antioxidant activity.
We developed an innovative single-step pyrolysis approach that combines microwave heating and activation by CO2 or steam to transform orange peel waste (OPW) into microwave activated biochar (MAB). This involves carbonization and activation simultaneously under an inert environment. Using CO2 demonstrates dual functions in this approach, acting as purging gas to provide an inert environment for pyrolysis while activating highly porous MAB. This approach demonstrates rapid heating rate (15-120 °C/min), higher temperature (> 800 °C) and shorter process time (15 min) compared to conventional method using furnace (> 1 h). The MAB shows higher mass yield (31-44 wt %), high content of fixed carbon (58.6-61.2 wt %), Brunauer Emmett Teller (BET) surface area (158.5-305.1 m2/g), low ratio of H/C (0.3) and O/C (0.2). Activation with CO2 produces more micropores than using steam that generates more mesopores. Steam-activated MAB records a higher adsorption efficiency (136 mg/g) compared to CO2 activation (91 mg/g), achieving 89-93 % removal of Congo Red dye. The microwave pyrolysis coupled with steam or CO2 activation thereby represents a promising approach to transform fruit-peel waste to microwave-activated biochar that remove hazardous dye.
This study was done to determine the effects of different thermal drying methods (sun drying, microwave drying and hot air oven drying) on the total phenolic content (TPC), total anthocyanin content and the antioxidant properties of Vitex negundo (VN) tea. Significant decline (P < 0.05) in antioxidant properties of hot air oven drying shows that this method is not the best method to preserve antioxidant compounds in VN tea. As a conclusion, microwave drying has been found to be a good method for maintain the TPC, anthocyanin content and AEAC in dried sample of VN tea.
Pectin is a heterogeneous branched polysaccharide with complex structure. Microwave-assisted
extraction (MAE) is more efficient in extracting pectin compared to conventional method. The objective of this study was to compare the efficiency of microwave-assisted pectin extraction against conventional extraction method. This study was also to investigate the effect of power level on yield and quality of extracted pectin from jackfruit rinds. Water-based extraction method was performed with the extraction duration for conventional extraction and MAE were 1 h and 10 min, respectively. The temperature of conventional extraction was set at 90°C and the power levels of MAE were 450 W, 600 W and 800 W. High yield of pectin was obtained from conventional extraction (14.59%) and MAE (16.72-17.63%). All quality characteristics determined were found to be insignificant different for pectin extracted from both conventional extraction and MAE except moisture and ash content. Increase in microwave power did not affect yield and quality characteristics of pectin from jackfruit rinds significantly. In conclusion, MAE requires shorter time than conventional extraction in extracting comparable amount and quality of pectin from jackfruit rinds. Microwave-assisted extraction at 450 W was the most effective and economic extraction condition among the different power levels tested.
Dielectric properties of natural rubber Hevea brasiliensis latex were measured at frequencies 0.2 to 20 GHz, at temperatures of 2, 15, 25, 35, and 50oC and around 30-98% moisture content. Measurements were done using open-ended coaxial line sensor and automated network analyzer. As expected, results showed that dielectric constant increased with increasing moisture. From 0.2 to 2.6 GHz, the losses were governed by conductive losses but for frequencies greater than 2.6 GHz, these were mainly due to dipolar losses. The former is due to conducting phases in hevea latex, while the latter is mainly governed by the orientation of water molecules. The results were analyzed at 2.6, 10, and 18 GHz, respectively. These were then compared with the values predicted by the dielectric mixture equations recommended by Weiner, Bruggeman and Kraszewski. All the measured values were found to be within the Weiner’s boundaries and close to the upper limit of Weiner’s model. It is also close to the predicted values of Bruggeman’s model with a/b = 0.1. All the models including Kraszewski are suitable for predicting the dielectric properties of hevea latex for frequencies 2.6 to 18 GHz, moisture content 30 to 98% and temperatures 2 to 50oC.
Optimization of microwave assisted extraction of dragon fruit peel pectin was conducted using respond surface methodology. Effect of extraction conditions, i.e. pH value (X1), extraction time (X2) and solid-liquid ratio (X3) on the extraction yield was investigated using a central composite experimental design. Optimization of microwave assisted extraction was performed and three-dimensional (3D) response surface plots were derived from the mathematical models. Analysis of variance (ANOVA) was conducted and indicated a significant interaction between extraction conditions (pH value and extraction time) and extraction yield. The optimum conditions of microwave assisted extraction were as follows: X1 = 2.07; X2 = 65 s and X3 = 66.57. The verification test on pectin extraction was performed and revealed a perfect agreement between experimental and predicted values. The maximum predicted yield of pectin extraction was 18.53%. Overall, application of microwave assisted extraction can give rise to high quality dragon fruit peel pectin.
An experimental study was performed to determine the drying characteristics of dried papaya using different drying methods. They were dried using several methods, such as sun drying, solar drying, oven drying, and microwave drying. The effects of different operating conditions on physical quality attributes were investigated. The papaya were cut into different thicknesses and cooked in sugar syrup with different sugar concentration for 24 hours. Three different temperature settings were used in oven and microwave drying. The drying curve and drying rate of each method, temperature, sample
thickness and sugar concentration were studied. The drying times were found as in 6-15 minutes, 5 to 11 h, 10 to 18 h, and 14 to 23 h for the microwave, oven, sun and solar drying, respectively. The drying time increased with the increase of sample thickness and sugar concentration, as well as with the decrease of the drying temperature. In this study, quality attributes like colours and textural property of dried papaya were explored. Among the various methods of the drying characteristics
of papaya halwa, oven drying was preferred with the optimum sample in 5 mm thickness and at the air temperature of 70ºC as it saved up to 40% of the drying time as compared to other methods, except microwave, and produced acceptable physical quality of product.
Microwave Remote sensing data have been widely used in land cover and land use classification. The objective of this research paper is to investigate the feasibility of the multi-polarized ALOS-PALSAR data for land cover mapping. This paper presents the methodology and preliminary result including data acquisitions, data processing and data analysis. Standard supervised classification techniques such as the maximum likelihood, minimum distance-to-mean, and parallelepiped were applied to the ALOS-PALSAR images in the land cover mapping analysis. The PALSAR data training areas were chosen based on the information obtained from
optical satellite imagery. The best supervise classifier was selected based on the highest overall accuracy and
kappa coefficient. This study indicated that the land cover of Butterworth, Malaysia can be mapped accurately
using ALOS PALSAR data.
Triyttrium Pentairon (iii) Oxide (Y3Fe501,2) or familiar called as Yttrium Iron Garnet (YIG) is successfully prepared using a conventional mixed-oxide method of 5:3 Fe to Y ratios. YIG prepared from conventional mixed-oxide usually produced some associated phase which surely will affect electrical properties. In this study, various temperature used in the sintering process to induce associated phases (YIP) to be fully reacting to form single phase of YIG and the effect on resonance frequency is studied for resonator applications. The mixtures of oxide powders are calcined at 1100 "C and sintered at various temperatures of (1350, 1380, 1400, 1420 1450 QC, respectively). Cubic phase is detected from the formation of YIG. Some other phases such as YIP and hematite also present as secondary phase. However, it is seen that, based on the Rietvield refinement method, the total amount of secondary phase simulated are inversely proportional with sintering temperature. The powder was pressed into cylindrical pellet and tested as a microwave resonator in antenna application. It was found that, on the actual antenna circuit the operating frequencies measured are in the range of 10-12 GHz for all samples which suitable for X-band. At the end, overall radiation pattern for all samples exhibit an omnidirectional behavior.
Nanocrystalline lead sulfide (PbS) thin films have been successfully grown on glass substrate using the chemical bath deposition technique. Microwave oven was used as a heating source to facilitate the growth process of the thin films. Aqueous solutions of lead nitrate Pb(NO3) and thiourea [SC(NH2)2] were used as lead and sulfur ion sources, respectively. Structural, morphological and optical analyses revealed good quality growth of nanocrystalline PbS thin films. This study introduced a facile and low cost method to prepare high quality nanocrystalline PbS thin films in a relatively short growth time for optoelectronic applications.
Microwave imaging is the technique to identify hidden objects from structures using electromagnetic waves that can be applied in medical diagnosis. The change of dielectric property can be detected using microwave antenna sensor, which can lead to localization of abnormality in the human body. This paper presents a stacked type modified Planar Inverted F Antenna (PIFA) as microwave imaging sensor. Design and performance analysis of the sensor antenna along with computational and experimental analysis to identify concealed object has been investigated in this study. The dimension of the modified PIFA radiating patch is 40 × 20 × 10 mm³. The reflector walls used, are 45 mm in length and 0.2-mm-thick inexpensive copper sheet is considered for the simulation and fabrication which addresses the problems of high expenses in conventional patch antenna. The proposed antenna sensor operates at 1.55⁻1.68 GHz where the maximum realized gain is 4.5 dB with consistent unidirectional radiation characteristics. The proposed sensor antenna is used to identify tumor in a computational human tissue phantom based on reflection and transmission coefficient. Finally, an experiment has been performed to verify the antenna's potentiality of detecting abnormality in realistic breast phantom.
Dielectric properties study is important in understanding the interaction between materials within electromagnetic field. By knowing and understanding the dielectric properties of materials, an efficient and effective microwave heating process and products can be designed. In this study, the dielectric properties of several encapsulation wall materials were measured using open-ended coaxial probe method. This method was selected due to its simplicity and high accuracy. All materials exhibited similar behavior. The result inferred that β-cyclodextrin (BC), starch (S), Arabic (GA) and maltodextrin (M) with various dextrose equivalent exhibited effective encapsulation wall materials in microwave encapsulation-drying technique owing to loss tangent values which were higher than 0.1 at general application frequency of 2.45 GHz. Thus, these were found to be suitable as wall material to encapsulate the selected core material in this microwave encapsulation-drying method. On contrary, sodium caseinate showed an ineffective wall material to be used in microwave encapsulation-drying. The differences in the values of dielectric constant, loss factor and loss tangent were found to be contributed by frequency, composition and bulk density.
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.
This paper investigates micromachined antenna performance operating at 5 GHz for radio frequency (RF) energy harvesting applications by comparing different substrate materials and fabrication modes. The research aims to discover appropriate antenna designs that can be integrated with the rectifier circuit and fabricated in a CMOS (Complementary Metal-Oxide Semiconductor)-compatible process approach. Therefore, the investigation involves the comparison of three different micromachined antenna substrate materials, including micromachined Si surface, micromachined Si bulk with air gaps, and micromachined glass-surface antenna, as well as conventional RT/Duroid-5880 (Rogers Corp., Chandler, AZ, USA)-based antenna as the reference. The characteristics of the antennas have been analysed using CST-MWS (CST MICROWAVE STUDIO®-High Frequency EM Simulation Tool). The results show that the Si-surface micromachined antenna does not meet the parameter requirement for RF antenna specification. However, by creating an air gap on the Si substrate using a micro-electromechanical system (MEMS) process, the antenna performance could be improved. On the other hand, the glass-based antenna presents a good S11 parameter, wide bandwidth, VSWR (Voltage Standing Wave Ratio) ≤ 2, omnidirectional radiation pattern and acceptable maximum gain of >5 dB. The measurement results on the fabricated glass-based antenna show good agreement with the simulation results. The study on the alternative antenna substrates and structures is especially useful for the development of integrated patch antennas for RF energy harvesting systems.