Fwen Hoon Wee

Free space measurement technique on dielectric properties of agricultural residues at microwave frequencies

Principles to determine dielectric properties measurement using microwave free-space transmission measurements technique is presented in this paper. The projects main objective was to measure the dielectric properties of different agricultural waste material at microwave frequencies, which in turn, can serve as a potential alternative, replacing conventional printed circuit board (PCB) using FR4 material. A system, which includes a PNA vector network analyzer, horn antennas, and Agilent Technologies 85071E material measurement software were used and described in detail. Techniques and procedures essential in obtaining reliable permittivity data for agricultural waste products were also discussed. The waste products - rice husk, rice straw, and kenaf were studied in the frequency range of 2.2 to 3.3 GHz. These agricultural waste materials were mixed with two distinct resins, namely, Urea Formaldehyde (UF) and Phenol Formaldehyde (PF). Each type of resin was also investigated using different percentage of resin moisture content, and the results were analyzed thoroughly.

Setup and results of pyramidal microwave absorbers using rice husks

Agricultural wastes are considered not useful and are commonly dumped or burned after crop harvesting. Rice husks from paddy (Oryza sativa) are example of agricultural wastes. Rice husks have been investigated as the material for the pyramidal microwave absorbers. The setup for the fabrication and measurement of the rice husks pyramidal microwave absorbers are discussed. An 8£8 array of pyramidal microwave absorber using the rice husks-polyester-MEKP mixture has been designed and fabricated. There are four main stages in this work: the collection of the raw rice husks materials, the mould fabrication, the pyramidal microwave absorber fabrication and the experiments performed to determine the re∞ection loss performance of the rice husks pyramidal microwave absorbers. Experimental

Specific Absorption Rate (SAR) Evaluation of Textile Antennas

This paper presents a detailed and systematic investigation of the reproducibility of specific absorption rate (SAR) measurements using textile antennas and their simulation accuracy. The ability to accurately predict the SAR is very important for practical textile antenna designers since certified SAR measurements are costly. To that goal, the SAR values of a range of textile antennas operating in various bands of the IEEE 802.15.6 and 802.11 standards are evaluated. The selected textile antenna topologies for the evaluation differ in terms of the bandwidth behavior (broadband, dual band, and ultrawideband). They are chosen to be distinct, have been fabricated using an array of conductive textiles, and are benchmarked against similar structures made from a flexible conductor. SAR values are evaluated at three different frequencies, i.e., 2.45, 5.2, and 5.8 GHz, respectively, using a commercial electromagnetic solver and a certified experimental setup. Factors affecting the SAR behavior are presented and discussed. Results indicate that antennas without a rear ground plane are producing almost three times the SAR of textile antennas that feature a full ground plane. The results of this paper point out that the repeatability of the measurements is about 10% and that the agreement between simulations and measurements is on the order of about 17%.

INVESTIGATION OF THE CHARACTERISTICS OF BARIUM STRONTIUM TITANATE (BST) DIELECTRIC RESONATOR CERAMIC LOADED ON ARRAY ANTENNAS

We investigated a dielectric resonator ceramic microstrip patch antenna. The antenna was formed using barium strontium titanate (BST), which had a dielectric constant of 15. A new approach,i.e., the use of a high temperature dielectric probe kit, was used to determine the dielectric constant of BST. A computer simulation technology (CST) microwave studio was used to simulate the BST array antennas, taking into consideration the dielectric constant. We also measured the gain of the antennas loaded with two-, four, and six-element arrays of the BST antenna and found that the gain of a six-element BST array antenna was enhanced by a gain of about 1.6 dB over the four-element BST array antenna at 2.3 GHz. The impedance bandwidths of these BST array antennas for voltage standing wave ratio (VSWR) < 2 were in the application ranges,i.e., 2.30 to 2.50 GHz, established for Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN). Compared with the conventional array antenna with the same aperture size, the performance of the antenna obviously was improved, and the design is suitable for array applications, including base stations, for example.

Experimental determination of the performance of rice husk-carbon nanotube composites for absorbing microwave signals in the frequency range of 12.4-18 GHz

Composites of rice husks and carbon nanotubes (RHC- NTs) are an innovation in improving the absorption of microwave sig- nals. Rice husks, which are an agricultural waste material, have been found to possess a signiflcant propensity for absorbing microwave sig- nals. Studies have shown that both rice husks and carbon nanotubes (CNTs) have high percentages of carbon. Thus, in this paper, we present the results of our experimental study in which we varied the ratios of rice husks and CNTs in the composite materials and deter- mined the dielectric properties of the composites and measured their abilities to absorb microwave signals. The experimental microwave

Specific Absorption Rate (SAR) evaluation of biomedical telemetry textile antennas

This investigation aims at determining the Specific Absorption Rates (SARs) of textile antennas for on-body biomedical telemetry applications. The dual-band antennas are designed to operate at 2.4 GHz and 5.2 GHz with unidirectional radiations and broad bandwidths. Fractal Planar Inverted-F Antennas (F-PIFAs) are fabricated using different materials to assess factors influencing SAR levels. Simulations and measurements indicated a maximum SAR and uncertainty of 0.6 W/kg and 10%, respectively.

Effect of two different superstrate layers on bismuth titanate (BiT) array antennas.

The microwave industry has shown increasing interest in electronic ceramic material (ECM) due to its advantages, such as light weight, low cost, low loss, and high dielectric strength. In this paper, simple antennas covered by superstrate layers for 2.30 GHz to 2.50 GHz are proposed. The antennas are compact and have the capability of producing high performance in terms of gain, directivity, and radiation efficiency. Bismuth titanate with high dielectric constant of 21, was utilized as the ECM, while the superstrate layers chosen included a split ring resonator and dielectric material. The superstrate layers were designed for some improvement in the performance of directivity, gain, and return loss. The proposed antennas were simulated and fabricated. The results obtained were small antennas that possess high gain and high directivity with 360°, omni-directional signal transmission that resonant types of conventional dipole antenna cannot achieve. The gain of the antenna with the superstrate layer was enhanced by about 1 dBi over the antenna without a superstrate layer at 2.40 GHz.

High Gain and High Directive of Antenna Arrays Utilizing Dielectric Layer on Bismuth Titanate Ceramics

A high gain and high directive microstrip patch array antenna formed from dielectric layer stacked on bismuth titanate (BiT) ceramics have been investigated, fabricated, and measured. The antennas are designed and constructed with a combination of two-, four-, and six-BiT elements in an array form application on microwave substrate. For gain and directivity enhancement, a layer of dielectric was stacked on the BiT antenna array. We measured the gain and directivity of BiT array antennas with and without the dielectric layer and found that the gain of BiT array antenna with the dielectric layer was enhanced by about 1.4 dBi of directivity and 1.3 dB of gain over the one without the dielectric layer at 2.3 GHz. The impedance bandwidth of the BiT array antenna both with and without the dielectric layer is about 500 MHz and 350 MHz, respectively, which is suitable for the application of the WiMAX 2.3 GHz system. The utilization of BiT ceramics that covers about 90% of antenna led to high radiation efficiency, and small-size antennas were produced. In order to validate the proposed design, theoretical and measured results are provided and discussed.

Composites Based on Rice Husk Ash/Polyester for Use as Microwave Absorber

This paper is to study the dielectric properties and microwave absorption of rice husk ash/polyester (RHAP) composites. The RHAP composites prepared with different weight ratio (40–80 wt. %) of rice husk ash (RHA) loading into polyester was fabricated. A rectangular waveguide transmission line method was used to measure the dielectric properties of the RHAP composites. The RHAP samples were designed and simulated with different thickness and percentage of RHA loading by using Computer Simulation Technology Microwave Studio (CST-MWS) software. The materials, their dielectrics properties measurement and microwave absorption result over 12.4–18 GHz (Ku-Band) frequency range are discussed. The dielectric properties of composites increase with increasing loading the RA wt%. The RHAP sample with different thickness was investigated in Ku-Band. The microwave absorption was up to 99.84 %, using 80 % loading of RHA with thickness 15 mm at 13.81 GHz, and showing the RHAP composites is applicable as microwave absorber.

Dielectric spectroscopy of pharmaceutical drug (Paracetamol) dosage in water

This paper discuss about the dielectric measurement on different concentration of pharmaceutical drug using Agilent 85070E High-Temperature and Slim form probe. A microwave dielectric measurement is set up to measure dosage of drug in solution. It is well-known as non-destructive and rapid method. In this work, the drug used is paracetamol because it is a common consumed pharmaceutical drug by public as mild painkiller. The dielectric measurement was conducted on paracetamol from 200 MHz to 10 GHz. The solution of paracetamol was prepared in various concentrations (molarity). Solution with different concentration will exhibit different dielectric properties. A P-Series Network Analyzer (PNA) is used to measure the dielectric properties.