See-Khee Yee

Design and Calibration of a Compact Quasi-Optical System for Material Characterization in Millimeter/Submillimeter Wave Domain

A compact quasi-optical setup based on conventional rectangular horn antennas and two symmetrical parabolic mirrors is designed to provide a plane wave on the material under test. To measure the scattering parameters at millimeter/submillimeter wavelengths, a commercial vector network analyzer and waveguide frequency extension units are used. The calibration of the system is performed with a simple practical deembedding process to determine the S-parameters on the material surface without using high-cost micrometer positioners. A reliable extraction method is presented to derive the material permittivity and calculate the errors and uncertainties as direct functions of the sample and setup geometry and their physical characteristics. Several materials are measured and the complex permittivity is presented together with a detailed uncertainty budget.

Design and calibration of a wideband TEM-cell for material characterization

A wideband TEM-cell is designed for dielectric measurements to operate over a 50 MHz - 800 MHz frequency range by using transmission/reflection method. This cell is compact, easy to fabricate, and useful for measuring porous samples such as concrete. The classic dielectric measurement setup is usually based on rectangular TE10-mode waveguides which become very large, expensive, and non-practical for lower frequencies. As for a classic coaxial cell, non-uniformity of the electromagnetic field and the difficulty to obtain sample in a toroidal shape for coaxial cells are overcome using the proposed TEM-cell. Wideband matching is performed using a coaxial to waveguide connector based on a tapering technique. A specific calibration is used and the complex permittivity and permeability are calculated from the measured S-parameters. Preliminary experimental results are presented.

Optimization of the EMI shielding effectiveness of fine and ultrafine POFA powder mix with OPC powder using Flower Pollination Algorithm

In order to solve the electromagnetic interference (EMI) issue and provide a new application for palm oil fuel ash (POFA), POFA was used as the cement filler for enhancing the EMI absorption of cement-based composites. POFA was refined by using water precipitation for 24 hours to remove the filthiness and distinguish the layer 1 (floated) and layer 2 (sink) of POFA. Both layers POFA were dried for 24 hours at 100 ± 5 °C and grind separately for sieve at 140 μm (Fine) and 45 цш sizes (Ultrafine). The micro structure and element content of the both layers POFA were characterized by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) respectively. The results showed layer 1 POFA has potentialities for EMI shielding effectiveness (SE) due to its higher carbon content and porous structure. The study reveals that EMI SE also influenced by the particle size of POFA, where smaller particle size can increase 5 % to 13 % of EMI SE. When the specimen consists of 50% POFA with passing through 45 μm sieve, the EMI was shield -13.08 dB in between 50 MHz to 2 GHz range. Flower Pollination Algorithm (FPA) proves that POFA passing 45 μm sieve with 50% mixed to OPC is optimal parameter. The error between experimental and FPA simulation data is below 1.2 for both layers POFA.

Shielding effectiveness of concrete with graphite fine powder in between 50MHz to 400MHz

The shielding effectiveness (SE) of building materials is of concern due to the possibility of electromagnetic interference on sensitive equipment located inside the building. The SE of building material could be obtained directly using measurement but it requires expensive and elaborate setup. Alternatively, analytical method is preferable to predict the SE of building material for various conditions regarding the parameters to be evaluated such as thickness, moisture content, percentage of conducting materials added and so forth. Since most of the building materials are non-magnetic, its relative permittivity will be an important parameter for SE calculation. The effective permittivities of the concrete samples between 50 MHz to 400 MHz are measured using a TEM parallel plate. In this work, the SE of concrete samples are compared for various concentrations of graphite fine powder. It is found that a concrete of thickness 20 cm with 12wt% of graphite fine powder is able to provide a maximum of 2.4 dB additional shielding at 360 MHz. It is also observed that reflection loss is the dominant mechanism that contributes on the SE of a concrete with graphite fine powder.

Design and calibration of a compact quasi-optical system for material characterization in millimeter/sub-millimeter wave domain

A compact spectrometer setup based on conventional rectangular horn antennas and two symmetrical parabolic mirrors is designed to provide a plane wave on the material-under-test. A commercial Vector Network Analyzer (VNA) and waveguide frequency extension units are used to measure the scattering parameters. A simple practical calibration process is used to determine the S-parameters on the material surface without need of high-cost micrometer positioners. Several materials are measured and the complex permittivity is presented.