Design and Evaluation of Microwave Antennas for Abdominal Fat Measurement Systems
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Availability of accurate, low cost and non-invasive devices for the measurement of abdominal fat is an important factor for early diagnosis of the obesity-related diseases. To achieve this, a wideband (WB) system was developed that includes the advantages of high range resolution due to the wide bandwidth (BW 0.5 GHz) and acceptable penetration depth due to the low centre frequency (1 – 3.5 GHz). For the pulse transmission, double-ridged horn (DRH) antennas were proposed because of their wide bandwidth, high gain, and impedance matching capability. Simulation studies suggested that optimal pulse focus and minimal interference to be introduced into the system by pyramidal- and elliptical-DRH, especially when extended to locate the antenna in the far-field region. Since these shapes are complex to manufacture, 3D printing was employed to fabricate low-cost antennas with high resolution. A further improvement in system performance as well as a reduction in system size was achieved by embedding the antenna in a high dielectric material, which further reduced the reflections caused by impedance differences. Previously proposed high dielectric materials such as Barium Titanate-based ceramics and canola oil were characterised during this study and combined with different percentages of Titanium Oxide to increase their dielectric constant, while retaining good conductivity. In addition, Paraffin was preferred over oil, as it has the same dielectric properties but solidifies at room temperature. Analyses were conducted based on a three-layer dielectric tissue model mimicking human tissue thicknesses. To measure the extent of the fat layer, a parameterised WB pulse was transmitted through the tissue model and its reflections were recorded. Evaluation metrics including the reflection coefficient were employed to investigate the pulse magnitude reduction and time of arrival at the fat layer. Results indicate that the proposed system is able to measure fat thickness with the accuracy within ±1 mm.
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