Abstract
This article presents the design of a droplet shape ultra-wide band antenna for imaging of wood. The proposed antenna is designed on PTFE substrate with a dielectric constant of 2.55, loss tangent of 0.001- and 2.4-mm thickness. The antenna is loaded by a stub to resonate at lower band frequency, strip loading at the back, and a chamfered ground to increase the bandwidth. Despite having miniaturized dimensions of 15 mm × 15 mm, it shows better results compared to recent studies. The simulation results depict a good ultra-wide bandwidth from 3.26 GHz to 20 GHz, and 21.5–25 GHz; Besides, the proposed antenna has two bands at 1.25–1.35 GHz and 1.7–1.81 GHz. In addition to that, the antenna achieved a maximum gain of 5.69 dB and directivity of 7.3 dBi. The measurement results of S-parameters transmitted and received signals performed in air, plywood, and high-density wood show a good agreement with the simulated results. In addition, the measured results illustrate a good isolation and uniform illumination among arrays as well as the received signals’ shapes do not change in different environments, but only the amplitude. Hence, the proposed antenna seems to be adequate for microwave imaging of wood.
Highlights
Many types of microwave sensors exist such as special transmission sensors, guided wave transmission sensors, freespace transmission sensors, time domain reflectometry (TDR) and tomographic sensors
Measurements are performed on high-density wood, soft plywood and in air. This might not be as realistic as the work presented in Refs. 28–31; It can still be considered as a promising method in the microwave imaging of wood in terms of the antennas’ and system dimensions, and not being destructive
The scattering parameters for each array are extracted from Performance Network Analyzer (PNA) and imported to MATLAB to be evaluated for time domain considerations
Summary
Many types of microwave sensors exist such as special transmission sensors, guided wave transmission sensors, freespace transmission sensors, time domain reflectometry (TDR) and tomographic sensors. 28–31; It can still be considered as a promising method in the microwave imaging of wood in terms of the antennas’ and system dimensions, and not being destructive (recent similar such as Gamma scorpion and ECTV showed in Table I in supplementary material, applied bulky systems with large dimension antennas and were destructive like X-ray and Gamma but the proposed system is smaller with high gain and broad BW, and beneficial for detecting of defects in wood). The key challenges in MWT of wood can be listed as follows (the advantages and disadvantages of the methods are presented in Table I in supplementary material): dimensions of the applied antennas and systems, ability of obtaining 3D image with high resolution.
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