Abstract
Microwave tomography is a microwave imaging method in which the resolution is not limited by wavelength, but rather by measurement noise and modelling errors. Inversion algorithm is used for obtaining an image from the measured scattered waves. Performance improvement of the inversion algorithm is introduced by approximately modelled antennas as a point, line or plane source. Such modelling of antennas introduces modelling errors. Antenna array in the unshielded measurement chamber will pick up external interference, as well as backscattering of array’s own radiation. Multipath occurring in measurement chamber has a large impact on the measurement performance. The wave propagated through the air and reflected from the chamber walls could mask a weaker wave scattered by the object under imaging. Also, a larger number of the antennas improves inversion and gives a more accurate image. This paper proposes a novel design of enclosed measurement antenna array for microwave tomography. To obtain an accurate and efficient antenna model in 3D FDTD, a square spiral wire antenna is used in this design. A metal shield protects the process of measurement from external interference and backscattering. Between the antenna array and the metal shield an absorption wall is introduced, which decreases multipath and partially prevents signal masking. Square spiral wire antennas are overlapped and packed, giving a larger number of antennas in the same space. Enclosed antenna array is modelled in 3D FDTD. Proposed antenna array is compared with solutions found in literature. Comparison is done using metrics relevant for antenna array measurement in microwave tomography.DOI: http://dx.doi.org/10.5755/j01.eie.23.2.17999
Highlights
Microwave tomography (MWT) [1], [2] is a microwave imaging method for acquiring images from microwaves scattered by the object under imaging
This paper offers a novel design of overlapped square spiral antenna array enclosed with an absorption wall and a metal shield
Most significant novelty presented in this paper is absorption wall for decreasing multipath along with overlapped square spiral antennas
Summary
Microwave tomography (MWT) [1], [2] is a microwave imaging method for acquiring images from microwaves scattered by the object under imaging. MWT, as an inverse problem, is inherently illconditioned, which means that a small change in measurement has a large impact on the resulting image. Inversion methods based on Born approximation work properly only if the aforementioned contrast is low Another purpose of the lossy matching fluid is lowering multipath effect and signal masking. An Archimedean square spiral wire antenna [29], [30] matches the aforementioned geometry of the grid This antenna is perpendicular to the direction of radiation, occupying less volume in the simulation space and making modelling more efficient. Two antenna array designs with multiple configurations are simulated and compared using metrics relevant for MWT: computation and memory performance, radiation from the chamber and fidelity of the measured signal.
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