Submitted to: Sensors
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/1/2010
Publication Date: 9/10/2010
Citation: Pelletier, M.G., Viera, J., Wanjura, J.D., Holt, G.A. 2010. Accurate permittivity measurements for microwave imaging via ultra-wideband removal of spurious reflectors. Sensors. 10(9):8491-8503. Interpretive Summary: This paper reports on a method for removing the distortion that hard reflectors, such as metal bale ties, create for microwave imaging sensors. The research development produced a technique based upon the use of ultra-wideband signals for removal of the spurious reflections created by the local proximity hard reflectors in the Mie scattering region. This improvement enables accurate microwave measurements of moisture as well as other physical properties such as density or material composition in such products as cotton bales. The proposed algorithm was shown to reduce errors from +/- 20% to less than 1-2% and is an enabling technology for imaging applications in the presence of metal bale ties and other hard reflectors such as drip-lines in sub-surface imaging applications.
Technical Abstract: The use of microwave imaging is becoming more prevalent for detection of interior hidden defects in manufactured and packaged materials. In applications for detection of hidden moisture, microwave tomography can be used to image the material and then perform an inverse calculation to derive an estimate of the variability of the hidden material, such as internal moisture, thereby alerting personnel to damaging levels of the hidden moisture before material degradation occurs. One impediment to this type of imaging occurs with nearby objects create strong reflections that create destructive and constructive interference at the receiver as the material is conveyed past the imaging antenna array. In an effort to remove the influence of the reflectors, such as metal bale ties, research was conducted to develop an algorithm for removal of the influence of the local proximity reflectors from the microwave images. This research effort produced a technique based upon the use of ultra-wideband signals for the removal of spurious reflections created by local proximity reflectors. This improvement enables accurate microwave measurements of moisture in such products as cotton bales, as well as other physical properties such as density or material composition. The proposed algorithm was shown to reduce errors from +/- 20% to less than 1-2% and is an enabling technology for imaging applications in the presence of metal bale ties.