success of the tags were associated to the RF signal attenuation. The free water content of the bread mostly absorbs RF energy. Tags before row five that have been missed may have had a smaller gap between them and the pallet next to them. Air
has minimal interference with RF propagation (Penttilä et al., 2006). Position (b) read all the tags that were on top of the load,
but missed nine tags out of the 17 tags placed at the bottom of each pallet (Fig. 3). Bottom tags could also only be read up to
row five. Position (c) delivers the same results as the omni-directional antenna (a) in terms of percentage of readability (Table 2). However missed tags were in different locations and again the only tags missed were from the bottom of the pallets.
All missed tags were forward of the antenna placement, which shows the effect of the load on 915 MHz wave readability.
Each of these tags were placed on the forward face of the pallets (Fig. 1), therefore all tags behind the antenna were facing
it, whereas all tags in front of the antenna were facing away from it; suggesting that the frozen bread was acting as an RF
absorbent (for 915 MHz) between the antenna and the tag. As Zhao et al. (2000) reported, the effect of the package can be
significant in RF propagation. The bread boxes were cardboard and the entire pallets were shrink-wrapped. Condensation on
the inner face of the shrink wrap contributed to the moisture content of the cardboard. Position (d) resulted in lower read
rates than position (c) even if they were both placed symmetrically (Figs. 2 and 3). More tags were missed in the forward
portion of the container than the back, as explained earlier. Compared with antenna (c), both were circular polarized, but
antenna (d) had a higher gain: 8.5 dBi vs. 6 dBi (Table 1) that explains the longer read range