## 4 Experiment and Discussion
### Results for the Accuracy of the Measurement Distance and Inventory Location Recognition  
With values of 125\({}^{\circ}\) in \(\theta\) and 72 cm in \(T\), _Th_ and _Rh_ were calculated as less than or equal to 1.4 m and 38.06 cm by Equations (3) and (4), respectively; that is, the measurement distance between the RFID reader and the tags should be less than or equal to 38.06 cm. The UIDs for the three reference tags of areas 1-1, 1-2, and 1-3 were e000864, 0000617, and 6000897, respectively. The experiment aimed to evaluate the recognition accuracy of the reference tag for area 1-2 (UID: 0000617), by means of the RFID reader, when the measurement distance was increased in 5 cm intervals from 20 cm to 60 cm. The MSR layout for the experiment is presented in Figure 5. The tests were replicated 30 times, and the average recognition results are plotted in Figure 6. Only the reference tag of area 1-2 was recognized when the measurement distance was increased from 20 cm to 40 cm. Thus, only the targeted reference tag can be recognized without the recognition of other adjacent reference tags when the measurement distance is set to be less than or equal to 38.06 cm. However, the chance of recognizing the adjacent reference tags is significantly increased when the measurement distance is more than 45 cm. Therefore, this experiment shows that the estimated measurement distance is practically applicable to the identification of the inventory locations of stock items with great recognition rates for passive RFID tags. We then analyzed the inventory location identification based on the change in the number of stock items to be loaded in zone (area) 1-2 and the tag recognition interval of the RFID reader. The tag recognition speed of the RFID reader was fixed at 0.15 m/s. The number of stock items in each zone was changed from one to seven, and the tag recognition interval of the RFID reader was changed to 0.3, 0.5, 1, 2, 3, 4, and 5 sec. Table 2 shows the mean recognition rates when the measurement was carried out 30 times for each setting. The recognition rate was 100% when the number of stock items was less than or equal to two and the tag recognition interval was less than or equal to 1 sec. In addition, the recognition rate was 100% even when the tag recognition interval was 0.3 sec and the number of stocked items was less than or equal to three. The larger the number of stock items loaded in each zone, the greater the variability in recognition rates together with the lower the mean. The same trend applies to the recognition intervals. Figure 7 shows the influence of the number of stock items and tag recognition intervals on mean recognition rates. The plot indicates that the tag recognition interval had greater effect on the recognition rate than the number of stock items (Figure 7a), and the higher number of stock items lead to worse recognition rates (Figure 7b). It could be interpreted that smaller recognition intervals (or number of stock items) contribute positively to a greater recognition rate. According to  
Figure 4: RFID reader with aluminum conical structure (mockup). the observations, it is found that both the recognition intervals and the number of stock items have a significant effect on the recognition rates in an inverse manner. It means that the recognition rate could be improved when the recognition interval or/and the number of stock items decrease/s. Therefore, the experiment results recommend managers load fewer than three items in a zone and scan the reference tag with an RFID reader with a recognition interval lower than 1 sec in order to have a 100% recognition rate. Figure 5: MSR areas with three items. Figure 6: Recognition of the reference tags with an increase in _Rh_ at a propagation angle of 125\({}^{\circ}\).