Optimal Setup
The reason why some tags are read and others not is due to the RSSI (tag sensitivity). If you put tags one over the other, the antenna of the bottom tag obstructs the antenna of the top tags.Therefore, to always read well, spread the tags so the antennas do not block. In additional, the environmental issue plays a role due to the fact that the tags does not go through the same reflection path than the previous scan because of collision avoidance protocol.
Typically, RFID reader software is designed to read continuously to read all surrounding tags. Therefore, you can press the scan button continuously or modify the java code so the scan button scans more than one time.You may also increase the Scan Time to allow more time to read tags.
This is a standard behavior of any UHF RFID reader in which the first iteration may not find all surroinging tags, but in the second and successive iteration it will find the tags. This is the reason why there is Merge button in the demo software. This keeps record of the previously detected tag.
Use the Merge button. Right now the Scan button only scan once. But this is a demo software, so we didn’t use multiple scans with a single button press. In a professionally coded software, scans should be done multiple times. You can modify the software to scan several time with single press or just use the Merge option. With that said, we will add option in our future demo that will have the option to set number of scans per Scan button press. Our next software release will have this feature.
Typically, RFID reader software is designed to read continuously to read all surrounding tags. Therefore, you can press the scan button continuously or modify the java code so the scan button scans more than one time.You may also increase the Scan Time to allow more time to read tags.
This is a standard behavior of any UHF RFID reader in which the first iteration may not find all surroinging tags, but in the second and successive iteration it will find the tags. This is the reason why there is Merge button in the demo software. This keeps record of the previously detected tag.
COLLISION
UHF RFID have this behavior due to Collision in which after a Collision the tag stops transmitting for a short moment. This is not a problem with the device, instead this is how the UHF RFID protocol work.The rule is, if the tag could not be found in the first iteration, it will be found in successive iterations. Eventually all surrounding tags would be found.In addition, the tag itself could be the cause of the problem. In your case, it does not seem that the tag is an issue because it is found eventually.Use the Merge button. Right now the Scan button only scan once. But this is a demo software, so we didn’t use multiple scans with a single button press. In a professionally coded software, scans should be done multiple times. You can modify the software to scan several time with single press or just use the Merge option. With that said, we will add option in our future demo that will have the option to set number of scans per Scan button press. Our next software release will have this feature.
ANTENNA LOBE
With the reader on the table, draw a 1 meter diameter circle reader as shown below. This is the sensitive area of the reader. If the tag is within the circle, most likely the reader will catch it in the first scan. Otherwise, it may get it in successive scan or not at all if it is way out of the cone.LONG RANGE
If you need long range, use tags with bigger antenna. Make sure that your desk is not made of Glass. Glass is a high dielectric material which significantly affects the reader’s impedance matching as well as the tag’s impedance.Having Glass in close proximity will reduce the read range. If you have Glass desk, use a 1″ thick book to place your reader and tags. This is shown below.
