Chapter two: Far is not always better

In the last post we discussed about the importance of the long-distance reading capability of the RAIN RFID technology stating that this is one of the main aspects of the technology success. But this is not the whole story.

Many applications do not require reading distances of more than 1 mt hence HF/NFC or LF RFID seem to be the right technologies to implement solutions for those scenarios. So why and when RAIN RFID should be preferable in sub-meter reading distance applications?

There are some characteristics of RAIN RFID that makes it a good choice even in medium/short range applications:

• RAIN RFID tags are typically less expensive than LF or HF/NFC, not only because RAIN tags are produced in larger quantities (that lower the production costs) but also because they are intrinsically simpler in the design. LF and HF/NFC antennas are designed as multiple coils, and this requires at least two planes to close the circuit on the chip with the complexity of making a hole on the substrate. RAIN tags, on the contrary, need just one plane reducing the complexity of the manufacturing process and, even more important, reducing the index of defectiveness.
• RAIN RFID technology is more efficient in transmitting the power to the tag and the tags require less power to be energized. This results in the need of lower power readers and smaller reader antenna and smaller tags compared to LF/HF/NFC systems to reach the same reading distance.

Anyway, there are some specific applications where the required reading distance is even less and, sometimes, it is required a limitation to few centimeters or even to read at contact (contactless applications) i.e. where the reader antenna and the tag are put in contact, like when you tap a NFC tag with your smartphone.

For these applications the natural choice is NFC and, in many cases, it’s also the right choice, but there are applications where RAIN RFID technology would fit better or be the only viable solution.

As we have seen in our last post, RAIN RFID technology uses electromagnetic field while LF/HF/NFC RFID use magnetic field to exchange power and data, but this is not true in all the cases. Magnetic field, and hence inductive coupling, can be used also at the UHF frequencies of RAIN RFID technology with some advantages.

At UHF frequencies the efficiency of power transmission is higher so, to reach the same reading distance, the dimension of the tag antenna can be much smaller for RAIN RFID than LF/HF/NFC and, most of the time, UHF requires just one coil for the purpose (that, again, means a single layer tag). Smaller tags, some of them just 1mm. by 2mm., open a new range of use cases. Examples are the identification of small objects like pharmaceutical vials or embedding tags into smartwatches, surgery tools, climbing carabiners or any other small object that need to be identified and/or authenticated.

In the RFID jargon this is called near field RAIN RFID technology where readers and chips for tags are exactly the same of the ones used for far field (long distances) but both reader and tag antennas need to be specifically designed to obtain the maximum performances from the inductive coupling.