Research & Development at STEIM
initial idea was finding potentials of RFID in performance domain. Marc supervised and worked together with me to test low frequency RFID reader. Thanks Marc!
following is the Marc's report on this issue.
Marc Boon, June 18, 2010
We tried the following 125kHz RFID reader modules:
Manufacturer: ID Innovations, Australia Supplier: Sparkfun, USA Antenna: internal http://www.sparkfun.com/datasheets/Sensors/ID-12-Datasheet.pdf
Manufacturer: SonMicro, Turkey Supplier: SonMicro, Turkey Antenna: external, 3 different sizes http://www.sonmicro.com/en/downloads/125/ds_SM125_V30.pdf
Manufacturer: Shenzhen RDM Tag Master, China Supplier: Seeedstudio, China Antenna: external http://www.seeedstudio.com/depot/datasheet/RDM630-Spec..pdf
The most common tag type for 125 kHz is the EM4100 series tag. Another type is the T5557 tag, which supports anti-collision. All readers support EM4100 tags, the SM125 also supports T5557 tags. For our tests we used EM4100 disc tags of two different diameters: 20mm and 50mm.
Another type of tag is the glass capsule tag, designed for implants. These tags are very small (2x5mm), and use a ferrite core antenna. We did not test this tag.
3. Reading speed
Both the ID-12/ID-20 and SM125 readers suffer from long recovery time after reading a tag, limiting the tag read rate to about two tags per second. The RDM630 is much faster and can read about 4 tags per second.
4. Reading distance
The reading distance is dependant on the tag size and the antenna diameter. Larger tags have better reading distance, but a larger antenna does not necessarily give a better reading distance for smaller tags. The best reading distance is obtained when the antenna size is slightly larger than the tag size. The reading distance of the 20mm tags is about 6cm, and about 8cm
for the 50mm tags.
5. Tag orientation
To be detected, the tag has to be in a certain orientation to the antenna, so that the field lines of the radiating antenna of the reader will intersect with the tag antenna. This will not always be the case when the tag is perpendicular to the reader antenna.
We tried folding the tag by heating it up and bending it in different shapes, so the loop antenna would catch the RF field independently of tag orientation, but that did not give satisfactory results.
EM4100 tags can not be read simultaneously. If more than one tag is in the RF field of the antenna, none of the tags can be read. The T5557 tags support a anti-collision scheme, which (when also supported by the reader) can identify multiple tags in the RF field. We could not test this because we don’t have T5557 tags. It is unknown if the SM125 reader (the only reader that can read these tags) supports this anti-collision protocol in its firmware.
7. Ball detection
We used two types of juggling balls, both hollow plastic balls of 80mm diameter, but with different wall thickness and stiffness. We outfitted one ball with four 20mm tags equally spaced on its surface. The softer ball was cut open to place a single loose tag in the hollow space. Because the other readers are too slow, we only tested ball detection with the RDM630 reader.
Problem with the multiple tag configuration is that sometimes two tags are in range of the reader, so they can not be read (no anti-collision). On the other hand, a minimum of four tags is required to ensure at least one tag to be in range.
The inside tag solution uses only one tag, so the collision problem does not occur. However, tag orientation and reading distance can be a problem. If the tag is loose inside the ball, the probability of perpendicular orientation is very low, because the tag will not stand up vertically by itself. A solid ball with a fixed internal tag would have this problem. A solid ball would also suffer more from reading distance limitations, because the tag has to be in the center of the ball in order to be read from all angles. A loose tag will be closer to bottom side (where the hand containing the reader is located), but a combination of rapid movement and inertia of the tag can place it outside of the reading range.
In short: both solutions do not give a 100% reliable detection.