RAIN RFID, explained without the jargon
A tag answers when a reader asks. No line of sight, no one holding a scanner on each item. What changes from one site to another is how well the answer reaches the reader.
What actually happens in a read
The reader sends a radio signal through an antenna. Tags in range use that energy to wake up and reply with their code. Many tags can answer in the same second, so a full box can be read without opening it. The tags follow the EPC Gen2 standard, and you choose them. Our readers work with the standard ones.
How a reader counts hundreds of tags at once
When many tags answer together, their replies collide. The reader solves this by splitting the tags into time slots, so each one answers on its turn. How many slots it opens depends on how many tags it expects in the field, the population estimate. The reader normally works this estimate out by itself, in real time. In a controlled setup with a known, fixed number of tags, you can set it by hand and read a little faster.
What makes a read better or worse
Reads are a negotiation between several things. Change one and the result changes. When a project reads badly, the cause is almost always on this list.
- Antenna type and where it points
- Reader output power, and how much the cable and splitter eat
- Tag orientation against the antenna's polarization
- Metal and liquids near the tag, which block or detune it
- Distance between tag and antenna
Sessions and search modes: who gets read again
Every tag keeps a flag, A or B, for each of four sessions (S0 to S3). When the reader inventories a tag, the flag flips, and the tag goes quiet until the flag returns. How long that takes is the persistence, and it depends on the session. The search mode decides what the reader does with the flag, so it decides how often you see the same tag.
- Dual target: alternates between A and B tags, so tags keep being read
- Single target: reads A tags and moves them to B, where they rest until they return to A
- Single target B to A: the same, with the flags inverted
- TagFocus (single target with suppression): after being read, tags stay silent while they remain in the field, which cuts repeated reads in dense, static populations
RF mode: speed or sensitivity
The RF mode sets the modulation, the timing and the data rate between reader and tag. Lower data rates give more sensitivity and better resistance to radio interference. Higher data rates read faster, but suffer more from interference. Pick a slower mode for noisy sites with many readers, and a faster one when tags pass quickly.
Near-field or far-field
Near-field antennas read in a tight zone close to the antenna, up to about 1 m on the larger ones. Use them where you must read one item and not its neighbor: a checkout counter, a sorting table. Far-field antennas throw a wider beam over more distance. Use them for doors, aisles and docks.
Think in read zones, not in readers
Start by drawing the space where tags must be read, and the space where they must not. A dock door is a zone. The shelf next to it is not. Then pick antennas whose beam fits the first shape, and set power to stop short of the second. Test with your real items before you install.
What the reader tells you about each read
Besides the tag code (EPC), a read can carry the signal strength (RSSI), the phase, the frequency channel, the antenna that heard the tag and the moment of the read. RSSI helps to compare distances and spot weak reads. Phase is used in movement and location work. The antenna tells you in which zone the tag was. Each reader sends only the fields you switch on.
{"epc":"3035000000000000000121","rssi":-5320,"antenna":1,"timestamp":"1790000000000"}Test with your real items before you install
Tags behave differently on cardboard, plastic, glass and metal. A bench test with your own items and tags answers most doubts before anyone drills a wall.
- Place the items as they will really move: in the box, on the pallet, on the shelf
- Start with the antenna you plan to use and a moderate power, then raise it only if needed
- Watch the read count and the RSSI while you move the items through the zone
- Check the neighbors: items that must not be read should stay silent
- Repeat with the worst case: the fullest pallet, the densest box
Questions we hear
Does RAIN RFID work through boxes?
Yes, through cardboard and plastic. Metal and liquids are the problem. They can block the signal, so test with your own packaging.
Do you sell the tags?
No. Identix makes readers, antennas, modules and portals. They work with standard EPC Gen2 RAIN RFID tags, which you choose for your items.
Why do I read tags I did not want?
The beam or the power is too wide for the space. Use a narrower antenna, lower the power, or move the antenna so it points away from the neighbors.
Why do I keep reading the same tag?
Because the tag keeps answering. The search mode and the session decide how often that happens. A mode with suppression, like TagFocus, makes a tag stay silent after the first read while it is still in the field.
What is the RSSI for?
It shows how strong the tag signal arrived. Use it to compare positions, find weak spots in a zone and tell a close tag from a distant one. It is a relative indicator, not a distance in meters.