RFID tags are everywhere, but they’re rather primitive as high-tech devices go. They’re programmed to do one thing: repeat a message over and over, like so many seagulls chanting, “Mine. Mine. Mine.” And, like a flock of seagulls, if you get a bunch of them going, then it’s hard to tell what any one of them is saying.
This can limit usage of RFID tags in situations where there are a lot of them very close together – say, in the back of a delivery truck. If you want to do an inventory (of sorts), given a strong enough field to activate everything, they will all talk on top of each other.
Imec took a stab at the first bidirectional RFID tags – ones that would take direction from the reader before just chattering away. The idea is that the RFID reader could ask that only tags with a particular characteristic respond; any tags not meeting that characteristic would be powered up, but remain silent.
In this use model, for instance, a dairy delivery truck could be queried to ensure that there was milk on board; any non-milk items would not respond. The query could then be refined by, say, brand.
This has its limits, of course. You have to know what you’re asking for in this model. I asked the presenter after his ISSCC presentation about this, and he agreed that for broader capability, new protocols are needed. For example, there’s no way to say, “OK, roll call: who’s on board?” and have the tags all respond in some kind of order, one at a time. And, of course, it may not help at all with security considerations – something snuck into the mix with no RFID tag would remain undetected.
But, ultimately, that wasn’t their goal; they were simply demonstrating the first bidirectional communication, and further work can go from there. In particular, this was the application that featured their new metal oxide (“MOxFET”) thin-film transistors.
You can find more details in the ISSCC proceedings, session 18.3