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It's important to understand the difference between UHF RFID (this technology) vs. others like BLE. UHF RFID tags harvest all of their operating power from a r
by beambot 11y ago
It's important to understand the difference between UHF RFID (this technology) vs. others like BLE.
UHF RFID tags harvest all of their operating power from a reader's transmitted RF signal. Multi-access is handled at the protocol layer via probabilistic time-division multiplexing. The tag doesn't actually "transmit" -- rather, it is a cooperative radar target that reflects RF power back to the reader (sort of like an SOS mirror) by intelligently, electronically changing its radar cross section. The tags contain a single IC, and the antennas (for commercial ID-only tags) are roll-to-roll printed... to the tune of Billions of tags per year. The net effect: Tags cost around $0.10 each in volume. The read range is practically limited to around 20 feet, as dictated by FCC limits on the reader's RF output power (1Watt). Nominally, gen2 UHF RFID tags operate at bitrates up to ~500kbps, but there are some specialized tags that can transmit at 100Mbps using just a few microwatts (we used them to transmit dragonfly neural signals during flight!).
Meanwhile, BLE technologies can do push notifications, mesh networking, and the like. The beacon (tag) may contain a full TX-RX transceiver. However, due to the tight spectral requirements of their transmissions, they generally require an external (off-IC) crystal oscillator. The net effect is that BLE beacons are more costly -- on the order of $2-3 ea. This means that they are much less likely to be used to tag everyday items (like a carton of milk) or deployed in the billions for outdoor monitoring.
Source: I'm an expert on these systems as applied to robotics, healthcare, and remote sensing [1,2,3,4]. I'm giving a talk on them next week at IEEE RFID / RFID Live. Oh, and you can also buy WISP-like tags from a company called Farsens.
[1] http://www.travisdeyle.com http://www.travisdeyle.com
[2] http://www.travisdeyle.com/research.html http://www.travisdeyle.com/research.html
[3] http://www.hizook.com/blog/2015/08/10/mobile-robots-and-long-range-uhf-rfid-sensor-tags-internet-things http://www.hizook.com/blog/2015/08/10/mobile-robots-and-long...
[4] http://www.wired.com/2013/06/dragonfly-backpack-neuron/ http://www.wired.com/2013/06/dragonfly-backpack-neuron/
- joshu 11y agoI have been meaning to research this stuff for a crazy automotive application I have in mind. thanks for the pointers. (Ps hello fellow TR35er!)
- beambot 11y agoHi Joshua -- wow, small world! Feel free to ping me (email in profile). I'm happy to chat about sensing or robotics...
- lolidaisuki 11y agoAnd if these limitations (frequencies, output power) for radio technology were lifted do you think we would have something that has the benefit of both worlds? What would be the negative effects, if there are even any?
- elcritch 11y agoThank you for the Farsens link! Really interesting RFID tags. Out of curiosity, do you know any good sources for programmable, or better yet, open source UHF RFID readers? I've gone through lots of options but none seem quite flexible enough.
- beambot 11y agoThe two most-common commercial options are Impinj and ThingMagic readers. Neither are open-source (hardware or firmware) -- they just have APIs. If you go back to the old ThingMagic M5e (rather than newer M6e), there are high-level open source libraries that I wrote: Documentation: http://wiki.ros.org/hrl_rfid http://wiki.ros.org/hrl_rfid On GitHub: https://github.com/gt-ros-pkg/hrl/blob/master/hrl_rfid/src/hrl_rfid/lib_M5e.py https://github.com/gt-ros-pkg/hrl/blob/master/hrl_rfid/src/h... You can buy single-chip readers from AMS (eg. on DigiKey) and build your own reader -- not a light undertaking due to RF PCB layouts, but manageable. I've also heard of people using the USRP (GNU Radio) to build gen2-compliant UHF RFID readers, but I believe they require the PCI-bus variant to adhere to protocol timing standards.
- elcritch 11y agoFantastic! I appreciate the heads-up. The open source ThingMagic drivers would be very handy. It has crossed my mind to try integrating a single-chip reader but I'm unsure of what the FCC requirements would be for selling it as part of a commercial product. It's a little surprising that there hasn't been a kickstarter type of project to build an open source reader chip and get it FCC spec'ed.
- beambot 11y agoThe AMS chip itself is probably FCC compliant, since the output power is so low (10-13dBM, IIRC). The problem arises when you add an external PA to get the full 30dBm output power permitted by the FCC; then you need to re-certify.