Small RFID for tracking position

February 9, 2008 10:52 AM

Where can I find small (passive) RFID tags with a reader that can record their position in space with relatively high precision? Sort of like a Nintendo Wii remote without the gaming option and on a much smaller scale..

I am interested in finding RFID tags with a reader that will be able to report their position in space (a confined space) with a roughly mm resolution or better. Using multiple small tags to do the job is definitely an option. They should be small and light and therefore probably passive tags. The intended use is sort of like a Nintendo Wii remote on a much smaller scale. I happen to know that there are RFID tags out there as small as 0.3x0.3x0.1mm that can do the trick, even using a single tag. The problem is that when I search for them the results are overwhelmed by the multitude of companies that offer help with keeping track of inventories of some kind or another. Would anybody happen to know about manufacturers of small RFIDs that enable spatial tracking (from a short distance) or at least have an idea on how to narrow the search?
Thanks.

posted by wyzewoman to technology (13 comments total)

I thought the position in space aspect of the Wii was due to an infrared camera detecting the position of the sensor bar. From Wiki:

Use of the Sensor Bar allows the Wii Remote to be used as an accurate pointing device up to 5 meters (approx. 16 ft) away from the bar. The Wii Remote's image sensor is used to locate the Sensor Bar's points of light in the Wii Remote's field of view. The light emitted from each end of the Sensor Bar is focused onto the image sensor which sees the light as two bright dots separated by a distance "mi" on the image sensor. The second distance "m" between the two clusters of light emitters in the Sensor Bar is a fixed distance. From these two distances m and mi, the Wii CPU calculates the distance between the Wii Remote and the Sensor Bar using triangulation.

This is not the same as RFID. Please correct me if I'm wrong or I misunderstood your question.
posted by ALongDecember at 10:58 AM on February 9, 2008

That's not how the Wii remote works.

And the problem with your idea is that I don't see any way to make it work.
For instance, measuring the round trip message time doesn't help. The time it would take the RFID chip to power up and respond is variable enough so that you couldn't take any meaningful measurements.

Measuring the received signal strength from the RFID is also useless. That would depend as much on orientation of the RFID, both in terms of how much energy it absorbs that can be used for the return, and because it won't radiate with equal amplitude spherically.

How do you plan to figure out where the RFID is located?
posted by Steven C. Den Beste at 11:01 AM on February 9, 2008

ALongDecember is correct the wii remote uses a camera an infrared not rfid.


you hay find johnny lee's wii remote hacking page interesting though.
posted by phil at 11:04 AM on February 9, 2008

It's a very interesting idea. About 20 years ago I wrote an application in Forth that used a so-called "3D Spatial Locator" to identify a point in 3D space. It was meant to be a kind of 3D mouse. Basically it generated a spark at the end of a wire, then listened for the sound at three or four (I forget) evenly spaced microphones about 3 feet away, and based on the time it took for the sound of the spark to reach the microphone I could identify the point in space. I can't find anything about the device with google - I seem to... eureka, I just found mention of it here!

I've worked with RFID tags (more recently) and never thought about your idea before, but I think I'll talk to some of the RF guys where I work, raise some venture capital, and make millions of dollars with 3D spatial locating RFID tags. What's the application?
posted by thomas144 at 11:28 AM on February 9, 2008

I did some looking for this sort of localization stuff once, and as of a year ago the technology didn't really seem to be there, and certainly not with mm resolution.
posted by TheOnlyCoolTim at 12:23 PM on February 9, 2008

Texas Instruments has some zigbee chips with built in location engines. Unfortunately, the chips are not even close to providing the resolution and speed you need.
posted by rdr at 12:43 PM on February 9, 2008

Doing that using sound is a lot easier because sound moves a lot slower. Light moves about 11 inches in a nanosecond, so if you want to locate the object to a resolution of 1 inch, you have to measure the round-trip travel time with accuracy better than 200 picoseconds.
posted by Steven C. Den Beste at 1:05 PM on February 9, 2008

Yeah, that basically won't work. I worked at the Virtual Reality Applications Center and they did lots of tracking stuff, and they used gyroscopic velocity sensors to track fine detail movement. I think they used radio interference to track location. The idea being that if you have transmitters at fixed positions broadcasting a known signal, you could measure the interference pattern and figure out where you were. I think they were somewhat precise by not 1mm.
posted by delmoi at 2:12 PM on February 9, 2008

Your best bet is implementing some sort of inertial navigation.
posted by phrontist at 2:31 PM on February 9, 2008

Oh, sorry, didn't read the more inside. Ignore me.
posted by phrontist at 2:31 PM on February 9, 2008

To button up the Wiimote science, what you may be thinking of is Bluetooth in the Wiimote and nunchuck. While the infrared is used to sense "pointing," the Bluetooth is used to transmit data from the accelerometers that measure tilt, thrust and speed.
posted by rhizome at 3:35 PM on February 9, 2008

Long story short, RFID technology can't get you to mm precision, and it never will. Other technology might, although that's more cutting-edge / exploratory at the moment. Look into ultra-wideband.
posted by allkindsoftime at 9:34 PM on February 9, 2008

My interpretation of the question is that you're not looking for the RFID tags to provide location information, but rather that when you scan a tag, you want to know exactly where the scanner was (and therefore where the tag was) at that time. That doesn't seem out of the question, if you strap something like an Ascension Technologies position tracker to your RFID reader and record the position and orientation information each time you scan a tag. To get millimeter precision you'd have to hold the tip of your scanner within a millimeter of the RFID tag when you scan it, which eliminates a lot of the convenience of RFID.
posted by moonmilk at 12:25 AM on February 10, 2008