Posts: 2
Registered: ‎11-02-2010

RFID as a locating device?

I've never designed an RFID device, and wonder if it can be used to solve the following "needle-in-a-haystack" problem:


I have a small widget, about the diameter of a pencil and 5-7cm long. The widget is valuable but can be lost in a pile of foriegn material which makes it hard to find.


Is there a RFID tag that is small enough to be embedded into this device, and a RFID reader that could then sense it from 4-8 meters away? Using a reader with a very directional antenna, the returned signal strength could be used to "zero in" on the widget's position.


So the questions are:

(a) is there a RFID tag that can fit in 5mm diameter x 50mm long device (cost < $5 @ qty=1000)?

(b) is there a RFID reader that (with appropriate antenna) can "see" the tag from 4-8m away ( cost < $100 @ qty =100)?

(c) is there a better way to do this?

Avnet Employee (Super Contributor)
Avnet Employee (Super Contributor)
Posts: 56
Registered: ‎11-04-2010

Re: RFID as a locating device?

This could possibly be achieved with a 2.4GHz active tag with something like Texas Instruments CC2500 or similar.  The eZ430-RF2500 kit may be a good start.  The board could probably be layed out to fit within the 5mm x 50mm device.  BOM cost might meet the less than $5 budget. It will require a microcontroller, transceiver, battery, antenna.


Does the pile of foreign material contain metal or liquids? If it does it might be an issue with the reading of the tag.

Posts: 2
Registered: ‎11-02-2010

Re: RFID as a locating device?

I don't think there's any way to get an active tag with uC, xcvr, battery, & antenna in something the size of a crayon, so it would have to be a passive tag. I've seen tags used in the truck/offroad tire industry that look like a small axial inductor coil, but I haven't found any tech info.


The pile of material would not contain metal, but may have some moisture in the form of leaves or dirt.

Thanks for the ideas.


Avnet Employee
Posts: 5
Registered: ‎03-04-2015

Re: RFID as a locating device?

Use a UHF tag. These can be passive tags, but the reader sends out enough energy to power the tag that transmits a signal back. On the reader side, At 915MHz, you could design a pseudo Yagi antenna (directional) on your PCB.

Check out Impinj. They make both tag and reader chips. Conversely you could make your own reader but buy tags in the form of "stickers." These are cheap and can be bought from Smartrac.

Have Fun!

Raman Sharma, FAE
Avnet Inc.