Sep 06, 2012We have a customer that needs to count 750,000 fish within a tank. The diameter of each fish is about 50 millimeters (2 inches). The customer is tagging the fish with low-frequency (LF) glass tags. Can we track the 750,000 fish tags using some type of reader? Are there any long-range readers that can work? And is this possible using handheld scanners with antennas?
I reached out to James E. Heurich, the president of RFID Inc., a company that sells passive LF systems, as well as high-frequency (HF), ultrahigh-frequency (UHF) and active RFID solutions. Here is an edited version of James' response:
"I'm not sure that reading tags on 750,000 fish simultaneously would be possible at any RFID frequency, but there are a couple of issues with LF tags. The first is read range. You can only read an LF glass ampoule from several centimeters away (similar to the ranges exhibited by HF tags). I've seen high-powered interrogators that can read a glass ampoule at a distance of 18 inches, in the correct orientation—but these devices exceed the power output allowable under U.S. Federal Communications Commission (FCC) regulations.
"The second issue involves reading the tags simultaneously. It sounds as if the inquirer would like to read all 750,000 tags using an RFID reader employing an anti-collision algorithm, which allows a user to singulate one tag, then the next and so on. There has been little calling for anti-collision with LF tags, so we've never really instituted this as an option on our product line. And from a purely timing perspective, I don't think you could singulate that many tags. In fact, I don't think you could do it with 750,000 UHF tags, which has a much faster tag transmission rate than LF tags. Simply put, I don't believe there to be an RFID technology that can provide a solution to the inquiry.
"Perhaps the fish owner could create a process whereby fish swim from one tank to another, through a tube that has a pass-through antenna on it. However long it takes for 750,000 fish to swim through the pipe, one at a time, would be the amount of time it would take to inventory all of them. You would probably need someone to begin hand-processing them through at some point (it's not like they can be herded), and you would need some sort of a one-way valve that does not allow the fish to return through the tube.
"A reader could also have an input/output port onboard, with two proximity or light sensors to close the tube if a fish's tag is not operating. Let's say a fish enters the tube, and a sensor closes a circuit to the reader, letting it know that a tag read is expected. If the reader does not interrogate a tag after the sensor senses the fish, the tube closes down, trapping the fish for removal and tag inspection."
—Mark Roberti, Founder and Editor, RFID Journal