I am interested in adding to my home a system for detecting which room each occupant is in. It would need to be passive, because asking everyone to place their hand on a reader each time they passed through a doorway wouldn’t be practical. Instead, I’m wondering if it might be possible to adapt a portal system like those used as antitheft systems in retail establishments. I understand how those work—a tag is detected if it passes through the portal without being deactivated—and that the system would have to be rather different to work by reading the ID of a tag as I would need for my application. I also understand that RFID tags like the xEM are very short range (<10cm) devices when used with the normal readers designed for them.
But, if it were possible to embed a large coil in a doorframe (alternatively, it could be mounted on the surface of the frame for minimum attenuation—I don’t really care what it looks like as long as it works reliably) and feed it enough power to create a strong field, might it be possible to create a circuit capable of activating an xEM RFID implant and detecting its return signal over a distance of, say, 50cm?
Surely I’m not the first person to have thought of this idea, but days of Googling all the variations I can think of have hasn’t gotten me anywhere. Opinions on whether it might be a practical idea? If so, could someone point me to any resources that might help me get started? I’d like to build the system myself if possible (I’m experienced with electronics), but I’d very much like to have it happen in any case so if necessary I’m willing to throw a fairly large amount of money at it to make it work. Also, I’m currently doing a major remodeling project on my house, so I have complete access to the interiors of the walls and doorframes and could easily install any size coil of antenna wire in a loop all the way around each doorframe if that would be the most effective configuration to work with the coil antennas in the Dangerous Things implants.
This would be possible with UHF tags like they use for inventory in warehouses, but they don’t come in an implantable version. Their antennas are very large. And I wouldn’t want UHF antennas transmitting in my house 24/7
I believe there are some long(er) range readers for 125khz but even then you are talking maybe 1 meter with card style tags. An implant would get much less than that. I’m pretty sure Amal has tested these.
Without doing the math, I might be wrong, but I highly doubt a giant loop around the door frame would do you any good. Not sure how easy it would be to tune. You’d need a massive driver to power it too… Not to mention all the RF noise it would create.
If I might ask, what is the purpose of tracking everyone in your house?
The serious purposes are: 1) to produce a smart intercom that knows how to direct messages to individuals and avoid bothering others without having to rely on everyone carrying their smartphones, and 2) to keep track of my wandering mom who has dementia. The more frivolous purpose is to have the room say “Hi, Tom” when I enter.
I recognize that I might have to go with card-style tags for some family members, but I was hoping to use an implant for myself and possibly my wife. A one meter range, if achievable, would be more than adequate for a detecter in a doorway.
A simple proximity detector could be used to switch the loop power on when someone was nearby, and it could otherwise remain off. So, on average no large power drain and no continuous energy fields.
You’re most likely looking at UHF tags. I’ve seen them get multiple meters of communication but it also means higher power, more expensive readers, custom implants, and higher radio power. Probably not very easy or practical to do. An easier solution would be to use iBeacons or Bluetooth devices in conjunction with your cell phone to identify that.
Power isn’t always the issue; there’s passive noise and receiver sensitivity. That, plus when you crank the power high enough and have long enough exposure you can damage your body. The best option I can think of is a parking garage reader and card style tokens. But even that isn’t guaranteed.
Have you looked into how the security gates at libraries operate? Many of those are 13.56MHz and have a range of a few feet. The only problem I foresee from an implant perspective is the sheer size of the tags they use. You might need to scale down the coil such that it is can only cover the right/left side of the abdomen of the person coming through the door for it to properly couple with a receiving coil on the scale of an implant. That seems like it would address your need, though.
Wow what libraries are you visiting? Honestly… even the fancy libraries out here on the west coast still use magnetic resonating “bit” tags and giant eletromagnet gates that jiggle magnet implants real good.
Oh you can do this with passive RFID tags if;
you are ok spending thousands of dollars.
are ok setting up UHF panel antennas in every room.
you’re ok wearing a UHF tag around your neck or in your clothing.
There are no UHF tag implants I’m aware of and the range would be absolute crap since backscatter has a seriously hard time with water… and you’re a giant bag of salty water.
You could technically wrap wire around the entire doorway and make a door portal … it would need to be integrated into the frame of the door, and you’d have these two issues;
you would still not necessarily get a guaranteed read. Every type of RFID system is notorious for not getting 100% reliable reads and often readers are re-positioned or the objects that fixed readers are scanning are moved or moving and scanned continuously until a good scan is achieved. if you’re looking for a completely passive method of getting a passive implant to scan without the user needing to even think about it, you will have reliability issues.
you will also have issues with occupancy synchronization. since there is no way to guarantee reliability and no way to know which direction a person is moving through the portal (in or out), imagine a read failing upon entry and working upon exit… the system would then assume the person is in the room… or a person enters only to turn around and exit while still within the read range of the door portal.
I hate to say it, but you might look into some of the wifi and RF bouncing technology being developed… you think cameras are invasive… check this out;
Now imagine this technology souped up to actually ID people using heartbeat… not with lasers as this tech does but with that same wifi tech above;
@ReactiveLight What kind of system did you end up going with? I’m looking at a similar project but in my case I’m interested in tracking the locations of our dogs within the home (1 is deaf/blind and another is deaf so we’re constantly looking for them). I’m also looking to use the RFID to trigger their automatic feeder and dog door. Right now, my front-runner is a combination of the SparkFun M6E Nano + ISO18000-6C UHF Laundry Tags.
Biometrics for dogs isn’t really there from a technology perspective and I tried using QR codes on their collars but getting the QR to reliably read (even when only applied to the feeder) was dicey at best. I’m curious to hear more about what you ended up doing.
Because the checkout is completely handled by the library patron, I assume that the security at the door also uses the NTAG cards. I can take another look next time I’m at the library (which will likely be a while, I’m currently not at my usual base of operations)