2
$\begingroup$

Let's say a three letter agency wants to track everyone using an ID card tied to a database. It's simple enough to put an RFID chip in it that gets read at some point of contact, but let's say we want ad hoc scans at any time. Existing RFID requires close contact, but supposedly specialized equipment can do it in hundreds of feet in certain conditions.

To maximize this agency's dystopic surveillance powers how far can we extend the range? Can we penetrate walls? Can we plausibly equip law enforcement with handheld battery powered scanners with a range of 10s of meters that can pull the ID numbers of everyone in a crowd in seconds? Can we scan someone from orbit? What kind of tech is behind the power transfer and signal?

The only requirement here is that the passive ID side of this needs to require no power and fit in a credit card sized package. The active scanning side of things can use whatever tech is needed, and be any size, but the possibility of a handheld device is ideal.

$\endgroup$
11
  • $\begingroup$ Sub cutaneous maybe too? It's a fascinating and valuable issue to deal with, but a tiny bit unfocused at present. I'm not voting to close because the main question is in the title, but the list of requirements - yeah, I want to know, but a bit broad. Just a comment not strict advice. $\endgroup$ – A Rogue Ant. Jul 21 at 15:51
  • $\begingroup$ Hardscience to fish some imaginary tech? Well ... not neccessarly new, but ... $\endgroup$ – MolbOrg Jul 21 at 16:08
  • $\begingroup$ I'm pretty sure "pull the ID numbers of everyone in a crowd in seconds" and "scan someone from orbit" are impossible. The latter I suspect is just plain impossible short of some novel discovery in physics. The former is going to have non-trivial signal collision issues. $\endgroup$ – Matthew Jul 21 at 16:11
  • 1
    $\begingroup$ Realistically, an RFID transducer might be possible both to power and to read from low orbit satellites in the next century. If there are any true technical obstacles to this, it will be with aiming for a device that small on the surface, rather than anything RF-related. And as computing power increases/miniaturizes, it might be true that there'd be even more to snoop on within the device. But using such a system to track billions of people seems slightly absurd. Nor can you hope to do this if the target is effectively in a Faraday cage. $\endgroup$ – John O Jul 21 at 16:28
  • $\begingroup$ @John O You suggest a highly directional antenna which would target passive RFID tag from a great distance and power it up? $\endgroup$ – Alexander Jul 21 at 17:26
4
$\begingroup$

If we mix and match wireless tech - 100m with passive RFID is possible.

Johns well researched answer covers all of the basics and I'm not going to duplicate his work or references (as doesnt forbid building on other answers), but he shows:

  • Passive RFID (no battery in the card) can transmit 10m.
  • Active RFID (where the card has a tiny little battery to help with power) can transmit 100m.

The question excludes active RFID and demands no on board power. So we need a way to charge up the rfid transmitter's capacitors to store enough power to get the range of an active rfid tag without relying on an on board battery.

I think the best way to do this is have them constantly trickle charging the capacitors from a remote power source of some kind. And I mean trickle - these power over distance calculations come out in microWatts. Pretty useless for on demand transmission requiring 10000 times that, unless the crowd is willing to wait a few hours for their rfid transmitters to charge while the cop scans them.

Look into research for power over wifi, in which devices can be charged using idle spectrum from a household 2.4ghz wifi router. This requires the router to detect and charge the card, and the user to opt into that behavior in the settings, even if it also charges the users phone wirelessly in your pocket (and most people opt in due to that convience), it may not be 1984 enough for your needs.

In which case your more interested in the later parts of that linked article, in which they're able to utilise the TV signal from a tower 10km away to trickle charge a tiny device.

So the secret is to have 3 devices

  • A big antenna that trickle charges every card in town at a rate of microwatts, but a range of several km. Looks like a large TV tower mounted on a hill. May actually also broadcast real TV.
  • The card in peoples wallet that discretely hides the rfid chip is trickle charged passively by the large antenna.
  • The agent uses a handheld device to contact all the the tags, the tags then respond, using the capacitors (that have probably been on charge non stop since manufacture) to boost their signal such that it can travel ~100m and penetrate some thin walls.
$\endgroup$
1
  • $\begingroup$ The problem is to make wireless power powerful enough at the needed distance, it will harm people who get near the transmitter. It also makes RHID itself impossible as the magnetic field interferes with it. even normal phones and radio will have big problems. you can make safe point chargers such as walkthrough a doorway or within a dozen feet of a coil, but long distance is incompatible with the other technology you need to work for the rest of the system. $\endgroup$ – John Jul 21 at 19:11
5
$\begingroup$

Frame challenge you need powered tags so use Phone ID or RFID implant

There is a limit to the amount of radio energy you can subject a human body to, and passive tags need far more energy than that to work at hundreds of meters. So you really need active AKA powered tags.

We could do it today if you are willing to spend enough money, what you need is transmitter density a few changes to laws.

Ultra high frequency tags have an effective range of about 10-12 meters. UHF suffer from signal interference but that is more about software and how quickly you can refresh you signals. It won't stop you it just makes it more expensive.

Hundreds of meters needs powered tags. Oddly a implanted tag works better than a card, you can supply power to an implant tag.

but really just build it into every phone, make your phone part of your ID, several states are already testing phone based ID's. now your tags hove power even if the phone is turned off, so you have your hundreds of meters. you will want to make wireless charging far more common place so people can't drain their phones too easily.

If you don't want powered tags you are limited to having transmitters every 10 meters or so. which is possible but will be amazingly expensive. but you will still have dead zones, mostly lakes. https://ieeexplore.ieee.org/abstract/document/6400261

$\endgroup$
4
  • $\begingroup$ +1 for including the references demanded by the hard-science tag. I'd +1 again if I could for pointing out that the OP's expectations can't be met with tech we understand today. Theoretically, a sensitive-enough receiver with great enough noise discrimination would read passive RFID from orbit, but I'd hate to be the engineer who designs that puppy (and it can't be done with today's tech). $\endgroup$ – JBH Jul 21 at 18:30
  • $\begingroup$ @JBH it could read an active RFID a passive one would be too weak to make it out of the atmosphere, without the initial signal harming people on the ground. $\endgroup$ – John Jul 21 at 19:03
  • $\begingroup$ I get what you're saying, but I've already lived through something being mathematically impossible (1nm FET geometries) and time proving the math wrong. As I said, if the receiver were sensitive enough and the filter discriminating enough.... BUT, there's a bazzilion things that would go wrong (lightening, thermal gradients in the ground plane, ionization... ) Are you getting the limits from the spec sheet? That's only the practical engineering limit. $\endgroup$ – JBH Jul 21 at 19:12
  • 1
    $\begingroup$ @JBH yes I am assuming a modern RHID lags level of return, which is the downside of the hard science tag, yes it might be possible to build something else but not with anything but purely hypothetical technology. $\endgroup$ – John Jul 21 at 19:17
1
$\begingroup$

To add to the technical discussion, perisens.de/wp-content/uploads/2018/09/publication2011_RFIDSystech.pdf has an analysis of attempting to extend the range of standard credit card RFID tags. The conclusion was that with special transmitters and antennas, the tags could be read up to several meters, but to go further required huge equipment.

A more reliable method is to use what is currently used by police: the cell tower logs. How does Google, Uber, and Lyft know where you are? By using the cell phone's own idea of location which is transmitted back to the server on a regular basis. That three letter agency simply needs to ask Google where everyone is.

Considering the cost of the special tags (in bulk, the current RFID credit cards still cost several dollars each), it would be far cheaper to simply require every citizen to have a phone that can be tracked.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.