Resonant Repeater Stickers

I want to create flex PCB stickers that are cheap and you can just slap on stuff to reshape the field to couple better with implants.

I did some calculations about “on-board” capacitors that are just copper pours so we can create the stickers without needing to populate parts or add any z-height. My calculations indicate that two 1cm² copper plates on a 0.13mm thick polyimide flex PCB will create a capacitor of 22.5pF

C = ε0 * εr * (A/d)

1cm2 on 0.13mm thick polyimide:
C = 8.85⋅10−12 * 3.3 * (0.0001m2 / 0.00013m)

C = 22.5pF

It also scales linearly with the copper area, so this is definitely doable in a larger sticker form factor in parallel with some antenna traces to get a resonant repeater to reshape the field.

Unfortunately there’s less than 1cm² of area in the center of a flex implant so I’ll have to get crafty if I want to create a resonant repeater board small enough to be installed with the 5mm flex needle and work with the Coil on Module (CoM) credit cards.



Would that be two different products? A board for COM cash cards as part of an implant, and a separate board that could be attached to places to increase the range of readers?

How about a third like the second but more durable and carried? I’m thinking of a key replacement solution, where your implant(s) open doors, but maybe one or two locations (where you can’t attach stickers) are problematic. A credit card sized resonant repeater would be easy to carry, and could be used in such circumstances. The antenna for some door locks is around a keypad for example, in those cases you may not be able to put a sticker on, but a card held between the implant and the lock could work.

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Yeah, two separate ideas, but the execution is almost identical other than scale.

Honestly the diagnostic card already does that. Give it a try and you’ll see what I mean. Worst case, just don’t pull off the Adhesive on the sticker and use that as part of your every day carry.

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Does this mean I could put a diagnostic card on a reader, and have better luck with my payment flex ?

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The reason I didn’t suggest this for payments is that you are back to carrying/using a card for payments…but for id purposes it isn’t identifying you but making it easier to identify you.

If the sticker is small enough and (for example) says “tap here” I could see it being put on a payment reader without complaints.

Not looking at it as a true solution, but something to know if I run into a reader that really doesn’t want to work… and the diagnostic card is something I might have around

I would love to have a repeater sticker and stick it near my phones antenna to get a smidge more range

Would this project also fall inline with the Flexible PCB/ Coil for for increasing Phone NFC antenna performance



I’ve actually been meaning to ask about these things. Would it be possible to have a repeater in something like a ring? Even if it works, I doubt it’d be anywhere near as good as the sticker form factor, I’m just curious if it’s possible.

I assume the goal is to have a range extender right beside an implant to make it easier to use.

Some of the payment chips include a small coil in the module, they then use a resonant repeater in the card to extend the antenna and get a usable range.

I am guessing that the idea would be to allow a flex conversion of those coil on module chips into an implant.

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Yeah, that. In the US at least banks save a bit of money by buying cards with CoM packages instead of soldered connections. They’re becoming pretty prevalent. I want to create an avenue for conversion of those payment cards in a conventional flex implant form factor.


Sorry, it may seem unrelated to the stickers, but from a technical perspective they’re functionally identical. My development and testing on one will directly translate to the other, so I grouped them here. This is just the first time I’ve mentioned the CoM packages on the forum, but we’ve been talking about them on the discord for a bit now.


Nope, it doesn’t

Yep, Figured

That was my subtle way of asking…


Lovin’ ya work Satur9

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Here’s a thought for a product: how about a universal “glassie booster”?

Picture this: a planar coil, say an inch across, connected to a small 4 mm diameter inductor coil in the middle. No electronics, no nothing: just the two coils. The whole thing is encapsulated in magic Amal goop, apart from the core of the center coil that would have a 3 mm diam. hole through it, leaving a 0.5 mm coating inside the coil. Somehow… Easier said than done, I’m sure.

If someone wants an extended range version of a glassie, they buy the glassie and the universal booster, slip the glassie through the center hole, and implant the complete “assembly”.

That would instantly upgrade the entire range of DT glassies currently on offer - including, crucially, those with blinkies - and give them all a extra range option for those willing to go through the installation of a big-ass disc. Hell, it would even generate a sale if someone wants an extended version of a competitor’s glassie.

Why would you buy an xseries and a big booster?
I’d just get a flex.


If its your lock maybe put the booster internally? Then you only need xseries implants.

Well, this: where do you get a flex NTAG21x with a LED? Oops, you don’t. Or a flex NTAG21x (real NTAG) with a LF side? Same thing. Or a ISO15693 flex? Or a LED-only flex?

My point is, if you decouple the extended range bit and the functional bit, DT only has to invest in the development of short-range glassies. And DT gets to reuse existing designs.

Not to mention reliability: the glassie will always work even if the extended range add-on fails - and it’s less likely to fail presumably, if it’s just two loops of copper wire soldered together.

True. But for me, implants should let me interface with the existing world. They should not require me to adapt the rest of the world to me.

It’s already half the case now: you’re limited in your choice of working NFC products with implants. Fortunately, there are enough that it doesn’t feel too much like a limitation. But it is a limitation.

I for instance had to carefully choose the lock to my main door: only one choice available at the end of the day for my style of door, but I wish I had had more choice, because my lock isn’t what I would have normally chosen. And I had to pay top dollar to equip doors at my workplace with implant-compatible door handles - that are barely compatible, to boot. And I can’t get any of my glassies read by any cellphones with 100% certainty.

Yeah I get that, I’m kinda annoyed with my walletmor trying to get a good couple with 1 type of reader is really hard and it seems to be the most common type in my area atleast. What’s even worse is that 2 identical readers preform entirely different.

I’ve actually found already that my shipping habits are changing based on the ease of use of my payment implant.

That too is keeping me from deciding on getting a Walletmor.

A few weeks ago, I was ready to order and I pinged Wojtek. Fortunately, he was out of 9-year chips, because since then I’ve had second thoughts.

There are essentially only two types of payment terminals in my neck of the woods, and I think I run a very real chance of implanting the Walletmor essentially for nothing, and being massively disappointed. Basically there would be 3 outcomes:

  • Both types work great with the Walletmor: I’m a happy camper
  • One type doesn’t, I’ll have implanted the Walletmor uselessly 50% of the time
  • Both types don’t work: I’ll have implanted the Walletmor for nothing.

That’s a 75% chance of disappointment. When you play poker, you fold with outs like that.

So what you are saying is walletmor is saving you money, it is basically paying for itself :interrobang:

oops, Sorry

On track

So how about those Resonant Repeater Stickers ?

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I’d secretly ask amal for a flexSIID. If not that, there are still other options like a ~2mm blue disc amal never made into a product afaik.

Surely amal can put a flexNT on a flexEM for some $$.

Reliability is ofc an issue with custom flex LED imlants, valid point.