Help? Making rfid antennas, math is not my forte. Resonance and capacitance

Projects
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Hey all you lovely folks,

I’ve got a two led implants, love them. I want to make something similar to these led nail stickers I see sold about, even on dangerous things:
https://dangerousthings.com/product/nfc-nails/

My wife is awesome with almost any medium artistically, and she’s taken up nail art. I have a few smt leds, and want to make some of these style leds for her to encapsulate in the acrylic nail gel.

I’ve run through a number of resonance calculators, i kind of understand: have to match resonance of coil (+ capacitor option) to the frequency of the signal; in our case i 13.56 mghz would probably be best.

I have yet to successfully wrap an “antenna” from magnet wire, on purpose. Once, years ago, i randomly wrapped in a rectangular shape, some 30ish gauge magnet wire, no capacitor, and it worked!
But since i’ve started trying to do it with “math”, i can’t; i should note, i’m a total amateur and haven’t used heavy math since highschool/college, and these appear to be fickle.

Anyone know how many loops those fingernail stickers have? Or an idea of the right capacitors/30 gauge wire combination would work? Or without the cap is fine too.
Or help me fill in a calculator? I have handy (not smt) caps in 1 and 0.1 uf caps, and 100 or 10000Pf caps.
I think aiming for 10-20mm across square/rectangle/circle flat antenna, using 30 gauge (too small for my cheap calipers. wrapped 10 loops, tried to be tight, and got 1 cm. so i think 0.1 mm diameter best i can see).

I’ve seen some “wireless power” circuits running at waaay higher frequencies, and will give those a shot for a bigger set of leds soldered onto jelly bean pcb mount inductors, but wouldn’t want to risk that kind of power with a) my implants b)fingernails. What i’ve seen in a few of those is that they may use different number/size of loops on the receiver than the transmitter. Can i guess, that with high enough frequency/power, you can get more of a range of coupling?

Would it be easier for my purpose, to make a higher frequency transmitter (i’m thinking 3 point resonator, found one that says it’s around 27mghz) and try to use that for the nail? I’d probably wear some kind of tinfoil glove to protect my implants :laughing:

Thanks a tonne!

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Hey @erischilde

First off check out this thread for some pointers:

It sounds like you already have a handle on tank circuits. You shouldn’t need a capacitor in this case, because the LED has around 20pF of capacitance in the junction for red and green, and about 45 for white and blue. Check out this thread for an inductance calculator:

Here’s a good LC tank calculator

If you have a 20pF LED you can use the inductance calculator to create an inductor that fits your maximum dimensions and is about 6.89uH. A 45pF LED would need an inductor of about 3.06uH. You can indeed put a capacitor in parallel to the LED to allow for smaller inductors, but you would need ones in the tens of pico Farad range not the hundreds.

If you want any help learning how to make flex PCB antennas feel free to hit me up. They’re expensive up front (~$150 for MOQ 300) but they’re much more reliable. We have an unofficial dangerous things Discord which has robust voice chat and screen sharing capabilities that I usually use to get people started. If I can motivate myself soon I’ll be releasing a long YouTube video explaining the process.

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I have a shitload of NFC nail stickers I’m not using now. Want a deal?

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lol, could be fun! What are you thinking? Feel free to dm me, or email me. I’m going away for a few weeks, can’t order anything till mid Nov, but yeah, you’re awesome!

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Hey! Thanks!
The capacitance of the LEDs, i was wondering, It hit me while slogging through traffic yesterday, that that could explain why single wire loops worked without caps… i’m elated i was actually on the right path for once.

Funny thing, i downloaded that Java calculator from the second thread you posted; just was at work and realized i shouldn’t run it there :smiley:

Vis-a-vis the Discord, i feel so old, i’ve never taken to Discord. Where can i find the discord server in question? I may not be much for voice, but text i am. I get social in ebbs and flow, but i’d love to give it a shot.

And, as for the flex PCB antennas, i appreciate it, but i don’t think that’s where i am right now. I’m very much at the beginning of learning electronics, something i wish i did long ago. If i get there, i’ll ping you directly for it. If you put up videos, i’ll definitely watch them. It’d be interesting for the learning part, but i’m unlikely to be using that type of tech for a bit.
Actually, the type of little toys i might be trying in the near future are more like using smd inductor packages and LEDs, like the sell via Aliexpress. Useless really, but cute.

again, you gave me a tonne to work with, thanks a chunk.

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The mind control lasers are still working.

:artificial_satellite:

:unicorn_clap_clap:

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Try this
from inside discord
discord.gg/implants

or
this from outside

one or t’other should get you in.
you will need to read and abide by the rules before you can enter the server fully.

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ty very much!

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Hola! this might be a bit of a book, but i think i will take you up on that offer about learning about flexy pcbs. I actually haven’t had any pcbs printed yet, was thinking about trying that out later this year.

I still haven’t had much luck. Either imprecise in the size of the rectangle/circular shapes, or i am not anywhere near knowing the gauge of the wire i was using. Going to try weighing a meter, then figuring it out from there.

I did have a bit of a brain-gasm while driving this morning though! Some experiments:

  1. see if can 3d print directly onto very thin copper with PLA. That could maybe act as mask for etching, or a really janky diy proto board.
  2. We’ve experimented with silicone as a molding/sugru kind of tool. Have a few recipes we tested. One recipe that worked well for us was 100% silicone (from hardware store. nice and cheap), and corn starch. (also added a couple drops of acrylic paint. Some say online it helps it set, others say just for color).
    I made some, stuck it in a ziploc bag, and rolled it flat. Got pretty thin, and once cured, very flexible.
    For at home, diy, “lifehack” type flexible circuit, that might be a thing too!

Of course, i have to figure out how the silicone and pla will play with ferric acid, but overall it’s a cheap set of supplies that i mostly have.

I’d have to investigate masking copper for etching though, would absolutely want prints, 2d or 3d, because hand drawing/cutting that would be awful.
Heck, could even embed some smd leds into the thin silicone “skin” and add flare to some kind of costumage… or something.

Cheers!

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I definitely recommend you reconsider acid etching. You’re introducing so much hardship into your life (not to mention danger from the caustic chemicals), and you’ll never be satisfied with the results. If you’re willing to spend a couple hours learning a free ECAD software like Autodesk Eagle or KiCAD, you can order rigid PCBs in batches of 10 for $25 including shipping. For learning and testing that will work fine, and then once you’re comfortable you can move on to a big order of flex PCBs if you want.

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Ahh. I kinda wondered, etched ones online always kind of look like butt.

Yeah I’ve poked around places like jlpcb. Really neat how cheaply and quickly end users can order things, as opposed to the past. Kinda wild actually.

I do kind of like the hardship, if that makes sense. For learning and hands on doing, but for functionality, you’re right.

You suggest KiCad? I’ll grab it. I’ve tried one or two designers. The most uncomfortable has been on my phone. Would be a great place to sketch. Using every circuit has been irritating though, due to the free version ads taking up so much of the screen, and refusing to emulate.

Thanks for the tips.

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EasyEDA is browser based and pretty good because it integrates octopart and JLCPCB ordering in the UI. KiCAD is very good, and open source which is nice. I usually use Autodesk Eagle myself. The free version is very robust. Let me know if you want a walkthrough on any of those. I train people in PCB design.

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I found a solid chunk of information, a paper from Stanford, where they created tiny implantable led units for light application inside a test mouse, and they hand made them.
34 gauge magnet wire, 3 turns (1.6 or 1.8mm dia), and a voltage doubler/rectifier with a pair of schottky diodes and i think a 10nf and 10pf caps.
They solder it onto a teeny tiny piece of pcb board, and encapsulate in UV curing resin.
Pretty neat to read!

They have the construction details of their implants.

Montgomery2015.pdf (2.2 MB)

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I updated your post to include the actual PDF because links often die and this is an interesting document.

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