Resonant repeater

Did anyone ever tried to use flexible PCB’s instead of wire coil antennas?

Yes, the flexNExT had a prìnted antenna. Didn’t turn out too well… hence the flexMN.

I expect some PCB stuff in future, but this is the current best method.

No, the flexNExT bullseye tags use a aluminum foil not pcb material.

I believe amal has mentioned using pcbs before or it might have been the other guy with the tiny flex pcb / programmable blinky

Edit: was Paul the guy who made the programmable blinky and amal said they could potentially package it up into an implant (that was a flex pcb)

Amal has done it before with some success (see original flexDF). I’m trying some stuff out now but as I’m sure you can imagine it takes several iterations to make a good antenna and flex PCB orders are a bit expensive. There’s also the reliability of the solder joints that needs to be tested over time, but they’re pretty robust and Amal has some new tricks in his toolkit for securing things that he didn’t have last time around.

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Hey, let me know if you guy’s need some support with things like that.

Cool, I definitely will. We like to keep the VivoKey dev stuff close to the chest understandably, but there’s some awesome community projects that are either ongoing or stalled. Check around in the projects category for stuff like the open-source source door lock and the xLED power bracelet and the tragus monophone.

There is one thing that people here need that only someone comfortable with flex PCBs could pull off, if you want to take a crack at it. Many access control systems have a flat NFC antenna that is not shaped well to couple with x-series implants. We need a small device that people can permanently affix to the face of their readers to reshape the field. I was thinking a small flex PCB trace antenna (roughly 3cm x 3cm) with footprints on one side for a coil antenna and a surface mount capacitor (all in series). This could be used to create some kind of resonant repeater circuit that would reshape the field from flat to cylinder.

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I’ve noted the open source door lock and the xLED bracelet projects, unfortunately is nothing coming up for tragus monophone.

This now is some challenge, an antenna which is tuned to resonate to the readers antenna and changes the polarization of the EMW. I assume you’re talking about the antenna polarization when you say:

As you might know antennas can have 3 main polarizations, horizontal or vertical, circular or elliptic. The RF field reshaping is the smallest problem, its much harder to find the correct resonance because every reader is somewhat different. Also, you’ll loose energy if you use only passive elements.
Please let me know what exactly you mean by “reshape the field from flat to cylinder”.

Here is a point in the right direction


This is what I was thinking. Basically two different inductors in series with a tuning capacitor. It would require some very careful tuning optimization to make sure it didn’t completely fudge up the reader communication by introducing phase lag or lead, but it might work. That’s kind of why I thought a bare flex PCB with a trace antenna and some unpopulated footprints would be ideal. That way the only thing that is static is the trace antenna inductance and we can try several different coil winding techniques for the second inductor and change the capacitor value.

It will basically relay the reader signal, but in so doing it will change the shape of the magnetic field from 1 to 2:


I was thinking about this a while ago, though it would work well built into a phone case.

Kinda like this?


A little off topic, but I really wish that US Moto phones had NFC. I don’t understand why they don’t include it with US models.

My US Moto Z2 Force has great NFC

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That’s cool! I just know that pretty much all of they’re other lines only have it in non-US markets for some reason. I mean, what is it like 10 cents to put it in there?

Not quite. I mean something like what @Satur9 posted.

A coil in a case like that one you just posted that couples well with the phone that then has a wound ferrite core antenna along the top edge for example.

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Yeah, my previous phone was a Moto G7 Power, no idea why it didn’t have NFC, was extremely annoying. I generally liked the phone otherwise, it had a 3 day battery which was neat. Had to upgrade to my current phone (a Pixel 4a) for NFC.