Short range but wide area antenna design?

Well, after almost a month of waiting, I finally got the thing in the mail and installed it at my desk at work. I have to say, it’s pretty awesome. It locks the session as soon as I get out of my chair, and wakes up the screensaver as soon as I come back, without fail. I don’t even need my overly-complicated screensaver killer trick no more.

It’s a very old product though: the configuration utility doesn’t know anything beyond Windows 2000. But it still works fine, so no problem there.

I still need to present my hand to the reader to log in, but at least Windows is all woken up and waiting for me to do so, so I don’t have to do wake it up manually. Now if only my piercer would reopen his parlor so I can get that transponder implanted in my rear-end. Damn virus…


If it ain’t broke…

I think that will complete it, ultrasound wakes it just in time to sit and sign in. For sure beats the AnusID™

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Yeah but that’s the thing: I don’t want to sign in - at least, I don’t want to have to do it manually by showing my hand to the reader. I want to be authenticated by sitting down.

So yeah, the sonar thing is nice to automatically lock the session, but it alone doesn’t solve the log-back-in part.

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Augment one of these. NXqnaAz

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How about this guy? With the edges sandblasted or otherwise rounded off, so they don’t cut into your biopolymer coating later on, it might work. What do you think? Care to quote me for an implantable one of those?

I doubt it actually… this looks like a ceramic resonator which is very thick. I was thinking more about inlays. Super flat, thin, flexible uhf tags… I can easily convert those.

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This one caught my eye as very implantable:

Okay I thought you could safely encapsulate anything of any thickness, provided the would-be implantee is okay with implanting it.

Right, back to the search engine then :slight_smile: Maybe Leumas95’s find would work… But I want more information first. Of course Amal, if you yourself are already eyeing something that would be suitable, don’t hesistate: all I’m doing is googling around without any real clue as to what’s suitable or not…

Yeah I have not tested them, just size wise it seemed decent.

The manufacturer won’t say anything about read range (wisely, probably). I’d like to find out what range I can expect “ideally”: if it’s 5 inches, it’ll likely be 1 when it’s implanted, so there wouldn’t be any real point.

Interesting video of a guy testing the read range with a UHF bird ring tag, first alone, then wearing it around his finger: in the second test, the range is dramatically reduced:

I’m tempted to order a reader and a tag, and try to read it with it inside my mouth. Then possibly swallow it and see if it still reads at all. A small tag obviously :slight_smile:

Yeah… Die-cut Size: 11 x 25 mm … the implant would be 13 x 27ish. Not awesome but not bad.

This is the biggest issue. You can see this effect on UHF badges… wearing as they lay on your chest the range is reduced by about 80% … this is why schools that have these badges for kids must put uhf panel antennas directly over the door facing both directions so they are sure to get a 90% read rate on tags passing through… while if the badge was simply held out from the chest by about 12 inches (about a full wavelength) then range dramatically increases since the body is not absorbing the radiation.

The problem with UHF is that it is not a magnetically coupled system. It uses EM field pulse transmissions which sort of “bounce” off the tag… the method is actually called backscatter. Because UHF tags only get a super tiny fraction of the energy the reader panel puts out, and the fact the EM emissions are readily absorbed by water and reflected by metals, interference is a serious problem for UHF. Unlike coupled systems though, if proper conditions are in place, extremely long range is possible. Certain lab conditions set up by RFID hackers achieved over 100 feet!!

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Yeah my reader picks up my tags by bouncing off my roof when I’m working on it :sweat_smile: can be annoying

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The thing is with UHF tags and to an extent HF tags they are never platform independent as I’m sure you know. An NFC tag in ‘air’ resonant at 13.56MHz will generally shift upwards a couple of MHz when placed on the skin and even more when placed under the skin. Implanting an ‘air’ designed tag is not really the best thing for optimum performance. The thing becomes a headache at UHF, you optimise a design for one person and it won’t fit all. Build and even ethnicity screws things up. For a small optimised UHF antenna mounted upon the palate of the mouth you’ll get about 0.8m read-range when everything is aligned and with a good reader. If you’re in the states then you might get a bit more as you’ve double the power of what we’ve got in Europe. Here’s a short conference paper . It was just to see if we could get some RF out the mouth! It has since progressed to a mouth mounted sodium measuring tag :wink:
Similarly for finger mounted ring type UHF tags you are looking at a 2 - 5m read-range dependent on substrate height from the finger. Coincidentally details are here :wink:

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Really interesting papers. Thank you for sharing! Also, I finally meet someone who seems to have a job as cool as mine :slight_smile:

Re UHF performances under the skin, I’m nowhere near the specialist you are on the subject, but two simple facts seem quite clear: the higher the frequency, and the more you work in the far field, the more attenuation you get if the transponder is near or behind wet ionized meat. This is even quite obvious with NFC tags: HF implant performances are rather pathetic compared to similar sized LF implants in-situ.

I’m actually surprised you got 0.8 m out of a UHF transponder on the palate - which essentially means the antenna is surrounded by 2" of flesh in all directions.

As for the mouth being a hostile RF environment, as described in your first paper, it’s only true if you try to go through it. But here’s a fun trick I use all the time: open your mouth, put your car’s remote inside it, face your car, and you’ll be able to unlock it from a lot further away. Those remotes work at 433 MHz, so your open mouth becomes a resonant cavity.

Anyway, apart from performance issues, the other practical factor that made me give up the UHF implant idea is that the working frequencies in Europe and in the US are different. That means if I want to buy hardware from outside Europe, there’s a 50-50 chance I’ll get something with the wrong frequency, or that it won’t be offered with the European frequency. I can foresee right now that it’ll get frustrating in a hurry - especially considering the price of that hardware.

Care to elaborate? I’m curious to know what you mean by that.

I think you might mean UHF here… because our experience has been that 13.56MHz magnetic coupling only detunes by about 1kHz to 2kHz only.

agree, thanks for sharing!

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Ha ha, thanks, I’m not so sure about the cool bit though. People after many years still say to me “now what is it you actually do?” Even family!

Yes it’s interesting coupling your fob to the body or road furniture to see the range improvement, even though things are unlikely to be matched in anyway…unless you’re lucky.

This is useful multi-region development kit which I use. Depending on what you want/need to spend. It has some basic software and an SDK.

This is for patient health monitoring of sodium intake based on this rather old device……

I wish it was only a few MHz at UHF Amal but unfortunately that has been my experience at HF, both in simulation using CST Microwave Studio and practical on/off body measurements. But I’ve never practically measured an implanted tag…yet :wink: Out of interest I wonder what your measurement technique is?

A basic SDR vector network analyzer with coupler. The tuning adjustments we make to out antennas only require ~ 2khz bump to maximize peak.


Amal gives the megahurtzmeter dial a tap, needle jumps to the other side of the scale

“Uh oh…”