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Transponder Tags on Carbon Fibre

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atlas_shrugged View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote atlas_shrugged Quote  Post ReplyReply Direct Link To This Post Posted: 08 September 2020 at 5:50pm
OK sounds like you intend to mount the tag on the *outside* of the carbon fibre wheel hub cover. In other words the tag will be visible by the track antenna. Naturally it may be best to avoid putting the tag *inside* anything that is carbon fibre.
 
No urgency with the map.
 
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Kim View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Kim Quote  Post ReplyReply Direct Link To This Post Posted: 09 September 2020 at 10:58pm
Natalya and I did SCIENCE:

(This is in the somewhat RF-hostile environment of our downstairs hallway, with assorted nearby metal objects and electrickery that wouldn't be around at the trackside, so take the longer range values with a pinch of salt.)

Re-configured MultiReader to do an inventory run using the trackside aerial at full power.  This reads all tags within range many times per second, with an indication of how long since each one was last successfully read.  It therefore becomes immediately clear when a tag is failing to read reliably.  We want a reliable read for race timing, as the more reads Impinj gets, the more accurately it can determine exactly when the tag crossed the finish line.

A brand new tag (SMARTRAC DogBone, Impinj Monza R6) attached (using masking tape, so I could re-stick it without damaging the tag with a peeling action) to a Mk 1 sheet of correx was readable at ~10m.

The same tag stuck directly to a sheet of 3mm aluminium was unreadable, even when physically touching the RFID aerial.

We then started adding shims of 1mm ABS between the tag and the aluminium, and recording the distance (to within 0.1m) where the tag was starting to miss reads:
Shim Range
1mm 0.4m
2mm 1.2m
3mm 4.2m
4mm 5.4m
5mm 5.7m
6mm 6.0m

And then using the 5mm adhesive foam from the timing kit:
5mm 5.8m
10mm 7.1m
15mm 7.7m
20mm 9.0m

Sadly the only carbon fibre I have to hand is the suspension fork on my Streetmachine, but I suspect that it's either going to be effectively the same as metal, or vary with the exact structure of the carbon fibre composite.  Metal should represent the worst-case scenario.

Anyway, on this basis, I'd suggest that 10mm or more of shim is best to get reliable reads on a wider track (or somewhere like Stourport or Derby Velodrome where we can only use an aerial on one side of the track), but you could probably get away with 4-5mm under most circumstances.  This is with the tag mounted horizontally at the same height as the aerial; performance will degrade somewhat if it's incorrectly polarised or significantly off-beam.


Edited by Kim - 09 September 2020 at 11:07pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2020 at 8:48am
Thank you so much Kim. I'm sending you a PM.

All the best.
Roy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 11 September 2020 at 11:54am
Hi Kim
I will send my race number plate as a control test. Known to work at distances over 10 meters (even when behind the antenna) but under 20 meters. Also a replacement wheel access cover made of ABS. And finally a carbon fiber sheet with an ABS transponder mounting plate on it.
Thanks for your help with this.
All the best.
Roy



Edited by RoyMacdonald - 11 September 2020 at 11:56am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 11 September 2020 at 4:00pm
Here is a photo showing the distance the antenna picked up my tag. My Sprint was behind the railings by the entrance.
 
All the best
Roy
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Kim View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kim Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2020 at 9:23pm
Thanks to Roy for providing a piece of carbon fibre.  We did some more testing, this time outdoors, using the same RFID configuration and tag as last time.

The tag without conductive material was now readable at 14.5m: performance was, unsurprisingly, better than indoors.  This is consistent with the "Range 14m" sticker that Andrew has at some point attached to the aerial, and the way the system regularly picks up tags on people milling around from the opposite side of the track.  (The race timing software can show us which aerial the read comes from, and it's usually the one on the far side, rather than the nearer one picking them up behind its back.)

The tag mounted directly to carbon fibre was unreadable, even touching the aerial.
On CF with various shims:
1mm 1m
2mm 1.5m
3mm 2.4m
4mm 3m
5mm 3m
6mm 8m
7mm 11m
8mm 10.5m
9mm 11m
10mm 9.5m
15mm 11.5m

We also repeated a few measurements on aluminium:
2mm 1m
3mm 2m
4mm 3m
5mm 10m

The difference in performance between materials with a 5mm shim is interesting.

So yeah, you might want a bit more than 5mm on carbon fibre, but should be safe with 10mm or so.


Edited by Kim - 12 September 2020 at 9:35pm
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RoyMacdonald View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2020 at 9:48pm
Thanks Kim, brilliant.
What was the replacement access cover in ABS reading?
Was it the same as my race number plate I labeled control?
All the best.
Roy


Edited by RoyMacdonald - 12 September 2020 at 10:16pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2020 at 10:02pm
ABS replacement cover 18 grams



Original carbon fiber access panel 14 grams.

Thanks for the new tags Kim.
All the best.
Roy


Edited by RoyMacdonald - 12 September 2020 at 10:17pm
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Kim View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Kim Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2020 at 10:56pm
Yeah, no difference between the ABS and any other non-conductive material.  Cardboard, correx, wood, polystyrene, air, etc, may as well not be there.

Edited by Kim - 12 September 2020 at 10:57pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote AlanGoodman Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2020 at 11:00pm
Air?!
I think Kim may have found the backing material light enough for the new velo Roy!

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