Transponder Tags on Carbon Fibre
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Forum Name: Building
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URL: https://forum.bhpc.org.uk/forum_posts.asp?TID=7130
Printed Date: 27 March 2026 at 4:46am
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com
Topic: Transponder Tags on Carbon Fibre
Posted By: RoyMacdonald
Subject: Transponder Tags on Carbon Fibre
Date Posted: 07 September 2020 at 8:38am
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Does anyone know how much isolation from carbon fiber our transponder tags need? Do you think 1mm ABS sheet will be enough isolation from the carbon fiber? All the best. Roy
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Replies:
Posted By: AlanGoodman
Date Posted: 07 September 2020 at 8:48am
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I think there are some foam strips around somewhere but Kim or Andrew are best to answer that - looking forward to seeing you and your new machine on track!! ------------- |
Posted By: atlas_shrugged
Date Posted: 07 September 2020 at 9:06am
| I put my tags on my helmet. |
Posted By: richforrest
Date Posted: 08 September 2020 at 7:33am
Does that not chafe a bit!!  (Sorry, had to be said
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atlas_shrugged wrote:Posted By: RoyMacdonald
Date Posted: 08 September 2020 at 9:40am
Already asked Kim but she did not know for sure. I'm inclined to think they will be OK, because when I mount the transponders on my ABS race numbers on my ICE trike the range the clubs sensors can pick the tags up is ridiculous. I left the trike behind the steel railings and well behind the sensors at the entrance to the changing rooms at Hillingdon and the sensors still picked up my tags. In fact while I was changing Chris came in and said I had won the fast race! I'm wondering if ABS boosts the efficiency of the tags somehow. All the best Roy
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Posted By: HeatherF
Date Posted: 08 September 2020 at 11:12am
| Foam strips do exist and should be in the box with the kit which I think Neil Hood has. We have more and Andrew can bring them to Gravesend. |
Posted By: Kim
Date Posted: 08 September 2020 at 11:18am
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ABS, foam, cardboard, wood, etc. is effectively invisible at 860MHz. The question is how close to a conductive surface the tag can be positioned without significant de-tuning of its antenna. There is adhesive foam in the box of timing kit. Its thickness is about 5mm. If this is known to work for applying a tag to a conductive surface, then there's your answer.
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Posted By: RoyMacdonald
Date Posted: 08 September 2020 at 11:45am
Hi Kim I take it the tag/reader operate at 860Mhz then? I would like to use 1 mm if possible because that will sit inside the front wheel access hole on the carbon fiber cover nicely. I could even replace the carbon fiber covers with ABS but that would add weight and Daniel worked so hard to make it the lightest Velomobile in the UK. Roy
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Posted By: atlas_shrugged
Date Posted: 08 September 2020 at 2:43pm
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Roy It is not quite clear what you mean by 'inside' the access cover. It sounds like the carbon fibre access cover is going to cover (obscure) the path to the track antenna from the tag. If this is the case the RF signal may be attenuated and the transponder may not work. Why not mount the tags on your helmet? Even if you have to use a foam spacer if your helmet is carbon fibre. The tags work OK on my helmet. Later if you use a race hood you can mount the tags on the side of the hood visor. The tags will have the highest chance of working if they have line-of-sight with the track antennas. |
Posted By: RoyMacdonald
Date Posted: 08 September 2020 at 5:36pm
Hi Brian. It isn't clear is it? inside the front wheel recess on the outside of the removable carbon fiber cover which fits into the recess. My helmets have always been damaged by the glue on the tag. Might just be a Giro thing though. I may fit the tag on the visor if all else fails. I thought that the access panels would be the best place to avoid disrupting the airflow. Can I bring your map to the AGM? I don't have a suitable box to post it in? I will still send your tie by post though. All the best. Roy
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Posted By: atlas_shrugged
Date Posted: 08 September 2020 at 5:50pm
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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. |
Posted By: Kim
Date Posted: 09 September 2020 at 10:58pm
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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.
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Posted By: RoyMacdonald
Date Posted: 10 September 2020 at 8:48am
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Thank you so much Kim. I'm sending you a PM. All the best. Roy
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Posted By: RoyMacdonald
Date Posted: 11 September 2020 at 11:54am
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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 |
Posted By: RoyMacdonald
Date 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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Posted By: Kim
Date Posted: 12 September 2020 at 9:23pm
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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.
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Posted By: RoyMacdonald
Date Posted: 12 September 2020 at 9:48pm
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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
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Posted By: RoyMacdonald
Date 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
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Posted By: Kim
Date 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. |
Posted By: AlanGoodman
Date Posted: 12 September 2020 at 11:00pm
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Air?! I think Kim may have found the backing material light enough for the new velo Roy!  ------------- |
Posted By: RoyMacdonald
Date Posted: 13 September 2020 at 8:52am
Thanks Kim. New access panels it is then. The better aerodynamics will outweigh the extra 8 grams of weight. All the best. Roy
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Posted By: RoyMacdonald
Date Posted: 13 September 2020 at 9:09am
 All the best Roy
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Posted By: legs_larry
Date Posted: 13 September 2020 at 11:54am
I remember a certain Matthias König saying “I wish he'd make them stronger instead of lighter!”  ------------- ==================== a bit ov a lyv wyr by slof standirds |
Posted By: RoyMacdonald
Date Posted: 13 September 2020 at 12:10pm
He makes them however you ask him to. His own one is the same weight as mine. He test rode mine and immediately took it all apart again and redid the tracking and suspension. He isn't satisfied until it feels perfect to him. All the best. Roy
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Posted By: Kim
Date Posted: 13 September 2020 at 10:13pm
And you can stick the tag to the inside, for an even more marginal gain
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Posted By: RoyMacdonald
Date Posted: 14 September 2020 at 8:17am
Hadn't thought of that one Kim.  All the best. Roy
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