High data rates through slip ring or equivalent - Page 1
Forum section: electronics / projects

author: nfmax
author_rank: Super Contributor
timestamp: April 25, 2025, 08:38:08 pm
content: So, today I went for a CAT scan, and realised that someone has already solved a problem we have been working on - getting high data rates (20 to 50 MB/s) from a continuously rotating assembly to a fixed assembly, without access to the axis of rotation. Does anyone know how they do it?We have used a repurposed video SERDES chipset, and a commercial slip ring assembly. But it’s not impedance controlled and this limits the data rates. It’s not a show stopper, but we would dearly like to make longer measurements more frequently than we currently can.What have you used?

author: TimFox
author_rank: Super Contributor
timestamp: April 25, 2025, 09:21:05 pm
content: Quote from: nfmax on April 25, 2025, 08:38:08 pmI was involved with CAT scan development in the late '80s and early '90s.By the way, the acronym is "Computed Axial Tomography", not "computer-aided".Two practical methods of data transmission from the rotating platform (which contained the x-ray tube and an arc of detectors, possibly with multiple rows) and the stationary platform:Optical transmission using clever arrangements of mirrors and optoelectronics.Non-contact capacitive coupling between a ring (that formed a transmission line) and an electrode spaced away from it. This works best with balanced transmission line and differential sensor, with multiple rings to increase the word width being transmitted.The big mechanical problem is that the slip ring requires a very large bore (roughly 1 m diameter) to clear the patient.

author: thm_w
author_rank: Super Contributor
timestamp: April 25, 2025, 09:33:29 pm
content: Google search "optical slip ring" and "high data rate slip ring" finds relevant results.https://www.grandslipring.com/slip-ring-data-speeds/https://www.moog.com/products/fiber-optic-rotary-joints.htmlhttps://www.rotarx.com/en/slip-rings/fiber-optical-slip-rings/

author: amyk
author_rank: Super Contributor
timestamp: April 25, 2025, 10:02:38 pm
content: Look up Ethernet Slip Rings. Many of those can transfer Gigabit Ethernet, which is beyond your requirements.

author: temperance
author_rank: Super Contributor
timestamp: April 25, 2025, 10:33:52 pm
content: Video records, DAT cassette players,... used transformers. One side was stationary while the other side was mounted on the rotating head.

author: Smokey
author_rank: Super Contributor
timestamp: April 25, 2025, 11:06:07 pm
content: Is this not a thing you can just solve with wireless link these days? All boards connect to a wifi router maybe?That has to be cheaper than a mechanical solution.

author: TimFox
author_rank: Super Contributor
timestamp: April 25, 2025, 11:13:37 pm
content: Quote from: temperance on April 25, 2025, 10:33:52 pmRemember the large bore required to insert the patient into the scanner.

author: temperance
author_rank: Super Contributor
timestamp: April 27, 2025, 02:29:16 am
content: Quotehttps://patentimages.storage.googleapis.com/1a/68/57/abd0c743077d94/US7717619.pdfSome use rotating transformers for power transfer and optical means for data transmission. Long ago I've seen some of those being taken apart on YT. A custom piece of ferrite is no big deal for companies developing such machines.Slip rings might work for power transmission but for data it will probably not work because of the high data rates.An other patent: wireless data transmission.https://patents.google.com/patent/US6914957B2/en

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 27, 2025, 04:36:03 am
content: Another method is to parallelize the data prior to going across the slip rings. You can re-serialize after if needed. Reduces the bandwidth as much as you need at the cost of some latency. But as others have said, large bore slip rings are going to be expensive custom items. The good news is that adding channels won't add that much to the cost.

author: nfmax
author_rank: Super Contributor
timestamp: May 03, 2025, 08:18:24 pm
content: Thanks for all the comments and suggestions - some good ideas there! The gigabit Ethernet slip rings look like a strong possibility, as they provide the bidirectional paths we need, and we could use standard MAC controllers instead of our current tricks with SERDES chips or FPGAs. I've looked at optical solutions before, but we don't have a lot of room to handle fibre management. WiFi is another idea: again, we might use standard chipsets, though I am a bit worried about EMC with the low-level analogue signals on our rotating assembly.Thank you all!