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Bunnie Huang has published a reference design for a near-ultrasound data link.
We were requested to investigate “near ultrasound” (NUS) links as part of our research on developing the Simmel reference design for a privacy-preserving COVID-19 contact tracing device. After a month of poking at it, the TL;DR is that, as suspected, the physics of NUS is not conducive to reliable contact tracing. While BLE has the problem that you have too many false positive contacts, NUS has the problem of too many false negatives: pockets, purses, and your own body can effectively block the signal.
That being said, we did develop a pretty decent-performing NUS data link, so we’ve packed up what we did into an open source reference design that you can clone and use in your own projects.
Previously:
(2020) Your Apps Can Pick Up Ultrasonic Signals You Can't Hear
(2017) Ultrasound Tracking Could be Used to Deanonymize Tor Users
(Score: 2) by VLM on Saturday July 11 2020, @02:21PM
The idea of data carried over plain old sound link is like moth to flame for tech people.
Historically for decades now the standard way to demonstrate various ham radio data modulations, most famously PSK31 back when it was new and FT-series stuff now, is just two laptops running the sound modems with speaker and laptop microphone in free air.
Its not exactly hard to set two laptops to 13 KHz or any frequency low enough for the laptop hardware to operate and talk across the room digitally or send FAXes or slow scan TV. Obviously error correcting systems like FEC AMTOR or packet are a bit more error free than classic 1950s FSK RTTY.
For many years the broadcast engineers know all about this weird data carrier they transmit for ratings tracking.
I'm just saying someone "invents" sending data in free space over speakers roughly every 30 to 45 days for many decades now.
Generally I'd say based on experience that free space data transmission is slower but more reliable than turn of the century IRDA, and shorter range and slower yet easier to set up than bluetooth serial RFCOMM protocol.
Its fun and all you need is two computers (raspi?) with some pretty simple software to experiment.
Note that ham radio operators are used to the sounds and find slow speed fsk rtty or multi-tone "modern" modes to be melodious whereas things like 60 lpm fax are rhythmic and generally OK to hear, whereas the general public hears the whine of a nice multi-level QAM and scream "shut that GD noise down it hertz (ha ha) my ears"