Great accomplishment, but people were building 3D ultrasonic scanners back in 80-ies, for much less than $100:
[didn't read your article, your claim has put me off, sorry]
-- use an electric spark gap as the wideband acoustic source
-- use 3 simple electret mikes on 3 axes. Mikes don't need to be high quality (spark intensity can always be raised as necessary), so they were hand-assembled using metallised mylar film (used nowadays to pack some food, or ESD-sensitive electronics components).
I definitely would like an English translation. Though, from what I understand (the diagram and the translation of the title) it's a graphic input device that can work out a few points at the time, and not in the same sphere (as echos will overlap, a point I develop in my article).
So it's not properly able to scan an object like I did?
Apart from that, how have you found that untranslated 1975 Russian patent? Google Scholar?
It's impressive what they were able to build with such low-tech.
Phased array ultrasonics[0] and Multibeam echo sounding[1] has been around for decades[2]. This project in particular is an example of what's called an air coupled ultrasonic phased array. It's an interesting project, but it's not first. Congrats on making it happen though, and thanks for the write up.
Author here, the title is a bit misleading. In the article, I specify that it's the first 3d ultrasonic scanner (of my knowledge) that works in the air.
Have you seen the way lasers are used to do this? NDT or non destructive testing has use dual laser systems to create ultrasound for several decades. Check it out if you are interested.
I think one of the subjects of my exam for entering engineering schools (a thing we do in France) was about that.
Would really like to see papers on the subject, because I don't really understand how you can use lasers in opaque materials. Will also look at my test to see if it's really about that.
I don’t speak French either but I like the etymological sense that Superior school means Post-Secondary/College better than the English version. It seems like a logical and efficient way to get the meaning across.
Not at all! There are many "Ecole Normale" which are just schools for teachers. The "Superieure" refers to the fact that you have to pass a hard exam to get in. And once there you can do research or become a teacher in a preparatory school (which prepares you to do the ENS's exams, in a pyramidal way)
I guess that the main option is the second one. Lidars, once they are solid-state and cheaper will be a better alternative (smaller, more precise and much faster).
The first option isn't the good one. Ultrasounds are already used in car parking assists and people trying to improve them would have gone the same route as I did.
Not sure about the first, but it is really cool regardless. I tried doing a similar thing once upon a time with RFID (SAR), but I couldn’t figure out how it would work.
This seems even lower level, since I was basically using off the shelf components, and you built the whole thing yourself!
Radar is at its simplistic sensing a pulse out and listening for a return. But then the engineers wanted more.. of course home radar would not be really safe.
Hah! Back in my undergrad days I’ve thought about doing exactly this, but I couldn’t figure out the beamforming part, so I just measured distances in (microcontroller) software by correlating transmitted x received waveforms.
Awesome project! I’m happy the author figured it out! I feel vindicated :)
Thank you!I've been helped a lot by how technology changed for the past few years (lots of good resources online, was able to do simulations easily, MCU programming a lot easier, etc).
Interesting, but yeah, he fought way too hard with the analog part driving the transducers
I get it, it's a hobby project, but I feel the knowledge of analog electronics is getting lost in a way (and yes the analog people are the worse at explaining things - I think I saw YT videos more informative than whole university courses)
There were definitely well-known circuits for driving transducers, but I had to improvise to make a circuit small and simple enough to build 100 of them.
Building new circuits requires tinkering and many tries, regardless of the builder's knowledge.
> well-known circuits for driving transducers, but I had to improvise to make a circuit small and simple enough to build 100 of them
Yes, maybe an Opamp that works at 40V could have worked (with an appropriate feedback config), but your end result looks ok. I'm just saying that putting the transducer in the emitter was a non-starter (as you correctly pointed out)
> Building new circuits requires tinkering and many tries, regardless of the builder's knowledge.
Absolutely, I'm not denying it :) It's a great job nonetheless
You need to be more verbose as you say analog tech is pretty unusual knowledge so even though I've fought through the 101 course you still make no sense to me. It's really sad and I think it's a provlem I share with many.
There are two reasons why you don't put it there, one of which you explained "The NPN capacitor here only cuts out the alimentation of the capacitor, but there's nothing to discharge it.". Yes, the transducer has (theoretical) infinite resistive load.
But another reason (which would be valid for a resistive load as well) is that anything plugged into the emitter will have its impedance "reflected" to the base.
Even if you're talking about a digital circuit you need to think about transistor biasing. A pure capacitive load on the emitter means no biasing.
One of the ways you could work around this is to have an inductor in parallel with the transducer so it would resonate at the frequency you want https://en.wikipedia.org/wiki/LC_circuit (though not very practical to your case) - but ideally this would go on the collector, not on the emitter
Your 3 transistor solution is ok for the most part. Maybe it's doable with only one transistor but probably would need an inductor and/or wouldn't be too efficient.
(Not the best explanation, but this would require some trial and error and actually thinking a bit about the analog aspects of the circuit)
Though, the emitter is pulsed and I also rely on the fact that it stops resonating after I cut out the power. Unless my LC oscillator has a low Q, it will keep oscillating after I cut out the supply, which is something I'd prefer to avoid.
> Unless my LC oscillator has a low Q, it will keep oscillating
Correct! You can add a resistor in parallel to reduce Q (but it will naturally "not be perfect" since the transducer is putting energy out as sound waves and it's not really a capacitor.
[didn't read your article, your claim has put me off, sorry]
-- use an electric spark gap as the wideband acoustic source
-- use 3 simple electret mikes on 3 axes. Mikes don't need to be high quality (spark intensity can always be raised as necessary), so they were hand-assembled using metallised mylar film (used nowadays to pack some food, or ESD-sensitive electronics components).
The rest was data processing.