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Comment by tyingq | Hacker News Reader

The most enlightening comment there was the one that contained this:

"Still I ended up north of $3k for hardware, and several hundred projected work-hours. A lot of the cost comes from needing 50-100 transducers to get a useable image."

https://news.ycombinator.com/item?id=13231831

So you can make a very low cost one, but you trade off what use cases it's good for.

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Ah, that makes a lot of sense - I was trying to find information on how ultrasound machines worked awhile ago, and most of the information I found just said that a ceramic piezo is used to emit the sound and measure the time until it returned. I could not fathom at the time what kind of math must be required to get a 2D image out of a single data point like that, and I couldn't find much elaboration on the subject.

But if it's just a few hundred piezos in an array, now THAT makes a lot more sense.

Yep. Array is the keyword that makes it easier to Google...phased arrays, curved arrays, etc. And of course, with a bunch of piezos, your signal processing problem is larger.

The point being that on these experiments, the sensor isn't an array of piezos, rather a single-element piezo. Cuts the costs (a fab invoices around 100-200e for such a sensor), but lowers the overall image quality.

I wonder if two sensors placed at a distance can make a huge difference, and how/if the image quality converges as you increase sensors.

One of the next experiment is to try with 8 small elements ;)

It's not an array of piezos (or at least, not a one-per-column array of transducers). It's a phased array which they use to rapidly scan the volume, iirc something like 32 emitters and a single receiver in a commercial unit.

Source: I looked into building one last time we had a baby but didn't get around to it.

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