> direct sampling ADC at 80 MHz or less is far from an impossible task
The Sonix linked below has 32 40MHz 10bit ADC channels, which is a factor of 64 off from the 80 MHz figure if one were to assume 8 bit, and places us firmly into the realm of several-hundred-dollar ADCs.
Not impossible, but I'm pretty sure that's where much of the cost is hidden.
That kind of figures is better than nothing but is exactly what I had in mind between toy systems and what good quality ones are able to provide. 80MHz is actually not mandatory but 40MHz starts to be really on the low end side, I think, but for low frequency probes that should still be quite good. Of course if you stick to simple B-mode you can get something visible with pretty much anything. 32 channels seems to start to be quite low, though, but yeah, better than nothing.
If you start to drive your TX path with "small" (depending on the number of channels) FPGA or CPLD, yeah this is more possible than with a raspberry pi GPIOs, this is even how some good ultrasound machines are build (depending on the volume)
In the end the cost of the hardware will be not far from the production cost of a "conventional" ultrasound machine. Because that industry has "low" volumes and very high R&D costs (especially for machines intended for diagnostic use), the difference between production cost and market price is very high. If you can eliminate part of that difference because you operate in another context, that's one way to drive the price down.
So yes, it should be possible to build one with limited capabilities for a few k$ per unit. (Spending various amount of money on R&D, depending what you're doing precisely.)
> Because that industry has "low" volumes and very high R&D costs (especially for machines intended for diagnostic use), the difference between production cost and market price is very high.
This is true, but this is only half of the story : the market price is also high because the elasticity of the demand for medical devices is really low. The hospitals charge a lot of money to their customers and their willingness to pay is also high.
I've developed software for customers working in the legal industry and it's the same kind of market: these people pay a lot for really simple stuff because they have money and want to get things done.
Hm, on the buyer side, it depends on the country but in some it is actually very competitive. So smaller players have a hard time to survive simply because of their lower volumes but similar R&D costs...
Plus an ultrasound exam is not too expensive in some (most?) countries.
10 bit, 32 channel, 80 Msample ADC is <$300 [1] at prototype quantities, and <$150 at production quantities. 12 bit, 64 channel, 80 Msample ADC could be done with 4 of these [2] for $620.
An AM5716 or 5726 would be $30-$40 (although buying one is a little trickier). Thats 7-8 processors in one, plus 1-2 DSPs. Plenty of power to handle all the processing required. Even a 128 channel device should only be ~$2000 in parts (minus the transducer). One with limited capabilities should be <$500 (again, minus transducer). Much less if you make a few more compromises in the ADCs.
We can make SDRs for incredibly low prices nowadays, the only real difference between that and ultrasound is the number of channels. The only reasons ultrasound machines cost more than 5 grand are economic inefficiencies. The engineering has been solid for a long while now.
Very old machine did some analog processing. Then it switched to digital on dedicated hardware. New machines can do all the processing in software, running on conventional hardware.
There is all kind of fun stuff that you can do with ultrasound, and some are similar to 'synthetic aperture radar'. However, 32 channel is still quite low. Lots of probes for humans are commonly using ~100 channels.
I would expect that they are looking at the return as an amplitude modulated and phase-shifted signal at the carrier frequency. They remove the carrier frequency and then look at the (much slower) modulation frequency.
I'm not sure what you gain from looking directly at the carrier frequency...
The relative bandwidth in ultasound is immense conpared to radar etc where a relatively narrow bandwidth is used. As an example one of our probes in university days was something like from 5 to 30MHz. Doesn't save much if we would mix it down that 5. Instead of 60MHz ADC we would need 50MHz. Not worth it.
Phase information is preserved when down converting. But resolution certainly will depend on bandwidth. I read that ultrasound propagation delay is ~650 ns / mm... this is something like 500 KHz for 1 mm (using rise-time * bandwidth = .35 approximation).
It's definitely one of the most expensive parts, but its still a factor of 100 cost difference in parts to product. Even assuming there are 10 parts that all cost a few hundred dollars each (processor, memory, transducer, ADC, amplifier), thats still a 90% profit margin before r&d and other overhead. It's very high.
The Sonix linked below has 32 40MHz 10bit ADC channels, which is a factor of 64 off from the 80 MHz figure if one were to assume 8 bit, and places us firmly into the realm of several-hundred-dollar ADCs.
Not impossible, but I'm pretty sure that's where much of the cost is hidden.