> Making a photo sensor must be thousands of times more complicated than ultrasounds sensors. What makes you think that? Photo sensors have no moving parts, p

> Making a photo sensor must be thousands of times more complicated than ultrasounds sensors. What makes you think that? Photo sensors have no moving parts, photons are the carriers of the electromagnetic force, so they readily interface with electronics given the right interface material; any semiconductor material with a matching bandgap will do, photons interacting with a bandgap produces free charge carriers; this is exactly what you're after. The rest is chipscale manufacturing, i.e. lots of sensor cells in a repetetive pattern. You can easily mass produce that in large quantities using photolithography methods, yet even if your process were to bad, that you'd get a low yield it would still be profitable. Ultrasound on the other hand is acoustics, i.e. mechanical waves. So you're dealing with moving parts, mechanics. Transducers are discrete parts, they can't (yet) be manufactured at chip scale. They're ceramics, and there are lot of parameters that go into manufacturing ceramics which limit the amount that can be produced in a single batch. And then you've to deal with electronics that's not over waaay beyond your typical hobbist level; it's in fact so complex that it goes over the head of most professional electrical engineers and there are companies who are specialised in ultrasonics transducer electronics consulting, doing the difficult design work for the large brand names.