making a sonic lens

>>1193903
I assume you'd ideally want a parabolic lens instead of a spherical one? One way to get that would be to spin the molten plastic; the centripetal force will pull more material to the perimeter and make a parabola, just like with early spinning-mercury telescopes.

I think you'll have to heat (and cool) the plastic uniformly, otherwise you'll get stress gradients within it. The surface made by a ball-bearing simply being pressed into place might not be perfect enough, and you'll probably have to polish it regardless, so maybe try bolting a rod onto a ball-bearing and putting it in a drill so you can rotate it within the lens' hollow with polish on it. Might I ask what you're using to produce and detect these ultrasonic waves/phonons?

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>>1193912
Spherical will do for now.
An even earlier prototype has a surface milled with a round bit and has been somewhat pollished. Still with noticable scores and works ok so far. So I think the bearing surface will be good enough.
I don't know about stress gradients, guess thats up to test.
>Might I ask what you're using to produce and detect these ultrasonic waves/phonons?
A custom transceiver hooked up to a piezo element that gets glued to the flat side of the lens. Here's a image of the Signal I get out of it so far.

>>1193912
>the centripetal force will pull more material to the perimeter
Not really, but I know what you mean.

>>1194172
Well I guess technically the centripetal force is pulling inwards, not outwards. But there aren't really defined terms for describing individual unbalanced racial forces.

>>1193912
>the centrifugal force will push more material to the perimeter

OP again. So far Acrylic seems to be a good choice. I guess I can heat the bearing up to ~110°C press it in and pull it out when cold. If necessary I could reheat and cool the entire thing later.

>>1194511
Are you getting any differential heating/cooling artefacts?

>>1194341
I suppose you could say that the centripetal force acted by walls of the mould on the molten acrylic pushes the acrylic up. Or that the centrifugal force acted by the molten acrylic on the immovable walls of the mould exponentially increase the pressure in the smelt radially from the centre. I don't know how to word it. Anyway, it's like asking what is shaping a sword; the hammer, or the anvil? It's both. Where centripetal force goes, centrifugal force follows. One can not exist without the other.

>>1195255
Ah, so that's what centrifugal force refers to. We kind of skirted around the term in class in much the same way that we skirt around the strong and weak nuclear forces, or around general relativity with respect to special relativity.

>>1194551
haven't done it yet and propably won't get around it this week. But I guess if it happens I could probably find a way to heat up the enire thing and cool it down slowly without destroying the shape.

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>>1193903 scanning ultrasonic microscope
>I casted this lens out of some clear resin

Doesn't know what plastic he used....

"I builded me this here micro-skope outa stuff I had lay'in around.