[WJW]

You could have at least three types of linear mixers:

- One where some type of spoon goes back and forth. This would probably just be worse than a rotary mixer though.

- One where the entire "basin" oscillates back and forth like a seesaw, like the machines they have at the blood bank to make sure the blood mixes well with the anticoagulant in the bag(s).

- One where the basin is airtight and vibrated up and down vigorously. I could see this work quite well for dry-ish mixtures of different particles, like if you have flour and sugar together in a container and want them mixed.

[echoangle]

I think the third point (vibrating a container to mix different dry particles) is actually the worst way to do it. If the particles have different sizes (or densities technically, I think), they will separate when vibrated, not mix together. If you ever tried to mix Cereals by shaking, you know what I mean. The proper technique is turning over the container continuously to mix the different layers, like in a cement mixer.

[WJW]

I was thinking more about "tossing a salad" type vibrations that get high enough to completely get all the particles airborne, possibly with some sort of mechanical structure above the mixture interfering with the mixing. If you just vibrate everything in-place then all the smaller particles will obviously just fall to the bottom.

I got curious and found https://making.com/equipment/high-frequency-vibratory-mixer, but that is for liquids and not for solids.