[MUSIC PLAYING]
DIANA COWERN: Thank you to 23andMe
for supporting PBS Digital Studios.
It sounds terrible.
It does.
I guess you go more that way.
We might want to try--
Something's wrong.
--messing around with these wires too, you know.
Let's turn it off.
Hey, I'm Diana.
[COUGH]
[GROANING]
We're going to get through this.
I'm Diana.
You're watching Physics Girl.
And that was us trying to make a levitator.
A few months back I got this email out of the blue
from the University of Bristol about this DIY,
make it at home acoustic levitator kit.
Have you ever heard of an acoustic levitator?
What?
I haven't
Yes.
I have.
DIANA COWERN: Yes?
Yeah.
I thought it was some sort of guitar
that like flew up in the air.
Magic.
I get it.
You may not have heard of this.
But the idea is that you use sound waves
from a bunch of different speakers pointed
in different directions, focused on a point.
And you can levitate something at that point in mid air.
This is real, yo.
I showed one of these from another research group
at the University of Tokyo three years ago in a video.
But this email was saying that anyone
can make one of these at home.
I was skeptical.
Then this one.
[KNOCK KNOCK]
Come in.
Hello.
Divosh!
Welcome to the party.
Oh, you guys are already started.
We already started.
This is a pencil sharpener.
Uh, no.
[CHUCKLING]
[MUSIC PLAYING]
DIANA COWERN: We're in America.
This is a problem.
Let's see if I got this.
OK.
You read to try?
Are you ready?
Five.
Oh!
Oh my god.
It's going.
DIANA COWERN: Oh my god.
Oh, yeah it is.
[SHRIEKING]
And my god.
It's so cool.
DIANA COWERN: Houston, we have levitation.
We just made this happen here.
[INAUDIBLE]
Yeah.
It's going to get ripped apart.
Oh!
It did get ripped apart.
[DIANA GIGGLING]
I'm serious.
DIANA COWERN: Are you guys excited?
This is amazing.
DIANA COWERN: How do you feel?
Really excited.
I think-- look, look, look.
I think this is half of the spacing we had before.
DIANA COWERN: Oh cool.
Yeah.
The technology behind this has been around for decades.
And I'm going to explain it later in this video,
for those of you who are like me and cannot go through the rest
of your life without understanding how something
works.
But the genius of this little at home project
is making it available for everyone.
Why did the original group from the University of Bristol
design this?
Don't get me wrong.
I'm appreciative.
This is super dope.
But that was the mystery to me.
And so I traveled to the University of Bristol
in England to ask.
[MUSIC PLAYING]
ASIER MARZO: So my name is Asier Marzo.
I'm a research assistant at the mechanical engineering
department.
And I always work with acoustic levitation.
It's open for everyone.
They can build it at home and experiment as they wish.
But that's the good thing about democratizing the technology.
You know, it's out there.
And everyone can do with it whatever they want.
Some people had very nice suggestions,
like could we put a seed and germinate it
while it's levitating.
Or can we put a neck of an insect,
and will it hatch while it's levitating?
Acoustic levitation in practice seems complicated.
So how is it possible to make a kit that someone like me,
and Dan, and Kyle could make in three hours?
So I should confess, Dan is a physicist.
Kyle's an engineer.
And all three of us have at least some electronics
and soldering experience.
But we're not frequent hobbyists.
We just like making things that inspire us to say,
I don't know if this is actually going to work.
But it does work.
So let's see how.
The main concept here is standing waves.
Standing waves are not normal waves.
They need very special conditions.
A regular wave in physics is just a disturbance
traveling through a medium.
Like when you disturb a slinky at one end,
the disturbance, or wave, travels to the other and.
If I then constrain or bound the slinky at the other end,
the wave will reflect back.
You can test this out by being that weird person that
yells at canyons.
Your vocal disturbance reflects back.
Now, if I send wave after wave down the slinky,
they continue to reflect back.
And what I get is two waves, one moving at me, one moving away
from me.
But obviously the slinky can't be in both places at once.
So the waves combine.
They interfere.
They add when they're on top of each other,
and they subtract when they're not.
And something very special can happen
when the two waves interfere at just the right conditions.
You can get a wave that doesn't appear
to be moving in any direction.
That's a standing wave.
The places along the standing wave that aren't moving at all
are called nodes.
Remember the nodes.
They're important, y'all.
Standing waves can happen anywhere you
use the right frequency on a confined medium.
They can also happen in two dimensions
by vibrating or sending waves along a 2D plate.
With the right frequency, on a confined medium.
The places where the sand collects are the nodes.
Remember the nodes.
Now, in three dimensions--
I think you see where this is going-- we need a 3D medium we
can send waves through.
Air.
And we can create a three dimensional wave profile
with nodes.
The nodes here are the places where the air is not moving,
even though it's moving a lot everywhere
else around the node.
The nodes are the zen zones.
If you're at the node, you can chill there.
Anywhere else and you'll get knocked away.
So in our levitator our little pieces of styrofoam and lint
hang out at the nodes.
They get held there at the nodes,
because if they're anywhere else they'll
get pushed back in or pushed out.
And there you have acoustic levitation.
It's more like acoustic tweezers.
Acoustic straightjackets?
Mosh pits?
Metaphors are failing today.
Ugh.
So how is it possible to make an acoustic levitator
with a perfect 3D wave profile in your home?
The key is this 3D printed shape.
ASIER MARZO: All these speakers, they
need to be at a specific position,
and within a specific angle.
And one way of achieving that is to design this base and 3D
print it.
If you tried to put them in a flat surface,
it wouldn't work as well.
You can see that there is only one signal
going through all the thopter's users.
And that's possible because the focusing
is done because the shape.
This has a ball shape that naturally
focus all the acoustic power in the center of the levitator.
And if you have sources in a flat surface
with the same face, that would not create levitation.
The structure puts all the transducers
at just the right distance so that all the waves
add and cancel in just the right way.
I had been curious about why they designed this DIY kit.
And as Dr. Marzo said, it was so they could
democratize the technology.
And plus, it's super cool, which I
think should be the only prerequisite for doing science.
You can quote me on that.
But there are other practical reasons
for perfecting levitation with sound.
People are very familiar with magnetic levitation.
And it's good because it's very strong.
But it has a big limitation.
And that's the materials that you can levitate.
They need to be ferromagnetic, diamagnetic, or paramagnetic.
With acoustic levitation you can levitate any sort of material.
So it could be liquids.
It could be powder.
It could be electronic components, insects.
Basically you name it.
Any material with a certain limit intensity.
Yeah.
So you want to be able to levitate
any kinds of materials.
Although there is a limit with current technology in size
and density of things that you can levitate.
So I was also curious about what other kinds of research they'll
be doing into acoustic levitators.
ASIER MARZO: All the levitators that we have seen,
they are a standing wave levitator.
DIANA COWERN: Yeah.
Meaning that there are waves coming from the top and waves
coming from the bottom.
They interfere and create a standing wave.
This one is different.
There is only one wave.
DIANA COWERN: Yeah.
It looks like a plunger.
ASIER MARZO: Yeah.
This one can still levitate particles
because it creates a field that looks like a pair of fingers
holding the particle.
DIANA COWERN: OK.
ASIER MARZO: It doesn't create a standing wave,
but it can still levitate a particle.
[MUSIC PLAYING]
As I said, we have the challenge of size.
Can we levitate particles bigger than half the wavelength?
That's something that we are working on.
And another challenge is manipulating multiple particles
individually, having a group of particles
and they are all moving independently from one another.
That would be so cool, to have like synchronized dancing
of bugs.
Fake ones?
The last thing if you want to do this at home,
I've got just some tips and tricks that we figured out.
Dr. Marzo's team put up a really easy to follow instructables
project online.
I will link to that in the description.
And when you get to the step where he says,
check the polarity of these transducers, the plus
and minus, heed that warning.
They're marked plus and minus, but we tested them all.
And they were completely random.
Don't trust the manufacturer.
Also, make sure all of your soldering connections are good.
We were not able to get water to levitate with this one, yet.
We need an oscilloscope to test that all the transducers are
working, and we didn't have one in time to make this video.
But that just means that our 3D wave profile in here
is not ideal.
Oh my gosh, yes!
If you're filming this thing your microphone
may not be happy.
These transducers are putting out 40,000 hertz,
which is above human hearing.
It's about twice the frequency of the top of human hearing.
But some microphones pick it up.
So be aware of that.
And yeah, happy levitating.
And thanks for watching.
And have happy physicsing.
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[MUSIC PLAYING]