40KHz xducer, I finally Get It

[Bill Beaty]

Stick your little ultrasound transducer on a sig generator, and at 10Vrms or so, it starts to create detectable "levitation" forces. Feeble though.

But instead, sprinkle tiny styrofoam beads on the bench, and fire the sound beam sideways. Wind! You can cause the fragments to scatter. It's clearly not just radiation pressure; the beam is moving the air as well. (Same as water jets created by ultrasonic humidifiers.)





((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty a chem washington edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph X3-6195 http://staff.washington.edu/wbeaty/

 

[John Larkin]

On Tue, 30 Apr 2019 17:05:46 -0700 (PDT), Bill Beaty
<billb@eskimo.com> wrote:

Stick your little ultrasound transducer on a sig generator, and at 10Vrms or so, it starts to create detectable "levitation" forces. Feeble though.

But instead, sprinkle tiny styrofoam beads on the bench, and fire the sound beam sideways. Wind! You can cause the fragments to scatter. It's clearly not just radiation pressure; the beam is moving the air as well. (Same as water jets created by ultrasonic humidifiers.)

I guess if you have a surface that's vibrating hard enough, air can be
compressed more on one sweep than on the other, since air can't go
below -1 atm. Sort of a rectifier.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Bill Beaty]

On Tuesday, April 30, 2019 at 6:17:25 PM UTC-7, John Larkin wrote:

I guess if you have a surface that's vibrating hard enough, air can be
compressed more on one sweep than on the other, since air can't go
below -1 atm. Sort of a rectifier.

Exactly that. This also explains the "sound laser" or "hypersonic
loudspeaker," the Woody Norris LRAD, where AM or DSB-modulated ultrasound
will spontaneously transduce itself into the audible spectrum. Air
itself is the detector diode? That means we can bounce a small air-jet
off a mirror surface, by bouncing the ultrasound.

I wonder how much of "sonic levitation" is from this fluid-streaming
effect, rather than exotic "acoustic pressure." When underwater, a
transducer can actually provide significant propulsion, via the water
jet coming off the vibrating surface. I've seen a patent for a "stomach
camera" micro-drone that free-swims in a water-filled gut, propelled by
tiny sonic-streaming transducers. Build a very confusing RC boat with
no visible props or even jet orifices, with ultrasound propulsion
through flexible solid surfaces.

Anyway, if you have any of those 40KHz transducers ($1 cheap from various
surplus mailorder,) just poke at styrofoam to get some low-mass frag-
ments. Then blow them around on the desk. Also: electrostatics! The
styro-bits will easily roll around at first, but then they charge up
and start attracting to the table. Same with aluminum surface. Maybe
with extremely clean pcb copper they'll keep rolling under acoustic power.
That, or extremely damp weather. (Also, I cheated by using the extremely
spherical 4mm beads from a 70s-era beanbag chair.)


---
((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty a chem washington edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph X3-6195 http://staff.washington.edu/wbeaty/

 

[amdx]

On 4/30/2019 7:05 PM, Bill Beaty wrote:

Stick your little ultrasound transducer on a sig generator, and at 10Vrms or so, it starts to create detectable "levitation" forces. Feeble though.

But instead, sprinkle tiny styrofoam beads on the bench, and fire the sound beam sideways. Wind! You can cause the fragments to scatter. It's clearly not just radiation pressure; the beam is moving the air as well. (Same as water jets created by ultrasonic humidifiers.)





((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty a chem washington edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph X3-6195 http://staff.washington.edu/wbeaty/

20 years ago I worked manufacturing an ultrasonic transducer and
amplifier. One of our demos was putting the transducer in an aquarium
face up with about 5" of water above it. Then pulsing the transducer
with ultrasound. We could get about a 6" plume of mist/water above the
water.
The piezo was a 2" ceramic on a 4" faceplate. The amp pulsed it at
660kHz. We had two models 250Watt and 1000watt.
Plume pictures, >
https://web.archive.org/web/20060127221507/http://www.ultrasonic-energy.com/yadda.html
Should have been better pictures, but the best I got.

Mikek

 

[Tim Williams]

Related:
https://www.eevblog.com/forum/projects/how-goos-is-this-ultra-thin-piezo-electric-blower/

It's not always easy to experience or appreciate, but waves do indeed carry
momentum. A wave is the medium moving out of the way of something, after
all! With the right phase and polarization (give or take the multiple modes
and dispersion that acoustic waves support), the momentum can be forwards or
backwards, or rotating!

I don't know if nonlinear effects (jetting, rarefaction) apply to the first
example, but they aren't necessary to explain the observation. And also,
they surely do occur at some intensity, which probably helps even more!

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Bill Beaty" <billb@eskimo.com> wrote in message
news:5cd07bc3-3aca-4393-bb0f-9b4d024823af@googlegroups.com...

Stick your little ultrasound transducer on a sig generator, and at 10Vrms or
so, it starts to create detectable "levitation" forces. Feeble though.

But instead, sprinkle tiny styrofoam beads on the bench, and fire the sound
beam sideways. Wind! You can cause the fragments to scatter. It's clearly
not just radiation pressure; the beam is moving the air as well. (Same as
water jets created by ultrasonic humidifiers.)





((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty a chem washington edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph X3-6195 http://staff.washington.edu/wbeaty/

 

[John Larkin]

On Tue, 30 Apr 2019 19:06:26 -0700 (PDT), Bill Beaty
<billb@eskimo.com> wrote:

On Tuesday, April 30, 2019 at 6:17:25 PM UTC-7, John Larkin wrote:

I guess if you have a surface that's vibrating hard enough, air can be
compressed more on one sweep than on the other, since air can't go
below -1 atm. Sort of a rectifier.


Exactly that. This also explains the "sound laser" or "hypersonic
loudspeaker," the Woody Norris LRAD, where AM or DSB-modulated ultrasound
will spontaneously transduce itself into the audible spectrum. Air
itself is the detector diode? That means we can bounce a small air-jet
off a mirror surface, by bouncing the ultrasound.

So could we focus ultrasound and make a spot of air glow, like the
soniluminescence thing in water? Cavitate air?

Probably not. Bummer. Maybe some less dramatic optical effects.

Perpendicular sound beams could mix and scatter and make sum and
product frequencies.

There are no longitudinal (compression) electromagnetic waves, so no
equivalent rectification of light, but aren't gravitation waves
longitudinal?

I wonder how much of "sonic levitation" is from this fluid-streaming
effect, rather than exotic "acoustic pressure." When underwater, a
transducer can actually provide significant propulsion, via the water
jet coming off the vibrating surface. I've seen a patent for a "stomach
camera" micro-drone that free-swims in a water-filled gut, propelled by
tiny sonic-streaming transducers. Build a very confusing RC boat with
no visible props or even jet orifices, with ultrasound propulsion
through flexible solid surfaces.

Anyway, if you have any of those 40KHz transducers ($1 cheap from various
surplus mailorder,) just poke at styrofoam to get some low-mass frag-
ments. Then blow them around on the desk. Also: electrostatics! The
styro-bits will easily roll around at first, but then they charge up
and start attracting to the table. Same with aluminum surface. Maybe
with extremely clean pcb copper they'll keep rolling under acoustic power.
That, or extremely damp weather. (Also, I cheated by using the extremely
spherical 4mm beads from a 70s-era beanbag chair.)

Nothing worse than a million charged styrofoam bits all over the room.
The only cure for that is to burn the building down.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Tim Williams]

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:jn7icedcfn6egq2vsqpm7okvt7j3sm18ud@4ax.com...

There are no longitudinal (compression) electromagnetic waves, so no
equivalent rectification of light, but aren't gravitation waves
longitudinal?

There's an equivalent gravitomagnetic effect, which is (IIRC) a 3+1D
equivalent (albeit possibly a low-rate approximation?) of the 4D (spacetime)
warping. (This explains why g-waves can travel at the speed of light
without orbits being unstable.)

(A reminder that, in Einstein tensor notation, Maxwell's equations are
practically trivial, a single expression. So a lot of functionality is
encoded in that format.)

G-waves are also quadrupole or higher, although I don't know if that has any
relevance for apparent direction of the field.

L-waves can't be polarized, right? G-waves are, AFAIK. That would be a
problem.

I'm not aware of any linearity quirks in g-waves until relativistic levels,
i.e., until you're in the Planck energy scale, or orbiting a small black
hole, everything works the same. Same with E&M, except the energy levels
are rather more easily accessible thanks to QM (pair production and such, on
the scale of ~1 MeV).

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Bill Beaty]

On Tuesday, April 30, 2019 at 9:35:07 PM UTC-7, John Larkin wrote:

So could we focus ultrasound and make a spot of air glow, like the
soniluminescence thing in water? Cavitate air?

Probably not. Bummer.

Or maybe yes, because "bubble resonance" is a real effect in
fluids. Is there an air analog? Maybe a gas-cavitation pocket
would slam shut and then bounce repeatedly (so try driving it at
resonance for better efficiency.)

> Maybe some less dramatic optical effects.

I have an old 1920s book on "supersonics" which shows it.

They photographed a little silvery donut shape hanging
in space in front of a compressor-powered ultrasonic
whistle. It's a cavitation in air, and reflects light
just like a thermal mirage, when viewed at grazing angle.

I've often wondered if the giant subsonic meter-scale version
might exist, using an empty room as a 100Hz resonator. Try to
pass your hand through it, and find a back-pressure, an invisible
wall? (While maybe your ears bleed, and also your lungs cave in.)

Perpendicular sound beams could mix and scatter and make sum
and product frequencies.

A PVdF piezo-membrane, if bent, makes a good audio transducer.
If slathered on density-neutralized mylar balloon, we might propel
the balloon by ultrasonic gas-streaming, by driving a section of
the membrane at 100KHz or so. Sell it to NASA (who had plans for
using little fans to propel their zero-gee drones around the ISS
in free fall.)

Nothing worse than a million charged styrofoam bits all
over the room. The only cure for that is to burn the
building down.

I have a cubic meter of 2mm styrofoam spheres. Once they
get loose on wood floors, you can see all the room air motions
and traveling vorticities (and 40KHz ultrasound beams if more
than a few tens of mW.) Anybody want a sample?

PS

Goldmine is selling at $1 until midnight:
https://www.goldmine-elec-products.com/prodinfo.asp?number=G19049
This so-called "receiver" is really just a standard transceiver,
but slightly de-tuned from 40KHz, for use as security prox sensors
when paired with a "transmitter" version. Use as rocket engines
for propelling very tiny low-mass vehicles?



--
((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty a chem washington edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph X3-6195 http://staff.washington.edu/wbeaty/

 

[nuny@bid.nes]

On Tuesday, April 30, 2019 at 5:05:52 PM UTC-7, Bill Beaty wrote:

Stick your little ultrasound transducer on a sig generator, and at 10Vrms
or so, it starts to create detectable "levitation" forces. Feeble though.

But instead, sprinkle tiny styrofoam beads on the bench, and fire the sound
beam sideways. Wind! You can cause the fragments to scatter. It's clearly
not just radiation pressure; the beam is moving the air as well. (Same as
water jets created by ultrasonic humidifiers.)

I just wanted to thank you for existing and starting threads like this one.

You've been talking mostly about micropower uses, but the topic reminded me of the SciAm article about sticking large artificial quartz crystals into microwave cavities to transduce microwaves into high-power "kilomegacycle" ultrasound beams in air.

https://www.jstor.org/stable/24936184?seq=1#page_scan_tab_contents

So maybe those lab-scale "levitation" tricks can actually be scaled up to picking up cars and stuff?


Mark L. Fergerson

 

[Bill Beaty]

On Saturday, May 4, 2019 at 2:07:33 AM UTC-7, nu...@bid.nes wrote:

I just wanted to thank you for existing and starting threads like

CL Stong will never die!

https://www.jstor.org/stable/24936184?seq=1#page_scan_tab_contents

Coooool! Parametric microwave audio amplifiers. In an old 70s-era
physics dictionary, they called this spectrum "hypersound" rather
than "ultrasound." At some point the wavelength comes close to
lattice spacing of solid objects, and the speed of sound slows
down to the speed of heat conduction.

So maybe those lab-scale "levitation" tricks can actually
be scaled up to picking up cars and stuff?

Besides the "wind," wouldn't the nonlinearity cause an
acoustic standing wave to have slightly higher net pressure
than ambient? A "sound pillow" trapped between floor and
object then lifts the object.

Also, ultrasound in water, at optical wavelengths, can form
off-axis holograms on the water surface, producing images of
submerged objects (such as animals with invisible flesh, moving
skeletons.) Need laser ref beam, also acoustic ref beam.


((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
wbeaty a uw edu UW Chem Dept, Bagley Hall RM74
billb a eskimo com Box 351700, Seattle, WA 98195-1700
ph X3-6195 http://staff.washington.edu/wbeaty/

 

[whit3rd]

On Thursday, May 9, 2019 at 7:18:27 PM UTC-7, Bill Beaty wrote:

On Saturday, May 4, 2019 at 2:07:33 AM UTC-7, nu...@bid.nes wrote:

Besides the "wind," wouldn't the nonlinearity cause an
acoustic standing wave to have slightly higher net pressure
than ambient? A "sound pillow" trapped between floor and
object then lifts the object.

At 40 kHz, wavelength in air is 8mm or so; a standing wave
might easily have higher air temperature at antinodes than
at nodes. Even light solids might dissipate energy as heat.

So, maybe your 2mm beads can become hot-air bouyant?