Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: mriver8 on 08/01/2015 16:15:59

Title: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 08/01/2015 16:15:59
http://sara.com/DE/high_power_acoustics/high_power_acoustic_tech.html

I specifically need to construct a helmet myself but I must do it for under $300.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: alancalverd on 08/01/2015 17:25:35
You could try active noise-cancelling headphones.
Title: Could a wall of piezo materials, like barium titanate or PVDF, stop sound?
Post by: mriver8 on 08/05/2015 19:23:32
Could a wall of piezo materials, like barium titanate or PVDF, act as a shield preventing ultrasound directed through the air from reaching a target? See the attached diagram and assume the wall was instead constructed of piezo materials. Would a wall contructed of such material be enough? Or would it need a layer of piezo material, and other construction elements in your opinion?
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: evan_au on 08/05/2015 23:12:18
Much more cheaply (and lighter), a wall composed of foam packing sheets would prevent an ultrasound cannon from reaching the target.
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: alancalverd on 08/05/2015 23:34:53
Ultrasound in rapidly attenuated in air. Probably no need for a wall at all, and as Evan says, a soft, absorbent material or a dispersive matrix would be more use than an elastic material like barium titanate.
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: RD on 09/05/2015 02:23:05
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2Fforum%2Findex.php%3Faction%3Ddlattach%3Btopic%3D57270.0%3Battach%3D19650%3Bimage&hash=df5e31f3612c2944fc042fb1d478cc7a)
It would take something like a the engine of a jet aircraft (https://youtu.be/ZJ9uWsvR1l0?t=2m41s) to demolish a wall.
Even if you could miniaturise the jet so it could be hand-held, the user would be propelled (https://youtu.be/jEvdvnSqJbM?t=18s) backwards when they activated it , if they could hang on.
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: mriver8 on 09/05/2015 04:33:10
Much more cheaply (and lighter), a wall composed of foam packing sheets would prevent an ultrasound cannon from reaching the target.

No regular acoustic foam doesn't work. Neoprine and poly rubber for anechoic chambers works a little at about an inch thick but is not enough at that thickness. I should add the wall has to be under 1 inch thick.
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: mriver8 on 09/05/2015 04:35:31
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2Fforum%2Findex.php%3Faction%3Ddlattach%3Btopic%3D57270.0%3Battach%3D19650%3Bimage&hash=df5e31f3612c2944fc042fb1d478cc7a)
It would take something like a the engine of a jet aircraft (https://youtu.be/ZJ9uWsvR1l0?t=2m41s) to demolish a wall.
Even if you could miniaturise the jet so it could be hand-held, the user would be propelled (https://youtu.be/jEvdvnSqJbM?t=18s) backwards when they activated it , if they could hang on.

I used the diagram as an example. Assume sound was being projected at a different frequency and intensity and the wall is constructed of a piezo material.
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: alancalverd on 09/05/2015 09:41:18
Your attacker would be at less risk if he used dynamite, artillery, or a rocket.

Your defender would stand some chance if he knew the frequency and intensity of the sound wave, and had access to Google. You can't solve an unstated problem, but all the engineering data you need for this job is freely available.
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: evan_au on 09/05/2015 09:53:07
Quote from: mriver8
Neoprene and poly rubber for anechoic chambers works a little at about an inch thick but is not enough

OK, what is your application, and how much attenuation is needed, at what frequencies?

A set of earplugs from your local hardware store is very effective.

The most common exposure to powerful ultrasound is probably for pre-natal imaging of pregnant women. I think a thin layer of foam would be pretty effective at providing privacy for the fetus.

Walking down the street surrounded by a set of spiky pyramids (as found in anechoic chambers) would keep most people away...
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 10/05/2015 04:35:53
Yes that works but headphones don't cover the entire head and wearing headphones on the head all day with sound running isn't practical.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 10/05/2015 04:36:29
What about piezo materials?
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: mriver8 on 10/05/2015 06:00:36
What about silica sand?
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: evan_au on 10/05/2015 08:06:04
Quote from: mriver8
What about silica sand?
You seem to be proposing solutions, without knowing what the problem is...

How about you state your problem, and then solutions will flow.

Unfortunately, if the ultrasound is purely in your head, then no amount of external shielding will protect you.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: alancalverd on 10/05/2015 09:11:52
As on your other thread: what is the incoming spectrum and power, and what are your outgoing limits?

Nobody can help you design a solution if you haven't specified the problem, so let's start at the beginning.

In the wise words of my old navigation instructor: "start from where you are, then you won't get lost before you take off." 
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: evan_au on 10/05/2015 09:55:27
A mouthguard from your local sports store?

This protects a very common route by which ultrasound gets inside your head (http://en.wikipedia.org/wiki/Scaling_and_root_planing#Periodontal_Intervention) (and which won't be blocked by a helmet).
Title: Re: Could a wall of piezo materials, like barium titanate or PVDF, stop sound?
Post by: alancalverd on 10/05/2015 15:07:12
What about silica sand?

Cheese would be better. Difficult to build a wall out of sand, but the original model of the Manchester Ship Canal that was presented to Parliament for funding, was made of cheese and did the job very well. Processed mild cheddar is best
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: evan_au on 10/05/2015 21:48:17
Due to their similar nature, posts on "Could a wall of piezo materials, like barium titanate or PVDF, stop sound?" (from the same author) have been merged with this thread.

Future posts will carry the title: "What type of technology can deflect or block high powered acoustics?"

- Moderator

Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: evan_au on 10/05/2015 21:50:21
Seriously, you should talk to your doctor about this.

There are medications today that can attenuate the impact of external sources on your thoughts.
Title: Re: Could a wall constructed of piezo materials such as barium titanate, or PVDF?
Post by: mriver8 on 11/05/2015 08:02:04
Quote from: mriver8
What about silica sand?
You seem to be proposing solutions, without knowing what the problem is...

How about you state your problem, and then solutions will flow.

Unfortunately, if the ultrasound is purely in your head, then no amount of external shielding will protect you.

Ultrasound directed at over 140DB according to citations from various reports. High intensity ultrasound. Specifically at a intensity and freq that damages hair follicles due to friction.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 11/05/2015 08:39:04
As on your other thread: what is the incoming spectrum and power, and what are your outgoing limits?

Nobody can help you design a solution if you haven't specified the problem, so let's start at the beginning.

In the wise words of my old navigation instructor: "start from where you are, then you won't get lost before you take off."

See this jpeg
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 11/05/2015 08:41:45
This is the other part of the text.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: alancalverd on 11/05/2015 09:08:04
The references you quote are pretty consistent with everything I've said in this conversation:

damage mainly occurs to the auditory system, so blocking the ears alone will be effective

ultrasound disperses rapidly in air, so distance is effective

impulse pressure has the same effect independent of source, so a conventional explosive would present less danger to the attacker 

Best of all, find out what the attacker is wearing in your diagram. The backscatter from his weapon will be far greater than the forward transmission through a brick wall, so if it works for him, it will work for you. And don't forget the conservation of momentum: find out what he uses to absorb the recoil from his impulse weapon.

You can get a really good blast wave from any high explosive, and if you want to demolish a wall, water or sand bags will intensify the effect.

You can't protect yourself against every conceivable threat but you might take a look at the specification of the Kelvedon "secret nuclear bunker" - also worth a visit! - which was designed to protect my co-workers (I was to be located elsewhere, now demolished) against a direct 10 megaton airburst.

If you are concerned about longterm exposure, stay indoors. Ordinary brick walls and double-glazed windows are extremely effective against ultrasound.

If you are concerned about an actual, ongoing exposure, please measure it and let us know the spectrum and intensity. 
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 11/05/2015 21:39:12
The references you quote are pretty consistent with everything I've said in this conversation:

damage mainly occurs to the auditory system, so blocking the ears alone will be effective

ultrasound disperses rapidly in air, so distance is effective

impulse pressure has the same effect independent of source, so a conventional explosive would present less danger to the attacker 

Best of all, find out what the attacker is wearing in your diagram. The backscatter from his weapon will be far greater than the forward transmission through a brick wall, so if it works for him, it will work for you. And don't forget the conservation of momentum: find out what he uses to absorb the recoil from his impulse weapon.

You can get a really good blast wave from any high explosive, and if you want to demolish a wall, water or sand bags will intensify the effect.

You can't protect yourself against every conceivable threat but you might take a look at the specification of the Kelvedon "secret nuclear bunker" - also worth a visit! - which was designed to protect my co-workers (I was to be located elsewhere, now demolished) against a direct 10 megaton airburst.

If you are concerned about longterm exposure, stay indoors. Ordinary brick walls and double-glazed windows are extremely effective against ultrasound.

If you are concerned about an actual, ongoing exposure, please measure it and let us know the spectrum and intensity.


Double glazed windows and a dewar vessel I know about. The problem being presented is an attempt to develop protective headwear. The reason I asked about silica sand is because it's what shuttle tiles are made of but I think the tile fibers are fused at a few thousand degrees so I couldn't do that by any normal means. I was interested in piezo materials because if effective I beleive there is film that is pliable. The problem is I need a layer less than 2 inches thick and my initial design calls for a layer of polyhedral vacuum cells within a helmet layer so I was looking for a cheaper alternative to see if I can develop protective headwear. I'm curious how the sound would react to a helmet of piezo material. Specifically I'm wondering could a helmet turned into a passive ultrasonic transducer of sorts be an effective solution.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: Colin2B on 11/05/2015 23:48:59
Quote from: alancalverd link=topic=53767.msg458282#qmsg458282 date=1431331684
....Kelvedon "secret nuclear bunker" ..... ..... which was designed to protect my co-workers (I was to be located elsewhere, now demolished) against a direct 10 megaton airburst.
Kelvedon, that takes me back! Like you I was to be elsewhere, but I did go 'down the Hatch' for some tests and exercises. I assume you had to go through the survival training? I kept it up due to an interest in outdoors and wildlife tracking and some previous experience in civil defence. Scary times.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 12/05/2015 09:28:35
Let me reword what I'm asking then. If ultrasound was being projected at a high intensity what would happen once it hits a one inch barrier composed of a piezo material? Would all of the sound be converted to electricity or would some make it though if the barrier was made up of silica fibers like shuttle tiles, barium, polyvinylidene fluoride, etc.? At the intensities listed in the charts I posted sound still passes through about a one inch shield of ultrasound absorbing polyrubber specially made by the National Physics Labratory. The rubber I used is specifically made to absorb ultrasound in anechoic chambers and definately reduces the effect but not enough at only one inch, and the rubber is also a bit too stiff for me to easily work with.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: evan_au on 12/05/2015 12:37:48
Quote from: mriver8
could a helmet turned into a passive ultrasonic transducer of sorts be an effective solution [to block ultrasound]

If you wanted to irradiate your skull with ultrasound, a helmet with piezoelectric transducers would be an effective way to do it.

Injecting ultrasound into your body involves placing a piezoelectric transducer directly against your body, with a film of gel to give a good contact between the transducer and the skin.

If you want to stop the ultrasound, lift the transducer by just 1cm/half an inch, and almost no ultrasound passes the air gap.

So if you want to keep out the ultrasound, just stay at least 1cm away from any piezoelectric transducers in the environment.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: alancalverd on 12/05/2015 13:30:39
The rubber I used is specifically made to absorb ultrasound in anechoic chambers and definately reduces the effect but not enough at only one inch, and the rubber is also a bit too stiff for me to easily work with.

Please provide some numbers. "Not enough" is hardly a design specification.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 13/05/2015 01:17:43
The rubber I used is specifically made to absorb ultrasound in anechoic chambers and definately reduces the effect but not enough at only one inch, and the rubber is also a bit too stiff for me to easily work with.

Please provide some numbers. "Not enough" is hardly a design specification.

Blue polyurethane rubber material, single-ply nominally homogeneous layer
Thickness of tile: 10mm, tile dimensions: 300mm by 300mm o
Density of 1.01g/m3, is close to that of water
Specific gravity 1.01
Longitudinal wave speed (1-10MHz)  approx 1500m/s
Acoustic impedance 1.5MRayls
High insertion loss, approximated by 30dB/cm/MHz. Insertion loss at frequencies greater than 2MHz is in excess of 60dB.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: alancalverd on 14/05/2015 17:47:11
So there you have it (except that the density of water is 106 g/m3) All you need is to define the input amplitude and frequency (i.e. the numbers I keep asking for) and you can calculate the attenuation in decibels.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 14/05/2015 20:30:30
So there you have it (except that the density of water is 106 g/m3) All you need is to define the input amplitude and frequency (i.e. the numbers I keep asking for) and you can calculate the attenuation in decibels.

The attenuation of what? The rubber doesn't work well enough at 1 inch and isn't pliable enough to easily work with. What about a noise cancelling helmet do they exist?
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: alancalverd on 15/05/2015 00:14:00
The attenuation of what?
whatever it is you want to attenuate - presumably ultrasound
Quote
The rubber doesn't work well enough at 1 inch and isn't pliable enough to easily work with.
At what frequency and amplitude does it not "work well enough"? What value of attenuation would be "well enough"?

I can't solve a problem if you won't tell me what the problem is, so for the last time before I leave this thread altogether, what frequency and amplitude are you trying to shield against?

Quote
What about a noise cancelling helmet do they exist?
No. Only headphones.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 24/12/2015 09:03:19
The attenuation of what?
whatever it is you want to attenuate - presumably ultrasound
Quote
The rubber doesn't work well enough at 1 inch and isn't pliable enough to easily work with.
At what frequency and amplitude does it not "work well enough"? What value of attenuation would be "well enough"?

I can't solve a problem if you won't tell me what the problem is, so for the last time before I leave this thread altogether, what frequency and amplitude are you trying to shield against?

Quote
What about a noise cancelling helmet do they exist?
No. Only headphones.

It's an LRAD like SARA device. It projects sound that itches, heats, and can remove hair. That's all I know but it has to be similar to ultrasound hair removal.
Title: Re: What type of technology can deflect or block high powered acoustics?
Post by: mriver8 on 26/12/2015 05:58:28
What about this? Or a vacuum ice bucket?
Jem v. the US Navy's latest weapon - Bang Goes th…: