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Author Topic: What type of technology can deflect or block high powered acoustics?  (Read 8631 times)

Offline mriver8

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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.


 

Offline alancalverd

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You could try active noise-cancelling headphones.
 

Offline mriver8

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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?
« Last Edit: 10/05/2015 21:40:38 by evan_au »
 

Offline evan_au

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Much more cheaply (and lighter), a wall composed of foam packing sheets would prevent an ultrasound cannon from reaching the target.
 

Offline alancalverd

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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.
 

Offline RD

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It would take something like a the engine of a jet aircraft to demolish a wall.
Even if you could miniaturise the jet so it could be hand-held, the user would be propelled backwards when they activated it , if they could hang on.
« Last Edit: 09/05/2015 02:48:17 by RD »
 

Offline mriver8

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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.
 

Offline mriver8

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It would take something like a the engine of a jet aircraft to demolish a wall.
Even if you could miniaturise the jet so it could be hand-held, the user would be propelled 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.
 

Offline alancalverd

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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.
 

Offline evan_au

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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...
 

Offline mriver8

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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.
 

Offline mriver8

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What about piezo materials?
 

Offline mriver8

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What about silica sand?
 

Offline evan_au

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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.
 

Offline alancalverd

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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." 
 

Offline evan_au

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A mouthguard from your local sports store?

This protects a very common route by which ultrasound gets inside your head (and which won't be blocked by a helmet).
 

Offline alancalverd

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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
 

Offline evan_au

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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

 

Offline evan_au

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Seriously, you should talk to your doctor about this.

There are medications today that can attenuate the impact of external sources on your thoughts.
 

Offline mriver8

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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.
 

Offline mriver8

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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
 

Offline mriver8

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This is the other part of the text.
 

Offline alancalverd

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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. 
« Last Edit: 11/05/2015 09:44:20 by alancalverd »
 

Offline mriver8

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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.
 

Offline Colin2B

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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.
 

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