The Naked Scientists

The Naked Scientists Forum

Author Topic: Can neodymium magnets be used to shield against ultrasound?  (Read 26795 times)

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4696
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: Can neodymium magnets be used to shield against ultrasound?
« Reply #50 on: 05/05/2015 00:06:51 »
I don't know much about engineering.

So it would appear. However you might consider the use of active noise reduction (ANR) headphones. We use them in aircraft (particularly helicopters) and MRI machines. A transducer listens to the incoming noise and generates a signal in antiphase to cancel the pressure wave. You can see the best ones in TV news reports: Bose trademark is a black headset, David Clark makes military green ones. Not cheap but amazingly effective.
 

Offline mriver8

  • Sr. Member
  • ****
  • Posts: 120
    • View Profile
Re: Can neodymium magnets be used to shield against ultrasound?
« Reply #51 on: 05/05/2015 04:08:33 »

[/quote]

So it would appear. However you might consider the use of active noise reduction (ANR) headphones. We use them in aircraft (particularly helicopters) and MRI machines. A transducer listens to the incoming noise and generates a signal in antiphase to cancel the pressure wave. You can see the best ones in TV news reports: Bose trademark is a black headset, David Clark makes military green ones. Not cheap but amazingly effective.
[/quote]


I think the headphones I have have a bit of piezo material inside that is converting the ultrasound into electricity and thereby blocking it somewhat. However I was interested in constructing something larger. I've never built speakers with piezoeletic material or a transducer so I would have to research the construction of one to see if I could apply the principles into something else. I don't know anything about engineering but my first thought was an outer layer of a piezo material like used in transducers, and an inner layer of some sort of conductive material, or poly rubber might be effective
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4696
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: Can neodymium magnets be used to shield against ultrasound?
« Reply #52 on: 05/05/2015 09:42:24 »
The problem with active noise reduction over a large area is the short wavelength of ultrasound. At 20 kHz the wavelength is around 1.7 cm so the peak of the incoming pressure wave at any point on, say, a 20 cm sphere (physicist's model of a head) is going to be quite different from the measured value a centimeter away.

You could produce a fairly soundproof planar wall with an array of independent transducers. This works OK for low frequency deadening of large rooms but you will need a vary large number of transducers. If you are to intercept and cancel, say, 50 MHz transmissions over a  30 cm square, you need 3600 independent elements, each consisting of a signal generator, an amplifier and a receiver.

I think the first step in your mission is to measure whatever it is that you think you are trying to nullify. Start with a broadband ultrasound receiver and a spectrum analyser. I recommend the Picoscope range of USB plug-in analysers - good value and the software is ridiculously easy to use. Not sure what transducer to use but http://parsonicscorp.com/  may be helpful. The problem is that most commercial transducers are tuned to send and receive at a sharp resonant frequency. However as you are looking for damage-inducing pressure levels, you might find that an old television remote control or a parking sensor does the job adequately.
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8122
  • Thanked: 53 times
    • View Profile
Re: Can neodymium magnets be used to shield against ultrasound?
« Reply #53 on: 05/05/2015 13:01:51 »
I think the first step in your mission is to measure whatever it is that you think you are trying to nullify. Start with a broadband ultrasound receiver and a spectrum analyser.

Or a cheap bat-detector ... http://www.thenakedscientists.com/forum/index.php?topic=52647.msg442735#msg442735  [ reply #9 ].

I appreciate mriver8's reluctance to accept voices they hear are almost-certainly endogenous, rather than exogenous, but hearing-voices is a well-recognised mental-health problem, see ... http://www.hearing-voices.org/voices-visions/comment-page-1/ . Some suffers incorrectly believe the voice is being beamed into their skull , usually via radio or some other technology, but this is incorrect.
« Last Edit: 05/05/2015 13:21:08 by RD »
 

Offline mriver8

  • Sr. Member
  • ****
  • Posts: 120
    • View Profile
Re: Can neodymium magnets be used to shield against ultrasound?
« Reply #54 on: 06/05/2015 05:23:23 »
The problem with active noise reduction over a large area is the short wavelength of ultrasound. At 20 kHz the wavelength is around 1.7 cm so the peak of the incoming pressure wave at any point on, say, a 20 cm sphere (physicist's model of a head) is going to be quite different from the measured value a centimeter away.

You could produce a fairly soundproof planar wall with an array of independent transducers. This works OK for low frequency deadening of large rooms but you will need a vary large number of transducers. If you are to intercept and cancel, say, 50 MHz transmissions over a  30 cm square, you need 3600 independent elements, each consisting of a signal generator, an amplifier and a receiver.

I think the first step in your mission is to measure whatever it is that you think you are trying to nullify. Start with a broadband ultrasound receiver and a spectrum analyser. I recommend the Picoscope range of USB plug-in analysers - good value and the software is ridiculously easy to use. Not sure what transducer to use but http://parsonicscorp.com/  may be helpful. The problem is that most commercial transducers are tuned to send and receive at a sharp resonant frequency. However as you are looking for damage-inducing pressure levels, you might find that an old television remote control or a parking sensor does the job adequately.

It's my understanding piezo materials convert sound waves into electricity? So what about a 30cm x 30cm roll of PVDF film or Piezo Ceramic? This material is used in ultrasound transducers so wouldn't ultrasound passing through it be converted into an electric current and eliminate the need for a bunch of transducers? Just one large transducer sort of. Why do say 3600 transducers?
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4696
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: Can neodymium magnets be used to shield against ultrasound?
« Reply #55 on: 06/05/2015 11:30:01 »
1. The conversion is unlikely to absorb 100% of the incident energy, so you need to generate a nulling signal to counteract whatever the enemy/government/mafia/aliens are beaming at your head.

2. The phase of the incoming signal will vary significantly with position, so you need to generate a separate nulling signal at each point over your head, preferably sampled at points a wavelength  (1 - 2 cm) apart.

But the important thing to do is to identify and measure the incoming signal before designing the countermeasure, so get cracking with the bat detector and spectrum analyser - it's all standard laboratory kit.
 

The Naked Scientists Forum

Re: Can neodymium magnets be used to shield against ultrasound?
« Reply #55 on: 06/05/2015 11:30:01 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length