What materials would produce an impedance mismatch?

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Discussion Overview

The discussion revolves around the concept of impedance mismatch in materials as a means to shield or redirect ultrasound waves traveling through air. Participants explore the acoustic impedance values necessary for effective shielding, particularly for frequencies ranging from 20 kHz to above 1 GHz.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants inquire about materials that could prevent ultrasound from reaching a second layer when stacked, specifically with the first layer exposed to ultrasound at 1 MHz.
  • Others express interest in creating impedance mismatches to shield ultrasound up to 3 GHz, noting that materials with an acoustic impedance around 1.5 may require a shielding material with an impedance of around 7.
  • One participant mentions the lack of available literature on tests regarding various materials' effects on ultrasound traveling through air at different frequencies.
  • Several participants seek clarification on the application and intensity range of the ultrasound being discussed, indicating a need for context in the conversation.
  • There is a reference to military applications potentially related to the topic, although the specifics are not detailed.
  • A participant shares a link to a document for further reference, indicating pages of interest for the discussion.
  • One participant notes the forum's policy against discussing dangerous activities or weapons, leading to a closure of related threads.

Areas of Agreement / Disagreement

Participants generally express curiosity about the topic, but there is no consensus on the specific materials or methods that would effectively create an impedance mismatch for ultrasound shielding. The discussion remains unresolved regarding the best approaches and materials.

Contextual Notes

Participants mention various acoustic impedance values and frequencies, but there are limitations in the available literature and empirical data to support their claims. The discussion also touches on the implications of the applications being considered, which remain vague.

mcriv880
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sufficient enough to redirect/shield against ultrasound 1MHz being directed through the air. i know a vacuum would. What I'm questioning is if you had 2 layers of different materials stacked on top of each other what could prevent the ultrasound from reaching the 2nd layer assuming the 1st layer is on the outside. The acoustic impedance of the second layer is somewhere between 1.5 and 2.
 
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I'm interested in methods of deflecting/shielding ultrasound up to 3GHz traveling through air as a medium. My search lead me to the study of creating impedance mismatches to affect sound wavess. I'm looking specifically for the acoustic impedance necessary to act as a shield of sorts for materials with an acoustic impedance around one and a half. Some of my searches have said an impedance of around 7 would suffice however I can not find any papers on such tests, and how various materials affected ultrasound traveling through air as a medium at different frequencies. I'm guessing that there have been tests in this area with military applications which would suffice if readily available. To my knowledge this is the best way to affect sound waves, if there are any other methods please feel free to share.
 
mcriv880 said:
sufficient enough to redirect/shield against ultrasound 1MHz being directed through the air. i know a vacuum would. What I'm questioning is if you had 2 layers of different materials stacked on top of each other what could prevent the ultrasound from reaching the 2nd layer assuming the 1st layer is on the outside. The acoustic impedance of the second layer is somewhere between 1.5 and 2.

mcriv880 said:
I'm interested in methods of deflecting/shielding ultrasound up to 3GHz traveling through air as a medium. My search lead me to the study of creating impedance mismatches to affect sound wavess. I'm looking specifically for the acoustic impedance necessary to act as a shield of sorts for materials with an acoustic impedance around one and a half. Some of my searches have said an impedance of around 7 would suffice however I can not find any papers on such tests, and how various materials affected ultrasound traveling through air as a medium at different frequencies. I'm guessing that there have been tests in this area with military applications which would suffice if readily available. To my knowledge this is the best way to affect sound waves, if there are any other methods please feel free to share.

Can you say more about your application? Those are very high frequencies for ultrasound in air...
 
Yes I realize they are very high frequencies for air being above 1MHz but I was looking for the entire range from 20KHz-Above 1GHz with air as a medium. Not just one specific frequency.
 
mcriv880 said:
Yes I realize they are very high frequencies for air being above 1MHz but I was looking for the entire range from 20KHz-Above 1GHz with air as a medium. Not just one specific frequency.

Can you say anything about the application? What intensity range are you looking at?
 
berkeman said:
Can you say anything about the application? What intensity range are you looking at?



https://docs.google.com/viewer?a=v&pid=explorer&srcid=0B-C2IpG-te-Lblhhd2V2eEh6WUk

Please see pages 20, and 25.
 
mcriv880 said:
https://docs.google.com/viewer?a=v&pid=explorer&srcid=0B-C2IpG-te-Lblhhd2V2eEh6WUk

Please see pages 20, and 25.

Ah, I understand. Thanks.

But sorry, we don't discuss dangerous activities/weapons here on the PF. Your threads on this subject are now closed.
 

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