Featured Research

from universities, journals, and other organizations

How do liquid foams completely block sound?

Date:
April 24, 2014
Source:
CNRS
Summary:
Liquid foams have a remarkable property: they completely block the transmission of sound over a wide range of frequencies. Physicists have studied how sound is attenuated in liquid foams. Their findings open the way to the development of tools called acoustic probes that could be used to monitor the quality of foams used in industry, especially in the mining and petroleum sectors.

This image shows a fine view of the distribution of the liquid phase in a liquid foam. The liquid channels that support the thin films, some of which can be seen here, are clearly visible. The behavior of both channels and films caused by an acoustic wave explains the unusual acoustic properties of liquid foams.
Credit: © Laboratoire "Matière et systèmes complexes" (CNRS/Université Paris Diderot)

Liquid foams have a remarkable property: they completely block the transmission of sound over a wide range of frequencies. CNRS physicists working in collaboration with teams from Paris Diderot and Rennes Universities* have studied how sound is attenuated in liquid foams. Their findings, published in Physical Review Letters, open the way to the development of tools called acoustic probes that could be used to monitor the quality of foams used in industry, especially in the mining and petroleum sectors.

Related Articles


Much research has been carried out in acoustics in order to understand how sound propagates through a material. One of the classic approaches is to send an acoustic wave through it and listen to the response, which provides key information about the material, in the same way as listening to the sound produced by tapping on a wall indicates whether it is hollow. This is why researchers analyze how various materials, from the simplest to the most complex, react when they are struck.

One of these is however keeping its secrets: liquid foam. This is a difficult material to study since it is short-lived and sound does not travel through it easily. Until now, there has been no acoustic probe for foams. The most frequently used probes rely on electrical conductivity to determine the amount of liquid contained in a foam. However, some of these substances are made up of non-conducting liquid, making it impossible to characterize them. Adding liquid foams to the list of materials that can be probed by acoustic waves is therefore central to ensuring that every type of foam used can be fully characterized.

How do liquid foams block sound? A key finding has been revealed in a recent study by researchers from the 'Matière et Systèmes Complexes' Laboratory (CNRS/Université Paris Diderot) and the Institut de Physique de Rennes (CNRS/Université Rennes 1).  Characterization of foams is essential for measuring the speed and attenuation of sound in foams of known composition. The results show that sound propagation varies greatly according to the frequency of the wave used. The researchers propose a simple interpretation of these observations. Foams are made up of 90% air plus a liquid, and this liquid is distributed between films and channels that support them.

However, these two structures have very different geometries and masses: films have a large surface area and a small mass, while channels are narrower but have greater mass. The vibration of air caused by the acoustic wave displaces the films, which in turn pull on the channels. At low frequencies, the speed of sound is very low (around 30 meters per second): the sound is slowed down by the coordinated motion of the films and channels, but is not blocked. At high frequencies, the speed of sound increases (approximately 220 meters per second): only the films move, thus also allowing the sound to travel through the foam. However, at intermediate frequencies, the films behave anomalously: they move in the "wrong" direction, in other words towards the left when the air displaced by the sound pushes them to the right, which prevents the channels from moving. The sound is therefore blocked in the bubbles over a wide range of frequencies.

This work thus helps to solve the mystery of acoustics in liquid foams. It will pave the way for the development of acoustic probes that can be applied to such materials, which are an everyday part of life as well as being widely used in industry.

* From the 'Matière et Systèmes Complexes' Laboratory (CNRS/Université Paris Diderot) and the Institut de Physique de Rennes (CNRS/Université Rennes 1).

The study, which is part of a project funded by the French National Research Agency (ANR), brings together for the first time acoustics experts and foam specialists.


Story Source:

The above story is based on materials provided by CNRS. Note: Materials may be edited for content and length.


Journal Reference:

  1. Juliette Pierre, Benjamin Dollet, Valentin Leroy. Resonant Acoustic Propagation and Negative Density in Liquid Foams. Physical Review Letters, 2014; 112 (14) DOI: 10.1103/PhysRevLett.112.148307

Cite This Page:

CNRS. "How do liquid foams completely block sound?." ScienceDaily. ScienceDaily, 24 April 2014. <www.sciencedaily.com/releases/2014/04/140424102254.htm>.
CNRS. (2014, April 24). How do liquid foams completely block sound?. ScienceDaily. Retrieved December 19, 2014 from www.sciencedaily.com/releases/2014/04/140424102254.htm
CNRS. "How do liquid foams completely block sound?." ScienceDaily. www.sciencedaily.com/releases/2014/04/140424102254.htm (accessed December 19, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Friday, December 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Navy Unveils Robot Fish

Navy Unveils Robot Fish

Reuters - Light News Video Online (Dec. 18, 2014) — The U.S. Navy unveils an underwater device that mimics the movement of a fish. Tara Cleary reports. Video provided by Reuters
Powered by NewsLook.com
3D Printed Cookies Just in Time for Christmas

3D Printed Cookies Just in Time for Christmas

Reuters - Innovations Video Online (Dec. 18, 2014) — A tech company in Spain have combined technology with cuisine to develop the 'Foodini', a 3D printer designed to print the perfect cookie for Santa. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
First Etihad Superjumbo Flight in December

First Etihad Superjumbo Flight in December

AFP (Dec. 18, 2014) — The first flight of Etihad Airways' long-awaited Airbus A380 superjumbo will take place later in December, the Abu Dhabi carrier said Thursday, also announcing its first Boeing 787 Dreamliner route. Duration: 01:09 Video provided by AFP
Powered by NewsLook.com
Ford Expands Air Bag Recall Nationwide

Ford Expands Air Bag Recall Nationwide

Newsy (Dec. 18, 2014) — The automaker added 447,000 vehicles to its recall list, bringing the total to more than 502,000. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins