Featured Research

from universities, journals, and other organizations

Random Noise From Within Objects Reveals Their Internal Structure

Date:
November 26, 2001
Source:
University Of Illinois At Urbana-Champaign
Summary:
By picking up the tiny vibrations of thermal energy that exist naturally in all objects, researchers at the University of Illinois have performed ultrasonic measurements without using a source. Potential applications range from seismology to materials science.

CHAMPAIGN, Ill. — By picking up the tiny vibrations of thermal energy that exist naturally in all objects, researchers at the University of Illinois have performed ultrasonic measurements without using a source. Potential applications range from seismology to materials science.

As reported in the Sept. 24 issue of Physical Review Letters, UI professor of theoretical and applied mechanics Richard Weaver and research associate Oleg Lobkis measured minuscule sound waves – called phonons – propagating within a block of aluminum at room temperature.

"The sound we were listening to was created by arbitrary thermal fluctuations generated elsewhere in the sample, such as an electron hitting a lattice imperfection or an air molecule striking the surface," Weaver said. "While no one had really doubted that these tiny fluctuations existed, no one had ever measured them before."

Weaver and Lobkis not only proved that the vibrations were indeed measurable, they also showed that by correlating what appeared to be random noise, considerable information could be gleaned about an object’s interior. First, they listened to the noise, then they used mathematical operations that looked for patterns and repetitions – a process called autocorrelation.

"Like BBs rattling inside a box, phonons will bounce off the walls of the aluminum, ricochet off some internal structure, and bounce off the walls again, corresponding to the round-trip travel time of an echo," Weaver said. "We looked for correlations within the echoes."

Weaver and Lobkis validated their technique by autocorrelating the noise from a passive piezoelectric transducer mounted to the sample and then comparing that result with an active measurement they obtained using conventional ultrasonics."The waveforms were almost identical," Weaver said. "When you autocorrelate the ambient noise, you see nearly the same signal as when you pulse the transducer and listen to the echoes."

This surprising result is something scientists have been overlooking for decades, Weaver said. "We’ve been throwing away this noise – not realizing that it’s full of useful information."

In principle, the passive technique could work on nearly any object, but would be most helpful in applications where conventional sound sources are scarce. At very low frequencies, for example, seismologists could pick up the random vibrations from distant earthquakes to obtain local stratigraphic information without setting off directed explosives. At extremely high frequencies, the technique could be used to noninvasively probe micron-sized features and material properties in microchips.

"The technique also might be useful for monitoring building vibrations to anticipate potential collapse," Weaver said. "By measuring the natural frequencies of the building as it responds to random vibrations in the neighborhood, even subtle changes in structural rigidity could be detected."

The National Science Foundation funded the research.


Story Source:

The above story is based on materials provided by University Of Illinois At Urbana-Champaign. Note: Materials may be edited for content and length.


Cite This Page:

University Of Illinois At Urbana-Champaign. "Random Noise From Within Objects Reveals Their Internal Structure." ScienceDaily. ScienceDaily, 26 November 2001. <www.sciencedaily.com/releases/2001/11/011120054110.htm>.
University Of Illinois At Urbana-Champaign. (2001, November 26). Random Noise From Within Objects Reveals Their Internal Structure. ScienceDaily. Retrieved August 30, 2014 from www.sciencedaily.com/releases/2001/11/011120054110.htm
University Of Illinois At Urbana-Champaign. "Random Noise From Within Objects Reveals Their Internal Structure." ScienceDaily. www.sciencedaily.com/releases/2001/11/011120054110.htm (accessed August 30, 2014).

Share This




More Matter & Energy News

Saturday, August 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Australian Airlines Relax Phone Ban Too

Australian Airlines Relax Phone Ban Too

Reuters - Business Video Online (Aug. 26, 2014) Qantas and Virgin say passengers can use their smartphones and tablets throughout flights after a regulator relaxed a ban on electronic devices during take-off and landing. As Hayley Platt reports the move comes as the two domestic rivals are expected to post annual net losses later this week. Video provided by Reuters
Powered by NewsLook.com
Hurricane Marie Brings Big Waves to California Coast

Hurricane Marie Brings Big Waves to California Coast

Reuters - US Online Video (Aug. 26, 2014) Huge waves generated by Hurricane Marie hit the Southern California coast. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Chinese Researchers Might Be Creating Supersonic Submarine

Chinese Researchers Might Be Creating Supersonic Submarine

Newsy (Aug. 26, 2014) Chinese researchers have expanded on Cold War-era tech and are closer to building a submarine that could reach the speed of sound. Video provided by Newsy
Powered by NewsLook.com
Breakingviews: India Coal Strained by Supreme Court Ruling

Breakingviews: India Coal Strained by Supreme Court Ruling

Reuters - Business Video Online (Aug. 26, 2014) An acute coal shortage is likely to be aggravated as India's supreme court declared government coal allocations illegal, says Breakingviews' Peter Thal Larsen. Video provided by Reuters
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:
from the past week

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