Quantcast
Connect with us

Scientists discover how to control heat and sound with magnetic fields

Published

on

Sound is carried by periodic vibrations of atoms in gases, liquids and solids. When we talk to each other, the vocal chords of the speaker vibrate, causing the air coming from his lungs to vibrate as well. This creates sound waves, which then propagate through the air until they hit a listener’s eardrums and make them vibrate as well. From these vibrations, the listener can then reconstruct the speaker’s words.

ADVERTISEMENT

Sound is affected by the surroundings in which it travels and by the frequency of the sound waves. We design musical instruments to manipulate the sound waves they produce. Further, we know that there are sound waves that are outside the range of human hearing, such as those produced by a dog whistle. As physicists have researched sound both inside and outside the range of human hearing, interesting properties have been discovered.

More than a hundred years ago, physicists understood that heat is simply the energy stored in the vibrations of atoms, and therefore realized that heat and sound are related. Now my lab showed experimentally for the first time that these atomic vibrations have magnetic properties too.

Building our knowledge of sound

In the 1930s, physicists started modeling atomic vibrations as particles. This is similar to the concept of light as both a wave and a particle we call a photon. Physicists called the sound wave particles “phonons,” derived from the Greek word for sound.

Today, physicists treat phonons as quasi-particles, having both wave and particle properties. Phonons carry both sound and heat. In metals, heat is carried primarily by the movement of electrons in the atoms. However, in all other materials, heat is carried almost exclusively by the phonons.

So the mechanical, acoustic and thermal properties of sound waves have long been established. Yet, before now, nobody ever imagined that sound waves might also have magnetic properties.

ADVERTISEMENT

A lopsided tuning fork, made of the semiconductor indium antimonide, used in the experiment.
Kevin Fitzsimons, The Ohio State University, CC BY-NC-ND

Heat, sound… and magnetism?

In the March 23 issue of Nature Materials, we offer experimental proof that sound waves do interact with external magnetic fields.

The experiment was carried out on a large, single crystal of a very pure semiconductor, indium antimonide, which had been cut into two unequal sections and then cooled to about -445F (-265C). A controlled amount of heat was made to flow in each section separately. At these temperatures, the phonons can be thought of as individual particles, like runners on a racetrack each carrying a little bucket of heat.

In the small section, the phonons often run into the walls, which slows them down. The small section is used as a reference, to make the experiment independent of the other properties of the solid that might interfere. In the large section, the phonons can go faster, and they don’t run into the walls as much as into each other. When we apply a magnetic field, they tend to run into each other more frequently. Because the magnetic field increases the number of collisions, it also slows the phonons down and lowers the amount of heat they carry by 12%.

ADVERTISEMENT

We think this is due to the electrons that rotate in orbits around each atom in the solid. The orbital motion of these electrons emits a very small intrinsic magnetic field that interacts with the externally applied field – an effect called “diamagnetism.“ This property exists even in substances we don’t traditionally think of as magnetic, such as glass, stone or plastic. When the atoms vibrate due to the passing of the phonons, this interaction creates a force on the atoms that makes the phonons collide with each other more often.

What can we do with these results?

At this point, we’ve just described a new concept, something that had never been thought of before. Engineers can perhaps use this concept to control heat and sound waves magnetically. Sound waves can be effectively steered already by using multiple sources of sound, as is done in ultrasound imaging systems, but controlling heat conduction is much harder.

ADVERTISEMENT

Conversion of heat into electrical or mechanical power, as is done in engines and in power stations, supplies over 90% of the energy humanity uses. Therefore, being able to control heat conduction at will could have an enormous impact on energy production, though, obviously, applications of this emergent concept are still quite a way in the future.

The Conversation

By Joseph Heremans, The Ohio State University

ADVERTISEMENT

This article was originally published on The Conversation.
Read the original article.


Report typos and corrections to: [email protected].
READ COMMENTS - JOIN THE DISCUSSION
Continue Reading

Breaking Banner

Fox News host: Teachers practicing COVID safety are like ‘George Wallace standing in the school door’

Published

on

Fox News host Mark Levin on Sunday accused teachers who want COVID-19 safety measures of re-enacting Jim Crow-era segregation rules.

Levin made the remarks during a rant about President Donald Trump's executive action on COVID-19 financial relief.

"Democrat governors have shut down this economy from sea to shining sea," Levin opined. "And they like it both ways, the Democrats. They want to lock up everybody like we're lamb in cages and then they want to complain about the economic consequences."

"And then they say, this president, look what he's doing," he continued. "Let me tell you, payback is a bitch. You remember Obama with his phone and his pen. Well, apparently he left his phone and his pen and President Trump picked it up."

Continue Reading

Breaking Banner

Mnuchin threatens to make taxpayers pay back COVID money unless Trump is reelected

Published

on

Treasury Secretary Steve Mnuchin suggested on Sunday that Americans will have to pay the government back for any payroll tax reduction unless President Donald Trump is reelected.

In an interview on FOX, host Chris Wallace noted that the president's latest executive action on COVID-19 financial relief is "not a tax cut."

"It's a payroll tax suspension," Wallace explained. "Isn't there a danger that a lot of businesses won't pass these saving through to workers because they're going to hold on to the money because at some point, according to this executive action by the end of the year, those payroll taxes are going to be have to be paid anyway?"

Continue Reading
 

Breaking Banner

Virtual learning means unequal learning

Published

on

WASHINGTON — Karen Reyes, who teaches deaf and hard-of-hearing children in Austin, Texas, worries about her first-grade pupils who will be learning online this fall. She’s concerned that virtual learning is harder for younger, special needs children, especially those who may not have as much support at home as students in more affluent communities.“It has brought out a lot of the inequities in our district, especially in special education,” Reyes said of the distance learning program.In her school, 93% of the students are considered economically disadvantaged, according to a city estimate.“Eit... (more…)

Continue Reading
 
 
You need honest news coverage. Help us deliver it. Join Raw Story Investigates for $1. Go ad-free.
close-image