Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Promising new metamaterial could transform ultrasound imaging

02.06.2006


UC Berkeley researchers borrow principles of resonance to develop a new material that captures a sound wave’s fine details



Using the same principles that help create a guitar’s complex tones, researchers at the University of California, Berkeley, have developed a new material that holds promise for revolutionizing the field of ultrasound imaging.

The substance, dubbed an "ultrasonic metamaterial," responds differently to sound waves than any substance found in nature. Within a decade, the researchers report, the technology they developed to create the material could be used to vastly enhance image resolution of ultrasound, while at the same time allowing for the miniaturization of acoustic devices at any given frequency.


"We’ve been very interested in developing artificial materials with extraordinary properties that do not exist in nature," said Xiang Zhang, Chancellor’s Professor in Mechanical Engineering at UC Berkeley and principal investigator of the study that describes the new material.

Zhang’s interest in acoustic metamaterials was inspired by the five years he and his group have already spent exploring optical metamaterials. "The goal is to create artificial materials that will be useful in both optical and acoustical applications," Zhang said.

The study, "Ultrasonic metamaterials with negative modulus," will be published June 1 in Nature Materials. The journal released the study in its early online version on April 30.

Metamaterials are novel, manmade structures designed to have properties that respond to light, sound and other waves in ways that do not occur in naturally occurring substances. An example would be a material created to have a negative refractive index, which means that it could bend light in a different direction than normal materials do, explained Cheng Sun, a senior scientist in Zhang’s group and one of the paper’s authors.

A basic element of metamaterial design is a lattice of identical building blocks, each smaller than the wavelength of the light wave or sound wave with which the material is designed to interact. As a result, when waves move through the material, they do not "see" individual blocks, but respond to the material as a whole, as if it were a homogeneous substance.

The material designed by Zhang and his colleagues consists of a series of water-filled chambers connected by a long channel built into a bar of aluminum. Known as Helmholtz resonators, the rigid-walled, narrow-mouthed chambers are designed to vibrate - or resonate - in response to the sound of a certain pitch. A better-known example of a Helmholtz resonator is the body of a guitar, which resonates when the instrument’s strings are plucked.

Designed to respond to 30 kHz sound waves moving through water, each chamber in the aluminum is a little smaller than a pencil’s eraser. Their spacing at 9.2 mm is one-fifth the length of one 30 kHz sound wave.

As sound waves pass through the water-filled channel, a significant amount of their energy gets stored in the connected chambers, explained Nicholas Fang, who designed the metamaterial when he was a post-doctoral researcher in Zhang’s lab. Now an assistant professor of mechanical engineering at the University of Illinois at Urbana-Champaign, Fang is lead author of the study.

"There is a natural frequency that determines the tone of a resonator," Fang said. "In this material, we are trying to excite the resonators with a tone that is higher than the one that they are tuned to. And because there are so many resonators in the series all tuned to the same frequency, every one lags just a bit behind the other."

In the complex dynamics of acoustical physics, this triggers various phenomena:

  • As opposed to natural materials that compress when a force (such as a sound wave) is applied to them, the metamaterial expands. This response, called "negative modulus," occurs when the fluid in the neck of the resonators oscillates in and out, causing the fluid in the chambers to spread apart and push into its walls.
  • The response makes it appear as if the sound wave is propagating backward instead of moving forward.
  • The material supports sound waves that are shorter and finer than sound waves that propagate through any other material.

The result?

"Basically, the resonators work together, supporting a much higher modulation of the acoustic wave," Fang said. "They are reacting as a very precise ruler, allowing us to measure the finer features of the wave."

This ability provides the basis for the material’s usefulness in ultrasound imaging. One of the factors limiting resolution quality of sonograms is the ability of the ultrasound lens to capture sound waves. Currently, these lenses are made with elastic materials such as polymers. The elasticity of the materials is what allows them to capture and focus the waves. But there is a limit to the finest resolution that they can capture.

"With this new material with a negative modulus, all the limits can be overcome," Fang said.

The material that Zhang’s research group fabricated is 55 centimeters long and houses 60 resonators. In its present form, it can be used only for one frequency and can capture sound from only one direction. The group’s plan, said Zhang, is to develop "three-dimensional" materials that will not only be able to capture sound from every direction, but will also be tunable. That is, the size of the resonators will be adjustable so that the material can respond to any frequency. Once they have designed and tested such a material, Zhang expects to be able to use microfabrication techniques to build materials with hundreds of thousands of resonators.

Because its resonators are many times smaller than wavelengths of the sound wave, Zhang said, the material can be used to make compact sonar and ultrasonic devices. Conventional lenses in these devices must be at least as large as the waves they are meant to capture. Sonar devices, which use long-length waves, would particularly benefit from this miniaturization.

The other researchers who contributed to the study are Dongjuan Xi, a former graduate student of Zhang’s; Jianyi Xu, a visiting scholar from Nanjing University, who was a member of Zhang’s lab when the work was conducted; and Muralidhar Ambati and Werayut Srituravanich, Ph.D. students of Zhang’s.

Liese Greensfelder | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Materials Sciences:

nachricht New material for digital memories of the future
19.10.2017 | Linköping University

nachricht Electrode materials from the microwave oven
19.10.2017 | Technical University of Munich (TUM)

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Electrode materials from the microwave oven

19.10.2017 | Materials Sciences

New material for digital memories of the future

19.10.2017 | Materials Sciences

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>