UC Berkeley researchers borrow principles of resonance to develop a new material that captures a sound waves fine details
Using the same principles that help create a guitars 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.
"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 materials 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 Zhangs 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 groups 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 Zhangs; Jianyi Xu, a visiting scholar from Nanjing University, who was a member of Zhangs lab when the work was conducted; and Muralidhar Ambati and Werayut Srituravanich, Ph.D. students of Zhangs.
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