Acoustic Metamaterial Could Enable Ultrahigh-Resolution Ultrasound Imaging

The acoustic metamaterial lens is composed of a planar network of subwavelength Helmholtz resonators. Image courtesy of Nicholas Fang.

Using an acoustic metamaterial, researchers at the University of Illinois at Urbana-Champaign succeeded in focusing ultrasound waves so that it exhibits a negative dynamic modulus–a phenomenon that doesn’t occur in nature. Ultrasonic imaging systems likely will be the first application of the technology. According to Nicholas Fang, an assistant professor at the university who led the research, an acoustic, metamaterials-based lens could dramatically improve the resolution of ultrasound imaging without pumping more energy into tissue.

In the past, diffraction of light and sound has limited the resolution that can be achieved with optical and acoustic lenses. In recent years, researchers have worked to solve that problem by developing lenses with a negative index of refraction (or in the case of acoustic lenses, a negative dynamic modulus), perhaps enabling the creation of the “perfect lens,” as Imperial College physics professor John Pendry has put it. Such a negative-index planar lens theoretically would provide perfect image reconstruction, enabling breakthroughs in imaging resolution.

Nicholoas Fang

The sound-focusing metamaterial-based device developed by Fang’s group is an aluminum array of resonant cavities with dimensions tuned to interact with ultrasound waves. Filled with water, the cavities behave similar to wind instruments such as the flute, which resonates when a stream of air blows across a hole in the instrument. Though the ultrasound system has yet to beat the diffraction limit, it may not be long before they do. “I am sure that we shall not have long to wait,” Imperial College physics professor John Pendry told the MIT Technology Review.

You can read an abstract on Fang’s recent research at the Physical Review Letters.

Tags: Nicholas Fang