First Acoustic Hyperlens Boosts Power of Ultrasound and Sonar

Imaging an unborn fetus and and spotting a lurking submarine
could both become much easier with the world's first acoustic
hyperlens. The device manipulates imaging sound waves to
provide an eightfold increase in the magnification power of
technologies such as ultrasound and sonar.

Hyperlenses use specially engineered materials that combine
metals and dielectrics, and allow scientists to image
features much smaller than typical light wavelengths.
Researchers at the U.S. Department of Energy's Lawrence
Berkeley National Laboratory applied this approach to capture
information in evanescent sound waves, which have higher
resolution and more detail but dissipate much more quickly
than typical waves.

The acoustic hyperlens consists of 36 brass fins arrayed in
a pattern resembling a hand-held fan. The fins remain
embedded in a brass plate from which they were shaped, and
extend from an inner radius of just 2.7 centimeters to
an outer radius of 21.8 centimeters.

"As a result of the large ratio between the inner and outer
radii, our acoustic hyperlens compresses a significant
portion of evanescent waves into the band of propagating
waves so that the image obtained is magnified by a factor of
eight," said Lee Fok, one of the researchers in the Berkeley
Lab.

The same lab group, led by materials scientist Xiang Zhang,
demonstrated a similar feat in 2007 by breaking the
"diffraction limit" that usually prevents researchers from
imaging features smaller than typical light waves.

Zhang's group is now upgrading their approach to produce 3-D
images, and wants to make the technique compatible with the
pulse-echo technology found in medical ultrasounds and
underwater sonar.