Improving Ultrasound Penetration Into Metal and Bone
Researchers from North Carolina State University (NC State) have developed a technique that allows ultrasound to penetrate bone or metal, using customized structures that offset the distortion usually caused by bone or metal.

"We've designed complementary metamaterials that will make it easier for medical professionals to use ultrasound for diagnostic or therapeutic applications, such as monitoring blood flow in the brain or to treat brain tumors," says Tarry Chen Shen, a PhD student at NC State and lead author of the study. "This has been difficult in the past because the skull distorts the ultrasound's acoustic field."

The researchers addressed the problem of physical characteristics that block or distort ultrasound's acoustic waves, called aberrating layers, by designing customized metamaterial structures that take into account the acoustic properties of the aberrating layer and offsetting them. The metamaterial structure uses a series of membranes and small tubes to achieve the desired acoustic characteristics.

The researchers have tested the technique using computer simulations and are in the process of developing and testing a physical prototype.

In simulations, only 28% of ultrasound wave energy makes it past an aberrating layer of bone when the metamaterial structure is not in place. But with the metamaterial structure, the simulation shows that 88% of ultrasound wave energy passes through the aberrating layer.

"In effect, it's as if the aberrating layer isn't even there," Jing says.

The technique can be used for ultrasound imaging, as well as therapeutically—such as using ultrasound to apply energy to brain tumors, in order to burn them.