Ultrasound is a great imaging modality that’s also used in a number of therapeutic applications. Its advantages include being able to penetrate tissue without using ionizing radiation, as well as the ability to see moving objects in real-time. A serious limitation, though, is that ultrasound waves are dispersed when they meet a hard object on the way to their real target. This, for example, makes non-invasive monitoring of blood flow in the brain and ultrasound targeting of brain tumors particularly difficult. Researchers from North Carolina State University and Massachusetts Institute of Technology have seemingly overcome this limitation that may open new doors for ultrasound in clinical use.
The technique relies on a special metamaterial that restores the sound waves that have been affected by the dense material in the way of the target. The technique has only been tested in a computer simulation so far, but the researchers are already building a prototype that will take advantage of the metamaterial. In the simulation, 28% of energy was able to make it past a layer of bone, while 88% made it through when taking advantage of the metamaterial.
Details from the study abstract:
In this paper, we investigate a type of anisotropic, acoustic complementary metamaterial (CMM) and its application in restoring acoustic fields distorted by aberrating layers. The proposed quasi two-dimensional (2D), nonresonant CMM consists of unit cells formed by membranes and side branches with open ends. Simultaneously, anisotropic and negative density is achieved by assigning membranes facing each direction (x and y directions) different thicknesses, while the compressibility is tuned by the side branches. Numerical examples demonstrate that the CMM, when placed adjacent to a strongly aberrating layer, could acoustically cancel out that aberrating layer. This leads to dramatically reduced acoustic field distortion and enhanced sound transmission, therefore virtually removing the layer in a noninvasive manner. In the example where a focused beam is studied, using the CMM, the acoustic intensity at the focus is increased from 28% to 88% of the intensity in the control case (in the absence of the aberrating layer and the CMM). The proposed acoustic CMM has a wide realm of potential applications, such as cloaking, all-angle antireflection layers, ultrasound imaging, detection, and treatment through aberrating layers.
Study in Physical Review X: Anisotropic Complementary Acoustic Metamaterial for Canceling out Aberrating Layers…