Acoustic Hyperlens

High resolution ultrasound scans and greatly improved sonal imaging may become possible because of a technique using metamaterials to create a hyperlens that can focus sound to a fraction of its wavelength.

Acoustic Hyperlens Could Sharpen Ultrasound Imaging – [ieee.org]

In the past few years, researchers have created artificial materials known as metamaterials, which bend and focus light in unnatural ways. While a microscope’s glass lens can detect only objects larger than half a wavelength of light, metamaterials could enable ultrahigh-resolution imaging of much tinier features.

A new device made by researchers at the University of California, Berkeley, does a similar trick with sound waves. Just as with its optical counterpart, imaging with sound is limited by the wave’s length, a phenomenon called the diffraction limit. But the acoustic metamaterial that mechanical engineering professor Xiang Zhang and his colleagues presented yesterday on the online version of the journal Nature Materials magnifies and detects features that are just one-seventh of the sound signal’s wavelength.

Berkeley Researchers Create First Hyperlens for Sound Waves – [lbl.gov]

In the world of optical imaging, hyperlensing is enjoying a hyper rage. Fabricated from metamaterials – composites of metals and dielectrics whose uniquely engineered structures give rise to extraordinary optical properties – hyperlenses make it possible to overcome the so-called “diffraction limit” by imaging features that are significantly smaller than the wavelengths of incident light. Zhang called the capturing of information carried by evanescent waves “the Holy Grail of optical information” in 2007, when he and his research group announced a hyperlens made from nanowires of silver and aluminum oxide that was able to use visible light to image objects smaller than 150 nanometers, well below visible light’s diffraction limit of 260 nanometers.

Sound waves are also hampered by an intrinsic diffraction limit when deployed for imaging purposes – objects that can be seen with conventional acoustic imaging are limited by the length of the sound wave. Once again, Zhang and his colleagues have overcome this diffraction limit by employing carefully engineered wave dispersion surfaces. This time they’ve demonstrated the first broad-band low-loss imaging with large magnification, where evanescent waves carrying information about subwavelength features are gradually converted into propagating waves.

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