Metamaterials: Acoustic lenses to shout about

An acoustic hyperlens that is able to magnify and image objects much smaller than the probing wavelength promises new applications in sonar imaging is discussed. The mathematical equations that describe the waves making up the transmitted image of an object suggest that this image can be decomposed into two different types such as propagating and evanescent waves. The use of metamaterials in the design of hyperlenses meant losses through dissipation and in some instances also a narrow operation frequency range. The air channels separated by narrow fins are at the heart of this hyperlens design. The combination of low effective bulk modulus and the large mass density perpendicular to the fins helps to convert evanescent waves into propagating waves, leading to hyperlensing. The requirement of a small bulk modulus also implies that the structure is relatively soft overall.