Ultrasonic waveguide based super resolution imaging using structured channel metamaterial lenses

The extension of metamaterial concepts to the ultrasonic domain is challenging because of the shorter wavelength, which necessitates the use of spatially narrow band receiving techniques to capture wavefields past fine features of the metamaterial. Currently, the Laser Doppler Vibrometer is the only option with several drawbacks hampering its widespread practical implementation, including cost and sensitivity to external disturbances. This paper proposes a novel waveguide based reception technique to capture the amplified evanescent fields transmitted through the subwavelength features of the metamaterials. Numerical simulations and experiments are carried out on a structured channel metamaterial and a thin stainless steel waveguide attached to a commercial transducer. A practical super resolution ultrasonic imaging down to a third of the operating wavelength is successfully demonstrated in comparison with a commercial laser receiver. The physics of the imaging and dispersion characteristics of the waveguide enabling the process are discussed. The promising results showcase broadband, low-cost, portable alternatives with important implications for high-resolution ultrasonic imaging in industrial and biomedical applications.