Studies in optics and acoustics have employed metamaterial lenses to achieve sub-wavelength localization, e.g. a recently introduced concept called ‘acoustojet’ which in simulations localizes acoustic energy to a spot smaller than λ/2. However previous experimental results on the acoustojet have barely reached λ/2-wide localization. Here we show, by simulations and experiments, that a sub-λ/2 wide localization can be achieved by translating the concept of a photonic jet into the acoustic realm. We performed nano- to macroscale molecular dynamics (MD) and finite element method (FEM) simulations as well as macroscale experiments. We demonstrated that by choosing a suitable size cylindrical lens, and by selecting the speed-of-sound ratio between the lens material(s) and the surrounding medium, an acoustic jet (‘acoustic sheet’) is formed with a full width at half maximum (FWHM) less than λ/2. The results show, that the acoustojet approach can be experimentally realized with easy-to-manufacture acoustic lenses at the macroscale. MD simulations demonstrate that the concept can be extended to coherent phonons at nanoscale. Finally, our FEM simulations identify some micrometer size structures that could be realized in practice. Our results may contribute to starting a new era of super resolution acoustic imaging: We foresee that jet generating constructs can be readily manufactured, since suitable material combinations can be found from nanoscale to macroscale. Tight focusing of mechanical energy is highly desirable in e.g. electronics, materials science, medicine, biosciences, and energy harvesting.

Propeller inspection is mandatory for safe operation of aircraft. Damage evaluation on such rotating structures requires dedicated measurement techniques. In this study efforts to create a stroboscopic technique are reported. Lamb waves were excited on a rotating blade with a Qswitched Nd:YAG laser synchronized to the sample rotation, whereas the wave amplitude was obtained by a laser Doppler vibrometer. A surface breaking notch on an aluminum sample rotating at 415 rpm was detected and sized with millimeter accuracy. The technique has potential for automatic non-contacting damage detection on rotating structures such as helicopter blades and turbines.

People suffering from glaucoma often endure high intra-ocular pressure (IOP). Methods for determining IOP either contact the eye or are unpleasant to some patients. There is therefore a need for a rapid and patient friendly non-contacting method to determine IOP. To address this need, we developed a tonometer prototype that employs spark-gap induced shock waves and a laser Doppler vibrometer (LDV) that reads the amplitude of membrane waves. The IOP was first identified from the membrane wave propagation velocity first in a custom-made ocular phantom and was then verified in ex vivo porcine eyes. The time-offlight (TOF) of the membrane wave travelling on a hemispherical membrane was compared to reference IOP values in the sample obtained with an iCare TA01 tonometer. The shock front was characterized by high speed photography. Within one eye, the method achieved an agreement of 5 mmHg (1.96 standard deviation between the shock wave tonometer and the commercial manometer) and high method-to-method association (Pearson correlation, R 2 = 0.98). The results indicate that the presented method could potentially be developed into a non-contacting technique for measuring IOP in vivo.