We report extraordinary effects in the transmission of sound through periodically perforated plates, supported by both measurements and theory. In agreement with recent observations in slit arrays, M. H. Lu et al. [Phys. Rev. Lett. 99, 174301 (2007)10.1103/PhysRevLett.99.174301], nearly full transmission is observed at certain resonant frequencies, pointing out similarities of the acoustic phenomena and their optical counterpart. However, acoustic screening well beyond that predicted by the mass law is achieved over a wide range of wavelengths in the vicinity of the period of the array, resulting in fundamentally unique behavior of the sound as compared to light.

In recent years, natural materials are becoming a valid alternative to traditional sound absorbers due to reduced production costs and environmental protection. This paper reports the acoustical characterization of sheep wool. Measurements on normal incidence and diffuse-incidence sound absorption coefficients of different samples are reported. The airflow resistance has also been measured. The results prove that sheep wool has a comparable sound absorption performance to that of mineral wool or recycled polyurethane foam. An empirical model is used to calculate the sound absorption of sheep wool samples. A reasonable agreement on the acoustic absorption of all sheep wool samples is obtained.

We study the angle and frequency dependence of sound transmission through water-immersed perforated aluminum plates. Three types of resonances are found to govern the acoustic properties of the plates: lattice resonances in periodic arrays, Fabry-Perot modes of the hole cavities, and elastic Lamb modes. The last two of them are still present in random arrays and have no parallel in optical transmission through holes. These modes are identified by comparing experiment with various levels of theoretical analysis, including full solution of the elasto-acoustic wave equations. We observe strong mixture of different transmission mechanisms, giving rise to unique acoustic behavior and opening new perspectives for exotic wave phenomena.

The development of flat acoustic lenses for different applications such as biomedical engineering is a topic of great interest. Flat lenses like Fresnel Zone Plates (FZPs) are capable of focusing energy beams without the need of concave or convex geometries, which are more difficult to manufacture. One of the possible applications of these type of lenses is tumor ablation through High Intensity Focused Ultrasound (HIFU) therapies with real time Magnetic Resonance Imaging (MRI) monitoring. In order to be MRI compatible, the FZP material cannot have electromagnetic interaction. In this work, a Phase-Reversal FZP (PR-FZP) made of Polylactic Acid (PLA) manufactured with a commercial 3D printer is proposed as a better, more efficient and MRI compatible alternative to conventional Soret FZPs. Phase-Reversal lenses, unlike traditional FZPs, take advantage of all the incident energy by adding phase compensation regions instead of pressure blocking regions. The manufactured PR-FZP achieves 21.9 dB of focal gain, which increases the gain compared to a Soret FZP of its same size by a factor of 4.0 dB. Both numerical and experimental results are presented, demonstrating the improved focusing capabilities of these types of lenses.

Surface acoustic-wave phenomena span a wide range of length scales going from the devastation of earthquakes down to image reconstruction of buried nanostructures. In solid-fluid systems, the so-called Scholte-Stoneley waves (SSWs) dominate the scene at the interface with their evanescent fields decaying away into both media. Understanding and manipulating these waves in patterned surfaces would enable new applications of sound to be devised for imaging and acoustic signal processing, although this task has so far remained elusive. Here, we report SSW modes displaying directional gaps and band folding in fluid-loaded solid phononic plates. The plates are inhomogeneously patterned with in-plane periodic modulations of the elastic constants, but present flat surfaces free of corrugations. We experimentally demonstrate control of SSWs, which opens a promising route toward acoustic fluid sensing, microscopy, and signal processing.