Giant extraordinary transmission of acoustic waves through a nanowire.

Wave concentration beyond the diffraction limit by transmission through subwavelength structures has proved to be a milestone in high-resolution imaging. Here, we show that a sound wave incident inside a solid over a diameter of 110 nm can be squeezed through a resonant meta-atom consisting of a nanowire with a diameter of 5 nm equal to λ/23, where λ is the incident acoustic wavelength, corresponding to a transmission efficiency of 500 or an energy densification of ~14,000. This remarkable level of extraordinary acoustic transmission is achieved in the absence of ultrasonic attenuation by connecting a tungsten nanowire between two tungsten blocks, the block on the input side being furnished with concentric grooves. We also demonstrate that these "solid organ pipes" exhibit Rayleigh end corrections to their effective longitudinal resonant lengths notably larger than their in-air analogs. Grooves on the output side lead to in-solid directed acoustic beams, important for nanosensing.