Additive manufacturing using two-photon polymerization (TPP) lithography is increasingly used in industry and research. Parameter sweeps of cuboid structures fabricated using TPP lithography were investigated across the parameters of the laser power and scan speed to find dependent mechanical material properties. The employed photoresists were examined using Raman spectroscopy to find the degree of conversion (DC) of monomer to polymer, and subsequently, micro-or nanoindentation was used to find Young's modulus (E). For the photoresist IP-Dip, the attained DC and E ranged from 20% to 45% and 1 to 2.1 GPa, respectively. The results were compared with reports found in the literature. For IP-Q, the attained DC and E ranged from 53% to 80% and 0.5 to 1.3 GPa, respectively. The characterized properties of IP-Q manifest as the current state of knowledge of the material.

The recently proposed bianisotropic acoustic metagratings offer promising opportunities for passive acoustic wavefront manipulation, which is of particular interest in flat acoustic lenses and ultrasound imaging at ultra-high frequency ultrasound. Despite this fact, acoustic metagratings have never been scaled to MHz frequencies that are common in ultrasound imaging. One of the greatest challenges is the production of complex microscopic structures. Owing to two-photon polymerization, a novel fabrication technique from the view of acoustic metamaterials, it is now possible to precisely manufacture sub-wavelength structures in this frequency range. However, shrinking in size poses another challenge; the increasing thermoviscous effects lead to a drop in efficiency and a frequency downshift of the transmission peak and must therefore be taken into account in the design. In this work three microacoustic metagrating designs refracting a normally incident wave toward −35°at 2 MHz are proposed. In order to develop meta-atoms insensitive to thermoviscous effects shape optimization techniques incorporating the linearized Navier-Stokes equations discretized with finite element method are used. The authors report for the first time microscopic acoustic metamaterials manufactured using two-photon polymerization and, subsequently, experimentally verify their effectiveness using an optical microphone as a detector in a range from 1.8 to 2.2 MHz.

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