A bioinspired metagel achieves broadband tunable acoustic impedance matching.

We design an acoustic switch based on a spiral kirigami metasurface using numerical simulations and evaluate its performance experimentally. By etching an Archimedean spiral on a thin aluminum sheet, a band gap in out-of-plane vibration modes can be generated. The band gap is significantly suppressed by axially stretching the kirigami spiral structure, extending sound propagation to a broader frequency range. The kirigami metasurface is easily deformed and manipulated and can switch the energy transmission on and off in the desired operating-frequency range, providing an alternative design strategy for acoustic metasurfaces.

Assessment of the compressibility of marine mammal airways at depth is crucial to understanding vital physiologic processes such as gas exchange during diving. Very few studies have directly assessed changes in cetacean and pinniped trachea-bronchial shape, and none have quantified changes in volume with increasing pressure. A freshly deceased harbor seal, grey seal, harp seal, harbor porpoise, and common dolphin were imaged post mortem via CT in a radiolucent hyperbaric chamber as previously described in Moore et al (2011). Volume reconstructions were performed of segments of the trachea and bronchi of the pinnipeds and bronchi of the cetaceans for each pressure treatment. All specimens examined demonstrated significant decreases in volume with increasing pressure, with the harbor seal and common dolphin nearing complete collapse at the highest pressures. The common dolphin bronchi demonstrated distinctly different compression dynamics between 50% and 100% lung inflation treatments, indicating the importance of air in maintaining patent airways, and collapse occurred caudally to cranially in the 50% treatment. Dynamics of the harbor seal and grey seal airways indicated that the trachea was less compliant than the bronchi. These findings indicate potential species-specific variability in airway compliance, and cessation of gas exchange may occur at greater depths than those predicted in models assuming rigid airways. This may potentially increase the likelihood of decompression sickness in these animals during diving.

The sound-transmission, beam-formation, and sound-reception processes of a short-finned pilot whale (Globicephala macrorhynchus) were investigated using computed tomography (CT) scanning and numerical simulation. The results showed that sound propagations in the forehead were modulated by the upper jaw, air components, and soft tissues, which attributed to the beam formation in the external acoustic field. These structures owned different acoustic impedance and formed a multiphasic sound transmission system that can modulate sounds into a beam. The reception pathways composed of the solid mandible and acoustic fats in the lower head conducted sounds into the tympano-periotic complex. In the simulations, sounds were emitted in the forehead transmission system and propagated into water to interrogate a steel cylinder. The resulting echoes can be interpreted from multiple perspectives, including amplitude, waveform, and spectrum, to obtain the acoustic cues of the steel cylinder. By taking the short-finned pilot whale as an example, this study provides meaningful information to further deepen our understanding of biosonar system operations, and may expand sound-reception theory in odontocetes.

A finite element method was used to investigate the temperature influence on sound beams of the Indo-Pacific humpback dolphin. The numerical models of a dolphin, which originated from previous computed tomography (CT) scanning and physical measurement results, were used to investigate sound beam patterns of the dolphin in temperatures from 21 °C to 39 °C, in increments of 2 °C. The −3 dB beam widths across the temperatures ranged from 9.3° to 12.6°, and main beam angle ranged from 4.7° to 7.2° for these temperatures. The subsequent simulation suggested that the dolphin's sound beam patterns, side lobes in particular, were influenced by temperature.