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In this research, we propose and design an acoustic metamuffler (AMM) by coupling a micro-perforated plate and a composite waveguide formed by a main waveguide and a Helmholtz resonator. The proposed mechanism and the deliberately designed structure are conducive to generating multimode resonances which help to improve the coupling absorption effect and lead to a broadband (4 octaves) sound insulation. We develop an effective circuit model to analytically predict the insulation bandwidth and put forward numerical and experimental measurements that demonstrate the effectiveness of the proposed concept. The designed AMM produces sound insulation with an average of 20 dB of sound transmission loss at a low frequency range extending from 100 to 1600 Hz while having an ultrathin thickness of 6.2 cm (1/55λ for the lowest working frequency). Our findings could have pragmatic applications for acoustic insulators or absorbers.

The accurate description of the total diffuse-photon-density-wave field inside turbid media, especially in the near-field region, is extremely critical but challenging for many decades. Here, the total diffuse-photon-density-wave field of semi-infinite turbid media was calculated by the third-order simplified spherical harmonics approximation (SP3) and compared with Monte Carlo simulations. To improve the SP3 approximation, the extrapolated Beer–Lambert law model considering the contribution of the coherent-photon-density-wave in the near-field region was proposed and implemented by Levenberg–Marquardt and universal global optimization methods. Last, we demonstrated the superiority of the proposed model over the existing model in fitting the accuracy and applicable source–detector distance range. The high accuracy and simplicity of the proposed model would be extremely helpful for biomedical applications involving photothermal radiometry, and rapidly determining optical properties of media, along with photoacoustic imaging and photodynamic therapy.

We report a sound impedance matching induced by asymmetry coupling vibrations. To achieve the vibration, acoustic waveguides with two different winding branch pipes are designed. In the acoustic device, the coupling effects of the two different winding branch pipes generate resonant vibrations, which constructs an impedance matching layer and produces a sound transmission with a wide band at lower frequencies. Importantly, multi-mode vibration can be adjusted by adding water. Consequently, the asymmetry winding branch pipes realize multi-mode vibrations that have the potential for use in sound control in broad frequencies.