High-Temperature and Low-Frequency Acoustic Energy Absorption by a Novel Porous Metamaterial Structure

In this paper,we propose a novel porous metamaterial structure with an improved acoustic energy absorption performance at high-temperature and in the low-frequency range.In the proposed novel porous metamaterial structure,a porous material matrix containing periodically perforated cylindrical holes arranged in a triangular lattice pattern is applied,and additional interlayers of another porous material are introduced around these perforations.The theoretical model is established by adopting the double porosity theory for the interlayer and the cylindrical hole which form an equivalent inclusion and then applying the homogenization method to the porous metamaterial structure formed by the equivalent inclusion and the porous matrix.The temperature-dependent air and material parameters are considered in the extended theoretical model,which is validated by the finite element results obtained by COMSOL Multiphysics.The acoustic or sound energy absorption performance can be improved remarkably at very low frequencies and high temperature.Furthermore,the underlying acoustic energy absorption mechanism inside the unit-cell is investigated by analyzing the distribution of the time-averaged acoustic power dissipation density and the energy dissipation ratio of each constituent porous material.The results reveal that regardless of the temperature,the acoustic energy is mostly dissipated in the porous material with a lower airflow resistivity,while the acoustic energy dissipated in the porous material with a higher airflow resistivity also becomes considerable in the high-frequency range.The novel porous metamaterial structure proposed in this paper can be efficiently utilized to improve the acoustic energy absorption performance at high temperature.

A new broadband differential phase shifter fabricated using a novel CRLH structure

Broadband phase shifters are mostly proposed and fabricated based on the scheme proposed by Shiffman, which uses a coupled line with far ends connected together and a uniform transmission line to give a differential phase shift. Based on the unique dispersion property of the composite right/left-handed (CRLH) metamaterial structure, a new configuration is presented in this paper for fabricating the broadband differential phase shifter, which employs a novel CRLH metamaterial structure as one of the differential phase-shift arms, instead of the conventional coupled line. The new circuit can achieve a phase shift of 90° in an operational bandwidth as broad as one octave and its phase deviations are quite small. An original design of the novel broadband phase shifter is presented, in which the artificial CRLH structure was implemented by microstrip quasi-lumped elements. Both the simulated and measured results of the 90° broadband differential phase shifter are presented.