This thesis proposes an acoustic metamaterial structure that effectively blocks the transmission noise of the muffler. In addition, a metamuffler is designed to block noise in the selective frequency band using an optimal design technique. Instead of designing the entire structure of the muffler, only one unitcell is designed and arranged repeatedly inside the muffler to block noise at the target frequency. The noise blocking effect of metamaterials can be explained by the bandgap in the dispersion curve. Dispersion curve is the relationship between natural frequency and wave number. In some frequency bands of the dispersion curve, a region that doesn't have a natural frequency is called a band gap. Sound waves are blocked in this section. Target frequency bands extend from low frequency bands to middle/high frequency bands. The unit cell is designed that target frequency band is included in the bandgap. These unit cells are repeated periodically to form a metamuffler. Transmission loss is used to evaluate the acoustic performance of the designed muffler. Finally, the validity is verified by comparing the results of the finite element analysis and the acoustic experiment.
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2016R1D1A1B03932357) and by the Center for Advanced Meta-Materials (CAMM) funded by the Ministry of Science and ICT as a Global Frontier Project (CAMM-No. 2020M3A6B3074299).
