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An ultra-sparse, broadband programmable Active Acoustic Meta-surface (AAMS) that is demonstrated to function as a multi-functional Active Acoustic Meta-device is developed. Functionalities Acoustic Barrier (AB), Acoustic Switch (AS), and Acoustic Transmitter (AT) have been successfully explored. AB functions at a broadband frequency of 455 to 679 Hz as an approximately 100 % acoustic reflector. The functional range of the AS is 425 to 800 Hz, and similarly, the functional range of the AT is 300 to 800 Hz (the full range of the applied frequency sweep). Being a re-configurable device, the AAMS has variable thickness. On a wavelength scale, it varies from 0.10 λ to 0.99 λ for the said functionalities. Here, λ is the wavelength. [ABSTRACT FROM AUTHOR]

This paper addresses the acoustical performance of a cylindrical expansion chamber muffler with single inlet, single outlet configuration. Analytical result for the transmission loss for the muffler has been derived by using the plane wave theory and the results are compared with the finite element analysis. The analysis for both the cases is done for the frequency varying from 50 Hz to 1500 Hz. The general peak value for transmission loss for the analyzed geometry was 13.16 dB, however a sharp transmission loss peak was also observed. The critical values for the transmission loss at three different frequencies are studied with the aid of finite element simulation. [ABSTRACT FROM AUTHOR]