Manipulation of double acoustic defect states based on connection phase mismatching

Abstract

Defects in periodic structures always lead to the defect states, which can modulate the physical or chemical properties of materials to realize devices with very high performance. To form defects in periodic waveguides, we connect the three periodically corrugated ducts with different initial phases, which result in the double transmitted peaks in the forbidden band. These two peaks, known as the defect states, correspond to the acoustic energy localizations at the two different defects and highly rely on the connection phases, which are defined as the difference of initial phases. For opposite connection phases, the frequencies of two defect states shift in the opposite directions with the connection phase increasing. However, there exists a frequency cutoff region when the connection phase equals π. The transmitted peaks cannot shift continuously but jump over this region. This phenomenon is explained theoretically with the coupled-mode theory on the periodic acoustic waveguides and the frequency cutoff region can be determined by the geometry parameters of the structure. For the same connection phase, the cutoff region disappears and the two defect states shift continuously from the low frequency to the high frequency with a fixed interval when the connection phase increases. The proposed double defects manipulation can help us to better understand the interactions of different defect states, and pave the way for functional devices in various applications including sound detection, underwater communication, and other wave control fields.