Unidirectional acoustic transmission in asymmetric bull＇s eye structure

Unidirectional acoustic transmission has been investigated in an asymmetric bull＇s eye structure, which consistes of a sub- wavelength hole with concentric grooves on one side of a thin steel plate. When acoustic waves impinge normally on the groove side of the asymmetric structure, a strong acoustic transmitted energy flux is observed in the frequency range of 400-450 kHz, while there is no obvious transmitted energy flux in the same frequency range if the acoustic waves impinge normally on the other side. Thus, a remarkable unidirectional acoustic transmission behavior is exhibited by the current struc- ture. With changing the period of the grooves, it is found that the transmitted acoustic energy flux keeps unchanged while the frequency of the transmitted waves can be modified. The experiments are performed, which has confirmed the unidirectional acoustic transmission behavior in the asymmetric bull＇s eye structure. The asymmetric bull＇s eye structure may have potential application in ultrasound diagnosis and therapy.