Effective impedance boundary optimization and its contribution to dipole radiation and radiation pattern control.

Radiation pattern control has generated much interest recently due to its potential applications. Here we report the observation of high-efficiency dipole-like radiation of sound with broad bandwidth through a decorated plate with periodical two-dimensional Helmholtz resonators on both sides and a single slit at the centre. The decorated plate was optimally designed to adjust the effective impedance of the boundary, and the underlying mechanism of radiation pattern control is attributed to wave vector tailoring. The high radiation efficiency is due to the Fabry-Perot resonances associated with waveguide modes in the centre slit. The method to obtain a collimated beam without any sidelobes is also provided. Our findings should have an impact on acoustic applications.