  In PT-symmetric gratings, asymmetric diffraction can be generated by
modulating the ratio between imaginary and real refractive indices. In this
paper, a rigorous coupled-wave analysis (RCWA) has been developed to analyze
the diffraction properties of acoustic PT-symmetric gratings with two kinds of
modulating approaches, including modulating the effective modulus and the
effective density. Asymmetric diffraction with both Bragg incident angles and
perpendicular incident angles is discussed by using the RCWA method. Results
show that the modulation ratio for the diffraction vanishing point changes with
the modulation amplitude differently for two kinds of modulating approaches.
Moreover, the sound energy will be weaken or be enhanced at Bragg incident
angles depending on the sign of incident angles and the modulation ratio.
