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Quantitative conversion of evanescent into propagating SH guided waves is demonstrated.Complex dispersion and group velocity curves are used to study conversion process.Amplitude coefficient of the converted propagating wave is obtained.Power analysis is performed on evanescent and propagating SH guided waves.Conversion efficiency is strongly frequency dependent and can be significant.Conversion of evanescent shear horizontal (SH) guided waves into propagating is presented in this paper. The conversion is exemplified by a time-harmonic SH evanescent displacement prescribed on a narrow aperture at an edge of a semi-infinite isotropic plate. The conversion efficiency in terms of the amplitude of the propagating SH mode converted from evanescent can be expressed in a very simple compact form. The magnitude of the conversion efficiency can be quantified through a derived semi-analytical form based on the complex reciprocity theorem in conjunction with a two-dimensional (2-D) finite element analysis (FEA). Through power conversion analysis, it can be shown that the power flow generated into the plate due to evanescent incident is complex valued. It is theoretically proved that the real part of the complex power flow is associated with the propagating SH modes, while the imaginary part is confined due to the evanescent modes at the plate edge. The conversion efficiency and converted modes are dependent on the geometric configuration of the aperture as well as the selection of the excitation frequency.