The classical single bubble's acoustic emission equation has been used for a long time to describe the sound filed of the bubble radiation, however, this formula does not consider the influence of the viscosity of the medium in the process of sound wave propagation, so in some special cases, it is more reasonable to make corresponding corrections to it.
Based on the boundary condition of the bubble, i.e., the vibration velocity of the bubble wall is equal to the velocity of the particle vibration velocity of the external medium at the bubble's boundary, the acoustic wave equation in spherical coordinate system in viscous medium is solved, then the modified acoustic emission formula of the bubble in the viscous medium is given.
In the numerical calculations part, the bubble radius R(t) is solved from the bubble dynamics equation using the fourth-fifth order Runge-Kutta method. Then the bubble's radiation sound field is obtained using the direct substitution method and the finite element (The pressure acoustics module; 2D axisymmetric geometric model) method respectively to find out that, the modified expression " ppresent" given in this paper is more accurate to describe the bubble's radiation than the classical expression " pclassical" at the high-viscosity, high-frequency and long-distance case. In these cases, if the acoustic emission of bubbles continues to be measured using the classical expression, it may have an impact on the characterization of cavitation, such as the inaccurate description of parameters like cavitation intensity and cavitation threshold.