I want to simulate simple ripples for rain drops. I don't need a surface displacement, just an effect in bump option.

I want to get something like these, but a bit more simple:

Fresnel shader w/wave equation

2d wave equation

And I have found this equation:

z=(cos( 0.5sqrt(x^2+y^2)-6n)/(0.5(x^2+y^2)+1+2n), n={0…10}

but i need some heelp to adapt to AOI