The peak silicon strains occur at peaks and troughs of the waves, and are calculated using ?? Si peak = h 2 R c , where h is the Si thickness, and Rc is the radius of curvature at peak or trough, which is given by R c = 1 y ?????? ??? x = ??? [ ( 2 n - 1 ) ?? 2 k ] where n is an integer and y??? is the second derivative of y with respect to x.