see Ref. 6. This is given solely by material parameters and has no user input.
where x0 is the user-specified location of the point source generating the spherical waves,
x is the position of the boundary, and
rb is the distance between the two.
where is the Hankel function of the second kind of order m given in terms of the Bessel functions of order
m of the first and second kind,
Jm(
x) and
Ym(
x), respectively. Notice that the source axis vector
esa is automatically normalized in this implementation.