vector poynting

It is unclear which version of Mathcad you are using . If you're referring to the impulse of Dirac, it is a special function of an independent variable. In your formula appears only the delta symbol. Instead, you should write a function. If, moreover, the symbol delta, is referred to any increase , it must have been previously defined so that the formulas give a result.

To get a result from your equations, you have to use the appropriate symbol of  equality, ie that corresponding to the assignment (obtained with a colon).

The Bessel functions must be written according to the definition of Mathcad, ie: J0 (x), Jn (n, x), K0 (x), Kn (n, x), ...

Hi.

Poynting vector is S = 1/μ E x B. As you subscript it with z1, it's assumed that E = (E,0,0) and B = (0,B,0). But in your expression can't identify E nor B.

Also, what are J and K? Bessel functions? If that, in Mathcad you don't have J2, but have Jn with two args. And for K2 must to write your own Bessel function.

For functions in general, you must to write exponents as (J.1(UR))^2, but not J.1^2(UR).

From the fisrts equations, those for a,b and F you can't derive S, at least without explain from where came R, n1 or phi.

Finally, Delta seems to be a small displacement from some equilibrium position, and guess that it is the small of the problems for write the equation for the Poynting vector.

Best regards.

Alvaro.

Could you please post a worksheet. Without a worksheet we can only guess what your problem actually is.