External library to define Coefficient Funtion

General
1

I am now trying to define a CoefficientFunction using other library named Radia.
but the NGSolve says

TypeError: float() argument must be a string or a real number, not 'ngsolve.fem.CoefficientFunction'

Are there any alternatice ways to define such a CoefficientFunction?

import radia as rad
def H(x,y,z):
	c1 = rad.ObjRaceTrk([0,0,0],[0.7,0.8],[0,0],0.1,12,10,"auto")
	Hx = rad.Fld(c1,"bx",[x,y,z])
	Hy = rad.Fld(c1,"by",[x,y,z])
	Hz = rad.Fld(c1,"bz",[x,y,z])
	return (Hx,Hy,Hz)

Hs = CoefficientFunction(H(x,y,z))