The Biot-Savart law for calculating magnetic fields due to a current is presented in my freshman physics book as a general way of getting B from I. But there's no time delay implied by the integral. Can I just manually throw the time delay into the integral? For instance, to numerically calculate the magnetic field at some point due to a time harmonic current in, say, an antenna, can I just: 1. Break the antenna up into known discrete current elements, 2. Calculate the delay between each element and the point of interest, 3. Use Biot-Savart to find B due to each element, and multiply each term by it's associated phase shift (exp(-i*w*delay)). 4. Add em up. It may not be computationally efficient but it would be simple. But would it give the right answer?