The 3D equal diameter Helmholtz coil is a unique, custom-made 3D Helmholtz coil. The three dimensions of the coil are identical, with each having the same diameter, number of turns, uniform area, volume, size, and internal space. The frame is nonmagnetic, making the 3D equal diameter Helmholtz coil especially suitable for use within the shield. The coil can also generate an AC magnetic field. The resistance and inductance of the three axes is the same, so the same AC power supply can be used for three axis switching to control the magnetic field with a voltage. The maximum magnetic field in each dimension of the 3D equal diameter coil ranges from 1-5Gs.