Final answer:
The zipper artifacts may occur in both the frequency and phase encode directions due to RF interference. Electric and magnetic fields of an electromagnetic wave are in phase and perpendicular, which is relevant to understanding wave interference and the development of directional antenna systems.
Step-by-step explanation:
The question concerns the orientation of zipper artifacts which may be related to interference from RF (radio frequency) signals in medical imaging, specifically in the context of MRI (Magnetic Resonance Imaging). According to the information provided, zipper artifacts are oriented perpendicular to the frequency encode direction, meaning that they can occur in either the frequency or phase encode directions, not exclusively in one or the other.
In regards to electromagnetic waves, as described in the reference material, electric and magnetic fields (E and B) produced by an antenna are in phase and perpendicular to each other and to the direction of propagation, characterizing a transverse wave. The fields propagate in the form of electromagnetic waves at the speed of light, which is the same across all frequencies. Whenever rays emanate from a source and travel at different angles, they can interfere constructively or destructively, depending on whether they are in phase or out of phase, respectively.
The reference to interference patterns formed by electromagnetic waves is analogous to those produced by sound waves from two speakers, suggesting applications like creating directional antenna systems that preferentially emit in certain directions based on the principle of interference.