So.. I'm a biomedical engineer, and a new technology that is arising is being able to control magnets that "swim" around the body using electromagnets oriented around the outside of the patients body. It has been said that electromagnets can't be used on the inside of the patient because they get too hot. What is the source of the majority of the heat? Is it the current moving through the wire, or the current induced in the core of the electromagnet? Are there methods to make electromagnets more efficient to reduce heat?