Are iCoupler products sensitive to external magnetic fields?

No – unless such fields are extremely strong and of high frequency. Since the transformers used within iCoupler devices typically measure about 0.5 mm in diameter, it takes a very high magnetic field rate-of-change to induce a voltage large enough to cause a performance error. For example, if a wire carrying a current oscillating at 1 MHz were to be placed 5 mm away from an iCoupler transformer, the current amplitude that would be required in order to cause a problem with the iCoupler's performance is 500A! (An analysis of this can be found in the Applications section of any iCoupler data sheet.)