The electromagnetic coils. By coil we mean colloquially a solid core on which thread-like or ribbon-like material can be wound, such as textile fibers, films, electrical conductors or other, can be compensated or not and are technically called EMI Filters (ElectroMagnetic Interference) is a passive filter present in most electronic equipment, to allow these devices to comply with electromagnetic compatibility regulations, in particular those concerning conducted emissions. Basically, the EMI filter is a low-pass filter which is connected as the last stage between the equipment and the power supply, so as to attenuate the disturbing components that any electronic device would tend to emit. Obviously, the filter must be transparent at the power supply frequency (50-60 Hz) to allow the correct functioning of the device, while it must act in the range of frequencies established by the legislation (150 kHz-30 MHz).
In physics, the coil is a set of turns, the number of which can vary from a fraction of a turn to many thousands, made with a conductive material. The fields of application are the most varied, from electronics to medicine (magnetic resonance). Its main electrical parameter is called inductance.
A traditional coil has a resonant frequency defined by its geometry and electrical characteristics, and a non-zero impedance, so that when an electric current flows through the coil, it generates heat.