Electromagnetic interference (EMI), also known as adverse electromagnetic impact (ansson index), is the adverse influence of electric equipment and electronic systems to work acceptably within their electromagnetic environment, limiting the undesired generation, transmission and reception of electromagnetic energy that can create harmful disturbance to health and/or damage. Many types of electromagnetic interference result from communication systems. Some are caused by communications networks. Others may be from power lines, medical imaging equipment, military radar systems and air traffic control systems. All of these sources generate EMIs, some of which can be very severe.
EMC stands for Electromagnetic Compatibility. A mismatch occurs when a transmitter transmits energy at a higher frequency than that which is allowed by the human body. The human body is not designed to receive electromagnetic frequencies from sources above frequencies which it is designed to handle. When this happens the potential health risks are great. EMC problems can occur from many sources and are often difficult to determine.
EMC problems occur mostly with electrical engineering devices such as headphones, power supplies, and receivers. There are solutions which address these issues but in general they are more expensive and sometimes impossible, to correct once the apparatus has been purchased. Many engineers consider this to be a defect in the design of the device rather than a problem caused by electromagnetic interference.
EMC problems also exist in devices which rely primarily on electrical equipment for operation. Some medical devices used in hospitals and assisted living facilities contain a metal shield or brace. This brace or shield consists of several individual components, one for the transmission of electromagnetic waves and one for the decibel reduction of unwanted emissions. This is designed to reduce the potential damage from electromagnetic interference while keeping the electrical equipment operational. Without this shield, the possibility of EMC issues is higher since the metal itself would be exposed to EMC and electrical emissions at the same time.
One method of protecting against interference is the use of a CISPR or Common Standard Protocol for Personal Computer Protection. This standard was developed by three U.S. organizations namely, The American Society for Testing and Materials (ASTM), The United Kingdom’s Health Forum, and the European Computer Manufacturers Association. The primary goal of the CISPR is to set down guidelines for EMC practices to protect computer systems and apparatus from unwanted electromagnetic interference. In addition, the standard requires manufacturers to provide evidence that they have used their products in compliance with the standards.
The principal method of protection is for switching power supplies to shut off when electromagnetic interference is detected. Although this may seem like an effective solution, it is only a temporary measure. For one, the switch must recognise the existence of an electromagnetic field and generate an appropriate shutdown command. In most cases, the command to turn off is generated from software.
Another option to consider is shielding sensitive electronic equipment with electromagnetic-absorbing materials. Currently, a number of choices are available in the market. For instance, conductive foil is used as an effective means of preventing EMC interference since the material has a thickness that is equal to the thickness of sensitive electronic components such as microprocessors. Moreover, shielding using bismuth metal or steel reinforcement has been found to be quite effective in blocking the radiation that is radiated by power lines.