Introduction to EMI/EMC
Electromagnetic Radiation (EMR) and its Effects
In recent years there has been considerable discussion and concern about the possible hazards of electromagnetic radiation (EMR), including both RF (Radio Frequency) energy and power frequency (50-60 Hz) electromagnetic fields.
All life on Earth has adapted to survive in an environment of weak, natural low-frequency electromagnetic fields (in addition to the Earth's static geomagnetic field). Natural low-frequency EM fields come from two main sources: the sun and thunderstorm activity. But in the last 100 years, man-made fields at much higher intensities and with a very different spectral distribution have altered this natural EM background in ways that are not yet fully understood. It has been known since the early days of radio that RF energy can cause interference in most of the wireless operated systems and in devices which process extremely low power signals associated with control systems and in medical equipments. Very high density of Electromagnetic Fields have been known to have resulted in injuries by heating body tissue. These heat-related health hazards are called thermal effects. In addition, there is evidence that magnetic fields may produce biological effects at energy levels too low to cause body heating. The proposition that these thermal effects may produce harmful health consequences has produced a great deal of research. Human body nervous system is also known to work on extremely low intensities of electrical signals. Very little has been done to investigate the effect of Electromagnetic Fields on the human nervous and control system which as such leaves a lot of scope for future research.
Potential Sources of EMR
The list could be endless starting with seemingly harmless AC (alternating current) operating devices to all the intentional and non- intentional transmitters. Appreciable radiation occurs as the size of the components and connecting wires approaches one tenth of the wavelength of the operating frequency. The intensity of the field so radiated also depends on the power handled by the device. To name a few tube lights, spark plugs, washing machines, music systems, power amplifiers, computers, lifts, air conditioners, cable TV, computer screen etc all fall in the category of non-intentional transmitters but can be potential source of Electromagnetic Radiations. All radio and TV broadcasting systems, telecommunication systems and equipments, RADARS, mobile phones etc are intentional transmitters of Electromagnetic Radiations and may result in typical effects on various systems in addition to causing serious interference problems and affecting human body.
With ever increasing use of modern digital technology in almost all the modern processing and communication equipments the threat of unintentional Electromagnetic Radiation is further enhanced. As all digital signals positively have a very large bandwidth, its increasing use will result in Electromagnetic Radiations in almost all the frequency ranges there by leaving a possibility of affecting most of electronic devices and also human beings.
Some Typical Effects of EMR
Electromagnetic Interference: Interference is the energy levels introduced by electronic or communications systems that have a detrimental effect on other systems. Any electronic system is capable of receiving Electromagnetic Radiations if the size of the components or connecting wires approaches one tenth of frequency that may be present in the surrounding environment due to any intentional or unintentional transmitter. Depending on the intensity of this unwanted received radiation there could be instances of malfunctioning of the device receiving this energy. There have been number of instances where such a condition had resulted in catastrophic failure of the equipments. The most famous example is the failure of the Electronic surveillance system installed at one of the ships of United Kingdom Naval forces during Falkland war due to operation of its own Radar system installed on the same warship. As a result of this only one system could be operated at one time resulting in the loss of the ship. Intentional Jamming of the radio receivers by the security and police forces is the utilization of this effect to make the enemies receivers inoperative, however it can also happen due to unwanted and unintentional Radiation of Electromagnetic fields.
Effects on Human Body: Body tissues that are subjected to very high levels of RF energy may suffer serious heat damage. These effects depend upon the frequency of the energy, the power density of the RF field that strikes the body, and even on factors such as the polarization of the wave.
At frequencies near the body's natural resonant frequency, RF energy is absorbed more efficiently, and maximum heating occurs. In adults, this frequency usually is about 35 MHz if the person is grounded, and about 70 MHz if the person's body is insulated from the ground. Also, body parts may be resonant; the adult head, for example is resonant around 400 MHz, while a baby's smaller head resonates near 700 MHz. Body size thus determines the frequency at which most RF energy is absorbed. As the frequency is increased above resonance, less RF heating generally occurs. However, additional longitudinal resonances occur at about 1 GHz near the body surface.
Health Care Engineering: Is electromagnetic Interference (EMI) becoming a problem in the healthcare environment? Although electrical interference in hospitals is often regarded as no more than a minor nuisance, there are documented cases in which equipment failures due to Electromagnetic Interference (EMI) have lead to injury or death. Some examples fare as follows: -