Electromagnetic Radiation (EMR) and its Effects
In recent years there has been considerable discussion and concern about 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 Earth's static geomagnetic field). Natural low-frequency EM fields come from two main sources: sun and thunderstorm activity. But in 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 early days of radio that RF energy can cause interference in most of 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 effect of Electromagnetic Fields on 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 intentional and non- intentional transmitters. Appreciable radiation occurs as size of components and connecting wires approaches one tenth of wavelength of operating frequency. The intensity of field so radiated also depends on power handled by 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 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 modern processing and communication equipments 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 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 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 size of components or connecting wires approaches one tenth of frequency that may be present in surrounding environment due to any intentional or unintentional transmitter. Depending on intensity of this unwanted received radiation there could be instances of malfunctioning of device receiving this energy. There have been number of instances where such a condition had resulted in catastrophic failure of equipments. The most famous example is failure of Electronic surveillance system installed at one of ships of United Kingdom Naval forces during Falkland war due to operation of its own Radar system installed on same warship. As a result of this only one system could be operated at one time resulting in loss of ship. Intentional Jamming of radio receivers by security and police forces is utilization of this effect to make 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 frequency of energy, power density of RF field that strikes body, and even on factors such as polarization of wave.
At frequencies near 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 person is grounded, and about 70 MHz if person's body is insulated from ground. Also, body parts may be resonant; adult head, for example is resonant around 400 MHz, while a baby's smaller head resonates near 700 MHz. Body size thus determines frequency at which most RF energy is absorbed. As frequency is increased above resonance, less RF heating generally occurs. However, additional longitudinal resonances occur at about 1 GHz near body surface.
Health Care Engineering: Is electromagnetic Interference (EMI) becoming a problem in 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: - • In 1992, a patient attached to a monitor-defibrillator in an ambulance died because of interference from ambulance radio prevented machine from working (1). • In 1987, patient monitoring systems failed to sound alarms because of interference; two patients died as a result (2).
• In 1993, a patient fitted with a pacemaker went into ventricular fibrillation shortly after being scanned with a metal detector outside a courtroom (2).
As in many other fields, amount and complexity of electronics in hospitals and other medical environments is increasing year by year. Despite this, number of reported incidents of EMC (Electromagnetic Compatibility) problems fortunately does not appear to be growing. This is probably because most manufacturers and designers of medical electronic products have developed a good awareness of EMC. Pacemakers are typical examples, where their design with respect to compactness and immunity to radio frequency interference has greatly improved over years. Nowadays, pacemakers are very reliable, but can still fail under extreme conditions. Pacemakers have failed in patients undergoing electro surgery (2) and in other cases where patients kept mobile phones in their chest pockets, a few centimeters from pacemaker leads (3). The powered Wheelchair is another typical example: there are many stories of radio frequency interference. (RFI) from mobile phones or police ‘walkie-talkies’ causing wheelchair to drive itself and its occupant into traffic. These stories are based on real occurrences; reports of incidents in USA in early 1990s prompted Food and Drug Administration (FDA) to investigate problem and recommend that manufacturer change design to give an immunity of at least 20V/m to RFI.