Waves of despair
IT WAS almost the last flight for passengers on board a commuter aircraft thattook off from Washington D C one nightin April last year. As the aircraft gainedheightthe pilot set its course for a shortflight to NewarkNew Jersey. Then suddenlythings went wonky. The air trafficcontrol radioed the pilot that the aircraftwas 16 km off course. Attempts to correct the plane's course failed becausealthough the on-board navigationalinstruments showed that it was headingin the right directionair-traffic controlknew it was not.
Oblivious to the crewone of thepassengers was using a laptop computerthat emitted stray radiation at a frequency that happened to match thatof the broadcasts from the beacons onthe ground. This was confusing theinstruments on the aircraft. When aflight attendant spotted the laptop andasked the passenger to switch it offeverything returned to normal.
This is not just one isolated incidentinvolving electromagnetic interferenceor EML Ratherinvisible electromagneticfields can be emitted by almost all electrical and electronic gadgets. Accordingto the International Federation ofAirline Pilotsthere are at least 20 EMIincidents involving aircrafts each year.Pilots have reported that EMi due to theuse of cellular phones and portablecompact disk players can block communications between aircraft and groundcontrol.
EMI can stop pacemakers in heartpatients and heart monitors in hospitals.Over the past 15 yearsthe us Food andDrug Administration (FDA) has receivedmore than 100 reports Of EMI-relatedincidents in hospitals. Researchers alsoclaim that prolonged exposure to EMIthrough high voltage transmission linesand cellular phones - among otheragents - can cause cancer in humans.In large databasesEMI can erase all thestored data. It can interfere with a fly-by-wire system or missile circuitrywreaking havoc in aviation and militaryinstallations. The effects are insidiousand frightening. "Most worrisome is thefact that the number of Emi incidents areon the increasesays Jocelyn Kaiser, a reporter with the American journal Science.
The hidden enemy It is gradually being realised that every electrical or electronic equipment, be it a microwave oven, mixer, television, mobile phone, high voltage distribution line or computer, can generate electromagnetic 'noise'. Radio waves are created whenever an electric field changes rapidly. A simple transmitting antenna, for instance, consists of a pair of wires pointing in opposite directions and carries a rapidly changing electrical field. The direction of the signal and its strength depend on factors such as length, spacing and orientation of the conducting wires.
Almost all modern electrical and electronic gadgets are potential transmitting antennae. They are packed with intricately spaced conducting wires. And the microprocessors in such devices rely on pulses of data that switch between zero and five volts, upto 100 million times a second. As a result, they generate stray electromagnetic noise or disturbance which could have debilitating effects.
The crux of the problem ties in the high-speed circuits that are now routinely used in video games, laptop computers and camcorders and a growing number of other devices such as computers built into car engines. Tens of millions of data pulses flow through their circuits every second. As a result, these circuits emit radiations at high frequencies.
The relatively slow chips that were in vogue in the early '80s hardly approached the frequency of 30 mega- hertz (mhz) and above. But the latest state-of-the-art microprocessors work at speeds of 100 mhz or more at each of the harmonics. And as we continually try to develop faster microprocessors, the problems stemming from EMi are likely to get even more acute in the near future.
In the past, electrical and electronics engineers have minimised Emi by shielding sensitive instruments inside ferrite sleeves or behind metal foils. Traditionallymuffling electromagnetic noise has been a somewhat desperate affair - slapping on more andmore shielding to the product so as toensure that the deleterious EMi effectscan be avoidedsays James Drewniak, an electrical engineer studying Emi at the University of Missouri in Rolla, us.Look at thepower cables in almost any computer today. The big neck is wherecomputer manufacturers add ferrite sleeves to cut down emissions he adds. But these methods are hardly effective in the case of high- speed circuits now being designed. As computers get smaller andfasterthe problems have out-stripped the solutionsasserts Drewniak, whose four-year-long research appears to have finally paid off.
Drewniak and his colleagues adopted a different strategy to deal with the EMI problem. Instead of trying to soak up stray radiations, they attempted to design circuit boards in a way that minimises the amount of electromagnetic radiation they produce in the first place. They began by measuring the radiation produced by common arrangements of components on the circuit boards and also identifying those which act as miniature transmitting antennae. Very soon, they were able to produce.a database of simple geometric arrangements of those components that always generate high levels of electro-magnetic radiation. They also worked out how to rearrange the circuit so as to reduce the noise.
The team has now developed a computer programme that looks for similar patterns in other circuit board designs.When it finds onewethen focus on the area to see how theproblem can be solvedDrewniak explains. He is already helping companies such as General Motors solve EMI problems. He claims that in future, designers of computer circuit boards will be able to check their layout within minutes with the help of his programme.
Crisis in the hospital
But preventing electronic and electrical devices from producing unwarranted electromagnetic signals is only half the problem. It is also imperative to shield components which are sensitive to stray radiation, such as medical equipment. As Drewmak puts it,A device that produces electromagnetic radiation is alsosusceptible to it because receivingantennae act much like transmitters inreverse."
According to himthough avionicscomputer and auto industries have agood record in dealing with electromagnetic noisemost companies manufacturing medical equipment do not.Several cases of the effects of Emi in hospitals have been reported to the FDA. Inone instanceEMI from a paging systemtriggered an electric knife that burntthrough a nurse's apron. It has alsobeen reported that EMI could kill thefoetus in a mother's womb. Two yearsagothe FDA began persuading medicalequipment manufacturers to reduce EMIsensitivity.
Awareness of the problem is risingin Indiawhich recently hosted aninternational conference on Emi. Testingof electronic goods for EMI is done bythe Madras-based Centre forElectromagnetics (CEM)which hascomputer-aided design facilities toassess the problem and offer solutions.Says S K Sinhaprogramme director ofcEmBy doing an EMI test at the design stage itself, manufacturers can make their products Emi-free at a small cost. This would definitely improve the quality. cEm has now offered design consultancy services to agencies such as the Mahanagar Telephone Nigam Limited, Oil and Natural Gas Commission, State Bank of India and Delhi Electric Supply Undertaking, among others, for ensuring EMI-ftee operation of their communications network.
Working towards a similar goal, researchers at the Bhabha Atomic Research Centre (BARC), Bombay, have developed a high power microwave generator which could be used for testing electrical and electronic equipment. Christened KALI or kiloampere linear injector, BARc has given the first machine to Electronics Research and Development Establishment (ERDE), Bangalore, which is using it to test electrical components and equipment for electromagnetic compatibility.
Though there exist some standards that stipulate the allowed levels Of EMI for electrical and electronic devices, these differ from country to country. Says P N A P Rao, project director (systems), Aeronautical Development Agency, Bangalore, and chairperson of the Society Of Emc Engineers (India), As the risks involved are high in strategic applicationscertain standards havebeen set. Howeverthere is no awareness at all among common consumersespecially in countries like Indiaaboutthe gravity of the problem." As a resultmanufacturers do not make theirproducts EMI-ftee. "UnlessIndian consumers demand such productsthey willnot make ithe asserts.