A Primer On Automotive EMC For Non-EMC Engineers
A Primer on Automotive EMCfor Non-EMC EngineersBY GARY FENICALThe automotive industry has changed drastically in recentyears. Advancements in technology paired with tighter federalfuel and emissions regulations have resulted in the needto place more electrical systems into vehicles. This in turnplaces a greater emphasis on keeping the ElectromagneticInterference (EMI) of these systems from interfering with eachother through radiated and conducted emissions, as well ascrosstalk between the multitudes of on-board systems.In addition to the sources withinthe vehicle, there are externalsources of EMI that could interferewith vehicle electronic systems. Thesesources include, but are not limitedto, cell phone towers, commercialbroadcast signals of all sorts, remoteentry devices as well as RADAR nearairports and other such places. Thereare devices brought on board bypassengers such as Bluetooth devices,DVD players, video games and prettymuch anything else you or yourchildren can think of that must also betaken into consideration by automakers.Before discussing the best solutionsfor common EMI issues, it is helpful20In ComplianceJune 2013to understand EMI; its influenceson vehicle EMC (ElectromagneticCompatibility) and where EMIshielding is often used in automobiles.Once engineers have all the informationand have considered all of the factorsaffecting EMI, then they can choose theproper shielding material for their need.WHAT IS EMI?EMI is a process by which disruptiveelectromagnetic energy is transmittedfrom one electronic component ordevice to another via radiated orconducted paths, or both. There arealways both paths there but many timesone is more prevalent than the other. Inwww.incompliancemag.com
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Consumers have become more interested in the optional convenience and entertainmentsystems available in vehicles today. These options include rear-view cameras, back-up radar andcomplicated infotainment systems.an automotive electronic system, EMIcan adversely affect the performance ofan integrated circuit internally, as wellas that of other electronic componentsin close proximity.There is a root cause to most EMInoise. In a digital system, clock pulsesare generated to operate the logic. Asthese clock pulses are developed, theyhave a given rise time. The rise time,as it gets shorter, has a tendency tocreate a broadband energy pulse on theleading edge. This is commonly knownas overshoot and/or ringing.The energy present in the overshootand ringing is the basis for generatingother higher frequencies calledharmonics. These higher frequenciesare multiples of the clock frequency.Both odd and even multiples(harmonics) exist. In most cases, theodd harmonics (observed at 3, 5, 7,and 9 etc. times the fundamental ofthe clock frequency) create most of theEMI noise problems. However, evenharmonics do exist and must not beignored.Placing more and more electronicsystems into the confined spacesof vehicles poses a potential EMIproblem. If not properly addressed,the interference can cause each systemto malfunction or even fail. Currenttrends and technology advancementsare introducing new electronic systems,and with that, new potential EMIissues into vehicles at a rapid pace.And, of course, every new device orsystem must meet all mandatory EMCrequirements that give a reasonableassurance that the device or system willoperate as intended and will not causeany other devices or systems to not22In ComplianceJune 2013operate as intended. This is especiallycritical where safety is concerned.becomes more difficult to meet radiatedemission standards.CURRENT TRENDSINFLUENCINGVEHICLE EMIAdditionally, consumers have becomemore interested in the optionalconvenience and entertainment systemsavailable in vehicles today. Theseoptions include rear-view cameras,back-up radar and complicatedinfotainment systems. As moreelectronic applications are added tovehicles, additional EMI shielding forthese systems is necessary to ensurethe safety and functionality of theautomobile. And let us not forget thePEDs (Portable Electronic Devices)many of us like to bring into thevehicle. Although the PEDs must meetFCC radiated and conducted emissions,these devices have not been specificallytested for use in an automotive system.Generally, conducted emission willnot matter because there are onlyrequirements for conducted emissionon the AC mains.As the automotive industry hasprogressed, there have been severalfactors external to the business whichhave influenced the evolution oftoday’s vehicle. Between increasedfuel and emissions standards by thefederal government to the consumer’sinterest in additional convenience andentertainment options, the automotiveindustry must address these trends andthe additional potential sources forEMI.With the new fuel efficiency standardsissued by the TransportationDepartment and EnvironmentalProtection Agency stating vehicles mustget an average of 35.5 miles per gallonby 2016, automakers are increasing theuse of electronic engine controls. Theseelectronic controls allow more precisecontrol of the engine and therefore, fueluse, helping to achieve the increasedfuel efficiency standards. The use ofthese controls also means additionalelectronics introduced into the car,resulting in potential EMI issues.As fuel efficient automobiles become afocus, hybrid and electric vehicles aregaining popularity with consumers.These types of vehicles feature somedegree of electronic drive systems,introducing new EMI issues forengineers, which must be dealt with tomaintain the “mission critical” systems.These types of drives are high currentdevices. As current increases in acircuit, emissions increase. Therefore itwww.incompliancemag.comSHIELDINGShielding is the practice of reducingthe electromagnetic field in anenvironment by blocking it, or isolatingit from the “outside world” withsome type of conductive or magneticmaterial. The amount of reductiondepends on the material used,thickness of the shield, amplitude andthe frequency of the fields. Shieldingis noninvasive and does not affecthigh-speed operation of componentsand systems. Other solutions such asfilters, ferrites and/or absorbers canchange the signal characteristics andaffect circuit operation. Shielding canbe a stand-alone solution, but is morecost effective when combined withother suppression techniques such asfiltering, absorbers, grounding and,
As more electronic applications are added to vehicles, additional EMI shielding for thesesystems is necessary to ensure the safety and functionality of the automobile. And let us notforget the portable electronic devices many of us like to bring into the vehicle.most importantly, proper design.The use of shielding can take manyforms, from RF gaskets to board levelshielding (BLS) and there are severalfactors to consider when choosingshielding material.SELECTING PROPERMATERIALSThere are many factors that affect theproper selection of RF gasket materials.The following list identifies some ofthe key issues that must be consideredwhen choosing a material. Operating frequency Cycle life Materials compatibility Electrical requirements Corrosive considerations Materials thickness/alloy EMC compliance specification Space and weight considerations Operating environment (In thepassenger compartment, under thehood, etc.) Product safety Load and forcesWHERE IS EMI SHIELDINGUSED ON A VEHICLE? Cost Attenuation performance Storage environment Oil and fuel resistanceDSA815 Ad-InComp Layout 1 9/6/12 2:22 PM Page 1 RecyclabilityAs stated previously, there are bothinternal and external sources ofEMI to vehicles. The automotiveIt's time to rethink EMCpre-compliance testing! Make limit lines for the EMI tests you need Load correction tables for your antenna and connection Set scans as quickly as 10 ms for a first look Use RBWs down to 100 Hz to find error sources Special EMI option & tracking generator for evenmore accurate readingsSave one trip to the compliance laband the DSA815 pays for itself!Get our New EMC App Note @ RigolEMC.comwww.incompliancemag.comJune 2013In Compliance23
electromagnetic environment is verycomplex, requiring automakers toconsider both these external andinternal sources prior to production ofvehicles.Internal EMI problems can range fromsimple static on the radio to a loss ofcontrol of the vehicle. Internal electricalsystems that can affect the vehiclefunction include: Collision avoidance radar Navigation-radio combination Power steering module Airbag inflator Adaptive cruise control Infotainment systems Tire pressure monitor, etc.Vehicles’ electronics can be affectedby harsh external EMI environments.EMI can be generated from powertransients, radio frequency interference,electrostatic discharge and power lineelectric and magnetic fields. Theseexternal sources can include: Garage door openers Remote entry devices Cell phones Bluetooth devices Third party navigation DVD players Pretty much anything that useselectricity but especially digitaldevicesVehicle electronics must be designedfor extremely high reliability at thelowest possible cost. If EMI is notconsidered at the beginning stagesof the design process, it becomesmore difficult and expensive todeal with later. All these issues haveto be overcome through optimalelectromagnetic compliance (EMC)design and the correct EMI shieldingmaterials selection.24In ComplianceJune 2013EXAMPLES OF EMISHIELDING USED INVEHICLESEMI shielding can be found in virtuallyany electronic system in a vehicle.Because of the confined space andthe number of electronic systemswithin a vehicle, engineers often useEMI shielding as an efficient andcost-effective means of addressinginterference issues.Audio Systems – Audio andentertainment systems can be oneof the largest sources of EMI invehicles due to AM/FM radios andadditional electronics including GPSand navigation or satellite radio.Other considerations include incar entertainment options such astelevisions and DVD players and theconvenience of after-market itemsincluding multi-programmable wirelesscontrols. Common shielding solutionsused in these systems include boardlevel shielding, metal fingerstock,conductive Fabric-over-Foam andspring gaskets.Interior Systems – These systemsinclude the lighting (which is only aproblem during turn-on and turn-offunless it is electronic lighting), powermodules, rearview mirrors and displayscreens found in most cars today.These electronics are more vital to thefunction of the vehicle and EMI issuesshould be carefully considered. Typicalsolutions used in these systems includeboard-level shields, metal fingerstock,spring gaskets, Form-in-Place gasketsand conductive elastomers. Forexample, in a rearview mirror witha camera, a board-level shield couldbe used to prevent crosstalk amongcomponents on the circuit board. For asystem that is exposed to the elements,conductive elastomers are a goodchoice as it is an environmental seal aswell as an EMI gasket.Safety and Security Systems – Thesesystems, often considered “missionwww.incompliancemag.comcritical”, include cruise control, driverinformation systems, tire pressuremonitors, blind spot detectors andnigh vision systems. If these systemsfail, then the safety of passengers isimmediately at risk. Often engineerswill use board-level shields, fingerstock,spring gaskets and microwaveabsorbers to mitigate the EMI in thesesystems. Microwave absorbers areused in some blind-spot detectorsand side-view radar to help alleviatecavity resonance and reduce crosstalkbetween boards and elements. Asfrequencies get higher, absorbersbecome a more efficient solution. Itis difficult to put a number on justwhen to rely on absorbers as opposedthe shielding but in the low gigahertzregion is a good rule of thumb.EMI SHIELDING OPTIONSFOR AUTOMAKERSThere is a wide variety of solutionsavailable to automakers to help solveEMI issues. The following discussesthe shielding options most oftenused in vehicles. It is important toremember that considering EMI earlyin the design process is not only morecost-effective, but also more efficient.Automakers and design engineersshould consider all factors whenchoosing the proper EMI material fortheir needs.Fingerstock and SpringContactsMetal RF gaskets are made fromvarious materials. The standard productis offered in Beryllium Copper (BeCu),but phosphor bronze and stainless steelare also available.The metal must be conductive andhave good spring properties. The metalRF gaskets generally have the largestphysical compression range and highshielding effectiveness holding steadyacross a wide frequency range. BeCu isthe most conductive and has the bestspring properties.
Fingerstock and spring contactproducts are ideal for high cyclingapplications requiring frequentaccess. Hundreds of standard shapesare available, as well as cut-to-lengthand modified standards. Fingerstockand spring contacts offer superiorperformance at elevated temperatures,often a concern in automotiveapplications. Metal fingerstock can beused from as low as 20% to 90%or moredepending upon the geometry andmaterial.Fabric-over-Foam (FoF)FoF EMI gaskets offer highconductivity and shielding attenuationand are ideal for applications requiringlow compression force. The FoFprofiles are available in a UL 94V0flame retardant version and offer highabrasion and shear resistance. TypicalFoF EMI gasket applications includeshielding or grounding of automotiveelectronic equipment seams andapertures.There are a wide range of shapes andthickness to meet any design need.Compression of the gasket from 30%to as high as 75% can be alloweddepending on the geometry and FoFmaterial, thereby accommodating thetolerances of many systems.Form-in-Place (FiP)Form-in-Place (FiP) EMI gaskets canbe dispensed onto any conductivepainted, plated, or metallic surface ofan electronics enclosure that requiresenvironmental sealing. It can be appliedon complex or rounded surfaces aswell as miniature devices requiring aprecision gasket. In return FiP gasketsprotect the enclosure against internallyand externally radiated interferenceand environmental elements.Facility SolutionsFor Global EMCThese EMI gaskets save costs in theform of raw materials, labor andassembly time. FiP gaskets allowfor more critical packaging spacefor board-level components. Roomtemperature curing gasket materialseliminate the need for costly heatcuring systems because singlecomponent compounds eliminateingredient mixing, thus shorteningproduction cycles. They have shieldingeffectiveness in excess of 70-100 dB to18 GHz and beyond.Electrically ConductiveElastomersConductive elastomers are ideal forautomotive applications requiringboth environmental sealing and EMIshielding. Compounds can be suppliedin molded or extruded shapes, sheetstock, and custom extruded or diecut shapes to meet a wide variety ofapplications. Conductive elastomersLet Panashield help you with yourEMC facility project.Our experienced personnelwill provide technical supportto guide you throughdesign, supply and certification.EMC ChambersP3 RF Sliding DoorsRF Shielded EnclosuresTurnkey ServicesMilitary Test ChambersFacilityAvionics Test ChambersRelocations/UpgradesFree Space ChambersAntennaMeasurement SystemsReverberation Chamberswww.panashield.comwww.panashield.co.ukTel: 203.866.5888Fax: .comJune 2013In Compliance25
Automakers must take into consideration a number of factors when choosing materials for theirEMI needs, including internal and external sources of EMI and cost.provide shielding effectiveness up to120dB at 18GHz and beyond and comewith many different material choicesfor both the conductive filler andelastomer compound.Conductive FoamConductive foam (CF) offers unlimitedcompression performance whileproviding a relatively soft CompressionLoad Deflection (CLD) curve. LowerCLD properties further reduce thepotential distortion in the application.CF can be die cut into or supplies asgaskets or in sheet stock.Board-Level Shielding (BLS)When electrical and electronic circuitsare in nonconductive enclosures, orwhen it is difficult or impossible to useRF gasketing, BLS provides the bestoption for EMI suppression. It is wellknown that the closer you are to thesource of an EMI problem, the moreefficient and less expensive it is to fix,and using a board-level shield is asclose as you can get to the problem.If done well, PCB level shielding canbe the most cost-efficient means ofresolving EMI issues. The approachesinvolve proper shield selection andoptimal circuit design includingpartitioning, board stack-up, as wellas high-frequency grounding ofthe board and filtering techniques.Generally, shielding on a PCB is someform of conductive cover mountedover one or more components. Insome applications, a shielding barrierseparates board components to preventcrosstalk.Heat can be an issue when using PCBshields. Ventilation holes are usually anadequate way to address this problem.However, if ventilation holes do notprovide enough heat dissipation, PCB26In ComplianceJune 2013shields are available with integral heatsinks or other thermal dissipationsystems.For extremely high frequencyapplications board level shields areavailable for use in conjunction withmicrowave absorbers.As a low cost and common shieldingmethod, a variety of board-levelmetal can-type shields have beenused to eliminate EMI radiation fromentering or exiting sections of a PCB.This method has primarily employedsolder-attached perforated metalcans being attached and soldered tothe ground trace on a PCB directlyover the electrical components thatneed to be shielded. The can-typeshields are often installed in a fullyautomated fashion via a surface mounttechnology process at the same time thecomponents themselves are installedonto the PCB using wave soldering, orsolder paste and a reflow process. Suchcans offer very high levels of shieldingeffectiveness, are typically very reliable,and are widely used in the industry. Butremember that a board level shield isonly five sides. The manufacture (PCBdesigner) must provide the sixth sidein the form of a solid layer within theboard with properly spaced vias toattach the BLS.There are detailed articles available onBLS usage.CONCLUSIONWith the advancements in technologyand the increased emphasis on fuelefficiency, the automotive industryhas placed more and more electricalsystems into cars than ever before.These electrical systems present agreater need to control the EMI issuesthey often present in the vehicleenvironment. If EMI issues are notaddressed, automakers risk the properfunctionality of basic and complexsystems within the car, and evenpassenger safety.Automakers must take intoconsideration a number of factorswhen choosing materials for their EMIneeds, including internal and externalsources of EMI and cost. Engineersshould always consider the potentialEMI issues in the beginning phases ofthe design process, as it will be moreefficient and more cost-effective.There are a number of potential EMIshielding solutions for the automotiveindustry. With a variety of shapes,sizes, material options and mechanicalfactors, however, there is a product thatwill fit virtually any need.(the author)GARY FENICALSenior EMC Engineer and NARTE Certified EMC Engineer, Gary has been withLaird Technologies for 30 years. He is a specialist in RF shielded enclosures andhas been responsible for the design and/or measurement and quality control ofhundreds of large-scale shielded enclosures, as well as a number of shieldedequipment cabinets and housings. He was instrumental in the design andconstruction of Laird Technologies’ state-of-the-art World Compliance Centersand has authored many articles on EMC requirements for medical devices,mutual recognition agreements and guidelines to meet the essential requirements if the EUEMC Directive. He has also authored several seminars, presented worldwide, on the EU
A Primer on Automotive EMC for Non-EMC Engineers The automotive industry has changed drastically in recent years. Advancements in technology paired with tighter federal fuel and emissions regulations have resulted in the need to place more electrical systems into vehicles. This in turn places a greater emphasis on keeping the Electromagnetic Interference (EMI) of these systems from interfering .
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