Using low power transponders and tags for RFID applications.

When having determined L tx and L tag , theantenna design phase can start. To completethis study, we give in (15) an empirical formulafor antenna design which gives goodagreement between calculation andmeasurements.2 2008 . . d . nL( m H)=3d + 9l + 10ewhere ndle= number of windings,= coil diameter (cm)= coil width (cm)= coil thickness (cm)(15)Finally, all this shows the importance tomaximize antenna Q factor on both sides,reader and transponder but there are somelimitations. The frequency bandwidth of thereader antenna should not be forgotten as it isa function of the Q factor, and transponderdata rate must be included in this frequencybandwidth. Also, each antenna circuit has gotfrequency tuning tolerances due to componentvariations. It has to be reminded that to simplifythe previous calculation, a perfect frequencytuning between field frequency and antennasresonant circuit has been assumed. Therefore,after a first set of system parameters has beencalculated using above formulas, a seconditeration process should be done including theeffect of frequency detuning to check if thecomponents tolerances meet the overallsystem performance requirements.4. LF Read Only transponderapplicationsWhen in 1993, a major Germaninsurance company put up pressure to eitherprotect vehicles against massively increasingtheft or else renounce to full insurancecoverage, nobody believed that RFID as a thenemerging technology would see one of it's firstmajor successes, still unbeaten in numbers byany other application today. Objection wasraised as to the reliability of potential systems,their suitability in an automotive environmentand of course, the lack of standards in whatthen seemed to be a mystic collection ofproprietary systems, was seen to be a majorobstacle.An extremely fast but substantialdevelopment effort was undertaken by a fewpowerful automotive industry suppliers,resulting in a miniaturized "Inkey" system andit's car lock transceiver counterpart to be fittedto new cars as early as 1994 already. This firstgeneration system, still fitted to certain modelsof most major car makers, consisted of a 64 bitread-only, rod or brick type transponder,embedded in the ignition key of the vehicle anda transceiver antenna with it's electronicspackage on PCB, integrated around andbehind the lock. The functionality consists of5safely cutting power supply to the starter, thefuel pump, the system ignition and othersystem elements, required for the vehicle'soperation during driving for the case, where thepresented key does not match one of the prestoredcodes. Specifications for theminiaturized transponders were very stringent,requiring maximum read distance in a metalloaded environment over industry practicethermal ranges with only a few ppm failure rateadmitted! Three mainstream systems wereadopted by the majority of the automotiveindustry and have since been fitted to millionsof new cars with great success. Immobilizerstoday in Europe are part of the normalequipment of cars and whilst still no standardrules neither the application nor the products,several systems have established a de factostandard and wide public acceptance: What isgood for the automotive industry can be usedin many applications elsewhere!In parallel, a variety of retrofit systemswere developed to protect vehicles already putinto circulation. Most of these contactlesssystems rely on the same principle except thatthey use keyholders and that their transceiversare mounted inside a more convenient place inthe dashboard. Their success in the marketwas not as expected and their need is nolonger given, considering that almost allEuropean vehicles are now equipped with OEMsystems.The possibility to emulate the code withan unsophisticated reader/transponder blackboxand hence to circumvent the immobilizerwas early 1995 at the origin of a newdevelopment, aiming at increased securityfeatures. It was widely felt, that the barrier levelwas not high enough and that the target of an80% reduction of car thefts, mainly for high-endmodels, could be missed. Second generationproducts now interface with several moremotor management functions and the readwritetransponders feature encrypting in thecommunication with the lock, renderingfraudulent attempts to drive away with thevehicle almost impossible. As an example, atypical encrypted communication protocol socalled « challenge/response » is described infigure 4. Statistics of stolen cars, fitted with firstgeneration immobilizers, showed however, thatthe problem had been dramatically reducedand the objective had been met if notexceeded.One of the first RFID applications wasanimal ID and whilst this most usefulapplication never came to the importance thatit should have done, it still is the first domainwith an official standard. ISO 11784/11785,released in 1996/7 indeed lay down the rules,applying to a variety of ID products such asimplants, ear marks, bolus etc. and areintended for establishing a traceability,predominantly for herd animals. The standard

users to the same extent as are bar codeand/or magnetic stripe tickets.The watch application stands for a seriesof opportunities, where the digital interfacebetween human beings and machines greatlyfacilitates desired transaction; both in time andaccuracy. The fact that RFID watches areperceived to be a necessary, even fashionableaccessory of people will add to theunderstanding and public acceptance of thetechnique.Another important application field ofR/W transponder is the multi-tag identificationwhere sending information to the tag is anabsolute requirement. For applications likelaundry automation, textile rental, inventorycontrol, it is necessary to identify and countseveral transponders present at the same timewithin a reader RF field. One of most knownprotocol is the so called Supertagä anticollisionprotocol developed in CSIR (South ofAfrica) and licensed by BTG (United Kingdom).The main principle of this protocol is that thetransponders messages are very short andrandomly repeated during the time. Thissupposes an excellent on chip randomgenerator for the transponder IC. Someadditional features like temporary inhibition andfinal inhibition commands allow the reader tomute the identified transponder thus reducingthe number of message collisions allowing ahigher number of tags in the field.6. Low cost system designParticular emphasis is to be given tosystem design cost since most RFIDapplications do become price sensitive shortlyafter the start of the deployment phase; as andwhen number of installed items and/orquantities become significant. System costshall therefore mean Œthe applicationdevelopment cost, the cost of hardwareincluding tags, readers, network hardware andother peripherals as well as computingfacilities, their installation and commissioningand finally Ž the cost of system operationthroughout it's planned lifecycle. Since thequantifiable elements of the expected gains areoften difficult to demonstrate beyond doubt,such system cost have to be kept as low aspossible, yet without attempting to unprudentlysave money during development.Assuming the majority of developmentcost to lay within the proper translation of theperformance requirements, i.e. the definition ofthe intended functioning, the creation ofsoftware, the setting-up of operationalprocedures for all elements and finally thetesting of the system components, a big lumpof the available funding is already gone. Unlessthe application is intended to be a turnkeypackage to be sold many times "withoutadjustments" or alternatively a truly high7volume niche application with an useful lifetimeof several years, the development price of asystem represents by enlarge the major cost ofthe application project, relegating cost oftransponders and readers well below the levelof attention that these items are usually given.The recent emergence of single chipreader ASSP has greatly improved thepotential for low cost, handheld, medium rangereaders in the 120 to 150 kHz band. Severalsemiconductor producers now offercomparable solutions with auto-frequencyadjust features (PLL loops) for the design ofsimple, rugged transceiver units. Some ofthese reader ASSP are truly low power ICs andsimply interface with a microcontroller of thedesigners choice, hence leaving vast room forfeature incorporation. Provided that designersdo not want push communication performancebeyond reason, customized readers can bedeveloped in less than 3 months. An increasingnumber of products, ranging from OEM boardsthrough to handheld computers with an RFIDreading capability and an RFDC (or infrared)interface are now readily available on themarket and their prices are still falling.Often, the system low cost requirementis driven by the cross-subsidizing policy,applied by several system houses in overallproduct/system pricing. The art consists ofsqueezing the cost of "consumables" below thepublicly perceived level of item value in order tomaximize margins. The lure consists ofoverpricing mainly transponders or tags with aview to recover underpriced applicationdevelopment and costly adjustments of other,associated hardware items. This way ofproceeding is increasingly dangerous withemerging new component producers, enteringthe market and selling their hardware as offthe-shelfcommodity; mainly when the"consumables" are of mainstream technologyand therefore system compatible.The design of LF-transponders, i.e. tagsin the 120 to 150 kHz range make use, at least,of an IC, actually the heart of the features, andconnected to a copper antenna coil, sometimeseven a capacitor. Miniaturized rod typetransponders as used for animal implantable IDcarriers furthermore use a ferrite but inessence, the single most costly item remainsthe IC and therefore, considerations of wireoptimization, the use of bobbins etc. may beignored for the purpose of this paper.Designs nowadays incorporate singlechip solutions, mounted on PCB, TAB, leadframe or even better, connected without furthercarrier structure directly to the antenna. Thetrade-off between an onboard capacitor (singlechip) and a multicomponent subassembly, asfor instance required in half duplex systemsclearly favors in terms of cost and reliabilityproducts, that minimize the number of built-incomponents. Finally, consideration has to begiven to the packaging of transponders in line

with the intended use and lifetime, may beeven with respect of ultimate disposal after theend of it's useful life. Widespread use of cheapplastic encapsulation, including PVC laminatesmay well reduce item cost but later becomeunacceptable.Analyzing a straightforward AccessControl Application with an add-on benefit ofshopfloor data collection for a smaller company(50 to 100 employees) would show the use ofsome 10 transceiver stations for areaprotection and data collection and maybe 200tags for the employees. The system wouldhave to be wired to the company's IT facilityand off-the-shelf software adjusted to thecompany's particular situation (Logo displayetc.) At prices of $400.- per transceiver and$5.- of the badges and estimation theinstallation and wiring at $2000.-, one wouldinvest $7000.- in such a system with asemiconductor content of less that $300.- Ofcourse, the time it takes to issue the badges(with personal photo?), to re-engineer theoperation and to explain (and re-explain) thenew system to each employee would have tobe added.Not enough attention is given yet to thedetermination of saving potential andproductivity increases, resulting out of an RFIDapplication. It is widely felt that many currentinstallations are the fruit of an "imperative"situation or some "gadget" of an influentialgroup of people, insisting in their "solution".Overall system cost in all these cases is theminimum that one can get away with and it isneedless to add that such systems operatewith restrictions and that the reputation of autoID solutions suffers.Bertin, Faroux, Renault,« Electromagnétisme », DUNOD collection.« P4022, Supertagä Contactless IdentificationDevice », preliminary data sheet, CSIR,EM-Microelectronic MARIN SA« V4070, high security authenticationContacless Device », EM-MicroelectronicMARIN SA.7. ConclusionsA simple theory has been developed toallow non RF specialist to build up RFIDsystems using OEM products like transponderIC and RFID reader board. Some majorapplications have been described showing thelarge potential of the RFID market. Very highvolume applications are about to emergerequiring optimized low cost solutions like the« Retail tag » and contactless smart cardapplications.8. ReferencesJ :D : Etienne, « Lecteurs CID for Swatch âAccess », ASULAB Internal report - 1997RFID « How it works and How it profit from it »,ID Technologies. http ://www.id-tech.comW. Buesser, private communication,EM-Microelectronic MARIN SA8