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[Computer-Aided Engineering]
Electromagnetic Analysis Speeds RFID Design
Modeling and analysis performed with a suite of planar three-dimensional electromagnetic (EM) simulation tools simplifies the design of RFID tags.

James B. Rautio  |  ED Online ID #5474 |  February 2003

Radio-frequency identification (RFID) is one of the fast-growing wireless market segments. Strong competition among RFID suppliers, however, requires fast product design times and rapid time to market. Fortunately, fast and accurate electromagnetic (EM) analysis and simulation tools can shave design time. What follows is a demonstration of how software tools from Sonnet Software (Liverpool, NY) can quickly and accurately evaluate a 13.56-MHz inductor design for an RFID product.

The accuracy of the software is based on the use of Fast Fourier Transform (FFT) techniques while the processing speed is the result of Adaptive Band Synthesis (ABS) interpolation. In addition, the software's automated features, including parameterization and optimization, allow the designer to evaluate a large number of alternatives in a short period of time. As wireless markets consolidate, efficient use of effective computer-aided-engineering (CAE) tools, such as the Sonnet EM software, is a key to survival.

The EM software uses Maxwell's equations to analyze planar circuits. A user specifies a design geometry as input. Geometries can be drawn, or they can be imported as files in GDSII or AutoCAD format or from other simulation/analysis tools from Agilent Technologies (Santa Rosa, CA), Ansoft (Pittsburgh, PA), Applied Wave Research (El Segundo, CA), Cadence Design Systems (San Jose, CA), or Mentor Graphics (Beaverton, OR). Then, based directly on Maxwell's equations, Sonnet solves for the S-parameters or Z-parameters of the structure. Since the calculations are based on FFTs, they are extremely accurate. There is no numerical integration used at any time. The EM software analyzes a circuit contained in a rectangular shielding box. The top cover can be removed to allow radiation. Sonnet works well with nearly any number of substrate layers and the layers can be nearly any thickness, all with full accuracy and speed.

RFID systems have been designed at a variety of different frequencies, although 13.56 MHz is one of the more popular RFID frequencies. In operation, the tag coil (Fig. 1) draws power from the RF energy radiated by a reader coil. Then the RFID tag's integrated circuit (IC) alternately resonates and detunes the tag coil, thus modulating the tightly coupled reader coil with data stored in the tag IC. Unlike bar codes, which must be visible to be read, RFID tags can be read when hidden, even when used in conditions of snow, rain, or excessive heat. Since the power is supplied by the reader, the tag doesn't require a battery. The tags are extremely durable, often lasting longer than the equipment that they tag.

Figure 2 shows a typical RFID inductor modeled with Sonnet.1 It is a planar inductor with six turns, each 0.5 mm wide and separated by 0.5 mm. The coil is 78 × 41 mm. The input port is on the left-hand side. Metal loss is included in the planar EM analysis of this inductor. Analysis time is about 1 minute per frequency. Because this analysis uses the Sonnet ABS interpolation, accurate data at 300 frequencies is calculated from EM analysis at only four frequencies, thus requiring only four minutes for a full analysis.

A lumped equivalent-circuit can be generated by using the Sonnet option "Analysis → Optional files → Add SPICE."2 The result of this operation is a SPICE-format file. To perform an analysis on the equivalent circuit, two frequencies are required. For the purpose of checking the SPICE results, it is a good practice to create two SPICE files for comparison. For this example, the first SPICE file was generated from data at 12.1 and 13.3 MHz, with the resulting equivalent-circuit element values being C1 1 0 = 1.09 pF, L1 1 2 = 4523 nH, and RL1 2 0 = 1.71 Ω.

The second SPICE file was generated from data at the slightly higher frequencies of 13.3 and 14.65 MHz, with the resulting equivalent-circuit element values being C1 1 0 = 1.11 pF, L1 1 2 = 4521 nH, and RL1 2 0 = 1.77 Ω. Both analyses give almost exactly the same answer, implying that the SPICE model is an accurate representation of this inductor. With this confidence, the SPICE model can now be used in an RFID circuit design.

The Sonnet SPICE model of the inductor (Fig. 3, left) includes a resistor in series with the inductor. For some calculations, it is also desirable to know the equivalent parallel resistance, which can be easily calculated using the equation in Fig. 3. For a series resistance of 1.8 Ω, the equivalent parallel resistance is 82.4 kΩ. From the Sonnet generated SPICE model, the capacitance is 1.1 pF and the inductance is 4523 nH.

The RFID IC intended for the RFID circuit design has 23.5 pF total internal capacitance. The inductor calculated by the Sonnet SPICE model already has 1.1 pF of capacitance. In order to make a 4523-nH coil resonant at 13.56 MHz, a total of 30.5 pF capacitance is needed. As a result, it is necessary to add a 5.9-pF external capacitor to tune the inductor to 13.56 MHz when it is connected to the RFID IC.


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Reader Comments

sir,i a B.tech student we are doing a project on RFID based security system can u plz send me the circuit diagram and brief description about IC'S used in this circuit

ronald -January 02, 2009

sir may i ask how can i make the frequency of an rfid became narrower?

lhan -December 17, 2008   (Article Rating: )

Sir. i m a final year engineering student at jiit,noida (delhi) and want to do some relevent research on rfid and design.. could you please help me by sending me the information available on rfid, like its design, circuitry, working, applications, properties, and all tchnical aspects. kindly do the favour. i will b highly obliged 2 u.

Lovely -August 15, 2008

Dear sir, iam a student doing project on "securing rfid with ultra wide band time hopping pulse position modulation" i wanna a circuit diagram design for this project. can anybody please help me please.......

ragav -August 12, 2008

Dear Sir, I'm a computer engineering student who lives in Malaysia, I'm applying for a degree and doing final year project about RFID . I need some of the tag architectures to design simulation on low frequency RFID tag, most of my information collected from the net. Its useful but doesn't show how to design a full system or the basis of its work, like how data is handled in RFID and how the tag designed.

simon -April 18, 2008

sir,Iam science studentin msc electronics and communication.i want RFID reader,tags and antenna in my relative research.Pls help me with ideas how to start and how to come about with this idea.

karthik.s -March 07, 2008

sir, Iam working as software engineer in rfid, i am new to this field and getting problems in desinging rfid reader antenna.can you send me the relevent documents to design the microstrip rectangular circularly polarized antenna .please help me

Ramakrishna -March 07, 2008

sir i,m engg student and i wanna design rfid could u please help me i have only idea tht wht is rfid so it would be quite kind of u if send me how to design it with comp.to be uesd

vikas -February 29, 2008   (Article Rating: )

sir i,m engg student and i wanna design rfid could u please help me i have only idea tht wht is rfid so it would be quite kind of u if send me how to design it with comp.to be uesd

vikas -February 29, 2008   (Article Rating: )

i m an engineering student at IIT,Delhi and want to do some relevent research on rfid and design.. could you please send some information available on RFID, like its design, circuitry, working, applications, properties and cost estimates. kindly do the favour.I shall be highly obliged.

Rishav Gupta -February 19, 2008

I intend on designing Access control and recording everyone accessing Medical storage facilities using RFID as my final project for B-Tec Electronic Engineering.I also want to record every item taken out of storages automatically using RFID Technology. Pls help me with ideas how to start and how to come about with this idea.

Matthews Prince Ramotsisi -February 13, 2008

sir, im a computer engineering and we are doing our thesis right know could you help us or sending some RFID ciruit diagram and how this RFID made, like its design, applications and technical aspects.. thanks...

striker -September 01, 2007

respected sir, i,am doing my engineering.could you please give information regarding the power generated in a passive rfid tag,its principle and any ways to increase the output power? thanking you

narman -July 30, 2007

sir,can you send the pdf for me.now,i am final year student in university science malaysia and the rfid is my final year project topic.thank you.

edward tan -July 29, 2007

Dear Sir, Im a computer engineering student (MSA University Arak) who lives in IRAN.could you please help me by sending me the information available on rfid, like its design, circuitry, working, applications, properties, and all tchnical aspects. kindly do the favour.Thanks!

M.Yazdani -July 20, 2007   (Article Rating: )

Dear Sir, Im a computer engineering student (MSA University Arak) who lives in IRAN.could you please help me by sending me the information available on rfid, like its design, circuitry, working, applications, properties, and all tchnical aspects. kindly do the favour.Thanks!

M.Yazdani -July 20, 2007   (Article Rating: )

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xcvxcv -July 20, 2007

Sir. i m a final year engineering student at jiit,noida (delhi) and want to do some relevent research on rfid and design.. could you please help me by sending me the information available on rfid, like its design, circuitry, working, applications, properties, and all tchnical aspects. kindly do the favour. i will b highly obliged 2 u.

saurabh gandotra -May 26, 2007   (Article Rating: )

Can anyone giv any good links to some more information like this. Great article and would like to read up some more on RFID hardware and RFID in general.

Anonymous -April 27, 2007

hello sir would you please send some names off good books about rfid design and i will be so thankful for you

MUSTAFA ALANI -March 27, 2007   (Article Rating: )

I am senior in EE and working on RFID technology. ME and three more students are responsable for building an RFID reader to read at three different frequencies: 13.56, 433 and 915MHz. We are going to use a PDA as a handheld reader with an external circuit composed of a receiver, transmitter, FPGA and two antennas. I was wondering if you could send me some information on which are the best inductors to use, usefull tips for the PCB layout and how to translate the different tag's format into binary.

Sonny Milhem -February 20, 2007   (Article Rating: )

Sir! Im the final year student of electronics engg (from NED University,Karachi Pakistan) ..i have to decide my Final year project within this week...Please send me the related projects on RFID with neccessary infos such as schematics,datasheets, design, circuitry, etc. i will be very thankful for ur act..

-Faraz Azeem Karachi,Pakistan

Faraz Azeem -December 03, 2006

Sir, I am an EnC student doing my final year project on rfid based smart cards. Could you please give me the related circuit diagrams. I have not been able to find them on the net.

Rishabh -November 03, 2006

sir i am an engineering student doing my seventh semester in electronics n communication. our project is to model rfid reader n tag.could u please sent me the details on criterion for selection of freq n standards,basic block schematics,design aspects n related circuitry of rfid tag n reader. hope u would kindly consider my request.

Lekshmi S -October 28, 2006

Respected Sir, I'm doing my ME-wireless technology in thiagarajar college of engineering,madurai, student in India.I am currently doing my ME project on RFID reader design operating at 13.56Mhz for passive tags.If you don't mind can you please mail me the circuitry design datasheets

BALATHILAKAR.R -August 03, 2006

sir im an engineering student and i am coducting a project study about this RFID could u kindly send me all about this RFID, specially the circuit and schematic diagram that i could use, by the way my project study is concern about RFID using a Zilog microcontroller. . . thanks!!!

wblade -July 20, 2006   (Article Rating: )

nice site

rohit -May 30, 2006   (Article Rating: )

sir im an engineering student and i want to do a research project on rfid could you help me with resources such as cricutiry and books ...

aadhavan -May 28, 2006

sir, now i am doing my project in attendance automation using RFID . SO please give me a guidance and give related notes and full details about tne reader and tags with circuit diagram

arun -March 27, 2006   (Article Rating: )

sir, now i am doing my project in attendance automation using RFID . SO please give me a guidance and give related notes and full details about tne reader and tags with circuit diagram

arun -March 27, 2006   (Article Rating: )

hi there. just checking if you sent schematics etc to everyone whos been rashing you for stuff. Im also doing an engineering project in RFID, (surprise surprise), and if you have been handing out free info please can I have some too... I totally understand if you arent giving out stuff, just thought its worth a try. else guess il have to do the design on my own.. thanks cheers

Peter -March 09, 2006   (Article Rating: )

Nice article. I wonder is it very common to find new students these days asking for other people to do all their work for them! I can't believe there isn't a single comment besides "please email me info to build my girl robot, I am very lonely". Sorry, that was a cheap shot. Us students won't learn unless we do some work. I liked the article very much!

Anonymous -February 16, 2006   (Article Rating: )

Dear Sir, i'm a computer engineering student in MIT, Phil. and am very interested in RFID's. Can you kindly send me more information? Or better yet, some schematic diagrams of the RFID readers. Thanks in advance!

Ron -February 16, 2006   (Article Rating: )

Dear Sir, i'm a computer engineering student in MIT, Phil. and am very interested in RFID's. Can you kindly send me more information? Or better yet, some schematic diagrams of the RFID readers. Thanks in advance!

Ron -February 16, 2006

Respected Sir, I'm a engineering student in India.I am currently working on RFID reader operating at 13.56Mhz for passive tags.If you don't mind can you please mail me the circuitry design datasheets.thanks in advance pradeep

Pradeep -February 13, 2006   (Article Rating: )

Sir, I am working on a senior design project that requires the design of an RFID system. Can you please send to me relevant information such as schematics, datasheets, design, circuitry, etc. Anything that you feel I may need in order to begin designing my system, please send it. I will extremely appreciate it.

javier solorzano -January 17, 2006

i m an engineering student at michigan,currently I'm working on an RFID tag deisgn project.. could you please send me all info available on rfid, like its design, circuitry, working, applications, properties, and all tchnical aspects. kindly do the favour.

Sam -January 13, 2006   (Article Rating: )

Respected sir, I'm doing my final course(M.E., APPLIED ELECTRONICS). My final year project title is"AUTOMATIC CHECKING OF CONTROL PANEL USING ALLEN BRADLEY PLC".i have had doubts regarding software part. For a given electrical circuit, i need the PLC ladder diagram circuit.So i need the Software reg the above said conversion. NAMASHKAAR

A.Dyaneswaran -January 06, 2006

Respected sir, Currently i'm doing my PG course(M.E.- APPLIED ELECTRONICS). I belong to Tamilnadu.I'm doing my final year project in RFID entitled"DESIGN OF RFID 13.56MHz RFID READER/WRITER".I dohave some doubts reg. designing.Can u please send me the detailed schematic of 13.56MHz RFID READER/WRITER.I have had gone thro' many supported RFID related websites. But still i didn't get any favour result.

M.PARTHIBAN -January 06, 2006

sir, im a engineering student in malaysia. now im working on a rfid designing. im currently having problem on the hardware part. currentlt im suppose to design a 13.56MHz RFID reader with a passive tag. if you dont mind can u mail me any schematics or information regarding my project.i will very much appriciate your help. thank you very much.

eNdRAn -December 13, 2005

Sir, im a engineering student doing my project in RFID..how to design a circuit which does the following thing...."RF based message cryptography"..ie i want to give security to a message using RF.

Partha -November 26, 2005

Too bad I'll never use it, because "free trade"/outsourcing took my job, but...

Anonymous -October 29, 2005

Interesting article/app note. Thanks

Anonymous -October 29, 2005

Sir, i am a B.Mec student and currently doing research on RFID. Now i have a problem with designing tag front end and now i use ADS from Agilent Technology to do simulation. Can you please teach me how to design a tag front end for 13.56MHz. Thanks

Fong -October 04, 2005

Dear Sir, Im a computer engineering studen who lives in baghdad, I'm applying for a master degree and doing a research about RFID . I need some of the readers and tag architectures becouse this technology is new in the middle east and there is not many books about it in the middle east, so most of my information I've collected from the net Its useful but doesnt sho how to design a full system or the basis of its work, like how data is handled in RFID and how the tags and readers are designed.

Zaid -September 29, 2005   (Article Rating: )

Dear Sir, Im a computer engineering studen who lives in baghdad, I'm applying for a master degree and doing a research about RFID . I need some of the readers and tag architectures becouse this technology is new in the middle east and there is not many books about it in the middle east, so most of my information I've collected from the net Its useful but doesnt sho how to design a full system or the basis of its work, like how data is handled in RFID and how the tags and readers are designed.

Zaid -September 29, 2005   (Article Rating: )

i m an engineering student at mit, manipal and want to do some relevent research on rfid and design.. could you please send me all info available on rfid, like its design, circuitry, working, applications, properties, and all tchnical aspects. kindly do the favour.

mayank -September 16, 2005   (Article Rating: )

i m an engineering student at mit and want to do some relevent research on rfid and design.. could you please send me all info available on rfid, like its design, circuitry, working, applications, properties, and all tchnical aspects. kindly do the favour.

mayank -September 16, 2005   (Article Rating: )

Sir, I am a Student of engineering and am using an evaluation kit and working on enhancing the RFid range.Could you please inform me how i can increase the power at output of reader to antenna from 200mW to 1W.

Behlul -August 28, 2005

Sir, I a B.tech student of Pondicherry Enginnering college I want to design this rfid can u please send me all info abt reader.

Fathima Juhara -July 28, 2005

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