Antenna Circuit Design RFID Applications REVIEW BASIC THEORY RFID

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Antenna Circuit Design RFID Applications REVIEW BASIC THEORY RFID

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AN710
Antenna Circuit Design RFID Applications
REVIEW BASIC THEORY RFID ANTENNA DESIGN
Current Magnetic Fields
Ampere's states that current flowing conductor produces magnetic field around conductor. magnetic field produced current element, shown Figure round conductor (wire) with finite length given
INTRODUCTION
Passive RFID tags utilize induced antenna coil voltage operation. This induced voltage rectified provide voltage source device. voltage reaches certain level, device starts operating. providing energizing signal, reader communicate with remotely located device that external power source such battery. Since energizing communication between reader accomplished through antenna coils, important that device must equipped with proper antenna circuit successful RFID applications. signal radiated effectively linear dimension antenna comparable with wavelength operating frequency. However, wavelength 13.56 22.12 meters. Therefore, difficult form true antenna most RFID applications. Alternatively, small loop antenna circuit that resonating frequency used. current flowing into coil radiates near-field magnetic field that falls with r-3. This type antenna called magnetic dipole antenna. 13.56 passive applications, microhenries inductance hundred resonant capacitor typically used. voltage transfer between reader coils accomplished through inductive coupling between coils. typical transformer, where voltage primary coil transfers secondary coil, voltage reader antenna coil transferred antenna coil vice versa. efficiency voltage transfer increased significantly with high circuits. This section written coil designers RFID system engineers. reviews basic electromagnetic theories antenna coils, procedure coil design, calculation measurement inductance, antenna tuning method, read range RFID applications.
EQUATION
where: current distance from center wire permeability free space given 10-7 (Henry/meter) special case with infinitely long wire where: -180° Equation rewritten Weber
EQUATION
Weber
FIGURE CALCULATION MAGNETIC FIELD LOCATION CURRENT STRAIGHT CONDUCTING WIRE
Wire
(into page)
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magnetic field produced circular loop antenna given
EQUATION
FIGURE CALCULATION MAGNETIC FIELD LOCATION CURRENT LOOP
coil
where current radius loop distance from center loop permeability free space given 10-7 (Henry/meter) above equation indicates that magnetic field strength decays with 1/r3. graphical demonstration shown Figure maximum amplitude plane loop directly proportional both current number turns, Equation often used calculate ampere-turn requirement read range. examples that calculate ampere-turns field intensity necessary power will given following sections.
FIGURE DECAYING MAGNETIC FIELD DISTANCE
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INDUCED VOLTAGE ANTENNA COIL
Faraday's states that time-varying magnetic field through surface bounded closed path induces voltage around loop. Figure shows simple geometry RFID application. When reader antennas close proximity, time-varying magnetic field that produced reader antenna coil induces voltage (called electromotive force simply EMF) closed antenna coil. induced voltage coil causes flow current coil. This called Faraday's law. induced voltage antenna coil equal time rate change magnetic flux
EQUATION
where: magnetic field given Equation surface area coil inner product (cosine angle between vectors) vectors surface area Note: Both magnetic field surface vector quantities.
EQUATION
where: number turns antenna coil magnetic flux through each turn negative sign shows that induced voltage acts such oppose magnetic flux producing This known Lenz's emphasizes fact that direction current flow circuit such that induced magnetic field produced induced current will oppose original magnetic field. magnetic flux Equation total magnetic field that passing through entire surface antenna coil, found
presentation inner product vectors Equation suggests that total magnetic flux that passing through antenna coil affected orientation antenna coils. inner product vectors becomes minimized when cosine angle between degrees, field surface coil) perpendicular each other maximized when cosine angle degrees. maximum magnetic flux that passing through coil obtained when coils (reader coil coil) placed parallel with respect each other. This condition results maximum induced voltage coil also maximum read range. inner product expression Equation also expressed terms mutual coupling between reader coils. mutual coupling between coils maximized above condition.
FIGURE BASIC CONFIGURATION READER ANTENNAS RFID APPLICATIONS
Coil
V0sin(t)
I0sin(t) B0sin(t)
Reader Electronics
Tuning Circuit
Reader Coil
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Using Equations Equation rewritten
EQUATION
2fNSQB where: frequency arrival signal number turns coil loop area loop square meters (m2) quality factor circuit strength arrival signal angle arrival signal above equation, quality factor measure selectivity frequency interest. will defined Equations through
EQUATION
where: voltage coil current reader coil radius reader coil radius coil distance between coils mutual inductance between reader coils, given
FIGURE ORIENTATION DEPENDENCY ANTENNA
B-field
EQUATION
above equation equivalent voltage transformation typical transformer applications. current flow primary coil produces magnetic flux that causes voltage induction secondary coil. shown Equation coil voltage largely dependent mutual inductance between coils. mutual inductance function coil geometry spacing between them. induced voltage coil decreases with r-3. Therefore, read range also decreases same way. From Equations generalized expression induced voltage tuned loop coil given
induced voltage developed across loop antenna coil function angle arrival signal. induced voltage maximized when antenna coil placed parallel with incoming signal where
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EXAMPLE CALCULATION B-FIELD COIL EXAMPLE OPTIMUM COIL DIAMETER READER COIL
MCRF355 device turns when antenna coil develops across This voltage rectified device starts operate when reaches VDC. B-field induce coil voltage with standard 7810 card size (85.6 0.76 calculated from coil voltage equation using Equation optimum coil diameter that requires minimum number ampere-turns particular read range found from Equation such
EQUATION
EQUATION
2fNSQB 0.0449 2fNSQ µwbm
where:
where following parameters used above calculation: coil size Frequency Number turns antenna coil coil voltage turn (85.6 (ISO card size) 0.0046224 13.56 (normal direction,
taking derivative with respect radius
above equation becomes minimized when: above result shows relationship between read range versus optimum coil diameter. optimum coil diameter found
EXAMPLE
NUMBER TURNS CURRENT (AMPERE-TURNS)
EQUATION
where: radius coil read range.
Assuming that reader should provide read range inches (38.1 given previous example, current number turns reader antenna coil calculated from Equation
EQUATION
result indicates that optimum loop radius, 1.414 times demanded read range
0.0449 0.38 0.43 ampere turns
above result indicates that needs turn coil, 2-turn coil.
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WIRE TYPES OHMIC LOSSES
Resistance Conductor Wire Types
diameter electrical wire expressed American Wire Gauge (AWG) number. gauge number inversely proportional diameter, diameter roughly doubled every wire gauges. wire with smaller diameter higher resistance. resistance conductor with uniform cross-sectional area found where: frequency Permeability 10-7 (h/m) Copper, Aluminum, Gold, 4000 pure Iron Conductivity material (mho/m) (mho/m) Copper 3.82 (mho/m) Aluminum (mho/m) Gold (mho/m) Silver where: total length wire conductivity wire (mho/m) cross-sectional area radius wire
EQUATION
permeability (F/m)
EQUATION
Resistance Wire
(mho/m) Brass
EXAMPLE
skin depth copper wire 13.56 calculated
EQUATION
resistance must kept small possible higher antenna circuit. this reason, larger diameter coil possible must chosen RFID circuit. Table shows diameter bare enamel-coated wires, resistance. 0.0661 0.018 0.187 13.56
Resistance Conductor
charge carriers evenly distributed through entire cross section wire. frequency increases, magnetic field increased center inductor. Therefore, reactance near center wire increases. This results higher impedance current density region. Therefore, charge moves away from center wire towards edge wire. result, current density decreases center wire increases near edge wire. This called skin effect. depth into conductor which current density falls 1/e, 0.3679) value along surface, known skin depth function frequency permeability conductivity medium. result skin effect effective decrease cross sectional area conductor. Therefore, increase resistance wire. skin depth given
shown Example current flowing copper wire will flow within distance 0.018 outer edge wire 13.56 0.187 kHz. wire resistance increases with frequency, resistance skin depth called resistance. approximated formula resistance given
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EQUATION
active where skin depth area conductor active
freq
Resistance Conductor with Frequency Approximation
When skin depth almost comparable radius conductor, resistance obtained with frequency approximation[5]:
EQUATION
first term above equation resistance, second term represents resistance.
resistance increases with square root operating frequency. conductor etched dielectric, substrate given
EQUATION
where width thickness conductor.
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TABLE
Wire Size (AWG)
WIRE CHART
Dia. Mils (bare) 289.3 287.6 229.4 204.3 181.9 162.0 166.3 128.5 114.4 101.9 90.7 80.8 72.0 64.1 57.1 50.8 45.3 40.3 35.9 32.0 28.5 25.3 22.6 20.1 17.9 Dia. Mils (coated) 131.6 116.3 106.2 93.5 83.3 74.1 66.7 59.5 52.9 47.2 42.4 37.9 34.0 30.2 28.0 24.2 21.6 19.3 Ohms/ 1000 0.126 0.156 0.197 0.249 0.313 0.395 0.498 0.628 0.793 0.999 1.26 1.59 2.00 2.52 3.18 4.02 5.05 6.39 8.05 10.1 12.8 16.2 20.3 25.7 32.4
Wire Size (AWG)
Dia. Mils (bare) 15.9 14.2 12.6 11.3 10.0 1.76 1.57 1.40 1.24 1.11 0.99
Dia. Mils (coated) 17.2 15.4 13.8 12.3 11.0
Ohms/ 1000 41.0 51.4 65.3 81.2 106.0 1080 1320 1660 2140 2590 3350 4210 5290 6750 8420 10600
Note: 2.54 10-3
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INDUCTANCE VARIOUS ANTENNA COILS
electric current element that flows through conductor produces magnetic field. This time-varying magnetic field capable producing flow current through another conductor this called inductance. inductance depends physical characteristics conductor. coil more inductance than straight wire same material, coil with more turns more inductance than coil with fewer turns. inductance inductor defined ratio total magnetic flux linkage current through inductor:
INDUCTANCE STRAIGHT WOUND WIRE
inductance straight wound wire shown Figure given
EQUATION
0.002l where: length radius wire respectively.
EQUATION
where: number turns current magnetic flux coil with multiple turns, inductance greater spacing between turns becomes smaller. Therefore, antenna coil that formed limited space often needs multilayer winding reduce number turns. (Henry)
EXAMPLE
INDUCTANCE CALCULATION STRAIGHT WIRE:
inductance wire with feet (304.8cm) long diameter calculated follows:
EQUATION
0.002 304.8 304.8 0.60967 7.965 4.855
Calculation Inductance
Inductance coil calculated many different ways. Some readily available from references[1-7]. must remembered that coils actual resulting inductance differ from calculated true result because distributed capacitance. that reason, inductance calculations generally used only starting point final design.
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INDUCTANCE SINGLE TURN CIRCULAR COIL
inductance single turn circular coil shown Figure calculated
INDUCTANCE N-TURN MULTILAYER CIRCULAR COIL FIGURE N-TURN MULTILAYER CIRCULAR COIL
FIGURE CIRCULAR COIL WITH SINGLE TURN
N-turns coil
EQUATION
0.01257 2.303log where: mean radius loop (cm) diameter wire (cm)
Figure shows N-turn inductor circular coil with multilayer. inductance calculated
INDUCTANCE N-TURN SINGLE LAYER CIRCULAR COIL FIGURE CIRCULAR COIL WITH SINGLE TURN
EQUATION
0.31 where: average radius coil number turns winding thickness winding height
EQUATION
-22.9a 25.4l where: number turns length radius coil
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INDUCTANCE SPIRAL WOUND COIL WITH SINGLE LAYER
inductance spiral inductor calculated
INDUCTANCE N-TURN SQUARE LOOP COIL WITH MULTILAYER
Inductance multilayer square loop coil calculated
EQUATION
0.3937
EQUATION
0.008aN 2.303log 0.2235 0.726
FIGURE SPIRAL COIL
where: number turns side square measured center rectangular cross section winding winding length winding depth shown Figure Note: dimensions
FIGURE N-TURN SQUARE LOOP COIL WITH MULTILAYER
where: ro)/2
View
Cross Sectional View
Inner radius spiral Outer radius spiral Note: dimensions
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INDUCTANCE N-TURN RECTANGULAR COIL WITH MULTILAYER
Inductance multilayer rectangular loop coil calculated
INDUCTANCE THIN FILM INDUCTOR WITH RECTANGULAR CROSS SECTION
Inductance conductor with rectangular cross section shown Figure calculated
EQUATION
0.0276 1.908C
FIGURE STRAIGHT THIN FILM INDUCTOR
where:
number turns width coil length coil width cross section height (coil build cross section Note: dimensions
EQUATION
0.002l 0.50049 where:
FIGURE N-TURN SQUARE LOOP COIL WITH MULTILAYER
width thickness length conductor
View
Cross Sectional View
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INDUCTANCE FLAT SQUARE COIL
Inductance flat square coil rectangular cross section with turns calculated by[2]:
EQUATION
0.2235 0.0467aN 2.414a 0.02032aN 0.914
where: side length inches thickness inches width inches total number turns
FIGURE SQUARE LOOP INDUCTOR WITH RECTANGULAR CROSS SECTION
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EXAMPLE TURN READER ANTENNA
reader antenna made rectangular loop composed thin wire thin plate element, inductance calculated following simple formula [5]:
FIGURE TURN READER ANTENNA
EQUATION
where units radius wire
Example with dimension:
One-turn rectangular shape with 18.887 25.4 width 0.254 gives (nH) using above equation.
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INDUCTANCE N-TURN PLANAR SPIRAL COIL
Inductance planar structure well calculated Reference [4]. Consider inductor made straight segments shown Figure inductance self inductances mutual inductances[4]: consider conductor segments shown Figure
FIGURE CONDUCTOR SEGMENTS
MUTUAL INDUCTANCE CALCULATION
EQUATION
where: Total Inductance self inductances straight segments positive mutual inductances negative mutual inductances mutual inductance inductance that resulted from magnetic fields produced adjacent conductors. mutual inductance positive when directions current conductors same direction, negative when directions currents opposite directions. mutual inductance between parallel conductors function length conductors geometric mean distance between them. mutual inductance conductors calculated
above figure indices conductor, indices length difference length conductors. above configuration (with partial segments) occurs between conductors multiple turn spiral inductor. mutual inductance conductors above configuration
EQUATION
EQUATION
where length conductor centimeter. mutual inductance parameter calculated
EQUATION
length same l2), then Equation used. Each mutual inductance term above equation calculated follows using Equations
EQUATION
where following examples shows above formulas calculate inductance 4-turn rectangular spiral inductor.
where geometric mean distance between conductors, which approximately equal distance between track center conductors.
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EXAMPLE INDUCTANCE RECTANGULAR PLANAR SPIRAL INDUCTOR
other hand, currents segments opposite direction. Therefore, mutual inductance between conductors negative term. mutual inductance maximized segments parallel, minimum they placed orthogonal degrees). Therefore mutual inductance between segments etc, negligible calculation. Example total positive mutual inductance terms are:
EQUATION
total negative mutual inductance terms are:
EQUATION
indices conductor. four full turn inductor, there straight segments. spacing between conductor, distance track centers between adjacent conductors. length conductor length conductor length conductor segments are: total inductance coil equal self inductance each straight segment L16) plus mutual inductances between these segments shown Equation self inductance calculated Equation (28), mutual inductances calculated Equations (32) (34). four-turn spiral, there both positive negative mutual inductances. positive mutual inductance (M+) mutual inductance between conductors that have same current direction. example, current segments same direction. Therefore, mutual inductance between conductor segments positive.
Appendix calculation each individual mutual inductance term Equations (36) (37).
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EXAMPLE INDUCTANCE CALCULATION INCLUDING MUTUAL INDUCTANCE TERMS RECTANGULAR SHAPED TURN READER ANTENNA
calculate Inductance turn loop etched antenna board reader antenna (for example, MCRF450 reader antenna DV103006 development kit) with following parameters: 25.4 7.436" 18.887 7.62 1.4536" 3.692 trace width 0.508 trace thickness 0.0001
EQUATION
since direction current each segment opposite with respect currents other segments.
where
solving self inductance using Equation (28), 59.8 259.7
Negative mutual inductances solved follows: 1+gap 1+gap
turn rectangular shape inductor, there four sides. Because gap, there total conductor segments. one-turn inductor, direction current each conductor segment opposite directions each other. example, direction current segment opposite. There conductor segments that have same current direction. Therefore, there positive mutual inductance. From Equation total inductance
gap, gap, gap,
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solving above equation, mutual inductance between each conductor are: M2,4 30.1928 (nH), M1,3 5.1818 (nH) M1',3 Therefore, total inductance antenna 2(M2,4 M1,3) 797.76 81.113 716.64 (nH) been found that inductance calculated using Equation (38) about higher than result using Equation (30) same physical dimension. resulting difference formulas contributed mainly mutual inductance terms. Equation (38) recommended needs very accurate calculation while Equation (30) gives quick answers within about percent error. computation software using Mathlab shown Appendix formulas inductance widely published provide reasonable approximation relationship between inductance number turns given physical size[1-7]. When building prototype coils, wise exceed number calculated turns about then remove turns achieve right value. production coils, best specify inductance tolerance rather than specific number turns.
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CONFIGURATION ANTENNA CIRCUITS
Reader Antenna Circuits
inductance reader antenna coil 13.56 typically range microhenries (µH). antenna formed aircore ferrite core inductors. antenna also formed metallic conductive trace board flexible substrate. reader antenna made either single coil, that typically forming series parallel resonant circuit, double loop (transformer) antenna coil. Figure shows various configurations reader antenna circuit. coil circuit must tuned operating frequency maximize power efficiency. tuned resonant circuit same band-pass filter that passes only selected frequency. tuned circuit related both read range bandwidth circuit. More this subject will discussed following section. Choosing size type antenna circuit depends system design topology. series resonant circuit results minimum impedance resonance frequency. Therefore, draws maximum current resonance frequency. Because simple circuit topology relatively cost, this type antenna circuit suitable proximity reader antenna. other hand, parallel resonant circuit results maximum impedance resonance frequency. Therefore, maximum voltage available resonance frequency. Although minimum resonant current, still strong circulating current that proportional circuit. double loop antenna coil that formed parallel antenna circuits also used. frequency tolerance carrier frequency output power level from read antenna regulated government regulations (e.g., USA). limits 13.56 frequency band follows: Tolerance carrier frequency: 13.56 0.01% 1.356 kHz. Frequency bandwidth: kHz. Power level fundamental frequency: mv/m meters from transmitter. Power level harmonics: -50.45 down from fundamental signal.
transmission circuit including antenna coil must designed meet limits.
FIGURE VARIOUS READER ANTENNA CIRCUITS
Series Resonant Circuit
Parallel Resonant Circuit
(secondary coil)
(primary coil)
reader electronics Transformer Loop Antenna
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Antenna Circuits
MCRF355 device communicates data tuning detuning antenna circuit (see AN707). Figure shows examples external circuit arrangement. external circuit must tuned resonant frequency reader antenna. detuned condition, circuit element between antenna pads shorted. frequency difference (delta frequency) between tuned detuned frequencies must adjusted properly optimum operation. been found that maximum modulation index maximum read range occur when tuned detuned frequencies separated MHz. tuned frequency formed from circuit elements between antenna pads without shorting antenna pad. detuned frequency found when antenna shorted. This detuned frequency calculated from circuit between antenna pads excluding circuit element between antenna pads. Figure (a), tuned resonant frequency detuned frequency
EQUATION
detuned this case, detuned higher than tuned Figure 17(b) shows another example external circuit arrangement. This configuration controls tuned detuned frequencies. tuned untuned frequencies are:
EQUATION
tuned
EQUATION
detuned typical inductance coil about microhenry with turns. Once inductance determined, resonant capacitance calculated from above equations. example, coil inductance then needs capacitance resonate 13.56 MHz.
EQUATION
where: Total inductance between antenna pads inductance between antenna antenna pads inductance between antenna pads mutual inductance between coil coil
coupling coefficient between coils tuning capacitance
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CONSIDERATION QUALITY FACTOR BANDWIDTH TUNING CIRCUIT
voltage across coil product quality factor circuit input voltage. Therefore, given input voltage signal, coil voltage directly proportional circuit. general, higher results longer read range. However, also related bandwidth circuit shown following equation.
EQUATION
FIGURE VARIOUS EXTERNAL CIRCUIT CONFIGURATIONS
MCRF355 Ant. inductors capacitor MCRF355 Ant.
tuned detuned tuned detuned
Ant.
where: mutual inductance coupling coefficient inductors
Ant. capacitors inductor MCRF360 Ant. Ant.
tuned detuned
inductors with internal capacitor
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Bandwidth requirement limit circuit MCRF355
Since MCRF355 operates with data rate kHz, reader antenna circuit needs bandwidth least twice data rate. Therefore, needs:
Parallel Resonant Circuit
Figure shows simple parallel resonant circuit. total impedance circuit given
EQUATION
where angular frequency given maximum impedance occurs when denominator above equation minimized. This condition occurs when:
EQUATION
minimum Assuming circuit turned 13.56 MHz, maximum attainable obtained from Equations
EQUATION
96.8 practical resonant circuit, range 13.56 band about However, significantly increased with ferrite core inductor. system designer must consider above limits optimum operation.
EQUATION
This called resonance condition, resonance frequency given
EQUATION
applying Equation into Equation impedance resonance frequency becomes:
RESONANT CIRCUITS
Once frequency inductance coil determined, resonant capacitance calculated from:
EQUATION
practical applications, parasitic (distributed) capacitance present between turns. parasitic capacitance typical antenna coil (pF). This parasitic capacitance increases with operating frequency device. There different resonant circuits: parallel series. parallel resonant circuit maximum impedance resonance frequency. minimum current maximum voltage resonance frequency. Although current circuit minimum resonant frequency, there circulation current that proportional circuit. parallel resonant circuit used both high power reader antenna circuit. other hand, series resonant circuit minimum impedance resonance frequency. result, maximum current available circuit. Because simplicity availability high current into antenna element, series resonant circuit often used simple proximity reader.
EQUATION
where load resistance.
FIGURE PARALLEL RESONANT CIRCUIT
parallel resonant circuit determine bandwidth, circuit.
EQUATION
-2RC
quality factor, defined various ways such
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EQUATION EQUATION NQSB
Energy Stored System Cycle -Energy Dissipated System Cycle reac -resis
above equation indicates that induced voltage coil inversely proportional square root coil inductance, proportional number turns surface area coil.
inductance
Series Resonant Circuit
capacitance
simple series resonant circuit shown Figure expression impedance circuit
EQUATION
where: angular frequency ohmic resistance coil capacitor reactance coil capacitor, respectively, such that:
where:
resonant frequency bandwidth ohmic losses
EQUATION
applying Equation Equation into Equation parallel resonant circuit
EQUATION
parallel resonant circuit proportional load resistance also ratio capacitance inductance circuit. When this parallel resonant circuit used antenna circuit, voltage drop across circuit obtained combining Equations
EQUATION
impedance Equation becomes minimized when reactance component cancelled each other such that This called resonance condition. resonance frequency same parallel resonant frequency given Equation
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FIGURE SERIES RESONANCE CIRCUIT
above equation indicates that coil voltage product input voltage circuit. example, circuit with have coil voltage that times higher than input signal. This because energy input signal spectrum becomes squeezed into single frequency band. When circuit tuned resonant frequency such voltage across coil becomes: EQUATION
13.56
half power frequency bandwidth determined given
EQUATION
EXAMPLE
CIRCUIT PARAMETERS
ohmic resistance then values 13.56 resonant circuit with are:
quality factor, series resonant circuit given series circuit forms voltage divider, voltage drops coil given
EQUATION
2.347 13.56MHz
58.7 (pF) 13.56
EQUATION
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TUNING METHOD
circuit must tuned resonance frequency maximum performance (read range) device. examples tuning circuit follows: Voltage Measurement Method: voltage signal source resonance frequency. Connect voltage signal source across resonant circuit. Connect Oscilloscope across resonant circuit. Tune capacitor coil while observing signal amplitude Oscilloscope. Stop tuning maximum voltage. S-Parameter Impedance Measurement Method using Network Analyzer: S-Parameter Test (Network Analyzer) measurement, calibration. Measure resonant circuit. Reflection impedance reflection admittance measured instead S11. Tune capacitor coil until maximum null (S11) occurs resonance frequency, impedance measurement, maximum peak will occur parallel resonant circuit, minimum peak series resonant circuit.
FIGURE VOLTAGE FREQUENCY RESONANT CIRCUIT
FIGURE FREQUENCY RESPONSES RESONANT CIRCUIT
Note Response, Impedance Response Parallel Resonant Circuit, Impedance Response Series Resonant Circuit. (a), null resonance frequency represents minimum input reflection resonance frequency. This means circuit absorbs signal frequency while other frequencies reflected back. (b), impedance curve peak resonance frequency. This because parallel resonant circuit maximum impedance resonance frequency. shows response series resonant circuit. Since series resonant circuit minimum impedance resonance frequency, minimum peak occurs resonance frequency.
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READ RANGE RFID DEVICES
Read range defined maximum communication distance between reader tag. general, read range passive RFID products varies, depending system configuration affected following parameters: Operating frequency performance antenna coils antenna tuning circuit Antenna orientation Excitation current Sensitivity receiver Coding modulation) decoding demodulation) algorithm Number data bits detection (interpretation) algorithm Condition operating environment (electrical noise), etc. read range 13.56 relatively longer than that device. This because antenna efficiency increases frequency increases. With given operating frequency, conditions related antenna configuration tuning circuit. conditions determined circuit topology reader. condition communication protocol device, related firmware software program data detection. Assuming device operating under given condition, read range device largely affected performance antenna coil. always true that longer read range expected with larger size antenna with proper antenna design. Figures show typical examples read range various passive RFID devices.
FIGURE READ RANGE SIZE TYPICAL PROXIMITY APPLICATIONS*
0.5-inch diameter
1-inch diameter 2-inch diameter
inche
inch Reader Antenna
inches
2-inch 3.5-inch" (Credit Card Type)
FIGURE READ RANGE SIZE TYPICAL LONG RANGE APPLICATIONS*
0.5-inch diameter
1-inch diameter 2-inch diameter
inch Long Range Reader
ches
inches
inch
Note:
2-inch" 3.5-inch (Credit Card Type)
Actual results shorter longer than range shown, depending upon factors discussed above.
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APPENDIX CALCULATION MUTUAL INDUCTANCE TERMS EQUATIONS
Positive Mutual Inductance Terms:
EQUATION Mutual inductance between conductors
EQUATION Mutual inductance between conductors
where:
where:
where d1,5 distance between track centers conductor interspacing between conductors width track, F11,5 mutual inductance parameter between conductor segments viewing from conductor F51,5 mutual inductance parameter between conductor segments viewing from conductor F1,5 mutual inductance parameter between conductor segments viewing from length difference between conductors.
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EQUATION Mutual inductance between conductors
EQUATION Mutual inductance between conductors
where:
where:
EQUATION Mutual inductance between conductors
where:
EQUATION Mutual inductance between conductors
where:
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EQUATION Mutual inductance between conductors
EQUATION Mutual inductance between conductors
where:
where:
EQUATION Mutual inductance between conductors
EQUATION A.10 Mutual inductance between conductors
where:
where:
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EQUATION A.11 Mutual inductance between conductors
EQUATION A.13 Mutual inductance between conductors
where:
where:
EQUATION A.12 Mutual inductance between conductors
EQUATION A.14 Mutual inductance between conductors
where:
where:
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EQUATION A.15 Mutual inductance between conductors
EQUATION A.17 Mutual inductance between conductors
where:
where:
EQUATION A.16 Mutual inductance between conductors
EQUATION A.18 Mutual inductance between conductors
where:
where:
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EQUATION A.19 Mutual inductance between conductors
EQUATION A.21 Mutual inductance between conductors
where:
where:
EQUATION A.20 Mutual inductance between conductors
EQUATION A.22 Mutual inductance between conductors
where:
where:
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EQUATION A.23 Mutual inductance between conductors
EQUATION A.25 Mutual inductance between conductors
where:
where:
EQUATION A.26 Mutual inductance between conductors
where:
EQUATION A.24 Mutual inductance between conductors
where:
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EQUATION A.27 Mutual inductance between conductors
EQUATION A.29 Mutual inductance between conductors
where:
where:
EQUATION A.28 Mutual inductance between conductors
EQUATION A.30 Mutual inductance between conductors
where:
where:
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EQUATION A.31 Mutual inductance between conductors
EQUATION A.32 Mutual inductance between conductors
where:
where:
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EQUATION A.33 Mutual inductance between conductors
EQUATION A.35 Mutual inductance between conductors
where:
where:
EQUATION A.34 Mutual inductance between conductors
EQUATION A.36 Mutual inductance between conductors
where:
where:
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EQUATION A.37 Mutual inductance between conductors
where:
EQUATION A.39 Mutual inductance between conductors
where:
EQUATION A.40 Mutual inductance between conductors
where:
EQUATION A.38 Mutual inductance between conductors
where:
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EQUATION A.41 Mutual inductance between conductors
EQUATION A.43 Mutual inductance between conductors
where:
where:
EQUATION A.42 Mutual inductance between conductors
EQUATION A.44 Mutual inductance between conductors
where:
where:
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EQUATION A.45 Mutual inductance between conductors
EQUATION A.46 Mutual inductance between conductors
where:
where:
EQUATION A.47 Mutual inductance between conductors
where:
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EQUATION A.48 Mutual inductance between conductors
EQUATION A.50 Mutual inductance between conductors
where:
where:
EQUATION A.49 Mutual inductance between conductors
where:
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EQUATION A.51 Mutual inductance between conductors
EQUATION A.52 Mutual inductance between conductors
where:
where:
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EQUATION A.53 Mutual inductance between conductors
EQUATION A.54 Mutual inductance between conductors
where:
where:
EQUATION A.55 Mutual inductance between conductor other conductors
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EQUATION A.56 Mutual inductance between conductors
EQUATION A.58 Mutual inductance between conductors
where:
where:
EQUATION A.57 Mutual inductance between conductor other conductors
EQUATION A.59 Mutual inductance between conductor other conductors
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EQUATION A.60 Mutual inductance between conductor other conductors
EQUATION A.63 Mutual inductance between conductor other conductors
EQUATION A.61 Mutual inductance between conductor other conductors
EQUATION A.64 Mutual inductance between conductor other conductors
EQUATION A.62 Mutual inductance between conductors other conductors
EQUATION A.65 Mutual inductance between conductors other conductors
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APPENDIX
One_turn.m Inductance calculation with mutual inductance terms turn rectangular shape. Inductor type Etched MCRF450 reader antenna Youbok Microchip Technology Inc. (nH) unit where (self inductance) Negative mutual inductance positive mutual inductance turn coil Length each conductor l_1a l_1b 7.62 25.4 7.436" 18.887 3.692 %-Define segment length (cm) 0.508 0.0001 3.692 l_1A 7.62 w/2. l_1B 7.62 w/2. 25.4 18.887 25.4 distance between branches (cm) -d13 %-calculate self inductance -L1A 2*l_1A*(log((2*l_1A)/(w+t)) 0.50049 (w+t)/(3*l_1A)) 2*l_1B*(log((2*l_1B)/(w+t)) 0.50049 (w+t)/(3*l_1B)) 2*l_2*(log((2*l_2)/(w+t)) 0.50049 (w+t)/(3*l_2)) 2*l_3*(log((2*l_3)/(w+t)) 0.50049 (w+t)/(3*l_3)) 2*l_4*(log((2*l_4)/(w+t)) 0.50049 (w+t)/(3*l_4))
MATHLAB PROGRAM EXAMPLE EXAMPLE
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calculate mutual inductance parameters -Q1A_3 (d13/l_1A) Q1B_3 (d13/l_1B) Q_1A_gap (d13/(l_1A+gap)) Q_1B_gap (d13/(l_1B+gap))
(d13/l_3) Q2_4 (d24/l_2) calculate negative mutual inductance 2*l_1A*Q1A_3 2*l_1B*Q1B_3 M1A_gap 2*(l_1A+gap)*Q_1A_gap M1B_gap 2*(l_1B+gap)*Q_1B_gap 2*l_3*Q3 M1A_3 (M1A+M3 M1B_gap)/2. M1B_3 (M1B+M3 M1A_gap)/2. M2_4 (l_2*Q2_4) (M1A_3 M1B_3 M2_4) Total Inductance (nH) -L_T
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REFERENCES
Welsby, Theory Design Inductance Coils, John Wiley Sons, Inc., 1960. Frederick Grover, Inductance Calculations Working Formulas Tables, Dover Publications, Inc., York, NY., 1946. Keith Henry, Editor, Radio Engineering Handbook, McGraw-Hill Book Company, York, NY., 1963. H.M. Greenhouse, IEEE Transaction Parts, Hybrid, Packaging, Vol. PHP-10, June 1974. Fujimoto, Henderson, Hirasawa, J.R. James, Small Antennas, John Wiley Sons Inc., ISBN 0471 914134, 1987 James Hardy, High Frequency Circuit Design, Reston Publishing Company, Inc.Reston, Virginia, 1975. Simon Ramo, Fields Waves Communication Electronics, John Wiley, 1984.
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NOTES:
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Note following details code protection feature Microchip devices: Microchip products meet specification contained their particular Microchip Data Sheet. Microchip believes that family products most secure families kind market today, when used intended manner under normal conditions. There dishonest possibly illegal methods used breach code protection feature. these methods, knowledge, require using Microchip products manner outside operating specifications contained Microchip's Data Sheets. Most likely, person doing engaged theft intellectual property. Microchip willing work with customer concerned about integrity their code. Neither Microchip other semiconductor manufacturer guarantee security their code. Code protection does mean that guaranteeing product "unbreakable."
Code protection constantly evolving. Microchip committed continuously improving code protection features products.
Information contained this publication regarding device applications like intended through suggestion only superseded updates. your responsibility ensure that your application meets with your specifications. representation warranty given liability assumed Microchip Technology Incorporated with respect accuracy such information, infringement patents other intellectual property rights arising from such otherwise. Microchip's products critical components life support systems authorized except with express written approval Microchip. licenses conveyed, implicitly otherwise, under intellectual property rights.
Trademarks Microchip name logo, Microchip logo, KEELOQ, MPLAB, PIC, PICmicro, PICSTART, MATE PowerSmart registered trademarks Microchip Technology Incorporated U.S.A. other countries. FilterLab, microID, MXDEV, MXLAB, PICMASTER, SEEVAL Embedded Control Solutions Company registered trademarks Microchip Technology Incorporated U.S.A. Accuron, dsPIC, dsPICDEM.net, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP, ICEPIC, microPort, Migratable Memory, MPASM, MPLIB, MPLINK, MPSIM, PICC, PICkit, PICDEM, PICDEM.net, PowerCal, PowerInfo, PowerTool, rfPIC, Select Mode, SmartSensor, SmartShunt, SmartTel Total Endurance trademarks Microchip Technology Incorporated U.S.A. other countries. Serialized Quick Turn Programming (SQTP) service mark Microchip Technology Incorporated U.S.A. other trademarks mentioned herein property their respective companies. 2003, Microchip Technology Incorporated, Printed U.S.A., Rights Reserved.
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