Texas Instruments TIRIS SCBU025 User manual
Antenna
Reference Guide
November 1996
SCBU025
Antenna
Reference Guide
Literature Number: SCBU025November 1996
Contents
Preface ............................................................................................................................... 5
1 Introduction ............................................................................................................... 71.1 TIRIS ................................................................................................................. 71.2 Purpose .............................................................................................................. 71.3 About This Guide ................................................................................................... 8
2 How the System Works ............................................................................................... 92.1 Operating Principle ................................................................................................. 92.2 Charge-Up of the Transponder ................................................................................... 92.3 Transponder Orientation ........................................................................................... 92.4 Differences Between Antennas .................................................................................. 102.5 Isofield Diagram ................................................................................................... 102.6 How to Measure Antenna Voltages ............................................................................. 112.7 How to Use the Charge-Up Diagrams .......................................................................... 112.8 Separation Between Transponders ............................................................................. 162.9 Antenna Parameters .............................................................................................. 16
3 Noise Characteristics ................................................................................................ 173.1 Influence of Noise on Readout Range ......................................................................... 17
4 Antenna Voltage and Field Strength ........................................................................... 214.1 Maximum Antenna Voltage Allowed ............................................................................ 214.2 Maximum Magnetic Field Strength That Can Be Generated ................................................ 224.3 Magnetic Field Strength Boundaries for Countries With RMS Regulations ............................... 22
5 Speed Applications (Detecting Moving Transponders) .................................................. 235.1 Introduction ......................................................................................................... 235.2 Shorter Charge-Up (TX) Pulses for Speed Applications ..................................................... 24
6 Mechanical Characteristics ........................................................................................ 276.1 Mounting the Antenna ............................................................................................ 276.2 Cleaning the Antenna ............................................................................................. 276.3 Chemicals .......................................................................................................... 276.4 Metal in the Environment ......................................................................................... 276.5 Connection Leads ................................................................................................. 28
A Brief Theory of Magnetic Induction ............................................................................. 31A.1 Description ......................................................................................................... 31
B Theory of Coupled Inductors ..................................................................................... 33
C Glossary of Terms .................................................................................................... 35
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List of Figures
2-5 Charge-Up Diagram for the G01C Antenna Antenna Voltage From 40 V to 712 V in 96-V Steps(Peak-to-Peak) (Scale in Meters) ........................................................................................ 122-6 Charge-Up Diagram for the G02C Antenna Antenna Voltage From 100 V to 730 V in 90-V Steps(Peak-to-Peak) (Scale in Meters) ........................................................................................ 132-7 Charge-Up Diagram for the G03C Antenna Antenna Voltage From 20 V to 391 V in 53-V Steps(Peak-to-Peak) (Scale in Meters) ........................................................................................ 142-8 Charge-Up Diagram for the S01C Antenna 361 V, 393 V, and 650 V (Scale in Meters) ......................... 153-1 Readout Range of 32.5-mm Transponder With STU on Maximum Power (All Values Are Absolute) .......... 183-2 Readout Range (V
antenna
).................................................................................................. 195-1 Maximum Transponder Speed ........................................................................................... 236-1 Antenna Dimensions ....................................................................................................... 286-2 Antenna Connector ........................................................................................................ 296-3 Mounting a Gate Antenna ................................................................................................. 296-4 Mounting a Stick Antenna ................................................................................................. 29A-1 Magnetic Field Distribution Around a Single Conductor, Side View ................................................. 31A-2 Magnetic Field Distribution Around a Single Conductor, Cross-section View ...................................... 31A-3 Magnetic Field Distribution Around a Two Parallel Conductor ....................................................... 32A-4 Field Line Distribution Around a 6-Turn Inductor ....................................................................... 32B-1 Coupled Inductors .......................................................................................................... 33
List of Tables
2-1 Maximum Antenna Voltages (Peak-to-Peak) ........................................................................... 114-1 Magnetic Field Strength Generated With 1000-V Peak-Peak Antenna Voltage ................................... 225-1 Charge-Up Times, Multiplication Factors, and Transponder Charge-Up Levels ................................... 25
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PrefaceSCBU025 – November 1996
Third Edition - November 1996This is the third edition of this guide. It contains the same information as the second edition, except thatthe appendix containing the antenna specifications has been removed. This information should beobtained from the relevant data sheet.
This guide describes the following antennas:RI-ANT-G01C
RI-ANT-G02C
RI-ANT-G03C
RI-ANT-S01C
If You Need Assistance
Application Centers are located in Europe, North and South America, the Far East, and Australia toprovide direct support. For more information, please contact your nearest TIRIS™ Sales and ApplicationCenter. The contact addresses can be found on the TIRIS home page:
http://www.tiris.com
Trademarks
The TIRIS logo and the words TIRIS, TI-RFid, and Tag-it are trademarks of Texas Instruments.
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1.1 TIRIS
1.2 Purpose
Chapter 1SCBU025 – November 1996
Introduction
TIRIS stands for Texas Instruments Registration and Identification System, a Radio FrequencyIdentification (RFID) system.
The core of the system is a small device called a transponder that can be attached to or embedded in anobject. A stationary or handheld reader sends a low frequency signal to the transponder via an antenna.This signal charges up the passive (battery free) transponder in milliseconds. The transponder returns asignal that carries a unique, factory programmed, 64-bit binary code back to the reader.
The system is used to identify and track objects or animals.
This guide includes the most important information needed to select the best antenna for a specificapplications, to install it correctly, and to optimize its performance. Although the main focus is on TIRISstandard antennas, the guide also contains some theoretical information to help design custom antennas.
The antennas described in this guide, in combination with the other TIRIS system components, offer you acomplete radio frequency identification system.
There are two types of antennas available for use with a stationary TIRIS reader: gate (square orrectangular) antennas and stick (ferrite rod) antennas. These standard antennas come in different sizesfor maximum flexibility.
Target audience: This guide is for application center engineers and customers who are actively developingTIRIS RFID applications.
If you have questions, please contact your local TIRIS Application Center (http://www.tiris.com ).
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1.3 About This Guide
About This Guide
This guide contains the following parts:
Chapter 1: Introduction. A short introduction to TIRIS and a short description of the guide itself.Chapter 2: How the System Works. A description of how the system works, followed by a seriesof charts showing the "charge-up" distances for different countries for each of the TIRISantennas.Chapter 3: Noise Characteristics. A description of noise and its influence on the TIRIS system.Chapter 4: Antenna Voltage and Field Strength. A description of the allowed antenna voltagesand how to calculate other antenna voltages and what field strengths are generated.Chapter 5: Speed Applications. A description of how to read moving transponders.Chapter 6: Mechanical Characteristics. A description of the mechanical characteristics of theantennas and how to mount them.Appendix A: Brief Theory of Magnetic Induction. A short description of magnetic induction.Appendix B: Theory of Coupled InductorsAppendix C: Glossary of Terms. A list of the terms and phrases using in this guide together with ashort description of each of them.
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2.1 Operating Principle
2.2 Charge-Up of the Transponder
2.3 Transponder Orientation
Chapter 2SCBU025 – November 1996
How the System Works
The antenna has two tasks in the TIRIS system:1. Send an energizing signal to the transponder.2. Receive the resulting ID signal from the transponder.
When the transponder passes through the magnetic field created by the transmitting antenna, a capacitorin the transponder is charged up to a certain voltage. The energy thus created in the capacitor is used totransmit an ID code back to the readout antenna. For proper functioning, the transponder needs aminimum voltage of 5 V on its capacitor.
Because the charge-up takes place in a fixed time, the magnetic field strength of the charging signal isrelevant to the maximum readout range (see Appendix A ).
The 'readout diagram' of a transponder depends on the orientation of the transponder with respect to thereader antenna. The magnetic field lines of the reader antenna must incident (cross) the antenna of thetransponder, and vice versa, in order to achieve a proper reception. Figure 2-1 through Figure 2-4 showthe affect that orientation has on the readout diagram. They show, respectively, the diagrams fororientations of 0 °, 30 °, 60 °, and 90 °.
See Appendix B for an explanation of how these definitions of orientation are derived.
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2.4 Differences Between Antennas
2.5 Isofield Diagram
Differences Between Antennas
The performance of the TIRIS system is influenced by the reader antenna selected. Each antenna has itsown specific characteristics.
Figure 2-1. 0 °Transponder Orientation Figure 2-2. 30 °Transponder Orientation
Figure 2-3. 60 °Transponder Orientation Figure 2-4. 90 °Transponder Orientation
A charge-up (Isofield) diagram shows the field strength achieved by a specific antenna voltage against anaxis of length (the distance over which the transponder will be "charged-up" to the required level – theexample given in Figure 2-5 is 5 V).
For example: on a G01C antenna, an antenna voltage of 232 V will charge-up a transponder with a 0 °orientation to 5 V over a distance of up to 0.68 m.
An 'Isofield' diagram and a charge-up diagram are the same and are independent of noise. A readoutdiagram includes the effects of noise. Each antenna has its own specific 'Isofield' pattern. The fieldstrength decreases exponentially with the distance to the readout antenna. For short distances thisexponent differs for various antennas.
In Figure 2-5 to Figure 2-8 you will see isofield (charge-up) diagrams for the TIRIS antennas. Thesepatterns show you the charge-up of the transponder to 5 V in 50 ms for the 32.5 mm tube transponder.The top diagram on each page is the charge-up diagram with a transponder orientation of 0 °, and thebottom diagram on each page is the charge-up diagram with a transponder orientation of 90 °. With thischarge-up voltage, the transponder is able to reset completely. However, the transponder is able totransmit back its complete ID code with a lower voltage, so the readout distance could be even larger.
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2.6 How to Measure Antenna Voltages
2.7 How to Use the Charge-Up Diagrams
How to Measure Antenna Voltages
Each diagram has several lines or 'envelopes' on it, each representing a different voltage applied to theantenna. The smallest 'envelope' (that closest to the antenna) shows the magnetic field induced by thelowest voltage applied to the antenna, and the largest 'envelope' shows the field induced by the highestantenna voltage (see Table 2-1 ).
The antenna voltage applied is set according to the regulations of the country in which the system is to beused. Table 2-1 is a table of antenna voltages allowed for each country with a charge-up time of 50 msand a receive time of 40 ms. By comparing these voltages with the relevant line on the antenna isofielddiagram, you can see what the charge-up distance will be for the country that the system will be used in.
Table 2-1. Maximum Antenna Voltages (Peak-to-Peak)
(1)
AntennaCountry CommentsG01C G02C G03C S01C
Netherlands 39 98 21 361 CISPRGermany 43 107 23 393 CISPRDenmark 43 107 23 393 CISPRUnited Kingdom 94 236 51 650
(2) (3)
PEAKJapan 371 713
(2) (3)
203 650
(2) (3)
PEAK (provisional value only)United States 499
(2)
713
(2) (3)
272 650
(2) (3)
RMS (100 ms window)France 688
(2)
713
(2) (3)
375
(2)
650
(2) (3)
RMSAustralia 707
(2)
713
(2) (3)
386
(2)
650
(2) (3)
PEAK (provisional value only)
(1)
The figures given in this table have been agreed with the relevant government agencies and are for "portable equipment". Forsome countries, (for example, the Netherlands), if the equipment is made a permanent fixture, it is possible to obtain permissionfor higher antenna voltages to be used.(2)
These voltages cannot be achieved using the RF Module RI-RFM-001. It should be possible to achieve these levels if you usethe RF Module RI-RFM-002 which allows approximately twice the antenna voltage of the 001.(3)
Temperature limit of antenna.
The antenna voltages can only be measured using an oscilloscope with a 10 M Ωprobe across theantenna terminals (metal-to-metal contact). Check the peak-to-peak level and then reverse the probecontacts and check again; the highest reading is the correct reading.
To work out the charge-up range for a particular antenna, you must first look in Table 2-1 to see whatantenna voltage is allowed in the country that the system will be used in. Now go to the charge-updiagram for the antenna, and see where on the diagram (usually between two lines) that value falls. Thiswill show you the readout range (in a environment with an acceptable noise level).
The innermost line (or envelope) shows the reading range possible with the lowest allowed voltage, andthe outer line is the range possible with the maximum voltage. On Figure 2-5 A, we have marked thevoltage value for each line to show how this works.
Examples 1 and 2 provide two examples of how to work out the charge-up distance for a particularantenna in two different countries.
Example 1: Using Antenna G02C in Japan1. Look in Table 2-1 , and you will see that the allowed voltage for antenna G02C in Japan is 713 V.2. Now go to Figure 2-6 A. 713 V falls just inside the outer line, which represents 730 V.3. Using a ruler, line up the 713 V "spot" with the side axis. This shows you that you have a charge-updistance of just over 70 cm (just over 27.5 inches).
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A) 0°Orientation
B) 90°Orientation
How to Use the Charge-Up Diagrams
Example 2: Using Antenna G02C in Germany1. Look in Table 2-1 , and you will see that the allowed voltage for antenna G02C in Germany is 107 V.2. Now go to Figure 2-6 A. 107 V falls just above the first (inner) line which represents 100 V.3. Using a ruler line up the 107 V "spot" with the side axis. This shows you that you have a charge-updistance of just under 40 cm (just under 16 inches).
Figure 2-5. Charge-Up Diagram for the G01C AntennaAntenna Voltage From 40 V to 712 V in 96-V Steps (Peak-to-Peak)(Scale in Meters)
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2.8 Separation Between Transponders
2.9 Antenna Parameters
Separation Between Transponders
Separation refers to how close together transponders can be and still be individually read.
High selectivity means transponders can be close together while still achieving successful readings. Lowselectivity means that more distance is needed between transponders in order for them to be successfullyread.
The smaller the antenna, the smaller the major lobe.
The smaller the antenna, the greater the selectivity. The following list shows the TIRIS antennas in orderof increasing selectivity:
Least G03C large gateG02C medium gateG01C small gateGreatest S01C/S02C stick antenna
Each antenna has an induction of 27 µH±1µH, with a Q-factor larger than 100. These values are valid atroom temperature and a 134.2 kHz measuring frequency.
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3.1 Influence of Noise on Readout Range
Chapter 3SCBU025 – November 1996
Noise Characteristics
Noise has an impact on system performance. The most important consideration in solving noiseinterference problems is to choose the best antenna for the particular application. This section provides:•Explanation of noise•The effect of moving the transponder closer to the readout antenna
Noise is any signal that deteriorates the readout range of the system. The larger the antenna (surface ×number of windings) the larger the noise signal that will be induced.
Homogeneous noise includes sources like other TIRIS systems at a certain distance (more than10 meters), radio stations transmitting within the TIRIS bandwidth, other strong noise sources at a largedistance from the readout antenna. Inhomogeneous noise includes sources like monitors, auto engines,other transponders within the field of the antenna, switching relays, etc., close to the readout antenna.
The readout range can be increased by orientating the readout antenna away from noise sources. It isalways recommended to look for noise sources and try to eliminate them if possible.
The signal from the transponder must be larger than the noise level, otherwise the receiver will not identifythe transponder. When a transponder signal is overpowered by external noise, moving the transpondercloser to the readout antenna has two effects which influence the readout:The first is better coupling between the transponder and the readout antenna (the better the coupling,the larger the induced voltage on the readout antenna).The second is by charging the transponder capacitor up to a higher voltage, this means that thetransponder is then able to transmit a stronger signal back to the readout antenna.
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Influence of Noise on Readout Range
Figure 3-1 is a graph showing the readout range for the standard gate antennas as a function ofhomogeneous noise. This graph ignores government agency regulations (FCC, PTT, etc.)
Figure 3-1. Readout Range of 32.5-mm Transponder With STU on Maximum Power(All Values Are Absolute)
Note: With cases of inhomogeneous noise, working out the reading distance is more complexand very dependent on the type of noise source. A straightforward analysis cannot bepresented.
There is a relationship between the antenna voltage and the readout range in a homogenous noiseenvironment. The figure for this relationship is established with three sections:Vcl = 3.5 V boundary (the transponder must be charged-up to a very minimum of 3 V to be able toreturn its ID code – for example: in Figure 3-2 for the G03C antenna, the 3 V boundary is between50 V and 180 V).Noise limiting boundary (the reading distance over which a proper readout can be achieved takingnoise into consideration; in Figure 3-2 for the G03C antenna, this is between 180 and 950 V
ant
).Vcl = 7 V boundary (the maximum charge-up level of the transponder, in Figure 3-2 for the G03Cantenna, this is between 950 V and higher).
There are two principles involved in working out the read-out range:The first principle is that the higher the antenna voltage, the higher the field strength and the larger thecharge-up distances.The second principle is that if you achieved a longer charge-up distance, the level of charge on thetransponder capacitor was probably only about 5 V, thus restricting the distance over which the returnsignal can be read (not such a good coupling between the transponder and the read antenna). Forexample: if the transponder was a little closer to the reader antenna, the capacitor would havecharged-up a little more (say 5.5 V) resulting in a slightly stronger returned ID signal.
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