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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