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Summary of Contents for Texas Instruments 2000 LF Series
- Page 1 Series 2000 LF Antenna Design Guide Application Note 11-06-21-068, March 2003 Radio Frequency Identification Systems...
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Page 3: Table Of Contents
Lit Number: 11-06-21-068 Contents Contents ..........................i Edition 1 – March 2003 ......................i About this Manual ........................ii Abstract ..........................1 Why Custom Antennas may be Required..............2 Standard Antennas......................3 27 µH Inductance Antennas ..................3 47 µH Inductance Antenna..................4 116 µH Inductance Antenna.................. - Page 4 Lit Number: 11-06-21-068 Figure 2. MicroReader Antenna (47 µH)................4 Figure 3. Mini-RFM Antenna (116 µH) ................5 Figure 4. The RFM-104B RF Module.................. 6 Figure 5. Inductance Fine-Tuning ..................6 Figure 6. RFM-003B and RFM-007B Modules ..............7 Figure 7. Capacitance Fine-Tuning ...................
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Page 5: Edition 1 - March 2003
Customer to ensure that these products meet their needs, including conformance to any relevant regulatory requirements. Texas Instruments (TI) reserves the right to make changes to its products or services or to discontinue any product or service at any time without notice. -
Page 6: About This Manual
Lit Number: 11-06-21-068 PREFACE Read This First About this Manual This LF Antenna Design Guide Application Note (11-06-21-068} is written for the sole use by TI*RFID Customers who are engineers experienced with TI*RFID and Radio Frequency Identification Devices (RFID). Regulatory and safety notes that need to be followed are given Section XX. Conventions Certain conventions are used in order to display important information in this manual, these conventions are:... -
Page 7: Abstract
Abstract This document describes how to design and develop custom antennas suitable for attaching to Texas Instruments’ Low Frequency (LF) Radio Frequency (RF) modules and readers. It looks at the matching circuits of the standard RFMs and details the antenna requirements for each one. -
Page 8: Why Custom Antennas May Be Required
Lit Number: 11-06-21-068 1 Why Custom Antennas may be Required There are many reasons why custom built antennas may be required: • special sized antennas are needed • the antennas have to be built into structures/ equipment e.g. doors • very large antenna are required e.g. road loops •... -
Page 9: Standard Antennas
Lit Number: 11-06-21-068 2 Standard Antennas Because different RF Modules require antennas with different inductances, Texas Instruments have three categories of antennas available: 2.1 27 µH Inductance Antennas These antennas are used with the RFM-104B, RFM-007B and RFM-008B RF modules. RI-ANT-G02E RI-ANT-G04E RI-ANT-G02E... -
Page 10: Μh Inductance Antenna
Lit Number: 11-06-21-068 The RI-ANT-G01E, RI-ANT-G02E antennas have 1m tails and are nominally 27 µH and when connected to the appropriate RF Module can be tuned to resonate at 134.2 kHz. The RI-ANT-G04C antenna is provided with no tail and is nominally 26 µH. If 2.5 mm (14 SWG) wire is used, a 4m (12’) tail can be added and still be capable of being tuned to resonance. -
Page 11: 116 Μh Inductance Antenna
Lit Number: 11-06-21-068 2.3 116 µH Inductance Antenna The RFM-003B module requires an antenna with a self inductance of 116 µH and the following antenna is available: RI-ANT-P02A Figure 3. Mini-RFM Antenna (116 µH) Historically, the Mini-RF Module was intended for hand-held readers and so the antenna is supplied with a 100 mm (5”) tails. -
Page 12: The Rfm-104B Module
Lit Number: 11-06-21-068 Equation [1] is the formula that determines at what frequency the antenna circuit resonates and you can see how either the Capacitance (C) or the Inductance (L) can be varied to arrive at the required frequency (ƒ). Some RF modules tune to resonance by varying the capacitance, whilst the RFM-104B and the Remote Antenna Tuning Boards both vary the inductance. -
Page 13: Rfm-003B And Rfm-007B Modules
Lit Number: 11-06-21-068 3.1.2 RFM-003B and RFM-007B Modules The RFM-003B (Mini-RFM) and the RFM-007B (Power RFM) are shown in Figure 6 Figure 6. RFM-003B and RFM-007B Modules The RFM-003B and RFM-007B modules both use capacitance tuning (using jumpers) for the fine tuning. This circuit is represented in Figure 7. Capacitance (C) Antenna Inductance (L) -
Page 14: The Stu-Mrd1 Microreader
Lit Number: 11-06-21-068 Figure 8. RFM-008B RF Module and ACC-008A Tuning Board The board has a wide range of capacitance, which can be selected using on-board jumpers. This arrangement allows for antennas with inductances from 12 to 80 µH to be connected and fine tuned by a variable inductor. -
Page 15: Determining Self Inductance
For S2000 Series readers, antenna inductance can be calculated using the software utility “ADU.exe” (Antenna Design Utility). This program is available from your local Texas Instruments RFID representative and is shown in Figure 10. Note: Because of the different characteristics of various wire types, some experience with this program is required. -
Page 16: By Measurement
Lit Number: 11-06-21-068 Figure 10. “ADU.EXE” Screen The length and width of an antenna and the wire size can be specified and by adjusting the number of windings (or the size) you can decide what size antenna will give you the correct inductance. 4.1.2 By Measurement Relatively low cost LCR (Inductance, Capacitance and Resistance) meters are available that will measure the inductance of a loop accurately enough for our... -
Page 17: Antenna Q
Lit Number: 11-06-21-068 These meters normally measure the inductance at 1 kHz (not 134.2 kHz) but providing that the meter has a resolution of 0.1 µH, they can be used 4.2 Antenna Q The Q value of an antenna is a measure of the efficiency. For the same input power, high Q antennas have a much greater RF output than lower Q antennas. -
Page 18: Determing The Antenna's Q Value
Lit Number: 11-06-21-068 Which is why the MicroReader, which was designed for applications such as vehicle immobilizer systems (where the antenna is around the lock barrel) and hotel door locks, requires low Q antennas. 4.2.1 Determing the Antenna’s Q Value 4.2.1.1 By Measurement Q values are normally measured using a signal generator and a spectrum analyzer. -
Page 19: Controlling The Antenna's Q
Lit Number: 11-06-21-068 Example 1. RI-ANT-G01E antenna, Where: ƒ = 134200 Hz (134.2 kHz) L = 0.000027 H (27 µH) R = 0.2 Ohms Q = (2 * 3.142 * 134200 * 0.000027)/ 0.2 = 114 Example 2. MicroReader antenna, Where: ƒ... -
Page 20: Litze Wire
Lit Number: 11-06-21-068 4.3.1.2 Litze Wire Because a low resistance is required for high Q antennas, Texas Instruments use Litze Wire in their antennas. Litze wire uses multiple (e.g. 120) individually insulated (lacquered) wire stands, covered in silk to make up the wire. As each strand is twice the skin depth, total current flow occurs in each strand and for a particular wire size, eddy currents are eliminated. -
Page 21: Other Wires Used In Antenna Construction
Lit Number: 11-06-21-068 4.3.1.3 Other Wires Used in Antenna Construction Smaller antennas e.g. RI-ANT-G02C tend to have very strong RF fields but the field falls away rapidly, whereas larger antennas have a less intense field close to the antenna and the field strength falls off less rapidly. Litze wire will bring increased performance to small loops and ferrite cored antennas but has limited advantages as antennas get larger. -
Page 22: Antenna Size
Lit Number: 11-06-21-068 For low Q antennas e.g. for the MicroReader, we use lacquered transformer wire. Figure 18. Transformer Wire The increased resistance of this wire enables us to create low Q antennas. 4.4 Antenna Size It has already been mentioned that, in electrically noisy situations, large antennas can have less reading range than smaller ones G04E 32 mm TRANSPONDER... -
Page 23: Antenna Size Vs. Inductance
Lit Number: 11-06-21-068 Not shown in Figure 19 is the stick antenna (RI-ANT-S01C). This antenna does not have a long range but because of its small area, it picks up much less ambient noise and is often used below roller conveyor systems. -
Page 24: Adapting A Non 27Μh Antenna
Lit Number: 11-06-21-068 4.4.2 Adapting a non 27µH Antenna If you have to produce a loop to a particular size and the inductance is not 27 µH, there are 3 ways to allow you to adapt that loop to a reader. 1. -
Page 25: Table 2. External Capacitance Values
Lit Number: 11-06-21-068 Inductance Too High Inductance Too Low Inductance (µH) Capacitance (µF) Inductance (µH) Capacitance (µF) 54.0 0.051 25.5 0.003 51.0 0.064 25.0 0.004 48.0 0.067 24.5 0.005 45.0 0.076 24.0 0.007 43.0 0.089 23.5 0.008 41.0 0.100 23.0 0.009 40.0 0.110... -
Page 26: Figure 23. Polypropylene Capacitor De-Rating
Lit Number: 11-06-21-068 Note: The values in this table are calculated and because of component tolerances, may not be exactly right for a particular reader. The values in Table 2 assume that high voltage (1000 ~ 2000 VDC) polypropylene capacitors are used. When high Q antennas are in use be careful not to exceed the manufacturer’s ratings for these capacitors, because as frequency increases the AC voltage capability of these capacitors reduces. -
Page 27: Antenna Tails
Lit Number: 11-06-21-068 4.5 Antenna Tails The antenna tail serves only to allow the antenna loop to be separated from the RF module and the longer the tail, the greater the losses that are introduced. For every metre length of the tail, approximately 0.5 µH inductance is added. If we assume that the standard antenna has an inductance of 27 µH and the upper limit that is allowed with the on-board capacitance/ variable inductance is 28.5 µH, then we can add around 3 m of extra wire and still tune to resonance. -
Page 28: Ferrite Cored Antennas
Figure 26. Ferrite Cored Antenna 5 Other Antennas 5.1 Field Lines Texas Instruments LF system uses the magnetic (H) field to transfer energy to the transponder. When a current moves through an antenna it generates field lines similar as those shown in Figure 27. -
Page 29: Opposing Antennas (In-Phase)
Lit Number: 11-06-21-068 Figure 27. Field Lines The result is that in different parts of the field, the tag couples better and receives the charge-up energy, while in other parts of the field no energy transfer takes place. Stick Antenna Gate Antenna Figure 28. -
Page 30: Opposing Antennas (Out-Of-Phase)
Lit Number: 11-06-21-068 Figure 29. Opposing Antennas (In-phase) If standard antennas are used, they are connected in parallel and appear as a single 13.5 µH antenna. This means they have to be used with the Remote Antenna RFM. A better approach is to make two antennas that are 54 µH (double inductance). When these antennas are connected in parallel, they appear as 27 µH inductance and can be used with standard RF module. -
Page 31: Figure 31. Opposing Antennas (Out-Of-Phase)
Lit Number: 11-06-21-068 Figure 31. Opposing Antennas (out-of-phase) This arrangement is very useful for access control gates, where the badge is always worn at right angles to the antenna. Changing the field means it will read across the width without a hole. This technique is used for livestock applications, where the electronic ear tag is normally in the same orientation as the badge. -
Page 32: Noise Canceling Antennas
Lit Number: 11-06-21-068 5.4 Noise Canceling Antennas When antennas have to operate in an environment with homogeneous noise (not coming from any one direction), noise canceling antennas may help to restore some performance. These antennas have multiple loops that are equal and opposite and any (homogeneous) signal arriving at all loops is cancelled, whereas the tag signal will arrive at one loop and be received. -
Page 33: Appendix A - Microreader Antenna Designs
Lit Number: 11-06-21-068 Appendix A – MicroReader Antenna Designs Because of the Micro-reader’s modest power output and the requirements for antennas to perform next to metal, certain constraints have been imposed by design on antenna construction. • The antenna Q factor must be less than 20 •... -
Page 34: Figure 34. Microreader Antenna 1
Lit Number: 11-06-21-068 Antenna 1 This antenna is built from a standard inductor and the resistance reduced by a series resistor 47 µH INDUCTOR, 1.2 A (RS No. 228-450) 1Ω RESISTOR, 1W (RS No. 214-0734) Figure 34. MicroReader Antenna 1 Antenna 2 This antenna is constructed on a 40 mm diameter plastic tube former. -
Page 35: Figure 36. Microreader Antenna 3
Lit Number: 11-06-21-068 Antenna 3 Antenna three is 75 mm in diameter and formed around a slice of plastic water pipe. 15 TURNS (0.2 mm Enamelled wire) 75 mm Figure 36. MicroReader Antenna 3 Page (29) -
Page 36: Figure 37. Microreader Antenna 4
Lit Number: 11-06-21-068 Antenna 4 This antenna is constructed around a 6 mm thick MDF former. Tip: For such antennas, double sided Scotch tape will retain the thin wire in position during winding. 8 TURNS (0.312 mm Enamelled wire) 200 mm Figure 37. - Page 37 Lit Number: 11-06-21-068 Page (31)
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Page 38: Appendix B. Contacts
Lit Number: 11-06-21-068 Appendix B. Contacts Litze wire Rudolph Pack +49 2261 53185 Gummersbach Germany http://www.pack-feindraehte.de/packE.html The Deeter Group +44 1494 450020 High Wycombe http://www.deeter.co.uk/litz.htm New England Electric Wire Corp +1 603 838 6625 Boston, USA http://www.newenglandelectricwire.com/litzwire.shtml Yu Seung Electronics Co Ltd +82 41863 8100 Korea http://www.yuseung.com/frame.html...
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