Let RFID, Inc. get you up to speed on the basics of RFID – Radio Frequency Identification.
RFID Components and ABCs.
RFID – Radio Frequency Identification is a small chip, or RFID tag, attached to some object that can be read at short range via radio waves by a tag reader. These items can be close together or far apart and are used for everything from credit cards, to inventory tracking to ticketing.
Components can be broken down as a Tag (Transponder), a Reader, an Antenna, and sometimes an Interface. Sometimes the Reader and Antenna are enclosed into a single housing, sometimes they are 2 separate components. Sometimes there is added to this architecture an Interface which can translate data into other communication protocols and/or manage a network of many Readers.
Passive Tags – A Tag carrying data, which can be RO (read only) or RW (read write) lies dormant until it is activated by the RF signal of a Reader. Upon being woken or excited by the Reader, the Tags begins to transmit it’s data back to the Reader. Tags typically have an infinite life in terms of being read, and a finite life in terms of the amount of writes. 100k writes is typical.
Active Tags – A Tag that is battery powered, most of which are known as TTO (tag talk only) whereby the Tag continually transmits it’s data x amount of times per second, and if in range of a Reader, which is really more of a listening post, will be read. That range depends upon the frequency of the system, but our 433.92 MHz product operates up to several thousand meters. Tag life very much depends upon the size of the battery and number of data transmissions, but can be as high as 4 years.
Readers – Readers translate the 1’s and 0’s of Tag data into languages another machine or human can understand, like TTL or ASCII bytes. Readers can have other functions, like I/O, sound a horn, illuminate a light, etc., or even logic tasks. Most often Readers are capable of serial (RS232, RS485, RS422), USB, TTL, Wiegand and Ethernet communication protocols.
Interfaces – Although Readers could output more in depth language protocols, PLC languages, this would make a single Reader more expensive thus it makes more sense to network simple Readers and most often this is handled by an Interface which can also manage a network of Readers, each Reader having its own unique address. Typical are protocols specific to a particular PLC manufacturer like Ethernet/IP & DeviceNet (Allen Bradley PLC’s), Profibus & Profinet (Siemens), Modbus RTU and Modbus TCP (Modicon) although standard TCPIP Ethernet and serial communications can also be offered.
What frequency should I consider for my application?
First and foremost that depends upon the read range necessary, followed by, to what material will the Tag be mounted (metal or non-metal).
125 KHz LF passive & 13.56 MHz HF passive – read range of inches to a foot or two. 1 meter is possible but pushing the limits of the technology necessitating a large Tag and Antenna. LF is very metal friendly, HF not so much. See a full breakdown of LF vs. HF here.
UHF active 433.92 MHz – read range of 1 meter to several thousand feet, some Tag options are metal mountable.
UHF passive 868-928 MHz – read range of inches to 30 meters of range, some Tag options are metal mountable.
Summary and History of Frequencies (in general)
125 KHz LF (low frequency) Passive
First put to use commercially in the 1980’s (generally), most all systems today are based on 125 KHz however there is an ISO standard (11784 & 11785) based on 134.2 KHz used in the animal market. Our first frequency was 148 KHz and other vendors had their own as well. Most LF applications consist of read ranges from inches to a foot, although 1 meter of distance is possible but requires a large Tag and Reader Antenna.
LF Advantages – Tags on/in metal, Readers in close proximity to one another without interference, Tag speed.
LF Disadvantages – Tag memory size generally limited to 2k bits, Tag cost prohibitive for applications requiring millions of Tags, although anti-collision capable there are not many applications where hundreds of Tags are to be stationed within a foot. Click here to download a tutorial PowerPoint with application photos and view a video of Tag read speeds with networked Smart Antenna Readers.
13.56 MHz HF (high frequency) Passive
HF came of age in the late 1990’s as an answer to lowering Tag costs in order to address high volume Tag applications such as library books, laundered items, passports and credit cards to mention a few, as LF Tags contain a hard copper coil and are difficult to mass produce while HF Tags can use printed metals or metallic fluids as a Tag coil. Read ranges are similar to LF, most applications are inches to a foot, although 1 meter f distance is possible with a large Tag and Reader Antenna. HF did not take off into the hundreds of millions of Tags application as predicted but is still a solid choice for some applications.
HF Advantages – More Tag memory, slightly less cost per Tag in volume than LF.
HF Disadvantages – On metal mount or heavy metal environments, can be done but is finicky. Readers in close proximity will interfere with one another. Although anti-collision capable there are not many applications where hundreds of Tags are to be stationed within a foot. You may see a lot of vendors tout 13.56 MHz as being ISO standard. In general Tags are ISO standard, however you are still locked into a single vendor as Readers vary greatly from vendor to vendor and sometimes Tags are programmed with proprietary data.
433.92 MHz UHF (ultra high frequency) Active (some vendors offer 2.45 GHz Active with the same features detailed here)
Battery powered Tags have always been around but their applications are limited and very specific.
Active Tag Advantages – Read range of thousands of feet, the ability to tune to a specific read range, and anti-collision feature (the ability to read more than 1 Tag at a time).
Active Tag Disadvantages – Tag cost ($20 to $30), Tag size, finite battery.
868 to 928 MHz UHF (ultra high frequency) Passive
Generally known in the USA as 915 MHz or just “UHF”, each country or continent has its own specific frequency that is accepted by regulating authorities. For a list of those, see this GS1 document here (attachment). Since the early 2000’s, 915 MHz has been all the rage, the vogue technology of frequent press bringing the RFID industry into a global limelight, the epicenter of development efforts and dollars. Tags at this frequency also need not incorporate a hard copper coil, promising the least expensive RFID Tag to address high volume applications however Tag innovation and development did not bring the frequency to competitiveness until about 2006.
UHF Advantages – Read Range up to 90 feet, Tag cost, anti-collision feature, and truly being ISO standard across vendors.
UHF Disadvantages – Reader cost, range performance limited or even enhanced by liquids (like the human body), metal can be a friend or enemy depending upon the Tag chosen.