Active RFID Tags have many benefits when you want to identify items wirelessly. You can read a truck-load of tagged items in seconds. Private tag information can be secured by password or cleared on command.
They operate over distances up to 100 metres, have the intelligence to initiate conditional transmissions to a reader.
They can store a number that makes a tagged item ‘one-of-a-kind’ and even store instructions about how to manufacture it, use or look after it.
Usually these features are benefits, but not always...
It depends on the application.
One of the main differences between active tags and passive tags is that the active tag has a battery.
You’d expect an RFID tag manufacturer to have good reasons to integrate a battery into an RFID tag, because...
A battery will limit some applications
But there are significant benefits.
A manufacturer of RFID tags knows that the RFID tag benefits mostly outweigh the disadvantages, because...
Having power available from a battery supports a number of features that make active RFID tags superior.
Some tag manufacturers claim that their
tags have a battery life of ‘up to’ five years. How long depends mostly
on how often and how long the tag transmits, so the words ‘up to’
perhaps indicates a battery life of five years, if your tag doesn’t
spend a lot of time transmitting and spends most of its time asleep.
Check the specified battery life (for a given duty cycle) in the manufacturer’s data sheet.
Here are some important things about active RFID tags...
Let’s look at each of these in more detail...
Transmit power and receive sensitivity
Active RFID tags transmit RF energy.
This energy carries the ID and other information to RFID tag readers. The higher the transmit power the greater the range.
The battery in an active tag provides
enough energy to allow the tag to transmit up to the legal maximum
power, enabling it to operate over a greater distance than would
otherwise be possible.
Active RFID tags also receive RF energy, from a reader.
This RF energy carries the information
from the reader to the tag. A tag with higher receive sensitivity will
be able to receive weaker RF signals than a tag with lower sensitivity.
It will be able to ‘hear’ better. The battery powers the receiver
The antenna and its orientation
An active RFID tag antenna is used to transmit and receive, though not at the same time.
The RF signal is strongest when a tag antenna and reader antenna are ‘facing’ each other.
However in many applications you can’t guarantee they will
be facing each other, so it’s better to engineer an RFID system based
on the shortest range, arising from worst case tag orientation.
Whether a tag is transmitting to, or receiving a signal from a reader...
the RF signal strength is weakest when the RFID tag antenna is edge-on to the reader’s antenna.
Weaker RF signal strength means shorter operating range.
In many practical applications the tags
will be randomly arranged and so you’d expect some tags to be
positioned edge-on to the reader with the RF at its weakest and the
range at its shortest.
In general, the higher frequency active RFID tags have greater operating range.
So tags operating in the higher UHF or
microwave frequencies operate over greater distances than tags that
operate at lower frequencies. However, the higher frequencies have some
limitations of their own...
The RF, to and from tags operating at UHF
or microwave frequencies, is likely to be partially absorbed by water
and blocked, or reflected, by metal objects. This reduces the range they
can operate over.
Tags operating at lower frequencies aren’t affected to the same extent but may have other disadvantages.
You can get active RFID tags that are
specifically designed to operate while attached to metal items You have
to mount the tags in a specific way, and by design they’re spaced off
from the surface of the metal by an exact amount. The metal surface then
becomes a reflector and effectively part of the RFID tag antenna.
You can read active RFID tags much faster than passive tags.
Typically you can reliably read a hundred
or more tags every second. Important if you’re trying to identify tagged
items in a truck passing RFID tag readers, and only have a few seconds
to do it.
Here’s why they’re so fast because...
Some types can put themselves into a sleep mode,
when they don’t need to be read, to minimize the current drain from the
battery. When a reader wants the tags to respond, it can wake them all
simultaneously and read each tag individually.
But it’s not an ideal world and
anything that degrades the quality of the RF interaction between tags
and reader will slow the rate at which the tags can be read.
Long range RFID tags might be of benefit to one application but a disadvantage to another.
The longer range of an active tag may seem like one
of the more important RFID tag benefits, but if security is your main
priority, you may want short-range operation, to make it difficult for
anyone to ‘listen in’ on the RF signal.
If security is important, you might prefer to define your own identification format, instead of using a standard format, such as the Electronic Product Code (EPC), so that an unauthorized reader couldn’t interpret the data even if it could access it.
Lock your information - With some standards, including EPC, you can ‘lock’ the data stored in the memory of active RFID tags.
Kill the tag - To prevent
unauthorized access to private information stored on active RFID tags,
some standards, including EPC, have a password-enabled ‘kill’ command
that allows you to permanently disable a tag when you no longer need it.
A typical standard identifier formatting code may have this type of structure...
A custom identifier format may provide a
higher level of security, if you need it. However, this usually isn’t
necessary and a standard identifier format is often adequate.
Imagine a world where every RFID system
used the same identifier format, where the numbers were always the same
length and came out in the same order according to what they meant.
Then all tags and readers throughout the world could speak the same
language and understand each other.
We don’t have such a universal RFID data format
and in some applications, such as security, this could be a bad thing
rather than an advantage as it would make it easier for unauthorized
Identify individual items -
Whatever the format, you may want enough numbers available to let you
allocate one unique number to each individual item that you want to tag.
If you want to individually identify each of millions of products
coming out of your factory each year then you’ll need to have tens of
millions of unique numbers available. So you would need to use an
identifier that would support this.
Standards such as the Electronic Product Code (EPC)
will let you do this and may allow different organizations in different
countries to read active RFID tags that have been written to by others.
They are usually bigger because they contain a battery.
Lower frequency tags may have a large
area to support the larger RFID tag antenna needed for low frequency
(LF) operation, but can be made extremely thin. Some LF passive tags are
like a stick-on label. But active tags are usually thicker because of
In general, all other things being equal, the bigger the tag, the bigger the battery and the longer the battery will last.
They have sophisticated electronics that enables them to carry out sophisticated functions.
Depending on the degree of sophistication, tags may be able to...
RFID tag cost depends on...
In general, passive RFID tags cost cents, while active RFID tags cost dollars.
But don’t consider RFID tag cost in isolation, as it’s the total cost of the complete system and process, over its life, you need to consider.
If you do this, you may discover that
the difference in cost between active and passive systems isn’t as great
as the difference in cost between active and passive tags might
suggest. It depends on your application.
Tag inexpensive items with low cost passive tags. Otherwise the tag might become a significant proportion of the total cost of the item.
Tag expensive items, such as vehicles, with higher cost active RFID tags
As a tag user, you may need to recover the cost of your tags.
In a high volume operation, where profit margins are small and
competition fierce, you may not be able to pass all, or any of the RFID
tag cost onto your customers.
In this case you would need to cover the cost of an RFID operation through efficiency gains by reducing handling and other labor-intensive tasks.
Check the tag’s datasheet to
ensure that the tags and other components of your RFID system will
operate during the worst conditions you're ever likely to use them in.
The maximum storage temperature of
active RFID tags is typically higher than the operating temperature.
Some tags can survive at temperatures as high as 200 degrees C, but
their maximum operating temperature may typically be 70 degrees C.
An RFID system using active RFID tags can bring huge benefits to many applications... and these applications are only limited by your imagination.