RFID tags The TrailerTrailer overview

RFID tag - Frequencies

Teh frequency that tag operates at is one of the most important considerations that TrailerTrailers give when designing a solution to suit your requirements. The different frequencies have enourmous effect on price, performance, range and suitability for RFID projects.

Your business requirements are given carefull consideration by TrailersTrailers before we recomend and implement a RFID solution. The general bands used to broadly classify different RFID tag families are LOW, HIGH, and ULTRA HIGH and are desribed in a little further detail below. Special consideration is given to 915 MHz, an increasingly popular frequency.

RFID - Low frequency

Most commonly used for access control, animal tracking and asset tracking. Advantages are cost. (125khz/134khz)

RFID - High frequency

Used where medium data rate and read ranges up to about 1.5 meters are for acceptable for passive tagging. This frequency also has the advantage of not being susceptible to interference from the presence of water or metals. (13.56 MHz)

RFID - Ultra high frequency

Offers the longest read ranges of up to approximately 3 meters for passive tags and 100 metres for active tags. Relatively high reading speeds can be achieved with these frequencies. (850 MHz to 950 MHz.

RFID 915 Mhz

A particular frequency that is growing popularity due to its potential low costs because it does not need an expensive copper antenna coil. It also has longer read rangers and high read rates. Some of the drawbacks of 915 MHz tags are the degraded performance in the vicinity of water.

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RFID tags - Tag types

Active RFID tags

These tags have a small battery built into the tags, batteries can sometimes be replaceable or the unit will be replaced after certain time, normally between 1 year and 7 years.
The advantages and disadvantages of active tags can be summarised as follows;

• The active RFID tag cannot function without battery power, therefore they have a limited lifetime.
• More information can be read and written to the tag
• The active RFID tag is typically more expensive, costs typically start from $10 to $20 per tag
• The active RFID tag is physically larger and can be more fragile and prone to damage.
• Read and write distances are much greater than for passive tags
• Active tags can be connected to sensors, eg they could measure and log information such as temperature.

Passive RFID tags

Passive RFID tags rely on moving through an area of radio waves in proximity to a RFID reader. The tag draws tiny amounts of power from the magnetic field associated with the radio waves created by the reader, these tiny amounts of energy temporarily energise circuits in the tag. The tag then sends the information encoded in the tag's memory, often using a different frequency to the one used to energising the chip.

The main advantages and disadvantages of passive RFID tags are:

• The tag can be read only at very short distances, typically a few feet at most although some modern tags can operate up to 3m if care is taken with tag orientation.
• The tag is readable for a very long time.
• Passive tags are generally more resistant to corrosion and physical damage.
• The tag functions without a battery; these tags have a useful life of twenty years or more.
• The tag is typically much less expensive, you can typically expect to pay between 10cents and a few dollars.
• The tag is much smaller and it can be easily concealed
• Passive tags have many more potential uses due to reduced size and cost

Semi-active or semi-passive RFID tags

A variety of options exists for this class of tags. These tags use a combination of batteries,(normally used to run the chips circuits) and an induced current to transmit data to the RFID reader.
The main advantages of these tags are that they achieve longer read ranges than passive tags but generally at lower costs than active tags.

They can also have many of the features associated with Active tags such as memory but with costs nearer those of passive tags.

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