RFID engineering

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Principle of RFID tag and reader/writer

In the RFID industry, there are many types of RF tags from different manufacturers in different specification and different size and different material. We can roughly devide these many tags into three types of RF tags by the working principle. They are different in how it works, with or without battery and way of data transmission. 

-Passive tag
-Active tag
-Semi-active tag

1.Passive tag

Passive tags do not have their own power source, but are able to obtain power from the reader/writer’s transmitted energy. Passive tag is the most prevalent type of RFID tag which functions with no battery installed inside, because the antenna in the tag uses the radio wave as the power source. Technically, the radio wave is not the battery itself at all, but the interaction with the radio wave and antenna generates subtle but sufficient power to enable the tag works. Because of the absence of the battery, passive tag has the advantages in cost and size and also works semi-permanently.

1. Reader/writer send signals
2. The tag receive the signal from the reader and get charged for transmission
3. The charged tag responds back to the reader using the power generated by signal interaction



2.Active tag

Active tag is a type of tag with a small battery installed. Though the battery offers the tag longer read range compared with a passive tag, it is relatively expensive and is short-life because the service life depends on the life of the battery. Since it positively gives information without the charge from the reader, active tags can be integrated with other higher level sensors to make a network system.  In the logistics industry, passive tags are widely used for tracking and managing the sea freight containers.

1. Battery-powered tag automatically and continuously sends signals to reader.
2. The battery is used for date transceiver and also for driving the system inside RFID.
3. Thus the reader can be a fixed type which gets the signals at any time 

3.Semi-active tag

This tag is kind of between active and passive tag. Only when receiving signals from the outside the semi-active tag works temporally. The most familiar application is the record measuring system of a competition. The semi-active tag works when the runner or competitor pass through the gate embedded with tag, which records the time of starting and goal. The another application is for the counting of visitors in public facilities like library and museum.

1. Reader/writer send signals
2. The tag receive the signal from the reader and get charged for transmission
3. A battery is installed in the tag but exclusively for driving the system
3. The charged tag responds back to the reader using the power generated by signal interaction

Passive tag consists of an inlet and a base material which is usually made of plastic or paper. The inlet is the combination of an IC chip for data management and controlling of RF tag and antenna for data transmission. 
There are wide 

There are a wide variety of tags depending on shape and size of IC and antenna, and type of base material. 
NiGK Corporation has on-metal passive tag and on-metal heat-resistant tags in different sizes.

→TAGATTM passive tag (On-metal)
→TAGATTM passive tag (Heat-resistant)

4.Reader/writer

RFID reader and writer devices are used in wireless data communications.  The RFID readers and writers are able to communicate with active and passive RF tags. The reader can simultaneously scan for multiple tags whereas the barcode reader can only communicate with one other device at a time. They are also used to write the information to tags and devices.  There are lots of devices available on the market, in different size, spec, and design. The reader doesn't have to be conditioned specially for the tag as long as the reader emits the frequency spectrum used in the region. Note that if you use the wrong reader giving "irregular" signals at a different radio frequency band than permitted in your region, you not only have the trouble using the tags but also be punished because of the infringement of the law!

 

Principle of passive tag

Passive tags, as explained above, have no battery inside.  The radio wave and electromagnetic wave from a reader/writer give signals and the passive tag gets charged by the electromagnetic induction method for the transmission of the data and driving of the central system.  Let's go back to the school days and review basic physics to understand RFID technology more.

1.Electromagnetic method

A passive RFID tag and a reader/writer have coils inside and the tag gets charged with the electromagnetic method by magnetic flux, which are induced by the interaction between coil loop inside the tags and the reader/writer. The RFID tags of 13.56MHz uses this method.

・When electric current flows in antenna coil in a reader, electro magnetif wave is generated vertically through the coil loop.
・When the antenna coil inside the RFID tag receives this wave, the electromotive field is generated inside the RFID coil to make the current flow.

・The RF tags get charged with the current to drive the IC and transmit data.

2.Radiowave method

Radio wave is used for the data tranmission between a RFID tag and a reader.

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・The antenna inside a tag receives the radio wave from a reader.

・Rectifier circuit inside the antenna converts the radio wave into AC to generate electricity.

・The IC and memory work using this electricity generated.

・The antenna in the RF tag retunrs the wave back to the reader.



RFID and external environment

1.Effects from metal and water

As RFID uses the radio wave, even if there is a obstacle between RF tag and a reader, there is in general no problem when transmitting data. Thanks to this electromagnetic wave transmission trait, the reader can scan the data from the tags inside a box or the tags embedded inside of the objectives.
However, because the radio wave are reflected by metal saface, the tool box should be made of plastic or partly plastic for tool tracking. 


On the other hand, if RF tags are fixed on the metal materials, the radio wave from the reader reflects on the surface of the metal and the reflected wave causes the errors in transmission. In order to be used on metal, the RF tags must be "On-metal" 
We have on-metal proof, super small RF tags for the metal tool tracking and inventry management of metal objects like servers and computers. (Metal mount RF tag TAGATTM

Additionally, if water or moisture exists on the surface of the RF tag, the water absorbs the radio wave and can interfere the transmission of data. Therefore 135kHz and 13.56MHZ RF tag which  are relatavely resistant to water is widely used near water like kitchen ware, ski area, and public transfer card.


2.Influence by heat and microwave

RFID is an integration of electronics parts and materials, conventional RFID is susceptible to more or less to heat and microwave. So for the production line under heat like modling, steam sterilization, reflowing and microwave valcanization, Heat resistant RF tag is necessary.

Heat resistant TAGATTM C Series 
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