By Rfid (Radio-Frequency Identification) we mean those technologies which allow the identification of objects, animals and people from a distance using radio waves. A radio-frequency identification system consists of two main components: a transponder or tag and a reader. The tag, a label applied to the object, contains all the data related to the object that identify it univocally.
The data, stored in a microchip, can be read thanks to an antenna which receives and transmits radio signals from and to the Rfid reader. The microchip and the antenna constitute the Rfid tag and are fixed together on a physical support. The reader, stationary or hand held, is the device which is in charge of reading the Rfid tag and able to convert tag radio waves into a digital signal that can be transferred to a pc. To enable communication between the tag and the reader, they must be tuned in the same frequency.
Rfid systems use several frequencies that can be classified as follows:
- low frequencies (LF, between 125 and 134 kHz)
- high frequencies (HF, around 15 MHz)
- ultra high frequencies (UHF, between 860 and 960 MHz)
- microwaves (above 2.45 GHz)
The different frequency ranges have different characteristics and are therefore meant for different applications. In general, if the frequency increases, so does the reading distance and the quantity of data that can be transferred during the time unit reduces the capacity to resist operation conditions and costs. Low frequency tags use little power and are able to pass through non-metallic and liquid materials, but the signal for reading does not go beyond 30-40 centimetres. High frequency tags work better with metallic objects and can cover a distance of approximately one meter. Ultra high frequencies offer wider reading ranges and allow the fast transference of data, but do no pass through materials easily. The solutions with tags of 2.45 GHz are applied to telepass systems, dry ports and equivalents.
There are three types of Rfid tags: passive, battery assisted passive or active. Passive tags have no internal power supply and draw the power required to activate the circuits from radio waves sent by the reader that interrogates them and induces a current in the antenna. According to the Iso standards, LF and HF tags can be only passive, while UHF and microwave tags can be battery assisted passive or active as well. A battery assisted tag has a power supply which cannot power radio circuits, but additional devices such as temperature or movement sensors. Finally, active tags are powered by batteries offering a larger range to the radio signal and a longer reading distance. Active tags are more expensive than passive tags and are strongly recommended to trace means of transport of valuable goods at long distances.
Compared to barcodes and other identification technologies, the radio-frequency technology offers numerous advantages: Reading is not optical, does not require direct contact or line-of-sight scanning. Tags can be read simultaneously, work in dirty and polluted environments and withstand very hard (pollutant agents, thermal, chemical and mechanical stress) conditions. They are therefore, more durable. Compared to barcodes, tags contain more data; they can be rewritten and updated with new information. They can also work immersed in a fluid, inside the object to be identified or inside a container. Besides, barcodes identify only the lot number of a product, not the single item. Rfid tags, instead, contain the single and univocal serial number identifying each single product manufactured in the world. Rfid tags are more expensive than barcodes, but the benefit-cost ratio is generally favourable