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Home   >   R&D   >   RFID

Surface Acoustic Wave Radio Frequency Identification

(SAW RFID)

Surface Acoustic Wave (SAW) technology has been in commercial use as acoustic filters and resonators for more than 60 years primarily in the mobile cell phones, base stations and televisions. Lately, the products are widely used in wireless products such as wireless LAN, WiFi, BlueTooth, etc. However, it has not been fully exploited as an auto identification technology.

Basic Working Principle of SAW RFID

The SAW RFID solution comprises of the following components:-

  • SAW RFID device
  • SAW Reader Unit + Antennae (Interrogator)
    		•

    SAW RFID Working Principle

    The SAW RFID device is constructed using crystal and operates on piezoelectric effect, surface acoustics wave and pre-arranged reflectors principles. It has an IDT or Inter-Digital Transducer and a Transponder Antennae for receiving and sending the signal from and to the SAW Reader. To read the SAW RFID, the SAW Reader first sends an interrogation signal via its antennae to read the SAW RFID device. When the SAW RFID device receives the signal from the reader, the Inter-digital Transducer (IDT) converts it into surface waves and spread across the surface of the crystal. The waves are reflected by pre-arranged reflectors and are converted back to microwave signal and transmitted to the reader. The reader picks it up very much in similar fashion as the normal RFID reader.

    Advantages of SAW RFID

    SAW RFID device works in the microwave range typically 2.45GHz and communicates through radiation rather than induction, which mean they have better penetration level. SAW RFID device does not have any silicon circuits and therefore requires very little power to operate. The advantages of SAW RFID are as follows:

  • Reliable reading over a larger range (distance between the reader and tag) in passive mode without the assistance of battery (up to 15 meter is possible, with some up to 30m).
  • Low reader power required.
  • Smaller reader required.
  • Able to operate in liquids and metals without problem of signals being absorbed, diffused or reflected.
  • Accurate full pallet reading is possible with high data rate. Reading 1,000 items in a pallet is possible.
  • Able to operate over a very wide range of temperature as well as at very high temperature range from – 40OC to + 400OC. Some up to 1000 OC is possible.
  • Ability to report temperature due to its inherent physical characteristics without adding any circuitry to the tags.
    		•

    The Inherent Limitations of Silicon Chip Based RFID

    RFID is the latest major auto identification technology after barcode and magnetic strips. The one key feature of RFID technology is the ability to read the tag without the line of sight. There are several types of RFID technology, the most popular today being the silicon based RFID tags. Silicon chip based RFID tags can either be passive or active (battery powered), and read only or read-writeable. Smart chip based RFID has gained major market share replacing magnetic strip technology in some niche applications such as banking, security access control, toll and parking gates, passports, Identification Cards, etc,. However, mass usage of RFID in manufacturing and retail where bar code is dominant is still limited due to relative high cost and the inherent limitations. Research efforts are now focused on alternative auto identification technology that promised to fill the following gaps.

  • Low reading range (distance) for passive tags
  • Limited life span of batteries in active tags
  • Unable to operate properly in or around metal as well as liquids
  • Damaged when exposed to Gamma radiation
  • Damaged when exposed to high temperature for a long period of time
  • Failed to perform accurately for pallet reads with standard setup and tags
  • Sensitive to the orientation of tags and readers. Tag has to be perpendicular to the magnetic field produced by the reader.
  • High powered readers or larger readers are required to increase the reading range / distance
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