Q: What is the difference between passive, active and semi-passive tags?
A: A passive tag does not have its own power source (there is no onboard battery) or a radio transmitter. It obtains power from the RF waves emitted by the reader. Therefore, it can communicate only when inside the read zone and while energized by the RF waves. Power from the radio waves operates the tag’s integrated circuit, sending data back to the reader. These tags usually have read range of anywhere from few inches to 20 feet and inlays cost approximately $0.10 when purchased in large quantities. They are primarily used in the applications requiring low cost, simple and light-weight tags. Semi-passive (or also sometimes called Semi-Active) tag has a battery but no radio transmitter. The battery powers its integrated circuit (IC), which helps it to modulate the reflected signal. The advantage of this type of tag is that it does not entirely rely on power from the reader. Therefore, you can use low-power readers and store more data on the tag. This type of tags is used to get longer read range or to couple the tag with environmental sensors such as temperature, pressure, relative humidity, etc. This tag can be read at a longer range of up to 100 feet. Active tags have their own battery and radio transmitter. This tag communicates at a longer distance because it is not dependent on a reflected signal. Its communication distance ranges from 100 to 750 feet and it can have more memory to store data. However, the cost is higher, and tags have larger size and higher weight than passive tags.
Q: What are the advantages of RFID over barcode?
A: Barcodes require a line of sight scanning, usually within a short distance and cannot be read in bulk (many barcodes at the same time). This is all eliminated by RFID technology, where you can simply pass a large amount of tagged items through a relatively wide read zone and even tags that do not face the reader antennas will be read (unless of course shielded by materials that even RF waves cannot penetrate like metal or sometimes liquids). Therefore, using RFID is faster and more efficient, albeit slightly more expensive, due to the cost of tags and readers being higher than barcode labels and scanners.
Q: What is the difference between RFID and NFC?
A: Near Field Communication or NFC is basically part of RFID technology. NFC uses High Frequency (HF) for communication in very short read ranges. NFC has been implemented in several mobile devices (smart phones and tablets) and payment systems. It features enhanced security and encryption.
Q: What is RHCP and LHCP?
A: This is an acronym for Right Hand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP) The direction of polarization is important for circularly polarized antennas if they are facing each other and are run by different readers. In order to prevent interference within an interrogation zone, facing antennas should have the opposite polarization. One of them should be LHCP and the other RHCP. However, if all antennas are run by one reader, it does not really matter as they will be used round-robin and will never be active at the same time.
Q: When should I use a linearly polarized antenna versus circularly?
A: Linearly polarized antennas are best used in circumstances, when you know your tag orientation and when you need longer and/or more focused beam. Handheld readers have often linear antennas as they can be turned manually into various orientations. Circularly polarized antennas are best when your tags will be passing the zone in various orientations.
All prices are in USD.