Generally speaking, there are three fundamental parts that make up in a passive RFID system – an RFID reader(interrogator), an RFID antenna, and RFID tags(What is RFID tagging). Unlike active RFID tags, passive RFID tags only contain two main components – the antenna and the micro-chip or IC (integrated circuit), no bettary is included.
As the name infers, passive RFID tags wait for a signal from an RFID reader. The reader will send energy to an antenna, which converts energy into an RF wave that is sent into the read zone. Once the tag is within range of the read zone, the RFID tag’s internal antenna can draw in energy from the RF waves. The energy transfers from the tag’s antenna to the IC and powers the chip which generates a signal back to the RF system. This is called backscatter. The backscatter, or change in the electromagnetic or RF wave, is detected by the reader (via the antenna), which interprets the information.
Passive RFID Frequency
125 ~ 134 KHz – Low Frequency (LF) – An extremely long wavelength with usually a short read range of about 1 – 10 centimeters. This frequency is typically used with animal tracking because it is not affected much by water or metal.
13.56 MHz ~ High Frequency (HF) & Near-Field Communication (NFC) – A medium wavelength with a typical read range of about 1 centimeter up to 1 meter. This frequency is used with data transmissions, access control applications, DVD kiosks, and passport security – applications that do not require a long read range.
865 ~ 960 MHz – Ultra High Frequency (UHF) – A short, high-energy wavelength of about a one meter which translates to long read range. Passive UHF tags can be read from an average distance of about 5 – 6 meters, but larger UHF tags can achieve up to 30+ meters of read range in ideal conditions. This frequency is typically used with race timing, IT asset tracking, file tracking, and laundry management as all these applications typically need more than a meter of read range.
As a general rule, higher frequencies will have shorter, higher-energy wavelengths and, in turn, longer read ranges. Moreover, the higher the frequency, generally speaking, the more issues an RFID system will have around non-RFID-friendly materials like water and metal.
Pros of Passive RFID
Thinner and more adaptable tags
Higher range of tag options
Tags can last a lifetime without a battery (depending on the wear and tear)
RFID Keycard Lock Systems
Key card lock systems operate by physically moving detainers in the locking mechanism with the insertion of the card, by shining LEDs through a pattern of holes in the card and detecting the result, by swiping or inserting a mag stripe card, or in the case of RFID cards, merely being brought into close proximity to a sensor. Keycards may also serve as ID cards.
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