When deciding which RFID tag to use, many considerations need to be taken into account. There are three main options for tags: passive, active, and a combination of both. Each one has its own advantages and disadvantages that need to be considered. The three types have different costs, different hardware components, and different abilities. All three options work similarly in that they can store up to 2 kilobytes of data and are composed of a microchip, antenna and, in the case of active and semi-passive tags, a battery. The tag's components are enclosed within plastic, silicon or sometimes glass.
- A passive 96-bit EPC inlay (chip and antenna mounted on a substrate) costs from 7 to 15 U.S. cents, which is pretty inexpensive.
- The passive RFIDs are not dependent on a battery to work.
- Able to be disposed of if necessary.
- These tags are usually much smaller and can fit on a wide variety of surfaces.
- Depend on the reader for the supply of power to enable signal transmission, because it doesn’t have a battery.
- Since passive RFID tags are constrained by the need for strong signals to power the tag and the small amount of power to respond to the reader, the communication range of a passive tag is limited to 3 meters or less
- In a passive RFID, the data storage is less than 128 bytes with no search capabilities or data manipulation features.
- It can collect about 100 tags, since the communication range is limited to 3 meters or less.
- Can transmit wireless signals on its own to the reader autonomously and can continuously monitor and record sensor input.
- Active tags do not have the constraint of power and can thus transmit to as far as 100 meters or more.
- Active RFID tags have large read and write data storage almost 128 kilobytes and sophisticated data search and access capabilities.
- An active tag can collect more than 100 tags from a seven acre region using a single reader.
- Can provide a better layer of security than passive RFID.
- Depend on a battery to be able to work and power internal circuits. The tag cannot function without battery power, which limits the lifetime of the tag.
- Active tags are more expensive, ranging from $25 and up. Active tags with special protective housing, extra-long battery life or sensors can run $100 or more.
- The tag is physically larger, which may limit applications.
- Battery outages in an active tag can result in expensive misreads.
- Broadcast high frequencies from 850 to 950 MHz that can be read 100 meters or more away.
- Once the battery dies, it can still act as a passive RFID tag.
- Can collect more than 100 tags from a seven acre region using a single reader.
- They have large read and write data storage almost 128 kilobytes and sophisticated data search and access capabilities.
- Can provide a better layer of security than passive RFID.
- Uses a battery to power their circuits.
- A semi-passive tag relies on the reader to supply its power for broadcasting.
- Usually more expensive, because they contain more hardware.
How RFID Works
RFIDs can be used as a replacement for UPC bar codes that are normally found on items you buy from stores (Kevin Bonsor, 2007). UPS bar codes have some disadvantages, including the need to scan each bar code and the fact that bar codes are read-only. This is why RFIDs are an improvement over bar codes, because the tags have read and write capabilities. Also, data stored on RFID tags can be changed, updated, and locked. RFID tags basically work the same way. Data stored within an RFID tag's microchip waits to be read. Then the tag's antenna receives electromagnetic energy from an RFID reader's antenna. Using power from its internal battery or power harvested from the reader's electromagnetic field, the tag sends radio waves back to the reader. Finally, the reader picks up the tag's radio waves and interprets the frequencies as meaningful data. There are three main types of RFID tags: passive, active, and semi-passive. Both active and semi-passive RFID tags use internal batteries to power their circuits. An active tag also uses its battery to broadcast radio waves to a reader, whereas a semi-passive tag relies on the reader to supply its power for broadcasting. As a result of the extra hardware used to make these tags, they are more expensive.
Passive RFID Basics
Radio Frequency Identification (RFID) systems use radio frequency to identify, locate and track people, assets, and animals (Sorrels, 2004). Passive RFID systems are composed of three components – an interrogator (reader), a passive tag, and a host computer. The tag is composed of an antenna coil and a silicon chip that includes basic modulation circuitry and non-volatile memory. The tag is energized by a time-varying electromagnetic radio frequency (RF) wave that is transmitted by the reader. This RF signal is called a carrier signal. When the RF field passes through an antenna coil, there is an AC voltage generated across the coil. This voltage is rectified to supply power to the tag. The information stored in the tag is transmitted back to the reader. This is often called backscattering. By detecting the backscattering signal, the information stored in the tag can be fully identified.
LANDMARC: Indoor Location Sensing Using Active RFID
An RFID system has several basic components including a number of RFID readers, RFID tags, and the communication between them (Patil). The RFID reader can read data emitted from RFID tags. RFID readers and tags use a deﬁned radio frequency and protocol to transmit and receive data. RFID tags are categorized as either passive or active. Passive RFID tags operate without a battery (Lionel M. Ni). They reﬂect the RF signal transmitted to them from a reader and add information by modifying the reﬂected signal. Passive tags are mainly used to replace the traditional barcode technology and are much lighter and less expensive than active tags, offering a virtually unlimited operational lifetime. However, their read ranges are very limited. Active tags contain both a radio transceiver and a button cell battery to power the transceiver. Since there is an onboard radio on the tag, active tags have more range than passive tags. Active tags are ideally suited for the identiﬁcation of high-unit-value products moving through a tough assembly process.
Discussion and Pertinent Opinion
For this project, the option that makes the most sense is the semi-passive RFID tag. This is because it is a mix of both types of RFIDs. It has a battery, so it can act like an active RFID tag and it can continue to work as a passive RFID tag after the battery dies. The battery allows it to continuously monitor and record sensor input and boost backscattered signals when in range of a reader. It can also broadcast high frequencies that can be read 100 meters or more away. It is able to collect more than 100 tags from a seven acre region using a single reader. They have large read and write data storage almost 128 kilobytes and sophisticated data search and access capabilities. They can provide a better layer of security than passive RFID. Overall, it is the better of the three different types of technologies.