Passive
Passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming radio frequency signal provides just enough power for the CMOS integrated circuit (IC) in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier signal from the reader. This means that the aerial (antenna) has to be designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. The response of a passive RFID tag is not just an ID number (GUID): tag chip can contain nonvolatile EEPROM (Electrically Erasable Programmable Read-Only Memory) for storing data. Lack of an onboard power supply means that the device can be quite small: commercially available products exist that can be embedded under the skin. As of 2005, the smallest such devices commercially available measured 0.4 mm × 0.4 mm, and are thinner than a sheet of paper; such devices are practically invisible. Passive tags have practical read distances ranging from about 2 mm (ISO 14443) up to about few metres (ISO 18000-6) depending on the chosen radio frequency. Due to their simplicity in design they are also suitable for manufacture with a printing process for the antennae. A development target are polycarbon semiconductor tags to become entirely printed. Passive RFID tags do not require batteries, and can be much smaller and have an unlimited life span
Semi-Passive
Semi-passive RFID tags are very similar to passive tags except for the addition of a small battery. This battery allows the tag IC to be constantly powered. This removes the need for the aerial to be designed to collect power from the incoming signal. Aerials can therefore be optimised for the backscattering signal. Semi-passive RFID tags are faster in response and therefore stronger in reading ratio compared to passive tags.
Active
Active RFID tags or beacons, on the other hand, have their own internal power source which is used to power any ICs and generate the outgoing signal. They may have longer range and larger memories than passive tags, as well as the ability to store additional information sent by the transceiver. To economize power consumption, many beacon concepts operate at fixed intervals. At present, the smallest active tags are about the size of a coin. Many active tags have practical ranges of tens of metres, and a battery life of up to 10 years.
Three main Types of RFID Tags
Passive tags
Passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming radio frequency signal provides just enough power for the complementary metal-oxide-semiconductor (CMOS) integrated circuit in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier wave from the reader. This means that the antenna has to be designed both to collect power from the incoming signal and also to transmit the outbound backscatter signal.
Semi-passive tags
Semi-passive tags, also called semi-active tags, are similar to active tags in that they have their own power source, but the battery only powers the microchip and does not power the broadcasting of a signal.
Active tags
Unlike passive RFID tags, active RFID tags have their own internal power source, which is used to power the integrated circuits and to broadcast the response signal to the reader. Communications from active tags to readers is typically much more reliable (i.e. fewer errors) than from passive tags due to the ability for active tags to conduct a "session" with a reader.
Using the right tag in your application
Because passive tags are cheaper to manufacture and have no battery, the majority of RFID tags in existence are of the passive variety. As of 2005, these tags cost an average of Euro 0.20 ($0.24 USD) at high volumes. Today, as universal RFID tagging of individual products become commercially viable at very large volumes, the lowest cost tags available on the market are as low as 7.2 cents each in volumes of 10 million units or more. Current demand for RFID integrated circuit chips is expected to grow rapidly based on these prices.
Reading ratio close to 100% is a mandatory requirement for successful application. While the cost advantages of passive tags over active tags are significant, other factors including accuracy, performance in certain environments such as around water or metal, and reliability make the use of active tags very common today. The final quality metrics is a probed reading ratio for a representative statistical basic population (fairly 100 plus tags in minimum), this unfortunately never reaches the 100% ratio. Sound system designs with RFID therefore take the deficiencies into account and compare in real-time already known data with just captured data on the basis of fuzzy reasoning.
There are four main frequency bands for RFID tags commonly in use. They are categorized by their radio frequency: low frequency tags (125 or 134.2 kHz), high frequency tags (13.56 MHz), UHF tags (868 to 956 MHz) or 463 MHz, and microwave tags (2.45 GHz or 5.8 GHz). UHF tags can be used globally when specially tailored according to regional regulations; as there are no globally unified regulations for radio frequencies in this ISM band range.
There is a wide variation of transponder devices and contactless chip cards which deliver similar functions
