Glossary Of Rfid Terms -- D

Data carrier

A medium that holds machine-readable data. Bar codes and RFID tags are types of data carriers.The term is also applied to a carrier frequency used to transmit data.

Data field

An area of memory in RFID microchips that is assigned to a particular type of information. Data fields may be protected (see below) or they may be written over, so a data field might contain information about where an item should be sent. When the destination changes, the new information is written to the data field.

Data field protection

The ability to prevent data stored in a specific area of memory of an RFID microchip from being overwritten. Companies might want to protect the data field that stores an Electronic Product Code, which doesn't change during the life of the product it's associated with.

Data retention

The ability of a microchip to maintain the information stored in EEPROM. RFID tags and other microchips can typically retain data for 10 years or more, but data retention depends on temperature, humidity and other factors.

Data synchronization

The harmonisation of information between trading partners ensures that the master data is the same in all trading partners systems.

Data transfer rate

The number of characters that can be transferred from an RFID tag to a reader within a given time. Baud rates are also used to quantify how fast readers can read the information on the RFID tag. This differs from read rate, which refers to how many tags can be read within a given period of time.

dB

See decibel.

dBi

The gain of an antenna compared to an isotropic antenna—that is, an antenna that radiates energy equally in every direction. A typical dipole antenna has a dBi of 2.2 when compared to an isotropic antenna.

dBm

See decibel

dBw

Decibels (dB) referenced to 1.0 watt. Using the decibel formula: dB=10 log(P1/P2), P2 equals 1.0 watt and P1 is in units of watts.

De-tune

UHF antennas are tuned to receive RFID waves of a certain length from a reader, just as the tuner on the radio in a car changes the antenna to receive signals of different frequencies. When UHF antenna is close to metal or metallic material, the antenna can be detuned, resulting in poor performance.

Deactivation

Rendering an RFID transponder in operable or, in the case of anti-theft applications, indicating an item with a specific serial number has been sold, so it does not set off an alarm as the tagged item leaves the store.

Dead tag

An RFID tag that cannot be read by an interrogator.

Decibel

A unit used to express the ratio between two values, including antenna gain, cable losses and reader power output. The formula for decibel is: dB=10 log (P1/P2). In layman’s terms, dB represents the difference in the intensity of an emitted signal or power where 0 dB is the reference, 3 dB is twice the intensity of 0 dB, 10 dB is 10 times the intensity, and 20 dB is 100 times the intensity and so on. (See also dBi, dBm and dBw.)

Die

The silicon block onto which circuits have been etched to create a microchip.

Dielectric

Unable to conduct direct electric current. Dielectric substances are used as insulators.

Dielectric constant

The measure of a material’s ability to store a charge when an electric field is applied, or its “capacitance.” If a material has a high dielectric constant, it reflects more RF energy and detunes the antenna more, which makes it harder to tag. Examples of materials with a low dielectric constant are dry paper (2), plastics (most are between 2 and 4), and glass (between 5 and 10). Water’s dielectric constant changes: At room temperature it is 80; near boiling it is 55; and when frozen it is 3.2.

Digital certificate

A digital message that contains the identity of an company or organization, its public key combined and a signature of this data from a certificate authority (Trust Center) proving the correctness of this data.

Digital signal processor

As special kind of microprocessor that converts changes in analog waves into digital information. DSPs are used in RFID readers.

Digital signature

A cryptographic protocol that ensures the authenticity as well as the integrity of digital data. A digital signature typically is realized by encrypting the hash value of the data to be protected with the private key.

Digital signature algorithm

A cryptographic algorithm approved by the United States government for use in creating digital signatures.

Dipole

An antenna made of two straight electrical conductors (poles). In an RFID transponder, these are connected to a microchip. The antenna is typically 1/2 wavelength from end to end.

Discovery services

A component of the EPCglobal Architecture Framework consisting of a suite of services that enable users to find data held by individual companies related to a specific Electronic Product Code. Object Naming Service is one component of Discovery Services.

DSP

See digital signal processor

Dual dipole

An antenna that has two dipoles. In an RFID transponder, these are attached to a chip. The dual dipole design greatly reduces the tag’s orientation sensitivity.

Dual interface smart card

A card that contains a microchip that can be read either when in content with a reader or remotely using radio waves.

Dumb reader

A generic term for a reader with limited computing power. It generally converts radio waves from a tag into a binary number and passes it to a host computer with little or no filtering.

Duplex

A channel capable of transmitting data in both directions at the same time. (Half duplex is a channel capable of transmitting data in both directions, but not simultaneously.)

Duty cycle

The length of time the reader can be emitting energy. Regulations in the European Union say readers can be on only 10 percent of the time.