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Fujitsu Laboratories Ltd. has announced the development of a compact and slim passiveultrahigh-frequency (UHF) RFID tag designed for ID cards, wearable devices, metal parts, and other objects that pose limitations with regard to signal reception.
The new tag overcomes what Fujitsu says has been a long-standing problem: the development of a EPC Gen 2 passive UHF RFID tag compact and slim enough to be affixed to metals or ID cards that can be worn by individuals. Metallic objects and human bodies can hinder signal reception. For that reason, in order to ensure a communications range of 2 meters (6.6 feet), for example, radio wavelength constraints meant that the tag needed to be at least 75 millimeters (3 inches) long, to accommodate an antennas that is one quarter the UHF radio wavelength of approximately 300 millimeters (11.8 inches), or more than 5 millimeters (0.2 inch) in thickness, to accommodate a 5-millimeter spacer.
According to Fujitsu Laboratories, it has now developed a technology that uses a new looped structure in which the RFID tag antenna is wound around thin plastic so that its ends overlap, resulting in what it claims is the world's most compact and slim RFID tag, measuring 30 millimeters (1.2 inches) long and 0.5 millimeter (0.02 inch) thick. The tagcan be attached to a range of objects, and can be used in a variety of applications, such as in the management of machine parts, as well as in ID cards that people wear as a means of access control.
Because UHF radio waves have difficulty traveling through metal and the human body, tagmakers often incorporate spacers within a passive UHF tag in order to increase the distance between a tag's antenna and the object to which that tag is attached. For example, when using a spacer that is 1 millimeter (0.04 inch) thick, for communications to travel a distance of 2 meters (6.6 feet) or more, the RFID tag itself needs to be at least 75 millimeters long (one quarter the radio wavelength of approximately 300 millimeters), according to the company.
Conversely, to enable communications to travel the same distance, it is possible for theRFID tag's length to be reduced to 33 millimeters (1.3 inches)—one eighth the radio wavelength—but then the spacer needs to be at least 5 millimeters thick. In short, according to Fujitsu Laboratories, there has been a tradeoff between RFID tag length and spacer thickness that is dictated by radio wavelength, making it difficult to achieve tags that were both compact and slim.
Fujitsu Laboratories claims its new looped structure overcomes these limitations. When tags of this type are affixed to metal, the company explains, a large current (loop current) will flow in a manner that follows the shape of the loop, and a portion of that current will leak through to the metal surface to which the tag is attached The original radio waves generated by the loop current combine with the new radio waves being generated by the current leaking through to the adjacent metal, resulting in a combined signal that is emitted on the metal's surface. Adjusting the length and thickness of the overlap at the ends of the RFID tag can optimize the degree of leaked current (the ratio of the two radio waves that are combined) to maximize communications distance. In other words, the metal to which the tag is attached and the tag itself act as a coordinated source of current, functioning as an antenna emitting their combined radio waves, and thereby enabling communications to distances of several meters.
When the RFID tag is attached to a plastic ID card or cardboard instead of metal, there are only the radio waves generated by the loop current. This enables communications equivalent to metal, as the radio signal efficiently propagates in a loop shape outward from the RFID tag, due to the absence of a metal object that would hinder the radio signal. What's more, since the human body has a significant water component and is structured to easily carry an electrical charge, it can be treated the same as metal. An ID card with an embedded tag will act the same as when attached to metal, so the negative effects of being carried on the body are reduced.
The technology will make it feasible to attach tags to a wider variety of objects, such as for managing machine parts and in ID cards carried on the body as a means of access control, thus enabling RFID tags to be utilized in a variety of applications. The company hopes to commercialize this new technology by the start of its 2015 fiscal year, which begins on March 31.