Xerox Corporation (Norwalk, CT) reveals a two step printing process using nanoparticle inks to produce individually unique hybrid printed antennae for chipless RFID applications in U.S. Patent 7,653,982. The RFID tags may be read through paint, water, dirt, dust, human bodies, concrete, or through the tagged item itself. RFID tags may be used in managing inventory, automatic identification of cars on toll roads, security systems, electronic access cards, keyless entry and other security applications.
Xerox's method of printing chipless RFID tags with unique features, includes printing a RFID antenna pattern precursor using a first printing process, in which the RFID antenna pattern precursor includes a plurality of disconnected wire segments; then printing with a conductive ink in second print process to interconnect disconnected wire segments, to produce a final RFID antenna with a unique antenna geometry, according to inventors Naveen Chopra, Peter M. Kazmaier and Paul F. Smith. The first printing process is can use gravure, rotogravure, flexography, or screenprinting and the second printing process is an inkjet printing process using nanoparticle conductive inks.
There are numerous advantages to process. Speedy and efficient mass production of RFID antenna masters is achieved via analog printing, as large numbers of identical master patterns can be created by using a fast printing process. Additionally, customization of each individual mass-produced RFID tag is achieved by digital printing. Furthermore, using the relatively slower digital process (for example, inkjet printing) to add just a few unique features will minimize the time lag for printing.
Also, the use of inkjet printing allows for very fine variable features to be printed, thus widening the scope of unique features and materials that may be printed. For example, graphite inks and copper may be used. Conversely, printing of only small areas of the antenna with conductive ink (such as gold, for enhanced conductivity at the interconnections) saves considerable amount of money as when compared against printing an entire antenna. Thus, the ability to print a variable data RFID tag in large volumes at low cost is now possible for the first time.
Recently, radio frequency identification (RFID) technology has gained tremendous popularity as a device for storing and transmitting information. RFID technology utilizes a tag transponder, which is placed on an object, and a reader, also referred to herein as an interrogator, to read and identify the tag. RFID technologies are broadly categorized as using either "active" tags or "passive" tags. Active tags have a local power source (such as a battery) so that the active tag sends a signal to be read by the interrogator. Active tags have a longer signal range. "Passive" tags, in contrast, have no internal power source. Instead, passive tags derive power from the reader, and the passive tag re-transmits or transponds information upon receiving the signal from the reader. Passive tags have a much shorter signal range (typically less than 20 feet).
Both categories of tags have an electronic circuit that is typically in the form of an integrated circuit or silicon chip. The circuit stores and communicates identification data to the reader. In addition to the chip, the tag includes some form of antenna that is electrically connected to the chip. Active tags incorporate an antenna that communicates with the reader from the tag's own power source. For passive tags, the antenna acts as a transducer to convert radio frequency (RF) energy originating from the reader to electrical power. The chip then becomes energized and performs the communication function with the reader.
On the other hand, a chipless RFID tag has neither an integrated circuit nor discrete electronic components, such as the transistor or coil. This feature allows chipless RFID tags to be printed directly onto a substrate at lower costs than traditional RFID tags.
As a practical matter, RFID technology uses radio frequencies that have much better penetration characteristics to material than do optical signals, and will work under more hostile environmental conditions than bar code labels.
Both categories of tags have an electronic circuit that is typically in the form of an integrated circuit or silicon chip. The circuit stores and communicates identification data to the reader. In addition to the chip, the tag includes some form of antenna that is electrically connected to the chip. Active tags incorporate an antenna that communicates with the reader from the tag's own power source. For passive tags, the antenna acts as a transducer to convert radio frequency (RF) energy originating from the reader to electrical power. The chip then becomes energized and performs the communication function with the reader.
On the other hand, a chipless RFID tag has neither an integrated circuit nor discrete electronic components, such as the transistor or coil. This feature allows chipless RFID tags to be printed directly onto a substrate at lower costs than traditional RFID tags.
As a practical matter, RFID technology uses radio frequencies that have much better penetration characteristics to material than do optical signals, and will work under more hostile environmental conditions than bar code labels.
Although particulate metal materials may be used, the superior characteristics of nanoparticle metal materials in ink applications yields a better product. Metallic nanoparticles are particles having a diameter in the submicron size range. Nanoparticle metals have unique properties, which differ from those of bulk and atomic species. Metallic nanoparticles are characterized by enhanced reactivity of the surface atoms, high electric conductivity, and unique optical properties. For example, nanoparticles have a lower melting point than bulk metal, and a lower sintering temperature than that of bulk metal. The unique properties of metal nanoparticles result from their distinct electronic structure and from their extremely large surface area and high percentage of surface atoms.
Metallic nanoparticles are either crystalline or amorphous materials. They can be composed of pure metal, such as silver, gold, copper, etc., or a mixture of metals, such as alloys, or core of one or more metals such as copper covered by a shell of one or more other metals such as gold or silver. The nozzles in an inkjet printing head are approximately 1 micron in diameter. In order to jet a stream of particles through a nozzle, the particles' size should be less than approximately one-tenth of the nozzle diameter. This means that in order to inkjet a particle, its diameter must be less than about 100 nm.
Metallic nanoparticles are either crystalline or amorphous materials. They can be composed of pure metal, such as silver, gold, copper, etc., or a mixture of metals, such as alloys, or core of one or more metals such as copper covered by a shell of one or more other metals such as gold or silver. The nozzles in an inkjet printing head are approximately 1 micron in diameter. In order to jet a stream of particles through a nozzle, the particles' size should be less than approximately one-tenth of the nozzle diameter. This means that in order to inkjet a particle, its diameter must be less than about 100 nm.
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