Derrick Ongchin MS&E 542 Term Paper RFID Tags Radio Frequency Identification (RFID) is becoming more widely used to facilitate common day-to-day activities due to new developments in processing, wider reading ranges, and larger memory capacities, making it a key contributor to the growth of the radio technology industry. RFID is almost indispensable when it comes to tasks that include automated data capture and identification applications, where a contactless identification is possible through RF signals. Many large corporations are interested in research and development within the field of RFID due to potential growth in areas, such as car identification, which will allow emergency vehicles, for instance, to safely trip traffic signals, production automation, and many other applications. As new materials such as conductive inks are used, printing methods will drive the cost of tags down while enhancing their flexibility and allowing for a wide array of applications. In order for tags to be marketable, better read ranges, processing methods, printable materials, and lower cost materials and processes must be achieved. RFID History and Basics RFIDs were invented in 1969 and like many new technologies, the inventors built upon prior knowledge and combined well-known scientific concepts to create something that was versatile and practical1. RFID tags, also called smart labels, are simply microchips. They can either be an active tag, requiring a battery, or a passive tag, requiring no battery. Each tag has a scanning antenna, a transceiver with a decoder to interpret data, and atransponder that is programmed with information. The antenna places an RF signal within a short range. This RF field is responsible for providing a means of communication with the transponder and providing the device with energy if it is passive. The transceiver activates and reads signals from the transponder. It contains a microprocessor responsible for decoding, and performing simple calculations, then sending the information to a computer system for processing. The transponder is commonly referred to as the tag and is the white plastic rectangular object attached to items in stores to prevent shoplifting. It can be programmed with information, such as serial numbers, price, inventory date, which is broadcasted. Transponders are the main reason that RFIDs are versatile because no line-of-sight or direct contact is required with the reader. Another key element lending to the success of RFID is that passive tags contain no battery, leading to tag sizes as small as .3 mm2, presented by Hitachi3. Figure 1. Hitachi’s “mu-chip” is half the size of the smallest chip on the market. When RFID was first commercially used 30 years ago, it was developed as an electronic article surveillance (EAS) equipment to counter theft. These tags could be made inexpensively by a company called Knogo and functioned based on a 1-bit system, meaning a ‘1’ was detected if a tag was present and a ‘0’ if absent2. These systems required the use of microwave or inductive technology. Nowadays, it is not uncommon to see 64-bit, 90-bit, or even 128-bit RFID tags being powered by a radio signal, allowing for much more information to be passed along (about 18 thousand trillion values for 64-bit). These broadcasts of information can be read by an RFID from a few inches up to a few feet away, depending on the antenna size and power driving the tag. It is possible to have better read ranges by using active tags or a more sensitive RFID receiver, but increased size and cost are an issue. Current passive tags average around 50 cents but prices are decreasing2. As prices keep going down due to developments in processing and materials, manufacturers may foresee achieving the “holy grail” of 5 cents a tag, meaning it will be cost efficient to place an RFID tag on anything above a dollar. Types of RFID Tags The two types of RFID tags with read and write capabilities are the inductively coupled and capacitively coupled RFID tags. Inductively coupled RFID tags have been used for years and are the most common ones available. The three parts of the inductively coupled RFID tag are the microprocessor, metal coil, and encapsulating material. The microprocessors are made of silicon and vary in size depending on their purpose. The metal coil is made of either copper or aluminum wire that is wound in a spiral pattern on the transponder and acts as the antenna. The tag transmits signals to the reader with read distances that depend on the coil size. The coils can operate at frequencies of 13.56 MHz which is the industry standard. The encapsulating material is either a glass or polymer material that wraps around the chip and coil4. Figure 2. Inductively coupled RFID tag.These tags are powered by the magnetic field generated by the reader. The high cost of these tags can be as much as $1 for passive tags and $200 for active tags. This high cost is mainly due to the silicon, coil, and the process needed to wind the coil around the surface of the tag5. The second type of tag, the capacitively coupled RFID tag, was created in response to the high price of inductive RFID tags. These tags do away with the metal coil and use less silicon to perform the same function as previous tags. The three parts of the capacitive tag are the microprocessor, conductive ink, and paper. The microprocessor is made of silicon or polymer and can be as small as a few square millimeters. The special ink is a conductive carbon ink that acts as the antenna and can be printed onto a paper substrate by conventional printing methods. The paper substrate allows for low cost and disposability of the tag, as well as easy integration on conventional product labels. The price of the capacitive tag will be much lower than inductive tags due to the replacement of the metal coil by conductive carbon ink, the use of paper substrates, and roll-to-roll printing methods. Figure 3. Capacitively coupled RFID tag in a roll. In addition to low cost, the tags are more flexible than inductive tags. The tags can bent and crumpled and can still relay information to the reader. Another difference is that instead of being powered by a magnetic field, the tags are powered by an electric fieldfrom the reader. The disadvantage of these tags is their very limited range. Most capacitive tags have ranges of less than 1 cm. If the tag covered a larger