## RFID market for tags 2014-2025($ Billion)
### Identifying Core Academic Literature  
RFID was used for aircraft identification during World War II. Walmart, the largest retailer in the United States, required its 100 most important pharmaceutical suppliers to embed RFID in all products by the end of 2006 with the aim of accelerating product identification. This prompted a trend in RFID application in multiple industries. RFID is a contactless, automated identification technology that employs electronic tags, reader devices, and radio waves. The electronic tag, smaller than 2 mm in diameter, is the key component. A radio wave can be emitted to an electronic tag from a distance of millimeters to meters, and a sensor can then read information embedded in the tag, thus identifying the product, device, or personnel. On the basis of their operating frequency, RFID readers can be classified into low-frequency, high-frequency, ultra-high-frequency (UHF), and microwave readers. Similarly, electronic tags can be divided into passive, semi passive, and active tags depending on the degree to which they are semi battery powered [6]. The papers that form key nodes in a citation network are crucial in their field and are often referenced by researchers. The present authors reviewed the papers in the major paths of the citation network relating to RFID. [PERSON] and [PERSON] [7] proposed a fully integrated passive UHF RFID transponder integrated circuit with 4.5- or 9.5-m reading distance at 500-mW effective radiated power (16.7-\(\mu\)W radio frequency input power) or 4-W effective isotropic radiated power (EIRP), respectively. The reader was capable of operating in the 868/915-MHz ISM band with an antenna gain of less than 0.5 dB. In terms of the received power level required for a given base-station transmission power and tag antenna gain, the proposed reader outperformed other RFID readers by a factor of three. On the basis of the work by [PERSON] and [PERSON] [7], [PERSON] et al. [8] developed a remotely powered UHF RFID transponder operable at 2.45 GHz. The system achieved a 12-m operating range at 4-W EIRP in base-station transmission. When the reader design was fabricated using silicon on sapphire and embedded in a rectifier, the resistance between the tag antennas was reduced. This system represented a crucial improvement on the tag reader proposed by [PERSON] and [PERSON] [7]. [PERSON] [9] used the human body as an object to be tagged or biomotored and designed a geometrical tag antenna on a suspended patch and fed via a nested slot to study the compatibility of antennas with the human body. Building on this work, [PERSON] [10] reduced the size of the system and embedded electronic components to reduce the resistance. Additionally, researchers have suggested using three-dimensional spatial algorithms to simulate real environments; in applying the algorithm to automated indoor transportation devices, the deviation between the reader and tag antenna could be optimized [11]. [PERSON] et al. [12] revealed that sparsely distributing RFID tags results in higher localization accuracy than densely distributing them does. However, most researchers have proposed that the RFID tag density be increased or the localization algorithm be modified to improve the positioning accuracy. [PERSON] et al. [13] employed the simultaneous localization of multiple targets and received signal strength indicators (RSSIs) to test indoor localization using passive UHF RFID based on tag interaction analysis; a revised algorithm that was robust to different numbers, spacing, and materials of target objects was then devised to improve the localization accuracy. Researchers have also applied RFID tags to solve localization problems. [PERSON] [14] experimented with a passive RFID localization system and determined that it had higher localization precision than that of other passive RFID localization systems. Given that RFID uses unique identifiers, enables traceability, and has high security, and [PERSON] et al.