Anti-metallic passive RFID tags play a key role in manufacturing automation systems adopting RFID techniques, such as manufacturing tool management, logistics and process control. A novel long range passive anti-metallic RFID tag fabrication method is proposed in this chapter, in which a multi-strip High Impendence Surface (HIS) with a feeding loop is designed as the antenna radiator. Firstly, the bandwidth enhancement methods for passive RFID tags based on micro strips are discussed. Then, a RFID tag design based on multi-strip antenna is proposed and its radiation efficiency is analyzed. After that, some key parameters of the RFID antenna proposed are optimized from the viewpoint of radiation efficiency and impedance match performance. Targeted for manufacturing plants with heavy metallic interfering, the proposed RFID tag can significantly enhance the radiation efficiency to improve the reading range as well as the bandwidth. Finally, some RFID tag prototypes are fabricated and tested to verify their performance and applicability against metallic environment, and the experimental results show that these fabricated RFID tags have outstanding reading performance and can be widely used in manufacturing plant full of heave metallic interfering.
Top1. Introduction
With the trend of consumer personalization and demand diversification,an increasing number of manufacturing enterprises are employing the informationization of Manufacturing Execution System (MES) to realize the seamless integration between the resource management systems and the real-world production environment, which is achieved by the collection and synchronization of real manufacturing data (Dai et al., 2012; Liu et al., 2012). Traditionally, barcode techniques have been mainly used for MES data acquisition. However, a barcode can easily get scuffed, damaged or wrinkled, and the reading is unreliable in dirty environment. Also, due to the difficulties to store data or identify moving objects, a barcode cannot acquire varying production data correctly and efficiently (Chao et al., 2007; Gaukler, 2011). Recently, a new electronic tag technology, i.e. RFID (Radio Frequency Identification), has been introduced to manufacturing automation due to its advantages such as long recognition distance, fast reading speed, large storage and programmable memory. Providing a non-contact solution for automatic identification, RFID has been increasingly used for online data acquisition and process control in the modern manufacturing system (DiGiampaolo et al., 2012; Ngai et al., 2008; Saad et al., 2011; Shih-Kang et al., 2010; Zhou et al., 2007). Nowadays, many researchers have applied RFID techniques for accurate and on-line decision-making in production management, allowing for closed-loop manufacturing systems (Bottani et al., 2009; Guo et al., 2009; Kim et al., 2007).
A typical RFID system is composed of a RFID reader and a passive RFID tag attached on items or pallets, among which the RFID tag is the key component to determine the maximum reading range (Rao et al., 2005). In a manufacturing logistic system, supervision of forklifts and pallets get into or out of warehouse requires RFID tags that have a reading range more than 5 meters. Therefore, long range UHF (Ultra High Frequency) RFID tags are needed. However, when a RFID tag is used in manufacturing plant, metal environment will severely affects its radiation efficiency. Especially, when the RFID tag is mounted on or near to metal objects, the reading/writing performance of the RFID tag will be dramatically degraded due to the change of the antenna parameters (frequency, efficiency, bandwidth, radiation pattern, and input impedance) (Dobkin et al., 2005; Prothro et al., 2006). For example, the reading range of an ideal passive UHF RFID tag will sharply drop from 10 m to less than 0.5 m in air when it is placed close to a metallic object. The reason for the performance degradation is mainly because that the phase of the impinging wave is reversed by metal surface, resulting in destructive interference with the wave emitted in the other directions (Sievenpiper, 1999).