Shuai Shao

Item-Level RFID Tag Location Sensing Utilizing Reader Antenna Spatial Diversity

A robust estimation procedure for sensing the locations of passive UHF radio frequency identification (RFID) tags is introduced based on spatial deployment of the reader antennas for maximum signal diversity. A signal model is developed for the received signal strength indicator seen by each reader antenna and incorporated into a mean-square error testing function. The error function is minimized at each test point in the interrogation zone to find the point with the minimum mean-square error. The minimization is independent of the tag type and orientation, making the proposed method very robust compared with other methods that are based on reference tags and radio maps. Experimental results are presented for a realistic retail scenario with multiple tagged items achieving an estimation accuracy of 35 cm. The location sensing system uses conventional UHF RFID readers, antennas, and passive tags, providing additional capability to existing item-level RFID systems. This added value will help to offset the high cost of large-scale RFID infrastructure development.

Design Approach for Robust UHF RFID Tag Antennas Mounted on a Plurality of Dielectric Surfaces [Antenna Designer's Notebook]

A design approach is presented for passive UHF RFID tag antennas to function efficiently when mounted on a wide variety of dielectric materials of arbitrary thickness. It is well understood that the presence of materials can detune an antenna by shifting its operational band. It is therefore important to design tags that can accommodate such a shift in frequency due to material effects. In this paper, we propose a way to modify existing classical tag designs to enable them to operate over a wide range of materials (3 <; εr <; 13 ) and arbitrary thickness. Experimental results showed that when compared to commercially available tags, the modified tags achieved better performance when mounted on a wide range of materials.

Broadband Textile-Based Passive UHF RFID Tag Antenna for Elastic Material

We present a broadband textile-based UHF RFID tag antenna. Its wide bandwidth makes the tag less susceptible to objects and materials in the vicinity. Also high conductive textile material (E-fiber) is used to introduce elasticity, flexibility, and mechanical strength. As a result, the designed tag antenna can operate in a wide range of dielectric materials and various environments. By contrast, conventional RFID tag antennas have narrow bandwidth and must be designed for placement in different materials. The new tag is designed for implementing with elastic materials; as an example, the designed tags are tested on automotive tires. Experimental results show that the designed tag achieves much better performance compared with commercially available tags.

Physics-based approach for antenna design optimization of RFID tags mounted on and inside material layers

A design approach is presented for UHF RFID tag antennas operating in the vicinity of dielectric media using the layered Greens function and the effective permittivity of a material with finite thickness. It is noted that materials detune the antenna and alter the gain pattern. In this work we propose a broadband tag antenna design that functions on materials across various permittivity and thicknesses. The analytic approach allows optimal placement to be determined within the dielectric. Experimental results show that the proposed tag achieves better performance when mounted on a wide range of materials as compared to commercial tags.

Passive UHF RFID tag localization using reader antenna spatial diversity

A simple and robust RSSI based passive RFID localization technique has been investigated. The algorithm does not depend on the type of RFID tags or orientation, and is independent of the environment as long as there is a reasonable line of sight between the reader antennas and the interrogation zone. Experimental results show that the average estimated distance error is 17cm for a single tag in an open space, and 48cm for an area cluttered with many retail items. Our future work will focus on using phase information combined with RSSI to enhance the localization accuracy. Improved propagation models and positioning algorithms will be developed for robust estimation under varying environmental conditions.

Broadband and flexible textile RFID tags for tires

A flexible, passive UHF RFID (Radio Frequency IDentification) tag antenna is presented and tested for automotive tire applications. RFID tags on tires can be adapted to provide information on the tire health, retreading interval, pressure and temperature among others. However, typical tags are narrowband. In this paper, we propose a broadband tag that retains its functionality as the surrounding material and location of the RFID tag vary. The tag is fabricated on conductive textiles and embedded into polymer to improve its flexibility and bonding with the tire rubber. Experimental results show that the proposed tag antenna achieves excellent performance when mounted on tires.

RFID tags for in-situ tire monitoring

A broadband and flexible UHF RFID tag designed to overcome the challenges of placement in tires is presented. The tag antenna design is discussed and its performance is evaluated through read-range, threshold and stretch tests. Next a smart sensing and logging capable EPC Class-1 Gen-2 compliant UHF RFID prototype tag board is presented to demonstrate the feasibility of RFID sensors in tires.

Item-level passive UHF RFID tag locating using reader antenna spatial diversity

A new concept of passive RFID tag position finding is presented for real world item-level applications and provides automatic guidance for order fulfillment centers and retail stores. The new technique does not require a radio map, reference tags, or any additional hardware. This is accomplished by using precise signal models, a minimum mean-square error estimator and four spatially diverse CP reader antennas. Experimental results show that the proposed method can make unprecedented robust real time estimation practical regardless of the type and orientation of the tag and the operating environment.

Embedded UHF RFID tag antennas for automotive tire sensing

We present analysis and design optimization of passive UHF RFID (Radio Frequency Identification) tags for tracking automotive tires. The RFID tags are mounted on or embedded into tires to monitor their conditions, verify their history and track inventory. In this paper, we evaluated the performance of existing RFID tags designed specifically for tires. It is found that the current RFID tags do not operate well in the vicinity of adjacent tires. This is due to the tires dielectric structure and metallic radial plies inside the sidewalls. These factors were also verified in simulation models. Recommendations for new tag designs will be provided at the meeting.