Near-field UHF Research Articles

Inception Phase Angle and Shape of Partial Discharge Signals Detected by Nearfield UHF Sensors

Inception Phase Angle and Shape of Partial Discharge Signals Detected by Nearfield UHF Sensors

Near-Field UHF RFID Transponder With a Screen-Printed Graphene Antenna

As a method of producing RFID tags, printed graphene provides a low-cost and eco-friendly alternative to the etching of aluminum or copper. The high resistivity of graphene, however, sets a challenge for the antenna design. In practice, it has led to using very large antennas in the UHF RFID far field tags demonstrated before. Using inductive near field as the coupling method between the reader and the tag is an alternative to the radiating far field also at UHF. The read range of such a near field tag is very short, but, on the other hand, the tag is extremely simple and small. In this paper, near field UHF RFID transponders with screen-printed graphene antennas are presented and the effect of the dimensions of the tag and the attachment method of the microchip studied. The attachment of the microchip is an important step of the fabrication process of a tag that has its impact on the final cost of a tag. Of the tags demonstrated, even the smallest one with the outer dimensions of 21 mm * 18 mm and the chip attached with isotropic conductive adhesive (ICA) was readable from a distance of 10 mm with an RF power marginal of 19 dB, which demonstrates that an operational and small graphene-based UHF RFID tag can be fabricated with low-cost industrial processes.

Design of UHF fractal antenna for localized near-field RFID application

In this article, fractal structure is proposed for localized near-field UHF antenna of radio frequency identification (RFID) reader. In the design, traditional Koch fractal structure is modified by converting the direction of one fractal structure of each line segment. Parameters of the fractal structure are optimized to acquire strong and uniform magnetic field distribution within an interrogation zone at designated height over the antenna. Two Koch fractal near-field antennas fed from center or side are presented. And the side-fed fractal near-field antenna is fabricated and tested to demonstrate a localized coverage area with a perimeter of two wavelengths within a reading distance of 35mm above the antenna. For distance above 35mm, a sharp decrease of reading rate is observed, which demonstrates a satisfactory near-field UHF antenna.

Near-Field Modular Antenna Concept With Configurable Reading Area for RFID Applications

This paper presents a near-field antenna with significant reading area that is reconfigurable. This antenna is used to realize near-field radio frequency identification technology in the UHF band (UHF RFID) reader. The antenna is printed on a flexible plastic substrate and then cut to the desired dimensions to be positioned over the area where it is desired to carry out the reading of near-field UHF RFID tags. This new concept of configurable antenna on demand, which is cut to fix the reading zone, shows extremely modular characteristics and can be simply implanted in a real environment. The performances of different configurations of the antenna that tell about different reading surfaces are presented. Significant reading surfaces never obtained before for near-field UHF RFID tags ( $1\times1$ cm2) up to $42\times76$ cm2 with a minimum range of 15 cm for the 868 MHz band are reported. Reading areas in three dimensions of such antennas are characterized experimentally with commercial tags to confirm the performances in a real environment.

A Yagi–Uda Antenna With Load and Additional Reflector for Near-Field UHF RFID

In this letter, a Yagi–Uda antenna with load and additional reflector is proposed to achieve strong and uniform magnetic field distribution within the antenna area for near-field ultrahigh-frequency radio frequency identification (RFID). This proposed antenna is composed of one driven dipole to emit electromagnetic (EM) wave, several directors to direct the EM wave to the desired area, a load element at the end of the director array to absorb the wave, and two reflectors at both ends to reflect the EM wave. The proposed antenna can generate a uniform magnetic field distribution within the antenna area, meanwhile keeping the field strength outside the antenna area relatively small. A prototype, as an example, that contains 13 elements is designed and fabricated, with the measured bandwidth of 880–980 MHz. The achieved interrogation area is 440 × 160 mm2, measured by utilizing a commercial RFID reader and some near-field tags. It is worth mentioning that the interrogation area can be extended by adding more directors to the antenna.

Design of near‐field ultra‐high frequency radio‐frequency identification antenna with fragmented wires for electrically‐large coverage

Design of ultra-high frequency radio-frequency identification (UHF RFID) reader antenna covering electrically-large near-field area is still challenging for near-field UHF RFID applications. In such design, magnetic field distribution on a large coverage area is required to be as uniform as possible. Fragment-type wire antennas are quite suitable for such demand because distribution of fragmented wires in a designated electrically-large area can be optimised to counterpoise the magnetic fields generated by non-uniform current distribution. By optimisation searching with multiobjective evolutionary algorithm based on decomposition combined with enhanced genetic operators, fragment-type RFID reader antenna is designed to provide uniform magnetic field distribution within dynamic range of 4 dB in an electrically-large near-field coverage of 320 × 320 mm at 915 MHz. The designed antenna is fabricated and tested. Both simulation and measurement results show good impedance matching, satisfactory near-field coverage, and desirable omni-directional pattern.

Enhancement of the Near-Field UHF RFID With Ferrite Substrates

We study the influence of the ferrite substrates on the near-field UHF RF identification (RFID) systems by relating their effective permeability μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> to the tag resonance parameters (voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IC</sub> , center frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) and the system-level performance (reading distance RD). To this effect, a new method to predict the disc μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> is used (fluxmetric approach) with good fit to the measured values. In addition, whereas the magnetic substrate normally yields the decrement of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IC</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> it also enables the tag downsizing and the RD increase. The conducted RD measurements with planar hexaferrite discs support this theoretical capability. Moreover, further improvement in RD is achieved when the discs are loaded to the reader loop antenna. Our ferrite samples are also found effective in shielding RFID from the metallic environment's implications, yet no discernible difference between permeable and lossy samples is realized. Full understanding of the underlying mechanisms governing the materials-system interaction is thereby provided to the RFID designer.

Microstrip-based segmented coupling reader antenna for near-field UHF RFID applications

A microstrip-based segmented coupling reader antenna is proposed for near-field ultra high frequency radio frequency identification applications. The measured reading distance is 13.5 cm in the air and the measured bandwidth is around 55 MHz (895–950 MHz) under the condition of voltage standing wave ratio less than 2.0, which covers the Federal Communications Commission standard (902–928 MHz) completely. In addition, the simulated far-field gain is around 4.7 dBi. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26144

Ultrawideband Multi-Static Scattering Analysis of Human Movement Within Buildings for the Purpose of Stand-Off Detection and Localization

An efficient and accurate method for the analysis of human backscatter response to ultrawideband near-field UHF radar systems is presented. The method combines a full-wave analysis of a human body model with a PO-like indoor propagation code known as “brick-tracing.” This method allows for the analysis of radar detection and tracking of humans within a realistic building environment. Using this method multi-static radar imaging of a human in buildings is evaluated and certain special features are pointed out. The simulation results are validated with actual radar measurements of a mannequin in a lab environment. A viable method for real time detection and localization of moving human inside buildings is then applied to the simulated and measured data and the building effects on the detection and localization are discussed.