The design of a reader antenna is described for usage in radio frequency identification (RFID) systems at 13.56 MHz, as defined in the ISO-14443a standard. It presents the theory, with emphasis on the effect of the read out distance on the design, but also describes measurements on concrete designs to validate the formulas and statements. We also comment on practical problems that were encountered during the design process. The major contribution of this work is the generalization of the design theory for large read out distances where the conventional assumption of constant loop current no longer holds.

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Dependence of RFID Reader Antenna Design on Read Out Distance

This article deals with an approach to the design of planar antennas that use metamaterial-loaded substrates based on the effective medium approximations. Metamaterials are structured composite materials with unique electromagnetic properties due to the interaction of electromagnetic waves with the finer scale periodicity of conventional materials. They may be used to modify the effective electromagnetic parameters of planar antenna substrates and to design antennas with the improved coupling to the feed, increased impedance matching bandwidths, miniaturized dimensions, and narrower beamwidths compared to those that use conventional dielectric materials for the same purposes. The electromagnetic analysis and optimization based on the effective medium approximations of metamaterials is very convenient since it deals with only a few bulk medium parameters instead of a large number of parameters describing a discrete structure. At the same time, the most common way of obtaining these effective medium parameters is transmission/reflection simulations or measurements in free space or in a homogeneous background medium. For a host medium which is not homogeneous, as for a grounded substrate, the effective medium parameters are different from the free space ones. The scattering losses in a metamaterial medium need to be accurately taken into account and included as parameters in full-wave bulk medium models. For this reason, in the effective medium approach for antenna substrates, one needs to use the appropriate effective medium approximations that take the coupling between inclusions into account and also to evaluate the effects of the scattering losses. In practice, this is done by finding the effective medium parameters inside an arbitrary substrate medium, and not in a homogeneous host medium or in free space. This paper presents the methodology and the results of FDTD analysis of planar antennas that have substrates

/pdf/homogenization-of-metamaterial-loaded-substrates-and-4vv88y1kth.pdf

Homogenization of metamaterial-loaded substrates and superstrates for antennas

This paper details the design, fabrication and testing of flexible textile-concealed Radio Frequency Identification (RFID) tags for wearable applications in a smart city/smart building environment. The proposed tag designs aim to reduce the overall footprint, enabling textile integration whilst maintaining the read range. The proposed RFID filament is less than 3.5 mm in width and 100 mm in length. The tag is based on an electrically small (0.0033 λ 2 ) high-impedance planar dipole antenna with a tuning loop, maintaining a reflection coefficient less than −21 dB at 915 MHz, when matched to a commercial RFID chip mounted alongside the antenna. The antenna strip and the RFID chip are then encapsulated and integrated in a standard woven textile for wearable applications. The flexible antenna filament demonstrates a 1.8 dBi gain which shows a close agreement with the analytically calculated and numerically simulated gains. The range of the fabricated tags has been measured and a maximum read range of 8.2 m was recorded at 868 MHz Moreover, the tag’s maximum calculated range at 915 MHz is 18 m, which is much longer than the commercially available laundry tags of larger length and width, such as Invengo RFID tags. The reliability of the proposed RFID tags has been investigated using a series of tests replicating textile-based use case scenarios which demonstrates its suitability for practical deployment. Washing tests have shown that the textile-integrated encapsulated tags can be read after over 32 washing cycles, and that multiple tags can be read simultaneously while being washed.

Reliable UHF Long-Range Textile-Integrated RFID Tag Based on a Compact Flexible Antenna Filament.

Electromagnetic Techniques and Probes for Side-Channel Analysis on Cryptographic Devices

In Radio Frequency (RF)-powered networks, peak antenna gains and path-loss models are often used to predict the power that can be received by a rectenna. However, this leads to significant over-estimation of the harvested power when using rectennas in a dynamic setting. This work proposes more realistic parameters for evaluating RF-powered Body Area Networks (BANs), and utilizes them to analyze and compare the performance of an RF-powered BAN based on 915 MHz and 2.4 GHz rectennas. Two fully-textile antennas: a 915 MHz monopole and a 2.4 GHz patch, are designed and fabricated for numerical radiation pattern analysis and practical forward transmission measurements. The antennas’ radiation properties are used to calculate the power delivered to a wireless-powered BAN formed of four antennas at different body positions. The mean angular gain is proposed as a more insightful metric for evaluating RFEH networks with unknown transmitter-receiver alignment. It is concluded that, when considering the mean gain, an RF-powered BAN using an omnidirectional 915 MHz antenna outperforms a 2.4 GHz BAN with higher-gain antenna, despite lack of shielding, by 15.4× higher DC power. Furthermore, a transmitter located above the user can result in 1× and 9× higher DC power at 915 MHz and 2.4 GHz, respectively, compared to a horizontal transmitter. Finally, it is suggested that the mean and angular gain should be considered instead of the peak gain. This accounts for the antennas’ angular misalignment resulting from the receiver’s mobility, which can vary the received power by an order of magnitude.

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Real-World Performance of Sub-1 GHz and 2.4 GHz Textile Antennas for RF-Powered Body Area Networks

The purpose of this article is to derive approximate formulas for the radiation resistance (R), and the directivity (D) of circular loop antennas. It is shown that simple approximations to the Bessel functions can be employed, to accurately model the oscillatory behavior of the Bessel function integral for both small and intermediate-sized loop antennas. Furthermore, when these approximations are combined with the usual asymptotic contributions to the integral in the case of a large input parameter ka (a=loop radius, a=2/spl pi///spl lambda/) accurate and relatively simple results for R and D can be secured for all loop sizes. Numerical results can, if necessary, be obtained using a simple pocket calculator. >

J.D. Mahony

Papers

Approximations to the radiation resistance and directivity of circular-loop antennas