Daniel Valderas

Design of UWB folded-plate monopole antennas based on TLM

From the current distribution on planar monopoles, transmission line modeling is applied to study this kind of antennas. Some reported techniques for broadband monopoles are approached by using this model from a qualitatively point of view. Conclusions are derived that help to match the monopoles over an ultrawide bandwidth regardless of whether they are folded or not. Folded configurations are obtained in order to provide solutions to specific designs and improve radiation pattern maintaining the planar monopole broadband behavior. Three compact folded prototypes with greater than 1:38 bandwidth are implemented and tested. Pulse distortion is also discussed for this type of applications.

UWB Staircase-Profile Printed Monopole Design

In printed monopoles, the current distribution along the lower monopole sheet and upper groundplane edges can be made analogous to a transmission line distribution by an appropriate antenna feed design. Accordingly, the VSWR < 2 impedance bandwidth upper frequency limit can be estimated for staircase-profile printed 2D ultrawideband (UWB) monopoles. Following this guideline, three tailored-bandwidth prototypes are designed, implemented and measured. They retain their length and width while multiplying their upper frequency (4.87, 8.7, and 15.15 GHz) by the number of monopole profile steps (1, 2, and 3). The deviation is found mainly below 13% in relation to the reference formula. The concept of angular range based on pattern stability factor (PSF) is introduced to compare the solid angle of UWB pattern stability operation when increasing the bandwidth. The angular range degradation versus impedance bandwidth improvement shows all the possible performance levels of the antennas. Thus, the design of UWB printed monopoles is approached from both points of view, i.e., impedance bandwidth and pattern stability.

Inkjet Printed Planar Coil Antenna Analysis for NFC Technology Applications

The aim of this paper is to examine the potential of inkjet printing technology for the fabrication of Near Field Communication (NFC) coil antennas. As inkjet printing technology enables deposition of a different number of layers, an accurate adjustment of the printed conductive tracks thickness is possible. As a consequence, input resistance and factor can be finely tuned as long as skin depth is not surpassed while keeping the same inductance levels. This allows the removal of the typical damping resistance present in current NFC inductors. A general methodology including design, simulation, fabrication, and measurement is presented for rectangular, planar-spiral inductors working at 13.56 MHz. Analytical formulas, computed numerical models, and measured results for antenna input impedance are compared. Reflection coefficient is designated as a figure of merit to analyze the correlation among them, which is found to be below −10 dB. The obtained results demonstrate the suitability of this technology in the fabrication of low cost, environmentally friendly NFC coils on flexible substrates.

RFID Technology and Applications

RFID is emerging as one of most fundamental technologies to Internet of Things due to its attractive features such as good reading ranges, high data rates, and low cost. RFID has achieved a widespread success in various applications, ranging from asset tracking, highway toll collection, supply chain management, animal identification to surveillance systems. Moreover, there has been a wide scope of development in RFID standards, protocols, and middleware. However, a series of challenging issues should be properly addressed before a massive adaptation of RFID technology. In this special issue, we have received 24 paper submissions and accepted 9 papers finally according to the reviewers’ comment and associate editors’ suggestion. These accepted papers include RFID reader antenna design, RFID tag antenna design, RFID passive transponders, tag collision algorithm, and RFID application systems. B. Lee et al. from Kwangwoon University of Korea proposed a novel structure of an NFC loop antenna for mobile handset applications by improving the performance of an NFC loop antenna when a ferrite-polymer composite is attached between the embedded NFC loop antenna and the phone battery. The proposed loop antenna gives better performance than that of a conventional NFC loop antenna. L. X. Zheng et al. from South China University of Technology proposed a compact RFID reader antenna for UHF near-field and far-field operations. The structure of the antenna is a novel folded-dipole loop and is formed by a concentric metal ring with a split. It can provide uniform magnetic near-field distribution and available farfield gain. Y. Yao et al. from Beijing University of Posts and Telecommunications also proposed a novel RFID reader antenna. This antenna was fabricated using indium tin oxide film; thus, it has optically transparent characteristic.This kind of antenna can be used in clothing stores. P. Jankowski-Mihulowicz et al. from Rzeszów University of Technology proposed novel RFID passive transponders with additional energy harvester. They can recover energy from the electromagnetic field of read device and the harvested energy was utilized to supply a microprocessor acquisition block for developed LTCC pressure sensor. C. Wang et al. from Beijing University of Posts and Telecommunications proposed an advanced dynamic framed-slotted ALOHA algorithm based on Bayesian estimation and probability response to solve the tag collision problem of RFID system. The simulation results show that the proposed algorithm has better performance. We sincerely hope that this special issue can further help the readers to understand RFID antenna design and applications and explore the future development of the system.

Synthesis of TLM-Based UWB Planar Monopole Impedance Bandwidth

A simple formula based on transmission line modeling (TLM) is proposed to determine the impedance bandwidth upper frequency limit for a staircase-profile planar monopole antenna. After a brief description of TLM analogy for planar monopoles, the formula is derived from a theoretical exposition. Accordingly, four prototypes are designed, implemented and measured in such a way that they are required to cover direct sequence ultrawideband (DS-UWB) first band (up to 4.85 GHz), UWB (up to 10.6 GHz) and possible future broadband systems (e.g., up to 15 and 21.4 GHz). The formula predicts this limit with a maximum error of 7.4% in the prototypes studied. The height of the antennas is chosen so that they help to filter WLAN 5 GHz band on the H-plane. This condition determines the lower impedance bandwidth limit (1.3 GHz for all of them). The resulting improvement on antenna system transfer functions (ASTF) is also discussed.

Broadband UHF Implanted 3-D Conformal Antenna Design and Characterization for In-Off Body Wireless Links

A broadband UHF antenna for implanted central venous catheters (CVC) is designed, implemented, and properly characterized. According to the requirements, the CVC antenna (CVCA) is low profile, surface integrated, and 3-D conformal to a 16 mm base radius, 10 mm upper radius, and 16 mm high truncated cone. It operates at the MedRadio band (401-406 MHz) for implant communication and at the ISM 2.45 GHz band for electronics wake up. A prototype implementation including a test-bed within a phantom that is representative of a body is introduced. The antenna exhibits S11 <;-10 dB at the bands of interest with broadband behavior. The measured gain is -28.95 dBi in vertical and -36.9 dBi in horizontal polarization in the MedRadio band and -25.5 dBi and -19.9 dBi at 2.45 GHz. The gain is corroborated by the link characterization between an implanted node with electronics and an external base station. Base station antenna, electronics sensitivity, transmitted power, and path loss are independently measured and introduced in a broken down link budget for read range estimate. This is 18.95 m for the MedRadio band in free space conditions. By using the power saving mode at 2.45 GHz, it is reduced to an estimate of 1.88 m.

Broadband implanted UHF RFID antenna

One of the priorities for sustaining high standards of medium to long term health care is to provide an effective monitoring system thus reducing the need for multiple consultations and hospital visits. In this connection, implanted biosensors, equipped with a transceiver with an antenna to establish the wireless link either to an external wearable station or to a computer placed in the care unit or household, constitute an essential area for telemetry research. The major problem with this kind of application is due to the losses introduced by the body, which is very high at RF frequencies and beyond. For this reason the research today has tended to favor in magnetic coils. However, the magnetic coils have three major shortcomings: their intrinsic short range, the critical positioning required for the two coils (inside and outside the body), and the exhibited low data rate. Therefore, it is reasonable to conduct a further study on radiators based on electromagnetic coupling for subcutaneous wireless biosensors, where the distance between the implant and the interface body-air is below a few millimeters. This would be the case of certain applications such as glucose analysis for diabetes treatment, intracranial pressure characterization etc. The combination of biosensors with RFID, a well developed EM coupling technology, can offer a practical platform for a sustainable health care.

High-Resolution ACLR Measurement Architecture for Adaptive Feedforward Amplifiers

One of the most restrictive linearity constraints to RF transmitter nonlinearity is the unwanted emission immediately outside the channel bandwidth, mostly known as adjacent channel leakage ratio (ACLR). In this paper, novel architecture design rules are presented for ACLR-level measurement in feedforward adaptive amplifiers. Both main and distortion signal power levels are obtained without any masquerading effect and with minimum component utilization. A prototype implementation is introduced to validate the proposed design rules, and a commercial spectrum analyzer is used for accuracy checking. Finally, the thermal stability has been tested for the -20degC to 70degC range.

RF implanted antenna gain characterization: Procedures and challenges

Implanted biosensors and actuators constitute an essential area for present and future telemetry research. Alongside the actual sensor or actuator, they require a communication transceiver with an antenna to establish the wireless link to the outside of the body. At RF frequencies, the major problem with this kind of applications is due to the losses introduced by the body tissues, which increase considerably at this part of the spectrum and beyond and hinder the communication link. However, they present quite promising features when they are subcutaneously implanted compared to magnetic-coupled based systems, such as higher data rates, longer ranges once the signal is outside the body and robustness to misalignment between the two ends of the link. Therefore, quite a few applications have recently emerged based on this technology, such as blood pressure monitoring, prostheses control by myoelectric sensors, cochlea implants etc. The parallel development of RFID technology presents a promising synergy that is worth exploring.

Modeling Eddy Current Brake Emissions for Electromagnetic Compatibility With Signaling Devices in High-Speed Railways

This paper presents a model that anticipates the emissions from eddy current brakes (ECBs) installed in high-speed trains. The emissions are computed in the 10 KHz–1.3 MHz range, where trackside signaling devices operate and issues related to electromagnetic compatibility have arisen, hindering ECBs promise of full deployment. The electromagnetic model provides a transfer function in the frequency domain between the nondesired harmonic currents produced by the train power supply and the subsequent radiated emissions by the ECBs at the trackside. The model includes the influence of the on-board ECB systems electric circuitry on the three-dimensional field computation of the electromagnets by a cosimulation approach (circuit and electromagnetic cross talk). After the data are postprocessed, the simulated results are compared with the results of an extensive measurement campaign on board a high-speed ICE 3 train equipped with ECBs. The high correlation makes it possible to anticipate ECB emissions in order to save costly on-track test runs, to suggest ECB design strategies and to provide safe limits when the worst cases occur.