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Bi2Sr2Ca2Cu3O10+δ (Bi-2223) precursors for the fabrication of high temperature superconducting tapes were prepared by spray pyrolysis technique followed by a calcination process. The influences of precursor powder phase composition on the phase evolution dynamics and final current capacity of Bi-2223 superconducting tapes were systematically studied. It was interesting to notice that slight increase of Cu content in chemical composition could cause obvious variations of both the phase composition and the morphology of CuO particles in precursors. Therefore, the Bi-2223 phase formation process during the sintering process of tapes could be affected, and the current capacity changed accordingly. On the other hand, during the calcination temperature optimization process, the Bi-2223 phase content in precursors changed accordingly, thus the Bi-2223 phase formation dynamics were also studied. More Bi-2223 nuclei were formed due to the pre-existed Bi-2223 grains, which worked as inhomogeneous nuclei centers. Thus, although the final Bi-2223 phase contents were similar in all the tapes, the particle size and texture structure of Bi-2223 varied greatly, which caused a dramatic decrease of critical current in Bi-2223 tapes with the formation of Bi-2223 in precursors. Therefore, it could be concluded that both the morphology of CuO particles and the Bi-2223 phase content in precursors were the factors controlling the phase evolution dynamics during Bi-2223 tape sintering process.

FeSe superconducting bulks with different Fe contents were prepared by high energy ball milling aided sintering process followed by a post annealing process in low oxygen atmosphere. The influences of Fe content, annealing temperature and oxygen partial pressure have been systematically studied. It was found that both the critical temperature and superconducting phase volume ratio have been obviously improved with annealing. However, the effect of oxygen annealing process on FeSe polycrystalline bulks was different with that on FeSe single crystals. In polycrystalline bulks, the annealing process could further promote the phase transition from nonsuperconducting hexagonal δ-FeSe phase to superconducting tetragonal β-FeSe phase. Meanwhile, the chemical composition uniformity has also been enhanced with no obvious FeOδ phase detected by X-Ray Diffraction. With optimized annealing process under the oxygen partial pressure of 5% at 400 °C for 10 h, FeSe superconducting bulks have reached the critical temperature of 9.1 K.

Fluorine doping Fe1.2Se polycrystalline were prepared by solid-state sintering method. The influences of fluorine doping content and sintering temperatures on phase composition, lattice parameters, microstructure as well as superconducting properties were discussed in detail. It was found that fluorine doping could effectively reduce the content of non-superconducting hexagonal δ-FeSe phase. Besides, the content of hexagonal δ-FeSe phase and grain size of superconducting tetragonal β-FeSe phase were decreased with the sintering temperature increasing. Scanning electron microscopes (SEM) images indicated that the morphology of β-FeSe phase was a typical lamellar structure with the small particles of hexagonal δ-FeSe phase. Meanwhile, a higher critical temperature Tc of 8.3 K and larger shield volume fraction were obtained with high sintering temperature of 950 °C and proper F doping content.

Precursor powders of Bi2Sr2Ca2Cu3O10+δ (Bi-2223) high temperature superconducting tapes were prepared with spray pyrolysis technique. By tuning the oxygen partial pressure in calcination atmosphere as 1.0%, 7.5%, and 10.0%, respectively, the influences of calcination atmosphere on the phase evolution dynamics during the precursor powders calcination process have been discussed. Then the optimal calcination temperatures have been obtained correspondingly. Moreover, Bi-2223 multi-filament tapes have been fabricated with the precursor powders calcinated under different atmosphere. The effects of precursor powder calcination parameters on the phase composition, microstructures as well as the current capacity of final tapes have been systematically studied. Due to the proper secondary phase content and enhanced Bi-2223 texture structures, the maximum critical current of 109 A at 77 K, self-field, corresponding to the critical current density of 23.3 kA cm−2 has been obtained with the oxygen partial pressure of 7.5% in calcination atmosphere and the calcination temperature of 790 °C.

Bi 1.76 Pb 0.34 Sr 1.93 Ca 2.02 Cu 3.06 O 10+δ (Bi-2223) high temperature superconducting tapes were fabricated with Powder in tube (PIT) process. The traditional drawing process was partially replaced by groove rolling. The influence of cold working method on the filament density, the phase evolution mechanism as well as superconducting properties has been systematically studied. The groove rolling process could obviously enhance the filament density of Bi-2223 green wires, which thus led to the change of Bi-2223 formation rate. Meanwhile, although the heat treatment process has not been thoroughly optimized, the residual secondary phase content was still high, the critical current has been improved for more than 20% with groove rolling process, which should be attributed to the improved intergrain connections. On the other hand, the groove rolling process was also effective on the fabrication of Bi-2223 tapes with larger filament number, such as 85 or 121 to maintain the uniformity of filament deformation.

It is well known that the existence of interstitial Fe is a great obstacle to enhancing the superconducting properties of the Fe(Se, Te) system. In this work, a silver and oxygen codoping effect toward enhancement of the superconductivity and flux pinning in Fe(Se, Te) bulks is reported. The oxygen ions from SeO

Ag-sheathed Fe1.05Se superconducting wires were fabricated with ex-situ powder in tube (PIT) process. Fe and Se powders with molar ratio of 1.05 were firstly mixed and sintered under 600 °C for 12 h to form precursor powders. Owing to the complex Fe–Se binary phase diagram, both superconducting tetragonal FeSe and non-superconducting hexagonal FeSe could be formed simultaneously during sintering. Aiming at the reduction of hexagonal FeSe phase content and higher superconducting phase volume, the influences of key parameters, including sintering time, cooling rate and heating rate, on the phase composition of sintered wires were systematically studied. Optimal sintering parameters are obtained, and the maximum tetragonal FeSe phase content of ~ 97% is achieved. Meanwhile, the effects of packing density of precursor powders on the phase composition of final wires were also discussed. Owing to the shorter length of diffusion path, more tetragonal FeSe was formed with higher packing density. The superconducting transition signal with critical temperature of ~ 7.5 K was obtained, which proved the effectiveness of our optimal sintering process.

FeSe superconducting tapes with different sheath materials of Nb/Cu composite, Ag, and Fe have been fabricated with a traditional in situ powder-in-tube (PIT) process, respectively. With the same cold working process and heat treatment, the influences of different sheath materials on the phase composition and microstructures of FeSe filaments have been analyzed. Due to the reaction between Nb-Se and Ag-Se, Nb2Se and Ag2Se particles can be clearly observed embedded in the filaments. Therefore, it is necessary to introduce a new method for the fabrication of Ag or Nb sheath FeSe wires in order to avoid the introduction of metal Fe in magnet system during practical applications. Based on our previous study, a high-energy ball milling process has been performed to achieve precursor powders with amorphous FeSe binary compound instead of elemental Se. The formation of Ag-Se compounds has been successfully avoided and the superconducting tapes with high superconducting FeSe critical temperature of 9.0 K have been obtained.

FexSe superconducting bulks with different norminal Fe content from x = 1.00 to 1.20 have been fabricated with high-energy ball milling (HEBM) aided sintering process. The influences of original Fe contents on the phase composition, microstructures and superconducting properties were systematically investigated. It was noticed that with the increase of original Fe content, the nonsuperconducting δ-FeSe phase content decreased, while the content of residual Fe increased correspondingly. Meanwhile, the increasing original Fe content could also cause the increase of FeSe crystal size, therefore, the (00l) texture of FeSe bulks was enhanced, which would be beneficial to the intergrain connections. Mossbauer spectra have been performed to study the magnetic orders in obtained FeSe bulks. A clear hyperfine magnetic sextet corresponding to the magnetic ordering with Hf of 333.0 kOe can be related to residual Fe in the bulks with Fe content higher than 1.10. The magnetic and superconducting properties of obtained bulks underwent a systematical change with original Fe content. The increasing Fe content can obviously enhance the superconducting performance of FeSe bulks and the optimal critical temperature, Tc of 9.0 K was obtained with original Fe content of 1.20.

Bi2SrxCa2Cu3O10+δ (Bi-2223) precursor powders were fabricated by co-precipitation process with different Sr content of x = 1.93, 1.90, and 1.85. Multi-filamentary Bi-2223 high temperature superconducting tapes were fabricated by the traditional powder in tube process (PIT) with different precursor powders. The influences of Sr content on the phase formation dynamics as well as the superconducting properties of Bi-2223 tapes have been systematically investigated. With decreasing Sr content, the critical temperature of Bi-2223 tapes decreased from 109.9 K to 107.7 K, which implied that the change of Sr content could change the carrier concentration on Cu-O plane, thus led to the variation of intrinsic superconducting transition behavior. Besides, with the decrease of Sr content, the phase formation temperature decreased. Bi-2223 tapes with higher superconducting phase content were obtained with the Sr content of 1.85, which was beneficial to the improvement of intergrain connections. Thus, the Jc-B behavior was enhanced under the magnetic field parallel to the ab plane of Bi-2223. With further optimization of sintering process, the maximum Ic of 128 A was achieved on Sr = 1.85 tape, corresponding to the critical current density, Jc of ~ 25.8 kAcm−2.

Halogen doped Fe(Se, Te) superconducting materials were successfully synthesized through the eutectic transformation method. Both the distribution and morphology of the secondary hexagonal phase were tuned accordingly by substituting halogen elements. The morphology of the hexagonal phase was transformed from plate-like lamellar to agglomerated dots or bulk precipitates as the doping elements changed from F to Cl and Br. Moreover, the flux pinning mechanism, which represents the ability of materials to trap the penetrating magnetic field, was observed to change from Δκ to point pinning when doped by elements with heavier atomic mass. As a result, tremendous optimization of the critical current, upper critical field, and thermally activated flux flow activation energy were achieved in the as-prepared samples, with a specific value of 7 times, 2 times, and 3 times, respectively, in FeSe0.45Te0.5F0.05 compared with the values for the undoped sample. Our results reveal that the light-halogen element doping is a promising way to optimize the superconductivities in the Fe(Se, Te) systems and inspire us to manipulate the morphology of secondary phase to boost the superconductivities in iron-based superconductors.

This article demonstrates in-depth electromagnetic analysis of a radio frequency identification tag antenna manufactured by inkjet printing technology on different paper substrates to achieve ultra-low cost flexible radio frequency identification tags using a novel hole-matching technique for reducing the consumption of substrate material, and conductive ink. Nevertheless, the electromagnetic properties of the paper substrate are vulnerable to various environmental effects. Thus, the proposed antenna design is optimized for consistent wideband performance throughout the complete UHF radio frequency identification band (860–960 MHz) while presenting a greater degree of material insensitivity. An advanced antenna design methodological analysis is performed to accomplish an extended read range, while exhibiting benchmarking results when across cardboard cartons filled with metal or water containing objects.

An ID generating circuit is unquestionably the core of a chipless RFID tag. For convenience of printing process and cost consideration, the circuit should be kept as simple as possible. Based on the cognition, an 8-bit time-domain based ID generating circuit that merely consists of a ML and eight capacitors was offered, and implemented on photo-paper substrates via inkjet printing process. In addition to the experimental measurements, the circuit was also input into circuit simulators for cross-validation. The good agreement between simulations and measurements is observed, exhibiting the tag technical feasibility. Besides of low cost, the tag has wide compatibility with current licensed RFID spectrum, which will facilitate the future deployment in real applications.Compared to time-domain based chipless tags, frequency signatures based chipless RFID tags are expected to offer a larger coding capacity. As a response, we presented a 10-bit frequency-domain based chipless RFID tag. The tag composed of ten configurable LC resonators was implemented on flexible polyimide substrate by using fast toner-transferring process. Field measurements revealed not only the practicability of the tag, but also the high signal to noise ratio (SNR). Another frequency domain tag consists of a configurable coplanar LC resonator. With the use of all printing process, the tag was for the first time realized on common packaging papers. The tag feasibility was confirmed by subsequent measurements. Owing to the ultra-low cost potential and large SNR, The tag may find wide applications in typical RFID solutions such as management of paper tickets for social events and governing of smart documents.Ultra wide band (UWB) technology possesses a number of inherent merits such as high speed communication and large capacity, multi-path immunity, accurate ranging and positioning, penetration through obstacles, as well as extremely low-cost and low- power transmitters. Thus, passive UWB RFIDs are expected to play an important pole in the future identification applications for IoT. We explained the feature difference between UWB chipless tags and chip based tags, and forecasted the applications respectively based on the comparison between the two technologies. It is expected that the two technologies will coexist and compensate each other in the applications of IoT.Lastly, the thesis ends up with brief summary of the author’s contributions, and technical prospect for the future development of printable chipless RFID tags.

The letter presents the design, fabrication, and measurement of a configurable radio frequency identification (RFID) tag based on time-domain reflections. The tag circuit contains a microstrip line (ML) that propagates radio frequency (RF) signals, and a group of capacitors that introduce impedance discontinuities to encode binary codes. The configurability of the tag circuit is allowed by connecting the nearby-placed capacitors with the ML. Ink-jet printing technology is employed to implement the layout of the proposed tag on paper substrate. To overcome the limitations of printed metallic tracks, a linearly tapering technique is proposed. With this technique, a four-bit configurable passive chipless RFID tag is realized. Both time-domain reflectometry (TDR) measurements and ultrawideband (UWB) characterizations were conducted for the proposed tag, and the results are in good consistence with the simulation ones from the circuit simulator advanced design system (ADS). Owing to its low cost fabrication and environmentally friendly nature, the proposed tag has great potential to be widely employed in low-end RFID applications. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 2781-2786, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26412

This letter presents the design, simulation, fabrication, and characterization of an LC-resonator-based chipless RFID tag. The ID-generating circuit is designed based on a reconfigurable LC resonance circuit. Phase position modulation (PPM) coding is used for the enhancement of the coding capacity. The tag has been realized on packaging paper using all printing technique. In fabrication, overprinting process has been investigated as an effective pathway for the improvement of the conductivities. The tag with 4.25-bit coding capacity has been examined using a sweeping frequency signal transmitted from a vector network analyzer, and experimental results confirm the feasibility of the proposed chipless tag. With further optimizations, the tag can be used in the item-level tracking and identification applications, especially for the management of paper tickets and banknotes. QC 20130503

This paper reviews recent research on Ultra-Wideband (UWB) techniques for the next generation Radio Frequency IDentification (RFID) towards the Internet-of-Things (IoT), conducted by Vinn iPack Center at KTH, Sweden. First, we introduce an inkjet printed chipless UWB RFID for ultra-low cost applications such as item-level tracking. The identification number is coded by variations of the impedance over the transmission line, resulting in the OOK modulated data by means of pulse reflections in time domain. Prototypes were fabricated and measured for 4-bit tag and 8-bit tag, respectively. Thanks to the employment of fully printing process and paper substrates, the tag is potentially ultra-low cost in volume production. Second, a wirelessly powered RFID tag with an active UWB transmitter is studied for advanced applications such as wireless positioning and sensing. The tag is powered by UHF continuous waves, whereas it uses an UWB pulse generator to transmit data to the reader. It ensures the improved coverage and accurate positioning over traditional backscattering UHF tags. UWB readers, positioning, and sensing are also discussed in a system perspective. The two solutions reveal that UWB is a viable alternative to existing passive RFIDs adapting both low-cost applications and high-performance sensing and positioning applications.

The present state of the art research in the direction of embedded systems demonstrate that analysis of life-cycle, sustainability and environmental assessment have not been a core focus for researchers. To maximize a researcher's contribution in formulating environmentally friendly products, devising green manufacturing processes and services, there is a strong need to enhance life-cycle awareness and sustainability understandings among embedded systems researchers, so that the next generation of engineers will be able to realize the goal of a sustainable life-cycle. In this work an attempt has been made to investigate and evaluate the life-cycle management and environmental assessment in fabricating processes of the RFID based systems. We have chosen a general life cycle assessment approach which involves the collection and evaluation of quantitative data on the inputs and outputs of materials and energy associated with the RFID based systems. Based on the developed generic models, we have obtained the results in terms of environmental emissions for a production of paper substrate printed RFID antennas. We also make an attempt to raise several sustainability issues and quantify the toxic emissions during the manufacturing process.

The development of RFID technology are requiring high performance and low cost tag antennas than ever before. To meet these demands, linear tapering technique is firstly proposed in the design of planar tag antennas. With this strategy, the current distribution along antenna arms is effectively assigned by varying the antenna line width. Compared with conventional ones, the tapered antennas can reduce the material cost by over 40% not only for PCB (Printed Circuit Board) processed, but also for ink-jet printing produced dipole and meander line antennas, while they still maintain comparable performance. With an identical volume of conducting material, the tapered antennas can achieve better radiation performance than non-tapered ones on antenna gains and radiation efficiencies. The method has been successfully verified by applying it onto 869 MHz and 2.45 GHz antennas. The influence of the tapering technique on antenna bandwidth is also investigated.

This paper reports on the development of a 10-bit chipless RFID tag on flexible plastic substrate. This tag is based on sympathetic oscillations of a group of LC circuits with different resonant frequencies. Sophisticated designs including the placement of capacitors involved in each LC circuit, and various LC combinations are examined for the trade-off of the readability and the tag sizes. Moreover, the antennas for detecting the proposed tags are presented. The measurement results show that the proposed tag possesses remarkable readability for a read range up to 21 cm and more importantly, it is suited for tagging liquid-bearing containers, which are widely used in food and medical industries. In addition, this tag is reconfigurable on circuit level, enabling a potential pathway towards the realization of low cost RFID tags for HF/VHF band applications.

A fully metallic ink-jet printed passive chipless RFID tag on paper substrate is presented. The tag consists of an ultra-wide-band antenna, a microstrip transmission line with distributed shunt capacitors as information coding element which is reconfigurable by ink-jet printing process. Tapered microstrip line is employed to overcome the limitations of low conductivity and thin film thickness of ink-jet printed metal tracks. Measurement results show that the tag features a robust readability over 80 cm reading distance and a high data rate of 1.67 Gb/s.

This paper presents the characterization and modeling of inkjet printed interconnects on flexible polyimide substrate using nano-particle silver ink for low-cost RFID applications. Then TDR/TDT and S-parameter measurements are performed at high frequency from 30 kHz to 6 GHz. A lumped equivalent circuit and distributed parameter model of the printed interconnects have been developed for the realization of the full printed RFID tags. Additionally the related electrical properties of the printed interconnects are extracted.

In this paper, a novel fully reconfigurable chipless RFID tag has been presented. 8-bit data are encoded by impedance mismatches along transmission line. Inkjet printing is used to reconfigure for special tag IDs. By integrating inkjet printing technology, printable tags are not only economically feasible but also technically efficient. The remarkable idea has been successfully validated both by simulation and experimental measurements.

This work is focused on frequency domain electrical characterization of ink-jet printed coplanar waveguides (CPWs). The waveguides were designed and printed using conductive nanosilver ink at room temperature and sintered at 300degC. Distributed models, dependent on frequency, have been developed and some relevent parameters such as impedance, attenuation, are derived over frequency band from 30 kHz to 6 GHz. Two different widths of ground planes are investigated to examine the effects on CPW high frequency behaviors. In addition to these the obtained parameters have been compared and validated by theoretical calculations and momentum simulations.

Paper substrate is one of the paramount nominees for radio frequency identification (RFID) tags but at the same time it is extremely prone towards environmental changes. In this paper, antennas for UHF RFID tags on paper based substrate are investigated and analyzed for the first time to evaluate the effect of change in dielectric constant on the antenna parameters and performance. On the basis of analysis a concrete meander line antenna is proposed, designed and evaluated which has tremendous immunity towards variation in dielectric constant.

The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel fo ...