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The synergies between Sentinel-3 (S3) and the forthcoming fluorescence explorer (FLEX) mission bring us the opportunity of using S3 vegetation indices (VI) as proxies of the solar-induced chlorophyll fluorescence (SIF) that will be captured by FLEX. However, the highly dynamic nature of SIF demands a very temporally accurate monitoring of S3 VIs to become reliable proxies. In this scenario, this article proposes a novel temporal reconstruction convolutional neural network (CNN), named dual attention temporal CNN (DAT-CNN), which has been specially designed for time-resolving S3 VIs using S2 and S3 multitemporal observations. In contrast to other existing techniques, DATCNN implements two different branches for processing and fusing S2 and S3 multimodal data, while further exploiting intersensor synergies. Besides, DAT-CNN also incorporates a new spatial– spectral and temporal attention module to suppress uninformative spatial–spectral features, while focusing on the most relevant temporal stamps for each particular prediction. The experimental comparison, including several temporal reconstruction methods and multiple operational Sentinel data products, demonstrates the competitive advantages of the proposed model with respect to the state of the art. The codes of this article will be available at https://github.com/ibanezfd/DATCNN.

Wearable health monitoring systems that collect data in free-living environments are becoming increasingly popular. Flexible printed circuits provide a commercially available option that can conform to the shape of a wearable system and support electronic sensing and flexible interconnect. However, repetitive dynamic activity can stress and damage the interconnect of flexible PCBs which degrades data quality. This case study evaluated the performance of flexible PCBs providing interconnect between electrodes and sensing electronics for tissue bioimpedance measurements in a wearable system. Resistance data (1 kHz to 128 kHz) was collected from localized knee tissues of 3 participants using the wearable design with flexible PCBs over 7 days of free-living. From electrical and optical inspection after use trace cracking of the flexible PCBs occurred, degrading tissue resistances reported by the wearable system. Exploration of these results advances understanding of how flexible PCBs perform in free-living conditions for wearable bioimpedance applications.

Sentinel missions provide widespread opportunities of exploiting inter-sensor synergies to improve the operational monitoring of terrestrial photosynthetic activity and canopy structural variations using vegetation indices (VI). In this context, continuous and consistent temporal data are logically required to rapidly detect vegetation changes across sensors. Nonetheless, the existing temporal limitations inherent to satellite orbits, cloud occlusions, data degradation, and many other factors may severely constrain the availability of data involving multiple satellites. In response, this letter proposes a novel deep 3-D convolutional regression network (3CRN) for temporally enhancing Sentinel-3 (S3) VI by taking advantage of inter-sensor Sentinel-2 (S2) observations. Unlike existing regression and deep learning-based methods, the proposed approach allows convolutional kernels to slide across the temporal dimension to exploit not only the higher spatial resolution of the S2 instrument but also its own temporal evolution to better estimate time-resolved VI in S3. To validate the proposed approach, we built a database made of multiple day-synchronized S2 and S3 operational products from a study area in Extremadura (Spain). The conducted experimental comparison, including multiple state-of-the-art regression and deep learning models, shows the statistically significant advantages of the presented framework. The codes of this work will be made available at https://github.com/rufernan/3CRN.

The development of specific user-based wearable smart textiles is gaining interest. The reliability and washability of e-textiles, especially electronic-based components of e-textiles, are under particular investigation nowadays. This is because e-textiles cannot be washed like normal textile products and washing electronic products is not common practice in our daily life. To adopt the e-textile products in our daily life, new standards, based on product usage, should be developed especially for flexibility and washability. The wearable motherboards are the main component for e-textile systems. They should be washing reliable and flexible for better adoption in the system. In this manuscript, flexible wearable PCBs were prepared with different conductive track widths and protected with silicone coatings. The samples were washed for 50 washing cycles in the household washing machine, and provoked damages were investigated. The PCBs were also investigated for bending tests (simulating mechanical stresses in the washing machine), and resultant damages were discussed and co-related with washing damages. The bending test was performed by bending the FPCBs at 90° over the circular rod and under the known hanging load.

Sentinel missions provide widespread opportunities of exploiting inter-sensor synergies to improve the operational monitoring of terrestrial photosynthetic activity and canopy structural variations using vegetation indices (VI). In this context, continuous and consistent temporal data are logically required to rapidly detect vegetation changes across sensors. Nonetheless, the existing temporal limitations inherent to satellite orbits, cloud occlusions, data degradation, and many other factors may severely constrain the availability of data involving multiple satellites. In response, this letter proposes a novel deep 3-D convolutional regression network (3CRN) for temporally enhancing Sentinel-3 (S3) VI by taking advantage of inter-sensor Sentinel-2 (S2) observations. Unlike existing regression and deep learning-based methods, the proposed approach allows convolutional kernels to slide across the temporal dimension to exploit not only the higher spatial resolution of the S2 instrument but also its own temporal evolution to better estimate time-resolved VI in S3. To validate the proposed approach, we built a database made of multiple day-synchronized S2 and S3 operational products from a study area in Extremadura (Spain). The conducted experimental comparison, including multiple state-of-the-art regression and deep learning models, shows the statistically significant advantages of the presented framework. The codes of this work will be made available at https://github.com/rufernan/3CRN.

The estimation of biophysical variables from remote sensing data raises important challenges in terms of the acquisition technology and its limitations. In this way, some vegetation parameters, such as chlorophyll fluorescence, require sensors with a high spectral resolution that constrains the spatial resolution while significantly increasing the subpixel land-cover heterogeneity. Precisely, this spatial variability often makes that rather different canopy structures are aggregated together, which eventually generates important deviations in the corresponding parameter quantification. In the context of the Copernicus program (and other related Earth Explorer missions), this article proposes a new statistical methodology to manage the subpixel spatial heterogeneity problem in Sentinel-3 (S3) and FLuorescence EXplorer (FLEX) by taking advantage of the higher spatial resolution of Sentinel-2 (S2). Specifically, the proposed approach first characterizes the subpixel spatial patterns of S3/FLEX using inter-sensor data from S2. Then, a multivariate analysis is conducted to model the influence of these spatial patterns in the errors of the estimated biophysical variables related to chlorophyll which are used as fluorescence proxies. Finally, these modeled distributions are employed to predict the confidence of S3/FLEX products on demand. Our experiments, conducted using multiple operational S2 and simulated S3 data products, reveal the advantages of the proposed methodology to effectively measure the confidence and expected deviations of different vegetation parameters with respect to standard regression algorithms. The source codes of this work will be available at https://github.com/rufernan/PixelS3.

In this paper, we demonstrate a low-cost, 48-channel, high-speed, flexible printed circuit (FPC)-based interconnect packaging concept for on-board optical modules. Due to the good high-speed performance and low cost, the FPC board is used as the base carrier for both transmitter and receiver modules. The on-board transmitter and receiver are based on a commercial 1-mm-pitch ISI HoLi pin grid array connector. The size of each module is only 31.5 × 31.5 mm and offers a state-of-art bandwidth density of 0.483 Gb/s/mm 2 by using a compact design. Investigation of RF signal propagation on the FPC is carried out for design validation at 10 Gb/s and, in order to further explore the potential of the suggested platform, differential pairs are simulated up to 30 GHz. The low-cost packaging approach requires only several flip-chip bonding steps using industry-standard solder reflow and ultrasonic bonding processes. An 8 × 12 -channel optical straight lens connector is used to couple the light from the optics into two 48-fiber multi-fiber push on connectors with 8 × 12 -channel MT ferrules. The fully assembled transmitter and receiver are tested at 10 Gb/s demonstrating error-free operation with sensitivities comparable with those of commercial devices. Bit error rates for all 96 channels as well as representative eye diagrams at 10 Gb/s are reported.

In this paper, we demonstrate a low-cost, 48-channel, high-speed, flexible printed circuit (FPC)-based interconnect packaging concept for on-board optical modules. Due to the good high-speed performance and low cost, the FPC board is used as the base carrier for both transmitter and receiver modules. The on-board transmitter and receiver are based on a commercial 1-mm-pitch ISI HoLi pin grid array connector. The size of each module is only 31.5 × 31.5 mm and offers a state-of-art bandwidth density of 0.483 Gb/s/mm 2 by using a compact design. Investigation of RF signal propagation on the FPC is carried out for design validation at 10 Gb/s and, in order to further explore the potential of the suggested platform, differential pairs are simulated up to 30 GHz. The low-cost packaging approach requires only several flip-chip bonding steps using industry-standard solder reflow and ultrasonic bonding processes. An 8 × 12 -channel optical straight lens connector is used to couple the light from the optics into two 48-fiber multi-fiber push on connectors with 8 × 12 -channel MT ferrules. The fully assembled transmitter and receiver are tested at 10 Gb/s demonstrating error-free operation with sensitivities comparable with those of commercial devices. Bit error rates for all 96 channels as well as representative eye diagrams at 10 Gb/s are reported.

In this paper, we combine high functionality c-Si CMOS and digitally printed components and interconnects to create an mostly printed integrated electronic system on a flexible substrate that can read and process multiple discrete sensors. Our approach is to create an integrated platform for the fabrication of mechanically flexible sensor tags that can be powered and interrogated wirelessly, precluding the need of a separate on-board power source. The high level system design is aimed at minimizing the number of non-printed components and reducing power consumption to enable energy harvesting from the RF field. Digital fabrication of these systems requires a range of materials, feature sizes, and electrical characteristics. In order to integrate the various printed components on a single substrate, we developed an integrated printer to accommodate a range of inks for printing the antenna, different types of sensors, chip interconnects, and wiring. For chip attachment to the flexible substrate, a method of integrating the die within the thickness of the substrate was developed. With proper system design and fabrication, a complete integrated tag for wireless sensing of temperature, strain, and touch was demonstrated. Our approach facilitates customization to a wide variety of sensors and user interfaces suitable for a broad range of applications including remote monitoring of health, structures, and the environment.

This paper reports the first high speed roll-to-roll printable transistor using a carbon nanotube (CNT) semiconducting layer. The transistor is made possible through the development of a pulsed light curable CNT ink compatible with typical drop on demand inkjet cartridges. This CNT ink uses a xylene based solvent with methanol, glycerin, and Triton X-100 modifiers to create an evaporable solution with appropriate absorption spectra for a mercury or xenon flash lamp with strong energy transmission in the UVB to mid visible light range, allowing the solution to absorb the energy from the flash lamp and evaporate. Transistor dimensions were defined by the capabilities of a typical roll-to-roll drop on demand cartridge. The final device demonstrated an on/off ratio of 104, representing performance similar to gravure printed devices. This represents the first CNT ink which can be used in high speed production methods without long thermal curing steps in the workflow.

In this paper, we demonstrate a low-cost, 48-channel, high-speed, flexible printed circuit (FPC)-based interconnect packaging concept for on-board optical modules. Due to the good high-speed performance and low cost, the FPC board is used as the base carrier for both transmitter and receiver modules. The on-board transmitter and receiver are based on a commercial 1-mm-pitch ISI HoLi pin grid array connector. The size of each module is only 31.5 × 31.5 mm and offers a state-of-art bandwidth density of 0.483 Gb/s/mm 2 by using a compact design. Investigation of RF signal propagation on the FPC is carried out for design validation at 10 Gb/s and, in order to further explore the potential of the suggested platform, differential pairs are simulated up to 30 GHz. The low-cost packaging approach requires only several flip-chip bonding steps using industry-standard solder reflow and ultrasonic bonding processes. An 8 × 12 -channel optical straight lens connector is used to couple the light from the optics into two 48-fiber multi-fiber push on connectors with 8 × 12 -channel MT ferrules. The fully assembled transmitter and receiver are tested at 10 Gb/s demonstrating error-free operation with sensitivities comparable with those of commercial devices. Bit error rates for all 96 channels as well as representative eye diagrams at 10 Gb/s are reported.

This article reports the work on next generation transponders for optical networks carried out within the last few years. A general architecture supporting super-channels (i.e., optical connections composed of several adjacent subcarriers) and sliceability (i.e., subcarriers grouped in a number of independent super-channels with different destinations) is presented. Several transponder implementations supporting different transmission techniques are considered, highlighting advantages, economics, and complexity. Discussions include electronics, optical components, integration, and programmability. Application use cases are reported.

In November 2015, the FLuorescence EXplorer (FLEX) was selected as the eighth Earth Explorer mission of the European Space Agency. The tandem mission concept will provide measurements at a spectral and spatial resolution enabling the retrieval and interpretation of the full chlorophyll fluorescence spectrum emitted by the terrestrial vegetation. This paper provides a mission concept overview of the scientific goals, the key objectives related to fluorescence, and the requirements guaranteeing the fitness for purpose of the resulting scientific data set. We present the mission design at the time of selection, i.e., at the end of project phase Phase A/B1, as developed by two independent industrial consortia. The mission concepts both rely on a single payload Fluorescence Imaging Spectrometer, covering the spectral range from 500 to 780 nm. In the oxygen absorption bands, its spectral resolution will be 0.3 nm with a spectral sampling interval of 0.1 nm. The swath width of the spectrometer is 150 km and the spatial resolution will be $300 \times 300~\text{m}^{2}$ . The satellite will fly in tandem with Sentinel-3 providing different and complementary measurements with a temporal collocation of 6 to 15 s. The FLEX launch is scheduled for 2022.

This paper presents an accurate and flexible approach to the self-consistent electrothermal modeling of III-N-based HEMTs, combining a temperature-dependent electrical compact model with a novel behavioral nonlinear dynamic thermal model, suitable for circuit-level simulations. The behavioral thermal model is extracted, according to a Wiener-like approach, from a full-scale, finite-element-method-based time-domain 3-D solution of the heat equation. The electrothermal model, validated against dc, pulsed dc, -parameter and large-signal nonlinear measurements, is exploited to assess the impact of thermal memory effects on the device RF performances. In particular, the model allows for a detailed analysis and interpretation of the thermal memory effects on intermodulation distortion. Finally, the proposed approach enables to analyze such features for different thermal mountings, thus providing useful indications for technology assessment.

A novel vertical architecture for all-printed organic electrochemical transistors, based on poly(3, 4-ethylenedioxythiophene):poly(styrene sulfonate), realized on flexible substrates, is reported. The transistors are manufactured along both faces of plastic or paper substrates and via connections are realized using laser ablation or simple punch through using a pin. Successful modulation of the electric current that flows between the two sides of the substrate is achieved using electrolyte-gating and electrochemical modulation of the electronic charge transport of the bulk of the transistor channel. In addition to this, the transistors are exhibiting fast switching and high ON/OFF current ratios.

This paper presents a switched-capacitor (SC) current integrator circuit for impedance measurement of tethered bilayer lipid membrane (tBLM) biosensors. The circuit comprises a small number of high performance components enabling enhanced experimental flexibility and reliability. The sensitivity is improved significantly by suppressing the output offset through pseudo-differential operation, using R-C components for the reference impedance. The sensing and reference electrodes are excited with low-amplitude differential voltage pulses and the current response to membrane resistance (RM) change of the tBLM biosensor is converted to voltage by a precision, low-noise SC integrator available as a single-package IC. Tests with both electrical models and actual biosensors demonstrated that the proposed circuit operates with high sensitivity and can be used in single chip versions for low-cost and high-sensitive tBLM biosensor arrays, featuring multiple electrode sites.

International audience; Finite-difference techniques are very popular and versatile numerical tools in computational electromagnetics. In this paper, we propose a preconditioned finite-difference frequency-domain method (FDFD) to model periodic structures in 2D and 3D. The preconditioner follows from a modal decoupling approximation. Its use involves discrete Fourier transforms (via FFTs). We have set FDFD against an FDTD package for a typical test case, with identical spatial grids. We have observed that computation times for a full frequency sweep are comparable, while the accuracy is slightly better with FDFD.

Look-up table (LUT) is one of the most popular methods for simulating the nonlinear characteristics of radio frequency (RF) power amplifiers. In this paper two practical methods for minimizing the LUT size are assessed for fast and flexible simulations using field programmable gate array (FPGA) circuits. They are cubic-spline interpolation and segmented nonuniform table indexing methods. The implementation architectures for these two approaches were developed and implemented. In addition, a suitable evaluation criterion for this kind of new applications is proposed in this paper. Implementation complexity and goodness of curve reconstruction were both considered so that the evaluation process could be more accurate and complete. The numerical comparisons show that the reconstruction performance of the cubic-spline interpolation method outperforms the nonuniform table indexing method dramatically by the sacrifice of a number of multipliers and double memory resources. The results also show that different segmentation schemes can considerably affect the performance of the segmented nonuniform indexing method.

Flexible Printed Circuits (FPCs) have been vastly used in electronic devices such as mobile phones and sensors. This multi-layer polymer is used in electronic packaging to interconnect high performance devices. Electroless Nickel Immersion Gold (ENIG) is the final finishing method commonly applied on FPCs due to its excellent planarity, wear or abrasion resistance and electrical contact performance. However, corrosion problem on FPCs surface may influence the electrical conductivity, performance and thus affect the functionality of the end product. Previous published literature showed that Co-Ni-Fe enhanced the corrosion behavior of metals. Therefore, ternary Cobalt alloys (Co-Ni-Fe) have been synthesized as the protective coating on ENIG FPCs in this research. A low cost electrodeposition method is applied to produce a Co-Ni-Fe protective coating to improve the corrosion resistance of ENIG FPCs. The result will be compared between FPCs with and without protective coating. Co-Ni-Fe solution for electrodeposition process was prepared at pH 1. The current applied to coat the FPCs is 0.6 ± 0.05 A. The experiment conducted at 50 °C ± 0.5 and performed at 30s and 60s of deposition time. Irregular shape of microstructure with grain size range from 46 nm to 88 nm was observed under FESEM micrographs. Corrosion test was performed by using Potentiodynamic Polarization technique under acidic environment. The corrosion rate per year of the FPCs after coated with electrodeposited Co-Ni-Fe showed lower corrosion rate than ENIG FPC. The corrosion behavior and surface morphology studies have shown that the electrodeposited Co-Ni-Fe coating improved the corrosion rate of ENIG FPCs.

This paper deals with the effects of bending flexible circuits on liquid crystal polymer (LCP) substrates in the gigahertz range. It investigates how the performance of passive circuit elements is influenced by the bends. For this purpose, four common types of transmission lines and a band-pass filter on flexible LCP substrate are analyzed concerning possible effects caused by sharp bending. Field simulation and measurements up to 67 GHz show that the occurring effects are small and negligible for several broadband applications. However, bending the substrate leads to small material deformation which could shift the frequency characteristics of resonant structures in a significant manner.