decisive drawbacks are (i) only a low to moderate level of scalability, (ii) restrictions for the size as well as the material of the substrate due to high-vacuum processes at elevated temperatures, iii) a lack of mechanical flexibility and iv) optical transparency.A few of these obstacles have been overcome with the emergence of novel materials such as carbon nanotubes (CNTs), graphene, [2] graphene oxide, [3] poly (3,4ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), [4] metal nanomeshes, [5] silver-coated polyester films (AgHT), [6] silver flakes, [7] silver nanoparticles, [8] copper oxide nanoparticles [9] as well as metal nanowires. [10,11] For the majority of these materials, scalable and high-yield synthesis protocols or fabrication techniques exist and these materials can potentially be deposited at almost arbitrary scale and under ambient conditions. Due to the cost-effectiveness, the ease-of-processing and the scalability, deposition methods such as inkjet printing, [12] direct laser writing, [13] spray coating [14] or screen printing [15] have become increasingly popular over the last years and raised academic and industrial interest.A high optical transparency of the deposited films is already a requirement for numerous antenna applications including solar cells, [16] sun shields on satellites, [17] radio-identification tags (RFIDs), [18][19][20][21] smart glasses, [22] bandstop filters to reduce the interference from wireless local area networks (WLANs) [23] as well as for energy harvesting. [24,25] Due to this broad application spectrum and the commercialization potential, notable technology companies including the so-called Big Techs, have recently filed several patents related to transparent conductive films and their use for antennas. [26][27][28] The conducting and transparent films presented in this work were made of a commercially available silver nanowire (AgNW)-based screen print paste. The use of screen printed AgNWs for antennas has already been reported in 2014 by Song et al. [29] However, in that work, the antenna films were fully opaque, which is a criterion for exclusion in many applications. In this work, as transparent electrode (TE) material, AgNWs were selected since this material is currently considered as the most promising alternative to the prevailing TE material, i.e., indium tin oxide (ITO), [30] with regard to the electro-optical performance as well as the chemical and the mechanical stability. [31] The antennas presented in this work show a highThe advent of mobile communication has made antennas omnipresent. Conventional methods of antenna manufacturing cannot address the growing demands for novel applications requiring transparent and flexible antennas. In this paper, transparent silver nanowire films are studied with respect to their highfrequency properties. Transparent silver nanowire (AgNW)-based antennas that are screen printed onto flexible polyethylene terephthalate (PET) substrate are reported. Transparent films with a low sheet resistance of 8.5 Ω sq −...

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In this work, we report on the fabrication and characterization of sub-300 nm electrode films based on solution-processed silver nanoparticles (AgNPs). Following the deposition of the electrode material using a scalable and homogenous spray process, the films are treated with thermal or photonic sintering to promote the coalescence of the nanoparticles and in turn decrease the resistivity of the films. After sintering, a resistivity of 63 ± 13 nΩ m is achieved for the AgNP films, which is only by a factor of four larger than the literature value for bulk silver. Both post-deposition treatments show a similar performance with regard to the achieved resistivity. However, photonic sintering avoids the need for thermal annealing at substrate temperatures of 150 °C and above. In addition, the photonic sintering process can easily be embedded in a roll-to-roll process and is extremely fast with light exposure times below 3 ms. Thus, this manufacturing technique paves the way for the use of flexible substrates in electronics. As a simple and practical application, we present the use of AgNP films for antennas operating in the 5 GHz band on flexible polyethylene terephthalate substrate. An original coplanar design is employed for the fabrication of antennas with a single conductive layer that exhibit a maximum return loss and radiation of -27 dB and 95%, respectively.

A Bayesian optimization algorithm in combination with a scattering based simulation approach is used for the optimization of quantum cascade detectors (QCDs). QCDs operate in the mid-infrared and terahertz regime and are, together with quantum cascade lasers, appropriate for the integration into on-chip applications such as gas sensors. Our modeling approach is based on a rate equation model and a Kirchhoff resistance network for noise modeling, using scattering rates calculated with Fermi’s golden rule, or alternatively extracted from an ensemble Monte Carlo transport approach. The appropriate surrogate model of Bayesian optimization is based on Gaussian process regression, which can handle noisy offsets on the objective function evaluations inherent in ensemble Monte Carlo simulations. Here, we focus on the optimization of a matured mid-infrared QCD design detecting at 4.7 $$\upmu {\mathrm{m}}$$ μ m . For optimization we choose as figure of merit the specific detectivity, which is a measure for the signal-to-noise ratio. As the trade-off between high extraction efficiency and low detector conductance is important for good detection performance, we search for the perfect layer composition and vary the thicknesses of different cascade layers. Due to the high-temperature requirements interesting for cost-effective and mobile on-chip sensing applications, a simulation temperature of 300 K is selected. Our optimization strategy yields an improvement of specific detectivity by a factor of $${\sim 2-3}$$ ∼ 2 - 3 at room temperature using two different parameter sets. Furthermore, we investigate the sensitivity of our approach to fabrication tolerances, showing robustness of the optimized designs against growth fluctuations under fabrication conditions.

Flexible electronic devices have gained significant interest due to their different potential applications. Herein, we report highly flexible, stretchable, and sensitive sensors made of sprayed CNT layer, sandwiched between two polymer layers. A facile fabrication process was employed in which the CNT solution was directly sprayed onto a patterned bottom polymer layer, above which a second polymer layer was casted to get a sandwiched composite structure. Varying amounts of CNT solution (i.e., 10, 25, 40, 70, and 100 mL) were sprayed to get conductive CNT layers of different thicknesses/densities. The physical characteristics of the conductive CNT layers were studied through SEM and optical images. The starting electrical resistance values (without strain) as well as the changes in electrical resistance against human body motions were monitored. The synthesized samples exhibited good response against finger and wrist bending. The conductivity of the samples increased with increase of CNT solution volume while the sensitivity followed the inverse relation, suggesting that the sensors with controlled sensitivity could be fabricated for targeted strain ranges using the proposed method.

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The propagation of stochastic electromagnetic fields can be accurately modeled using the auto-and cross-correlation spectra of the field components. In this work, we introduce the framework of principal component analysis for reducing the computational cost of handling stochastic electromagnetic fields described by correlation matrices. We consider noisy electromagnetic fields originating from stationary random processes with Gaussian probability distribution. The amount of data obtained by 2-dimensional near-field measurements and by determining the autoand cross-correlation information of electromagnetic interference can become burdensome for further processing even for problems of moderate size. For obtaining the correlation data, 2 measurement probes have to scan a defined grid of measurement points. For each pair of points, the spatial correlations need to be calculated, and hence, the data obtained scales quadratically with the number of sampling points.To reduce the amount of data, we project the given data obtained by measurement or simulation onto directions of maximum variation, the so called principal components, and keep only those principal components which contribute most to the total variance. In this way, the memory demand for storage and further computation of stochastic electromagnetic fields can be reduced significantly. KEYWORDS electromagnetic interference, noisy electromagnetic fields, principal component analysis, stochastic electromagnetic fields Int J Numer Model. 2018;31:e2246.wileyonlinelibrary.com/journal/jnm

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