Search

Functional imaging methods such as resting-state fMRI allow to describe interactions among different areas of the brain, thus deriving a functional connectivity matrix of the entire brain network. Tracking functional relationships among different regions of interest can be applied, besides a pure modelling perspective, also to discovering procedures to detect brain diseases and anomalies, or pursuing rehabilitation of subjects with structural damages. However, network characterization is often regarded as frequency-independent, so that the frequency at which interactions take place among different regions is ignored. In this paper, we show how simple filtering procedures over different bands, applied to the resting-state fMRI signals, result in highly different connectivity matrices. Thus, it is highlighted that the functional network can be significantly dependent on the considered frequency range for the fMRI signal. This both justifies the need for a careful filtering of the signals, that avoids filtering out relevant frequencies, and also hints the possibility of classifying functional interactions according to the frequency where the connectivity among two areas is the strongest.

[EN] This article describes different tunable structures for typical waveguide combline filters. In this context, several configurations using dielectric tuners have been studied for resonators, inter-resonator couplings, and input/output couplings. All configurations are analyzed in a wide frequency range showing advantages and drawbacks. Using the best structures in terms of performance, a fully re-configurable filter has been designed. The filter provides a wide tuning range in terms of center frequency while maintaining a high Q factor, and a constant bandwidth and return losses. A first filter prototype has been designed at L-band. The structure demonstrates a tunability in terms of frequency range of about 400 %, thereby clearly demonstrating that the approach we propose is indeed a very promising candidate for implementing tunable combline filters based on dielectric tuners.

[EN] The objective of this paper is to describe the design of an innovative and low-cost diplexer for Ka-band multi-beam satellite applications. The device is based on the use of two quadruplets to implement a number of transmission zeros (TZs) thus obtaining high-selectivity quasi-elliptic transfer functions. The resulting diplexer structure is particularly flexible in terms of layout, does not require tuning and has an excellent high-power behavior. In addition to theory, we compare the results of our simulations with the measurements obtained with a manufactured breadboard. The comparison shows excellent agreement thereby fully validating both the design procedure, and the new diplexer structure., This work was supported in part by the MINECO (Spanish Government) through Research and Development Project under Grant TEC2016-75934-C4-1-R, and in part by the Research and Development Technicians under Grant PTA2015-10839-I.

Wireless body area networks (WBANs) are becoming increasingly popular as they allow individuals to continuously monitor their vitals and physiological parameters remotely from the hospital. With the spread of the SARS-CoV-2 pandemic, the availability of portable pulse-oximeters and wearable heart rate detectors has boomed in the market. At the same time, in 2020 we assisted to an unprecedented increase of healthcare breaches, revealing the extreme vulnerability of the current generation of WBANs. Therefore, the development of new security protocols to ensure data protection, authentication, integrity and privacy within WBANs are highly needed. Here, we targeted a WBAN collecting ECG signals from different sensor nodes on the individual's body, we extracted the inter-pulse interval (i.e., R-R interval) sequence from each of them, and we developed a new information theoretic key agreement protocol that exploits the inherent randomness of ECG to ensure authentication between sensor pairs within the WBAN. After proper pre-processing, we provide an analytical solution that ensures robust authentication; we provide a unique information reconciliation matrix, which gives good performance for all ECG sensor pairs; and we can show that a relationship between information reconciliation and privacy amplification matrices can be found. Finally, we show the trade-off between the level of security, in terms of key generation rate, and the complexity of the error correction scheme implemented in the system.

This paper presents a three-phase coil topology for high-power static WPT. With respect to a single-phase system, the proposed topology allows to increase the volume power density while reducing the magnetic stray field and the weight of the filtering elements of the power electronics on board. This topology is applied to the design of a 100 kW-85 kHz system whose performances are highlighted through the comparison with an equivalent single-phase system transferring the same power at the same frequency.

The objective of this paper is to describe dual-band filters in rectangular waveguide based on resonant apertures. In addition, we also discuss the use of several techniques like capacitive stubs, width alteration in the resonators and staircase configurations to improve both the selectivity and the out-of-band performance of the basic filter structure. Finally, we show in detail the simulated performance of several filter configurations, thereby fully validating the new filter topology.

The increasing requirements in terms of bandwidth and power efficiency demanded by telecommunication, automotive and datacenter applications are pushing copper-based interconnections close to their intrinsic limits [1]. On the same line, the emerging trends on new rack-scale multi-socket computational units are putting pressure on chip-to-chip interconnections, calling for high speed and low-latency performance at a reduced energy and cost [2]. These technological requirements are making copper-based interconnects the bottleneck of high-performance systems, suggesting the use of point-to-point optical connectivity not only for long range communications but also at short or ultra-short distances [3]. With respect to other solid-state solutions, Silicon Photonics (SiP) seems to be the ideal candidate to answer to these needs, as it shares the same fabrication technologies of the microelectronic industry and is therefore expected to play a significant role in the field.

In this work, corona discharge breakdown thresholds in microstrip bandpass filters are studied. If a gas is subjected to strong electric fields, gas breakdown may occur with severe consequences for microwave devices. The objective of this paper is to propose a solution for the mentioned problem for a microstrip bandpass filter, through the implementation of dielectric material covers over the open-circuit terminations of the resonators forming the filter, where the voltage magnification is maximum. A parametric study of covers' dimensions for an open-ended resonator is presented, and it is analyzed how the maximum electric field strength and the unloaded quality factor are affected. Finally, the aforementioned study is applied to the design of a fifth-order bandpass filter with hairpin resonator configuration centered at 1.6 GHz. Numerical results show that by using this strategy, the peak power handling capability (PPHC) of microstrip filters can be considerably enhanced without hardly degrading the filter response performance. This work has been supported by the University of Alicante through the fellowhip grant UAFPU2018-054 and the research project GRE16-17, by the ”Agencia Estatal de Investigación (AEI)” under the coordinated research project TEC2016-75934-C4, and by the Generalitat Valenciana under the research project GVA/2018/071.

The objective of this paper is to combine the power of Space Mapping (SM) with a well-known cavity-by-cavity filter design procedure to obtain an advanced, very simple and powerful filter design procedure. Following our technique, the filter is built progressively so that the optimization space in each step is limited to only a few variables. As an illustration, we compare our method to the classic SM procedure for the design of two filters. The comparison shows that our technique is considerably faster than the classic SM approach thereby fully validating our advanced filter design procedure.

The objective of this paper is to describe a number of different techniques to enhance the out-of-band performance of wide-band rectangular waveguide filters. In particular, we discuss the use of mixed inductive and capacitive (hybrid) couplings, in conjunction with a staircase configuration and E-plane T-junctions, to yield a significant improvement both in the out-of-band response and in the filter selectivity. In addition to theory, we also discuss the performance of several filter prototypes, thereby fully validating the new filter topology.

This work describes a new strategy for improving the peak power handling capability (PPHC) of microstrip bandpass filters (BPFs) without any degradation in the electrical performance. For this purpose, a new resonator topology with rounded open-circuit terminations is proposed. Using this strategy, sharp edges are avoided and a reduction of the maximum peak voltage (Vpeak) is obtained, leading to higher peak power thresholds. An in-depth analysis of the variation of Vpeak and PPHC as a function of the circle radius is also carried out. As a validation, two microstrip BPFs centered at 1.6 GHz with different end-circle sizes are designed, manufactured and measured, showing a PPHC enhancement of 2.10 dB and 1.15 dB, respectively, as compared to a standard microstrip BPF. This work has been supported by the University of Alicante through the fellowship grant UAFPU2018-054 and by the Ministry of Science and Innovation through the sub-projects C41 and C43 of the coordinated project PID2019-103982RB.

Nowadays power electronics is looking for more integrated and compact insulated DC/DC converters. Electrical machines, like transformers, have a fundamental role in those kinds of converters. One of the main integration issue is the thermal aspect due to the power losses. Moreover, in an insulated DC/DC converter the bulkiest device is the transformer. Based on the high frequency power application the adopted transformer could be planar or litz wounded technology. In this work a single phase planar transformer for high power application has been investigated. An IPOS structure connecting many planar transformers has been performed to cope with the limitations that a single component gives. An experimental set-up adopting a SiCH-bridge power module feeding the different transformer structure. A power losses comparison among different structures has been realized. Indeed, the comparison is made connecting the H-bridge to a: single phase planar transformer, IPOS with 2 transformers, IPOS with 5 transformers, IPOS with 6 transformers and IPOS with a 10 transformers. The paper proposes thermal simulations for the IPOS made by 10 transformers and experimental results.

The multimode equivalent network (MEN) formulation has been originally developed for the efficient and accurate analysis of waveguide devices. In this article, we extend the use of the MEN to the analysis of zero-thickness, planar printed circuits in a metallic enclosure. The formulation is developed for metallic areas of arbitrary shape and includes both internal and external ports in the transverse plane to model connections to external components, and coaxial input/output ports. The boundary integral resonant mode expansion (BI-RME) method is used for the analysis of the arbitrary shape metallizations. On this basis, shielded multilayered microstrip circuits of complex geometry are analyzed in the common frame of the MEN technique. To validate the theoretical formulation, several boxed microstrip structures are analyzed, including multilayered configurations with several metallization interfaces, showing good agreement with respect to both other commercial tools, and measurements. This work was supported in part by the Spanish Government through the Ministerio de Educación, Cultura y Deporte under Grant FPU15/02883 and in part by the Ministerio de Economía y Competitividad through the sub-projects 4, 2, and 1 of the coordinated project under Grant TEC2016-75934-C4-R.

In this article, we show how the multimode equivalent network (MEN) technique can be extended to the analysis of multilayer boxed planar microwave circuits that are built using a thick metallization. This analysis is carried out considering the thick metallic circuit as a length of the uniform waveguide. The problem is then divided into two waveguide steps (or junctions). We first obtain the equivalent network of the two junctions. Then, we cascade them to obtain the MEN of the complete circuit, thereby including the effect of finite thickness rigorously. A key aspect of the formulation that we propose is that it includes ports in the transverse plane of the circuit. In addition to theory, several shielded microwave filters using a thick metallization are also analyzed. An in-depth study of the numerical convergence is also performed for two practical examples. Simulation results are shown to be in good agreement with both commercial simulation tools and measurements, thereby fully validating our theoretical formulation. This work was supported in part by the Ministerio de Educación, Cultura y Deporte, Spanish Government, under Grant FPU15/02883; and in part by the Ministerio de Ciencia e Innovación through the sub-projects C41, C42 and C43 of the coordinated project under Grant PID2019-103982RB.

We consider the problem of computing (approximate) greatest common divisors for matrix polynomials and we present some related facts and applications in system and control theory. The main application is to compute the distance of a controllable multi-input multi-output system to the set of uncontrollable ones; then we describe some related results. Index Terms— Matrix polynomial common factor - Distance to uncontrollability - Behavioral approach