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Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved One of the major challenges in the field of ambulant stress detection lies in the model validation. Commonly, different types of questionnaires are used to record perceived stress levels. These only capture stress levels at discrete moments in time and are prone to subjective inaccuracies. Although, many studies have already reported such issues, a solution for these difficulties is still lacking. This paper explores the potential of unsupervised learning with Self-Organizing Maps (SOM) for stress detection. In unsupervised learning settings, the labels from perceived stress levels are not needed anymore. First, a controlled stress experiment was conducted during which relax and stress phases were alternated. The skin conductance (SC) and electrocardiogram (ECG) of test subjects were recorded. Then, the structure of the SOM was built based on a training set of SC and ECG features. A Gaussian Mixture Model was used to cluster regions of the SOM with similar characteristics. Finally, by comparison of features values within each cluster, two clusters could be associated to either relax phases or stress phases. A classification performance of 79.0% (±5.16) was reached with a sensitivity of 75.6% (±11.2). In the future, the goal is to transfer these first initial results from a controlled laboratory setting to an ambulant environment. no issn ispartof: pages:26-35 ispartof: Proc. of Biosignals 2018 vol:4 pages:26-35 ispartof: BIOSIGNALS 2017 location:Funchal, Madeira date:Jan - Jan 2018 status: published

ispartof: BHI ispartof: IEEE Biomedical and Health Informatics (BHI'18) location:Las Vegas date:4 Mar - 7 Mar 2018 status: accepted

We present the design and construction of Frequency Selective Surface arrays composed of two subarrays of different slot lengths. We investigated their response variations with the variation of slot length differences of the elementary sub-arrays. Such nonhomogeneous arrays cannot be simulated with Computer Aided Design (CAD) programs because the boundary conditions are not fulfilled by the simulator. In infinite array simulation, the periodic boundary conditions are prescribed on the walls of the unit cell, whereas in the case of sub-arrays of unequal slot length such boundary conditions are not applicable. The CAD simulation of such combined array gives incorrect values of amplitude and phase responses. In this work, we investigate the characteristics of such complex arrays by using heuristic experimental approach. The results of the experimental approach demonstrate that the resultant reflection amplitude and phase of such complex array depend on the difference of slot lengths (ΔL) of the two sub-arrays.

New semiconductor technologies, used in passive microwave applications, allow the integration of passives with high quality factors and the fabrication of novel RFMEMS components for switches and tunable capacitors and resonators. The use of these technologies results in a strong reduction of the size and the power consumption of wearable microwave systems. The scaling of silicon transistors, following Moore’s law, results in RF-CMOS devices approaching the performance of III-V and SiGe devices but at a considerably lower cost and much higher integration capability. The introduction of GaN based technologies offering new possibilities in the field of power microwave devices is discussed.

This work is a comprehensive experimental investigation of chip to package wirebond interconnects for chip-package co-design. Wirebonds are interconnect bottlenecks in RF design, but are difficult to avoid due to their low cost and manufacturing ease. We have shown measurements on wirebonds in coplanar configuration with different return paths and also the cross coupling. We have also extracted lumped and distributed models and demonstrate the excellent agreement with measurements atleast upto 15GHz. We have proposed multi-wirebonds as a potential solution for better impedance matching. Different types of inductors with Q-factors of upto 100 have also been illustrated. We show influence of encapsulant on wirebonds and finally we also demonstrate a methodology to extract the time-domain response from S-parameters.

Currently, the thin film microwave multi-chip module (MCM) technology offers many benefits for a compact, lightweight and low cost integration of RF and microwave circuits [see Carchon et al (1)]. This technology allows the realisation of low loss transmission lines with a variety of characteristic impedances (between 10 and 100 Ohm) up to the higher mm-wave frequencies (>50 GHz). The technology also allows mounting active circuits (such as MMICs) by e.g. flip-chip technology. However, when placing different functions closely together, an adequate shielding and also mechanical protection of the active dies may be required. For this purpose, we developed a wafer level (called 0- level) package concept using micromachined cavities to realise versatile, microwave compatible protection and shielding structures on the thin film substrate. 0-level packaging refers to packaging before separation of the dies of the thin film integration substrate. In order to illustrate this concept and the benefits in real microwave functions, the realisation of a Ka-band LNA module, including 0-level package, bias circuits and RF feedthrough structures is discussed in this contribution.

We evaluate an oscillator-amplifier MMIC submitted to high-temperature operating life time tests. To relate adequately these results with individual components’ results, it is important to realise that failure mechanisms in non-linear MMICs are governed by the maximally instantaneous voltages/currents and hence that comparisons should be conducted at equal instantaneous conditions.

We show that the "Nonlinear Network Measurement System" allows to accurately measure the real-time degradation of microwave active devices under large-signal RF overdrive stress. This new kind of measurements gives a better insight in the failure mechanisms. We present results of both off- and on-state degradation of InP based HEMT's.

In this paper, the performance of both GaAs and InP-based 0.15um dual-gate HEMTs in a cascode configu­ration is demonstrated by the successful design and realisation of a number of coplanar amplifiers. For a reactively matched single-stage GaAs PHEMT amplifier a gain of 20.9dB is obtained at 23GHz. At millimetre-wave frequencies, this gain can be further improved by using InP-based HEMTs as is shown by the realisation of a single-stage LM HEMT dual-gate amplifier with a stable gain of 16.4 dB and a good in-and output matching at 58.5 Ghz.