Characterization of dielectric charging in RF MEMS capacitive switches

RF MEMS capacitive switches show great promise for use in wireless communication devices such as mobile phones, but the successful application of these switches is hindered by reliability concerns: charge injection in the dielectric layer (SiN) can cause irreversible stiction of the moving part of the switch. We present a new way to characterize charge injection. By stressing the dielectric with electric fields on the order of 1 MV/cm, we inject charge in the dielectric, and use a new method to measure the effects it has on the C-V curve. Instead of measuring the change in the pull-in voltage, this method measures the change in the voltage at which the capacitance is minimal. This way, no extra charge is injected during the measurement of the amount of injected charge, which reduces the effect it has on the tested switches, so that the effect of the intentionally induced stress voltage is not obscured by the measurement method

Fast RF-CV characterization through high-speed 1-port S-parameter measurements

We present a novel method to measure the capacitance-voltage relation of an electronic device. The approach is accurate, very fast, and cost-effective compared to the existing off-the-shelf solutions. Capacitances are determined using a single-frequency 1-port S-parameter setup constructed from discrete components. We introduce a new way to correct for non-linearities of the used components, which greatly increases the accuracy with which the phase and magnitude of the reflected signal is measured. The measurement technique is validated on an RF-MEMS capacitive switch and a BST tunable capacitor. Complete capacitance-voltage curves are measured in less than a millisecond, with a measurement accuracy well below 1%.\ud \u

Math-Failure Associations, Attentional Biases, and Avoidance Bias: The Relationship with Math Anxiety and Behaviour in Adolescents

Background: Math anxiety in adolescence negatively affects learning math and careers. The current study investigated whether three cognitive biases, i.e. math-failure associations, attentional biases (engagement and disengagement), and avoidance bias for math, were related to math anxiety and math behaviour (math grade and math avoidance behaviour). Methods: In total, 500 secondary school students performed three cognitive bias tasks, questionnaires and a math performance task, and reported their grades. Results: Math-failure associations showed the most consistent associations with the outcome measures. They were associated with higher math anxiety above and beyond sex and education level. Those math-failure associations were also associated with lower grades and more avoidance behaviour, however, not above and beyond math anxiety. Engagement bias and avoidance tendency bias were associated with math avoidance behaviour, though the avoidance bias finding should be interpreted with care given the low reliability of the measure. Disengagement biases were not associated with any math anxiety nor behaviour outcome measure. Conclusions: Whereas a more reliable instrument for avoidance bias is necessary for conclusions on the relations with math performance and behaviour, the current results do suggest that math-failure associations, and not attentional bias, may play a role in the maintenance of math anxiety.</p

A Direct Elliptic Solver Based on Hierarchically Low-rank Schur Complements

A parallel fast direct solver for rank-compressible block tridiagonal linear systems is presented. Algorithmic synergies between Cyclic Reduction and Hierarchical matrix arithmetic operations result in a solver with $O(N \log^2 N)$ arithmetic complexity and $O(N \log N)$ memory footprint. We provide a baseline for performance and applicability by comparing with well known implementations of the $\mathcal{H}$-LU factorization and algebraic multigrid with a parallel implementation that leverages the concurrency features of the method. Numerical experiments reveal that this method is comparable with other fast direct solvers based on Hierarchical Matrices such as $\mathcal{H}$-LU and that it can tackle problems where algebraic multigrid fails to converge

Ensuring metrological control of the means of thermal control

В настоящее время все большее применение набирают приборы бесконтактного и быстродейственного контроля температуры приборами, регистрирующими излучения в световом и инфракрасном диапазонах.At present, more and more devices are being used to collect non-contact and high-speed temperature control instruments that register radiation in the light and infrared ranges

Precision surface characterization for finish cylindrical milling with dynamic tool displacements model

In this work a new approach to surface roughness parameters estimation during finish cylindrical end milling is presented. The proposed model includes the influence of cutting parameters, the tool’s static run out and dynamic phenomena related to instantaneous tool deflections. The modeling procedure consists of two parts. In the first stage, tool working part instantaneous displacements are estimated using an analytical model which considers tool dynamic deflections and static errors of the machine – tool-holder – tool system. The obtained height of the tool’s displacement envelope is then applied in the second stage to the calculation of surface roughness parameters. These calculations assume that in the cylindrical milling process, two different mechanisms of surface profile formation exist. Which mechanism is present is dependent on the feed per tooth and the maximum height of the tool’s displacement envelope. The developed model is validated during cylindrical milling of hardened hot-work tool steel 55NiCrMoV6 using a stylus profiler and scanning laser vibrometer over a range of cutting parameters. The surface roughness values predicted by the developed model are in good agreement with measured values. It is found that the employment of a model which includes only the effect of static displacements gives an inferior estimation of surface roughness compared to the model incorporating dynamic tool deflection

Газогидродинамические исследования скважин в условиях установившегося режима течения

Purpose: Interventional magnetic resonance imaging requires dedicated and MR-compatible devices. The guidewire is a key item for intravascular interventions. Mechanical stability, good visibility during real-time imaging, and RF safety are essential. A novel fiber-compound MR guidewire (GW) was evaluated in different MR-guided interventional scenarios. Materials and Methods: The GW (diameter 0.032") consists of a fiber-compound produced using a micropultrusion technique doped with iron particles and a 10-cm Nitinol tip. Several iron splints are additionally attached at regular distances to visualize GW-movement. A protective polymer jacket with hydrophilic coating covers the core material. As approved by the government committee on animal investigations, the GW was evaluated in 5 pigs. Under complete MR-guidance, catheterization of the carotid and renal arteries, segmental arteries of the kidneys, the contralateral inguinal artery, and the left ventricle was performed using real-time gradient echo sequences in a 1.5 Tesla scanner. Different interventional applications including balloon dilatation, stent deployment, and embolization of small vessels were investigated. The time to probe the vessels under magnetic resonance imaging guidance and visibility of the GW are assessed. Handling and visibility under fluoroscopy were compared with a standard Nitinol guidewire as a benchmark. Results: On real-time magnetic resonance imaging, the iron-induced artifacts enabled a distinct visualization of the GW shaft and of its markings with a mean size of 2.6 mm and 5.4 mm, respectively. This facilitated fast navigation to the target vessels (averages: renal arteries 16 seconds, carotid artery 5 seconds, and contralateral inguinal artery 42 seconds.) with an exact depiction of the respective vessel. All interventional procedures were performed successfully. No GW-related side effects as kinking or breakage of the wire or GW induced blood-clotting were observed. All interventionalists assessed handling of the GW to be nearly equal in terms of stiffness, flexibility, and guidance compared with a standard Nitinol guidewire. X-ray visibility was less distinct but still diagnostically good. Conclusion: With the aid of the GW, different fully real-time MR-guided endovascular interventions become feasible