1,720,996 research outputs found
Impact of the variability of microfabrication process parameters on CMUTs performance
No full textAs CMUT technology moves towards the industrial phase, the robustness of the fabrication process becomes a key aspect to produce reliable and well-performing devices. CMUT arrays typically show a variability of the electromechanical and acoustic behavior among the transducer elements, which is mainly ascribed to tolerances of process-related parameters. This paper investigates the impact of process-related parameters variability on the performance of CMUT arrays, by proposing a local sensitivity analysis technique performed according to a Design of Experiments (DoE) approach based on Vertex Analysis. The sensitivity analysis is performed by simulating a Reverse-Fabricated CMUT using Finite Element Modeling (FEM), and computing the CMUT electromechanical parameters by varying the thicknesses of the front membrane layer, of the top and bottom passivation layers and of the sacrificial layer within a 10% tolerance range around the nominal set of values. The sensitivity analysis results are then compared to the variability observed in the data obtained characterizing a 256-element Reverse-Fabricated CMUT linear array for medical imaging
Development of a Passive Skin for Glass Building Surfaces in a Smart Electromagnetic Environment
No full textElectromagnetic metasurfaces (MTS), also referred to as Reconfigurable Intelligent Surfaces (RIS) in their dynamic form, have the potential to actively shape the wireless communication environment, particularly in 5G and 6G systems. They help overcome significant path loss issues, especially at millimeter-wave (mmWave) frequencies within the FR2 band. Our study focuses on MTS from a fabrication standpoint, highlighting the microfabrication methods employed to create a static and passive MTS prototype on a 6′′-optically transparent wafer substrate. This MTS design is intended for integration onto large glass surfaces commonly found in urban settings
Assessing the Microfabrication-Related Variability of the Performance of CMUT Arrays
No full textThis paper addresses the assessment of the variability of CMUT arrays’ electro-mechanical and acoustic performance, as related to the tolerance of the CMUT vertical dimensions due to the microfabrication process. A 3-factors 3-levels factorial sensitivity analysis is carried out to compute the main effects and the interaction effects of the moving plate thickness, the passivation layers thickness, and the sacrificial layer thickness, on the CMUT resonance frequency, collapse voltage, and static capacitance, as well as on the transmission and reception sensitivity amplitude and bandwidth and time delay in water-coupled condition. The analysis is performed by means of FEM simulations of the CMUT static behavior and dynamic response, and the findings are compared to experimental data
Extreme value analysis of the impact of the effective gap tolerance on the acoustic transmit and receive performance of reverse-CMUT arrays
No full textWe assess the impact of the fabrication-related variability of the thickness of the effective gap layers on the transmission (TX) and reception (RX) performance of a reverse-fabricated CMUT array by means of finite element analysis (FEA). The extreme values of the thickness of the passivation layers and of the cavity height, obtained by interferometry measurements during in-line wafer inspection, are applied to the simulated design of a reverse-fabricated CMUT array of circular cells. The analysis follows a 2-by-2 factorial approach to evaluate the variability of the TX and RX sensitivity amplitude, phase, and bandwidth caused by the fabrication tolerances, and compute the main effects and interactions of the effective gap layers
Characterization of Oscillations during Flow Boiling of Water in Parallel Microchannels
No full textSeveral challenges coexist in the field of flow boiling in microchannels, ranging from high superheat required for boiling incipience to boiling instabilities and early dryouts. The aim of this study is to mitigate or solve some of the challenges and develop an image-processing algorithm for analysis of boiling oscillations in multiple parallel channels. The experimental results were acquired on an array of 64 parallel 25×25 μm microchannels using a synchronized high-speed visualization and measuring system. The small cross section of the microchannels allowed only the formation of annular two-phase flow, and a computer algorithm was developed for tracking the meniscus oscillations during boiling. The applied image analysis focuses on reliability with the simultaneous use of brightness variation and brightness derivative along with image subtraction. Moreover, the images were preprocessed to determine the number of microchannels and their orientation with applying different filtering and Radon transformations. The data extracted from the visualization helped determine the peak-to-peak amplitudes and fundamental frequencies of the oscillating meniscus. The results exhibit lower amplitudes and higher fundamental frequencies with increasing heat flux. The mass flux was kept constant at 83 kg/m2s, whereas the heat flux varied from 150 kW/m2 to 250 kW/m2. The amplitudes and the fundamental frequencies of the meniscus oscillations determine the length and duration of microchannel with periodically alternating liquid and vapor phases
Realization of 3D silicon structures using a DRIE technique
No full text3D manufacturing at micron scale with very low roughness is a key enabling technology for the realization of micromechanical parts both for mechanical devices and for critical components such as printer head nozzles and high precision molds. The only currently available technique in the field of IC micro technology is nanolithography by two photon absorption [1]. We report the implementation of a technique based on multiple Deep Reactive Ion Ecthing (DRIE) [2] that allows to realize complex 3D geometries in silicon with a limited number of lithographic steps. A mold is demonstrated with 1/30 aspect ratio, 6 depth levels, including wafer-through features, with a dimensional accuracy of 5um
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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