1,720,963 research outputs found
Flexible CMUT as smart tool for nondestructive testing of aircraft composite structures
No full textIn avionics, safety is a crucial aspect and nondestructive testing (NDT) is a mandatory inspecting procedure to ensure the quality of materials before and during the lifetime of the aircraft, evaluating both the status of the materials and the degradation of the different parts of an aircraft. Especially in recent composites like Carbon Fibre Reinforce Plastics the presence of defects or the disbonds caused from accidental impacts can be very dangerous for the integrity of the wings, fuselage, etc. Among the different methods implemented in non-destructive testing, ultrasonic testing is the most common sub-surface technique to detect defects in welds, fittings, joints, bolts and adhesive bond quality. Capacitive Micromachined Ultrasonic Transducers (CMUTs) can be utilized to this end, thus permitting portable and potentially low-cost inspection. In this work, we present the fabrication and characterization of flexible CMUTs, and we discuss their potential use in NDT probes to be embedded directly on the aircraft to allow continuous and real-time monitoring of the different parts of an aircraft
Demonstration of PolyimideBased Flexible CMUT Operation on Curved Substrates
No full textCapacitive micromachined ultrasonic transducers (CMUTs) represent a class of ultrasonic devices widely investigated for several applications such as medical imaging and non-destructive material inspections. Although many improvements, the possibility to successfully operate on nonplanar surfaces still remains challenging. In this respect, flexible electronics can represent a unique ally to enable the manufacturing ultra-thin highly conformable CMUTs. In this paper, we demonstrate a fully flexible fabrication process for a PI based CMUT device and a preliminary characterization. This flexible CMUT technology was conceived to achieve a final device composed of only two materials, i.e., Titanium for the electrodes and PI for the membrane and the backplate. The CMUT cavities were realized by Aluminium sacrificial release. We fabricated flexible CMUT test devices consisting of 7 membranes 50μm in diameter laying onto an 8μm-thick backplate. This configuration can allow the bending of the devices on very small curvature radii (down to 1 mm)
Dielectric Characterization of Structural and Passivation Films for Flexible CMUT Microfabrication
No full textPolymer-based CMUT microfabrication approaches allow low-cost fabrication of flexible transducers. However, they are characterized by processing limitations mainly related to the low glass transition temperature of polymers, reducing the possible choice of materials that can be used for electrodes and in-cavity passivation layers, the latter having a major impact on transducer performance and reliability. In this paper, we experimentally evaluate the electrical properties of these two materials in terms of dielectric dispersion and losses, and high electric field response with respect to state-of-the-art materials
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Fabrication and Characterization of Capacitive Micromachined Ultrasonic Transducers Integrated on Ultra-thin and Flexible Substrates
No full textPolymer-based microfabrication approaches have been recently proposed as a low-cost alternative to traditional Capacitive Micromachined Ultrasonic Transducers (CMUT) fabrication methods. In most of the CMUT structures fabricated using such approaches, the electrodes passivation is achieved by a spin-coated polymer layer, with dielectric properties typically unsuitable to withstand the high in-cavity electrical fields. Moreover, typical layer thicknesses achievable by spin-coating bring to a significant increase of the effective gap height, inducing a very high collapse voltage and thus the need to use unpractically high operating voltages. In this paper, we investigate a process aimed at fabricating flexible CMUTs, potentially enabling high-performance, low-cost, curved, and ultra-miniaturized transducer configurations. In the proposed process, CMUT fabrication is carried out on an ultra-thin Polyimide substrate spun on a silicon wafer. The electrodes passivation is achieved by a thin SiO2 layer with excellent dielectric properties. A thin layer of SU-8 is used for the membrane fabrication and for sacrificial etch holes sealing. The devices are mechanically peeled-off from the wafer at the end of the process
- …
