1,720,963 research outputs found
Air-Coupled Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) for High-Resolution Distance Sensing
No full textHigh-frequency airborne ultrasound enables high-resolution distance sensing for various applications, such as robotics, industrial automation, gesture control, and more. This paper presents a 1.5MHz, 12-element 2-D Piezoelectric micromachined ultrasonic transducer (PMUT) array for high temporal and spatial resolution distance sensing in air. Electrical impedance analysis and measured electroacoustic frequency response of the air-coupled PMUT array showed a resonant frequency fr of 1.5 MHz, an electromechanical coupling factor kT2 of 4.5%, and a -3 dB fractional bandwidth of 5% centered at 1.5 MHz, with high transmit and receive sensitivities of 70 Pa/V and 0.16 mV/Pa, respectively. Distance measurement on a curved surface using two matched PMUT arrays in pulse-echo proved the feasibility of sensitive and accurate high-resolution distance sensing in demanding scenarios
PMUT-Based System for Continuous Monitoring of Bolted Joints Preload
No full textIn this paper, we present a bolt preload monitoring system, including the system architecture and algorithms. We show how Finite Element Method (FEM) simulations aided the design and how we processed signals to achieve experimental validation. The preload is measured using a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) in pulse-echo mode, by detecting the Change in Time-of-Flight (CTOF) of the acoustic wave generated by the PMUT, between no-load and load conditions. We performed FEM simulations to analyze the wave propagation inside the bolt and understand the effect of different configurations and parameters, such as transducer bandwidth, transducer position (head/tip), presence or absence of threads, as well as the frequency of the acoustic waves. In order to couple the PMUT to the bolt, a novel assembly process involving the deposition of an elastomeric acoustic impedance matching layer was developed. We achieved, for the first time with PMUTs, an experimental measure of bolt preload from the CTOF, with a good signal-to-noise ratio. Due to its low cost and small size, this system has great potential for use in the field for continuous monitoring throughout the operative life of the bolt
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Design, Fabrication, Characterization, and System Integration of a 1-D PMUT Array for Medical Ultrasound Imaging
No full textMicromachined Ultrasonic Transducer (CMUT and PMUT) technologies are playing a fundamental role in the development of novel applications such as ultra-portable medical imaging systems. This paper presents the design, fabrication, characterization, and system integration of a 1-D PMUT array for low-frequency diagnostic imaging applications. The PMUT array was fabricated using a sol-gel PZT thin film-based MEMS technology from STMicroelectronics. The 1-D array was integrated into an ultrasound probe and acoustic characterization and imaging tests were carried out using the ULA-OP 256 open scanner. The two-way frequency response of the PMUT had a center frequency of 2.5 MHz and a -6dB fractional bandwidth of 81%, and peak transmit and receive sensitivities assessed at the transducer surface of 31 kPa/V and 3.2 mV/kPa, respectively. In vitro and in vivo scans of a tissue-mimicking phantom and of a carotid artery, respectively, were successfully carried out demonstrating the potentiality of this PMUT technology for medical imaging applications
Variations on the Author
Get PDF“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
Get PDFWe 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
Evaluating the Influence of PMUT Mechanical Support Properties on Power Conversion Efficiency in Ultrasonically Powered Implants
No full textMicromachined Ultrasonic Transducers (MUTs) are being explored as power converters in wirelessly powered biomedical implants. This paper investigates the role of mechanical support properties in piezoelectric MUTs (PMUTs) on their power conversion efficiency. For this purpose, a finite element model (FEM) of a PMUT array was developed and integrated with an equivalent circuit model (ECM). The study considered different mechanical support scenarios, from rigidly clamped to completely free. These were numerically analyzed and validated by impedance measurements and acoustic power transfer experiments on PMUT prototypes. The results show that reducing the mass of the mechanical support increases the Q factor, leading to a significant improvement in power conversion efficiency, with an efficiency increase factor of 5.6x from the clamped to the free case. This approach can potentially enhance overall power conversion efficiency, reduce the need for matching networks, and enable miniaturization in ultrasonically powered implants
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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