1,721,054 research outputs found
A Method for the Measurement of the k Factor in Lossy Piezoelectric Materials
No full textIn general the coupling factor k is a dimensionless parameter, defined as a particular combination of the dielectric, elastic and piezoelectric constants, and which may be useful for the internal energy conversion description in piezoelectric materials. In this paper, a method for k factor measurement in lossy materials is described: by using the 1D model of a piezoelectric element vibrating in the length extensional mode, it is shown that this parameter can be evaluated by measuring the velocity on the element external surfaces orthogonal to the wave propagation direction, and the voltage across the element, at the antiresonance frequency. The proposed measurement method was tested by using the same analytical 1D model to compute the coupling factor as a function of mechanical and dielectric losses; the obtained data show that the method gives good results for materials with any dielectric losses, while for very high mechanical losses the choice of the frequency at which the measurement is done is crucial
La modellistica della ceramica piezoelettrica come elemento attivo delle sonde a ultrasuoni
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Behaviour of the electromechanical coupling factor of cylinder shaped piezoceramics with different aspect ratios
No full textThe IEEE Standard on piezoelectricity defines the electromechanical coupling factor (k) in static conditions as the ratio between the energy converted from electric to mechanic form or viceversa. Recently, the authors have shown that this definition can be extended also to dynamic
cases, by analysing a rod piezoelectric element by means of a 1D distributed model. In this work, the dynamic coupling factor is computed for cylinder shaped piezoceramic elements of different aspect ratios by using classical 1D models and a 3D analytical model. It is shown that it can be correlated to the effective electromechanical coupling factor (keff) for any aspect ratio
Fe Analysis of a High Displacement Ultrasonic Actuator Based on a Flexural Mechanical Amplifier
No full textIn this work, a novel ultrasonic actuator, composed of a Langevin transducer and of a displacement amplifier vibrating in a flexural mode, is proposed, designed and experimentally characterized. The displacement amplifier is composed of a cylinder shaped base with the same radius of the Langevin transducer, of four arms, and of a thin disk acting as a displacement collector. The displacement amplifier is able to transform the almost flat axial displacement provided by the Langevin transducer at its back end into a flexural deformation that produces the maximum axial displacement at the center of its front end.
Design and analysis of the actuator have been performed by using a FEM software. In analogy to classical power actuators, the design criterion that has been followed was to separately design the Langevin transducer and the flexural amplifier at the same working frequency. Simulated results have shown that the proposed actuator presents two close working frequencies, which exhibits comparable maximum displacements even if with different deformed shapes. Measurements carried out on a manufactured prototype are presented and discussed
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
Design and Experimental Characterization of an Composite Longitudinal-Flexural Mode Ultrasonic Transducer
No full textIn this work a composite longitudinal-flexural mode ultrasonic transducer is proposed, designed and experimentally characterized. The transducer is composed of a Langevin transducer and of a displacement amplifier, which is composed of a cylinder shaped base with the same section of the Langevin transducer, of four arms, and of a thin disk acting as a displacement collector. The displacement amplifier is designed to convert the almost flat axial displacement provided by the Langevin transducer at its back end into a flexural deformation that produces the maximum axial displacement at the centre of its front end. Analysis and design and of the actuator are performed by using a FEM software. Besides the designed resonance frequency, the vibrational behaviour of the actuator is analysed also at a close frequency, where comparable performance are found. A prototype of the designed transducer is manufactured and experimentally characterized. Measurements of the electrical input impedance and of the displacement on the front surface are presented
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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