1,721,199 research outputs found
Self-excited piezoelectric cantilever oscillators
No full textWe describe a micromachined self-excited piezoelectric cantilever device whose oscillating frequency is in the audio range. The 2000 mu m X 2000 mu m X 2.8 mu m cantilever has a zinc oxide (ZnO) piezoelectric thin film between two aluminum (Al) layers on a supporting layer of low-pressure chemical-vapor-deposited (LPCVD) low-stress silicon nitride. The transducer and an amplifier that drives the cantilever via a driving electrode constitute a self-excited unit. If the gain of the amplifier is sufficient to overcome the loss of the transducer and the resonance frequency is in the amplifier passband, the device oscillates and produces significant acoustic output. The self-excited acoustic output transducer could serve as a sensor for environmental quantities such as relative humidity or chemical vapor concentration. Simulation results show that the gravimetric sensitivity exceeds 5000 cm(2) g(-1) when the whole cantilever is covered with the sorptive film
Piezoelectric cantilever voltage-to-frequency converter
No full textA micromachined piezoelectric cantilever acoustic device that functions as a microspeaker and a voltage-to-frequency converter has been designed, fabricated and tested. The 2 x 2 x 0.0047 mm(3) cantilever has a 1.3-mu m-thick zinc oxide (ZnO) piezoelectric thin film on a supporting layer of LPCVD low-stress silicon nitride. When measured with 8 VP-P (peak-peak) input drive, the sound pressure level (SPL) of the cantilever microspeaker output is higher than 70 dB at 5 kHz at a distance of 0.5 cm. The microspeaker also can be used as a voltage-to-frequency converter by the addition of a silicon top plate and an aluminum (Al) sputtered layer on the backside of the cantilever. The resonant frequency of the microspeaker is changed by the potential applied between the top plate and the backside Al layer. As the potential is changed from 0 to 40 VP-P, the resonant frequency shifts down from 14.5 to 11.5 kHz. In the potential range of 15 to 25 VP-P, the frequency shift is fairly linear with the potential change and the sensitivity (frequency shift/applied potential change) is 200 Hz/V around 13 kHz. (C) 1998 Elsevier Science S.A. All rights reserved
Piezoelectric cantilever acoustic transducer
No full textWe present a piezoelectric acoustic transducer fabricated on a bulk-micromachined cantilever diaphragm. Use of the cantilever as a supporting diaphragm produces a highly sensitive microphone. In addition, when the device is driven electrically as an output transducer, a microspeaker, the relatively large deflections produce significant acoustic output. A voltage-to-frequency converter has also been demonstrated with piezoelectric cantilever transducers. The 2 x 2 x 0.0047 mm(3) micromachined transducer has a zinc oxide (ZnO) piezoelectric thin film on a 1.5 mu m thick cantilever diaphragm, made of LPCVD low-stress silicon nitride. The measured cantilever microphone sensitivity is fairly constant around 3 mV mu bar(-1) in the low-frequency range below the first resonant frequency, which occurs at 1.8 kHz. The microspeaker output is approximately 100 dB SPL at 4.8 kHz and 12 VP-P (peak-peak) input drive. The voltage-to-frequency conversion is accomplished by the addition of a conducting plate and an aluminum (Al) sputtered layer on the underside of the cantilever. The resonant frequency of the microspeaker is changed by the potential applied between the top conducting plate and the lower Al layer. As the potential is changed from 0 to 40 VP-P, the resonant frequency shifts down from 14.5 kHz to 11.5 kHz while the amplitude of the output pressure is increased by 12.5 dB SPL. In the potential range of 15 to 25 VP-P, the frequency shift is fairly linear with the potential change and the sensitivity (frequency shift per unit applied potential change) is 200 Hz V-1 around 13 kHz
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
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
- …
