121,476 research outputs found
Avaliação de sensor SAW de temperatura
Get PDFDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2009Este trabalho objetiva estudar sensores de temperatura sem fio baseados na tecnologia SAW (Surface Acoustic Wave - ondas acústicas superficiais). Os sensores SAW utilizados são baseados na sensibilidade dos parâmetros de propagação de ondas SAW em um substrato piezelétrico encapsulado em um circuito integrado. Estes sensores dispensam alimentação e podem ser interrogados à distância, sem fio. O conhecimento dos parâmetros do sensor é necessário para possibilitar o projeto de um interrogador para com ele formar um sistema de medição. Foi utilizado um único modelo de sensor, que opera na faixa de frequência de 433 MHz, com faixa de medição de (0 a 120) °C. Para a avaliação, foram utilizados equipamentos de radiofrequência ligados através de cabos e interface de conectores, exigindo o emprego de técnicas específicas para desacoplá-los, pois interferem significativamente no resultado das medições. Os critérios de avaliação do sensores se basearam nos diferentes indicadores de ressonadores e a comparação com sensores convencionais de temperatura. Chegou-se à conclusão de que a interface de comunicação entre equipamentos e dispositivo sob teste é muito relevante, alterando de forma significativa os resultados. Também concluiu-se que os sensores SAW tem resposta linear e comportamento estável com o tempo
Efficient all-optical wavelength conversion scheme based on a saw-tooth pulse shaper
Get PDFWe experimentally demonstrate the use of saw-tooth optical pulses, generated using a superstructured fiber Bragg grating, to achieve high performance and efficient all-optical wavelength conversion in a scheme based on cross-phase modulation in a highly nonlinear fiber, with subsequent offset filtering. Compared to the use of more conventional waveforms, such as Gaussian pulses, the purpose-shaped saw-tooth pulses allow an improvement in the optical signal-to-noise ratio of the wavelength-converted signal of around 15 dB as well as a more than 6-dB improvement in receiver sensitivity
Methods for automatic grading of saw logs
Get PDFThe aim of log grading for pricing is to apply an economic value based on volume and log grade. However, unlike many other commodities logs are hard to characterize into different grades. The reasons are: internal properties are hard to decide from the external appearance, the wood properties are often heterogeneous and there are a variety of different grading criterias. In Sweden, as in many other countries, the log grading is based on visual assessment of log characteristics, which can be considered intricate, time consuming and monotonous. Moreover, factors like increasing labour cost, structural changes among sawmills and the introduction of new technology, are all changing the possibilities and demands for the sawmills. New technology is important in order for the sawmill industry to remain competitive and therefore the log grading system for pricing needs to become more flexible and adaptable to the new technology. This thesis investigates two different methods using automatic measuring techniques to grade logs for pricing. In the first method a 3D log scanner is used to estimate log shape and this information is used to grade the log. The accuracy when using 3D log scanning to grade logs, according to the grades in the current Swedish national grading system, was comparable with but somewhat lower than manual grading of logs. Scanner data were used to estimate curvature type and compression wood content. Models based on log scanner data could discriminate between curvature types if the curvature was severe and bow height larger than 0.8 %. The models predicting compression wood were significant even though models using log end information were better. Analysis of whole stems showed that compression wood content was most pronounced near ground level and that stems with basal sweep more often had large amounts of severe compression wood. The second technique used acoustics and the results indicate that the technique has potential for grading logs by the stiffness of the sawn timber. The stiffness criterion was more important for spruce saw logs since spruce lumber is more often used for construction purposes. Using 3D scanning, acoustic methods and other techniques would probably reduce costs and make log grading for pricing more efficient. To enable this, the log grading system needs to be simplified and adapted to the new automatic technologies. Based on the findings in this thesis, a base for a new grading system for pine and spruce is proposed
Pulse mode shear horizontal-surface acoustic wave (SH-SAW) system for liquid based sensing applications
No full textIn this work, we describe a novel pulse mode shear horizontal-surface acoustic wave (SH-SAW) polymer coated biosensor that monitors rapid changes in both amplitude and phase. The SH-SAW sensors were fabricated on 36degrees rotated Y-cut X propagating lithium tantalate (36 YX.LT). The sensitivity of the device to both mass loading and visco-elastic effects may be increased by using a thin guiding layer of cross-linked polymer. Two acoustic modes are excited by the electrodes in this crystalline direction. Metallisation of the propagation path of the 36 YX.LT devices allows the two modes to be discriminated. Successive polymer coatings resulted in the observation of resonant conditions in both modes as the layer thickness was increased. Using the 36 YX.LT devices, we have investigated the application of a novel pulse mode system by sensing a sequence of deposition and removal of a biological layer consisting of vesicles of the phospholipid POPC. A continuous wave system was used to verify the accuracy of the pulse mode system by sensing a series of poly(ethylene glycol) (PEG) solutions. The data clearly demonstrates the ability of the 36 YX.LT pulse mode system to provide rapid measurements of both amplitude and phase for biosensing applications
Flexible saw microfluidic devices as wearable ph sensors based on zno nanoparticles
Get PDFIn this work, a new flexible and biocompatible microfluidic pH sensor based on surface acoustic waves (SAWs) is presented. The device consists of polyethylene naphthalate (PEN) as a flexible substrate on which aluminum nitride (AlN) has been deposited as a piezoelectric material. The fabrication of suitable interdigitated transducers (IDTs) generates Lamb waves (L-SAW) with a center frequency ≈500 MHz traveling in the active region. A SU-8 microfluidics employing ZnO nanoparticles (NPs) functionalization as a pH-sensitive layer is fabricated between the IDTs, causing a shift in the L-SAW resonance frequency as a function of the change in pH values. The obtained sensitivity of ≈30 kHz/pH from pH 7 to pH 2 demonstrates the high potential of flexible SAW devices to be used in the measurement of pH in fluids and biosensing
180 DEGREE REFLECTIVITY AND VELOCITY PERTURBATION OF THIN METAL DOTS.
No full textReflective arrays of rectangular thin metal 'dots' spaced in a regular or near regular grid pattern, such as have been used in surface acoustic wave resonators and in-line dot RACs on LiNbO//3 , are analyzed. The half-wavelength spacing of dots required leads to capacitative coupling between adjacent dots. The charge distribution induced on the dots by the passage of the SAW is presented including the coupling. The 180 degree SAW reflectivity of the dots and the SAW velocity perturbation through the dot array are given for a range of dot sizes. These are shown to be in good agreement with experimental results. The work establishes that the method of analysis can form the basis of the design of 180 degree reflective weighted dot arrays, allowing them to be implemented through varying dot density and/or by varying dot dimensions
Storage ring free electron lasers and saw-tooth instability
No full textWe show that Free Electron Lasers (FEL) operating with storage rings may counteract beam instabilities of the Saw Tooth (STI) type. We use a model based on a set of equations that couple those describing the FEL evolution to those accounting for the STI dynamics. The analysis provides a clear picture of the FEL-STI mutual feedback and clarifies the mechanisms of the instability inhibition. The reliability of the results is supported by a comparison with fully numerical codes. (C) 1999 Elsevier Science B.V. All rights reserved
Efficient all-optical wavelength converter using saw-tooth pulses
Get PDFWavelength conversion is a key WDM function which is used to avoid wavelength blocking, thus allowing greater flexibility in the network design. Wavelength conversion of an intensity modulated signal can be simply achieved by employing cross-phase modulation (XPM) on a CW beam placed at the desired wavelength, normally followed by a band-pass filter and a narrowband notch filter to reject the pump and the carrier frequency respectively
Saw Tester
No full textPatent for a device that tests and trains saws for cotton gins. Detects cups and kinks in the saw and prevent the saw from being burned
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
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