1,721,055 research outputs found
On the piezoresistance coefficients of holes in Ge
No full textThe aim of this letter is to include the contribution of the optical phonon scattering mechanism in theory of piezoresitive effect for the case of holes in covalent semiconductors. In this way a more complete study of the dependence with temperature of the piezoresistance coefficients is made possible and a comparison between theory and experiment is carried out
Sensori e trasduttori a film spesso
No full textE' riportata una rassegna riguardante sensori a film spesso e tecnologia a film spesso. Essa intende illustrare conoscenze e processi sviluppati in attività che coprono un arco di tempo poco più che decennale ma in rapida, crescente espansione
Thick-film sensors: an overview
No full textSensors form a vital part of any measurement and control system,. Demand for sensors generally are increasing, but particularly for rugged, reliable, integrated sensors for computer control systems.Among the various sensor technologies, thick-film technology (TFT) does not really offer conceptually new sophisticated solutions, but does offer several appreciale capabilities, e. g., flexibility in chice of materials and design, easy integration with electronic circuits and packaging.This paer illustrates some specific features of TFT for sensor manufacture and overviews most of the types of devices used or developed at present. Moreover, some new sensors, which might be conceived and developed in the near future, are suggested
Some uniaxial piezoresistive effects in p-type silicon
No full textSome experimental results obtained at 300 K and 77 are presented regardind the silicon crystal doped with boron
Piezoresistive thick.film sensors
No full textSensors of strain-related mechanical quantities relying on the piezoresistive properties of thick-film resistors are being increasingly employed in various measuring and control systems; the purpose of this section is to explain how and why thick-film strain gauges differ from metal and semiconductor strain gauges widely employed in similar devices, and to remark the specific methods and materials enabling the design of variety of new classes of sensors for pressure, force weight and acceleration. The potentials of this technology are are illustred by many examples. It is clear that this class of sensors has not reached yet his full potentials; on one side performance of piezoresistors might be improved with satisfactory models of the physical behaviour of thick film resistors, on the other hand we see a continuous search of new materials and structure for increangly integrated and small sensors. However piezoresistive sensors are the field where the possibility of a dynamic evolution of thick film technology as an advanced sensor technology has been demonstrated by a variety of new sensors developed in a short lapse of time
Thick-film piezoelectric actuator for micripositioning
No full textDriven by the versatility of conventional thick-film technology , this work was aimed at investigating the application chances of the electric field induced strains in ferroelectric (thick-film) material layers. To this end an experimental investigation is described, which concerns the piezoelectric potenstial of PZT thick-films, screen printed and fired on ceramic substrates, for applications in actuator development. It was carried out on a structure consisting of an alumina plate, clamped as a cantilever beam, the faces of which were supporting two symmetrically placed ferroelectric layers. An interdigital electrode system, created inside them, enabled a polarization parallel to the substrate, hence bending occured in the regions of the beam that were coverted by the film when opposite driving voltages were applied. The deflection measurements and their voltage dependence are shown, together with: strcture design and realization, an analysis and the performance highlighted as a micro-displacement actuator
Dynamic torsion of laminar beams as a working principle for sensors
No full textABSTRACT: A method is presented in order to put planar structures in a pure torsion, bydirectly acting from their surfaces where a stress state is induced, taking advantage ofpiezoelectric layers that are integral with them. An experimental investigation was carriedout on alumina beams which, in a portion of their faces, support two ferroelectric layers ofPZT created using conventional thick-film technology processes. A suitable system ofcoplanar electrodes, embedded in the layers, promotes piezoelectric deformations parallel tothe substrate, induced by a voltage across them. At the layer-substrate interfaces,completely in-plane stresses are created and when they are conveniently oriented, the beamis prompted into pure torsion which takes on the characteristics of a vibration following theapplication of alternated voltage.Besides describing the design and realization of the sample beams, this work reports ontheir dynamic behaviour in torsion, the experimental set-ups and the procedures for itscharacterization. The results are discussed and highlighted in order to outline the potentialof the method with regard to using the realized beams as primary sensors for physicalquantities. To this end, proposals for possibl
The women scientists of Bologna
No full textShort biographies of four scientists women operating in Bologna (Italy) in eighteen century are reported. They refer to Laura Bassi (electricity and hydrodinamics topics), Anna Morandi Manzolini (reproduction of anatomical body organs), Maria Gaetana Agnesi (linguist and mathematician) and Maria Dalle Donne ((midwifery and newborn care)
New approach to the excitation of plate waves for piezoelectric thick-films devices
No full textA method is presented for exciting the propagation of plate waves in elastic guides. It is implemented in a device whose minimum working structure consists of a non-piezoelectric plane guide and two piezoelectric transducers operating as a generator and detector. The device is entirely in accordance with thick-film technology standard procedures. Both transducers are composed of a PZT ferroelectric layer deposited on a ceramic substrate and a suitable system of three coplanar metal electrodes placed inside the same layer. Beside setting the wavelength of propagation, the electrode system promotes piezoelectric deformations parallel to the substrate simultaneously contracting and extending contiguous active regions in the layer. Pure shear stresses are then induced on the involved guide surface, alternately distributed, with the spatial periodicity of the wave that will propagate in the guide. The propagation of several kinds of guided waves is possible so the selection of the one that meets a specific device design best is allowed. This work describes the design, realization and operation of a prototype structure consisting of an alumina plate guide and two pairs of piezoelectric thick-film transducers realized on it. The results related to the propagation of symmetric and asymmetric Lamb modes are reported. Moreover, the potential of the method is highlighted, emphasizing its effectiveness, easy implementation and application in the development of devices for the sensing and non-destructive testing areas
TRASDUTTORE PIEZOELETTRICO TORSIONALE
No full textOgetto dell'invenzione è un trasduttore piezoelettrico torsionale utilizzabile sia come attuatore che come sensore. Lo scopo dell'invenzione è la realizzazione semplice ed economica di tale trasduttore. Esso consiste di una struttura laminare che funge da substrato che in prossimità di un suo estremo supporta almeno uno strato di materiale piezoelettrico. Ad esso è associato internamente allo strato, almeno un sistema elettrodico interdigitato costituito da una pluralità di elementi orientato secondo una direzione inclinata rispetto all'asse longitudinale del substrato. L'ecitazione piezoelettrica dello strato induce in torsione la struttura laminare su cui esso è collocato
- …
