1,720,968 research outputs found
Elastic surface wave devices based on piezoelectric thick-films
No full textA study has been performed for the development of elastic-waves structures, involving screen printed and fired piezoelectric layers on nonpiezoelectric substrates, intended for new families of thick film sensors. This study approached the electroacoustic effects, i.e., the coupling between electromechanical. parameters of the layers and elastic properties of the substrate, related to the wave propagation. In this work, particular attention is devoted to devices implemented on alumina substrates where SAW as well as (symmetric and antisymmetric) Lamb's waves are generated. The realization processes and the performance characteristics of these structures are presented
A new ultrasonic composite transducer implemented with thick film technology
No full textA new ultrasonic transducer operating in air and fabricated by thick film technology is presented. It consists of a composite mechanical structure in which three active elements, made with planar alumina substrates supporting PZT-based piezoelectric films, behave as elastic guides. The active elements have a constant rectangular cross-section and are radially placed, 120 degrees apart. They are mounted between a rigid base (operating as the acoustic backing) and an alumina disk. On both sides of each substrate a piezoelectric layer las interdigital thick-film electrodes embedded in layer itself, so that it can be polarized parallel to the long side of the active element; consequently, it allows the creation of periodic surface stresses responsible for symmetric extensional strains in the alumina plates. The elements, synchronously driven in phase, form, with the disk, a vibrating resonant structure, which radiates acoustic energy perpendicular to the disk surface. The assembly of active elements, acoustic backing and radiating disk forms a composite ultrasonic transducer operating in air without the need of any acoustic matching layer. Among the prominent features offered by the transducer design are: a transduction efficiency of 25% at an exiting voltage of 100 V-p and a high directivity of the emitted beam
MAGNETORESISTIVE THICK-FILM SENSOR FOR LINEAR DISPLACEMENTS
No full textA new thick film material has been developed starting from Ni and Co powders in the ratio Ni:Co=3:1. The thermal treatment (in N,, up to 950 degrees C) of the metal films deposited on glazed alumina enables the in situ formation of the NiCo alloy. The films as created exhibit a high longitudinal (current I parallel to the field B) magnetoresistive response with Delta R/R approximate to 4% at 1.2 kGauss, and a negligible transverse one. The temperature coefficient of resistance (TCR) is approximate to 2700 ppm degrees C-1. These properties make the new material superior, from the point of view of magnetoresistive applications, to the Ni-based currently available thick film conductors. Contactless sensors for linear displacements have been created with the sensor's structure enclosing either Ni-based and Ni/Co-based meanders, having two magnetoresistive elements on each side of the substrate. This paper compares the magnetoresistive and thermoresistive properties of Ni and Ni/Co-based layers as well as the performances of the sensors in the range -20 to 120 degrees C
A THICK-FILM RESONANT SENSOR FOR HUMIDITY MEASUREMENTS
No full textThe paper describes the implementation and performance of a resonant humidity sensor relying on the piezoelectric properties of PZT-based thick films on an alumina diaphragm and the reversible hygroscopic behaviour of a cellulose acetate coating on the substrate. A shift of about 100 Hz of the resonance frequency f0 = 56.675 Hz (22-degrees-C, 35% RH) is obtained by changing the relative humidity from 10 to 95%, with a linear response over the whole range. In a time of 0.5 min the sensor changes its output when the relative humidity is varied from 10 to 40%. The dynamics of interaction between the water molecules and the organic film are discussed and related to the prompt response of the sensor to changes of environmental conditions. It is suggested that the joint exploitation of resonant techniques and thick-film technology can be a powerful strategy for manufacturing other inherently digital sensors of chemical species and biosensors
A NOVEL TORQUE SENSOR-BASED ON ELASTIC-WAVES GENERATED AND DETECTED BY PIEZOELECTRIC THICK-FILMS
No full textScreen-printed and fired PZT-based films have been used as the source and detectors of elastic waves near the surface of a torsional shaft. The change in wave propagation velocity due to applied torques has been taken as the operating principle of a torque sensor. The new opportunities opened by piezoelectric thick-film materials in the implementation of this novel sensor are demonstrated
RESONANT PRESSURE SENSOR BASED ON PIEZOELECTRIC PROPERTIES OF FERROELECTRIC THICK-FILMS
No full textThe paper describes the design, implementation and performance of a resonant sensor for gas-pressure measurement realized with screen-printed and fired PZT-based layers on an alumina diaphragm. The piezoelectric properties of these layers have been exploited to excite (with low voltage signals) and detect oscillations of the diaphragm. The layer configurations and associated vibrational modes of the diaphragm have been designed and a phase-locked loop (PLL) technique implemented in electronic circuits able to keep the resonant condition, despite the change of resonance frequency due to variation of the applied differential pressure. It is shown that for an adequate choice of operating frequency (i.e. of the vibrational mode) a good sensitivity and thermal stability of the sensor can be obtained; in this device, operating at frequency around 57.8 kHz, corresponding to the third-mode frequency f0.3, a shift DELTA-f0.3 = 650 Hz is found by changing the pressure from 0 to 900 mmHg. We found also that f0.3 changes less than 6 x 10(-3) by changing the temperature from 23 to 100-degrees-C. Moreover the sensor allows long-term measurements of static pressures without significant hysteresis effects
HYBRID THICK-FILM MAGNETORESISTIVE SENSORS
No full textThis paper describes a first prototype of a thick-film sensor using Ni-based pastes, whose resistance changes with the applied magnetic field. The magnetoresistive properties of thick films (Ital. Patent No. 9477/A86 (1986)) have been exploited for the development of hybrid sensors for proximity detection and rotational speed. The conditioning electronic circuits are specifically designed to compensate the relevant temperature effects, which otherwise would overwhelm the weak magnetoresistive effects. The electronic solution, though simple, proves to be very effective. On this basis integrated magnetoresistive sensors, with standard trimmable hybrid circuits and Ni-based films on the same substrate, have been developed in the framework of a collaboration aimed at looking for reliable integrated sensors for various applications. The design and operation of a prototype are described. Some areas of application of hybrid magnetoresistive sensors will be analysed
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
Preparation and properties of new thick-film magnetoresistive materials
No full textNixCoy-based thick-film magnetoresistors (TF-MRs) have been prepared with two different approaches: either the in situ alloy formation (and sintering) from fine powders of Ni and Co or the sintering of a Ni70Co30 powder obtained by co-reduction of Ni(II) and Co(II) acetates in diethyleneglycol. The pastes, printed on properly glazed alumina substrates in meander configuration, have been fired in N-2. The microstructure, electrical and magnetoresistive properties of these films have been studied. Both materials appear of interest for the implementation of contactless sensors
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