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March 1987 - present
January 1987 - present
January 1987 - present
Publications
Publications (151)
This paper describes a virtual instrument capable of the automatic and quasi-instantaneous classification of a vehicle according to category when it is driving along the road. The vehicle’s classification is based on accurate measurements of both the vehicle’s speed and its wheelbase. Our research is focused on achieving accurate speed and wheelbas...
In this paper, a new prospect using lead-free piezoelectric ceramics is presented in order to determine their behavior in piezoelectric-based road traffic energy harvesting applications. This paper will describe the low-cost and fully programmable novel test bench developed. The test bench includes a traffic simulator and acquires the electrical si...
New mixed composite conductors of compositions: Li 3 V 2−x [Cu] x (PO 4 ) 3 /C and Li 3 V 2−x [Nb] x (PO 4 ) 3 /C (x = 0.1; 0.2 and 0.3) have been synthesized by the sol-gel method using Citric and Oxalic acids as a primary carbon source and Carbon Black or Carbon Nano-Fibers as secondary carbon sources. The combination of these carbon forms with t...
A new virtual instrument (VI) has been designed to obtain the Fourier model of piezoelectric devices under test (PDUT) in road traffic environments, and the linear electrical model of the piezoelectric harvester circuit involved in energy harvesting applications. The VI provides a high grade of automatisation and high accuracy in the characterisati...
Infrared Thermography (IRT) is a widely used technique for the detection of temperature change patterns. In the present study, we are interested in its application to the non-invasive follow-up of temperature changes on emotionally stressed people. Nine subjects performed the arithmetic task of the Trier Social Stress Test (TSST) while IRT videos w...
Purpose
This study aimed to characterize the radiation exposure to patients and workers in a new vascular hybrid operating room during X-ray-guided procedures.
Methods
During one year, data from 260 interventions performed in a hybrid operating room equipped with a Siemens Artis Zeego angiography system were monitored. The patient doses were analy...
In the search of multiferroic materials with enhanced magnetoelectric response, the BiFeO3–Bi4Ti3O12 composite system has been proposed as a promising candidate. However, in order to ensure an effective coupling between the antiferromagnetic and the ferroelectric-order parameters, a high structural quality of the oxide heterostructure (well-matched...
A new Virtual Instrument (VI) system is presented in this paper. The VI is designed to obtain the linear electrical models of the piezoelectric elements involved in energy harvesting applications in road traffic environments. The system, the modelling and the verification methodology are described in this paper, comparing the obtained results. The...
Introduction
The development of biplane angiography systems is a huge advance in neurointerventional procedures but also a possible increase in patient doses.
Purpose
This work aims to evaluate dosimetric parameters associated with doses to patients during the first year of use of a biplane angiography system
Materials and methods
The angiography...
Introduction
Electron beams over an irregular surface produce localized hot and cold spots in the underlying medium due to scattering. This fact usually reduces the quality of the treatments. In practice, such sharp dose edges may be smoothed with an appropriately shaped bolus which has similar properties to the tissue when it is irradiated.
Purpo...
Introduction
When large volumes need to be irradiated multiple organs at risk are involved. There is no doubt about the preeminence for conformal index and sparing of critical structures for VMAT, but an alternative regarding the use of single or multiple isocenter shows a subject for detailed analysis.
Purpose
To compare VMAT in treatment of pelv...
In this paper a new computer controlled (C.C.) laboratory test bench is presented. The patented test bench is made up of a C.C. road traffic simulator, C.C. electronic hardware involved in automating measurements, and test bench control software interface programmed in LabVIEW™. Our research is focused on characterizing electronic energy harvesting...
Physiotherapy ultrasonic transducers are mainly composed by a piezoelectric ceramic bonded to a metallic thin membrane. These transducers vibrate at the thickness fundamental mode. The acoustic efficiency depends on the vibration pattern of the transducer face in contact with the human skin. Radial modes excited by the piezoceramic disc introduce a...
Electrical response changes due to the incorporation of alkaline-earth oxides in the vanadium–molybdenum tellurite glassy matrix have been studied. The results are explained by analyzing the electric formalisms representations. A non-straightforward relationship to the modifier oxide ionic radius was found and the results suggest poor charge carrie...
Glasses of composition 0.8 [xBaO.(1 − x)MgO]. 0.2TM.2TeO2 with TM: MoO3, WO3, V2O5 or Nb2O5 (x = mol content) were obtained by the melt quenching technique. Raman Spectroscopy, Density and Differential Scanning Calorimetry were used to infer their microscopic structure and electrical properties were studied using Impedance Spectroscopy. Some singul...
Se ha sintetizado titanato de bismuto puro y dopado con cerio, por el método de reacción de estado sólido. Se ha observado la presencia de fase romboédrica en los o de fases binarias con cerio y óxidos de bismuto en función del contenido de Ce y de la temperatura de calcinación. Las muestras dopadas con el 0,05 de cerio se someten a un tratamiento...
Resumen
En este trabajo se estudian diferentes tipos de causas de la degradación de materiales estructurales, y mediante la utilización de cerámicas piezoeléctricas se analizan el tipo, la magnitud y la distribución de microgrietas asociados a cada una de ellas. Los resultados se complementan con estudios adicionales (SEM, EDX, resistencia mecánica...
Son bien conocidas las aplicaciones de los ultrasonidos en tratamientos médicos y estéticos de piel y de movilización subcutánea de tejidos grasos. El transductor tipo utilizado consta de un disco piezoeléctrico adherido a una línea de retardo metálica en forma de cápsula. El diseño de la cápsula es un punto crítico, ya que el elemento piezoeléctri...
Carbon nanotubes (CNTs) growth on piezoelectric AlN substrates has appeared to be important in sensing purposes using acoustic technology. CNT forests can act as sensing layers with high surface active area. We study such growth by using Fe as active catalyst and Ti, Cr and Al as catalyst underlayers. All underlayers enable CNT growth at temperatur...
En este trabajo se caracterizan electromecánicamente materiales piezoeléctricos comerciales individuales y en diferentes configuraciones para su potencial uso en dispositivos de transformación de energía mecánica en eléctrica, con el objetivo de almacenarla y usarla en la alimentación de sistemas electrónicos de bajo consumo.
Se plantean modelos op...
Growing carbon nanotube (CNT) forests on metals for integrated circuits interconnections or active layers applications is currently a challenge. CNT forests easily develop on insulators but their growth on metallic substrates is subject to interdiffusion and wettability effects that hamper the formation of the catalyst nanoparticles. This paper rep...
Ceramic composites of the mixed system (BaTiO3)x(NiFe2O4)1−x (x = 1, 0.8, 0.65, 0.6, 0.5, 0.2, 0) have been prepared by hydrothermal synthesis and characterized through dielectric and magnetic measurements. It is shown that, when compared with the first-order phase transition of pure BaTiO3, the ferroelectric response of this mixed system is dramat...
In this paper we present the study of the glassy systems of formula: xMgO(1 − x)(0.5V2O5·0.5MoO3)2TeO2, with (0 < x < 1). The aim of the work is to understand the relationship between in the induced changes in the glassy matrix by the incorporation of MgO in a vanadium–tellurite glass and the electrical response of the material. It has been found t...
In the complex multicomponent formulation of standard commercial varistors used in high tension devices, those based in the ZnO–Bi2O3–Sb2O3 (ZBS) ternary system, the presence of iron is ordinarily prevented in any of its plausible sources: dopant, impurity and/or unwanted contamination. Otherwise the material undergoes a systematic degradation in i...
When electrical characterization of thin conductive coating is carried out, it requires an effective electrode configuration that prevents design problems due to low thickness, such as short circuits or electrode diffusion. In this work, two electrode configurations were carried out, surface and volume configurations, in order to compare and demons...
The structural, electrical, and magnetic properties of magnetite nanoparticles, with crystallite sizes 30, 40, and 50 nm, are studied. These crystallite sizes correspond to average particle sizes of 33, 87, and 90 nm, respectively, as determined by TEM. By HRTEM images, it is observed that grain boundary widths decrease as crystallite size increase...
espanolEn este trabajo, se estudia la evolucion desde su inicio de las fases de hidratacion de materiales cementicios a los que se incorporan cenizas volantes y escorias procedentes de centrales termicas. Mediante medidas de espectroscopia de impedancia electrica (EIS), y de difraccion de rayos X (XRD), se analiza el proceso desde la etapa inicial...
KNL-NTS powder with (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 stoichiometry was prepared following the conventional ceramic method of mixing carbonates and oxides. KNL-NTS powder synthesis is carried out in solid state at 700 ºC for 3h. To obtain ceramic samples with different porosity the sintering of pellets is carried out in air at different tem...
In this paper we study the structural and electrical behavior of glass-ceramic material of general formula: xMgO (1-x) (0.5V2O5.0.5MoO3)2TeO2 (0≤x≤0.9) through measurements of density, molar volume, oxygen packing density (OPD), differential scanning calorimetry (DSC) and Raman spectroscopy: electric behavior was studied by impedance spectroscopy....
The optimal topological structure of the piezoelectric materials involved in road traffic harvesters is covered with the linearized models obtained using practical measurements. The behavior of that harvesters is analyzed in order to obtain practical results that guarantees the optimal tracked maximum power point of operation. Our specifically desi...
Practical models of the input stage energy harvesting circuits, based on piezoelectric elements involved in road traffic environments, were obtained and optimized. The availability of power harvested at the optimal point of operation is determined assuming regular traffic, generated using a test bench designed to emulate the real road traffic. In o...
We have developed a system to verify that the Doppler kinemometers installed on the highway system are functioning correctly. An EMBEDDED SERVER is installed next to the test kinemometer (subject of the study) and the verification tasks are programmed and sequenced (in minutes, hours, days, months, etc) through a remote CLIENT subsystem. As the tas...
In this work, the hyperfine quadrupole interaction at Ta-doped PbTi1−xHfxO3 polycrystalline samples is studied for the first time. Powders with x=0.25, 0.50 and 0.75 were prepared and characterized by X-ray diffraction analysis. Perturbed Angular Correlation (PAC) analyses were done as a function of temperature, using low concentration 181Ta nuclei...
CaCu3(Ti4−xHfx)O12 ceramics (x = 0.04, 0.1 and 0.2) were prepared by conventional synthesis (CS) and through reactive sintering (RS), in which synthesis and sintering of the material take place in one single step. The microstructure and the dielectric properties of Hf-doped CCTO (CCTOHf) have been studied by XRD, FE-SEM, AFM, Raman and impedance sp...
CaCu3Ti4O12 (CCTO) was prepared by a conventional synthesis (CS) and through reaction sintering, in which synthesis and sintering of the material take place in one single step. The microstructure and the dielectric properties of CCTO have been studied by XRD, FE‐SEM, EDS, AFM, and impedance spectroscopy to correlate structure, microstructure, and e...
En este trabajo se presenta el estudio realizado para determinar los modelos electricos equivalentes de materiales de
tipo piezoelectrico, para evaluar su capacidad como elementos generadores de energia electrica. Los diferentes modelos
desarrollados a partir de los resultados experimentales registrados, se han utilizado para obtener la estructura...
En este trabajo, se estudia como generar de manera acelerada fenomenos expansivos en el interior de materiales cementicios
compuestos considerando la posibilidad de utilizar como elementos de adiccion tanto cenizas volantes como escorias. Se
presentan resultados de la monitorizacion de estos procesos desde su etapa inicial y se caracterizan quimica...
Se ha desarrollado un sistema electronico computerizado, portatil y de bajo consumo, denominado Medidor de Velocidad de
Vehiculos por Ultrasonidos de Alta Exactitud, VUAE. La alta exactitud de la medida conseguida en el VUAE hace que pueda
servir de medida de referencia de la velocidad de un vehiculo circulando en carretera. Por tanto el VUAE puede...
Eutectic temperature and composition in the CuO–TiO 2 pseudobinary system have been experimentally determined in air by means differential thermal analysis (DTA), thermogravimetry (TG) and hot-stage microscopy (HSM). Samples of the new eutectic composition treated at different temperatures have been characterized by X-ray diffraction (XRD) and X-ra...
In this work the dielectric properties of concrete with and without chlorides as a function of their water contents were studied by the Electrical Impedance Spectroscopy (EIS). Specimens of cement paste with different water/cement ratio and chlorides content was analyzed. After drying the specimens, the rehydratation was controled by the relative w...
With the objective to advance in the study of dimensional properties in ferroelectric materials, we have prepared a new kind of materials, which are going to be called “pseudoceramic”. These are, basically, composites that are constituted of milled single crystals packed tightly in different polymers. In these materials, we control, between other f...
Estudios recientes sobre la transición de fase en SrZrO3 haciendo uso entre otras técnicas de Difracción de Rayos X y de Neutrones, junto con espectroscopías de correlación angular o espectroscopía Raman, ponen de manifiesto que el diagrama de fases de estos compuestos no es simple, ni está claramente definido. Las temperaturas de transición propor...
The method to obtain electrical equivalent models of piezoelectric materials used in energy harvesting road traffic environment is presented in this paper. The experimental results are processed in order to determine the optimal topological structure and technology of the semiconductor elements used in the input stage of the power harvesting system...
The development of piezoelectric sensors for high frequency requires to work with very thin samples of material. At this thick nesses, the stress concentration produces strong perturbations in the materials, and the origin oF a non linear response, which depends field on working conditions. With the goal to advance in the knowledgement of this phen...
In this paper a comparative study of the hydration process in a very early age, first 20 hours, between a conventional cement paste and its equivalent with a replacement of slag of about 12%, is done. The study was undertaken through semiadibatic calorimetry, electrical impedance spectroscopy and X-ray diffraction. It shows that using electrical im...
The magnetoelectric coefficient, α = dE/dH, of different compositions of BaTiO3-CoFe2O4 composites was measured by using the dynamic method and also a new method developed in our laboratory which is based on pulsed magnetic fields. The values obtained by both methods are congruent, with the largest magnetoelectric coefficient obtained for the compo...
In this work, the dielectric behaviour and capacitance–voltage (C–V) curves under an applied DC bias field of 1wt% Nb-doped CaCu3Ti4O12 ceramics have been studied. The dielectric properties reveal the existence of grain boundaries of different electrical nature. A new model is proposed to simultaneously explain the presence of insulating and conduc...
In this work a complete piezoelectric and electromechanical characterisation of zirconium rich Nb 2 O 5 doped PZT ceramics obtained by means of new techniques is presented. The objective is to establish the correlation existing between the microscopic structure of these ceramic materials, the small variations in the cationic compositions and the di...
In the present work, the theory of charge transport through active interfaces is used to study the electronic properties of ZnO-based varistors. It has been observed that for a certain range of sintering temperatures the microscopic electrical response of the material is constant, so that the macroscopic response is microstructure controlled. This...
En este trabajo se define y propone un banco de ensayos que permite testar materiales piezoelectricos para aplicaciones
viales en sus diferentes configuraciones en un rango de velocidad entre los 14 y los 170 km/h, lo que cubre sobradamente
las condiciones de trafico real. Tanto el control del variador de velocidad del motor trifasico que realiza e...
In this paper a comparative study of the hydration process in a very early age, first 20 hours, between a conventional cement paste and its equivalent with a replacement of fly ash of about 7.9%, is done. The study was undertaken through semiadibatic calorimetry, electrical impedance spectroscopy and X-ray diffraction. It shows that using electrica...
Magnetoelectric composites were synthesized from piezoelectric BaTiO3 and ferrimagnetic NiFe2O4. These two phases are mixed, mechanically milled and heat treated. A characterization is made by means of electronic microscopy and x-ray diffraction. The results of the magnetic, electric, ferroelectric and piezoelectrical response of two different comp...
The obtaining of ZnO-Bi2O3-Sb2O3 (ZBS) based varistor thick films with high non-linear properties is constrained by the bismuth loss by vaporization that takes place during the sintering step of these ceramics, a process which is yet more critical in the thick film geometry due to its inherent high are/volume ratio. This volatilization can be contr...
The microstructure and electrical properties of varistors composed of (95-x) ZnO + x Pr6O11 + 5 CoO (ZPC), (x = 0.1, 0.5 and 1.0) and sintered at 1300 and 1350 °C, were investigated. According to X-ray diffraction, several phases (ZnO, Pr2O3 and Pr2CoO4) are present when x = 1.0. Using Scanning Electron Microscopy, all of these compositions contain...
La obtención de varistors en lámina gruesa basados en ZnO-Bi2O3-Sb2O3 (ZBS) y con propiedades altamente no-lineales está limitada por la perdida de bismuto por volatilización durante la sinterización de estos cerámicos, un proceso que es todavía más crítico en la geometría de lámina gruesa debido a su elevada relación área/volumen inherente. Dicha...
The objective of this study is to determine the influence of partial substitutions of Zr by Hf in the perovskite-type crystalline structure of PbZrO<sub>3</sub>. Different samples over the whole composition range (0 les x les 1) in the PbZr<sub>x</sub>Hf<sub>1-x</sub>O<sub>3</sub> family have been prepared. Phase transitions have been determined by...
Fe3+- or Nb5+-doped CaCu3Ti4O12 (CCTO) ceramics show higher values of both room-temperature (RT) grain conductivity and dielectric constant than undoped ceramics. Microstructural and structural characterization combined with magnetic properties reveal the coexistence of two components that seem relevant for the dielectric behavior of the material....
In this paper we evaluate different mortars, with varying degrees of damage by the action of ice-thawing cycles, and analyzing their status through various methods to assess usual. The results obtained by these methods are compared to an analysis by means of the technique of impedance spectroscopy and we analyzed the ability of this technique to as...
In this paper we evaluate different mortars, with varying degrees of damage by the action of ice-thawing cycles, and analyzing their status through various methods to assess usual. The results obtained by these methods are compared to an analysis by means of the technique of impedance spectroscopy and we analyzed the ability of this technique to as...
The aim of this work was to develop a methodology for the characterization of complex piezocomposites under external mechanical forces. In this specific procedure the samples were axially loaded in a universal mechanical test machine and monitored with an electrometer. The force versus displacement and the generated charge versus the applied force...
Thick films of ZnO-based ceramic varistors prepared by tape casting technique typically show a poor electrical response that
still limits their application as protective devices. The excessive volatilization of Bi2O3 during sintering at high temperatures, especially dramatic in the film geometry due to its high area–volume ratio, is found
to be the...
Even though the PZT ceramic system has been thoroughly studied and modified with different additives, no numerous reports have been published focusing on the PZT double ‘soft’ modification with La3+ and Nb5+ (PLZTN). In this paper, we explore the structural, morphological, dielectric, ferroelectric and piezoelectric properties of the PLZTN system f...
In this work, different mortars with different degrees of damage brought about by the action of the freeze-thawing cycles are evaluated. Analysis of its state is carried out by different usual evaluation methods. Results obtained through these methods are compared with the electrical impedance spectroscopy. Moreover, this non-destructive technique...
In this work, we present a compositional and electrical study of mixed presinterized systems following a solid-state and sol-gel rule in order to achieve mixed morphotropic PZT compositions with other compositions in different proportions. A complete characterization of the electrical response of the different PZT compositions is presented, as is t...
This work deals with the electrical properties of SnO2-based varistor systems with different area–volume (A/V) ratio of the green compact. The influence of A/V ratio specially
on microstructural homogeneity and different diameter-thickness (D/t) ratio of sintered compact mainly as a requisite to the
existence of non-Ohmic properties is evaluated. T...
Electroceramics with ferropiezoelectric and ferri-ferromagnetic properties have been studied. These ceramics consist of two phases, a ferroelectric one (commercial BaTiO3) and a ferromagnetic one (MFe2O4, with M = Ni, Zn, Co, obtained through co-precipitation methods), which are later mixed using mechanical milling. A characterization of the previo...
In this work a comparative study of undoped CaCu3Ti4O12 (CCTO) and doped with Fe3+(CCTOF) and Nb5+(CCTON) ceramics, was aimed to modify the electronic transport. XRD patterns, FE-SEM microstructural analysis, impedance spectroscopy and I–V response curves were afforded to correlate the microstructure with the nonlinear I–V behaviour. The appearance...
In the composition region of PZT rich in zirconium, (0.05 < x < 0.35) there are two phase transitions. The first takes place between the high and low temperature Rhombohedric phases FRL–FRH both of which are ferroelectric, and the second between the high-temperature ferroelectric Rhombohedric phase and the cubic phase which is paraelectric (FRH–PE)...
Thick films of ZnO-based varistors have been prepared by screen printing and tape casting techniques. The manufacture of varistor thick films by screen printing shows two critical problems; the excessive volatilization of Bi2O3 during the sintering step, due to the exaggerated area–volume ratio of these devices and the lack of density of the green...
The present work deals with the electrical characterization of undoped Zn2SnO4 (ZTO) and SnO2-doped ZnO bulk ceramics in order to clarify the role played by the ZTO spinel type phase in the electrical response of these materials. For this purpose, SnO2-doped ZnO materials with SnO2 concentrations of 0.1, 1 and 10 mol% have been prepared by co-preci...
Recent studies of the phase transitions in SrZrO3 using X-ray and Neutron Diffraction, together with Perturbed Angular Correlation spectroscopies reveal that the phase diagram of this compound is not simple. The temperatures of the transitions appear to be highly dependent of the thermal history. In this work we present for the first time a study o...
The recent interest in room temperature ferromagnetic semiconductors has led to an intense research in ZnO-based ceramics doped with different magnetic elements such as Mn, Co, Ni, etc. An improvement of the semiconductor behaviour of ZnO is also necessary to obtain good electrical properties and in this way tin oxide is expected to increase the el...
BaTiO3-CoFe2O4 composites synthesized by the ceramic method showed a magnetoelectric effect. The CoFe2O4 powders were synthesized by coprecipitation and mixed with Aldrich reactive quality BaTiO3 powders with particle size < 2 μm. The coupling of the magnetostrictive and the piezoelectric phases via elastic deformations of the properly polarized co...
One of the earliest technological applications of ferroelectric materials was in the area of electromechanical transducers, the physical basis of which is the piezoelectric effect. PbZrO3-PbTiO3 (PZ-PT) or PZT ceramics with base compositions close to the morphotropic phase boundary are potential materials for many applications such as transducers a...
We have characterized electroceramics of PNZT rich in zirconium, piezoelectric and dielectrically. We show the results obtained based on the field of excitation and the cycle of measurement and analyze the answer in each composition. For some of the samples, the relaxation of the initial state of polarization reduces the initial long-range ordered...
Bi 6 Ti 3 WO 18 is a ferroelectric phase which belongs to the Aurivillius family like Bi 4 Ti 3 O 12 or Bi 2 WO 6 layered phases. The present work is focused on the study of the sintering behaviour as well as on the electric and ferroelectric properties of this m = 2 Aurivillius phase. Ceramic samples were obtained by the conventional mixed oxides...
Sn:ZnO thin films with different Sn concentrations were grown by pulsed laser deposition (PLD) onto single-crystal Si(001) substrates at an oxygen pressure of 2 × 10–2 mbar and substrate temperature of 600 °C. The targets used were high density Sn:ZnO pellets with different Sn concentrations produced by mixing ZnO and SnO2 by conventional ceramic r...
Thick film varistors based on the ZnO-Bi2O3-Sb2O3 system have been prepared by screen printing on dense alumina substrates. Different processing parameters like the paste viscosity, burn out and sintering cycles, green and sintered thickness, have been studied to improve the processing of ZnO-based thick film varistors. Starting powders were pre-tr...
Tin (IV)-doped zinc oxide ceramics find its main application as specific gas sensor devices. The sensor ability of the mixture and its particular affinity for a particular gas (selectivity) depends both on the crystalline phases in the microstructure of the sintered semiconductor and on the degree of tin incorporation into ZnO lattice. By means of...
In this work a complete piezoelectric and electromechanical characterisation of zirconium rich Nb2O5 doped PZT ceramics obtained by means of new techniques is presented. The objective is to establish the correlation existing between the microscopic structure of these ceramic materials, the small variations in the cationic compositions and the diffe...
Broadband admittance spectroscopy measurements of ZnO-based varistors are analyzed in terms of charge transport theory through double Schottky barriers, hence obtaining empirical evidence on the minority of the shallow donor in n-type ZnO. The dominant defect species is found to be a deep donor, in agreement with recent first-principles calculation...
In the present work, a ‘soft-doped’ PZT ceramic system with a near MPB Zr/Ti ratio of about 54/46, is characterized when simultaneously modified with Lanthanum (La) and Niobium (Nb) at the same doping level, x = 0.4, 1.0 and 1.4 mol%. X-rays diffraction patterns showed the rombohedral/tetragonal perovskite phase coexistence as reported for Zr/Ti ra...
This article describes a virtual instrument that automates the obtaining of real vibration patterns of a piezoelectric device, based upon a set of displacement measurements collected for a discreet group of points of its surface. The real vibration pattern information is not easy to model when nonlinear effects appear in the piezoelectric devices....
In this paper we present a comparative analysis of the magnetic interactions and reversal mechanisms of two different systems: NdFeB-type alloys with grain sizes in the single domain range and Fe-SiO2 nanocomposites with Fe concentrations above and below the percolation threshold. We evidence that the use of the coercivity as the main parameter to...
In this work measurements on a piezoelectric sample in dynamic behavior were taken, in particular, around the frequencies of resonance for the sample where the nonlineal effects are accentuated. Dimension changes in the sample need to be studied as that will allow a more reliable characterization of the piezoelectric samples. The goal of this resea...
Broadband electrical response analysis and charge transport theory through double Schottky barriers in ceramic semiconductors, are both used in order to separately study the grain boundary, depletion layer, and bulk grain regions of ZnO-based varistor samples sintered at 1180 C for 0 h (no significant time at the sintering temperature), 2, 4, and 8...
In this work, a new experimental method, based on non-invasive infrared thermograph techniques, has been developed to visualize and quantify the spatial temperature distribution of the convective air currents generated by a heated body.
Starting from that distribution of temperature and using some theoretical models, the corresponding velocity dist...
In the present work, the theory of charge transport through active interfaces is used to study the electronic properties of ZnO-based varistors. It has been observed that for a certain range of sintering temperatures the microscopic electrical response of the material is constant, so that the macroscopic response is microstructure controlled. This...
We study the temperature dependence of grain resistivity in ZnO ceramic varistors (300–430 K), finding a positive temperature coefficient (PTC). We devise a high-frequency procedure that allow us to obtain the concentration and energy position of the shallow donor. The observed behavior is consistent with a shallow donor approaching complete ioniza...
