Examinando por Materia "PIEZOELECTRICITY"

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    Frictionless contact in a layered piezoelectric medium composed of materials with hexagonal symmetry
    (2014-05-06) Ramirez, G. (Guillermo)
    Se presenta una formulación matricial para la solución de problemas de contacto sin fricción en semiplanos piezoeléctricos elásticos de múltiples capas. Se consideran diferentes disposiciones de materiales piezoeléctricos elásticos y transversalmente ortotrópicos dentro del medio de múltiples capas. Se usa una deformación de plano generalizada para obtener las ecuaciones gobernantes de equilibrio para cada capa individual, que se resuelven con la técnica de transformada de Fourier infinita. Entonces el problema se reformula con el método de rigidez local/global, en el cual se formula para cada capa una matriz de rigidez local que relaciona los esfuerzos y el desplazamiento eléctrico con los desplazamientos mecánicos y el potencial eléctrico en el dominio transformado. En seguida se ensambla en una matriz de rigidez global para todo el semiplano imponiendo la continuidad interfacial de tracciones y desplazamientos. Este enfoque por rigidez local/global no sólo elimina la necesidad de hallar explícitamente los coeficientes de Fourier desconocidos, sino que también permite el uso de algoritmos numéricos eficientes, muchos de los cuales se desarrollaron para análisis por elementos finitos. A diferencia de los métodos de elementos finitos, este enfoque requiere una entrada miníma. El uso de condiciones de borde mezcladas reduce el problema a una ecuación integral, que se resuelve para la presión de contacto desconocida con una técnica basada en los polinomios de Chebyshev.
  • Miniatura
    PublicaciónAcceso abierto
    Inmunosensores piezoeléctricos: revisión general y su aplicación en el análisis de pesticidas
    (2014-05-08) Ocampo, Aquiles; March, Iborra, Carmen; Montoya, Ángel
    A bibliographic review about the main aspects concerning the development of immunosensors is presented in this article, as well as some of the experimental results in an application in the analysis of carbaryl plaguicide that illustrates the analytical methodology and the expected results. The quartz crystal microbalance immunosensor (QCM), known as piezoelectric immunosensor, is an analytical system which combines an immunoreagent as the biologic component, a quartz crystal transducer with an immobilized antigen or antibody on its surface, coupled to an information processing system. Due to its simplicity, convenience, low cost, accuracy, stability, and real time response, this device has become very important, especially for material analysis in biomedicine, food, environment, and veterinary.
  • Miniatura
    PublicaciónAcceso abierto
    Interface layer to improve polystyrene attachment on a quartz crystal resonator
    (2014-05-07) Llanes, D. S. (Doris Susana); Hempel, U. (Ulrike); Ocampo, Aquiles
    Technologies for thin film deposition have been used to improve the functionalization of quartz crystal resonators (QCR); such technologies, for example, are spin coating and Langmuir-Blodgett (LB) film preparation. These experiments are required because the film uniformity and homogeneity over the quartz crystal resonator are fundamental for its applications as chemical and biological sensors. Film deposition of polystyrene (PS) particles, as well as polyvinyl chloride (PVC), was performed in solvents such as cyclohexanone, tetrahydrofuran (THF), dimethylformamide and chloroform at different concentrations using the spin coating procedure on wafer targets. The film quality was determined by optical microscopy, ellipsometry, and profilometry. Additionally, films on wafers or QCR with gold surface have been prepared by spreading the mentioned substances on an aqueous subphase and transferring it by dipping from the subphase surface onto the target. For LB film preparation arachidic acid and PS particles have been used. Prepared mono- or multilayered films of these substances on wafer or gold quartzes have been controlled additionally by IR-spectrometry. The resonant behavior of QCR before and after surface coating has been measured with a network analyzer. In combination with a graphical user interface the data could be easily recorded and visualized.