Estudio de las diferentes alternativas para mejorar la respuesta de los filtros BAW (Bulk Acoustic Wave) con topología en escalera

Los requisitos de los dispositivos empleados en los nuevos sistemas de telecomunicaciones son: unas avanzadas prestaciones, reducido tamaño y bajo coste. Actualmente, se utilizan filtros basados en la tecnología SAW para trabajar a frecuencias de microondas. Dado los inconvenientes que presentan dicho tipo de filtros, se pretende substituirlos por filtros basados en tecnología BAW. La topología en escalera es hasta el momento la más extendida para diseñar estos filtros.

Could cell membranes produce acoustic streaming? Making the case for synechococcus self-propulsion

Sir James Lighthill proposed in 1992 that acoustic streaming occurs in the inner ear, as part of the cochlear amplifier mechanism. Here we hypothesize that some of the most ancient organisms use acoustic streaming not only for self-propulsion but also to enhance their nutrient uptake. We focus on a motile strain of Synechococcus, a yanobacteria whose mechanism for self-propulsion is not known. Molecular motors could work like piezoelectric transducers acting on the crystalline structure surrounding the outer cell membrane. Our calculations show that a traveling surface acoustic wave (SAW)could account for the observed velocities. These SAW waves will also produce a non-negligible Stokes layer surrounding the cell: motion within this region being essentially chaotic. Therefore, an AS mechanism would be biologically advantageous, enhancing localized diffusion processes and consequently, chemical reactions. We believe that acoustic streaming, produced by nanometer scale membrane vibrations could be widespread in cell biology. Other possible instances are yeast cells and erythrocytes. Flows generated by acoustic streaming may also be produced by silica coated diatoms along their raphe. We note that microelectromechanical (MEMS) acoustic streaming devices were first introduced in the 1990’s. Nature may have preceded this invention by 2.7 Gyr.

Clustering or scattering: the underlying reason for regulating distance among retail outlets

Concerns on the clustering of retail industries and professional services in main streets had traditionally been the public interest rationale for supporting distance regulations. Although many geographic restrictions have been suppressed, deregulation has hinged mostly upon the theory results on the natural tendency of outlets to differentiate spatially. Empirical evidence has so far offered mixed results. Using the case of deregulation of pharmacy establishment in a region of Spain, we empirically show how pharmacy locations scatter, and that there is not rationale for distance regulation apart from the underlying private interest of very few incumbents.

Diseño de filtros Bulk Acoustic Wave con topología en escalera de altas prestaciones

Degut als avenços als dispositius de telecomunicacions durant l’última dècada, els filtres integrats en aquests dispositius requereixen de millors prestacions, baix cost i, per sobre de tot, requereixen unes dimensions el més reduïdes possibles. Tot i que avui dia encara s’utilitzen el filtres SAW en aquests dispositius, cada cop més s’estan substituint pels filtres amb tecnologia BAW, ja que tenen millors prestacions. En l’actualitat la topologia BAW més extensa i utilitzada és la topologia en escala. En aquest projecte s’ha portat a terme un estudi en profunditat de les limitacions dels filtres en escala. A partir de les limitacions detectades s’ha presentat una nova estructura de disseny per aquest tipus de filtres que redueix les dimensions d’aquests i millora considerablement algunes de les limitacions de l’estructura convencional. Paral·lelament s’ha desenvolupat una metodologia sistemàtica pròpia pel disseny de la nova estructura.

Acoustic properties of polypropylene composites reinforced with stone groundwood

Currently, acoustic isolation is one of the problems raised with building construction in Spain. The publication of the Basic Document for the protection against noise of the Technical Building Code has increased the demand of comfort for citizens. This has created the need to seek new composite materials that meet the new required acoustical building codes. In this paper we report the results of the newly developed composites that are able to improve the acoustic isolation of airborne noise. These composites were prepared from polypropylene (PP) reinforced with mechanical pulp fibers from softwood (Pinus radiata). Mechanical and acoustical properties of the composites from mechanical pulp (MP) and polypropylene (PP) have been investigated and compared to fiberglass (FG) composites. MP composites had lower tensile properties compared with FG composites, although these properties can be improved by incorporation of a coupling agent. The results of acoustical properties of MP composites were reported and compared with the conventional composites based on fiberglass and gypsum plasterboards. Finally, we suggest the application of MP composites as a light-weight building material to reduce acoustic transmitions

Acoustic transport of charge and spins in GaAs-based heterostructures

Report for the scientific sojourn carried out at the Paul Drude Institut für Festkörperelektronik of the Stanford University, USA, from 2010 to 2012. The objective of this project is the transport and control of electronic charge and spin along GaAs-based semiconductor heterostructures. The electronic transport has been achieved by taking advantage of the piezolectric field induced by surface acoustic waves in non-centrosymmetric materials like GaAs. This piezolectric field separates photogenerated electrons and holes at different positions along the acoustic wave, where they acummulate and are transported at the same velocity as the wave. Two different kinds of structures have been studied: quantum wells grown along the (110) direction, both intrinsic and n-doped, as well as GaAs nanowires. The analysis of the charge acoustic transport was performed by micro-photoluminescence, whereas the detection of the spin transport was done either by analyzing the polarization state of the emitted photoluminescence or by Kerr reflectometry. Our results in GaAs quantum wells show that charge and spin transport is clearly observed at the non-doped structures,obtaining spin lifetimes of the order of several nanoseconds, whereas no acoutically induced spin transport was detected for the n-doped quantum wells. In the GaAs nanowires, we were able of transporting successfully both electrons and holes along the nanowire axis, but no conservation of the spin polarization has been observed until now. The photoluminescence emitted by these structures after acoustic transport, however, shows anti-bunching characteristics, making this system a very good candidate for its use as single photon emitters.

Desarrollo de tecnología Bulk Acoustic Wave

El creciente uso de dispositivos móviles y el gran avance en la mejora de las aplicaciones y sistemas inalámbricos ha impulsado la demanda de filtros paso banda miniaturizados, que trabajen a altas frecuencias y tengan unas prestaciones elevadas. Los filtros basados en resonadores Bulk Acoustic Wave (BAW) están siendo la mejor alternativa a los filtros Surface Acoustic Wave (SAW), ya que funcionan a frecuencias superiores, pueden trabajar a mayores niveles de potencia y son compatibles con la tecnología CMOS. El filtro en escalera, que utiliza resonadores BAW, es de momento la mejor opción, debido a su facilidad de diseño y su bajo coste de fabricación. Aunque el filtro con resonadores acoplados (CRF) presenta mejores prestaciones como mayor ancho de banda, menor tamaño y conversión de modos. El problema de este tipo de filtros reside en su complejidad de diseño y su elevado coste. Este trabajo lleva a cabo el diseño de un CRF a partir de unas especificaciones bastante estrictas, demostrando sus altas prestaciones a pesar de su mayor inconveniente: el coste de fabricación.

X-ray diffraction, thermal analysis, and Raman scattering study of K2BeF4 and comparation to other member of the (beta)-K2SO4 family with ferroelectric -paraelectric transition

Thermal analysis, powder diffraction, and Raman scattering as a function of the temperature were carried out on K2BeF4. Moreover, the crystal structure was determined at 293 K from powder diffraction. The compound shows a transition from Pna21 to Pnam space group at 921 K with a transition enthalpy of 5 kJ/mol. The transition is assumed to be first order because the compound shows metastability. Structurally and spectroscopically the transition is similar to those observed in (NH4)2SO4, which suggests that the low-temperature phase is ferroelectric. In order to confirm it, the spontaneous polarization has been computed using an ionic model.

Raman scattering and photoluminescence analysis of silicon on insulator structures obtained by single and multiple oxygen implants

An analysis of silicon on insulator structures obtained by single and multiple implants by means of Raman scattering and photoluminescence spectroscopy is reported. The Raman spectra obtained with different excitation powers and wavelengths indicate the presence of a tensile strain in the top silicon layer of the structures. The comparison between the spectra measured in both kinds of samples points out the existence in the multiple implant material of a lower strain for a penetration depth about 300 nm and a higher strain for higher penetration depths. These results have been correlated with transmission electron microscopy observations, which have allowed to associate the higher strain to the presence of SiO2 precipitates in the top silicon layer, close to the buried oxide. The found lower strain is in agreement with the better quality expected for this material, which is corroborated by the photoluminescence data.

Raman scattering of InSb quantum dots grown on InP substrates

In this paper we present the Raman scattering of self-assembled InSb dots grown on (001) oriented InP substrates. The samples were grown by pulsed molecular beam epitaxy mode. Two types of samples have been investigated. In one type the InSb dots were capped with 200 monolayers of InP; in the other type no capping was deposited after the InSb dot formation. We observe two peaks in the Raman spectra of the uncapped dot, while only one peak is observed in the Raman spectra of the capped dots. In the case of the uncapped dots the peaks are attributed to LO-like and TO-like vibration of completely relaxed InSb dots, in agreement with high resolution transmission electron microscopy photographs. The Raman spectra of the capped dot suggest a different strain state in the dot due to the capping layer.

Elastic constants of bcc Cu-Al-Ni alloys

We have measured the adiabatic elastic constants of two Cu-Al-Ni martensitic alloys using ultrasonic methods and we have compared the results to recent neutron-scattering experiments. It is shown that the elastic behavior of Cu-Al-Ni alloys follows the same trends exhibited by other Cu-based alloys; in particular, the TA2 long-wavelength acoustic modes are softer than all other modes.