Jose Maria Bravo

High sound screening in low impedance slit arrays

We report on the key role of the acoustical impedance ratio between the solid and the host fluid in the transmission properties of slit arrays. Numerical calculations predict huge sound screening effects up to 60dB for low impedance ratio values. The screening band appears over a broad frequency region and is very robust against dissipative losses of the material as well as against the sound incident angle. This counterintuitive result is discussed in terms of the hydrodynamic short circuit, where thefluid and the solid at the radiating interface vibrate out of phase, resulting in a huge sound blocking effect.

Application of Structured Light System Technique for Authentication of Wooden Panel Paintings.

This paper presents a new application of photogrammetric techniques for protecting cultural heritage. The accuracy of the method and the fact that it can be used to carry out different tests without contact between the sample and the instruments can make this technique very useful for authenticating and cataloging artworks. The application focuses on the field of pictorial artworks, and wooden panel paintings in particular. In these works, the orography formed by the brushstrokes can be easily digitalized using a photogrammetric technique, called Structured Light System, with submillimeter accuracy. Thus, some of the physical characteristics of the brushstrokes, like minimum and maximum heights or slopes become a fingerprint of the painting. We explain in detail the general principles of the Structured Light System Technique and the specific characteristics of the commercial set-up used in this work. Some experiments are carried out on a sample painted by us to check the accuracy limits of the technique and to propose some tests that can help to stablish a methodology for authentication purposes. Finally, some preliminary results obtained on a real pictorial artwork are presented, providing geometrical information of its metric features as an example of the possibilities of this application.

Influence of screw spacings on sound reduction index in lightweight partitions

Abstract In this paper measured sound reduction index data for lightweight partitions with gypsum board layers attached to the frame with two different screw spacings are presented. Data are used to show the effect of screw spacings and to quantify the effect on sound reduction index. The results show that screw spacing had a great effect in double walls where each gypsum board layer was attached to each side of a timber frame.

Application of ultrasound phase-shift analysis to authenticate wooden panel paintings

Artworks are a valuable part of the Worlds cultural and historical heritage. Conservation and authentication of authorship are important aspects to consider in the protection of cultural patrimony. In this paper we present a novel application of a well-known method based on the phase-shift analysis of an ultrasonic signal, providing an integrated encoding system that enables authentication of the authorship of wooden panel paintings. The method has been evaluated in comparison with optical analysis and shows promising results. The proposed method provides an integrated fingerprint of the artwork, and could be used to enrich the cataloging and protection of artworks. Other advantages that make particularly attractive the proposed technique are its robustness and the use of low-cost sensors.

Development of a Low-Cost Airborne Ultrasound Sensor for the Detection of Brick Joints behind a Wall Painting

Non-destructive methods are of great interest for the analysis of cultural heritage. Among the different possible techniques, this paper presents a low cost prototype based on the emission and reception of airborne ultrasound without direct contact with the test specimen. We successfully performed a method test for the detection of brick joints under a XVth century Renaissance fresco of the Metropolitan Cathedral of the city of Valencia (Spain). Both laboratory and in situ results are in agreement. Using this prototype system, an early moisture detection system has been installed in the dome that supports the fresco. The result is encouraging and opens interesting prospects for future research.

Influence of air layers and damping layers between gypsum boards on sound transmission

Abstract In this paper the influence on sound reduction index of a thin air layer between gypsum board layers of lightweight partitions has been examined. It has been shown that the air layer between gypsum boards causes a decrease in sound reduction index due to mass-air-mass resonance. When the thin air layer is filled with a damping layer, the sound reduction index is increased for frequencies around the critical frequencies. Predictions show similar effects to those measured.

Experimental Sound Insulation Performance of Single Frame Partitions with the Addition of a Sound-Absorptive Perforated Board

In this paper, the acoustical performance of a sound-absorptive facings added to a single frame partition is studied. Sound reduction index and sound absorption measurements were carried out to test the influence of the relative position of the frame with the perforated absorptive facing when it was added to a single frame partition. The results show that when a perforated absorptive facing is added to a single frame partition, the sound insulation improvements occur in the mid and high frequency range and the relative position of the frame with the perforated absorptive facing is noticeable in the low frequency range. The sound absorption curves have the typical shapes of that obtained for a series of Helmholtz resonators absorbers and their values are similar, although there are some differences due to the position of the peak of absorption that is linked with resonant frequency.

Technical Note: Comparison of the Sound Insulation of Lightweight Partitions with Different Sound Absorbing Infills

Measurements of sound reduction indices for lightweight gypsum board partitions filled with three different sound absorbing materials (rockwool, glasswool and polyurethane foam) are reported. For partitions where the gypsum panels are mounted on a common stud, with the sound absorbing infill in direct contact with both panels and for uncoupled double partitions, measurement results show that polyurethane foam, of high flow resistivity and stiffness, is less effective as an infill than either rockwool or glasswool.

PHYSICAL-MATHEMATICAL CONCEPTS IN A SIMPLIFIED STUDY OF THE PROTOCOL OF THE LAUNCH OF A ROCKET TO PUT A SATELLITE INTO ORBIT

The achievement of a comprehensive education of the students to provide a global knowledge that allows them to make appropriate decisions in the framework of their future work is one of the most important challenges of the Engineering degrees, especially in basic subjects as Physics or Mathematics. In this sense, a great effort has to be done by the teachers of the first year where the subjects are generally quite abstract and, as a consequence, the motivation of the students is hard to attain. Several are the conditions to obtain this goal successfully: First, a correct cross-coordination and a well-designed teaching of the basis subjects to avoid undesirable repetition of some concepts under different point of view and to show the basic knowledge as a uniform conceptual body ready to be applied to real situations. Second, the need to make attractive the study of these basic and abstract subjects by proposing the resolution of real problems related with the goals of each particular Degree, and adapted to the knowledge of the student of the first level. These problems have to be solved involving different branch of the basic subjects as Physics or Mathematics. In this paper we present a real project related to the professional skills of the Geomatic and Topography Degree, adapted for the first level, and involving three core subjects namely, Algebra, Calculus and Mechanics. The approach of this real project, proposed as an interdisciplinary practice, is related with the path followed by a rocket that puts a satellite in orbit. In real situations, sixteen are the steps of the protocol to achieve this goal, from the takeoff of the rocket to its entrance on the final elliptic orbit. To adapt this complicated protocol to our purposes, we have simplified the steps considering finally only four: (i) the takeoff of the rocket; (ii) the change of the upright path at a predetermined height from the ground to approach to the elliptical orbit; (iii) the link between the rise of the rocket and its placing in elliptical orbit; (iv) the putting into the elliptical orbit itself. Analysis of classic geometric figures as the conics, with their different forms of representation, becomes necessary to be able to develop this practice, since they adapt to the forms described by orbits of the satellites. Modeling makes it necessary to use different reference systems and their relationship between them. In addition, the simplified study of the satellite position vector in its different phases provides fundamental data such as speed, acceleration or balance of forces, related with the subjects of Dynamic or Kinematics, and where the concept of derivative plays a fundamental role. A later detailed study on the motion of the satellite would lead to propose systems of differential equations that relate the elements studied and whose complexity requires numerical methods for their resolution.

Sound Insulation of Lightweight Partitions with Circular Apertures with Varying Overlap

A simple prediction model is developed to predict the decrease in sound reduction index in single and double frame lightweight partitions with the space between gypsum boards filled mineral wool and with circular apertures. The calculation model shows how the distance between centres of the circular apertures on each side of the partition affects the sound reduction index of the whole partition. Calculated results are compared with measured ones. In general, the prediction model developed shows good agreement with the measured results.