Abstract
In the present moment, the sustainable water management is a major concern throughout the world. Mountain areas are more and more recognized as the world's water towers (UNESCO IHP-VI PROGRAMME). Since a large number of mountains are located at high altitude and are crossed by roads, deicing operations are inevitable. The use of deicing chemicals such as sodium chloride and calcium chloride to promote snow and ice melting in roads is an environmental problem of scientific, economic and social relevance. Due to its geological, geomorphological and climate characteristics, the Serra da Estrela mountain plays a strategic role in the water management in Portugal. This paper presents hydrogeochemical results that illustrate the process of groundwater contamination by road deicing salts in this mountain area. © 2012 LNEG.

Abstract

Abstract
Ultrasound transducers are typically based on piezoelectric materials, due to their good response at high frequencies. Depending on the application, ceramics, polymers and composite materials can be used. In this work, an optimization study of ultrasound transducers for underwater communications is addressed, focusing on a piston type emitter transducer operating in thickness mode (d(33)). The piston is constituted by an active element disk with optimized dimensions. It is discussed how the acoustic impedance, thickness, resonance frequency and structure affect the transducer performance. This work allows a better understanding of the emitter transducer characteristics allowing reaching the optimum point of operation for specific applications. Focusing on underwater communication, the acoustic channel is defined and the transducer is optimized by finite element computer simulations. The results were compared with experimental tests, which show that four-layer structures increase up to 16 dB in performance versus single-layer.

Abstract

Abstract

Abstract