IEEE International Ultrasonics Symposium 2019, Glasgow

Air-coupled Transducers for Quality Control in the Food Industry.

Alba Martín Ginel, Tomás Gómez Álvarez-Arenas

Food industry is continuously innovating its capability of analysis by incorporating new technologies aimed to meet increasing quality and safety requirements, concurrence and consumers demands. In this context, non-destructive and non-invasive techniques are demanded in different stages of the production chain for quality control and verification. Air-coupled ultrasound is a fully non-invasive and non-destructive technique that has already been successfully implemented in other industries (aeronautical, aerospace, etc.) with fast scan velocities, and compatibility with industrial environment. This technique is capable to determine mechanical and viscoelastic properties of different materials as well as the presence of discontinuities, cavities, and foreign objects. Clearly, these capabilities are extremely interesting for inline quality control in the food industry. Being the main challenge of air-coupled applications the performance of air-coupled transducers (bandwidth and sensitivity), the objective of this work is to show a transducer design approach to simultaneously optimize both sensitivity and frequency band that make possible to operate in through transmission. In addition, food industry requirements in terms of materials and working conditions are also reviewed and included in the transducers design. Transducers with centre frequency at 300 and 500 kHz has been designed, built and tested. A first verification of the use of this technology in food products is shown revealing the possibility to measure transmitted signal above the noise level.

Optimization of Ferroelectret Transducers for Pulse-Echo Water Immersion Operation

Julio Quirce Aguilar, Tomás Gómez Álvarez-Arenas

The adaptation and optimization of polypropylene ferroelectret (FE) films as the main piezoelectric element for water immersion ultrasonic transducers is studied. One of its main features is that they present a very wide band response so they can be an alternative for certain medical applications, especially those demanding intermediate frequencies and reduced size. The main problems of using this kind of materials are the poor sensitivity and the weak bonding of the metallization to the FE film that is easily degraded when entre in contact with water. The objective of this work is to optimize FE transducers for pulse-echo water immersion, while preserving the bandwidth, by: i) protecting the surface and ii) improving the impedance matching to the water.Metallization degradation produced by water has been quantified, then, main materials requirements to produce matching layers for this application are reviewed and potential materials to produce them proposed. A procedure to reinforce the metallization while preserving the electromechanical film response is proposed (based on Au sputtering) and first prototypes of transducers with a single matching layer are proposed, built and characterized.

Novel Nanocomposite Materials for Improving Passive Layers in Air-coupled Ultrasonic Transducer Applications

Lorena Amoroso, Sivaram Nishal Ramadas, Christoph Klieber, Tomas E. Gomez Alvarez-Arenas, Tony McNally

International Institute for Nanocomposites Manufacturing, University of Warwick, Honeywell Redditch, UK, ITEFI-CSIC, Spain, 

Recent research has focused on developing air-coupled transducers for use in industrial flow measurement application. Optimal performance of ultrasonic transducers is only achieved with maximum energy transfer. Unfortunately, the significant acoustic impedance mismatch between the active layer and the load medium (i.e. air) in sensors reduces considerably the effective ultrasonic energy transmission and reception, with most of the energy reflected at the interface. Improved matching layers with an appropriate acoustic impedance and attenuation coefficient as low as possible can significantly improve the power efficiency and sensitivity of devices, decreasing energy loss by scattering. The aim of this research is to evaluate novel acoustic materials for use in a new ultrasonic transducer assembly process involving cost effective advanced manufacturing methods. More efficient and consistent signal shapes could be achieved by substituting current matching layers (e.g. syntactic foams) with new materials. Nanocomposite foams can be obtained via cost effective extrusion/moulding processes where microbubbles are formed inside the polymer when heated above a certain temperature. The reduction in density affects acoustic impedence, ultimately creating light passive layers for ultrasonic applications manufacturable in high volumes.

The Role of Additive Manufacturing Technology in the Design of Sparse Transducer Arrays

Oscar Martiınez-Graullera, Virginia Yagüe-Jiménez∗, Adrián Blanco Paetsch, Alberto Ibá añeez Rodríguez  and Tomás Gómez Álvarez-Arenas Inst. Tecnol. Fïsicas y de la Información. Spanish National Research Council (CSIC),

Large two-dimensional (2D) arrays offer very promising prospects as an analysis tool due to their capability to obtain information of volumetric spaces. However, this kind of development has major drawbacks. The main challenge comes from the large number of elements required to achieve an acceptable image quality. The sparse arrays have been proposed as a compromise solution between the number of active elements and dynamic range. Although we can find in the literature a lot of examples about sparse arrays models, there is a significant lack of experimental prototypes. The main reason for this is that the manufacturing process is expensive and complex. In order to address this problem, the capabilities to develop structural parts of sparse arrays of manufacturing process based on Additive Manufacturing technology have been analyzed in this paper.