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Content archived on 2024-05-29

Miniaturised Ultrasonic, Engineered-Structure and LTCC-Based Devices for Acoustics, Fluidies, Optics and Robotics

Final Report Summary - MINUET (Miniaturised ultrasonic, engineered-structure and LTCC-based devices for acoustics, fluidies, optics and robotics)

Electroceramic materials are widely used in several application fields from medical diagnostics and therapy, through industrial processing and process control, to robotics and printing. In all these applications, electroceramics offer high efficiency, flexibility and wide operating temperature range. However, the general trend in the development of new or upgraded electronic equipment has been towards miniaturisation, increased flexibility and complexity, associated with reduced negative impact on the environment.

In order to meet these challenges, the MINUET project used an unusually broad approach: in the fundamental part it addressed single materials and complex structures consisting of several materials, both of which were investigated by modelling as well as laboratory development; in the applications part several specific devices were developed. The consortium comprised universities, institutes and companies, both Small and medium-sized enterprises (SMEs) and large enterprises, with complementary expertise in development and applications of electroceramics.

A very promising new modelling field based on ab initio calculations was applied, to begin with on relatively simple systems. It is still too early in the development to use this method for identifying new compositions with competitive properties, however. They have also performed a very interesting study of phase transformations in bulk ceramics from relaxor-based systems by means of strain measurements through acoustic emission and X-ray diffraction. Furthermore, they have investigated the influence of uniaxial compressive loads on single crystals from similar systems.

A very important part of MINUET was the development of new piezoelectric materials. LC-EPFL is among the leading laboratories in Europe in the field of lead-free piezoceramics based on the potassium sodium niobate system (KNN). These materials are quite promising for a number of applications, but there are also some difficulties not known from the conventional lead-based PZT system. The KNN materials developed here have been tested by other MINUET partners and several scientific papers have been published on the subject.

One of the applications of piezoelectric thick films developed in the project was a device for 'drop on demand' inkjet printing. The Department of Micro Technology and Medical Device Engineering (part of the Technische Universität München) developed and built a micro-dosing head. Droplets with a volume in the range of 50 pl and less are not only needed in office ink jet printers but also in medical, biological and industrial applications like drug delivery or for three-dimensional (3D) printing of computer generated objects.

Another fluidic application was an oil condition sensor developed by Centro Ricerche Fiat (CRF). In terms of engine lubrication, the current trend among car manufacturers is to extend the interval for oil change and to use a low-viscosity lubricant in order to reduce fuel consumption. This imposes quite severe demands on the performance of the lubricant oil and very advanced formulations and additives must be used.

CRF also worked on quite long-term development, namely adaptive photonic crystals. Within recent years, 'photonic crystals' have emerged as a new class of materials for the control and manipulation of light. A photonic crystal affects the properties of a photon in the same way a semiconductor affects the properties of an electron: electron waves travelling in the potential of a crystal are arranged into energy bands separated by gaps in which propagating states are prohibited.

The Swiss company MTB is specialised in ultrasonic probes and Doppler devices for liquid flow measurements. In this project two transducers for medical applications were addressed. The first one was a single-use blood-flow probe for intraoperative use. The other transducer developed by MTB was a transoesophageal Doppler probe for air embolism detection. Venous air embolism (VAE) may occur during surgery, especially during neurosurgery in sitting position, and represents a high risk for the patient. VAE can be monitored with a precordial Doppler device (Doppler probe positioned on the chest wall over the heart). The French company IMASONIC worked on no less than three devices in MINUET, two of which were focused transducers for ultrasonic imaging with working frequencies at 30 MHz and 50 MHz, respectively. The main applications of the 30 MHz transducer will be ophthalmology, dermatology and small animal imaging. For this transducer, several materials were tested, including lead titanate and composites with either PZT as active material or lead-free piezoceramics based on the KNN system described above.

The development of the 50 MHz transducer has been rather successful. In this case, single crystals were chosen as the active material and the performance proved to be very good. The relative bandwidth is as high as 80 % and the sensitivity is 5 times as high as for ceramic reference probes. This transducer will be commercialised in 2008 and is to be used for medical imaging in ophthalmology.

The third device that Imasonic worked on in the project was a 4 MHz transducer to be used in continuous mode for therapeutic applications. Due to the rather high power involved here and the need for relatively high permittivity, Ferroperm's new materials for High-intensity focused ultrasound (HIFU) applications were chosen for evaluation. They were shown to be very efficient compared to classical high permittivity materials, which showed much higher loss. This transducer is not yet fully developed, however.

Also Non-destructive testing (NDT) of industrial parts was addressed in the project, by the Czech company Starmans. Conventional ultrasonic NDT transducers are based on single-element piezoceramic bulk parts, but Starmans were able to develop a phased-array transducer using piezoceramic thick films.

More than a dozen different designs were presented using various combinations of standing and travelling ultrasonic waves:
- piezoelectric actuators driven by non-harmonic or asymmetric oscillations;
- piezoelectric actuators driven by trans-longitudinal and in-plane flexural oscillations;
- piezoelectric actuators driven by axial travelling wave motion;
- piezoelectric actuators driven by radial travelling wave motion;
- piezoelectric actuators with several degrees-of-freedom, incl. positioning systems on a plane;
- piezoelectric actuators with two active elements in contact zone (example of application: miniature valve for toys).

MINUET had a vertical structure from materials modelling, small scale testing of compositions, developing technology and scaling up to testing in actual devices, with feedback at each step. When forming the consortium, special care was taken to make it well balanced, representing complementary know-how without overlapping or conflicting interests, and this ensured a smooth work process. The 14 partners represented 9 European countries, all of these EU Members States except Switzerland. There were eight industrial partners, among them five SMEs.

The main project outputs were:
- theoretical model for predicting stability of perovskite phases and to a certain extent the piezoelectric properties;
- new perovskite-based compositions with high permittivity (relaxor-ferroelectrics);
- extended line of lead-free piezoceramics of the alkali niobates family;
- technology for manufacturing these materials, and their integration into thick-film structures;
- technology for materials with controlled microstructure and porosity;
- devices based on all the above mentioned materials and technology for medical diagnostics and therapy, NDT, environmental monitoring, robotics and optics applications.