Darko Belavic

The design, fabrication and functional evaluation of the radio-frequency dielectric heating of liquids in an LTCC-based ceramic microfluidic system are described and discussed. The device, which relies on the dielectric heating of liquids, was fabricated using a low temperature co-fired ceramic (LTCC) technology. A multilayered ceramic structure with integrated electrodes, buried channels and cavities in micro and millimetre scales was fabricated. The structure with the dimensions of 35 mm × 22 mm × 2.4 mm includes a buried cavity with a diameter of 17.3 mm and a volume of 0.3 mL. The top and bottom faces of the cavity consist of silver/palladium electrodes protected with 100 μm thick layers of LTCC. The power, used to heat a polar liquid (water) in the cavity with the volume of 0.3 mL, ranges from 5 to 40 W. This novel application of RF dielectric heating could enable the miniaturization of microfluidic systems in many applications. The working principle of such a device and its efficiency are demonstrated using water as the heated medium.

Purpose: The purpose of this study is to design, fabricate and investigate low-temperature co-fired ceramic (LTCC) structures with integrated microfluidic elements. Special attention is paid to the study of fluid properties of micro-channels and microvalves, which are important constitutive parts of both, microfluidic systems and individual microfluidic devices. Design/methodology/approach: Several test patterns of fluid channels with different geometry and different types of valves were designed and realized in LTCC technology. All test structures were tested under the flow of two fluids (liquids): water and isopropyl alcohol. Flow rates at different applied pressure were measured and hydrodynamic resistance and diode effect were calculated. Findings: The investigation of the channels showed that viscosity of fluidic media has significant influence on the hydrodynamic resistance in channels with rectangular cross-section, while this effect is small on channels with square cross-section. The viscosity also has a decisive influence on the diode effect of different shape of valves, and therefore, it is important in the selection of the valve in practical applications. Research limitations/implications: In this work, the investigation of hydrodynamic resistance of channels and diode effect of passive valves is limited on selected geometry and only on two fluidic media and two applied pressures. All these and some other parameters have a significant influence on fluidic properties, but this will be the topic of the next research work, which will be supported by numerical modelling. Practical implications: The presented results are useful in the future designing process of LTCC-based microfluidic devices and systems. Originality/value: Microfluidic in the LTCC structures is an unconventional use of this technology. Therefore, the fluid properties are relatively unsearched. On the other hand, the global use of microfluidic devices and systems is growing rapidly in various applications. They are mostly made by polymer materials, however, in more demanding applications; ceramic is a useful alternative.

Piezoelectric ceramic resonant pressure sensors have shown potential as sensing elements for harsh environments, such as elevated temperatures. For operating temperatures exceeding ~250 °C, conventional and widely used Pb(Zr,Ti)O₃ (PZT) piezoelectrics should be replaced. Here, a ceramic pressure sensor from low-temperature co-fired ceramics (LTCC) was constructed by integrating a piezoelectric actuator made from bismuth ferrite (BiFeO₃) on a diaphragm. This ferroelectric material was selected because of its high Curie temperature (T_C = 825 °C) and as a lead-free piezoelectric extensively investigated for high-temperature applications. In order to construct a sensor with suitable pressure sensitivity, numerical simulations were used to define the optimum construction dimensions. The functionality of the pressure sensor was tested up to 201 °C. The measurements confirmed a pressure sensitivity, i.e., resonance frequency shift of the sensor per unit of pressure, of −8.7 Hz/kPa up to 171 °C. It was suggested that the main reason for the hindered operation at the elevated temperatures could lie in the thermo-mechanical properties of the diaphragm and the adhesive bonding at the actuator-diaphragm interconnection.

In this work the screen-printed piezoelectric 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 thick films were prepared on metalized low-temperature co-fired ceramic substrates. Such substrates are interesting for micro-electro mechanical systems, for example for piezoelectric sensors and actuators. The prepared thick films exhibit the piezoelectric coefficient d33 equal to 120 pC/N.

In this paper, we present some techniques used to characterize the electrochemical cells. The main role of the batteries is to provide power and to recharge using DC. The research led to the identification of different charging methods which prevent battery damage. Conventional processes are highlighted and some of them provide the opportunity to stimulate battery electrodes and thus, prevent battery damage. In this regard, the most effective methods are processes using current pulses during charging and discharging.

In this contribution the design and fabrication of ceramic microsystems with integrated different microfluidic elements and sensors will be presented. Ceramic microsystems are based on unconventional application of low-temperature co-fired ceramic technology and materials. This unconventional application is related to three-dimensional ceramic structures, such as cantilevers, ledges, bridges, diaphragms, valleys, channels, holes and cavities, valves, mixers, diffusors, distributors, collectors, flow limiters, sensors, and actuators.

An exploratory study of the impact of housing on the characteristics of a low-temperature co-fired ceramic (LTCC) pressure sensor is presented. The ceramic sensor structure is sealed in a plastic housing. This may have non-negligible effect on the final characteristics and should be considered in the early design phase. The manufacturability issue mainly concerning the selection of available housing and the most appropriate materials was considered with respect to different requirements for low and high pressure ranges of operation. Numerical predictions showed the trends and helped reveal the critical design parameters. Proper selection of the adhesive material remains an essential issue. Curing of the epoxy adhesive may introduce non-negligible residual stresses, which considerably influence the sensor’s characteristics.

In this work the design aspects of a piezoelectric-based resonance ceramic pressure sensor made using low-temperature co-fired ceramic (LTCC) technology and designed for high-temperature applications is presented. The basic pressure-sensor structure consists of a circular, edge-clamped, deformable diaphragm that is bonded to a ring, which is part of the rigid ceramic structure. The resonance pressure sensor has an additional element – a piezoelectric actuator – for stimulating oscillation of the diaphragm in the resonance-frequency mode. The natural resonance frequency is dependent on the diaphragm construction (i.e., its materials and geometry) and on the actuator. This resonance frequency then changes due to the static deflection of the diaphragm caused by the applied pressure. The frequency shift is used as the output signal of the piezoelectric resonance pressure sensor and makes it possible to measure the static pressure. The characteristics of the pressure sensor also depend on the temperature, i.e., the temperature affects both the ceramic structure (its material and geometry) and the properties of the actuator. This work is focused on the ceramic structure, while the actuator will be investigated later.

Purpose: – The purpose of this paper is to present the research activity and results to research and development society on the field of ceramic microsystems. Design/methodology/approach: – The chemical reactor was developed as a non-conventional application of low temperature co-fired ceramic (LTCC) and thick-film technologies. In the ceramic reactor with a large-volume, buried cavity, filled with a catalyst, the reaction between water and methanol produces hydrogen and carbon dioxide (together with traces of carbon monoxide). The LTCC ceramic three-dimensional (3D) structure consists of a reaction chamber, two inlet channels, an inlet mixing channel, an inlet distributor, an outlet collector and an outlet channel. The inlet and outlet fluidic barriers for the catalyst of the reaction chamber are made with two “grid lines”. Findings: – A 3D ceramic structure made by LTCC technology was successfully designed and developed for chemical reactor – methanol decomposition. Research limitations/implications: – Research activity includes the design and the capability of materials and technology (LTCC) to fabricate chemical reactor with large cavity. But further dimensions-scale-up is limited. Practical implications: – The technology for the fabrication of LTCC-based chemical reactor was developed and implemented in system for methanol decomposition. Originality/value: – The approach (large-volume cavity in ceramic structure), which has been developed, can be used for other type of reactors also.