Advances in Science and Technology Vol. 54

Abstract: This paper reports experimental and modelling results on the manufacture and properties of hydroxyapatite / BaTiO3 ceramic composites and studies their electromechanical properties with ferroelectric ceramic volume fractions, mFC ³ 0.7. In these composites the bio-active properties of hydroxyapatite are combined with the electromechanical properties of a perovskite-type ferroelectric BaTiO3 ceramic in an attempt to create a novel polarised bone-substitute material. Experimental results of the volume fraction dependences of the effective piezoelectric coefficients * 31 d (mFC), * 33 d (mFC) and dielectric permittivity e *s 33 (mFC) of stress free samples are analysed within the framework of a modified model of a porous piezo-active material that is described in terms of 1–3 (one-dimensional rods in a continuous matrix) and 2–2 connectivity (laminates). The role of several structural elements and physical factors in forming the electromechanical properties of the composites is discussed. It is shown that performance of these materials typical properties are 5 pC / N < | * 31 d |< 45 pC / N, 20 pC / N < * 33 d < 100 pC / N and 400 < e *s 33 / 0 e < 1300.

Abstract: Barium titanate (BaTiO3) ceramics with a high-density were fabricated by two-step sintering method from hydrothermally synthesized 100 nm BaTiO3 nano-particles. The best specimen with an average grain size of 1.6 μm and a density of 5.91 g/cm3 (98.3% of the theoretical value). The dielectric constant was 4500 and electromechanical coupling factor kp was 45%. Large piezoelectric constants d33 = 460 pC/N and d31 = -185 pC/N were observed in the specimens. This was an important practical result towards obtaining a high d33 in non-lead-based BaTiO3 ceramics manufactured by a low-cost process. These results also indicated the possibility of using BaTiO3 ceramics in piezoelectric devices at room temperature. Temperature dependence of dielectric constant showed two peaks located at 24 and 126 oC, corresponding to orthorhombic-to-tetragonal phase transition temperature Tot and Curie temperature Tc, respectively. Owing to the size effect of nanocrystals, Tot shifted to 24 oC. The maximum of electromechanical coupling factor kp appeared close to the phase transition temperature. It also caused a very large temperature coefficient of resonance frequency from room temperature to 60 oC. Hysteresis curve measurement showed a very low coercive field Ec = 115 V/mm. A large Poisson’s ratio, about 0.38, was determined from the ratio of overtone frequency and resonant frequency in the planar mode. The high Poisson’s ratio and the large dielectric constants are most likely the origin of the high piezoelectric constants in the ceramics.

Abstract: A dynamic, nonlinear model for magnetic induction and strain response of cubic magnetostrictive materials to 3-D dynamic magnetic fields and 3-D stresses is developed. Dynamic eddy current losses and inertial stresses are modeled by coupling Maxwell’s equations to Newton’s second law through a nonlinear constitutive model. The constitutive model is derived from continuum thermodynamics.

Abstract: High performance biosensors are urgently needed from medical diagnosis, to food safety/security, to the war on bio-terrorist. Recently, magnetostrictive microcantilever (MSMC) and magnetostrictive particle (MSP) have been developed as high performance biosensor platform. Both MSMC and MSP are wireless sensors and exhibit advantages over current acoustic wave biosensor platforms. Theoretical analysis and experimental results indicate that micro/nano scale MSMC and MSP have ultra-high sensitivities. However, in real detection, there is a challenge faces all micro/nano scale sensors because of their small size. That is, a long time is required for the tiny sensors to react with the target species. Due to the magnetic and wireless nature, MSP provides a unique way to bring the nanosensors to target species. The fabrication of bar-like MSPs in nanoscale is reported. Amorphous Fe-B alloy was selected as target magnetostrictive materials for fabrication. The properties of these nanobars were determined. The morphology and magnetic properties of the nanobars were characterized. The results ware analyzed and the size effect on the microstructure and properties is discussed.

Abstract: The discovery of the magnetoimpedance (MI) effect in 1994 had a strong impact on the development of magnetic sensors, offering miniature, highly sensitive, and quick response elements. Along with traditional areas of sensing applications (data storage, bio-medical electronics, robotics and security), the MI elements have a high potential for non-destructive testing (as eddy current probes) and smart sensory systems (self-sensing composites). In certain soft magnetic materials, such as composites of amorphous thin wires, the impedance change (MI ratio) can be as high as 600 % in the MHz band and 50-100% at GHz frequencies subjected to small magnetic fields or stresses. Furthermore, special thin-film structures have been proposed to improve the MI performance in miniature elements. This paper discusses physical concepts of MI in multilayered structures including MI ratio enhancement and effect of anisotropy, experimental results proving high sensitivity to the external stimuli for excitation frequencies up to few GHz, practical sensor designs and, finally, the use of MI fibers for tagging the composites to build-in sensing functionality .

Abstract: In this study, aluminum nitride (AlN) thin films reactively sputter deposited from an aluminium target are characterized both under material related aspects as well as on device level for resonantly driven gyroscopes. The first topic comprises a qualitative evaluation of the c-axis orientation by applying a wet chemical etching procedure in phosphoric acid to specimens synthesized under varying sputter deposition conditions. Samples with a high c-axis orientation show a low etch rate and smooth surface characteristics on the etched areas and vice versa. Furthermore, a quantitative determination of the piezoelectric coefficients is presented including the impact of the silicon substrate on the change in AlN film thickness under excitation. With this advanced approach, the d33 and the d31 coefficients are gained simultaneously with high accuracy comparing FEM simulations and interferometric measurements. Finally, AlN are applied to bulkmicromachined gyroscopes to stimulate the drive mode. Parasitic effects on the performance generated by the microactuator elements are identified and potential improvements are proposed.

Abstract: The present research compares properties and behaviour of co-precipitated 3Y-PSZ powders submitted, after co-precipitation, to different milling treatments. The characteristics of the different products were evaluated by measurement of particle size distribution, thermogravimetric analysis, X-ray diffraction, specific surface area and scanning electron microscopy analysis. It has been demonstrated that 1h of attrition milling enables the production of powders with micrometric particles: the dispersing liquid used on milling has little influence. Crystallization of the amorphous powder is achieved after 1h of high energetic milling, without any thermal treatment.

Abstract: Quartz length-extension resonators have already been used to get atomically-resolved imaging by frequency-modulation atomic force microscopy. Other piezoelectric materials could be appropriate for this application. Theoretical study is reported on Langasite length extension resonator. In this paper, an attempt to fabricate similar micro resonators in Langasite temperaturecompensated cuts is prospected.