Jari Juuti

Manufacturing of prestressed piezoelectric unimorphs using a postfired biasing layer

A novel manufacturing method for prestressed piezoelectric unimorphs is introduced and the actuator properties are examined. Prestressed PZT 5A and PZT 5H unimorphs with piezo material thickness of 250 /spl mu/m and 375 /spl mu/m were manufactured by using sintering and thermal shrinkage of the prestressing material. The process was carried out by screen printing a layer of AgPd paste on one side of the sintered bulk ceramic. As an alternative method, dielectric low temperature co-fired ceramic (LTCC) tape was used as the prestressing material. Different configurations were tested to obtain high displacements and to make a comparison between materials. After firing, the samples were poled, and the displacement versus load characteristics of the resulting actuators were investigated. A maximum displacement of 118 /spl mu/m was obtained from a 250 /spl mu/m thick, prestressed PZT 5H actuator with a diameter of 25 mm, in which LTCC tape was used as the prestressing layer. Similarly, the PZT 5H material provided a maximum displacement of 63 /spl mu/m with a screen-printed AgPd prestressing layer. The manufacturing method described offers a novel approach for the production of a wide range of integrated active structures on, for instance, an LTCC circuit board. This is especially important because piezoelectric bulk materials with high piezoelectric coefficients can be used to produce high displacements.

Formulation of Screen Printable Cobalt Nanoparticle Ink for High Frequency Applications

In this work, magnetic metallic cobalt nanoparticles with an average particle size of 28nm were processed as a dry powder with surface coating material and other organic additives to form a screen-printable ink to be cured at 110 - C. EFTEM and TGA-DSC- MS-analyses were used to measure the thickness of the polymer, its coverage on cobalt nanoparticles and the inorganic solid content of the ink. The resolution of the printed patterns and the print quality were evaluated by surface profller, FESEM and optical microscopy. The relative permeability of the thick fllm patterns with good printability was measured with a shorted microstrip structure over the frequency range of 0.2 to 4GHz and complex permeability values were calculated from measured scattering parameter data. The ink attained real part of complex permeability values of up to 5.13 at 200MHz with 70wt.% of magnetic flller. The developed ink can be utilized in various printed electronics applications such as antenna substrates and magnetic sensors.

Method to characterize dielectric properties of powdery substances

An open ended coaxial cavity method for dielectric characterization of powdery substance operating at 4.5 GHz in TEM mode is presented. Classical mixing rules and electromagnetic modeling were utilized with measured effective permittivities and Q factors to determine the relative permittivity and dielectric loss tangent of different powders with er up to 30. The modeling enabled determination of the correction factor for the simplified equation for the relative permittivity of an open ended coaxial resonator and mixing rules having the best correlation with experiments. SiO2, Al2O3, LTCC CT 2000, ZrO2, and La2O3 powders were used in the experiments. Based on the measured properties and Bruggeman symmetric and Looyenga mixing rules, the determined dielectric characteristics of the powders exhibited good correlation with values in the literature. The presented characterization method enabled the determination of dielectric properties of powdery substances within the presented range, and therefore could be a...

Combined electrical and electromechanical simulations of a piezoelectric cymbal harvester for energy harvesting from walking

In this article, simulation combining real-life mechanical input energy with electromechanical and electrical behavior of piezoelectric energy harvester and electronics is demonstrated. A finite element method model for a piezoelectric cymbal harvester is developed and compared to measurements from an actual prototype. The measurements were taken using a piston imitating a measured walking pressure profile, which was also used in the simulations as an arbitrary input signal. The finite element method model was used to calculate the electrical power of the prototype under a resistive load. These results were then compared to the measured results, which showed that the error in the generated power between the model and the actual prototype was below 7% for stroke displacements below 1.3 mm. Such accurate modeling of full chain from mechanical to electrical energy will be an essential tool in optimization of the mechanics, electronics, and materials of the future energy harvesting devices.

An indirectly coupled open-ended resonator applied to characterize dielectric properties of MgTiO3–CaTiO3 powders

The effect of CaTiO3 addition on the complex permittivity of MgTiO3 powder was characterized with an open-ended coaxial cavity resonator in the range of 2.12–3.66 GHz. Permittivities and loss tangents of (1 − x)MgTiO3-xCaTiO3 composite powders with x of 0, 2, 5, and 10 mol. % were measured and compared to theoretical values. Inclusion permittivities and dielectric loss tangents were determined by using Bruggeman symmetric and Looyenga mixing rules and a general mixing model. Additions of CaTiO3 resulted in a clear increase in inclusion permittivities from 13.4 up to 14.9 and in loss tangents from 7.1 × 10−3 up to 8.5 × 10−3. Comparison with the theoretical loss tangent values and quantitative determination of CaTiO3 molar ratios by using measured loss tangents and a general mixing model gave a good correlation. The characterization method was proved to be capable of detecting dielectric changes of MgTiO3–CaTiO3 composite powder and of quantifying the amount of additional substances. This information can b...

Ferroelectric, pyroelectric, and piezoelectric properties of a photovoltaic perovskite oxide

A perovskite solid-solution, (1-x)KNbO3-xBaNi1/2Nb1/2O3-δ (KBNNO), has been found to exhibit tunable bandgaps in the visible light energy range, making it suitable for light absorption and conversion applications, e.g., solar energy harvesting and light sensing. Such a common ABO3–type perovskite structure, most widely used for ferroelectrics and piezoelectrics, enables the same solid-solution material to be used for the simultaneous harvesting or sensing of solar, kinetic, and thermal energies. In this letter, the ferroelectric, pyroelectric, and piezoelectric properties of KBNNO with x = 0.1 have been reported above room temperature. The investigation has also identified the optimal bandgap for visible light absorption. The stoichiometric composition and also a composition with potassium deficiency have been investigated, where the latter has shown more balanced properties. As a result, a remanent polarization of 3.4 μC/cm2, a pyroelectric coefficient of 26 μC/m2 K, piezoelectric coefficients d33 ≈ 23 p...

Use of an open-ended coaxial cavity method to characterize powdery substances exposed to humidity

The effect of moisture adsorption in the characterization of dielectric powders by an indirectly coupled open-ended coaxial cavity method operating at 4.5 GHz was analyzed. SiO2, Al2O3, and ZrO2 powders were exposed to 5% and 100% relative humidity levels and Bruggeman symmetric, Looyenga, and General Mixing Model equations were used to determine changes in permittivity and loss tangent of the inclusions. Low moisture adsorption (0.1–2.5 vol. %) induced only a small change in inclusion permittivity but had a pronounced impact on dielectric losses. Calculated moisture percentages based on responses of the resonator and the General Mixing Model correlated well with traditional mass based determination. The presented characterization method exhibited high sensitivity for the determination of dielectric properties of powders and their moisture content to be further utilized in, e.g., process and quality monitoring.

Electrical and electromechanical characteristics of LTCC embedded piezoelectric bulk actuators

Abstract Abstract Piezoelectric effect is a versatile method to generate force and movement in microsystems as well as electrical feedback in sensors and smart packages. On the other hand, low temperature cofired ceramic (LTCC) has been utilised as a base material for hybrid circuit boards, packages as well as some microfluidic devices; however, new means to introduce integrated functionalities for it are needed. In this paper, a 10×5 mm rectangle and 10 mm in diameter round PZT samples fully embedded and cofired with Heraeus HeraLock LTCC were manufactured and their hysteresis, dielectric, displacement and microstructure properties and coupling factors were characterised. Relative permittivity of the LTCC embedded varied from 1300 for the rectangle sample to 1500 for the round sample at 1 kHz, while r of 2209-2406 was obtained for corresponding bare bulk samples respectively. Measured piezoelectric d 33 coefficient was in the range of 324-441 pm V−1 for embedded structures, while 553-567 pm V−1 was obtained for free bulk samples at 100 Hz. Results show that LTCC has significant impact for electromechanical performance mainly due to constraining of the LTCC layers. In spite of this, feasible figures of merits were obtained for LTCC embedded PZT materials, while further improvements can be obtained by optimising the process and structures for LTCC based microsystems, sensors and actuators.

Multilayer BST-COC Composite with Enhanced High Frequency Dielectric Properties

The 0–3 composites with a mixture of randomly dispersed and separated ceramic particles and thermoplastic polymers provide flexible method to fabricate RF devices with adjusted mechanical and electrical properties. However, high ceramic loading levels are required to achieve high relative permittivity which, on the other hand, dramatically degrades the mechanical properties of the composite. In this work vertical and horizontal 2–2 type multilayer structures were fabricated by hot lamination of injection moulded 0–3 BST-COC composite materials with different loading levels of paraelectric ceramic (Ba 0.55 Sr 0.45 Ti 1.01 O 3 ). Each layer and the structures with gradient in permittivity and loss were characterized up to 1 GHz by impedance analyzer. The relative permittivity for the vertical and horizontal gradient structure with identical layer order and average ceramic loading of ∼ 16 vol.% was 6.54 and 10.60 at 1 GHz, respectively. The results showed that especially the horizontal structure is able to provide higher relative permittivity values than a vertical one with similar ceramic loading levels and with competitive dielectric losses. Since the introduced structure is composed of combination of ductile and brittle layers, it also offers a way to fabricate devices with improved mechanical properties.

A Game Changer: A Multifunctional Perovskite Exhibiting Giant Ferroelectricity and Narrow Bandgap with Potential Application in a Truly Monolithic Multienergy Harvester or Sensor

An ABO3 -type perovskite solid-solution, (K0.5 Na0.5 )NbO3 (KNN) doped with 2 mol% Ba(Ni0.5 Nb0.5 )O3-δ (BNNO) is reported. Such a composition yields a much narrower bandgap (≈1.6 eV) compared to the parental composition-pure KNN-and other widely used piezoelectric and pyroelectric materials (e.g., Pb(Zr,Ti)O3 , BaTiO3 ). Meanwhile, it exhibits the same large piezoelectric coefficient as that of KNN (≈100 pC N-1 ) and a much larger pyroelectric coefficient (≈130 µC m-2 K-1 ) compared to the previously reported narrow-bandgap material (KNbO3 )1-x -BNNOx . The unique combination of these excellent ferroelectric and optical properties opens the door to the development of multisource energy harvesting or multifunctional sensing devices for the simultaneous and efficient conversion of solar, thermal, and kinetic energies into electricity in a single material. Individual and comprehensive characterizations of the optical, ferroelectric, piezoelectric, pyroelectric, and photovoltaic properties are investigated with single and coexisting energy sources. No degrading interaction between ferroelectric and photovoltaic behaviors is observed. This composition may fundamentally change the working principles of state-of-the-art hybrid energy harvesters and sensors, and thus significantly increases the unit-volume energy conversion efficiency and reliability of energy harvesters in ambient environments.