The demand for the development of non-destructive techniques aiming to assess the reliability of adhesively bonded structures has greatly increased these recent years. The multilayered plates ...investigated can suffer from different defects, such as delaminations, inclusions and microcracks at interfacial areas. The aim of this paper is to study the effect of imperfect interfaces on the wave propagation in multilayered structures that represent the typical architecture of components present in several industrial fields. This study is based on the calculation of both the reflectance function and the guided waves dispersion curves for an anisotropic multilayer where two metallic layers are bonded together by an adhesive layer made of an epoxy resin. Comparisons were performed in order to evaluate numerically the influence of several properties of the adhesive layer on the resonance modes of the multilayer. In addition, an imperfect porous interface layer model is implemented in order to simulate different adherence qualities between the metallic layers.
•Porous interface layer embedded in a multilayered structure.•Influence of the interface layer on the resonance modes of the structure.•Comparison between resonance modes and dispersion curves of the free guided waves.•Identification of the modes most sensitive to interface changes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Numerical study of interface properties on resonance modes in an isotropic multilayer.•Imperfect interface models assessing adherence quality.•Identification of coupling modes most sensitive to ...interface changes.•Characterizing an adhesive layer by comparing resonance modes and dispersion curves.
The microelectronics industry is expressing an increased demand for the development of non-destructive tools and methods for health control and diagnostics in multilayered structures. The purpose of these tools is to detect problems such as delaminations, inclusions and microcracks. The aim of this paper is to study the effect of imperfect interfaces on the wave propagation in multilayered structures. This type of structure represents the typical architecture of many microelectronic components. This study will be based on the calculation of the reflection coefficient and the guided waves dispersion curves. The investigated structure is an isotropic trilayer where two metallic layers are bonded together by an adhesive layer made of an epoxy resin. Comparisons were performed in order to evaluate numerically the influence of several properties of the adhesive layer on the guided waves behavior. In addition, an imperfect viscoelastic interface layer model 1 has been implemented in order to simulate different adherence qualities between the metallic layers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A kerfed, annular-array, high-frequency, micro ultrasonic transducer was produced.•Low temperature deposition and MEMS techniques were used to produce the UT.•The annular UT had a 67MHz resonance ...frequency in air and can work in water.•A FD–PSTD method was used to simulate the annular-array UT.
In this work, low temperature deposition of ceramics, in combination with micromachining techniques have been used to fabricate a kerfed, annular–array, high–frequency, micro ultrasonic transducer (with seven elements). This transducer was based on PZT thick film and operated in thickness mode. The 27μm thick PZT film was fabricated using a low temperature (720°C) composite sol–gel ceramic (sol+ceramic powder) deposition technique. Chemical wet etching was used to pattern the PZT thick film to produce the annular array ultrasonic transducer with a kerf of 90μm between rings. A 67MHz parallel resonant frequency in air was obtained. Pulse-echo responses were measured in water, showing that this device was able to operate in water medium. The resonance frequency and pulse-echo response have shown the frequency response presented additional resonance mode, which were due to the lateral modes induced by the small width-to-height ratios, especially for peripheral rings. A hybrid finite-difference (FD) and pseudospectral time-domain (PSTD) method (FD–PSTD) was used to simulate the acoustic field characteristics of two types of annular devices. One has no physical separation of the rings while the other has 90μm kerf between each ring. The results show that the kerfed annular-array device has higher sensitivity than the kerfless one.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper presents a method for ultrasonic characterization of porous silicon in which a genetic algorithm based optimization is used to solve the inverse problem. A one-dimensional model describing ...wave propagation through a water immersed sample is used in order to compute transmission spectra. Then, a water immersion wide bandwidth measurement is performed using an insertion/substitution method and the spectrum of signals transmitted through the sample is calculated using Fast Fourier Transform. In order to obtain parameters such as thickness, longitudinal wave velocity or density, a genetic algorithm based optimization is used.
A validation of the method is performed using aluminium plates with two different thicknesses as references: a good agreement on acoustical parameters can be observed, even in the case where ultrasonic signals overlap.
Finally, two samples, i.e. a bulk silicon wafer and a porous silicon layer etched on silicon wafer, are evaluated. A good agreement between retrieved values and theoretical ones is observed. Hypothesis to explain slight discrepancies is proposed.
•Water immersed ultrasonic measurements are performed on a porous silicon sample.•An ultrasonic wave propagation through a liquid or solid layer is implemented.•An inverse problem resolution is performed using a genetic algorithm.•A good agreement is shown between porous silicon parameters and literature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•An original 1D analytical model dedicated to Rosen type piezoelectric transformers is described.•Different electro-mechanical transfer functions were derived from the matrix representation of this ...model.•The 1D analytical model results were compared with both 3D Finite Element Analysis and experimental measurements.•Eight parameters of the 1D analytical model were fitted by performing a least squares adjustment of the voltage gain.•The Rosen type piezoelectric transformer’s output impedance was calculated analytically.
This article is dedicated to the study of Piezoelectric Transformers (PTs), which offer promising solutions to the increasing need for integrated power electronics modules within autonomous systems. The advantages offered by such transformers include: immunity to electromagnetic disturbances; ease of miniaturisation for example, using conventional micro fabrication processes; and enhanced performance in terms of voltage gain and power efficiency. Central to the adequate description of such transformers is the need for complex analytical modeling tools, especially if one is attempting to include combined contributions due to (i) mechanical phenomena owing to the different propagation modes which differ at the primary and secondary sides of the PT; and (ii) electrical phenomena such as the voltage gain and power efficiency, which depend on the electrical load.
The present work demonstrates an original one-dimensional (1D) analytical model, dedicated to a Rosen-type PT and simulation results are successively compared against that of a three-dimensional (3D) Finite Element Analysis (COMSOL Multiphysics software) and experimental results. The Rosen-type PT studied here is based on a single layer soft PZT (P191) with corresponding dimensions 18mm×3mm×1.5mm, which operated at the second harmonic of 176kHz. Detailed simulational and experimental results show that the presented 1D model predicts experimental measurements to within less than 10% error of the voltage gain at the second and third resonance frequency modes. Adjustment of the analytical model parameters is found to decrease errors relative to experimental voltage gain to within 1%, whilst a 2.5% error on the output admittance magnitude at the second resonance mode were obtained. Relying on the unique assumption of one-dimensionality, the present analytical model appears as a useful tool for Rosen-type PT design and behavior understanding.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A screen-printed PZT thick film with a final thickness of about 40 mum was deposited on a porous PZT substrate to obtain an integrated structure for ultrasonic transducer applications. This process ...makes it possible to decrease the number of steps in the fabrication of high-frequency, single-element transducers. The porous PZT substrates allow high acoustic impedance and attenuation to be obtained, satisfying transducer backing requirements for medical imaging. The piezoelectric thick films deliver high electromechanical performance, comparable to that of standard bulk ceramics (thickness coupling factor over 45%). Based on these structures, high-frequency transducers with a center frequency of about 25 MHz were produced and characterized. As a result, good sensitivity and axial resolution were obtained in comparison with similar transducers integrating a lead titanate (PT) disk as active material. The two transducers were integrated into a high-frequency imaging system, and comparative skin images are shown
Electrophoretic deposition (EPD) was used for the fabrication of piezoelectric lead zirconate titanate (PZT) thick films on alumina substrates. The EPD was performed in constant current mode from an ...ethanol based suspension consisting of PZT and PbO particles. The influence of addition of ethyl cellulose (EC) and sintering temperature on the thickness, density, homogeneity and functional response of PZT thick films is studied. Results show that the highest electromechanical performance is obtained for the PZT thick films sintered at 900 or 950°C, with a thickness coupling factor k
t
of 50%. The addition of EC influenced the thickness of the PZT thick films but had only minor effect on the porosity content for sintering temperatures over 900°C. Moreover, elastic constants of the thick films based on the suspension with EC were lower, which leads to lower acoustic impedance (15 MRa) while maintaining high (k
t
) value. In this last case, a better acoustic matching can be expected with propagation media such as water or biological tissues for ultrasound medical imaging applications.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Issue Title: Special Issue on Advances in Piezoelectrics: Fundamentals, Characterization, Materials and Applications, Guest Editor: Dragan Damjanovic Porous ceramics are of interest for ultrasonic ...transducer applications. Porosity allows to decrease acoustical impedance, thus improving transfer of acoustical energy to water or biological tissues. For underwater applications, the d^sub h^g^sub h^ figure of merit can also be improved as compared to dense materials. In the case of high frequency transducers, namely for high resolution medical imaging, thick film technology can be used. The active films are generally porous and this porosity must be controlled. An unpoled porous PZT substrate is also shown to be an interesting solution since it can be used in a screen-printing process and as a backing for the transducer. This paper describes the fabrication process to obtain such materials, presents microstructure analysis as well as functional properties of materials. Modelling is also performed and results are compared to measurements. Finally, transducer issues are addressed through modelling and design of several configurations. The key parameters are identified and their effect on transducer performance is discussed. A comparison with dense materials is performed and results are discussed to highlight in which cases porous piezoceramics can improve transducer performance, and improvements are quantified.PUBLICATION ABSTRACT
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The present work investigates the possibility to charge a Lithium micro-battery (LiB) via direct conversion of ambient mechanical energy into electricity using piezoelectric ZnO nanowire (NW) based ...microgenerators (PGs). An estimate is provided for the power levels at the different stages of mechanical-to-electrical energy conversion chain, in the following areas: (1) PG output, (2) power management block and (3) LiB storage unit. Also covered in this work is the synthesis, which is a prerequisite for realising such PGs. ZnO NWs of 2μm in length and 200nm in diameter have been grown using a low temperature (<150°C) hydrothermal process on 100μm thick PET substrates (25 × 25 mm2). Substrates containing bi-layer metal layers with dissimilar electro-negativities functioned as a galvanic cell in the growth nutrients, which acted as an electrolyte medium. This necessitated ZnO NWs growth on conductive surfaces, even in the absence of seed layers and/or substrate with specific lattice parameters. Finally, the assembly steps undertaken to realise the fully functional PGs are discussed, and the performances of the final PG are described thereafter. Subjecting such devices to a 10Hz sinusoidal bending force resulted in a measured PG output of ∼56mV peak to peak, on 1 MΩ resistive load.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A new hybrid finite-difference (FD) and pseudospectral (PS) method adapted to the modeling of piezoelectric transducers (PZTs) is presented. The time-dependent equations of propagation are solved ...using the PS method while the electric field induced in the piezoelectric material is determined through a FD representation. The purpose of this combination is to keep the advantages of both methods in one model: the adaptability of FD representation to model piezoelectric elements with various geometries and materials, and the low number of nodes per wavelength required by the PS method. This approach is implemented to obtain an accurate algorithm to simulate the propagation of acoustic waves over large distances, directly coupled to the calculation of the electric field created inside the piezoelectric material, which is difficult with classical algorithms. These operations are computed using variables located on spatially and temporally staggered grids, which attenuate Gibbs phenomenon and increase the algorithm's accuracy. The two-dimensional modeling of a PZT plate excited by a 50 MHz sinusoidal electrical signal is performed. The results are successfully compared to those obtained using the finite-element (FE) algorithm of ATILA software with configurations spatially and temporally adapted to the FE requirements. The cost efficiency of the FD-PS time-domain method is quantified and verified.
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