2. Piezoelectric structures based on new modified PZT zirconate titanate designed for energy harvesting applications

We propose a piezoelectric ceramic material what can it be integrated into piezoelectric structures for energy harvesting applications. The piezoceramic element has the shape of a disk with diameter of 12 mm while the width is 0.3 mm. On each of the ceramic disk's sides, silver

Figure 13. XRD pattern of PZT doped with 1% Nb2O5 sintered at 1120C for 2 hours, [25].

Figure 14. Scanning electron microscopy images (SEM) image of PZT doped with 1% Nb2O5. Sintered at 1120C for 2 hours [25].

electrodes were attached. Perovskite ceramics based on lead zirconate titanate (PZT) modified with niobium (Nb) were used to obtain these active elements. A high temperature solid state reactions technique has been used to prepare the piezoelectric ceramic, [25, 26], described by the general formula Pb(Zr0.53Ti0.47)0.99Nb0.01O3. Based on their piezoelectric characteristics, modified PZT zirconate titanate ceramics have efficient applications in energy harvesting devices. The X-ray diffraction patterns of Pb(Zr0.53Ti0.47)0.99Nb0.01O3 ceramic are shown in Figure 13. The XRD results indicate the rovskite type tetragonal phase free from a pyrochlore phase. The SEM pattern of the same composition sample is shown in Figure 14 and it shows that the microstructure of our sample is very dense.

Figure 17. Computational domain for the flow problem (the plate is placed in a flow duct, as in a hydrodynamic test

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Figure 18. Solutions of the multiphysics problem: Fluid streamlines and electric potential color map on the surface of the

setting) (concept ECEE-UPB) [26].

plate (concept ECEE-UPB) [26].

Figure 15. The low energy source built with piezoelectric linear transducers system, INCDIE ICPE-CA concept [26].

Figure 16. The electrical circuit of the generator [26].

electrodes were attached. Perovskite ceramics based on lead zirconate titanate (PZT) modified with niobium (Nb) were used to obtain these active elements. A high temperature solid state reactions technique has been used to prepare the piezoelectric ceramic, [25, 26], described by the general formula Pb(Zr0.53Ti0.47)0.99Nb0.01O3. Based on their piezoelectric characteristics, modified PZT zirconate titanate ceramics have efficient applications in energy harvesting devices. The X-ray diffraction patterns of Pb(Zr0.53Ti0.47)0.99Nb0.01O3 ceramic are shown in Figure 13. The XRD results indicate the rovskite type tetragonal phase free from a pyrochlore phase. The SEM pattern of the same composition sample is shown in Figure 14 and it shows

32 Advanced Electronic Circuits - Principles, Architectures and Applications on Emerging Technologies

Figure 15. The low energy source built with piezoelectric linear transducers system, INCDIE ICPE-CA concept [26].

that the microstructure of our sample is very dense.

Figure 16. The electrical circuit of the generator [26].

Figure 17. Computational domain for the flow problem (the plate is placed in a flow duct, as in a hydrodynamic test setting) (concept ECEE-UPB) [26].

Figure 18. Solutions of the multiphysics problem: Fluid streamlines and electric potential color map on the surface of the plate (concept ECEE-UPB) [26].

A simple structure is analyzed in [25], by numerical simulation for the demonstration of its capacity to generate electric voltage under mechanical stress.

A multiphysics numerical simulation further illustrates such piezoelectric transducer operation. The numerical model was built and analyzed with Comsol Multiphysics [38], a technical software package based on the finite element method, which allows the coupling of different software modules specialized in modeling physical problems of different nature. An image of

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Often, due to the complexity of the mathematical model, the analytical solutions of the differential equations system are difficult to obtained. Thus, it is necessary to use the numerical

Interfacing of the low energy source built with piezoelectric linear transducers system is

3. Miniature planar transformer with circular spiral winding and hybrid core—ferrite and magnetic nanofluid designed for new energy harvesting

One of the novelties of the future harvesting devices is regarding the use of a magnetic liquid core micro-transformer for the DC-DC converter of the harvesting device. From the operating point of view, by replacing the solid core with a hybrid core—ferrite and magnetic nanofluid, we estimate to result in a better heat dissipation and a reduction the thermal stresses in the microtransformer leading to a longer life cycle of the device, maintaining or even improving the electric characteristics. Also, the dielectric properties of the micro-transformer will be improved.

3.1. Making a planar microtransformer with circular spiral windings with hybrid core ferrite and colloidal magnetic nanofluid: V1 by using LIGA technology (Litographie,

Energy harvesting is a relatively new research area, seen as a viable and affordable solution for powering small autonomous devices, such as wireless sensor networks. Energy harvesting devices use small scale parts with low power losses. The main components are the electrical transformers that convert the voltage/current parameters from the primary from the energy harvesting stage, to the secondary to energy storage and distribution level stage. Miniature construction of the transformers, whose implementation can benefit from the LIGA manufacturing technology (Litographie, Galvanoformung, Abformung or in English Lithography, Electroplating and Molding), are required for compact, small but energy-efficient solutions. The following steps are performed to manufacture a planar microtransformer with circular spiral windings and with hybrid core—ferrite and colloidal magnetic nanofluid—V1:

• the ceramic substrate preparation, 1, as well as surface preparation, (Figure 20a) and

• spin deposition (coat) of a uniform layer, 2, SU8 photoresist, (Figure 20a). The thickness of this layer will be slightly above the height of turns to be deposited;

depositing conductive uniform submicrometer layer, 3;

Galvanoformung, Abformung) and precision micromachining

A. Manufacture of the planar micro-coils:

the solution of this analysis is presented in Figures 17 and 18.

simulations method still from the design phase.

systems

achieved through four bridges, as shown in Figure 19.

Another piezoelectric transducer, consisting of a thin plate of piezoceramic material with dimensions (34 mm 14 mm 1 mm), is illustrated in Figure 15. A layer of conductive material is deposited on one side of the plate (see the lower picture in Figure 15) and four equal rectangular conductive areas are deposited on the other side (see the upper picture in Figure 15), [26]. If the plate is subjected to pressure and mechanical deformation, due to exposure to wind or being placed in a fluid flow, the piezoelectric material will be polarized and a non-uniform electrical potential distribution could be identified on the faces of the plate. Conductive surfaces behave like surface electrodes attached to the plate; they integrate the electric potential on the plate's surface and connect to an electric circuit, transferring the potential value of each plate to an output connector, Figure 16. The one face which is uniformly coated can be used for reference terminal (ground), while each of the four rectangular patches can be connected to an individual electrode (1, 2, 3, 4), Figure 16. If the deformation of the ceramic plate is not uniform (the case of a flexible material), the electrodes might take different potential values and the piezoceramic plate becomes an electrical generator with four different output voltages: U10, U20, U30, U40, Figure 16. If the plate is rigid and the deformations are identical, the four terminals provide equal output voltages, [26].

Figure 19. Interfacing of the low energy source built with piezoelectric linear transducers system [26].

A multiphysics numerical simulation further illustrates such piezoelectric transducer operation. The numerical model was built and analyzed with Comsol Multiphysics [38], a technical software package based on the finite element method, which allows the coupling of different software modules specialized in modeling physical problems of different nature. An image of the solution of this analysis is presented in Figures 17 and 18.

Often, due to the complexity of the mathematical model, the analytical solutions of the differential equations system are difficult to obtained. Thus, it is necessary to use the numerical simulations method still from the design phase.

Interfacing of the low energy source built with piezoelectric linear transducers system is achieved through four bridges, as shown in Figure 19.
