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

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:

#### A. Manufacture of the planar micro-coils:

A simple structure is analyzed in [25], by numerical simulation for the demonstration of its

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 deforma-

capacity to generate electric voltage under mechanical stress.

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

tions 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].


C. The assembling:

access;

ment, 5, (Figure 20g);

core—ferrite and colloidal magnetic nanofluid

core—ferrite and colloidal magnetic nanofluid: V2

• undismantled adhesion assembly (bonding);

• aligning the plates with micro-coils (two) by means of the separation and seal ele-

New Energy Harvesting Systems Based on New Materials

http://dx.doi.org/10.5772/intechopen.72613

37

• introducing a magnetic nanofluid, 6, (Figure 20g), in the cavity and sealing the nozzle

• mounting plate ferrite isolated from coils and making of electrical connections.

3.2. Making a miniature planar microtransformer with circular spiral windings obtained by machining, starting from a textolit board double plated with copper and with hybrid

3.2.1. Making a miniature planar microtransformers with circular spiral windings with hybrid

type NMF-UTR40-50G that having saturation magnetization of 50 Gs.

nanofluid—V2 and the equivalent simplified 2D axial model [30].

A key component of the devices used for energy harvesting from the environment is the electric transformer. In this case, we proposed a miniature planar transformer with circular spiral windings with hybrid core—ferrite and colloidal magnetic nanofluid, [27]. The proposed model has two circular spiral-wound, made from copper: 20 turns in primary and 40 turns in secondary. Windings, Figures 21 and 22, can be "grown" using LIGA technology on a ceramic substrate (Al2O3) as has been shown previously or can be obtained by machining, starting from a textolit board double plated with copper. Housing and central column are made of 3F3 ferrite. The cavity formed in the housing is filled with superparamagnetic colloidal nanofluid, NMF-UTR40-500G, Figure 21, having saturation magnetization of 500 Gs, [27]. The applications presented in [28, 29], uses a dilution of magnetic nanofluid acting also as a cooling agent,

Figure 21. The planar microtransformers with circular spiral windings with hybrid core—ferrite and colloidal magnetic

Figure 20. Manufacture of a planar microtransformer with circular spiral windings with hybrid core—ferrite and colloidal magnetic nanofluid—V1.


#### B. Manufacture of another parts:

• precision micromachining by CNC machine (KERN Micro) by laser ablation CompexPro/Coherent and by electrodischarge machine on SmartDEM/Kunth: separation and sealing element, 5, (Figure 20f) and ferrite clad, 7, (Figure 20h).
