**3. Magnetic-based effects of solid-state energy harvesters**

Electricity can be generated by operating on a coil with a variable magnetic field. Such a field can be induced by another coil, in which a variable current flows, we are talking about the mutual induction of coils. This is how the transformer works. By definition, a harvester should be designed so that it does not require additional power supply. Materials that can be used to generate a variable magnetic field are:


As part of our own research, we selected a group of smart materials for harvesting applications and developed many solutions and harvesting methods predestined for the SHM [28, 41] application. The scope of works on magnetic harvester is presented in **Figure 4** [42]. Harvesters with a smart magnetic core can be used as:

• Impulse power supply operating under the influence of mechanical impact with energy adjusted to the size of the harvester core, conditioning its electrical power

**41**

**Figure 5.**

*Development of the next generation of harvester with magnetic core and their applications.*

*Energy Harvester Based on Magnetomechanical Effect as a Power Source for Multi-node Wireless…*

• As an electric power transmitter operating under the influence of ultrasonic vibrations above 25 kHz, supplied either from an actuator or a specific techno-

*DOI: http://dx.doi.org/10.5772/intechopen.85987*

logical process

**Figure 4.**

*Types of harvesters with magnetic processing.*

*Energy Harvester Based on Magnetomechanical Effect as a Power Source for Multi-node Wireless… DOI: http://dx.doi.org/10.5772/intechopen.85987*

• As an electric power transmitter operating under the influence of ultrasonic vibrations above 25 kHz, supplied either from an actuator or a specific technological process

*A Guide to Small-Scale Energy Harvesting Techniques*

system as a whole.

ing characteristics.

core-coil system magnetostrictive core.

magnet-coil system against one another.

even for small power and efficiency, it can be a valuable power source. The development of the technology of constructing harvester, with similar electrical parameters as chemical cells, may reduce the production of the latter for ecological reasons. As harvesters acquire energy in a nonparasitic manner, i.e., they process energy considered as a by-product ("junk") process, they increase the efficiency of the

Both electricity and electric voltage must have the parameters necessary to supply both the sensors themselves and the built-in processor with the transmitter adapted to it, as well as the communication unit. Another problem is the conversion and conditioning of the voltage/current from the generator (**Figure 3**) [33, 34]. Designing electrical circuits for harvester requires knowledge of the device's operat-

Only harvesters based on a thermoelectric or photovoltaic effect generate DC current. Harvesters recovering energy from vibration, magnetostrictive, and piezoelectric, as well as based on the Faraday effect, are on the other hand alternating current sources. Harvesters powered by impact impulse are a special case [35]. The generation of electricity in pulsed power takes place for a very short time, but the current amplitude is very high. Harvesters "powered" by mechanical shock generate a variable voltage waveform and are characterized by a strong current pulse, and in the generated signal, there are frequencies related to magnetic resonance of the

Electricity can be generated by operating on a coil with a variable magnetic field. Such a field can be induced by another coil, in which a variable current flows, we are talking about the mutual induction of coils. This is how the transformer works. By definition, a harvester should be designed so that it does not require additional power supply. Materials that can be used to generate a variable magnetic field are:

• Permanent magnets (e.g., neodymium NdFeB), which are a source of constant magnetic field. In order to be able to recover energy through a coil, a source of an alternating magnetic field is necessary, which means movement of the

• Materials with gigantic magnetostriction (giant magnetostrictive material— GMM): Work on new materials has led to the development of materials with gigantic magnetostriction, which undergoes the action of force, deforming, while generating a variable magnetic field. If harvesters based on these methods are subjected to mechanical vibrations, which are a side effect of a certain process, they can be considered a "free" source of alternating electric current, resulting from the appearance of a variable magnetic field generated in the

As part of our own research, we selected a group of smart materials for harvesting applications and developed many solutions and harvesting methods predestined for the SHM [28, 41] application. The scope of works on magnetic harvester is presented in **Figure 4** [42]. Harvesters with a smart magnetic core can be used as:

• Impulse power supply operating under the influence of mechanical impact with energy adjusted to the size of the harvester core, conditioning its electri-

coil, obtaining the best energy conversion parameters [36–40].

**3. Magnetic-based effects of solid-state energy harvesters**

**40**

cal power

*Types of harvesters with magnetic processing.*

**Figure 5.** *Development of the next generation of harvester with magnetic core and their applications.*

## **3.1 Harvester construction: core modification**

In the next step, it was considered advisable to undertake the task of miniaturizing the harvester structure by modifying the harvester core. The magnetic circuit of the core consists of a set of permanent magnets coupled with magnetostrictive elements, which in turn are cores made of Terfenol-D, solid, as well as in the form of compressed flakes, which makes it possible to reduce eddy currents. Proper selection of parameters related to prestress and magnetization of the magnetostrictive material ensured the supply of the microprocessor even with much smaller dimensions than the one described in [33]. In addition to the typical design assumptions, it was necessary to formulate assumptions from the electrical and functional side, which would ensure a total possibility of working in the mode of actuator-harvester [33].

Previously, harvesters with magnetic processing have been described. The subgroup of magnetic harvester is top core coil magnet (TCCM) harvesters and its variants, double top core coil magnet (DTCCM) and TCCM model 2 [36]. In the work [36], it was shown that harvesters have low electric power yields in relation to dimensions and weight. Further work was aimed at developing a new harvester structure capable of miniaturizing the device without compromising performance and electrical efficiency. The schedule of work on the development of the structure is presented in **Figure 5**.

In order to develop a miniature harvester, the following assumptions were made:


**Figure 6** shows a comparison of the TCCM structure currently developed based on two solid Terfenol-D cores. The fact that two external NdFeB magnets have been placed inside nonmagnetic oscillating cones is noteworthy.

The prestress of the core is determined by tightening the thread between the clamp and the body. A hole has been made in the aluminum cover in which a cylindrical-shaped ring is received, which receives vibrations. Between the clamp and the washer, there is a rubber ring, which acts as a shock absorber for transmitted vibrations and determines the prestress. By changing the mutual position of the clamp and body, the force at which the polyurethane ring is compressed is influenced, which acts on the core-coupled washer as shown in **Figure 7**.

The harvester body is made of steel; it acts as a seismic mass, affecting the core through a cone embedded in the hole at its bottom. A hole has been made in the body with a diameter suitable for the coil with magnetostrictive cores and a supply opening for the coil wires. The advantage of the body is that it shields the magnetic field from the magnetic circuit. All elements and assembly of the harvester are shown in **Figure 7**.

#### **3.2 Review of prototypes of harvester with a smart magnetostrictive core**

The above described only selected own works which allowed to create a palette of harvesters. The type of work and power range of the harvester are shown in the graph below (**Figure 8**):

**43**

**Figure 7.**

**Figure 6.**

*Energy Harvester Based on Magnetomechanical Effect as a Power Source for Multi-node Wireless…*

*Comparison of the structure of harvester construction developed in the Laboratory of Dynamics of WRUT.*

*List of all elements of the harvester: (a) main body, (b) coil with inner elements.*

*DOI: http://dx.doi.org/10.5772/intechopen.85987*

*Energy Harvester Based on Magnetomechanical Effect as a Power Source for Multi-node Wireless… DOI: http://dx.doi.org/10.5772/intechopen.85987*

**Figure 6.** *Comparison of the structure of harvester construction developed in the Laboratory of Dynamics of WRUT.*

**Figure 7.** *List of all elements of the harvester: (a) main body, (b) coil with inner elements.*

*A Guide to Small-Scale Energy Harvesting Techniques*

**3.1 Harvester construction: core modification**

1.As a core solid Terfenol-D must be used.

3.Alignment will be followed by a "cone-hole" pair.

placed inside nonmagnetic oscillating cones is noteworthy.

enced, which acts on the core-coupled washer as shown in **Figure 7**.

crumbling.

magnetostriction.

the graph below (**Figure 8**):

In the next step, it was considered advisable to undertake the task of miniaturizing the harvester structure by modifying the harvester core. The magnetic circuit of the core consists of a set of permanent magnets coupled with magnetostrictive elements, which in turn are cores made of Terfenol-D, solid, as well as in the form of compressed flakes, which makes it possible to reduce eddy currents. Proper selection of parameters related to prestress and magnetization of the magnetostrictive material ensured the supply of the microprocessor even with much smaller dimensions than the one described in [33]. In addition to the typical design assumptions, it was necessary to formulate assumptions from the electrical and functional side, which would ensure a total possibility of working in the mode of actuator-harvester [33]. Previously, harvesters with magnetic processing have been described. The subgroup

of magnetic harvester is top core coil magnet (TCCM) harvesters and its variants, double top core coil magnet (DTCCM) and TCCM model 2 [36]. In the work [36], it was shown that harvesters have low electric power yields in relation to dimensions and weight. Further work was aimed at developing a new harvester structure capable of miniaturizing the device without compromising performance and electrical efficiency. The schedule of work on the development of the structure is presented in **Figure 5**. In order to develop a miniature harvester, the following assumptions were made:

2.The core of Terfenol-D will be wrapped with foil, which will protect it against

**Figure 6** shows a comparison of the TCCM structure currently developed based on two solid Terfenol-D cores. The fact that two external NdFeB magnets have been

The prestress of the core is determined by tightening the thread between the clamp and the body. A hole has been made in the aluminum cover in which a cylindrical-shaped ring is received, which receives vibrations. Between the clamp and the washer, there is a rubber ring, which acts as a shock absorber for transmitted vibrations and determines the prestress. By changing the mutual position of the clamp and body, the force at which the polyurethane ring is compressed is influ-

The harvester body is made of steel; it acts as a seismic mass, affecting the core through a cone embedded in the hole at its bottom. A hole has been made in the body with a diameter suitable for the coil with magnetostrictive cores and a supply opening for the coil wires. The advantage of the body is that it shields the magnetic field from the magnetic circuit. All elements and assembly of the harvester are shown in **Figure 7**.

**3.2 Review of prototypes of harvester with a smart magnetostrictive core**

The above described only selected own works which allowed to create a palette of harvesters. The type of work and power range of the harvester are shown in

4.An NdFeB magnet will be placed inside the coil, which will increase the obtained results with the Faraday effect under the influence of core

**42**
