**4. Harvesters based on mechanical impact and electronic converters for small power applications dedicated for them**

Generators of special characteristics are the explosive-driven ferromagnetic generators (EDFMG) producing an electromagnetic wave that arises as a result of immediate demagnetization of the magnet by a stroke following an explosion or other strong force impulse. The magnet then loses its magnetic properties but generates a strong pulsed magnetic field around it. During the impact it is possible to even destroy the magnet, but the amount of energy that will be induced in the coil is large, and it is enough to charge high-voltage capacitors with a large capacity. This issue is the subject of intense research, especially in the last decade, and their goal is applications, mainly military [43, 44].

One of the proposed methods of generating electricity directly from the impact was the impact demagnetization of NdFeB permanent magnets [35, 36]. Just as a spring has its constant, which is a measure of energy accumulated in it, the magnet has similar storage properties. Large diameter springs have large solid, strong magnets and have a high energy density. Permanent magnets containing components of rare earth have the highest energy density (see **Table 2**). This applies to the generation of electricity for the instantaneous supply of microprocessor systems from the impact demagnetization of permanent magnet-type NdFeB. Currently, NdFeB magnets are the most powerful permanent magnets. The advantages of NdFeB permanent magnets in impact harvesting:


The disadvantages of neodymium magnets include:



**Table 2.**

*Magnetic parameters of permanent magnets NdFeB divided into classes.*

Through the use of NdFeB magnets, harvesters feature the smallest possible external dimensions. The process of releasing energy through a surge load has become a determinant for the construction of a new generation harvester.

The limited availability and increasing price of rare earth elements are the reason for reducing their share in the composition of permanent magnets. At the same time, this is the reason for intensive research on improving the operational performance of magnets, with a significant reduction in manufacturing costs. On the other hand, you can see that, despite the popularity of the so-called neodymium magnets, not all of their capabilities have been noticed and fully used. There is little work on the use of NdFeB magnets as energy storage sources, which are used if necessary due to demagnetization as a result of mechanical impact. Due to the "longevity" of magnets, you can store "programmed energy" in them much longer than in typical alkaline batteries or accumulators. Of course, the amount of stored energy is much smaller than in typical lithium batteries, but in the case of energy recovered from magnets, there are no limitations in the type of leakage current, causing self-exhaustion of batteries. It is also possible to recycle magnets after fully demagnetizing them. Assumptions adopted during the construction of the impact harvester:


**47**

**Figure 10.**

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

There are examples of ferromagnetic generators which, thanks to the impact (explosion) against the neodymium magnet, obtain instantaneous powers reaching MW; however, in the energy-harvesting application, there is no need to destroy the magnet but only a "light" impact that would not cause its rapid destruction. The way to convert energy into electricity is to place the magnet in the induction coil, just as it is placed in it and other materials, e.g., in electromagnets or in the case of Terfenol-D [2]. Due to the wave phenomena resulting from the stroke, the coil must have a special construction, also due to the polarity of the NdFeB magnet. In the case of a wave transition, a large number of windings are not required

Due to the pulsed energy release, too high inductance of the magnetic circuit causes the reduction of the recovered current due to the increase of the substitute output impedance. The winding should be permanently attached to the magnet. One of the most important information about a magnet that cannot be omitted is the shape and arrangement of the zero line. The winding should be made only at one of the poles, N or S. This means that the magnet should have the largest possible height to diameter ratio but at \$ > 10 mm. Currently a 0.6 ratio is assumed to be the standard; however, there are solutions with a proportion close to 1. Be careful about the arrangement of the zero line, which shifts under the influence of demagnetization, and do not combine magnets in NSNS cascades, because the resulting relaxation of the NS transition results in a dramatic reduction in the performance of the magnetic circuit. A good chance to improve the performance of the recovered current is to use the Halbach matrix as the object to be

Harvesters using the mechanical impact phenomenon generate a variable voltage waveform. At the same time, it is characterized by a strong current impulse, and in the generated signal, there are frequencies associated with magnetic resonance of the core-coil system. Next, a new method of acquiring electric current is presented as a result of demagnetizing neodymium magnets in a circuit with a magnetostric-

The use of a small number of coils around the magnet enables the "capture" of rapid change of the magnetic flux and the generation of electricity directly from the magnet impact. However, a very low voltage level at a very high current requires the use of specialized electronic transducers capable of delivering the

**4.1 A dedicated low-power electronic system for impact harvesters**

*The scheme of MFT harvester construction together with the description of the relevant parameters.*

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

(**Figure 10**).

demagnetized.

tive core.

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

There are examples of ferromagnetic generators which, thanks to the impact (explosion) against the neodymium magnet, obtain instantaneous powers reaching MW; however, in the energy-harvesting application, there is no need to destroy the magnet but only a "light" impact that would not cause its rapid destruction. The way to convert energy into electricity is to place the magnet in the induction coil, just as it is placed in it and other materials, e.g., in electromagnets or in the case of Terfenol-D [2]. Due to the wave phenomena resulting from the stroke, the coil must have a special construction, also due to the polarity of the NdFeB magnet. In the case of a wave transition, a large number of windings are not required (**Figure 10**).

Due to the pulsed energy release, too high inductance of the magnetic circuit causes the reduction of the recovered current due to the increase of the substitute output impedance. The winding should be permanently attached to the magnet. One of the most important information about a magnet that cannot be omitted is the shape and arrangement of the zero line. The winding should be made only at one of the poles, N or S. This means that the magnet should have the largest possible height to diameter ratio but at \$ > 10 mm. Currently a 0.6 ratio is assumed to be the standard; however, there are solutions with a proportion close to 1. Be careful about the arrangement of the zero line, which shifts under the influence of demagnetization, and do not combine magnets in NSNS cascades, because the resulting relaxation of the NS transition results in a dramatic reduction in the performance of the magnetic circuit. A good chance to improve the performance of the recovered current is to use the Halbach matrix as the object to be demagnetized.

Harvesters using the mechanical impact phenomenon generate a variable voltage waveform. At the same time, it is characterized by a strong current impulse, and in the generated signal, there are frequencies associated with magnetic resonance of the core-coil system. Next, a new method of acquiring electric current is presented as a result of demagnetizing neodymium magnets in a circuit with a magnetostrictive core.

#### **4.1 A dedicated low-power electronic system for impact harvesters**

The use of a small number of coils around the magnet enables the "capture" of rapid change of the magnetic flux and the generation of electricity directly from the magnet impact. However, a very low voltage level at a very high current requires the use of specialized electronic transducers capable of delivering the

#### **Figure 10.**

*The scheme of MFT harvester construction together with the description of the relevant parameters.*

*A Guide to Small-Scale Energy Harvesting Techniques*

*Magnetic parameters of permanent magnets NdFeB divided into classes.*

**Material Energy density [kJ/m3**

Through the use of NdFeB magnets, harvesters feature the smallest possible external dimensions. The process of releasing energy through a surge load has become a determinant for the construction of a new generation harvester.

N27 199–223 25–28 10.2–11.0 Min. 9.6 N30 223–247 28–31 10.8–11.5 Min. 10.0 N35 263–286 33–36 11.7–12.1 Min. 10.9 N38 286–302 36–38 12.1–12.5 Min. 11.3 N40 302–326 38–41 12.5–12.8 Min. 11.6 N42 318–342 40–43 12.8–13.2 Min. 11.6 N45 342–366 43–46 13.2–13.8 Min. 11.0

**] Bhmax MGsOe Remanence kGs Coercion kOe**

The limited availability and increasing price of rare earth elements are the reason for reducing their share in the composition of permanent magnets. At the same time, this is the reason for intensive research on improving the operational performance of magnets, with a significant reduction in manufacturing costs. On the other hand, you can see that, despite the popularity of the so-called neodymium magnets, not all of their capabilities have been noticed and fully used. There is little work on the use of NdFeB magnets as energy storage sources, which are used if necessary due to demagnetization as a result of mechanical impact. Due to the "longevity" of magnets, you can store "programmed energy" in them much longer than in typical alkaline batteries or accumulators. Of course, the amount of stored energy is much smaller than in typical lithium batteries, but in the case of energy recovered from magnets, there are no limitations in the type of leakage current, causing self-exhaustion of batteries. It is also possible to recycle magnets after fully demagnetizing them. Assumptions adopted during the construction of the impact

• Neodymium magnet with "stored" energy (BH) max can be treated as a ware-

• The harvester can be stored in conditions much less favorable than typical

• In the magnetic circuit, the simplest construction of the magnetomechanical magnetic circuit should be used (application of pre-pressure, magnetic

• Energy "recovered" from a permanent magnet can be used to power a low-

have a minimum starting voltage of several mV.

• Electronics used in the input stage supplying microprocessor elements should

• The visible trend of reducing rare earth elements will result in a decrease in the cost of producing the harvester; however, a NdFeB magnet should be used as

house with energy that can be used with impact demagnetization.

**46**

harvester:

**Table 2.**

batteries, even in seawater.

the method of standard.

power sensor system.

screens).

#### **Figure 11.**

*Application of linear technology LTC3109 as a power conditioner for the microprocessor.*

appropriate voltage level to power the microprocessor system. The linear technology LTC3109 system dedicated to thermoelectric applications operating in a bipolar configuration was used in an original way, which, as it turned out, enables voltage processing from low-impedance magnetic circuits. The obtained results demonstrated the usefulness of the system to resonant frequencies close to 70 kHz. The most important features of the harvester with the LTC3109 system are shown in **Figure 11**.

Thanks to the LTC3109 system, which enables the capacitor to be charged for the shortest possible time (the dynamic resistance parameter (ESR)), the operating time of the microprocessor is extended. It is estimated that the harvester subjected to a stroke with a 1 ms force impulse at the energy storage capacitor 100 nF manages to extend the microprocessor operating time to 6 ms. This effect is presented in **Figure 12**, and the view of the prototype impacts harvester system on **Figure 13**.

It should be borne in mind that the estimated efficiency of transforming the impact of the magnetization of the neodymium magnet to electric current is only 0.02%. Therefore, the key challenge is better transformation of energy, which requires changes in the harvester construction. An important aspect is the standardization of the harvester, in terms of their geometric dimensions, conditioned by the application requirements. It is possible to create their series of types, from miniature versions to powers of several watts, as well as relatively large ones (e.g., with neodymium magnets Ø100 mm diameter) for applications in, for example, mining. Further works should also consider the possibility of replacing relatively expensive neodymium magnets with their counterparts lacking rare earth elements.

**49**

**Figure 13.**

**Figure 12.**

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

*(a) An example diagram obtained as a result of stimulation of a harvester by mechanical shock, (b) waveforms on the conditioner LTC3109, and microprocessor by Atmel together with a description of the parameters.*

*View of the impact harvester with the ball as the element receiving the impact.*

*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 12.**

*A Guide to Small-Scale Energy Harvesting Techniques*

appropriate voltage level to power the microprocessor system. The linear technology LTC3109 system dedicated to thermoelectric applications operating in a bipolar configuration was used in an original way, which, as it turned out, enables voltage processing from low-impedance magnetic circuits. The obtained results demonstrated the usefulness of the system to resonant frequencies close to 70 kHz. The most important features of the harvester with the LTC3109 system are shown

*Application of linear technology LTC3109 as a power conditioner for the microprocessor.*

Thanks to the LTC3109 system, which enables the capacitor to be charged for the shortest possible time (the dynamic resistance parameter (ESR)), the operating time of the microprocessor is extended. It is estimated that the harvester subjected to a stroke with a 1 ms force impulse at the energy storage capacitor 100 nF manages to extend the microprocessor operating time to 6 ms. This effect is presented in **Figure 12**, and the view of the prototype impacts harvester system

It should be borne in mind that the estimated efficiency of transforming the impact of the magnetization of the neodymium magnet to electric current is only 0.02%. Therefore, the key challenge is better transformation of energy, which requires changes in the harvester construction. An important aspect is the standardization of the harvester, in terms of their geometric dimensions, conditioned by the application requirements. It is possible to create their series of types, from miniature versions to powers of several watts, as well as relatively large ones (e.g., with neodymium magnets Ø100 mm diameter) for applications in, for example, mining. Further works should also consider the possibility of replacing relatively expensive neodymium magnets with their counterparts lacking rare earth elements.

**48**

in **Figure 11**.

**Figure 11.**

on **Figure 13**.

*(a) An example diagram obtained as a result of stimulation of a harvester by mechanical shock, (b) waveforms on the conditioner LTC3109, and microprocessor by Atmel together with a description of the parameters.*
